Remedial Action Report Construction Phase

Home Browse Search

Area 24 During completion of the ESA, Century West located a concrete manhole-type cover in the asphalt surface of the Senator parking lot (Century West 1997a). This feature was identified as a possible sump or septic tank. During pre-construction remedial actions, a test pit was completed in this area to investigate the subsurface (Century West 1998b). However, no evidence of subsurface contamination was observed in the test pit. During construction activities on June 29, 1999, a concrete sump (approximately 9 feet long, 3 feet wide, and 5 feet tall) was discovered approximately ten feet south of the pre-construction test pit. A diesel odor was noted in the soil surrounding the sump. Soil sample 24-1-1.0 was collected from the impacted soil and analyzed for NWTPH-HCID with quantification, PCBs, HVOCs, and leachable cadmium, chromium, and lead to characterize the contamination and evaluate disposal options. Approximately 170 tons of diesel impacted soil were removed from Area 24 for off-site disposal. Groundwater was not observed in the excavation. Confirmation samples 24-2-10.0 through 24-8-11.0 were collected from the excavation and analyzed for NWTPH-Dx. In addition, soil sample 24-5-11.0 was analyzed for PAHs. Figure 5 shows the location of the samples and the extent of contaminated soil removed from Area 24. Diesel and heavy oils were detected in soil sample 24-1-1.0 at concentrations of 328 mg/kg and 1,300 mg/kg, respectively (Table 3). No PCBs, HVOCs, or leachable metals were detected in this sample. Soil in the vicinity of sample 24-1-1.0 was removed during excavation and disposed of off- site. Diesel and heavy oils were detected in sample 24-5-11.0 at concentrations of 416 mg/kg and 2,200 mg/kg, respectively. This is the only confirmation sample with concentrations of diesel and heavy oils that exceed the 500 mg/kg soil matrix cleanup level. No PAHs w~ere detected in sample 24-5-11.0. UST-14 On July 1, 1999, a 250-gallon UST (labeled UST-14) was encountered approximately three feet below street grade in the northern portion of the Courthouse Square property. After the UST was removed, soil sample UST14-1-7.0 was collected from approximately six-inches beneath the tank and analyzed for NWTPH-HCID (see Figure 5 and Table 4). No visual or olfactory evidence of contamination was noted in the soil surrounding the UST. Groundwater was not observed in the excavation. Figure 5 shows the location of the former UST and the soil sample. No petroleum hydrocarbons were detected in soil sample UST-14 (Table 4). Construction Phase - Remedial Actions - 1 I- 4080600127 Courthouse Square November 9, 1999