guidelines for design and construction of water and wastewater systems

1. Water and Sewerage Authority
EDITED BY:
COMMITTEE OF THE BOARD OF
ENGINEERING OF TRINIDAD AND TOBAGO
AND THE WATER AND SEWERAGE AUTHORITY JUNE 2003
GUIDELINES FOR DESIGN AND
CONSTRUCTION OF
WATER AND WASTEWATER SYSTEMS IN
TRINIDAD AND TOBAGO

2. 2
1.1 SCOPE
The Approval of the Water and Sewerage is required, under the Water and
Sewerage Act Chapter 54:40 of the Laws of Trinidad and Tobago, for any
proposed water reticulation and wastewater collection, treatment and disposal
systems for all developments which involve the subdivision of land and
construction of non-simple buildings.
The object of approving applications for all Developments and Non-Simple
Buildings by the Authority is to ensure that all building sites are provided with an
adequate supply of potable water, as well as an efficient system of collection and
disposal of wastewater.
Applications submitted for approval are considered in the following stages:
1.1.1 Definitions
i) Outline Approval
This is approval in principle, which indicates that the quantity of water
which is needed, can be made available to the site and that the type of
wastewater collection, treatment and disposal system proposed is suitable
and acceptable to the Authority.
ii) Final Approval
This involves the approval of detailed designs of the water supply system
and wastewater collection, treatment and disposal facilities to be installed.
This approval must be obtained prior to the installation of any such
facilities.
iii) Completion Certificate
The Authority must inspect all water and wastewater treatment works
during construction. This will also involve the carrying out 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.

3. 3
1.2 OUTLINE APPROVAL
1.2.1 SUBMISSION REQUIREMENTS FOR OUTLINE APPROVAL
Applications shall be submitted to the Authority for Outline Approval by a
listed professional Engineer and must be accompanied by a completed
application form (See Appendix 3 for approved 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 or vicinity map which would enable
the site to be clearly identified in the field. The location plan should
be extracted from a Ward Sheet.
iii) Two (2) copies of a plan of the area showing topographical
information acceptable to the Authority.
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 or well are within 30m of the
nearest lot, details of the use to be made of the lots are required.
vii) Information on seasonal flooding and flood levels are required.
viii) Where it is proposed that the wastewater be treated at an existing
wastewater treatment plant not owned by the Authority, the existing,
the designed and the proposed load on the plant shall be provided.
ix) Where on-site wastewater treatment with sub-soil disposal is
proposed, the Authority will require the witnessing of a percolation
test and its results.

4. 4
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.
iv) The alternatives for providing the Development with
a potable water supply.
v) The proposed water supply connection and point of
interconnection.
1.2.2.2 Method of Wastewater Collection, Treatment and Disposal
a. The developer may propose and the Authority will consider
methods of disposal including:
i) Provision of on-lot treatment including septic tanks and
appropriate effluent disposal systems.
ii) Connection to the public/private sewers.
iii) Construction of conventional central collection treatment
and disposal systems.
b. The developer may propose and the Authority will consider the
approval of other methods of disposal.
Some of the factors that will influence the appropriate method of
disposal include:
i) Percolation test results where on-lot sub-soil systems are
being considered.
ii) Physical factors – These include location and proximity
the coast, beaches, rivers, swamps, the quality of the

5. 5
receiving waters and the existing well field in relation to
the proposed Development.
iii) The incidence of seasonal flooding.
iv) 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) The possibility of contamination of groundwater and
surface water supplies.
vii) Submission of proposals for projects in their entirety for
Outline Approval and the phasing of the developmental
works.
viii) Operation and Maintenance requirements and the
arrangement for meeting these requirements in both the
short and long term.
ix) Soil conditions
x) Topography
xi) Population density in the vicinity of the Development.
1.3 FINAL APPROVAL
1.3.1 SUBMISSION REQUIREMENTS 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 and size of all water supply lines, house connections, sluice
valves, fire hydrants and caps, anchor blocks and other special fittings.
ii) Four (4) copies of plans A – size of sections and elevations of all
communal storage tanks and pumping stations. Performance curves of all
pumps must also be submitted.

