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J C.WA.Ca0. BRowry JR. <br /> SOD6wV <br /> EC 5TAVY ° E2 <br /> Water Boards Frv"'"°NWIXI`°ROTE°"°" <br /> Central Valley Regional Water Quality Control Board <br /> RECEIVED <br /> 15 August 2016 <br /> AUG 1 u 2016 <br /> Dave Patten <br /> Chevron EMC ENVIRMAENTAL HEALTH 6101 Bollinger Canyon Road, BR1X-5535 PERMIT/ERVICES <br /> San Ramon, CA 94583 <br /> CHEVRON STATION #9-4054, 2103 COUNTRY CLUB BOULEVARD, STOCKTON, SAN <br /> JOAQUIN COUNTY (RB CASE# 390089) <br /> On behalf of the Central Valley Regional Water Quality Control Board (Central Valley Water <br /> Board), I am pleased to notify you that as of 1 June 2016, 1 am the assigned caseworker for <br /> Chevron Service Station #9-4054 in Stockton. My contact information is included at the end <br /> of this letter. <br /> I have reviewed the Semi-Annual Groundwater Monitoring Report— First Quarter 2016 dated <br /> 28 April 2016, submitted on your behalf by Stantec Consulting Services Inc. (Stantec), as <br /> well as other historical Site files. Four groundwater zones have been impacted by the <br /> release of petroleum fuels from the Chevron service station at 2103 Country Club Boulevard <br /> in Stockton (Site). The A Zone is represented by wells screened 5 to 35 feet bgs; the B <br /> Zone by wells screened 39 to 51.5 feet bgs; the C Zone by wells screened 65 to 81.5 feet <br /> bgs; and the D Zone by wells screened 95 to 101 feet bgs. Additional delineation of <br /> petroleum constituents in the B zone is needed at this Site. Below are my detailed comments <br /> on the current status of the assessment and cleanup of the petroleum release from the Site. <br /> 1. The majority of hydrocarbon impacts to groundwater appear to be in the B Zone, with <br /> recent total petroleum hydrocarbons as gasoline (TPHg) and benzene concentrations <br /> as high as 3,800 micrograms per liter (ug/L) and 1,200 ug/L, respectively. Water <br /> Quality Objectives (WQOs) for TPHg and benzene are 5 ug/L and 1 ug/L, <br /> respectively. These concentrations were reported in the down-gradient well MW-13B, <br /> which is approximately 180 feet north of the former USTs (source area) and marks <br /> the furthest downgradient assessment of hydrocarbon impacts to groundwater. <br /> Additionally, nearby well MW-12B recently contained 340 ug/L benzene. As such, <br /> additional delineation of B zone groundwater to the north is needed. As such, by <br /> 28 October 2016, please submit a Work Plan which includes a proposal for the <br /> collection of a sufficient number of groundwater samples to adequately delineate <br /> hydrocarbon impacts in B zone groundwater north of wells MW-12B and MW-13B. <br /> 2. While down-gradient groundwater impacts appear to be limited to the B zone, it does <br /> not appear that groundwater pollution has been fully delineated east of the Site in the <br /> A Zone. A zone well MW-6, located on the east side of Franklin Avenue, has recently <br /> been reported with TPHg and benzene concentrations of 3,400 ug/L and 310 ug/L, <br /> KMRL E. LONGLEY SCD, P.E., CHAIR I PAMELA C. CREEDON P.E., BCEE, EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200,Rancho Cordova,CA 85670 I www.waterboards.ca.gov/c.ntr.ivalley <br /> C"ae°ro.e°rn'en <br />