Summary of the Statement of Basis

Area of Concern 19 - Trench Disposal Area A4

Area of Concern 21 - Trench Disposal Area A6

at the Sunflower Former Army Ammunition Site

JUSTIFICATION:

AOC 19 is located immediately outside the southwest corner of the former Classification Yard (SWMU 01) and south of AOC 18 and is approximately 0.6 acres (Figure 1). AOC 21 is located southeast of AOC 19 and immediately south of the former Classification Yard (SWMU 01). The site is approximately 0.1 acres. The U.S. Environmental Protection Agency (EPA) identified a potential trench disposal area based on interpretation of 1948 aerial imagery. No other records are available regarding past activities at either AOC 19 or AOC 21. No contaminants have been detected above target media cleanup levels (TMCLs) in AOC 19 or AOC 21 soils. Two monitoring wells installed upgradient of the sites in SWMU 01 showed no contaminants above the TMCLs for the sites. Groundwater will be evaluated further during the assessment of Groundwater Operable Unit #4 (GWOU #4)

Contaminants of potential concern (COPCs) selection for AOC 19 and AOC 21 initially focused on contamination originating from historical activities at SWMU 01. Two RFIs were performed at SWMU 01 in 1994 and 2003 and are considered pertinent due to the geographic proximity to the three sites (Law, 1994 and Shaw, 2003). A total of 61 surface soil, 10 subsurface soil, three sediment, seven groundwater, and two surface water samples were collected between both RFIs (Tetra Tech, 2007). The presence of phthalates, metals, semi-volatile organic compounds (SVOCs), and volatile organic compounds (VOCs) in media at SWMU 01 was considered during development of the analytical suites for the subsequent RFIs at AOCs 19 and 21.

In 2003, a Relative Risk Site Evaluation (RRSE) for AOCs 01, 18, 19, 20, and 21 was performed (USACE, 2005). During this investigation, a total of eight surface soil samples were collected from AOC 19 and AOC 21 and analyzed for target analyte list metals, SVOCs, and VOCs. Analytical results for these surface soil samples were below their respective TMCLs and soil-groundwater risk levels. The RRSE recommended NFCAP at AOCs 19 and 21. KDHE requested that the Army collect additional subsurface soils and groundwater samples to determine potential impacts of historic disposal activities.

Between January 22, 2008 and July 16, 2010, RFI field activities (RFI Work Plan, Tetra Tech, Inc., 2007) were completed for AOCs 18-21. These activities included surface/subsurface soil sampling and groundwater sampling to close data gaps and identify any contaminants of concern (COCs) associated with historical activities. Nine exploratory trenches were excavated, and field screened. No evidence of contamination was documented during exploratory trenching. Ten surface and nine subsurface soil samples were collected and analyzed for RCRA metals, explosives, SVOCs, VOCs, ammonia, nitrate, and sulfate. Based on the analytical results, analytes were not detected above the TMCLs or soil-to-groundwater risk levels. Two groundwater samples were collected from AOC 19 and AOC 21. Because of low water production the samples were tested only for ammonia, nitrate, nitrite, sulfate, and VOCs. Analytes were not detected above the TMCLs or soil-to-groundwater risk levels. Analysis of two upgradient wells in SWMU 01 showed that all COCs were below the TMCLs for groundwater.

Corrective measures were not proposed for either AOC 19 or AOC 21 because the RFI (Louis Berger and Burns & McDonnell, 2016) data indicated no contaminants of concern COCs were present above TMCLs or soil-to-groundwater risk levels for soils or groundwater.

The two downgradient wells were not tested for all site-specific groundwater COCs because of low water volume (Louis Berger and Burns & McDonnell, 2016). Therefore, groundwater at the site will be evaluated for site wide COCs during the Army's assessment of Groundwater Operable Unit #4 (GWOU #4).

Proposed Remedial Measure

The recommended final corrective measures alternative for AOC 19 and AOC 21 is NFCAP for surface/subsurface soils and site-specific groundwater. No further actions will be taken to evaluate or reduce contaminant mass, address potential exposure pathways, or reduce the potential for contaminant migration because no contamination that posed a threat to human health and the environment was found at the site.

The site-specific contaminants that were evaluated in the soil were not all analyzed in groundwater due to low water volume. Therefore, all site-wide contaminants for groundwater will be evaluated at the two sites during the Army's assessment for site-wide contaminants in groundwater for Groundwater Operable Unit #4 (GWOU #4).

References

  • Law, 1999. Final RFI & QCSR, SWMU 1, Classification Area, SFAAP, De Soto, Kansas. February.
  • Shaw Environmental, Inc., 2005. Final RFI Addendum Solid Waste Management Unit 1, Classification Yard, Sunflower Army Ammunition Plant, De Soto, Kansas. June.
  • U.S. Army Corps of Engineers, 2005. Final Report for RRSE for AOC's 1, 18, 19, 20, 21 and SWMU 66 at SFAAP. July.
  • Tetra Tech, Inc., 2007. RCRA Facility Investigation Work Plan, Area of Concern (AOC) 18-21. November
  • Louis Berger and Burns & McDonnell, 2016. Final RCRA Facility Investigation Report and Focused Corrective Measures Study Areas of Concern 18-21 Potential Trench Disposal Area. November.

KDHE Site Documents