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terraphase <br />9r engineering <br />RECEIVED <br />JUL 2 6 2018 <br />July 25, 2018 <br />San Joaquin County <br />Environmental Health Department <br />1868 E. HazeIton Avenue <br />Stockton, CA 95205-6232 <br />ENVIRONMENTAL HEALTH <br />DEPARTNIENT <br />Subject: Work Plan for Additional Environmental Investigation for 371 South Garfield Avenue, <br />Manteca, California <br />Terraphase Engineering Inc. (Terraphase) has prepared this work plan to conduct additional soil gas <br />investigation work ("investigation") at the southern parking lot of Manteca High School, located at 371 <br />South Garfield Avenue in Manteca California (the Subject Property), Figure 1. Terraphase conducted a <br />Phase I Environmental Site Assessment (ESA) in May 2017 of a neighboring property which included <br />testing of soil, groundwater and soil gas in the Manteca High School Parking lot as a Limited Phase II <br />investigation of that property. The results of the limited Phase II investigation identified elevated <br />concentrations of tetrachloroethylene (PCE) in soil gas at approximately 15 feet below ground surface <br />(bgs). The purpose of the proposed additional soil gas sampling is to assess the lateral extent of PCE in <br />the vicinity and to locate its source if possible. <br />Objectives <br />The objectives of this Investigation are: <br />Assess the lateral extend and likely source of PCE in soil gas identified in one location during the <br />limited Phase ll investigation. <br />Obtain analytical laboratory data from soil gas samples of sufficient quality and detection limits <br />to allow comparison to environmental screening levels applicable to the Site. The applicable <br />screening levels for the Subject Property are a) U.S Environmental Protection Agency (EPA) <br />Regional Screening Levels (RSLs) and b) California Department of Toxic Substance Control <br />(DTSC), Human and Ecological Risk Office (HERO) Note 3, for school and residential properties. <br />Assess potential migration of VOCs toward Manteca High School. <br />To achieve these objectives, Terraphase will collect six soil-gas samples within the southern portion of <br />the Manteca High School parking lot from 15 feet bgs. The locations of the soil gas borings are shown <br />on Figure 2. <br />The following sections discuss the detailed scope of work for the proposed Investigation. <br />Terraphase Engineering Inc. 11404 Franklin Street, Suite 6001 Oakland, California 946121www.terraphase.com