wasa guidelines for design of water and wastewater systems

Reproduction in process by WSSM for Internal Use -Feb 2014

GUIDELINES FOR

DESIGN AND CONSTRUCTION OF

WATER AND WASTEWATER

SYSTEMS IN

TRINIDAD AND TOBAGO PREPARED BY:- COMMITTEE OF THE BOARD OF ENGINEERING OF TRINIDAD AND TOBACO AND THE WATER AND SEWERAGE AUTHORITY

JUNE 1995

PREFACE These Guidelines are intended to assist practitioners in the Water and Wastewater industry in the Design and Construction of these facil ities, and in meeting related statutory requirements in a simple and efficient manner while safeguarding the health and sanitation of the citizens of Trinidad and Tobago. They were compiled and revised by a Committee of the Boar d of Engineering of Trinidad and Tobago comprising the following members: Messrs.:

Carl De Four Committee Chairman Hamilton St. George Elton Asson Paul Taylor Harry Phelps Amna Sadeek-Tota John Comacho

The Committee recognizes the invaluable contribution of the Water and Sewerage Authority and the several persons who participated in developing these guidelines.

Part I - Administrative Procedures Part II - Water Part II I - Wastewater Part IV - Appendices

TABLE OF CONTENTS

DEFINITIONS PART I - Administrat ive Procedures 1 .1 INTRODUCTION 1.2 OUTLINE APPROVAL

1.2.1 Submission requirements for Out line Approval 1.2.2 Invest igations into the avai labi l i ty of water supply and

method of wastewater disposal. 1.3 FINAL APPROVAL

1.3.1 Submission requirements for Final Approval .

1.4 INSPECTION AND COMPLETION CERTIFICATE FOR WATER AND WASTEWATER SYSTEMS.

1.4.1 Procedure for inspect ion and issuance of completion

certi f icate. 1.5 CONNECTION TO WATER AND WASTEWATER SYSTEMS.

1.5.1 Water system 1.5.2 Wastewater system.

PART I I - DESIGN GUIDELINES FOR WATER SYSTEMS. 2.1 SCOPE 2.2 GUIDELINES FOR DESIGN OF PIPELINES AND RELATED STRUCTURES

2.2.1 Pipel ine 2.2.2 Pipel ine Appurtenances 2.2.3 Storage Faci l i t ies 2.2.4 Swimming Pool

PART I I I - DESIGN GUIDELINES - WASTEWATER 3 .1 SEWERS AND APPURTENANCES 3.2 SMALL DIAMETER GRAVITY SEWERS 3.3 FORCE MAINS 3.4 WASTEWATER PUMPING STATIONS 3.5 WASTEWATER TREATMENT PLANTS 3.6 ON-LOT WASTEWATER DISPOSAL SYSTEMS 3.7 PROCEDURES FOR CONDUCTING PERCOLATION TEST 3.8 OTHER ON-LOT SYSTEMS

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INTRODUCTION

DEFINITIONS Authority means the Water and Sewerage Authority of Trinidad and Tobago.

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1.1 INTRODUCTION

Under the Water and Sewerage Act Chapter 54 : 40 of the Laws of Trinidad and Tobago, the approval of the Authority is required for the proposed water reticulation and wastewater collection, treatment and disposal syst ems for al l developments which involve the sub -division of land and large scale building developments.

The process of approving applications for building developments by the Authority is designed to ensure that al l building sites are provided with an adequate supply of potable water, as well as an efficient system of wastewater collection, treatment and disposal.

Applications submitted are considered in the fol lowing stages:

i ) Outline Approval

This is approval in principle which indicates the quantity of water which can be made available to the site and makes recommendations on the type of wastewater collection, treatment and disposal system to be installed.

i i) Final Approval

This involves the approval of detailed designs of the water supply system and wastewater collection, treatment and disposal system to be instal led. This approval must be obtained prior to the installation of any such facil ities.

i i i) Inspection and Completion Certificate

Al l water and wastewater treatment works must be inspected by the Authority during construction. This will also involve the conducting and/or witnessing of al l tests. On satisfactory completion, the Authority will issue a Completion Certificate permitting the use of the wastewater system and the connection to the water supply system.

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1.2 OUTLINE APPROVAL 1.2.1 SUBMISSION REQUIREMENT FOR OUTLINE APPROVAL

Applications shall be submitted to the Authority for Outl ine Approval by a registered Engineer and must be accompanied by a completed application form (see Appendix 3 for recommended forms) as well as the following documents:

i ) Two (2) copies of the notice of Outl ine Planning Permission issued

by the Town and Country Planning Division.

i i) Two (2) copies of a Location Plan and Vicinity Map, which would enable the site to be clearly identif ied in the field. The Location Plan should be extracted from the Ward Sheet.

i i i) Two (2) copies of a plan of the area showing topographical

information acceptable to WASA.

iv) The estimated water demand for each type of occupancy i .e. residential , commercial, industrial etc.

v) The proposed method of wastewater collection, treatment and

disposal.

vi) Where the coast, r iver, swamp, spring and wells are within 30m from the nearest lot, details of their use are required.

vi i) Information on seasonal flooding, f lood levels are required.

vi i i) Where it is proposed that the wastewater be treated at an exist ing

wastewater treatment plant not owned by WASA, the existing and proposed load on the plant shall be provided.

ix) Where on-site wastewater treatment with sub -soil disposal is

proposed, the percolation test results wil l be required by WASA.

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1.2.2 INVESTIGATIONS INTO AVAILABILITY OF WATER SUPPLY AND METHOD OF WASTEWATER DISPOSAL.

