SWMU 44 - Tank T784 Site

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 44, Tank T784 Site, located in the northwest portion of the former SFAAP, encompasses approximately one acre within the former nitroguanidine (NQ) production area. It includes Tank T784, outbuildings, piping, and pump equipment. This site was used from 1981 to 1992 to store National Pollutant Discharge Elimination System (NPDES) permitted wastewater prior to discharge. The wastewater effluent from Tank T784 discharged through an approximately 3-mile underground transfer line which follows the north plant boundary in an easterly direction before turning directly north at Sunflower Road towards the former River Water Treatment Plant (RWTP) Lagoons (SWMU 2).  SWMU 44 was part of the NQ production area and included an aboveground, circular, metal, wastewater collection tank (Tank T784) that held cooling tower blow down, NQ crystallizer condensate, guanidine nitrate (GN) evaporator condensate, and noncontact cooling water. The capacity of Tank T784 was 100,000 gallons. Underground transfer line pipes discharged wastewater effluent from Tank T784 into the RWTP Lagoons (SWMU 2).  SWMU 2 was the NPDES permitted discharge point for the NQ wastewater.

Arsenic and total chromium were the COC) at this SWMU based on the surface and subsurface sampling of the soil during the initial  Resource Conservation and Recovery Act (RCRA) Facility Investigation (RFI) (Shaw, 2005) and the Final RFI (AECOM, 2020).

A site-specific RFI was conducted at SWMU 44 in August 2003. Three groundwater samples and 15 surface and subsurface soil samples were collected at the Tank T784 area. Samples were collected at biased locations around the perimeter of Tank T784, below the overhead transfer lines, and at various locations identified by KDHE. Soil and groundwater samples were analyzed for Target Analyte List metals, hexavalent chromium, semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs), explosives, nitroglycerine, NQ, guanidine nitrate (GN), polychlorinated biphenyls (PCBs), fluoride, cyanide, sulfates, nitrates, nitrites, ammonia-nitrate, and herbicides.

Laboratory analysis of surface soil samples identified metals, nitrate, ammonia, sulfate, PCBs, herbicides, and SVOCs. Thirteen metals were detected at concentrations exceeding their statistically estimated background concentrations (Law 1996). Laboratory analysis of subsurface soil samples identified metals, ammonia, nitrate, sulfate, SVOCs, and VOCs. Four metals were detected at concentrations exceeding their statistically estimated background concentrations (Law 1996). Laboratory analysis of three groundwater samples identified metals, nitrate, ammonia, sulfate, and one SVOC. Eight metals were detected at concentrations exceeding their statistically estimated background concentrations (Law 1996).

The 2019 RFI field activities were completed at SWMU 44 to determine whether historical contaminants impacted subsurface soil. To prepare for the subsurface soil sample collection, the field team completed potholing to daylight the 3 mile-long underground transfer line, confirmed lateral position and obtained vertical line depth. A total of 141 subsurface soil samples were collected from May 28 through October 2, 2019 and analyzed for RCRA metals, manganese, nitrate, ammonia, GN, and NQ. Additionally, two subsurface soil samples were collected for chromium VI analysis. 

Arsenic was above the residential Target Media Cleanup Level (TMCL) (18.9 mg/kg) at one subsurface soil sample location (30.2 mg/kg). The arsenic concentration of 30.2 mg/kg falls between the residential TMCL of 18.9 mg/kg and the non-residential TMCL of 63.2 mg/kg. Based on the 2019 RFI data, only one of 141 subsurface soil samples exceeded the residential TMCL of 18.9 mg/kg. Delineation was not pursued given the lack of exceedances along the underground transfer line. Total chromium was above the residential TMCL (33.6 mg/kg) at two subsurface soil sample locations (45.4 mg/kg and 34.0 mg/kg). Therefore, two chromium VI samples were collected at the same locations and intervals as the previous samples. The chromium VI concentrations were below the residential TMCL (33.6 mg/kg) at 1.3 mg/kg and 0.38 mg/kg. 

No wells were installed at SWMU 44 during the 2019 RFI. Groundwater will be further evaluated during the Army’s assessment of site-wide groundwater in operational unit GWOU-1

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 44 falls within the area designated as a Research and Technical Center (Johnson County, 1998).

The KDHE has determined that No Further Action for soil is the appropriate remedy for SWMU 44. The 2019 RFI sampling results show no contamination was identified above the site-specific TMCLs for the site.  This proposal is based upon EPA and KDHE’s review of all available historical documentation regarding the Site. The proposed decision is based upon KDHE’s review of all available historical documentation.