Area of Concern 25 - 1942 Gas Station and Vehicle Shops

Justification

The former Sunflower Army Ammunition Plant (SFAAP) is located near DeSoto, Kansas, in the northwest corner of Johnson County. It is approximately 30 miles southwest of Kansas City, Kansas, and 16 miles east of Lawrence, Kansas. The plant consisted of production facilities, administrative and storage facilities, powerhouses, landfills, lagoons, ditches, burning grounds, sumps, projectile ranges, and waste treatment facilities. The site is composed of 70 Solid Waste Management Units (SWMUs) where a release of hazardous waste was identified and 27 Areas of Concern (AOCs) where hazardous waste or constituents have been identified but are not linked to a specific solid waste management practice.

AOC 25, the 1942 Gas Station and Vehicle Shops, is in the north-central portion of the former SFAAP. It encompasses approximately five acres and once consisted of a Gasoline Station (Building 248), Body Repair Shop (Building 249), Gasoline Storage Tank (Tank 337112), Gasoline Storage Tanks (Tanks 337517-1 through 4), Heavy Equipment Storage (Building 509-1), Tire Repair Shop (Building 511), Car Wash Houses (Buildings 513-1 and 513-2), and Paint Shop (Building 514). These facilities were built in 1942 and dismantled in 1948. The tanks at AOC 25 were above ground. All tanks and building structures have been removed, with only cement foundations remaining. 

During the AOC 25, AOC 27, SWMU 68 Confirmatory Study from May to June 2021, 26 surface soil samples, 53 subsurface soil samples and 7 groundwater samples were collected and analyzed for Resource Conservation and Recovery Act (RCRA) metals, Semi-Volatile Organic Compounds-Polycyclic Aromatic Hydrocarbons (SVOCs-PAHs), Volatile Organic Compounds (VOCs,) and Total Petroleum Hydrocarbons-Low Range Hydrocarbons/Medium Range Hydrocarbons/High Range Hydrocarbons (TPH-LRH/MRH/HRH) (AECOM, 2022). TPH-MRH exceeded residential Target Media Cleanup Levels (TMCLs) in two soil samples. Chromium exceeded applicable residential TMCLs (but not non-residential TMCLs) at a soil sample collected at 15.0-17.0 feet below ground surface (bgs). All soil SVOC-PAH and VOC concentrations were below their respective residential and non-residential TMCLs (AECOM, 2022).

There are no permanent monitoring wells at AOC 25. Out of seven groundwater samples that could be collected during the 2021 study, three sample locations indicated TPH concentrations that exceeded residential and/or non-residential TMCLs. 

Pre-design soil and groundwater investigations (PDI) were performed August 2022. Soil samples were collected from just above the saturated zone at A25-AMSB025A to determine if prior detections of TPH in the saturated zone was representative of nearby soil concentrations. The final sample depth was from 13-14.8 ft bgs. It was determined that PDI sample results at this location were below TMCLs.  Eight temporary groundwater monitoring wells were installed as part of the August 2022 PDI. All wells were pumped dry and had less than one foot of water after 72 hours. This indicated that the groundwater yield does not meet KDHE’s determination of potable groundwater (100 gallons/day). 

Excavation and disposal of petroleum-impacted materials was selected as an interim corrective measure (ICM) for AOC 25. In August 2022, soil at areas with prior TPH detections was excavated to bedrock (6-9 feet bgs) and until sidewalls and floor samples no longer indicated dark staining or petroleum odors. Post-excavation sampling confirmed the completion of contaminated soil removal. Total soil removal was roughly 400 cubic yards. Groundwater was not encountered during any part of the excavation.

The Army conducted a streamlined health risk evaluation by comparing RCRA Facility Investigation (RFI) data to the approved TMCL. KDHE believes that proper employment of the KDHE (2015) Risk-based Standards for Kansas (RSK) Manual values result in risk-based remediation that is consistent with federally promulgated standards, including the Safe Drinking Water Act, 42 U.S.C. §300f – 300j-26, and is protective of human health as required by Resource Conservation and Recovery Act, 42 U.S.C. §6901 et seq., including the Hazardous and Solid Waste Amendments (HSWA) and 40 CFR Part 264.101. KDHE Tier 2 risk-based cleanup goals represent concentrations at which the contaminants pose an acceptable human health risk to receptors, including sensitive groups (e.g., children or the elderly), over a lifetime.

Cleanup goals were developed for two general categories of receptors, residents and non-residents, according to the appropriate land-use designation, exposure frequency, and exposure duration. According to the Conceptual Land Use Plan, AOC 25 falls within the area designated as a business center (Johnson County, 1998).

The KDHE has determined that interim actions completed for soil were the appropriate remedy for AOC 25. Contaminated surface and subsurface soils were excavated, and post-excavation sampling confirmed removal of all COCs. The prior excavation of surface and subsurface soil COCs is appropriate for the site to be protective of human health and the environment. The proposed decision is based upon KDHE’s review of all available historical documentation.