SWMU 50 - Disposal Site East of the SWMU 1 Classification Yard

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 50, Disposal Site East of the SWMU 1 Classification Yard, is in the northeast portion of the former SFAAP. SWMU 50 was used as a solid waste disposal area for construction debris during the 1940s and 1950s. Construction, renovation, and demolition activity generated asbestos containing material (ACM) that was disposed at SWMU 50. SWMU 50 consists of two historical construction debris disposal areas: Tract 1, an abandoned dump site located immediately west of Kill Creek comprising approximately 6.2 acres, and Tract 2, an abandoned dump site located approximately 1,000 feet north of Tract 1 (Figure 2). In total, SWMU 50 encompasses approximately 12.3 acres. Both tracts adjoin ditches that direct water flow into Kill Creek. 

Following a 1995 Resource Conservation and Recovery Act (RCRA) Facility Investigation (RFI) by Law Environmental, Inc., Asbestos Containing Materials (ACM) and lead impacted soil were removed at Tracts 1 and 2 in 1997 and 2011. Groundwater samples were collected from three wells. Manganese, zinc, and di-n-butyl phthalate were detected above background levels but did not exceed Target Media Cleanup Levels (TMCLs). Bis(2-ethylhexyl) phthalate marginally exceeded the TMCL (6.1 ug/L vs 6.0 ug/L) in one well; however, it was not detected in nearby wells and since 1995 all source material has been removed (Law, 1997).

From 2007 to 2017, annual inspections at both Tract 1 and Tract 2 routinely identified and removed surficial ACM. The ongoing detection of ACM at the surface of SWMU 50 was likely due to erosion of disposal areas. Due to the continuing detection of ACM at SWMU 50, the Army requested that the horizontal and vertical extent of the ACM debris be delineated through an RFI, and that the results be used to conduct a focused Corrective Measures Study (Louis Berger & Burns and McDonnell, 2018).

In 2017, RFI activities were conducted in which trenches were dug at Tracts 1 and 2 in areas where ACM was observed. Samples of suspect ACM were collected and analyzed to confirm the presence or absence of ACM. Waste characterization samples were collected and analyzed to manage the disposal of waste. Fifteen soil samples were collected and analyzed for volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPH), metals, and explosives. Two of the 15 soil samples indicated lead concentrations exceeding Target Media Cleanup Levels (TMCLs). A magnetometer survey was also conducted to identify the extent of the disposal area (SRS-CAPE, 2022). Previous investigations at SWMU 50 indicated that no residual chemical contaminant impacts were present at SWMU 50, and that soil impacted by previously detected lead contamination was removed during the interim corrective measures in 1997 (Louis Berger & Burns and McDonnell, 2018).

Corrective Measures Implementation (CMI) excavation and field activities were conducted from September 15, 2020 through November 3, 2021, in accordance with the SWMU 50 CMI Work Plan (CAPE, 2020). Vegetation was cleared and tree root balls containing ACM were placed in designated ACM stockpiles, then disposed offsite. The Johnson County Park Trail is located within the northern portion of SWMU 50 and crossed the 1.5-foot excavation area in Tract 2. SRS-CAPE excavated around the pathway and did not disturb the pathway during site activities (SRS-CAPE, 2022). Erosion controls were implemented, and ACM areas in Tract 1 and Tract 2 were excavated. Tract 1 was excavated to a depth of 3 feet below ground surface (bgs), and Tract 2 was excavated to a maximum depth of 6 ft bgs along the southern side. Additional ACM contaminated soils were identified on the west side of the mouth of the Tract 2 ditch; these soils were excavated to 1 ft bgs, or until ACM were no longer visible (SRS-CAPE, 2022). The excavation was considered remediated after a visual inspection by a Kansas-licensed asbestos professional. The excavated soil was stockpiled, sampled, and characterized for disposal. Excavated areas were backfilled with clean soil and the area was surveyed, graded, shaped and contoured (SRS-CAPE, 2022).

The Army conducted a streamlined health risk evaluation by comparing 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 (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, SWMU 50 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 SWMU 50. 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 regarding the Site.