WORK PLANS - Laserfiche WebLink

Home Browse Search

E vraxoxC.Bxowx Jx. neneu � Mnnxew goomouez Water Boards oxxrx,.r axa.r=r,ox Central Valley Regional Water Quality Control Board March 9, 2015 HEGEI Y ED MAR 31 2016 Mr. F. Wally Sandelin ENVIRONME TAL Public Works Director City of Lodi 221 West Pine Street, Lodi, CA 95240 REVIEW OF RECOMMENDED CENTRAL PLUME EXTRACTION WELL LOCATION—MID- PLUME AREA, LODI, SAN JOAQUIN COUNTY Staff of the California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) reviewed the Technical Memorandum Recommended Central Plume Extraction Well Location—Mid-Plume Area dated December 22, 2014 and prepared by Langan Treadwell Rollo (Langan) on behalf of the City of Lodi (City). The memorandum provides an evaluation of potential locations for new groundwater extraction and treatment (GWET) in the middle portion of the Lodi Central Plume. The memorandum also includes recommendations for the location and construction of a new extraction well to contain and capture the highest concentrations of tetrachloroethene(PCE) remaining in the Central Plume. In April 2011, the Central Plume Source Area GWET system started pumping from two source area groundwater extraction wells (EW-4 and EW-5) that were turned off in November 2011 due to low concentrations of PCE in the influent. Both EW-4 and EW-5 were constructed with screens starting below 100 feet deep, while PCE pollution at the source area appeared to be predominantly in shallower groundwater. The source area GWET system was restarted in April 2012 with newly installed EW-6, which was constructed with a screen from 50 to 90 feet deep. The influent concentrations of PCE in EW-6 started at 2,100 pg/L, decreased to 100 pg/L by January 2013, and further decreased to 32 pg/L as of July 2014. In August 2014, EW-6 was shut down and post-shutdown sampling indicated steady or decreasing PCE concentrations. Between April 2011-5nd July 2014, extraction wells EW-4, EW-5 and EW-6 removed approximately 226 pgdnds of PCE from groundwater in the Central Plume source area. Currently, the highest concentrations of PCE in the Central Plume are located down gradient of the source area in the middle portion of the plume. To address the PCE mass in the middle portion of the plume, the City is proposing to install a single new extraction well near the intersection of Church Street and West Tokay Street with the treatment system to be located on the Needham Elementary School property. This location is approximately 2400 feet down gradient of the source area. PCE at this location is encountered primarily in the intermediate Kae.E. Lunraev ScC, P.E.. -.+w I Pnutu C. CNt[UVx P.F.. BCEE,erecunve nrrwea 11020 P.on Cennr Drive 0200.Rancho Cordova.CA 95810 1 www.wabrboartls.Ca.Aov.'cemrawaney