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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 <br /> C510) 663-4100 • FAX (510) 663-4141 GEOMATRIX <br /> September 12,2002 <br /> Project 7243.008.3 <br /> Ms. Penny Fottrell <br /> Chevron Environmental Management Company <br /> P.O. Box 6012 <br /> San Ramon, CA 94583-0712 <br /> Subject; Work Plan for Soil and Groundwater Investigation <br /> Mountain House Site 3 <br /> Mountain House, California <br /> Dear Ms. Fottrell: <br /> Geomatrix Consultants,Inc. (Geomatrix),has prepared this work plan on behalf of Chevron <br /> Environmental Management Company.(ChevronTexaco) for the area designated by Geomatrix as <br /> "Site 3"in Mountain House, California(Figure 1). The purpose of the work proposed herein is to <br /> further investigate the nature and extent ofpetroleum hydrocarbon constituents detected in site <br /> soil during previous investigations conducted by Condor Earth Technologies Inc., (Condor)and to <br /> collect additional data needed to perform a human.health risk assessment. This work plan in- <br /> cludes the collection of soil and grab groundwater samples. A brief description.of the site back- <br /> ground and the proposed work plan are presented below. <br /> SITE BACKGROUND <br /> On behalf of Trimark Communities, Condor conducted soil and groundwater investigation activi- <br /> ties along Byron Road inJuneand July 2001 in preparation for development of the Mountain <br /> House community in the area. The future development is bisected by the right-of-way for <br /> Chevron.Texaco's former crude oil/Bunker C fuel oil pipelines. Investigation activities included <br /> advancing 185 soil borings along the right-of-way at intervals of 100 feet or less.Petroleum <br /> affected soil was observed in 20 of the soil borings at depths ranging from 4 to 46 feet below <br /> ground surface(bgs). Petroleum hydrocarbon constituents were detected in samples collected <br /> from 21 of the borings.. Grab groundwater samples were collected from selected borings. Based <br /> on results from Condor's investigation, Geomatrix identified six areas for further investigation <br /> (designated as Sites I through 6,Figure 2). This work plan discusses proposed activities at Site 3, <br /> which is located southeast of Mountain House Parkway and approximately 2,000 feet southeast of <br /> Mountain House Creek. <br /> Condor advanced sixteen borings in the vicinity of Site 3 to total depths ranging from 16 to 48 <br /> feet bgs;boring logs are attached. Petroleumhydrocarbon affected soil was observed in four <br /> borings clustered together(GP 96, GP 97, GP 117, and GP 173, Figure 3)at depths as shallow as <br /> 5.5 feet bes (GP 97)an dee as 4 f-et bg (GP 96 which was drilled to 48 feet bes) <br /> Affected soil was also observed in a single boring located approximately 200 feet southeast of the <br /> cluster at depths between 6.5 and 11 feet bgs (GP 120, which.was drilled to 16 feet bgs). Affected <br /> soil was not observed in the remaining 11 borings drilled in the site vicinity(GP 94, GP 95, <br /> GP 118, GP 119, GP 121, GP 122, GP 137 through GP 141; Figure 3). <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />