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ENV. <br /> A M E R I C A <br /> Mr. Duane White <br /> California Department of Toxic Substances Control <br /> September 24, 2004 <br /> Page 2 of 6 <br /> classified as a low-risk groundwater case based on the remediation activities completed to <br /> date, ongoing Site maintenance, Site conditions, and regional groundwater quality. A <br /> revised groundwater monitoring program is proposed for the Site based on an evaluation <br /> using the Groundwater Monitoring Decision Tree and data collected to date. <br /> LOW-RISK GROUNDWATER CASE <br /> The criteria for determining no further action required (NFAR) for a site classified as a low- <br /> risk groundwater case are described in a document prepared by the Central Valley <br /> Regional Water Quality Control Board (CVRWQCB)2. PG&E has completed substantial <br /> phases of investigation and remediation activities at the Site since 1986. The extensive <br /> data collected to date support the classification of the Site as a low-risk groundwater case. <br /> These reasons are summarized below. <br /> A. The source of COCs to groundwater (i.e., 24,654 tons of affected soil) has been <br /> removed to the extent practicable. <br /> B. Oxygen releasing compound was used to enhance in situ bioremediation of the <br /> residual COCs remaining after soil excavation. <br /> C. The Site has been capped and does not pose significant human health risks. <br /> D. PG&E has a routine cap inspection program to ensure the integrity of the cap is <br /> maintained. <br /> E. PG&E maintains access restrictions for the Site and will maintain a deed <br /> restriction for the site. <br /> F. Groundwater in the area of the Site and most parts of Stockton is not used for <br /> drinking water supply due to seawater intrusion from the west, a groundwater <br /> problem that has been widely documented for this region. Groundwater in this <br /> area has high concentrations of total dissolved solids (TDS) and specific electric <br /> conductance (SEC) due to soluble salts, including chloride. The Drinking Water <br /> Standard for SEC is 900 micromhos per centimeter (Nmhos/cm) (Title 22 <br /> California Code of Regulations, Section 64449). The SEC concentrations <br /> measured in the groundwater monitoring wells at the Site generally range from <br /> more than 900 to as high as 3,000 Nmhos/cm. As a result of the high salt <br /> concentrations, groundwater in this area is not suitable for most agricultural crop <br /> production; and there are no agricultural land uses in the area of the Site. <br /> 2 Appendix A— Reports, Tri-Regional Board Staff Recommendations for Preliminary Investigation and <br /> Evaluation of Underground Storage Tank Sites, prepared by CVRWQCB, April 16, 2004. <br /> C:\Documents and Settings\mjavierlocal Settings\Temporary Internet Fi1es\0LK86\DTSC response Itr Sep2004_revised.doc <br />