Area of Concern 01 – Monitoring Well West of Old Administrative Area

Proposed Remedial Measure

The proposed remedy for site-specific groundwater at AOC 01 is a land use restriction in the form of Groundwater Use Restriction cited in Sunflower Army Ammunition Plant, Consent Order No. 05-E-011, Exhibit 14a (Quit Claim Deed), (SRL Consent Order, 2005, Johnson County Kansas Register of Deeds); Section III (D) Groundwater Use Restrictions. The citation of the Groundwater Use Restrictions for AOC 01 is as follows:

“Grantee, for itself and its successors and assigns, covenants and agrees that no access or use groundwater underlying the property for any purposes shall be permitted unless the groundwater has been tested and found to meet applicable standards for human consumption by the KDHE and any other state and local regulatory authorities. The costs associated with obtaining use of such water, including, but not limited to, the costs of permits, studies, or analysis shall be the sole responsibility of the Grantee, its successors and assigns.”

For soils, the RFI/CMS (Burns and McDonnell, 2017) indicated that site-specific COCs for surface/subsurface soils were below the TMDLs for soils Therefore, soils require no further action.

Justification

The AOC 01 historical procedures and activities are unknown, but the site had recreational and residential buildings that were demolished from 1959-1966. During the RCRA Facility Investigation and Corrective Measures Study (RFI/CMS; Louis Berger 2017), surface and subsurface soil, and groundwater samples were collected and tested for nitrate/nitrite, ammonia, antimony, and cobalt. Surface and subsurface soil results showed no COCS above the residential TMCLs.

Groundwater showed levels of nitrate/nitrite above residential TMCL. While AOC 01 had no known activities or processes that could potentially be responsible for the comparatively high levels of nitrogen in ground water, several potential nitrogen sources exist in the vicinity of the site:

  1. A possible leak in an 8-inch diameter force main pipeline that conveyed wastewater from Tank T784 (SWMU 44) in the NQ area to the lagoons at the River Water Treatment Facility (SWMU 02) - this pipeline lies to the northwest of AOC 1 (Figure 2),
  2. A leak in a force main running between the Industrial Wastewater Treatment Plant (SWMU 68) and the Kansas River – this pipeline lies to the west of AOC 01 (Figure 2),
  3. A potentially undocumented septic system or former outhouse,
  4. Potential over-application of wastewater to land in the area of AOC 01,
  5. Agricultural storage or application of fertilizer, and/or
  6. Migration on site from an upgradient, off-property source (i.e., across Lexington Ave.).

Based on topography, the expected groundwater flow direction in the vicinity of AOC 01 is to the south.

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 AOC 01 is proposed to be non-residential. Based on this land-use, the potential current and future receptors include:

  • Current: soil samplers, environmental consultants
  • Future: Commercial workers, construction workers, utility workers, maintenance workers

The RFI identified nitrates and antimony as COCs at AOC 01 based on exceedances of the residential groundwater TMCLs, therefore, the exposure pathway for groundwater was considered during the assessment. Groundwater: Evaluated exposure pathways include incidental ingestion, and dermal contact (organic compounds only). Based on comparison of the RFI results to TMCLs, which identified exceedances and therefore pose a potentially unacceptable health risk, the following corrective action objective (CAO) was established for groundwater:

  • Mitigate risk to human health via direct contact with impacted groundwater with COC concentrations above TMCLs.

KDHE Site Documents