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Groundwater Monitoring Report for the Semiannual ARCADIS Period from January 1 through June 30,2012 Lincoln Center,Stockton, California Avenue, on the south by Douglas Avenue,and on the north by Lincoln Elementary School. Benjamin Holt Drive runs east-west through the middle of the Site. 1.2 Background In 1984,groundwater contamination was detected in a municipal supply well located along the western edge of the Site.Subsequent investigations began to assess the nature and extent of soil and groundwater contamination at the Site. Results of these investigations indicate that the main constituents detected in groundwater at the Site are perchloroethylene(PCE),trichloroethylene (TCE),cis-1,2- dichiorcethylene(cis-1,2-DCE),trans-1,2-dichloroethylene(trans-1,2-DCE), and vinyl chloride. PCE,TCE,cis-1,2-DCE,trans-1,2-DCE,and vinyl chloride are referred to collectively as"Hazardous Substances"in this report. 1.3 Overview of Groundwater Self-Monitoring Program This is the fifteenth groundwater monitoring report submitted in accordance with a semiannual schedule of groundwater monitoring and reporting, as proposed by LFR Inc. (now ARCADIS)in a letter dated June 24,2004 and approved by the RWQCB,Central Valley Region in a letter dated August 26,2004.The groundwater monitoring schedule divides the reporting year into two semiannual periods:January 1 through June 30 and July 1 through December 31.Selected groundwater monitoring wells are now sampled on a semiannual basis,with reports submitted on August 15 and February 15(45 days after the end of each semiannual period). Previously,three different monitoring schedules—routine monitoring, Phase IV IRA monitoring, and Phase V IRA monitoring—were Implemented at the Site. These three monitoring schedules were later combined into one in the letter from Mr. Roberto Cervantes, P.E.,of the RWQCB,dated January 4,2011 (RWQCB 2011). Furthermore, in the letter dated January 24,2012(RWQCB 2012),the RWQCB concurred with the Trusfs recommendation that MW-103A be abandoned because this well had been paved over by a contractor during street resurfacing activities and did not provide additional value for groundwater monitoring.MW-103A is no longer included as part of the groundwater monitoring schedule and will be abandoned after the appropriate permits have been obtained.The current consolidated monitoring schedule is summarized in the table below. . u,oN�w h,o,z.Emoonw.m< 2