Evaluation of SWMU 6 Data

Comparison to TCLP Criteria
The results of the laboratory analyses indicate that several of the TCLP analytes (for evaluation of overburden soils as hazardous waste) were reported at values that are above the laboratory detection limits. However,
none of the analytes detected exceeded the Regulatory TCLP limits for hazardous waste (see section 5.3 of URS, 2001). Based on these results, the soil excavated as part of the construction project will not require disposal as hazardous waste.

Comparison to Risk-Based Concentrations
Organic Data
As presented in the SWMU 6 Soil Sampling Results Report (Sections 5.4 and 5.5, URS, 2001), Maximum Detected Concentrations (MDCs) of TCL VOCs, SVOCs, Pesticide/PCBs and Explosives did not exceed either Residential or Industrial RBCs.

Inorganic Data
Table 1 presents the results of discrete sample data comparisons to screening criteria (USEPA Region III, April 2, 2002, RBCs, and background Point Estimates) for inorganic chemicals at SWMU 6. Seven
constituents were present above Residential RBCs. Aluminum (10,200 to 49,600 milligrams per kilogram [mg/kg]) detections were above the Residential RBC of 7,800 mg/kg. Arsenic detections (3.8 to 7.6 mg/kg)
were above the Residential RBC of 0.43 mg/kg. Chromium detections (18.6 to 51.5 mg/kg) were above the Chromium VI Residential RBC of 23 mg/kg. Iron detections (20,500 to 40,400 mg/kg) were above the Residential RBC of 2,300 mg/kg. Manganese detections (181 to 1,510 mg/kg) were above the Residential RBC Food value of 1,100 mg/kg. The Thallium detection (1.2 mg/kg) was above the Residential RBC of 0.55
mg/kg. Vanadium detections (45.9 to 89.9 mg/kg) were above the Residential RBC of 55 mg/kg.

Of the seven constituents present above Residential RBCs, only Arsenic detections (3.8 to 7.6 mg/kg) were above the Industrial RBC of 3.8 mg/kg. The MDC of arsenic at SWMU 6, detected above its Industrial RBC,
is below background Point Estimates (i.e., 95% UTL Point Estimates) established in the Facility-Wide Background Study (IT Corp., 2002). Additionally, the six constituents that had MDCs between Residential
RBCs and Industrial RBCs are below background Point Estimates (i.e., 95% UTL Point Estimates) with one exception, Aluminum. Aluminum was reported as present in sample 6SB12B at 49,600 mg/kg, which is above
the 95% UTL Point Estimate of 40,041 mg/kg. This detection of aluminum is well below the Industrial RBC value of 200,000 mg/kg. Given the nature of this site, the depth bgs, the lack of viable pathways, and the toxicity of the constituent, this exceedance is not considered a risk at SWMU 6.