Riverton Mill Site

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WYOMING UMTRA SITES

The Riverton and Spook former processing sites are two of 24 uranium mill processing sites designated by the Uranium Mill Tailings Radiation Control Act for remediation by the Department of Energy. During the 1960s, private firms processed most of the uranium ore mined in the United States for the Atomic Energy Commission, a predecessor of the Department of Energy. Congress passed the Act in 1978 in response to public concern regarding potential health hazards from long-term exposure to uranium mill tailings. It authorized the Department of Energy to stabilize, dispose of, and control uranium mill tailings and other contaminated material at 24 uranium mill processing sites and vicinity properties. For a general discussion of the UMTRA Program, see the overview presented in the New Mexico section of this report.

The cost estimate model used for this report provides costs for each of the UMTRA sites. All costs for waste management activities, program management, and relevant landlord activities attributable to the Department are provided for within the scope of the environmental restoration. There are no Uranium Mill Tailings Radiation Control Act sites with either current or planned nuclear material and facility stabilization activity needs. Funding for all sites is 100 percent nondefense.

RIVERTON, WYOMING (UMTRA SITE)

The Riverton mill site and tailings pile covered 88 hectares (218 acres) located four kilometers (2.5 miles) southwest of the center of Riverton on the north side of State Highway 789 in Fremont County, Wyoming. Before remedial action, the tailings pile occupied about 29 hectares (72 acres) at an average depth of 1.2 meters (4 feet). The site is located within the boundaries of the Wind River Indian Reservation, which is occupied by the Shoshone and Arapaho Tribes; however, the parcel of land upon which it sits is privately owned.

FACILITY MISSION

The mission of the mill site was to provide uranium for the United States Government. The source of contamination was the residual tailings that remained after the milling process extracted the uranium. In 1958, Susquehanna-Western, Inc., formerly known as Fremont Minerals, Inc., became the operational owner of the site. Solution Engineering Corporation of Alice, Texas, later acquired the mill and owned it until 1978 when Lome Drilling and Well Service, a Wyoming corporation, purchased most of the site. Western Nuclear, Inc. owned part of the mill area after Susquehanna-Western and operated a sulfuric acid plant at the site. In 1985, Chemical Marketing Services purchased the sulfuric acid plant, and this company operates it today. In 1987, the State of Wyoming acquired the tailings pile and mill site from Lome Drilling and Well Service and will participate in decisionmaking.

The Environmental Management program is responsible for cleaning up surface- and ground-water contamination at the UMTRA sites. The Uranium Mill Tailings Radiation Control Act designated the residual radioactive material found at this site for cleanup and stabilization. The Act directed the Environmental Protection Agency to promulgate standards (Code of Federal Regulations, Title 40, Part 192) and the Department of Energy to perform the cleanup. It also assigned the Nuclear Regulatory Commission to oversee and certify the cleanup, and license the completed disposal cell.

FUTURE USE

The site will be released for use consistent with existing land-use controls. Since the tailings were disposed of at an active Title II facility, the Department of Energy does not need to acquire the former mill site land. Ownership of the processing site will revert from the State of Wyoming to Industrial/Commercial use following completion of the UMTRA Surface Project. However, the Department of Energy must fulfill the requirements of the UMTRA ground-water restoration program and will maintain control of the property until all phases of the Riverton UMTRA Project are complete.

ENVIRONMENTAL RESTORATION

Surface remedial action has been completed and the source of contamination has been stabilized. However, residual milling-related contaminated ground water remains and will be addressed in the second phase of the UMTRA Project.

Surface Project

Remedial action at the Susquehanna-Western uranium mill tailings site began in May 1988 and was completed in September 1990. The Nuclear Regulatory Commission certified the processing site in January 1995. The cleanup involved relocating the tailings and contaminated materials from vicinity properties to the UMETCO facility located within the Gas Hills Uranium Mining District approximately 72 kilometers (45 miles) east of Riverton. The Gas Hills Uranium Mining District contains several active uranium mill sites licensed by the Nuclear Regulatory Commission. The tailings were consolidated and stabilized with the existing tailings at this Nuclear Regulatory Commission-licensed commercial disposal facility. UMETCO is responsible for all long-term surveillance and monitoring costs associated with the disposal cell.