6. 6
iii) Four (4) copies of plans (A – size) showing details of river, drain, culvert
and sewer crossings, service connections, gate valves, air valves,
washouts, fire hydrants and details of the connection between the Building
Development and the public water supply.
iv) Data on class of pipes, the material of which they are made and depth of
cover to be used.
v) Calculation sheets showing design flows, pressures head losses, system
curves etc.
vi) Structural designs and calculations for support and retaining structures.
vii) Electrical and mechanical details.
viii) Any other relevant design information that the Authority may request.
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 distances between manholes, invert and top
elevations of all manholes and other appurtenances.
(ii) Four (4) copies of plans (A – size) showing profiles along sewers,
showing ground elevation, invert elevations, manholes, clean outs
drain crossings, encasement and special bedding where
necessary.
(iii) Four (4) copies of plan (A – size) showing details of all manholes,
clean outs house connections, encasement, manhole covers, step
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.
(v) Where a wastewater treatment plant is to be provided, a process
design should be submitted and approved prior to the
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

7. 7
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, fences, 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, operators’ facilities,
operations building, pumping apparatus and the 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.
(xi) Where on-lot disposal systems are proposed:
a) A copy of the 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, effluent disposal system and outfall effluent
drain where applicable.
c) Four (4) copies of drawings (A – size) showing plan and
sections of septic tank and effluent disposal system,
including disinfection facilities where required.
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 shall submit a work
schedule and pay the relevant inspection fees to the Authority.

8. 8
(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 Authority, as a basis for granting the necessary
approvals, will accept the Engineer’s Certificate of the works.
(iii) The role of the Authority will involve occasional inspection of the
works and witnessing and approval of prescribed tests.
(iv) The Water and Sewerage Authority will issue a completion
certificate for the Development upon satisfactory completion of the
works.
1.5 CONNECTIONS TO THE WATER AND WASTEWATER SYSTEMS
1.5.1 WATER SYSTEM
Connections to the water system will normally be done by the Water and
Sewerage Authority at a cost of the Developer.
1.5.2 WASTEWATER SYSTEM
A Licensed Sanitary Constructor under the supervision of the Water and
Sewerage Authority and at a cost of the Developer shall make all the connections
to the public wastewater system.

9. 9
PART II
DESIGN GUIDELINES FOR WATER SYSTEM

10. 10
DESIGN GUIDELINES FOR WATER SYSTEM
2.1 SCOPE
Design guidelines for the following are included in this section: -
2.1.1 Design factors for pipelines, storage tanks and pump stations.
2.1.2 Material specifications to ensure quality requirements are met.
2.1.3 Typical details of appurtenances and other related structures.
2.1.4 Power requirements for pumpsets, identification of acceptable types of
pumps with considerations for quality reliability and maintenance.
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:

11. 11
Table 2.1
Water Consumption
NO. USER UNIT TYPICAL
CONSUMPTION
(lpd)
1 Residential Person 350
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
Commercial
Airport
Apartment House
Automobile Service Station
Boarding House
Department Store
Hotel
Lodging House & Tourist Home
Motel
Motel with Kitchen
Laundry (self service)
Office
Public Lavatory
Restaurant (including toilet)
Conventional
Short Order
Bar & Cocktail Lounge
Shopping Center
Theater
Indoor
Outdoor
Passenger
Person
Employee
Vehicle Served
Person
Toilet Room
Employee
Guest
Employee
Guest
Guest
Guest
Machine
Wash
Employee
User
Customer
Customer
Customer
Seat
Parking Space
Employees
Seat
Car
11
455
49
38
152
2083
38
189
38
152
111
152
2083
158
57
19
34
23
98
76
8
375
12
15
3 Industrial
4 Fire Fighting Purposes Lpm 2275

12. 12
NO. USER UNIT TYPICAL
CONSUMPTION
(lpd)
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
Institutional User
Assembly Hall
Hospital, Medical
Hospital, Mental
Prison
Rest Home
School Day with Cafeteria
Gym and Showers
With Cafeteria only
With Cafeteria and Gym (without)
School Boarding
Hotels
Seat
Bed
Employee
Bed
Employee
Inmate
Employee
Resident
Employee
Student
Student
Student
Student
(lcd)
12
568
38
455
38
455
341
341
38
95
57
38
284
350
Source: - (1) Water and Sewerage Authority
(2) Metcalf and Eddy, Wastewater Engineering,
Treatment, Disposal & Reuse; 3rd Edition

13. 13
2.2.1.2 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 fire fighting purposes
plus twenty percent (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 pipeline shall be 100mm.
A residual pressure of not less than 170Pa (25 psi) should be
considered in the design.
2.2.1.5 Vertical Alignment
Water mains shall be laid within the road reserve at a depth of not
deeper than 2m below the road surface.
2.2.1.6 Horizontal Alignment
Dual water mains may be installed to avoid water services from
crossing the carriageway.

