NPL Partial Site Deletion Narrative Mystery Bridge Rd/U.S. Highway 20 Evansville, Wyoming On August 29, 2017, the EPA deleted the former Kinder Morgan Inc. (KMI) Property of the Mystery Bridge Road/U.S. Highway 20 site located in Natrona County, Wyoming from the National Priorities List (NPL). This partial deletion pertains to the entire former KMI Property including the ground water [operable unit 1 (OU1)] and the soil/former source area (OU2). The remaining areas of OU1 and OU2 containing the volatile halogenated organic chemicals (VHOs) source soils and plume will remain on the NPL. The Mystery Bridge Road/U.S. Highway 20 site (EPA ID WYD981546005) is located northeast of Casper, Wyoming and one mile east of Evansville. The area is bordered on the north by the North Platte River, the south by U.S. Highway 20, the east by Mystery Bridge Road, and the west by the Sinclair Refinery. Residential properties comprise the northern two thirds of the site. The southern third of the site is made up of the KMI Property and the Dow Chemical Company and Dowell-Schlumberger, Inc. (DOW/DSI) facilities. The former KMI Property is in continued operation as a mid-stream gas processing facility. Residential complaints of poor water and air quality resulted in site investigations that were completed in 1986 and 1987. These investigations identified a benzene, toluene, ethylbenzene, and xylene (BTEX) plume originating from the former KMI Property and a VHOs plume originating from the DOW/DSI property. The site was listed on the NPL on August 30, 1990. The former KMI Property was the location of a natural gas fractionation, compression, cleaning, odorizing, and transmission plant that was operational beginning in 1965. During the plant start-up, 5,000-10,000 gallons of adsorption oil were injected into the subsurface when an underground pipe burst. Initially, spent material was collected in an earthen flare pit. Absorption oil, emulsions, anti-foulants, anti-corrosive agents, crude oil condensate, and liquids accumulated in the flare stack. Lubrication oils and blowdown materials from plant equipment along with potassium hydroxide treated waste were possibly collected in the flare pit. The initial absorption oil spill, leaks from the earthen flare pit, and a catchment area that collected surface water run-off are believed to have contributed to the BTEX contamination in soil and ground water. The site was divided into two media-specific OUs. OU1 includes the ground water at the site and OU2 refers to the source areas in the soil at the site. The OU1 response actions began in November 1989. A ground water pump and treat system was paired with a soil vapor extraction system to remove BTEX contaminants. This remediation system was in operation through August 1996. In 2010, it was confirmed that the remedial action objectives for OU1 were achieved. As part of the restrictive covenants at the site, institutional controls are in place to restrict ground water use except for sampling purposes at the former KMI Property. The EPA, with the concurrence of the state of Wyoming, through WDEQ, has determined that all appropriate response actions under CERCLA, other than maintenance of institutional controls and five-year reviews, have been completed at the former KMI Property. Therefore, the EPA is deleting the former KMI Property of the Mystery Bridge Road/U.S. Highway 20 site from the NPL. ------- |