After decontamination of the Susquehanna-Western mill tailings site, the disturbed areas at the site were backfilled with uncontaminated soil to a level compatible with the surrounding terrain, recontoured to promote surface drainage, and revegetated.

The Riverton remedial action program included cleanup of all offsite properties contaminated with tailings from the Riverton site. Contaminated materials from vicinity properties were also transferred to the UMETCO facility.

Ground-Water Compliance Project

The Department is developing a Programmatic Environmental Impact Statement pertaining to all 24 UMTRA sites. For a discussion of the Programmatic Environmental Impact Statement, see the UMTRA program narrative in the New Mexico section of this report. Site-specific National Environmental Policy Act documentation will be developed to propose an appropriate ground-water compliance strategy and reasonable alternatives for the Riverton site once the Programmatic Environmental Impact Statement is completed.

This report assumes a ground-water compliance strategy of natural flushing, based on data collected over the past decade and a site conceptual model. With this approach, contamination concentrations are expected to be reduced naturally to appropriate concentration limits within 100 years, as required by Environmental Protection Agency standards. If an alternate compliance strategy is selected, the Department will adjust the cost estimates accordingly. For all types of ground-water compliance strategies, once the Nuclear Regulatory Commission determines that the site is in compliance with Subpart B of the Environmental Protection Agency Standards and the site is certified, no additional long-term surveillance or monitoring will be conducted.

The total volume of contaminated ground water is estimated to be 870 million liters (230 million gallons). The contaminant plume extends offsite. The ground-water contaminants of potential concern are manganese, uranium, sulfate, vanadium, and nickel.

The following milestone dates have been established for planning purposes.

In January 1994, to obtain additional characterization information regarding contaminant distribution in the surficial, semiconfined, and confined aquifers, samples were collected from 15 monitoring wells that had been installed in 1993. Nine domestic wells located in the confined aquifer were sampled to complete an assessment of potential impacts to domestic water sources located near the site.

Other hydrologic data gathered during 1994 included ground-water and surface-water elevations. To collect nearly continuous data on ground-water levels, pressure transducers and data loggers were installed in nine monitoring wells in 1994. Ground-water level measurements were also made in 14 other wells. In addition, surface-water level measuring points were established near the Little Wind River and at the wetland east of the site. These points will be surveyed, and periodic readings will be made in the future.

Ground-water monitoring information obtained during 1994 confirmed the previously established concepts regarding the extent of contamination in the vicinity of the Riverton site. Environmental Protection Agency maximum concentration limits were only exceeded in surficial aquifer samples from beneath the southeastern edge of the former processing site and immediately downgradient (southeast) of the site. Samples from domestic wells located near the site confirmed that site-related contamination has not impacted the confined aquifer. Consequently, continued use of the ground water from the confined aquifer for domestic purposes is not expected to pose any risks to human health.

During the first ten years of remediation, verification monitoring will be performed to ensure that natural flushing is working according to predictions. The data collected during this phase will be provided to the Nuclear Regulatory Commission in a confirmation report. If the Nuclear Regulatory Commission accepts this report, the site will be turned over to the Grand Junction Projects Office's Long-Term Surveillance and Maintenance program. This program will conduct "compliance monitoring" for up to 90 years. When maximum concentration limits or background or alternate concentration limits have been achieved, a certification report will be prepared to close out all Department of Energy liability at this site.

Direct Program Management/Support

Program management supports management efforts for the National Environmental Policy Act process, site characterization and licensing, public information/participation, applicable state and federal regulator costs, quality assurance audits, program and management support for the technical assistance contractor, special studies, document control, technical assistance contractor site and technical management, cost and schedule controls, planning and preparation of the federal budget, and the Environmental Management Progress Tracking System.

FUNDING ESTIMATE

The following table presents estimated funding information for the Riverton site.