ADSSC Design Standards Manual

ABU DHABI MUNICIPALITY SEWERAGE PROJECTS COMMITTEE

DESIGN STANDARDS MANUAL

GUIDANCE NOTES

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Design Standards Manual Sewerage Projects Committee Abu Dhabi Municipality

1.

INTRODUCTION TO DESIGN STANDARDS MANUAL (DSM) The Design Standards Manual is presented in a single PDF document comprising the following separate sections. COVER SHEET GUIDANCE NOTES LIST OF CONTENTS SECTION 1 SECTION 2 SECTION 3 SECTION 4 SECTION 5 SECTION 6

GENERAL STORM WATER SYSTEM DESIGN SEWERAGE SYSTEM DESIGN SEWAGE TREATMENT PLANT DESIGN TREATED SEWAGE EFFLUENT SYSTEM DESIGN STANDARD AND TYPICAL DRAWINGS

The first issue for implementation of each section of the DSM will be at Revision 00. Subsequent revisions will be at 01, 02 etc. Future revisions to the DSM will be managed through annual review meetings when minor comments gained from experience of using the DSM and new technologies developed by the department/consultants will be incorporated in the DSM as discussed and agreed at the annual review meetings. 2.

NAVIGATING THROUGH THE DSM PDF DOCUMENT The DSM PDF document opens with the separate section bookmarks as identified above to the left of the screen and the DSM cover sheet at 100% magnification to the right of the screen. The contents of each section are also bookmarked and are shown by clicking on the + sign to the left of the section bookmark. The contents can be removed by clicking on the – sign to the left of the section bookmark. Clicking on a section bookmark or section contents bookmark will automatically take the user to that part of the DSM PDF document. Navigation through the DSM PDF document can also be achieved by clicking on the underlined section number in the list of contents section of the document. This will take the user to the cover page of the section. By scrolling down to the table of contents page for the section and clicking on a clause within the table of contents the user will automatically be taken to that part of the DSM PDF document. To return to the list of contents click on the back to previous view arrow in the tool bar or use the document drop down menu. The standards and typical drawings can also be accessed by clicking on the underlined drawing number in Section 6 of the DSM. To return to the DSM PDF document click on the back to previous view arrow in the tool bar or use the document drop down menu.

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LIST OF CONTENTS

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LIST OF CONTENTS

Volume No.

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SECTION 1

GENERAL

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SECTION 2

STORM WATER SYSTEM DESIGN

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SECTION 3

SEWERAGE SYSTEM DESIGN

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SECTION 4

SEWAGE TREATMENT PLANT DESIGN

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SECTION 5

TREATED DESIGN

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SECTION 6

STANDARD AND TYPICAL DRAWINGS

SEWAGE

EFFLUENT

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SECTION 1

GENERAL

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DOCUMENT CONTROL SHEET

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Revision Description / Purpose of Issue

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Updating of Design Standards Manual.

01 02 03 04 05 06 07 08 09 10

Approved for Implementation:_______________________________________________

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TABLE OF CONTENTS COVER SHEET..................................................................................................................... 1 DOCUMENT CONTROL SHEET .......................................................................................... 2 TABLE OF CONTENTS ........................................................................................................ 3 1.1

INTRODUCTION................................................................................................... 5

1.1.1

SCOPE.................................................................................................................. 5

1.1.2

CONTENTS AND ARRANGEMENT...................................................................... 5

1.2

RELATED DOCUMENTS...................................................................................... 5

1.3

MANUAL UPDATING............................................................................................ 5

1.4

DESIGN CONSIDERATIONS................................................................................ 6

1.4.1

DESIGN LIFE........................................................................................................ 6

1.4.2

DESIGN INFORMATION....................................................................................... 6

1.4.3

SITE INVESTIGATIONS ....................................................................................... 6

1.4.4

ENVIRONMENTAL IMPACT ................................................................................. 6

1.4.5

1.4.7

CLASSIFICATION OF POTENTIALLY EXPLOSIVE AREAS ................................ 6 TABLE 1 – SOURCES OF HAZARDS................................................................... 7 TABLE 2 – AREA CLASSIFICATIONS.................................................................. 9 FORMATION OF ODOROUS COMPOUNDS ..................................................... 14 TABLE 3 – ODOUR CONTROL GUIDELINES .................................................... 16 ENCLOSURES, COVERS AND ODOUR TREATMENT...................................... 25

1.4.8

HEALTH AND SAFETY IN DESIGN.................................................................... 27

1.4.9

VALUE MANAGEMENT AND VALUE ENGINEERING ....................................... 28

1.4.10

COST CONSIDERATION & FINANCIAL EVALUATION ..................................... 29

1.4.11

SPECIFICATIONS .............................................................................................. 31

1.4.12

DRAWINGS ........................................................................................................ 31

1.4.13

STRUCTURAL DESIGN...................................................................................... 31

1.4.14

CONCRETE STRUCTURES ............................................................................... 32

1.4.15

STEEL STRUCTURES........................................................................................ 32

1.4.16

DESIGN PRESENTATION.................................................................................. 33

1.5

MATERIALS........................................................................................................ 33

1.4.6

APPENDIX 1 – CLIMATIC DATA........................................................................................ 35 APPENDIX 2 – TYPICAL SEWAGE ANALYSIS................................................................. 36 APPENDIX 3 – TYPICAL GROUNDWATER ANALYSIS .................................................... 37 APPENDIX 4 – TYPICAL POTABLE WATER ANALYSIS .................................................. 38

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APPENDIX 5 – TYPICAL TREATED SEWAGE EFFLUENT ANALYSIS ............................ 39 APPENDIX 6 – MATERIALS SELECTION ......................................................................... 40 1. CONSTRUCTION MATERIALS .......................................................................... 40 2. MATERIALS SELECTION................................................................................... 40 3. PIPES ................................................................................................................. 41 4. STRUCTURES.................................................................................................... 50 5. MANHOLES ........................................................................................................ 59 6. MANHOLE COVERS........................................................................................... 59 7. STEP-IRONS AND LADDERS ............................................................................ 60 8. QUALITY CONTROL AND QUALITY ASSURANCE ........................................... 61 END OF SECTION.............................................................................................................. 61

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1.1

INTRODUCTION

1.1.1

SCOPE The Design Standards Manual (DSM) is for use by design consultants in carrying out the design of projects for the Sewerage Directorate. It presents guidelines for the design but it does not include design theories and methods of calculation but provides local practices and criteria to be adopted. Where any deviation from these criteria is considered necessary by the designer, the Directorate shall be consulted and their approval obtained. Copyright of the DSM in its current format is the property of the Directorate and it may not be reproduced in any format without express permission of the Directorate. Use of the DSM does not absolve design consultants from their normal responsibilities. It is meant as a guide and should be used only by competent practitioners, with due diligence.

1.1.2

CONTENTS AND ARRANGEMENT The DSM is divided into 6 separate sections as follows: • • • • • •

1.2

General. Storm Water System Design. Sewerage System Design. Sewage Treatment Plant Design. Treated Sewage Effluent System Design. Standard and Typical Drawings.

RELATED DOCUMENTS The Directorate’s companion documents to the DSM are: • • • • • • • •

1.3

Conditions of Engagement for Consulting Services. Quality Management System. CAD Manual. Geotechnical Design Manual. Construction Documents Manual. Irrigation and Landscape Re-engineering Manual. Safety Manual. Operation and Maintenance Contracts Manual.

MANUAL UPDATING Sections of the DSM will be revised from time to time and it will be the responsibility of all design consultants using the DSM to ensure that they are

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working to the current issue. Any errors or omissions, or recommendations should be notified to the Directorate. 1.4

DESIGN CONSIDERATIONS

1.4.1

DESIGN LIFE In general design life shall be as follows: • • • •

1.4.2

Pipelines Structures Mechanical and Electrical Equipment Instrumentation

50 – 60 years. 25 – 30 years. 10 – 15 years. 3 – 5 years.

DESIGN INFORMATION Design information relating to: • • • • •

Climatic Data. Typical Sewage Analysis. Typical Ground Water Analysis. Typical Potable Water Analysis. Typical Treated Sewage Analysis.

is given in Appendices 1 to 5 at the end of this section of the DSM. 1.4.3

SITE INVESTIGATIONS A description of the geology of Abu Dhabi and the requirements for site investigations is given in the Geotechnical Design Manual.

1.4.4

ENVIRONMENTAL IMPACT The designer shall address the environmental impacts of projects in accordance with the relevant legislation.

1.4.5

CLASSIFICATION OF POTENTIALLY EXPLOSIVE AREAS Classification of Potentially Explosive Atmospheres within sewerage systems and related operational processes are required to assess the risk of ignition in potentially explosive atmospheres and to remove or reduce them. A consistent and traceable approach shall therefore be made to each and every classification or ‘zoning’ exercise. This guidance note shall not be regarded as prescriptive, and is written to ensure that each zoning exercise complies with the relevant and current best industry engineering practice. Each installation shall be considered individually taking into account the civil structure and the proximity of other structures and plant. Consideration shall also

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be given to the consequences of an explosion when determining the subsequent classification. Reference should be made to the harmonised standard BS EN 60079-10, IEC 7910:1996 supersedes BS 5345 Part 2 which has been withdrawn. The classification and definitions of zones can be found in BS EN 60079-10 The design process shall attempt to remove or reduce the need for hazardous areas. Guidance as to the definitions of hazardous area zones is set out in BS EN 60079. In principle the classification of an area shall include the consideration of sources of hazards i.e. all potential releases of flammable substances. In the water industry the most common sources have been identified in Table 1 below. TABLE 1 – SOURCES OF HAZARDS

Flammable Material

Source

Density

Petrol/Hydrocarbons

Petrol station spillage into sewerage Heavier than system (Petrol tanker spillage not air considered significant) Other flammable liquids from industrial sources

Methane

Infiltration from leaking gas mains Cold digestion in poorly designed Lighter than air sewerage system Biogas production in digesters Geological infiltration

Hydrogen

By-product of (OSEC) plants

electrochlorination Lighter than air

Hydrogen sulphide

Sewers

Dust

Sludge dryers and pelletisers Powdered activated carbon (PAC) in water treatment plants

Heavier than air

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Lower Explosive Limit 1.0%

5.3%

4.0% 4.3% Varies

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Gases and vapours are only potentially explosive when mixed with air in certain quantities. Concentrations below the Lower Explosive Limit (LEL) or above the Upper Explosive Limit (UEL) are not potentially explosive. For the purposes of this guidance, the terms ‘flammable’ and ‘explosive’ shall be considered synonymous. For an explosion to occur there must be a source of ignition. The most common sources have been recognised as follows: • • • • • •

Electric arcing Hot surfaces Flames Friction and sparking from mechanical equipment and ferrous tools, manhole covers etc. Electrostatic discharges Spontaneous ignition.

The classification tables listed below include common items of plant relating to surface water and waste water treatment. The default zone classification may not necessarily be correct for every zoning exercise. Consideration shall always be given to site specific ventilation, structures and businesses that discharge (or could potentially discharge) chemicals into the sewerage system, which may change the extent of the zone or increase its severity.

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TABLE 2 – AREA CLASSIFICATIONS

Item

Plant / Process Equipment

Area Classification Zone 0

1.0 1.1 1.1.1

Sewerage & Storm Water Sewers Sewer

1.1.2 1.1.3 1.1.4 1.2 1.2.1 1.2.2 1.3 1.3.1

Manhole Chamber Outfall Sewer Vent Areas Vent Stack Air Valve Pumping Stations Wet Well

1.3.2 1.3.3 1.3.4 1.3.5 1.3.6

Zone 1

Zone 2

Remarks

NonHazardous

! ! !

Zone 1 unless solely used for domestic sewage with a low risk of flammable substance contamination ! !

Pumping Main Enclosure Above Wet Well (enclosed) Dry Well Valve Chamber Interconnecting Paths

! !

! !

!

!

! !

!

!

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! !

Consider flap valve

Wet wells are Zone 1 or Zone 2 up to coping level. Areas above coping are deemed non-hazardous if open to atmosphere ! ! !

Similar to Enclosed Channels, ventilation dependent Unzoned if sealed from wet well The area between 2 sets of doors between wet well and dry well is Zone 2

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Item



2.0 2.1 2.1.1

Sewage Preliminary Treatment Sewage P.S

2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.2 2.2.2 2.2.3 2.2.4 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5

Screens Forebay Odour Control Open Channels Enclosed Inlet Works Screen Houses (covered) Storm Tanks Primary Treatment Low Lift P.S. PST Distribution

Zone 1

Zone 2

!

!

! !

! !

! !

! ! !

Remarks

NonHazardous

Below coping level is Zone 1 or Zone 2 depending upon ventilation, above coping is non-hazardous if open to atmosphere The zoning of any ducting depends upon amount of dilution of air. Ventilation calculations required Below Coping ! !

!

Storm first flush may be a source of hazard

!

!

!

!

Below Coping is Zone 1 or Zone 2 depending upon ventilation Below Coping is Zone 1 or Zone 2 depending upon ventilation

!

Primary Settlement Secondary Treatment SBRs Aeration Blowers Aeration Lanes/Tanks Anoxic Lane RAS/SAS

Depends upon ventilation

! ! ! ! !

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Item



2.3.6 2.3.7 2.3.8 2.3.9 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.4.5 2.4.6 2.4.7 2.4.8 2.4.9 2.4.10 2.4.11 2.4.12 2.4.13 2.5

Biological Filters Final Effluent Humus Tanks Final Settlement Sludge Handling Primary Sludge Transfer Surplus Sludge Transfer Raw Sludge Tanks Digested Sludge Storage tanks Centrifuges Thickening Plant Digesters Dryers Pelletisers Bagging Plant Gassifiers Gas Holders Flare stack

Zone 1

Zone 2

Remarks

NonHazardous ! ! ! ! ! !

!

! !

!

! ! ! ! ! ! !

Tertiary Treatment UV Disinfection

! ! ! ! ! ! !

Open topped tank is non hazardous, however beware junction boxes etc. below coping Indoor centrifuge locations shall be ventilated Review manufacturers risk assessment with regard to hazardous areas caused by presence of combustible dusts Similar to vent stack when unlit, also consider this as a source of ignition

!

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Item



3.0 3.1

Water Treatment Electrochlorination

3.2

Zone 1

Zone 2 ! !

Ammoniation

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NonHazardous Electrochlorination Plants generate H2, review manufacturers risk assessment, ventilation required Where possible store NH3 containers in open air, NH3 can react with other materials to form explosive compounds, keep away from Chlorine.

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Potentially Explosive Atmosphere Area Classification Project: ….......................................................... File Ref.: …………………………………………... Plant / Process Equipment

Project No. …...................... Sheet No. ….....……………..


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Zone 1

Zone 2

Date: ………………………. Table Revision No. …....... Remarks

Flammable Material; Source, Ventilation, Process Conditions, Reasons, PEXA Drawing, Other Relevant Details

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1.4.6

FORMATION OF ODOROUS COMPOUNDS Odorous compounds only cause a problem if they are released to atmosphere and if there are residential areas close to the site which may be affected. To ensure that development does not encroach too near to a pumping station or treatment works and lead to odour related complaints, a new site should be selected so that ideally the boundary fence should be a minimum of 400m from the nearest residential property for small works and pumping stations, and 1km for large works and large pumping stations. Odour problems are associated with the development of anaerobic conditions (septicity) in sewage or sludge resulting in the formation of a range of malodorous compounds by the action of bacteria. The main compound associated with sewage and sludge odours is hydrogen sulphide (H2S), which is also a toxic and corrosive gas. The amount of H2S that can be formed is dependent on the strength of the sewage (or sludge) and the retention time under anaerobic conditions. Nutrient availability and the initial concentration of sulphate limit the maximum concentration that will develop. Saline intrusion increases the sulphate concentration of the sewage, which can increase the values of sulphide developing, especially in sludges. In sludges, other compounds such as mercaptans, dimethyl sulphide and volatile fatty acids are also formed and may be as important as H2S in adding to the total odour. The resultant lowering of pH value in sludges in the presence of volatile fatty acids enhances the release of odours. Anaerobic digestion reduces the volatile fatty acid content of the sludge with a consequent reduction in total odour and a reduction in the potential release of sulphide. However, the digester gas produced may contain up to 3000 parts per million (ppm) of hydrogen sulphide, which, unless treated, will have an odour impact. Oxidation of H2S and the other malodorous products of septicity to less odorous compounds will occur during aeration in activated-sludge treatment or during aerobic digestion. Odorous chemicals present in sewage or sludge cause a problem only when they are released to the atmosphere. This typically occurs at effluent discharge points and weirs where odour containing sewage or sludge is turbulent and there is good opportunity for odours to be transferred to the atmosphere. If the odorous compounds can be retained in solution, for example by retaining in pipes they will not cause nuisance. H2S e can be smelt at a concentration of 0.5 parts per billion (ppb) under laboratory conditions (the threshold odour concentration). Nuisance concentrations are typically 5-10 times the threshold odour value. H2S can cause corrosion of concrete and mortar fixtures when oxidised to sulphuric acid, e.g. on moist walls of sewers and manholes. Metal work and electrical equipment is vulnerable to H2S corrosion. Measures to control odours shall therefore aim to:

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• • • •

Prevent/reduce the development of septicity. Reduce the release of odours. Contain and treat odours. Locate odorous processes as far away from potential complainants as possible.

Specific guidelines for different stages in wastewater and sludge treatment are given in Table 3 below.

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TABLE 3 – ODOUR CONTROL GUIDELINES Process stage

Minimum provision

Sewerage system

• • • • • • • • • •

Enhanced provision

Use gravity system rather than rising • mains • Ensure adequate velocity to prevent deposition of grit and sediments Minimise turbulence, sharp bends and drops Ensure adequate ventilation of gravity sewers Minimise length of siphon sections Minimise length of rising main sections Seal manholes at discharge points Discharge at low levels to minimise turbulent drops Minimise retention time in sumps Ensure grit and screenings can be removed from sumps (e.g. good benching, access for pumping out)

Pumping stations

•

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Comment

Chemical dosing Seal manholes

Reduce the height of hydraulic drops • Provide OCU if identified into sumps problem • Minimise operational volume of sumps • Provide sufficient slopes and benching so that there is no accumulation of rags or sediments

•

Pumping stations can be a source of odour release due to turbulence, and odour formation if sumps are oversized or if sediments can accumulate

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Process stage

Minimum provision • • • • •

Inlet discharge – rising main/septic

Enhanced provision

Comment

Allow intermittent drain down to clear rags and sediments Where rags and screenings accumulate, include regular cleaning out in operational procedures Do not use screw pumps Avoid turbulence of flow in channels and at the discharge Cover wet well

• •

Do not locate near sensitive boundary Minimise turbulence at discharge points, including at intermediate pumping stations and all downstream locations prior to secondary treatment stage • Cover channels, sumps, detritors, screens receiving pumped sewage • Ensure materials below covers are resistant to sulphide/sulphate attack

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• • • • • •

Chemical dosing to upstream • Sewage can become very sewerage system, nitrate salts, septic in rising main sewers or STW, iron salts with consequent impact on odours at intermediate Minimise turbulence of pumping stations and the discharge discharge point. Sulphide Cover channels and sumps will also cause corrosion Ensure materials below covers and will pose a health and resistant to sulphide/sulphate safety risk to workers attack Vent from below covers to OCU Consider using gravity sewerage system with lift stations rather than long rising mains

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Process stage

Minimum provision

Inlet discharge - gravity

• •

Install away from sensitive boundary • Minimise turbulence of discharge Avoid cascades and other areas of turbulence • Covers and OCU • Keep channels non turbulent, minimise bends • Ensure liquor/returned storm sewage/imported wastes discharged at low level to reduce splashing

•

Sewage smells even when fresh and draws air along the sewer which may be unpleasant. Turbulence exacerbates release of odour

Imported wastes and sludges

•

Discharge at low level to covered sump • Treat displaced air in OCU or use close coupling • Connect tanker vents to OCU if • Locate tanker discharge point away air mixing employed from sensitive boundary

•

Imported wastes are generally odorous

Grit removal

• •

•

Aerated grit channels can lead to a significant release of odours

Inlet screens and screenings handling

•

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Do not select aerated grit channels Ensure grit is washed

Provide local covers and minimise turbulence as far as possible • Ensure materials below covers are resistant to sulphide/sulphate attack • Wash screenings

Enhanced provision

•

Do not select aerated grit channels • Cover unit • Ensure grit is washed • Enclose grit conveyor and classifier

Comment

•

House screens in a building actively vented to OCU • Provide local covers and minimise turbulence as far as possible

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Process stage

Minimum provision

Enhanced provision

Comment

•

Ensure materials below covers are resistant to sulphide/sulphate attack • Provide a gas alarm system as high levels of H2S could accumulate if ventilation system fails • Discharge washed screenings to enclosed skips • Do not store on site Inlet channels

•

Ensure a reasonable slope so that there is no grit deposition but not so much that there is turbulence • Avoid drops and sharp bends • Minimise height of discharges for example of return liquors, to reduce splashing

• •

Storm/balance tanks

•

•

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Ensure overflow weir is upstream of any liquors or tanker discharge • Discharge to base of storage tank to minimise splashing

Cover Ensure materials below covers are resistant to sulphide/sulphate attack

Use an effective cleaning system such as rotating jets. Operation should be stopped when the jet is exposed • Use an automatic system of return

•

Discharges into tanks release odours unless at low level. The impact is increased if the sewage discharging to the tank contains odorous wastes or liquors

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Process stage

Minimum provision

Enhanced provision

•

Design to ensure tank and associated • Ensure associated feed and channels and pipelines can be return channels can drain back completely drained of sewage, sludges, • Cover with air displaced during sediments and debris filling vented to odour control • Use an effective cleaning system such as rotating jets • Use an automatic system of return • Return storm/balanced flows downstream of the overflow weir and are at low level in the channel to minimise splashing

