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0 APPENDIX G GROUNDWATER DIRECTION, AND FLOW RATE CALCULATIONS Groundwater elevations in the monitoring wells were obtained this semester. These measurements were used to define the direction and gradient of groundwater flow in the vicinity ' of the Foothill Sanitary Landfill. The groundwater flow direction is to the southwest. The average groundwater velocity in this area was calculated using the following equation (Darcy's Law): ' V=Ki n 0 1!� C n n J i1 V = maximum linear velocity K = permeability i = hydraulic gradient n = porosity K= 9.8 x 10-3 centimeters per second (cm/s) = 10,100 feet per year (ft/yr) i = 0. 00 16 foot per foot (ft/ft) n= 0.30 The groundwater flow velocity was 53.86 ft/yr for the second quarter and was calculated as follows: V = 10,100 ft/yr (0.0016 ft/ft) 0.30 = 53.86 ft/yr The permeability coefficient was determined with a slug test in well G-1 at the North County Recycling Center and Sanitary Landfill to be 9.8 x 10"3 cm/s. Well G-1 at North County monitors similar soil types at the equivalent horizon as the water -bearing zone beneath the Foothill Sanitary Landfill. The hydraulic gradient for the second quarter 2007 was calculated by dividing the difference in groundwater elevations between contour lines 52.00 and 50.00 by the lateral distance between the two elevations in the direction of groundwater flow (1,275 ft). An average porosity value of 0.3 was used, based on published porosity values for similar geologic materials. The groundwater flow velocity was 63.96 ft/yr for the first quarter and was calculated as follows: V = 10,100 ft/31_(0.0019 ft/ft) 0.30 = 63.96 ft/yr Permeability coefficients determined with a slug test in well G-1 ranged from 8.3 x 10-3 to 9.8 x 10-3 cm/s in the water -bearing zone beneath the landfill. The highest measured permeability Foothill Sanitary Landfill Public Works/Solid Waste V4 Semester 2007 Groundwater Monitoring G-1 County of San Joaquin — July 31, 2007