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GAVIN NEWSOM GOVERNOR Water Boards v ENV E qF°R ENVIRONMENTAL PROTECTION Central Valley Regional Water Quality Control Board 25 April 2023 Tim Cosgrave Director, Environmental, Health & Safety UniFirst Corporation 68 Jonspin Road Wilmington, MA 01887-1090 REVIEW OF 2019 GROUNDWATER INTERIM REMEDIAL ACTION WORK PLAN — REVISION 3, UNIFIRST, 819 HUNTER STREET, STOCKTON, SAN JOAQUIN COUNTY Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff have reviewed the 31 March 2023 2019 Groundwater Interim Remedial Action Work Plan — Revision 3 (Interim Work Plan #3) submitted on your behalf by WSP USA Environment & Infrastructure, Inc. (WSP) for the UniFirst Corporation (UniFirst) property located at 819 Hunter Street in Stockton, California (the Site). UniFirst has been monitoring and remediating tetrachloroethene (PCE), trichloroethene (TICE), and their daughter products in soil vapor and groundwater at the Site. Past investigations indicated that these Volatile Organic Compounds (VOCs) originated from spills and leaks from UniFirst's prior dry-cleaning operation and are found in soil vapor and groundwater beneath and down-gradient of the Site. In short, the Interim Work Plan #3 extends the monitoring area to better inform remedial action strategies. In response to a 30 December 2022 letter from Central Valley Water Board staff, and consistent with the recommendations made in the 2022 Second Semiannual Groundwater Monitoring Report, the Interim Work Plan #3 proposes installing monitoring well MW-11 on the north side of East Poplar Street and west of North Hunter Street. MW-11 will be screened in the C-Zone, between approximately 94.5 feet below the ground surface (bgs) and 104.5 feet bgs, in an effort to delineate the impacts of VOCs in groundwater and better determine the groundwater gradient on the north side of the facility. The Interim Work Plan #3 maintains the original remedial concept of installing three injections wells, IW-5A, IW-5B, and IW-5C in the A-Zone, B-Zone, and C-Zone, respectively, and conducting enhanced in-situ bioremediation at the appropriate time. Furthermore, the Interim Work Plan #3 highlights the need for the collection and analysis of groundwater samples taken from MW-11 prior to installing injection wells. Central Valley Water Board staff concur with this approach, and look forward to discussing injection well placement once data from MW-11 is available. At that time, Central Valley Water Board staff will finish preparing Monitoring and Reporting Program MARK BRADFORD, CHAIR I PATRICK PULUPA, ESQ., EXECUTIVE OFFICER 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvalley