The test compared pumping results from three power sources: 1) direct electrical power, 2) solar power with batteries and 3) solar power alone. Pressure transducers were installed to record levels every 15 minutes in each of three low-flow gas-collection wells, all exceeding depths of 50 feet. Methane and oxygen percentages were measured prior to and during operation.
The test showed that the low-flow pumps reduced average 24-hour liquid levels to satisfactorily address the migration issues, and the levels were consistently maintained by all power options, including solar-only.
Concomitantly, the lower liquid levels attained by all three options exposed an additional 15-18 feet of screen in each well, which resulted in an increased gas flows of at least 15% in all wells. The solar-only system demonstrated consistent recharge rates with a simple, low-maintenance linear-rod drive-motor design, at lower costs to purchase and operate.
Methods
The engineers initiated the test during December 2011. Linear-rod reciprocating-piston drive motors were identical, but each utilized a different power source: Direct electric power converting 220-volt AC to 24-volt DC in well GW-01, direct power from 12-volt DC batteries charged through a mounted solar panel in GW-02, and power from a solar panel alone in GW-05.
The pumping flow rates were a maximum of 2.25 gallons (8.5 liters) per minute. Pump intakes were set 1 to 3 feet above well bottom to avoid accumulated silt or debris. GW-02 began operating on Dec. 13, 2011, followed by the other two wells on Dec. 21.
Liquid levels were measured periodically through March 2012, and pressure transducers were installed March 6. The transducers recorded liquid elevations every 15 minutes. Percentages of methane and oxygen were measured periodically before and during pump operations.
Results
Average 24-hour groundwater levels were satisfactorily reduced and consistently maintained at pump intake by all three power options, including the solar-only system. Depending upon the well, between 15.6 and 18.4 feet of additional screen was exposed -- between 75% and 93.6% -- equating to methane-flow increases of at least 15% at GW-01 and GW-02 and approximately 20% at GW-05.
Solar-only power at GW-05 produced minor fluctuating liquid levels corresponding with the on/off cycle during daylight/nighttime hours. Approximately 3 to 4 feet of liquid accumulated while the pump was not running. The pump switched on during daylight hours, removing the liquid and maintaining liquid level at intake. The degree of daily fluctuation in GW-05 was relatively minor compared with length of additional screen exposed (17.0 feet).
