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6.1.5 Area 22 <br />Based on field observations and the analytical results for the Area 22 soil samples, the estimated <br />volume of gasoline impacted soil left in place with concentrations above the 80 mg/kg matrix <br />cleanup level is 100 cubic yards. Figure 6 shows the estimated lateral extent of Area 22 impacted <br />soil left in place. The estimated vertical extent of impacted soil left in place is limited to a three-foot <br />thick layer of soil located between 15 and 18 feet below street grade. <br />A comparison between the BTEX concentrations detected in the Area 22 samples and the applicable <br />RBCA Tier I RBSLs indicates that the impacted soil left in place does not pose a threat to human <br />health or the environment. <br />6.2 Groundwater <br />During the construction phase, water samples were collected in the vicinity of Remediated Areas 2, <br />6, 18, 19, 22, and 23. Diesel was detected in water samples collected from Areas 6 and 22. <br />Although Sumps 2 and 6 were installed to dewater Area 22 excavations, the detection of diesel in <br />the water samples collected from these sumps is attributed to the UST-9 release since Area 22 is <br />associated with a gasoline source not a diesel source. <br />The maximum concentration of diesel detected in the Area 22 water samples (representative of Area <br />18) was 0.59 mg/L. However, after seven days of groundwater pumping in Area 22, concentrations <br />of diesel decreased to non-detectable levels. All other water samples collected from the Remediated <br />Areas had concentrations of diesel below the DEQ preliminary screening level of 0.5 mg/L. <br />BTEX was detected in the water samples collected in the vicinity of Areas 2, 6, 19, 22, and 23 at <br />concentrations significantly below the applicable RBCA Tier I RBSLs. <br />Cons[ruction Phase - Remedial Actions - 23 - 4080600127 <br />Courthouse Squaze November 9. 1999 <br />