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_ri <br />'y£ <br /> F✓z <br /> `r, Ric _Notini ?aye <br /> :.Iav 25. 1991 <br /> ZRM-West, Inc.. water levels were measured in the pre-existing wells. The <br /> -measurements verified that groundwater flows in a south. southwesterly <br /> direction. The gradient was found to van, as a result of tidally induced <br /> water level fluctuations in the nearby Stockton deep water channei. <br /> F. <br /> Coni cions and 13Pcommenda1iong <br /> The extent of the released gasoline appears to be limited both areally and <br /> with depth. The maximum lateral extent of affected soil and groundwater <br /> is approximately 30 feet in a downgradient direction Froin the tank(see <br /> Figure 1). <br /> The maximum concentrations encountered were at or near the <br /> groundwater surface, then decreased quickly with depth. The limiting <br /> factor for downward migration therefore was the presence of groundwater <br /> 4 at a shallow depth. <br /> fai <br /> San Joaquin County s next required phase of work is the preparation of a <br /> Problem Assessment Report (PAR). ERM-West, Inc. understands that the <br /> County has requested Catellus Development Corporation to submit a PAR <br /> by June 17, 1991 (copy of letter enclosed). ERM-West, Inc. recommends that <br /> ' an initial step in address�nR the request,the results of the latest fieldwork <br /> should be released to the Colanty. And at the same time, open discussions <br /> t with the County regarding their concerns and potential clean-up standards <br /> for the site. <br /> Secondly, ERM-West, Inc. recommends that the County be approached <br /> about postponing the June 17th deadline,pending the removal of two <br /> additional underground omstAssessmage ent Report addressing all ths. If problems are encountered <br /> ee sit sites <br /> � � those tanks. one <br /> .i ; instead of three reports would be more cost effective. <br /> i Well inurn i n <br /> Two monitoring wells were constructed by ERM-West, Inc. on April 12, <br /> 3 1991. The wells, labeled MW-4 and MW-5 were located hydraulically <br /> downgradient from the tank site and within the tank site respectively (see <br /> Figure I). The sail borings at each location were drilled to 30 feet and <br /> sampled at 5 foot intervals. .A portion of the sample at each depth interval <br /> k„a was preserved for subsequent laboratory- analyses. The remainder of the <br /> sampled soils were used for classification according to the Unified Soil <br /> t ; Classification System (see enclosed goring logs) and for preliminary <br /> iVs <br /> screening by head space analysis. <br /> � r <br /> After the borings were advanced to a depth of 30 feet, they were completed <br /> as monitoring wells. The wells were constructed of 2-inch diameter, flush- <br /> threaded, Schedule 40 PVC. The well screen was sF!t at a depth interval of <br /> -approximately 10 to-15 feet♦-The remainder of the boring,-from_15-tod witht, ---- - - - - <br /> ' was filled with sand. At the ground surface both wells were covered with <br /> traffic boxes. <br /> t:7 <br />