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NPL Site Narrative for Mystery Bridge Rd/U.S. Highway 20
MYSTERY BRIDGE ROAD/U.S. HIGHWAY 20
Evansville, Wyoming
Federal Register Notice: August 30, 1990Conditions at proposal (June 24, 1988): The Brookhurst residential subdivision and an industrial area border on Mystery Bridge Road and U.S. Highway 20 in Evansville, Natrona County, Wyoming. To date, several sources of contamination have been identified at the site, which covers approximately 200 acres. The search continues for other sources.
One source is KN Energy, Inc., which has operated a natural gas processing and transmission facility since 1963 on about 25 acres south of the subdivision at 5500 Yellowstone Highway (U.S. Highway 20/26) east of Casper. Until 1985, wastes drained into an unlined pit on the northeast corner of the facility. This unlined pit, which was replaced in December 1984 by a concrete-lined structure, contains numerous hazardous substances, including xylenes, ethylbenzene, toluene, naphthalene, chrysene, methylnaphthalene, and benzene, according to EPA tests conducted in 1987. These substances were detected in the shallow alluvial aquifer immediately north of the pit, including private wells in the subdivision. Within 3 miles of the site, this aquifer has been the sole source of drinking water for about 400 people, an alternate source for about 2,500 people, and a source to irrigate cropland.
EPA's 1987 tests indicate that Elkhorn Creek, which passes through the middle of the KN Energy facility, is contaminated with toluene and fluoroanthene. Within 3 miles downstream of KN Energy the North Platte River is used for irrigation and recreational activities.
The Dowell Schlumberger oil field service facility is also south of the subdivision. The facility occupies 10 acres on the east side of KN Energy at 5750 Yellowstone Highway. EPA determined that this facility was the source of chlorinated organic solvents, including trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, and 1,2-dichloroethylene, in private wells in the Brookhurst subdivision as far as 0.5 mile away, and also in Elkhorn Creek.
EPA detected pentachlorophenol in monitoring wells along the Burlington Northern Railroad and U.S. Highway 20 rights-of-way and at several locations in the subdivision. The source or sources of this contamination is unknown.
The State provided bottled water to about 400 subdivision residents for 1 month in late 1986. Using CERCLA emergency funds, EPA supplied water until December 1987, when EPA provided the homes a permanent water supply.
KN Energy, Dowell Schlumberger, and its parent company, Dow Chemical Co., signed a Consent Agreement with EPA on December 15, 1987 in which they agreed to conduct a remedial investigation/feasibility study (RI/FS) to determine the type and extent of contamination at the site and identify alternatives for remedial action. On the same day, KN Energy and Dowell Schlumberger/Dow Chemical signed separate Consent Agreements to conduct removal actions on their properties.
Status (August 30, 1990): KN Energy is extracting vapors from soil and pumping and treating ground water. The other two companies have removed some contaminated soil and are operating two soil vapor extraction systems. The RI/FS is nearing completion.
For more information about the hazardous substances identified in this narrative summary, including general information regarding the effects of exposure to these substances on human health, please see the Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs. ATSDR ToxFAQs can be found on the Internet at http://www.atsdr.cdc.gov/toxfaq.html or by telephone at 1-888-42-ATSDR or 1-888-422-8737.