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• S ECOR --- • -
<br /> PREVIOUS INVESTIGATIONS
<br /> Environmental investigations have been conducted at the Site since 1989. A summary of
<br /> previous assessments conducted at L&M OU, UOU, and MOU is presented below.
<br /> In August and September 1989, Applied Geosystems (AGS) conducted a soil gas survey (VP-1 xJ `
<br /> through VP-14) at the Waterfront Redevelopment Property, and subsequently installed three ,
<br /> groundwater monitoring wells (MW-1 through MW-3) at the Site. A water supply well survey
<br /> was also performed, which confirmed the presence of two municipal water supply wells in the r
<br /> vicinity of the Site. One of the municipal water supply wells, owned by the City of Stockton and p,^ i
<br /> constructed in 1972, was identified approximately 2,200 feet east of the Waterfront
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<br /> Redevelopment property. Another municipal water supply well, maintained by California Water r„,.
<br /> Service, was identified approximately 5,000 feet southeast of the Site. A total of six industrial ViV
<br /> wells were located at the Fiberboard Paper Company, approximately 2,000 feet southwest of ygt
<br /> the Site; these wells were reportedly installed between 1921 and 1954 (AGS, October 31, NFA
<br /> 1989).
<br /> In July 1990, sixteen soil borings (B-4 through B-19) were drilled by AGS to investigate the
<br /> extent of petroleum hydrocarbons beneath the Site. Four of the soil borings (B-4 through B-7)
<br /> were converted to groundwater monitoring wells (MW-4 through MW-7). Results are included in
<br /> AGS' report entitled Evaluation of Hydrocarbons in Soil and Ground Water at City of Stocktonk
<br /> Waterfront Redevelopment Property, West Weber Avenue and North Lincoln Street, Stockton,
<br /> California, dated January 29, 2001. t
<br /> In October 1996, a total of 22 additional soil borings (TR-1 through TR-22) were drilled across Q,
<br /> the site to determine the type and assess the extent of petroleum hydrocarbons in shallow soil ?10
<br /> and in groundwater. Four of the borings were converted to groundwater monitoring wells
<br /> (MW-8 through MW-11). Results are presented in Treadwell & Rollo's (T&R) report entitled tXVi
<br /> Subsurface Investigation, South Parcel, West Weber Avenue & North Lincoln Street, Stockton, 4
<br /> California, dated November 8, 1996.
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<br /> In January and February 1999, Environmental Resolutions Inc. (ERI) conducted a tidal study to n;,`r
<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 7i
<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 multi-
<br /> 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, 38-1, 36-2,
<br /> and 4B-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
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