•

•

•

Provide close-coupled pumped • Design without a primary desludging to avoid exposure of sludges sedimentation stage or to the atmosphere • Provide covers vented to odour • Desludge frequently and remove control. Ensure materials below sludges at a low concentration to avoid covers are resistant to excessive retention sulphide/sulphate attack • Design arrangement so that tanks can be removed from operation at times of low flow to avoid excessive retention of sewage • Minimise the height of drop over weirs to reduce splashing

Primary tanks

Comment

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Storm/balance tanks can cause problems if sludges accumulate or if sewage is retained for excessive periods • Cleaning is important, but jet cleaners can cause odour release when the jet is exposed

Primary sedimentation is a very odorous stage allowing septicity to develop in sewage and sludges if retained for excessive periods with release mainly at PST weirs and downstream channels and from sludge withdrawal handling and treatment

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Process stage

Minimum provision

Enhanced provision

Comment

Lamella separators

•

•

•

Activated sludge/ membrane Bioreactors/ sequencing batch reactors

• •

•

Conventional biological • filters •

•

Can be a cause of odours if overloaded and ponding

•

Septic areas can develop, particularly in fixed media systems

Minimise need for manual cleaning of plates • Do not select systems that incorporate sludge thickening within the unit

Provide covers vented to odour control. Ensure materials below covers are resistant to sulphide/sulphate attack

Ensure adequate aeration and mixing • Cover distribution chambers, inlet channels and anoxic zone Fine bubble aeration systems are areas preferred to mechanical surface aeration systems • Minimise the loading rate • Use submerged or non-turbulent inlet and outlet arrangements

Ensure operating correctly Minimise the height of drop between distributor and media surface • Use recirculation if signs of ponding • Ensure adequate ventilation

Submerged biological • Fluidised media preferred to fixed media aerated filters fixed or • Avoid turbulence at inlet and during fluidised media backwashing

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•

Cover and vent to odour control

The level of septicity and odours developing is in proportion to the retention time

At normal loadings, activated sludge has a low odour level, decreasing as the loading rate decreases • FBDA systems release less aerosol and odours than mechanical surface aerators. There also is less risk of septic pockets developing

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Process stage

Minimum provision

High rate biological filters

•

Enhanced provision

Cover and vent filter and effluent sump • Replace with an alternative to odour treatment system. Draw air system or from the base of the filter • Cover and vent by drawing air • Do not co-settle sludge down to the base i.e. in the same direction and the sewage flow. Treat the vented air • Ensure materials below covers are resistant to sulphide/sulphate attack

Comment •

Can be a significant source of odours due to the development of thick biofilms with release of odours from the top of the filter in the ventilation

Final sedimentation, • Recycle backwash waters from sand tertiary sand filter, UV filters without storage treatment Picket fence thickeners • Cover and vent tanks to OCU, passive • Replace with mechanical and raw sludge storage may be sufficient. Toxic levels of thickeners hydrogen sulphide will develop below • Active venting to OCU covers • Site away from sensitive boundary • Non-turbulent low-level inlet, outlet and supernatant discharge • Locate motors for mixers outside tanks, use external pumps • Mix at low, rather than high, speed • Minimise the number of times that sludge is handled before thickening

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•

Odours in sludges and sludge liquor strength increase with storage • PFTs can be a significant source of odour formation with release of odours from: the surface of the PFT, the overflow weir, the sludge liquor drainage system and from subsequent handling of the sludge

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Process stage

Minimum provision

Enhanced provision

•

Minimise retention time prior to thickening, digestion and dewatering stages

Secondary sludge storage

• •

Minimise retention prior to thickening • Aeration may be used to maintain condition of sludge

Mechanical sludge thickening and dewatering

•

•

Sludge liquors

•

Ensure that there is more than sufficient capacity, including standby, so that raw sludge does not back up in the system • Minimise turbulence of liquor discharge e.g. below belts, into sludge liquor system • Enclose, vent covers to OCU • Minimise retention time of raw or secondary sludges prior to thickening, treatment and dewatering stages

Cover tank, vent to OCU

Comment

•

Biological sludges are odorous if they become anaerobic

Locally enclose and actively vent to OCU • A building may be required

Discharge at level to reduce odour • Chemical dosing e.g. using emission permanganate or iron salts, may be used to reduce sulphide • Balance flow and composition release • Return to secondary treatment, not primary or inlet, if imported sludges on site

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Process stage

Minimum provision

Anaerobic sludge digestion

•

Ensure that there is more than sufficient • Chemical dosing of sludge with capacity iron salts to reduce sulphide level in off-gas • Cover tanks, feed, mixing and take-off points • Ensure the gas handling system is fully operational. Whessoe valves, gas storage flare stack, CHP units and/or gas engines • If gas is not required for heating or engines, it should be flared

•

Aerobic digestion

•

Ensure that there is more than sufficient • Cover tanks and ventilate to capacity OCU • Cover feed, mixing and take-off points

•

Odours will be released during aeration of raw and secondary sludges.

Thermal treatment processes and drying

•

•

Volatilisation of a range of organic compounds may occur to due the high temperature

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Odour control, possibly by thermal oxidation • Tall stack

Enhanced provision

Comment Capacity is required to prevent the risk of sludge backing up in the system causing upstream odour problems • Digester gases can contain significant levels of H2S which is oxidised by flaring or burning

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1.4.7

ENCLOSURES, COVERS AND ODOUR TREATMENT In some instances covers, or an enclosed building, to contain and collect odours will be the only way to ensure that odour release can be controlled. If processes are enclosed within a building, additional local covering is likely to be necessary to ensure that the working atmosphere is safe. Processes that are commonly provided with local covering are: • • • • • •

Inlet works (may also be within a building). High rate filters. Sludge storage tanks. Sludge thickening and dewatering processes (may also be within a building). Sludge liquor sumps. Sludge import facilities.

Provision of covers will create a confined space where high concentrations of potentially hazardous gases may develop, requiring appropriate measures in terms of zoning (including for ventilation fans and/or odour treatment) and personnel access. Fan assisted ventilation may be needed to: • • • • • • •

•

• • •

Convey odours to an odour treatment system. Prevent the accumulation of high levels of odours that could be displaced during operations. Reduce the level of corrosion below covers. Reduce condensation and consequent corrosion. Prevent the accumulation of high levels of potentially hazardous chemicals. Ensure that working conditions meet Health and Safety requirements. Choice of materials for covers will need to take into account: strength and thickness, durability, weight, cost, aesthetics, supplier and operational requirements. Covers must be resistant to corrosion, both from external forces such as weathering and UV radiation, as well as internal chemical attack due to the hydrogen sulphide, sulphuric acid or organic acids below covers. Fibre reinforced plastic (with appropriate choice of resin, UV absorbers and light stabilisers) and aluminium are commonly used. Vinyl ester resin is considered to have excellent corrosion resistant properties. Aluminium with the correct choice of alloy is also corrosion resistant, although susceptible to corrosion if splashed with sewage. Covers should withstand wind loadings and static loads. Materials for covers and supports, and any equipment below the cover should be resistant to corrosion. Where possible motors etc should be located outside the cover. Suitable platform access and walkways should be provided to any equipment. In general facilities to allow access of personnel onto covers should not be provided.

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• • • •

Inspection and access hatches will be required for repair and maintenance purposes. Alternatively cover sections may be designed to be removable. Where possible, design should be such that equipment below covers can be easily and quickly removed to minimise time when covers need to be opened. Covers should be sealed as far as possible. Inspection /access hatches should be sufficiently durable so that they continue to be effectively sealed for the design life of a piece of plant. Overflow and discharge pipes should be designed and constructed to prevent a route for air under covers being discharged to the atmosphere.

All buildings containing sewage or sludge processes will need some form of ventilation to avoid build up of potentially hazardous (explosive or toxic) atmospheres. Where housing is close to the STW, this ventilation air will require odour treatment. Design of the ventilation and odour control system may need to take in to account the handling of potentially hazardous gases, and the zone requirements of the area in which it is installed. Odour releasing units (such as screens or belt presses) within a building should be locally enclosed, and a proportion of the required ventilation air drawn from the body of the building towards the odorous unit to ensure odours do not escape into the body of the building. The siting of stacks and emergency vents should be away from potential complainants. The choice of odour treatment process and the number of treatment stages depends on: • • • •

Flow rate of air to be treated. The strength and composition of the incoming air and whether intermittent or continuous. The percentage removal required (the standard of odour treatment required to avoid an odour problem can be derived from odour dispersion modelling). Space availability and zoning requirements of proposed location.

Design of odour control unit, ductwork, chemical storage and associated equipment should take into account expected temperatures: • • • •

o

25-35 C sewage. o 0-50 C ambient. o 85 C maximum radiating temperature (surfaces). o up to 30 C air vented from the sewerage system to an OCU.

Preferred odour treatment technology is:

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• •

Wet chemical scrubbing employing as a minimum single stage treatment using alkali/oxidant such as sodium hypochlorite with sodium hydroxide. Polishing treatment or treatment at small or remote sources (such as pumping stations) using activated carbon. In most cases carbon regenerated using alkali (caustic soda or potash) is preferred.

Post treatment of vented air or lightly odorous air by ducting to the activated sludge process should be considered. Post treatment of ventilation air for example using carbon should be considered at sensitive sites and at pumping stations. The same technology should be used throughout a site, for ease of operation. At existing sites, existing technology should be duplicated. Several sources should be combined to a single odour control unit, possibly providing more than one stage of treatment. Odour control equipment should be designed to remove the range of odorous compounds expected. The factors influencing the treatment process, the number of units provided on a site and the number of stages of treatment would be: •

Odours from buildings housing sewage processes (e.g. screening) will include: a) b)

•

Hydrogen sulphide (typically up to 10 ppm in ventilation air). Lower concentrations (typically less than 1ppm) of other sulphurous and nitrogen compounds (such as ammonia). c) Trace levels of solvent type odours. d) Odours from below vented covers could be ten times these values. Odours below unvented covers could be one hundred times these values. Odours from buildings housing sludge processes will include: a) b) c) d) e) f)

1.4.8

Hydrogen sulphide (typically 3 to 50 ppm in ventilation air). Mercaptans (typically 3 to 50 ppm in ventilation air). Dimethyl sulphide (typically 3 to 50 ppm in ventilation air) and similar organic sulphides. Ammonia if handling digested sludge/sludge liquors or if lime addition employed. Polyelectrolyte breakdown products (amines). Odours from below the covers of vented sludge storage tanks could contain ten times the above concentrations. Concentrations below the covers of un-vented tanks could be one hundred times these levels (toxic levels).

HEALTH AND SAFETY IN DESIGN

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The designer must be aware of all his responsibilities in the design and detailing of a project and shall: •

Ensure that any design he prepares and which he is aware will be used for the purposes of construction work includes among the design considerations adequate regard to the need: a)

b)

c)

•

•

1.4.9

To avoid foreseeable risks to the health and safety of any person at work carrying out construction work or cleaning work in or on the structure at any time, or of any person who may be affected by the work of such a person at work. To combat at source risks to the health and safety of any person carrying out construction work in or on the structure at any time, or of any person who may be affected by the work of such a person at work. To give priority to measures which will protect all persons at work who may carry out construction work or cleaning work at any time and all persons who may be affected by the work of such persons at work over measures which only protect each person carrying out such work.

Ensure that the design includes adequate information about any aspects of the project or structure or materials (including articles or substances) which might affect the health and safety of any person at work carrying out construction work or cleaning work in or on the structure at any time or of any person who may be affected by the work of such a person at work. Co-operate with the planning supervisor and with any other designer who is preparing any design in connection with the same project or structure so far as is necessary to enable each of them to comply with the requirements and prohibitions placed on him in relation to the project by or under the relevant statutory provisions.

VALUE MANAGEMENT AND VALUE ENGINEERING Value management (VM) can be defined as “A service which maximises the functional value of a project by managing its development from concept to completion and commissioning through the examination of all decisions against a pre-defined value system.” Value engineering is defined as the “The application of VM techniques within the design process”. The principles of value management are: • • • • •

Agreeing clear objectives. Agreeing value criteria. Ensuring that they are understood by all parties. Generating ideas for options. Validating outputs against agreed objectives and value criteria.

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•

Identifying value enhancements on the selected option.

Value

=

Satisfaction of needs / Resources used.

Value management: • • • • • • •

Provides a structured approach to decision making. Provides a common focus on value and objectives. Limits misunderstandings & misinterpretations. Delivers cost benefits by eliminating unnecessary work. Increases team building, shared knowledge and understanding. Ensures that the project outcome will correspond to the Client’s needs and aspirations. Enhances the value of projects.

Value management reviews should be carried out throughout the project life cycle, as set out in the value management plan, and the number required will depend on the project complexity. The reviews should generally follow the following sequence: • • • • • •

VM1 VM2 VE1 VE2 a,b,c VM3 VM4

Project definition. Concept design. Preliminary design and engineering. Detailed design. Procurement and contract strategy. Post project feedback.

The ability to add value is at it’s highest during the early stages of a project and reduces rapidly as decisions are taken and work implemented. The cost of adding value is at it’s lowest at the outset but increases rapidly as the project progresses. The aim should be to focus on the 20% of the project that accounts for 80% of the total project cost. Value management should be carried out through structured value engineering workshops, as well as being an integral part of the day to day design development. Formal workshops should be run by a trained facilitator and include all stakeholders including the design team; the client project team; the operations and maintenance teams who will operate and maintain the works on project completion. 1.4.10

COST CONSIDERATION & FINANCIAL EVALUATION Robustness and redundancy is an essential part of the design of works as obtaining spare parts at a later date can be problematic. Minimising capital expenditure resulting in a works that will require a lot of maintenance is not what is required.

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Civil works cost estimates may be built up using local rates and allowing further margins for overhead and profit of any overseas involvement. Major mechanical and electrical equipment cost estimates can be obtained from international suppliers of equipment. Allowances must be made for shipping costs, installation, overhead and profit and local agents’ costs. These can more than double the base price. Cost estimates should also allow for the consideration of: • • • • •

Project complexity. Levels of competition. Current and international workload. Unusual project scope. Operations expenditure.

Operations expenditure (Opex) covers the following aspects: • • • • •

Labour. Power. Chemicals. Sludge disposal. Maintenance and spares.

Currently labour costs are generally low therefore high manning levels are acceptable. Chemicals can be difficult to obtain and can be expensive. They will be required for certain processes but if their use can be avoided it is desirable. Maintenance costs should be based on 1% of the capital value of the plant costs. Net Present Value Net present value (NPV), or discounted cash flow (DCF), calculations are a method of comparing capital and operations costs over a period to determine which has the lowest overall value. In essence all costs are reduced back to present day prices. Capital costs for expenditure in the first year, year 0, are the actual costs whereas costs for future capital expenditure e.g. phased construction or replacement of plant are represented by the sum which invested now would build up to the capital sum needed in the future. Operations costs are represented by the present day sum that invested now will enable the annual running costs to be paid and reduce to zero at the end of the term.

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A discount rate is chosen on which to base the assessment. Normally this is between 3%-7%. A sensitivity analysis can be done at different discount rates if required. Inflation need not be considered as all sums are reduced to present day values. The period of the NPV calculations should be at least 20 years. Replacement of items of computer hardware should be allowed for every 5 years, machinery 15 years and civil structures 30 years. In all but the most sensitive calculations there is no need to consider residual values i.e. the remaining value of the item at the end of the term under consideration. The NPV may be calculated according to the following equation: NPV = Cost/(1-r)

n

Where n= number of years and r = discount rate 1.4.11

SPECIFICATIONS The basic specifications for use on projects are the General Specification for Civil Works and the General Specification for Mechanical and Electrical Works. Where used in contract documents they shall remain unaltered and may be referred to without the need to incorporate as hard copies into all documents.

1.4.12

DRAWINGS A complete list of standard and typical drawings is given in Section 6 of the DSM. The standard drawings should be used in their original format without alterations. Where used in contract documents their numbers shall remain unaltered and may be referred to without the need to incorporate as hard copies into all documents. Typical drawings are presented as an indication of standard format and quality. These may be used as the basis of individual contract drawings but must be renumbered and edited accordingly for specific projects.

1.4.13

STRUCTURAL DESIGN Structural design calculations shall be submitted to the Municipal Engineer’s Department of Abu Dhabi Municipality for approval. Design should be generally in accordance with their publication “Building Regulations & Recommendations for Structural Design & Concrete Practices”. The structural design submission shall include a separate design information sheet which contains the following: •

Code of practice adopted for design.

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• • • • • • • • • • • 1.4.14

Imposed loadings. Clear cover to main reinforcement. Concrete properties. Protective methods used for concrete. Reinforcement properties and coating. Safe allowable bearing capacity of soil, soil report to be attached. Pile foundation arrangement where appropriate. Types of structures. Dewatering requirements. Concrete curing methods. Formwork removal notes.

CONCRETE STRUCTURES Calculations should satisfy the requirements of ACI 318-63 or ACI 318-83, BS 8007 or BS 8110 or any equivalent and acceptable international code of practice. For serviceability limit state the following apply: • • • • •

Partial safety factor for all loads is 1. Factor of safety against flotation is 1.1. Design crack width is 0.2mm. Liquid level to be the working top water level. 2 Allowable steel stress in direct or flexural tension is 130N/mm .

For ultimate limit state the following apply: • • •

Partial safety factor for earth and water pressure is 1.4. 2 2 Allowable anchorage bond stress is 1.6N/mm and 2N/mm compression. 2. Maximum sheer stress is 4.75N/mm

Other principal factors are: • • • • 1.4.15

2

Characteristic strength of concrete is 40N/mm . 2 Yield strength of steel is 460N/mm for high yield defined bars. Minimum reinforcement is 0.35% of the cross section in each direction and in both faces. Maximum bar spacing is 300mm or the thickness of the section.

STEEL STRUCTURES In general the design of structural steelwork shall be in accordance with AISC Manual of Steel Construction or BS 5950 or other equivalent and acceptable international standard. Both the working stress and the ultimate stress methods of calculation are acceptable but it should be in accordance with the recognised standard.

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Steel should be A36 to ASTM & AISC and grade 43 to BS. Consideration must be given to fire and corrosion protection and appropriate methods applied. 1.4.16

DESIGN PRESENTATION All calculations are to be presented on standard A4 size calculation sheets. All information contained on the sheets is to be printed and the title blocks are to be filled in completely. All pages are to be numbered and sketches used as required to clarify the calculations. All assumptions, references, units and calculations are to be clearly stated. The originals of all calculations are to be indexed and bound for submittal. Drawing format as specified in the CAD Manual shall be adopted for all design projects. All drawings are to be signed by a professional engineer and two initials of the draughter, designer and checker must be included as appropriate in the title block. All design dimensions shall be expressed in metric units only. Drawings should generally be presented in the following arrangement: • • • • •

Cover sheet. Index of drawings. Location plan. Project drawings. Standard drawings.

The Consultant has total responsibility for the accuracy and completeness of the plans, calculations and related documents as required under the scope of work. Prior to final design submittal, the Consultant is expected to perform an internal quality control review carried out by engineers experienced in the appropriate disciplines to ensure a product of neat appearance, technically and grammatically correct and checked and signed by the draughter, designer and checker where appropriate. 1.5

MATERIALS Materials shall be chosen which result in the least maintenance and are not prone to decay by weathering or corrosion causing structural deterioration, leakage and infiltration.

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Established International Standards and guides such as ASTM, BS, EN, ISO and WIS should be followed in the selection of and specification for construction materials. Ideally the material product should be covered by an established ISO 9000 Quality Control system and wherever possible a third party quality assurance scheme. A discussion on materials selection is given in Appendix 6 for the designers information.

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APPENDIX 1 – CLIMATIC DATA

Temperature Degree C Mean Dry Bulb for Month Daily Ave. Max. Daily Ave. Min. Absolute Max. Absolute Min. Ground Min. Daily Ave. Absolute Ground Min. Earth 50cms. Daily Ave. Earth 100cms. Daily Ave. Relative Humidity % Mean RH for Month Daily Ave. Max. Absolute Max. Daily Ave. Min. Absolute Min. Wind Speed (46' above ground) Knots Mean Wind for Month Absolute Max. (for at least 10 mins) Highest Gust Precipitation (Rainfall) mm Total Amount Max. for any one day No. of days with Rain

JAN

FEB

MAR APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

19.8 24.4 15.2 30.1 12.0 13.2 9.0 25.2 26.8

20.7 25.3 14.5 32.7 10.5 13.0 8.3 24.4 25.7

23.1 28.5 19.6 39.8 13.2 15.7 11.6 25.8 26.1

27.1 33.4 22.0 41.7 15.6 19.7 13.3 29.4 28.6

29.4 36.7 23.6 41.9 18.6 21.3 15.7 31.5 30.5

32.0 38.5 27.4 44.6 24.5 25.6 22.8 34.7 33.2

30.9 41.3 31.1 44.8 26.5 30.2 24.5 36.8 34.9

33.5 39.2 29.8 45.5 26.0 28.9 24.6 36.8 34.9

30.9 37.3 26.7 43.0 24.7 24.9 21.8 36.5 35.8

28.9 35.7 23.0 39.6 21.0 21.0 17.8 34.1 34.2

25.3 30.1 20.3 36.7 15.4 18.7 13.9 30.8 31.8

22.0 26.3 16.9 31.3 13.3 15.1 10.4 27.5 29.0

68 83 100 51 37

65 88 100 43 15

56 82 100 36 10

50 71 84 28 13

55 79 97 28 11

58 80 91 33 17

57 79.3 92 32.8 17

66 84.7 92 42.2 13

67 85 94 41 13

65 86 100 29 16

63 78 9 45 1

68 85 10 5 27

7.2 24.0

6.5 32

7.4 31

8.2 27

7.3 25

8.5 27

8.9 26

8.8 25

7.9 22

7.3 19

8.1 23

6.9 32

30.0

45

39

39

32

33

30

34

30

25

29

30

Nil Nil Nil

20.1 10.5 5

0.8 0.7 2

2.7 2.1 4

TR TR 2

Nil Nil Nil

TR TR 3

Nil Nil Nil

Nil Nil Nil

Nil Nil Nil

Nil Nil Nil

0.3 0.3 1

999

997

997 1005 1012 1016 1019

0.8

2.1

1.4

0.8

0.3

1.0

1.6

Nil

0.3

0.2

0.4

0.3

0.4

1.0

N/A 29.0

456 24.2

382 19.3

316 339 16.5 16.10

30.9 19.8

24.8 17.0

637 21.6

537 22.8

515 20.1

507 19.3

487 23.2

363 15.2

313 16.0

Nil

1

1

2

6

Nil

7

Atmospheric Pressure mbs (MSL) Mean for Month 1019 1018 1014 1010 1006 Cloudiness-Oktas (Eighths of Sky) Total Cloud-Mean for 1.8 2.6 1.8 2.7 0.6 Month Low Cloud (8000) - Do 1.4 1.5 0.8 0.5 0.1 Evaporation mm (Standard Piche) Total for Month 464 413 517 404 482 Max. for 24 hours 28.1 28.0 29.0 25.0 28.5 Solar Radiation mls Total Distillation of Water 306 354 506 501 607 Maximum Distillation of 14.2 16.6 22.4 21.2 24.5 Water for 24 hours Visibility (vis 1000m in 24 hours) No. of Fog Days 7 7 4 Nil 2

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APPENDIX 2 – TYPICAL SEWAGE ANALYSIS The following is typical sewage analysis, as recorded at Mafraq sewage treatment works inlet, during the period January to December 1998.

