Water Stewardship

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

Part 1

6. Guidelines for Well Development

6.1 General Considerations

An important factor in well development is that the development work be started slowly and gently and increased in vigour as t he well is developed.

When to stop well development is to a large extent a matter of experience and judgement; periodic pumping or bailing will indicate whether the sand content in the well is decreasing and whether for a given rate of flow and period of test the drawdown becomes less as well development proceeds.

6.2 Water for Well Development

Under no circumstances should water be introduced into a well for jet development, etc., that does not meet the recommended water quality standards published by the Provincial Ministry of Health, without prior approval from the local health officer.

6.3 Acids or Other Chemicals

If acids or other chemicals are introduced into the well to develop the well, the well water should be pumped until all traces of the chemical are dissipated, before being connected up to a piped system.

6.4 Sand Content

The contractor should attempt to meet the following recommended limits for sand content in well water:

(a) Sprinkler systems, industrial evaporative cooling systems and other uses where a moderate amount of sand is not especially harmful 10 ppm (mg/L).

(b) Wells supplying water to be used directly in contact with or on the processing of food or beverages — 1 ppm (mg/L).

(c) Wells supplying water to homes, institutions, municipalities and industries — 5 ppm (mg/L).

Information on Well Development Methods is given in Appendix 4.

7. Guidelines for Well Testing

7.1 Water Wells for Single Family Dwellings (Domestic Wells)

Domestic water wells should be test pumped, bail tested or air lifted for a minimum of one hour following construction of the well. The static water level should be recorded prior to testing, the change in water level within the well should be recorded if possible, and recovery measurements taken to give some idea of well capacity. Domestic wells constructed in bedrock require a longer test period.

In testing a well by means of a simple bail or air lift test, the amount of water taken out in a given time has to be approximated. However, when a well is test pumped there are several procedures that can be used to obtain information on well capacity.

Firstly, a step-drawdown test may be sed. In this procedure, the well is pumped at several rates starting with a minimum rate and increasing in several "steps" to the maximum rate desired. Each step is continued until the level in the well becomes approximately stable, or until the rate of decline of water level becomes constant. Secondly, a constant rate test can be run. In this case the well discharge should remain constant for the duration of the test.

A recovery test may also be used. Here the well is pumped at a fixed rate for a number of hours during which the level in the well is observed. Pumping is stopped abruptly and the water level is recorded as the water level rises in the well. In using this method it is important to record the time of starting and stopping of pumping and the time of all observations, and it is particularly important to observe the last part of the well recovery as it approaches the original level. This may mean taking observations for many hours after pumping has been stopped. The following two tables (Tables 7 and 8) illustrate the type of information recorded in pumping and recovery tests.

For domestic water wells constructed in bedrock, longer more sophisticated tests may have to be undertaken and where only a one hour minimum bail test, pump test or air lift test is done followed by the recovery test, the well owner should be informed that the yield may differ considerably from the test result obtained, particularly during summer drought conditions.

Pump testing of wells constructed in fractured bedrock must be done with considerable care. Experience shows, that the amount of water entering a well from fractures during sustained pumping usually decreases before becoming approximately constant. Rock wells should be pumped for a long period (usually more than two days) at a constant rate in order to detect the decrease in well capacity with time.

In testing rock wells at locations where the distribution of rainfall is very uneven throughout the year and where the well is fairly close to its source of recharge, the results of pump testing may vary considerably with the season. For example, certain wells located on the Gulf Islands of British Columbia, where there is normally a long, dry summer, show lower capacity when tested in early autumn than when tested in winter.

7.2 Industrial, Irrigation and Community Water Supply Wells

Large capacity wells for industrial or irrigation use should be test pumped at rates at least equal to the expected pumping rate for a period of up to 24 hours, or for a longer time period in certain circumstances as in the case of wells constructed in fractured bedrock. The pumping rate should be held constant during the final pumping test and the reader is referred to the tables in Appendix 5 for the type of information to be recorded in pumping and recovery tests. In large capacity wells, a pumping test for maximum information may include one or more observation wells near the well being pumped, and this test is frequently run under the supervision of a consulting ground water geologist or a professional engineer, whose field of competence lies within the ground water field. In this test the observation well(s) should, of course, be in the same aquifer as the pumped well. In this procedure, pumping is started at a steady rate which is sustained for at least several hours. The drawdown is measured in observation wells and in the pumped well at frequent intervals during the pumping. Tests may be conducted at several different pumping rates. The analyses of these pumping data are rather involved. A number of assumptions are made concerning the nature of the aquifer, now to the well and other factors. These assumptions may not be correct, but they are usually close enough to give an approximate idea of the conditions prevailing. The analyses determines aquifer constants called "Transmissivity" and "Coefficient of Storage' " These measure the ability of the aquifer to transmit and store water. From the aquifer constants, predictions can be made concerning well yield drawdowns at various distances from the well and other factors. In this type of test, the performance of the well may be separated from the performance of the aquifer.
For community water supply wells, instruction and procedures for preparation of ground water reports and for undertaking well tests in support of a Certificate of Public Convenience and Necessity, see Appendix 5. Further information should also be obtained from the Water Management Branch of the Ministry of Environment.

Table 7. Pumping Test

Depth to water in well from top of casing before test _____________ ft.

For the above table, readings should be taken every minute from 1 to 10 minutes and then every 10 minutes from 10 to 120 minutes (2 hours), then readings every 1 1/2 hours thereafter.

Table 8. Recovery Test

For the above table, readings should be taken every minute from 1 to 10 minutes and then every 10 minutes from 10 to 120 minutes (2 hours), then readings every 1 1/2, hours thereafter. Slow recovery may require that the last readings be spaced as much as 8 to 12 hours apart.

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