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I Ms. Margaret Lagorio, SJCEHD January 5,2005 Work Plan for Additional Site Assessment and Project No. 2033-15600-01 Evaluation of Remedial Alternatives Joe's Truck Plaza,Lathrop,California Page 4 In Sand A, TPHG and MTBE are currently reported (third quarter 2004) in wells MW-2 and MW-3. MTBE is also reported in wells MW-7 and MWO-2. MTBE impact east and northeast of the site has not been fully characterized in Sand A. The lateral extent of dissolved MTBE impact is shown on Figure 4. i One well (MWO-1X) is currently screened in the depth range of Sand B. TPHG and MTBE are currently reported in this well. MTBE was also reported in grab samples collected in Sand B at CPT-8, but was not reported in samples collected within Sand B at CPT-5. TPHG or other fuel oxygenates (including MTBE) were not reported in grab samples collected within Sand C at any of the CPT locations. PROPOSED SCOPE OF WORK i To address the concerns outlined in SJCEHD's letter of November 10, 2004, to further characterize the lateral extent of dissolved MTBE impact in Sands A and B, and to move the project toward implementation of active remediation, Stratus proposes to: i • Install two additional off-site groundwater monitoring wells (MW-9 and MW-11), screened within Sand A, at the locations of CPT-5 and CPT-8. • Install one additional on-site monitoring well (MW-10), screened within Sand A, south of well MW-3. I • Install one off-site well (MW-8), screened within Sand B, at the location of CPT-8. • Evaluate remedial options, including C-Sparge ozone injection, batch extraction of groundwater, DPE, and air sparging (AS). The proposed scope of work presented above has been subdivided into tasks 1 throughh 5. All geologic work will be conducted under the supervision of a State of California Registered Geologist or Registered Engineer, and will be conducted in accordance with standards established by Appendix A-Reports, Tri-Regional Board Staff Recommendation for Preliminary Investigations and Evaluation of Underground Tank Sites (April 2004) and SJCEHD guidelines. Additional information regarding Stratus' field practices and 1 procedures is presented in Appendix A. Task 1: Pre-Field Activities Following approval of this work plan by SJCEHD, the following activities will be implemented: • Secure an access agreement and an encroachment permit for installation of j off-site wells. K:Uoe's Truck Plaza\Work PlansUoes workplan 010505.doc 1