Mystery Bridge Rd/U.S. Highway 20
National Priorities List (NPL) History
Construction Completion Date
Site Type: Final NPL
Street Address: U.S. Hwy 20, 28 and Mystery Bridge Rd.
ZIP Code: 82636
EPA ID: WYD981546005
Site Aliases: Brookhurst Subdivision, Evansville
Congressional District: At Large
Updated August 2010
EPA and WDEQ Announce Proposed Plan
The public is invited to review and comment on a proposed plan to address the remaining environmental contamination at the Mystery Bridge Road/US Highway 20 Superfund Site (Mystery Bridge), Operable Unit 2 (Source Control).
The public comment period runs from August 23 through September 21, 2010. Feel free to submit your comments in writing via mail or email by close of business September 21, 2010 to Frances Costanzi. Or attend our public meeting to comment on the proposed plan in person:
Thursday, September 2, 2010
Evansville Town Hall
235 Curtis Street
The majority of the cleanup work needed at this site has been completed. EPA’s preferred remedial alternative for Operable Unit 2 (OU2) addresses the remaining work needed to ensure protection of human health and the environment. The proposed remaining work necessary involves adding institutional controls to the two industrial properties.
Although the previous work on OU2 was conducted under Administrative Orders on Consent (AOCs) and overseen by EPA, a Record of Decision (ROD) was not written for OU2. EPA anticipates finalizing a ROD after this public comment period closes. The ROD will document the work that has been completed as well as identify the selected actions needed for future protectiveness.
See Cleanup nears final stage in the Casper Star-Tribune, September 2, 2010.
The Mystery Bridge site is located in Natrona County, northeast of Casper, Wyoming. A residential area comprises the majority of the site, and an industrial area where hazardous substances were used lies along the southern and western site boundary. The site is bordered to the north by the North Platte River and on the west by the former Little America Refining Company (LARCO) refinery, which is currently operated by Sinclair Refining under a RCRA permit (see WDEQ fact sheets in the Links section below). Mystery Bridge Road and the Brookhurst subdivision extend along much of the northern and eastern perimeters of the site. The site was listed on the National Priorities List (NPL) in 1990 after several removal actions and significant public input.
Map of the Mystery Bridge Rd/U.S. Highway 20 Superfund Site boundaries (PDF, 1 pg, 313K, about PDF )
The two responsible parties are Kinder Morgan Energy Partners, L.P. (KMI), which own and operate a gas compression and transmission plant, and Dow Chemical Company/Dowell Schlumberger, Inc. (DOW/DSI), which operated an oil field services and truck washing facility, now closed. Two separate groundwater plumes emanated from the two facilities and flowed towards the Brookhurst subdivision and the North Platte River.
Two separate groundwater plumes were identified. One groundwater plume, which originated from the KMI property, contained benzene, ethylbenzene, toluene and xylene (BETX). The KMI plume has now met cleanup standards. The other groundwater plume originated from the DOW/DSI property and extended underneath part of the subdivision. The DOW/DSI plume is primarily composed of volatile halogenated organic compounds (VHOs) including perchloroethylene (PCE).
|Media Affected||Contaminants||Source of Contamination|
|groundwater, surface water, soil, liquid waste, sold waste, air||benzene, ethylbenzene, toluene, xylene (BETX), volatile halogenated organics (VHOs)||unlined waste pond at a natural gas processing facility, toluene storage area, a truck wash drain, abandoned sump at oil field service company site|
In response to citizen complaints, studies were started in 1986, which found VHOs in area drinking-water wells. Many homes in the Brookhurst subdivision were affected. The site was then proposed for the NPL in June 1988.
EPA initial response actions included connecting residents to the Evansville municipal water system. This work was completed in January 1989 under a removal action. The site was placed on the NPL in August 1990.
The site was divided into two operable units. Operable Unit 1 (OU1) includes the groundwater contaminant plumes and OU2 includes the contaminated soils on the industrial properties, which represent a source for the groundwater contamination.
A ROD for OU1 was signed in September 1990, and a consent decree between EPA and KMI and DOW/DSI to conduct the groundwater remedy selected in that ROD was signed October 1991. The groundwater cleanup involved extracting and treating the contaminated groundwater.
Although a ROD was not written for OU2, the OU2 work was conducted under two AOCs, one with KMI and one with DOW/DSI. These AOCs concerned the work involved in reducing sources of contamination in the soil by excavating and removing these soils and by operating soil vapor extraction (SVE) systems. The source control work was completed on the KMI property in 1998 and on the DOW/DSI property in 1993.
Groundwater extraction and treatment systems were shut down for the KMI property in 1996 and for the DOW/DSI property in 2001.
Groundwater monitoring has been conducted on both properties since that time.
Isoconcentration map of PCE and benzene in January 1993 (PDF, 1 pg, 393K, about PDF )
Isoconcentration map of PCE and benzene in January 2010 (PDF, 1 pg, 335K, about PDF )
Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, on-going, meaningful community involvement. The goals of the Superfund community involvement program are to:
- Keep communities affected by sites informed throughout the cleanup process
- Provide opportunities for communities to comment and offer their input about site cleanup plans
- Facilitate the resolution of community issues tied to a site
A public meeting is scheduled for Thursday, September 2, 2010 to discuss the proposed plan. The meeting is scheduled from 6:30–8:30 p.m. and will be held at the Evansville Town Hall at 235 Curtis Street in Evansville, Wyoming.
