Safe Drinking Water Act and Consumer Right-To-Know: Some Statistical Gauges
Draft from Saturday, August 29, 1998 at 1:14 AM
Safe Drinking Water and Consumer Right-to-Know: Some Statistical Gauges
James Hilden-Minton, Ph.D.
National Institute of Statistical Sciences
Research Triangle Park, North Carolina
August 29, 1998
Central to the Safe Drinking Water Act (SDWA) is the principle of community right-to-know and citizen involvement. The 1996 amendments expanded provisions for consumer involvement and notification. Presently, the Environmental Protection Agency (EPA) is proposing a rule to require most water systems to report annually water quality information to consumers. In this period of rapidly expanding access to information, it is vital that the public is given appropriate tools to digest and interpret data. This report supposes that the public has access to drinking water sampling data and shows four statistical and graphical methods, in order of difficulty, that the involved citizen may use to interpret such data. These four gauges may be used to address questions concerning 1) degree to which water is safe, 2) certainty or assurance that water is safe at this moment, 3) variation of water quality over time including prediction of future safety, and 4) extent of unsafe water in a large population by size.
Safe Drinking Water Act
Community water systems serve about 84 percent of the nations 102 million households.[1] In 1974, Congress enacted the Safe Drinking Water Act charging the Environmental Protection Agency (EPA) to establish national drinking water standards for public water systems. Congress further revised and strengthened the Act with amendments in 1986 and 1996. States are given some flexibility to establish their own more stringent standards and administrative programs.
Presently, there are about 55,000 community drinking water systems nationwide. As SDWA defines it, a community water system is any “public water system which serves at least 15 service connections or regularly serves at least 25 year-round residents.”[2] They may serve, for example, a municipality or a mobile home park. Non-community water systems, such as for schools, restaurants or highway rest stops, serve non-residential customers. Private wells and very small public systems are not within the purview of SDWA.
Public water systems deliver water to customers. Source water may be obtained from ground water, surface water, or purchased wholesale. Ground water is from wells, while surface water may come from lakes, rivers, or reservoirs. Water from separate sources is sometimes mixed or blended. Before water is distributed, it may be treated at one or more treatment facilities. Untreated water is at least pumped into the distribution system. In this case, the pumping station is considered a treatment facility. Thus, each water system has at least one treatment facility, and water leaving a treatment facility may or may not be treated water.
Under SDWA, public water systems are required to monitor their water for over 70 contaminants. These include volatile organic compounds such as from solvents, coliform and viruses often from fecal matter, inorganic contaminants such as nitrate, and other organic contaminants including pesticides. Lead, copper and trihalomethanes, water chlorination by-products, receive special monitoring as well.
The EPA has established maximum contaminant level (MCL) for each contaminant.[3] Maximum contaminant level is defined as “the maximum permissible level of a contaminant in water which is delivered to any user of a public water system.” Thus, MCLs are legal thresholds. Related to the MCL is the maximum contaminant level goal (MCLG) which is a health-related threshold. The regulatory language defines this as “the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. Maximum contaminant level goals are nonenforceable health goals .”[4] The EPA has proposed simple definitions for MCL and MCLG for communication with the public. Specifically, the MCLG would be “the level of a contaminant in drinking water below which there is no known or expected risk to health,” and the MCL would be “the highest level of a contaminant that is allowed in drinking water.”[5] Clearly, the intent is to distinguish between regulatory issues and health-related issues. Although MCLGs are never greater than MCL, any water with all contaminant levels below MCL is officially safe, whether or not the MCLGs are achieved.