1.2.2.1 Water Supply

In determining the feasibi lity of supplying potable water to a development, the Authority will consider the fol lowing:

i ) The source of supply

i i) The existing and projected water demand in the area.

i i i) The existing and operating condit ions and schedules.

iv) The possible alternatives for providing the development with a

potable water supply.

A schematic of the proposed water supply connection wil l be prepared to assist the applicant with final design drawings.

1.2.2.2 Method of Wastewater Collection, Treatment and Disposal

The proposed method of wastewater collection, treatment and disposal may include:

I ) Provision of on-lot treatment plant or septic tanks and appropriate

eff luent disposal systems.

I I) Connection to the public/private sewers.

I I I) Construction of conventional central collection, treatment and disposal.

Some of the considerations for determining the appropriate method of wastewater disposal include:

I ) Percolation test results where on-lot sub-soil systems are being

considered. I I) Physical factors - A site visit is necessary to determine physical

factors including location of coast, beaches, river, swamp, the quality of the receiving waters and well f ield in relation to the proposed development.

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I I I) Information on seasonal flooding. IV) Technical feasibil ity of connection to the public wastewater system. V) Advice from the Institute of Marine Affairs where developments are in

close proximity to the coast. VI) Hydrology data from the Water Resources Agency when there is the

possibil ity of contamination of groundwater supply and surface water within catchments in use.

VII) Developers should submit their proposals for projects in their entirety

for Outline Approval providing the phasing of the development. VIII) Operation and maintenance requirements. IX) Soil conditions. X) Topography. XI) Population density in the vicinity of the development . XII) Size of the development.

1.3 FINAL APPROVAL 1.3.1 SUBMISSION FOR FINAL APPROVAL

Submission for Final Approval should include the fol lowing: 1.3.1.1 Water Supply

i ) Four (4) copies of plans A - s ize of proposed water reticulation system showing lot layout, principal drains, all roads, walkways and reserves, the location, s ize of all water supply l ines, house connections, sluice valves, f ire hydrants and caps, anchor blocks and other special f itt ings.

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i i) Four (4) copies of Plans A - s ize showing sections a nd elevations of all communal storage tanks and pumping stations. Performance curves of all pumps must also be submitted.

i i i) Four (4) copies of Plans A - s ize showing details of river, drain, culvert

and sewer crossings; service connections, s luice valves, air valves, washouts, fire hydrants, valve chambers, anchor blocks, thrust blocks, and details of connection from the building development to public water supply.

iv) Data on class of pipes and materials and depth of cover. v) Calculation sheets, showing design flows, pressures, head losses

systems curves etc. vi) Structural designs and calculations; vi i) Electrical and mechanical details; vi i i) Any other design information, which WASA may require.

1.3.1.2 Wastewater

i ) Four (4) copies of plans A - s ize showing lot layout, p rincipal drains, all roads, walkways and reserves and layout of the wastewater collection system showing connections, s izes, gradient of sewers and distance between manholes invert and top elevations of all manholes and other appurtenances.

i i) Four (4) copies of plans A - s ize showing profi les along sewer, showing

ground elevation, invert elevations, manholes, cleanouts, drain crossings, encasement and special bedding where necessary.

i i i) Four (4) copies of plans A - s ize showing details of al l manholes,

cleanouts, house connections, encasement, manhole covers, steps, supports etc.

iv) Calculation sheets showing depth of flow in sewer at minimum,

average and peak f lows, minimum and peak velocities, capacity of sewer and length, s lope and diameter of each section.

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v) Where a wastewater treatment plant is to be provided, a process design should be submitted prior to commencement of detailed design.

vi) Four (4) copies of plans A - s ize showing detailed designs of

wastewater treatment plant including plans and sections of all process units, air supply piping, sludge/wastewater piping, electrical and mechanical details.

vi i) Layout of plant on site showing location of pumping facil it ies, s ludge

drying beds, operations building, fence, road reserve, drains, distance of plant from nearest habitable plot, point of ful l discharge of eff luent and other pertinent details.

vi i i) Four (4) copies of plans A - s ize showing detailed designs of li ft

station, s ludge drying beds, equipment room, operator’s faci lities, operations building, pumping apparatus, chlorine contact chamber.

ix) Work sheets showing hydraulic and biological designs, computations

for sizing of treatment units and electrical and mechanical equipment as well as structural design calculations.

x) Detailed manufacturers specif ications for al l equipment such as

pumps, blowers, chlorinators and other equipment.

x i) Where on-lot disposal systems are proposed:

a. A copy of percolation test certificate issued by the Authority.

b. Four (4) copies of plans A - s ize of typical lot, showing maximum building coverage, location of treatment plant or septic tank and eff luent disposal system and outfal l effluent drain where applicable.

c. Four (4) copies of plans A - s ize showing plans and sections of

septic tank and eff luent disposal system including disinfe ction facil it ies where required.

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d. Work sheet showing design computation for sizing of septic tank and eff luent disposal system.

1.4 INSPECTION AND COMPLETION CERTIFICATE FOR WATER AND WASTEWATER

SYSTEMS 1.4.1 PROCEDURE FOR INSPECTION AND ISSUANCE OF COMPLETION CERTIFICATE

i ) Prior to commencement of construction of the water and wastewater infrastructural works, the applicant submits a work schedule and pays the relevant inspection fees to the Authority.

i i) These works shall be inspected during constructi on by a Registered

Engineer who shall be required to certify in writ ing the quality of the works. The Engineers Certif icate of works wil l generally be accepted by the Authority as a basis for granting the necessary approvals.

i i i) The role of the Authority wil l involve occasional inspection of the works

and witnessing and approval of prescribed tests.

iv) A Completion Certificate for the development will be issued by the Authority upon successful completion of al l tests.

