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City of Pleasanton Water Quality Division's Report on Water Quality Relative to Public Health Goals 2022 June 2022 -Page 6 of 8 The remaining 20% of the City's water supply, as noted, comes from local groundwater. Groundwater is water that comes from wells and springs. Both the City and Zone 7 use local groundwater to increase the volume of water available for their use. However,groundwater is used the most during the hot summer months, when demand for water increases dramatically. In the summer,the amount of groundwater in the City's distribution system can be as much as 50%of the water used on any given day. All of the City's water is disinfected with chloramine to rid the supply of any harmful bacteria and is fluoridated prior to delivery. Water Quality Data Considered All of the water quality data collected by the City's water system in calendar years 2019,2020, and 2021 for purposes of determining compliance with drinking water standards was considered. This data is summarized in our Annual Water Quality Reports that are provided to all of our customers prior to July 1 of each year(Reference No. 2). Constituents Detected That Exceeded a PHG or a MCLG during CY 2019-2021 The following is a discussion of constituents that were detected in one or more of the City's drinking water sources at levels above the PHG, and where there were no PHG levels, above the MCLG, during Calendar Years 2019—2021. Inorganic Chemical Constituents Copper Currently, there is no established MCL for Copper. Instead, the regulations recommend that the 90th percentile value of all samples collected from a predetermined number of household taps in the distribution system cannot exceed an Action Level of 1.3 mg/L for Copper. The PHG for Copper is 0.3 mg/L. Health Risk Category: The California Department of Public Health(CDPH), which sets drinking water standards, has determined that copper is a health concern at certain exposure levels. Copper, a reddish brown metal, is often used to plumb residential and commercial structures that are connected to water distribution systems.Copper contaminating drinking water as a corrosion by-product occurs as the result of the corrosion of copper pipes that remain in contact with water for a prolonged period of time. Copper is an essential nutrient, but at high doses it has been shown to cause stomach and intestinal distress, liver and kidney damage, and anemia. Level of Copper in City Drinking Water: Based on the 2019 copper resident tap samples from selected homes in Pleasanton, the 90th percentile value for copper was 0.65 mg/L,which is over the PHG of 0.3 mg/L, but below the action level of 1.3 mg/L. 6