ARCHIVED REPORTS_QUARTERLY GROUNDWATER MONITORING REPORT 1ST QUARTER 2016

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QUARTERLY GROUNDWATER MONITORING REPORT— FIRST QUARTER 2016 L&M Operable Unit—West Weber Avenue and North Lincoln Street, Stockton, CA Appendix B is Page 10 complete shutdown of the onsite remedial systems to evaluate for rebound of petroleum hydrocarbon concentrations in groundwater and soil vapor at the Site. All on-Site systems have been shut down since October 16, 2013. On November 6, 2013 the RWQCB-CVR concurred with the rebound test but requested a vapor intrusion contingency plan be submitted should soil vapor monitoring results demonstrate hazardous vapor intrusion levels to Delta View Apartment residents during the period the systems are down. A contingency plan was submitted by Stantec dated January 17, 2014. Stantec met with the RWQCB on March 7, 2014, at which time a discussion of the path forward with regard to on-Site system operations and a plan of action to address data gaps in apartment soil vapor wells as well as re-evaluating groundwater plume contaminant zones on-Site in source areas was discussed in order to continue on a path toward Site closure. The RWQCB-CVR issued a letter on April 7, 2014 that summarized the meeting and directed CEMC to address the following action items by May 30, 2014: • The L&M Group will submit a proposal to remove the existing on-Site SVE/DPE remedial equipment. System piping, manifolds, and other infrastructure will remain to allow for system optimization to occur using a mobile treatment unit, if necessary; and, • The L&M Group will submit a work plan identifying additional soil vapor sampling locations to confirm the source area has been cleaned up. The RWQCB-CVR concurred that the system will remain off pending the results of the rebound test. Stantec completed these action items with a Work Plan for Additional Soil Vapor Survey and a Remediation Equipment Removal Proposal submitted on May 30, 2014. A meeting was held between Stantec and the RWQCB-CVR on October 23, 2014 to help introduce the site to the newly assigned regulator for the case and to discuss the work plan approval, scope, and data gaps. Following the October 23, 2014 meeting and after receiving the CRWQCB letter dated November 3, 2014, the following objectives were identified by Stantec to address agency concerns and to report findings from additional soil vapor survey: 5 Stantec