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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 <br /> • (510) 663-4100 • FAX (510) 663-4141 GEOMATRIX <br /> March 29, 2000 <br /> Project 6115.019 <br /> Ms. Katie Hower <br /> Chevron Environmental Management Company <br /> P.O. Box 6012 <br /> San Ramon, California 94583-0712 <br /> Subject: Response to DTSC Comments <br /> Burns Property (San Joaquin County APN 232-170-05) <br /> Tracy, California <br /> Dear Ms. Hower: <br /> Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter in response to comments <br /> provided by the California Environmental Protection Agency, Department of Toxic <br /> s Substances Control (DTSC) (copy attached) regarding Geomatrix's report entitled, "Soil and <br /> Groundwater Investigation Report and Human Health Screening Evaluation, Burns Property, <br /> Tracy, California" dated January 17, 2000. The DTSC letter presented three specific <br /> comments. These are presented below in italics; Geomatrix's responses follows. <br /> Specific comment number 1 - "The use of Friedman and Bruya, Inc. of Seattle Washington <br /> for the analysis of the petroleum-related hydrocarbons was a good idea. The laboratory <br /> identified the probable source of the contamination as crude oil. The results of the analysis <br /> (on the) soils and one grab groundwater sample indicated the BTEX was not detected. Soil <br /> and groundwater samples contained low levels of PAH compounds. " <br /> Response: No response required. <br /> Specific comment number 2 - "Text states petroleum-affected soils were observed from 7 to <br /> 14 feet bgs. However, the tables reflect the depths as 8.5 to 11 feet bgs. The text should be <br /> revised appropriately" <br /> Response: The tables do not reflect the vertical extent of affected soil; they only show the <br /> depth at which a particular sample was collected and are not meant to suggest that this depth <br /> represents the entire range of affected soil in a particular boring. The text of the report states <br /> that petroleum hydrocarbon affected soil was observed from 7 to 14 feet below ground <br /> surface, this is also supported by the attached boring logs. <br /> Specific comment number 3 - "HERD reproduced the risk screening calculations. The risk <br /> calculated for the property was at 1 x 10-8, which is within the range that is considered <br /> • acceptable (1 x 10-8 to 1 x 10-4). The risk calculations were based on the use of the equivalent <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />