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 April 29, 2016 • • Dissolved phase TPHg and benzene concentrations in C-Zone wells were generally delineated during 1 Q16. Dissolved phase TPHd, and TPHo concentrations in C-Zone wells were generally delineated to the west. Dissolved phase MTBE concentrations were generally delineated to the west and south. Dissolved phase TBA concentrations were generally delineated to the south. • In the D-Zone wells, dissolved phase TPHg is delineated to the south. Dissolved phase MTBE is delineated. Dissolved phase TPHd and TPHo are not delineated. Dissolved phase benzene is delineated except to the north. Dissolved phase TBA is generally delineated. • The extent of petroleum-affected deeper (B-, C-, and D-Zones) groundwater was not investigated by the City of Stockton at the LOU and MOU to the east. However, using historical data, the deeper groundwater plumes are considered to be stable. 5.2 PLUME STABILITY The petroleum hydrocarbon plume appears stable and concentration data are consistent with the historical range for the Site. 5.3 REMEDIATION SYSTEM . The on-site systems have been fully decommissioned as of February 2015. Pertinent infrastructure such as wells, piping, manifolds, gas and electrical connections were left in place to allow for the possibility of future use. The off-site product recovery remediation system was 787o operational during the reporting period. Since startup the product recovery remediation system has removed approximately 682.2 gallons of SPH from the subsurface. The off-site system will remain on. Recharge rate measurements will be conducted periodically to aid in site remediation progress and for system optimization. 5.4 SOIL VAPOR In the report Soil Vapor Investigation Report of Findings submitted January 29, 2016, Stantec demonstrated that there is a bio-barrier in the shallow soil fit hology between the surface and 3-4 feet bgs. This bio-barrier currently provides health protection from both VOCs and methane gas to residential and commercial/industrial receptors from vapor intrusion to indoor/outdoor air at the Delta View Apartment Complex and within the vicinity. Stantec is continuing to monitor soil vapor on a quarterly basis and is planning to further investigate methane and VOC's at depth to develop remedial alternatives. • ® Stantec 16