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3 . RESULTS <br /> 3 . 1 SITE HYDROGEOLOGY <br /> The three new off-site soil borings encountered similar sediments <br /> to those underlying the site. The area is underlain mainly by <br /> silty and clayey sediments to the maximum investigated depth of <br /> ` 38 feet (MW10 ) , intermingled with more sandy lenses of variable <br /> thickness . These sandy lenses ( Figure 3 ) ranged in thickness <br /> from 3 feet at MW10 to 12 feet at MW8 . Table 1 shows the refer- <br /> ence elevations of the tops of well casings and the ground-water <br /> elevations between 6 November 1987 and it April 1988 . Ground <br /> water on 11 April 1988 was at depths between 20 and 24 feet-- <br /> elevations below mean sea level ranging from -12 . 47 feet at MW8 <br /> r <br /> to -14 . 57 feet at MW10 . Ground-water movement was northeasterly <br /> at a gradient of 0. 006. Well gauging indicated that the ground- <br /> water level fell about two feet between February and April (Table <br /> 1 ; Figure 3 ) . <br /> The ground-water velocity in sandy lenses may be estimated as <br /> V = Ki/n <br /> where <br /> K = hydraulic conductivity = 10-5 m/s ( Freeze and Cherry <br /> 1979 ) <br /> i = hydraulic gradient 0 . 006. <br /> n = effective porosity = 0. 3 for silty sand ( Freeze and <br /> Cherry, 1979 ) . <br /> r <br /> The resulting estmate is <br /> V = 2 x 10-7 meters per second ( about 20 feet/year ) . <br /> e20/73942 5 <br /> r <br />