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Atlantic Richfield Company Page 7 ARCO Station No 4932 Stockton California August 29 2002 3.0 SUMMARY OF CURRENT ACTIVITIES Elevated concentrations of MtBE in wells MW-4, MW-6, SVE-1, and EW-1 led the SJCEHD to the conclusion stated in their February 14, 2002, letter(Appendix A) that "Interim remediation begin Immediately, and must be extended to include all known areas of the plume with contaminant concentrations greaten than 10,000 ug/U' The SJCEHD requested that additional site assessment be performed to delineate the vertical and downgradient extent of the plume as well as Install an extraction well to aid in interim remediation by groundwater batch extraction SECOR submitted a Response to SJCPHS Letter Dated December 7, 2001 and Work Plan for Additional Site Assessment and Feasibility Testing dated January 15, 2002, and an Addendum to Work Plan for Additional Site Assessment and Remedial System Feasibility Testing dated March 11, 2002, which was approved by the SJCEHD in their February 14, 2002 letter and March 13, 2002 letter, respectively (Appendix A) Discussion of the Installation and advancement of one extraction well (EW-2), two monitoring wells (MW-10 and MW-11), and two deep monitoring wells (DMW-2 and DMW-3) is included in the following section Extraction well (EW-2) and monitoring wells (MW-10, MW-11, DMW-2, and DMW-3) were installed on June 10 through 13, 2002 Quarterly monitoring and sampling of the existing well network continues to be implemented at the site Wells are sampled and analyzed for the presence of TPHg, BTEX, MtBE and other fuel oxygenates by EPA Method 8260 Fuel oxygenate data is presented in Table 5 3.1 Additional Site Assessment On June 10 through 13, 2002, SECOR performed additional subsurface assessment activities at the site The findings of this Investigation are discussed in the following sections 3.1.1 Description of Site Assessment Activities On June 10 through 13, 2002, two monitoring wells (MW-10 and MW-11), two deep monitoring wells (DMW-2 and DMW-3), and one extraction well (EW-2) were installed at the site by West Hazmat (Figure 2) Monitoring wells MW-10 and MW-11 were completed at 40 feet bgs, and were Installed with a 2-inch PVC well casing screened from 20 to 40 feet bgs These wells are located off-site to the north, MW-10 is in an alley off El Dorado Street and MW-11 is on the corner of El Dorado Street and Sperry Avenue Deep monitoring wells (DMW-2 and DMW-3) were completed at 82 feet bgs, and were installed with a 2-inch PVC well casing screened from 77 to 82 feet bgs Extraction well (EW-2) was completed at 43 feet bgs, and was Installed with a 6-Inch PVC well casing with a stainless steel wire-wrap screen extending from 20 to 40 feet bgs Wells DMW-2,DMW-3, and EW-2 are located off- site north across E Harding Way from the site Boring logs showing well construction details for wells MW-10, MW-11,DMW-2, DMW-3, and EW-2 are Included in Appendix B Field and laboratory procedures are presented as Appendix H I URCOW32TARIPAR doc