SITE INFORMATION AND CORRESPONDENCE

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It is the writer ' s understanding that the primary concern pf the San Joaquin Co. regulatory authorities in this matter is potential pollution of the ground water resulting from this , incident. Hence the requirement of a ground water sample down gradient from the site of the spill . Unfortunately, the ground water flow direction keeps changing with time. ^ ' Migration of pollutants in ground water is highly dependent on the permeability of the formations - through which the pollutants are flowing. The soils that underlie this site, to a � depth of at least 25 feet are clays, clayey silts and silty clays. Soils of this type are generally considered to be very low permeability soils to impervious soils. Relative values of permeability for various soils are shown in the following table: very high over 1 x 10 to minus 1 coarse gravel medium 1 x 10 to minus 1 -- 1 x sand, fine 10 to minus 3 sand ` low 1 x 10 to minus 3 -- 1 x silty sand , ' 10 to minus 5 dirty sand very low 1 x 10 to minus 5 -- 1 x silt, fine 10 to minus 7 sandstone ' impervious less than 1 x 10 to minus 7 clay � ( Sowers and Sowers, p 93 ) These coefficients of permeability were determined by laboratory tests of undisturbed soils samples. By definition, ` the hydraulic gradient is 1 ft fall per 1 ft plan distance. The soils beneath the site, based on the above experimental data, can be assumed to have a coefficient of permeability of between 10 to the minus 5 to 10 to the minus 7 cm/sec. Since the spill happened about 1 . 5 years ago, about 47 million seconds have elapsed since then. In order to get a handle on the maximum distance that any oil which might have entered the ground water at the site of the spill might have traveled, one must perform. some mathematics. ' ` 4