Geohydrology and Contamination at the Michigan Department of Transportation Maintenance Garage Area, Kalamazoo County, Michigan, 1996

By: Erin A. Lynch and Gary C. Huffman

Abstract

A leaking underground storage tank was removed from the Michigan Department of Transportation maintenance garage area in Kalamazoo County, Mich., in 1985. The tank had been leaking unleaded gasoline. Although a remediation system was operational at the site for several years after the tank was removed, ground-water samples collected from monitoring wells in the area consistently showed high concentrations of benzene, toluene, ethylbenzene, and xylenes -- indicators of the presence of gasoline.

The U.S. Geological Survey did a study in cooperation with the Michigan Department of Transportation, to define the geology, hydrology, and occurrence of gasoline contamination in the maintenance garage area. The aquifer affected by gasoline contamination is an unconfined glacial sand and gravel aquifer. The average depth to water in the study area is approximately 74.7 ft. Water-level fluctuations are small; maximum fluctuation was slightly more than 1 ft during August 1993 - August 1994. Hydraulic conductivities based on aquifer-test data collected for the study and estimated by use of the Cooper-Jacob method of solution ranged from 130 to 144 feet per day. Ground water is moving in an east-southeasterly direction at a rate of about 1 foot per day.

Leakage from perforated pipes leading from the underground storage tanks to the pump station was identified as a second source of gasoline contamination to saturated and unsaturated zones. The existence of this previously unknown second source is part of the reason that previous remediation efforts were ineffective. Residual contaminants in the unsaturated zone are expected to continue to move to the water table with recharge, except in a small area covered by asphalt at the land surface.

The gasoline plume from the perforated pipe source has merged with that from the leaking underground storage tank, and the combined plume in the saturated zone is estimated to cover an area of 30,000 square feet. The combined plume is in the upper 20 feet of the saturated zone. The relative distribution of benzene, toluene, ethylbenzene, and xylenes indicate that factors such as sorption, solubility, and susceptibility to microbial degradation are affecting the movement of the combined plume. Given these factors, the plume is expected to move at a rate of less than 1 foot per day.

Publication
Lynch, Erin.A., and Huffman, Gary C., 1996, Geohydrology and Contamination at the Michigan Department of Transportation Maintenance Garage Area, Kalamazoo County, Michigan: U.S. Geological Survey Water-Resources Investigations Report 96-4010, 31 p.

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