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7A <br /> City of Redwood City <br /> Page 5 <br /> 2007 Public.Health Goal Report <br /> LEAD <br /> The PHG for lead is 2 parts per billion (ppb). Lead enters drinking water primarily through <br /> leaching of lead-containing materials in household piping. The corrosion of household plu.mbing <br /> systems such as those containing iead-based soitier used #o join copper pipe, brass and c'hrome- <br /> plated brass faucets, lead pipe connections from homes to the water main, brass/bronze water <br /> meters, brass/bronze curb valves, and brass/hronze corporafiion valves can all contrihute to lead <br /> leaching <br /> Although the Ciry of Redwood Ciry's wat�r sourccs are free of lead, several of the homes that <br /> participated in the Redwood City's 2004 and 2006 Lead and Capper Sampling had lead levels <br /> that exceeded the P�TG of 2 ppb. Results from the Lead an.d Copper sampling represent the worst <br /> case conditions for Icad levcls in the distribution system. These samples are cattected under a <br /> �rst-�raw condition; vvhieh means that water must s:t:n the eustomer's piping fox 6 hours before <br /> it is collected. These samples were taken from homes that are considered to be the highest risk <br /> locations. Lead levels at these iocations may be higher than others because of the plumbinb <br /> material used when these homes were built. Many of the samples collected during the Lead and <br /> Copper Sampling tested below the PHG for lead. The probable reason for the difference in lead <br /> concentration at the individual residences can be attributed to the plumbing components at these <br /> residences. <br /> As sliowra in the following chaYt, SS%of t�ie sarrtples collected irt 2006 tesded below the PHG; alI <br /> but one sample tested below the MC.L. <br /> REDWOOD C{TY 2006 LEAD SAMPLING RESULTS <br /> (First�raw Samples trom Customer's 7ap} <br /> so <br /> 5D <br /> _ _.. .. _ _ _.... ... _. <br /> 40 <br /> .0 <br /> �. <br /> t7. <br /> 0 3D <br /> Q <br /> LU <br /> J <br /> 20 <br /> MCL 15 ppb <br /> io <br /> ' i'HG 2 b <br /> 0 <br /> -,-. . . <br /> 1 2 3 4 5 6 7 8 9 10 11 '12 13 14 15 16 17 16 19 2D 21 22 23 24 25 26 27 28 29 30 31 <br /> FIRST DRAW SAMPLE <br /> For. water samples collected From a custorner's tap, there is an action level adopted by the CDHS <br /> instead of an MCL. The 90U' percentile va�ue for samples collected From appropriate househotd <br /> 3 <br />