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Stantec
<br /> Report of Findings for the Waterfront Towers Separate Phase Hydrocarbon Investigation
<br /> and Unocal Extraction Well Pilot Study
<br /> Waterfront Towers Parking Lot
<br /> March 4, 2011
<br /> Service, was identified approximately 5,000 feet southeast of the Site. Six industrial wells were
<br /> located at the Fiberboard Paper Company, approximately 2,000 feet southwest of the Site;
<br /> these wells were reportedly installed between 1921 and 1954 (AGS, October 31, 1989).
<br /> In July 1990, 16 soil borings (B-4 through B-19) were drilled by AGS to investigate the extent of
<br /> petroleum hydrocarbons beneath the Site. B-4 through B-7 were converted into groundwater
<br /> monitoring wells (MW-4 through MW-7). Results are included in AGS' Evaluation of
<br /> Hydrocarbons in Soil and Ground Water at City of Stockton Waterfront Redevelopment
<br /> Property, West Weber Avenue and North Lincoln Street, Stockton, California, dated January 29,
<br /> 2001.
<br /> In October 1996, 22 additional soil borings (TR-1 through TR-22) were drilled across the Site to
<br /> determine the type and assess the extent of petroleum hydrocarbons in shallow soil and in
<br /> groundwater. Four of the borings were converted into groundwater monitoring wells (MW-8
<br /> through MW-11). Results are presented in Treadwell & Rollo's (T&R) Subsurface Investigation,
<br /> South Parcel, West Weber Avenue & North Lincoln Street, Stockton, California, dated
<br /> November 8, 1996.
<br /> In January and February 1999, Environmental Resolutions Inc. (ERI) conducted a tidal study to
<br /> determine the influence of tidal fluctuations on the direction of groundwater flow, collected
<br /> additional data to evaluate concentration trends, and collected inorganic water quality data to
<br /> investigate whether natural attenuation is occurring beneath the Site. Pressure transducers/data
<br /> loggers were installed in wells MW-5, MW-8, and MW-9 to monitor changes in water levels
<br /> within the monitoring wells over a 48-hour period. Results of the tidal study indicated that over
<br /> the testing period, observed tidal changes (up to 4 feet) had little influence on the southerly
<br /> direction of groundwater flow in the monitoring wells (less than 0.1 feet). Results of this
<br /> multi-phase assessment are provided in ERI's Groundwater Monitoring and Sampling and Tidal
<br /> Influence Study Report, The Stockton Group Site, West Weber Avenue and North Lincoln
<br /> Street, Stockton, California, dated June 11, 1999.
<br /> Between August and October 1999, T&R oversaw a geophysical survey on Parcels 2A, 3, and
<br /> 4, which involved the excavation of exploratory test pits (2ATP-1 through 2ATP-5, 2BTP-1,
<br /> 3TP-1 through 3TP-4, 4TP-1 through 4TP-3) to determine the location of suspected
<br /> underground structures including underground storage tanks (USTs), sumps, and pipelines.
<br /> Additional soil borings were drilled (2AB-1 through 2AB-4, 2BB-1 through 2BB-3, 313-1, 313-2,
<br /> and 413-1) and groundwater monitoring wells were installed (2BMW-1, 3MW-1, and 2AMW-12
<br /> through 2AMW-15) in suspected areas of contamination. A preliminary endangerment
<br /> assessment was performed on the parcels to evaluate the environmental health risk associated
<br /> with residual petroleum hydrocarbon concentrations in soil and groundwater. Details are
<br /> • presented in T&R's Site Characterization Report, South Shore Parcels, Stockton, California,
<br /> dated December 13, 1999.
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