United States Government Accountability Office

GAO Report to Congressional Requesters

SAFE DRINKING 

WATER ACT 

EPA Should Improve 

Implementation of 

Requirements on 

Whether to Regulate 

Additional 

Contaminants 

May 2011 

GAO-11-254 
 United States Government Accountability Office 

Accountability • Integrity • Reliability 

Highlights of GAO-11-254, a report to 

congressional requesters 

May 2011 

SAFE DRINKING WATER ACT 

EPA Should Improve Implementation of 

Requirements on Whether to Regulate Additional 

Contaminants 

Why GAO Did This Study 

Under 1996 amendments to the Safe 

Drinking Water Act, every 5 years the 

Environmental Protection Agency 

(EPA) is to determine for at least five 

contaminants, such as chemicals, 

whether regulation is warranted, 

considering those that present the 

greatest public health concern. Since 

1996, EPA had not recommended any 

new contaminants for regulation until 

February 2011, when it reversed its 

controversial 2008 preliminary 

decision to not regulate perchlorate, 

an ingredient in rocket fuel and other 

products. GAO was asked to (1) 

evaluate the extent to which EPA’s 

implementation of the 1996 

amendments has helped assure the 

public of safe drinking water and 

(2) review the process and scientific 

analyses used to develop the 2008 

preliminary regulatory determination 

on perchlorate. GAO analyzed 

relevant statutory provisions and 

regulatory determination documents 

and interviewed EPA officials. 

What GAO Recommends 

GAO’s 17 recommendations include 

that the EPA Administrator require 

(1) development of criteria to identify 

contaminants that pose the greatest 

health risk, (2) improvements in its 

unregulated contaminants testing 

program, and (3) development of 

policies or guidance to interpret the 

broad statutory criteria. EPA agreed 

with 2 recommendations but took the 

position that developing guidance 

and taking the other recommended 

actions are not needed. GAO believes 

EPA needs to adopt all of the 

recommendations to better assure 

the public of safe drinking water. 

What GAO Found 

Systemic limitations in EPA’s implementation of requirements for determining 

whether additional drinking water contaminants warrant regulation have 

impeded the agency’s progress in assuring the public of safe drinking water. 

EPA’s selection of contaminants for regulatory determination in 2003 and 2008 

was driven by data availability—not consideration of public health concern. 

EPA does not have criteria for identifying contaminants of greatest public 

health concern and based most of its final determinations to not regulate 20 

contaminants on the rationale of little or no occurrence of the contaminants in 

public water systems. Moreover, EPA’s testing program for unregulated 

contaminants—which can provide key data to inform regulatory 

determinations—has fallen short in both the number of contaminants tested 

and the utility of the data provided because of management decisions and 

program delays. In addition, EPA has not developed policies or guidance for 

interpreting the amendments’ broad statutory criteria for selecting 

contaminants and making regulatory determinations, increasing the potential 

for inconsistent decision making. Also, the credibility of some of EPA’s 

regulatory determinations is limited by a lack of transparency, clarity, and 

consistency of key documents. For example, EPA made decisions on nine 

contaminants relying on tests that were not sensitive enough to detect them at 

the agency’s health risk benchmarks. Furthermore, EPA did not clearly and 

consistently disclose this limitation and its effect on EPA’s analysis. 

In making its preliminary regulatory determination on perchlorate in 2008, 

EPA used a process and scientific analyses that were atypical, lacked 

transparency, and limited the agency’s independence in developing and 

communicating scientific findings. First, while an intra-agency workgroup 

typically makes recommendations to the Assistant Administrator for Water on 

whether to regulate evaluated contaminants, in this case, the Assistant 

Administrator directed the staff to develop a determination to not regulate 

and to support a specified exposure level as protective of all populations. This 

direction was outlined in an agreement between high-level officials at EPA 

and other federal agencies that is not part of the perchlorate regulatory 

determination record. Moreover, EPA adopted the National Academies’ 2005 

perchlorate health assessment—a foundation for EPA’s regulatory 

determination—without using EPA’s standard internal scientific review 

process. This assessment is controversial, especially its sufficiency to protect 

infants. Also, the credibility of EPA’s exposure estimate for perchlorate, 

which is based on a novel analysis, is reduced by the lack of a comprehensive 

explanation of the methodology’s limitations and uncertainties in the 

preliminary determination notice. Finally, according to key EPA scientists, the 

agency mischaracterized important scientific findings on the sensitivity of 

various age groups to perchlorate exposure. EPA scientists who managed the 

sensitivity analysis did not agree that it supported the conclusion that the 

selected exposure level was protective of all populations, which was one 

component of the aforementioned agreement between EPA and other federal 

agencies. 

View GAO-11-254 or key components. 

For more information, contact David C. 

Trimble at (202) 512-3841 or 

trimbled@gao.gov. 
Page i GAO-11-254 

Contents 

Letter 1

Background 5 

Systemic Limitations in EPA’s Implementation of Requirements for 

Determining Whether to Regulate Additional Contaminants Have 

Impeded Progress in Helping Assure the Public of Safe Drinking 

Water 17 

The Process and Analyses EPA Relied on to Support Its 

Preliminary Determination on Perchlorate Were Atypical, 

Lacked Transparency, and Limited the Agency’s Independence 

in Developing and Communicating Its Scientific Findings 50 

Conclusions 79 

Recommendations for Executive Action 82 

Agency Comments and Our Evaluation 85 

Appendix I Objectives, Scope, and Methodology 92 

Appendix II Information on EPA’s Regulatory Actions under 

the 1974 Safe Drinking Water Act 95 

Appendix III Information on U.S. Public Drinking Water Systems 101 

Appendix IV Calculations EPA Uses to Develop Health Reference 

Levels for Drinking Water Contaminants Being 

Considered for Regulation 104 

Appendix V Calculations of Relative Source Contribution 

Using the Percentage and Subtraction Methods 105 

Appendix VI Supplemental Information on EPA’s 2003 Regulatory 

Determination for Manganese and Its 2008 

Determination for Boron 108 

 Safe Drinking Water Act 
Appendix VII EPA’s Evaluation of Perchlorate Occurrence at 

Two Levels—5 Parts and 15 Parts per Billion of 

Perchlorate in Water 122 

Appendix VIII Supplemental Information on Limitations and 

Uncertainties of EPA’s Perchlorate 

Exposure Analysis 124 

Appendix IX Calculations for the Perchlorate Health Reference 

Level in EPA’s 2008 Preliminary Regulatory 

Determination and the Related 2010 Journal Article 

on EPA’s Exposure Analysis Methodology 128 

Appendix X Comments from the Environmental 

Protection Agency 130 

Appendix XI GAO Contact and Staff Acknowledgments 139 

Tables 

Table 1: EPA’s Contaminant Candidate Lists 7 

Table 2: Information on EPA’s Unregulated Contaminants Testing 

Program 10 

Table 3: Comparison of the Impact on Health Reference Levels of 

Three Different Relative Source Contribution Factors, 

Assuming a Reference Dose of 0.5 Micrograms per 

Kilogram per Day 13 

Table 4: Drinking Water Contaminants with Final EPA Regulatory 

Determinations 15 

Table 5: Nine Contaminants Whose Minimum Reporting Levels 

Exceeded EPA’s Health Reference Levels 46 

Table 6: U.S. Public Drinking Water Systems by Size 102 

Table 7: U.S. Public Drinking Water Systems by Source Water 103 

Page ii GAO-11-254 Safe Drinking Water Act
Table 8: Hypotethical Data Used in Examples 106 

Table 9: Example of How the Relative Source Contribution Is 

Determined Using the Perentage Method 106 

Table 10: Example of How the Relative Source Contribution Is 

Determined Using the Perentage Method 107 

Table 11: Perchlorate Occurrence and Population Exposure 

Estimates at Various Potential Health Reference Levels 

Reported in EPA’s Preliminary Regulatory Determination 

for Perchlorate 123 

Table 12: Comparison of the Health Reference Level Calculations 

Used in EPA’s Preliminary Perchlorate Regulatory 

Determination and Its Subsequent Article on the 

Perchlorate Exposure Methodology the Agency Used in Its 

Preliminary Regulatory Determination, Based on a 

Reference Dose of 0.7 Micrograms per Kilogram per Day 129 

Figures 

Figure 1: Health Reference Level Equation for Contaminants with 

Carcinogenic Health Effects 104 

Figure 2: Health Reference Level Equation for Contaminants with 

Noncarcinogenic Adverse Health Effects 104 

Figure 3: Health Reference Level Equation 105 

Page iii GAO-11-254 Safe Drinking Water Act
Abbreviations 

ATSDR Agency for Toxic Substances and Disease Registry 

CDC Centers for Disease Control and Prevention 

DOD Department of Defense 

EPA Environmental Protection Agency 

HHS Department of Health and Human Services 

IRIS Integrated Risk Information System 

MTBE methyl tertiary-butyl ether 

NASA National Aeronautics and Space Administration 

NAWQA National Water-Quality Assessment 

NIRS National Inorganic and Radionuclide Survey 

OMB Office of Management and Budget 

PBPK physiologically based pharmacokinetic 

PCE tetrachloroethylene 

TCE trichloroethylene 

USGS U.S. Geological Survey 

VOC volatile organic compounds 

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Page iv GAO-11-254 Safe Drinking Water Act
 

Page 1 GAO-11-254 

United States Government Accountability Office

Washington, DC 20548 

May 27, 2011 

The Honorable Barbara Boxer 

Chairman 

Committee on Environment 

 and Public Works 

United States Senate 

The Honorable Henry A. Waxman 

Ranking Member 

Committee on Energy and Commerce 

House of Representatives 

The Honorable Edward J. Markey 

House of Representatives 

The overall goal of the Safe Drinking Water Act, originally enacted by 

Congress in 1974, is to ensure that public drinking water is safe.1

Nonetheless, more than 35 years later, the safety of drinking water 

remains a significant concern. For example, according to a 2010 Gallup 

survey on the environment, the safety of drinking water continues to be 

the environmental issue of greatest concern to Americans, with 50 percent 

worrying “a great deal” about drinking water pollution. In addition, 

Members of Congress continue to express concerns regarding the impacts 

of contaminated drinking water on public health, particularly on children.2

While 89 contaminants have been regulated pursuant to the act, the 

number of potential drinking water contaminants is vast.3

 For example, as 

many as tens of thousands of chemicals may be used across the country, 

and the Environmental Protection Agency (EPA) has identified more than 

 

1

Pub. L. No. 93-523 (1974), codified as amended at 42 U.S.C. §§ 300f–300j-26 (2010). 

2

See, for example, Oversight of Recent EPA Decisions Hearing Before the Senate 

Committee on Environment and Public Works, 110th Cong. (Feb. 6, 2007) (statement of 

Sen. Barbara Boxer); Endocrine Disrupting Chemicals in Drinking Water: Risks to 

Human Health and the Environment Hearing Before the House Committee on Energy 

and Commerce, Energy and Environment Subcommittee, 111th Cong. (Feb. 25, 2010) 

(statement of Rep. Edward Markey); Oversight Hearing on Public Health and Drinking 

Water Issues Hearing Before the Senate Committee on Environment and Public Works, 

112th Cong. (Feb. 2, 2011) (statements of Sen. Barbara Boxer, Sen. Benjamin Cardin, and 

Sen. Frank Lautenberg). 

3

Under the Safe Drinking Water Act, a drinking water contaminant is defined as any 

physical, chemical, biological, or radiological substance or matter in water. 

 Safe Drinking Water Act 
 

6,000 chemicals that it considers the most likely sources of human or 

environmental exposure. The potential health effects of exposure to most 

of these chemicals, and the extent of their occurrence in drinking water, 

are unknown. Several studies since the 1980s have examined the 

occurrence of unregulated contaminants in public drinking water systems 

and their source waters. Typically small in scale—focusing on 60 or fewer 

contaminants—these studies have nonetheless detected hundreds of 

unregulated contaminants in public drinking water systems and source 

waters, some of which are known to have adverse health effects. 

Under the Safe Drinking Water Act, EPA is authorized to regulate 

contaminants in public drinking water systems. Since 1974, EPA has 

implemented its drinking water program under three separate legislative 

frameworks—first under the initial statute and subsequently under major 

amendments in 1986 and 1996. Under the 1996 amendments, which remain 

in effect, EPA is to select for consideration those unregulated 

contaminants that present the greatest public health concern, evaluate 

their occurrence and the potential health risks associated with them, and 

decide whether a regulation is needed for at least five contaminants every 

5 years. This regulatory determination process includes EPA’s publication 

in the Federal Register of a preliminary decision on whether the agency 

will propose a drinking water regulation for each contaminant evaluated—

called a preliminary regulatory determination—and provides for a public 

comment period, followed by a final decision, or regulatory determination, 

also published in the Federal Register. 

In 2003 and 2008, EPA issued final regulatory determinations on a total of 

20 contaminants, deciding in each case that a drinking water regulation 

was not warranted. Thus, EPA had not recommended any new 

contaminant for regulation under the provisions of the 1996 amendments 

until February 2011, when the agency issued a final determination to 

regulate perchlorate—reversing a separate preliminary determination to 

not regulate perchlorate that the agency had issued in 2008. EPA had first 

formally identified perchlorate, an ingredient in such products as rocket 

fuel and fireworks, as a contaminant that may require regulation in 1998. 

Perchlorate can interfere with the normal functioning of the thyroid gland 

by inhibiting the transport of iodide into the thyroid, an essential step in 

the synthesis of thyroid hormones. According to EPA’s preliminary and 

final determination notices on perchlorate, iodide uptake inhibition from 

perchlorate exposure has been identified as a concern in connection with 

Page 2 GAO-11-254 Safe Drinking Water Act
 

increasing the risk of neurodevelopmental impairment in fetuses of 

hypothyroid mothers.4

 In addition, poor iodide uptake and subsequent 

impairment of thyroid function in pregnant and lactating women have 

been linked to delayed development and decreased learning capability in 

their infants and children. As we recently reported, perchlorate has been 

found in water, soil, and sediment at varying levels in 45 states, as well as 

in the food supply.5

 Over the last decade, issues surrounding the health 

risks of and the potential drinking water regulation for perchlorate have 

generated considerable interest and debate among such federal agencies 

as the Department of Defense (DOD) and the National Aeronautics and 

Space Administration (NASA) that use perchlorate in carrying out aspects 

of their missions. Moreover, EPA’s 2008 preliminary determination to not 

regulate perchlorate in drinking water was controversial, generating 

significant public comment. In August 2009, the EPA Administrator 

announced that the agency would consider additional public comments on 

alternative analyses regarding perchlorate prior to making its final 

regulatory determination. In February 2011, the EPA Administrator 

announced that the agency intends to propose a perchlorate drinking 

water regulation within 24 months of the regulatory determination—that 

is, by February 2013. 

In this context, this report responds to your request that we conduct a 

review of EPA’s implementation of the Safe Drinking Water Act’s 

provisions on unregulated contaminants.6

 Our objectives were to (1) 

evaluate the extent to which EPA’s implementation of the 1996 

amendments’ requirement for determining whether to regulate potentially 

harmful contaminants has helped assure the public of safe drinking water 

and (2) review the process and scientific analyses EPA used to develop its 

2008 preliminary regulatory determination on perchlorate. 

To assess EPA’s implementation of the 1996 amendments’ requirement to 

determine which potentially harmful drinking water contaminants should 

be regulated, we reviewed the statute, legislative history, and relevant 

amendments and analyzed relevant documentation, such as Federal 

 

4

Hypothyroidism is a condition in which the body lacks sufficient thyroid hormone. 

5

GAO, Perchlorate: Occurrence Is Widespread but at Varying Levels; Federal Agencies 

Have Taken Some Actions to Respond to and Lessen Releases, GAO-10-769 (Washington, 

D.C.: Aug. 12, 2010). 

6

Unless otherwise stated, in this report we refer to the Safe Drinking Water Act as 

amended. 

Page 3 GAO-11-254 Safe Drinking Water Act
 

Register notices and regulatory determination support documents;7 EPA’s 

information on the potential adverse health effects of, and the extent to 

which the public may be exposed to, individual contaminants in public 

drinking water systems; and public comments on EPA’s determinations. 

We interviewed officials from EPA’s Office of Water and Office of 

Research and Development. We also reviewed health effects and public 

drinking and source water occurrence information from other entities, 

such as the Department of Health and Human Services’ (HHS) Agency for 

Toxic Substances and Disease Registry (ATSDR), California’s Office of 

Environmental Health Hazard Assessment, and the U.S. Geological Survey 

(USGS). In evaluating EPA’s implementation of the regulatory 

determination process, we analyzed information developed under two 

processes integral to the regulatory determination process—development 

of contaminant candidate lists and implementation of the unregulated 

contaminants monitoring rule—but did not evaluate EPA’s implementation 

of them. To review the process and scientific analyses EPA used to 

develop a preliminary determination on perchlorate, we interviewed 

officials in EPA’s Office of Water and Office of Research and Development 

and reviewed relevant Federal Register notices; public comments; and 

EPA documents, including documentation of the agency’s review process 

for its Integrated Risk Information System (IRIS) assessment for 

perchlorate and its scientific analyses of (1) exposure to perchlorate in 

drinking water and related external peer review comments and (2) the 

sensitivity of various age groups to perchlorate exposure and related 

agency documents. Appendix I provides a more detailed description of our 

scope and methodology. We conducted this performance audit from 

March 2009 to May 2011, in accordance with generally accepted 

government auditing standards. Those standards require that we plan and 

perform the audit to obtain sufficient, appropriate evidence to provide a 

reasonable basis for our findings and conclusions based on our audit 

objectives. We believe that the evidence obtained provides a reasonable 

basis for our findings and conclusions based on our audit objectives. 

 

7

In this report, we refer to Federal Register notices regarding EPA’s regulatory 

determinations (notices) and EPA’s regulatory determination support documents 

individually and collectively, as appropriate. When referring to these documents 

collectively, we use the term “regulatory determination documents.” 

Page 4 GAO-11-254 Safe Drinking Water Act
 

The following provides information on the act, its requirements and 

amendments, completed regulatory determinations, EPA health advisories, 

and federal advisory committees for drinking water issues. 

Background 

The Safe Drinking Water 

Act 

Among other things, the Safe Drinking Water Act requires EPA to establish 

legally enforceable standards for public water systems—called national 

primary drinking water regulations—which generally limit the levels of 

specific contaminants in drinking water that can adversely affect public 

health. States typically have the lead role in implementing and enforcing 

these federal drinking water regulations.8

 Under state laws, some state 

environmental agencies have the authority to establish more stringent 

standards than federal regulations and regulate additional contaminants 

than federal regulations, while others lack these authorities. 

EPA’s regulatory actions under the Safe Drinking Water Act have varied 

over time as the agency’s legal authority to determine which drinking 

water contaminants to regulate, if any, has changed from discretionary to 

prescriptive and back to largely discretionary. While the statute was 

enacted in 1974, EPA promulgated most of the existing national drinking 

water regulations under the framework established by the 1986 

amendments, which mandated, among other things, that EPA regulate 

specific contaminants and established a testing program whereby EPA 

was to require public water systems to test for unregulated contaminants. 

As discussed later, with the 1996 amendments, Congress established a 

framework under which EPA is to periodically identify contaminants that 

may warrant regulation, and it revised EPA’s authority related to the 

existing testing program for unregulated contaminants. The 1996 

amendments mandate that EPA focus on unregulated contaminants that 

present the greatest public health concern. EPA completed its first cycle of 

regulatory determinations in 2003 and a second cycle in 2008, and plans to 

 

8

The public drinking water systems regulated by EPA and delegated states and tribes 

provide drinking water to 90 percent of U.S. residents. These public drinking water 

systems, which may be publicly or privately owned, serve at least 25 people or 15 service 

connections for at least 60 days per year. Private, individual household wells are not 

regulated by EPA. States can seek lead enforcement responsibility (called primacy) for 

public water systems if they adopt drinking water regulations that are no less stringent 

than the national primary drinking water regulations and meet other statutory and 

regulatory requirements. 

Page 5 GAO-11-254 Safe Drinking Water Act
 

complete a third cycle in 2013.9 As noted earlier, EPA had decided to not 

regulate any additional contaminants since the enactment of the 1996 

amendments10 until February 2011, when the EPA Administrator 

announced that the agency had made a final determination to regulate 

perchlorate. The Administrator also announced plans to develop a 

regulation addressing a group of carcinogenic volatile organic compounds 

(VOC)—chemicals such as industrial solvents. The announced plan to 

regulate carcinogenic VOCs stemmed from EPA’s effort to revise the 

existing drinking water regulations for trichloroethylene (TCE) and 

tetrachloroethylene (PCE) and the Administrator’s 2010 Drinking Water 

Strategy that includes a goal of addressing contaminants as groups rather 

than one at a time to enhance drinking water protection in a timely and 

cost-effective manner. According to EPA, the agency plans to include up to 

eight unregulated VOCs in this regulatory action covering a group of 

related contaminants.11 (App. II provides additional information on EPA’s 

regulatory actions under the statute as enacted in 1974, the 1986 

amendments, and the 1996 amendments.) 

In addition to requiring EPA to periodically make regulatory 

determinations on unregulated contaminants, the 1996 amendments also 

require that EPA identify and publish a list every 5 years of unregulated 

contaminants that may require regulation; the list is called the 

contaminant candidate list. EPA selects the contaminants for which it will 

make regulatory determinations from the relevant candidate list.12 EPA has 

 

9

Under the statute, the first regulatory determination cycle was to have been completed—

including notice and public comment—by August 2001; the second by August 2006; and the 

third by August 2011—requiring determinations on at least 15 contaminants. EPA did not 

meet the time frames in the statute but has made determinations on 21 contaminants as of 

February 2011. 

10Since the 1996 amendments, EPA has finalized national primary drinking water 

regulations that it had previously proposed; the regulations address several previously 

unregulated contaminants. 

11The planned regulation of a group of carcinogenic VOCs includes contaminants that are 

not regulated as well as contaminants that are regulated individually, such as benzene, 

TCE, PCE, and vinyl chloride. EPA stated it was moving toward establishing a drinking 

water standard to address a group of up to 16 toxic chemicals but has not provided details 

on how the planned regulation of a group of both regulated and currently unregulated 

contaminants would be handled. The EPA Administrator stated, for example, that the 

agency would be “working towards developing an update to the Safe Drinking Water Act 

[regulations]” to address this planned action. 

12EPA could also make a regulatory determination for a contaminant not on the 

contaminant candidate list but has not done so. 

