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Technical LA/V&A/%J IKEAUWLLL HULLO Memorandum 555 Montgomery Street,Suite 1300 San Francisco,CA 94111 T:415.955.5200 F:415.955.5201 To: Nathan Casebeer, Regional Water Quality Control Board, Central Valley Region cc: F. Wally Sandelin, City of Lodi Public Works � r From: Varinder Oberoi and Phil Smith Date: 22 December, 2014 MAR 31 2016 Project: Lodi Central Plume— Mid-Plume Area Remediation rrl0NtVtG� B Subject: Recommended Central Plume Extraction Well Location—Mid-Plume i i6 THDFPARTMEi``T Introduction This Memorandum has been prepared for the City of Lodi (City) to address the down-gradient groundwater contamination that has moved beyond the Lodi Central Plume (LCP) source area remediation system capture zone. The LCP source area extraction well, EW-06, was shut down on 19 August 2014, and monthly monitoring indicates that contaminant concentrations have remained stable in the source area. The City, as part of its ongoing remediation efforts, is evaluating the placement of a single or multiple extraction well/s to remediate the down-gradient groundwater contamination of the LCP, especially in the intermediate zone, which is located between 75 to 125 feet below ground surface (ft-bgs). This memorandum evaluates several possible locations of the proposed extraction well/s, and identifies the preferred location for the proposed extraction well/s, recommended screened intervals, and the recommended extraction rate. The modified City of Lodi transient groundwater flow and contaminant transport model (Model) was applied to meet the objectives of this task. Five groundwater contaminant plumes, comprised primarily of halogenated volatile organic compounds (HVOCs), principally tetrachloroethene (PCE) and trichloroethylene (TCE), have been identified impacting the groundwater beneath the City. The LCP has been extensively studied as it is the primary contaminant plume in Lodi. It is primarily a PCE contaminant plume with minimal TCE and other HVOC daughter products present. The current on-going groundwater monitoring program in Lodi is centered on the LCP, and there is a detailed record of the lateral and vertical extent of contamination in the LCP. Additionally, the LCP has undergone several years of source area remediation and is currently being evaluated for closure. Data collected by the City has been used to develop the technical basis of this memorandum. The memorandum is not meant to provide a complete description of the area's geology and hydrogeology, but rather to describe the overall hydrogeologic model for the migration of the LCP and to present an optimized location, extraction rate, and screened intervals for capturing down-gradient groundwater contamination that has moved beyond the LCP source area remediation system capture zone.