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II <br />r—. <br />i <br />u <br />Fi <br />u <br />fl <br />P <br />I'. <br />I <br />r' <br />0 <br />r <br />iI <br />u <br />d - <br />H <br />GROUNDWATER11 <br />DIRECTION, RATE CALCULATIONS,D <br />HYDROGRAPHS <br />Groundwater elevations in the monitoring wells were obtained this semester. These <br />measurements were used to define the direction and gradient of groundwater flow in the vicinity <br />of the Foothill Sanitary Landfill. The groundwater flow direction is to the southwest. The <br />average groundwater velocity in this area was calculated using the following equation (Darcy's <br />Law): <br />V=Ki <br />n <br />V = maximum linear velocity <br />K = permeability <br />i = hydraulic gradient <br />n = porosity <br />K= 9.8 x 10-3 centimeters per second (cm/s) <br />= 10,100 feet per year (ft/yr) <br />i = 0.0038 foot per foot (ft/ft) <br />n= 0.30 <br />The groundwater flow velocity was 127.9 ft/yr for the second quarter and was calculated as <br />follows: <br />V = 10,100 ft/yr ft/ft) <br />0.30 <br />= 127.9 ft/yr <br />The permeability coefficient was determined with a slug test in well G-1 at the North County <br />Recycling Center and Sanitary Landfill to be 9.8 x 10-3 cm/s. Well G-1 at North County <br />monitors similar soil types at the equivalent horizon as the water -bearing zone beneath the <br />Foothill Sanitary Landfill. The hydraulic gradient for the second quarter 2008 was calculated by <br />dividing the difference in groundwater elevations between contour lines 49.00 and 48.00 by the <br />lateral distance between the two elevations in the direction of groundwater flow (260 ft). An <br />average porosity value of 0.3 was used, based on published porosity values for similar geologic <br />materials. <br />The groundwater flow velocity was 134.66 ft/yr for the first quarter and was calculated as <br />follows: <br />V = 10,100 ft/y(0.004 ft/ft) <br />0.30 <br />= 134.66 ft/yr <br />Perineability coefficients determined with a slug test in well G-1 ranged from 8.3 x 10-3 to 9.8 x <br />10-3 cm/s in the water -bearing zone beneath the landfill. The highest measured permeability <br />value of 9.8 x 10-3 cm/s was selected because it would produce the greatest groundwater <br />Foothill Sanitary Landfill Department of Public Works/Solid Waste <br />1" Semester 2008 Groundwater Monitoring County of San Joaquin — July 31, 2008 <br />