1.5 CONNECTIONS TO THE WATER AND WASTEWAT ER SYSTEMS 1.5.1 Water System

i) Connections to the water system wil l normally be done by the Authority at the cost of the developer.

i i) Subject to the approval of the Authority, the developer can make

alternative arrangements for the connections to be made.

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1.5.2 Wastewater System

All the connections to the public wastewater system must be done by a l icensed sanitary constructor under the supervision of the Authority.

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PART II

DESIGN GUIDELINES FOR WATER SYSTEM

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DESIGN GUIDELINES FOR WATER SYSTEM

2.1 SCOPE

Design guidelines for the following are included in this section:

2.1 Design factors for pipelines, storage tanks and pump stations.

2.2 Material specif ications to ensure that quality requirements are met.

2.3 Typical details of appurtenances a nd other related structures.

2.4 Power requirements for pumpsets, identif ication of acceptable

type of pumps with considerations to quality, reliabil ity, maintenance, spares etc.

2.2 GUIDELINES FOR DESIGN OF PIPELINES AND RELATED STRUCTURES 2.2.1 PIPELINE 2.2.1.1 General

Pipeline sizes should be determined from estimates of water consumption and allowable velocity.

2.2.1.2 Water Consumption

Table 2.1 provides estimates of the average daily demand for potable water.

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Table 2.1 Water Consumption

NO. USER UNIT TYPICAL (LPD)

CONSUMPTION

1.0 Residential Person 350

2.0 Commercial

2.1 Airport Passengers 11

2.2 Apartment House Person 455

2.3 Automobile Service Station Employee 49

Vehicle Served 38

2.4 Boarding House Person 152

2.5 Department Store Toilet Room 2083

Employee 38

2.6 Hotel Guest 189

Employee 38

2.7 Lodging House & Tourist Home Guest 152

2.8 Motel Guest 111

2.9 Motel with Kitchen Guest 152

2.10 Laundry (Self Service) Machine 2083

Wash 158

2.11 Office Employee 57

2.12 Public Lavatory User 19

2.13 Restaurant (including toilet) Customer 57

Conventional Customer 34

Short Order Customer 23

Bar & Cocktail Lounge Seat 76

2.14 Shopping Centre Parking Space 8

Employees 375

2.15 Theater

Indoor Seat 12

Outdoor Car 15

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CONSUMPTION

3.0 Industrial

4.0 Fire Fighting lpm 2275

5.0 Institutional User

5.1 Assembly Hall Seat 12

5.2 Hospital (Medical) Bed 568

Employee 38

5.3 Hospital (Mental) Bed 455

Employee 38

5.4 Prison Inmate 455

Employee 341

5.5 Rest Home Resident 341

Employee 38

5.6 School (Day with Cafeteria)

Gym & Showers Student 95

Cafeteria only Student 57

Cafeteria & Gym Student 38

School (Boarding) Student 284

5.7 Hotels (lcd) 350

Source: ( i) Water & Sewerage Authority

( ii ) Metcalf and Eddy, Wastewater Engineering, Treatment, Disposal & Reuse (3rd Edit ion)

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Pipelines shall be designed to accommodate a peak flow rate of twice (2) the average demand for residential, commercial and industrial usage plus the value estimated for firefighting purposes plus 20% of the total which is considered as unaccounted for water in the system.

2.2.1.3 Velocity

The velocity of flow in any pipeline whether for the average or the peak value shall normally be between 0.91 m/s to 1.52 m/s.

2.2.1.4 Head Losses

(a) Frict ion Loss

Frict ion loss can be computed using either Hazen Wil liams formula or Darcy’s equation.

(b) Minor losses in bends, valves and other fittings should be computed

and included.

For network analysis the Hardy Cross method of design can be util ized to determine the required pipe sizes.

The minimum size of any distribution pipe l ine shall be 100mm.

A residual pressure of not less than 170Pa (25psi) should be considered in the design.

2.2.1.5 Vertical Al ignment

Water mains shall fol low the general contour of the land. 2.2.1.6 Horizontal Alignment

Water mains shall be laid within the road reserve at a depth of not less than 0.76m below the road surface.

Dual water mains may be installed to avoid water services from crossing the carriageway.

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2.2.1.7 Right of Way

A right of way of at least 3.0 metres wide shall be provided for water mains not located within a road reserve.

2.2.1.8 Location in Relation to Sewers

Al l water mains shall be placed above sewers so as to ensure a minimum clearance of 0.45m above the top of the sewer.

2.2.2 PIPELINE APPURTENANCES 2.2.2.1 Gate valves shall be located to ensure that sections of the pipelines and the

development can be locked off without disruption of the total water supply to other areas. Valves shall be provided for control and isolation purposes in accordance to:

(a) Pipeline sizes less than 200mm, valv es shall be placed at intervals of

500m.

(b) Pipeline sizes greater than 200mm, valves shall be placed at intervals of 1000m.

(c) In al l situations valves shall be placed at connection points to the exist ing

system, at street intersections to facil itate isolatio ns and at dead ends. 2.2.2.2 Air release and vacuum valves shall be located at the highest points. Other

air valves shall be placed at other high points. The size of air valves shall be in accordance with the relevant AWWA Standards or Approved Equivalent .

2.2.2.3 Washout and pumpouts shall be provided at all low points. In cases where

the ground level is f lat a 0.002 grade on the pipeline is required to facil itate adequate drainage.

2.2.2.4 Fire hydrants spacing shall be located so as to not exceed 90m apart or as

approved by the fire services department.