Regulations[6] lay out how each contaminant is to be sampled, which systems must sample and how frequently they must sample. Most contaminants are sampled at the point-of-entry, between treatment facility and distribution system, since this is where they are most likely to be greatest. In contrast, water disinfection by-products, trihalomethanes, are sampled widely in the distribution system.[7] This is because trihalomethanes increase with time in the distribution system. Similarly, lead and copper are sampled at residential taps.[8]
Most contaminants are sampled quarterly, once per year, or once per three-year period. Microbiological contaminants are typically sample more frequently than once per month. Non-community water systems sample less frequently than community water systems. Systems meeting certain criteria may be exempted from monitoring for a particular contaminant or be placed on a reduced schedule. For some contaminants, surface water systems are sampled more frequently than those with ground water are. For example, all public water systems must sample for nitrate quarterly if distributing surface water or annually if ground water. If, after one year, all nitrate samples are below one half the maximum contaminant level (10 parts per million), then the system may be put on an annual schedule.[9] The question of sampling frequency is truly complex. The EPA recommends, “To find out how frequently your drinking water is tested, contact your water system or state agency in charge of drinking water.”[10]
Expanding the public right-to-know
Drafted into the Code of Federal Regulations (CFR) 141 National Primary Drinking Water Regulations are provisions for public notification. Essentially, the consumer has the right to be informed of any violations. First, systems are required to publish any MCL, treatment technique, or variance and exemption schedule violations in local newspapers within 14 days. Second, systems in violation must report to their customers by mail or hand delivery within 45 days, unless they correct the problem within that period. Finally, if an MCL violation poses a serious short-term risk to health, that system must report within 72 hours of the violation.[11] Also, drinking water systems must provide the most recent notification to new billing units. Not required to do so, the EPA publishes all violations on the World Wide Web.[12] Thus, at any moment, an individual may query (with ease) the Safe Drinking Water Information System (SDWIS) to obtain the latest list of violations for any public water system within the United States.
There are three types of violations, which must be reported. Variance and exemption violations refer to a failure to monitor or report according to a specific sampling schedule. While such a violation is not direct evidence that water may be unsafe, it does indicate that the system has had difficulty complying with regulations. Furthermore, where sampling is delayed or neglected the consumer has diminished assurance that their water is safe. Simply put, the water provider has failed to demonstrate to the state or EPA that their water is indeed safe.
Treatment technique violations indicate that a system is failing to treat water or to remedy other features of water delivery with methods prescribed by the National Primary Drinking Water Regulations (NPDWR). While this may not mean that the water is unsafe, as with the monitoring and reporting violations, consumer confidence is not bolstered.
Of immediate significance to the safety of water are MCL violations. For most contaminants, an MCL violation occurs when the average level over the last twelve months for that contaminant is above MCL. This may indicate that the contaminant level has been near or above MCL for most of the preceding year. Thus, water may be unsafe, i.e. above MCL or MCLG, for one or more contaminants for a year or more before regulatory actions are triggered and the community is notified under NPDWR. We will discuss below ways of interpreting sampled water data should those ever become available.[13]
Consumers not only have the right to know when their drinking water provider is in violate, but they also have the right to be informed of the possible health risks. Care has gone into the specific wording of health risk statements. When a system notifies users of violations, mandatory health effects language for the relevant contaminants must be included along with a plain English (non-technical) description of the violations. For example, if there is an MCL violation for tetrachloroethylene the following paragraph must included.
The United States Environmental Protection Agency (EPA) sets drinking water standards and has determined that tetrachloroethylene is a health concern at certain levels of exposure. This organic chemical has been a popular solvent, particularly for dry cleaning. It generally gets into drinking water by improper waste disposal. This chemical has been shown to cause cancer in laboratory animals such as rats and mice when the animals are exposed at high levels over their lifetimes. Chemicals that cause cancer in laboratory animals also may increase the risk of cancer in humans who are exposed over long periods of time. EPA has set the drinking water standard for tetrachloroethylene at 0.005 part per million (ppm) to reduce the risk of cancer or other adverse health effects which have been observed in laboratory animals. Drinking water that meets this standard is associated with little to none of this risk and is considered safe with respect to tetrachloroethylene. [40 CFR 141.32(e)(48)]
This mandatory language addresses several important points. What is the contaminant? Where does it come from? How does it get into drinking water? What are the known or anticipated health effects? How are these health effects known or derived? Are these effects acute or long term? What standard has EPA set? And what does the EPA consider safe? In all this, there is effort to make the language accessible to nearly all adults.
The pending amendment to the National Primary Drinking Water Regulations would expand community right-to-know. The proposed rule would add a subpart mandating consumer confidence reports. These reports would exceed the current public notification of violations. Consumers would receive annual reports on water quality whether or not there were violations. Consumer confidence reports would “raise consumers’ awareness of where their water comes from, show them the processes by which safe drinking water is delivered to their homes, [and] educate them about the importance of prevention measures such as source water protection to a safe drinking water supply.”[14] The EPA anticipates that these reports will initiate a “dialogue” between the public and drinking water providers.
The proposed consumer confidence reports would contain the following information. Source water used by the water system will be identified. Terms such as MCL and MCLG will be defined with jargon-free language. Central to the report is the reporting of contaminant levels. For some contaminants, the highest test result within the last twelve months will be reported, and for others, particularly those with compliance criteria based on averages, the average over the last twelve months will be reported. These maximums and averages will be reported along with the related MCLs and MCLGs. Violations will be identified, and variances and exemptions will be explained.
Important changes are proposed for required health information. All consumer confidence reports will display “prominently” a disclaimer concerning individual susceptibility. Specifically, “Some people may be more vulnerable to contaminants in drinking water than the general population.”[15] Immunocompromized individuals are encouraged to “seek advice…from their health care provider” or call the Safe Drinking Water Hotline[16]
Violations will trigger the inclusion of health effects information in consumer confidence reports. Under this proposal the mandatory health effects language is somewhat simplified. For example, the paragraph above on tetrachloroethylene would be replaced by “People who drink water containing tetrachloroethylene in excess of the MCL over many years could have problems with their liver, kidney or nervous system, and may have an increased risk of getting cancer.”[17] While this single sentence does not cover all the points of the previous mandatory paragraph, combined with the rest of the consumer confidence report all the necessary issues are covered. Missing, perhaps for its technicality, is reference to how this cancer risk is extrapolated from tests on laboratory animals.
The proposed rule to establish consumer confidence reports expands the role of public right-to-know while being careful to employ principles of effective risk communication. These include the use of non-technical, jargon-free language and the avoidance of “information overload.”[18] This latter concern is of particular importance to the question of which statistic or statistics on monitoring levels should be reported. The decision in this proposed rule was to require either the annual mean or the annual maximum depending on the contaminant. Reporting only one value per contaminant helps avoid information overload. However, “as far as accuracy is concerned, the Agency [EPA] is aware that choosing one number to put into the report which gives a true representation of the water that customers may have consumed during the year will sometimes be difficult [as t]he quality of water is subject to spatial and temporal variability.”[19] The difficulty is that one number is never sufficient to describe both the typical level and the degree of variability. To do that, one needs at least two statistics. Furthermore, to address variation over time and location, not even two statistics are sufficient.
While information overload is a sensible restraint to reporting requirements, it does not mean that more information should not be given to those who ask for it. Individuals may ask state drinking water authorities or their water providers for more information. Specifically, one may ask for the records of water sample test results. Neither state agencies nor public water systems are required to provide this detailed information, but may grant it under some circumstances. We obtained data from a particular state agency for research purposes. We use it here to demonstrate the sort of variability inherent in the monitoring program under SDWA and to suggest ways to understand such information, should one obtain access to it.
Four additional questions
Regulations as regulations must define what is and is not legally acceptable. MCLs are the mandated thresholds. For most contaminants under the NPDWR, a twelve-month average above MCL is not legally acceptable. Penalties, correction, and public notification may be demanded of drinking water systems in violation. Violation is a more or less black-and-white construct, though determining whether a violation has occurred may involve some ambiguity. The NPDWR recognizes that the enforceable threshold, the MCL, may not be adequate as a health-based threshold. The MCL Goal (MCLG) serves this function. Unfortunately, the MCLG may be so low that enforcement would not be practical. Different thresholds may be needed to answer different questions.
Our purpose here is to develop alternative thresholds, or gauges, to help answer additional questions which the public may ask, especially if the public becomes informed of the drinking water sampling records. We will address four questions.
- To what degree is our drinking water safe?
- How confident can we be that our drinking water is safe?
- If our drinking water is now unsafe, when did it become unsafe?
- How many people in this state are receiving unsafe drinking water?
Surely, the public may have additional questions, and many of these are addressed in “Water on Tap: A Consumer’s Guide to the Nation’s Drinking Water”[20] and other EPA documents.
Question 1 moves us beyond the black-and-white formulations of drinking water regulation. Obviously, there is a difference between water at 95 percent of MCL and at 65 percent; however, both are below MCL and are treated the same under present regulations. Our first set of gauges on comparing measurements with MCL will help us examine measurements at any level and help us appreciate the imprecision of the measurement process.
Appreciation of measurement imprecision is essential to the second question. Greater precision in the measurement process leads us to greater confidence in determining whether drinking truly below a threshold of safety. Thus, measurement error is related to our confidence that drinking water is safe, especially on those days when the water is sampled. However, suppose three months pass between two sampling dates. How certain can we be that our water remained safe throughout that interval of time? To address that question, we must consider how variable contaminant levels are over time. We will present some gauges for measuring process variation. These gauges, to be sure, are only descriptive statistics. They cannot tell us why contaminant levels vary; they only quantify how much they vary. Similarly, gauges for measurement error cannot explain why the measurement process is imprecise.