SWMU 69 - Disposal Area Southeast of AOC 22 Old Reclamation Area

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.

SWMU 69, Disposal Area Southeast of AOC 22 Old Reclamation Area, is located in the northeastern portion of the former SFAAP and consists of approximately 2.75 acres. No former use was identified for SWMU 69 and there is no historical record of dumping in the area. However, due to a small pile of railroad ties, the area was originally identified in 2012 during a site inspection by the Army. During the inspection, multiple animal burrows exposed significant amounts of ACM, empty drums, and other assorted debris associated with the SFAAP operation. Two separate disposal areas (North Waste Disposal Area and South Waste Disposal Area) with debris were visually delineated in 2013 through an additional inspection by the Army.

RFI field activities were conducted during 2017 and included exploratory trenching, soil sample collection, and groundwater sample collection. To delineate the vertical and horizontal extent of suspected ACM, 24 exploratory trenches were excavated. Fifteen trenches were excavated in the North Waste Disposal Area, while nine were excavated in the South Waste Disposal Area (Berger and Burns & McDonnell, 2019). Twenty-five soil samples were collected from the North Waste Disposal Area, while 15 soil samples were collected from the South Waste Disposal Area. Samples were collected from the side walls and bottoms of the trenches. 

Soil samples obtained from the North and South Disposal Areas were analyzed for Volatile Organic Compounds (VOCs), Semi-Volatile Organic Compounds (SVOCs), explosives, metals and total petroleum hydrocarbons (TPHs). Exceedances of the residential TMCLs for arsenic, chromium, and lead were detected in the North Waste Disposal Area. In the South Waste Disposal Area, one sample exceeded the residential TMCL for mercury (Berger and Burns & McDonnell, 2019). 

Nine samples of suspected ACM (debris, transite, and TSI) were collected from both disposal areas during RFI trenching activities. Samples comprised of greater than one percent asbestos are considered ACM. All nine samples detected the presence of chrysotile fibers ranging from three percent up to 85 percent suggesting SWMU 69 was previously utilized as a disposal area for building material containing ACM (Berger and Burns & McDonnell, 2019). 

Two monitoring wells were installed downgradient of the suspected contaminated areas in October 2017. Groundwater samples (including one duplicate) were collected from both newly installed wells and one existing upgradient well. These samples were analyzed for the same constituents as the soil samples, with the addition of herbicides and pesticides. None of the groundwater sample results exceeded associated residential TMCLs (Berger and Burns & McDonnell, 2019). 

Pre-design investigation (PDI) sampling was conducted in September 2019 by CAPE Environmental Management Inc (CAPE). Fifteen soil samples and two field duplicates were collected and analyzed for arsenic, chromium (including hexavalent and trivalent), lead, and mercury. The results indicated that all but four of the sample locations exceeded the residential TMCLs (CAPE, 2020). 

Following the results of the PDI sampling, Corrective Measures Implementation (CMI) activities were conducted at SWMU 69 from September 16, 2020 through April 21, 2021 in accordance with the SWMU 69 CMI Work Plan (CAPE, 2020). A hydraulic excavator was used to excavate to a depth of approximately 5 feet below ground surface (bgs) to remove asbestos, arsenic, chromium, lead, and mercury in soil (CAPE, 2021). A total of 6,263 tons of ACM special waste and RCRA Non-Hazardous soil were removed and disposed off-site (CAPE, 2021). Confirmation soil samples collected following excavation actives were below the TMCLs for arsenic, chromium, lead, and mercury (CAPE, 2021). This indicates that CMI activities sufficiently removed the impacted soil at SMWU 69.

The Army conducted a streamlined health risk evaluation by comparing RCRA Facility Investigation (RFI) data to the approved TMCLs for the site. 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  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, SWMU 69 falls within the area designated as park land (Johnson County, 1998).

KDHE has determined that NFA for surface soil, subsurface soil and groundwater is the appropriate remedy for SWMU 69. The prior excavation and disposal of surface and subsurface soil exhibiting TMCL screening exceedances for ACM (asbestos), arsenic, chromium, lead, and mercury was appropriate for the site to be protective of human health and the environment. This proposed remedy is based upon KDHE’s review of all available historical documentation regarding the Site.