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 facilities, 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 Board 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 III - Wastewater
Part IV - Appendices

TABLE OF CONTENTS
DEFINITIONS
PART I - Administrative Procedures
1.1 INTRODUCTION
1.2 OUTLINE APPROVAL
1.2.1 Submission requirements for Outline Approval
1.2.2 Investigations into the availability 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 inspection and issuance of completion
certificate.
1.5 CONNECTION TO WATER AND WASTEWATER SYSTEMS.
1.5.1 Water system
1.5.2 Wastewater system.
PART II - DESIGN GUIDELINES FOR WATER SYSTEMS.
2.1 SCOPE
2.2 GUIDELINES FOR DESIGN OF PIPELINES AND RELATED STRUCTURES
2.2.1 Pipeline
2.2.2 Pipeline Appurtenances
2.2.3 Storage Facilities
2.2.4 Swimming Pool
PART III - 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 all
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 all 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 following 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.
ii) Final Approval
This involves the approval of detailed designs of the water supply
system and wastewater collection, treatment and disposal system
to be installed. This approval must be obtained prior to the
installation of any such facilities.
iii) Inspection and Completion Certificate
All water and wastewater treatment works must be inspected by
the Authority during construction. This will also involve the
conducting and/or witnessing of all 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 Outline 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 Outline Planning Permission issued
by the Town and Country Planning Division.
ii) Two (2) copies of a Location Plan and Vicinity Map, which would
enable the site to be clearly identified in the field. The Location
Plan should be extracted from the Ward Sheet.
iii) 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, river, swamp, spring and wells are within 30m
from the nearest lot, details of their use are required.
vii) Information on seasonal flooding, flood levels are required.
viii) Where it is proposed that the wastewater be treated at an existing
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 will 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 feasibility of supplying potable water to a development,
the Authority will consider the following:
i) The source of supply
ii) The existing and projected water demand in the area.
iii) The existing and operating conditions and schedules.
iv) The possible alternatives for providing the development with a
potable water supply.
A schematic of the proposed water supply connection will 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
effluent disposal systems.
II) Connection to the public/private sewers.
III) 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.
II) 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 field in relation to the proposed
development.

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III) Information on seasonal flooding.
IV) Technical feasibility 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
possibility 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 following:
1.3.1.1 Water Supply
i) Four (4) copies of plans A - size of proposed water reticulation system
showing lot layout, principal drains, all roads, walkways and reserves,
the location, size of all water supply lines, house connections, sluice
valves, fire hydrants and caps, anchor blocks and other special
fittings.

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ii) Four (4) copies of Plans A - size showing sections and elevations of all
communal storage tanks and pumping stations. Performance curves of
all pumps must also be submitted.
iii) Four (4) copies of Plans A - size showing details of river, drain, culvert
and sewer crossings; service connections, sluice 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;
vii) Electrical and mechanical details;
viii) Any other design information, which WASA may require.
1.3.1.2 Wastewater
i) Four (4) copies of plans A - size showing lot layout, principal drains,
all roads, walkways and reserves and layout of the wastewater
collection system showing connections, sizes, gradient of sewers and
distance between manholes invert and top elevations of all manholes
and other appurtenances.
ii) Four (4) copies of plans A - size showing profiles along sewer, showing
ground elevation, invert elevations, manholes, cleanouts, drain
crossings, encasement and special bedding where necessary.
iii) Four (4) copies of plans A - size showing details of all manholes,
cleanouts, house connections, encasement, manhole covers, steps,
supports etc.
iv) Calculation sheets showing depth of flow in sewer at minimum,
average and peak flows, minimum and peak velocities, capacity of
sewer and length, slope 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 - size 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.
vii) Layout of plant on site showing location of pumping facilities, sludge
drying beds, operations building, fence, road reserve, drains, distance
of plant from nearest habitable plot, point of full discharge of effluent
and other pertinent details.
viii) Four (4) copies of plans A - size showing detailed designs of lift
station, sludge drying beds, equipment room, operator’s facilities,
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 specifications for all equipment such as
pumps, blowers, chlorinators and other equipment.
xi) 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 - size of typical lot, showing maximum
building coverage, location of treatment plant or septic tank and
effluent disposal system and outfall effluent drain where
applicable.
c. Four (4) copies of plans A - size showing plans and sections of
septic tank and effluent disposal system including disinfection
facilities where required.

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d. Work sheet showing design computation for sizing of septic tank
and effluent 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.
ii) These works shall be inspected during construction by a Registered
Engineer who shall be required to certify in writing the quality of the
works. The Engineers Certificate of works will generally be accepted by
the Authority as a basis for granting the necessary approvals.
iii) The role of the Authority will 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 all tests.
1.5 CONNECTIONS TO THE WATER AND WASTEWATER SYSTEMS
1.5.1 Water System
i) Connections to the water system will normally be done by the Authority
at the cost of the developer.
ii) 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
licensed 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 specifications to ensure that quality requirements are
met.
2.3 Typical details of appurtenances and other related structures.
2.4 Power requirements for pumpsets, identification of acceptable
type of pumps with considerations to quality, reliability,
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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NO. USER UNIT
TYPICAL (LPD)
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 Edition)

