Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

Page 4 production wells. The difference between water levels inside a well casing and in the adjacent aquifer formation refers to the well efficiency needed for well capacity estimates. For example, if the water level in the wells declines by 100 feet during pumping but the aquifer groundwater level just outside the well filter pack declines by 50 feet, the well efficiency is considered to be 50%. A reasonable well efficiency target to strive for in most high-capacity production well drilling operations is 70 to 80%. For the purposes of the well capacity estimates (based on 24-hour specific capacity) described below, it was assumed that a production well at the Del Prado Park site could achieve a 75% well efficiency, while the production wells at the Tennis Court and Hansen Park sites were conservatively estimated to have 50% well efficiency. Lower well efficiencies were assumed at the higher specific capacity sites (Tennis and Hansen) primarily because in highly permeable sediments,the flow of water at higher pumping rates has a greater tendency to become turbulent, which increases friction losses and reduces well efficiencies. ĞůWƌĂĚŽWĂƌŬtĞůůĂƉĂĐŝƚǇƐƚŝŵĂƚĞ The upper end well capacity estimate for the Del Prado Park test well is summarized in Table 4. The average pumping rate of 252 gpm combined with a projected 24-hour drawdown of 15.6 feet yields a specific capacity of 16.2 gpm/ft. The April 2025 static water level of 17 feet below ground surface (bgs), combined with depth to top of first screen of 170 feet bgs, yields an available drawdown of 153 feet. Multiplying the specific capacity of 16.2 gpm/ft times the available drawdown of 153 feet yields an interim well capacity calculation of about 2,500 gpm. Applying a well efficiency factor of 75% yields a final upper- end well yield estimate of approximately 1,900 gpm. The lower end well capacity estimate is based on the same specific capacity, top of upper well screen, and well efficiency calculations/assumptions as summarized above. However, the April 2025 static water level of 17 feet bgs was substituted with a drought year assumed depth to water of 65 feet bgs based on review of groundwater elevation contour maps for 2021 and 2022, which yields an available drawdown of 105 feet compared to 153 feet for the upper end well capacity calculation. Multiplying the specific capacity of 16.2 gpm/ft times the available drawdown of 105 feet yields an interim well capacity calculation of 1,700 gpm. Applying a well efficiency factor of 75% yields a final lower-end well yield estimate of approximately 1,300 gpm (Table 4). Tennis Park Well Capacity Estimate The upper end well capacity estimate for the Tennis Park test well is summarized in Table 4. The average pumping rate of 549 gpm combined with a projected 24-hour drawdown of 9.6 feet yields a specific capacity of 57.2 gpm/ft. The April 2025 static water level of 17 feet below ground surface (bgs), combined with depth to top of first screen of 195 feet bgs, yields an available drawdown of 178 feet. Multiplying the specific capacity of 57.2 gpm/ft times the available drawdown of 178 feet yields an interim well capacity calculation of 10,200 gpm. Applying a well efficiency factor of 50% yields a final upper-end well yield estimate of approximately 5,100 gpm. The lower end well capacity estimate is based on the same specific capacity, top of upper well screen, and well efficiency calculations/assumptions as summarized above. However, the April 2025 static water level of 17 feet bgs was substituted with a drought year assumed depth to water of 75 feet bgs based on review of groundwater elevation contour maps for 2021 and 2022, which yields an available drawdown of 120 feet compared to 178 feet for the upper end well capacity calculation. Multiplying the specific capacity of