ARCHIVED REPORTS XR0003979 - Laserfiche WebLink

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' DRAFT 2.2 Problem Assessment ' Between 1987 and 1993, a total of nine soil borings were drilled at the site. Eight of these soil borings were completed as monitoring wells (MW-1 through MW-8); the ninth boring ' was completed as a vadose zone remediation well (RW-1). The locations of all wells are illustrated in Figure 2. A complete history of the soil and groundwater assessment of the site was included in the PAR prepared by GeoAudit. 2.3 Groundwater Monitoring ' Between August 1987 and March 1994, wells at the site have been sampled up to six times. Since 1987, groundwater depth at the site has dropped below the screened interval in MW-2 and MW-3. Table 1 summarizes the analytical results of the groundwater samples. The depth to groundwater has fluctuated by several feet since 1987 due to seasonal variations. Initially, the depth was 50 feet, but fell to more than 60 feet by November 1991. ' Groundwater depths have fluctuated between 55 and 60 feet since 1992. As of March 1994, groundwater remained at a depth of approximately 60 feet. The direction of groundwater flow has changed considerably at this site, but has been consistently southwestward since ' 1993. 2.4 Hydrocarbon Impacted Soil During the assessment, a total of 27 soil samples were analyzed for total petroleum hydrocarbons (TPH as gasoline) and volatile aromatics (BTE&X). Selected samples were ' also analyzed for total lead. The sample depths and analytical results are summarized in Table 2. ' All analyzed samples from MW-1 and RW-1 contained gasoline and BTE&X. No samples from any of the other borings contained TPH. These results indicate that impacted soil is Iimited beneath the former UST, and does not extend far beyond MW-1 (Figures 3 and 4). ' Gasoline and volatile aromatics were detected at moderate to high concentrations at the bottom of vadose zone well RW-1 at a vertical depth of 48 feet. Similar concentrations were detected at 50 feet in MW-1 (near the groundwater interface in 1987), and organic vapor readings taken during drilling of MW-1 suggest that hydrocarbons may extend to the bottom of the well at 70 feet (see Weiss Associates report dated October 16, 1987). Contaminated soil below 50 feet is within the capillary fringe ("smear zone"), and contaminated soil below 60 feet has been within the saturated zone since before investigation began at this site. The zero line of vadose-zone contamination lies between MW-1 and MW-3 on the east and between MW-1 and-MW-4 on the north. Contamination probably extends southward into the alley behind the building, but underground utilities there prevent drilling to delineate the southern limit. Based on data from the other wellsjt appears that gasoline migration .wA rrw17-M.47 � II