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I <br />7 <br />�.J <br />J <br />J <br />J <br />APPENDIX G <br />GROUNDWATER DIRECTION, FLOW RATE CALCULATIONS, AND <br />HYDR®GRAPHS <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 = 0.0036 foot per foot (ft/ft) <br />n= 0.30 <br />The groundwater flow velocity was 120.2 ft/yr for the first quarter and was calculated as follows: <br />V = 10,100 ft/yr (0.0036 ft/ft) <br />0.30 <br />= 120.2 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 first quarter 2009 was calculated by <br />dividing the difference in groundwater elevations between contour lines 56.00 and 55.00 by the <br />lateral distance between the two elevations in the direction of groundwater flow (280 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 127.04 ft/yr for the second quarter and was calculated as <br />follows: <br />V = 10,100 ft/yr (0.0037 ft/ft) <br />0.30 <br />= 127.04 ft/yr <br />Permeability 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 />velocity. The hydraulic gradient for the second quarter 2009 was calculated by dividing the <br />Foothill Sanitary Landfill <br />1 " Semester 2009 Groundwater Monitoring <br />Department of Public Works/Solid Waste <br />County of San Joaquin —July 31, 2009 <br />