SWMU 63 – Water Towers
Proposed Remedial Measure
The proposed remedy for SWMU 63 was excavation and off-site disposal of soils. Excavation and removal of soil off-site to an appropriate landfill or treatment facility was completed as an Interim Corrective Measure (ICM) as summarized in the RFI/CMS (BMcD, 2018) and the Corrective Measures Implementation Completion Report (CAPE, 2020).
The RFI/CMS indicated that site-specific COCs for groundwater were below the TMDLs for the COCs. Therefore, site-specific groundwater will be included in the NFA remedy. Surface water and sediment were sampled from a cattle pond at the SWMU 63-1 site. Both media had COCs below the TMDLs. Surface water and sediment are included in NFA for the SMWU 63-1 site.
Groundwater at the site will be evaluated for sitewide COCs during the Army’s site-wide assessment of Groundwater Operable Unit (GWOU #2). A GWOU is 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.
A Relative Risk Site Evaluation (RRSE) was conducted in 2003 by Battelle Memorial Institute. Four composite soil samples were analyzed for RCRA metals. A concentration of lead of 596 mg/kg was detected at SWMU 63-2, which exceeded the Target Media Cleanup Level (TMCL) of 400 mg/kg (Battelle, 2003). Based on this result, SWMU 63 received a low hazard score in the RRSE, and further investigation was recommended (Battelle, 2003).
An RFI/CMS was finalized in 2017 by Louis Berger and Burns & McDonnell in which field activities were performed between June 1, 2009 and February 17, 2011. In-situ and ex-situ x-ray fluorescence (XRF) readings, surface and subsurface soil samples, sediment samples, surface and groundwater samples were collected. Ninety-eight surface soil samples were selectively analyzed for general chemistry, toxicity characteristic leaching procedure (TCLP), metals, munitions/explosives, nitro parameters, polycyclic aromatic hydrocarbons (PAHs), semi-volatile organic compounds (SVOCs), and total petroleum hydrocarbons (TPH) (BMcD, 2018). Only chromium and lead exceeded TMCLs at SWMU 63.
Out of 67 surface soil locations for chromium, three exceeded the residential soil TMCL of 33.6 mg/kg. Given the limited exceedances and the intent of the TMCL to manage hexavalent chromium, the RFI/CMS recommended that additional samples be analyzed for hexavalent chromium prior to deciding whether to designate chromium as a COC (BMcD, 2018). Based on the Pre-Design Investigation (PDI), chromium was not determined to be a COC (CAPE, 2020).
Lead was detected at a concentration below the residential TCML from a single subsurface soil sample that was collected during the RFI (BMcD, 2018). Lead exceeded the residential TMCL at 89 ex-situ XRF (X-Ray Fluorescence) sampling locations and eight surface soil sampling locations. Exceedances ranged from 405.1 mg/kg to 3,582 mg/kg in surface soil. Approximately 28 of these exceedances were greater than the non-residential TMCL for lead of 1,000 mg/kg. Due to the historical sandblasting activities to remove lead-based paint from the water towers at SWMU 63, elevated lead concentrations appear to be due to anthropogenic sources (BMcD, 2018). Therefore, lead was considered a COC for surface soil.
Monitoring well 063MW001 was installed at SWMU 63 in June 2018 to a depth of 20 feet bgs and screened at an interval of 10 to 19.6 feet bgs (BMcD, 2018). Two groundwater samples were filtered and collected on July 12, 2010 and analyzed for dissolved lead. Dissolved lead was not detected in either sample; therefore, no contaminants of potential concern (COPCs) were identified for groundwater at SWMU 63 (BMcD, 2018).
One surface water and two sediment samples were collected from the pond northeast of Water Tower 127-1 (Cattle Pond) during Phase II (BMcD, 2018). Both the surface water and sediment samples were analyzed for SFAAP metals. Metals concentrations in both surface water and sediment samples were below residential TCMLs (BMcD, 2018).
Pre-Design Investigation sampling was conducted by CAPE at SWMU 63 in August 2019. Three soil samples were collected from a depth of 0-1 feet bgs and analyzed for lead, chromium, and hexavalent chromium to determine chromium speciation in areas that had historical high chromium TMCL exceedances. The presence of lead was detected from twenty-four wipe samples that were collected from the support legs of the water towers (CAPE, 2020). Lead also exceeded its TMCL of 400 mg/kg in the northern portion of SWMU 63 and at 063 - CPGC00026-SO-ER00026 in the central portion of SWMU 63-2 (CAPE, 2020). Based on the results, it was determined that excavation of surface soil was required to address lead contamination above residential TMCLs.
Additional PDI sampling was conducted for total chromium and hexavalent chromium to determine whether to designate chromium as a COC. Three historical sample locations that contained total chromium TMCL exceedances were resampled for total chromium and hexavalent chromium. Neither chromium nor hexavalent chromium exceeded the respective TMCLs of 33.6 mg/kg at any location sampled; therefore, chromium and hexavalent chromium were not considered COCs in the surface soils at SWMU 63 (CAPE, 2020).
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 (2021) 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 Johnson County Rural Comprehensive Plan Resolution No. 079-98. Conceptual Land Use Plan, Sunflower Army Ammunition Plant. July 23, 1998, the area encompassing SWMU 63 is proposed to be redeveloped as a Business Center, which will accommodate mixed office, research and development, technology, and similar uses. The area encompassing Water Towers 127-5, 128-3, and 130-4 is proposed to be the site of the Town Center, which will accommodate mixed-use retail, office, public facilities, civic, cultural and entertainment, and residential uses (BMcD, 2018). Water Tower 128-8 is located within the proposed Single-Family Residential area (Johnson County, 1998). Based on this land-use, the potential current and future receptors include:
- Current: Construction and excavation workers.
- Future: Future residents of the SWMU 63 area could be exposed to contamination through ingestion or dermal contact of surface soils or inhalation of dust, although business center and town center uses would be more transient than residential locations.
The RFI identified lead as a COC at SWMU 63 based on exceedances of the residential soil TMCLs, therefore, the exposure pathway for soil was considered during the assessment. Soil evaluated exposure pathways include incidental ingestion and inhalation of airborne particulates (dusts). Based on comparison of the RFI results to TMCLs, which identified exceedances and therefore pose a potentially unacceptable health risk, the following corrective action objectives (CAOs) were established for surface soil SWMU 63:
- Mitigate risk to human health via direct contact with impacted surface soil with COC concentrations above TMCLs.
- Mitigate the potential future migration of contaminants from impacted surface soil to surface soil in drainage pathways leading to Kill Creek.
The removal of debris and the excavation of the surface soil removed the COCs for future use at the site. No contaminants, including lead, were identified in the one groundwater sample collected at the site. Additional evaluation of groundwater in the area will occur when work on GWOU-#2 is done.
- SWMU63 Statement of Basis, March 2022 (PDF)
- Site Wide Work Plan, August 2019 (PDF)
- RCRA Facility Investigation Report and Focused Corrective Measures Study, July 2018 (PDF)
- Relative Risk Site Evaluation, November 2003 (PDF)
- Risk-based Standards for Kansas (RSK) Manual - 6th Version, July 2021 (PDF)
- Conceptual Land Use Plan Sunflower Army Ammunition Plant (PDF)