Salmon Site

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The Salmon Site is administered by the Nevada Operations Office. A more thorough description of the environmental activities managed by the Nevada Operations Office can be found in the Nevada Offsite Program narrative. The Salmon Site is located 34 kilometers (21 miles) southwest of Hattiesburg, Mississippi, and was used for the Salmon and Sterling tests, as well as for nonnuclear gas detonations in the Miracle Play program.

FACILITY MISSION

The Department used the site for two nuclear detonations, Salmon and Sterling, to evaluate the seismic response of salt deposits to nuclear explosives. Salmon Site was also the location for two nonnuclear gas detonations used for seismic decoupling studies in the Miracle Play Program. The Department conducted the Salmon test at a depth of 828 meters (2,717 feet) in the Tatum Salt Dome in October 1964. It detonated the Sterling test in the Salmon cavity in December 1966. The Miracle Play program consisted of two methane-oxygen explosions conducted in the Salmon/Sterling cavity and included Diode Tube in February 1969 and Humid Water in April 1970. Following testing, a 1972 cleanup operation provided for soil excavation and recovery and decommissioning of the facilities.

Contamination consists of low-level radioactive contamination of the salt around the shot cavity; contamination of a deep zone in the Cook Mountain Limestone, in which contaminated water from the drill-back operation for the first test was injected; surface contamination from the drill-back operations; and near-surface hazardous waste contamination from the closed mud pits and burial of debris in near-surface burial pits.

Migration of the contamination from the shot cavity is unlikely because the only possible pathway is through an improperly abandoned drill hole. Ground water is the most likely transport medium for the contamination in the Cook Mountain Limestone. However, because of the very slow ground-water velocity in the formation, calculations suggest that by the time the material has migrated offsite, it will have decayed to the point where it is no longer dangerous. The possible exposure to humans or the environment from this material is unlikely.

The near-surface contamination consists of tritium, heavy metals, and diesel fuel in abandoned mud pits, disposal pits, and burn pits. The near-surface ground water is the most likely transport mechanism for this contamination. However, monitoring has shown none of the contamination has migrated offsite. Surface contamination is due to disposal of materials that were not considered hazardous waste at the time of disposal and insufficient cleanup of some of the mud pits.

FUTURE USE

Characterization of the site is currently under way; therefore, no definitive plan for future use has been developed. The Department is involved in discussions with the State of Mississippi and Congress concerning transfer of the land back to the State after cleanup is complete. However, this report assumes the surface of the site will be cleaned to a level that permits Recreational use. The future use designation for the subsurface of the site will remain Controlled Access. The Department of Energy will maintain institutional control of the subsurface and retain all mineral rights; any disturbance of the subsurface (e.g., well drilling, mining, excavation) will require Department approval. The final future use will be negotiated with the State of Mississippi. The Department will maintain the entire site as a mix of Industrial, Open Space, and Controlled Access use until remedial action is complete.

ENVIRONMENTAL RESTORATION

Following the Salmon test, water contaminated by radioactivity was injected into the Cook Mountain Limestone for disposal. In addition, radioactively contaminated soil and water were injected into the shot cavity for disposal during site cleanup. This should not impact the surface of the site, because the implacement wells, drill-back wells, and injection wells were all sealed with concrete and bentonite when the site was decommissioned. Work on the site is performed under an Agreement-in-Principle between the Department and the State of Mississippi.

The cleanup strategy includes characterizing ground-water flow, defining the area of contamination, assessing risk, and modeling contaminant movement away from the shot cavities. The focus will be on tritium, since it is the most mobile of the potential radiological contaminants. Attenuation characteristics provide for little migration of other radionuclides and will indicate whether other radionuclides should be included in the source evaluation. Maximum use will be made of existing data, including monitoring data collected from the Long-Term Hydrologic Monitoring Program well networks.

This report assumes subsurface waste in and around the shot cavities will not be removed, and long-term monitoring will continue. The surface sites and facilities will be cleaned up and the waste will either be left in place, treated and disposed of onsite, or transported offsite. Based on discussions with the State, if it can be demonstrated that the hazardous contamination does not migrate, the installation of monitoring wells around the contaminated area will be sufficient for the surface and near-surface sites.

ASSESSMENT

The Department conducted an extensive sampling program in 1977, with more than 170 exploratory borings, extensive soil sampling and analysis, and ground-water sampling. The result of the study showed that tritium contamination was left in the mud pits during site cleanup in 1972. This has resulted in a plume of tritium extending northwest from the surface-ground-zero mud pits. The tritium concentration in this plume is mostly below the 20,000 picocuries per liter Safe Drinking Water standard; however, a few of the samples were above that level. The plume did not reach Half Moon Creek at the time of the testing.

The site will conduct a Remedial Investigation/Feasibility Study according to the requirements of the Resource Conservation and Recovery Act and the State of Mississippi. The study will address the tritium plume in the shallow aquifer, potential leakage of contaminants from the shot cavity, characterization of the mud and disposal pits and analysis of risk pollutant rate, and assessment of remediation strategies. To support the study, the site will perform sampling and analysis activities, risk analysis, and methodology screening activities.

Assessment activities began in 1992 with National Environmental Policy Act surveys and surface geophysical surveys, and continued in 1993 with biota, soil, and water sampling, more geophysical surveys, cone penetrometer testing, and test pit excavation.

As the Department further defines the extent and magnitude of contamination, it will take appropriate remedial action as required by the State. Any requirements for site cleanup or long-term monitoring will be part of this activity.

Major Environmental Restoration Activity Milestones

TASK	COMPLETION DATE Fiscal Year
Installation of Additional Monitoring Wells	1997
Surface Remedial Action	1999
Assessment	2001
Long-Term Hydrologic Monitoring Program	2025

REMEDIAL ACTION

Surface contamination is the result of drill-back operations at the surface-ground-zero area and the disposal of site waste in surface and near-surface disposal pits. Contamination consists of soil contaminated with metals and petroleum hydrocarbons and drilling mud contaminated with tritium.

After the first tests, contaminated water was injected into a deep brine aquifer for disposal. During the surface cleanup, contaminated soil and water were placed in the shot cavity and sealed in 1972. The waste in the shot cavity and the brine aquifer will remain in place. The tritium-contaminated mud pits at surface-ground-zero may be excavated and shipped to a disposal facility. The metals-and petroleum-contaminated soils in the REECo Disposal Pits will remain in place unless it is proven contaminant migration is occurring.

This estimate assumes remediation includes removal of the buried mud pits at surface ground zero and installation of monitoring wells around the contaminated surface soils associated with disposal activities at the REECo Pits on the Salmon site. It further assumes remediation activities will begin in FY 1996 and be completed in FY 1999. The only approvals necessary are those from the Mississippi Department of Environmental Quality regarding the investigation approach, remedial action technical strategy, and final remediation goals.

This baseline report estimates the total volume of waste requiring treatment and/or disposal consists of 15,000 cubic meters (19,650 cubic yards) of stabilized tritiated drilling mud (low-level waste) that will be transferred to the Nevada Test Site.

COMPARISON WITH PREVIOUS ESTIMATE

Environmental Management costs at the Salmon site are limited to Environmental Restoration program assessment, remediation, and surveillance and maintenance costs. The 1996 life-cycle cost estimate is $7.7 million, an increase of approximately $4 million over the 1995 estimate. This increase is due to increased remediation costs in response to the State of Mississippi requirement for additional monitoring wells. The application of a three percent annual escalation factor and the adjustment of pre-FY 1996 costs to reflect actual costs through FY 1995 also contributed to the increase.