Page 6 GAO-11-254 Safe Drinking Water Act
 

published three candidate lists of unregulated contaminants that may 

warrant regulation: in 1998, 2005, and 2009 (see table 1).13

Table 1: EPA’s Contaminant Candidate Lists 

Contaminant candidate list 

Date published in the 

Federal Register 

Number of 

contaminants on the list

1 March 2,1998 60

2 February 24, 2005 51

3 October 8, 2009 116

Source: Federal Register notices. 

For each regulatory determination cycle (2003 and 2008), EPA developed a 

preliminary determination notice that provided its proposed 

determinations for the contaminants addressed in that cycle, as well as its 

rationale and primary support for individual determinations. The final 

determination notice for each cycle addressed public comments received 

on its preliminary determination notice and briefly summarized its final 

determinations. In the two completed cycles to date, EPA did not change 

any determination in response to public comments.14

EPA’s regulatory determinations can have long-term implications for the 

safety of public drinking water. For example, a decision to not regulate 

tends to limit or remove the focus and resources that may be applied to 

further developing and evaluating data on the occurrence of the 

contaminant, as well as on treatment technologies to remove it from 

drinking water. On the other hand, a decision to regulate places emphasis 

on and commits resources: first, to development of a regulation and, later, 

to actions by some public water systems to limit public exposure to the 

contaminant. Specifically, if EPA determines that a regulation is needed 

for a contaminant, under the 1996 amendments, the agency has 24 months 

to publish a proposed regulation for comment and up to an additional 27 

months to promulgate a final regulation. With regard to developing 

drinking water regulations, the 1996 amendments added a requirement 

that EPA conduct a cost-benefit analysis as part of the standard-setting 

 

13Under the statute, the candidate list was to be published in 1998 and every 5 years 

thereafter—therefore, in 2003 and 2008. EPA did not meet the time frame for publishing the 

second and third candidate lists. 

14As discussed earlier, EPA reversed its 2008 preliminary determination to not regulate 

perchlorate in February 2011. The determination was made as an out-of-cycle action. 

Page 7 GAO-11-254 Safe Drinking Water Act
 

process. The amendments further require that in carrying out the 

provisions concerning listing, selecting, and regulating contaminants, to 

the degree that an action is based on science, EPA use the best available 

peer-reviewed science and data collected by accepted or best available 

methods. EPA is also to ensure that the presentation of information on 

public health effects is comprehensive, informative, and understandable. 

Once established, federal drinking water regulations generally apply to the 

approximately 153,500 public water systems that provide drinking water to 

at least 15 service connections or that regularly serve at least 25 people. 

Nearly 52,000 of these systems are community water systems that serve 

year-round residents, providing drinking water to approximately 294 million 

people. Small systems—those serving 3,300 or fewer people—account for 

most of the community water systems, while large systems—those serving 

more than 10,000 people—provide drinking water to 82 percent of the 

population served by community water systems. Similarly, more than threequarters of community water systems have groundwater sources, such as 

underground aquifers, but a much larger percentage of the population 

receives water from systems that have surface water sources, such as 

streams, rivers, and lakes. Appendix III provides further information on 

public water system types, sizes, sources, and populations served. 

EPA’s Office of Water has primary responsibility for implementing the 

requirements of the Safe Drinking Water Act. Office of Water staff have 

described the agency’s process for assessing contaminants being evaluated 

for regulatory determination as one that continues to evolve. While the 

regulatory determination process is not a rulemaking process, EPA uses 

the administrative process it established for developing and processing 

regulations to govern the development and processing of its regulatory 

determinations. Moreover, according to EPA, the Office of Management 

and Budget (OMB) views the regulatory determinations as equivalent to 

“significant” rulemakings under Executive Order 12866, which establishes 

procedures for OMB to review certain regulations.15

 

15Executive Order 12866 directs agencies, among other things, to “identify for the public, in 

a complete, clear, and simple manner, the substantive changes between the drafts 

submitted to [OMB] for review and the action subsequently announced,” “identify for the 

public those changes in the regulatory action that were made at the suggestion or 

recommendation of [OMB],” and make available to the public the draft action as sent to 

OMB for review. 

Page 8 GAO-11-254 Safe Drinking Water Act
 

The 1996 amendments stipulate that EPA assess contaminants against 

statutory criteria to make determinations on whether they warrant 

regulation. In making regulatory determinations, EPA is to consider 

contaminants that present “the greatest public health concern,” taking into 

account sensitive populations—such as children—that may be at greater 

risk of adverse health effects from exposure to contaminants in drinking 

water, among other factors. EPA’s regulatory determinations are to be 

based on three broad statutory criteria, all of which must be met for EPA 

to decide that a regulation is needed: 

Statutory Criteria for 

Assessing Drinking Water 

Contaminants for 

Regulation 

• the contaminant may have an adverse effect on the health of persons; 

• 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 

• 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. 

Data on Occurrence and 

Health Risks of 

Unregulated Contaminants 

in Drinking Water to 

Support Regulatory 

Determinations 

To assess unregulated contaminants against the statutory criteria, the 

Office of Water needs sufficient information on both (1) the occurrence of 

these contaminants in drinking water—called occurrence data—to assess 

the population potentially being exposed and the levels of that exposure 

and (2) the human health effects that may result from exposure to the 

contaminants in drinking water. Regarding occurrence data, the agency 

has stated that it needs occurrence data that can provide “a generally 

representative idea of known and/or likely occurrence in public water 

systems.”16 As required by the 1996 amendments, EPA has developed a 

new testing program for unregulated contaminants to collect nationally 

representative samples from a subset of public water systems on up to 30 

 

16EPA, “Drinking Water: Regulatory Determinations Regarding Contaminants on the Second 

Drinking Water Contaminant Candidate List—Preliminary Determinations,” Federal 

Register (Washington, D.C.: May 1, 2007). 

Page 9 GAO-11-254 Safe Drinking Water Act
 

contaminants every 5 years.17 Thus, the 1996 amendments placed a limit on 

the number of unregulated contaminants that certain public water systems 

would be required to test for in each 5-year testing cycle.18 In this report, 

we refer to the unregulated contaminant monitoring program as EPA’s 

testing program for unregulated contaminants. EPA completed one testing 

cycle in 2005 and expects to complete the second cycle later in 2011. On 

March 3, 2011, EPA issued a proposed rule for the third cycle and plans to 

publish a final rule in 2012. The published testing program rules identify, 

among other things, the contaminants to be tested, the testing (analytic) 

methods to be used, and the time frames for the testing. As shown in table 

2, data from the first testing cycle was available for EPA to use in 

developing its second cycle of regulatory determinations in 2008, and data 

from the second testing cycle will be available to support EPA’s third cycle 

of determinations in 2013. 

Table 2: Information on EPA’s Unregulated Contaminants Testing Program 

Unregulated 

contaminants 

testing cycle 

Date testing program rules 

published in Federal Register

Date testing program cycle 

completeda

Related regulatory determination 

cycle and completion date 

Cycle 1 September 1999 December 2005 Cycle 2, 2008 

Cycle 2 January 2007 Fall 2011 (planned) Cycle 3, 2013 (planned) 

Source: GAO analysis of EPA data. 

a

We consider completion of a testing program cycle to be the date at which EPA presents the final 

results. 

 

17Under its unregulated contaminants testing program, during each testing cycle, EPA has 

generally required public water systems serving more than 10,000 people, and a 

representative sample of those serving 10,000 or fewer people, to test for the presence of 

selected contaminants either two or four times during a consecutive 12-month period; 

testing frequency depends on whether the public water systems are served by ground or 

surface water. Under the statute, EPA was to promulgate the first list for testing up to 30 

specified unregulated contaminants in 1999 and every 5 years thereafter. EPA published the 

first rule in 1999 but did not meet the time frame for the second rule, which was published 

in 2007. EPA proposed the third rule for the testing program in March 2011 and plans to 

issue a final rule in 2012. 

18The 1996 amendments modified the authority EPA had under the 1986 amendments to 

require public water systems to test for unregulated contaminants, limiting the number of 

(1) unregulated contaminants for which some systems would be required to test and (2) 

public water systems serving populations of less than 10,000 that EPA could require to 

conduct such testing. (See app. II for more information on the testing programs established 

by the 1986 and 1996 amendments.) 

Page 10 GAO-11-254 Safe Drinking Water Act
 

Regarding the information EPA needs to assess health risks from exposure 

to unregulated drinking water contaminants, the Office of Water generally 

considers agency-approved health risk assessments, such as those 

available from the agency’s Integrated Risk Information System (IRIS), 

sufficient to characterize potential health risks for the purpose of making 

regulatory determinations.19 IRIS assessments, which are critical to the 

drinking water program, provide EPA’s toxicity assessments of 

contaminants that may cause cancer and those that may cause 

neurological or other noncancer effects, or both. 

Health Reference Levels 

That EPA Develops to 

Assess Contaminants for 

Regulation 

Using an IRIS or comparable toxicity assessment, the Office of Water 

calculates the health reference level—the estimated level of exposure to a 

contaminant in drinking water below which adverse health effects are not 

likely. The health reference level is critical to EPA’s implementation of the 

1996 amendments because it is the benchmark the agency uses to evaluate 

whether contaminants occur in public drinking water at levels of public 

health concern. That is, levels of contaminants in drinking water that 

exceed the health reference level are deemed to represent exposure that is 

of public health concern. The health reference level is determined in one 

of two ways depending on whether the potential health effects are cancer 

(i.e., carcinogenic) or other adverse effects (i.e., noncarcinogenic). For 

carcinogens, the Office of Water generally develops the health reference 

level using a quantitative estimate of carcinogenic risk—from, for 

example, an IRIS assessment—to calculate a concentration in drinking 

water equivalent to a one-in-a-million increased risk of getting cancer from 

a lifetime of exposure to a contaminant. In making this calculation, EPA 

applies its standard metrics for the weight of an adult—70 kilograms (154 

pounds)—and the daily drinking water intake—2 liters (60 fluid ounces). 

For contaminants with noncarcinogenic adverse health effects, such as 

perchlorate and manganese, the Office of Water develops the health 

reference level using the IRIS reference dose, which is an estimate of the 

total daily oral exposure to a contaminant—for example, from food and 

water—that is not likely to cause “appreciable risk of deleterious effects 

during a lifetime” and is expressed as milligrams (or micrograms) per 

 

19The IRIS database contains EPA’s scientific position on the potential human health effects 

of more than 540 chemicals. According to EPA documents, health risk assessment data that 

would be deemed sufficient to characterize the potential health effects include assessments 

from the IRIS program, the Office of Pesticide Program in a Reregistration Eligibility 

Decision, the National Academies, or ATSDR. 

Page 11 GAO-11-254 Safe Drinking Water Act
 

kilogram of bodyweight per day (mg/kg/day or μg/kg/day).20, 21 EPA 

generally uses the reference dose to calculate a daily safe dose of the 

contaminant in drinking water for a healthy adult by applying (1) its 

standard metrics for the weight of an adult and the daily drinking water 

intake and (2) an allocation of the estimated oral exposure to the 

contaminant from drinking water alone, called the relative source 

contribution. (Stemming from the general assumption that there is no safe 

level of exposure to a carcinogen, EPA has not used the relative source 

contribution in developing health reference levels for carcinogenic 

contaminants.)22 Appendix IV provides examples of the calculations for 

health reference levels for carcinogenic and noncarcinogenic adverse 

health effects. 

The Relative Source 

Contribution Component 

of the Health Reference 

Level 

The Office of Water applies the relative source contribution estimate when 

calculating the health reference level for noncarcinogens to ensure that 

the level of a contaminant in drinking water, when combined with other 

sources of exposure (e.g. food and air) will not result in a total exposure 

for an individual that exceeds the reference dose. The relative source 

contribution has a significant impact on the health reference level that the 

agency derives for contaminants with noncancer adverse health effects. As 

shown in table 3, the lower the relative source contribution, the lower and 

more protective the health reference level. Conversely, a higher relative 

 

20EPA defines a reference dose as an estimate (with uncertainty spanning perhaps an order 

of magnitude) of a daily oral exposure to the human population (including sensitive 

subpopulations) that is likely to be without an appreciable risk of deleterious effects during 

a lifetime. It can be derived from a no-observed-adverse-effect level, a lowest-observedadverse-effect level, or a benchmark dose, with uncertainty factors generally applied to 

reflect limitations of the data used. 

21IRIS information includes the reference dose for noncancer health effects resulting from 

oral exposure, the reference concentration for noncancer health effects resulting from 

inhalation exposure, and the cancer assessment for both oral and inhalation exposure. 

Combined with specific situational exposure assessment information, the summary health 

hazard information in IRIS may be used as a source in evaluating potential public health 

risks from chemical substances found in the environment. 

22For the carcinogens EPA has evaluated for regulatory determination, EPA’s assessments 

have assumed that no level of exposure is safe, with the health reference level reflecting 

the concentration of the contaminant in drinking water equivalent to a one-in-a-million 

increased risk of getting cancer from a lifetime of exposure. EPA’s cancer risk policy 

provides guidance on the data needed for EPA to assume that there is a threshold below 

which a carcinogenic contaminant does not pose a risk. For health problems other than 

cancer, EPA has generally posited that there is some safe level of exposure to a 

contaminant before adverse health effects occur. 

Page 12 GAO-11-254 Safe Drinking Water Act
 

source contribution results in a higher and less protective health reference 

level. 

Table 3: Comparison of the Impact on Health Reference Levels of Three Different Relative Source Contribution Factors, 

Assuming a Reference Dose of 0.5 Micrograms per Kilogram per Day 

[(Reference dose 

(micrograms per 

kilogram per day)a

x 

Body weight) 

(kilograms) ÷ 

Drinking water 

intake] 

(liters per day) x 

Relative source 

contribution 

(percentage) = 

Health reference 

level 

(parts per billion)b

[(0.5 x 70) ÷ 2] x 20 = 3.5 

[(0.5 x 70) ÷ 2] x 50 = 8.8 

[(0.5 x 70) ÷ 2] x 80 = 14 

Source: GAO. 

a

1 microgram = 0.001 milligrams. Therefore, 0.5 micrograms per kilogram per day also equals 0.0005 

milligrams per kilogram per day. 

b

The parts per billion unit is equivalent to the micrograms per liter unit. Therefore, 3.5 parts per billion 

is the same as 3.5 micrograms per liter. 

According to EPA’s guidance on methods for developing relative source 

contribution estimates,23 in deciding what method to use, the agency must 

determine whether adequate data are available on the extent of exposures 

to the contaminant from drinking water and all other relevant sources, 

including other oral exposures, inhalation exposures, and dermal 

exposures. According to an Office of Water official, in most cases the 

agency lacks adequate data to fully characterize the extent of exposure 

from the various sources. In the absence of sufficient data, the guidance 

recommends the use of a conservative default assumption—that the 

relative source contribution from drinking water is 20 percent, leaving 80 

percent of the total reference dose to account for all other sources of 

exposure. With the exception of perchlorate, EPA has used the default 20 

percent when using a relative source contribution to determine the health 

reference level for its regulatory determinations. 

 

23EPA, Office of Science and Technology and Office of Water, Methodology for Deriving 

Ambient Water Quality Criteria for the Protection of Human Health (Washington, D.C.: 

October 2000). This guidance document includes discussions of the two approaches the 

drinking water program has used for estimating the relative source contribution and 

criteria for selecting the appropriate approach. While the guidance was developed in the 

context of Clean Water Act water quality criteria, the Office of Water uses it in making its 

drinking water regulatory determinations as well as in establishing primary drinking water 

regulations. 

Page 13 GAO-11-254 Safe Drinking Water Act
 

If the agency determines it has adequate exposure data to estimate the 

relative source contribution, rather than applying the default assumption, 

according to the guidance, the agency may choose one of two methods—

the percentage method or the subtraction method.24 EPA characterizes the 

percentage method as conservative in that it preserves the proportion of 

existing daily exposure from drinking water relative to other exposure 

sources when allocating the reference dose. That is, if the daily exposure 

to a contaminant in drinking water is currently low compared to food, for 

example, the portion of the reference dose allocated to exposure from 

drinking water will also be relatively low. In contrast, the subtraction 

method allocates 100 percent of the reference dose among the various 

sources of exposure. Specifically, under the subtraction method, the daily 

exposure from all nondrinking water sources is first subtracted from the 

reference dose, and the remainder is allocated to drinking water, thereby 

generally resulting in a higher relative source contribution factor for 

drinking water than the percentage method. The guidance generally 

provides that, using either method, the relative source contribution 

selected should not be lower than 20 percent or higher than 80 percent. 

(Appendix V provides example calculations of the relative source 

contributions that result from each of these methods.) 

EPA’s Completed 

Regulatory Determinations 

EPA completed two cycles of regulatory determinations in 2003 and 2008 

addressing a total of 20 contaminants—in each case, it decided not to 

regulate. In addition, EPA addressed perchlorate in 2011—deciding to 

regulate using an out-of-cycle determination. First, in 2003, EPA made final 

regulatory determinations to not regulate 9 contaminants on its 1998 

candidate list of 60 contaminants. Second, in 2008, EPA made final 

regulatory determinations to not regulate 11 of 51 contaminants on its 

2005 candidate list and issued a preliminary determination to not regulate 

perchlorate. As discussed earlier, on February 11, 2011, EPA reversed its 

preliminary determination and made a determination to regulate 

perchlorate—representing the first determination to regulate a 

contaminant under the 1996 amendments. Table 4 identifies the 

contaminants for which EPA has made regulatory determinations to date. 

 

24According to the guidance, adequate data are available data that describe central 

tendencies and high ends for relevant exposure sources and pathways. In addition, 

adequacy depends on whether the data are relevant to and representative of the population 

at risk; therefore, data may be adequate for some decisions and inadequate for others. 

Page 14 GAO-11-254 Safe Drinking Water Act
 

Table 4: Drinking Water Contaminants with Final EPA Regulatory Determinations 

Regulatory determination cycle Contaminants 

Cycle 1 (2003) Acanthamoeba, aldrin, dieldrin, 

hexachlorobutadiene, manganese, metribuzin, 

naphthalene, sodium, and sulfate. 

Cycle 2 (2008) Boron; dacthal (DCPA) mono-acid degradate; 

dacthal (DCPA) di-acid degradate; DDE; 

1,3-dichloropropene; 2,4-dinitrotoluene; 

2,6-dinitrotoluene; EPTC 

(s-ethyl-dipropythiocarbamate); fonofos; 

terbacil; and 1,1,2,2-tetrachloroethane. 

Out of cyclea (2011) Perchlorate. 

Sources: 68 Fed. Reg. 42898 (July 18, 2003); 73 Fed. Reg. 44251 (July 30, 2008); 76 Fed. Reg. 7762 (Feb. 11, 2011). 

a

The 2011 regulatory determination on perchlorate represents the first time EPA has made an out-ofcycle determination, issuing it while EPA is working on the third cycle of regulatory determinations 

expected to be completed in 2013. 

EPA’s Health Advisories EPA’s Office of Water has issued health advisories for different durations 

of exposure for regulated and unregulated drinking water contaminants, 

including some for which EPA made regulatory determinations to not 

regulate.25 According to EPA documents, health advisories provide 

technical guidance on health effects, analytical methodologies, and 

treatment technologies to assist EPA regional offices, state governments, 

and public health officials in cases of emergency spills or contamination 

situations. EPA has issued new or updated health advisories for 9 of the 20 

contaminants it determined did not warrant regulation under the 1996 

amendments.26 These advisories establish 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. A key difference between the utility of health advisories for 

regulated contaminants and health advisories for unregulated 

 

25EPA health advisories for regulated and unregulated contaminants are provided in EPA’s 

2009 Edition of the Drinking Water Standards and Health Advisories, EPA 822-R-09-011 

(Washington, D.C., October 2009). 

26Although EPA announced in its July 2008 Federal Register notice that it would issue an 

updated health advisory for a 10th contaminant that the agency decided to not regulate—

1,3-dichloropropene—as of February 2011, the agency had not issued an updated health 

advisory for this contaminant. 

Page 15 GAO-11-254 Safe Drinking Water Act
 

contaminants is that states, localities, and consumers may obtain testing 

data on the levels of regulated contaminants from their public water 

systems, but information on levels of unregulated contaminants may be 

outdated or unavailable from public water systems because these systems 

are not typically required to test for the presence of unregulated 

contaminants. 

EPA’s Federal Advisory 

Committees for Drinking 

Water Issues 

The Office of Water has two key EPA federal advisory committees that can 

assist it in implementing the numerous requirements of the Safe Drinking 

Water Act. First, EPA’s Science Advisory Board’s Drinking Water 

Committee, composed of non-EPA technical experts, provides 

independent advice and recommendations to EPA on the technical aspects 

of its drinking water program.27 For example, in 2009, the Drinking Water 

Committee issued a report on EPA’s processes for developing its third 

contaminant candidate list.28 In addition, EPA’s National Drinking Water 

Advisory Council, a federal advisory committee created in 1974 by the Safe 

Drinking Water Act, also provides independent advice and 

recommendations to EPA on various aspects of its drinking water 

program. The council is composed of 15 members representing (1) state 

and local agencies concerned with safe drinking water, (2) water-related 

or other organizations and interest groups having an active interest in safe 

drinking water, and (3) the general public. In June 2000, the council 

provided EPA with recommended protocols for evaluating contaminants 

for regulatory determination, including a semiquantitative evaluation tool 

that highlighted the relative importance of various factors in making 

regulatory determinations.29

 

27EPA’s Science Advisory Board is a federal advisory committee established by Congress in 

1978 with a broad mandate to advise the agency on technical matters. The Board has 

established several standing committees, including the Drinking Water Committee. 

28SAB Advisory on EPA’s Draft Third Drinking Water Contaminant Candidate List 

(CCL3), EPA-SAB-09-011 (Washington, D.C., Jan. 29, 2009). 

29National Drinking Water Advisory Council, Report of the National Drinking Water 

Advisory Council Working Group on CCL & Six-Year Review, Recommendations on the 

CCL Regulatory Determination Protocol (May 23, 2000). The council approved the report’s 

recommendation that EPA use the protocol for making regulatory determinations on June 

14, 2000. 

Page 16 GAO-11-254 Safe Drinking Water Act
 

Since the enactment of the 1996 amendments to the Safe Drinking Water 

Act, EPA has made limited progress in prioritizing drinking water 

contaminants on the basis of greatest public health concern, and the lack 

of data on the public’s exposure to potentially harmful drinking water 

contaminants and their health effects continues to limit EPA’s ability to 

make regulatory determinations. In addition, during the nearly 15 years 

since the 1996 amendments were passed, EPA has not developed policies 

or guidance providing its interpretation of, or guiding personnel in how to 

implement, the broad statutory criteria for selecting contaminants and 

making regulatory determinations on them. Moreover, the credibility of 

some of EPA’s regulatory determinations is reduced because of a lack of 

transparency, clarity, and consistency in the regulatory determination 

notices and primary support documents. 