14. 14
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 the 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 isolated without disruption of the total
water supply to other areas. Valves shall be provided for control and
isolation purposes generally in accordance with the following criteria:
(a) Pipeline sizes less than 200mm, valves shall be placed at intervals
of 500 metres.
(b) Pipeline sizes greater than 200mm, valves shall be placed at
intervals of 1000 metres.
(c) Valves shall generally 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 Wash out and pump outs 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.
2.2.2.5 Thrust Restraints
All tees, bends, caps, 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.

15. 15
2.2.2.6 Service Connections
Each plot shall have an individual water service connection not less
than 20mm in diameter. Double service connections 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.
2.2.2.8 Meter Box
All water service pipes shall be terminated just inside the boundary line
or property line with a typical meter box as approved by the Authority.
2.2.2.9 Testing
Testing of water mains and appurtenances shall conform to AWWA
Standards C 600-82. The test pressure shall be equal to 1.5 times the
working pressure.
2.2.3 Storage Facilities
Central water storage facilities shall be provided for all public,
commercial and industrial buildings and other building developments.
The water storage facilities shall have the capacity equivalent to the
average daily requirement of the establishment.
Where applicable, central storage facilities that are provided shall be
adequately fenced, illuminated and accessible to vehicular traffic.
2.2.4 Swimming Pool
2.2.4.2 Detailed Considerations
These include: -
a. All water for use must be obtained from a source approved
by the Water and Sewerage Authority.

16. 16
b. Water should be introduced into the suction side of the recirculation
pump, preferably through a make-up water tank.
c. Chlorine residual should be 0.6 ppm on the suction side of the
recirculation pump.
d. The recirculation 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 private pools.
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 a subsurface
wastewater absorption unit.
DESIGN GUIDELINES FOR WATER SYSTEM
3.1 Sewers
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 to be designed for maximum flow i.e., peak flow and
infiltration.
3.1.3 Estimated contributing population for residential developments shall be 4.5
persons per dwelling unit. Population densities for other types of
developments shall be in accordance with the requirements of the Town
and Country Planning Division.
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 the population in thousands.
5
P1/6

17. 17
3.1.6 Ground water infiltration should be estimated at 5000 l/ha/day, or based
on actual investigation or established data, if available, in case of existing
systems.

18. 18
Table 3.1
Wastewater Flow
NO. USER UNIT TYPICAL
CONSUMPTION
(lpd)
1 Residential Person 280
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
Commercial (working)
Airport
Automobile Service Station
Bar
Hotel
Industrial Building
(Excluding Industry & Cafeteria)
Laundry (self service)
Guest House
Guest House with Kitchen
Office
Restaurant
Rooming House
Department Store
Shopping Centre
Passenger
Vehicle Served
Employee
Customer
Employee
Guest
Employee
Employee
Machine
Wash
Person
Person
Employee
Meal
Resident
Toilet Room
Employee
Parking Space
Employees
10
40
50
8
50
190
4
55
2198
190
120
200
55
10
150
2000
40
4
40

19. 19
NO. USER UNIT TYPICAL
CONSUMPTION
(lpd)
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
Institutional
Hospital, Medical
Hospital, Mental
Prison
Institutional (School)
School Day with Cafeteria, Gym and
Showers
With Cafeteria only
With Cafeteria and Gym
School Boarding
Retirement Home
Apartment, Resort,
Recreational Cabin,
Resort
Cafeteria
Campground (development)
Cocktail Lounge
Coffee Shop
Day Camp (No Meals)
Dining Hall
Dormitory, Bunkhouse
Hotel, Resort
Laundromat
Store Resort
Swimming Pool
Theatre
Visitor Center
Country Club
Bed
Employee
Bed
Employee
Inmate
Employee
Student
Student
Student
Student
Resident
Employee
Person
Person
Customer
Employee
Person
Seat
Customer
Employee
Person
Meal Served
Person
Person
Machine
Customer
Employee
Customer
Employee
Seat
Visitor
Member Present
Employee
78.2
48
482
48
541
48
96
72
48
336
421
48
264
192
7
48
144
90
24
48
60
36
180
240
2641
12
48
48
48
12
42
482
60

