Pump test procedures

The pump test must be performed at or above the pumping rate for which approval will be sought in the water supply application. If multiple wells are to be pumped simultaneously to achieve the necessary yield, the test should incorporate such a pumping plan. To reproduce the anticipated stress on the aquifer, the pump test should be done when nearby wells normally in operation are running.

For unconfined aquifers the test should be conducted for a minimum of 72 hours.

For confined aquifers the test should be conducted for at least 48 hours.

Pumping of other wells in the test area should be monitored.

No pumping should be conducted at or near the test site for at least 24 hours prior to the test. Static water levels at the pumping well and observation wells should be measured one day prior to the start of the test and again immediately prior to the start of the test.

A constant pumping rate should be maintained throughout the test. The pumping rate should be measured accurately and recorded at least as often as water level measurements. A decrease in discharge from the pump will normally occur with increasing drawdown, as the pump works against a greater hydraulic head and increasing friction in the system. These effects should be compensated for during the test. Water discharged during the pump test should be conducted away from the pumping well to minimize or eliminate recharge of this water to the aquifer. If the aquifer is confined or if it can be otherwise demonstrated that discharged water will not recharge the aquifer being tested, a more convenient method of discharge can be used.

Water levels in observation wells and at the pumping well should be measured to give at least ten observations of drawdown within each log cycle of time, beginning one minute after the start of pumping. A suggested schedule of measurements at all wells is as follows:

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Fluctuations in nearby surface water stages should be monitored to the nearest cm unless it can be demonstrated prior to the test that there is no connection between the aquifer and nearby surface water.

At least three observation wells should be monitored during the pump test. The horizontal distance between each observation well and the pumping well should be measured to the nearest dm (0.1m). The vertical elevation of a fixed reference point on each observation well and on the pumping well should be established to the nearest cm. One observation well should be located outside of the expected influence of the pumping well; this observation well should serve to monitor background conditions during the pump test. The remaining observation wells should be placed so as to best define the hydrogeologic characteristics of the aquifer with respect to the pumping well.

Observation wells should be just large enough to allow accurate and rapid measurement of the water levels. Small diameter wells are recommended because the volume of water contained minimizes time lag in drawdown changes. Existing wells can be utilized if they are in good condition and were properly installed.

For unconfined aquifers, at least two observation wells should generally be placed no farther than 100 m from the pumping well and at least one additional observation well should be placed beyond the 100m radius. For thick confined aquifers that are considerably stratified, at least two observation wells should be placed within 200 m of the pumping well and at least one observation well located further than 200 m from the pumping well.

Observation wells should be screened in, or open to, the same formation as the pumping well. Additional observation wells beyond the specified minimum number may be screened in, or open to, formations above or below the one tapped by the pumping well to determine if there is any hydraulic connection between formations.

Water level measurements should be collected during the recovery period for all wells using the same procedure and time pattern followed at the beginning of the pump test. Measurement should commence at least one minute prior to shutdown of the pumping well and continue for at least 12 hours. Water level measurements should be made to the nearest cm. To obtain accurate data during the recovery period, a check valve must be installed at the base of the pump column pipe in the pumping well to eliminate backflow of water into the well. Water level measurements should also be collected during the recovery period in all off-site monitoring wells, such a homeowners private wells.

Rainfall should be measured to the nearest mm and recorded daily at or near the site for one week preceding the pump test, during the test, and during the recovery period. A log of weather conditions during this period should also be kept, including barometric pressure recorded on the same schedule as rainfall. Weather station data available from within a reasonable distance of the test site can be utilized.

Fluctuations in surface water stages for all surface waters within 500 feet of the pumping well should be measured to the nearest cm. Measurements should be made and recorded at least once daily for one week prior to the start of the test and at least twice per log cycle, after the first ten minutes, for the duration of the test. Measurements should be made more frequently if surface water levels are changing rapidly. The degree and nature of hydraulic connection with the surface water body should be quantified.

If the pumping well is, or may be, hydraulically connected to a surface water body, water samples from the well should be analyzed in the field at least once every four hours for the following parameters:

1. pH,
2. temperature,
3. conductivity, and
4. hardness.

Water samples should be obtained from the pumping well at least twice during the test: once during the first hours of pumping and again during the last hour of pumping.

Water level data, graphs, and interpretations should be corrected, as appropriate or deemed significant, for the effects of: ambient water level trends; partially penetrating production well(s); partially penetrating observation wells; delayed yield from unconsolidated aquifers; recharge and/or impermeable boundaries; barometric pressure changes; changes in stage in nearby surface water bodies; recharge events (rainfall, snow melt) during the week preceding the test, during the test, or during the recovery period; influence from nearby pumping wells; and any other hydrogeologic influences. All such data and calculations should be included in the test information package.

In order to accurately analyze pump test data, it is necessary to use the methods and formulae appropriate for the hydrogeologic and test conditions encountered at, and specific to, the pump test site. Knowledge of the hydrogeologic conditions of the area is necessary in order to ensure the use of appropriate techniques of analysis. Accordingly, analysis of pump test data should be carried out by a hydrogeologist or other appropriately trained staff. Recovery data should be analyzed in a similar manner to drawdown data.

Theoretical distance-drawdown graphs should be prepared from the recorded drawdown graphs. The graphs should be derived from the pump test data, setting time equal to 180 days and groundwater withdrawal equal to the pump test production rate. The theoretical cone of depression so determined should be used to establish the area of influence of the well(s) and a conditional wellhead protection area.

Data submitted in support of a requested groundwater withdrawal should include

• the raw pump test data;
• engineering diagrams showing construction details and depths of pumping wells and observation wells;
• graphs, formulae and calculations used to estimate transmissivity and storage coefficient;
• scaled site plan showing water level elevation controls for all wells and the location of nearby surface water bodies;
• interpretations including methodology, references and rationale.