Systemic Limitations 

in EPA’s 

Implementation of 

Requirements for 

Determining Whether 

to Regulate Additional 

Contaminants Have 

Impeded Progress in 

Helping Assure the 

Public of Safe 

Drinking Water 

EPA Has Neither Identified 

the Drinking Water 

Contaminants of Greatest 

Public Health Concern 

Nor Fully Used Its 

Authority to Obtain Data 

for Making Regulatory 

Determinations 

The 1996 amendments require EPA to consider for regulatory 

determinations contaminants that present the greatest public health 

concern, but the agency has not effectively implemented this requirement. 

In addition, while EPA has made some progress in developing the 

occurrence and health effects data it needs, for many contaminants EPA 

lacks sufficient occurrence and health effects data to support regulatory 

determinations, which continues to limit its ability to make these 

decisions. Further, some management decisions and implementation 

delays have limited the extent and utility of the occurrence data EPA 

collected under its unregulated contaminants testing program. Moreover, 

as a result of the IRIS program’s inability to provide timely health 

assessment data, EPA regulatory determinations have been delayed on 

some unregulated contaminants. 

In light of the potentially large number of contaminants in public drinking 

water and limited government resources to address them, the 1996 

amendments to the Safe Drinking Water Act directed EPA to consider for 

regulatory determination contaminants that present the greatest public 

health concern. As discussed earlier, the occurrence in drinking water and 

potential health effects of tens of thousands of chemicals that may be in 

use in the United States are largely unknown. Although the candidate list 

represents one level of prioritization by having EPA identify contaminants 

that warrant consideration for regulation from a larger universe, EPA 

officials told us that the Office of Water has not (1) further ranked or 

EPA Has Not Effectively

Implemented the Act’s 

Requirement to Prioritize Its 

Regulatory Determinations by 

Selecting for Consideration 

Contaminants of Greatest 

Public Health Concern 

Page 17 GAO-11-254 Safe Drinking Water Act
 

otherwise prioritized the contaminants on the list on the basis of public 

health concern or (2) prioritized contaminants on the basis of public 

health concern when selecting them for regulatory determinations. In fact, 

for 16 of the 20 regulatory determinations made through January 2011, 

including all 11 decisions for the second cycle of determinations 

completed in 2008, EPA based its decisions not to regulate on the rationale 

of no or limited occurrence—that is, EPA assessed public exposure to 

these drinking water contaminants as minimal. An EPA official described 

these determinations as addressing the “low hanging fruit”—rather than 

the contaminants of greatest public health concern. In making regulatory 

determinations, EPA has selected contaminants from its candidate lists for 

which it decided that sufficient occurrence and health effects data were 

available.30 Consequently, data availability—not consideration of greatest 

public health concern—has been the primary driver of EPA’s selection of 

contaminants for regulatory determinations. EPA officials told us that the 

agency has not needed to prioritize among contaminants because a lack of 

occurrence and health effects data, rather than agency resources, has 

limited the number of determinations. According to EPA officials and 

regulatory determination documents, most contaminants on the candidate 

lists have lacked sufficient occurrence data, health effects information, or 

both. 

EPA has acknowledged the significant gaps in its data for contaminants on 

its candidate lists. After EPA completed 20 regulatory determinations from 

1996 through 2008, 40 of the 60 contaminants on its 1998 and 2005 

candidate lists remained unaddressed as a result of insufficient data.31 In 

2009, EPA published its third and latest candidate list, which contains 116 

contaminants32—including 18 from the previous lists.33 EPA’s Federal 

Lack of Coordinated 

Occurrence and Health Effects 

Data Continues to Limit EPA’s 

Ability to Make Regulatory 

Determinations 

 30EPA uses occurrence data to identify human exposure to contaminants in drinking water. 

31Perchlorate was one of the 40 contaminants that remained unaddressed because, as EPA 

explained, “additional information may be needed to more fully characterize perchlorate 

exposure” to support a regulatory determination during this period. In October 2008, EPA 

issued a preliminary determination on perchlorate, and in February 2011, EPA issued a 

final regulatory determination. 

32The third candidate list includes 104 chemical and 12 microbial contaminants. 

33EPA made substantial changes in its methodology for developing the third candidate list, 

including implementing a criteria-based screening process. The 40 contaminants from the 

previous candidate lists for which the agency had not made regulatory determinations were 

included among the contaminants that were subject to the screening process. Using the 

new screening process to re-evaluate these contaminants, EPA selected 18 to carry forward 

to the third candidate list and did not select the other 22. 

Page 18 GAO-11-254 Safe Drinking Water Act
 

Register notice on the third candidate list indicated that the agency lacked 

sufficient occurrence or health effects data, or both, for making regulatory 

determinations for at least 100 of these contaminants. Further, in many 

cases, gathering sufficient data to address contaminants awaiting 

determinations has taken EPA more than 10 years, and obtaining data on 

other contaminants on the current list may well take decades. 

Moreover, 17 contaminants that have been on all three candidate lists lack 

the needed occurrence data and health effects information. One such 

contaminant is RDX—a powerful explosive used by the U.S. military in 

thousands of munitions and classified by EPA as a possible human 

carcinogen. Although RDX first appeared on a candidate list in 1998, EPA 

still lacks the data it needs to make a regulatory determination.34

Specifically, EPA expects to have nationally representative occurrence 

data on RDX from the second testing cycle by the fall of 2011, in time for 

the third cycle of regulatory determinations that EPA expects to complete 

in 2013. However, it is not known at this time whether the minimum 

reporting level of the test methods EPA is using to collect occurrence data 

on RDX under its testing program will be sufficiently sensitive to identify 

exposure at the health reference level, because the IRIS assessment on 

which the health reference level will be based is in progress. Regarding the 

IRIS assessment, we have previously reported that EPA started an IRIS 

assessment of RDX in 2000, suspended it to await research, and then 

restarted it in 2007.35 Subsequently, EPA’s Office of Research and 

Development placed the ongoing IRIS assessment of RDX and other 

contaminants on hold for about a year to enable the IRIS program to focus 

on completing what it defined as its priority assessments.36, 37 In October 

 

34EPA had planned to test for RDX in the first testing cycle, but the agency did not require 

testing for this contaminant during the first cycle as it awaited refinement of the testing 

(analytic) method. EPA subsequently selected RDX again for testing under the second 

cycle, allocating 2 of the 60 available testing slots for the first two testing cycles to RDX. 

35GAO, Chemical Assessments: Low Productivity and New Interagency Review Process 

Limit the Usefulness and Credibility of EPA’s Integrated Risk Information System, 

GAO-08-440 (Washington, D.C.: Mar. 7, 2008). 

36To make progress on its backlog of 70-plus ongoing assessments, the IRIS program 

identified a subset of assessments for completion, taking into account such factors as the 

assessment stage (with priority generally given to assessments in the later stages of 

development) and input from program offices. 

Page 19 GAO-11-254 Safe Drinking Water Act
 

2010, an official from the Office of Research and Development told us that 

the IRIS program had just begun to work on the IRIS assessment again and 

estimated its completion in the third or fourth quarter of 2012. Under 

EPA’s IRIS assessment process, this approximately 2-year time frame 

reflects EPA’s estimate for completion of a standard, noncontroversial 

assessment.38 However, RDX is among the contaminants EPA considers to 

have a greater level of controversy or visibility. As we reported in 2008, 

several IRIS assessments of contaminants of key concern to other federal 

agencies—stemming from potential impacts on agencies’ operations and 

associated environmental cleanup costs—involved extensive interagency 

reviews and ultimately long delays.39 Because RDX is such a contaminant 

of concern, the IRIS assessment may similarly be subject to extended 

reviews and delays.40 Moreover, the potential for the continuation of 

previous IRIS assessment delays for this contaminant raises concerns. 

Thus, the outlook for a regulatory determination on RDX in 2013 is 

uncertain. 

Other contaminants that have been on all three candidate lists that lack 

the needed occurrence and health effects data include terbufos, a 

pesticide that is highly toxic; and methyl tertiary-butyl ether (MTBE), a 

gasoline additive whose potential health effects EPA is currently assessing 

under its IRIS program. EPA has a risk assessment for terbufos but does 

not yet have nationally representative occurrence data on it.41 The agency 

has nationally representative occurrence data for MTBE but lacks an IRIS 

assessment. We note that addressing data gaps for regulatory 

 

37According to OMB documents, EPA is the only federal agency that conducts quantitative 

cancer assessments of chemicals. Moreover, the World Health Organization, ATSDR, and 

the California Environmental Protection Agency—entities EPA has cited as potential 

sources for health assessment data for regulatory determinations—do not have health 

assessments on RDX. 

38The IRIS program provides an assessment time frame for standard assessments—23 

months—but not for more complex or controversial assessments. Rather, the IRIS program 

indicates such assessments may take longer. 

39As of February 2011, EPA had not finalized IRIS assessments for the six key contaminants 

that we reported in 2008 had been in progress for a number of years. 

40For example, along with contaminants such as perchlorate and hexavalent chromium, 

RDX is on DOD’s emerging contaminants program’s action list. Under this program, a DOD 

team on “materials of evolving regulatory interest” focuses on a number of contaminants to 

develop actions to respond to such potential factors as health impacts, cleanup costs, 

compliance costs, readiness impacts, and facilities’ life-cycle costs. 

41Because terbufos degrades quickly in water, EPA is currently testing for its longer-lived 

degradate, terbufos sulfone. 

Page 20 GAO-11-254 Safe Drinking Water Act
 

determinations generally requires coordinated and timely efforts between 

the agency’s testing program and its IRIS program. However, while data on 

exposure and health effects from similar time frames are generally needed 

to develop credible determinations and drinking water regulations, the 

current process is not producing such data, largely because EPA is 

collecting nationally representative occurrence data on some 

contaminants to identify exposure at levels of public health concern but is 

not at the same time actively pursuing IRIS assessments or other credible 

sources for health effects information. For example, in the case of RDX, 

while the Office of Water is obtaining testing data on this contaminant, we 

found that the Office of Water did not list RDX among the contaminants 

for which it needed an IRIS assessment in responding to the Office of 

Research and Development’s 2010 survey of program offices on IRIS 

assessments needs for the next few years. 

Although occurrence data on unregulated contaminants are critical for 

informed regulatory determinations and may also help EPA identify 

contaminants of greatest public health concern, EPA has not fully used its 

authority to gather these important data. To obtain information on how 

frequently and in what locations unregulated contaminants occur in public 

water systems for EPA’s assessments of public exposure to such 

contaminants, the agency requires a subset of public water systems to test 

for the presence of selected contaminants either two or four times during 

a consecutive 12-month period during a testing cycle.42 While the 1996 

amendments authorized EPA to require certain public water systems to 

conduct such testing for the presence of up to 30 unregulated 

contaminants every 5 years, EPA’s implementation of this authority has 

limited the agency’s progress in obtaining this important information. 

Specifically, by the fall of 2011, EPA expects to have occurrence data for 

51 contaminants the agency included in its first two testing cycles; 

however, according to the testing provisions in the 1996 amendments, EPA 

could have (1) obtained occurrence data for up to 60 unregulated 

contaminants and (2) begun the process of obtaining such data for up to 

Some Management Decisions 

and Implementation Delays 

Have Limited the Extent and 

Utility of the Occurrence Data 

EPA Collected under Its 

Unregulated Contaminants 

Testing Program 

 42Public water systems served by surface water are to test four times, and systems served 

by groundwater are to test two times, during a consecutive 12-month period. 

Page 21 GAO-11-254 Safe Drinking Water Act
 

30 more.43 The difference between the occurrence data that EPA could be 

obtaining under its authority to support its regulatory determinations and 

the data it currently has or is in the process of obtaining largely stems 

from the agency not fully using its testing authority, not adhering to the 

testing program schedule, and requiring testing for some contaminants 

that are not on its candidate list. 

First, despite having the authority to require testing for up to 30 drinking 

water contaminants in each 5-year cycle, in implementing the first two 

cycles of the testing program, EPA required that only 51 contaminants be 

tested—thereby not availing itself of its authority to obtain occurrence 

data for 9 additional contaminants. EPA officials who manage the testing 

program said that EPA chose to limit the number of contaminants tested in 

the first two testing cycles so that, if additional emerging contaminants of 

concern were identified, the agency would be able to incorporate them 

into its testing schedule without exceeding the statutory limit of 30 per 5-

year cycle. However, these officials also said they have now concluded 

that this approach was not practical or necessary, given the logistical and 

operational challenges the agency and water utilities would face in testing 

for additional contaminants and because the 1996 amendments provided 

other authority to test for other emerging contaminants, if needed. In 

August 2010, these officials told us they were likely to recommend that the 

agency use its full testing authority in the next testing cycle, and EPA did 

so—proposing to require testing for 30 unregulated contaminants in its 

March 3, 2011, proposed rule for the third testing cycle. 

Second, delays in implementing the testing program have reduced its 

productivity in obtaining occurrence data on contaminants on the 

candidate list. If EPA had met the statutory time frames for the testing 

program,44 it would likely have completed two testing cycles and begun the 

third cycle in 2009 by identifying up to 30 contaminants for which it would 

require testing to be conducted. Based on the first two rules, the testing 

would likely have started in January 2011. However, as of March 2011, 

 

43Under the time frames set out in the statute for identification of contaminants to be 

tested, EPA would have issued the list of contaminants for the third testing cycle in 2009, 

and based on past time frames between publishing a list and beginning testing, public water 

utilities in the testing program sample would have started to test for up to 30 contaminants 

in January 2011. EPA has recently proposed the list and time frames for the third testing 

cycle (2012 through 2016), with testing to be conducted from January 2013 through 

December 2015. 

44See footnotes 17 and 43. 

Page 22 GAO-11-254 Safe Drinking Water Act
 

EPA had obtained testing data on 26 contaminants from the first testing 

cycle and was still collecting final testing data for the 25 contaminants 

from the second cycle.45 While the reasons for the delays in the testing 

program are outside the scope of this report, EPA officials who manage 

the testing program told us that the delays stemmed from implementing 

the 1996 amendments’ new and technically challenging requirements for 

testing unregulated contaminants, including developing testing methods 

for selected contaminants, developing quality assurance and quality 

control standards for the tests, and certifying laboratories to conduct the 

tests. They indicated, however, that they should be in a position now to 

manage the program more efficiently, beginning with the planned 

publication in 2012 of the final list of contaminants to be tested in the third 

cycle and adhering to 5-year cycles in the future. 

Third, EPA has required a sample of public water systems to test for some 

contaminants that are not on its candidate lists, which has further limited 

the capacity of the testing program to support EPA’s regulatory 

determinations. According to EPA, the purpose of the testing program is to 

provide the data necessary to determine if a contaminant occurs with a 

frequency and at levels of public health concern to warrant regulatory 

determination; the testing program also informs the development of 

candidate lists, EPA’s primary mechanism for identification of 

contaminants that may require regulation.46 In the second testing cycle, 9 

of the 25 contaminants selected for testing did not appear on the candidate 

list. As a result, EPA has required a subset of public water systems to test 

for 9 contaminants not on the list that represents the primary source from 

which EPA selects contaminants for regulatory determinations.47 To the 

extent that EPA has tested for contaminants not on its candidate lists, the 

agency has reduced the capacity of its testing program to address the 

occurrence data gaps that EPA officials said have precluded the agency 

from making regulatory determinations for contaminants on the candidate 

lists. 

 

45According to EPA officials, the agency expects to have complete data from the second 

testing cycle by the fall of 2011. 

46EPA, “Drinking Water Contaminant Candidate List 3—Final Notice,” 74 Fed. Reg. 51850 

(Washington, D.C., Oct. 8, 2009). 

47EPA is authorized to make regulatory determinations for contaminants that are not on the 

candidate list, but has not done so to date. For these 9 contaminants, the agency could 

make determinations for any of them either as part of a regulatory determination cycle or 

out of cycle, or could add any of them to the next candidate list. 

Page 23 GAO-11-254 Safe Drinking Water Act
 

In addition to decisions and program delays that have limited the total 

number of contaminants tested, EPA’s decisions on the type of sampling 

approach to use have limited the utility of some of the testing program 

data obtained. Regarding sampling, EPA has used two approaches—

”assessment monitoring” and “screening survey.” EPA officials described 

assessment monitoring as “the gold standard” for obtaining sufficient data 

on national occurrence of drinking water contaminants to support 

regulatory determinations. This approach can provide nationally 

representative occurrence data with low levels of uncertainty.48

Nonetheless, under the first two testing cycles, EPA required assessment 

monitoring testing—conducted at approximately 4,000 public water 

systems—for less than half (22) of the 51 contaminants in the unregulated 

contaminants testing program.49 EPA has used the more limited “screening 

survey” for a majority of the contaminants tested to date—29—under the 

unregulated contaminants testing program.50 The screening survey—which 

required testing at 300 and 1,200 public water systems for the first and 

second cycles, respectively—results in greater uncertainty because it tests 

a smaller sample of public water systems. In fact, the Office of Water did 

not make regulatory determinations for 12 contaminants tested under the 

screening survey in the first cycle of testing. In EPA’s 2008 regulatory 

determination notice, the agency classified these 12 contaminants as 

having insufficient occurrence data for making regulatory determinations. 

Thus, nearly half of the contaminants in the first testing cycle were 

nonetheless found to have insufficient occurrence data for making 

regulatory determinations. EPA stated in a Federal Register notice that it 

increased the sample size of the screening survey in the second testing 

cycle so that “the data can be used to support regulatory determinations 

EPA Used a Limited Testing 

Approach for More Than Half 

of the Contaminants Tested 

 48According to EPA testing program documentation, EPA believes assessment monitoring 

represents “the most effective and accurate survey approach,” providing “a confidence 

level of 99 percent with an allowable error of plus or minus 1 percent.” The documentation 

notes that using an approach with a greater margin of error, and the resulting smaller 

sample size, could cause the occurrence of the many contaminants that occur in 1 percent 

or less of drinking water systems on a national basis to be “missed entirely.” The 

documentation further notes that even a small percentage of systems with detections can 

affect a significant population. 

49The first cycle testing included approximately 3,800 systems and the second cycle about 

4,200. Assessment monitoring includes all systems serving over 10,000 people and a 

representative sample of 800 smaller systems. 

50The 29 contaminants tested under the screening survey include 14 contaminants from the 

first testing cycle and 15 from the second cycle. 

Page 24 GAO-11-254 Safe Drinking Water Act
 

and rule development, if warranted.”51 For example, EPA testing program 

documentation states that if a contaminant is found with some 

significance during the screening survey, EPA may be able to forgo 

assessment monitoring and make a regulatory determination based on 

these data to protect public health more quickly. We note, however, that 

this screening survey will provide estimates with greater uncertainty than 

those provided by assessment monitoring. Despite EPA’s intent that 

screening survey data indicating significant occurrence of a contaminant 

may be sufficient to support a regulatory determination, whether EPA 

finds such data to be sufficient will not be known until EPA announces 

whether it will proceed with determinations for the contaminants on the 

second testing cycle screening survey list—or why it will not proceed. This 

is an important point as three times as many contaminants on the current 

candidate list (12) will have second testing cycle screening survey data as 

will have the more robust assessment monitoring data (4) for EPA to 

consider as it develops the third cycle of regulatory determinations, 

expected to be finalized in 2013. 

According to an EPA testing program document, assessment monitoring 

was selected for contaminants that could be tested for using analytical 

methods that “utilize widely available technologies,” with decisions on 

which testing approach to use for each contaminant based primarily on 

the availability of the analytical methods used and the associated issue of 

laboratory capacity. The document also states that the screening survey 

“primarily targets contaminants with analytical methods that generally 

utilize more sophisticated technology that may not be widely established 

in drinking water laboratories.”52 However, in August 2010, EPA officials 

who manage the testing program said the number of laboratories with the 

capacity to conduct the more sophisticated testing technologies has 

grown, in part because recent concerns about low levels of 

pharmaceuticals found in drinking water increased demand for these more 

advanced technologies. In August 2010, the officials told us they now 

anticipate that most, if not all, of the testing under the next cycle will be 

conducted using assessment monitoring. EPA’s March 2011 proposed rule 

 

51EPA, “Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems Revisions: Proposed Rule,” Federal Register (Aug. 22, 2005). 

52As noted earlier, we did not evaluate the testing program. As such, we did not examine 

issues such as the extent to which the tests used widely available technologies and national 

laboratory capacity to conduct more sophisticated tests. 

Page 25 GAO-11-254 Safe Drinking Water Act
 

for the third testing cycle proposes assessment monitoring testing for 28 of 

the 30 contaminants.53

In some cases, the benefit of the occurrence data collected under the 

testing program was reduced because EPA required public water systems 

to use testing (analytic) methods that were not sufficiently sensitive to 

identify the presence of contaminants at EPA’s health reference level—the 

health benchmark that EPA uses in assessing whether to regulate specific 

contaminants. For 9 of the 20 contaminants for which EPA made 

regulatory determinations in 2003 and 2008, the minimum reporting 

level—the lowest level of a contaminant at which detections can be 

reported under testing protocols—exceeded EPA’s health reference level.54

As a result, occurrence of these 9 contaminants at a level higher than the 

health reference level but lower than the minimum reporting level may not 

have been detected.55 For four of the nine contaminants, EPA obtained 

occurrence data in the first cycle of its testing program.56 According to 

EPA officials, the minimum reporting levels were developed for these 

contaminants before the health reference levels were developed. These 

officials told us that the agency used its best professional judgment and 

the information available at the time in developing the minimum reporting 

levels that, in retrospect, were higher than the health reference levels.57

According to a 2010 USGS report that presents information from that 

agency’s National Water-Quality Assessment Program—a long-term effort 

EPA’s Testing Methods Were 

Not Sufficiently Sensitive in 

Some Cases to Identify the 

Presence of Contaminants at 

EPA’s Health Reference Level 

 53The 28 contaminants with proposed assessment monitoring testing are chemicals. For the 

other 2 contaminants—microbials (biological substances), which present different testing 

challenges than chemicals—EPA proposed “pre-screen testing” at 800 targeted, 

undisinfected groundwater wells from systems that serve 1,000 or fewer customers. 

54In addition, according to its February 11, 2011, final regulatory determination notice for 

perchlorate, the agency developed a range of health reference levels for 14 life stages, some 

of which are lower than the minimum reporting level the testing program used for 

perchlorate. 

