This section presents information on (1) regulated and unregulated contaminants in drinking water, (2) the UCMR program and SDWA requirements, and (3) laboratories and methods used to analyze drinking water. Drinking water contaminants include chemical and microbial substances, some of which can harm human health. For example, prolonged exposure to arsenic in drinking water can cause skin damage or circulatory problems and, over time, may increase cancer risks. Contaminants may be naturally occurring or introduced through other means. EPA has identified three ways that drinking water generally becomes contaminated. First, contaminants can find their way into drinking water sources from industrial waste releases, agricultural runoff, and other pollution sources. Second, contamination can occur during the treatment of water by forming what are known as “disinfection by-products.” Third, contaminants can “leach” or dissolve out of the materials used for treatment, storage, and distribution of water. EPA regulates drinking water contaminants under SDWA by issuing legally enforceable standards, known as National Primary Drinking Water Regulations or “primary standards” that generally limit the levels of these contaminants in public water systems. EPA has issued primary standards addressing more than 89 contaminants. States generally enforce these standards through compliance monitoring. Under compliance monitoring, public water systems collect a sample of drinking water, analyze the sample for specific contaminants, and report the results to states. To analyze the samples, water systems and states use analytical methods developed by government agencies, universities, and other organizations. EPA evaluates analytical methods for drinking water and approves those it determines meet agency requirements for monitoring contaminants. Laboratories analyzing drinking water compliance samples must be certified by the state or EPA. EPA establishes schedules for how often water systems must monitor for regulated contaminants. The monitoring frequency generally depends on the contaminant, previous monitoring results, the type of source water, and the size of the population served by the water system. Unregulated drinking water contaminants include chemical and microbial substances and are not currently subject to primary standards under SDWA. Exposure to unregulated drinking water contaminants may pose a human health risk, particularly to vulnerable subpopulations such as pregnant women, infants, the elderly, and those with compromised immune systems. Unregulated contaminants include industrial chemicals, military chemicals, pesticides, bacteria, and other microbes and chemicals. They also include contaminants of emerging concern— contaminants characterized by a perceived, potential or real threat to human health or the environment or by a lack of published health standards. Examples include pharmaceuticals, such as prescription and over-the-counter drugs, and ingredients in personal care products, such as cosmetics and soaps. A contaminant may also be considered to be emerging because a new source of public exposure has been discovered or a new detection method or treatment technology has been developed. Under the UCMR program, EPA collects data about the occurrence of unregulated contaminants in drinking water. The UCMR program collects data on the extent of the occurrence of unregulated contaminants in all public water systems serving more than 10,000 people and in a nationally representative sample of smaller systems. These data inform EPA’s decisions about whether to issue primary standards for unregulated contaminants. Under the UCMR, EPA is to identify up to 30 unregulated contaminants that may be present in drinking water and establishes a monitoring program to obtain data on the extent of their occurrence. These data help EPA determine whether drinking water contamination is occurring and estimate its level and frequency. EPA established a three- tiered approach for monitoring UCMR contaminants that includes (1) assessment monitoring, (2) screening survey, and (3) pre-screen testing. EPA’s approach is based primarily on the availability of analytical methods to monitor the contaminants. Assessment monitoring is used to monitor contaminants that can be detected by well-established analytical methods that are widely used in drinking water laboratories. The screening survey is used to monitor contaminants that can be detected by more recently developed analytical methods that are used in fewer drinking water laboratories. Pre-screen testing is used to monitor contaminants that can be detected by very new or specialized analytical methods that are used in a small set of drinking water laboratories. Approximately 6,000 public water systems are currently participating in the UCMR program. Participating public water systems are monitoring for contaminants under one or more of the three tiers. EPA varies the number of public water systems required to monitor under each tier. UCMR monitoring is conducted by all large community and nontransient, noncommunity public water systems serving more than 10,000 people. Monitoring is also conducted by a nationally representative sample of other public water systems that EPA selects (see table 1). In addition, a sample of community and nontransient, noncommunity water systems, and transient water systems are required to allow