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ON <br /> ;.m <br /> 4.4 DISCUSSION <br /> 4.1 Hydrogeology <br /> F , The ground-water gradient remains to the south-southwest at approximately 0.004 feet/fect <br /> (21 feet/mile). This is similar to the November data when the water table was at a lower <br /> level (ESE, 1991). No wells exist within a mile of the subject site in the present dow. <br /> gradient direction (Figure 4 - Site Vicinity Wells). <br /> In a telephone conversation on February 21, 1991 with Mr.Jack Merrill of the Mainland <br /> Nursery, he revealed that the water levels in the nursery's two water supply wells are <br /> significantly lower (at least 11 feet) during the warm months when the water demands o <br /> the nursery are much greater. Pumping of these two wells may depress the water table thus <br /> 1.� <br /> causing the ground-water gradient at the site to switch to the north at that time. <br /> Water in the unlined Woodbridge Canal immediately to the cast of the site is at an <br /> E elevation at least 30 feet higher than the water table. On November 5, 1990 the relative <br /> elevation of water in the canal was surveyed at 31.56 feet or 30.79 feet higher than the <br /> ground water in MW-3. Thus the canal is a losing stream and considering the current <br /> ground-water gradient,water from the canal must percolate towards the site. <br /> 4.2 Ground Nater Analysis <br /> " The reported concentration for Toluene, the only hydrocarbon detected, at a maximum 0.8 <br /> ug/L remains well below the State of California Action Level for drinking water based on <br /> K toxicity 100 ug/L (Regional Board, 1989). No Xylenes were detected during recent <br /> t sampling. On November 5, 1990 Toluene and Total Xylenes were detected in MW-2, a <br /> cross-gradient well, and Toluene in MW-1, a down-gradient well from the former <br /> t.1 underground tank site (ESE, 1991). On February 6, 1991 Toluene was only detected in <br /> MW-1 and MW-3, a currently up-gradient well. A temporary gradient to the north due to <br /> ave caused some hydrocarbons to migrate in that <br /> the pumping of the nursery wells might h <br /> direction. The stronger influence (in temporal terms) of the regional gradient to the <br /> southwest should cause most hydrocarbons to back track across the site. The remainder of <br /> .A, <br /> 10 _.._ ...._..____... <br />