55Determinations for five of the contaminants with minimum reporting levels greater than 

health reference levels were based on state testing data collected under the testing 

program pursuant to the 1986 amendments to the Safe Drinking Water Act. 

56Three of the contaminants were part of the first testing cycle. The fourth—1,3-

dichloropropene—was not officially part of the first testing cycle, but EPA conducted 

analyses on samples collected from 796 of the small drinking water systems that provided 

samples for assessment monitoring in conjunction with the first testing cycle. 

57Because the second cycle of testing will support the third cycle of regulatory 

determinations in 2013, it is not known at this time the extent to which minimum reporting 

levels for the contaminants could exceed the health reference levels developed as part of 

the regulatory determination process. 

Page 26 GAO-11-254 Safe Drinking Water Act
 

to assess the status and trends of national water quality conditions58—the 

reporting level for contaminant occurrence data should be below the 

human health benchmark, which is analogous to EPA’s health reference 

level,59 to ensure that the tests are adequate to detect concentrations 

relevant to human health. Further, USGS has reported that when the 

reporting level exceeds the health benchmark, a contaminant may be 

present at a concentration greater than the health benchmark but remain 

undetected, resulting in greater uncertainty in evaluating the contaminant 

concentration in the context of public health. We note that EPA’s testing 

program obtains data using minimum reporting levels that are often higher 

than those used by USGS in its National Water-Quality Assessment 

Program—ranging from 2 to more than 600 times higher.60 In addition to 

the potential for underestimating occurrence at the health reference level, 

using high minimum reporting levels also prevents EPA from obtaining 

information on lower levels of contamination—such as at one-half the 

health reference level, as recommended by EPA’s National Drinking Water 

Advisory Council, or the 1/10th health reference level used by USGS. 

According to the USGS report, these lower levels can provide “early and 

conservative indications of contaminant concentrations that may at some 

time approach or exceed benchmarks.” While EPA may have different 

factors to consider in selecting methods for use in its testing program than 

USGS, the USGS report shows that more sensitive methods for testing 

unregulated contaminants have been available. 

 

58USGS, Quality of Source Water from Public-Supply Wells in the United States, 1993-

2007 (Reston, Va., May 2010). This report is part of the USGS National Water-Quality 

Assessment (NAWQA) Program, which was established in 1991 to develop long-term, 

nationally consistent information on the quality of the nation’s streams and groundwater, 

and thereby support scientifically sound decisions for water-quality management, 

regulation, and policy decisions. The objectives of NAWQA are to assess the status and 

trends of national water-quality conditions and to understand the factors and processes 

that govern those conditions.

59USGS’s health benchmarks are comparable in concept to EPA’s health reference levels, 

although USGS does not use its benchmarks for regulatory decisions. USGS uses EPA’s 

maximum contaminant levels for regulated contaminants and develops health-based 

screening levels for unregulated contaminants using EPA Office of Water methodologies 

for establishing drinking water guidelines. 

60In its 2010 report on its national water-quality assessment program from 1993 to 2007, 

USGS reports that its results for three contaminants included in EPA’s testing program 

differ, “perhaps because the reporting levels in this study were about 170-fold to 670-fold 

lower than in the UCMR2 program [cycle 2 of EPA’s testing program].” 

Page 27 GAO-11-254 Safe Drinking Water Act
 

The other key gap in data that are critical for informed regulatory 

determinations is a lack of health assessment data on drinking water 

contaminants. This gap has been largely caused by long-standing 

productivity problems in EPA’s IRIS program, which is managed by the 

Office of Research and Development. EPA established the IRIS program in 

1985 to develop EPA consensus opinions about the health effects that may 

result from chronic exposure to various substances found in the 

environment, thereby helping EPA program offices reduce inconsistency 

in toxicity assessments and, therefore, risk assessments. The IRIS 

database contains toxicity assessments providing health effects data for 

more than 540 chemicals. The Office of Water typically uses these 

assessments, along with exposure assessments, to characterize the public 

health risks of exposure to a chemical or contaminant in drinking water.61

IRIS assessments are a cornerstone of scientifically sound EPA decisions, 

policies, and regulations under a variety of statutes and programs, such as 

the Safe Drinking Water Act, the Clean Air Act, and the Superfund 

program.62 We reported in March 2008 that EPA has not been able to keep 

its existing chemical toxicity assessments current or to complete 

assessments of the most important chemicals of concern.63 We 

subsequently added transforming EPA’s processes for assessing and 

controlling toxic chemicals as a high-risk area in our January 2009 report 

on governmentwide high-risk areas requiring increased attention by 

executive agencies and Congress, and we published our biennial update 

report on the high-risk areas in February 2011.64 In 2009, EPA issued a 

revised IRIS assessment process in response to our recommendations.65

The IRIS Program’s Inability to 

Provide Timely Health 

Assessment Data Has Delayed 

Some Regulatory 

Determinations 

The inability of EPA’s Office of Research and Development to provide the 

Office of Water with new and updated assessments in a timely manner has 

 

61The Office of Water uses occurrence data from public water systems to assess exposure. 

62The Superfund program, established under the Comprehensive Environmental Response, 

Compensation, and Liability Act of 1980, is to protect human health and the environment 

from the effects of hazardous substances. Under this program, EPA has the authority to (1) 

clean up hazardous waste sites and then seek reimbursement from the nonfederal parties 

legally responsible for contaminating them or (2) compel such responsible parties to clean 

up these sites. 

63GAO-08-440. 

64GAO, High-Risk Series: An Update, GAO-09-271 (Washington, D.C.: January 2009); and 

High Risk Series: An Update, GAO-11-278 (Washington, D.C.: February 2011). 

65We are currently evaluating this program and EPA’s progress in completing assessments 

in a separate review. 

Page 28 GAO-11-254 Safe Drinking Water Act
 

impeded effective implementation of EPA’s regulatory determinations. 

From 1998 through 2008, the Office of Water lacked current IRIS 

assessments or other sufficient health information for 24 chemical 

contaminants on its candidate lists, and the Office of Research and 

Development completed assessments for only 2 of the 24.66, 67 Moreover, the 

Office of Water’s needs for health effects information for contaminants on 

the current candidate list, which contains about twice as many 

contaminants as the prior lists, have roughly doubled. Specifically, when 

publishing the third candidate list in 2009, EPA identified health effects 

information gaps for 44 of the 104 chemicals on the list. Further, this 

number may be understated because it excludes 24 contaminants for 

which EPA does not have an IRIS assessment or for which an IRIS 

assessment is either in progress or has not yet begun. It is not clear why 

EPA has not also categorized these contaminants as having health effects 

information gaps, given the challenges that the IRIS program continues to 

face in timely completion of assessments and the related uncertainty as to 

when these ongoing and planned assessments may be completed. Further, 

most of the 44 contaminants with health effects information gaps that EPA 

did identify (1) are not on the IRIS agenda (i.e., assessments are neither 

under way nor planned) and (2) have not been identified by the Office of 

Water as priorities for IRIS assessments. For about half of the 44 

contaminants with health effects information gaps, EPA has indicated that 

assessments containing sufficient toxicity information to initiate an IRIS 

toxicity assessment may be available from other government entities, such 

 

66A total of 24 chemical contaminants lacked health effects information; in 2008, EPA listed 

19 contaminants with health effects information gaps and had removed 5 of the 

contaminants the agency originally identified as lacking health effects information in 1998. 

Of the 5 contaminants removed from the list, EPA completed IRIS assessments for 2 (boron 

and perchlorate), used the existing assessment for 1,1,2,2-tetrachloroethane that the IRIS 

program was in the process of updating, and used the assessment of the parent compound 

dacthal (DCPA) for the two dacthal (DCPA) degradates. 

67In the Federal Register notice announcing its preliminary regulatory determinations for 

cycle 2, EPA reported using IRIS health risk assessments, in some cases augmented by 

subsequent Office of Pesticides Program assessments, for the 11 contaminants the agency 

determined had sufficient health risk data. EPA outlined its process for evaluating studies 

published after the assessments used were completed and for making needed adjustments 

on the basis of new data and to update the assessments to follow the agency’s updated 

guidelines for carcinogen risk assessments. Office of Water officials told us that sometimes 

the office develops it own health assessment or uses other available assessments. 

Page 29 GAO-11-254 Safe Drinking Water Act
 

as the World Health Organization, ATSDR, and the California 

Environmental Protection Agency.68

While problems with the IRIS program are beyond the purview of the 

Office of Water, to some extent the Office of Water’s failure to develop and 

communicate its assessment priorities to the Office of Research and 

Development during this period may have contributed to the Office of 

Water’s inability to obtain sufficient health effects information. 

Specifically, the Office of Research and Development periodically 

requested that program offices identify their IRIS priorities and needs 

throughout the 2000s, and as we reported in 2008, some EPA program 

offices responded and specifically requested that IRIS program 

management focus its resources on expediting the completion of specific 

ongoing IRIS assessments important to their missions.69 However, our 

review of program offices’ responses to the Office of Research and 

Development’s periodic requests for priorities showed that the Office of 

Water did not respond to the requests. Further, while Office of Water 

officials told us that they met with Office of Research and Development 

staff to request status updates of key IRIS contaminants “on a number of 

occasions,” the officials confirmed they did not take the initiative to 

communicate the office’s IRIS assessment needs in writing. We note, 

however, that the Office of Water did respond to the IRIS program’s 

request for input on IRIS assessment priorities in 2010. Also, in November 

2010, EPA Office of Water officials said that the office is developing health 

assessments for some contaminants internally in lieu of depending solely 

on the IRIS program, a situation that highlights the need for EPA to 

effectively implement its revised IRIS assessment process. That is, when 

EPA lacks an effective IRIS process, individual EPA program offices may 

respond by developing health risk assessments of contaminants, using 

varying assessment methods and potentially producing different risk 

estimates—a problem EPA hoped to mitigate by creating the IRIS 

program. 

 

68EPA has yet to use an assessment by these entities to support its completed regulatory 

determinations. In its 2009 notice announcing its third candidate list, EPA indicated that 

the agency would need to evaluate the existing assessments from these other entities to 

determine whether the data on which they are based meet EPA data quality guidelines and 

are compatible with EPA risk assessment policies. 

69GAO-08-440. 

Page 30 GAO-11-254 Safe Drinking Water Act
 

Although the Safe Drinking Water Act requires EPA to select contaminants 

for regulatory determinations that present the greatest public health 

concern, EPA has not developed policies or guidance defining the 

characteristics that would constitute a contaminant of greatest public 

health concern or established a process for identifying such contaminants. 

Moreover, the Office of Water has not developed guidance on when and 

how to conduct additional analyses focused on the effects of drinking 

water contaminants on children and other sensitive subpopulations. While 

the statutory criteria from the 1996 amendments that EPA is to apply in 

making regulatory determinations are generally broad and open to 

interpretation, EPA has not developed policies or guidance for applying 

them. Finally, EPA has not developed guidance on, or a process for, 

reconsidering final regulatory determinations to not regulate. 

EPA has not defined the characteristics of contaminants of greatest public 

health concern or developed a process for prioritizing the contaminants on 

its candidate list for regulatory determination on this basis. As a result, 

EPA lacks criteria and a process for identifying those contaminants on its 

candidate list that pose the greatest public health concern. Contaminants 

of greatest public health concern could be defined on the basis of various 

characteristics. For example, a contaminant that poses a significant health 

hazard, such as cancer or a serious adverse neurological effect, could be 

considered a contaminant of greatest health concern. Along these lines, a 

1993 EPA report to Congress on the drinking water program discussed 

criteria the agency could use in selecting additional contaminants for 

regulation, including that “contaminants posing acute risks or very potent 

chronic health risks would be more likely to be regulated even if 

occurrence tended to be low.”70 In addition, the occurrence or likely 

occurrence of a contaminant in many public drinking water systems or in 

source water could also characterize a contaminant of greatest public 

health concern. For example, an extensive USGS report71 on the quality of 

source water from public-supply wells based on tests of water samples for 

215 regulated and unregulated contaminants conducted from 1993 through 

2007 identified 10 contaminants that occurred most frequently above 

EPA Lacks Policies or 

Guidance on Applying the 

Broad Statutory Criteria 

for Selecting Contaminants 

for Regulatory 

Determinations and 

Making the Determinations 

EPA Has Not Defined 

Characteristics of 

Contaminants of Greatest 

Public Health Concern for the 

Purpose of Selecting Them for 

Regulatory Determinations 

 70At the time of this statement, EPA was operating under the framework of the 1986 

amendments, rather than the 1996 amendments which are the focus of this section. 

71USGS, Quality of Source Water from Public-Supply Wells in the United States, 1993-

2007 (Reston, Va., May 2010). 

Page 31 GAO-11-254 Safe Drinking Water Act
 

USGS health benchmarks72—5 of the 10 were unregulated contaminants.73

These USGS data are limited to the source water for public water systems 

served by groundwater, but they nonetheless represent the type of data 

available for EPA to consider in identifying contaminants on its candidate 

lists as those of greatest public health concern.74

Moreover, EPA’s Science Advisory Board has recommended that EPA 

prioritize among the contaminants on the candidate list. Specifically, in a 

2009 report on the agency’s draft third candidate list, EPA’s Science 

Advisory Board said that the draft list of 104 contaminants was too large to 

effectively prioritize for the purpose of making regulatory determinations. 

The Science Advisory Board recommended that EPA prioritize the 

contaminants on the list to help the agency meet its goal of selecting 

contaminants that “have the greatest opportunity to improve the safety of 

drinking water and protect public health.” In its 2009 Federal Register

notice publishing the final candidate list, EPA stated that it would 

continue to work to prioritize the 116 contaminants on the third candidate 

list, both for regulatory determination and for additional research and data 

collection. As noted earlier, it is important that such efforts relating to IRIS 

assessments and the unregulated contaminants testing program be 

effectively coordinated—that is, focused on priority contaminants of 

greatest public health concern. 

In selecting contaminants that present the greatest public health concern, 

under the Safe Drinking Water Act, EPA is to consider the effect of these 

contaminants on subpopulations at greater risk of adverse health effects, 

such as children. Further, Office of Water officials stated they are required 

to consider effects on sensitive subpopulations in making regulatory 

determinations. Such subpopulations, which may be at greater risk for 

adverse health effects from exposure to drinking water contaminants, may 

include infants, children, those with kidney or liver diseases or weakened 

immune systems, and the elderly. In fact, some of these subpopulations, 

The Office of Water Has Not 

Developed Guidance on 

Considering Adverse Health 

Effects of Drinking Water 

Contaminants on Children and 

Other Sensitive Subpopulations 

to Identify Contaminants of 

Greatest Concern or in Making 

Determinations 

 72As noted earlier, USGS’s health benchmarks are comparable in concept to EPA’s health 

reference levels, although USGS does not use its benchmarks for regulatory decisions. 

73This specific USGS report was not available at the time EPA made regulatory 

determinations on these contaminants, but most of the occurrence data in the report were 

available to EPA at the time the agency was developing regulatory determinations on these 

contaminants. 

74EPA has used these USGS data for other purposes, such as evaluating chemicals for 

inclusion on its candidate lists. 

Page 32 GAO-11-254 Safe Drinking Water Act
 

such as children and individuals with liver or kidney disease, are identified 

as sensitive subpopulations for many of the contaminants EPA determined 

did not warrant regulation. For example, according to EPA documents, 

because children consume more water per unit of body weight than adults, 

they may be more highly exposed to toxic substances in drinking water 

and therefore at greater risk of adverse health effects than adults. In 

addition, children may have increased susceptibility following exposure to 

drinking water contaminants because they continue to develop both 

behaviorally and physiologically throughout childhood. 

In 1995, EPA published its Policy on Evaluating Health Risks to Children, 

which states that the agency will “consider the risks to infants and 

children consistently and explicitly as a part of risk assessments generated 

during its decision making process,” and to “the degree permitted by 

available data in each case, the Agency will develop a separate assessment 

of risks to infants and children or state clearly why this is not done.”75 In 

2006, EPA developed a general guidance document for all EPA program 

offices on implementing its 1995 children’s health policy,76 as well as 

several technical guidance documents (in 2005, 2006, and 2008) that could 

help the Office of Water develop its own guidance specific to assessing the 

sensitivity of children to drinking water contaminants.77 For example, 

EPA’s 2005 guidance on assessing childhood exposures to environmental 

contaminants in general recommends that chronic risks be assessed by 

summing time-weighted exposures that occur at each life stage and states 

that adjustments for variations in toxicity may also need to be made for 

 

75EPA, Policy on Evaluating Health Risks to Children (Washington, D.C.: Oct. 20, 1995). 

76EPA, EPA’s Action Development Process-Guide to Considering Children’s Health When 

Developing EPA Actions: Implementing Executive Order 13045 and EPA’s Policy on 

Evaluating Health Risks to Children (Washington, D.C.: Oct. 2006). EPA published this 

guide to consider children’s health when developing actions, such as policies, regulatory 

actions, or risk assessments. Under this guidance, for example, if health risks will be 

considered to inform a policy or decision, the children’s health policy applies and EPA 

should develop a separate assessment of risks to infants and children, evaluate health risks 

of infants and children in risk characterizations, or state clearly why this was not done. 

Office of Water officials told us that they did not use this guidance in the 2008 regulatory 

determinations because the office developed the framework for the analyses that 

supported the 2008 regulatory determinations in 2003. 

77EPA, Child-Specific Exposure Factors Handbook, EPA/600/R-06/096F (Washington, D.C.: 

Sept. 2008); A Framework for Assessing Health Risks of Environmental Exposures to 

Children, EPA/600/R-05/093F (Washington, D.C.: Sept. 2006); and Guidance on Selecting 

Age Groups for Monitoring and Assessing Childhood Exposures to Environmental 

Contaminants, EPA/630/P-03/003F (Washington, D.C.: Nov. 2005). 

Page 33 GAO-11-254 Safe Drinking Water Act
 

different age groups.78, 79 Finally, EPA has stated that in making a regulatory 

determination, “the [act] requires EPA to take into consideration the effect 

contaminants have on subgroups that comprise a meaningful portion of 

the general population (such as infants, children, pregnant women, the 

elderly, individuals with a history of serious illness or other 

subpopulations) that are identifiable as being at greater risk of adverse 

health effects than the general population.” 

Notwithstanding the requirements of the Safe Drinking Water Act and 

EPA’s 1995 children’s health policy, in developing the 2008 regulatory 

determinations, the Office of Water did not implement a specific approach 

to considering children’s health. In addition, the Office of Water has not 

developed guidance for when and how to analyze the effects of drinking 

water contaminants on children—or other sensitive subpopulations—for 

the purposes of identifying the drinking water contaminants of greatest 

concern on which to make regulatory determinations and to ensure it 

consistently and explicitly considers risks to children in making these 

determinations. While EPA identified children as a sensitive population in 

11 of the 20 regulatory determinations it completed in 2003 and 2008, 

Office of Water officials confirmed that for these 20 determinations, EPA 

did not develop separate health reference levels for children or make 

adjustments to its health assessments. Office of Water officials said, 

however, that they believe their evaluation of the health risks of 

contaminants takes into account sensitive subpopulations, including 

children, as required by the Safe Drinking Water Act. For example, the 

officials said that if they had determined children were “particularly 

sensitive” to the adverse health effects of contaminants being considered 

for regulatory determinations, they could have developed a separate 

assessment of risks for that population, using weight and drinking water 

intake for children, rather than the agency’s standard approach using an 

adult’s weight and water intake.80 Office of Water officials said that, 

alternatively, they could have adjusted the reference dose to account for 

increased sensitivity. As discussed later, EPA’s regulatory determination 

documentation does not explain how or whether the agency determined 

that a separate assessment for children or an adjustment to the health 

 

78EPA/630/P-03/003F. 

79EPA has identified 10 life stages for children from birth up to 21 years of age. 

80According to EPA’s guidance documents on assessing childhood exposures to 

environmental contaminants, EPA historically used a standard approach assuming a 

lifetime of constant exposure for an adult (EPA/630/P-03/003F). 

Page 34 GAO-11-254 Safe Drinking Water Act
 

reference level was not warranted. In light of the children’s risk issues 

discussed earlier—their consumption of more water per unit of body 

weight and other susceptibilities that may occur during childhood—EPA’s 

approach to considering sensitive subpopulations in regulatory 

determinations may not fully account for the risks to children of exposure 

to drinking water contaminants and does not align with current agency 

guidance. 

The 1996 amendments also provide three broad criteria for EPA to use in 

making regulatory determinations, all of which must be met for EPA to 

determine that regulation is warranted. Notably, two of the criteria are so 

broadly stated that they could potentially be interpreted so as to lead to 

regulating all of the contaminants on candidate lists, some of them, or 

none of them. Specifically, the second statutory criterion—that a 

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”—is susceptible to varying 

interpretations. For example, different people may reasonably have 

differing views on the frequency and levels of occurrence that represent a 

public health concern. The third criterion—that regulation of the 

contaminant presents “in the sole judgment of the Administrator . . . a 

meaningful opportunity for health risk reduction”—is expressly 

discretionary, and similarly open to differing interpretations. Importantly, 

the Office of Water has not developed policies or guidance to help EPA 

staff apply these broad criteria. Guidance that might help EPA staff apply 

the criteria transparently and consistently could, among other things, (1) 

define or set thresholds or parameters for assessing whether a 

contaminant occurs, or is substantially likely to occur, in public water 

systems with a frequency and at levels of public health concern and (2) 

provide factors or characteristics of situations that would present 

meaningful opportunities for health risk reduction. We note that such 

guidance could also serve as the basis for an internal review mechanism to 

help EPA ensure consistent implementation of the statutory criteria. Office 

of Water officials could not describe examples of what would meet the 

three criteria beyond stating that “there are no bright lines” and that they 

would “know it when we see it.” Without clarifying guidance, EPA’s 

regulatory determinations lack transparency, and EPA is at risk of making 

inconsistent determinations, undermining the program’s credibility and 

the agency’s ability to assure the public of safe drinking water. 

EPA Has Not Developed 

Policies or Guidance for 

Applying the Broad Statutory 

Criteria for Making Regulatory 

Determinations 

We note that, in 2000, EPA’s National Drinking Water Advisory Council 

provided EPA with a suggested approach for making regulatory 

determinations, including a tool to transparently and semiquantitatively 

Page 35 GAO-11-254 Safe Drinking Water Act
 

evaluate relevant data on known or likely occurrences of contaminants in 

drinking water. Under this approach, data on both known occurrences and 

the substantial likelihood of occurrence would be identified and weighted 

on the basis of such factors as number of detections in excess of the 

health reference level as well as in excess of one-half the health reference 

level, geographic distribution of occurrence, trends in the production and 

use of the chemicals, and direct releases into surface waters.81 While EPA 

has generally provided the types of occurrence data identified by the 

council in its regulatory determination documents, it has not adopted a 

quantitative or other systematic method that would transparently identify 

how and to what extent these data are used to support the agency’s 

determinations. 

While the Office of Water has not established regulations or guidance for 

applying the broad statutory criteria, EPA appears to apply an informal 

policy that contaminants warranting regulation should occur in public 

water systems on a “national” scale. That is, as illustrated in the following 

examples, EPA officials and regulatory determination documents indicate 

that occurrence is, at least to some extent, evaluated from a national 

perspective. 

• Some EPA officials serving on regulatory determination workgroups 

told us that a contaminant must occur “nationally” to warrant a 

determination to regulate. 

• Documents supporting EPA’s first cycle of regulatory determinations 

state that the consideration of geographic distribution “is important 

because the agency is charged with developing national regulations, 

and it may not be appropriate to develop [national primary drinking 

water regulations] for regional or local contamination problems.” 

• In response to public comments about certain preliminary regulatory 

determinations, EPA stated that contaminants “were evaluated in terms 

of national significance” and that EPA considers “both the extent of 

national occurrence and the severity of health effects” when deciding if 

a regulation would provide a meaningful opportunity for health risk 

reduction. 

 

81The council approach outlined geographic distribution using the USGS codes for the 

nation’s 21 water-resources regions and the more than 200 water-resources subregions. The 

approach defined national occurrence as detections in more than 4 of the 21 USGS waterresources regions, and regional occurrence as detection in 2 or more of the subregions but 

fewer than 4 of the regions. 

Page 36 GAO-11-254 Safe Drinking Water Act
 

• In addressing public comments from a state that had requested EPA 

reconsider its preliminary determination to not regulate two 

contaminants (2,4-dinitrotoluene and 2,6-dinitrotoluene), EPA stated 

that these chemicals did not occur “nationally in public drinking water 

systems at health levels of concern” and that if a contaminant appears 

to be “highly localized,” it does not meet the statutory criterion. 

In the cases of 2,4-dinitrotoluene and 2,6-dinitrotoluene, the state 

requesting reconsideration of the preliminary determination reported to 

EPA that it had found high levels of 2,4-dinitrotoluene in groundwater (in 

one case, 200,000 times greater than EPA’s health reference level) in 

numerous locations in their state, including around ammunition and 

military sites.82 EPA’s Federal Register notice does not disclose that the 

state detections reported to the agency, as well as the one detection of 2,4-

dinitrotoluene identified by EPA’s unregulated contaminants testing 

program, involved levels of the contaminant significantly in excess of 

EPA’s health reference level.83 In issuing its final regulatory determination, 

EPA declined to change its decision and referred the state to its revised 

drinking water health advisory, issued in conjunction with the 

determination. EPA’s health advisory for these contaminants presented 

some data on contamination at military sites in two states, stating that 

these data demonstrate the risk for contamination of groundwater at 

military bases where dinitrotoluene munitions have been used or stored. 

Guidance addressing such issues as what circumstances would meet an 

occurrence characterization of “highly localized” could help EPA reach 

consistent judgments over time in cases such as these. Further, while 

EPA’s regulatory determination notice acknowledges that the agency was 

aware that these contaminants may be found at some military sites, the 

notice and support documents do not discuss how and whether this 

information was used to assess occurrence and gauge the likelihood of 

occurrence, which might include considering how many military and 

industrial sites may potentially be contaminated with 2,4- and 2,6-

 

82Another state has found high levels of these contaminants near military facilities; in this 

case, the state has regulated these contaminants. 

83According to EPA’s June 2008 regulatory support document for the second cycle of 

regulatory determinations, the concentration of 2,4-dinitrotoluene detected through EPA’s 

unregulated contaminants testing program was 333 micrograms per liter—more than 6,000 

times the health reference level. 

Page 37 GAO-11-254 Safe Drinking Water Act
 

dinitrotoluene.84 We note that EPA’s occurrence testing methodology is not 

designed to identify localized but high contaminant occurrences in public 

water systems that stem from specific land uses that may be associated 

with likely contamination—such as military and industrial activities—or 

associated with Superfund sites with known contamination and releases of 

these contaminants reported to EPA under its Toxics Release Inventory. 

Notably, the Safe Drinking Water Act does not require that contaminants 

be found in public water systems on a national basis for an Administrator 

to find a meaningful opportunity for health risk reduction. In fact, other 

parts of the statute provide for relief from monitoring and flexibilities for 

instances in which a contaminant occurs in certain areas but not in others. 

Moreover, there is nothing in the act’s committee reports suggesting that a 

contaminant need occur nationally to support a decision to regulate. 

Without EPA guidance providing a definition or parameters, an informal 

“national occurrence” standard is open to shifting interpretations, 

potentially affecting the consistency and credibility of EPA’s decision 

making. Importantly, to the extent EPA is informally applying an 

unspecified national occurrence requirement for contaminants to be 

evaluated as occurring “with a frequency and at levels of public health 

concern,” EPA is implementing a critical policy and interpretation of the 

Safe Drinking Water Act that has neither been defined nor subjected to 

public review. 

Further, aside from stating in its regulatory determination notices that 

applying the third statutory criterion involves evaluating a contaminant’s 

potential health effects and the related occurrence and exposure estimates 

at the “health level of concern,” EPA has not articulated guidelines or 

thresholds for how it is to assess whether regulating a specific 

contaminant would provide a meaningful opportunity for health risk 

reduction. The absence of guidelines on what scenario or scenarios might 

illustrate “a meaningful opportunity for health risk reduction” increases 

the potential for inconsistent decision making and reduces the decisions’ 

transparency. 

 

84According to EPA documents, these contaminants are released into the environment 

primarily from facilities that manufacture and process dinitrotouluene. A mixture of 

dinitrotoluene is used in automobile airbags, as an intermediate in the production of 

urethane foams, and for smokeless powders in the munitions industry. 

Page 38 GAO-11-254 Safe Drinking Water Act
 

EPA Has Not Developed 

Policies or Guidance on 

When the Agency Would 

Reconsider a Regulatory 

Determination to Not 

Regulate and What Process 

EPA Would Use to Do So 

Office of Water officials told us that EPA could subsequently reconsider a 

determination to not regulate a contaminant on the basis of new scientific 

data. Office of Water officials said, for example, that a new IRIS health 

assessment on a contaminant could lead to a re-evaluation of a prior 

regulatory determination to not regulate that contaminant. EPA has not, 

however, developed any guidance on the circumstances that would trigger 

such a re-evaluation or on the process the agency would use in conducting 

a re-evaluation. In fact, in at least one instance—1,1,2,2-

tetrachloroethane—new or revised scientific data became available after 

EPA’s determination to not regulate, but the agency has not announced 

whether it will reconsider the determination. Specifically, subsequent to 

its negative regulatory determination in 2008, EPA’s IRIS program finalized 

an updated health assessment in 2010, reclassifying this contaminant from 

a “possible” to a “likely” human carcinogen and decreasing the 

concentration in drinking water equivalent to a one-in-a-million increased 

risk of getting cancer. The new assessment would have produced a more 

stringent health reference level than the one EPA used in assessing the 

health risks of exposure to 1,1,2,2-tetrachloroethane for the regulatory 

determination. In addition, this contaminant is a VOC related through 

either production of, or degradation to, several other VOCs—namely, 

trichloroethylene (TCE), tetrachloroethylene (PCE), and vinyl chloride—

that are (1) also associated with cancer, (2) currently regulated by EPA, 

and (3) among those contaminants EPA announced in February 2011 

would be included in a planned new drinking water regulation of a group 

of VOCs. As there is no policy or guidance, it is not clear whether EPA will 

re-evaluate 1,1,2,2-tetrachloroethane as a result of the updated IRIS 

assessment or the planned action on carcinogenic VOCs in drinking water. 

EPA cannot ensure consistency in its re-evaluations of completed 

regulatory determinations in the absence of guidance on the 

circumstances under which, and the process the agency will use, to 

reconsider determinations. For example, potential process choices may 

include reconsidering such contaminants as a part of the agency’s current 

regulatory determination cycle, adding the contaminants to the existing or 

next candidate list, or in the case of a planned regulation for a group of 

chemicals, adding the contaminant to that regulatory action. 

Page 39 GAO-11-254 Safe Drinking Water Act
 

The Credibility of Some of 

EPA’s Regulatory 

Determinations As 

Presented in Federal 

Register Notices and 

Support Documents Is 

Limited by a Lack of 

Transparency, Clarity, and 

Consistency 

The Safe Drinking Water Act requires EPA to ensure that, in its regulatory 

determinations, among other things, the presentation of information on 

public health effects is comprehensive, informative, and understandable. 

In addition, to the extent that EPA’s regulatory determination notices and 

key support documents are transparent, clear, and consistent regarding 

the occurrence and health effects data the agency relied on, the credibility 

of the determinations is enhanced. However, for the regulatory 

determinations that EPA has made to date, some of the notices and 

support documents lack these key qualities. 

EPA discussed the health risks to infants of exposure to manganese in 

drinking water in an inconsistent and, at times, incomplete manner in its 

regulatory determination documents. For example, EPA’s 2003 regulatory 

determination support document for manganese states unequivocally that 

there are “no data to indicate children are more sensitive to manganese 

than adults.” However, EPA’s 2003 health effects support document for 

manganese discusses studies that identify an association between 

exposure to manganese in drinking water and learning disabilities in 

children and concludes that additional studies are needed to investigate 

the possibility that children are more sensitive than adults. In addition, 

while EPA’s regulatory determination support document for manganese 

notes that infants and newborns may be potentially susceptible to 

manganese toxicity, this key document does not disclose that newborns 

may be exposed to high levels of manganese from infant formula or that 

these high levels of manganese in formula can be magnified when it is 

reconstituted with manganese-contaminated water. In contrast, the health 

advisory EPA issued in conjunction with the regulatory determination 

notice on manganese identifies “concerns for differences in manganese 

content in human milk and formula and the possibility of higher 

absorption and lower excretion in young infants.” At a minimum, EPA’s 

varying statements on the health risk that exposure to manganese in 

drinking water may pose to infants and children do not comport with the 

act’s requirement to present information on health effects in a 

comprehensive, informative, and understandable manner. 

EPA’s Presentation of Health 

Effects Information on Some 

Contaminants Lacked Clarity, 

Consistency, and Transparency 

In addition, EPA’s presentation of the health risks of exposure to boron in 

the documents supporting its 2008 regulatory determination is also 

inconsistent and lacking in clarity. For example, in its regulatory support 

document, the Office of Water identified the primary adverse effects 

identified from studies of animals after chronic exposure to low doses of 

boron as generally involving the testes and the developing fetus. In this 

Page 40 GAO-11-254 Safe Drinking Water Act
 

document, EPA stated that animal studies identify the developing fetus as 

potentially sensitive to boron and concluded that boron concentrations 

greater than the health reference level “might” have an effect on prenatal 

development.85 In contrast, the Office of Water’s May 2008 Drinking Water 

Health Advisory for Boron—developed in conjunction with the regulatory 

determination and published just 2 months before the regulatory 

determination was published—states that there are “compelling lines of 

evidence to suggest that the testicular morphological effects” reported in 

studies of animals are applicable to children. In this document, EPA also 

concluded that exposure to boron between birth and puberty may result in 

adverse cellular effects that would “affect testicular function” and that 

“testicular toxicity in males is the most sensitive endpoint relevant to 

children.” In addition, a third related document—EPA’s Summary 

Document from the Health Advisory for Boron and Compounds—

provides an important warning regarding infants’ exposure to boron in 

drinking water that is not included in either EPA’s drinking water advisory 

for boron or its regulatory determination support document. Specifically, 

the summary document states that water containing boron “at levels above 

the HA [health advisory]” should not be used to prepare food or formula 

for infants. EPA does not identify which of the exposure duration health 

advisories it is referring to in this warning.86

As discussed earlier, EPA has issued new or updated health advisories for 

9 of the 10 contaminants it determined did not warrant regulation under 

the 1996 amendments but which it decided warranted the issuance of 

health advisories. In its regulatory determination notices, EPA identified 

the purpose of the advisories variously, such as providing “guidance to 

communities that might be exposed to elevated concentrations” of the 

contaminants and “information to any states with public water systems 

that may have” contaminants at levels above the health reference level.87

However, EPA’s discussions of these health advisories in the regulatory 

determination notices for the contaminants lack clarity and transparency 

EPA’s Regulatory 

Determination Notices Lack 

Transparency and Clarity 

Regarding the Limitations of 

Health Advisories Issued in 

Conjunction with 10 Decisions 

to Not Regulate 

 85The regulatory determination support document also states that individuals with severely 

impaired kidney function might also be sensitive to boron exposure. 

86EPA’s boron health advisory provides, for a child weighing 10 kilograms, a 10-day (acute) 

health advisory level of 3 milligrams of boron per liter of drinking water and a “longer-term” 

level of 2 milligrams per liter. The advisory also provides, for an adult, a longer-term health 

advisory of 5 milligrams per liter and a lifetime health advisory of 5 milligrams per liter. 

87The purpose presented in the health advisories themselves is as follows: “Health 

advisories serve as technical guidance to assist federal, state, and local officials responsible 

for protecting public health when emergency spills or contamination situations occur.” 

Page 41 GAO-11-254 Safe Drinking Water Act
 

regarding the limitations of the advisories.88 Specifically, the regulatory 

determination notices do not acknowledge that when EPA determines 

regulation is not warranted but a health advisory is needed, it will 

generally be up to states, localities, and consumers to determine whether 

such contaminant levels are found in public water systems in their 

jurisdiction. Importantly, because public water systems are not typically 

required to test for the presence of unregulated contaminants, information 

on the levels of the contaminants in individual public water systems may 

be outdated or unavailable. Some regulatory determination notices do, 

however, state that EPA “encourages” those states with public water 

systems that have contaminants at concentrations greater than the health 

reference level “to evaluate site-specific protective measures and to 

consider whether state-level guidance (or some other type of action) is 

appropriate.” EPA officials have noted that individual states can 

promulgate their own drinking water regulations, but some states have 

legal or other constraints on their ability to regulate contaminants that 

EPA does not. For example, while some states—such as California and 

Massachusetts—have issued drinking water standards for contaminants 

that EPA has not regulated, others are statutorily prohibited from, or 

otherwise constrained in, enacting more stringent regulations than EPA 

has promulgated or promulgating their own drinking water regulations for 

contaminants that EPA does not regulate.89 In addition, it would be 

difficult for many people to determine how much of these unregulated 

contaminants are present in their drinking water, which would be 

required, for example, to heed EPA’s warning in some cases to not use 

drinking water with contaminants in excess of certain levels to prepare 

infant food or formula. As EPA has acknowledged in some of its health 

advisory documents, individuals may have to have their water tested by a 

laboratory for the presence of the contaminants since EPA typically does 

not require water systems to test for them. Moreover, according to EPA 

officials, the agency releases its drinking water advisories by posting them 

 

88These contaminants are boron; dacthal (DCPA) mono-acid degradate; dacthal (DCPA) diacid degradate; 1,3-dichloropropene; 2,4-dinitrotoluene; 2,6-dinitrotoluene; 1,1,2,2-

tetrachloroethane; manganese; sodium; and sulfate. EPA also issued a health advisory in 

conjunction with its preliminary determination on perchlorate. 

89For example, in May 2008, the President of the Association of State Drinking Water 

Administrators told a congressional committee that “most states do not have the resources 

or expertise to independently develop drinking water regulations and therefore look to 

EPA to conduct the necessary research and collect the data and information needed to 

make regulatory decisions.” 

Page 42 GAO-11-254 Safe Drinking Water Act
 

on its Web site and does not issue public notification of them, such as a 

press release, which potentially limits awareness of the health advisories. 

EPA’s regulatory determination notices and support documents generally 

lacked transparency and clarity and, in some cases, consistency, regarding 

the occurrence data the agency used in supporting its determinations. For 

example, in its preliminary regulatory determination notices, the Office of 

Water provided occurrence data on the number of public water systems, 

and the populations served by them, with contaminant detections (1) 

greater than the health reference level and (2) greater than one-half of the 

health reference level.90 However, in its notices and support documents, 

EPA provides other data potentially relevant to assessing known or likely 

occurrence of contaminants in drinking water, such as data on releases to 

the environment as reported in the Toxics Release Inventory91; 

contamination at Superfund (National Priorities List) sites; and other data 

such as those provided by states, USGS, and others. The regulatory 

determination documents lack transparency because they do not explain 

the extent to which, if any, EPA used these data in its assessment of the 

contaminants’ known or likely occurrence in public water systems. In 

addition, we found that EPA does not consistently disclose information 

about the occurrence of the contaminants at Superfund sites. For 

example, the regulatory determination notices and support documents did 

not report that ATSDR had found a particular contaminant at more than 50 

percent of Superfund sites, while EPA did report such information from 

ATSDR about some contaminants found less frequently. 

EPA Explanations of the 

Occurrence Data EPA Relied 

on to Assess Known and Likely 

Occurrence of Contaminants in 

Drinking Water Lack 

Transparency, Clarity, and 

Consistency 

In addition, while EPA’s regulatory determination notices for the 20 

determinations completed in 2003 and 2008 present actual detections from 

unweighted occurrence data from public water systems that tested for the 

contaminants—rather than extrapolated estimates of national 

occurrence—EPA includes extrapolated estimates of national occurrence 

in its support documentation. However, it is not clear whether and to what 

extent EPA used these national occurrence estimates in assessing 

occurrence at levels of public health concern. For example, EPA’s 

 

90As discussed earlier, in some cases the data represented detections in excess of minimum 

reporting levels. 

91The Emergency Planning and Community Right-to-Know Act of 1986 requires EPA and 

states to collect data annually on releases and transfers of certain toxic chemicals from 

industrial facilities and make the data available to the public in the Toxics Release 

Inventory. 

Page 43 GAO-11-254 Safe Drinking Water Act
 

explanation in the notices that it does not provide estimates of national 

occurrence because presenting the data on actual detections is “the most 

straightforward and accurate way” to present the occurrence data does 

not address or clarify how the extrapolated data are used, if at all. 

Additionally, focusing on the actual detections rather than national 

projections in its determination notices has the effect of downplaying the 

potential occurrence of the contaminants nationally. For example, for 

manganese, EPA highlighted in the regulatory determination notice that 

3.2 percent of groundwater public water systems serving approximately 

39,000 people had at least one detection above the level of public health 

concern. In its support document for manganese, EPA reported that, 

according to its national estimates based on these groundwater data alone, 

approximately 2.3 million people could be affected. 

As noted earlier, EPA identified children as a sensitive subpopulation for 11 

of the 20 contaminants with final regulatory determinations.92 However, the 

regulatory determination notices and support documents in these cases lack 

clarity regarding how EPA determined that the health reference levels used 

to assess public health risk were adequately protective of this sensitive 

subpopulation. For example, in its 2003 regulatory determination notice 

addressing seven contaminants for which children were identified as a 

sensitive subpopulation, EPA stated that the agency had not yet determined 

a protocol for making a regulatory determination for a chemical for which 

body weight and drinking water intake of infants or a particular childhood 

age group would be the basis of a regulatory action. As discussed earlier, 

health assessments based on adult weight and drinking water intake may 

not fully account for the risks to children of exposure to drinking water 

because they consume more water per unit of body weight and may have 

other susceptibilities, as well. However, in its 2003 determination notice, 

EPA did not explain the potential effect of not developing separate health 

reference levels for children (or not making adjustments to its health 

assessments to reflect increased sensitivity) on its ability to ensure that the 

health reference levels used in the regulatory determinations were 

protective of children. In contrast to its 2003 determination notice, EPA was 

silent on the issue of separate assessments for children in its 2008 notice 

that included four contaminants for which children were identified as a 

sensitive subpopulation. As discussed earlier, Office of Water officials told 

us they would have developed separate assessments for children if they had 

Regulatory Determination 

Documents Lack Transparency 

and Clarity Regarding How 

EPA Determined Its Health 

Reference Levels Were 

Protective of Children 

 92These contaminants are aldrin; boron; dieldrin; DDE; 2,4-dinitrotoluene; 2,6-

dinitrotoluene; hexachlorobutadiene; manganese; naphthalene; sodium; and sulfate. 

Page 44 GAO-11-254 Safe Drinking Water Act
 

determined children were “particularly sensitive” to the adverse health 

effects of contaminants being considered for regulation. However, EPA did 

not explain in its regulatory determination notices or support documents 

the basis for its determinations that children were not particularly sensitive 

to the adverse health effects of the contaminants considered for 

regulation—even for those contaminants that EPA had determined children 

are sensitive subpopulations; EPA also did not explain how the sensitivity of 

children can be evaluated in the absence of a separate assessment based on 

the weight and drinking water intake of children. 

EPA relied primarily on nationally representative but older data from its 

National Inorganic and Radionuclide Survey (NIRS) on systems served by 

groundwater to assess (1) manganese occurrence in public water systems in 

2003 and (2) boron occurrence in 2008. Discussing the use of the NIRS data 

(from the 1980s) in its 2003 Health Effects Support Document for 

Manganese, EPA said “these estimates are based on very limited and 

outdated data. The possibility exists that the number of people served by 

groundwater with [manganese] levels above the HRL [health reference 

level] could be higher than these estimates; however the data are lacking at 

this time to develop a more timely assessment.” Moreover, EPA 

acknowledged that it did not have national data on manganese or boron 

occurrence in public water systems that use surface water—systems that, 

according to EPA, serve about 70 percent of community water system 

customers. As discussed in appendix VI, which provides additional 

information on the regulatory determinations for manganese and boron, the 

supplementary data EPA provided on surface water systems in its support 

documents for these contaminants were limited and, in the case of 

manganese, presented in a manner that may have understated the 

occurrence. For example, EPA acknowledged that the industry-sponsored 

survey data on boron were not statistically representative. Also, the agency 

characterized drinking water occurrence data on manganese from five 

states as showing “substantial low-level manganese occurrence,” but did not 

reconcile this assessment with the data it presented showing that the 

percentages of state populations served by public water systems with levels 

that exceed the health reference level as ranging from 2.4 percent to 27.2 

percent.93 EPA’s regulatory determination documents did not explain why, 

in light of these data deficiencies, it (1) deemed the occurrence data it relied 

EPA’s Regulatory 

Determinations Lack Clarity 

Regarding Its Reliance on 

Outdated and Limited 

Occurrence Data to Support 

Some Determinations 

 93The five states, listed in order of the size of populations served by public water systems 

with manganese levels in excess of the health reference level, are Alabama (2.4 percent); 

Oregon (3.2 percent); New Jersey (9.1 percent); Illinois (14.7 percent); and California (27.2 

percent). 

