CANNON, ROBERT P., Cannon@AGandE.com, ROGERS, GARY D., Rogers@AGandE.com, and BILLINGTON, EDWARD, Billingt@ AGandE.com, Applied Geosciences and Engineering Inc., 405-A Parkway Dr., Greensboro, NC 27401

Groundwater levels rose significantly after the first filling of the upper reservoir at the Ludington Pumped Storage Plant (LPSP) in 1972. A groundwater control system composed of 45 pumping wells and 156 piezometers were installed to control and return the groundwater levels to pre-filling levels. This system has been monitored, adjusted and maintained in excellent condition since that time, and has successfully maintained groundwater at pre-construction levels.
    The LPSP is located on the shore of Lake Michigan near Ludington, Michigan. The plant consists of a powerhouse with reversible pump/turbines, six 28 foot diameter penstocks, and an upper reservoir. During operation, water is pumped up from Lake Michigan into the man-made upper reservoir during times when demand for electricity is low, then released back into Lake Michigan to generate electricity during high demand periods. The plant is the second largest pumped storage facility in the US and is capable of storing up to 27 billion gallons of water. It can generate 1872 megawatts of power by lowering the water level of the 843 acre upper reservoir by up to 6 feet per hour.
    The upper reservoir consists of a 5.5 mile long continuous embankment ranging from 60 to 170 feet in height and constructed on a bluff over 250 feet above Lake Michigan. The reservoir is founded on glacial tills and outwash sands, the lower units of which were folded by glaciotectonic deformation. The upstream slope of the embankment is covered with an asphalt liner with an internal drainage system and the bottom of the reservoir is covered with a 3 to 5 foot thick layer of compacted clay.
    Upon initial filling, the seepage rate from the reservoir was measured at 23.8 cfs in January 1973, significantly higher than expected. During the initial filling, piezometers installed at the toe of the embankment recorded significant rises in groundwater levels in the three separate aquifers between the base of the reservoir and the elevation of Lake Michigan. An extensive groundwater control program was installed at the downstream toe of the embankment to return the water levels in the aquifers to pre-construction levels.
    Subsequent studies found that this seepage was caused by trenches that had formed through the clay liner and extending over 40 feet into the foundation materials. As the trenches have been repaired, the average pumping rate from the pumping wells required to maintain pre-construction water levels has decreased from 0.22 to 0.10 cubic feet per second and total seepage from the reservoir has decreased from 15.5 to 8.3 cubic feet per second over this same period.