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PARSONS 100 West Walnut Street•Pasadena,CA 91124•(626)440-2000•Fax:(626)440-2630•w .parsons.wm February 11, 2011 z9 9 Mr. Mike Inf irna / San Joaquin Coutny Environmental Health Department(EHD) 600 E. Main Street, Stockton, CA 95202 (209) 468-3420 (209)464-0138 (FAX) RE: Geotechnical and Environmental Investigation for Further Delineation of Remedial Areas of Impact Prior to Excavation Former Tracy Manufactured Gas Plant Site,Tracy, CA PROJECT UNDERSTANDING Based on the data generated during the RI, impacted soil and soil gas with concentrations above human health screening criteria were identified at the Site. Additionally, low level impacts were also identified in groundwater. The Draft Final HRA/RAW (approval email attached) addresses remedial activities that will restore, to the extent practicable,the Site to background conditions such that potential future residents who might be living at the Site would have no significant incremental risk above background from exposure to PAHs. Based on a Site walk conducted in mid-October with Mr. Rudy Millan(PG&E) and Pivox, supplemental environmental and geotechnical information was discussed that would be beneficial in developing the shoring design and further delineating remedial areas of impact outlined in the Draft Final HRA/RAW(excavation). Implementation of Supplemental Geotechnical and Environmental Borings Based on the Site walk previously referenced, there are six areas of impact(AOI-1 through AOI-6) that will benefit from further delineation; thus, reducing the future cost of remediation. In addition, two areas of impact (AOI-3 and AOI-4) require a geotechnical investigation to develop the necessary information to design the appropriate shoring approach for implementation of the RAW. Boring locations are presented on the attached figure. The following general procedures will be implemented at the Site to facilitate this scope of work: • Obtain boring permits from the San Joaquin County Environmental Health Division; • Notify Underground Service Alert a minimum of 48-hours in advance of invasive operations;