Page 45 GAO-11-254 Safe Drinking Water Act
 

on as sufficient for purposes of making regulatory determinations on these 

contaminants and (2) decided not to obtain current, nationally 

representative data on both ground and surface water occurrence of these 

contaminants through its unregulated contaminants testing program. 

As discussed earlier, for nine of EPA’s 20 regulatory determinations, EPA 

based its conclusions on occurrence data for which some or all of the 

minimum reporting levels were above the health reference levels.94

However, EPA’s 2003 and 2008 regulatory determination documents for 

these contaminants lack transparency and clarity regarding the agency’s 

use of minimum reporting levels in these cases and its potential effect on 

EPA’s occurrence analyses. As table 5 shows, in these nine cases, the 

minimum reporting levels were from 1.25 to 2,200 times greater than the 

health reference levels. 

Regulatory Determination 

Documents Lack Transparency 

and Clarity Regarding EPA’s 

Reliance on Minimum 

Reporting Levels Greater Than 

Its Health Reference Levels 

Table 5: Nine Contaminants Whose Minimum Reporting Levels Exceeded EPA’s Health Reference Levels 

Contaminant 

Health reference level 

(micrograms 

per liter - μg/L)

Minimum reporting level 

or range (micrograms 

per liter - μg/L)

Extent to which minimum reporting level 

was greater than health reference level 

Aldrina0.002 0.1 – 0.84b50 to 420 times 

DDEc 0.2 0.8 4 times 

1,3-Dichloropropenec0.4 0.5 1.25 times 

Dieldrina0.002 0.02 – 4.4b10 to 2,200 times 

2,4-Dinitrotoluenec 0.05 2 40 times 

2,6-Dinitrotoluenec 0.05 2 40 times 

Hexachlorobutadienea0.9 0.05 – 10d

0.1 – 1.5b

Up to 11 times at upper end of range 

Up to 1.7 times at upper end of range 

Sulfatea500,000 1 – 800,000 b Up to 1.6 times at upper end of range 

1,1,2,2-Tetrachloroethanec0.4 0.01 – 10d

0.1 – 2.5b

Up to 25 times at upper end of range 

Up to 6.25 times at upper end of range 

Source: GAO analysis of EPA data. 

a

Contaminant from regulatory determination Cycle 1, 2003. 

b

Unregulated contaminant monitoring program round 2 data. EPA provided estimates of the wide 

range of minimum reporting levels reported by states. 

c

Contaminant from regulatory determination Cycle 2, 2008. 

d

Unregulated contaminant monitoring program round 1 data. EPA provided estimates of the wide 

range of minimum reporting levels reported by states. 

 

94In six of the nine cases, EPA had no testing data that would identify exposure at the 

health reference level, and in three cases, EPA had only limited data on exposure at the 

health reference level. 

Page 46 GAO-11-254 Safe Drinking Water Act
 

The regulatory determination notices for four of the contaminants from 

the 2003 regulatory determination cycle with minimum reporting levels 

greater than the health reference levels did not disclose that the 

occurrence data EPA provided as a basis for its conclusions could be 

understated because of this detection issue. The understatements could 

occur in these cases because some or all of the tests supporting the data 

presented were not sufficiently sensitive to detect occurrence at the 

agency’s level of health concern (i.e., the health reference level).95

Specifically, the regulatory determination notices present the occurrence 

data for the contaminants addressed in this determination cycle in a table 

identified as containing occurrence data for the number of systems with 

detections greater than the health reference level and one-half the health 

reference level, as well as the population served by these systems. 

However, there is no disclosure in the notice, the table, or a table note 

that, for four of the contaminants, the detections reported represent 

detections at minimum reporting levels that are higher than the identified 

health reference levels. In some cases, the undisclosed minimum reporting 

levels were significantly greater than the health reference levels. For 

example, for dieldrin, the agency relied on testing data obtained using 

minimum reporting levels ranging from 10 to 2,200 times higher than EPA’s 

health reference level. Using these data, dieldrin was detected in 0.06 

percent of samples (0.09 percent of public water systems). Using more 

sensitive tests with minimum reporting levels near and below EPA’s health 

reference level, USGS’s subsequent testing of source water for drinking 

water wells detected dieldrin in 3.1 percent of public well samples.96

Importantly, essentially all of the detections were at levels above the 

health reference level, yet below EPA’s minimum reporting levels. Thus, 

dieldrin would not have been found in these groundwater well samples if 

USGS had used the minimum reporting levels EPA used for its regulatory 

determination.97 Further, while related regulatory determination support 

documents for the four contaminants with minimum reporting levels 

greater than EPA’s health reference levels in some cases disclose the fact 

 

95The contaminants are aldrin, dieldrin, hexachlorobutadiene, and sulfate. 

96Dieldrin was banned by EPA in 1974 for most uses, except for the control of termites, and 

banned for all uses in 1987 because of concerns about environmental damage, harm to 

human health, and its ability to persist in the environment for decades. 

97According to USGS, because water samples were collected prior to any treatment or 

blending that potentially could alter contaminant concentrations, the sampled groundwater 

represents the quality of the source water and not necessarily the quality of finished water 

ingested by the people served by these public wells. Water utilities, however, are not 

required to treat water for unregulated contaminants. 

Page 47 GAO-11-254 Safe Drinking Water Act
 

that the data provided are detections above the minimum reporting level, 

EPA’s explanations are unclear and incomplete. Specifically, the 

documents state that the detections above the health reference level 

represent detections above minimum reporting levels because (1) the 

estimated health reference levels are lower than the minimum reporting 

levels or (2) a simple meaningful summary statistic is not available to 

describe the various reported minimum reporting levels, and to avoid 

confusion, minimum reporting levels are not reported. Importantly, the 

documents do not identify the minimum reporting levels, explain the 

impact of this limitation on EPA’s occurrence analyses and its reliability, 

or explain why EPA considered these reporting levels appropriate for 

assessing occurrence at levels of public health concern. 

The other five contaminants with some or all minimum reporting levels 

greater than EPA’s health reference level were addressed in the 2008 

regulatory determination cycle. For these contaminants, all of which are 

classified as possible or likely carcinogens, EPA did disclose in its 

determination notices that the minimum reporting levels used in the 

testing program were greater than the health reference levels—and that it 

therefore evaluated occurrence and exposure to the contaminants at the 

minimum reporting levels.98 However, EPA did not clearly explain the 

effect that this approach has on the reliability of its analysis or clearly 

explain why the minimum reporting levels were appropriate for assessing 

occurrence at levels of health concern. That is, EPA explained in the 

regulatory determination notices that, for each of these contaminants, the 

minimum reporting levels were “within the 10-4 to the 10-6 cancer risk 

range,” without providing the specific risk level value associated with the 

minimum reporting level for each contaminant. This range represents an 

increased risk of cancer to 1 in 10,000 persons (the 10-4 risk level) to 1 in 1 

million persons (the 10-6 risk level). Since the minimum reporting levels of 

the different contaminants fall at different points within the risk range, 

EPA’s assessments of occurrence and public exposure to contaminants at 

levels of public health concern for carcinogens are based on differing risk 

levels. For two contaminants for which we calculated the specific risk 

level values, the minimum reporting levels would limit cancer risk to 

 

98The contaminants are DDE; 1,3-dichloropropene; 2,4-dinitrotoluene; 2,6-dinitrotoluene; 

and 1,1,2,2-tetrachloroethane. In the cases of 1,1,2,2-tetrachloroethane and some of the 

data for 1,3-dichloropropene, some minimum reporting levels exceeded health reference 

levels. For these data sources, EPA evaluated occurrence at the health reference level, but 

stated that because some reporting limits exceeded the thresholds of interest, the 

occurrence analyses may result in an underestimate of systems affected. 

Page 48 GAO-11-254 Safe Drinking Water Act
 

approximately 1 in 25,000 persons; in contrast, EPA generally establishes 

health reference levels to limit cancer risk to 1 in 1 million persons. EPA 

also is not clear in its determination documents about (1) its rationale for 

applying risk standards for some contaminants that are less stringent than 

for others to identify occurrence at levels of public health concern or (2) 

the effect of the differing standards on the reliability of its estimates of 

occurrence at levels of public health concern. 

An EPA document listing 14 contaminants the agency was evaluating for 

regulatory determinations in 2008 indicated that there was a “strong 

possibility” that several of the contaminants may not make the cutoff date 

for regulatory determinations because of outstanding risk assessments. In 

fact, the agency decided not to consider MTBE or bromobenzene for 

regulatory determination in 2008 because risk assessments for these 

contaminants were in process. However, EPA did make a regulatory 

determination in 2008 on 1,1,2,2-tetrachloroethane despite an update to an 

existing IRIS assessment being underway, without explaining why the 

agency did not await its completion.99 As discussed earlier, the IRIS 

assessment for 1,1,2,2-tetrachloroethane was finalized in 2010 and would 

have produced a more stringent health reference level than the one EPA 

used to assess the health risks of exposure to this contaminant in its 2008 

regulatory determination. 

EPA Lacked Consistency and 

Clarity in Making 

Determinations When IRIS 

Assessments Were Either in 

Process or Needed to Be 

Updated 

 99In addition, in 2003, EPA made a regulatory determination on hexachlorobutadiene while 

a new risk assessment was underway. This IRIS assessment is still at the initial stage (draft 

development). 

Page 49 GAO-11-254 Safe Drinking Water Act
 

An understanding of the process and analyses EPA used to develop its 

2008 preliminary determination to not regulate perchlorate can provide 

context for EPA’s 2011 decision to reverse its preliminary determination. 

In addition, key analyses EPA relied on for its preliminary determination 

to not regulate perchlorate remain relevant to EPA’s subsequent 

determination to regulate perchlorate. We found that in making its 

preliminary determination on perchlorate, EPA used a separate process 

that was less inclusive, less transparent, and more directive than the 

process it used to develop its other regulatory determinations. In addition, 

the agency used nontraditional approaches to three key analyses it relied 

on to support its preliminary determination. First, in developing an IRIS 

assessment for perchlorate, EPA established a reference dose on the basis 

of recommendations from the National Academies100, 101 but subjected it to a 

more limited review than the agency’s standard IRIS assessment review 

process. Second, to determine the relative exposure to perchlorate from 

drinking water versus food, EPA relied on an exposure estimate that it 

developed using a novel analysis and then used a nontraditional method to 

calculate the relative source contribution. Third, according to key EPA 

scientists, the agency mischaracterized important scientific findings that 

emerged from the novel analysis it conducted to determine the sensitivity 

of various age groups, particularly infants and children, to the agencycalculated health reference level. Furthermore, EPA’s independence in 

developing and communicating its scientific findings was limited by the 

agency’s acceptance of external input on its preliminary determination 

notice for perchlorate. 

The Process and 

Analyses EPA Relied 

on to Support Its 

Preliminary 

Determination on 

Perchlorate Were 

Atypical, Lacked 

Transparency, and 

Limited the Agency’s 

Independence in 

Developing and 

Communicating Its 

Scientific Findings 

EPA Used a Less Inclusive, 

Less Transparent, and 

More Directive Process in 

Developing Its Preliminary 

Regulatory Determination 

on Perchlorate Than Its 

Usual Process 

Perchlorate was initially among the contaminants EPA was evaluating in 

its second cycle of regulatory determinations, which were to be finalized 

by 2008. However, in 2007, when EPA published its preliminary 

determinations on these contaminants, which the agency was reviewing 

under its usual process for developing regulatory determinations, EPA 

indicated that it was not making a preliminary determination on 

perchlorate at that time, stating that additional information may be needed 

to more fully characterize perchlorate exposure. EPA stated that it would 

 

100The National Academies consists of four private, nonprofit organizations that advise the 

federal government on scientific and technical matters: the National Academy of Sciences, 

National Academy of Engineering, Institute of Medicine, and National Research Council. 

101National Academies, Health Implications of Perchlorate Ingestion (Washington, D.C., 

2005). 

Page 50 GAO-11-254 Safe Drinking Water Act
 

continue to seek and evaluate the information it needed—primarily 

regarding exposure to the contaminant—and would issue a preliminary 

determination on perchlorate either in time for it to be finalized along with 

the other contaminants’ determinations in 2008 or as soon as possible 

following final determinations for the other contaminants. In conjunction 

with EPA’s decision to issue a separate preliminary regulatory 

determination for perchlorate, EPA officials decided that the agency’s 

continuing deliberations would be conducted using a different process, 

which differed substantially from its usual process “because of the 

sensitive nature of the perchlorate regulatory determination.” 

In developing its regulatory determinations for the first two determination 

cycles (2003 and 2008), EPA used its usual process, which the Office of 

Water initiated by establishing intra-agency regulatory determination work 

groups.102 The work groups were composed of professional staff with 

relevant expertise from various EPA program, support, and regional 

offices.103 Under this process, the intra-agency work groups identified 

contaminants on the candidate list for which it determined sufficient 

information was available to characterize both the potential health effects 

and the known or likely occurrence of the contaminants in drinking water; 

analyzed the health effects information and occurrence data for each 

selected contaminant with respect to the three statutory criteria; 

presented regulatory determination options104 for each contaminant to the 

Office of Water’s Assistant Administrator and the Assistant and Regional 

Administrators from offices participating on the work group, who selected 

a final option for the regulatory determination; and developed draft 

notices for review and obtained written position statements, generally in 

 

102EPA uses its Action Development Process—an agency administrative process for 

developing rules, policy statements, risk assessments, guidance documents, models that 

may be used in future rulemakings, statutorily mandated reports to Congress, and 

strategies related to regulations—to govern the agency’s development and review of 

regulatory determinations. Regulatory determinations are not rules; however, if a positive 

determination is made to regulate a contaminant, a rulemaking would follow. 

103For the 2003 regulatory determination process, the participating intra-agency offices were 

the Office of Prevention, Pesticides, and Toxic Substances; the Office of Research and 

Development; the Office of General Counsel; the Office of Policy, Economics, and 

Innovation; and Regions 1, 3, 5, 8, and 9. For the 2008 regulatory determination process, in 

addition to these offices, the Office of Enforcement and Compliance Assistance also 

participated, and regional office participation included Regions 1, 2, 6, and 8. 

104Regulatory determination options for each contaminant presented to senior management 

could include to regulate, not to regulate, or not to regulate but to issue a health advisory. 

Page 51 GAO-11-254 Safe Drinking Water Act
 

the form of concurrence memorandums, from all Assistant and Regional 

Administrators from participating offices.105

Under this usual process, after obtaining concurrence within EPA on the 

draft regulatory determinations, the Office of Water sent draft notices of 

its preliminary determinations to OMB for review, which could solicit and 

coordinate input from other federal agencies. Upon addressing comments 

from OMB and other federal agencies, as applicable, and receiving final 

clearance from OMB and final approval from the EPA Administrator, EPA 

published the preliminary regulatory determinations in the Federal 

Register, provided a public comment period, and subsequently published 

the final regulatory determinations in the Federal Register.

106 Throughout 

this process, EPA documented the meetings and decisions of the intraagency work group, concurrence memos from office leadership, and 

communications between EPA and external reviewers. 

In contrast to EPA’s usual process, which is managed by a work group of 

professional staff with relevant expertise from across the agency, EPA 

officials decided that the agency’s continuing deliberations on perchlorate 

would be managed by a less inclusive, small group of high-level officials, 

such as the Deputy Administrator and several Assistant Administrators.107

This group of high-level officials managed the regulatory determination 

process for perchlorate both within EPA and externally with the 

Perchlorate Interagency Working Group,108 whose work was coordinated 

 

105While consensus is not required, officials said that the work groups try to obtain 

consensus on the selected option among senior management officials. Officials could not 

recall a work group that did not achieve consensus. 

106The draft final determinations underwent the same concurrence and OMB review as the 

preliminary determinations before being finalized and published in the Federal Register. 

107According to Office of Water officials, this group was primarily composed of the EPA 

Deputy Administrator and the Assistant Administrators for the Office of Water; Office of 

Research and Development; Office of Solid Waste and Environmental Remediation; Office 

of Policy, Economics, and Innovation; and Office of General Counsel. Select program office 

staff were involved in some non-decision-making activities of the group. 

108The Perchlorate Interagency Working Group includes officials from OMB and the Office 

of Science and Technology Policy, both part of the Executive Office of the President; DOD; 

NASA; the Department of Energy; the Department of Health and Human Services’ Food and 

Drug Administration and ATSDR; the Department of Agriculture; and the Department of 

the Interior. 

Page 52 GAO-11-254 Safe Drinking Water Act
 

by the Council on Environmental Quality.109 According to an EPA briefing 

document, the Perchlorate Interagency Working Group was established in 

2002 “to identify and help resolve perchlorate science and science policy 

issues.”110 EPA officials told us that one of the aims of the Perchlorate 

Interagency Working Group was a “no-surprises policy” concerning any 

issues related to perchlorate. Thus, in addition to reviewing EPA’s 

activities and analyses related to the perchlorate preliminary regulatory 

determination, the Perchlorate Interagency Working Group reviewed 

multiple products such as articles for scientific journals prior to 

dissemination by researchers and scientists from EPA and other agencies, 

such as the Centers for Disease Control and Prevention (CDC) and Food 

and Drug Administration. In addition, while the usual process for 

regulatory determinations provides multiple opportunities for input from 

participating EPA offices and results in documentation of meetings and 

analyses, the activities and decisions of the small group of high-level 

officials managing perchlorate were less inclusive and transparent. That is, 

relevant EPA staff, such as Office of Water managers, scientists 

conducting perchlorate analyses requested by the Assistant Administrator 

of the Office of Research and Development and the Perchlorate 

Interagency Working Group, officials from the Office of Children’s Health 

Protection, and regional office staff from areas with extensive perchlorate 

contamination, had limited input into the preliminary regulatory 

determination. Moreover, according to an EPA official, meetings of the 

small group of high-level officials were not documented, and while the 

usual process involved developing a document providing the supporting 

analysis for the determination for each contaminant, EPA did not prepare 

such a document for the perchlorate preliminary determination. Also, in 

contrast to EPA’s usual process, according to EPA officials, the Office of 

Water provided updates on the status of the perchlorate regulatory 

determination to the leadership of the EPA program and regional offices 

not included in the small group—such as the Office of Prevention, 

Pesticides, and Toxic Substances and the 10 regional offices—rather than 

seeking input and agreement from them. Specifically, agency program and 

regional offices were not asked by the small group of high-level officials to 

provide concurrence on the draft preliminary perchlorate determination. 

 

109The Council on Environmental Quality, which is part of the Executive Office of the 

President, coordinates federal environmental efforts in the development of environmental 

policies and initiatives. 

110This working group stemmed from interagency work groups that were established as 

early as 1998. 

Page 53 GAO-11-254 Safe Drinking Water Act
 

EPA further limited participation by relevant EPA staff. For example, EPA 

did not include the Office of Children’s Health Protection in its small 

group of high-level officials despite EPA’s and the National Academies’ 

conclusion that iodide uptake inhibition from perchlorate exposure had 

been identified as a concern in connection with increasing the risk of 

neurodevelopmental impairment in fetuses of pregnant women with iodine 

deficiency and to developmental delays and decreased learning capability 

in infants and children.111, 112 The lack of participation by the Office of 

Children’s Health Protection in developing the preliminary regulatory 

determination for perchlorate is noteworthy for two reasons: (1) This 

office was established in 1997 to work with EPA program and regional 

offices to promote a safe and healthy environment for children by ensuring 

that all regulations, standards, policies, and risk assessments take into 

account risks to children113 and (2) the Safe Drinking Water Act directs 

EPA to consider at several key points in the regulatory determination 

process the effect of contaminants on such subpopulations as infants, 

children, pregnant women, and others that may be at greater risk of 

adverse health effects than the general population as a result of exposure 

to those contaminants, among other factors.114 Overall, by excluding 

relevant EPA offices from a more participatory role, the agency did not 

avail itself of the expertise that resides in those offices. 

 

111We recently reported that EPA has not fully used the Office of Children’s Health 

Protection and other child-focused resources. GAO, Environmental Health: High-level 

Strategy and Leadership Needed to Continue Progress toward Protecting Children from 

Environmental Threats, GAO-10-205 (Washington, D.C.: Jan. 28, 2010). 

112According to officials from the Office of Children’s Health Protection, their office was 

excluded from the small group of high-level officials and from providing input into the 

perchlorate preliminary determination because it had not been part of the original work 

group for the second cycle of regulatory determinations. Office of Children’s Health 

Protection officials said they were involved only informally and intermittently in the 

regulatory determination work groups largely as a result of its staff and resource 

limitations. 

113EPA established the Office of Children’s Health Protection to implement Executive Order 

13045: Protection of Children from Environmental Health Risks and Safety Risks (signed 

in 1997) directing all federal agencies to assess health and safety risks to children, 

coordinate research priorities on children’s health, and ensure that their standards take 

into account special risks to children. 

114See 42 U.S.C. § 300g-1(b)(1)(C) (requiring consideration of such factors, among others, in 

selecting unregulated contaminants for consideration); § 300g-1(b)(3)(C)(i)(V) (requiring 

EPA to publish an analysis of such effects when proposing a national primary drinking 

water regulation). 

Page 54 GAO-11-254 Safe Drinking Water Act
 

Finally, in contrast to the usual process EPA used for its regulatory 

determinations, in which EPA staff with relevant expertise develop and 

submit options to the Assistant Administrator for the Office of Water for 

review and selection, the Assistant Administrator directed the Office of 

Water staff in developing the preliminary determination for perchlorate. 

Specifically, according to officials in the Office of Water and the Office of 

General Counsel, in August 2008 the Assistant Administrator directed the 

staff to draft a preliminary determination that reflected the agency’s 

decision to not regulate perchlorate and to support it with a detailed and 

specific rationale that EPA and other members of the Perchlorate 

Interagency Working Group had agreed to, under the leadership and 

coordination of the Council on Environmental Quality.115 EPA Office of 

Water officials told us that they believed this agreement—which is not part 

of the record for the preliminary regulatory determination—was 

developed by senior officials from the Council of Environmental Quality, 

the Department of Health and Human Services (HHS), EPA, OMB, and the 

U.S. Department of Agriculture. The agreement focused on how EPA 

should address the key science issues concerning perchlorate in its 

preliminary regulatory determination and specified (1) a health reference 

level of 15 parts per billion of perchlorate in drinking water and (2) the 

rationale for EPA to support the conclusion that this health reference level 

would be protective of pregnant women and their fetuses as well as of 

infants and children. 

