Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

REGIONAL GROUNDWATER FACILITIES PROJECT FEASIBILITY STUDY 17 Zone 7 Water Agency December, 2025 3.3. Project Alternative Production Rates Each of the four project alternatives is capable of producing a range of instantaneous and annual volumes, with actual groundwater production influenced by both hydrogeologic setting/conditions and engineered well materials and pump equipment design features. Hydrogeologic setting/conditions include the thickness and continuity of water-bearing sands and gravels relative to less permeable materials, which determine aquifer transmissivity, defined as the aquifer’s ability to yield water when pumping induces drawdown. Seasonal water level fluctuations and long-term basin trends further affect available drawdown and, therefore, sustainable production. Siting of a production well site a significant distance from the test well site may result in different hydrogeologic conditions (e.g. yield and/or water quality). Well construction characteristics also play a critical role. Production capacity depends on drilling contractor performance/efficiency, selection and placement of well screens, screen length, and gravel pack design. The position of the uppermost screen interval is particularly important for accessing available drawdown in the well (defined as the difference between the static water level and the top of the well screen). Collectively, these factors establish the specific capacity (Q/s) and ultimately the production rate of the well, defined as the pumping rate achieved per unit of drawdown (expressed in gpm/ft). Pump equipment design must then be optimized in consideration of site-specific hydrogeologic and well construction conditions. Properly sized bowls, column, shaft, and motors allow the pump to utilize the full drawdown range from static water levels down to the top of the screen. If any one of these system components (hydrogeologic setting/conditions, well design/construction, or pumping equipment) is suboptimal, the overall capacity of the well is constrained. Conversely, when all three are optimized together, wells can reliably achieve their design production rates and sustain long- term groundwater development. Table 4 summarizes the estimated production capacities for each project alternative under drought-year, average-year, and wet-year conditions. Annual production estimates assume an 18-hour daily runtime (6,570 hours per year), consistent with Zone 7’s 75-percent reliability factor for facility operation and provide a common basis for comparison against Zone 7’s 7,000 AFY drought-year production objective. Results indicate that Alternatives 1 and 3 cannot meet the 7,000 AFY target while operating within the 18- hour limit and therefore are not considered viable for Zone 7’s production goals, though they are carried forward for informational and comparative purposes. At the upper end, Alternative 4 is capable of producing approximately 9,800 AFY under drought conditions; however, Zone 7 does not intend to produce more than 9,000 AFY during drought years, as groundwater sustainability impacts have not been modeled beyond this annual production total for drought years. As a result, the additional production capacity represented by Alternative 4 would not be utilized under normal operating conditions, effectively increasing capital cost without a proportional supply benefit leaving Alternative 4’s only primary advantage of enhanced operational flexibility and reliability beyond Zone 7’s standard policy requirements.