No. of samples Mean Maximum Minimum Standard deviation

pH

TSS

BOD

NH3

COND

64 7.0 7.2 6.9 0.1

64 182 259 123 28.2

64 233 340 170 39.4

64 27 30 24 1.4

121 3192 3800 3000 214

Legend to Appendix 2 TSS BOD NH3 COND

Total suspended solids (mg/l) Biochemical oxygen demand (mg/l) Ammoniacal nitrogen (mg/l) Electrical conductivity (µ S/cm)

1

12 monthly averages of hourly readings

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APPENDIX 3 – TYPICAL GROUNDWATER ANALYSIS The following are typical analyses of groundwaters that have been encountered in Abu Dhabi.

Location Abu Dhabi Island Mussafah Khalifa City A Khalifa City'B

pH

Chloride (g/l)

Sulphate (g/l)

6.5 - 8.3 7.0 - 7.2 6.3 - 7.5 6.7 - 7.9

13 - 120 148 - 188 40 - 210 70 - 205

2.2 - 6.1 2.6 - 4.6 1.5 - 6.8 2.1 - 3.6

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APPENDIX 4 – TYPICAL POTABLE WATER ANALYSIS The following is typical potable water analysis, based on data from Umm al Nar desalination plant.

Parameter

Typical values

Units

8.3 - 8.8 250 - 500 20 - 30 20 - 35 60 - 120 5-7 0.4 - 0.8 8 - 15 4-7

µ S/cm mg/l mg/l mg/l mg/l mg/l mg/l mg/l

PH Conductivity Total alkalinity as CaC03 Hardness as CaC03 Chloride Sulphate Residual chlorine Calcium Magnesium

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APPENDIX 5 – TYPICAL TREATED SEWAGE EFFLUENT ANALYSIS The following is typical sewage effluent analysis, as recorded at Mafraq sewage treatment works outlet, during the period January to December 1998.

No. of samples Mean Maximum Minimum Standard deviation

pH

TSS

BOD

NH3

CL2

64 6.9 7.2 6.7 0.1

64 3.3 9.4 1.0 1.3

64 0.9 2.4 0.2 0.4

64 0.4 2.1 0.1 0.3

121 1.5 2.1 1.1 0.3

Legend to Appendix 2 TSS BOD NH3 CL2

Total suspended solids (mg/l) Biochemical oxygen demand (mg/l) Ammoniacal nitrogen (mg/l) Total residual chlorine (mg/l)

1

12 monthly averages of hourly readings

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APPENDIX 6 – MATERIALS SELECTION

1.

CONSTRUCTION MATERIALS As materials on storm water and groundwater control, sewerage and treated sewage effluent contracts can constitute up to 60% of the capital costs of a project it is essential that suitable materials are selected for the long term benefit of the Client. The design principles adopted for a particular system may reduce the number of options on material selection either from cost or geological/geographical standpoint. Established International Standards and guides such as ASTM, BS, ISO, WIS, and WRC should be followed in the selection of and specification for construction materials. Ideally the material product should be covered by an established ISO 9000 Quality Control system and wherever possible a third party quality assurance scheme. In selecting standards to specify materials it should be noted that European Standards are normally written for temperate climates whereas American Standards can reflect the diversity of climates experienced within the American continent e.g. Alaska to California in order to achieve materials/products that will perform under Abu Dhabi climatic and geophysical conditions. It may be necessary to combine standard specifications with technical data on testing of materials at temperatures equivalent to those experienced in Abu Dhabi.

2.

MATERIALS SELECTION General In order to determine if a material is suitable for inclusion in storm water and groundwater control, sewerage and treated sewage effluent projects, several factors have to be considered. These include: • • • • • • • • • •

Suitability for intended purpose. Availability of material locally and cost. Capital cost of selected material offset against reduction or elimination of maintenance costs. Capital cost of installation by Non Destructive Methods (NDM) or Microtunnelling offset by reduction in disruption to traffic etc. Quality of the medium being transported. Ground conditions (strata and groundwater). Difficulties in handling, transporting and installing the material. Environmental conditions within the network such as high temperature, poor ventilation, high levels of corrosive products and significant sand accumulation. Future use of land. Future expansion of the network.

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The selection of materials should strive to maximise all options available to provide the lowest total installed cost of the system without compromising the long term performance. The conveyance of sewage, combined with poor ventilation and high temperatures creates anaerobic conditions resulting in the creation of hydrogen sulphide gas, which has the familiar rotten egg smell. This in turn will convert to sulphuric acid which is highly corrosive to cementitious and ferrous materials. Hence, if the practice of discharging sewage into the stormwater network is practised, materials must be selected to withstand such an environment. Caution should be exercised in industrial areas where dumping of neat waste into sewerage or drainage networks, in the absence of local legislation, may result in abnormal high concentrations of corrosive products in specific locations of the network. The accumulation of sand and silt in storm water systems is a frequent occurrence of a predominately arid climate such as in Abu Dhabi. Wind blown sand and silt can easily enter the system. The lack of vegetation gives higher overland flows and allows more material to be washed off the open areas than otherwise would be the case. The pipes and culverts are sized for peak design flows, which occur infrequently and as a result self cleansing velocities are not achieved and the sediment cannot be flushed away regularly. Accordingly even with a correctly designed system, maintenance of the network and removal of sand and debris is necessary and has to be carried out on routine basis. In reviewing possible materials for inclusion in storm water and groundwater control, sewerage and treated sewage effluent, materials have been considered which are currently included in the existing networks as well as some newer materials which are now available to the local and regional construction industry. The two largest volumes of material utilised on storm water and groundwater control, sewerage and treated sewage effluent systems are concrete and pipeline materials. This appendix concentrates on the major items.

3.

PIPES Good guidelines to follow are WRC Pipe Materials Selection Manual and EN 1295-1:1997 Structural design of buried pipelines under various conditions of loading. The material for a pipeline must be selected to suit the liquid being conveyed and the installation conditions. General guidelines on the selection of pipe materials and the properties of pipe materials are given in the tables below.

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SUITABILITY OF PIPE MATERIALS FOR USE IN STORM WATER, SEWERAGE AND TREATED SEWAGE EFFLUENT

Pipe Material

Class

Storm Water

Sewerage

Treated Sewage Effluent

Manufacturing Base

Relative Cost per m

Gravity

Pressure

Gravity

Pressure

Gravity

Pressure

Rigid

Yes

No

No

No

Yes

No

UAE Saudi Arabia

Medium

Semi rigid

No

Yes

No

Yes

No

Yes

Europe USA

High

GRP

Flexible

Yes

Yes

Yes

Yes

Yes

Yes

UAE

Medium

HDPE

Flexible

Yes

Yes

Yes

Yes

Yes

Yes

UAE

Medium

MDPE

Flexible

Yes

No

Yes

No

Yes

No

UAE

Medium

PVCu

Flexible

Yes

No

Yes

No

Yes

No

UAE

Low

Rigid

Yes

No

Yes

No

Yes

No

Saudi Arabia

Low

Lined and coated RC DI

VC

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SUMMARY OF PROPERTIES OF PIPE MATERIALS

Property

DI

GRP

Specification

ISO 2531 ISO 8179 Coating BS EN 545 BS EN 548

HDPE

ASTM C128 ASTM D1447 ASTM D3262 ASTM D3035 AWWA C400 DIN 8074 BS 486 ISO 4427 BS 5480 ISO R160

PVCu

VC

ASTM D1784 ASTM D1785 ASTM D2241 ASTM D2665 BSEN 1452-2 ISO 11922-1

ASTM C700 BS 65 BS EN 295 DIN 1230

Maximum operating pressure

Maximum 25 Bar

Maximum 25 Bar

2.5 Bar to 30 Bar

16 Bar

10 Bar

Structural type

Semi rigid

Flexible

Flexible

Flexible

Rigid

Standard length

5/6m length

6m max

100m coil up to 110mm dia > 12m length above 110mm dia

6m

2m

Jointing

Push fit spigot and socket, Flanged joints

Push fit rubber gasket collar joint, Spigot and socket with gasket, Slip on collar flange

Butt fusion welding, Electrofusion , Flange

Push fit spigot and socket, Solvent welding

Push fit with rubber gasket

Anchor blocks

Required

Required

Not required on welded lines

Required

Required

Fittings

DI fittings

GRP

HDPE fabricated fittings, Standard mechanical joints

PVCu

VC limited

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Property

DI

GRP

HDPE

PVCu

VC

Deflection allowed

Only on long length

Max 50

More than 50 35D

1 to 50

Up to 200mm 0 2.9 , For 1000mm 0 0.6

Trench required

Wide trench

Wide trench

Narrow trench

Wide trench

Wide trench

Installation

Overground, Underground

Underground

Can be laid overground /underground on slopes

Underground

Underground

Corrosion

Effected by certain soil chemicals

Resistant to soil corrosion, Chemically inert




Heavy

Lightweight

Lightweight

Lightweight

Heavy

Handling

Cam be damaged by heavy handling

Careful handling, cracks if badly handled

Easy handling, not easily damaged

Careful handling because of brittle nature

Careful handling, can be easily damaged

Hydraulic properties

High frictional loss, High pumping cost

Low frictional loss, low pumping cost

Low frictional loss, low pumping cost

Low frictional loss, can be susceptible to fatigue, surge failures have been known

Low frictional loss

Abrasion resistance

Lining suspect to abrasion

Good

Good

Limited

Good

Breakage

Damaged due to heavy impact loads

Impact loads cause cracks

Impact resistant, unbreakable

Damaged by impact

Damaged by impact

Weight

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Property

DI

GRP

HDPE

PVCu

VC

Easy installation, larger sizes need craneage

Careful installation, required

Easy installation, Less time required, Only very large sizes need craneage

Easy installation but subject to poor installation methods

Easy installation, many joints due to small length

Bedding requirements

As dug material

As dug material, important to support along entire length must be self compacting

Selected as dug material, target 90% standard Proctor

Selected as dug material or processed granular materials, target 90% standard Proctor

Selected as dug material or processed granular materials, target 90% standard Proctor

Supports, clamps

Supports required

Not applicable, Above ground installation not possible

No support required, frequent clamping



Low maintenance

Low maintenance

No maintenance

No maintenance

No maintenance

Leakages

Frequent if corroded

Normal

No Leakage

Normal allowances for push fit joints

Normal

Surge head

High surge pressure

Medium surge pressure

Low wave velocity, Less surge pressure

Medium surge pressure

Not suitable for pumping

Depending on water quality cement internal lining is provided

Common

Recommend ed all over world

Commonly used in distribution

Not applicable

Installation

Maintenance

Water supply

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Property

DI

GRP

HDPE

PVCu

VC

Common in pump mains

Common in Middle East

New to UAE

Common in UAE

Common throughout World

Test pressure times operating pressure

1.5 times operating pressure



Air/gravity test

Design life

35 years depending on environment

50 years

50 years minimum

50 years (without brittle failures)

50 years

Deterioration with time

Corrosion encrustation etc

Joints deteriorate encrustation etc

Nil

Joint deterioration

Joint deterioration

Imported

UAE

Local up to 1200mm dia UAE

Commonly available up to 400mm dia

Saudi Arabia

Not affected

Deteriorates in UV

Stabilised

High

Moderate

Moderate

Sewage

Availability

UV light Cost

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Low

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GENERAL USE OF MATERIALS IN PIPELINES

Material Size

Storm water

Sewage

Treated sewage effluent

Trunk 300mm up to 2400mm dia

Distribution ≥50mm, generally300mm to 800mm dia

Services ≤50mm dia

Pumping Stations

Lined and coated RC, GRP, PVCu, VC

Lined and coated RC, GRP, PVCu, VC

Not applicable

DI

Lined and coated RC, DI, GRP, HDPE, VC

GRP, HDPE, PVCu, VC

Not applicable

DI

GRP, HDPE, MDPE, VC

HDPE, MDPE, PVCu, VC

HDPE, MDPE

DI, MDPE, HDPE

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Structural Behaviour & Classification of Pipes A buried pipe and the soil surrounding it are interactive structures. The extent of the interaction and hence the magnitude of the pipe loads arising depends on the relative stiffnesses between the pipe and the pipe bedding and native soil. Pipes are generally classed into rigid, semi-rigid or flexible, depending on the degree of this interaction. Rigid pipes are those where due to the nature of the pipe material, only very small diametrical deflections are possible before fracture occurs at a well defined limiting load. These deflections are too small to develop significant lateral passive pressure in the pipe zone fill material due to external vertical loading. Thus all the external load is taken by the pipe itself and bending moments are induced in the pipe wall. The design of rigid pipes is based upon the concept of a maximum loading at which failure occurs. Some examples of rigid pipe are reinforced concrete pipe (RC), vitrified clay pipe (VC) and asbestos cement pipe (AC). Semi-rigid pipes are capable of being distorted sufficiently without failure to transmit a part of the vertical load to the pipe zone fill material, thus mobilising a measure of lateral passive support from the surrounding soil, with the pipe wall continuing to take the remainder of the load in bending. Resistance to vertical loading is thus shared between the pipe wall itself and the lateral support from the pipe zone fill material, the proportions of this distribution depending upon the relative stiffnesses of the pipe and the soil surround. Some examples of semirigid pipe are ductile iron (DI) and cylinder type pre-stressed concrete. Flexible pipes are capable of being distorted sufficiently without failure to transmit virtually all vertical load to the surrounding pipe zone fill material for lateral support; the proportion of the load resisted by the pipe wall itself is very small. Flexible pipes are designed on the basis of maximum acceptable deflection, or strain induced in the pipe wall and resistance to buckling under load. The ability of the pipe zone material to provide support is a function of its stiffness, or modulus of reaction. Some common flexible types of pipe are un-plasticised polyvinyl chloride pipe (PVCu), polyethylene pipe (PE), glass reinforced plastic pipe (GRP) and glass reinforced epoxy pipe (GRE). Pipe Bedding The selection of the proper type of bedding and surround material is important in the long-term integrity and performance of both rigid and flexible pipes. Although rigid pipes support vertical loads mostly through their inherent strength and little support is generated by the horizontal soil reaction, nonetheless the selection of an appropriate pipe bedding installation can significantly increase its load bearing capacity by ensuring a more even distribution of vertical loads onto the pipe itself and also by transmission of the load by the pipe to the trench formation beneath.

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There is a much greater interaction between flexible pipes and the pipe zone material. The integrity of a flexible pipe is therefore critically dependent on the width and degree of compaction of the pipe bedding material and the stiffness of the native soil. A flexible pipe should be totally surrounded with granular bedding material. Sufficient trench width each side of the pipe is essential to allow correct placement and compaction of the granular bed and surround. Incorrect placement will lead to distortion of the pipe walls. A geotextile membrane is often employed to avoid loss of fines from the native soil and/or to stiffen up the pipe zone material. Due care should be exercised during placement of aggregates so as not to damage any of the pipes, especially the flexible types which are more susceptible to such type of damage. Flexible pipes may require import of backfill if the existing material is too coarse and contains large amounts of sharp pieces. Joints Joints are an essential component of any pipeline system providing continuity between individual pipes. The number and type of joints can considerably affect cost and timescales for a particular pipeline. Flanged joints for rigid connections are normally employed for above ground use and within pumping stations. Cautionary notes should accompany any joints between GRP and DI flanged pipes/fittings as the correct bolt tightening sequence should be followed to prevent damage. Nuts, bolts and washers should be specified to suit the prevailing conditions e.g. stainless steel in wet and/or corrosive environments. For buried pipelines it is important to allow for some movement of the pipeline which occasionally occurs through differential settlement of the soil. There are three principal types of flexible joint: • • •

Spigot and socket. Sleeve coupling. Bolted coupling.

Push fit spigot and socket joints comprise a belled end integrally formed at one end of the pipe. This has a slightly enlarged internal diameter sized to receive the spigot end of the next pipe. Sealing of the joint is achieved with flexible elastomeric gaskets which allow a limited degree of angular rotation and longitudinal movement without risk of leakage or fracture. A sleeved coupling comprises a short cylinder into which the machined ends of the two pipes are inserted. Sealing is affected by two elastomeric gaskets, one for each end of each pipe, which also allow movement of the joint. The sleeve can have a raised ring, or central locating register on the inside to ensure that the pipes are correctly inserted.

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Bolted couplings comprise a cast iron or steel sleeve which is located over the ends of the two pipes to be joined. Detachable flanges, located outside the sleeve are bolted together compressing rubber gaskets on the outside edges of the sleeve to effect sealing of the joint. All metal parts should have a protective coating e.g. fusion bonded epoxy or nylon. Joints can also be formed by solvent welding (PVCu pipes) and in-situ lamination (GRP pipes). The pipes themselves are flexible and can accommodate limited differential settlement through longitudinal bending. For HDPE pipes and fittings two types of fusion welding of joints is available buttfusion welding and electrofusion welding. The latter method is expensive and should be avoided where possible. Universal mechanical couplers are also available particularly for jointing HDPE to pipes/fittings composed of different material. Flanged joints can also be formed, generally comprising a slip-on galvanised mild steel flange restrained by an integral stub return on the pipe end. Pipe Handling, Storage and Laying It is imperative that manufacturers’ recommendations for handling, storage and laying are strictly followed. Each material has its frailties and rejection and repair strategies should be assessed at tender stage. The manufacturer should be encouraged to attend site to evaluate the performance of the contractors’ personnel to handle, store and more importantly to correctly install and backfill the pipes to provide optimum performance throughout the lifetime of the pipes.

4.

STRUCTURES Structures within the networks are usually constructed using concrete, either insitu poured or with pre-cast elements or a combination of both. Concrete is a relatively cheap material produced locally using locally sourced materials, cement, aggregates, clean water, admixtures etc. Approved readymix companies and precast yards should be selected to provide concrete. Auditing of the facilities is essential to verify that a quality product is supplied. A good guide for properties of concrete constituents and properties is provided in the CIRIA Guide to concrete construction in the Gulf region. Also useful is ACI 305R Hot weather concreting. Generally two classes of concrete are required to be designed for use on networks- a structural grade which will reflect the compressive and tensile strength and durability requirements and a non-structural grade for blinding etc where strength and durability are not a major requirement.

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Concrete mix designs should be designed to BS 5328 or equivalent. Trial mixes should be conducted on each trial mix to confirm the suitability and the properties of fresh concrete and hardened concrete. The approved mix designs should be continually assessed by frequent site sampling and testing. Limits should be derived from the trial mix which will govern the quality of the concrete supplied throughout the remainder of the project using that particular mix design. Tests for concrete are generally: • •

For fresh concrete bleed, setting time, slump and slump retention, temperature, bulk density. For hardened concrete 7 & 28 day compressive strength, density and durability tests such as rapid chloride penetrability (RCP) test to ASTM C1202 and /or Water penetration to BS EN 12390-8.

