Laserfiche WebLink
1 / <br /> 5.0 EXISTING CONDITIONS <br /> 1 <br /> 1 5.1 Soil Conditions <br /> Soils encountered beneath the site consist primarily of well graded sand and well graded sand with slit <br /> to approximately 40 feet below grade Below 40 feet interbedded lenses of well to poorly graded sand <br /> with silt and clay, and elastic silt and sandy clay are present to 85 feet, the total depth explored <br /> Soil samples have not been collected from the site since October 1993 Confirmation soil boring were <br /> not advanced following soil remediation activities at the site based on the approval of PHS/EHD <br /> Historical analytical results of soil samples indicate that residual petroleum hydrocarbons have been <br /> 1 delineated and are limited to the vicinity of the former gasoline tanks and pump island at depths <br /> between 10 and 45 feet below grade Soil impacted with TPHd remains in place beneath California <br /> Street in the vicinity of the former diesel tank At the direction of PHS/EHD no further investigation <br /> 1 or remedial action is warranted at this location it is estimated that approximately 900 cubic yards of <br /> soil have been impacted by petroleum hydrocarbons but have been remediated by soil vapor extraction <br /> and natural biodegradation The estimated areal extent of residual hydrocarbons prior to remediation is <br />' shown on Figure 6 <br /> 1 5_2 Groundwater Conditions <br /> Shallow groundwater beneath the site is encountered at approximately 68 feet below grade and <br /> PPgenerally flows to the west with a gradient of 0 002 ft/ft, or approximately 11 ft/mile The <br /> groundwater gradient measured on January 9, 1996 is depicted on Figure 3 <br />' Results from the most recent groundwater sampling event indicate that TPHg and BTEX are below <br /> method detection limits in wells MW 1 through MW4 TPHd was detected only in wells MW2 and <br /> MW3 at concentrations lust above the detection limit but were reported as a non-diesel mix These <br /> 1 results are consistent with historical data(Table 2) <br /> 6.0 SPECIFIC INFORMATION FOR CLOSURE REQUEST <br />' 6.1 Introduction <br /> 1 This section provides information specifically required for closure review as per the October 7, <br /> 1993 Addendum to Appendix A of the Tri-Regional Recommendations <br /> 1 6_2 Rationale for Closure <br />' Based on the analytical results of the vapor samples collected from the vapor extraction <br /> system, it appears that TPHg and BTEX in soil have been remediated to concentrations at or <br /> near nondetectable levels Extracted soil vapors have contained concentrations of TPHg and <br /> benzene near or below their respective detection limits during the last six months of system <br /> w 1951411quan1yl4gr-1995 dm 9 <br /> S <br /> • <br /> 1 <br /> SIY�TH <br />