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1 Introduction
<br /> On behalf of UniFirst Corporation (UniFirst), WSP USA Environment& Infrastructure Inc. (WSP)
<br /> has prepared this 2019 Groundwater Interim Remedial Action Work Plan—Revision 3 for the UniFirst
<br /> facility located at 819 North Hunter Street in Stockton, California (the site; Figure 1). Groundwater
<br /> beneath the site and in the vicinity contains chlorinated volatile organic compounds (CVOCs). The
<br /> sources of these chemicals in groundwater include past operations at the site. Other sites nearby are
<br /> also sources of these chemicals in groundwater in this part of Stockton.
<br /> Between 2005 and 2008, UniFirst conducted a series of groundwater investigations on and off the
<br /> site under the direction of the Central Valley Regional Water Quality Control Board (RWQCB).
<br /> The investigations included drilling a series of soil borings to collect grab groundwater samples and
<br /> installing groundwater monitoring wells based on the results of the borings. These investigations are
<br /> summarized in the April 18, 2008, Monitoring Well Installation and First Quarter 2008 Groundwater
<br /> Monitoring Results(Geomatrix, 2008). The results of these investigations indicated that the primary
<br /> constituents of concern (COCs)were tetrachloroethylene (PCE) and trichloroethylene (TCE).
<br /> The CVOCs in groundwater were being degraded by natural processes, and the highest CVOC
<br /> concentrations were in the vicinity of the MW-5 well cluster located immediately downgradient of the
<br /> site. In addition, soil samples were analyzed for the presence of dehalogenating organisms.
<br /> These organisms were detected in the deeper soil samples.
<br /> In an August 2, 2010, letter to UniFirst, the RWQCB requested that UniFirst propose remedial actions
<br /> to reduce the mass of CVOCs in groundwater more rapidly than by natural processes alone. UniFirst
<br /> proposed a pilot test of in-situ bioremediation for CVOCs using injections of hydrogen-release
<br /> compound (HRC) in borings drilled adjacent to the MW-5 well cluster(AMEC Geomatrix, 2010b).
<br /> The RWQCB approved the pilot test and issued a May 26, 2011, Notice of Applicability of General
<br /> Order No R5-2008-0149-029 (NOA). The NOA authorized injections of HRC and provided a
<br /> monitoring and reporting program for the remedial action. UniFirst conducted the injection work in
<br /> 2011 and reported the results in the October 31, 2011, Groundwater Remediation Pilot Test
<br /> Installation Report(AM EC Geomatrix, 2011 b).
<br /> Following the pilot test, PCE and TCE concentrations in groundwater at the MW-5 well cluster
<br /> generally declined over time as shown in the time concentrations charts in Appendix A and tables
<br /> included in semiannual groundwater monitoring reports. The concentration of daughter compounds
<br /> such as vinyl chloride also increased somewhat following the pilot test, a further indication that the
<br /> degradation of PCE and TCE via dechlorination was occurring. However, over time, the PCE and TCE
<br /> concentrations in groundwater rebounded and concentrations of vinyl chloride have not decreased to
<br /> their concentrations from before the pilot test in all wells (appendix A).
<br /> UniFirst met with the RWQCB on August 20, 2019, to propose additional interim remedial actions to
<br /> promote in-situ bioremediation in groundwater at the site. UniFirst submitted the 2019 Groundwater
<br /> Interim Remedial Action Work Plan, dated October 14, 2019, to the RWQCB proposing installation of
<br /> injection wells near the MW-5 well cluster and injection of materials designed to stimulate naturally
<br /> occurring bioremediation of CVOCs. After reviewing the work plan, the RWQCB issued a November 19,
<br /> 2019, letter, requesting UniFirst revise the work plan to address the potential that the plume of CVOCs
<br /> extends north of the MW-5 well cluster and prepare a revised Notice of Intent.
<br /> To address the RWQCB comments, UniFirst submitted the 2019 Groundwater Interim Remedial
<br /> Action Work Plan—Revision 1, dated January 14, 2020, that proposed the installation of an additional
<br /> groundwater monitoring well cluster on East Poplar Street. In a February 3, 2020, email, the RWQCB
<br /> requested UniFirst perform additional assessment to optimize the location of the proposed monitoring
<br /> well cluster. As requested, UniFirst submitted the 2019 Groundwater Interim Remedial Action Work
<br /> Plan—Revision 2, dated April 17, 2020, proposing to install and sample two soil vapor borings to
<br /> obtain these data.
<br /> On November 6, 2020, samples were collected from soil probes installed in borings B-12 and B-13
<br /> in general accordance with the Department of Toxic Substances Control (DTSC)Advisory using the
<br /> methodology described in Appendix B of the DTSC Advisory. The findings were reported in the
<br /> January 5, 2021, Soil Vapor Sampling Results letter to the RWQCB (Wood, 2021 a). Following their
<br /> 2019 Groundwater Interim Remedial Action Work Plan—Revision 3 Page 1
<br /> UniFirst Facility,Stockton,California
<br /> Project No.0132902023
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