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URS tMs Margaret Lagorio, Supervising REHS Page 5 of 7 • San Joaquin County Environmental Health Department February 16, 2005 8260B (preparation EPA Method 5030), and total lead by EPA Method 6000/7000 series Analytical results from this sample are included in Table 1 On December 31, 2004, Dillard Environmental Services picked up waste drums from the site Soil cuttings were transported to Republic Services Vasco Road, LLC, in Livermore, California Drilling equipment decontamination water was transported to the Instrat Inc disposal facility in Rio Vista, California Both soil cuttings and decontamination water were disposed of as non-hazardous waste Disposal documentation is included as Attachment F CONCLUSIONS AND RECOMMENDATIONS Petroleum hydrocarbons were reported as below laboratory detection limits for all off-site and on-site soil and grab groundwater samples collected In addition,petroleum hydrocarbons were reported as below laboratory detection limits in groundwater samples collected from off-site well MW4 Relatively low concentrations of petroleum hydrocarbons were reported in groundwater samples collected from deep on-site monitoring well MW-5 URS will add the groundwater monitoring well MW-5 to the quarterly groundwater monitoring program for a minimum of one year to determine whether further investigation and/or additional remedial action will be necessary This subsurface investigation, conducted in November and December 2004, concludes our efforts to 1 assess the vertical and lateral extent of 1,2-DCA-impacted groundwater beneath the site, as requested by the SJCEHD Groundwater grab samples collected from boring B-28, southwest of the site, and from the two newly installed groundwater monitoring wells (MW-4 and MW-5) reported no detectable concentrations of 1,2-DCA These data, combined with data collected in March 2004, define the lateral and vertical extent of 1,2-DCA to the area of the site property and slightly off-site, to the southwest, as reported in samples collected from boring B-25 and monitoring wells MW-1, MW-2, and MW-3 Definition of the plume is as follows • Laterally defined to the north by boring B-26 dnlled in March, 2004, • Laterally defined to the south by boring B-27 drilled in March 2004, • Laterally defined to the west by boring B-28 drilled in November 2004, • Laterally defined to the east by monitoring well MW-4 sampled in December 2004, and • Vertically defined by on-site deep monitoring well MW-5, which is screened from 99 to 104 feet bgs Lateral and vertical definition of the 1,2-DCA-impacted groundwater is shown on Figures 2 and 3 URS recommends that this site be considered a low risk groundwater case and be closed by the SJCEHD URS will continue quarterly groundwater monitoring until closure is granted i 0 K 1Wprocessl15 BP ARCO\0076012004 Asscssment1760 additional assessment report 04 doc