SEEPAGE MEASUREMENTS FROM LONG LAKE, INDIANA DUNES NATIONAL LAKESHORE

Long Lake, located near Lake Michigan within the dune-complexes of Ind iana Dunes National Lakeshore, USA, was formed some time during the Pl eistocene and Holocene epochs. A surficial or sink for the later. The hydrologic processes in the lakeshore and surrounding environs have be en significantly altered during the agricultural, municipal, and indus trial development of the region. Limited data suggest that the organis ms of Long Lake have elevated levels of several contaminants. This stu dy attempts to quantify seepage within the lake to assess the potentia l threat to groundwater quality. Seepage measurements and minipiezomet ric tests were used to determine seepage within the lake. Seepage meas urements and minipiezometric tests suggest that water seep out of Long Lake, thus recharging the groundwater that flows southwest away from the lake. There is a great deal of variability in the seepage rate, wi th a mean of 11.5 x 10(-4) +/- 11.2 x 10(-4) m d(-1). The mean seepage rate of 0.3 m yr(-1) for Long Lake is greater than the 0.2 m yr(-1) r echarge rate estimated for the drainage basin area. The Long Lake rech arge volume of 2.5 x 10(5) m(3) yr(-1) is approximately 22% of the vol ume of the lake and is significant when compared to the total surface recharge volume of 4.8 x 10(5) m(3) yr(-1) to the upper aquifer of the drainage area. There is a potential for contamination of the groundwa ter system through seepage from the lake from contaminants derived fro m aerial depositions.