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1 <br /> Geomatrix <br /> • accordance with EHD and State of California well destruction requirements after <br />' site closure <br /> 9 Groundwater Level Data. Measured water level data and calculated groundwater <br />' elevations through second quarter 2006 are provided in Table 1 <br /> 10 Groundwater Analytical Data. Analytical results of groundwater samples <br />' collected from the Site are summarized in Table 2 Time concentration plots of <br /> groundwater analytical data are included on Figures 5, 6, and 7 <br />' 11 Concentration Trends. The concentration trends for benzene, toluene, <br /> ethylbenzene, and xylenes (BTEX) and TPHg in groundwater samples collected <br /> from the monitoring wells at the Site are provided on Figures 5, 6, and 7 These <br />' data indicate stable concentration trends and no apparent upward trends <br /> Concentrations of BTEX and/or TPHg exceeding the water quality objectives <br /> (WQOs) (Table 1 of the TRR [CVRWQCB, 2004]) are reported in the groundwater <br />' samples collected from four of six existing on-site monitoring wells MW3-1, <br /> MW3-2, MW3-3, and MW3-6 <br />' 12 Extent of Residual Petroleum Hydrocarbons in Soil and Groundwater. The <br /> lateral and vertical extent of TPHg in soil is illustrated on Figures 8, 9, and 10 The <br /> lateral and vertical extent of TPHg in groundwater 1s illustrated on Figures 2, 11, <br /> lieand 12 <br /> 13 Remediation. Source removal was conducted in 1988 when approximately <br />' 180 cubic yards of affected soil were excavated from the Site following removal of <br /> the former USTs <br />' 14 Best Available Technologies. The residual petroleum hydrocarbons remaining at <br /> the Site primarily are trapped within the fine-grained sediments in the saturated <br /> zone Several remedial technologies were evaluated for the Site (Geomatnx, 2003) <br />' • Oxygen Release Compound could be injected to enhance in situ aerobic <br /> biodegradation of residual petroleum hydrocarbons in the saturated zone <br />' Liquid oxidants also could be infected to oxidize residual petroleum <br /> hydrocarbons in the saturated zone However,because of the fine-grained <br /> sediments and the naturally-reducing conditions in the saturated zone at the Site, <br />' densely-spaced infection points and numerous applications of chemicals would <br /> be necessary These Site conditions would make remedial technologies that <br /> involve infection of liquid chemicals costly <br /> • The effectiveness of air spargxng to strip the volatile organic compounds <br /> (VOCs) or infection of gaseous-phase chemicals to oxidize the residual <br /> petroleum hydrocarbons in the saturated zone would be hindered by the fine- <br /> grained sediments at the Site In addition, the layer of fine-grained sediments <br /> could potentially promote the vapor-containing VOCs to migrate laterally <br />' beneath the layer as a result of air sparging or gas injection The uncertainty in <br />' 116000s16437 0001Archrve16437 041 doe 3 <br />