The Mystery Bridge at Highway 20 site is an industrial area with two onsite residential subdivisions, in Natrona County, one mile east of Evansville, Wyoming. A portion of the site lies within the 100- and 500-year floodplains of the North Platte River and Elkhorn Creek. Two plants are located at the site: the DOW/DSI facility, an oil and gas production enhancement service facility; and the KN plant, which is a natural gas fractionation, compression, cleaning, odorizing and transmission plant. The site overlies a contaminated alluvial aquifer. In 1965, an underground pipe burst, releasing 5,000 to 10,000 gallons of absorption oil from the KN facility into the soil. From 1965 to 1987, a flare pit was used by KN to collect spent materials and wastes, and an onsite catchment area was used to collect the contaminated surface runoff etc. In 1987, site investigations revealed the presence of aromatic hydrocarbons in the soil in this area. The Record of Decision (ROD) addresses remediation of the onsite ground water emanating from the DOW/DSI and KN facilities; the VHO and BETX plumes respectively. The primary contaminants of concern affecting the ground water are VOCs including benzene, PCE, TCE, toluene, and xylenes.