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PP 1 GROUNDWATER•W 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 North County Sanitary Landfill. The groundwater flow direction is to the south-southeast. The average groundwater velocity in this area was calculated using the following equation (Darcy's Law): Where V = Ki n 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 = 0.00045 foot per foot (ft/ft) n = 0.30 The groundwater flow velocity was 15.30 ft/yr for the third quarter and was calculated as follows: AMNL V = 10,100 ft/yr (0.00045 ft/ft) 0.30 = 15.30 ft/yr The hydraulic gradient for the third quarter 2012 was calculated by dividing the difference in groundwater elevations between contour lines -45.0 and -45.0 by the lateral distance between the two elevations in the direction of groundwater flow (1,100 ft). An average porosity value of 0.3 was used, based on published porosity values for similar geologic materials. The groundwater flow velocity was 19.23 ft/yr for the fourth quarter and was calculated as follows: V = 10,100 ft/yr (0.00057 ft/ft) 0.30 = 19.23 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 value of 9.8 x 10"3 cm/s was selected because it would produce the greatest groundwater velocity. The hydraulic gradient for the fourth quarter 2012 was calculated by dividing the ® difference in groundwater elevations between contour lines -47.0 and -47.5 by the lateral North County RC&SL Public Works/Solid Waste 2ntl Semester and Annual 2012 Groundwater Monitoring County of San Joaquin — January 15, 2013