Contents of this · Web viewTemporary casing may be installed in the borehole to prevent formation heave or collapse or sloughing. Installation and diameter of any temporary casing

ANNEX A: FRT-WSH-13401 – Technical Specifications and Drawings

Water, Sanitation and Hygiene Programme

GOAL

Technical Specification and DrawingsFor

Siting, Drilling, Pump Installation and Associated Works For

Construction of 15 Boreholes in Communities Gaura and Tunkia Chiefdoms in Kenema District in Sierra Leone

February 2018

Contents of this Technical Specification1. Technical Specification

GOAL Sierra Leone– Borehole Technical Specification 2017Page 1 of 35

2. Annex 1: Standard Borehole Designs3. Annex 2: Borehole apron design4. Annex 3: Typical Reporting Forms5. Annex 4: List of Communities

Technical Specification1.0 Scope of works

The scope of the works require that contractors furnish only successful boreholes to the client. A successful borehole is defined as one conforming to all the requirements for the siting, drilling, pumping testing, yield and water quality requirements. The well delivers at least 1000 l/hr, has an aquifer recovery of at least 65% in one hour and passes the minimum acceptable potable water quality standards as defined by the Government of Sierra Leone (GOSL) By this definition, the bidder MUST include costs of replacement of unsuccessful boreholes (poor water quality and dry boreholes) in their BoQ.

Dry wells or wells with poor water quality according to GOSL standards will be replaced by the contractor at no further cost to GOAL. The drilling records for all unsuccessful wells must be provided to GOAL including for poor quality wells the water quality test certificates.

All the wells successfully drilled and tested will be installed with India mark 2 hand pumps with stainless steel (G316 steel) pipes and rods.

The depths of installation of hand pumps must be approved by GOAL

The successful contractor will carry out the siting/hydrogeological survey for the borehole locations,

carrying out the drilling works, pumping tests, water quality tests and the installation of the pumps and

aprons ready for use.

1.1 Location of the works

The works are located in communities in Gaura and Tunkia Chiefdom in Kenema districts. See the

attached list of communities in Annex 4

1.2 Borehole siting The contractor is to carry out detailed geophysical analysis in the communities listed in the attached

Annex 4.

GOAL Sierra Leone – Borehole Technical Specification 2017 Page 2 of 35

A method of geophysical survey best suited to the geography/geology of the area is to be employed

The geophysical analysis will include the desk study, the hydro census and the geophysical survey.

The reports of the surveys will be included as part of the final reports submitted for the whole works.

The desk study will include a review of existing reports, borehole logs, topographical, geological and

hydro geological maps, previous geophysical surveys and the evaluation of aerial photographs if any.

The contractor’s hydro-geologist should carry out a hydro census in the vicinity of the target areas.

This will include a detailed inventory of all existing water supplies to ensure that the current site does

not influence nearby wells and to be able to make decisions that could affect the success of the new

boreholes.

The contractor should ensure that the siting/Geophysics work is to be carried out by suitably qualified

and experienced person(s). The nominated person(s) shall be available for the specified contract

period. Proposed changes to the hydro-geologist should be agreed with the supervising

engineer/GOAL.

During the siting, the hydro-geologist should ensure that representatives of the local community shall

be involved. GOAL will assist with community liaison activities.

2.0 Drilling site

Borehole locations shall be identified in agreement with the local communities and in consultation with

the Client. The process for community involvement is set out in the Memorandum of Understanding

that is signed between community leaders, District Council, the contractor Goal and the land owner if

required. Sites selected for the hand pump should preferably be within the communities and not

further away than 0.5km from 80% of people of the village. If preferred site are not suitable for

technical reasons, this must be explained to the community. Boreholes should not be sited in or near

to places that get flooded during rains. Flood plains should be avoided. Additional measures should

be taken to ensure that sites are located outside the minimum distances prescribed from sanitation

installations, sources of pollution, landfills, grave yards and animal kraals.


It is advisable that the hydrologist uses their experience to determine alternative suitable sites for

borehole construction for each village so that these can be developed if initial sites are abandoned for

any reasons including dry wells or unsuitable water quality wells.

The contractor shall drill the well(s) at location(s) as determined by their hydrogeological surveys.

Access to the site shall be the responsibility of the Contractor. Tracks required for access of drilling

plant, gear, camp and accessories to the well site shall be made by the contractor, and shall minimize

as much as possible interference with existing fences and cultivated land.

The table below shows the Minimum distances from the borehole that are to be observed

Souce: Ministry of Water Resources: Principles of Borehole Drilling, 2014

3.0 HydrogeologyWhile deep wells have been constructed in these areas before, there is inadequate information

regarding success rates and soil profiles. The conditions of drilling cannot therefore be precisely

described for these two Chiefdoms. Boreholes drilled in other parts of Kenema district have averaged

between 50- 60 meters in depth with some wells being deeper than that while others are shallower.

