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California Regional Water Quality Control Board 0 Central Valley Region Winston H.Hickox Robert Schneider,Chair Secretoryfor Gray DavisFresno Branch Office Governor Environmental Internet Address: httpJ/www.swrcb.ca.gov/-rwgcb5 Protection 1685 E Street,Fresno,California 93706-2020 Phone(559)445-5116•FAX(559)445-5910 28 February 2003 [RECEIVED] AR 0 4 2Em irnnrnental Mu Ms. Penny T. Fottrell ChevronTexaco Chevron Environmental Management Company P.O. Box 6012 San Ramon, CA 94583 REVIEW OF OFFSITE GROUNDWATER INVESTIGATION WORKPLAN, U.S. CAN/WELTY ROAD PROPERTY, VERNALIS, SAN JOAQUIN COUNTY We have reviewed the Off-Site Soil and Groundwater Investigation Workplan, U.S. Can/Welty Road report, dated 18 February 2003 submitted by Geomatrix Consultants, Inc. on behalf of ChevronTexaco. The Workplan proposes collecting additional offsite data regarding the crude oil pollution downgradient and adjacent to the U.S. Can/Welty Road property at 35275 Welty Road in Vernalis. The Workplan summarizes the results of a data review and proposes two offsite borings to collect soil and groundwater samples for delineating the extent of petroleum hydrocarbons generally downgradient of site monitoring wells MW-1 and MW-2. We concur with the installation of the two boring at the locations proposed in the 18 February 2003 Workplan. However, additional boring(s) with soil and groundwater sampling and analyses are needed in the area between proposed boring location GMX-10 and MW-2. This data gap is downgradient (east- northeast) of MW-2 (and the western "pod") where elevated concentrations of petroleum hydrocarbon compounds were previously reported in soil and groundwater. In accordance with ChevronTexaco's draft CTA (consistent technical approach) report, groundwater and soil samples should be collected immediately outside the western pod area of petroleum hydrocarbon- impacted soil. During fieldwork, the findings should be evaluated to determine if one or more of the borings should be converted to monitoring wells for future groundwater sampling. Additionally, according to the draft CTA, long term quarterly groundwater monitoring may be needed to confirm that concentrations of petroleum hydrocarbon are gradually decreasing as the mass is depleted over time. California Environmental Protection Agency .e 0th Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/rwgcb5