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00:00 Water Boards EDMUND G. BROWN JR. GOVERNOR MATTHEW FloORIOUEZ SECRETARY FOR ENVIRONMENTAL PROTEC/ION Central Valley Regional Water Quality Control Board 15 August 2016 Dave Patten Chevron EMC 6101 Bollinger Canyon Road, BR1X-5535 San Ramon, CA 94583 CHEVRON STATION #9-4054, 2103 COUNTRY CLUB BOULEVARD, STOCKTON, SAN JOAQUIN COUNTY (RB CASE# 390089) On behalf of the Central Valley Regional Water Quality Control Board (Central Valley Water Board), I am pleased to notify you that as of 1 June 2016, I am the assigned caseworker for Chevron Service Station #9-4054 in Stockton. My contact information is included at the end of this letter. I have reviewed the Semi-Annual Groundwater Monitoring Report — First Quarter 2016 dated 28 April 2016, submitted on your behalf by Stantec Consulting Services Inc. (Stantec), as well as other historical Site files. Four groundwater zones have been impacted by the release of petroleum fuels from the Chevron service station at 2103 Country Club Boulevard in Stockton (Site). The A Zone is represented by wells screened 5 to 35 feet bgs; the B Zone by wells screened 39 to 51.5 feet bgs; the C Zone by wells screened 65 to 81.5 feet bgs; and the D Zone by wells screened 95 to 101 feet bgs. Additional delineation of petroleum constituents in the B zone is needed at this Site. Below are my detailed comments on the current status of the assessment and cleanup of the petroleum release from the Site. The majority of hydrocarbon impacts to groundwater appear to be in the B Zone, with recent total petroleum hydrocarbons as gasoline (TPHg) and benzene concentrations as high as 3,800 micrograms per liter (ug/L) and 1,200 ug/L, respectively. Water Quality Objectives (WQ0s) for TPHg and benzene are 5 ug/L and 1 ug/L, respectively. These concentrations were reported in the down-gradient well MW-13B, which is approximately 180 feet north of the former USTs (source area) and marks the furthest downgradient assessment of hydrocarbon impacts to groundwater. Additionally, nearby well MW-12B recently contained 340 ug/L benzene. As such, additional delineation of B zone groundwater to the north is needed. As such, by 28 October 2016, please submit a Work Plan which includes a proposal for the collection of a sufficient number of groundwater samples to adequately delineate hydrocarbon impacts in B zone groundwater north of wells MW-12B and MW-13B. While down-gradient groundwater impacts appear to be limited to the B zone, it does not appear that groundwater pollution has been fully delineated east of the Site in the A Zone. A zone well MW-6, located on the east side of Franklin Avenue, has recently been reported with TPHg and benzene concentrations of 3,400 ug/L and 310 ug/L, KARL E. LONGLEY ScD, P.E., CHAIR I PAMELA C. CREEOON PE., BCEE, EXECUTIVE OFFICER 11020 Sun Center Drive Or200, Rancho Cordova, CA 95670 I www.waterboards.ca.govicentralvalley elp RECYCLED PAPER