14 ATTACHMENT 1 EXHIBIT B - Laserfiche WebLink

Zone 7 Water Agency Executive Summary ES.2.4. Groundwater Quality Groundwater quality is an important factor in achieving and maintaining sustainable groundwater resources. The main purpose of monitoring groundwater quality is to assure that remediation of past groundwater degradation is proceeding, and that no new degradation has occurred or is currently taking place. Zone 7 maintains a robust monitoring network of wells for annual sampling and reporting. Each well in the program is monitored and/or sampled to fulfill one or more specific objectives. The groundwater monitoring program conducts annual sampling and analysis for inorganic constituents of concern for meeting the Livermore Basin groundwater quality objectives. The four main constituents of concern that are monitored and have set minimum thresholds are total dissolved solids (TDS), nitrate, boron, and chromium (Cr). In addition, per- and polyfluoroalkyl substances (PFAS) were added to the list of analytes for all municipal supply wells and select monitoring wells in the 2019 WY. Zone 7 also has programs that review permits, correspondence, and monitoring reports required by other agencies related to contamination and nutrient loads (see ES 3.1, Water Quality Sustainability). Overall, there were no significant groundwater quality changes relative to the minimum thresholds encountered during the 2019 WY. A brief summary of the results of each of these constituents for the 2019 WY are provided below. TDS Many of the municipal supply wells in the Pleasanton area produced water having TDS concentrations greater than the minimum threshold of 500 milligrams per liter (mg/L) during 2019 WY. For the 2019 WY, the highest TDS concentration in Zone 7 wells was detected in samples collected from the Mocho wellfield (962 mg/L in Mocho 4) and a monitoring well located central to four active wellfields used for municipal and public supply (921 mg/L in 3S/1E 17B 4). These concentrations are down from the 2018 WY when TDS was detected at over 1,000 mg/L in these wells. Zone 7 used its Mocho Groundwater Demineralization Plant (MGDP) to help reduce the TDS in delivered water in the 2019 WY. Other planned corrective actions and strategies are described in Section 5.3.3.2, Salt Management Strategy of the Alternative GSP. Nitrates In the Lower Aquifer, nitrate was only detected above the minimum threshold in one Area of Concern (AOC), the Buena Vista AOC, during the 2019 WY. Nitrate concentrations exceeded the minimum threshold in two monitoring wells (10.2 mg/L in 3S/2E 5N 1 and 10.0 mg/L in 3S/2E 15E 2) and one municipal supply well (11.0 mg/L in CWS 19). The nitrate plumes appear to be stable and will continue to be monitored. Boron Boron has been detected above the minimum threshold of 1.4 mg/L in a handful of lower aquifer monitoring wells in the past and again in the 2019 WY. Boron was detected at slightly above 3.0 mg/L in monitoring well 3S/1E 171D11 in the Hopyard Wellfield (compared to 2.8 mg/L in the 2018 WY). Boron has never been detected above 1 mg/L in the Hopyard municipal supply wells. Annual Report for the Sustainable March 2020 Groundwater Management Program 2019 WY ES -10