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Nftw-1 r,/ TETRA TECH, INC. 1.0 INTRODUCTION Tetra Tech, Inc. (Tetra Tech) will provide project management and technical environmental services in support of a groundwater sampling effort at Tracy Mansfield Property (also referred to herein as the "Site")under contract with LDK Ventures,LLC. 1.1 PURPOSE OF THE PLAN The purpose of the Work Plan is to detail the field effort that will be conducted in order to evaluate the rate of natural attenuation of contaminants of concern(COCl)in groundwater and soil at the Site, and the potential presence of COCs in soil gas. 1.2 PROPERTY DESCRIPTION The Site is contained within one(1)parcel,Assessor's Parcel Number 209-27-030, in Tracy, San Joaquin County, California, 95304. A San Joaquin County Assessor's map, taken from that agency's website, is provided below as Figure I-1. 1.3 SITE HISTORY AND PREVIOUS INVESTIGATIONS Chevron's former Old Valley Pipeline (OVP) was located in a right-of-way (ROW) along the southern edge of the Site. The former OVP transported heavy petroleum (crude and fuel oil) from Bakersfield to Richmond, California, from the early 1900s to the 1950s. Leaks from the OVP have impacted the subsurface soil. Geomatrix Consultants(Geomatrix)conducted a soil and groundwater investigation of the OVP on behalf of Chevron(Geomatrix 1999a). In this investigation,Geomatrix advanced 16 soil borings in the southern portion of the Site along the former OVP location,and collected 14 soil samples(at depths ranging from 5 to 16.5 feet below ground surface [bgs]) and six groundwater samples. Soil samples were analyzed for the following contaminants of concern (COCs): total petroleum hydrocarbons as crude oil (TPH-c), benzene, toluene, ethylbenzene, and xylenes (BTEX), and polynuclear aromatic hydrocarbons (PAHs). Groundwater samples were analyzed for the following COCs: TPH as gasoline (TPH-G), TPH as diesel (TPH-D),BTEX,and PAHs. TPH-c was detected in four soil samples, with a maximum concentration of 20,000 milligrams per kilogram (mg/kg). PAHs and BTEX were below residential screening levels. TPH-G and TPH-D were detected in one groundwater sample at maximum concentrations of 660 and 700 micrograms per liter (pg/L), respectively. PAHs and BTEX were below screening levels. Geomatrix concluded, "These data indicate that future use of the site for residential purposes should not be restricted due to the presence of residual petroleum hydrocarbons along the ROW." Geomatrix also prepared a Site Soil Management Plan for Chevron,which stated that the if the Site owner encounters oil-affected soil during excavation,Chevron should be notified and the oil-affected soil should be identified, segregated, and stockpiled on-Site. Chevron will consult with the appropriate party to evaluate the final soil disposition or reuse options and will inform the San Joaquin County Public Health Services—Environmental Health Division of the status(Geomatrix 1999b). 1.4 SUMMARY OF PLANNED ACTIVITIES In order to evaluate the rate of natural attenuation of COCs in groundwater and soil at the Site, and the potential presence of COCs in soil gas, six borings will be drilled until groundwater is reached, and Sampling Effort Work Plan Page 1-1 Tracy Mansfield Property