While drilling conditions are not expected to be difficult, the driller should be prepared to deal with dry wells and wells whose water quality is unsuitable for portable water supply as recommended by the GOSL water quality standards.


4.0 Environmental protection of the site

Care must be taken in the handling and storage of drilling fluids, oils, greases and fuel to avoid

introducing environmental contaminants and pollutants. The Contractor shall dispose of any toxic

materials including drilling fluids, cuttings and discharged waters in a manner approved by the Client

and so as not to contaminate/pollute public and private property. The contractor shall adhere to

relevant National regulations and guidelines on Environmental protection that apply to drilling. The

Contractor shall ensure that all their personnel are aware of Environmental protection requirements.

5.0 Materials for the works and Workmanship

Materials that will form part of the complete works must be supplied new and never used. Materials

must comply with the minimum specifications in the relevant codes. Materials not specified here must

comply with the minimum specifications in the relevant codes of practice. Where a national standard

does not exist for the material, the relevant British Standard shall apply.

The Contractor is expected to carry out all works as specified and in a professional manner. The

Contractor shall carry out operations in accordance with the terms of the contract and to the

satisfaction of the Client. The Contractor shall use suitable equipment, and supply efficient and

experienced staff.

a) The Contractor will provide an experienced project Coordinator to oversee the drilling and testing

to be carried out under this Contract.

b) The Contractor will maintain a full crew on each drilling unit and pump test unit. If a member of

crew quits for personal reasons or must leave because of illness or injury, the Contractor will replace

him as soon as possible with a worker of similar experience.

c) If the Client is dissatisfied with the performance of members of the crew, such members shall be

informed of their shortcomings and warned by the contractor. If no change results within a reasonable

period, the Contractor will be notified and requested to take necessary measures on the

unsatisfactory crewmember.

d) If the Client wishes to operate drilling equipment more than one shift per day that can only be done

upon agreement between the Contractor and the Client.

e) In the case of absence of one or more members of the drilling crew the decision of whether to

proceed with drilling operations will be at the discretion of the Client

6.0 Contractor to provide all equipment for the works

All necessary machinery, equipment and materials to carry out the drilling, test pumping, headwork

construction shall be provided by the contractor. Test pumping equipment shall be independent from


the drilling rig(s). Prior to mobilization the Client shall verify the specifications and state of repair of all

major items of plant and transport, and shall have the right to order the removal and/or replacement

of any items which in his opinion are insufficient or in unsatisfactory condition. Acceptance by the

Client of the Contractor’s proposed plant and transport does not relieve the contractor of his

obligations under this contract, in cases where such plant and transport accepted by the Client fails to

successfully complete the required works.

7.0 Drilling method

The Contractor should make exclusive use of direct or reverse circulation rotary and down-the-hole

hammer drilling techniques, using an appropriate (biodegradable) drilling fluid.

The drilling fluids and additives shall consist of water, bio-degradable drilling mud, weight materials

(barite or equivalent), fluid loss control materials, and foam. The selection, supply and use of drilling

additives shall be the responsibility of the Contractor. Toxic or dangerous substances that may

adversely affect the quality of the water shall not be added to the drilling fluid.

The Contractor shall be responsible for maintaining the quality of the drilling fluid to assure the

protection of the aquifer and other potential water bearing formations and ensure that good

representative samples of the formation material are obtained.

The Contractor may use any motorized drilling technique that will achieve the depth and diameter

required of the well, provided that the techniques used are those specified in his proposal and

approved by the Client. The rig to be deployed must be capable of drilling to at least a depth of 25%

beyond the anticipated final depth at the required diameter. . If the Contractor wishes to cease drilling

at a shallower depth and complete the borehole at this depth, he must first get the approval of the

Client This approval will be provided in writing and will be signed by the Client. This approval will be

provided in writing and will be signed by the Client. If the Contractor is unable to drill to the required

depth due to unsuitable or defective drilling equipment and/or inadequate operator competence, the

Client shall not be held accountable for any costs associated with that particular borehole.

Temporary casing may be installed in the borehole to prevent formation heave or collapse or

sloughing. Installation and diameter of any temporary casing required for the construction of the

borehole shall be the responsibility of the Contractor so long as the finished product meets the

specifications outlined in this document.

The average anticipated borehole depth will be in the region 60m. Shallower or deeper boreholes

may be encountered.


During rotary drilling using air as the circulating fluid, approved surfactants and artificial foam

stiffening additives may be used if ground conditions warrant their use.