20. 20
3.1.7 No public sewers shall be less than 100mm 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, of not less than 0.6 m/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
protect against displacement by erosion, abrasion and movement.
3.1.10 Table 3.2 shows the maximum lengths between manholes and
absolute minimum slopes that should be provided for various pipe
sizes. However, slopes greater than these are desirable:
Table 3.2
Sewer Size
mm / ins
Maximum
Distances/Lengths
m ft
Minimum Slope
ft/100ft-m/100m
200 8
250 10
300 12
350 14
375 15
400 16
450 18
525 21
600 24
90 300
110 350
110 350
110 350
110 350
120 400
120 400
120 400
150 500
0.40
0.28
0.22
0.17
0.15
0.14
0.12
0.10
0.08
3.1.11 Sewers 600 mm or less shall be laid with straight alignment between
manholes.
3.1.12 Where one sewer joins another of larger diameter, the invert of the
larger sewer shall 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;
b) Concrete – Concrete pipes shall be manufactured to meet the
requirements of BS 556 or approved equivalent international
standard.

21. 21
3.1.14 Manholes shall be installed at the upper end of each line, at all
changes in grade, size or alignment, all inter-sections and in
accordance with distances at Table 3.2. A drop manhole shall be
provided for a sewer entering a manhole at an elevation of 0.6m or
more, above the manhole invert. Where the difference in elevation
between the incoming sewer and the manhole invert is less than 0.6m,
the invert shall be filleted to prevent solids deposition. The minimum
diameter of manholes shall 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 Water and Sewerage 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 Authority shall
approve the design, spacing and materials for manhole steps.
3.1.15 There shall be no physical connection between a public or private
potable water supply system and a sewer. Sewers 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.
3.1.17 The top of the 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 of at least 3.0 metres wide shall be provided for sewer
mains not located within a road reserve.
3.2 SMALL 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 Water and Sewerage Authority may be
used.
3.2.2 The minimum pipe diameter shall not be less than 100mm.

22. 22
3.2.3 The minimum design velocity of 0.46 m/s at half full pipe shall be used.
3.2.4 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 force main shall be 100mm diameter.
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 wet well shall provide a minimum holding period of 10 minutes for
the design flow.
3.4.3 Pumps shall be sized and operated so that their rate of discharge is at
least equal to the rate of flow into the wet well.
3.4.4 A coarse screen with a spacing of no less than 50 mm, shall be
provided before the wet well. Adequate provisions must be made for
the removal and disposal of screenings.
3.4.5 Pumping stations must be provided with standby power generation
units.
3.4.6 In areas affected by seasonal flooding, precautionary measures shall
be taken to guard against flooding of the wet well.
3.4.7 Adequate and safe access shall be provided for dry and wet wells to
allow for inspection and maintenance.
3.4.8 Adequate ventilation must be provided either naturally or by forced
means.
3.4.9 The distance between a pumping station and a residence shall not be
less than 50 metres.
3.4.10 The installation shall have paved vehicular access, surface drainage,
security lights and shall be adequately fenced.

23. 23
3.4.11 A potable water supply must be provided, including adequately sized
storage tank with a pump capable of delivering a minimum of 90 lpm at
30m head.
3.5 WASTEWATER TREATMENT PLANTS
3.5.1 The standard for domestic effluent shall be the Trinidad and Tobago
Bureau of Standards (T.T.S – 417 1993) – “Specifications for liquid
effluent from domestic wastewater treatment plants into the
environment”. This standard has been assigned 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 provided tolerance limits for industrial effluent discharged
into public sewers.

