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Ot W¢psver 9creev <br /> 1 <br /> 210 FlO <br /> Oakland. 1 94612 GEOMATR IX <br /> (5101 663-41[ • FAX (5101663-4141 <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 /> Pombo Property(San Joaquin County APN 232-170-07) <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 /> Substances Control(DTSC)(copy attached) regarding Geomatrix's report entitled,"Soil and <br /> Groundwater Investigation Report and Human Health Screening Evaluation,Pombo Property, <br /> Tracy, California,'dated January 17,2000. The DTSC letter presented seven specific <br /> comments. These are presented below in italics; Geomatrix's responses follow. <br /> Specific comment number 1 - "The background information indicates that a former <br /> Mohawkgas station was located on the property. No location is provided in the text or <br /> Figure. From the sampling locations it is assumed that the former location was at or near the <br /> southeast corner of the property. Please clarify." <br /> Response: Geomatrix has added the interpreted location of the former Mohawk gasoline <br /> station to Figure 2 (attached). The approximate location of structures is based on an undated <br /> Sanborn Fire Insurance map. <br /> Specific comment number 2 - "The test states that nine offifteen samples (sic) werepositive <br /> for petroleum related hydrocarbons based on staining while the results of the OVA screening <br /> indicates eight offifeen samples (sic) were positive. Is this correct or there was (sic)staining <br /> without OVA positive readings?" <br /> Response: In one soil boring(GMX-5)staining was observed without positive detections <br /> using a photoionization meter. Because of the highly weathered nature of the residual crude <br /> oil,this is not uncommon and has been observed many times at similar sites. <br /> Specific comment number 3 - "All of the petroleum related hydrocarbons were identified in <br /> the "lean clays"horizon of the soil. Petroleum related hydrocarbons were identified at up to <br /> 18,000 mg/kg for crude oil and up to 6,800 mg/kg for diesel along the former pipeline. <br /> Gasoline was identified along the pipeline and where the suspected former Mohawk gas <br /> Geomatrix Consultants, Inc. <br /> Engineers. Geobrysa. antl Emimnmen[al ScienusW <br />