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 Page 2 attenuation is occurring beneath the Site. Pressure transducers/data loggers were installed in wells MW-5, MW-8, and MW-9 to monitor changes in water levels within the monitoring wells over a 48-hour period. Results of the tidal study indicated that over the testing period, observed tidal changes (up to 4 ft) had little influence on the southerly direction of groundwater flow in the monitoring wells (less than 0.1 ft). Results of this multi-phase assessment are provided in ERI's Groundwater Monitoring and Sampling and Tidal Influence Study Report, The Stockton Group Site, West Weber Avenue and North Lincoln Street, Stockton, California, dated June 11, 1999. Between August and October 1999, T&R oversaw a geophysical survey on Parcels 2A, 3, and 4, which involved the excavation of exploratory test pits (2ATP-1 through 2ATP-5, 2BTP-1, 3TP-1 through 3TP-4, 4TP-1 through 4TP-3) to determine the location of suspected underground structures including underground storage tanks (USTs), sumps, and pipelines. Additional soil borings were drilled (2AB-1 through 2AB-4, 2BB-1 through 2BB-3, 36-1 , 36-2, and 413-1) and groundwater monitoring wells were installed (2BMW-1 , 3MW-1, and 2AMW-12 through 2AMW-15) in suspected areas of contamination. A preliminary endangerment assessment was performed on the parcels to evaluate the environmental health risk associated with residual petroleum hydrocarbon concentrations in soil and groundwater. Details are presented in T&R's Site Characterization Report, South Shore Parcels, Stockton, California, dated December 13, 1999. In 2001 , additional assessment activities were conducted by T&R in the vicinity of the Site within Parcel 3. Results are included in T&R's report entitled Subsurface Investigation for Area 3, dated August 17, 2001 . In September 2001, a total of 11 Cone Penetrometer Test (CPT) borings (DP-1 through DP-11) were drilled to investigate the following: (1 ) subsurface lithology; (2) the presence of SPH; (3) the lateral extent of petroleum hydrocarbon impacted groundwater east, south, and west of the Site; and (4) to investigate potential off-site sources upgradient (north-northwest) of the Site. Surficial soil samples were also collected from depths up to 5 ft below ground surface (bgs) to evaluate whether the presence of residual concentrations of metals present a threat to groundwater quality. Results are presented in the Clayton Group Associates (Clayton) report entitled Further Characterization at the West Weber • Avenue and North Lincoln Street Site, Parcel 2A, dated December 18, 2001 . Stantec