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r Groundwater Monitoring ARCADIS Report for the Semiannual Period from January 1 through June 30,2012 Lincoln Center, Stockton, California between 1995 and 2005 was presented in LFR's"Groundwater Monitoring Report for the Biannual Period from July 1, 2005 through December 31,2005,"dated February 15, 2006 (LFR 2006). During the June 2012 sampling event, chloroform was detected In two monitoring wells, MW-001A and MW-110A, at concentrations of 19 and 1.6 pg/I,respectively. In addition, 1,2-dichloroethane was detected at an estimated concentration of 3.6 pg/I In one monitoring well,MW-101 2.3.3 Phase V IRA Monitoring ResUItS As discussed in Section 1.3, Phase V IRA monitoring is included as part of routine monitoring at the Site.The Phase V IRA monitoring well network consists of two monitoring wells located upgradient from the ERD injection area,six monitoring wells located within the ERD injection area, and seven monitoring wells and three piezometers located downgradient from the ERD injection area. During the reporting period,groundwater samples were collected from eight monitoring wells to monitor ongoing performance of the Phase V IRA: • Monitoring well MW 020B, located upgradient from the ERD injection area; • Monitoring wells MW-122A-U, MW-124A-L, MW-2148, and MW-301C,located within the ERD injection area, and • Monitoring wells MW-121A-U, MW-123A-L,and MW-2158,located downgradient from the ERD injection area. The remaining Phase V IRA monitoring wells were sampled during the December 2011 event in accordance with the RWQCB-approved sampling schedule(see Section 1.3). The Phase V IRA consisted of(1) implementing an ERD program in the A-zone,and (2)assessing the need for ERD technology in the B-zone.A figure illustrating the locations of the Phase V IRA components is presented in Appendix B. During construction of the Phase V IRA system,two well clusters were installed downgradient from the injection array,in accordance with LFR's"Phase V Interim Remedial Action Detailed Plan,"dated September 27, 2007(LFR 2007). Each cluster Includes three wells,one screened in the upper A-zone(MW-121A-U and MW-122A-U),one screened in the lowerA-zone(MW-123A-L and MW-124A-L),and one screened in the B-zone (MW-2148 and MW-215B).The first and second well clusters,respectively,are located �"_w cw worzeiwmrsoa"" 9