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8.A. - Page 7 ctry ofxedwood ctry <br /> 2013 Public Health Goal Report <br /> II. CONSTITUENTS DETECTED THAT EXCEED PHG OR MCLG <br /> In reviewing water quality monitoring data collected during 2010, 2011, and 2012, City of <br /> Redwood City staff have concluded that a PHG report is required that addresses the <br /> contaminant lead. The following section presents a discussion of lead which was detected <br /> in customer's homes at levels above the PHG: <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 /> plumbing systems such as those containing lead-based solder used to join copper pipe, <br /> brass and chrome-plated brass faucets, lead pipe connections from homes to the water <br /> main, brass/bronze water meters, brass/bronze curb valves, and brass/bronze corporation <br /> valves can all contribute to lead leaching <br /> Although the City of Redwood City's water sources are free of lead, several of the homes <br /> that participated in Redwood City's 2012 Lead and Copper Sampling had lead levels that <br /> exceeded the PHG of 0.2 ppb. Results from the lead and copper sampling represent the <br /> worst case conditions for lead levels in the distribution system. These samples are collected <br /> under a first-draw condition; which means that water must sit in the customer's piping for 6 <br /> hours before it is collected. These samples were taken from homes that are considered to <br /> be the highest risk locations. Lead levels at these locations may be higher than others <br /> because of the plumbing material used when these homes were built. Many of the samples <br /> collected during the lead and copper sampling tested below the PHG for lead. The probable <br /> reason for the difference in lead concentration at the individual residences can be <br /> attributed to the plumbing components at these residences. <br /> As shown in the following chart, 14 of 34 samples collected in 2012 tested below the PHG for <br /> lead. One sample tested above the Action Level for lead, but the MCL was not exceeded <br /> because 90°0 of the samples were below the Action Level. <br /> is <br /> 16 <br /> 15 <br /> 14 - <br /> 12 <br /> lfl �Resuk <br /> -AL <br /> 8 <br /> PHG <br /> 6 <br /> [90[h Percentilej <br /> 4 z'4 <br /> az IIII � � � � � � � � � IIIII <br /> o , - __ ,,---r-�_r__r_,_,__�_- _ <br /> 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 <br /> 3 <br />