Testing should also be conducted on constituent materials within the concrete mix e.g. aggregates, water, cement, admixtures, mineral additives to the relevant standards. In addition to trial mixes, site dummy trials should be carried out to assess the ability of the contractor to work and compact the proposed mix designs and the equipment he will use. The dummies should reflect the structural designs e.g. shutter material and releasing agent, reinforcement type and spacing, spacers to be used, wall and floor/base dimensions, curing regime, striking shutters. The dummy and cubes from the same mix should be cored at 7 and 28 day age and tested for compressive strength, RCP, Water Penetration and water absorption. The results should be compared to cube trials. In the event of a dispute on placed concrete quality, the structure can be cored and tested and the results compared to the trial. The dummies should be assessed for finish and defects. The dummies can also be utilised to provide surfaces for further site demonstrations e.g. repair materials, coatings, tanking. For tanking demonstrations, pipe entries should be introduced into the dummy to demonstrate the contractor’s ability to successfully overcome this detail. Care should be taken as to the temperature of water being used in the mixes. Most readymix companies have chillers and large capacity reservoirs to keep o water below 5 C, but in Middle East summer months the high temperatures require the addition of ice to control the concrete temperature. This ice should be flaked to allow access to more surface area and therefore to melt quicker. o Concrete temperature as delivered to site should not exceed 32 C, and no o concrete should be poured when ambient temperature is 40 C and rising. Care should also be taken to shade reinforcement prior to pouring as the surface o temperatures of exposed steel can exceed 70 C. Curing is an important process for obtaining successful concrete structures. Wet curing is the preferred method although there are many curing compounds that

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could be assessed for use. Caution should be taken that curing compounds do not affect any finish coats that are required. Consideration should be given to the new generation of concretes available in the market. These include cement replacement with mineral additives and selfcompacting concrete. Self compacting concrete as it infers does not require any compaction and as such there is no need for concrete vibrators and allows a reduction in manpower. Reinforced Concrete pipes can differ in their manufacture depending on the application. GRP concrete surround pipes for sewage application are generally constructed using the approved structural grade concrete and an applied external protective coating. A new concrete design may be necessary for these pipes if they are to be jacked in Non Disruptive Method as opposed to open-cut laying. RC pipes for stormwater or irrigation are generally produced in a factory with a factory prepared mix design with a reduced w/c ratio of 0.28-0.30 with integral HDPE internal liner and a spray applied protective external coating. All concrete used in construction work must have a certain strength, regardless of its application. The strength of concrete lies in its ability to resist various types of forces. These may result from applied loads, from the weight of concrete itself, or more commonly, from a combination of both. However, a high strength alone does not guarantee long-term performance of a concrete structure. The durability of concrete is probably the single most important property. The durability of concrete can be defined as its ability to resist weathering action, chemical attack, abrasion, or any other form of deterioration. A durable concrete should maintain its original form, quality and serviceability when exposed to surrounding environment for a long service life. Water is responsible for many types of physical processes of degradation. It also serves as the carrying agent of soluble aggressive ions that can be the source of chemical processes of degradation. Tests and field experience have demonstrated that compressive strength is the most important single factor controlling the physical degradation of concrete. Generally two factors leading to the chemical degradation of reinforced concrete is sulphate and chloride attack. Sulphates and chlorides are found in abundance in the soil and groundwater in Middle East. The sulphates attack the concrete, while the chlorides cause corrosion of reinforcing steel. The chemical processes involved in both cases are complex and these are described briefly in the following section. Ordinary Portland Cement (OPC) Versus Sulphate Resisting Cement (SRC)

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The British and American Standards governing Portland Cement classify several different types of cement based on their chemical compositions. The differences in chemical composition impart different properties to the cements. The resistance of Portland cement to sulphate attack is traditionally related to the proportion of C3A (tricalcium aluminate) in the cement. It is known that C3A combines with any available pre-setting and post-setting sulphates causing swelling, when excessive, and thus resulting in early cracking of concrete, caused by an increase in solid volume. Later, durability problems can also be caused by crystallisation of calcium sulphate when appreciable amounts of C3A are available simultaneously with abundant sulphate ions in contacting water or soil. Experience has shown that the maximum allowable proportion of C3A in cement, which will not render itself to sulphate-related problems, about 5%. This sets the upper permissible limit for SRC. Most other types of Portland cements, as classified by international standards, have maximum C3A limit ranging from about 7% to 15%. Such proportions of C3A can be alarming, if the concentration of sulphate ions is excessive. OPC has no specified limit on C3A content. Therefore, it can contain significantly higher amounts of it and any concrete made with OPC will be more susceptible to sulphate attack. Another property of OPC which can have a detrimental effect on the performance of concrete is the heat of hydration. Heat of hydration is the heat generated when cement and water react. A key concern for concrete in the field is thermal cracking. Because the cement hydration reactions are exothermic, large temperature gradients of the order of 50°C may be generated within a concrete structure. The large temperature gradients can cause thermal cracking. The major components which contribute to the heat of hydration in Portland cement are tricalcium aluminate, tricalcium silicate, tetracalcium aluminoferrite and dicalcium silicate. The combined content of the aforementioned components of cement are significantly lower in SRC than in OPC. Thus, as a consequence SRC will generate less heat during the hydration process. No concreting should take place at above 40°C. Classification and Applicable Standard There are five general types of cement classified by ASTM C 150. The five types are designated as Type I through Type V with each classified for a particular type of application based on its properties. OPC in designated as Type I and SRC is designated as Type V. Additives Relatively small quantities of other materials, called additives or admixtures, can be added to concrete to modify its properties in either fresh or hardened state. The additives used to modify the properties of fresh and hardened concrete are of the following general categories:

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• • • • • • • • •

Water-reducing admixtures and workability aids. Superplasticizers and high-range water-reducing admixtures. Air-entraining agents. Accelerators. Retarders. Waterproofers. Viscosity modifiers. Resin bonding agents. Fungicides, etc.

Additives may be useful for specific applications, but the claims made by manufacturers of such products should be well supported with long-term, impartial test results. This applies particularly to the permanence of the effects claimed. Extensive field data indicates that most of the additives used to modify the properties of fresh concrete, to aid in its ease of placement, such as waterreducing agents, workability aids, and superplasticisers, do possess the properties claimed and are beneficial. The other types of admixtures which modify the properties of hardened concrete have frequently been controversial with conflicting results, obtained by different parties involved in testing. Additionally, the increase in unit costs of concrete associated with the use of such types of additives cannot be justified, in most cases. In general a well-produced Portland cement concrete, with appropriate protection when necessary, will perform adequately for the duration of its design life without the need for any expensive property-modifying additives. The following simple measures if implemented and strictly enforced will significantly improve the durability of concrete. • • • • •

Use of high quality aggregates. Use of minimum water-cement ratio. Avoidance of segregation and elimination of bleeding. Use of properly-timed finishing and curing procedures. Use of surface barrier sealants and coatings, waterproofing membranes, etc.

The use of concrete additives should be evaluated on a case-by-case basis for particular applications. If required to be used, ASTM C 494 and BS 5075 should be referred to for specification requirements. Cement Replacement There are cementing materials which are sometimes used as a partial replacement of Portland cement in concrete mixes to achieve certain desired properties. Such types of materials are widely used in Europe , USA and recently in Middle East for special applications. They have certain benefits over plain Portland cement concrete and their use should be evaluated on an as-needed basis Three of the most common one are briefly discussed below:

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•

•

•

Ground Granulated Blast-Furnace Slag (GGBS) is a by-product of the manufacture of iron from iron ore. The slag is composed mainly of calcium and magnesium silicates and alumino-silicates. Blending of GGBS with a Portland cement produces a slower and sometimes useful strength gain. BS 6699 gives composition and performance requirements for GGBS. GGBS is available in the Gulf region and is manufactured to high standards. Its use increases density and also provides good resistance to sulphates. A maximum cement replacement of 70% GGBS / 30% OPC is allowable and is recommended in Europe for concreting in the marine environment. Pulverised Fuel Ash (PFA) is the most common cementing material used as a partial replacement in concrete. It is electrostatically precipitated from the exhaust fumes of coal-fired power stations burning pulverized coal. Blending of PFA with Portland cement slows the rate of strength development, however, the cement may generate heat less quickly and be more chemically resistant in some circumstances. BS 3892 gives composition and performance requirements for PFA. Condensed Silica Fume (Micro-Silica) is a high purity silica cementing material which has a very fine particle size; much smaller than that of cement or PFA. Silica fume is so fine that it can be used to fill the interstices between cement particles and it reacts rapidly with the cement hydration products. It is a by product of the production of silicon and ferrosilicon being collected by cooling and filtering of furnace gases. When mixed correctly in proportion of 6% to 10% by weight of OPC, silica fume can result in producing dense concrete with very high strengths and good chemical resistance.

Protective Coatings The service environment of network structures such as pipelines, manhole chambers, culverts, outfalls, etc. in the Middle East is considered very severe. High concentrations of sulphate and chloride ions in the surrounding soil, groundwater and effluent present an environment which makes all concrete structures susceptible to significant deterioration. New structures should be properly protected by means of surface barrier sealants, coatings and membranes in order to preclude chemical attack and significantly improve their service life. The protection of concrete will be necessary for buried structures such as manholes, inlets, catch basins, etc. and exposed structures such as outfalls, headwalls, etc. For buried structures, an external waterproofing membrane should be applied to all surfaces. The membrane can be either a self-adhesive or a torch applied type, consisting of a rubberised bituminous compound coated to one side of a polyethylene sheet. Alternatively, the waterproofing membrane may be a liquidapplied elastomeric type.

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It is worth noting that in hot climates, problems can be experienced with the selfadhesive type membrane. The bituminous compound softens in the heat when exposed to direct sun light for long periods of time and the membrane will sag or slide off vertical surfaces if not protected or backfilled soon after application. The torch applied protective membrane is much more robust in this regard. The membrane, whatever the type, should be protected by a suitable protection board so that no damage occurs to it during backfilling operations. For structures in splash zones such as headwalls, outfalls, etc. where exposure to wetting and drying cycles are expected, the exposed concrete surfaces can be coated with a protective coating, 200-500 microns thick, of a solvent free polyamide epoxy coating or other suitable system such as an elastomeric aliphatic acrylic on a silane-siloxane, impregnating, internal membrane-forming, concrete clear sealant primer. Regardless of the system used, the coating system should possess the following performance criteria, as a minimum: • • • • • •

Reduction in water absorption per BS 1881, equal to or better than 95%. Reduction in chloride ion penetration per BS 1881, equal to or better than 99%. Solids content by volume, equal to or better than 50%. 0 Crack spanning ability, equal to or better than 2mm at 40 C. Tear resistance per ASTM D624, equal to or better than 12 N/mm. Resistance to salts, alkalies and acids.

Reinforcement Bars Steel reinforcing bars when correctly placed in a concrete matrix permit it to be formed into many structural shapes which can carry bending moments and their associated tensile and shear forces. Without this reinforcement it would not be possible to, cost effectively, construct most of the structures commonly found today in infrastructure projects. Plain (Uncoated) Reinforcing Steel Until recently the reinforcement employed in reinforced concrete was almost always uncoated mild or high yield steel. If the workmanship was poor: e.g. reduced cover to the reinforcement; porous concrete, or the environmental conditions were aggressive: e.g. heat; moisture; high concentration of chlorides, then corrosion of the steel would ensue reducing the service life of the structure. Corrosion of steel is an electrochemical process. In order for corrosion to take place in reinforced concrete, there must be an anode where oxidation occurs, a cathode where reduction occurs, an electrical conductor and an aqueous medium. Both oxygen and moisture must be present in order for corrosion to occur. Normally the alkaline environment of concrete provides a natural degree of protection against corrosion to the reinforcement where the pH is greater than 12.5. The concrete reacts with the steel to form a film that passivates and

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protects the steel. However, the intrusion of chlorides and other ions can undermine these protective qualities and may cause steel corrosion if oxygen and moisture are also present. These conditions are commonly found in stormwater drainage concrete structures which are constantly exposed to seawater and saline groundwater. Chlorides may also be introduced into the concrete through admixtures, contamination of concrete mix water or aggregates, or industrial chemicals. Carbonation can also reduce the alkalinity of concrete thereby permitting corrosion to occur Carbonation occurs when carbon dioxide from the air reacts with the concrete to reduce concrete's pH. It is normally a slow process, but can be accelerated by concrete cracking or inadequate concrete cover. Other factors that influence the rate of corrosion include concrete resistivity and permeability, temperature and depth of cover over the reinforcement. Cracks in concrete and galvanic effects due to contact with dissimilar metals can accelerate corrosion. When steel corrodes it forms rust that occupies a volume much greater than the steel itself. This exerts large expansive stresses on the surrounding concrete. Because the concrete is low in tensile strength, these stresses cause cracking and spalling, which, in turn, permits faster ingress of water, oxygen and chlorides, accelerating corrosion further. Corrosion adversely affects the structural performance of reinforced concrete by reducing the cross-sectional area of the steel thus reducing the steel’s tensile strength. Epoxy Coated Reinforcing Steel Epoxy coatings were first used on steel reinforcing bars on a bridge deck constructed in Philadelphia, Pennsylvania in 1973. Since that time, it has been increasingly adopted throughout North America, Europe and the Middle East for reinforced concrete structures exposed to potentially corrosive environments. Fusion-bonded epoxy coating principally protects against corrosion by serving as a barrier that isolates the steel from the oxygen, moisture, and chloride ions that are needed to cause corrosion. Epoxy coating also has a high electrical resistance, which blocks the flow of electrons that make up the electrochemical process of corrosion. In addition to serving as a circuit breaker, the coating protects in a way that is less obvious by reducing the size and number of potential cathode sites, which will limit the rate of any corrosion reaction that could occur. Epoxy coating starts out as a dry powder. When heated, the powder melts and its constituents react to form complex cross-linked polymers. The process of applying fusion-bonded epoxy coating to steel reinforcement involves four major steps of surface preparation, heating, powder application and curing.

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Proper surface preparation is important to assure that maximum adhesion will develop at the interface between the steel and the coating. The reinforcing steel is blast-cleaned to a near white metal finish using abrasive grit. This cleans the steel of contaminants, mill scale and rust. It also roughens the surface in order to give it a textured, anchor profile which provides mechanical anchorage. Texturing the surface also facilitates adhesion by increasing the exposed surface area of the steel and by providing more opportunity for the coating to chemically bond. Chemical pre-treatments are sometimes used to supplement blast cleaning and improve the long term adhesion of the coating. After blast-cleaning, the bars are heated to approximately 2300C. using electrical induction heaters. The heated bars are then passed through a powder spray booth where dry epoxy powder is emitted from a number of spray nozzles. As the powder leaves the spray nozzle, an electrical charge is imparted to the particles. These electrically charged particles are attracted to the grounded steel surface providing an even coverage of the coating. When the dry powder hits the hot steel, it melts and flows into the anchor profile and conforms to the ribs and deformations of the bar. The heat also initiates a chemical reaction that causes powder molecules to form the complex cross-linked polymers that give the epoxy coating its beneficial properties. Following powder application, the coating is allowed to cure for a short period of approximately 30 seconds during which it hardens. To facilitate handling, the curing period is often followed by an air or water quench that quickly reduces the bar temperature. The advantages and disadvantages of epoxy coated reinforcing steel are as follows: • • • •

Significantly improves the long-term durability of concrete, due to corrosion resistance against chloride attack. Damaged coating can be easily touched up onsite prior to concrete placement. Increased construction cost for reinforced concrete. Possibility of damaged epoxy coating being undetected and used. Damaged coating can make the steel prone to severe chloride attack. Inspection of epoxy coated rebar should be routinely conducted during construction to ensure that severe damages are detected and properly rectified prior to concrete placement. Note that ASTM standards for rebar coating do allow a certain amount of discontinuities in the coating layer.

Classification and Applicable Standards Reinforcing steel is classified according to its yield strength or ultimate tensile strength. ASTM A615M and BS 4449 are two of the most commonly used standards which govern the requirements of reinforcing steels. ASTM A 775 provides detailed specifications for the epoxy coating material and its application to the steel.

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5.

MANHOLES Manholes are generally designed in both cast in-situ and precast concrete with protective coatings on internal and external faces. For sewage applications the internal liner must be corrosion resistant and generally GRP with vinylester resin rich outer layer is used. For ease of construction it has been found that use of double-skin GRP units as shuttering has proved successful. The units can be manufactured in one piece for small depths but generally come as separate units that have to be in-situ laminated together. For stormwater and irrigation the manholes are constructed by conventional shuttering methods with external bituminous tanking and an internal coating of solvent free epoxy resin.

6.

MANHOLE COVERS Manhole covers are used to provide access to manholes and chambers which are typically constructed with a frame cast into the top opening area. Manhole covers are then installed in the frames to be flush with the top of the structure. The manholes are often located within road carriageways or footpaths and are thus subjected to vehicular and pedestrian traffic. In addition to being capable of withstanding applied loads, the covers must be durable. Many different types of materials, such as reinforced concrete, steel, and aluminium have been used for manhole covers but the most common material now in use is ductile cast iron. The early manhole covers were manufactured from grey cast iron which contains filamentous graphite particles. This has good corrosion resistance but is susceptible to brittle fracture and has to be manufactured in heavier sections to offset this characteristic. Today most manhole covers are manufactured from ductile cast iron which contains spheroidal graphite particles which reduces the risk of brittle fracture by providing slightly greater elasticity. Lighter sections can therefore be manufactured than for an equivalent strength grey cast iron cover making it easier to lift. However it is less corrosion resistant. Cast iron manhole covers are manufactured in several countries in the Gulf region, Europe and Australia. Care should be taken to the quality of the products offered both from a structural point of view and aesthetics. For sewage manholes and chambers the frames need to be gastight and watertight. This can be achieved by inclusion of a separate removal plate often manufactured in GRP with an EPDM rubber seal. Manhole covers are classified according to load classes in relation to the areas in which they will be installed. BS EN 124 provides detailed requirements regarding manhole covers. A durable coating should be applied to cast iron manhole covers for long-term corrosion protection. The coating should be a solvent-free,

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polyamine-cured epoxy paint, which should be applied to a minimum thickness of 400 microns.

7.

STEP-IRONS AND LADDERS Step-irons and ladders are used to access manhole chambers for maintenance and inspection. The steps or ladders are permanently attached to the internal wall of the manhole chamber and upon removal of the manhole cover an operator can climb down into the chamber. The steps or ladders must have sufficient strength to resist point loads or pullout forces which may be imparted to it. The top of the rungs should have a non-slip surface for safety reasons. Furthermore to avoid failure during use it is of the utmost importance for steps and ladders to be resistant against corrosion which can result from high temperatures, humidity, chlorides and hydrogen sulphide gas where sewage effluent is present. There are several types of materials which are used for steps and ladders in manholes which are discussed below. Step-irons and ladders are manufactured from stainless steel or cast-iron which are bolted or embedded into the concrete wall of the manhole to allow access. There are various types of stainless steel available for use in construction. They are more expensive than normal steels or cast-iron. Of the various types of stainless steel available, austenitic steel containing nickel and chromium has the greatest corrosion resistance for use in structural and civil engineering works. The minimum grade is to be grade 316 S31 to BS 790 Pt. 1. It is durable in most situations encountered in marine applications with the exception of anaerobic conditions, which may occur due to marine growth and in stagnant conditions where the oxygen supply is low. Under these circumstances, stainless steel, owing to the breakdown of the protective oxide film, is subject to pitting and crevice corrosion, a tendency that is increased in the presence of chlorides. To protect metal step-irons from corrosion they can now be obtained in encapsulated form in which they are totally sealed from the aggressive environment by either a plastic, e.g. HDPE, or an epoxy resin. The coating needs to be robust to withstand abrasion and impact loadings but these have generally proved to be very effective in eliminating corrosion failures. The increased degree of safety they provide justifies the small additional cost. Access ladders for manhole chambers can also be manufactured from corrosion resistant GRP. These are commonly manufactured by hand lay-up or pultrusion methods. The ladders are normally fixed to the internal wall of the manhole chamber by means of bolts embedded into the concrete or incorporated into GRP internal liner. In the hand lay-up method of production, a mould is used to cast a GRP laminate against it. A mould release agent is applied to the mould followed by alternating layers of resin and glass fibre reinforcing with hardwood rails and

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rungs until the desired thickness is achieved. The moulding is then allowed to cure before release from the mould. The pultrusion process of manufacture generally consists of drawing resin impregnated glass rovings or other specialist reinforcements, through a heated die in which cure takes place. However, pultruded GRP has not been very widely applied to the manufacture of manhole ladders probably due to the ease and simplicity of the hand lay-up method

8.

QUALITY CONTROL AND QUALITY ASSURANCE Quality of a material can be defined as the ability to satisfy defined, and implied, needs. This will often include compliance with national or international standards. Quality is rarely achieved without a formal system of controls being established, and implemented. There are three main requirements to ensure that quality standards can be achieved in a reliable and predictable manner: • • •

Quality control (QC) which is a system of documented procedures for manufacturing and inspection. Quality assurance (QA) which is the implementation of the quality control system by routinely providing evidence that all reasonable actions have been taken to achieve the required quality. Auditing which is routinely providing evidence that the quality control system is being implemented and that all reasonable actions have been taken to achieve the required quality

Quality management systems are now governed by ISO 9001:2000 Quality Management Systems – Requirements. It is becoming increasingly recognised worldwide that mandatory implementation of these standards does significantly help achieve desired quality standards and Directorate should insist that suppliers have quality systems in place which are regularly verified by certified external auditors before their materials are approved for use. A project is made up of a series of activities that contribute to its success. The choice of material and a high standard of specification alone cannot guarantee the satisfactory performance of a drainage system. Improper handling or installation of a high quality product will render it inferior. For example, GRP pipes are susceptible to impact damage during installation, which can easily occur without proper training of operatives and with poor supervision. Such damage is not easily detected by visual examination and can cause cracking of the fibre-resin matrix leading possibly to the eventual failure of the pipe. In concrete construction, the durability of an otherwise superior mix is significantly reduced if poor placement practices result in inadequate compaction, honeycomb formation, and insufficient hydration due to improper curing.

END OF SECTION

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SECTION 2


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STORM WATER SYSTEM DESIGN ..................................................................... 4

2.1.1 2.1.1.1 2.1.1.2

GENERAL ............................................................................................................. 4 Overall System Planning ....................................................................................... 4 System Performance Requirements...................................................................... 5 TABLE 1 – PRIORITY GROUPS ........................................................................... 5 2.1.2 RAINFALL & RUNOFF .......................................................................................... 5 2.1.2.1 Storm Profiles........................................................................................................ 5 2.1.2.2 Storm Return Period.............................................................................................. 5 2.1.3 DESIGN ................................................................................................................ 6 TABLE 2 – DESIGN FLOWS ................................................................................. 7 2.1.4 OTHER CONSIDERATIONS................................................................................. 8 2.1.4.1 Flow Attenuation.................................................................................................... 8 2.1.4.2 Collection ..............................................................................................................9 2.1.4.3 Soakaways............................................................................................................ 9 2.1.4.4 Groundwater Control ............................................................................................. 9 2.1.4.5 Lifting Pumping Stations...................................................................................... 10 END OF SECTION.............................................................................................................. 10

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2.1


2.1.1

GENERAL

2.1.1.1

Overall System Planning Overall system planning shall take account of the following: • • • • •

•

Stormwater drainage must be considered in the context of an overall drainage plan. Drainage of each site should be considered for the effect it may have on the overall drainage area. Watershed lines should be identified to establish the drainage basin. Stormwater collection can then be developed for sub areas to suit outfall locations and topography and to offer a cost effective solution. The approach should reduce drain lengths and hence depths which is especially important when considering an outfall adjacent to the sea. System planning should endeavour to achieve a fully gravitational arrangement whenever possible. Town Planning Development plans indicate the land use within the drainage area. These plans identify principal roads, access and service roads, parking facilities and footpaths, residential, industrial and recreational areas and landscape/park areas. This information should be used to assign system performance and runoff factors. Service reservations are allocated by Town Planning Department and best use of these should be made to ensure optimum design. Conflict with other services is always a potential problem and should be considered and clarified at the earliest.

