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To date, active groundwater remediation has not been pursued at the site. Due to the general <br />poor quality of groundwater in the area, the shallow aquifer beneath the site is not considered, <br />a viable water supply. This was confirmed by Mr. Elmer 'Fowler of Cal Water Service. <br />1 <br />Biophysical laboratory results suggest that natural degradation of petroleum hydrocarbons in the <br />subsurface is occurring. This is supported by the apparent decrease in concentration of <br />petroleum hydrocarbons in the former tank pit area from 12,000 ppb TPHG in September 1995 <br />(Hydropunch sample from SB1) to 5,500 ppb TPHG in June 1996 (Hydropunch sample from <br />. SB8). Although the reproducability of Hydropunch sampless somewhat questionable, these two <br />samples were collected from approximately the same location (within approximately 6 feet) from <br />the uppermost water bearing zone. Further, Hydropunch samples generally represent a worst- <br />case scenario of groundwater contamination because they are discrete samples that do not allow <br />any purge volume of groundwater prior to sampling and are subject to contaminants introduced <br />by soil disturbance. <br />y <br />Ground Zero proposes passive groundwater remediation to 'mitigate groundwater contamination <br />{ beneath the site. <br />4.0 EXISTING CONDITIONS <br />4.1 Soil <br />The site is currently an undeveloped parcel. Soils beneath the site are fine grained, consisting <br />3 � l <br />of clays, silts, and poorly graded sands. No residual soil contamination remains in the <br />I <br />a unsaturated zone. The lateral and vertical extent of saturated soil contamination has been <br />defined. The impacted soil in the saturated zone is limited to a relative small area in the vicinity <br />of the former tanks (near SB1 and SB8) between the depths of approximately 20 to 35 feet bgs. <br />A stratigraphic cross section is shown on Figure 4. <br />1 groundzeVanuioklosure 9 <br />i <br />