EPA to conduct pre- screen testing under UCMR3. The UCMR program is part of a larger framework established by SDWA that also includes the CCL and requires EPA to make regulatory determinations for at least five of the contaminants on that list every 5 years. The CCL is a list of unregulated contaminants that are known or anticipated to occur in public water systems and that may require regulation. SDWA directs EPA to select contaminants that pose the greatest public health concern for consideration for the CCL and regulatory determinations. A regulatory determination is a formal decision on whether EPA should initiate a rulemaking process to develop a primary standard for a specific drinking water contaminant. The UCMR, CCL, and regulatory determinations framework is implemented by three different branches within EPA’s Office of Ground Water and Drinking Water’s Standards and Risk Management Division: the Technical Support Center administers the UCMR program; the Targeting and Analysis Branch develops the CCL; and the Standards and Risk Reduction Branch leads the development of the regulatory determinations. SDWA requires EPA to make regulatory determinations for at least five of the contaminants on the CCL every 5 years. Regulatory determinations can be positive (i.e., a primary standard is needed) or negative (i.e., no primary standard is needed). Under SDWA, EPA is to make a positive regulatory determination and subsequently issue a primary standard when (1) the contaminant may have an adverse effect on the health of persons; (2) the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern; and (3) in the sole judgment of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems. EPA can make a negative regulatory determination when the SDWA conditions are not met. SDWA set recurring 5-year deadlines for the CCL, UCMR, and regulatory determinations. The initial deadlines were staggered such that EPA was required to publish the CCL in the Federal Register first (February 1998), the UCMR list 18 months later (August 1999), and the regulatory determinations 2 years after that (August 2001). The cycle restarts with the next CCL, UCMR, and regulatory determinations due 5 years after the first set of deadlines. However, EPA has not always met the SDWA deadlines. Moreover, EPA has not issued the CCL, UCMR, and regulatory determinations separated by the 18-month and 2-year time frames that were originally established by statute. The cycle is currently in its third iteration. EPA refers to the programs in the current cycle as CCL3, UCMR3, and the CCL3 regulatory determinations (see table 2). The UCMR program’s primary purpose is to inform regulatory determinations, but EPA can also use the UCMR data to develop health advisories for some of the contaminants it decides not to regulate. Health advisories provide information on contaminants that can harm human health and are known or anticipated to occur in drinking water. They provide technical guidance on health effects to assist EPA regional offices, states, and other public health officials. EPA has issued new or updated health advisories for nine contaminants it decided not to regulate. The advisories identify concentrations of contaminants at which adverse health effects are not anticipated to occur over specific exposure durations (1 day, 10 days, several years, and a lifetime). Drinking water health advisories are not legally enforceable standards and, according to EPA, are subject to change as new information becomes available. Private analytical laboratories and some water utilities’ laboratories conduct the analytical testing for the UCMR contaminants. All laboratories conducting analyses for UCMR3 must be approved by EPA. In general, laboratories must first successfully complete the registration and application process, which includes testing for contaminants using EPA- specified analytical methods, before receiving EPA’s approval. Approved laboratories must adhere to the quality assurance and quality control procedures and criteria outlined in the methods and rule language to maintain their approval status and may be subject to on-site laboratory or paper audits. Laboratories also post occurrence data and required quality control data electronically in EPA’s data system, the Safe Drinking Water Accession and Review System, within 120 days of the sample collection date. EPA specifies the analytical methods that laboratories participating in the UCMR program use to detect contaminants. Some methods can detect a single contaminant while others can detect a group of similar contaminants. Because the UCMR collects nationwide data, agency officials told us EPA’s goal is to use analytical methods that yield consistently high-quality monitoring data from public water systems across the country. EPA officials told us that the agency develops or uses analytical methods for the UCMR program that enable it to meet this goal. In particular, agency officials told us these methods must (1) have sufficient “holding times”; (2) be able to be used successfully by a variety of labs with varying levels of expertise; and (3) be used effectively in different types of drinking water. EPA officials said it typically takes 1 or 2 years to develop a standard analytical method that meets these requirements and up to 3 years or longer to develop more complex methods. See appendix III for more information on analytical methods.