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2.1.1.2

System Performance Requirements The performance required is dependent on the importance of the catchment area and the possible consequences of it flooding. Areas under consideration should be classified into the priority groups given in Table 1 below to establish the level of service to be provided. TABLE 1 – PRIORITY GROUPS

Priority

Catchment Type

1

Major roads, freeways, arterials and underpasses

2

Business sector, minor and service roads

3

Residential sector roads

4

Industrial sector roads

5

Open areas, parks and areas of infrequent use and not subject to building flooding

In the case where the route of a drain travels through areas of differing priority, the criterion applied to the upstream area of higher importance should be carried through the downstream area of lower importance. 2.1.2

RAINFALL & RUNOFF

2.1.2.1

Storm Profiles In the Gulf Region, storms are historically intense, of short duration and very infrequent. Average annual rainfall in the Abu Dhabi area is generally less than 100mm and occurs on but a few days during the year between the month of October and April. Analysis of available rainfall records has produced graphs numbers 1 and 2 for storm frequencies of 1 in 1 year to 1 in 100 years. Graphs are attached in Appendix 1 to this section of the DSM.

2.1.2.2

Storm Return Period The approach to stormwater drainage design should achieve a sensible balance between cost and acceptable level of performance.

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For the most part of the year, the Abu Dhabi area has no rainfall and it would be uneconomic to provide a system with a long return period except in very specific locations. In Abu Dhabi, storm drainage and foul sewerage are provided as separate systems. The consequences of flooding in the stormwater drainage system due to the design storm being exceeded is less of a health hazard than in a combined system. In addition, the mode and amount of rainfall allows ample time for draining away the surface water. With these prevailing conditions, it is generally considered acceptable to tolerate some temporary ponding or surface storage of rainfall. It must also be remembered that stormwater drainage systems have inherent storage capacities. Actual surface flooding will probably occur at a much lower frequency, between 1 in 3 and 1 in 5 years, depending upon the amount of surcharge that the system can tolerate. A system may flow surcharged without surface flooding. A 1 in 2 year return period should be chosen for design as standard with a 1 in 5 or 10 year storm being used for critical areas. 2.1.3

DESIGN Design parameters are as follows: •

General: a) b)

c)

d)

The design procedure adopted is dependent on the system outlet condition and whether or not it is submerged. For systems with a free outlet, the design shall use the Rational Method with pipe sizes chosen to match the design peak flow, commencing with the most upstream length on the longest line. Where the outlet is submerged normally when outfalling to the sea, much of the system will be below high tide level and thus will remain full of water most of the time. In such cases, pipes are sized using a backwater hydraulic grade line computation commencing at the most down stream section and using the design flows calculated by the Rational Method. Total friction loss for the main pipeline must not exceed available head difference between street level on the most upstream end and design elevation on outlet. Moreover losses at manholes and junctions must also be included. Both methods involve reiterative computation to determine the optimum pipe sizes and it is preferable to carry out detailed design by

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computer to enable the designer to examine system performance and be assured of its suitability. •

Storm return period: a) b) c)

•

1 in 2 year generally 1 in 5 to 10 years if area considered particularly sensitive or prone to flooding However, if a higher level of performance is considered necessary then this shall be discussed and approved by the Directorate.

Storm duration for the priority groups defined in Table 1 shall be as given in Table 2 below. TABLE 2 – DESIGN FLOWS

Priority

•

1

Time of concentration

2

1.5 X Time of concentration

3


4


5


Rainfall intensity: a)

•

Duration Equal To

Use graphs numbers 1 and 2 attached in Appendix 1.

Runoff coefficients: a) b) c)

Paved areas Unpaved areas Walled plots

0.9. 0.25. 0.2.

In low density residential areas it is common practice for individual properties to have boundary walls which effectively contain the runoff within the property and delay/reduce potential runoff onto the roads and into the drainage system. Ignoring the effect of these boundary walls would lead to unrealistically high flows and uneconomic design.

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•

Time of entry: a)

•

Hydraulic design: a)

•

0.75m/s desirable but dependent on system planning.

Pipes should be sized to take the design flow but with a minimum diameter of 300mm. Oversizing in the upper reaches of the system should be avoided as greater flows would be passed more quickly when the design storm frequency is exceeded. This could cause flooding in the lower reaches of the system at an earlier stage.

Minimum gradient: a)

•

0.013. 0.6. 140 for pipe diameters >500mm. 135 for pipe diameters< 500mm.

Minimum pipe diameter: a)

•

Manning Colebrook-White Hazen Williams

Minimum velocity: a)

•

Design of sewers should be based on equations such as Manning, Colebrooke-White and Hazen Williams.

Pipe roughness factors shall be as follows: a) b) c)

•

5 minutes

0.04% desirable but dependent on system planning.

Collection of runoff: a)

By kerb inlet with catchbasins at 20m to 50m spacing dependent on road grading and system performance requirements.

2.1.4

OTHER CONSIDERATIONS

2.1.4.1

Flow Attenuation The design philosophy already incorporates an overall attenuation of flow and provides for some surface ponding. However, further localised control and balancing of flows should be examined. It could prove cost effective to store flows from upstream areas and hence reduce the required carrying capacity of the down stream system.

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Oversized trunk sewers or controlled surface ponding in paved areas are most suitable for urban areas where land is at a premium. In some locations where ground conditions allow, overflow to soakaways could provide a practicable solution. 2.1.4.2

Collection Wind blown sand is a particular feature of the Abu Dhabi region causing sand to accumulate against road kerbs. Special measures need to be taken to prevent the passage of sand into the system to minimise maintenance requirements. The preferred method of collection of stormwater runoff is by kerb inlet catch basin structures. The clearance rate should correspond to the level of service required for the catchment area with kerb inlets spaced to suit. Catchbasins should be provided at each kerb inlet and at bends in the collector drains.

2.1.4.3

Soakaways Soakaway arrangements should be flexible to suit the requirements of the location and layout. Various combinations of chamber/pit and trench or mattress should be examined. The mattress type has particular suitability where the ground water table is high. A site investigation should be carried out to determine the soil gradation, structure and density and hence infiltration rate. Consideration should be given to the sinking of cased boreholes to sub strata aquifers to enhance the outflow rate.

2.1.4.4

Groundwater Control Consideration should be given to installing groundwater collection systems at the same time as the stormwater system. French drains comprising porous pipes and granular material wrapped in geotextile are the preferred arrangement. These can be constructed within the stormwater drain trench and connected to it at suitable locations. The drawdown required is normally in the 1.5m to 2.0m range.

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Rates of flow from groundwater systems is relatively low compared to stormwater design flows. It is not considered to include an allowance for groundwater flows in the stormwater drainage system. 2.1.4.5

Lifting Pumping Stations The provision of low lift pump stations should be considered so that the drainage system can be emptied for maintenance and to keep flow moving through the system in conjunction with groundwater lowering. A submersible type station with a suitable capacity should be designed in accordance with Section 3.2 of this manual - sewerage system design, but taking account of the following amendments: • •

• • • •

The determination of flow rates shall be based upon the design flow rates calculated for the run-off area Odour control facilities shall not be required for surface water pumping stations, but consideration shall be given to install more high powered water jetting facilities than that normally provided for Sewage Pumping Stations. This will allow for proper cleaning down of the Station before dormant periods of the year Axial type impellers may be considered in addition to mixed flow type Screens and macerators are not required for storm water pumping stations Because storm water can contain significant quantities of sand, the design of the sump shall ensure adequate provision to prevent the deposition of sand The area of land required for storm pumping stations shall be considered on a case by case basis and shall not comply with Table 4E of section 3.2.2.3 of this manual

Health & Safety requirements shall be as Section 3.3 of this manual - Sewerage System Design END OF SECTION

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SECTION 3

SEWERAGE SYSTEM DESIGN

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SEWERAGE SYSTEMS........................................................................................ 5

3.1.1 3.1.1.1 3.1.1.2 3.1.1.3 3.1.1.4 3.1.1.5 3.1.1.6 3.1.1.7 3.1.1.8

SEWERS .............................................................................................................. 5 Design Requirement.............................................................................................. 5 Design Capacity .................................................................................................... 5 System Layout....................................................................................................... 5 Site Features......................................................................................................... 6 Population/Water Usage Statistics ........................................................................ 6 Trade Effluents...................................................................................................... 7 Hydraulic Design Equations .................................................................................. 7 Design Flows......................................................................................................... 7 TABLE 1 – DESIGN FLOWS ................................................................................ 8 3.1.1.9 Other Criteria......................................................................................................... 9 3.1.1.10 Structural Design................................................................................................. 10 3.1.1.11 Manholes............................................................................................................. 10 3.1.2 PROPERTY CONNECTIONS ............................................................................. 11 3.1.2.1 Limit of Works ..................................................................................................... 11 3.1.2.2 Pipework ............................................................................................................. 11 3.1.2.3 Chambers............................................................................................................ 12 3.1.2.4 Sand Traps.......................................................................................................... 13 TABLE 2 – SAND TRAPS CAPACITIES ............................................................. 13 3.1.2.5 Grease Separators .............................................................................................. 14 3.1.2.6 Petrol/Oil Interceptors.......................................................................................... 15 3.2 PUMPING STATIONS......................................................................................... 16 3.2.1 3.2.1.1 3.2.1.2 3.2.1.3 3.2.1.4 3.2.1.5 3.2.1.6 3.2.2 3.2.2.1 3.2.2.2 3.2.2.3

GENERAL ........................................................................................................... 16 Location of Pumping Stations.............................................................................. 16 Selection of Equipment ....................................................................................... 16 Determination of Flow Rates ............................................................................... 16 TABLE 3 – MINIMUM PUMPED FLOWS ............................................................ 17 Electrical Equipment............................................................................................ 17 Environmental Aspects........................................................................................ 17 Arrangement Considerations............................................................................... 18 DESIGN .............................................................................................................. 19 Site Investigation ................................................................................................. 19 Substructure Configuration.................................................................................. 19 General Requirements ........................................................................................ 19 TABLE 4A – DESIGN PARAMETERS................................................................. 20 TABLE 4B – WET WELL ARRANGEMENT ........................................................ 21 TABLE 4C – DRY WELL ARRANGEMENT......................................................... 22 TABLE 4D – SUPERSTRUCTURE ..................................................................... 23

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3.2.3.2 3.3

TABLE 4E – EXTERNAL WORKS ...................................................................... 24 TABLE 4F – ANCILLARIES................................................................................. 25 TABLE 4G – INSTRUMENTATION ..................................................................... 26 PUMPING/FORCE MAINS .................................................................................. 27 Hydraulic Design ................................................................................................. 27 TABLE 5 – ENERGY LOSSES THROUGH FITTINGS........................................ 28 Other Features .................................................................................................... 29 HEALTH AND SAFETY....................................................................................... 31

3.3.1

DESIGN CONSIDERATIONS.............................................................................. 31

3.4

TRENCHLESS TECHNOLOGIES....................................................................... 31

3.4.1

ALTERNATIVE TECHNIQUES............................................................................ 31

3.5

SEWER REHABILITATION TECHNIQUES ........................................................ 32

3.5.1

ALTERNATIVE TECHNIQUES............................................................................ 32

3.2.3 3.2.3.1

END OF SECTION.............................................................................................................. 32

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3.1

SEWERAGE SYSTEMS

3.1.1

SEWERS

3.1.1.1

Design Requirement The Department will approve plans for new systems, extensions to new areas or replacement sewers only when designed upon the separate system, in which rain water from roofs, streets and other areas, and groundwater from foundation drains are excluded.

3.1.1.2

Design Capacity In general, sewer capacity should be designed for the estimated ultimate contributing population, except in consideration of parts of the systems that can be readily increased in capacity. A similar consideration should also be given to the maximum anticipated capacity of institutions, industrial parks etc. In determining the required capacity of sewers, the following factors should be considered: • • • • • •

Maximum hourly domestic sewage flow. Additional maximum sewage or waste flow from industrial plants. Topography of the area. Location of the sewage treatment plant. Depth of excavation. Pumping requirements.

The basis of design for all sewer projects shall accompany the plan documents. More detailed computation may be required by the Department Design SubCommittee for critical projects. 3.1.1.3

System Layout The layout should take account of the following: • • •

Best use of available reservations should be made to ensure economy of design. Sewer depths should be sufficient to accommodate not only all existing properties but also any future properties likely to be erected within the area. In certain cases, the depth of basements may need to be borne in mind. Where main sewers are laid at considerable depths it may be more economic to lay shallow rider sewers to receive the local house connections and to connect the riders at a small number of convenient points into the main sewer.

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• • • • • • • •

Consideration should be given to the likely form and method of construction as a consequence of depth and other factors such as nature of ground, groundwater and the proximity of foundations, services etc. Sewers should generally be kept as short as possible and unproductive lengths avoided. Sewer gradients should be chosen to ensure velocities are high enough to prevent deposition of solid matter in the invert. Where a scheme is to be developed in phases, consideration should be given to the likely flows following the initial stages of construction so that self cleansing velocities are attained at times of peak flow each day. The route and depth of a new sewer should take account of land where there is a possibility of future development. Steep gradients/high velocities should be avoided to reduce problems of turbulence and the consequent gas/odour release and increased corrosion potential. Adequate access provision for maintenance Consideration should be given to such aspects as: a) b) c)

• • • 3.1.1.4

The position of other existing or proposed services. The proximity of existing buildings and their foundations. The nature of the road construction.

The impact of the construction of the sewer and subsequent maintenance activities upon road users and the general public. When areas are being improved or redeveloped the possibility of replacing the existing sewerage system should be considered with a view to its relocation to a more suitable layout. Septicity development should be avoided as far as possible.

Site Features Information on topography, below ground conditions, existing services, service reservations, future development etc should be collected. Ground investigation should be considered in the light of the knowledge of site conditions already gained and of the probable disposition and depths of excavation. The positions of all existing services should be ascertained as accurately as possible and physically checked by exploratory holes if considered necessary Service reservations are prescribed by Town Planning Department.

3.1.1.5

Population/Water Usage Statistics Potable water consumption is not monitored and hence statistics are not available for assessment.

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In this region a large quantity of potable water is drawn from the distribution system and used for irrigation purposes both for private developments and by the Agricultural Section. 3.1.1.6

Trade Effluents The discharge of trade effluents to a sewer is subject to conditions prescribed by the Department. Compliance with such conditions may require the discharge to be pretreated.

3.1.1.7

Hydraulic Design Equations Design of sewers should be based on equations such as Manning, ColebrookeWhite and Hazen Williams Pipe roughness factors shall be as follows: • • •

3.1.1.8


0.013. 0.6. 140 for pipe diameters >500mm 135 for pipe diameters< 500mm

Design Flows •

Per capita flow: a)

Sewer systems shall be designed on the basis of details given in Table 1 below.

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TABLE 1 – DESIGN FLOWS

Development Type

Occupancy rate

Daily Flow Litres/Head

Low Cost Residential

12 - 16

180

Medium Cost Residential

12 - 16

225

High Cost Residential

12 - 16

275

Large Villas/Palaces

15 - 50

275

High Rise

Number of flats X 5

275

Educational

Number of pupils + staff

70

Number of beds + staff

350

Commercial

Number of staff

50

Mosques

Floor area m

Wet Industry

Not applicable

Varies to be advised

Dry Industry

Number of staff

50 at 8 per m

Army Camps

Number of occupants

100

Hospital

1

1

2

100

2

Number of persons taken as twice the number of beds

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•

Peak flow. Sewers shall be designed on a peak flow basis using one of the following methods: a)

b) c)

3.1.1.9

The ratio of peak to average daily flow as determined from the equation Qmax / Qave = 18 + √P / 4 + √P where P is the population in thousands. Value established from a study acceptable to the Directorate. Use of other values for peak design flow if justified on the basis of extensive documentation

Other Criteria •

Depth of flow: a)

•


•

No gravity sewer conveying raw sewage shall be less than 150mm in diameter.

Minimum and maximum velocity: a)

•

The design depth of flow should be 0.7 of the pipe diameter at peak flow.

The minimum velocity should be about 0.75 m/s at peak flow and in general the maximum mean velocity should not exceed 3 m/s at the design depth of flow.

Minimum gradient: a) b)

150mm diameter 200mm diameter

0.75%. 0.30%.

The Operating Division shall be notified of those locations where gradients are less than those associated with minimum velocity. •

Maximum depth to invert: a)

•

Nominally 10m.

Minimum cover: a) b) c)

Without protection With protection Under existing services

1.2m (depth to top of pipe). 0.5 m (depth to top of protection). 0.3m (minimum distance between).

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•

Protection: a) b)

Concrete bed and surround. Bunds can be used in ground to be raised if initial cover is 1.0 to 1.5m.

When at shallow depth beneath highway then design check to be carried out. 3.1.1.10 Structural Design •

Soil loading: a)

•

Superimposed loading: a)

•

Use highway design standards as appropriate.

Bedding factors (or load factors): a)

•

Use the Marston formulae

Refer to standard drawings.

Pipe strength: a) b)

National standards specify strengths for diameters and class of rigid pipe. For flexible pipe use the Spangler equation. The initial pipe stiffness should be used for calculating the initial pipe deflection expected after backfilling. For long term deflection, the pipe stiffness taken as 0.4 x initial pipe stiffness for GRP pipes and 0.2 x initial pipe stiffness for PVCu pipes.

3.1.1.11 Manholes •

Location: a) b) c) d) e) f)

•

At changes of slope in pipeline. At changes of direction. At junctions including property connections. At changes of pipe diameter. At termination of sewers. At any designated special locations.

Spacing: a) b) c)

150mm 200mm to 500mm 600mm to 1000mm

up to 60m. up to 100m. up to 120m.

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A greater spacing of 120m or more may be used for larger sewers. •

Types: a) b)

•

Manhole cover levels: a) b) c)

•

Paved areas Landscaped areas Open, unpaved areas

Rectangular Circular

Use to be limited to unavoidable situations. Minimum drop for 150mm diameter pipe is 0.7m. See standard drawing.

3.1.2

PROPERTY CONNECTIONS

3.1.2.1

Limit of Works Works within property lines: a) •

Refer to "Developer's Guide to Building Drainage."

Future connection provision: a)

b)

3.1.2.2

600mm x 750mm. 750mm diameter.

Drop manhole or backdrop connection: a) b) c)

•

cover level = final paved level. cover level = final ground level +0.1m. cover level = final ground level +0.25m.

Manhole covers: a) b)

•

Refer to standard drawings. Use of manholes is preferred on 200mm diameter. pipes if depth is less than 2.0m.

A chamber to be constructed in the approved reserve at the boundary of each known plot such that a connection can be made at any time in the future. Approval is required from the Directorate for each Contract. Also, stub pipes to be incorporated in selected manholes to facilitate system extension and property connection of possible future development.

Pipework •

General arrangement: a)

Each plot to drain separately to an inspection chamber outside boundary.

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•

Minimum diameter: a)

•

Gradient: a) b)

•

150mm. 100mm pipes may be used if necessitated by existing drainage.

Minimum Maximum

0.75%. 10%.

Minimum Cover: a) b) c)

1.2m (depth to top of pipe). 0.5m (depth to top of protection). 0.3m (minimum clearance between services) If plot internal system requires, then minimum cover with protection can be reduced to 0.3m. •

Protection: a)

3.1.2.3

Without protection With protection Under existing services

Concrete bed and surround. When at shallow depth beneath highway then design check to be carried out.

Chambers •

Classification: a) b)

•

Spacing: a)

•

Spacing of collection chambers and inspection chambers should be between 20m and 50m.

Chamber cover levels: a) b) c)

•

Refer to standard drawings. Non standard chambers may be required to accommodate the arrangement and number of outlets from the property internal drainage layout. Also in restricted areas where plan area/depth requirements are not available.

Paved areas Landscaped areas Open and unpaved areas

cover level = final paved level. cover level = final ground level +0.1m. cover level = final ground level +0.25m.

Chamber covers:

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a) b) •

600mm x 750mm. 750mm diameter.

Venting: a)

3.1.2.4

Rectangular Circular

Should be provided at head chamber of every branch if not already installed within the property and should extend to 1m above roof of building.

Sand Traps Sand traps should be installed on property connections where required and approved by the Directorate. •

Location: a)

•

The trap should be installed at the upstream end of the property connection and upstream of the grit separator or petrol interceptor. It should be located to afford adequate access for maintenance and emptying.

Capacity: a)

As per German Standard DIN 1999 Part 2, provide recommended minimum capacities for flows up to 6 l/s as follows. TABLE 2 – SAND TRAPS CAPACITIES

Flow (l/s)

2

3

4

5

6

Internal Dimensions mm

1000 X 800

1400 X 800

1750 X 1000

2000 X 1000

2500 X 1000

Minimum Capacity Litres (l)

520

840

1400

1800

2500

Also the minimum capacity for car wash plants should be 5000 litres even when the rate of flow is under 6l/s. These capacities assume an emptying schedule which ensures that only half the trap capacity has been utilised and a maximum interval of six months.

