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WORKPLAN SUMMARY <br /> Stockton A Substation <br /> Site Visit: September 4, 2007 <br /> Site Description and History <br /> Substation site located on southeast comer of East Church Street and Center <br /> Street in Stockton, CA <br /> • Currently major building structures includes an electric substation building and <br /> communications building on the southwest end of the site and a transfer switch <br /> house on the east side of the site; remainder of site contains electrical equipment <br /> and transformer hoist (and associated tracks), and is largely unpaved (i.e., gravel <br /> base) (Figure 1) <br /> • Identified Key Oil Handling Features: Based on historical PG&E plans and the <br /> site visit, key features include: an existing transformer hoist and associated tracks <br /> to old transformer bank to east, two former mineral oil ASTs, a former <br /> Transformer House, and former/existing underground piping used to transfer <br /> mineral oil (Figure 1) <br /> • Location of PG&E former Stockton manufactured gas plant (MGP); no <br /> information on former MGP structure layout available <br /> Previous Environmental Investigations/Removals <br /> • Remedial Investigation and Risk Assessment conducted in 1993 (CH2M Hill, <br /> 1993) to characterize former MGP site (includes surface soil samples collected in <br /> vicinity of former Transformer House, old transformer banks along tracks, and <br /> former mineral oil ASTs); elevated concentrations of PCBs (up to 81 mg/kg <br /> Aroclor 1254), arsenic (up to 230.9 mg/kg) and lead (up to 409.8 mg/kg) detected <br /> in surface soil adjacent to oil handling features <br /> • Transformer House removed prior to 1950; concrete foundation remains, though <br /> former sumps/access trenches were filled with concrete <br /> • Two former mineral oil ASTs removed in past; underground piping associated <br /> with ASTs and transformer banks may remain <br /> Proposed Sampling Activities <br /> • Collect a total of 36 soil samples from 12 borings drilled to a total depth of 10 feet <br /> bgs. Collect one grab groundwater sample (if encountered). Analyze all samples <br /> for: <br /> o Extractible TPH (Carbon Chain)by EPA Method 8015M <br /> o CAM 17 metals by EPA Method 601013/7470A <br /> o PCBs by EPA Method 8082 <br /> • See Table 1 for detailed soil sampling program and rationale and Figure 1 for <br /> sample locations <br /> Page 1 of 7 <br />