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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 <br /> ICI : <br /> C510) 663-41 00 • FAX (51 0) 663-4141 #L�,.jG.y;�j'�' gi'�C' `���1� GEOMATRIX <br /> July 12, 2001 01 JUL 16 PM.. 2*. 18 <br /> Project 002463.002 <br /> Mr. Robert Mihalovich <br /> Chevron Environmental Management Company <br /> 6001 Bollinger Canyon Rd <br /> Post Office Box 6012 <br /> San Ramon, California 94583-0712 <br /> Subject: Response to RWQCB May 10, 2001 Comments <br /> Grant Line and Corral Hollow Roads Site <br /> Tracy, California <br /> Dear Mr. Mihalovich: <br /> Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter on behalf of Chevron Envi- <br /> ronmental Management Company(Chevron) for the subject site. This letter responds to the <br /> California Regional Water Quality Control Board—Central Valley Region (RWQCB) com- <br /> ments on Chevron's request for no further action at the site. The RWQCB comments are pre- <br /> sented in a May 10, 2001 letter to Chevron (RWQCB, 2001). Additionally, this letter provides <br /> an update of potential development activities at the site. <br /> As requested by the RWQCB, remedial alternatives for the site were evaluated in the 2nd <br /> Semiannual 2000 Groundwater Monitoring and Additional Information for Site Closure <br /> Report (Geomatrix, 200.0). The alternatives evaluated were natural attenuation (NA), <br /> monitored NA, enhanced(with the use of an oxygen releasing compound [ORC]) in situ <br /> bioremediation(EISB), and excavation. Based on the results of this evaluation, data collected <br /> to date, and a human health risk assessment, NA is recommended as the remedial action, and <br /> "no further action"was requested for the site. Based on RWQCB staff review of this report <br /> (RWQCB, 2001), the RWQCB commented that: <br /> 1. NA is not acceptable because Chevron must monitor the site to ascertain that NA is <br /> continuing to occur. <br /> 2. Chevron should provide clarification on how the rate of declining benzene concentra- <br /> tions, ranging from 0.1 to 0.29 percent, was derived. <br /> 3. Chevron should provide (a) the basis for replacing ORC at a rate of 3 times per year in <br /> the cost estimate, and(b)justification for using 15 years as the time to remediate the <br /> site using ORC. <br /> The RWQCB additionally requested the submittal of a work plan describing field procedures f <br /> for conducting a pilot study at the site using ORC. The objective of the pilot study would be <br /> to obtain"more concrete" information regarding the use of ORC at the site so that a direct <br /> comparison with monitored NA can be made. <br /> I <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />