ARCHIVED REPORTS XR0000257 - Laserfiche WebLink

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Project No S8100-06-IIA June 29, 1995 Benzene, toluene, ethylbenzene, and total xylenes (BTEX) exist in capillary fringe soil beneath ' the former fuel USTs location with concentrations in VW-1 at 0 13 mg/kg benzene, 0 061 mg/kg toluene, and 0 034 mg/kg total xylenes ' The low concentrations of TPHg in vadose zone soils in SB-1, SB-2, MW-1, MW-2, MW-3 and VW-1 that surround the former USTs location, combined with the existence of TPHg impacted groundwater beneath the former USTs indicate that a vadose zone soil plume exits beneath the former USTs • The vadose zone soil plume bounded by SB-1, SB-2, MW-1, MW-2, MW-3, and VW-1 has an ' approximate volume of 350 cubic yards, however, the location of the central portion of the soil plume has not been identified Consequently,the concentration of impacted soil and the resulting mass of TPHd and TPHg cannot be estimated ' A minimum of one additional soil boring would be required within the former UST excavation in order to attempt to better estimate the location and volume of the central portion of vadose zone soil impacted with TPHg ' Initial evaluation of soil remediation options indicates that soil vapor extraction is the most cost effective soil remediation technology available to reduce the mass of TPHg in vadose zone and capillary fringe soil • Groundwater exits beneath the project boundaries at a depth of approximately 19 5 meters (64 ' feet) bgs with a general flow direction trending from southeast to northwest at a gradient of 0 0002 to 0 001 ' Groundwater quality data indicates that dissolved TPHd, TPHg and benzene exist beneath the site at maximum reported concentrations of 600 micrograms per liter (ug/L) TPHd, 28,000 ug/L TPHg, and 5,300 ug/L benzene • Benzene concentrations in groundwater are in excess of the California Maximum Contaminant Level (MCL) of 1 0 ug/L The lateral limits of TPHg in groundwater have not been established to allow for the implementation of a groundwater remedial action plan • Additional investigation would be required to further delineate the extent of TPHg impacts in groundwater The installation of four additional groundwater monitoring wells is recommended to attempt to establish the lateral extent of TPHg groundwater impacts • Initial evaluation of groundwater remediation options indicates that several feasible alternatives exist to facilitate groundwater restoration Site specific data collected to date indicates that groundwater extraction and treatment (pump and treat), in-situ bioremediation and air sparging remain as feasible groundwater remediation alternatives