Remedial Action Report Construction Phase

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During the construction phase, additional excavation of contaminated soil was completed east of the pre-construction excavation limits. Approximately 191 tons of contaminated soil were removed from the excavation for off-site disposal. Groundwater was observed in the Area 6 excavation. Soil sample 6-49-16.0 was collected from the excavated soil and analyzed to evaluate disposal options. Confirmation samples 6-50-16.0 through 6-57-16.0 were collected from the completed excavation and analyzed forNWTPH-Gx, NWTPH-Dx, and BTEX. Figure 8 shows the location ofthe samples and the extent of contaminated soil removed from Area 6 during the construction phase. Sump 1 was installed to dewater the southeast portion of the Courthouse Square property, including Area 6. After pumping from the sump for at least 24 hours and allowing groundwater to recharge, seven water samples (labeled Influent and SE-Influent) were collected from Sump 1 between April 14, 1999 through May 19, 1999. The samples were analyzed for NWTPH-Dx and BTEX. Figure 4 shows the location of Sump 1. No diesel or heavy-oil range petroleum hydrocarbons were detected in the confirmation samples. Gasoline was detected at concentrations exceeding the matrix cleanup level of 80 mg/kg in soil samples 6-50-16.0 (480 mg/kg), 6-51-16.0 (230 mg/kg), and 60-52-18.0 (86 mg/kg). However, the BTEX concentrations detected in these samples were below the applicable RBCA Tier I RBSLs (Table 10). Diesel was not detected in any of the water samples collected from Sump 1 except the May 4, 1999 water sample which contained diesel at a concentration of 0.28 mg/L (Table 15). BTEX concentrations detected in the Sump 1 samples were significantly below the applicable RBCA Tier I RBSLs. Area 7 During pre-construction remedial actions, approYimately 15 tons of lube oil range impacted soil was removed from Area 7, located in the southeast corner of the Courthouse Square property (Century West 1998b). During the construction phase, additional excavation of contaminated soil was required in this area due to the unsuitable geotechnical properties of the soil. Approximately 115 tons of contaminated soil was removed for off-site disposal. Soil sample 7-SP-1 was collected from the e~cavated soil pile and analyzed for NWTPH-HCID to evaluate disposal options. Confirmation samples 7-4-12.5 through 7-8-14.5 were collected from the bottom of the excavation and analyzed for NWTPH-HCID and NWTPH-Dx. Figure 8 shows the location of the samples and the extent of contaminated soil removed from Area 7 during the construction phase. No petroleum hydrocarbons were detected in the confirmation samples (Table 11). Construction Phase - Remedial Actions - l7 - 4080600127 Courthouse Square November 9. 1999