SWMU 56 – Monitoring Well South of Facility 211
Proposed Remedial Measure
The proposed remedy for SWMU 56 is No Further Action (NFA). Long term monitoring (LTM) of groundwater concluded that groundwater at SWMU 56 is no longer impacted above acceptable standards, and that soil and groundwater data demonstrate that there is no current or future potential risk from soil or groundwater at SWMU 56. No excavation or remedial measures were taken.
Groundwater samples collected from Monitoring Well 003MW003 in September 1996 showed concentrations of nitrate/nitrite at 99,200 microgram per liter (μg/L), above the current USEPA Maximum Contaminant Level (MCL) of 10,000 μg/L and below the Consent Order’s performance standard of 250,000 μg/L. While the source of the nitrates is uncertain, land application of treated wastewater from the nitroguanidine (NQ) process area was known to be conducted near SWMU 56 for several years. In addition, the area has been used for livestock grazing and non-point source impacts are a possibility (Tetra Tech 2008). In 1996 lead was detected in groundwater collected from Monitoring Well 003MW003 at a concentration of 15.5 μg/L. This result slightly exceeds the Risk Based Standards for Kansas (RSK) value of 15.0 μg/L (KDHE, 2021). There is no known source of lead in the vicinity of SWMU 56.
Monitoring Well 003MW003 was subsequently sampled as part of the Relative Risk Site Evaluation (RRSE) conducted by Battelle in 2003. Nitrate/nitrite was not detected in groundwater samples collected from Monitoring Well 003MW003. Soil samples collected at SWMU 56 during the RRSE showed a maximum concentration of nitrate at 6.18 milligram per kilogram (mg/kg). While the maximum soil concentration was slightly higher than background conditions calculated for SFAAP, it was below the TMCL presented in the 2003 RRSE of 1,000 mg/kg (TMCL Source = 2000 USEPA preliminary remediation goals [PRGs]), and updated TMCL of 200 mg/kg (TMCL Source: (KDHE 2021) Residential RSK value) as presented in a March 22, 2011 request for no further action prepared by Tetra Tech. A map showing the historical sample locations and aerial photography is found in Attachment 2 of the 2003 RRSE Report.
In response to KDHE’s comments on the 2003 RRSE Report, long term monitoring (LTM) of groundwater was performed at SWMU 56 to evaluate trends for nitrogen in groundwater and determine the need for additional actions at SWMU 56. Groundwater samples were collected from Monitoring Well 003MW003 in November of 2007, May and November of 2008, and in July and December of 2009 as part of the LTM activities. While the sampling list varied over the course of LTM, analyses were performed for nitrogen (total organic), ammonia (as N), nitrate, nitrate/nitrite, nitrite, and nitrogen (TKN). All nitrate, nitrate/nitrite, and nitrite sample results were below their respective TMCLs referenced above. LTM sampling results were summarized in the Long Term Monitoring Report (May 2008) and the Long Term Monitoring Report for 2008 and 2009, Solid Waste Management Unit 56, Former Sunflower Army Ammunitions Plant, Desoto, Kansas (LTM Report) which was prepared by Tetra Tech (2010). The LTM report concluded that groundwater at SWMU 56 is not impacted, and that laboratory data demonstrate there is no current or future potential risk from soil or groundwater at SWMU 56.
Buildings 210 and 211 are not located within the SMWU 56 boundaries but are adjacent to the SWMU (Figure 2). These building were observed to have no exterior environmental risks. They are built of concrete and were not painted so there is no risk of LBP, pesticides, or lead. Inside the building suspected ACM floor tiles and possibly some pipe wrap may be present, but soil testing revealed no asbestos contamination. No work is necessary until demolition or remodeling.
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 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, and considered 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 56 is proposed to be a Business Center. Based on this land-use, the potential current and future receptors include:
- Current: Construction workers
- Future: Construction workers, facility employees and visitors.
The LTM plan identified nitrates as COCs at SWMU-56 below TMCLs, but above the EPA MCL, therefore, the exposure pathway for soil was considered during the assessment. Soil: Evaluated exposure pathways include incidental ingestion, inhalation of airborne particulates (dusts), and dermal contact (organic compounds only). Groundwater for potable use is restricted at this property. Based on comparison of the LTM results to TMCLs, there is no future potential risk from soil and groundwater at SWMU-56. Potential sitewide groundwater contaminants in the northeast area of the SFAAP site will be evaluated during the US Army’s assessment of Groundwater Operable Unit #2 (GWOU #2).
KDHE determined in 2013 that lead concentrations identified in the groundwater were of minimal risk and no source of lead was identified. No additional lead sampling is required due to the intended use of the property.
- SWMU 56 Statement of Basis, March 2022 (PDF)
- Long-Term Monitoring Report, October 2010 (PDF)
- Long-Term Monitoring Report, May 2008 (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)