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r � \_1 groundwater flow direction indicate that a dissolved plume has migrated to and is assumed to have crossed the Delta Disposal property line. 2.0 2000-foot Radius Well Survey Sensitive Receptor Survey Wright performed a 2000-foot radius search for wells around the Delta Disposal site. The search will use the available information from the Department of Water Resources files and City of Tracy files to document municipal, domestic, agricultural, industrial and other wells. The information is compiled into a summary table together with a map showing the well locations (see Figure 1 and Table 1). The well locations are approximate on Figure 1 and based upon the information on the individual well log; in some cases the well location, logging and well construction information may not be precise or incomplete from the well search information on the Well Completion Reports. Also in most cases the current use status of individual wells is not known. Groundwater monitoring wells installed for regulatory compliance issues are not plotted on this search. The well search revealed City of Tracy-owned wells, and domestic wells occur in the area in and around the search radius. Several domestic wells are beyond the 2000-foot radius search radius and two domestic wells have been destroyed. Two Tracy Unified School District wells were destroyed in 2000. One irrigation well noted numerous screened intervals but no seal is reported. Based on the available well screen information, the wells appear to be screened below the uppermost aquifer sampled for this study. Well annular seals on the available State reports appear to extend at least 50 feet or greater below the ground surface (except the irrigation well). Some City of Tracy wells did not have a seal depth noted on the reports, however it is assumed these wells were sealed. In our opinion based upon the well information available there does not appear to be a threat to sensitive receptor wells since the contaminant plume appears relatively small and well seals extend through the shallow aquifer and screened intervals are below the shallow aquifer. 3.0 Field Methods—Drilling and Sampling Exploratory Borings Three (3) exploratory borings were drilled at the locations shown on Figure 1. Drilling and well installation permits were secured from the SJC/EHD, and an underground utility clearance was performed prior to doing the fieldwork. A site safety plan and traffic control plan was prepared for the site work. The wells were installed on the north and south side of 6'h Street. The wells were advanced to depths of about 25 feet into the shallow aquifer. The boreholes were drilled with a truck-mounted hollow-stem auger rig. All drilling equipment and sampling tools were cleaned prior to arriving, and before leaving the site. The decontamination process used a tri-phosphate soap to wash the soil sampler between each sample run and each borehole. Augers and drill rods were decontaminated in similar fashion between each borehole using a pressure washer to clean and remove soil/sediment adhering to the augers, rods and drill bits. The hollow-stem augers were advanced and discrete soil samples were collected at five-foot intervals of depth from each borehole. The augers and drill rod was Page 2 of 11