EPA Established a 

Reference Dose for 

Perchlorate on the Basis of 

the National Academies’ 

Recommendations, but 

Subjected It to a More 

Limited Review Than the 

Agency’s Standard IRIS 

Assessment Review 

Process 

In developing an IRIS assessment of perchlorate, EPA established a 

reference dose on the basis of the National Academies’ recommendations, 

but subjected it to a more limited review than the agency’s standard IRIS 

assessment review process. Typically, to establish a reference dose for a 

contaminant, EPA conducts an IRIS assessment, a draft of which 

undergoes internal and external scientific peer reviews and is also made 

available for public comment in the Federal Register before being 

finalized. In its initial effort to develop an IRIS assessment of perchlorate, 

EPA followed its usual process, and in 2002, the agency provided a draft 

IRIS assessment to the public for comment. 

 

115According to an EPA official, the agreement was documented in an unattributed two-page 

white paper and faxed to EPA from the Council on Environmental Quality in early August 

2008; EPA made some editorial changes to the document but did not alter the substance of 

the agreement. 

Page 55 GAO-11-254 Safe Drinking Water Act
 

EPA’s 2002 draft IRIS assessment of perchlorate—which proposed a 

reference dose of 0.03 micrograms per kilogram of body weight per day 

and a related drinking water equivalent level of 1 part per billion116—drew 

significant attention, including from such federal agencies as DOD, the 

Department of Energy, and NASA, because of the implications such a level 

could have on their operations if EPA were to develop a drinking water 

regulation for perchlorate.117 According to a senior EPA official, the 

controversy that arose over the draft IRIS assessment of perchlorate “was 

like nothing I had ever seen or have seen since.” As a result of the 

divergent views between EPA and the other federal agencies, the 

Administrator of OMB’s Office of Information and Regulatory Affairs 

urged the four interested agencies to convene a National Academies panel 

to review the draft IRIS assessment. Convened in October 2003, the panel 

conducted this review and issued its report in January 2005.118

In its 2005 report, the National Academies made several key 

recommendations to EPA on the basis of a different study from those on 

which EPA had based its draft IRIS assessment. The National Academies’ 

recommended reference dose was more than 20 times higher than the one 

proposed in EPA’s 2002 draft IRIS assessment and, according to an IRIS 

official, was a recommendation that EPA neither specifically requested nor 

expected the panel to issue.119 However, the IRIS official also told us that in 

discussions regarding the National Academies’ recommendations, EPA 

management indicated that quickly incorporating the National Academies’ 

perchlorate recommendations into the IRIS assessment would help the 

agency bring some closure to the controversy surrounding its draft 

 

116This drinking water equivalent level was calculated using EPA’s default assumptions for 

adult weight—70 kilograms (154 pounds) and daily drinking water intake—2 liters (60 fluid 

ounces). 

117EPA noted in the Federal Register notice that the final health reference level in the final 

regulatory determination for perchlorate would serve as the basis for the agency’s health 

advisory for perchlorate and that thereafter it might be appropriate to use the health 

advisory value as a “to be considered” value in developing potential cleanup levels for 

perchlorate pursuant to Superfund. A federal drinking water standard for perchlorate could 

also serve as a possible basis for environmental cleanup goals, potentially affecting some 

federal agencies’ as well as perchlorate manufacturers’ cleanup requirements at Superfund 

and other contaminated sites. 

118National Academies, Health Implications of Perchlorate Ingestion (Washington, D.C., 

2005). 

119The National Academies’ recommended reference dose for perchlorate was 0.7 

micrograms per kilogram of body weight per day. 

Page 56 GAO-11-254 Safe Drinking Water Act
 

assessment. In February 2005, just 5 weeks after the National Academies 

issued its report, EPA adopted the National Academies’ recommendations 

with unprecedented expediency, finalizing its IRIS assessment on 

perchlorate using the National Academies’ recommended reference dose. 

Other EPA officials told us that this swift action was possible because the 

National Academies had “taken the unprecedented step of completing 

what amounted to a toxicological review itself and derived a 

recommended reference dose.” 

EPA’s final internal review of the revised IRIS assessment for 

perchlorate—termed a consensus review—differed from the agency’s 

usual consensus review process for IRIS assessments at that time in terms 

of scope, time frames, and public comment. The scope of the review was 

limited in that the IRIS program did not seek input from consensus 

reviewers on the scientific basis for the assessment as it typically does. 

Instead, the IRIS program director stated in the request for consensus 

reviews that because the assessment had undergone several external peer 

reviews, including a recent review by the National Academies, the purpose 

of the consensus review of the revised IRIS assessment for perchlorate 

was to “ensure that the science in the IRIS Summary is clearly summarized 

and not inconsistent with the major conclusions of the [National 

Academies’] report.”120 At least two EPA offices essentially opted out of the 

consensus review process because of this limitation, which was a 

significant departure from the usual IRIS consensus practice.121 For 

example, the Office of Children’s Health Protection’s response to the IRIS 

program’s request for consensus review stated that because the IRIS 

assessment did not represent the “traditional end-of-process consensus 

review for IRIS,” that office chose to neither approve nor disapprove the 

IRIS assessment, opting instead to identify concerns about the 

consideration of children’s health in the IRIS perchlorate assessment, as 

discussed later. A second difference between the consensus review for the 

draft IRIS assessment and the typical consensus review was the speed 

 

120Under the typical process, at that time, the IRIS program would circulate an IRIS 

Toxicological Review support document in addition to the IRIS Summary among the 

consensus reviewers, generally allowing 45 days for the review. The program manager 

noted in the request for the perchlorate IRIS assessment consensus review, however, that 

EPA would not develop and post an IRIS Toxicological Review support document as part 

of the IRIS assessment. 

121The IRIS program officials could not provide copies of the consensus review 

memorandums. However, we were able to obtain comments from 5 of the 18 individual 

consensus reviewers. 

Page 57 GAO-11-254 Safe Drinking Water Act
 

with which it was conducted. The IRIS program allowed reviewers only 1 

week—rather than the 45 days that is typically afforded—to complete their 

reviews before finalizing the revised assessment and posting it on its Web 

site.122 Finally, while EPA had provided a public comment period for its 

2002 draft IRIS assessment before the National Academies review began, it 

did not offer a public comment period on the 2005 revised assessment, 

even though it was based on different data than the 2002 draft assessment. 

Specifically, EPA’s 2002 draft assessment was based primarily on data 

from several toxicological (animal) studies, while the National Academies’ 

2005 assessment was based primarily on the results of a single 14-day 

clinical study from 2002—the Greer study, which was funded by the 

National Institutes of Health and perchlorate manufacturers and users.123

EPA has received both internal and external criticisms of its decision to 

accept the National Academies’ recommended reference dose as its IRIS 

assessment. These criticisms—which generally focused on limitations of 

the 2002 Greer study from which the National Academies derived its 

reference dose and the extent to which EPA mitigated those limitations to 

help ensure that sensitive subpopulations were adequately protected—

were communicated to EPA before it finalized its IRIS assessment and 3 

years before the agency issued its preliminary determination for 

perchlorate. For example, in 2005, the Office of Children’s Health 

Protection articulated concerns in a memorandum to the IRIS program 

director during the week allowed for consensus review for the IRIS 

assessment that the uncertainty factor124 of 10 that the National Academies 

used in developing its proposed reference dose might not sufficiently 

protect the sensitive subpopulations, which the National Academies 

identified as including fetuses, preterm newborns, infants, and developing 

 

122The final IRIS assessment for perchlorate was posted on the Web site 11 days after the 

IRIS program requested the consensus reviews. 

123M. A. Greer et al., “Health Effects Assessment for Environmental Perchlorate 

Contamination: The Dose Response for Inhibition of Thyroidal Radioiodine Uptake in 

Humans,” Environmental Health Perspectives, vol. 110, no. 9 (2002). The published article 

notes that the study was supported by a National Institutes of Health grant and the 

Perchlorate Study Group—whose members included such perchlorate manufacturers and 

users as Aerojet, American Pacific Corporation, Kerr-McGee Chemical, and Lockheed 

Martin. 

124Uncertainty factors, also called variability factors, are default factors used in deriving a 

reference dose from experimental data. The factors are intended to account for such things 

as variation in susceptibility among the members of the human population, extrapolating 

from data obtained in a study with less-than-lifetime exposure, and uncertainty associated 

with extrapolation when the database is incomplete. 

Page 58 GAO-11-254 Safe Drinking Water Act
 

children. The National Academies concluded this uncertainty factor was 

sufficient because its recommended reference dose was based on a 

nonadverse effect that was a precursor to any adverse effects that may 

result from exposure to perchlorate. However, the Office of Children’s 

Health Protection stated in its memorandum to the IRIS program that the 

Greer study—which examined the effect of perchlorate exposure on 

iodide uptake inhibition of the thyroid in 37 healthy adults—did not 

provide data to consider variability among humans at different life stages, 

during pregnancy, and as a result of health status (such as 

hypothyroidism)—or even to consider variations among healthy adults. (In 

fact, the National Academies’ recommended reference dose was derived 

from data on a subgroup of study participants comprised of seven healthy, 

nonpregnant adults.125) As a result, the Office of Children’s Health 

Protection expressed its concern that the uncertainty factor of 10 the 

National Academies’ recommended to account for variations among 

humans may not be adequately protective of sensitive subpopulations. The 

Office of Children’s Health Protection also stated concerns that the effects 

observed during the 2-week Greer study may not be indicative of potential 

effects from lifelong exposure to perchlorate. Consensus reviewers from 

two other EPA offices identified similar concerns. For example, a 

consensus reviewer from a regional office, while expressing an 

understanding that accepting the National Academies’ reference dose 

reflected “the best course of action for the agency, given the history of this 

compound,” nonetheless provided substantive comments on a number of 

scientific issues, including the uncertainty factor. This reviewer stated that 

the National Academies’ uncertainty factor apparently reflects a 

conclusion that pregnant women, pregnant women with subclinical 

hypothyroidism, preterm infants, and newborns would be no more 

sensitive to perchlorate than nonpregnant adult women and men—a 

conclusion the reviewer stated was questionable. Nonetheless the IRIS 

Summary that EPA posted on its Web site shows that the agency adopted 

the National Academies’ reasoning, including its recommended 

uncertainty factor, which did not address the concerns raised by the Office 

of Children’s Health Protection or reviewers from other offices. 

 

125In calculating the reference dose, the National Academies applied the uncertainty factor 

to the no-observed-effect level reported for the group of seven healthy, nonpregnant adult 

subjects in the study that received the lowest dose of perchlorate—the level selected by the 

National Academies as the point of departure for determining the reference dose. The noobserved-effect level represents an exposure level at which there is no statistically or 

biologically significant difference in the frequency or severity of any effect between the 

exposed population and its appropriate control. 

Page 59 GAO-11-254 Safe Drinking Water Act
 

In addition, in September 2005—3 years prior to EPA’s preliminary 

determination for perchlorate—public health officials from Connecticut 

and Maine published a detailed critique of the Greer study that expressed 

concerns similar to those raised by the Office of Children’s Health 

Protection, as well as additional concerns.126 For example, these public 

health officials stated that the National Academies’ consideration of 

uncertainties was insufficient. They said, among other things, that in 

addition to the uncertainty factor of 10 that the National Academies 

applied to account for variability among humans, an additional 3- to 10-

fold uncertainty factor was warranted to account for the potential for 

greater toxicity to breastfeeding newborns,127 as well as the potential for 

greater perchlorate toxicity resulting from exposure lasting more than 2 

weeks.128 These state public health officials concluded that risk assessors 

should carefully evaluate whether the IRIS reference dose was the most 

appropriate value for assessing perchlorate risk. 

The concerns regarding the reference dose in the IRIS assessment noted 

earlier continued to be raised when EPA issued its preliminary regulatory 

determination for perchlorate in 2008. This preliminary determination 

generated substantial public comment regarding EPA’s assessment of the 

health risks to sensitive subpopulations—issues that had been raised when 

EPA first adopted the reference dose. For example, in official comments 

on EPA’s preliminary regulatory determination on perchlorate, officials 

from the states of Washington and Oregon asked EPA to reconsider its 

decision, citing, among other things, their view that the 10-fold uncertainty 

factor EPA used to derive a reference dose and to formulate a healthbased drinking water level was insufficient. As with other comments, the 

officials stated that a higher uncertainty factor was warranted given the 

data gaps in the limited studies available on perchlorate. The state officials 

 

126G. Ginsberg and D. Rice, “The NAS Perchlorate Review: Questions Remain about the 

Perchlorate RfD,” Environmental Health Perspectives, vol. 113, no. 9 (2005). 

127Perchlorate is actively transported into breast milk, where relatively high levels have 

been reported in the United States and Chile. The public health officials noted that there 

has been a lack of useful studies examining lactation as a route of exposure, resulting in a 

critical data gap that has added uncertainty to perchlorate risk assessment. Since the 

National Academies study, however, new studies have provided information on perchlorate 

in breast milk that could help reduce this uncertainty, several of which EPA references in 

its August 2009 perchlorate supplemental request for comments. 74 Fed. Reg. 41883 (Aug. 

19, 2009). 

128The public health officials cited a 1998 study in rats that suggests greater perchlorate 

toxicity to the thyroid from 90-day exposure than from 14-day exposure. 

Page 60 GAO-11-254 Safe Drinking Water Act
 

noted that the state of Massachusetts’s risk assessment of perchlorate 

used a higher uncertainty factor—100 versus EPA’s 10. In fact, two states 

that promulgated perchlorate limits for drinking water and one state that 

proposed such limits each relied primarily on the Greer study but, because 

of variations among the states regarding the values they chose for three 

key variables,129 developed more stringent limits than EPA’s assessment. 

Specifically, EPA’s health reference level for purposes of its preliminary 

regulatory determination was 15 parts per billion of perchlorate per liter of 

water, while California’s health limit is 6 parts per billion, Massachusetts’s 

is 2 parts per billion, and New Jersey’s proposal was 5 parts per billion.130

Nonetheless, in its public comment response document associated with 

EPA’s February 2011 final regulatory determination for perchlorate, EPA 

stated that it “believes that the [reference dose] indicated by the [National 

Academies] is appropriate.” In its determination notice, EPA used the 

National Academies’ reference dose—which EPA had adopted as its IRIS 

assessment for perchlorate in 2005—and life stage-specific exposure 

information to derive a range of health reference levels for 14 life stages 

(age groups). EPA stated in its final determination notice that it considers 

these potential alternative health reference levels—which range from 1 to 

47 parts per billion—levels of public health concern for purposes of its 

final determination. 

 

129The variables are (1) the uncertainty factors; (2) the dose used as the starting point, or 

point of departure, for the health-risk computation (i.e. whether to use the no-observedeffect level; the lowest-observed-adverse-effect level; or the benchmark dose level); and (3) 

the relative source contribution. EPA defended its decision not to use any additional 

uncertainty factors, stating that it was relying on the findings of the National Academies’ 

study. 

130California’s and Massachusetts’s limits are set in state drinking water regulations; New 

Jersey’s limit was a proposed drinking water standard that lapsed in March 2010 when the 

state’s newly appointed Commissioner of the Department of Environmental Protection 

decided to delay adopting a standard until EPA made its regulatory determination. 

Page 61 GAO-11-254 Safe Drinking Water Act
 

EPA conducted a novel analysis to develop estimates of exposure to 

perchlorate for various subpopulations that it would use to calculate the 

relative source contribution—the allocated exposure to perchlorate from 

drinking water alone. Independent scientists who reviewed EPA’s analysis 

noted that it had several limitations—in particular, uncertainties specific 

to the exposure estimate for pregnant women. Nonetheless, EPA relied on 

the exposure estimate for pregnant women to calculate the relative source 

contribution, stating that the National Academies had identified pregnant 

women and their fetuses as the most sensitive subpopulation.131 Further, in 

calculating the relative source contribution, EPA used a nontraditional 

method—the subtraction method—that was less conservative than the 

default approach it had used for its other completed regulatory 

determinations, and was less conservative than other available methods. 

While EPA identified some of the limitations of the exposure analysis in its 

preliminary regulatory determination notice for perchlorate, it did not 

discuss the effects of the limitations on EPA’s exposure analysis. 

Moreover, although the agency’s guidance for calculating the relative 

source contribution cautions against using the subtraction method in the 

absence of adequate data representative of at-risk populations—and EPA 

lacked data to estimate exposure to perchlorate for certain populations—

the agency did not explain that the method it used to calculate the relative 

source contribution for perchlorate was the subtraction method or its 

reasoning for selecting this method. 

In developing its 2008 preliminary determination for perchlorate, EPA 

sought information on actual perchlorate exposure from food to enable 

EPA to estimate a “better informed relative source contribution and health 

reference level that is more appropriate for fetuses of pregnant women 

(the most sensitive subpopulations identified by the NRC [the National 

Academies]).” EPA decided to obtain data on perchlorate exposure after it 

evaluated the extent of perchlorate occurrence in public water systems 

using the 20 percent default relative source contribution it used for its 

other regulatory determinations. The default relative source contribution 

resulted in a health reference level of 5 parts per billion. In evaluating 

exposure at this level, some agency officials concluded that perchlorate 

EPA Relied on an Estimate 

of the Relative Exposure 

to Perchlorate from 

Drinking Water and Food 

That It Derived from a 

Novel Analysis and Used a 

Nontraditional Method to 

Calculate the Relative 

Source Contribution 

Developing the Perchlorate 

Exposure Estimates 

 131The 2005 National Academies report on perchlorate contained varying characterizations 

of sensitive subpopulations, sometimes referring to pregnant women and their fetuses 

alone as the most sensitive subpopulation and other times including infants in this 

designation. In addition, the National Academies identified developing children as a 

sensitive population and people with compromised thyroid function and people who are 

iodide-deficient as potentially sensitive populations. 

Page 62 GAO-11-254 Safe Drinking Water Act
 

warranted regulation.132 (See app. VII for more detailed information about 

EPA’s evaluation of exposure at this level.) According to an Office of 

Water official, EPA had not obtained data for other regulatory 

determinations because the conservative default relative source 

contribution had not previously resulted in occurrence analyses that 

suggested regulation was warranted. In commenting on the exposure 

analysis, another Office of Water official explained that “there were too 

many stakeholders with high interest in the outcome” of the perchlorate 

regulatory determination for EPA “not to go out and get the data [it] 

needed.”133 This interest arose, in part, because a federal drinking water 

standard for perchlorate could also serve as a possible basis for 

environmental cleanup goals, potentially affecting some federal agencies’ 

and perchlorate manufacturers’ cleanup requirements at Superfund and 

other contaminated sites.134

The primary data sources EPA used to develop perchlorate exposure 

estimates were (1) CDC’s National Health and Nutrition Examination 

Survey (CDC’s biomonitoring study),135 which included information on 

perchlorate exposure for a nationally representative sample of 2,820 U.S. 

residents, and (2) perchlorate occurrence data from EPA’s testing program 

for drinking water contaminants. Merging CDC’s biomonitoring data with 

perchlorate occurrence data from EPA’s testing program for drinking 

 

132In fact, the Office of Water had developed a draft perchlorate section to include in the 

second cycle regulatory determination preliminary notice indicating regulation of 

perchlorate in drinking water was warranted. 

133Key entities that might be impacted by EPA regulation of perchlorate include perchlorate 

manufacturers, public drinking water systems, companies and federal agencies that use 

perchlorate, and others that could be responsible for clean up of perchlorate 

contamination. 

134While the Superfund program does not establish cleanup standards, it requires, among 

other things, that long-term cleanups meet applicable requirements based on standards for 

contaminants set under state or federal laws or regulations and in consideration of other 

guidance. A federal drinking water standard for perchlorate could supply cleanup values at 

sites where existing or potential sources of drinking water are contaminated, unless a more 

stringent state standard applies. See 40 C.F.R. § 300.430(e)(2)(i) (2010). For discussion of 

state standards, see GAO, Perchlorate: Occurrence Is Widespread but at Varying Levels; 

Federal Agencies Have Taken Some Actions to Respond to and Lessen Releases, 

GAO-10-769 (Washington, D.C.: Aug. 12, 2010). 

135Biomonitoring is a method to identify exposure to environmental chemicals by measuring 

chemicals in people’s tissue or body fluids such as blood and urine. CDC’s National Health 

and Nutrition Examination Survey conducts biomonitoring on a nationally representative 

sample of the U.S. population every 2 years, testing blood and urine to identify exposure to 

hundreds of chemicals, including perchlorate. 

Page 63 GAO-11-254 Safe Drinking Water Act
 

water contaminants—a methodology EPA described as novel—EPA 

developed estimates of daily exposure to perchlorate from drinking water 

for various age and gender groups. EPA stated in its preliminary 

determination notice that the analysis of the merged data provides the best 

available information to characterize non-drinking-water exposures to 

perchlorate for what it identified as the most sensitive subpopulation—

pregnant women and their fetuses. EPA also noted that the primary 

contribution of using this new exposure methodology is that the 

biomonitoring data can provide more direct estimates of exposure to the 

perchlorate that individuals consume in their diets. EPA also considered 

an alternative method for estimating perchlorate exposure in food that 

does not use biomonitoring data. In this method, perchlorate intake from 

food was estimated by combining two sets of estimates—FDA’s estimates 

of perchlorate levels in different food groups136 and USDA’s estimates of 

food and beverage consumption—for different age and gender groups. 

Although EPA’s exposure analysis had several key limitations that were 

identified by peer reviewers, the extent to which the agency identified 

them and explained their significance in its preliminary regulatory 

determination notice was limited. Prior to its 2008 preliminary 

determination for perchlorate—in which EPA relied on the results of this 

exposure analysis—EPA had the analysis peer reviewed by three 

independent scientists. EPA also received comments from CDC officials, 

including the official who conducted the CDC biomonitoring study and coauthored, with an EPA scientist, the subsequently published 2010 article in 

the Journal of Exposure Science and Environmental Epidemiology that 

presented the exposure analysis methodology EPA used to support its 

 

136EPA also considered the Food and Drug Administration’s 2006 Total Diet Study, which 

reported in 2008 that at least one sample in 74 percent of the 285 foods tested contained 

detectable levels of perchlorate. The Food and Drug Administration’s Total Diet Study is a 

food-monitoring study that the agency has conducted periodically since 1961. In 2005 and 

2006, the Food and Drug Administration tested a set of 285 representative foods for 

perchlorate, among other things, making it the most comprehensive information available 

on the occurrence of perchlorate in the diet at that time. The 285 food items tested 

represented the major components of the American diet, such as dairy, meat, fruits, and 

vegetables. Using the analytical results for the food samples collected, Food and Drug 

Administration researchers calculated the estimated average daily perchlorate intake from 

food for the total U.S. population and for 14 age and gender subgroups. For more 

information on the Food and Drug Administration’s Total Diet Study, see 

http://www.fda.gov/Food/FoodSafety/FoodContaminantsAdulteration/ 

TotalDietStudy/default.htm. 