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For a more frequent emptying schedule of say once per month, the following guidelines can be used: a)

b)

c)

3.1.2.5

For every l/s wastewater throughflow, a multiple of 100 litres of trap capacity shall be provided for an anticipated small accumulation of sediment. For every l/s wastewater throughflow, a multiple of 200 litres of trap capacity shall be provided for an anticipated normal accumulation of sediment. For every l/s wastewater throughflow, a multiple of 300 litres of trap capacity shall be provided for an anticipated large accumulation of sediment.

Grease Separators Property connections to such premises as catering establishments, butchers and meat factories, fish processing establishments and some aspects of slaughter houses first require the elimination of grease. The wastewater should be taken to a grease separator prior to connection to the sewer. •

Location: a)

•

Grease separators should be provided as closely as possible to the outlet from the premises and wherever possible in the open and away from traffic but readily accessible for cleaning.

Arrangement: Provision of the following is emphasised. a) b) c) d) e)

•

Adequate ventilation. Odour seals to upstream outlets like flow drains and to the separator outlet. Secure covers. Adequate access to all parts requiring maintenance including the inlet and outlet pipes. A minimum gradient of 1 in 50 on the inlet pipe.

Capacity: Provide, according to German Standard DIN 4040, a period of stay of wastewater in the separation compartment as follows: a) b) c)

3 mins minimum for 2 l/s to 9 l/s throughflow. 4 mins minimum for 10 l/s to 19 l/s throughflow. 5 mins minimum for 20 l/s and over throughflow.

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For example a catering establishment serving 400 hot meals per day will discharge a peak flow of around 4 l/s. A further 0.25 l/s should be added for every additional 100 heads. Also consider the following: Compartment water surface should be 0.25m2 per l/s inflow. Ratio of width and length should be 1 : 1.8.

a) b) 3.1.2.6

Petrol/Oil Interceptors Petrol interceptors should be provided on the outlets from vehicle washing bays, maintenance areas and the like prior to connection to the sewer. •

Location: a)

•

Interceptors must be installed as closely as possible to the point of wastewater source. Adequate access is essential so that the removal of its contents can be conveniently and effectively carried out. Interceptors should not be installed in closed premises.

Arrangement: Provision of the following shall be taken into consideration. a) b) c) d)

•

Note: a) b) c)

•

Adequate ventilation. Odour seals at inlet and outlet. Secure, non inflammable covers. Uniform flow through the separation compartment.

Domestic wastewater may not be taken to the interceptor. Pumping installations must be located after the separation of the petrol/oil. Collection chambers are normally provided into which the separated petrol/oil is drawn off. This enables further separation in a non-agitated environment.

Capacity: Comply with the following recommendations. a) b) c)

For vehicle washing facilities allow 2 l/s per wash line. Size of separator should be based on double the wastewater flow. For light liquids retention time should be a minimum of 3 minutes up to a design flow of 20 l/s. For higher flows an additional minute can be added per 10 l/s increase.

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d) e)

For vehicle maintenance bays where heavier liquids can be expected the retention time should be increased to 6 or even 9 minutes. Width to length ratio should be 1 : 1.8.

Specialist input should be sought for the provision of a purpose designed interceptor for wastewater from commercial or industrial manufacturing processes. 3.2

PUMPING STATIONS

3.2.1

GENERAL

3.2.1.1

Location of Pumping Stations The pumping station shall be readily accessible by maintenance vehicles during all weather conditions. The facility should be located off the trafficway of streets and alleys. Pumping stations shall be of the submersible type designed in accordance with the typical pumping station layout drawings in Section 6. Pumping stations’ structures and electrical and mechanical equipment shall be protected from physical damage and fully operational and accessible during the 25 year flood.

3.2.1.2

Selection of Equipment Commercially standard available pumps should be chosen and should be capable of impeller adjustment to modify output. Pump type, size and numbers shall be selected to achieve the desired maximum and minimum pumping rates and so accommodate the variations in rate of discharge from the station. Pumping stations serving only a small tributary area shall have a minimum of two identical units, either one capable of handling the design flow. In large stations the number of duty pump and standby units should be chosen appropriate to the strategic importance of the station. The possible consequences of pump failure at a time of peak incoming flow or with one pumpset undergoing maintenance at such a time should be considered

3.2.1.3

Determination of Flow Rates In pump selection the following flow rates shall be considered: • •

The design peak flow. The initial and design average flow.

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•

The initial minimum flow.

The pumps shall be capable of handling the design peak flow. The initial and design average flow rates shall be considered for efficient operation of the equipment whereas the initial minimum flow rate shall be considered in sizing the force main so that the solids at low velocity may not plug the main. Initial minimum flows to be pumped may be approximated by using the multipliers in Table 3 below. TABLE 3 – MINIMUM PUMPED FLOWS

Average Flow l/s

50

500

2500

5000

Minimum Flow Factor

0.25

0.35

0.45

0.50

3.2.1.4

Electrical Equipment Electrical equipment located in the wet well shall be suitable for use under corrosive conditions. A fused disconnecting switch located above ground shall be provided for all pumping stations. When such equipment is exposed to weather, it shall meet the requirements of weather equipment (NEMA IP65 or approved equal).

3.2.1.5

Environmental Aspects Pumping stations are conspicuous by their function and every effort should be made to disguise them and reduce to a minimum their environmental impact. Architectural and layout design and materials should be chosen for access roads, boundary walls, building superstructures and landscaping to ensure that the general appearance of the above ground structures blend in naturally with the neighbouring arrangements. Odour control is of primary importance to ensure that such nuisance does not arise.

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3.2.1.6

Arrangement Considerations The following should be incorporated so that the pumping station installation facilitates operations and maintenance work: • • • • • •

•

• •

• • • • • • • • • • •

The provision of facilities and standards of equipment that are considered suitable and acceptable to the Abu Dhabi environment and are necessary in the types of pumping stations adopted. The provision of all necessary health, safety and welfare features appropriate to the numbers of personnel and the frequency of visits to the station. Where applicable duplication of incoming sewers, inlet sumps, valves, penstocks, control panels, pumps and incoming power supplies. Pump operation should be automatically controlled using a wet well level sensing system which sequences pump operation with the rise and fall of the water surface. Consideration of planned capacity in relation to development phasing. Appropriate wet well and sewer inlet design to minimise turbulence and air entrainment and so reduce odour emission, corrosive potential of the atmosphere and possible pump cavitation. For large stations model tests should be considered. The wet well volume between high level and low level and the number of pumps should be such that the pumps will not be cycled more often than recommended by the manufacturer and that the retention time of the sewage will be as short as possible. The lower part of wet well or sump should be shaped to suit the pump suctions and to prevent deposition of grit and sewage solids. Well arranged all flanged pipework including proper support and anchorage, drainage facilities for emptying isolated pumps and pipework, cross connections and valves to enable suction lines to be back flushed, flexible and dismantling couplings and station bypass connection. Liberal dimensional tolerance in level and location for all installed items so that they can be conveniently fitted together and fixed to the structure. Good access facilities and working space to and around all equipment. Adequate access openings for the introduction and removal of all operational and safety items. Adequate ventilation to all areas to be accessed. Exhausted gases from the wet well should be deodorised before discharge to the atmosphere. Provision of proper lighting and electrical power points for portable lights and tools. Hosing facilities for cleaning. Floor drainage in the pump well and valve chambers. Provision for emptying the wet well and the activated carbon vessels. Good access to site for vehicles and plant for maintenance and emergency considerations. Provision of irrigation connection to wet well for flushing.

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3.2.2

DESIGN

3.2.2.1

Site Investigation Should be carried out to establish: • • • • •

3.2.2.2

Substructure Configuration • • • •

•

• • 3.2.2.3

Topographical features. Subsoil conditions and physical properties of the soil to a depth of at least 1.5 x depth to station foundation. Safe allowable bearing capacity of formation. Nature of groundwater and its normal level. Historical and predicted maximum flood level.

Unless specific or special circumstances prevail the arrangement is circular. Refer standard and typical drawings. In all cases the ground floor slab level should be 300mm above predicted maximum flood level. The wet well should be designed to minimise retention time and ensure still areas cannot develop which can lead to deposition and accumulation of solids. Pump start/stop levels should be spaced to suit a pumping regime which produces the best compromise between stop/starts and continuous flow. The minimum live volume in the sump per pump is V = 0.25 QT where Q is the pump capacity and T is the minimum on/off cycle time offered by the pump manufacturer. For an installation with several identical duty pumps, the start and stop levels of all the pumps differ by a constant value determined by the characteristics of the control system. The difference in levels should be large enough to eliminate accidental pump starts and is normally in the range 200mm to 300mm. The inlet arrangement shall minimise turbulence and hence emission of gases. o o Side slopes to wet well benching should be a minimum of 40 to 45 .

General Requirements Three pumping station types have been identified which are related to design flow: • • •

Type 1 - design flow up to 100 l/s. Type 2 - design flow up to 300 l/s. Type 3 - design flow greater than 300 l/s.

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The factors and general requirements for each type of pumping station are given in Tables 4A to 4G below. TABLE 4A – DESIGN PARAMETERS

General Requirement

Pumping Station Type 1



Number of duty pumps

1

2

3

Number of standby pumps

1

1

1

Number of pumps depends on flow regime favoured Service rating

25 years design life

Type of impeller

Mixed flow

Solids handling capacity

100mm

Running hours per day per pump

8 to 10 hours

Pipework velocity at: Maximum flow Minimum flow

2.5m/s 1.0m/s

Maximum velocity through valves

2.5m/s

Maximum speed

1500rpm

For small pumps up to 5l/s

3000rpm

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TABLE 4B – WET WELL ARRANGEMENT

General Requirement




Number of wells

1

2

2

Number inlets

1

2

2

Inlet control

Penstock motorised or manual

Screens

To be used only where required when possibility of large size material is anticipated Manual

Raked Either manual or automatic

Raked Motorised Automatic

Macerators

Submersible type and used an alternative to screens

Inlet baffle

To be considered

Benching

Shaped to suit pump suctions and to prevent deposition of solids

Access

Temporary access used

Landings, handrailing and ladders provided only if directed by the Directorate

Deodorisers

Activated carbon or chemical scrubbing units depending on H2S concentration anticipated

Internal finish

Protective liners or coatings

Lifting equipment

Portable davit or fixed frame

Provided in stations as overhead crane as fixed installations

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TABLE 4C – DRY WELL ARRANGEMENT

General Requirement

Number of pumps and arrangement




1 duty 1 standby

1 duty 1 standby

2 duty 1 standby

At least 1m clear access around pumps Station pipework

Protective coatings internally and externally

Suction line control

Not applicable

Delivery line control

Isolation valves required

Isolation valves required Throttling valves not recommended All valves manual unless size requires motorisation

Station bypass

Provision to be considered for each installation

Sump pump provision

Not applicable

Access Internal finishes

Not required Protective liner or coating

Lifting equipment

Portable davit

Fixed permanent motorised lifting equipment

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TABLE 4D – SUPERSTRUCTURE

General Requirement


Wet well no superstructure



RC cover slab with protective coating to underside Openings with covers and sealing plates sized and located to suit access needs

Wet well with superstructure

Not applicable

Not applicable

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On large stations construction integral with pump well

Page 23


TABLE 4E – EXTERNAL WORKS

General Requirement


Minimum area of land required Delineation of boundary

2

100m

Pumping Station Type 2 2

400m

Pumping Station Type 3 2

900m

Preferably wall with pedestrian and vehicular access for operation and maintenance

Access

At least 6m wide turning circle with hardstanding for vehicles preferably with loading bay

Landscaping

Directorate’s instructions to be obtained

Services

Not required

Watchman facilities

Telephone lines for outstation telemetry and hand set Water supply for mess room and possible irrigation

Toilet facilities required plus mess room fully equipped on larger stations

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TABLE 4F – ANCILLARIES

General Requirement

Small power provisions

and


lighting

Fire protection and detection (Detectors, alarms, portable hosereel system, electrical protection) Earthing system



Full internal and external site site lighting All stairways and landings provided with emergency DC lighting Fire detection and alarm

Fire detection, alarm and optional firefighting

Fire detection, alarm and fire fighting system

All pumping stations rely on earth rods Recommendation is to use neutral as a PME system

Standby generator

Always provide socket for portable generator but on larger stations fixed generators should be considered

Welfare facilities

To be provided

WED supply – Transformer requirements

Not applicable

Possible space requirement

Vehicular access for sump to clean sand debris

Not applicable

Always required to access sump

Ventilation equipment for personnel and auxiliary cooling

Portable only

Provide minimum air change capacity of: 15 per hour during maintenance 5 per hour at other times

Air conditioning

Air conditioning of control panel rooms only

Surge protection and auxiliary equipment

Sometimes not required

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Always provided

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TABLE 4G – INSTRUMENTATION

General Requirement


Wet well water level sensor



Ultrasonic level detection for sump level monitoring and pump control

Wet well H2S level sensor

None

SCADA equipment

Provide data transmission through Etisalat lines compatible with existing system

Pumping monitoring

Hours run only

Flow monitoring

Larger motor units will be fitted with temperature monitors for alarm and protection circuits

Electromagnetic flowmeters to provide integrated flow

Valve status indication

None

If motorised valves then valve status indication provided

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3.2.3

PUMPING/FORCE MAINS

3.2.3.1

Hydraulic Design •

Design basis: a)

•

Pipe roughness factors shall be as follows: a) b) c)

•

Equations such as Manning, Colebrook-White and Hazen Williams should be used.


0.0075 0.06 140 for pipe diameters >500mm 135 for pipe diameters< 500mm

Energy losses through fittings given as equivalent pipe length i.e. factor x pipe diameter as given in Table 5 below.

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TABLE 5 – ENERGY LOSSES THROUGH FITTINGS

Fitting

Factor

Non return valve

45

Gate valve

7

Butterfly valve

45

Radial tee

22

Tee piece

54

Taper 15o - 60o angle

22

Bellmouth exit

9

22½o Bend

r=d

7

o

r=d

14

o

r=d

34

22½ Bend

o

r = ≤ 7d

5

45o Bend

r = ≤ 7d

9

90o Bend

r = ≤ 7d

18

45 Bend 90 Bend

•

Minimum velocity: a)

•

Maximum velocity: a)

•

1.0m/sec.

2.5m/sec.

Minimum gradient: a)

None.

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•


•

Maximum bend: a) b)

•

100mm.

90o with radius to suit deflection measurement requirements. Sharp bends to be avoided as much as possible.

Surge protection: Maximum negative pressure specified as 1.0m water head.

•

Means of surge control: a) b)

c) •

Surge: a)

3.2.3.2

Air valves. Means adopted generally depends on dimension of control required. Regulating valves/Regulating vessels. Preferred method is regulating vessels. The use of controlled valve closure only as a last option. Air valves along the main not to be included in surge analysis. Pump flywheel. Pump flywheel not suitable for submersible type pumps.

Pressure and velocity changes can be calculated by the Joukowskey or an equivalent equation.

Other Features •

Minimum cover: a) b)

•

Refer to standard drawings.

Pipeline protection: a)

•

1.2m (depth to top of pipe). 0.5m (depth to top of protection).

Pipe bedding: a)

•

Without protection With protection

Use of concrete slab where required.

Thrust blocks: a) b)

See standard drawings. Check manufacturer’s recommendations for maximum bend without restraint.

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c)

d) e) f) •

Washouts: a) b)

•

b)

b)

Should be so arranged to avoid turbulence or splashing. Vertical drop pipes should be avoided and the end of the pumping main should always be full. Surfaces of structure should be protected against corrosion. Refer standard drawing.

Twin mains: a)

b) •

Cleaning chamber at start of main in vicinity of pumping station for all diameters and on 100mm and 150mm diameter mains chambers to be provided at 200m spacing.

Discharge chamber: a)

•

At all high points along pumping main. Also, at selected locations to suit isolation and emptying of main including in vicinity of pumping station so that station pipework can be dismantled without emptying the whole main. Maximum spacing in the order of 1000m. Refer standard drawings.

Provision of access: a)

•

At all low points along pumping main. Refer standard drawings.

Air valves: a)

•

Wherever possible blocks should take the form of a cradle wedged against the undisturbed trench side and design based on the safe bearing pressure of the ground. Piling may be required to achieve support from the ground at depth, subject to results of soils investigation. Arrangement should not impede flexibility or expansion. Check for friction factor of safety 1.5, sliding factor of safety 2.0, overturning factor of safety 2.0 and bearing capacity.

To accommodate short term/long term requirements of pumping arrangement. Duplication could be limited to critical lengths if restraints applied. Also used where pump characteristics do not lend themselves to combined working through a single main. Space between must ensure no interaction.

Cross over chambers: a)

At selected locations for isolation and emptying and hence dependent on individual configuration.

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3.3

HEALTH AND SAFETY

3.3.1

DESIGN CONSIDERATIONS Considerations in design to mitigate risks will include but not be limited to: • • • • • • • • • • • • • • •

The designer must design out the need for entry into all confined spaces wherever possible. Safe access should be provided to all plant requiring maintenance. All above ground must be fenced off and inaccessible to the general public. Craneage or mobile lifting facilities must be provided for all heavy equipment. Stairways should be equipped with handrailing and toe plates in accordance with the relevant standards. Tripping hazards should be avoided, likewise overhead obstructions. Barriers should be provided to prevent falling from height. All hazards should be signposted. Adequate lighting to be provided wherever access is required. Welfare facilities should be provided to allow operatives to clean up after maintenance work. Manholes must be equipped with covers which are secure yet can be easily removed for maintenance purposes. Covers should be a minimum size to allow operatives wearing breathing apparatus. A minimum of 650mm square should be appropriate in most cases, but will depend upon the apparatus used. Flow isolation facilities. Access to long tunnels to allow desilting equipment as necessary. Zoning classification should be established for all work carried out on existing and proposed infrastructure.

3.4

TRENCHLESS TECHNOLOGIES

3.4.1

ALTERNATIVE TECHNIQUES A brief summary of the typical purpose and diameter range appropriate for each technique is presented below. • • • •

Pipe jacking open/closed face. Purpose new installation by tunnelling in diameter range 900mm and above. Microtunnelling closed face. Purpose new installation by tunnelling in diameter range 300mm to 900mm. Directional drilling. Purpose new installation by drilling in diameter range 300mm to 1500mm. Impact moling. Purpose new installation by moling in diameter range 20mm to 90mm. With multiple passes diameter range can be increased to 1000mm.

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• • • •

Pipe ramming. Purpose new installation by moling in diameter range 50mm to 1800mm. Non steerable auger boring. Purpose new installation by boring in diameter range 100mm to 1600mm. Guided auger boring. Purpose new installation by boring in diameter range 150mm to 1500mm. Heading. Purpose new installation by tunnelling in diameter range man entry size and greater.

3.5

SEWER REHABILITATION TECHNIQUES

3.5.1

ALTERNATIVE TECHNIQUES The acceptable systems for the rehabilitation of sewers are considered to be: • • • •

Cured in place pipe liner. Deformed and reformed high density polyethylene (HDPE) pipe liner. Spiral wound pipe liner with stainless steel reinforcement. Only for sewers of 250mm diameter and greater. Sliplining.

The liner shall be designed to support all combinations of imposed loads including earth, traffic, hydrostatic etc and have a minimum service life of 50 years. For the purposes of calculations it shall be assumed that the ground water table is at ground level. Host pipes shall be considered to be fully deteriorated. The liner 2 shall have a minimum allowable long term stiffness of 2500N/m and be designed to have a factor of safety of 2. The normal requirement will be that the liner shall provide the least possible thickness or decrease in diameter to meet the requirements of this section and consequently shall be of the close fit type.

END OF SECTION

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SECTION 4

SEWAGE TREATMENT PLANT DESIGN

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Sewage Treatment Plant Design

Page 1



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01

02

03

04

05

06

07

08

09

10


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DESIGN CONSIDERATIONS................................................................................ 5

4.1.1

PLANT LOCATION ............................................................................................... 5

4.1.2

FLOOD PROTECTION ......................................................................................... 5

4.1.3

QUALITY OF EFFLUENT...................................................................................... 5

4.1.4 4.1.4.1 4.1.4.2 4.1.5 4.1.5.1 4.1.5.2 4.1.6

HYDRAULIC DESIGN ........................................................................................... 5 New Systems ........................................................................................................ 5 Existing System..................................................................................................... 6 ORGANIC DESIGN............................................................................................... 6 New System Minimum Design............................................................................... 6 Existing Systems ................................................................................................... 6 CONDUITS ........................................................................................................... 6

4.1.7

ARRANGEMENT OF UNITS ................................................................................. 7

4.1.8

INSTRUMENTATION ............................................................................................ 7

4.1.9

FLOW DIVISION CONTROL................................................................................. 8

4.1.10

EMERGENCY OUTFALL ...................................................................................... 8

4.1.11 4.1.11.1 4.1.11.2 4.1.11.3 4.1.11.4 4.1.12

PLANT DETAILS................................................................................................... 8 Unit Bypasses ....................................................................................................... 8 Drains.................................................................................................................... 8 Painting ................................................................................................................. 8 Operating Equipment: ........................................................................................... 9 GRADING AND LANDSCAPING........................................................................... 9

4.1.13

EMERGENCY POWER FACILITIES..................................................................... 9

4.1.14 4.1.14.1 4.1.14.2 4.1.15

WATER SUPPLY .................................................................................................. 9 General: ................................................................................................................ 9 Water Connections:............................................................................................... 9 SANITARY FACILITIES ...................................................................................... 10

4.1.16

SAFETY .............................................................................................................. 10

4.1.17 4.1.17.1 4.1.17.2 4.1.17.3 4.1.17.4 4.2

LABORATORY.................................................................................................... 10 General ............................................................................................................... 10 Location & Space: ............................................................................................... 10 Sinks: .................................................................................................................. 11 Ventilation and Lighting: ...................................................................................... 11 PROCESS DESIGN ............................................................................................ 11

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4.2.1 4.2.1.1 4.2.1.2 4.2.1.3 4.2.2

PRELIMINARY TREATMENT ............................................................................. 11 Inlet Works .......................................................................................................... 11 Screens ............................................................................................................... 11 Grit Removal ....................................................................................................... 12 PRIMARY TREATMENT ..................................................................................... 12

4.2.3

BIOLOGICAL TREATMENT................................................................................ 12

4.2.4

SECONDARY SETTLING TANKS ...................................................................... 13

4.2.5

TERTIARY TREATMENT.................................................................................... 13

4.2.6 4.3

SLUDGE TREATMENT....................................................................................... 15 TABLE 1 – SLUDGE PRODUCTION DESIGN CRITERIA .................................. 15 SMALL TREATMENT PLANTS (INCLUDING PACKAGE PLANTS) .................. 17

4.3.1

APPROPRIATE USES ........................................................................................ 17

4.3.2

LOCATION.......................................................................................................... 17

4.3.3

ARRANGEMENT ................................................................................................ 17

4.3.4

DESIGN CRITERIA............................................................................................. 18

4.3.5

EFFLUENT DISPOSAL/REUSE.......................................................................... 19

4.4

SEPTIC TANKS .................................................................................................. 19

4.4.1

LOCATION.......................................................................................................... 19

4.4.2

ARRANGEMENT ................................................................................................ 19

4.4.3

CAPACITY .......................................................................................................... 20

4.4.4

FURTHER TREATMENT OF TANK EFFLUENT ................................................. 20

4.4.5

EFFLUENT DISPOSAL ....................................................................................... 20

END OF SECTION.............................................................................................................. 20

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4.1

DESIGN CONSIDERATIONS

4.1.1

PLANT LOCATION The following items shall be considered when selecting a plant site: • • • • • • •

Proximity to residential areas. Direction of prevailing winds. Accessibility by all weather roads. Area available for expansion. Local soil characteristics, geology, hydrology and topography available to minimise pumping. Access to disposal point. Compatibility of treatment process with the present and planned future land use, including noise, potential odours, air quality, and anticipated sludge processing disposal techniques.

