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~ BROWN AND CALDWELL CONSULTING ENGINEERS WATER STABILITY, CORROSION, AND LEAD CONTROL FOREWORD The nationwide concern about lead toxicity and the U, S. Environmental Protection Agency's proposed new lead-copper regulation have heightened the interest of water supply professionals in the topics of water stability, internal piping corrosion, and lead leaching, Brown and Caldwell engineers Douglas T. Merrill, Ph.D., PE, and Gary P. Silverman, PE prepared this compendium to give an understandable overview of these topics. This overview covers some practical relationships between chemical stability and lead leaching, but readers should be aware that no single index or set of parameters provides simple operating guidelines for control of these potential problems in water distribution systems . Water chemistry changes proposed to solve one problem should always be checked for their effect on other water characteristics, Regulations Since 1980, the U.S. Environmental Protection Agency (EPA) has required a one-time monitoring of parameters related to internal corrosion. These include pH, calcium, alkalinity, temperature, total dissolved solids (TDS). and calculation of the Langelier Saturation Index (LSI). EPA has also estab- lished a qualitative secondary drinking water standard for corrosivity that requires water to be "noncorrosive," This requirement has often been interpreted to mean an LSI between -0.2 and +0.2, On August 18,1988, EPA proposed a new regulation for controlling lead and copper in drinking water' These constituents primarily occur as corro- sion by-products from household piping and plumbing fixtures, Since water utilities typically have no jurisdic- tion over household plumbing, EPA has proposed a corrosion control treatment standard as well as numerical standards for lead and copper, The EPA proposal sets up three criteria for determining if corrosion treatment beyond current levels is needed. These require that (1) average lead levels be 10 ppb or below, (2) pH be 8.0 or greater in at least 95 percent of the samples, and (3) copper levels be 1 .3 ppm or less in at least 95 percent of the samples. These parameters are to be measured in first- draw samples from buildings targeted as being likely to have lead in the drinking water. If any of these cri- teria are violated, the water utility must develop a treatment program detailing methods for complying. Any treatment program must either achieve the criteria listed above or, alternatively, demonstrate that treatment is optimal to minimize lead and copper leaching. Operations at pH values iess than 8.0 may be ail owed in certain cases. In addition, if average lead levels are greater than 10 ppb, or if lead levels exceed 20 ppb more than 5 percent of the time, the utility must conduct a public education program to en- courage consumers to reduce their exposure to lead in drinking water, Stability A stable or saturated water is in equilib- rium with respect to a particuiar solid it contacts. An oversaturated water tends to precipitate that solid, forming a scale, Small amounts of scale, which tend to form on the active areas of corroding pipe, can ar- rest or retard the corrosion process. However, a highly oversaturated water can deposit excessive scale, reducing flow and increasing maintenance and pumping costs. On the other hand, an undersaturated water usually cannot deposit a protective scale. Such waters are often described as aggressive or corro- sive, but "nonprotective" is probably a more accurate description. Without protection, the pipe corrodes. Corrosion can cause leakage or tuberculation, which results in loss of hydraulic capacity,2 It can also cause adverse health and aesthetic effects when pipe materials like lead, copper, and iron are released into the water.