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` US Ms Margaret Lagorio Page 2 i San Joaquin County Environmental Health Department ARCO 760 February 15, 2006 depth-discrete soil and grab groundwater samples were collected to assess the western and southern lateral extent of 1,2-DCA in groundwater beneath the site Analytical data from the March 2004 investigation determined that the western extent of 1,2-DCA-impacted groundwater was not yet defined and that more sampling would be required during the second phase of the assessment In addition, in its letter dated October 14, 2004, SJCEHD reaffirmed its interest in defining/monitoring the eastern extent of impacted groundwater between the site and City of Lodi municipal well #1R (812 feet east of the site) Between November 20, 2004, and November 30, 2004, URS conducted the following field activities as part of phase II of the assessment r • One vertical soil boring (B-28) was advanced to first encountered groundwater on the northern side of Lodi Avenue, approximately 180 feet west of the site, and depth-discrete soil samples and a grab groundwater sample were collected to define the western extent of 1,2-DCA-impacted groundwater • One vertical soil boring was advanced to 70 feet bgs on the eastern side of S Cherokee Lane, and a 2-inch diameter monitoring well (MW4) was installed to monitor the eastern extent of impacted groundwater between the site and the City of Lodi municipal well ��. C One vertical soil boring was advanced to 105 feet bgs onsite and a 2-inch diameter deep groundwater monitonng well (MW-5) was installed in the area reporting the highest 1,2- DCA concentration to assess the vertical extent of impacted groundwater The Phase 11 did not identify any petroleum contamination in the soil samples, grab groundwater sample, or the groundwater sample from MW4 The groundwater- sample collected from MW-5 only r identified toluene (0 55p.g/L) and total xylenes (0 84 j,g1L) at or above the method detection limits This investigation resulted in establishment of vertical and horizontal extent of contamination at this site Quarterly groundwater sampling has occurred at the site from October 2002 to present The sampling results are presented in Tables 1 and 2 Site Geology and Hydrogeology Soil encountered during these activities consisted of sand, silty sand, sandy silt, and silt Boring logs, are presented in Attachment D A geologic cross-section is presented in Attachment E Based on quarterly water-level measurements from October 2002 through October 2005, the inferred groundwater flow direction is generally to the south at a gradient of 0 001 to 0 06 feet/foot Groundwater gradients and flow directions are summarized in Table 3 Contarmnant Mass Remaining and distribution �i K 1WprocessV5 BP ARCO\007601Closure Rpt1760 Closure Report doc