8.0 Strata sampling and borehole geo data

While the drilling operation progresses, representative samples (min. 100 grams) of strata penetrated

shall be collected at every Two (2) meters intervals by whatever method is standard for the drilling

technique in use. The Contractor shall take every possible precaution to guard against sample contamination. Strata samples will also be taken at every change in the profile and where water or

an aquifer is struck

At completion of drilling, the contractor will be required to complete the borehole geo-log with all

information describing the properties of the samples, appearances of water and aquifers, rock types

and sampling details.

The contractor will then complete the borehole log reports forms and supply them together with the

borehole completion records including water quality test certificates to the client. Incomplete records

or un-obtained samples are a reasonable ground for rejection of a borehole. ).NOTE

The contractor will be required to hand to the client at the end of the drilling operation borehole logs and pumping test data including information from dry boreholes and boreholes considered unsuccessful as a result of poor water quality.

9.0 Borehole depth and diameter

The Contractor shall drill to the total appropriate depth depending on the geological formation

required to meet the sufficient yield and borehole diameter requirements and the small diameter

pumps now on the market mean that 4” (~100mm) internal diameter cased boreholes are sufficient for

the hand pump cylinder and rising main. Unless otherwise instructed by the Client, uPVC

casing/screen is specified which has a minimum internal diameter of 103mm and an outside diameter

of 113mm.

Expected borehole depths are an average 60 meters depth however the contractor will be required

to drill deep enough to meet the acceptable yield.

The minimum acceptable stable yield at test pumping shall be 1000 L /hr. and aquifer recovery rate of

65% in one hour.


Drilling diameter should be a minimum of 6.5” (165mm) through unconsolidated formations such as

sands, gravels, clays and silts using mud rotary methods (or similar approved methods)

Drilling diameter should be a minimum of 5.875” (150mm) through consolidated rock utilizing down-

the-hole hammer and compressed air supply – augmented as required by water foam injection

The Contractor shall however drill to the total depth and at such diameter as will be instructed by the

Supervising Engineer. No borehole will be accepted if drilled to such depth and diameter other than

agreed by the Supervising Engineer.

In collapsing formations, the borehole drilling will be telescopic. In this case 200mm (8 inch) or of

appropriate diameter drilling (approved by the Engineer) is required to allow installation of temporary

casing. This temporary casing must enable further drilling of 200mm (8 inch) boreholes for the

installation of 100mm (4inch) nominal internal diameter PVC casing and screen.

When rotary-drilling method is used, either a water meter or a 90-degree V-notch flow measurement

device or a drainpipe shall be permanently set up in an approved manner and level, so that

continuous monitoring of airlift yields can be obtained. Average yields shall be read every 3 meters of

penetration and recorded in the driller’s log. Care should be taken to ensure that the flow of water

through the meter, over the V-notch or through the drainpipe is not impeded by debris.

Boreholes shall be drilled to such depths as to penetrate below the shallow water table aquifers and

tap the first potential deeper aquifer in confined/semi confined conditions with a discharge rate above

1000l/hr to sustain a continuous and reliable operation of hand pumps fitted on them, subject to water

quality considerations. The depth to be drilled should be at least 5 to 10 meters below the main

aquifer to provide proper installation of a hand pump and to provide a sand trap of at least 1 – 2

meters. If the discharge is less than 1000 l/hr a decision to abandon the borehole or continue to drill

deeper will be at the discretion of the Contractor.

10. Temporary casingIn order to prevent the collapse of unstable strata, the contractor may use temporary casings. These

temporary casings will be provided by the contractor and removed after use. Installation and diameter

(which should not be less than 8 inches) of any temporary casing required for the construction of the

borehole will be at the discretion of the Contractor provided that the finished product meets the

specifications and is approved by the Supervising Engineer. Cost for supply, installation and removal


of temporary casing shall be borne entirely by the Contractor. Casings left in the borehole, which is

not retrievable, cannot be claimed by the Contractor from the Client.

11 Casing and screens

Aquifer zones shall be completely or partly lined with UPVC screens supplied by the contractor. The

casings and screens shall be OD 113 mm, ND 100 mm . The Client however reserves the right to

vary these specifications if deemed necessary. The collapse resistance of the casings shall normally

be a minimum of 6.5kg/cm2, while that for screens shall be a minimum of 50% of that of the casing.

The screen open area shall be between 6-10%and shall have a uniform slot size of between 0.5-

1mm. Screen length should not be compromised to save cost as this can result in a dry borehole.

Sections of the screen shall be provided in maximum 3m lengths and joined water tight by either flush

threaded connections, or by an appropriate method recommended by the screen manufacturer or an

equivalent standard, so that the resulting joint shall be strong and have the same structural integrity

as the casing and the screen themselves. In particular cases the lower end of the screen shall be

completed with a sump of minimum 0.5m and maximum 2m length. The bottom end shall be sealed

with a suitable bottom cap.

