Region 8

Mystery Bridge Rd / U.S. Highway 20

site location map Site Type: Final NPL
City: Evansville
County: Natrona
Street Address: U.S. Hwy 20, 28 and Mystery Bridge Rd.
ZIP Code: 82636
EPA ID: WYD981546005
SSID: 0883
Site Aliases: Brookhurst Subdivision, Evansville
Congressional District: At Large

What's New?

Updated January 2014

A five-year review of the remedy at the Mystery Bridge site will be conducted in 2014 by EPA in coordination with the Wyoming Department of Environmental Quality (WDEQ). The five-year review process will include a request for comments from the local community as well as community interviews. The five-year review report will be signed no later than September 30, 2014.

The majority of the cleanup work needed at this site has been completed. EPA is working with WDEQ to determine if any additional work needs to be conducted before deleting all or a portion of the site from the National Priorities List. Any deletion proposed will include the opportunity for public comments to be considered prior to deletion.

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Site Description

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. 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 site boundary, Operable Units and Institutional Controls

The two responsible parties are Kinder Morgan Energy Partners, L.P. (KMI), which owned and operated 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 previously emanated from the two facilities and flowed towards the Brookhurst subdivision and the North Platte River. The KMI facility was sold in 2012 and is now owned and operated by Tallgrass Energy Partners, LP.

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Site Risk

Two separate areas of soil contamination and groundwater plumes were identified related to each of the industrial facilities. All the soil contamination has been remediated. 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). The extent of this plume has been greatly reduced and cleanup standards have been met in the majority of the monitoring wells.

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

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Cleanup Progress

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.

KMI facility during a 2009 site visit

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 Administrative Orders on Consent (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

Isoconcentration map of PCE and benzene in January 2010

On September 30, 2010, EPA signed a record of decision (ROD) to document the work completed and to address the remaining environmental contamination at the Mystery Bridge Road/US Highway 20 Superfund Site (Mystery Bridge), OU2 (Source Control). The Wyoming Department of Environmental Quality (WDEQ) concurred with this ROD. This remaining work involved adding institutional controls (ICs) to the two industrial properties.

The ICs required by the RODs for OU1 (groundwater) and OU2 have been implemented. For further information see Land Use Controls section below.

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Community Involvement

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

There will be an opportunity for public comment and community interviews will be conducted during the five-year review in 2014. Any deletion or partial deletion from the National Priorities List will include the opportunity for public comment as well.

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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 former 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.

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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 ICs required by the RODs for OU1 (groundwater) and OU2 have been implemented.

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 implemented the necessary ICs on their respective properties. On the KMI property, the ICs are implemented through restrictive covenants within a deed. On the DOW/DSI property, the ICs are implemented through a notice of use restrictions and restrictive covenant.

Map of site boundary, Operable Units and Institutional Controls

KMI and DOW/DSI Institutional Controls

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Five-Year Reviews

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 fourth five-year review of the remedy at the Mystery Bridge site will be conducted in 2014 by EPA in coordination with the Wyoming Department of Environmental Quality (WDEQ). The five-year review report will be signed no later than September 30, 2014.

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Site Documents

You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.

Update to the Five-Year Review, January 2011

Record of Decision for OU2 (Industrial Properties), September 30, 2010

Technical Memorandum: Revised Summary of Vapor Intrusion Modeling for the Kinder Morgan Portion of the Mystery Bridge Superfund Site, August 5, 2010

Letter re: Dow/Dowell Brookhurst/Mystery Bridge Site, Technical Memorandum Evaluating Vapor Intrusion (Revision 2), August 3, 2010

Technical Memorandum and Report: Summary of Remediation Actions Related to OU2 at the Casper Compressor Station, June 22, 2010

Third Five-Year Review Report (PDF), September 30, 2009(27 pp, 4.8 MB)

Record of Decision for OU1 (Groundwater) (PDF), September 24, 1990(36 pp, 92 K)

Administrative Order on Consent for Removal Action – KN Energy, December 13, 1987

Action Memorandum (Removal Request for the Brookhurst Subdivision, Natrona County, WY), January 7, 1987

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Frances Costanzi
Project Manager
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)

Site Information Repositories:

Natrona County Public Library
Reference Desk
307 East 2nd Street
Casper, WY 82601-2593

EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
To request copies of administrative record documents call:
800-227-8917 ext. 312-7273 (toll free Region 8 only)


Jane Francis
Wyoming Department of Environmental Quality
Water Quality Division
122 West 25th Street
Herschler Building, 4-W
Cheyenne, WY 82002

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Photo/Video Gallery

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The following links exit the site Exit

Wyoming Department of Environmental Quality, Water Quality Division

Natrona County Public Library

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