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2.2.2.5 Thrust Restraints

Al l tees, bends, cape, reducers, wyes, valves and hydrants shall be restrained by either concrete thrust blocks or thrust rods where applicable. Thrust restraining structures shall be designed in accordance to the relevant AWWA Standards or approved equiva lent.

2.2.2.6 Service Connections

Each plot shall have an individual water service connection not less than 20mm in diameter. Double service connection shall not be permitted.

Al l water service pipes shall be connected to the water main by means of a ferrule or corporation valve and shall be laid at a depth of not less than 450mm.

2.2.2.7 Kerb Valves

Kerb valves shall be installed on water service connections outside the property boundary.

Meter Box

All water service pipes shall terminate just insid e the boundary l ine or property l ine with a typical meter box as approved by the Authority.

2.2.2.8 Testing

Testing of water mains and appurtenances shall conform to AWWA Standards C 600-82. The test pressure shall equal 1.5 times the operating pressure at the point of testing for two (2) hours.

2.2.3 STORAGE FACILITIES

Central water storage facil it ies shall be provided for all public, commercial and industrial buildings and other building developments as st ipulated by the Water and Sewerage Authority.

The water storage tank shall have the capacity equivalent to the average daily requirement of the establishment.

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Where applicable central storage facil ities are provided they shall be adequately fenced, i l luminated and accessible to vehicular traff ic.

2.2.4 SWIMMING POOL 2.2.4.1 General considerations

Design of a swimming pool involves the fol lowing factors:

a. capacity of pool b. daily water requirement c. estimated evaporation losses d. change of water e. total water requirement f . f i lter rate and area g. capacity of recirculation pump h. turnover duration/recirculation period i . method of disinfection

2.2.4.2 Detailed Considerations

These include:

a. All for potable use must be obtained from a source approved by the Authority

b. Fresh water should be introduced into the suction side of the

recirculaton pump, preferably through a make -up water tank. An air gap not less than 100mm shall be provided.

c. Chlorine residual should be 0.6ppm on the suction side of the

recirculation pump.

d. The recirculaton pump shall be capable of recycl ing or dewatering the pool at least once every 6 hours for commercial pools and once every 8 hours for domestic pools.

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e. Daily partial renewal of clear water should be on average one twentieth of the total vo lume of swimming pool water.

f . Pool water shall not be drained into a private or public wastewater

collection system.

g. Swimming pools should not be located less than 3.0m from any building sewer or septic tank and 7.5m from subsurface wastewater absorption unit.

DESIGN GUIDELINES - WASTEWATER 3.1 Sewers & Appurtenances Factors that must be considered in determining the required capacit ies of

sanitary sewers include: 3.1.1 Sewers shall be designed for the estimated ultimate tributary population. 3.1.2 Sewers are not to be designed for maximum flow i.e. peak flow and

infi ltration. 3.1.3 Total contribution population for residential developments shall be 4.5

person per dwelling unit. Population densities for other establishments as obtained from the Town and Country Planning Division would be admissible.

3.1.4 Per capita daily contribution of wastewater should be in accordance with

Table 3.1. 3.1.5 The peak f low should be calculated based on the peak factor t imes the

dry weather f low plus infi ltra tion.

The peak factor shall be calculated based on the formula, peak factor =

where P is population in thousands.

3.1.6 Ground water infiltration should be at 5000 l/ha/day, or based on actual

investigation or established data, if available, in case of exist ing systems.

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Table 3.1 Wastewater Consumption


CONSUMPTION

1.0 Residential Person 280 (170 GPD)

2.0 Commercial (working)

2.1 Airport Passengers 10

2.2 Automobile Service Station Vehicle Served 40

Employee 50

2.3 Bar Customer 8

Employee 50

2.4 Hotel Guest 190

Employee 4

2.5 Industrial Building (excluding industry & cafeteria)

Employee 55

2.6 Laundry (self service) Machine 2198

Wash 190

2.7 Motel Person 120

2.8 Motel with Kitchen Person 200

2.9 Office Employee 55

2.10 Restaurant Meal 10

2.11 Rooming House Resident 150

2.12 Store (department) Toilet Room 2000

Employee 40

2.13 Shopping Centre Parking Space 4

Employees 40

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CONSUMPTION

3.0 Institutional

3.1 Hospital, Medical Bed 78.2

Employee 48 3.2 Hospital, Mental Bed 482

Employee 48 3.3 Prison Inmate 541

Employee 48

3.4 Institutional (school)

School (Day with Cafeteria), Gym & Showers

Student 96

Cafeteria only Student 72

Cafeteria & Gym Student 48

School (Boarding) Student 336

3.5 Rest Home Resident 421

Employee 48 3.6 Apartment, resort, recreational Person 264

Cabin, resort, cafeteria Person 192

Customer 7 Employee 48

3.7 Campground (development) Person 144

Cocktail Lounge Seat 90

Coffee Shop Customer 24

Employee 48

3.8 Day Camp (No meals) Person 60

Dining Hall Meal Served 36

Dormitory, Bunkhouse Person 180

Hotel, Resort Person 240

Laundromat Machine 2641

Store Resort Customer 12

Employee 48

3.9 Swimming Pool Customer 48

Employee 48

3.10 Theater Seat 12

Visitor Centre Visitor 24

Country Club Member Present 482

Employee 60

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3.1.7 No public sewers shall be less than 20mm in diameter except where permitted by the Authority.

3.1.8 All sewers shall be so designed and constructed to give self cleansing

velocit ies, when flowing ful l, or not less than 0.6m/s. 3.1.9 Velocit ies in sewers should not normally exceed 3.00 m/s. Where greater

velocit ies are attained special provision shall be made to project against displacement be erosion, abrasion and movement.

