Original Date: 09/14/1998
Revision Date: 01/18/2007
Best Practice : Pumping Very Low Water Yield Wells with Conventional Submersible Pumps
Raytheon Missile Systems Company (RMSC) builds water wells in tight, low permeability clay units as part of a pump-and-treat redemption system for a zone of contaminated shallow groundwater. Conventional 0.5-horsepower, 480-volt submersible pumps are the most cost-effective devices to use in these areas, but draw at ten gallons per minute (gpm), which rapidly deplete the well’s water. As a result, the pumps burn out when operated under this no- load condition. Although very low yield pumps are available, they are expensive and not as reliable as submersible pumps. Their associated submersible controllers with downhole probes are also unreliable and require high maintenance.
RMSC resolved this problem by installing electrical load-sensing motor controllers on 41 of its low water yield redemption wells. When a no-load current condition is detected, the controller turns the pump off for a pre- designated period of time. This above ground device cycles the pump on and off according to the flow of groundwater into the well. As a result, the company can use conventional submersible pumps to draw low yield (0.1 gpm continuous flow) water wells. The controller also measures the amperage of the pump’s motor in addition to other operating parameters. When a well pumps dry, the load on the motor drops and the amperage decreases accordingly. The controller senses this decrease and shuts off the motor. After a pre-programmed time, the controller restarts the pump. The pre-programmed time is determined by measuring the amount of time it takes for the well casing to refill with groundwater.
The motor controllers enable RMSC to use its existing, readily available, low cost submersible pumps in very low water yield wells. The controllers cost $170 each compared to the $500-a-piece replacement cost for existing submersible pumps. Alternatively, retrofitting submersible pumps with low rate bladder pumps or centrifugal pumps with controllers would cost between $1,000 and $2,000, and these devices are not designed for continuous use. RMSC’s motor controllers have been in operation for more than a year, and are quite reliable.
For more information see the
Point of Contact for this survey.