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s YS1 <br />AS <br />n <br />TECHNICAL MEMORANDUM <br />DATE: April 18, 2017 <br />Project No.: 213-17-17-37 <br />SENT VIA: EMAIL <br />TO: Nathan Casebeer <br />Regional Water Quality Control Board, Central Valley Region <br />CC: Mr. Lyman Chang <br />Deputy Public Works Director, City of Lodi <br />FROM: Varinder Oberoi, PE, RCE #69037 <br />REVIEWED BY: Jim Strandberg, PG #1685, CHG #800 <br />SUBJECT: Recommended Lodi Central Plume Mid-Plume Replacement Extraction Well <br />Location <br />INTRODUCTION <br />This technical memorandum (TM) has been prepared for the City of Lodi (City) to evaluate and <br />identify the location for the replacement extraction well EW-7R that will capture the <br />down-gradient groundwater contamination that has moved beyond the Lodi Central Plume (LCP) <br />source area (i.e., mid-plume area). This work follows a determination that the current extraction <br />well (EW-7), which was installed in October 2016 along with the newly constructed groundwater <br />treatment system at 531 Church Street, did not meet the stated requirements of an appropriate <br />extraction rate that would hydraulically contain and capture groundwater contamination in the LCP <br />mid-plume area. The original location of EW-7 was approved by the Regional Water Quality <br />Control Board, Central Valley Region (Water Board) in a letter dated March 9 2015. This TM <br />summarizes the results of our evaluation of EW-7 and provides a recommendation for the location <br />of replacement extraction well EW-7R for the City. <br />BACKGROUND <br />The LCP, which is one of five groundwater contaminant plumes, has been extensively studied as <br />it is the primary contaminant plume impacting groundwater beneath the City. It is primarily a <br />tetrachloroethylene (PCE) contaminant plume with minimal trichloroethylene (TCE) and other <br />halogenated volatile organic compound (HVOC) daughter products present. The current on-going <br />groundwater monitoring program in Lodi is centered on the LCP, and there is a detailed record of <br />the lateral and vertical extent of contamination in the LCP. Additionally, the LCP has undergone <br />several years of source area remediation. <br />6800 Koll Center Parkway, Suite 150 <br /> Pleasanton, CA 94566 westyost :.;orr