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1 ' Unique site features, One ( Sand zone at 20-25' ) . . . . . . . . . . . . . . . . . . . . . Score 9 1 TOTAL SCORE 43 pts ' Based on this analysis the site has a medium leaching potential therefore maximum allowable levels of diesel ( the site contamination below 11 feet ) which can reasonably be left without ' threat to groundwater is 1000 ppm. The residual contamination has even a greater safety factor when the entire area is repaved to eliminate surface water and rainfall penetration. The precipitation will then go to zero . DISPERSION MODEL The most probable vadose zone dispersion pattern is a pattern driven by matric gravity (osmosis) . This will yield a ' dispersion pattern with a greater vertical than horizontal component . Assuming 2: 1 horizontal to vertical dispersion of the diesel . This model will allow us to use a vertical arithmetic ' decrease away, from our sample points to model a 1000 ppm overdig cutoff line . We can use samples; SB-1 @ 4 ' (2600 ppm-D in fill ) , SB-1 a 10.5' ( 1300 ppm--D) and @ 24 ' (BRL , use 10 ppm) , SB-2 @ 14 .5 (210 ppm-D) and a 24 ' ( BRL , use 10 ppm) , SB-3 n0 9.5' ( 1500 t ppm-D and @ 24.5' ( BRL , use 10 ppm) and SB-4 @ 23' (290 ppm-D) to set vertical dispersion gradients. ' Therefore: SB-1 Gradient= (2600-1300 ppm) - 200 ppm/f t* 6.5 ' ' SB-1A Gradient - ( 1300-10 m) - 95.6 ppm/ft 13.5' ' SB-2 Gradient - (210-10 m) = 21 ppm/ft 9.5' SB-3 Gradient ( 1500-10 m) - 99 . 3 ppm/ft 15' *Should not use due to the sample at 4 ' being in fill material . ' Knowing that the Vadose Zone dispersion will not only go vertically but horizontally the application of the worst vertical gradient to S8--4 should give a Conservative margin of error for establishing it 's gradient in the zone above 23 feet . T & T EARTH SERVICES