The casing and screens must be centralized in the well so that an annular space of at least 25mm

exists between the well wall and the casing. Suitable centralizers shall be provided to allow the casing

screen to be set correctly in the center of the well. A centralizer shall be used every 3m.

The screen shall be joined water tight in an approved manner by either flush threaded connections or

by an appropriate method. Screened sections shall be attached to the plain casing using the

manufacturer’s standard connections.

The casing should extend 0.3 metres above the ground surface.

The contractor will transport and store the casing pipe at the drilling site, to prevent distortion and

bending of the pipe.


12. Verticality and Alignment

All wells shall be vertical, shall be drilled and cased straight, and all casings/screens shall be set

round, plumb and true to line. If required by the Client, the Contractor shall make a verticality test

during and after drilling by approved methods and at his own expense to demonstrate that the

departure from the vertical does not exceed 3mm for every 100m between ground level and the

bottom of the well. If this departure is exceeded, the Contractor shall make the necessary corrections

to the approval of the Client, without additional payment. If the error cannot be corrected, then drilling

shall cease, and a new well shall be drilled. The abandoned well shall be backfilled and /or capped.

No payment shall be made for re-drilling, the sealing/backfilling of the abandoned well, or for moving

to a new site. Any materials (i.e. casing, screens, gravel pack, cement, etc) lost in the abandoned well

shall be at the contractor’s cost.

13. Loss of equipment

Any equipment lost down a well must be removed by the Contractor or the well shall be considered a

lost bore. A replacement well shall have to be constructed at the Contractor’s expense. The

contractor shall not be entitled to further payments for such a well.

14. Lost bore

If completion of the well is prevented by any of incident to the plant, behavior of the ground, jamming

of the tools, or casing or any other cause, the well shall be deemed to be lost and no payment shall

be made for that bore or for any materials not recovered there from, nor for any time spent during

drilling or while attempting to overcome problems.

In the event of a lost bore, the Contractor shall construct a new well. The option of declaring any bore

lost shall rest with the Contractor, subject to the approval of the Client.

A lost bore shall be treated as follows:

a) The Contractor may salvage as much casing and screen from the lost well as possible, and

may use it if not damaged in a replacement well, with the approval of the Client.

b) Any material supplied by the Client and salvaged damaged shall become the property of the

Contractor, and the Contractor shall compensate the Client accordingly.

c) The lost bore shall be sealed by concrete or cement grout, which shall be placed from the

bottom upward by methods approved by the Client.


d) The upper 2 meters of the lost bore shall be backfilled with native top soil. Sealing of such

abandoned wells shall be done in such a manner as to avoid accidents or subsidence, and to

prevent it from acting as a vertical conduit for transmitting contaminated surface or subsurface

waters into the water bearing formations.

15. Water supply for drilling

The contractor shall make his own arrangement for obtaining, transporting and pumping of water

required for drilling purposes and for use by the drilling crew at their camp site.

16. Well design

The final design of the borehole shall be confirmed by the Client in consultation with the Contractor

during the drilling process, or immediately after drilling is completed using the tabulated borehole strata data log. Typical standard borehole designs are described below:

• Design 1 - Drilled at 10 5/8" through soft collapsible overburden until firm rock is encountered.

Drilled further with 8" or 6" bit for 3m or more through non-collapsing formation. Cased with 4"

ND uPVC Class D casing, 10mm wall thickness. Drilling to continue with 6” or 6½”" bit to final

depth. Bottom annular space between uPVC casing and borehole to be grouted with cement

slurry of 1.67-2.08 Kg cement/litre (24-30 litres of water per 50 Kg bag of cement). Grout is to

be injected into the annulus using tremie pipes, or a method approved by the Client, in a

continuous operation so that a complete and continuous seal is achieved.

• Design 2 - Drilled with 10 5/8" bit to final depth where necessary finished with 8" bit to final

depth. Cased with 4’’ND uPVC Class D casing, 6mm wall thickness. Screened sections

adjacent to aquifer zones at depths as instructed by the Client. The screened sections are to

be gravel packed.

• Design 3 - Refer to specifications in drawing attached in Annex 1.

