Annex D - Recommended format for technical specifications for water well construction
Key:
A = Number of wells to be drilled
B = Location of
drilling sites
C = UNHCR's implementing partner for the
project
1. GENERAL CLAUSES
1.1. Subject of the Contract
The subject of the contract comprises the construction of (A)
water wells for potable water supplies for refugee settlements in (B).
The contractor will carry out the drilling work and provide the
proper tools, machinery, implements, materials and labour for due construction
of the wells, their development and pump testing. He will also provide the
casing and screen materials according to the quality specifications given
hereunder.
1.2. Information supplied by (C)
(C) will supply all available information about the possible
hydrogeological conditions at each drilling site. It should be clear that this
information does not hold (C) responsible for the locally different conditions
at the specific drilling site or for the particular problems the contractor may
face while carrying out his work.
1.3. Drilling Sites
(C) will indicate the drilling sites and provide the required
permits for the use of the land where the contract is to be carried out.
The contractor will be responsible for all damages occurring
outside the allocated land.
The contractor will clear all debris of any kind, and leave the
land, as far as it is possible, in the original condition, once the well has
been finished, developed and pump-tested.
1.4. Abandoned Well
If the contractor is not able to finish the drilling or has to
abandon the well due to loss of tools or any other accident or contingency, he
should remove the casing or drive pipes already placed in the hole and refill it
with clay or concrete, at his own expense. All material extracted from such
holes, after refilling them will be considered the property of the contractor.
In this case, (C) will not pay for any of the work carried out,
and will authorize in advance the drilling of a new hole, at a site near the
abandoned one.
2. TECHNICAL SPECIFICATIONS
2.1. Boreholes
2.1.1. Information concerning each borehole
The contractor will supply a detailed borehole log, in which all
relevant information on drilling velocity, well casing and other well
construction operations will be recorded.
The contractor will also annotate all information pertaining to
the appearance of water filtrations and aquifer, types of rock found and rock
sampling details.
2.1.2. Casing and diameters
The drilling of each hole will be carried out according to the
characteristics specified in the Appendix of these specifications, using the
proper drilling tools, drive pipes, casing pipes, gravel packs and sanitary
protection (see 2.5.), based on the real characteristics of the aquifer
formations. The casing pipe and sanitary protection (seals) should isolate the
aquifers from other formations, which are considered improper for the
exploitation of wholesome water.
The well design is to be authorized by (C) before the casing pipes
and screens are introduced into the well.
2.1.3. Pipes and screen filters
The contractor will supply all pipes, screen filters and fittings
for the proper casing of the wells at the agreed price.
2.1.4. Drilling equipment and depth of drilling
The contractor will use drilling equipment capable of drilling
down 25 per cent deeper than indicated in Appendix I. The use of cable tool,
rotary or down the hole hammer (air percussion) rigs is acceptable. The depths
indicated in the Appendix are tentative and should only be regarded as a guide.
If the real characteristics of the wells being drilled justify any
change in these specifications, the contractor will request the authorization of
(C) for such changes to be made.
These communications will be made verbally and shall be properly
recorded by (C).
In every case, if the actual characteristics of the well differ
from those indicated in the Appendix I, and once these changes have been
authorized by (C), a proper price adjustment will be made according to the final
depth of the well, and the unit price rendered by the contractor in his original
proposal.
2.2. Well Completion and Test Pumping
2.2.1. Pumping tests
The contractor will have a pumping unit capable of discharging 50
per cent more water, at the well's pumping water level, than the maximum
yield indicated for each well in the Appendix.
Once the well construction is finished, the well will be developed
by hydraulic surging (by means of a packer piston, compressed air of dry ice
treatment). Immediately after this operation is completed, the well will be
cleaned and the pumping unit introduced into the well. The contractor will
communicate (3 days in advance) the date the pumping test is to be carried out.
The test pumping of the well will be performed according to
2.2.1.1.
2.2.1.1. Pumping test
The test will consist of continuously pumping the well at the
maximum yield specified in Appendix I for the respective well (or at any other
previously defined rate, according to the results of the drilling work, between
the contractor and (C). The duration of this test will be 48 hours. The
measuring of the dynamic water levels will be performed according to the
logarithmic time-scale schedule normally used for test pumping water wells.
2.2.1.2. Other specifications
The contractor will evacuate all the pumped water in such a way
that no impoundments are produced at distances less than 200 m from the well.
