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r.. ,wo", <br /> California Regional Water Quality Control BoarAj <br /> vft-; Central Valley Region C__ .1 �`# <br /> Steven T.Butler,Chair C- / <br /> �„�`v�,, <br /> Winston H.Hickox Gray Davis <br /> Secretaryfor Sacramento Main Office Q0 Governor <br /> Environmental Internet Address: http://www.swrcb.ca.gov/—rwgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 -� <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> hJ , <br /> O <br /> 18 July 2000 <br /> Mr. Robert Mihalovich <br /> Chevron Environmental Management Company <br /> 6001 Bollinger Canyon Road <br /> P. O. Box 6012 <br /> San Ramon, CA 94583-0712 <br /> LOW-RISK CLOSURE REQUEST, CORRAL HOLLOW AND GRANT LINE ROADS SITE, <br /> TRACY, SAN JOAQUIN COUNTY <br /> I have reviewed Geomatrix Consultants' March 2000 Second Semi-Annual 1999 Groundwater <br /> Monitoring, 1999 Annual Progress Report, Low-Risk Closure Request(report) for Chevron <br /> Environmental Management Company's (Chevron) site at Corral Hollow and Grant Line Roads in <br /> Tracy. My comments on the report are presented below. <br /> Second Semi-Annual 1999 Groundwater Monitoring <br /> 1. The report states that total petroleum hydrocarbons quantified as diesel (TPHd)were analyzed using <br /> U.S. EPA Methods 3630M (silica-gel cleanup) and 8015M. The report also states that benzene, <br /> toluene, ethylbenzene, and xylenes (BTEX) were analyzed using U.S. EPA Method 8021. The use of <br /> Methods 8015 and 8021 are appropriate. However, we do not accept the use of silica-gel cleanup <br /> when testing for TPHd. Silica gel cleanup is performed to remove interferences from polar materials <br /> which are either naturally occurring or petroleum degradation byproducts. If these materials are the <br /> latter, then they should be identified and their respective water quality objectives applied. The <br /> attached 14 March 2000 letter and memorandum document our discussions with Chevron and our <br /> final decision regarding this issue. Future monitoring for TPHd at the site should not include <br /> silica-gel cleanup. <br /> 2. Figure 2 shows analytical results and groundwater elevations from the December 1999 sampling <br /> event. It also shows the northern half of the BTEX plume. The southern half of the plume is missing <br /> due to the absence of monitoring points in the southern section. Based on current and historical data, <br /> this plume most likely extends into Grant Line Road, but not all the way to the median strip,which <br /> can serve as a monitoring well location. Thus, Chevron should install a monitoring well along the <br /> median strip of Grant Line Road to define the southern extent of the plume. <br /> California Environmental Protection Agency <br /> A011 Recvcled PaDer <br />