Municipal Water Supply Hydrogeologic Assessment: Madison, Minnesota
Leggette, Brashears & Graham, Inc. (LBG) conducted two aquifer pumping tests for a municipality based on a request to supply water to a proposed 45 million gallon ethanol plant located approximately 1½ miles east of Madison, Minnesota. The tests were conducted to determine if the existing and newly installed city wells were capable of handling the increased water demand that would be required for the proposed ethanol plant and the city’s needs.
SUMMARY OF TASKS
Installed pressure transducers and data loggers;
Collected manual water-level measurements from wells with transducers to validate transducer readings and from wells without transducers;
Test #1 was conducted in November 2006 by pumping two city wells at a combined
rate of 1,060 gallons per minute (gpm) for approximately 7 days, and monitoring water levels in 15 wells;
Test #2 was conducted in June and July 2007 by pumping three city wells in three different pumping scenarios for 35 days at a combined rate of 960 gpm. Water levels were monitored at 26 stations (24 wells and 2 are surface water stations); and,
Completed data analyses, evaluation, and reporting.
Approximately 150 feet of glacial till along with shallow and deep outwash sand and gravel aquifers underlie the area. The deeper sand and gravel aquifer is more extensive and thicker (generally 30 to 125 feet) than the shallow aquifer and supplies water to the city wells and other high-capacity wells.
Aquifer parameters were determined by analyzing the drawdown versus time data from Test #1 using Aqtesolv for Windows Pro. A qualitative evaluation of Test #2 data was conducted to evaluate the ground-water flow systems and evaluate how the aquifer responds to pumping under different pumping scenarios. The tests showed that by using different pumping scenarios, the city would be able to meet its demand of approximately 960 gpm if managed properly, while keeping drawdown levels above the MN DNR safe yield thresholds set forth to protect groundwater resources.