Water Stewardship

Guidelines for Minimum Standards in Water Well Construction, Province of British Columbia — June 1982

Part 1

8. Guidelines for Well Disinfection

8.1 General Considerations

All wells should be disinfected by the drilling contractor following completion. The quantity of chlorine compounds used for disinfection should be sufficient to produce a 50 ppm chlorine solution when thoroughly mixed with the total volume of water retained within the well.

Following installation of the pump and fittings, the pump installer should further chlorinate the well to 50 ppm, making sure the chemical is thoroughly mixed within the well. Before being used for consumption the chlorine solutions should be pumped to waste and until the smell of the chlorine has dissipated. To protect aquatic life or vegetation, the disposal point for the waste water from the well must be carefully selected.

Further information on well disinfection can be obtained by referring to Appendix 6 and the local health district.

9. Guidelines for Water Samples and Analyses

9.1 General Considerations

Water in all wells should be sampled and the necessary field and laboratory tests made so that the ground water chemical and bacteriological quality of each well and its suitability for its intended use can be determined. Recommended Water Quality Standards have been published by the Provincial Ministry of Health for drinking water and the reader is referred to this publication and the local Medical Health Officer for further details. The Ministry of Health should be contacted for advice on what additional analyses may be required and on any constituents present in well waters which are above the recommended safe limits. All proposals for sampling and analyses for public drinking water supplies serving more than one single family residence should be reviewed by the Medical Health Officer.

For chemical analyses, sample collection procedures vary from the use of a bailer common to the cable tool method to more sophisticated samplers which can take a water sample at a specific depth. Usually samples are collected from the discharge during test pumping or after the production pump is installed. A list of recommended parameters for chemical analyses and further details on water quality are given in Appendix 7, and in the Ministry of Environment publication entitled Practical Information on Ground Water Development.

A sample should be taken on all wells to determine bacteriological quality. For new or repaired wells AWWA A100-66 recommends the collection of any sample for determination of bacteriological quality be taken following the disinfection of the well. Chlorine solution must first be removed from the well by pumping, and the chlorine residual reduced to less than 2 ppm before the sample is taken.
The local public health inspector should be requested to obtain a sample for bacteriological analyses where the water is to be used for a public water supply system. In situations where this is not possible, sample bottles and advice on sampling techniques may be obtained through the local health district.

The quality of any drinking water supply cannot be determined with confidence from the result of a single sample, but rather is possible only by observing the results of several samples over a long period of time. Shallow wells that may be influenced by surface contamination near the well may produce water of varying quality depending on climatic and physical conditions. Therefore if a sanitary survey shows a well water supply to be obviously subject to pollution, the water may be condemned, irrespective of the test results.

10. Guidelines for Permanent Well, Test Well and Test Hole Abandonment

10.1 General Considerations

All test holes, test wells, mineral drill holes and abandoned water wells should be sealed in such a way as to protect any aquifers penetrated. The sealing material should be safe from a health point of view and be more 'impervious than the material encountered during the drilling of the hole.

Accurate records should be kept of all abandoned holes showing their location, the well log and the methods and materials used in the abandonment procedure.

Because of the complexities involved in some cases of well abandonment, each case should be considered as an individual problem and the design, construction of the well and the hydrogeology must be considered and studied before final selection of materials, methods and procedures can be realized. It would be wise, where there is doubt as to the well construction or the hydrogeology, to adopt those materials and procedures which will give the greatest possible chance for a successful and permanent sealing operation. Further information on permanent well, test well and test hole abandonment is given in Appendix 8.

11. Guidelines for Well Head Completions and Pump Installations*

11.1 General Considerations

(a) All pump installations which involve below-surface well-head works should include waterproof pitless adapters or waterproof drained pits. (Further information on pitless adapters is given in Appendix 10).

(b) The well casing should not be cut off below ground surface unless it is enclosed in a waterproof drained pit and fitted with an enclosing cap.

(d) To prevent backflow into any well it is good practice to install a swing check valve or a backflow preventer on the well-head pipework. To minimize surge pressures on pump start up or shut down, a pump control valve should be fitted. The prevention of backflow is essential where the well is to be used for filling containers or where the potential for contaminated backflow is particularly significant.

(e) Pumps should not be in contact with the well screen and large capacity pumps should be installed in a manner which allows the weight of the pump and/or column to be fully supported at the surface on a foundation independent of the well casing.

(f) All well-pump installations should include provision for venting air from and into the well and the well head pipework, and for taking water level soundings in the well.

(g) Metering facilities are essential in order to effectively monitor the performance of the well and pump. All wells used for industrial and public water supply should be equipped with a suitable water meter.

(h) Provision should be made in the pump house design for maintenance equipment, drilling rigs, etc. to operate at the well head in case it is necessary to redevelop or remove the pump, etc.

(i) Thermoplastic water well casing should be protected by steel casing at the ground surface in such a way as to prevent damage to the plastic. The steel casing must be firmly anchored into the ground.

Back to Contents