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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) Friction Loss
Friction loss can be computed using either Hazen Williams 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 utilized to
determine the required pipe sizes.
The minimum size of any distribution pipe line shall be 100mm.
A residual pressure of not less than 170Pa (25psi) should be considered in
the design.
2.2.1.5 Vertical Alignment
Water mains shall follow 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
All 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, valves shall be placed at intervals of
500m.
(b) Pipeline sizes greater than 200mm, valves shall be placed at intervals of
1000m.
(c) In all situations valves shall be placed at connection points to the existing
system, at street intersections to facilitate isolations 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 flat a 0.002 grade on the pipeline is required to facilitate
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
All 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 equivalent.
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.
All 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 inside the boundary line or
property line 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 facilities shall be provided for all public, commercial
and industrial buildings and other building developments as stipulated 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 facilities are provided they shall be
adequately fenced, illuminated and accessible to vehicular traffic.
2.2.4 SWIMMING POOL
2.2.4.1 General considerations
Design of a swimming pool involves the following factors:
a. capacity of pool
b. daily water requirement
c. estimated evaporation losses
d. change of water
e. total water requirement
f. filter 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 recycling 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 volume 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 capacities 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
infiltration.
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 flow should be calculated based on the peak factor times the
dry weather flow plus infiltration.
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 existing systems.

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Table 3.1
Wastewater Consumption
NO. USER UNIT
TYPICAL (LPD)
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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NO. USER UNIT
TYPICAL (LPD)
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
velocities, when flowing full, or not less than 0.6m/s.
3.1.9 Velocities in sewers should not normally exceed 3.00 m/s. Where greater
velocities 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,
slopes 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 all changes
in grade, size or alignment, at all 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 filleted to
prevent solids deposition. The minimum diameter of manholes should be
1.2m. Solid and watertight manhole covers are to be used in all 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 installation of the manhole bases. The design, spacing
and materials for manhole steps shall be approved 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 existing or proposed water main. Whenever sewers
cross under water mains, the sewer shall be laid at least 3.0m
horizontally from any existing 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 the 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
rigid 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 full pipe shall be used.
3.3 FORCE MAINS
Considerations for velocity and friction 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 flows 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 flow into 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 allow for
inspection and maintenance.

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3.4.8 Adequate ventilation 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 lights and shall be adequately fenced.
3.4.11 A potable water supply must be provided including a 4000 litre 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) - “Specifications for Liquid
Effluent from Domestic Wastewater Treatment Plants into the
Environment”. This standard has been compulsory status. Appendix 3
refers.
3.5.2 The standard for all other wastewater effluents (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 effluent 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, O
C, 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

25
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 all 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 lighting of Wastewater Treatment Plants shall be provided.
3.5.7 Adequate land shall be provided for the treatment facilities including
additional land area for future plant expansion.
3.5.8 The treatment facilities shall be made accessible to vehicular traffic.
Paved roadways, including on-site vehicular parking and paved walkways
between treatment units and buildings must be provided.
All treatment units shall be provided with service access - steps/ladders,
cat walks and handrails. All 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 litre 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 facilities.
3.6 ON-LOT WASTEWATER DISPOSAL SYSTEMS
3.6.1 Where on lot wastewater disposal systems are permitted the following
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
Authorities (Local Health, WASA) and may be used where no public or
private sewerage system is:
i. available within 50m (150 ft.) or
ii. likely to become available within a reasonable time.
3.6.3 The on-lot disposal system shall be designed to receive all domestic
wastewater from the building.
3.6.4 Storm-water, wastewater from a commercial water softener, water filter,
or other commercial water treatment device or commercial 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 drilled, bored or dug well
ii. an aquifer
iii. 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
ii. a paved road
iii. 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 effluent
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 required,
be submitted to the Water and Sewerage Authority and/or the Approving
Authority for locating test points
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.
All loose material shall be removed from the bottom of the holes and
coarse sand or fine gravel shall be added for a depth of about 50mm to
protect the bottom of the holes from scouring and sediment
3.7.4 Soaking Period
Carefully fill the holes with at least 300mm of clear water above the
Gravel or sand or to a height where the water surface is visible and leave
overnight to allow ample opportunity for soil swelling 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 calculate the percolation rate.
In sand/porous soils with little or no clay, soaking may not be necessary.
If after filling the holes twice with 300mm of water, water seeps
completely away in less than 10 minutes, the test can proceed
immediately.
From a fixed, 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 fall 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 will 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
effluent 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 GUIDELINES
4.1 GENERAL
4.1.1 The installations shall have paved vehicular access, surface drainage,
security lights and shall be adequately fenced.
4.1.2 A minimum of one (1) metre working space is to be provided around blowers,
Iift pumps, sludge pumps and standby generators.
4.1.3 Adequate lifting equipment is to be provided for all 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 flows with 100% standby capacity including blowers, lift pumps and
sludge/recirculating pumps.
4.1.5 All installations shall be designed to allow 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 installations shall conform to the requirements of the Trinidad and
Tobago National Electrical code as administered 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 installed to
115Vfor socket outlets and possible lighting.

4.2.1.4 Adequate layout lighting 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 lighting equipped with auto transfer switches
4.3 MOTOR REQUIREMENTS
4.3.1 Motors shall operate at the above power supply and shall be vertical or horizontal,
weather proof and vermin proof.
4.3.2 Motors shall be rated to drive pumps for the full range of flows 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 ample safety factor.
The factor shall be based the average life expectancy of five 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 writing
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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