24. 24
TABLE 3.3
TOLERANCE LIMITS FOR INDUSTRIAL EFFLUENTS DISCHARGING INTO PUBLIC SEWERS
NO. CHARACTERISTIC TOLERANCE LIMITS INTO
PUBLIC SEWERS
1
2
3
4
5
6
7
8
9.
10.
11.
12.
13.
14.
15.
16.
17.
Colour and odour
Suspended solids, mg/l, Max
Particle size of suspended solids, mm
Dissolved solids (inorganic), mg/l, Max
pH value
Temperature, o
C, Max
Oil and grease, mg/l, Max
Total residual chlorine, mg/l, Max
Ammoniacal nitrogen (as N) , mg/l, Max
Total nitrogen (as N), mg/l, Max
Free ammonia (as NH3) , mg/l, Max
Biochemical oxygen demand (5 days at 200
C) Max
Chemical oxygen demand, mg/l, Max
Arsenic (as As) , mg/l, Max
Mercury (as Hg) , mg/l, Max
Lead (as Pb) , mg/l, Max
Cadmiun (as Cd) , mg/l, Max
-
350
3
2100
5.5 to 9.0
45 at the point of discharge
20
0
50
0
0
300
0
0.2
0.01
1
1

25. 25
NO. CHARACTERISTIC TOLERANCE LIMITS INTO
PUBLIC SEWERS
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
Hexavalent chromium (as Cr +6
) mg/l, Max
Total chromium (as Cr), mg/l, Max
Copper (as Cu), mg/l, Max
Zinc (as Zn), mg/l, Max
Selenium (as Se), mg/l, Max
Nickel (as Ni), mg/l, Max
Boron (as B), mg/l, Max
Percent sodium, Max
Residual sodium carbonate, mq/l, Max
Cyanide (as CN), mg/l, Max
Chloride (as Cl), mg/l, Max
Fluoride (as F), mg/l, Max
Dissolved phosphates (as P) mg/l, Max
Sulphate (as S) , mg/l, Max
Sulphide (as S) , mg/l, Max
Pesticides (See note 5)
Phenolic compounds I (as C6H5OH) , mg/l, Max
Radioactive materials:
(a) Alpha emitters, uc/ml, Max
(b) Beta emitters, uc/ml, Max
2
2
3
15
0.05
3
2
60
-
2.0
1000
15
-
1000
1000
Absent
5
10 – 7
10 – 6

26. 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 25 metres
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 50 metres. A thick green belt (for
example tall pine trees) shall be provided between the pond and the
habitable premises.
3.5.6 Adequate land shall be provided for the treatment facilities including
additional land area for future plant expansion.
3.5.7 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.
3.5.8 All treatment units shall be provided with service access –
steps/ladders, catwalks and handrails. All works must be painted. The
compound shall be properly landscaped. Adequate surface drainage
must be provided. All works must be adequately fenced and protected
against unauthorized interference. Adequate lighting of Wastewater
Treatment Plants shall also be provided.
3.5.9 Adequate accommodation by means of a room equipped with storage
cupboards, toilet, face basin and shower facilities with hot and cold
running water, shall be provided.
For installations serving 500 lots and more, an operator room shall be
provided.
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 metre head pressure.
3.5.11 Treatment plants shall be provided with appropriate laboratory
facilities.

27. 27
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 the Water and Sewerage
Authority.
3.6.2 On-lot systems shall be constructed in accordance with approvals of
the relevant Authority’s (Local Health, Water and Sewerage Authority)
and may be used where no public or private sewerage system is:
i. available within 50m 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 development.
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 only 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 (12ft)
from the surface; or

28. 28
3.6.6 An absorption system shall not be located under:
i. a roadway or driveway
ii. a paved road
iii. a vehicle parking lot
iv. any building
TABLE 3.4

29. 29
Minimum Distance for Location of On-site/Lot Wastewater System
Feature Septic Tank
(Metre)
Absorption
Unit
(Metre)
Building
Property Boundary
Wells, Springs or any water source
Potable Water Pipes
*Cuts or Embankments
Paths
Swimming Pools
Shore line/high-water mark
Underground Water Storage Tank
Large Trees
Septic Tank
Soakaway
1.50
1.50
30.00
7.50
3.00
7.50
1.50
3.00
30.00
7.50
1.50
1.50
3.00
1.50
30.00
3.00
30.00
1.50
7.50
30.00
15.00
1.50
1.50
-
Note
+ Ground Water Level
Notes:
* These distances should be increased to 60
metres, if the installation is on a water supply
watershed.
+ The minimum clearance between the bottom
of an absorption unit and the ground water
level.
1.20 1.20

