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• SOIL GAS SURVEY RESULTS FOR UNOCAL SERVICE STATION 5417 MANTECA, CALFORNIA INTRODUCTION This report presents the results of a soil gas survey completed at UNOCAL Service Station 5417 The soil gas survey was performed by Pacific Environmental Group, Inc (PACIFIC) on September 19, 1997 The work was performed in accordance with a scope of work prepared by Tosco Marketing Company (Tosco), dated August 25, 1997 The purpose of the soil gas survey is to provide baseline data regarding the occurrence of petroleum hydrocarbon vapors in soil near potential source areas at the site referenced above This report presents a discussion of field data collection methods and • analytical procedures, and the survey results The following information is attached to this report, a Field Data Sheet, a Site PIan, a Soil Gas Sampling Analysis Report, and chain-of custody documentation for the soil gas samples FIELD AND LABORATORY PROCEDURES The scope of work included the following procedures (1)perform a presurvey site visit to mark soil gas probe locations for utility clearance, (2) collect organic vapor measurements from beneath product dispensers and within manways for the underground storage tank (UST) turbines, (3) collect soil vapor samples from near USTs, product islands, and product lines, and (4) submit soil gas samples to Sequoia Analytical Laboratories for chemical analyses These procedures are described below in further detail Prefield Preparation Prior to initiating the soil gas survey, PACIFIC personnel performed a site visit to mark proposed probe locations, check accessibility, and to notify the UNOCAL station manager of the proposed survey schedule Probe locations were selected based on PACIFIC's under- standing of underground facilities as shown on the attached Site Plan which was provided by Tosco In some cases probe locations were adjusted in the field to avoid overhead or under- 311163 1A\5417 nder-3111631A15417 I October 29, 1997