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Abstract: Gas Chromatography -Its Not Just For Source Rocks Anymore: An Environmental Case Study At The Lexington-Bluegrass Army Depot Site, Fayette County, Kentucky


Use of gas chromatography as a tool for characterizing source rocks, and understanding hydrocarbon migration and emplacement is well established in petroleum geology. Unfortunately, environmental professionals lacking experience with gas chromatography, and certain concepts such as structural and stratigraphic trapping, and reservoir compartmentalization can bias field sampling and analysis of hydrocarbons at environmental sites. This problem was recognized at the Lexington-Bluegrass Army Depot Site near Lexington, Kentucky where hydrocarbon contamination up gradient hydrologically from known underground storage tanks has not been adequately deciphered. The nearly 800-acre site, situated near the crest of the Cincinnati Arch, is located on the Lexington Limestone, which is composed of about 50 percent shale. At this site, the Lexington displays epikarst features, and contains two contaminated aquifers associated with the Tanglewood and Grier limestone members. Original remediation plans at the site were to pump and treat groundwater, based on the belief that all detected hydrocarbons were anthropomorphic. Fortunately, expensive remedial efforts will probably be avoided since it has been suggested to site officials that a significant portion of the site may be "contaminated" by naturally occurring hydrocarbons. The revised sampling and analysis plan considers the following: 1) retention times required to detect naturally occurring hydrocarbons versus refined product 2) regional structural position of the site 3) chemical variations in formation waters versus compartmentalization of aquifers and 4) characteristic gas chromatograph signatures associated with source rocks in adjacent basins.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky