Remedial Action Report Construction Phase

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to extend off-site. Field observations and analytical results for the Area 6 soil samples collected during construction activities indicated that the gasoline impacted soil extended further north than previously estimated. Although remedial excavation was completed in this area, the presence of the sidewalk limited access for further removal of contaminated soil. The total estimated volume of gasoline impacted soil left in place with concentrations above the 80 mg/kg matrix cleanup level is 250 cubic yards. Figure 8 shows the estimated lateral extent of Area 6 impacted soil left in place. In the northern portion, the estimated vertical extent of impacted soil left in place is limited to a two-foot thick layer of soil located between 16 and 18 feet below street grade. In the southern portion, the estimated vertical extent of impacted soil left~in place is limited to a four-foot thick layer of soil located between 14 and 20 feet below street grade. A comparison between the BTEX concentrations detected in the Area 6 samples and the applicable RBCA Tier I RBSLs indicates that the impacted soil left in place does not pose a threat to human health or the environment. 6.1.3 Area 9 Based on field observations and the analytical results for the Area 9 soil samples, the estimated volume of diesel impacted soil left in place with concentrations above the 500 mg/kg matrix cleanup level is 5 cubic yards. Figure 9 shows the estimated lateral extent of Area 9 impacted soil left in place. The estimated vertical extent of impacted soil left in place is limited to two-foot thick layer of soil located between 10 and 12 feet below street grade. A comparison between the PAH concentrations detected in the Area 9 samples and the applicable RBCA Tier I RBSLs indicates that the impacted soil left in place does not pose a threat to human health or the environment. 6.1.4 Area 18 Based on field observations and the analytical results for the Area 18 soil samples, the estimated volume of diesel impacted soil left in place with concentrations above the 500 mg/kg matrix cleanup level is 25 cubic yards. Figure 6 shows the estimated lateral extent of Area 18 impacted soil left in place. The estimated vertical extent of impacted soil left in place is limited to three-foot thick layer of soil located between 14 and 17 feet below street grade. A comparison between the PAH concentrations detected in the Area 18 samples and the applicable RBCA Tier I RBSLs indicate that the impacted soil left in place does not pose a threat to human health or the environment. Construction Phase - Remedial Actions - 22 - 4080600127 Courthouse Square November 9. 1999