Where a site must be used which is critical with respect to these items, appropriate measures shall be taken to minimise adverse impacts. 4.1.2

FLOOD PROTECTION Treatment works should remain fully operational and accessible during the 25 year flood. This applies to new construction and to existing facilities undergoing major modification.

4.1.3

QUALITY OF EFFLUENT The required degree of wastewater treatment shall be based on the effluent requirements and water quality standards as decided by the Directorate. To ensure an effluent is satisfactory for reuse, the following effluent standards shall be achieved: • • • • •

BOD SS Ammoniacal Nitrogen Coliforms Salinity

4.1.4

HYDRAULIC DESIGN

4.1.4.1

New Systems

10mg/l. 10mg/l. < 1mg/l. < 100/100ml. < 4000 micromho/cm.

The design for sewage treatment plants shall be based on average daily flow 275 l/cap unless water use data or other justification upon which to better estimate flow is provided. Peak factor on design should be two as a minimum.

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Allowance should be made for recycled works liquors within the proposed plant or tankered wastes from septic tanks. For commercial flow, the design load should be the actual peak period discharge plus 10%. 4.1.4.2

Existing System Where there is an existing system, the volume and strength of existing flows shall be determined. The determination shall include both dry-weather and wetweather conditions. At least one year's flow data should be taken as the basis for the preparation of hydrograph for analysis to determine the following types of flow conditions of the system: • • • • •

The annual average daily flow as determined by averaging flows over one year, exclusive of inflow due to rainfall. The minimum daily flow as determined by observing 24 hours flows during dry weather. Wet weather peak flows as determined by observing 24 hour flows during a period of one year. Peak hourly flows as determined by observing the maximum hydraulic load to the plant. Industrial wasteflows as determined by flow data, including water use records, for each of the industries contributing to the sewer system.

4.1.5

ORGANIC DESIGN

4.1.5.1

New System Minimum Design Domestic waste treatment design shall be based on at least 0.08 kg of BOD per capita per day and 0.09 kg of suspended solids per capita per day, unless information is submitted to justify alternate designs. Domestic waste treatment plants that will receive industrial wastewater flows shall be designed to include these industrial waste loads. Significant industrial discharges may need to be separately examined

4.1.5.2

Existing Systems When an existing treatment works is to be upgraded or expanded, the organic design shall be based upon the actual strength of the wastewater as determined from the measurements listed above in 4.1.4, with an appropriate increment for growth.

4.1.6

CONDUITS All piping and channels shall be designed to carry the maximum expected flows. The incoming sewer should be designed for unrestricted flow. Bottom corners of

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the channels must be filleted. Conduits shall be designed to avoid creation of pockets and corners where solids can accumulate. 4.1.7

ARRANGEMENT OF UNITS Component parts of the plant should be arranged for greatest operating and maintenance convenience, flexibility, economy, continuity of maximum effluent quality and ease of installation of future units.

4.1.8

INSTRUMENTATION When considering the control regime for a particular works, full consultation with the Department must be carried out. The choice of automatic or manual control will depend on the strategic importance of the works, the process item and the interconnection/relationship required with other sites. The parameters to be measured/archived are to be agreed and can include flow, level, pressure, quality, temperature, speed, position, motors, valves etc. Critical conditions requiring alarm annunciation must be identified. The Plant Management Information System (PMIS) should consider: • • • • • • •

Main operator interface. Local operator interface. Discrete displays (non PMIS). Facilities such as screen, printers, database etc. Alarms, reports, trends, text. Ability to hold historical data. PLC protocol requirement.

SCADA facilities must be compatible with existing installations. features should be incorporated: • • • • • • • • • •

The following

Microprocesscor based. Expansion capabilities. Ease of maintenance. Components to operate with compatible protocol/language, programmes, programme development units, file management routines, data storage facilities etc to the existing system. Programme modifying facilities. Marshalling station for input/output signals. Minimum time delays in signalling. Fully operational during periods of mains failure through UPS system. Isolating transformers and surge suppression components in modem links for transmission over land lines. Electronic pattern RTU’s.

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Mimic panels should be sized to clearly indicate all operations and process measuring parameters in the form of a flow line diagram with illuminated symbols and indicating instruments and should incorporate sufficient spare space to permit the display of all future plant extensions. 4.1.9

FLOW DIVISION CONTROL Flow division control facilities shall be provided as necessary to ensure organic and hydraulic loading control to plant process units and shall be designed for easy operator access, change, observation and maintenance. Appropriate flow measurement shall be incorporated in the flow division control design.

4.1.10

EMERGENCY OUTFALL Storm conditions can double the design flow. Consideration should be given therefore to providing an overflow at the inlet to the works with connection to the sea or a lagoon for eventual loss through evaporation and percolation.

4.1.11

PLANT DETAILS

4.1.11.1 Unit Bypasses Properly located and arranged bypass structures and piping shall be provided so that each unit of the plant can be removed from service independently. The bypass design shall facilitate plant operation during unit maintenance and emergency repair so as to minimise deterioration of effluent quality and ensure rapid process recovery upon return to normal operational mode. 4.1.11.2 Drains Means shall be provided to dewater each unit to an appropriate point in the process. Pipes subject to clogging shall be provided with means for mechanical cleaning or flushing. 4.1.11.3 Painting The use of paints containing lead or mercury should be avoided. In order to facilitate identification of piping, particularly in the large plants, the different lines shall be colour-coded. The following colour scheme is recommended for purpose of standardisation: • • • • • •

Sludge line Gas line Potable water line Chlorine line Sewage line Compressed air line

grey. orange. blue. yellow. brown. green.

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•

Water lines for heating digesters -blue with 150mm red bands 750mm apart.

The contents shall be stencilled on the piping in a contrasting colour. 4.1.11.4 Operating Equipment: A complete outfit of tools, accessories, and spare parts necessary for the plant operators use shall be provided. Readily accessible storage space and workbench facilities shall be provided, and consideration be given to provision of a garage for large equipment storage, maintenance and repair. 4.1.12

GRADING AND LANDSCAPING Upon completion of the plant, the ground should be graded. Concrete or gravel walkways should be provided for access to all units. Surface water shall not be permitted to drain into any unit. Provision should be made for landscaping.

4.1.13

EMERGENCY POWER FACILITIES All plants shall be provided with an alternate source of electric power to allow continuity of operation during power failure, except as noted below. Methods of providing alternate source, include: • • •

4.1.14

The connection of at least 2 independent public utility sources such as substations. A power line from each substation is recommended. Portable or in-place internal combustion engine equipment which will generate electrical or mechanical energy. Portable pumping equipment when only emergency pumping is required.

WATER SUPPLY

4.1.14.1 General: An adequate supply of potable water should be provided for use in the laboratory and for general cleanliness inside buildings. 4.1.14.2 Water Connections: Potable water from a Municipal or separate supply may be used directly for the following: • • • •

Lavatory. Water closet. Laboratory sink with vacuum breaker. Showers.

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• • • 4.1.15

Drinking fountain. Eye wash fountain. Safety shower.

SANITARY FACILITIES Toilet, shower, lavatory and locket facilities should be provided in sufficient numbers and convenient locations to serve the expected plant personnel.

4.1.16

SAFETY Adequate provision shall be made to effectively protect the operator and visitors from hazards. The following shall be provided to fulfil the particular needs of each plant. • • • • • • •

4.1.17

Enclosure of the plant site with a fence designed to discourage the entrance of unauthorised persons and animals. Handrails and guards around tanks, trenches, pits, stairwells, and other hazardous structures. First Aid equipment. No smoking signs in hazardous areas. Protective clothing and equipment, such as air pack, goggles, gloves, hard hats, safety harnesses, etc. Portable blower and sufficient hose. Appropriately placed warning signs for slippery areas; non potable water fixtures, low head clearance areas, open service manholes, hazardous chemical storage areas, flammable fuel storage areas etc.

LABORATORY

4.1.17.1 General Where required by the Department, treatment works shall include a laboratory for making the necessary analytical determinations and operating control tests. The laboratory shall have sufficient size, bench space, equipment and supplies to perform all self monitoring analytical work required, and to perform the process control test necessary for good management of each treatment process included in the design. The layout should consider future needs for expansion in the event that more analytical work is needed. 4.1.17.2 Location & Space: The laboratory should be located on ground level, easily accessible to all sampling points. It shall be located away from vibrating machinery or equipment which might have adverse effects on the performance of laboratory instruments or the

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analyst etc. A minimum of 50 square metres of floor space should be allocated for the laboratory. 4.1.17.3 Sinks: The laboratory should have a minimum of 3 sinks. Additional sinks should be provided in separate work areas as needed. The sinks should be constructed of material highly resistant to acids, alkalis, solvents and salts and should be abrasion and heat resistant, non-absorbent and light in weight. Trap should be easily accessible for cleaning. 4.1.17.4 Ventilation and Lighting: The laboratory should be separately air conditioned, with external air supply for 100% make-up volume. In addition, separate exhaust ventilation should be provided. Good lighting, free from shadows, shall be provided in the laboratory.

4.2

PROCESS DESIGN The designer should liaise closely with the Operational Manager. The general aim of process selection should be to provide operational efficiency in terms of both manpower and energy in achieving the required standard. The nature and relative volumetric proportions of any trade wastes should be considered. Sewage treatment works comprise all or some of the following processes: • • • • •

Preliminary treatment Primary treatment Secondary treatment Effluent polishing Sludge handling

4.2.1

PRELIMINARY TREATMENT

4.2.1.1

Inlet Works

screenings and grit removal. sludge removal. oxygenation and clarification. tertiary and chlorination. removal, digestion, drying.

Inlet works should be designed for the ultimate flow. 4.2.1.2

Screens Bar spacing and general requirements are: •

Protection of machinery

50mm (Range 40 - 100).

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• • • • • • • • 4.2.1.3

Prevention of blockages 15mm (Range 15 - 20). Special application 12mm (Range 10 - 15). Screens with bar spacings of less than 40mm in duty situations should be mechanically raked. Maximum velocity through screen bars 0.9m/s (may vary with local circumstances). Minimum velocity through screen bars 0.3m/s. Hand raked by-pass screens should be provided with mechanically raked screens and in line macerator/comminutor/muncher/rotodisintegrator /Aquaguard units. 3 Volume of screenings for disposal 0.01 to 0.03m /d/1000 population. Disposal of screenings by in-line macerators preferred.

Grit Removal Grit tank method of grit removal is preferred. • • • •

4.2.2

The design layout should follow manufacturer's requirements. A by-pass should be provided. The tanks should be designed for 0.3m/s velocity at maximum flow with the water level controlled by hydraulic gradient through the plant. Organic content to be removed and the organic solution returned to the flow.

PRIMARY TREATMENT The following criteria should be used: • • • • • • •

Detention time of 1 to 2 hours at average flow. 3 2 Surface loading of 30 to 36m /m /d at average flow. 3 Weir overflow rate in range of 100 to 150m /m/d at average flow. Sludge hopper capacity to suit operational method. Minimum sidewall depth of 2.0m. Rectangular tanks should have a length/breadth ratio 4:1. Floor slopes as follows: a) b)

o

Circular tanks 3 to 9 . o Rectangular tanks 1 in 100 (self draining slope) with 60 side slope provided at the inlet end on sludge hoppers.

In difficult ground conditions the economics of flat bottomed tanks with associated scraper mechanisms should be compared. 4.2.3

BIOLOGICAL TREATMENT The following criteria should be used:

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• • • •

In sizing the units, consideration must be given to the plant manufacturer's recommendations. 3 Organic loading of 0.48 to 0.80 kg BOD/m /d. This is based upon settled sewage, but allowance must be made for any returned liquors etc. Aeration period of 4 to 8 hrs at average flow. Air requirements for: a) b)

•

Surface aeration see manufacturer's requirements. 3 3 Diffused air 3.5 to 15m /m at average flow. 3 30 to 55 m /kg BOD removal for conventional works. 3 75 to 115 m /kg BOD removal for nitrifying works.

Mixed liquor suspended solids (MLSS). a) b)

1500 to 3000 mg/l for conventional works. 2000 to 3500 mg/l for nitrifying works.

The following is suggested: • • • 4.2.4

Select trial MLSS and by using design BOD, calculate tank capacity. Check other design parameters. Recalculate capacity if necessary by using adjusted MLSS within the ±20% range.

SECONDARY SETTLING TANKS The following criteria should be used: • • •

Tanks should be designed for the maximum flow to treatment. Sidewater depth to be 3.65 to 6m. Overflow rate to be: a) b)

• •

Detention time to be 1 to 2 hours at peak flow Solids loading to be: a) b)

•

2 4 to 6kg/m /h at average flow. 2 9 to 10kg/m /h at peak flow.

Configuration: a) b)

4.2.5

3

15 to 35m /m/d at average flow. 3 40 to 50m /m/d at peak flow.

Circular Rectangular

Radius < 5 x height. Length < 10 to 15 x height.

TERTIARY TREATMENT

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Rapid downward flow sand filters: • • • • •

In sizing units, consideration must be given to the plant manufacturers recommendation. Max flow rate range 1 to 2 x DWF. SS and BOD reduction in the order of 60% to 80% to be achieved. 3 2 Surface loading 200 to 300m /m /d at max flow rate dependent on influent quality and effluent requirements. Backflow for washing approximate requirements: a) b)

0.01m3 effluent per m2 of sand per second. 3 2 0.02m air per m of sand per second.

Chlorination: •

To achieve a residual chlorine content of not less than 0.5mg/l after 24 hours and be capable of varying the dosage from 0 to 10mg/l. Effluent storage/chlorine contact tank to have a storage capacity of not less than 48 hours.

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4.2.6

SLUDGE TREATMENT Sludge production design criteria to be as given in Table 1 below. TABLE 1 – SLUDGE PRODUCTION DESIGN CRITERIA

Sludge Type

Mass of Dry Solids gm/head/day Range

Average

Raw primary sludge

40 to 70

52

Activated sludge: • Settled sewage, nitrifying • Settled sewage, high rate • Unsettled sewage, nitrifying • Unsettled sewage, high rate

40 to 60 50 to 80 15 to 30 25 to 40

48 70 22 35

1 to 4

2

55 to 100

74

27 to 48 40 to 70 33 to 60

36 55 45

Raw tertiary sludge Raw co settled sewage • Primary and nitrifying activated Anaerobically digested sludge • Primary • Primary and nitrifying activated co-settled • Primary and low rate humus

In addition the following should be taken into account: •

Works liquor

• •

Trade effluent Imported sludge

Likely assessment only made dependent on sludge dewatering process. Calculated from design allowance. Calculated or measured from a sludge survey.

Sludge consolidation/thickening tanks: •

Fill and displacement type one to three days capacity provided with surface 3 2 loading not exceeding 30m /m /d at maximum sludge input rate.

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•

Quiescent type tank capacity should be capable of dealing with 7 days sludge in 5 days. i.e. 34 hours sludge production. Provision is to be made for supernatant liquor to be drawn off at various levels.

Heated anaerobic digestion: • • • • •

Tank shape, height = diameter. Fixed roof. Floor slope should be as steep as practicable. Fully mixed system to be provided to prevent dead areas and deposition. Detention period

a) b)

Standard High rate

• •

3 Solids loading 1 to 2kg/m /d. Secondary digestion tanks should have a large area/volume ratio to promote rapid cooling to aid thickening. Gas holder design should ensure that the ingress of air into the methane collection system and associated appliances is prevented. Gas pipework and associated plant should be designed as far as is reasonably practicable to avoid gas leakage and should preferably be in the open air. Buildings housing plant should be provided with adequate natural ventilation and explosion relief. Lockable valves should be provided in water drain lines from the gas pipes. Compressors for flammable gases should not be sited within buildings but in the open air or under a structure with a lightweight roof and open sides. Where security measures are necessary open sides may be covered with wire mesh or similar. Electric motors sited indoors shall have compressors outdoors and driven by shafts passing through glands in the wall. A high standard of permanent natural ventilation should be provided in pump and boiler rooms at all times. Gas burners should comply with the requirements of the relevant Code of Practice. A facility for gas composition monitoring should be provided to ensure it is safe and stable for combustion. Methane detectors installed in sludge digestion plants shall have alarm setting below 25% of the LEL for methane. Detectors shall be interlocked to trip out compressors and gas burners with manual reset after an alarm.

• • • • •

• • •

25 to 30 days. 15 days.

Other methods of sludge dewatering may be considered: • • • •

Plate press. Belt press. Vacuum filter. Centrifuge.

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Storage and dosing facilities should be provided for the conditioning chemicals. Sludge Drying Beds: • •

Bed depth range is 0.6 to 1.5m. Removal by hand, shovelling or mechanical means.

Mechanical drying fluidised beds, rotatory drum & kiln type etc can be considered where appropriate. 4.3

SMALL TREATMENT PLANTS (INCLUDING PACKAGE PLANTS)

4.3.1

APPROPRIATE USES Small treatment plants serve populations up to 15,000. Package type plants are generally used in locations such as: • • • • • •

4.3.2

Military camps. Villages. Hospitals. Hotels/recreational facilities. Construction camps. Pretreatment of trade waste.

LOCATION The plant should be as far away from habitable buildings as is economically possible. The direction of the prevailing wind should be considered when siting the works. Special provisions to reduce noise and screening from blowing sand should be incorporated where required.

4.3.3

ARRANGEMENT The following features should be incorporated into the installation: • • • • • • •

Adequate protection against corrosion. Standby equipment with automatic changeover. Automatic restarting in the event of a power failure. Standby generator with automatic mains failure start. Adequate flow control or flow balancing. When flow pumped to plant, maceration prior to pumping. When flow to plant by gravity, for population greater than 1,000 maceration with screening of macerated plastics, rags etc at convenient stage in process as site conditions allow. Use 2.5 to 5mm screen, run down, brush type, rotary or a fine submerged bag type with bypass provision/overflow.

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• • • • • • • • • • 4.3.4

Provide grit/sand trap with simple removal mechanism. For population greater than 5,000 extend to include bypass channel together with provision of aerated type mechanical grit trap and removal system. Air blowers to be filtered and duty, duty assist and standby units provided. Effluent/water retaining structures to be suitable for the purpose and proposed life of the plant. Odour control. Proper vehicle access for maintenance and sludge removal. Adequate and safe access and egress provision to all plant. Provision of a central control building or machine house. Basic health and welfare provision. Watchman's accommodation. Security fence or boundary wall. Telemetry provision of on line quality and flow instrumentation for turbidity, pH, residual chlorine.

DESIGN CRITERIA Plants to be designed for peak flows of 3 x average daily flow. Process design to produce better than BOD 10/SS 15 prior to tertiary treatment and based on: • • • •

BOD loading of 80gm/per capita/day. Hydraulic loading of 275 l/capita/day. Septic sewage with soluble sulphides around 35mg/l. o Crude sewage temperatures of up to 40 C.

Standard of final effluent for reuse to be: • • • • • •

5 day BOD SS pH Ammoniacal nitrogen Coliforms Salinity

< 5mg/l. < 5mg/l. 6.5 to 8.5. <1mg/l. < 100/100ml. < 4000 micromho/cm.

Actual process used must be specified to suit the locality and climate conditions which it is required to operate under and offer a performance and quality guarantee. Tertiary Treatment: • • •

Sand filters rapid gravity or pressure sand filtration. Consider micro and nano filtration for filtering out particles size>2 microns. Disinfection after filtration using chlorine gas or liquid sodium hypochlorite solution or UV/ozone.

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•

If reuse for agriculture, further chlorination required to provide a residual of 0.5mg/l.

