Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

Zone 7 Water Agency – Hansen Park Test Well Summary and Production Well Design Recommendations 5 Zone 7 Water Agency December 2025 requirements of the City’s Waste Discharge Permit. Benzo-a-pyrene was not detected in that testing. Based on the fact there have been no detections of benzo-a-pyrene in other wells in Pleasanton area and the non-detect in the initial sample from the well, LSCE believes that sample was contaminated and is not representative of groundwater. Based on a review of water quality data for the City of Pleasanton and Zone 7 wells, iron, aluminum, and manganese concentrations are typically non-detect or below their respective MCLs. Iron and aluminum concentrations can be elevated in a turbid sample. Aluminum has typically been non-detect in the City of Pleasanton and Zone 7 wells. The concentration of aluminum in the Hansen Park well was 0.44 mg/l. The concentration of iron in the well was 0.54 mg/l. LSCE believes that, based on the water quality of other wells in the area and the elevated turbidity of samples, the levels of aluminum and iron are not representative of groundwater. The concentration of manganese was 0.045 mg/l, below its MCL of 0.050 mg/l. It has been our experience that manganese concentrations in monitoring wells and test wells can be higher than observed in production wells. That is, water produced from monitoring wells or test wells will have elevated manganese concentrations, whereas production wells completed in the same formations have lower concentrations or are non-detect for manganese. LSCE has recognized this phenomenon in monitoring and test wells across the state, in different geologic environments, using different drillers and drilling techniques, and different laboratories. In our experience, this only occurs with manganese. The most probable cause for elevated concentrations of manganese in the test well is related to well development techniques and limitations. Due to the size of the well casing, limited screen section lengths, water levels during pump and surge development, pump size limitations, and well yield, the development of a small-diameter well can be less effective than can be achieved in a large-diameter well. The development of a full-size production well can be more vigorous and effective than is possible in a small- diameter well with isolated zones. LSCE believes that the large discharge volumes and development techniques utilized in production wells results in more effective well development and removal of residual drilling fluids and formation material than is possible in small diameter wells. Based on our experience and the water quality of other wells in the vicinity of the Del Prado test well, and the limitations of development of a small-diameter well, we believe that the elevated concentration of manganese is not representative of groundwater. While meeting Title 22 water quality standards, hardness and total dissolved solids values exceed Zone 7/City of Pleasanton’s water quality targets. The exceedances are summarized in Table 5. Table 5. Water Quality Targets and Exceedances Parameter Target Result Hardness 150 mg/l 410 Total Dissolved Solids 500 mg/l 542