(Example borehole designs drawings are included towards the end of this document. Alternative Ministry of Water Resource drawings are attached as Annex 1)

17. Gravel pack

The Contractor shall supply suitable gravel pack. Prior to delivery, samples of the gravel pack shall be

subjected to a grain size analysis at the Contractors expense and the Client must approve the results

before the gravel pack is used. Gravel pack shall consist of washed, well-rounded particles of a

uniform grading of between 2.5 and 4.0mm, shall comprise at least 95% siliceous material and must

contain no clay, shale, silt, fines, excessive amounts of calcareous material or crushed rock. The

gravel pack needs to be installed slowly and carefully, preferably with a tremie pipe and a funnel


18. Sanitary seal

To provide an effective seal to the entry of contaminants, the upper 3 meters of the annular space

between the casing and the well wall shall be grouted using suitable prepared cement slurry. Grout is

to be injected into the annulus in a single operation so that a complete and continuous seal is

achieved.

19. Development and cleaning of wells

Well development must be undertaken before the contractor moves to the next site. Development and

cleaning of the wells, in order to remove native silts, clay and drilling fluid residues deposited on the

well wall during the drilling process, shall be carried out by the Contractor upon completion of the

drilling and installation of casings. The borehole should be flushed until it is free of fines and turbidity

for a continuous period of not less than 30 minutes or until the water has fully cleared.

Whenever possible, natural well development must be used. If organic drilling fluids are used, they

shall be broken down chemically according to manufacturer’s recommendations before or during

development. Cleaning may be carried out by airlift pumping, surging, backwashing or jetting, to the

approval of the Client. Clay de-segregation by means of Sodium Hexametaphosphate (“Calgon”)

treatment may, in some cases, also be called for by the Client.

The method proposed by the contractor for development of wells shall be submitted to the Client in

writing for his approval. Development of wells shall be effective from the depth at which water is

encountered to the bottom of each well. Development shall continue for such time as directed by the

Client and until the Client is satisfied that the water is as free from fine particles as possible. Upon

completion of development, any accumulation of material shall be removed from the bottom of the

well by airlifting.

20. Pumping Tests

Pumping test will take place for 6-hours depending on the drillers yield estimate. For Boreholes with a

drillers yield being more than 0.7l/s, a step drawdown test (each step running for one hour) for up to a

maximum of 3 steps shall be carried out. This shall be followed with 3 hours of continuous test at a

predetermined optimum yield. A minimum of 1-hour recovery test or until the water level returns to

80% of the static water level should then conducted to determine the Borehole recharge ability.


Pumping rates for the step drawdown test will commence at 0.42l/s for the initial 60 minutes. The next

steps will be pumped depending on the aquifer behavior and in agreement with the supervisor on site.

Constant rate pumping test pumping rates will normally range between 0.5l/s and 2.5l/s but may not

fall below 1000l/hr. If the pumping rate is below 1000 l/hr then the borehole will be regarded as dry.

Once the flow rate has been determined and preliminary adjustments made, the measured discharge

rate shall be maintained within 15% of the required rate for the duration of the test. Persistent

fluctuations beyond this tolerance will require abortion of the test.

Failure of the operation to produce the desired minimum pumping rate for a period greater than one

percent of the elapsed pumping time shall also require abortion of the test.

Any test, which is aborted due to the reasons above, shall be repeated after recovery of the water

level. The contractor will not claim stand by time for aborted tests or for standing time during water

level recovery after aborted tests.

Discharge measurements shall be made by using a flow meter or other measuring device approved

by the supervising engineer. During pumping tests, the discharge water will be diverted in an

appropriate manner over a distance of at least 50 m downslope from the wellhead. Water discharge

measurements shall be taken at appropriate time intervals as instructed by the Supervising Engineer,

while at the same time Electrical Conductivity readings are to be taken.

After completion of the test the contractor shall remove by bailing and pump or other methods any

sands, stone or other foreign materials that may have become deposited in the borehole and with

consent of the Engineer, the borehole shall be chlorinated.

Pumping test data shall be supplied to the Supervising Engineer from all pumping tests conducted at

the borehole. These will show dates, water levels, discharge rates, electrical conductivity values,

times of starting and stopping the pump, changes in discharge, weather, and other conditions that

could affect the test data.

The Contractor shall supply appropriate electric contact water level gauges for measuring water

levels in the borehole to the nearest 10 mm at pre-determined intervals. The minimum length of the

electrical dipper shall be 250 metres. Wellhead arrangements shall permit these gauges to be

inserted and passed freely. Hereto the Contractor shall be required to install a dipping tube, minimum


3/4" inner diameter, lowered to approximately 2 metres above the pump intake or the anticipated

maximum drawdown level.

Other methods of measuring water levels are subject to approval by the Supervising Engineer.

The method for varying the discharge rate of the pumps shall depend on the type of pump used. The

Contractor shall ensure the provision of a suitable means of achieving the range of constant flow

rates specified.

21. Water level observation

The contractor shall apply appropriate electronic contact water level gauges for measuring water level

in the wells. Measurements shall be made at predetermined intervals, depending on the nature of the

test. Well head arrangement shall permit these gauges to be inserted.

