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North County RC&SL Public Works/Solid Waste <br />First Semiannual 2024 Groundwater Monitoring ©2024 COUNTY of San Joaquin. All Rights Reserved. <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 North County Sanitary Landfill. The average groundwater velocity in <br />this area was calculated using the following equation (Darcy’s Law): <br /> V = Ki <br /> n <br />Where <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 = (difference between groundwater elevations) / distance <br />between measuring locations) in foot per foot (ft/ft) <br /> n = 0.30 <br />Permeability coefficients determined with a slug test in well G-1 ranged from 8.3 x 10-3 to <br />9.8 x 10-3 cm/s in the water-bearing zone beneath the landfill. The highest measured <br />permeability value of 9.8 x 10-3 cm/s was selected because it would produce the greatest <br />groundwater velocity. An average porosity value of 0.3 was used, based on published <br />porosity values for similar geologic materials. <br />First Quarter 2024 <br />Between wells G-12 and G-5B <br />The hydraulic gradient (0.0005 ft/ft) was calculated by dividing the difference in <br />groundwater elevations between wells G-12 and G-5B by the horizontal distance between <br />the two wells (2,070 feet). <br />The groundwater flow velocity was 17 ft/yr was calculated as follows: <br /> <br /> V = 10,100 ft/yr (0.0005 ft/ft) <br /> 0.30 <br /> = 17 ft/yr <br /> <br />Between wells G-7 and G-9 <br />The hydraulic gradient (0.001 ft/ft) was calculated by dividing the difference in <br />groundwater elevations between wells G-7 and G-9 by the horizontal distance between <br />the two elevations (3,050 feet).