30. 30
3.7 PROCEDURE FOR MAKING PERCOLATION TEST
3.7.1 General
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 applicable
standards.
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 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 unit(s)
(soakaway pit 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 3.0 metres 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
300 mm and vertical sides to a depth of the proposed soakaway pit or
absorption trench (min. depth 1.3m).

31. 31
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 shall be noted over a 120
minutes period at intervals of 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.

32. 32
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 the
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 60min/25mm Unsuitable for absorption trenches
3.7.8 Absorption – Area Requirements
For Private Residences
PERCOLATION RATE REQUIRED ABSORPTION AREA
(TIME REQUIRED TO FALL SQUARE METERS PER BEDROOM
25MM IN MINUTES) FOR BOTTOM ABSORPTION
TRENCHES OR SIDE WALL AREA
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

33. 33
3.7.9 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 alternative on-lot systems may be used. These
include: -
(a) Evapo-transpiration system including use of the mound system;
(b) Use of separate dual system.
Notes on Percolation Test when compared with Standard TTS 16 80
400
 The minimum distances as stipulated in Table 3.4 in this doc
varies slightly from the TTBS standard.
 The procedure for the percolation test is essentially the same
except that this doc requires that the test pit be filled to 300 mm
and the test conducted over 2 hrs, while the TTBS standard
requires that the test pit be filled to 150 mm and the test
conducted over 4 hours.
 Also Section 3.7.9 of this document specifies the absorption
areas in terms of no of bedrooms of residence while the TTBS
standard specifies it in terms of 1000litres usage. The latter is
recommended.

34. 34
APPENDIX 1

35. 35
APPENDIX 1
MECHANICAL AND 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, lift pumps, sludge pumps and standby generators, surface
aerators drives and related equipment.
4.1.3 Adequate lifting equipment are 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 INSTALATION
4.2.1 GENERAL
4.2.1.1 The characteristics for the electrical power supply to these
installations shall be 400V, 3 phase, 60 Hz, 4 wire and for
the operation of all major equipment 230V, 1 phase, 60 Hz
for lighting and single phase loads.
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 and the Trinidad
and Tobago Electricity Commission.
4.2.1.3 Single-phase step down 230V/115V transformers shall be
installed to 115V for socket outlets and possible emergency
lighting.
4.2.1.4 Where a starter house is used, adequate internal fluorescent
lighting and at least two (120V/115V) electrical outlets shall
be provided.

36. 36
4.2.1.5 External lights shall be controlled by photoelectric sensors.
4.2.1.6 All electrical system shall be constructed for explosion proof.
4.2.2 WASTEWATER PLANTS – ELECTRICAL POWER
4.2.2.1 Adequate outdoor lighting shall be provided specifically over
all processes at treatment plants.
4.2.2.2 A standby generator shall be provided for at least (50%)
pumping capacity, surface aerators/blower capacity
recirculation pumps. Emergency lighting equipped with auto
transfer switches must be provided.
4.3 MOTOR REQUIREMENTS
4.3.1 Motors shall operate at the above power supply and shall be
vertical or horizontal, weatherproof and vermin proof,
explosion proof and shall be of the totally enclosed for
cooled type.
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 an ample safety factor. The factor shall
be based on the average life expectancy of five years
operating at 24 hours per day and must be manufactured to
AFBMA standards.
4.3.5 The motors shall be of the full voltage starting, squirrel cage
induction type and must be manufactured for inverter duty.
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 NEMA Class II type B
standards, the requirements of the Trinidad and Tobago
Electrical Inspectorate, and the requirements of the Trinidad
and Tobago Electricity Commission.

