Mystery Bridge Rd/U.S. Highway 20

Overview

Two industrial properties near a residential subdivision called Brookhurst drove the creation of this Superfund site in Natrona County, Wyoming. Starting in the 1960s, a gas compression plant run by Kinder Morgan Energy Partners and an oil service facility run by Dow Chemical/Dowell Schlumberger released wastewater, oils, and solvents into the ground. Residents reported poor water quality in 1986, and testing confirmed halogenated organic chemicals in their drinking water wells. The EPA responded by connecting residents to the Evansville municipal water supply by 1989.

EPA identified 15 contaminants of concern at the site. These include volatile organic compounds such as trichloroethene, tetrachloroethene, benzene, toluene, ethylbenzene, and xylene, along with chlorinated compounds like 1,1,1-trichloroethane, 1,1-dichloroethane, 1,1-dichloroethene, and trans-1,2-dichloroethene. Both soil and groundwater were affected across two cleanup areas: a source control zone and a groundwater zone.

Cleanup actions included excavating contaminated soils, running soil vapor extraction systems to pull solvents from the ground, and pumping and treating groundwater. The Kinder Morgan source area cleanup finished by 1996, with groundwater monitoring ending in 2010. The Dow/DSI source area cleanup wrapped up by 2001, with monitoring ending in 2015 after cleanup goals were met. The site is divided into three operable units. Operable Unit 1 covers groundwater and uses extraction wells, air stripping, and monitored natural attenuation. Operable Unit 2 addresses source control through institutional controls. Operable Unit 3 focuses on PFAS (per- and polyfluoroalkyl substances), though no cleanup decision has been issued for that unit yet.

Both properties now carry restrictive covenants that limit use to industrial activities, ban new groundwater wells until federal drinking water standards are met, and restrict soil excavation. Human exposure is currently under control across the entire site, and contaminated groundwater is stable with no unacceptable discharge to surface water. The site was deleted from the National Priorities List in two phases, with the Kinder Morgan property removed in August 2017 and the rest of the site removed in September 2019. The most recent five-year review was completed in July 2024 and confirms the remedy continues to protect human health and the environment.

Community members who want more information can contact the EPA Remedial Project Manager or the Wyoming Department of Environmental Quality project geologist. Site documents, including the 6th Five-Year Review, are available at the Natrona County Public Library Reference Desk in Casper, Wyoming, and at the EPA Superfund Records Center in Denver, Colorado. Copies can be requested by calling 303-312-7273 or 800-227-8917 ext. 312-7273.