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EDMUND G. BROWN <br />GOVERNOR <br />Water Boards <br /> <br />MATTHEW RODRIQUEZ <br />(1110.S :N'Cvl'ReOTNAM%N'T°ARL PROTECTION <br /> <br />Central Valley Regional Water Quality Control Board <br />JUL 20 2010 <br />17 July 2018 <br />ENN I IZONINIENTA I I EALEI I <br />Mr. Carl Knowles DEPAIZT1EINT <br />P.O. Box 640 <br />Woodbridge, CA 95258 <br />RESPONSE TO ADDENDUM TO WORK PLAN FOR GROUNDWATER REMEDIATION, <br />KNOWLES STATION, 1120 WEST HAMMER LANE, STOCKTON, SAN JOAQUIN COUNTY, <br />CASE #390107 <br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br />reviewed the 20 April 2017 Addendum to Work Plan for Groundwater Remediation (Work Plan <br />Addendum) submitted on your behalf by Stratus Environmental, Inc. (Stratus) for the <br />unauthorized underground storage tank (UST) release at 1120 West Hammer Lane in Stockton, <br />San Joaquin County (Site). During a 23 August 2017 Project Execution Plan meeting, Central <br />Valley Water Board staff stated that they would not approve additional remediation until the <br />downgradient extent of the petroleum hydrocarbon plume had been delineated. Stratus did not <br />detect petroleum hydrocarbon constituents in the 25 June 2018 sample collected from newly <br />installed downgradient monitoring well MW-13. Therefore, this letter represents Central Valley <br />Water Board staff's response to the remedial approach presented in the 6 February 2017 Work <br />Plan for Groundwater Remediation (Work Plan) and the Work Plan Addendum. <br />Work Plan Timeline <br />The potential need for a remediation work plan was initially introduced in a 21 October 2016 <br />Central Valley Water Board staff letter which states "By 15 February 2017 submit a work plan to <br />delineate the downgradient extent of the groundwater plume and conduct additional <br />remediation, as appropriate." The letter also requested "an evaluation of the effectiveness of the <br />ozone sparge activities conducted between 2012 and 2015 and also evaluate the potential that <br />these sparge activities contributed to the offsite migration of petroleum constituents." On <br />6 February 2017, Stratus submitted the Work Plan which proposed: <br />Installing a new soil vapor extraction (SVE) system consisting of two new vapor <br />extraction wells (VE-1 and VE-2), a regenerative blower, two 1,000-pound granular <br />activated carbon (GAC) vessels, and treated vapor discharge to the atmosphere; <br />Installing a new groundwater extraction system consisting of two new groundwater <br />extraction wells (EX-1 and EX-2) with submersible pumps, three 1,000-pound GAC <br />vessels, and sprinkler lines for treated water discharge to ground surface; and <br />Connecting an air compressor to wells IW-1A/B through IW-4A/B for use as air sparging <br />wells <br />The Work Plan did not include a plan to delineate the downgradient extent of the groundwater <br />plume nor an evaluation of historical sparging activities, as was requested in the 21 October <br />KARL E. LONGLEY ScD, P.E., CHAIR I PATRICK PULURA, EXECUTIVE OFFICER <br />11020 Sun Center Drive #200. Rancho Cordova, CA 95670 www.waterboarcis.ca.gov/centralvalley <br />C.,) RECYCLED PAPER