37. 37
4.4.2 Starters shall be of the reduced voltage type unless
otherwise approved in writing by Trinidad and Tobago
Electricity Commission.
4.4.3 Starters shall be outfitted with phase failure and overload,
ground fault under voltage protection.
4.4.4 Starters shall include circuit breakers, hand-off-auto
switches, voltmeters, ammeters, push button on-off switches
and adequately sized motor starter contactors.
4.4.5 Direct on-line starters shall be explosion proof and be
capable of being pole mounted.
4.4.6 Reduced voltage starters shall be NEMA type 12 ventilated
enclosure and shall be housed in a covered enclosed
building.
4.5 INSTRUMENTS – WATER PUMP STATIONS
4.5.1 Provision shall be made for the measurement of the suction
and discharge pressure at each pump and the common
discharge line pressure.
4.5.2 Provision shall also be made for the measurement of flow
using a flow meter or other reputable flow-measuring device
at each pump station.
4.5.3 Pressure switches shall be installed at the suction line of
each pump at water pump stations.
4.5.4 A common discharge pressure switch shall be installed at
water pump stations.
4.5.5 The pressure switches shall be set so as to trip pumps at low
suction and high discharge pressures and to start pumps at
the required NPSH.
4.5.6 All pump stations shall be designed with due consideration
for the effects of water hammer. Adequate protection for
adverse effects should be included in the design.

38. 38
4.6 INSTRUMENTS
Flow meter for Pump Stations and Plants
- Turbine type meters (accuracy -+ 1-2% of Actual)
- Flow nozzles (accuracy - + 1-2% of Actual)
- Ultra Sonic – (transit time type) (accuracy - + 1-2% of Actual)
- Flow tubes – (accuracy - + 0.5 – 2% of Actual)
- Venturi – (accuracy - + 0.5 – 2% of Actual)
- Magnetic – (accuracy - + 1 – 2% of Actual)
Recommendation of use in Wastewater Plants and Pump
Station assuming full flow in pipes.
- Flow nozzles (accuracy - + 1 – 2% of Actual)
- Ultra Sonic – (transit time type) (accuracy - + 1 – 2% of
Actual)
- Flow tubes – (accuracy - + 0.5 – 2% of Actual)
- Venturi – (accuracy - + 0.5 – 2% of Actual)
- Magnetic – (accuracy - + 1 – 2% of Actual)
Recommendation for use in Wastewater Plants – open
- Panshall Flume – (+ 3 – 8% of Actual)
- Open Flow nozzles – (+ 3 – 8% of Actual)
4.7 DISINFECTION – WASTEWATER PLANTS
4.7.1 Adequate disinfection is to be provided for the Treatment Plant’s
effluent in accordance with TTS 417.1993 prior to its discharge
into a receiving stream.

39. 39
APPENDIX II

40. 40
APPENDIX 2
LIST OF APPLICABLE STANDARDS
5.1 SPECIFICATIONS OF MATERIALS AND WORKMANSHIP
All materials for potable water shall meet the ASTM Standard or approved
equivalent standard. The Standards also provide literature on Workmanship.
For guidance the appropriate standards are listed.
5.2 Water
SUBJECT STANDARD
Storage Tanks
Welded Steel Tank
Painting for Welded Steel Tanks
Factory Coated Tanks
Disinfection
Concrete Structures for retaining liquids
ANSI/AWWA D100-84
ANSI/AWWA D102-78
ANSI/AWWA D103-80
ANSI/AWWA D152-86
AS 3735 1991
Pipelines
Polybutylene (PB)
Polyethylene (PET)
Poly Vinyl Chloride (PVC)
Fabricated Steel Pipe and Fittings
Steel Pipe Flanges Class D
Coal tar protection coatings and
Linings for steel water pipelines
Flanged Ductile Iron Pipelines
Rubber Gasket
Disinfection
Pressure Test
Grey Iron Casting
Elastometrix Joint Rings for pipework and
pipelines
Flanges and bolting for pipes valves and
fittings metric series
(copper alley and composite flanges)
Metal Washers for General Engineering
Purposes Metric Series
AWWA C-902-78
AWWA C-901-78
AWWA C-900-75
AWWA C-208-83
AWWA C-207-86
AWWA C-203-86
AWWA C-115/A21
AWWA C-111/A21
AWWA C-651-86
AWWA C-600-82
BS 1452:1977
BS 2494:1986
BS 4504: Part 2 1974
BS 4320:1968