The contractor will provide all the necessary elements for this purpose.
The contractor will provide all necessary implements (weirs,
pipes, gauges, etc.) for the proper measurement of discharge rates and water
levels.
2.2.2. Well yield
After the pumping tests have been carried out, (C) will decide the
recommended yield for each well, according to the test results, appropriate
hydrogeological techniques and the actual needs.
2.3. Well Plumbness and Alignment
2.3.1. Tests
The well will be tested for plumbness and alignment by means of a
12 metre long, and perfectly straight, steel pipe that will be introduced along
the whole well. The external diameter of this will, at the most, be 13 mm less
than the well casing inside the diameter. This pipe will be supplied by the
contractor.
2.3.2. Minimum requirements
Such a test pipe, as described in 2.3.1. should easily move
through the whole well. The loss of plumbness of the well's axis should
never be more than 2/3 the smaller inside diameter of casing. If these minimum
requirements are not met by the well, the contractor will, if possible, correct
the defects. If not, (C) will reject the well and no payments will be made for
its drilling and completion. This test should normally be made before pump
testing the well.
2.4. Protection of the Water Quality, Disinfection and
Sampling
2.4.1. The contractor will take maximum care to avoid the
physical, chemical or bacteriological contamination of the well water, during
the construction operations. In any case, where water is polluted due to the
contractor's neglect, he will be obliged to carry out all the necessary
operations, at his own cost, in order to extract such pollution from the well.
2.4.2. Well sterilization
Once the well has been completed and tested, the contractor will
sterilize the well with a chlorine solution yielding at least 50 mg/l of active
chlorine in all parts of the well.
The chlorine solution may be prepared for this purpose, by
disolving calcium hypochlorite, sodium hypochlorite or gaseous chlorine in
water. The chlorine solution should stay in the well for at least four hours, at
the specified concentration.
2.4.3. Rock samples
The contractor will keep a complete record of the rock samples
taken during the drilling operations, in properly packed and identified sample
bags, and will make them available to (C) upon his request.
The contractor will take at least one sample every three metres of
drilling, unless a change in rock formations is spotted by the driller. In such
cases, additional samples should be taken. The minimum weight for each sample
should be 500 grammes.
For each rock sample that has not been taken, the contractor will
be fined a penalty amounting to 1 per cent of the total value of the well and
this will be deducted from the final payment. If the total amount of samples not
taken is more than 15 per cent of the specified number, the well should be
started again and (C) will not make any payments for the work already done.
2.4.4. Water samples
The contractor will take two water samples for laboratory
analysis, after completion of the long duration pumping test. One sample will be
used for physical and chemical analysis. It should be put in a clean and
properly sealed plastic or glass container. Its volume should not be less than 5
litres. The other sample will be used in a bacteriological analysis. It should
be collected in triplicate, in sterilized, properly sealed and protected
containers. The volume of such containers should not be less than 100
millilitres. The samples will be handed to (C) as soon as the samples have been
taken.
2.4.5. Sand particle content in pumped water
The water drawn out of the well will be acceptable if it has a
sand particle content of less than 5 grammes per cubic metre. In case this
maximum limit is not kept, the contractor will make all necessary adjustments to
the well structure, at his own expense, in order to meet this specification.
2.5. Finishing Works
2.5.1. Temporary lid
The contractor will pay close attention to the due protection of
the well's mouth against the entrance of water or any other pollutants
while drilling or after the completion of the well. For this purpose, he will
provide a lid to be placed at the well's mouth at any time the drilling rig
is not in operation. This lid will also be placed after the well has been
completed.
2.5.2. Artificial filter packs
An artificial properly graded gravel pack will be placed in the
annular space between the hole wall and the outer face of the casing according
to Annex 1. Proper techniques should be used for the accurate placing of this
pack on the site. The gravel to be used should be clean, well-rounded and the
grains should be hard and of alluvial origin and in size between 0.5 and 2.5 cm
diameter. This gravel has to be approved by (C).
2.5.3. Sanitary protection seal
All the wells that have been completed and tested with success,
should have a proper sanitary seal protection built of concrete.
This protection will be placed from 3.5 metres below the ground to
0.25 metres above the ground and will occupy all the annular space between the
hole face and the outer face of the casing.
APPENDIX I.
Characteristics of the Water
Wells
Tentative Specifications (see 1.2 Technical
Specifications)
