SWMU 13 - South Acid Area Evaporative Lagoons and Liquid Waste Treatment Plant

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 13, South Acid Area Liquid Wastewater Treatment Plant (LWTP) Evaporative Lagoons, is in the central-eastern portion of the former SFAAP. SWMU 13 was used to store treated wastewater from the Sulfuric Acid Regeneration (SAR) and calcium sulfate sludge from the treatment of wastewater produced in the acid production area and nitroguanidine (NQ) area. The LWTP contained five aboveground tanks and four unlined earthen cells used as evaporative lagoons, which each measured approximately 10 feet deep. Calcium sulfate sludge that resulted from the wastewater treatment was settled in the lagoons to evaporate by solar energy. However, the influent rate exceeded the evaporation rate which prompted a land application program in the mid-1980s for the wastewater treatment. The land application ceased in December 1998. Currently, the site is an open grassy field used for cattle grazing with no roads crossing the area. In total, SWMU 13 encompasses approximately 28 acres.

A RCRA Facility Investigation (RFI) was conducted by Law Environmental in 1999 to collect subsurface soil, sludge, surface water, and groundwater samples and install monitoring wells. There were fourteen wells that had previously been installed in the area; however, six of those wells were private. Therefore, six new monitoring wells were installed as part of the RFI field work and sampled for groundwater. Several RCRA metals were detected above background levels in all media and the sludge was identified as a potential source of nitrate/nitrite and sulfate contamination (Law 1999). Nitroglycerin (NG) and NQ were detected in the groundwater samples, but not in the surface water. The results of the RFI samples indicated that contamination was migrating from the lagoons via groundwater.

A closure plan developed in 1995 and approved by KDHE in 1996 addressed the remediation/denitrification of the sludge present in the lagoons by mixing soil and vegetation with the sludge, capping the lagoons with a clay cover, and grading, then seeding the area with perennial grasses (AECOM 2022). Following this closure plan, primary and secondary sources of groundwater contamination were addressed through the removal of wastewater and remediation of sludge. 

Soils associated with the excavation and removal of explosive foundations were characterized and remediated in the Interim Corrective Measures (ICM) performed by Zapata Incorporated, Burns & McDonnell (BMcD), and Envirocon Incorporated (2019). The rind soils and foundations associated with Account 731 (Waste Water Treatment Facility) were evaluated and remediated based on sampling results. The building in Account 731 had been removed prior to the start of the ICM field activities. Rind soils in SWMU 13 that were previously analyzed by AECOM did not require remediation in the ICM activities. There were no interior sewer removals required for Account 731. However, there were several foundation slabs and concrete gutters that required sampling and removal. Following removal, the screening samples taken for soil below the foundations and gutters were below the TMCLs and MEC screening levels (Zapata, Burns & McDonnell, and Envirocon, Inc., 2019). The site was backfilled and seeded with grass following the completion of MEC removal activities in 2017.

During the RFI conducted by AECOM in 2022, 16 surface soil samples, 101 subsurface soil samples, and 25 stepout/stepdown soil samples were collected and analyzed for chemicals of interest at SWMU 13. RCRA metals, guanidine nitrate (GN) and (NQ), sulfate, and hexavalent chromium did not exceed their respective soil TMCLs. Ammonia, arsenic, cadmium, and nitrate exceeded their respective TMCLs and are considered COPCs for soil at the site. 

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) 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 13 is proposed to be split between multi-family residential, light manufacturing, and green space. The KDHE has determined that no further action for soil is the appropriate remedy for SWMU 13. The prior excavation of ammonia and nitrate contaminated soils was appropriate for the site to be protective of human health and the environment. This proposal is based upon KDHE’s review of all available historical documentation regarding the Site.