In January 2004, the Washington Post reported that the DC Water and Sewer Authority (WASA) had found elevated lead levels in the drinking water of more than 4,000 homes in Washington, DC, during testing done in 2003. Subsequently, water suppliers, local officials, and regulators have undertaken numerous actions intended to respond to citizens' concerns; to abate further exposures to lead from tap water; to identify the cause of the problem; and, ultimately, to reduce the occurrence of lead in DC's water and assess whether similar problems are occurring in other cities. To determine whether the problem in Washington, DC, is more widespread and to evaluate the effectiveness of the lead rule, EPA has undertaken a national review of lead monitoring conducted by water systems from 2000 through 2003. As of June 2004, EPA had received monitoring data for 744 (89%) of the 834 systems that serve more than 50,000 persons. EPA reported that 27 (3.6%) of these systems exceeded the action level of 15 parts per billion (ppb) at least once since 2000, and that 12 of 316 systems reported exceeding the action level during the monitoring period ending after January 2003. (These 12 systems serve a total population of 5.2 million people.) Among all systems serving more than 50,000 persons, 66% reported that the highest level observed during any monitoring period since 2000 was less than 5 ppb. EPA also received data for 6,678 (91%) of 7,833 systems that serve from 3,300 to 50,000 people. Of these systems, 237 (3.4%) reported exceeding the action level at least once since 2000, and 76 systems (serving a total population of 5.2 million) reported exceeding the level for a monitoring period ending after January 2003. In this size category, 71% of systems reported that the highest level observed since 2000 was less than 5 ppb. In each size category, 1% of water systems reported exceeding 25 ppb. Last autumn, news reports of possible manipulation of lead monitoring data by some systems to avoid noncompliance with the lead rule raised concern that a larger number of systems may have exceeded the action level. In response, several Members of Congress asked the EPA Inspector General to examine the adequacy of enforcement of the lead rule, and to determine whether elements of the rule allow data manipulation so that systems remain in compliance. EPA announced that if utilities have violated the law by providing false or misleading data, EPA or the state would take appropriate enforcement actions. However, in its evaluation of the rule and monitoring concerns, EPA did determine that systems needed more guidance for collecting samples and calculating the lead 90 th percentile to determine compliance with the rule. In November, EPA issued a memorandum clarifying these requirements. The guidance reflects requirements of the lead rule as currently written and may be modified if EPA decides to revise the rule. Lead exposure is considered a major environmental health threat to young children, because lead affects their developing nervous systems and intellectual and behavioral development. Fetuses and children under six years of age are most at risk. In 1991, the Centers for Disease Control (CDC) adopted a blood lead level of concern for children of 10 micrograms per deciliter (μg/dl) in response to evidence associating adverse health effects with blood lead levels above that level. Recent studies indicate that blood lead levels below 10 μg/dl also may be associated with negative effects on children's intellectual development. In adults, lead may increase blood pressure. Lead is widespread in the environment and can be found in older homes with leaded paint, and in soil, plumbing materials, pottery glazes, pewter, and elsewhere. The main source of lead exposure for children is house dust from lead-based paint; exposure to small amounts of paint dust and flakes can elevate blood lead levels. Another major source is soil contaminated by lead-based paint and past vehicle and industrial emissions. EPA estimates that 10% to 20% of exposure to lead may come from drinking water, but notes that infants who consume mostly mixed formula can receive 40% to 60% of their lead from water if lead levels are elevated in tap water. Lead is rarely present in water when it leaves a treatment plant. The most common sources of lead in water are lead service lines that connect water mains to homes, lead solder and pipes within homes, and brass plumbing fixtures. Although older homes are most likely to have lead pipes, joints, and solder, new homes may also be at risk, because under the Safe Drinking Water Act, "lead-free" pipes may contain up to 8% lead. These pipes can leach lead for several months following installation. The most common cause of lead in drinking water is corrosion, a reaction between the lead pipes or solder and the water. The corrosivity of water depends on the water's characteristics (such as acidity). The Safe Drinking Water Act (SDWA) directs EPA to promulgate National Primary Drinking Water Regulations for contaminants that may pose public