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QUARTERLY GROUNDWATER MONITORING REPORT—FIRST QUARTER 2016 <br /> L&M Operable Unit—West Weber Avenue and North Lincoln Street, Stockton, CA <br /> Appendix B <br /> Page 11 <br /> 1) Report results from the work proposed in Stantec's May 30, 2014 work plan <br /> for additional soil vapor survey; <br /> 2) Provide additional support for Stantec's position on the presence of <br /> methane in soil vapor wells; <br /> 3) Update and/or modify appropriate screening levels presented in the <br /> original Vapor Intrusion Contingency Plan, submitted January 17, 2014; <br /> and <br /> 4) Address how and when a soil vapor extraction system may be restarted in <br /> the future if proposed soil vapor concentration screening levels are <br /> exceeded in specified probes. <br /> Stantec received approval of the May 30, 2014 Remediation Equipment <br /> Removal Proposal from the RWQCB-CVR in a letter dated November 3, 2014. <br /> Stantec removed both SVE systems and the vapor component of the DPE <br /> • system between January 12 and 14, 2015. The offsite skimmer system remained <br /> in place and operational. <br /> Another meeting was held on April 15, 2015, at which time Stantec proposed to <br /> suspend adherence to the original Vapor Intrusion Contingency Plan as there <br /> did not appear to be a threat to human health for residents at the Delta View <br /> Apartment complex which would warrant a complete mobilization and re-start <br /> of a soil vapor extraction system without further investigation. <br /> On May 15, 2015 Stantec submitted a soil vapor assessment report of findings <br /> following the installation of seven off-Site Delta View Apartment complex <br /> locations (APSV-11, APSV-12, APSV-14 through APSV-18) and two on-Site <br /> locations (UPSV-7 and UPSV-8) across the L&M OU. The primary objective of this <br /> assessment work was to obtain soil vapor data from newly installed vapor <br /> probes at previously compromised locations (APSV-2 and APSV-4) and other <br /> locations representing data gaps that were warranted to comply with Stantec's <br /> Vapor Intrusion Contingency Plan, submitted January 17, 2014 (provided in the <br /> work plan). The investigation also included a methane survey that provided <br /> confirmation that there is no immediate threat to receptors due to elevated <br /> methane in sub-surface soil gas. However; further investigation of methane at <br /> depth and around the apartment buildings is being proposed to assess risk of <br /> • any utility/construction worker exposed to methane at depth. <br /> Stantec <br />