Sludge Treatment: • • • •

Dependent on ultimate reuse and/or disposal route. In smaller plants tanker off site to larger treatment plant. Digestion in larger plants followed by mechanical dewatering/thickening, sludge drying beds and/or chemical treatment with lime or cement kiln dust, storage and then reuse. Drying beds: a) b)

•

Consolidation tanks. a)

4.3.5

2

0.2 to 0.4m /person. 225mm.

Area Max depth

Capacity

30 days production

EFFLUENT DISPOSAL/REUSE Effluent disposal or reuse to be agreed with the Directorate.

4.4

SEPTIC TANKS

4.4.1

LOCATION In the case of single plot septic tanks, the location should be within the plot boundary. A tank serving several plots should be sited in public open space reserved for the purpose at an adequate distance from the development and downwind wherever possible. In all instances consideration should be given to: • •

4.4.2

Adequate access for tankers to empty and operate within suction lift capacity. Future connection to the probable or planned main sewerage network.

ARRANGEMENT The following points are highlighted: • • • •

Tanks should be divided into two compartments. First compartment, length = twice width. Second compartment, length = breadth. Inlets and outlets should be such as to introduce the crude sewage and to remove the clarified liquid with the least possible disturbance of the settled sewage or the surface scum. For smaller tanks, populations <30, the use of tees within the tank on the inlet and outlet pipes are recommended. In

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• • •

4.4.3

larger tanks dual submerged inlets with baffle board and scumboard/weir arrangement at the outlet end are preferred. For populations >60 duplicate tanks each of half the capacity required should be considered and operated in parallel. To facilitate desludging of the first compartment the floor of the tank should slope at 1 in 4 to the inlet end. For populations >100 consideration can be given to the provision of two single compartment tanks operating in parallel as surge flows are likely to cause less disturbance.

CAPACITY BS 6297 gives capacity = 180 x population + 2000 litres The minimum value for population is 4. The maximum number of people that can be served by a septic tank is very much dependent on the suitability and capability of the receiving medium for the effluent. Ground percolation potential must be assessed against peak flow predictions.

4.4.4

FURTHER TREATMENT OF TANK EFFLUENT This should be considered where there is a need to ensure a higher quality of effluent.

4.4.5

EFFLUENT DISPOSAL The most common means is by soakaway pit particularly in the case of single plot septic tanks. In some circumstances a system of shallow drains may be a more practicable alternative.

END OF SECTION

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SECTION 5

TREATED SEWAGE EFFLUENT SYSTEM DESIGN

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Treated Sewage Effluent System Design

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GENERAL............................................................................................................. 4

5.1.1

SYSTEM ............................................................................................................... 4

5.1.2

EFFLUENT QUALITY ........................................................................................... 4

5.1.3 5.1.3.1 5.1.3.2 5.1.3.3 5.1.3.4 5.1.3.5 5.1.3.6 5.1.3.7 5.2

WATER DEMAND................................................................................................. 4 Plant Type ............................................................................................................. 4 Application Losses: ............................................................................................... 5 Leaching Requirements ........................................................................................ 5 Soil Classification .................................................................................................. 5 Groundwater Table Level ...................................................................................... 5 Climate .................................................................................................................. 5 Irrigation Management .......................................................................................... 5 DESIGN CRITERIA............................................................................................... 5

5.2.1

WATER DEMAND................................................................................................. 5

5.2.2 5.2.2.1 5.2.2.2 5.2.2.3 5.2.2.4 5.2.2.5 5.2.3 5.2.3.1 5.2.3.2 5.2.3.3 5.2.3.4 5.2.3.5 5.2.3.6 5.2.4

PIPEWORK........................................................................................................... 6 Hydraulic Design ................................................................................................... 6 Surge Protection ................................................................................................... 6 System Losses ...................................................................................................... 6 Valve Chambers.................................................................................................... 6 Flowmeters............................................................................................................ 7 UNDERGROUND RESERVOIRS (UP TO 500,000 GALLON CAPACITY)............ 7 Configuration......................................................................................................... 7 Inlet Arrangement.................................................................................................. 7 Outlet Arrangement ............................................................................................... 7 Overflow and Washout .......................................................................................... 7 Access .................................................................................................................. 7 Ventilation .............................................................................................................7 AT GROUND LEVEL RESERVOIRS (1,000,000 GALLONS CAPACITY AND ABOVE):................................................................................................................ 8 Configuration......................................................................................................... 8 Inlet Arrangement.................................................................................................. 8 Outlet Arrangement ............................................................................................... 8 Overflow and Washout .......................................................................................... 8 Access .................................................................................................................. 8 Ventilation .............................................................................................................9 Water Level Indication........................................................................................... 9 PUMPING STATIONS........................................................................................... 9

5.2.4.1 5.2.4.2 5.2.4.3 5.2.4.4 5.2.4.5 5.2.4.6 5.2.4.7 5.2.5

END OF SECTION................................................................................................................ 9

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5.1

GENERAL

5.1.1

SYSTEM The treated effluent transfer and distribution system has the following main component parts: • • •

5.1.2

Pipework for transfer and distribution. Reservoirs for storage. Pumping stations to supply through the primary distribution lines.

EFFLUENT QUALITY To ensure the treated sewage effluent is of a very high standard and satisfactory for all irrigation requirements the following parameters are to be controlled: •

Trade/Industrial discharges: a)

•

Salinity: a)

•

Tertiary treatment to produce a 10 mg/l BOD and 10 mg/l SS effluent preventing buildup of solids in the irrigation distribution system and stable and pure enough to reliably disinfect. Process should achieve full nitrification.

Disinfection: a)

5.1.3

Should be as low as possible but a maximum of 4000micromho/cm to ensure growth of the plant types adopted.

Sewage treatment: a)

•

The pH, temperature, concentrations of dissolved and suspended solids, organic and non-organic pollutants and radioactivity of the discharge must be within acceptable and prescribed standards.

By chlorine injection to render the effluent virtually harmless and to control the growth of algae in the system A chlorine residual of 0.5 mg/l at the outlet of the irrigation system should be available.

WATER DEMAND The demand for water is the basis for the planning and design of the irrigation supply network. This demand should take account of the following variables:

5.1.3.1

Plant Type

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Plant growth must not be inhibited by lack of water. 5.1.3.2

Application Losses: Proper equipment selection, system layout and irrigation scheduling to provide an efficient application of water.

5.1.3.3

Leaching Requirements If the ground water table or soil stratum is such that leaching cannot occur, a drainage system should be considered to provide the required downward movement of salts.

5.1.3.4

Soil Classification Water infiltration rate and resulting water holding capacity to be assessed. Also, estimated reduction in infiltration rate as more water is absorbed during application.

5.1.3.5

Groundwater Table Level Affects on the infiltration rate of the soil and therefore the leaching capability and requirements to be considered.

5.1.3.6

Climate Higher demand for water in the summer months to satisfy the higher rates of evaporation and plant evapotranspiration.

5.1.3.7

Irrigation Management Consider provision of the following: • • • • •

Field measurement of soil moisture levels at the beginning and end of an irrigation cycle. Installation of flow meters at strategic locations to monitor actual losses and uses. Salinity measurement to establish leaching requirements and actual salt conditions. Evaluation of the irrigation systems performance in the distribution of the water as forecast. Scheduling the irrigation cycle.

5.2

DESIGN CRITERIA

5.2.1

WATER DEMAND

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• •

2

12 litres/m conditions. 2 15 litres/m conditions.

for grass and 35 litres each for trees and shrubs during normal Application over a 12 hour period. for grass and 50 litres each for trees and shrubs during summer Application over a 15 hour period.

These figures allow for demand losses. 5.2.2

PIPEWORK

5.2.2.1

Hydraulic Design Design of sewers should be based on equations such as Manning, ColebrookeWhite and Hazen Williams Pipe roughness factors shall be as follows: • • •

5.2.2.2


0.013. 0.6. 140 for pipe diameters >500mm 135 for pipe diameters< 500mm

Surge Protection To be based on: • • •

5.2.2.3

Maximum velocity of flow of 1.1m/s. Balancing tank. Pressure relief valves.

System Losses 12½% to be allowed

5.2.2.4

Valve Chambers • • • • • • • •

Network isolation. Valves installed at strategic locations to enable isolation of portions of the network. Also provided at cross connections between primary/secondary mains and secondary/ distribution mains. Irrigation T-connection pipe. Maximum spacing up to 500m in green areas. Air release. Air release valves to be installed at all high points. Washout. Washout facilities to be installed at the low points.

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5.2.2.5

Flowmeters Provide at suitable locations to monitor consumption and irrigation efficiencies.

5.2.3

UNDERGROUND RESERVOIRS (UP TO 500,000 GALLON CAPACITY) Normally constructed in reinforced concrete. See standard and typical drawings.

5.2.3.1

Configuration • • • • •

5.2.3.2

Inlet Arrangement • •

5.2.3.3

Separate pipework and valves to each compartment with discharge to a common collection chamber either for disposal to an adjacent sewer or a soakaway or removal by tanker.

Access • • • • •

5.2.3.6

Depends on downstream requirements related to irrigation system pumps and suction head, normally 150mm or 200mm diameter.

Overflow and Washout •

5.2.3.5

Splitting chamber to provide separate feed, normally 400mm diameter, to each compartment with appropriate valves and fitting. Ball float valve in each compartment for automatic water level control.

Outlet Arrangement •

5.2.3.4

Rectangular or square depending on plan area of allocated site. Two equal compartments. Sloping floor to outlet at a gradient of 1 in 70. Internal height 3m. Roof supported on columns to suit structural design.

Ladders for man and equipment entry to each reservoir compartment plus the inlet and outlet chambers. Intermediate platform, removable, to facilitate valve operation in inlet chamber. Covers above ball float valves to afford access for maintenance and possible removal. Water level check facility to each compartment. Lockable covers.

Ventilation

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• 5.2.4

Two number. to each compartment each with integral deodoriser and mosquito screen.

AT GROUND LEVEL ABOVE):

RESERVOIRS (1,000,000 GALLONS CAPACITY AND

Constructed in reinforced concrete or steel. See standard and typical drawings. 5.2.4.1

Configuration • • • • •

5.2.4.2

Inlet Arrangement •

5.2.4.3

•

Similar to inlet arrangement with connection to distribution centre pump suction line. Control of outflow through valve on outlet with remote operation at distribution centre. Grating over outlet bellmouth and retained in upstand. Vortex inhibitor installed either within or over outlet bellmouth.

Overflow and Washout •

5.2.4.5

Single feed pipe under reservoir and up through floor terminating in a bellmouth 150mm above floor level. Control inflow through valve on inlet pipe with remote operation at distribution centre.

Outlet Arrangement •

5.2.4.4

Rectangular with actual dimensions dependent on capacity required, land availability and shape. Length to breath ratio recommended as 1.5 : 1. One compartment. Sloping floor to outlet end at 1 in 200. Maximum height above ground 5m (check with Planning Department restriction). roof supported on columns to suit structural design.

Overflow level at 100mm above top water level connected to outfall and designed to be capable of passing maximum inflow. Washout at floor level in bellmouth and connected to same outfall. Washout usually 300mm diameter. Both pipelines installed at outlet end of reservoir with control valves.

Access • • • •

Lockable covers. Openings sufficient to afford suitable access for men and equipment and over all pipe entries and exits to facilitate inspection. Ladders at each access openings. Staircase access to roof with handrailing.

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5.2.4.6

Ventilation •

5.2.4.7

Water Level Indication •

5.2.5

150mm diameter pipe with integral deodoriser and mosquito mesh provided 2 for every 400m of roof.

Manometer tube 80mm diameter fixed to outside of reservoir wall with fliptype colour indicators and relayed to distribution centre.

PUMPING STATIONS The overall approach to sewage pumping station design, general layout and mechanical/electrical requirements is appropriate to treated sewage effluent pumping stations. The major aspects which can differ are: •

Inlet arrangement: a)

•

Inlet control: a)

•

Pressure sensors/relays are required on the suction side of the pumps to signal the pumps to trip in the event of a set maximum negative pressure being exceeded.

Pump selection: a) b)

•

System between the reservoirs and the pumps is continuous without a break to atmosphere. The suction head on the pipes is directly related to the reservoir level.

Double entry split casing type with double entry impellers are preferred. Construction materials for the parts in contact with the effluent should be resistant to corrosion from the chlorine content.

Outlet control: a) b) c)

Design to maintain a fixed pressure head to allow pump speed/flow characteristics to develop. Bypass line to the pressure control should be provided with pressure sustained by partial closure of a valve. Pressure sensing/relays to be installed on the delivery main.

END OF SECTION

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SECTION 6

STANDARD AND TYPICAL DRAWINGS

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TABLE OF CONTENTS COVER SHEET..................................................................................................................... 1 DOCUMENT CONTROL SHEET .......................................................................................... 2 TABLE OF CONTENTS ........................................................................................................ 3 STANDARD DRAWINGS...................................................................................................... 4 GENERAL SD100 SERIES ................................................................................................... 4 STORM WATER SYSTEM SD200 SERIES .......................................................................... 4 SEWERAGE SYSTEM SD300 SERIES ................................................................................ 4 SEWAGE PUMPING MAIN SD400 SERIES ......................................................................... 5 SEWAGE PUMPING STATION SD500 SERIES................................................................... 5 IRRIGATION SYSTEM SD600 SERIES ................................................................................ 5 IRRIGATION RESERVOIR AND PUMP CHAMBER SD700 SERIES.................................... 5 MISCELLANEOUS SITE WORKS SD800 SERIES............................................................... 5 SEWAGE TREATMENT PLANT SD900 SERIES ................................................................. 6 TYPICAL DRAWINGS .......................................................................................................... 7 GENERAL TD100 SERIES ................................................................................................... 7 STORM WATER SYSTEM TD200 SERIES .......................................................................... 7 SEWERAGE SYSTEM TD300 SERIES ................................................................................ 7 SEWAGE PUMPING MAIN TD400 SERIES ......................................................................... 7 SEWAGE PUMPING STATION TD500 SERIES................................................................... 7 IRRIGATION SYSTEM TD600 SERIES ................................................................................ 8 IRRIGATION RESERVOIR AND PUMP CHAMBER TD700 SERIES.................................... 8 MISCELLANEOUS SITE WORKS TD800 SERIES ............................................................... 8 SEWAGE TREATMENT PLANT TD900 SERIES.................................................................. 8 END OF INDEX..................................................................................................................... 9

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STANDARD DRAWINGS GENERAL SD100 SERIES (SD100 to SD149 Civil, SD150 to SD199 Mechanical and Electrical) Number

Title

SD101 STORM WATER SYSTEM SD200 SERIES (SD200 to SD249 Civil, SD250 to SD299 Mechanical and Electrical) Number SD201 SD202 SD203 SD204 SD205 SD206 SD207 SD208 SD209 SD210 SD211 SD212

Title GA of Storm Water Manholes on Pipelines 200-500mm Dia. GA of Shallow Storm Water Manholes on Pipelines 600-1400mm Dia. GA of Deep Storm Water Manholes on Pipelines 600-1400mm Dia. GA of Shallow Storm Water Manholes on Pipelines 1500-2400mm Dia. GA of Deep Storm Water Manholes on Pipelines 1500-2400mm Dia Lateral Connections to Storm Water Manholes Cover Details for Storm Water Manholes Connection Details for Storm Water Manholes and Structures Storm Water Inlet Details Storm Water Grating and Cover Details Storm Water Catch Basin Details Typical Details of Storm Water Outlet SEWERAGE SYSTEM SD300 SERIES (SD300 to SD349 Civil, SD350 to SD399 Mechanical and Electrical)

Number SD301 SD302 SD303 SD304 SD305 SD306 SD307 SD308 SD310 SD311

Title GA of Sewerage Manhole on Pipelines 150-500mm Dia. GA of Sewerage Manhole on Pipelines 600-1600mm Dia. Sheet 1 of 2 GA of Sewerage Manhole on Pipelines 600-1600mm Dia. Sheet 2 of 2 GA of Sewerage Manhole on Pipelines 1800-2400mm Dia. Sheet 1 of 2 GA of Sewerage Manhole on Pipelines 1800-2400mm Dia. Sheet 2 of 2 Connection Details for Sewerage Manholes and Chambers Cover Details for Sewerage Manholes and Chambers GRP Liner Joint Details for Sewerage Manholes and Chambers Collection and Inspection Chambers Details Small Rectangular Inspection Chambers and House Connection Details

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SEWAGE PUMPING MAIN SD400 SERIES (SD400 to SD449 Civil, SD450 to SD499 Mechanical and Electrical) Number SD401 SD402

Title Discharge Chamber for Sewage Pumping Main Pumping Main Marker Details SEWAGE PUMPING STATION SD500 SERIES (SD500 to SD549 Civil, SD550 to 599 Mechanical and Electrical)

Number SD501 SD502 SD503 SD504 SD505 SD506

Title Builders Works Typical Door Details Builders Works Doors, Steps and Lintels Builders Works Floor Details and Surface Finishes Builders Works Roof Slab and Parapet Details Cover Details Miscellaneous Details IRRIGATION SYSTEM SD600 SERIES (SD600 to SD649 Civil, SD650 to SD699 Mechanical and Electrical)

Number SD601

Title Irrigation Main Marker Details IRRIGATION RESERVOIR AND PUMP CHAMBER SD700 SERIES (SD700 to SD749 Civil, SD750 to SD799 Mechanical and Electrical)

Number

Title

SD701 MISCELLANEOUS SITE WORKS SD800 SERIES (SD800 to SD849 Civil, SD850 to SD899 Mechanical and Electrical) Number SD801 SD802 SD803 SD804 SD805 SD806 SD807

Title Pipe Bedding and Backfill Details Thrust Blocks General Arrangement Detail of Internal Backdrop on Existing Manhole Adjusting Cover Levels for Manholes and Collection Chambers Typical Details Tanking Details Sand Trap and Grease Trap Petrol Interceptor Type 1

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SD808 SD809 SD810 SD811 SD812 SD813 SD814 SD815 SD816 SD817 SD819 SD820 SD821

Petrol Interceptor Type 2 Collection Tank for Petrol Interceptor GRP Ladder Ladder, Walkway, Stairs and Handrailing Details Details of Perforated Pipes for Groundwater Lowering Blockwork Boundary Wall Details Sheet 1 of 2 Blockwork Boundary Wall Details Sheet 2 of 2 Precast Boundary Wall Details Sheet 1 of 2 Precast Boundary Wall Details Sheet 2 of 2 Aluminium Site Entrance Gate Cable Draw Pits. Earth Pits and Cable Ducts Details Street Lighting Works 8.0m Pole Details Paving Details SEWAGE TREATMENT PLANT SD900 SERIES (SD900 to SD949 Civil, SD950 to SD999 Mechanical and Electrical)

Number

Title

SD901

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TYPICAL DRAWINGS GENERAL TD100 SERIES (TD100 to TD149 Civil, TD150 to TD199 Mechanical and Electrical) Number TD100 TD101

Title Project Signboard Site Safety Notice Board STORM WATER SYSTEM TD200 SERIES (TD200 to TD249 Civil, TD250 to TD299 Mechanical and Electrical)

Number TD200 TD201

Title Overall Plan General Layout Plan Sheet 1 of 16 SEWERAGE SYSTEM TD300 SERIES (TD300 to TD349 Civil, TD350 to TD399 Mechanical and Electrical)

Number TD300 TD301

Title Overall Plan General Layout Plan Sheet 1 of 16 SEWAGE PUMPING MAIN TD400 SERIES (TD400 to TD449 Civil, TD450 to TD499 Mechanical and Electrical)

Number TD400 TD401

Title Overall Plan Plan and Profile Sheet 1 of SEWAGE PUMPING STATION TD500 SERIES (TD500 to TD549 Civil, TD550 to TD599 Mechanical and Electrical)

Number TD500 TD501 TD502 TD503 TD504 TD505 TD506 TD507 TD550

Title Site Plan Two Pump Submersible General Arrangement Plan (With Options) Two Pump Submersible General Arrangement Sections (With Options) Control Building Sheet 1 of 2 Control Building Sheet 2 of 2 Control and Generator Building Sheet 1 of 3 Control and Generator Building Sheet 2 of 3 Control and Generator Building Sheet 3 of 3 Typical Curves

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TD551 TD552 TD553 TD554 TD555 TD556 TD557 TD558

Typical Operating System Curves Typical Process and Control Diagram Typical Arrangement Drawing Single Line Diagram Standards Symbols General Notes Typical Drawing Weather Proof Junction Box Typical P&I Diagram IRRIGATION SYSTEM TD600 SERIES (TD600 to TD649 Civil, TD650 to TD699 Mechanical and Electrical)

Number TD600 TD601

Title Overall Plan Plan and Profile IRRIGATION RESERVOIR AND PUMP CHAMBER TD700 SERIES (TD700 to TD749 Civil, TD750 to TD799 Mechanical and Electrical)

Number TD701 TD702 TD703 TD704 TD705 TD710 TD711 TD712 TD713

Title 0.50MG Reservoir General Arrangement Sheet 1 of 2 0.50MG Reservoir General Arrangement Sheet 2 of 2 0.50MG Reservoir General Arrangement Sections 0.50MG Reservoir General Arrangement Inlet Chamber 0.50MG Reservoir General Arrangement Pump Chamber 0.35MG Reservoir General Arrangement Sheet 1 of 2 0.35MG Reservoir General Arrangement Sheet 2 of 2 0.35MG Reservoir General Arrangement Sections 0.35MG Reservoir General Arrangement Inlet Chamber MISCELLANEOUS SITE WORKS TD800 SERIES (TD800 to TD849 Civil, TD850 to TD899 Mechanical and Electrical)

Number TD801 TD802 TD803

Title Thrust and Receiving Pits Details Sheet1 Thrust and Receiving Pits Details Sheet 2 Pipe Details SEWAGE TREATMENT PLANT TD900 SERIES (TD900 to TD949 Civil, TD950 to TD999 Mechanical and Electrical)

Number

Title

TD901

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END OF SECTION

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ADSSC Design Standards Manual

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