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Mr. Russell Chapin <br /> 1766 W. Monte Diablo Avenue <br /> Page 3 of 3 <br /> In QR, your consultant recommended: <br /> • Continued quarterly groundwater monitoring; <br /> • Discontinuation of monitoring for monitored natural attenuation (MNA) <br /> parameters; <br /> • Operation of the existing groundwater extraction and treatment system <br /> with installation of additional groundwater extraction wells; <br /> • Testing dual-phase extraction (DPE) on the site; <br /> • Installation of additional assessment soil borings to sample soil, soil gas <br /> and groundwater along the eastern and southern property boundaries; <br /> and <br /> • Collection of soil vapor samples below the building on your site to evaluate <br /> the risk from vapor intrusion in the building from impacted soil and <br /> groundwater underlying the building. <br /> The EHD approves continuation of the quarterly groundwater monitoring <br /> program, discontinuation of monitoring for MNA parameters, and reinitiating the <br /> groundwater extraction and treatment system. Submit a technical justification for <br /> the additional groundwater extraction wells and a feasibility analysis of DPE so <br /> the EHD can evaluate these proposals. The EHD believes the site can benefit <br /> from additional assessment, but an evaluation of the proposal should be <br /> prepared to demonstrate that the proposed borings along the eastern and <br /> southern property margins are adequate and necessary to address site <br /> conditions and complete the onsite assessment. The EHD approves preparation <br /> of a work plan for assessment of soil gas beneath the building on site. <br /> Please submit your technical justifications, feasibility analyses and work plan(s) <br /> addressing the issues noted above to the EHD by 15 December 2006. Questions <br /> and/or comments may be directed to Nuel Henderson at (209) 468-3436. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> Nuel C. Henderson, Jr., PG Margare Lagorio, REHS <br /> Engineering Geologist Program Coordinator, Unit IV <br /> Unit IV - Site Mitigation <br /> C: Mr. James L.L. Barton — CVRWQCB <br /> Mr. Dennis Parfitt- SWRCB <br /> Mr. William Little - AGE <br /> Supervisor Victor Mow— San Joaquin County Board of Supervisors <br />