EPA places a high priority on land reuse as part of its Superfund response program mission. The Agency tries to select cleanup options that encourage and support future use of a site. We use two fundamental methods to facilitate reuse of Superfund sites:
- Exploring future uses before the cleanup remedy is implemented, an approach that gives the Agency the best chance of designing cleanup remedies to support the likely future use of a site
- Working with landowners and communities to remove barriers not considered necessary for the protection of human health or the environment at those sites where remedies are already in place
One option for reuse is the siting of clean and renewable energy projects on contaminated (or formerly contaminated) lands. As part of this effort, EPA is evaluating the potential for energy projects on these properties and working with landowners and communities to identify ways to remove barriers to such projects.
At the Mystery Bridge site, the KMI property remains in use as a gas compression and transmission plant. It is anticipated that the land use at the DOW/DSI property will remain industrial, although it currently has no active operations on-going. It is anticipated that the Brookhurst subdivision will remain a residential area.
Land Use Controls and Other Institutional Controls
Land use controls are the most common type of institutional control (IC). ICs are administrative or legal controls that help reduce the likelihood for human exposure to contamination. ICs can also help protect the integrity of the remedy. Examples of ICs are:
- Zoning ordinances
- Environmental covenants
- Deed notices
- Well-drilling restrictions
- Building permits
- Informational advisories
The proposed plan currently available for public comment for the Mystery Bridge site describes the ICs that are currently being proposed for the KMI and DOW/DSI properties. Because soil cleanup was not performed to levels appropriate for residential use, ICs are necessary to provide information and controls for future protectiveness.
The objectives of the ICs are to:
- Restrict the use of the KMI and DOW/DSI properties to industrial uses
- Restrict the use of groundwater under the KMI and DOW/DSI properties until drinking water standards are met
- Control handling of excavated soils on the KMI and DOW/DSI properties
KMI and DOW/DSI have agreed to implement necessary ICs on their respective properties, pending the results of this public comment period. On the KMI property, the ICs are proposed to be implemented through restrictive covenants within a deed. On the DOW/DSI property, the ICs are proposed to be implemented through a notice of use restrictions and restrictive covenant.
EPA or the lead agency conducts five-year reviews following the start of a Superfund cleanup when contamination is left on the site. These reviews are repeated every five years. We use these reviews to determine:
- How the remedy is working
- If the remedy remains protective of human health and the environment
In September 2009, EPA conducted a five-year review of the remedial actions performed under the Superfund program for the Mystery Bridge site. This was the third five-year review for the site.
The review confirmed that the remedy continues to be protective of human health and the environment. The next five-year review will be completed in 2014.
You will need Adobe Acrobat Reader to view some of the files on this page. See EPA's PDF page to learn more.
Best way to open a very large file: right-click and save it to a folder.
Update to the Five-Year Review, January 2011 (PDF, 2 pp, 35K)
Proposed Plan, August 2010 (PDF, 8 pp, 575K)
Summary of Institutional Controls for Industrial Properties, Mystery Bridge Superfund Site, August 18, 2010 (PDF, 2 pp, 61K)
Technical Memorandum: Revised Summary of Vapor Intrusion Modeling for the Kinder Morgan Portion of the Mystery Bridge Superfund Site, August 5, 2010 (PDF, 111 pp, 6.4MB )
Letter re: Dow/Dowell Brookhurst/Mystery Bridge Site, Technical Memorandum Evaluating Vapor Intrusion (Revision 2), August 3, 2010 (PDF, 197 pp, 8MB )
Technical Memorandum and Report: Summary of Remediation Actions Related to OU2 at the Casper Compressor Station, June 22, 2010 (PDF, 294 pp, 13.4MB )
Third Five-Year Review Report, September 30, 2009 (PDF, 27 pp, 4.8MB )
Record of Decision for OU1 (Groundwater), September 24, 1990 (PDF, 36 pp, 92K)
Administrative Order on Consent for Removal Action – KN Energy, December 13, 1987 (PDF, 26 pp, 850K)
Action Memorandum (Removal Request for the Brookhurst Subdivision, Natrona County, WY), January 7, 1987 (PDF, 49 pp, 2MB)
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (8EPR-SR)
Denver, CO 80202-1129
800-227-8917 ext. 312-6571 (toll free Region 8 only)
Community Involvement Coordinator
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (8OC)
Denver, CO 80202-1129
800-227-8917 ext. 6633 (toll free Region 8 only)
Wyoming Department of Environmental Quality
Water Quality Division
122 West 25th Street
Herschler Building, 4-W
Cheyenne, WY 82002
View Documents at:
Natrona County Public Library
307 East 2nd Street
Casper, WY 82601-2593
EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
800-227-8917 ext. 312-6473 (toll free Region 8 only)