3.1.10 Table 3.2 shows the maximum lengths between manholes and absolut e

minimum slopes that should be provided for various pipe sizes. However, s lopes greater than these are desirable:

Table 3.2

Sewer Size Maximum

Distances/Lengths Minimum Slope

mm ins m ft. ft./100 ft.-m/100m

200 8 90 300 0.4

250 10 110 350 0.28

300 12 110 350 0.22

350 14 110 350 0.17

375 15 110 350 0.15

400 16 120 400 0.14

450 18 120 400 0.12

525 21 120 400 0.1

600 24 150 400 0.08

3.1.11 Sewers 600mm or less shall be laid with straight alignment between

manholes. 3.1.12 When a sewer joins a larger one, the invert of the larger sewer should be

lowered sufficiently to maintain the same energy gradient. 3.1.13 Pipe material shall be of PVC or concrete or any other material as

approved by the Authority.

a) PVC - All PVC pipe shall be manufactured according to BS 5481 or approved equivalent international standard;

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b) Concrete - concrete pipes shall be manufactured to meet the requirements of BS 556 or approved equivalent international standard.

3.1.14 Manholes shall be installed at the upper end of each line, at al l changes

in grade, size or alignment, at al l inter -sections and in accordance with distances at Table 3.2. A drop manhole should be provided for a sewer entering a manhole at an elevation of 0.6m or more, above the manhole invert. Where the difference in the elevation between the incoming and the manhole invert is less than 0.6m, the invert should be f i l leted to prevent solids deposit ion. The minimum diameter of manholes should be 1.2m. Solid and watertight manhole covers are to be used in al l cases. Manhole covers shall be fitted with a gasket to the approval of the Authority. Manholes should be constructed of precast reinforced concrete cylinders. The base of the manhole shall be such as to permit the flushing of solids. Sulphate resistant cement shall be used in the construction and instal lation of the manhole bases. The design, spacing and materials for manhole steps shall be approve d by the Authority.

3.1.15 There shall be no physical connection between a public or private potable

water supply system and a sewer. Sewers should be laid at least 3.0m horizontally from any exist ing or proposed water main. Whenever sewers cross under water mains, the sewer shall be laid at least 3.0m horizontally from any exist ing or proposed water main. Whenever sewers cross under water mains, the sewer shall be laid at such elevation that the top of the sewer is at least 0.45m below the bottom of th e water main.

3.1.16 In roadways where cover is less than 1.2m or in open areas where cover

is less than 0.9m, the pipe shall be structurally reinforced to perform as a r igid pipe system.

3.1.17 The top of a sewer shall be at least 0.6m below the bottom of any drain it

crosses. Where this distance is less than 0.6m, the sewer shall be encased in concrete.

3.1.18 A right-of-way at least 3.0m wide shall be provided for sewer mains not

located within a road reserve.

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3.2 SEWER DIAMETER GRAVITY SEWERS 3.2.1 Where small diameter gravity sewers are permitted the EPA Manual

Alternative Wastewater Collection Systems, the design of small bore sewer systems by R. J. Otis and D. Duncan Mara, or any other standard acceptable to the Authority shall be used.

3.2.2 The minimum pipe diameter shall not be less than 100mm. 3.2.3 The minimum design velocity of 0.46 m/s at half ful l pipe shall be used. 3.3 FORCE MAINS

Considerations for velocity and frict ion losses in the Design of Force Mains shall be similar to those applied to the design of water mains. The minimum size of force main is 100mm.

3.4 WASTEWATER PUMPING STATIONS 3.4.1 Pumping stations shall be designed to handle peak f lows with 100%

standby capacity. 3.4.2 The wetwell shall provide a minimum holding period of 10 minutes for

the design flow. 3.4.3 Pumps should be sized and operated so that their rate of discharge is

nearly equal to the rate of f low i nto the wetwell . 3.4.4 A coarse screen shall be provided before the wetwell. Adequate

provisions must be made for the removal and disposal of screenings. 3.4.5 Pumping stations must be provided with standby power generating units. 3.4.5 In areas affected by seasonal flooding, precautionary measures shall be

taken to guard against flooding of the wetwell . 3.4.7 Safe access shall be provided for dry and wet wells to al low for

inspection and maintenance.

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3.4.8 Adequate venti lat ion must be provided. 3.4.9 The distance between the compound of a pumping station and a

residential building shall not be less than 50m. 3.4.10 The installation shall have paved vehicular access, surface drainage,

security l ights and shall be adequately fenced. 3.4.11 A potable water supply must be provided including a 4000 l itre storage

tank with a pump capable of delivering a minimum of 90 lpm at convert to in head 30m head.

3.5 WASTEWATER TREATMENT PLANTS 3.5.1 The standard for domestic effluent shall be the Trinidad and T obago

Bureau of Standards (TTBS - 417 : 1993) - “Specif ications for L iquid Effluent from Domestic Wastewater Treatment Plants into the Environment”. This standard has been compulsory status. Appendix 3 refers.

3.5.2 The standard for al l other wastewater e ff luents (Municipal, commercial,

agricultural etc.) shall be the World Health Organization (WHO) Standards, or any other standards acceptable to the Authority.

3.5.3 Table 3.3 provides tolerance limits for industrial eff luent discharged into

public sewers .

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TABLE 3.3

TOLERANCE LIMITS FOR INDUSTRIAL EFFLUENTS BEING DISCHARGED INTO PUBLIC SEWERS.

