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May 31,2023 <br /> Ms.Amber Ginorio,GIT <br /> Central Valley Regional Water Quality Control Board <br /> 11020 Sun Center Drive,#200 <br /> Rancho Cordova,California 95670 <br /> Subject: 2023 Biennial Monitoring and Sampling Report <br /> Monitoring and Reporting Program Order Number <br /> RS-2012-0813 <br /> Olin Chlor Alkali Facility <br /> Tracy,California <br /> Project 6107210034 <br /> Dear Ms.Ginorio: <br /> On behalf of Olin Corporation (Olin),Wood Environment& Infrastructure <br /> Solutions, Inc. (Wood) has prepared this 2023 Biennial Monitoring and <br /> Sampling Report for the Olin Chlor Alkali facility(the"Site") located at 26700 <br /> South Banta Road in Tracy,San Joaquin County,California (Figure 1).The Site <br /> was previously operated by Pioneer Americas Inc.;Olin purchased Pioneer <br /> Americas Inc. in August 2007. In compliance with the Revised Monitoring <br /> and Reporting Program (MRP) R5-2012-0813, issued by the Central Valley <br /> Regional Water Quality Control Board (CVWB) on June 2,2022 ("Revised <br /> MRP"),this biennial report presents data collected during the March 2023 <br /> (first quarter 2023) groundwater monitoring event. <br /> Geology and Hydrogeology <br /> The Site is located in the San Joaquin Valley and overlies recent Quaternary <br /> deposits and the Tulare Formation.The upper 30 feet of the subsurface <br /> comprises recent Quaternary silt and clay alluvial deposits,which are <br /> difficult to distinguish from the underlying deposits of the Tulare Formation. <br /> In this area,the Tulare Formation is divided into Upper, Middle, and Lower <br /> Members.The Upper Tulare Member is further subdivided into four geologic <br /> units,designated "horizons"as follows:Above Upper, Upper, Middle,and <br /> Lower, referred to herein as the Upper, Middle,and Lower Horizons. In this <br /> report,the Above Upper Horizon is included in the Upper Horizon.The <br /> depth,thickness,and I ithology of the horizons vary across the Site.The <br /> horizons comprise fine-to medium-grained deposits of sand and gravel with <br /> varying amounts of sand,separated by fine-grained deposits of silt and clay. <br /> A more detailed description of the Site geology and hydrogeology was <br /> provided in the Conceptual Site Model Report Olin Chlor Alkali facility, <br /> Tracy, California, (Amec Foster Wheeler,August 31,2017). <br /> wsp.com <br /> https://woodplc.sharepoint.com/teams/olintracy/shared documents/general/03.0 docctrl/2021 biennial report/01_text/tcy 2021 biennial_text_rev.docx <br /> Page 1 <br />