ENGINEERING GEOLOGY STUDY TO DETERMINE SOURCE OF ELEVATED ARSENIC VALUES IN GROUNDWATER NEAR MT. VERNON, IN

Mt. Vernon, Posey County, Indiana is located in the southwest corner of the state, just west of Evansville, along the Ohio River. Elevated levels of arsenic, above the MCL of 10 ppb have been found in wells tapping the overburden soils. Houses on domestic wells east and beyond Mt. Vernon’s water supply, have experienced arsenic levels up to 100 ppb. The elevated arsenic levels were first found in a community well for a mobile home park just east of the city. A 12-inch city waterline was extended to this site to mitigate the problem and subsequently individual residential wells were tested for arsenic. An extensive area of high arsenic levels was found. To solve this problem, the city water line was extended eastward to provide city water. A group of students at Purdue, under the direction of Dr. West, studied the details of the area with the high arsenic levels. Overburden consists of sandy silts of alluvial and lacustrine origin. This part of Indiana lies beyond the boundary of Pleistocence glacial contact deposits. Bedrock is Pennsylvanian sandstone and shale yielding shallow, low production oil wells. A port facility on the Ohio River is located adjacent to the contaminated area and about a mile upstream a coal fired power plant is in operation. Fire at a plastic pipe manufacturing plant which lies upstream on the drainage to the mobile home park may have contaminated the groundwater along the stream. An abandoned sanitary landfill lies to the west of the city and down gradient from the contamination and it was ruled out. These items are all possible sources for the elevated arsenic levels. Pennsylvanian bedrock does not seem to be a logical arsenic source and the overburden soil seems innocuous as well. There are some abandoned oil wells in the area which may yield some leakage of petroleum. The configuration of the plume related to the various houses does not point to an obvious source either. The study is currently on hold while more information on arsenic contamination is being explored in the literature.