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2101 Webster Street 12th Floor Oakland, CA 94612 G�OMATRIX C5107 663-4100 • FAX C5101 663-4141 September 9, 1999 Project 5650 F Eu` FE: E Mr. Michael J. Infama SEP 0 9 1999 San Joaquin County Public Health Services 304 East Weber Avenue, Third Floor ENVIRON141EN CAL HEALTH Stockton, CA 95202 PERMIT / SERVICES Subject: Soil and Groundwater Sampling Work Plan Ridgeway-Pombo Property Tracy, California Dear Mr. Infurna: Geomatrix Consultants, Inc. (Geomatrix)has prepared this work plan on behalf of Chevron Environmental Management Company(Chevron) for the investigation of petroleum hydrocarbons in the subsurface at the subject site. This work plan includes collecting additional soil and groundwater data at the Ridgeway-Pombo property located at Corral Hollow and 11th Street in Tracy, California(the "Site") as necessary to conduct a health risk assessment for the Site. The proposed work plan was developed based on the results of an initial investigation conducted at the Site by others. Soil borings advanced as part of the initial investigation indicate that petroleum hydrocarbons are present in site soil. The objective of the work is to confirm that the presence of petroleum hydrocarbons in the subsurface does not pose an unacceptable risk to future commercial, construction and maintenance workers at the Site. The proposed scope of work is described below. On July 29, 1999 Earth Systems Consultants advanced six soil borings along the northern property boundary of the Ridgeway property(EB-1 through EB-6) and four along the northern property boundary of the Pombo property (EB-7 through EB-10). Petroleum hydrocarbon- affected soil was observed in four of these borings (EB-2, EB-3, EB-7, and EB-9; Figure 2). Geomatrix will contract with Precision Sampling, Inc. to advance approximately 15 soil borings in the vicinity of borings EB-2, EB-3, EB-7, and EB-9 to assess the lateral and vertical extent of petroleum hydrocarbon-affected soil. Prior to field activities, Geomatrix will contract a private utility locator to identify potential underground utilities at proposed boring locations, notify Underground Service Alert(USA), and obtain a boring permit from San Joaquin County Public Health Services (SJCPHS). Borings will be advanced using a hydraulically driven, direct push core barrel and drive sampler. Soil recovered from continuous cores will be examined and logged in accordance with the Unified Soil Classification System (USCS) as presented in the American Society of Testing and Materials Standard D2488-90. One soil sample will be collected for chemical analyses from each boring at either the area of soil core most visibly affected with petroleum hydrocarbons, or from just above the groundwater table if petroleum hydrocarbons are not identified visually or through screening using an organic vapor meter. Soil samples will be collected in brass or stainless steel liners, sealed with Teflon Geomatrix Consultants, Inc. Engineers, Geologists, and Environmental Scientists