Record of Decision System (RODS)
HILL AIR FORCE BASE
|Site Name:||HILL AIR FORCE BASE|
|City & State:||HILL AFB UT 84056|
|NPL Status:||Currently on the Final NPL|
|ROD Type:||Record of Decision|
|Media:||Groundwater, Liquid Waste, Sediment, Soil, Surface Water|
|Contaminant:||Base Neutral Acids, Metals, Nitroaromatics, PAH, PCBs, Pesticides, Petroleum Hydrocarbon, VOC|
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.
The U.S. Department of Energy's (DOE) Weldon Spring site consists of two distinct geographical areas: 1) the quarry area, and 2) the chemical plant area. Both areas are located in St. Charles County, Missouri. Much of the land surrounding the quarry consists of state-owned conservation areas containing second growth forest. Non-forested areas are largely used for crop production and pasture or are old-field habitat. Aquatic habitats in the vicinity of the site include the Missouri River, Little Femme Osage Creek, Femme Osage Slough and numerous small unnamed creeks, drainages and ponds throughout the Weldon Conservation Area.
The quarry was used by the Army for disposal of chemically contaminated materials in the 1940s and was later used for the disposal of radioactively contaminated material by the Atomic Energy Commission in the 1960s.
Unconsolidated surficial materials are present in the area of the Weldon Spring quarry. The uppermost bedrock unit in the vicinity of the quarry is the Kimmswick Limestone. The contact between the Kimmswick Limestone and the underlying Decorah Group, which may provide primary pathways for contamination migration from the quarry area, is in contact with fine-grained soils, silty clay, and organic silt and clay north of Femme Osage Slough.
A Record of Decision (ROD) was completed in 1990 for the Quarry Bulk Waste Operable Unit (OU). A ROD was completed in 1998 for the Quarry Residuals OU.
The selected remedy for operable unit 1 (OU1) is part of a Basewide effort to clean up contaminated soil, surface water, and groundwater. At Hill Air Force Base (HAFB), there are nine OUs, all of which are in different stages of investigation or cleanup. OU1 is located along the eastern Base property and is comprised of the following individual on-Base areas of potential concern: Landfills 3 and 4, Fire Training Areas 1 and 2, Chemical Disposal Pits 1 and 2, the Waste Phenol/Oil Pit, the Waste Oil Storage Tank Site, and the contaminated groundwater emanating from the individual on-Base areas of potential concern. Specific off-Base areas have been impacted by on-Base groundwater migrating off-Base. The selected remedy addresses on-Base (Source Area) waste disposal areas and associated contaminated environmental media including air, soil, and groundwater. The area containing contaminated groundwater emanating from the Source Areas is identified as the Non-Source Area. The selected remedy includes the following components: dewatering of the Source Area with extraction trenches; light non-aqueous phase liquid (LNAPL) recovery from the extraction trenches followed by proper disposal of the LNAPL; Groundwater treatment at the Operable Unit 2 Air Stripper Treatment Plant (ASTP) or the HAFB Industrial Wastewater Plant (IWTP); Repair as well as operation and maintenance of the landfill caps and passive gas vent system. Non-Source Area: Upgrade the spring collection system and treatment of the collected surface water at the Operable Unit 2 ASTP, a new remote treatment plant, or the IWTP; Excavate arsenic-contaminated spring sediments. The sediments will be properly disposed of offsite at an appropriate disposal facility; Monitored natural attenuation of contaminants in the groundwater of the Non-Source Area. This component of the selected remedy depends on intercepting contamination in the Source Area. Other remedies will be implemented if concentrations are notattenuating in a reasonable time frame. Both Source and Non-Source Areas: Environmental monitoring; Institutional and engineering controls designed to prevent potential unacceptable risks to human health and the environment; Designation of a Corrective Action Management Unit (CAMU) to facilitate remedial actions. The CAMU will be designed as the contiguous area of contamination. The selected remedy for OU1 addresses the principal threats posed by the site by minimizing or preventing direct contact with contaminated soils and landfill contents, preventing ingestion of and direct contact with contaminated groundwater, surface water, and sediments as well as preventing further off-site transport of contaminants.
Estimated Capital Costs: $2,959,100
Estimated Annual O&M Costs: $416,520
Estimated Present Worth Costs: $8,214,700
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