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0 2010 TIDEWATER STOCKTON WORK PLAN PREVIOUS INVESTIGATIONS Summary of Site Investigations by Others Environmental investigations have been conducted at the Site since 1989. A summary of previous assessments conducted at L&M OU, UOU, and MOU is presented below. In August and September 1989, Applied Geosystems (AGS) conducted a soil gas survey (VP-1 through VP-14) at the Waterfront Redevelopment Property, and subsequently installed three groundwater monitoring wells (MW-1 through MW-3) at the Site. A water supply well survey was also performed, which confirmed the presence of two municipal water supply wells in the vicinity of the Site. One of the municipal water supply wells, owned by the City of Stockton and constructed in 1972, was identified approximately 2,200 feet east of the Waterfront Redevelopment property. Another municipal water supply well, maintained by California Water Service, was identified approximately 5,000 feet southeast of the Site. A total of six industrial wells were located at the Fiberboard Paper Company, approximately 2,000 feet southwest of the Site; these wells were reportedly installed between 1921 and 1954 (AGS, October 31, 1989). In July 1990, sixteen soil borings (B-4 through B-19) were drilled by AGS to investigate the extent of petroleum hydrocarbons beneath the Site. Four of the soil borings (B-4 through B-7) were converted to groundwater monitoring wells (MW-4 through MW-7). Results are included in AGS' report entitled Evaluation of Hydrocarbons in Soil and Ground Water at City of Stockton Waterfront Redevelopment Property, West Weber Avenue and North Lincoln Street, Stockton, California, dated January 29, 2001. In October 1996, a total of 22 additional soil borings (TR-1 through TR-22) were drilled across the site to determine the type and assess the extent of petroleum hydrocarbons in shallow soil and in groundwater. Four of the borings were converted to groundwater monitoring wells (MW-8 through MW-11). Results are presented in Treadwell & Rollo's (T&R) report entitled Subsurface Investigation, South Parcel, West Weber Avenue & North Lincoln Street, Stockton, California, dated November 8, 1996. In January and February 1999, Environmental Resolutions Inc. (ERI) conducted a tidal study to determine the influence of tidal fluctuations on the direction of groundwater flow, collected additional data to evaluate concentration trends, and collected inorganic water quality data to investigate whether natural 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 feet) had little influence on the southerly direction of groundwater flow in the monitoring wells (less than 0.1 feet). Results of this multi- phase assessment are provided in ERI's Groundwater Monitoring and Sampling and Tidal