health risks and that are likely to be present in public water supplies. These regulations generally include an enforceable numerical standard (maximum contaminant level (MCL)) to limit the amount of a contaminant that may be present in drinking water. If it is not economically and technically feasible to determine the level of a contaminant, EPA may establish a treatment technique in lieu of an MCL (§1412(b)(7)(A)). At least once every six years, EPA must review, and revise as needed, each drinking water regulation (§1412(b)(9)). The 1986 SDWA Amendments directed EPA to issue a new lead regulation, and in 1991, EPA issued the Lead and Copper Rule (56 FR 26460, June 7, 1991). This rule replaced an interim lead standard of 50 parts per billion (ppb), which was outdated and not protective of public health. Moreover, the interim regulation did not require sampling at the tap to show compliance with the standard. In 1988, EPA had proposed a lead rule that would have lowered the MCL for lead to 5 ppb (applied to water leaving the plant) and also would have required a treatment technique (corrosion control) to further reduce lead in water. Many expressed concern with the proposed rule, arguing that a standard applicable at the treatment plant would not indicate the amount of lead in tap water, and that compliance at the tap was essential. EPA and utilities were concerned that an MCL applied at the tap was not workable, because lead in household plumbing could be a major cause of violations—a situation beyond the control of the water system. Some utilities also were concerned that setting an MCL for source water in addition to a treatment technique for corrosion control would result in confusion among the public and the regulated community (56 FR 26472). The final 1991 Lead and Copper Rule (LCR) did not include an enforceable standard (MCL). Instead, the LCR established a treatment technique (corrosion control) to prevent lead and copper from leaching into drinking water. Other requirements include tap water monitoring, public education, source water treatment, and lead service line replacement. Some Members of Congress and environmental groups argued that, because lead is measurable, the law required EPA to establish an MCL rather than a treatment technique. However, EPA concluded that an MCL at the tap was not feasible because lead levels are often influenced by factors beyond the control of the water utility. The rule generally required all large water systems (serving more than 50,000 people) to conduct corrosion control studies and recommend an optimal corrosion control treatment to the state or EPA. Smaller systems were required to optimize corrosion control when tap water monitoring showed that it was necessary. The state or EPA then approved or designated a treatment as optimal, and water systems were given two years to install optimal corrosion control and one year to conduct further monitoring. The lead rule also established a lead "action level" of 15 ppb at the tap, based on the 90 th percentile level of water samples. Water systems are required to sample tap water in locations that are at high risk of lead contamination (primarily homes with lead pipes and/or lead service lines). The number of samples a water system must take depends on the system's size and the results of earlier testing. Large systems generally must take 100 samples in a six-month monitoring period. However, systems that meet the action level or maintain optimal corrosion control treatment for two consecutive six-month periods may reduce the number of sampling sites (to 50 sites for systems serving more than100,000 people) and reduce collection frequency to once a year. Monitoring may be reduced to once every three years if the 90 th percentile lead levels are 5 ppb or lower. If lead concentrations exceed the action level in more than 10% of samples, the water system has 60 days to deliver an EPA-developed public education program to customers. The education program must contain information about lead's health effects and sources, and explains steps to take to reduce exposure to lead. The water system also must offer to sample the tap water of any customer who requests it. (The system is not required to pay for sample collection or analysis.) If a water system still exceeds the action level after installing optimal corrosion control treatment and source water treatment, it must replace annually 7% of the lead service lines under its ownership. The water system must offer to replace the privately owned portion of a service line (at the owner's expense). The Safe Drinking Water Act allows EPA to delegate primary enforcement authority (primacy) for the Public Water System Supervision (PWSS) Program to states. States that have primacy oversee water systems and their compliance with federal drinking water regulations. If primacy is not delegated to a state, EPA is responsible for implementing the program. (All states except Wyoming have primacy for the PWSS program.) EPA Region 3 directly implements the program for the District of Columbia.