Water level shall be measured to 10mm accuracy during test pumping by the Contractor by means of

an electronic contact gauge (dipper). The frequency of measurement shall be as specified on the

agreed test pumping data form, or one otherwise determined by the Client.

Discharge shall be measured by volumetric methods, or means of approved measuring device.

During test pumping, discharged water shall be disposed-off sufficiently far from the well to prevent

recharge.

22. Water Quality Testing

Water quality

Water quality analysis shall be done in line with the national guidelines.

On completion of test pumping, The contractor should contact Ministry of Water Resources (MoWR) to arrange for the collection of water samples. The samples will be used for physical and chemical analysis. The samples should reach the

laboratory within 6 hours from the time of collection. Specific parameters to be measured include

Physical Parameters – Colour apparent (PtCo), Turbidity (NTU), Electrical Conductivity

(µS/cm), TSS (mg/L)

Chemical Parameters – Nitrate(mg/L N), Total Hardness (mg/L), Fluoride (mg/L F), Chloride

(mg/L Cl-), Sulphate (mg/L SO42-), Total Iron (mg/L Fe) Manganese (mg/L Mn), TDS (mg/L),


Calcium (mg/L Ca2+), Magnesium (Mg/L Mg2+), Bicarbonate (mg/L CaCO3), Alkalinity (total

mg/L CaCO3)

23. Capping of well

During well construction, installation, development and test pumping, the Contractor shall use all

reasonable measures to prevent entrance of foreign matter into the well. Well caps should be used at

all times. Wooden logs shall not be used to replace well caps. The Contractor shall be responsible for

any objectionable materials that may fall into the well and any effect it may have on water quality or

quantity until completion of the Works and acceptance by the Client.

24 Acceptance of well

The Client shall accept the well upon satisfactory completion of all drilling operations, installation of casings and screens, development works, pumping tests, presentation and approval of complete drilling reports and logs and provided the well yield is above minimum recommended values and water quality tests are suitable for potable water according to the GOSL standards.

25. Standby time

The Contractor shall provide the Client with 24 hours’ notice before starting any works that need to

have the Client’s supervisor on site as well as 24 hours’ notice when mobilizing to the next site. The

Client shall allow for an additional 24 hours for the Client’s supervisors to arrive on site.

26. Concrete apron/platform casting and hand pump installation.

Upon receipt of satisfactory water quality results and after being verified by the Client, the contractor

shall cast a concrete slab on the wells according to these specifications

The Contractor shall construct concrete platform for each successful borehole carrying out the

following activities in order:

Excavate square pit 760x760x400mm deep around casing pipe.

a) Place stand assembly (pedestal) over casing pipe, ensuring third leg (corresponding to the

water tank spout pipe position) faces the proposed direction of the drain.

b) Making sure the pedestal is vertical, construct concrete in layers of 100mm up to top of legs.

c) Cover stand assembly with a cover plate and, level the ground around the pump pedestal.


d) Lay the mild steel shuttering (molds), place 10mm ribbed r/f bar to the channel thickness and

wire mesh fabric to the apron (refer to the drawings) and cast platform in mass concrete (mix

1:2:4/20mm agg.) conforming to the dimensions and other specifications shown in drawings.

e) Cure concrete for 5 days and protect it from excessive sunshine (using gunny bags and thorny

bushes, etc).

f) Plaster platform and drain in cement screed to a smooth finish, then engrave the borehole

details provided by the Client on the platform

27. Hand pump equipment and installation

The Contractor shall supply pipes and pump parts, to cast and install India Mark II Deep well Hand

pump as per Bureau of Indian Standard Specifications IS-13056: 1991, Bureau of Indian Standard

Specifications IS-13056: 1991 – Amendment 6, with 50mm dia. cast iron brass sleeved open top

cylinder assembly with extractable plunger and foot valves assemblies or a similar specification

according to Sierra Leone standards. Note that all pipes and rods are to be replaced with stainless

steel G316 unless specified by the Client. If conditions allow, where pH >6.75, and when directed by

the Client, uPVC pipes may be substituted for stainless steel.

The Contractor shall supply Either Grade 316 Stainless steel pipes, 1¼” Nominal pipe diameter, 3m

long with average weight of 2.73 Kg/m and Stainless steel rods of grade 316, not less than 17mm

diameter together with two rod centralizers for pump installation greater than 36m deep or 3m in

length uPVC 40mm diam. riser pipes with stainless steel coupler design; male threads insert fitted

and crimped at one end and female threaded stainless steel socket fitted and crimped at the other.

