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~ Former Beacon Station No. 12474 March 18,2002 Stockton California Problem Assessment Report/Corrective Action Plan 4 of groundwater within the San Joaquin River hydrologic basin is from the adjacent flanks of • the Sierra Nevada and Coast Ranges provinces toward the axis of the Great Valley structural trough, which is generally located in the western portion of the Central Valley, nearer to the Coast Ranges and west of the site. The natural, regional groundwater flow then generally runs north-northwest parallel to the axis of the structural trough. Depth to groundwater at the site has risen from approximately 80 feet below surface grade (bsg) in 1993 to approximately 55 feet bsg in 2001. During the most recent four quarters of monitoring, groundwater flows were northeast to southeast under gradients of 0.001 to 0.004 as shown on Figure 5. 4.0 SENSITIVE RECEPTOR SURVEY AND WELL SEARCH Horizon conducted a sensitive receptor survey for the area within a 2000-foot radius of the site. The sensitive receptor survey included identification of natural surface water bodies and a water well search in the survey area. Mormon Slough trends roughly east-west at the southern edge of the survey area. Flow in Mormon Slough is diverted into Stockton Diverting Canal approximately 3 miles east (upstream) of the survey area. The cut off Mormon Slough is tributary to the Stockton Deep Water Channel at Morelli Boat Ramp Park approximately 4 miles west of the survey area. No other naturally occurring surface water bodies were identified within the survey area. Authorization to review well records at the California Department of Water Resources (DWR) was obtained from San Joaquin County Environmental Health Division (SJCEHD). Vista Information Solutions (Vista) was contracted to perform a search for wells within one- half mile of the site. The Water Well Report is contained in Appendix C of this report and includes a map showing the position of the wells relative to the site. Twelve well locations were identified within the 2000-foot radius of the site as summarized in Table 2. Eleven 474PARCAP3-02.doc 5 Project No. 1474.23 HORIZON ENVIRONMENTAL INC.