ITEM NUMBER

CHARACTERISTIC TOLERANCE LIMITS

INTO PUBLIC SEWERS

1 Colour & Odour -

2 Suspended Solids, mg/l, max. 350

3 Particle size of suspended solids, mm 3

4 Dissolved Solids (inorganic), mg/l max. 2100

5 pH value 5.5 to 9.0

6 Temperature, OC, max. 4.5 at the point of

discharge

7 Oil, grease, mg/l, max. 20

8 Total residual chlorine, mg/l, max. -

9 Ammoniacal nitrogen, (as N), mg/l, max. 50

10 Total nitrogen (as N), mg/l, max. -

11 Free ammonia (as NH3 ), mg/l, max. -

12 Biochemical oxygen demand (5 days at 20O , max.) -

13 Chemical oxygen demand, mg/l, max. 300

14 Arsenic (as As), mg/l, max. 0.2

15 Mercury (as Hg) mg/l, max. 0.01

16 Lead (as Pb), mg/l, max. 1

17 Cadmin (as Cd), mg/l, max. 1

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ITEM NUMBER

CHARACTERISTIC TOLERANCE LIMITS

INTO PUBLIC SEWERS

18 Hexavalent chromium (as Cr + 6) mg/l, max. 2

19 Total chromium (as Cr), mg/l, max. 2

20 Copper (Cu), mg/l, max. 3

21 Zinc (as Zn), mg/l, max. 15

22 Selenium (as Se), mg/l, max. 0.05

23 Nickel (as Ni), mg/l, max 3

24 Boron (as B), mg/l, max 2

25 Sodium, max. 60

26 Residual sodium carbonate, mg/l, max. -

27 Cyanide (as Cn), mg/l, max. 2

28 Chloride (as CI), mg/l, max. 1000

29 Fluoride (as F), mg/l, max. 15

30 Dissolved phosphates (as P), mg/l, max. -

31 Sulphate (as S), mg/l, max. 1000

32 Sulphide (as S), mg/l, max. -

33 Pesticides (see note 5) Absent

34 Phenolic compounds I (as C6H5OH), mg/l, max. 5

35 Radioactive materials:

a.) Alpha emitters, uc/ml, max. 10 to 7

b.) Beta emitters, uc/mg, max 10 to 6

26

3.5.4 The Authority may consider any technically feasible method of wastewater treatment providing it can produce effluent of the required quality and which can satisfy the Authority’s other requirements such as location. All relevant references must be provided.

3.5.5 Treatment plants are to be located downwind of al l residential premises.

Treatment tanks shall not be located less than 50m from habitable premises. Where treatment is done at waste stabilization ponds the distance from the pond to any habitable premises shall not be less than 100m. A thick green belt (for example, tall pine trees) shall be provided between the pond and the habitable premises.

3.5.6 Fencing and l ighting of Wastewater Treatment Plants shall be provided. 3.5.7 Adequate land shall be provided for the treat ment facil ities including

addit ional land area for future plant expansion. 3.5.8 The treatment faci lit ies shall be made accessible to vehicular traff ic.

Paved roadways, including on -site vehicular parking and paved walkways between treatment units and bui ldings must be provided.

Al l treatment units shall be provided with service access - steps/ladders, cat walks and handrails. Al l works must be painted.

3.5.9 Adequate accommodation by means of a room equipped with storage

cupboards, lavatory 3.5.10 A potable water supply must be provided, including - a 4000 l itre water

storage tank with a pump capable of delivering a minimum of 90 lpm at 30 m pressure.

27

3.5.11 Treatment plants shall be provided with laboratory faci lities. 3.6 ON-LOT WASTEWATER DISPOSAL SYSTEMS 3.6.1 Where on lot wastewater disposal systems are permitted the fol lowing

manual may be used:- (a) EPA Design Manual ‘On -Site Wastewater Treatment and Disposal

System’ (b) the Trinidad and Tobago Bureau of Standards - T.T.S 16 80 400 (c) or any other standard acceptable to Water and Sewerage Authority

shall be used.

3.6.2 On-Lot systems shall be constructed in accordance with approvals of the Authorit ies (Local Health, WASA) and may be used where no public or private sewerage system is: i . avai lable within 50m (150 ft.) or i i . l ikely to become available within a reasonable time.

3.6.3 The on-lot disposal system shall be designed to receive all domestic wastewater f rom the building.

3.6.4 Storm-water, wastewater from a commercial water softener, water f i lter,

or other commercial water treatment device or co mmercial or industrial process, wastes shall not be discharged into an on -lot system designed to receive sanitary sewage .

3.6.5 Sewage or sewage effluent shall not be discharged into : i . a dri lled, bored or dug well i i . an aquifer

i i i . an excavation, seepage pit or cesspool deeper than 3.66m (12 ft.) from the surface; or

iv. an abandoned water well

3.6.6 An absorption system shall not normally be located under i . a roadway or driveway

28

i i . a paved road i i i. a vehicle parking lot iv. any building

TABLE 3.4

Minimum distance for location of On-Site/Lot Wastewater Systems

FEATURE SEPTIC TANK

METRE

ABSORPTION UNIT METRE

Building 1.50 3.00

Property Boundary 1.50 1.50 Wells, Springs or any water source 30.00 30.00

Potable Water Pipes 7.50 3.00 * Cuts or Embankments 3.00 30.00 Paths 7.50 1.50 Swimming Pools 1.50 7.50 Shore line / high-water mark 3.00 30.00 Underground Water Storage Tank 30.00 15.00 Large trees 7.50 1.50 Septic Tank 1.50 1.50 Soakaway 1.50

Note * Ground Water Level 1.20 1.20

Notes:

* These distances should be increased to 60 meters, if the installation is on a water supply watershed.