41. 41
SUBJECT STANDARD
Specifications for Poly Vinyl Chloride
(PVC) solvent Cement for use with un-
plasticized PVC Pipes and fittings for cold
water applications
Cast Iron Non-pressure pipes and pipe
fittings metric units
TTS 413-1992
AS 1631 – 1974
Safety Valves
Safety Valves
Specification for safety valves for steam
and hot water
BS 6759
PT 1 1984
Mixing Valves
Mixing Valves
Non-Thermostatic, Non-Compensating
mixing valves
Specification for Thermostatic mixing
valves
BS 1415
PT 1 1976
PT 2 1986

42. 42
SUBJECT STANDARD
Water
Glass Filament Reinforced thermosetting
plastics (GRP) Pipes Polyester Based –
Water Supply. Sewerage and Drainage
Applications.
Water Supply Metal Bodied Taps –
Specified by performance
Water Well Casing
Specification for steel tubes for casing
Specification for thermoplastics tubes for
casing and slotted casing.
Stationery circulation pumps for heating
and hot water service system.
Specification for Cold Water Storage and
combined feed and expansion cisterns
(polyolefin or olefin copolymer) up to 500 L
capacity used for domestic purposes
Multi Standard
Measurement of flow of cold potable water
in closed conduits
Safety and Control Devices for use in hot
water systems
Code of Practice for test pumping of Water
Well
Storage Cisterns up to 500 L Actual
Capacity for water supply for domestic
purposes
Bitumen – based coatings for cold
application, suitable for use in contact with
potable water
Bitumen based hot applied coating
materials for protecting iron and steel
including suitable primers were required
AS 3571 1989
AS 3718 – 1990
BS 879
PT 1-1985
PT Z-1988
BS 1394
BS 4213 - 1991
BS 5728
BS 6283
BS 6316 – 1992
BS 7181 – 1989
BS 3416 – 1980
BS1 4147 – 1980

43. 43
5.3 Wastewater Systems
SUBJECT STANDARD
Cement
Aggregate
Steel (Reinforcer)
Structural Steel
Manhole Bricks
Precast Sections
Manhole Frames Cones
Reinforced Concrete Pipes
Non Reinforced Concrete Pipes
Gaskets
Welded Steel Pipe
Steel Fitting Couplings
Gate Valves
Sluice Valves
Drain Pipes and Fittings
Sewer
Grey Iron
Ductile Iron
Thermoplastic Pipe for Sewers
Thermoplastics waste pipes and fittings
Polypropylene Waste pipe and fittings
(External Diameter 34.6 mm 41.0 mm 54.1
mm)
ASTM C-150-60
ASTM C-33-59
ASTM A- 15-58T
ASA – ASA A57 1-1952
ASTM C- 32-58 Grade MA
ASTM C-478-61T using type II cement
ASTM A48-60T
ASTM C76-60T
ASTM C14-59
Flexible joint gasket manufactured by lock joint
Co or Equal
AWWA C 202-59
AWWA (Same as Water)
ASA B16 10-1957
AWWA C 501-41T
BS 4660 or American Equivalent
BS 4660, BS 5481 or Class B, BS 3505
BS 4622
BS 4772
ASTM D 2321, F-894
BS 5255 – 1989
BS 5254 – 1976
Sewer
Unplasticized PVC (UPVC) Pipes and Fittings
for storm and surface water applications
Unplasticized PVC (UPVC) Pipes and Fittings
for soil waste and vent (SWV) applications
Design charts for water supply and sewerage
Water Supply – Mechanical backflow
prevention devices
Plastics Waste Fittings
Specifications for compact type float operated
valves for the WC Flushing Cisterns (including
floats)
Specification for Galvanized low Carbon Steel,
Cisterns, Lids, Tanks and Cylinders
Specification for unplasticized PVC Drain,
Waste and Vent Pipes
Technical Drawing Installation, Graphical
symbols for supply water and drainage
systems
Recommendations for the Design of buildings,
plumbing and drainage systems
AS 1254
AS 1415 PT 1-4
AS 2200-1978
AS 2845-1986
AS 2887-1986
PT 4 - 1991
BS 417
TTS 414-1992
TTS 31 85 006
PT 6 – 1988
TTS 16 90 400
PT 4 - 1985