Summary of the Statement of Basis

Area of Concern 20 - Potential Trench Disposal Pit Area

at the Sunflower Former Army Ammunition Site

PROPOSED REMEDIAL MEASURE

The proposed remedy for AOC 20 is No Further Corrective Action Planned (NFCAP) for soils and site-specific groundwater. Excavation activities were performed as Interim Corrective Measures between October 28, 2019 and June 11, 2020. A total of 48 cubic yards (CY) of lead-contaminated soil was excavated and disposed of off-site at the Johnson County Landfill. The result of the post-excavation confirmation composite sample was below the TMCL of 400 mg/kg for lead. Therefore, no additional excavation was necessary. According to the Conceptual Land Use Plan for SFAAP, the area of AOC 20 is designated for redevelopment as parks, trails, or open space (Johnson County Rural Comprehensive Plan Resolution No. 079-98, 1998).

One well is located downgradient of the area with the excavated lead contaminated soil. Sampling during the 2008-2010 RFI (Louis Berger and Burns and McDonnell, 2016) showed that lead was below the MCL of 15 micrograms per liter (µg/L) and all other detections in the groundwater at the site were below the TMCLs.

Sitewide COCs in groundwater will be evaluated during the Army's assessment of Groundwater Operable Unit #4 (GWOU #4). GWOU means a discrete area consisting of a single to many SWMUs and/or AOCs with actual or potential for releases to groundwater, grouped together for purposes of assessment and cleanup. The primary criteria for placement of sites with actual or potential groundwater releases into an operable unit include geographic proximity, similarity of waste characteristics and site type, and the possibility for economies of scale.

JUSTIFICATION:

AOC 20, Potential Trench Disposal Pit Area, is one of a group of four AOCs (AOCs 18-21) located adjacent to the former Classification Yard (SWMU 1; Figure 1). AOC 20 is approximately 0.5 acres in size. However, the Army identified a disturbed area (from a 1948 aerial photograph) of approximately 10 acres southeast of the official boundary and included it with the AOC 20 RFI (investigations 2005 and 2008-2010, Figures 1 and 2).

Initial field work done by the USACE in 2005 collected four surface soil samples at the four corners of the identified disposal area. The samples were tested for semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs), and target analyte list (TAL) metals; all of which were below the target media clean up levels (TMCLs).

The majority of the RFI work at the site occurred in 2008-2010 including eight exploratory trenches to determine if debris disposal occurred at the site (Figure 2). A total of eight surface soil samples (one per trench) were collected from AOC 20 as part of the RFI and reported by Louis Berger and Burns and McDonnell in 2016. Only one surface soil sample showed a lead exceedance of 1470 milligram per kilogram (mg/kg). One discrete subsurface soil was collected from the soil loader for each of the 8 trenches. All samples were non-detect for explosives and semi-volatile organic compounds (SVOCs). Metals and volatile organic compounds (VOCs) were detected below their TMCLs.

The AOC 20 Corrective Measures Implementation (CMI) Report (CAPE, 2020) presented the results of the removal activities for the site. Corrective measures included excavation and disposal of 48 CY of lead-contaminated soil that exceeded the 400 mg/kg TMCL for lead, with a confirmation sample of 26 mg/kg (Figure 2).

One well was located southeast of AOC 20 (Figures 1 and 2). This well had lead concentration below the detection limit for groundwater (15 micrograms per milliliter (µ/ml). Sitewide contaminants in groundwater will be evaluated during the Army's assessment of Groundwater Operable Unit #4 (GWOU #4).

AOC 20 and Trench 1 Location.

AOC 20 and Trench 1 Location.
Site Location and Detail Map

Site Location and Detail Map.

KDHE Site Documents