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e 2101 Webster Street' • 12th Floor Oakland, CA 24612 (51 0) C63-41 00 • FAX (51 0) 663-4141 GEMP+/9A1 RIX April 4,2002 Project 7243.008 Mr. Robert Mihalovich Chevron Environmental Management Company 6001 Bollinger Canyon Road P.O. Box 6012 San Ramon, California 94583 Subject: Project Approach and Proposed Schedule Mountain House Sites, Byron Road Mountain House, California Dear Mr. Mihalovich: Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter to present our approach and proposed schedule for investigating the areas where petroleum hydrocarbon affected soil has been identified along Byron Road in Mountain House, California (Figure 1). BACKGROUND On behalf of Trimark Communities, Condor Earth Technologies, Inc. (Condor) conducted soil and groundwater investigation activities along Byron Road in June and July 2001 in prepara- tion for the future development of the Mountain House community in the area. The future development is bisected by the right-of-ways of ChevronTexaco's former crude oil/Bunker C fuel oil pipelines. Investigation activities included excavating 13 trenches at areas where future utilities may cross the former pipeline right-of-way along the south side of Byron Road and advancing 185 soil borings along that right-of-way at intervals of 100 feet or less. Petro- Ieum affected soil was not observed in any of the trenches, however it was observed in 20 of the soil borings at depths ranging from 4 to 46 feet below ground surface (bgs). A minimum of one soil sample from each boring was analyzed for total petroleum hydrocarbons quantified as crude (TPHc). Selected soil samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) and polynuclear aromatic hydrocarbons (PAHs). Petroleum hydrocarbon constituents were detected in samples collected from 21 of the borings (Figure 2). Grab groundwater samples were analyzed from seven borings where stained soil was observed and from one boring in an alfalfa field southeast of the intersection of Mountain House Park- way and Byron Road. Groundwater samples were analyzed for total petroleum hydrocarbons quantified as gasoline (TPHg) and diesel (TPHd; with and without a silica gel preparation pro- cedure), BTEX, and PAHs. Petroleum hydrocarbons and PAHs were detected in the seven samples collected from the borings where stained soil was observed; they were not detected in the sample from the alfalfa field. It should be noted that grab groundwater samples collected in 2001 were intended to identify potential issues pertaining to construction dewatering activi- ties and may not reflect dissolved constituents in groundwater. Engineers, Geologists, and Envirormental Scientists