* The minimum clearance between the bottom of an absorption unit and the ground water level.

29

3.6.7 Table 3.4 gives details of minimum distances for location of On -Lot Wastewater Systems from various features

3.7 PROCEEDURE FOR MAKING PERCOLATION TEST 3.7.1 Where the effluent of an on-lot system is to be disposed of in a sub-

surface system, the design of the system shall be based on the results of a Percolation Test performed in keeping with the building procedures

Percolation tests shall be conducted under the supervision of the Water and Sewerage Authority. A test certificate shall be issued following these tests.

These tests ascertain the suitability of a receiving soil to, absorb eff luent from an on-lot: system. Prior to the percolation tests, a subdivision/site plan for the proposed development showing contours at 1m or 2m intervals should if requi red, be submitted to the Water and Sewerage Authority and/or the Approving Authority for locating test poi nts

3.7.2 Location and Number of test holes

The test shall be conducted at points where the disposal units (soakaway pit and or absorption trenches) are to be located. A minimum of three shall be bored or dug across the test area. At least one hole shall be bored or dug to a depth of about 3m at the lowest site elevation in order to determine the existence of ground water or impervious strata.

3.7.3 Preparation of test holes

Each hole shall have a diameter or side width respectively of 150 to 300mm and vertical sides to a depth of the proposed soakaway pit or absorption trench (min. depth 1.3m)

30

The bottom and sides of the holes shall be carefully scratched in order to remove any smeared soil surface and to provide a natural soil/water interface into which water may percolate . Al l loose materia l shall be removed from the bottom of the holes and coarse sand or f ine gravel shall be added for a depth of about 50mm to protect the bottom of the holes from sco uring and sediment

3.7.4 Soaking Period

Carefully f il l the holes with at least 300mm of clear water above the Gravel or sand or to a height where the water su rface is visible and leave overnight to al low ample opportunity for soil swell ing and saturation.

The percolation test shall be determined 24 hours after the water is added

3.7.5 Measurement of Percolation Rate

Adjust the water level to 300mm above the gravel or sand . From a fixed reference point the drop in water level is noted over a 120 minutes period at intervals 30 minutes. After each measurement the water level is adjusted to the 300mm level. The last water level drop is used to calc ulate the percolation rate. In sand/porous soils with l itt le or no clay, soaking may not be necessary. If after fi l l ing the holes twice with 300mm of water, water seeps completely away in less than 10 minutes, the test can proceed immediately. From a f ixed, reference point the drop in water level shall be noted over a 60 minutes period at intervals of 10 minutes adjusting the water level to 300mm after each measurement. The last water level drop is used to calculate the percolation rate .

31

3.7.6 Calculation of Percolation Rate

The percolation rate is the time taken, in minutes, for the water level in a test hole to fal l 25mm. To determine the percolation rate for the area, the rates obtained for each hole are averaged. If the rates in area vary by more than 20 minutes/25mm, variations in the soil type are indicated. Under these circumstances percolation rates should not be averaged.

3.7.7 Interpretation of Results Absorption System Percolation Rate Slower than 30 min./25mm Unsuitable for soakaway

Slower than 60 min./25mm Unsuitable for absorption trenches

3.7.8 The final choice of which wastewater disposal system is adopted in a

particular case wil l depend on many factors. 3.7.9 Absorption - Area Requirements For Private Residences

PERCOLATION RATE (TIME REQUIRED TO FALL 25MM IN MINUTES)

REQUIRED ABSORPTION AREA SQUARE METERS PER BEDROOM FOR BOTTOM ABSORPTION TRENCHES OR SIDE WALL FOR SOAKAWAY PITS

1 or less 6.5

2 7.9

3 9.3

4 10.7

5 11.6

10 15.3

15 17.6

30 23.2

45 27.9

60 30.7

32

3.7.10 Table 3.4 provides details of minimum distances for location of on -lot Wastewater systems

3.8 Other On-Lot Systems

Where percolation rates do not permit sub-soil disposal of wastewater eff luent the following on-lot systems may be used. These include: (a.) Evapo-transpiration system including use of the mound system (b.) Use of separate dual system

Guidelines for Design and Construction of Water and Wastewater Systems in Trinidad and Tobago Page 1

APENDIX I


APPENDIX 1

4.0 MECHANICAL & ELECTRICAL GUIDEL INES 4.1 GENERAL 4.1.1 The installations shall have paved ve hicular access, surface drainage,

security l ights and shall be adequately fenced. 4.1.2 A minimum of one (1) metre working space is to be provided around blowers,

I i ft pumps, sludge pumps and standby generators. 4.1.3 Adequate l ift ing equipment is to be provided for al l pumps as well as

blowers rated at 15 Hp and larger. 4.1.4 Wastewater pump stations and treatment plants shall be designed to handle

peak f lows with 100% standby capacity including blowers, l i ft pumps and sludge/recirculating pumps .

4.1.5 All installations shall be designed to all ow for unmanned operations 4.2 ELECTRICAL POWER/LIGHTING REQUIREMENT FOR WATER AND WASTEWATER

INSTALLATION 4.2.1 GENERAL 4.2.1.1 The character for the electrical power supply to these installations shall be

400V, 3 phase, 60Hz, 4 wire or 230 V, 1 pH, 60 Hz. 4.2.1.2 These instal lations shall conform to the requirements of the Trinidad and

Tobago National Electrical code as a dministered by the Electrical Inspectorate of the Trinidad and Tobago Electricity Commission.

4.2.1.3 A single phase step down 230V/115V transformer shall be instal led to

115Vfor socket outlets and possible l ighting.


4.2.1.4 Adequate layout l ighting shall be provided where a starter house is used adequate internal fluorescent lighting shall be provided and at least two (120V/115V) electrical outlets.

4.2.1.5 External lights shall be controlled by photo electric sensors. 4.2.2 WASTEWATER PLANTS - ELECTRICAL POWER 4.2.2.2 A standby generator shall be provided for at least fifty percent (50%)

pumping capacity, surface aerators/blower capacity recirculating pu mps as well as emergency l ighting equipped with auto transfer switches

4.3 MOTOR REQUIREMENTS 4.3.1 Motors shall operate at the above powe r supply and shall be vertical or horizonta l,

weather proof and vermin proof. 4.3.2 Motors shall be rated to drive pumps for the full range of f lows and heads. 4.3.3 Motors shall be rated to be able to operate in tropical countries. 4.3.4 Motor thrust bearings shall have capacity to carry the weight of all the rotating

parts plus the hydraulic thrust of the pump impellers and have a mple safety factor. The factor shall be based the average l ife expectancy of f ive years’ operating at 24 hours per day.

4.3.5 The motor shall be of the full voltage starting, vertical hollow shaft, squirrel cage

induction type 4.3.6 The motor speed shall not exceed 1800 rpm for motors larger than 30 Hp (no load)


4.4 MOTOR STARTER/CONTROL REQUIREMENTS 4.4.1 Starters shall conform to the latest HEMA Class II type B standards, the

requirements of the Trinidad and Tobago Electrical Inspectorate, and the requirements of the Trinidad and Tobago Electricity Commission

4.4.2 Starters shall be of the reduced voltage type unless otherwise approved in writ ing

by T&TEC.

SUBJECT STANDARD

Storage Tanks

Welded Steel Tanks ANSI/AWWA D100-84

Painting for Welded Steel Tanks ANSI/AWWA D102-78

Factory Coated Tanks ANSI/AWWA D103-80

Disinfection ANSI/AWWA D652-86

Concrete Structures for retaining liquids AS 3735 1991

Pipelines

Polybutylene (PB) AWWA C-902-78

Polyethylene (PET) AWWA C-901-78

Poly Vinyl Chloride (PVC) AWWA C-900-75

Fabricated Steel Pipe and Fittings AWWA C-208-83

Steel Pipe Flanges Class D AWWA C-207-86

Coal tar protection coatings and linings for steel water pipelines

AWWA C-203-86

Flanged Ductile Iron Pipelines AWWA C-1l5/A21

Rubber Gasket AWWA C-111/A21

Disinfection AWWA C-651-86

Pressure Test AWWA C-600-82

Grey Iron casting BS 1452:1977

Elastomeric Joint Rings for pipework and pipelines BS 2494:1986

Flanges and bolting for pipes valves and fittings metric series (copper alloy and composite flanges)

BS 4504: Part 2 1974

Metal Washers for General Engineering purposes metric series

BS 4320:1968

Specifications for Poly Vinyl Chloride (PVC) Solvent Cement for use with unplastized PVC Pipes and fittings for cold water applications

TTS 413-1992

Cast Iron Non-pressure pipes and pipe fittings metric units

AS 1631-1974


SUBJECT STANDARD

Valves

Balls Valves AWWA C-507-35

Rubber Sealed Butterfly Valves BS 2494:1986

Sluice Valves AWWA C-501-56

a) Water Service Connections

b) Fire Hydrant

c) End Cap

d) Washout

e) Valve Chamber and Assembly

f) Trench Cross Section

g) Culvert Crossing

h) Thrust Block

Predominately key Operated Cast Iron Valve for waterworks purposes

BS1 5163:1986

Butterfly Valves BS 5155:1984

Copper Alloy Gate Valve and Non-Return Valve for use in water supply and hot water services

AS 1628: 1917


ABSORPTION RATES

Percolation Rate [time taken for water level to drop 25mm]

(minutes)

Required Absorption Area

m2 per 1000 l per day m3/m2/day

2 or less 12.1 0.0830

3 14.6 0.0708

4 17.1 0.0585

5 18.4 0.0543

6 19.5 0.0516

7 20.6 0.0489

8 21.7 0.0462

9 22.8 0.0435

10 24.5 0.0408

11 25.2 0.0397

12 26.0 0.0386

13 26.7 0.0375

14 27.5 0.0364

15 28.2 0.0354

16 28.8 0.0349

17 29.3 0.0343

18 29.8 0.0338

19 30.3 0.0332

20 30.8 0.0327

21 31.3 0.0321

22 31.8 0.0316

23 32.3 0.0310

24 32.8 0.0305

25 33.3 0.0299

26 33.8 0.0294


27 34.3 0.0288

28 34.8 0.0283

29 35.3 0.0277

30 36.8 0.0272

31 37.3 0.0269

32 37.8 0.0265

33 38.3 0.0261

34 38.8 0.0257

35 39.3 0.0253

36 39.8 0.0249

37 40.3 0.0247

38 40.8 0.0243

39 41.3 0.0241

40 41.8 0.0237

41 42.3 0.0234

42 42.8 0.0230

43 43.3 0.0227

44 43.8 0.0223

45 44.5 0.0220

46 44.8 0.0223

47 45.1 0.0227

48 45.4 0.0220

49 45.7 0.0219

50 45.96 0.0217

51 46.2 0.0216

52 46.5 0.0215

53 46.8 0.0213

54 47.1 0.0212

55 47.4 0.0211

56 47.7 0.0210


57 48 0.0208

58 48.3 0.0207

59 48.6 0.0206

60 48.9 0.0204

over 60 Unsuitable for shallow absorption systems

wasa guidelines for design of water and wastewater systems

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