ARCHIVED REPORTS XR0001824 - Laserfiche WebLink

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September 30, 1999 47491 1 Harding Lawson Associates Margaret Lagono, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 4 activities The analytical results indicated that for both sampling events none of the analytes were detected above their respective reporting limits This provided an additional confirmation that the remaining impacted ' soils did not pose a threat to groundwater quality at this Iocation Based on the analytical results and the observations made in the field, and the quarterly monitoring results, HLA concluded that the soils remaining in place adjacent to the former UST sidewali do not pose a threat to groundwater quality and do not require any ' additional sampling or investigation (HLA, 1998b) As discussed further below, two additional quarterly monitoring events performed during 1999, further support this conclusion REQUESTED ADDITIONAL CLOSURE INFORMATION This section presents the additional information required for closure that was requested in the PHS/EHD letter dated February 25, 1999 Compilation of Monitoring Well Data ' Groundwater monitoring has been performed for Newark by several different contractors at four monitoring wells located adjacent to the former location of the 210,000-gallon UST The RWQCB required installation M and sampling of these four wells to obtain a variance (Title 23, Chapter 3, Subchapter 16, Article 4, Section 2641, Alternative Number 2) from required vadose zone monitoring for the UST After acquiring all the data available at the Newark facility,HLA contacted PHS/EHD to see if their files included additional data Additional data are apparently not available at PHS/EHD ' As requested b the PHS/EHD, HLA has reviewed available documents and has compiled a table of existing �1 Y groundwater elevations, depths to groundwater, and groundwater sample analytical results Groundwater monitoring reports for wells MW-1 through MW-4 were reviewed and data were compiled into the summary table attached to this report (Table 1) Table 1 is organized with all results for well MW-1 on pages 1 and 2, all well MW-2 results on pages 3 and 4, and so on With the exception discussed below, none of the analytes tested for have been detected above the respective method reporting limits The exception occurred in June 1993 when TRPH was detected near method reporting limits at concentrations of 0 9 mg/I, I I mg/l, and 0 9 mg/l in wells MW-I, MW-2, and MW-3, respectively In approximately February 1993,the UST was inadvertently overfilled by the fuel supplier, and heavy rams occurred during late winter and early spring After Newark communicated this information to the RWQCB in ' their August 6, 1993 letter, the wells were resamplcd and TRPH was not detected in any of the wells during following two sampling events performed in August 1993 and January 1994 Only one additional detection (also near the reporting limit) of TRPH has ever occurred, this was 0 7 mg/l from well MW-1 during April I 1994 sampling event TRPH(and subsequently TPHd) has not been reported in any of the monitoring wells in any of the following years of monitoring In addition, none of the other EPA 61018310/8270 analytes were detected above normal reporting limits in any of the samples from any of the wells This includes the third and ' fourth quarter 1998 and first and second quarter 1999 monitoring events performed after the completion of UST removal activities These data strongly support the conclusions of the HLA reports (HLA 1988b and • 1998c)cited above,that the remaining impacted soils do not pose a threat to groundwater quality I