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' 8 Average annual rainfall in Stockton is 14 inches, more than 80% of which falls between November and March Average monthly rainfall from May to September is less than 0 5 inches Eleven of the last 14 years (1984-1997) have been dner than the annual average of 14 q��,q7 inches with a particularly dry 3 year period from 1988 through 1990 where annual rainfall was q-1^�� ' less than 10 inches ' 3.2 SITE SOIL CONDITIONS Previous investigations indicate that the Site is underlain by primarily fine-grained ' deposits consisting of interlayered clays and silts to an approximate depth of 50 feet Silts and silty sands occur to a depth of approximately 25 feet Occasional urterlayered silty sands(up to 50 feet duck)were reported to the total depth investigated ' Previous investigations also indicate that hydrocarbon concentrations in the soul appear to be limited to the area around the former product islands Sods in the vicinity of the northern product island at location VW-2,within the depth interval of 20 to 30 feet bgs, were found to ? p, 606 have TPHg concentrations ranging from 1,400 e00 g kg v�nth benzene concentrations ' ranging from 0 27 to 28 mg/kg Within 15 feet of VW-2, at locations MW-2 and KB-2, soil concentrations decreased to below 28 mg/kg TPH, and less than 1 mg/kg benzene between depths of 25 and 30 feet bgs In the area around the southern product island, Boring KB-3 ' contained 239 mg/kg TPN and 112 mg/kg benzene ' 3.3 SITE GROUNDWATER CONDITIONS ' Groundwater occurs beneath the Site within fine-grained deposits Groundwater at the Site has been consistently observed to flow northeast, since 1988, at an approximate gradient ' of 0 002 The maximum groundwater fluctuation of 17 5 feet was measured in well MW-1 between 1988 and 1993 Because of the fluctuations in groundwater, wells MW-1 and MW-2 ' were dry between 1990 and 1992 Well MW-3 continued to be dry through the first quarter 1993