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7.B.- Page 9of15 City of Redwood City 2019 Public Health Goal Report less than the DLR should be considered zero. This approach is consistent with DDW practice for treating non-detected results as zero. Water Quality Data Reviewed for this Report Water quality data collected by the City of Redwood City during 2016, 2017, and 2018 for the purpose of determining compliance with drinking water standards were reviewed in order to prepare this PHG report. This data was summarized in our 2016, 2017, and 2018 Annual Water Quality Reports (also known as Consumer Confidence Reports (CCRs)) which were distributed to all of our customers through direct mail, and are available on the City website. Best Available Treatment Technology and Cost Estimates Both the USEPA and DDW adopt Best Available Technologies (BATs) for the purpose of reducing contaminant levels below the MCL. While a BAT may identify a process that can reduce the presence of a contaminant, the cost of implementation can be a major factor in deciding whether or not to adopt the process. For a system that is in compliance with MCL levels, cost considerations must be a factor. Striving to keep contaminants below PHG/MCLG levels must be evaluated with costs in mind. Costs are estimated for the implementation of BATs for each constituent exceeding a PHG or MCLG. The PHGs and MCLGs are set much lower than the MCL, and it is not always possible or feasible to determine what treatment is needed to further reduce a constituent to, or below, the PHG or MCLG. In some cases, such as when the MCLG or PHG is set at zero, there may not be commercially available technology to reach that level. The issue is further complicated because it is often not possible to verify by analytical means that the contaminant has been totally eliminated. In some cases, installing a treatment technology to try and further reduce very low levels of one constituent may, in turn, have adverse effects on other aspects of water quality. This report presents the required cost estimates to implement the BATs to reduce a contaminant to a level at or below the PHG/MCLG. II. CONSTITUENTS DETECTED THAT EXCEED PHG OR MCLG In reviewing water quality monitoring data collected during 2016, 2017, and 2018, City of Redwood City staff have concluded that a PHG report is required that addresses the contaminant lead. The following section presents a discussion of lead which was detected in customer's homes at levels above the PHG. LEAD The PHG for lead is 0.2 parts per billion (ppb). Lead enters drinking water primarily through leaching of lead -containing materials in household piping. The corrosion of household plumbing systems such as those containing lead-based solder used to join copper pipe, brass and chrome -plated brass faucets, lead pipe connections from homes to the water 3 322