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F-1 <br /> <br />APPENDIX F <br />GROUNDWATER DIRECTION AND FLOW RATE CALCULATIONS <br /> <br />Groundwater elevations in the monitoring wells were obtained this semiannual period. <br />These measurements were used to define the direction and gradient of groundwater flow <br />in the vicinity of the Foothill Sanitary Landfill. The groundwater flow direction is to the <br />south. The average groundwater velocity in this area was calculated using the following <br />equation (Darcy’s Law): <br /> <br /> V = Ki <br /> n <br /> V = maximum linear velocity <br /> K = permeability <br /> = 9.8 x 10-3 centimeters per second (cm/s) <br /> = 10,100 feet per year (ft/yr) <br /> i = hydraulic gradient <br /> = 0.002 foot per foot (ft/ft) <br /> n = porosity <br /> = 0.30 <br /> <br />Permeability coefficients were determined with slug testing in well G-1, located at the <br />North County Landfill, and ranged from 8.3 x 10 -3 to 9.8 x 10-3 cm/s in the water-bearing <br />zone beneath the landfill. The highest permeability (K) value of 9.8 x 10 -3 cm/s was <br />selected because it would produce the greatest groundwater velocity. Well G-1 (North <br />County Landfill), located approximately 10 miles NW of the Foothill Landfill, monitors <br />similar soil types at the equivalent horizon as the water-bearing zone beneath the Foothill <br />Sanitary Landfill. <br /> <br />An average porosity value of 0.3 was used, based on published porosity values for similar <br />geologic materials. <br /> <br />First Quarter 2025 <br /> <br />The groundwater flow velocity was 84.2 ft/yr for first quarter and was calculated as follows: <br /> <br />V = 10,100 ft/yr (0.0025 ft/ft) <br />0.30 <br /> = 84.2 ft/yr <br /> <br />The hydraulic gradient for first quarter 2025 was calculated by dividing the difference in <br />groundwater elevations between wells MW-4A and MW-6 by the horizontal distance <br />between the two elevations in the direction of groundwater flow (6,400 ft). <br /> <br />Second Quarter 2025 <br /> <br />The groundwater flow velocity was 80.8 ft/yr for second quarter and was calculated as <br />follows: