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Geomatrix Mr. Dean Hubbard California Regional Water Quality Control Board - Central Valley Region January 30, 2007 Page 2 WORK PLAN Prior to advancing the test trenches and grab groundwater borings,Underground Service Alert(USA) will be notified, the trench and boring locations will be marked and cleared by a private underground utility locator, and appropriate permits and access will be obtained from the City of Tracy and San Joaquin County Public Health Services,Environmental Health Division(SJEHD). Soil Investigation Geomatrix will advance up to 95 test trenches to a depth below visually affected soil to assess the lateral and vertical extent of affected soil(Figure 3). The test trench locations are planned to be advanced on the northern half of the site on 100 foot centers. Geomatrix will contract a California-licensed surveyor to layout the grid and sampling locations. The trenches will be advanced using a standard backhoe, small excavator or equivalent. At each location the lithology will be logged by a Geomatrix field geologist under the supervision of a California Professional Geologist or Engineer. In addition, organic vapor meter(OVM)readings will be obtained at various depths and recorded on trench logs. From each trench location, up to two soil samples will be collected in the upper 10 feet. If affected soil is observed, a sample of affected soil will be collected and one sample below affected.soil will be collected to vertically delineate the impacted soil. If no visually affected soil is identified, soil samples will be collected-at 5 and 10 feet bgs. Soil samples will be collected in stainless steel soil tubes, or equivalent, sealed with Teflon sheets, end caps, and silicon tape. Soil samples will be analyzed for TPHd and TPHmo using EPA Method 8015M, and PAHs using EPA Method 8270 with a selective ion monitoring system (SIM). Several soil samples may be analyzed for Title 22 Metals (using EPA Method 6020) depending on the trench location. Due to matrix interference in soil samples collected during the previous Geomatrix investigations, PAH reporting limits were raised above typical risk- based screening levels (RBSLs). Geomatrix will communicate with the laboratory ahead of the investigation to discuss the need for reporting limits below RBSLs. Additional steps may be taken at the laboratory to remove matrix interference (sample cleanup using silica gel, alumina, or equivalent)to improve PAH reporting limits. All trenches will be backfilled in lifts and bucket compacted using the original soil from the trench.