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

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

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

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

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

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

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

(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

PART II

DESIGN GUIDELINES FOR WATER SYSTEM

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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, oC, 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 200C) 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

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

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

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

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

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

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

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

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

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

APPENDIX 1

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

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

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

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

APPENDIX II

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

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

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

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