(Preferably AJAY manufactured); Each pipe fitted with two centralizers and stainless steel rods of

G316 and not less than 17mm diameter for pump installations not greater than 36m.

29. Clearing the site

Upon completion of works on a well site, the site must be left free from debris, hydrocarbons and

waste, and all pits must be filled up. A site not delivered clean may render the well unacceptable.

30. Records and Reporting (see Annex 3)

The Contractor shall prepare a Borehole Completion Report; including drilling and pump testing and water quality data, according to the provided lists of standard forms in section 5.53, as well as provide photographs of materials installed and all work progress on completion that shall be laid out as described below:

Site Identification

The Contractor shall provide the following information:


Site Name Borehole Name GPS Coordinates correct to 2 decimal places Height above sea level

Drilling Details

The Contractor shall provide the following information:

Make and model of Drilling Rig Name of Driller in charge Date and time drilling start Date and time drilling ended Drilling method used Drilling fluid used Drilling additives used Drilling diameter(s) – where different diameters used, depths (from & to m.b.g.l.) must be

provided for each diameter.

Table 13: Example of rate of Penetration table and graph (similar to below)


Sampling

The Contractor shall provide a geological log table with the following information:

Example of geological Log table.

Drilling Log no.

Depth (m bgl) Rock / soil description & remarksFrom To

1 0 22 2 4Etc.

The Contractor shall also provide a sieve analysis for each aquifer encountered. The Contractor shall take a large representative sample (approx. 1kg) and provide the following information in a table:

Table 15: Sieve Analysis.

Sieve Size (mm) Weight Passing (kg) Percentage passing

Borehole Design information.

The Contractor shall provide the following details about the borehole design:

Casing & Screen type (solvent / threaded) Screen Design (E.g. Slotted pipe, Bridge-slot, louvered, continuous slot) Casing and screen material Internal diameters of screens and casings Slot size of the screens Percentage open area of the screens Plain casing & screen placement, from and to depths below ground level

The Contractor shall show all borehole design calculations using the Logan method or similar approved method. The contractor shall clearly show the following:

The stated desired flow rate from the borehole The assumed hydraulic conductivity of the aquifer(s) The maximum desired drawdown in the well The calculated length of screen required The calculated entrance velocity The calculated up flow velocity in the borehole


Gravel Pack Design

A well-graded pack will be placed in the annular space between the borehole wall and the outer surface of the casing. Proper techniques should be used for the accurate placing of this pack to ensure its even placement. The gravel to be used should be clean, well rounded and the grains should be hard, of alluvial origin, and a size between 2mm and 4mm diameter.

The Contractor shall provide a grading profile for the gravel pack and show by means of a graph (similar to below) how the gravel pack is compatible with the aquifer grading profile.

Example of aquifer grading Profile


Annex 1: Standard borehole designsBorehole design 1: Unconsolidated formations


Borehole design 2: consolidated formations


Borehole design 3: Consolidated formation


Annex 2: Borehole Apron: – Drawings (Plan & Sections).


Annex 3: Typical FormsTest Pumping: Step Draw Down (Typical format)

PUMP TEST - STEP DRAW DOWN TEST REPORTVillage; GPS Co-ords N…………….…… E……………….…STEP 1 : Discharge set at ( Liters/Second): 0.25TIME ELAPSED (In Minutes)

DEPTH TO WATER LEVEL (Meters)

DRAWDOWN (In meters) REMARKS

0 1 2 3456789101520STEP 2: Discharge set at ( Liters/Second):TIME ELAPSED (In Minutes)



0 1 2 3 4 5 6 7 8 9 10 15 20 STEP 3 : Discharge set at ( Liters/Second): TIME ELAPSED (In Minutes)



( 20 MINUTES) 0 1 2 3 4 5 6


7 8 9 10 15 20 Pump Supervisor Sign Drilling Supervisor Sign Drilling Manager

Sign


Test Pumping: Constant DischargePUMP TEST - 4 HOURS AQUIFER TEST Village:___________________________

GPS Coords N……………… E …………….Date:___________

Start Time…………….

