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City of Redwood City 2016 Public Health Gc 9.A. - Page 9 <br /> less than the DLR should be considered zero. This approach is consistent with DDW practice <br /> for treating non-detected results as zero. <br /> Water Quality Data Reviewed for this Report <br /> Water quality data collected by the City of Redwood City during 2013, 2014, and 2015 for <br /> the purpose of determining compliance with drinking water standards were reviewed in <br /> order to prepare this PHG report. This data was summarized in our 2013, 2014, and 2015 <br /> Annual Water Quality Reports (also known as Consumer Confidence Reports (CCRs)) which <br /> were distributed to all of our customers through direct mail, and are available on the City <br /> website. Hexavalent chromium is not included in the Water Quality Reports because the <br /> levels detected were below the DLR established by DDW. <br /> Best Available Treatment Technology and Cost Estimates <br /> Both the USEPA and DDW adopt Best Available Technologies (BATs) for the purpose of <br /> reducing contaminant levels below the MCL. While a BAT may identify a process that can <br /> reduce the presence of a contaminant, the cost of implementation can be a major factor in <br /> deciding whether or not to adopt the process. For a system that is in compliance with MCL <br /> levels, cost considerations must be a factor. Striving to keep contaminants below <br /> PHG/MCLG levels must be evaluated with costs in mind. <br /> Costs are estimated for the implementation of BATs for each constituent exceeding a PHG <br /> or MCLG. The PHGs and MCLGs are set much lower than the MCL, and it is not always <br /> possible or feasible to determine what treatment is needed to further reduce a constituent <br /> to, or below, the PHG or MCLG. In some cases, such as when the MCLG or PHG is set at <br /> zero, there may not be commercially available technology to reach that level. The issue is <br /> further complicated because it is often not possible to verify by analytical means that the <br /> contaminant has been totally eliminated. In some cases, installing a treatment technology <br /> to try and further reduce very low levels of one constituent may, in turn, have adverse <br /> effects on other aspects of water quality. This report presents the required cost estimates <br /> to implement the BATs to reduce a contaminant to a level at or below the PHG/MCLG. <br /> II. CONSTITUENTS DETECTED THAT EXCEED PHG OR MCLG <br /> In reviewing water quality monitoring data collected during 2013, 2014, and 2015, City of <br /> Redwood City staff have concluded that a PHG report is required that addresses the <br /> contaminant lead and hexavalent chromium. The following section presents a discussion of <br /> lead which was detected in customer's homes at levels above the PHG and hexavalent <br /> chromium which was detected at the water supply source and distribution system: <br /> LEAD <br /> The PHG for lead is 0.2 parts per billion (ppb). Lead enters drinking water primarily through <br /> leaching of lead-containing materials in household piping. The corrosion of household <br /> 3 <br />