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7C Page 7 City of Redwood City 2010 Public Health Goal Report II. CONSTITUENTS DETECTED THAT EXCEED PHG OR MCLG In reviewing water quality monitoring data collected during 2007, 2008, and 2009, 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 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 main, brass/bronze water meters, brass/bronze curb valves, and brass/bronze corporation valves can all contribute to lead leaching Although the City of Redwood City's water sources are free of lead, several of the homes that participated in Redwood City's 2009 Lead and Copper Sampling had lead levels that exceeded the PHG of 2 ppb. Results from the lead and copper sampling represent the worst case conditions for lead levels in the distribution system. These samples are collected under a first-draw condition; which means that water must sit in the customer's piping for 6 hours before it is collected. These samples were taken from homes that are considered to be the highest risk locations. Lead levels at these locations may be higher than others because of the plumbing material used when these homes were built. Many of the samples collected during the lead and copper sampling tested below the PHG for lead. The probable reason for the difference in lead concentration at the individual residences can be attributed to the plumbing components at these residences. As shown in the following chart, 43% of the samples collected in 2009 tested below the PHG for lead; all the samples tested below the lead MeL I I ~ Result .".,.,.",. PHG -MCL 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 For water samples collected from a customer's tap, there is an action level adopted by the CDPH that Redwood City considers to be an MCL. The 90th percentile value for samples collected from appropriate household taps cannot exceed CDPH's action level (MCL) of 15 ppb, as prescribed in Chapter 17.5 of Title 22, California Health and Safety Code. During the 2009 Lead and Copper Sampling Redwood City's 90th percentile values for lead were below the 15 ppb MCL. 3