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Record of Decision System (RODS)



City & State:  CHEYENNE  WY  82005
County:  LARAMIE
EPA ID:  WY5571924179
EPA Region:  08
NPL Status:  Currently on the Final NPL
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-96/126
ROD Date:  03/13/1996
Operable Unit(s):  03
Media:  groundwater
Contaminant:  Trichloroethylene
Abstract:  Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.

F.E. Warren Air Force Base (the base), occupies approximately 5,866 acres immediately adjacent to the west side of Cheyenne, Wyoming.

Historically, the base has served a number of military functions, including: cavalry outpost; quartermaster depot; and intercontinental ballistic missile operations base. Operations began at the U.S. Army outpost named Fort D.A. Russell in 1867. The name was changed to Fort F.E. Warren in 1930. The base was a major training facility during and after World War II. Fort F.E. Warren was transferred to the newly formed U.S. Air Force base in 1947 and was subsequently names F.E. Warren Air Force Base.

After World War II, the base underwent extensive renovation and the majority of the Army training facilities were torn down. Beginning in 1958, F.E. Warren Air Force Base became a Strategic Air Command Base.

The base is bordered by agricultural land and rural or suburban residential areas. The base contains 831 housing units and several unaccompanied personnel housing units, along with all of the services required by residents.

Operable Unit (OU) 3 consists of Landfill 3, Landfill 6, and Nob Hill. This Record of Decision (ROD) discusses the selected interim action for Nob Hill. Remedial Investigation (RI) activities conducted as part of OU 3 identified the off-base movement of a groundwater contaminant plume originating from the Landfill 3 area. The contaminant plume was determined to be migrating down-gradient toward the Nob Hill subdivision.

A search of available records indicated that Landfill 3 was a trench-and-fill operation from 1941 until 1947, and that hardfill was deposited at the site after 1947. Some burning probably occurred in Landfill 3 based on results obtained in 1992 that indicated the presence of ash, cinder, general debris, and construction material at the surface of Landfill 3. The general waste deposited at Landfill 3 includes waste from the base shops. A driver training area was located around the landfill area during World War II. Construction of Happy Jack Road in 1988-89 involved the area to the southwest of the landfill, but the landfill itself was not disturbed.

Leachate originating from the Landfill 3 area is the source of the groundwater contaminant plume that has reached the Nob Hill residential area. The Landfill 3 plume was identified as containing trichloroethylene (TCE).

No specific characterization has been performed for the Landfill 3 contents. Based on guidance on landfills, the source of contamination is considered to be the entire landfill area.

The Landfill 3 is a single area covering approximately 7 acres and is located near the southeastern boundary of the base, north of Happy Jack Road and northwest of the Nob Hill area. Workshop, domestic, and construction wastes were disposed of here. Burning probably occurred in the area as a means to reduce waste volumes.

Leaching of contaminants from a landfill into the groundwater and/or having landfill contents in contact with the groundwater are the primary release mechanism for landfill contaminant movement. Leachate originating from the landfill may occur as the result of rain water infiltration and reaction with landfill contents, or from the movement of liquid waste from the contact with the groundwater. Also, the contents of the landfill may be in direct contact with the groundwater. As the leachate is mixed and dispersed through groundwater transport, contaminants may undergo degradation and transformation reactions, producing additional groundwater contaminants. The movement of groundwater transports contaminants away from the landfill toward potential receptors such as the Nob Hill residents.
Remedy:  The selected remedy for Nob Hill involves including the Nob Hill residential area within the City of Cheyenne's water supply system. This remedy involves expanding Cheyenne's current water supply system by constructing a water supply line to the Nob Hill Area, permitting the residents of Nob Hill access to an alternate water supply.

This remedy for Nob Hill is considered final and supplants the current action of supplying the Nob Hill residents with bottled water. The remedy described above is specific to the Nob Hill portion of OU 3. Remedies selected for the remaining portions of OU 3 will be described under separate RODs for OU 3.
Text:  View full-text ROD [ 34K ]
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