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" <br /> . � <br /> ! <br /> | <br /> � It is the writer ' s understanding that the orimary concern of / <br /> the San Joaquin Co. regulatory authorities in this matter is � <br /> potential pollution of the ground water resulting from this | <br /> ! <br /> i incident. Hence the requirement of a ground water sample down � <br /> gradient from the site of the spill . Unfortunately, the ground i <br /> / <br /> i water flow direction keeos changing with time. i <br /> � <br /> � | <br /> Migration of pollutants in ground water is highly dependent <br /> on the permeabiIity of the formations through which the i <br /> � <br /> / <br /> pollutants are flowing The soils that underlie this site to a <br /> ' . , � <br /> depth of at least 25 feet are clays, clayey silts and silty <br /> ! clays. SpiIs o+ this type are generally considered to be very <br /> / low permeability soils to impervious soils. <br /> '| <br /> Relative values of permeability for various soils are shown / <br /> following in `he lowing table: � <br /> � ` ^ l <br /> ' <br /> | <br /> � Permeability k in cm/sec� 0 i]� te i <br />� very high over 1 x 10 to minus 1 coarse gravel | <br />, medium 1 x 10 to minus 1 -- 1 x sand, fine <br /> 10 to minus 3 sand ! <br /> i <br /> ' low l x 10 to minus 3 -- 1 x silty sand, <br /> 10 to minus 5 dirty sand <br /> | <br />} <br /> � very low 1 x 10 to minus 5 -- 1 x silt, fine / <br /> � ` <br /> 10 to minus 7 sandstone <br /> � imoervious less than 1 x 10 to minus 7 clay <br /> � <br />! ' <br />| ( Sowers and Sowers, p 93 ) <br /> � <br /> � <br /> � These coefficients of oermeability were determined by <br /> laboratory tests of undisturbeo soils samples. By definition, <br /> � the hydraulic gradient is 1 ft fall per 1 ft Van distance. <br />/ The soils beneath the site, nased on the aoove experimental ' <br /> data, can be assumed to have a coefficient of permeability of <br /> i between 10 to the minus 5 to 10 to the minus 7 cm/sec. Since the <br />' spill happened about 1 . 5 years ago, about 47 million seconds have ' <br />' elapsed since then. In order to get a handle on the maximum | <br />! distance that any oil which might have entered the ground water <br />| at the site of the spill might have traveled, one must oerform <br /> t <br /> some mathematics. <br />� . <br />| <br /> � <br />� | <br />' l <br /> x � <br />