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Module 3 — Design and Construction of Water Wells
Yield Test
A yield test is important because the information gathered during the test assists the
driller in determining the:
Rate at which to pump the well
Depth at which to place the pump.
Provincial regulations outline the requirement for a minimum yield test to be performed
on all new wells. After drilling and developing a well, the licensed water well contractor must
remove water from the well for at least 2 hours. If a pump is used to remove the water, then
water level measurements can be recorded as the water level draws down during pumping. If
the yield test is performed using a bailer or air compressor to remove the water, water level
measurements cannot be taken during the water removal portion of the test.
After 2 hours, water removal must be stopped and the recovery of the water level then
monitored and recorded. Measurements must be taken at specific time intervals for a 2 hour
period or until the water level returns to 90 percent of its original level.
Once the yield test is complete, the driller will decide at what rate the well can be
pumped without lowering the water level below the top boundary of the aquifer, the top of
the perforations or below the pump intake.
Your pump should have a capacity equal to, or less than, the rate at which the well can
supply water for an extended period of time without lowering the water level below the pump
intake. That pumping rate is considered the long-term, safe and sustainable pumping rate
for the well.
The value of using a pump to perform the yield test is the test will be repeatable. You
should periodically conduct a similar yield test to collect new data that can be compared to
previous tests. If you notice a decline in well performance you can have your licensed water
well contractor back to rehabilitate or repair your well. Keeping a watchful eye on your well
will enable you to recognize the symptoms of declining performance before it is too late to
economically repair the well.
Disinfecting the Well
Provincial regulations require the licensed water well contractor to disinfect new wells
with chlorine. The concentration is calculated on the volume of water that is in the well.
The concentration must be at least 200 milligrams of chlorine per litre of water present in
the well and must be left in the well for at least 12 hours to ensure any bacteria present are
destroyed. Disinfection is done after the pumping equipment is installed and before the well
is put into production.
The yield test provides a benchmark of your
well's performance. Repeating this test at a
later date can be used to assess any changing
conditions in well performance and indicate
when maintenance is required.