End Time……………

S.no Time elapsed in minutes Drawdown (meters) Yield ( ltr / sec) Remarks

1 0 2 13 24 35 46 57 68 79 810 911 1012 1513 2014 2515 3016 3517 4018 5019 6020 7021 8022 9023 10524 12025 13526 15027 16528 18029 19530 21031 22532 240 33 260 34 280 35 300 Pump Supervisor Sign Drilling Supervisor Sign Drilling Manager Sign


Recovery MeasurementsBORE HOLE - RECOVERY TEST Village:……………………………GPS Co-ords N…………………… E ……………………

Date:…………………… Start Time……………………….End Time……………………..…

S.NO

TIME ELAPSED IN MINUTES

DRAWDOWN (METERS)

YIELD ( LTR / SEC) REMARKS

1 0 2 1 3 2 4 3 5 4 6 5 7 6 8 7 9 8 10 9 11 10 12 15 13 20 14 25 15 30 16 35 17 40 18 45 19 50 20 55 21 60 22 23 24 25 26 27 28 29

30 Pump Supervisor Drilling Drilling Manager


Supervisor


Borehole log sheet (Typical)

Bore Hole Litho log and drill time log with water strike zones

Drilling Company:Village Borehole Number

GPS Cords. N_______________________________ E________________________________

Dates Started:Date Ended :

Water strikes Litho-logical LogDepth in Meters

Drill Time Log

Ground Surface

Minutes / per meter drilled

BO

RE

H

OLE



Bore Hole Completion Record

Bore Hole No……………………………………………………..Bore Hole Name…………………………………………………._______________________________________________________________________1. Village………………… Parish ……………………..District……………………….. Coordinates; N ………………E………………… Elevation …………………..ASL 3. Contactor/Driller………………………………………… Address……………………. …………………………………………………………………………………………

4. Type of Bore Hole; Drilled; Driven; Bored; Jetted; Other……………………………… ………………………………………………………………………………………….. Type & Make of the drilling Rig………………………………………………………...

5. Bore Hole Design & Construction (Sketch to accompany) Drilling Started………………………… Drilling Completed…………………………. All work completed……………………………………………………………………… Total Depth: Reported………m; Measured…….m; Final (Backfilled) Depth;……..m Hole Diameter………………mm. From ……….m to……………….m ……………….mm From ……….m to……………….m ……………….mm From ……….m to……………….m ……………….mm From ……….m to……………….m Permanent Casing: Plain: Type………..; Dia……..mm; Length………m; From………m to……….m Type………..; Dia……..mm; Length………m; From………m to……….m Type………..; Dia……..mm; Length………m; From………m to……….m Type………..; Dia……..mm; Length………m; From………m to……….m Screen: Type & Make……………………………………………………………………………… Diameter………mm; Length……….m Set from…….m to……………m

Gravel Pack: Size of grains…………mm, Roundness (Good, Fair, Poor)……………………….. Volume inserted to the annular space………cu.m, from………….m to…………..m


6. Aquifer: 1st Water Struck at ……………….m.; Water rest level………………………….m Main Aquifer struck at …………...m. ; Water rest level…………………………m Water bearing material…………………………, from……..m to………………..m Other Aquifers, Remark etc……………………………………………………………………... ……………………………………………………………………………………………………. ………………………………………………………………………………………………

7. Yield: SWL………m.; DWL……….m. below GL; Discharge………………….Ltrs/min after pumping ……………..Hrs; Recovered to SWL in …………….Minutes;

Recommended production discharge………….Ltrs/Hr, with pump set at …………..m below GL

8. Bore Hole Development Start……………. Finish …………… Hrs…………………

9. Pumping Test Record in summary (Attach detailed test records – Test pumping & BH recovery tests) – All depth measurements to be in Metres below GL

DescriptionDate of Test (Day, Month, Year)Depth of BH at time of test (m)Static Water Level (SWL) before test (m)Type of Pump usedDepth of Pump Intake (m)Discharge (Ltrs/Minute)Dynamic/Pumping water level (m)After Pumping continuously for (Hrs)Time of recovery to original SWL (Minutes)Rate of Recovery – WL after 5 Minutes (m) WL after 20 Minutes (m) WL after 60 Minutes (m) WL after 180 Minutes (m) WL after 360 Minutes (m)

Additional pumping tests to be mentioned in Remarks

10. Quality of Water: (Water Quality Test Certificates to accompany) Sample (Yes/No) collected at …………………………. Hour on …………………….. (Date) Sediment………………………….., Taste ……………………….., Odour……………………. Colour………………………………; Specific conductivity……………….μmho/cu. m; Temperature……...oC

11. Remarks: (Drilling difficulties, gravel pack details, all pertinent information about drilling and completion of the Bore Hole) …………………………………………………………………………………………………………………………………………………………………………………………………………………………


………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

12. Sketch of Bore Hole Construction ( Sketch to include depth, & changes of hole diameter; casing positions, manner of casings (if different diameters), connections, and casing connection to the screen; depths of screen, how casing is closed at the bottom, formation caving zones and any other pertinent information)


Annex 4: List of Communities Chiefdom Community Name Number of Boreholes to

be drilled


Map of Chiefdoms in Kenema District in Sierra Leone


Contents of this · Web viewTemporary casing may be installed in the borehole to prevent formation heave or collapse or sloughing. Installation and diameter of any temporary casing

Documents