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R603 UPDATE-27 5/17/94 1 .0 INTRODUCTION This update, STATUS UPDATE #27 , presents data from February 21, through March 29, 1994, collected at the site on March 3 , 4 , 7, 23 and 29, 1994 Since the repairs, completed on February 1, 1994 , the system has operated at 1000 The permit to dump treated ground water to the sewer was received and presently we are batch dumping the treated water from the "ConVault" monthly This water is collected from the vapor recovery condensate dropouts and the water produced from the sampling and monitoring of the monitor wells by Lawrence Tank Testing (LTT) pumping service We are presently evaluating the need for a continuous pump and treat system If it is determined that continuous pumping of ground water is needed, monitor wells MW1 and MW3 will be continuously pumped, see Appendix B - Sewer Discharge Report LOCATION The station is located at 6425 Pacific Avenue at the intersection of Douglas Road, Stockton, in San Joaquin County, California The site lies in Section 21, T2N, R6E, MDB&M at approximately 12 feet above mean sea level (MSL) (see Figures 1 , 2 , 3 ) The parcel is # 31 and can be located in Assessor' s Book 97 on page 41 (97-041-31) On October 2 , 1992 , a licensed surveyor with Nolte & Assoc surveyed all monitoring well locations and top of casing elevations to a known datum, ie City of Stockton Bench Mark Number 12 , elevation 11 74 ' above mean sea level 2 . 0 GROUND WATER LOCAL GROUND WATER FLOW Ground water flow direction in this region is to the west and towards south Stockton from the foothills of the Sierra Nevada Mountain Ranges, and towards the east from the Sacramento-San Joaquin Delta At present, encroachment of saline waters from the Delta is impairing the quality of the ground water in the Stockton area Vapor extraction has created a ground water potentiometric low (an apparent mounding) beneath the site near MW1, MW2 , MW3 and MW10 Measurements obtained on February 10 , 1994 , represents ground water gradient the day following restart of the vapor extraction system Vapor extraction is being concentrated on MW9 MMI arra MW10 see Figure 4A Figure 4B (March 29 , 1994) , shows the effective potentiometric lows at these wells, with flow occurring towards MW10 Currently the ground water is in a continuation of a recharge cycle produced from the Winter of 1993/1994 precipitation, see Depth to Water measurements on Table 1 As would be expected, changes in vacuum at the wells influences the shape of the potentiometric surface PAGE 1