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' Harding Lawson Assoc Ates <br /> findings that the primary direction of flow is north-northeast, <br /> with an average gradient of 0. 009 feet per foot. <br /> rPublished hydraulic conductivity values (Todd, <br /> 1976) for the types shallow subsurface materials found on the <br /> site are approximately 1 x 10-8 feet per second. This zone <br /> appears to be confined or semi-confined, as evidenced by the site <br /> stratigraphy and the elevation of the potentiometric surface. <br /> ' The potentiometric surface is also subject to seasonal <br /> fluctuations, as noted in Table 1. <br /> C. Potential Sources of Petroleum Hydrocarbons <br /> The source of gasoline hydrocarbons is believed to be the <br /> former 10, 000-gallon unleaded gasoline tank. The dry well <br /> (Plate 2) may have served as a conduit for petroleum products <br /> ' that spilled to the ground surface to reach the groundwater. <br /> With the decommissioning of the 10, 000-gallon tank, the major <br /> source of gasoline hydrocarbons was removed. The dry well <br /> continues to serve as drainage for the parking area but should no <br /> longer serve as a conduit because gasoline is no longer <br /> ' distributed on site. <br /> In December 1986, approximately two gallons of floating <br /> product were balled from MW-A and MW-B. These wells were <br /> installed by Southland to warn of gasoline leaks in the tank <br /> ' backfill. In December 1987 , MW-B was redrilled and converted to <br /> MW-7 . During excavation of the underground tanks in 1989, MW-A <br /> and MW-7 were destroyed. <br /> 5 <br />