ARCHIVED REPORTS XR0001826 - Laserfiche WebLink

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December 22, 1998 Harding Lawson Associates 4034405 Margaret Lagorio, Supervising RENS San Joaquin County Public Health Services Environmental Health Division Page 10 sample from SB-1 did not contain detectable TPHd or BTEX, the presence of 1 8 mg/l of TPHd in the Hydropunch sample collected from the screened-interval depth of 21 5 to 24 feet bgs is somewhat enigmatic In addition, the Hydropunch sample was collected from boring SB-1 in which impacted soils were exposed in the borehole from near the ground surface to depths of at least 15 feet bgs After encountering groundwater in the 20 foot sample from boring S13-1, static water level rose to approximately 16 feet bgs Because solid-flight augers were used, the augers were pulled to pound the 20-foot soil sample and then the Hydropunch sample Pulling the augers is likely to have resulted in impacted soils falling into the boring and contaminating the groundwater in the borehole The potential exists for down- hole contamination of the Hydropunch sample by contaminated bore hole water derived from shallower depths These conditions suggest that the results are suspect and do not in fact reflect formational waters This is corroborated by the soluble analyses which indicated that impacted soils (maximum detected concentrations) do not contain detectable concentrations of soluble TPHd, TPHmo, or BTEX ' Another objective of the investigation was to assess the feasibility of insitu passive bioremediation of impacted soils As discussed above, the results of feasibility studies indicate that a subpopulation of microorganism capable of degrading petroleum hydrocarbons is present in soils at the site and that this ' population is within the range acceptable for biological degradation of TPH as a viable remedial alternative One of the criteria for no further action on low risk sites is that the Site must not pose a significant risk to human health or safety (RWQCB, 1996) As discussed above a RBCA assessment of the Site consisting of a Tier 1 evaluation performed in accordance with ASTM-E 1739-95 (ASTM, 1995), indicates that the Site does not pose a significant risk to human health or safety CONCLUSIONS Based on the results of previous investigations, the data collected during this investigation, and the information discussed above, HLA makes the following conclusions • Potential leaks have been eliminated by closure activities which removed all former product, cleaned and backfilled the USTs/sump with concrete • The lateral extent of the impacted soil associated with the courtyard USTs/sump location has been determined • The vertical extent of impacted soil has been determined and does not extend to depths of 20 feet bgs at the source • The areal extent of impacted soil is less than 700 square feet ' • The Hydropunch groundwater data aie suspect and groundwater is not likely to be impacted based on the available data • The lack of detectable benzene in all soil samples collected to date and the lack of detectable PAHs in the soil with the maximum TPH concentrations indicates that the remaining impacted soils do not contain the CDCs associated with # six fuel that would typically pose a potential threat to health or safety • The soluble data from the courtyard samples and the additional soluble data from the six UST- removal samples indicate that the impacted soils remaining on site do not pose a threat to . groundwater quality • Z he RBCA assessment shows that the Site does not pose a threat to human health or safety 0