GROUNDWATER PRODUCTIVITY IN GLACIAL AQUIFERS AS INFLUENCED BY VARIATION IN GLACIAL GEOLOGY AND BEDROCK TOPOGRAPHY IN EAST CENTRAL INDIANA

East Central Indiana is an excellent place to study groundwater situations in the Midwest as there is an almost 50/50 split between glacial and bedrock wells ranging over 100 meters depth. There are two geologic factors leading to these variations. There are over 200 meters of relief on the bedrock surface with deep glacial drift in two distinctly different buried valleys. Also, the glacial drift consists of two distinctly different till plains; one a clay till formation and the other a loamy mix. Over 33000 UTM located water well records are examined from a 17250 km2, 13 county area of East Central Indiana. The area is underlain by nearly horizontal Silurian sedimentary rocks which are covered by 2 to 150 meters of Wisconsin glacial deposits. Prior to glaciation, bedrock was deeply incised by the Teays River Valley to the north and the earlier more maturely developed Anderson Valley to the south. Regarding glacial wells over 50 meters deep, there are more wells in glacial sand and gravels in the southern Anderson area where there are many tributaries. In the north deep wells are restricted to just the deep course of the Teays with less glacial productivity in the steep immature tributary streams. With regard to the shallowest glacial wells (less than 16 meters deep), most are found to the south where the top glacial layer is the loamy Trafalgar Formation and there are less to the north in the clay till Lagro Formation. To the north glacial wells are mostly limited to depths of 15 to 50 meters between the Lagro and the buried bedrock plateau. Glacial groundwater transmissivity is studied using selected well log specific capacity data and the TGuess program. Plots of these data suggest areas for possible high glacial well productivity at various depths, but do not suggest that deeper sand and gravels in the buried valleys would be any more transmissive than others as a general rule.