Page 64 GAO-11-254 Safe Drinking Water Act
 

preliminary determination for perchlorate.137 In general, reviewers 

commented that EPA’s exposure analysis using the merged CDC and EPA 

data was a novel and defensible approach to examining perchlorate 

exposure from food and water, but they also recognized a number of 

limitations. EPA identified a few of the significant limitations of its 

analysis from the peer review in its 2008 preliminary regulatory 

determination notice that was published in the Federal Register, but did 

not explain the effect of these limitations on the analysis. Further, the 

Federal Register notice did not include some important limitations of this 

novel methodology. Some of these limitations were raised by reviewers 

before EPA issued its preliminary determination, and others were 

subsequently identified in the 2010 journal article.138

On the basis of our review of the Federal Register notice, reviewers’ 

comments, and the journal article, we found that the lack of a 

comprehensive explanation for the methodology’s limitations and 

uncertainties reduce the credibility of EPA’s use of the methodology to 

support its decision. Three key limitations are highlighted: 

• First, because data were not available to assess the exposure to 

perchlorate of infants and children younger than 6 years of age,139 EPA’s 

analysis of perchlorate exposure using biomonitoring data does not 

include some age groups that are also sensitive subpopulations. 

Nonetheless, EPA stated that all sensitive subpopulations are protected 

by the health reference level of 15 parts per billion that the agency used 

as its level of public health concern in its 2008 preliminary regulatory 

determination for perchlorate. EPA did not identify or discuss this 

limitation of the biomonitoring data (e.g., lack of data on infants and 

children) in its presentation of the exposure analysis in the preliminary 

determination notice. EPA did a separate sensitivity analysis to justify 

the protectiveness of the health reference level for infants, as described 

later. The Office of Children’s Health Protection noted in its comments 

 

137D. R. Huber et al., “Estimating perchlorate exposure from food and tap water based on 

U.S. biomonitoring and occurrence data,” Journal of Exposure Science and 

Environmental Epidemiology (2010). Other contributing authors cited in the article 

include EPA contractors with Danya International and The Cadmus Group. 

138In addition to the three independent scientists who reviewed the analysis prior to EPA’s 

use of the results in its preliminary determination for perchlorate, the analysis was 

reviewed by OMB and other members of the Perchlorate Interagency Working Group as 

well as reviewers for the Journal of Exposure Science and Environmental Epidemiology. 

139CDC’s biomonitoring study included data on children 6 years of age and older and adults. 

Page 65 GAO-11-254 Safe Drinking Water Act
 

regarding the exposure analysis that since the “real target life stage for 

EPA to protect are newborn infants,” its usefulness may be limited. In 

addition, reviewers stated that infants who are breast feeding may have 

a much higher exposure than the populations analyzed in the study 

(children 6 years of age or older and adults) because, for example, data 

demonstrate that perchlorate in breast milk may be 10 times more 

concentrated than perchlorate found in urinary estimates. Further, 

according to a 2007 study EPA cited in its determination notice, 

perchlorate was measured in infant formula at levels as high as 4 parts 

per billion. As a result, the perchlorate dose to which formula-fed 

infants are exposed could be further increased if the formula is 

prepared with water contaminated with perchlorate. We note that, in a 

different section of EPA’s preliminary regulatory determination for 

perchlorate, the agency showed that formula-fed infants can be 

exposed to more than twice the dose that breast-fed infants receive. 

However, the implications of this information were not discussed in the 

context of EPA’s exposure analysis for perchlorate. 

• Second, the exposure estimates that resulted from EPA’s analysis of 

the CDC biomonitoring data—particularly those for pregnant women—

reflect some significant uncertainties associated with inherent 

limitations in the method used for extrapolating an estimate of daily 

exposure to perchlorate from CDC’s biomonitoring data. Specifically, 

to estimate daily exposure to perchlorate, EPA had to make an 

adjustment—called a creatinine adjustment—to the CDC 

biomonitoring data because only one urine sample was collected from 

each participant—called spot testing. This adjustment is especially 

uncertain when made for pregnant women because of the numerous 

physical changes women undergo during pregnancy. The 2010 journal 

article on the exposure assessment states that some caution should be 

used when interpreting perchlorate exposure estimates for pregnant 

women, noting the “profound changes in a woman’s body during 

pregnancy.” In addition, a technical addendum to the journal article 

identifies other problematic aspects of applying the creatinine 

adjustment to pregnant women that make the exposure estimates 

“tenuous.” EPA officials said they believed EPA disclosed all significant 

uncertainties of the exposure assessment that the agency was aware of 

at the time it used the assessment in supporting its preliminary 

regulatory determination notice. However, other reviewers that 

commented on the study prior to EPA’s 2008 preliminary determination 

expressed similar concerns about the reliability of the creatinine 

adjustment for pregnant women. While a single statement in EPA’s 

preliminary regulatory determination notice regarding these 

uncertainties reflects EPA’s recognition of these issues, EPA does not 

Page 66 GAO-11-254 Safe Drinking Water Act
 

explain or assess them: “A limitation is in the use of NHANES’ [CDC 

biomonitoring study’s] spot urine testing, and creatinine corrections for 

a population with diverse physiological characteristics to calculate the 

daily perchlorate dose.” This statement does not identify, for example, 

the “population”—pregnant women—to which it is referring and does 

not identify the effects of these limitations on EPA’s exposure analysis. 

This lack of disclosure is significant because of the direct impact the 

exposure estimates have on the relative source contribution 

calculation, which, in turn, directly affects the health reference level—

the benchmark EPA uses to determine whether perchlorate occurs in 

drinking water with a frequency and at levels of public health concern. 

• Third, EPA relied on an exposure estimate that the agency itself had 

identified as anomalous as the basis for calculating its relative source 

contribution. According to the principal EPA scientist conducting the 

analysis, EPA expected that the perchlorate exposure for individuals in 

the group exposed to perchlorate from food and water would be 

greater than from food or water alone. FDA’s findings from its 2006 

Total Diet Study that perchlorate is widespread in the food supply 

seem to corroborate this as a logical and reasonable assumption. For 

most of the age and gender groups, the data met this expectation. 

However, at both the mean and the 90th percentile, pregnant women’s 

exposure to perchlorate from food alone was higher than for pregnant 

women exposed to perchlorate from both food and water. Specifically, 

in a table in EPA’s preliminary regulatory determination, the agency 

estimated that, at the 90th percentile, pregnant women’s exposure to 

perchlorate from food only was 0.263 micrograms per kilogram per 

day, while the exposure for those who ingested perchlorate through 

both food and water was 0.121. While EPA stated in its draft 

preliminary regulatory determination sent to OMB that such anomalous 

results added uncertainty to this exposure analysis, this disclosure was 

deleted during OMB’s review and thus did not appear in EPA’s 2008 

preliminary regulatory determination notice. Some reviewers 

specifically questioned the analysis’s conclusions regarding pregnant 

women’s exposure to perchlorate in drinking water and stated that 

issues identified in their comments would need to be addressed before 

this approach was used in a larger context. 

Further, in response to reviewers’ comments, the authors of the 2010 

journal article on this methodology removed four data points that were 

determined to be outliers—two of which were data points that 

corresponded to women. As a result, in the article the authors reported 

pregnant women’s exposure to perchlorate from food alone at 0.198 

micrograms per kilograms per day—compared with EPA’s 0.263 estimate. 

Page 67 GAO-11-254 Safe Drinking Water Act
 

Even with this downward adjustment in the food exposure estimate for 

pregnant women, the anomalous relationship between exposure from food 

alone and from food and water likely persisted. However, readers of the 

journal would not be aware of such an anomaly because for pregnant 

women—the population of greatest significance in this study, according to 

EPA—the authors included only the data for those most likely to have 

been exposed to perchlorate through food alone and omitted data for 

those who were more likely to have been exposed to perchlorate through 

food and water. For all other populations in the study, such as children 

aged 6 to 11 and women aged 15 to 44, the authors report all exposure 

data. Appendix VIII provides greater detail on these and other limitations 

of EPA’s perchlorate exposure analysis. In addition, we found that while 

the downward adjustment in the food exposure estimate for pregnant 

women in 2010 resulted in a relative source contribution estimate for 

perchlorate exposure from water of 72 percent compared with the 62 

percent relative source contribution derived for EPA’s preliminary 

determination in 2008, the 2008 and 2010 analyses both specifically 

support the same health reference level of 15 parts per billion—the level 

EPA and the Perchlorate Interagency Working Group agreed to. Appendix 

IX shows how making small changes in the standard assumptions for 

weight and drinking water intake that were used to calculate the health 

reference levels in 2008 and 2010 allowed EPA and the journal authors to 

maintain consistency in the health reference levels reported. 

Notwithstanding the limitations of the exposure analysis discussed earlier, 

EPA used the exposure estimate for pregnant women to calculate a 

relative source contribution for perchlorate using a nontraditional 

method—that is, the subtraction method—rather than applying the default 

20 percent relative source contribution it has used for its other regulatory 

determinations. EPA officials said they used the subtraction method for 

perchlorate because they had the data to estimate exposure for 

perchlorate, whereas they had not for other contaminants. As previously 

discussed, however, according to EPA’s guidance on methods for 

developing relative source contribution estimates,140 if the agency 

Calculating the Relative Source 

Contribution 

 140EPA, Office of Science and Technology and Office of Water, Methodology for Deriving 

Ambient Water Quality Criteria for the Protection of Human Health (Washington, D.C., 

October 2000). This guidance document includes discussions of the two approaches the 

drinking water program has used for estimating the relative source contribution and 

criteria for selecting the appropriate approach. While the guidance was developed in the 

context of Clean Water Act water quality criteria, the Office of Water uses it in making its 

drinking water regulatory determinations. 

Page 68 GAO-11-254 Safe Drinking Water Act
 

determines that it has adequate exposure data to estimate the relative 

source contribution, rather than apply the default assumption, either of 

two methods may be applicable—the percentage method or the 

subtraction method. 

EPA’s decision to use the subtraction method rather than the percentage 

method to calculate the relative source contribution had a significant 

effect on the resulting health reference level, and consequently on EPA’s 

evaluation of whether (1) perchlorate occurred at a frequency and at levels 

of public health concern and (2) the regulation of perchlorate would 

provide a meaningful opportunity for public health risk reduction. 

Significant differences in the resulting health reference levels can occur 

because the subtraction method allows health reference levels to be set at 

the highest levels short of exceeding the reference dose. In contrast, the 

percentage method allows for a cushion between actual exposure levels 

and the reference dose, allowing for other sources of exposure and risk 

assessment uncertainties, including uncertainties related to the exposure 

data. For example, using EPA’s exposure estimates for people 20 years of 

age or older,141 the health reference level for perchlorate would be 19.6 

parts per billion using the subtraction method.142 In contrast, the health 

reference level would be 5 parts per billion using the percentage method.143

The sensitivity of the resulting health reference level—which can drive 

policy decisions—underscores the need for transparency in EPA’s 

regulatory determination notices regarding the relative source 

contribution methodology the agency selects. 

EPA’s guidance on relative source contribution methods indicates that the 

subtraction method may be used in some cases in which data are 

available—relevant to and representative of populations at risk—to 

describe central tendencies and high-end exposure. Further, the guidance 

 

141These calculations are based on EPA’s exposure data at the 90th percentile, the exposure 

level EPA used in calculating the relative source contribution for perchlorate in its 

preliminary regulatory determination. Because of the anomalies in the exposure data for 

pregnant women at the 90th percentile that EPA used as the basis for its relative source 

contribution, we cannot calculate what the relative source contribution would have been if 

EPA had chosen to use the percentage method in its preliminary regulatory determination. 

142Using the exposure analysis data to derive the relative source contribution under the 

subtraction method resulted in a relative source contribution of 80 percent. 

143In this scenario, the calculated relative source contribution was 15.2 percent. However, 

we rounded this number to 20 percent per EPA’s guidance that generally specifies a 20 

percent floor and an 80 percent ceiling for the relative source contribution. 

Page 69 GAO-11-254 Safe Drinking Water Act
 

generally advises that the subtraction method should be used with caution 

because it removes any cushion between existing exposure levels and the 

reference dose.144 An Office of Water official said that it is extremely rare 

for EPA to have the exposure data it needs to use the subtraction method. 

Because EPA did not document a determination that it had sufficient data, 

it is not clear why EPA deemed it appropriate to use the subtraction 

method to calculate the relative source contribution for perchlorate in 

light of the exposure analysis’s lack of data on infants—another sensitive 

subpopulation identified by the National Academies and EPA—as well as 

the uncertainties in EPA’s exposure analysis of pregnant women. In 

November 2010, Office of Water officials told us that they believe the use 

of available exposure information using the subtraction method for 

relative source contribution was consistent with the requirement in the 

Safe Drinking Water Act to use “the best available, peer-reviewed science 

and supporting studies conducted in accordance with sound and objective 

practice.” Office of Water officials also said that EPA’s 2000 guidance on 

when to use the percentage and subtraction methods “does not reflect 

more current thinking.”145 We note, however, that EPA’s 2008 preliminary 

regulatory determination notice on perchlorate did not expressly disclose 

(1) that the agency was using the subtraction method, (2) that this was the 

first use of this method in a preliminary (or final) regulatory 

determination, or (3) any guidance or rationale for the use of the 

subtraction method. Office of Water officials told us that the choice of 

relative source contribution methodology was either using the 20 percent 

default assumption when exposure information is not available or using 

the subtraction method in cases where information is available to develop 

estimates of exposure to drinking water contaminants from multiple 

sources. However, without EPA documentation, it remains unclear 

whether this position is consistent with the Office of Water’s existing 

guidance on relative source contribution, which provides that there may 

 

144EPA, Office of Science and Technology and Office of Water, Methodology for Deriving 

Ambient Water Quality Criteria for the Protection of Human Health (Washington, D.C., 

October 2000). 

145According to its December 2010 Exposure and Relative Source Contribution Analysis 

for Fluoride (820-R-10-015), the Office of Water is in the process of considering 

refinements to the 2000 guidance for determining the relative source contribution for 

ambient water and drinking water. However, this document states that EPA developed the 

relative source contribution for fluoride using the 2000 guidance because those 

modifications were not available for the fluoride exposure assessment. 

Page 70 GAO-11-254 Safe Drinking Water Act
 

be a choice between the use of the percentage or subtraction method—

depending, in part, on the scope and quality of the exposure data. 

Throughout the time that the agency was considering its course of action 

regarding a relative source contribution for perchlorate, the small group of 

high-level EPA officials—in accordance with the Perchlorate Interagency 

Working Group’s “no-surprises policy”—was sharing preliminary 

information and analyses with OMB and other members of the Perchlorate 

Interagency Working Group, and receiving direction and feedback from 

OMB. For example, documents we reviewed indicated that OMB officials, 

along with EPA management, directed the Office of Water to obtain 

additional data on sources of perchlorate exposure in order to estimate 

the relative source contribution rather than rely on the more conservative 

20 percent default. In addition, the documents show that, as early as 2006, 

OMB had concluded that the exposure data EPA was in the process of 

obtaining and analyzing would support a determination not to regulate 

perchlorate. Further, according to these documents, OMB expected that 

EPA would be able to strengthen its case for not regulating perchlorate by 

2007, when the agency was expected to make its second cycle of 

regulatory determinations. 

According to Key EPA 

Scientists, the Agency 

Mischaracterized 

Important Scientific 

Findings That Emerged 

from Its Novel Analysis of 

the Sensitivity of Various 

Age Groups to Perchlorate 

in Drinking Water 

In early 2008, EPA used a physiologically based pharmacokinetic (PBPK) 

model146 to (1) evaluate the relative sensitivity of sensitive subpopulations 

to the health reference level the agency had developed based on pregnant 

women and their fetuses and (2) address concerns that some sensitive 

subpopulations, such as infants, exposed at the health reference level may 

receive concentrations of perchlorate above the reference dose.147 For its 

preliminary regulatory determination, the agency used the model in a 

novel way and, according to some key EPA scientists, mischaracterized 

the findings of the modeling analyses by selecting and presenting 

information in such a way as to support the agreed-upon conclusion that a 

 

146PBPK models are complex and involve numerous underlying assumptions that are 

imbedded in mathematical representations of the processes associated with how a 

contaminant behaves within, and is eliminated from, the body. 

147As discussed earlier in the report, the reference dose is an estimate of the total daily oral 

exposure to a contaminant that is not likely to cause an “appreciable risk of deleterious 

effects during a lifetime.” 

Page 71 GAO-11-254 Safe Drinking Water Act
 

health reference level of 15 parts per billion was protective of all sensitive 

subpopulations, including infants.148

Specifically, in January 2008, EPA’s Office of Water asked the Office of 

Research and Development to review the PBPK model—which had 

recently been used by other scientists to estimate the effects of exposure 

to perchlorate and how the body processes it149, 150—to determine whether 

(1) that model represented the best available science and (2) there were 

scientifically defensible applications of the PBPK model for EPA’s purpose 

of assessing the risks of exposure to perchlorate. Office of Research and 

Development officials told us that this was different from how PBPK 

models are traditionally used because in this case, EPA was using the 

model to estimate an effect—that of perchlorate exposure on inhibition of 

iodide uptake on the thyroid at specific drinking water concentrations—

rather than to estimate the amount of perchlorate (the dose) that would 

adversely affect the thyroid. After examining the model in detail and 

making some minor adjustments to it, the Office of Research and 

Development concluded that it was appropriate to use the PBPK model for 

assessing exposure risks. Over the next several months, the Office of 

Research and Development used the model to conduct numerous 

sensitivity analyses for sensitive subpopulations, applying various sets of 

assumptions. As it conducted this work, the Office of Research and 

Development kept the Office of Water apprised of its results, some of 

which indicated that to prevent some infants from receiving a perchlorate 

dose greater than the reference dose, the concentration of perchlorate in 

water should not exceed 2 parts per billion. During this time, members of 

EPA’s small group of high-level officials continued to meet with the 

Perchlorate Interagency Working Group, and, in early July 2008, the 

Assistant Administrator of the Office of Research and Development told 

his staff that the Perchlorate Interagency Working Group had requested a 

 

148As discussed above, EPA agreed with other federal agencies on this conclusion and the 

rationale to support its regulatory determination using a health reference level of 15 parts 

per billion of perchlorate in drinking water, focusing on pregnant women and their fetuses 

as the most sensitive population. 

149E. A. Merrill et al., “PBPK Model for Radioactive Iodide and Perchlorate Kinetics and 

Perchlorate-Induced Inhibition of Iodide Uptake in Humans,” Toxicological Sciences, vol. 

83 (2005). 

150R. A. Clewell et al., “Perchlorate and radioiodide kinetics across life stages in the human; 

using PBPK models to predict dosimetry and thyroid inhibition and sensitive populations 

based on developmental stage,” Journal of Toxicology and Environmental Health Part A,

vol. 70, no. 5 (2007). 

Page 72 GAO-11-254 Safe Drinking Water Act
 

particular analysis using the PBPK model. Specifically, the Perchlorate 

Interagency Working Group asked EPA to use the model to show the 

iodide uptake inhibition rate for each sensitive subpopulation at water 

concentrations of 20 and 15 parts per billion. According to the Assistant 

Administrator, this was an effort to explore ways the PBPK model could 

be used to evaluate the effects of perchlorate exposure “instead of using 

default approaches.” 

EPA presented the results of such a PBPK analysis in its October 2008 

preliminary regulatory determination for perchlorate to support its 

conclusion that a health reference level of 15 parts per billion was 

protective of all sensitive subpopulations, including infants, and stated 

that using the model in this way could reduce some of the uncertainty 

regarding the sensitivities of subpopulations other than pregnant women. 

The analysis EPA presented in its preliminary regulatory determination 

compared the (1) estimated iodide uptake inhibition rate predicted by the 

model for various age groups with the (2) iodide uptake inhibition rate 

corresponding to the no-observed-effect level for the seven healthy adults 

from which the reference dose was derived (point of departure), at the 

health reference level of 15 parts per billion. From this comparison, the 

agency concluded that the 2.2 percent iodide uptake inhibition rate 

estimated by the model for the formula-fed infant—the age group with the 

highest inhibition rate—was comparable to the 1.8 percent inhibition rate 

for a healthy adult, noting that the difference in the inhibition rates was 

“within the statistical uncertainty in the data.” 

According to Office of Research and Development officials overseeing this 

work, however, this comparison was “misleading and incomplete” because 

it does not account for the uncertainty and variability inherent in 

comparisons of the responses of adults with those of other age groups, 

such as infants and children. These officials also stated that the 

comparison in the preliminary determination notice of the modelpredicted iodide uptake inhibition to the iodide uptake inhibition 

associated with the point of departure151 identified by the National 

Academies was inappropriate. They also said that a comparison of the 

model-predicted iodide uptake inhibition would also need to be made with 

the iodide uptake inhibition associated with the reference dose to 

 

151The no-observed-effect level was the starting point (point of departure) to which the 

National Academies applied an uncertainty factor of 10 to arrive at its recommended 

reference dose. 

Page 73 GAO-11-254 Safe Drinking Water Act
 

understand whether a drinking water concentration of 15 parts per billion 

would be protective of all subpopulations. Further, Office of Research and 

Development officials said they disagreed with the way EPA presented the 

information in its preliminary regulatory determination notice, saying the 

agency did not sufficiently explain the uncertainties and limitations, 

instead presenting the information more conclusively than was 

appropriate. In discussing these issues regarding the comparison with 

Office of Water officials, however, they said the comparison was valid on 

the basis that EPA agrees with the National Academies identification of 

iodide uptake inhibition as a valid measure to protect against the potential 

for an adverse health effect from perchlorate.152

While EPA relied on the modeling results and comparison discussed 

earlier to support its conclusion that a health reference level of 15 parts 

per billion was protective of all subpopulations, the table EPA published in 

the preliminary regulatory determination notice presenting the results of 

this analysis also included data that may not be consistent with that 

conclusion. That is, while the table providing the estimated daily dose of 

perchlorate to which infants and children up to age 2 would be exposed at 

a drinking water concentration of 15 parts per billion did not present a 

comparison of these estimated exposures with the reference dose, the 

table did provide sufficient data for informed readers of the preliminary 

determination to calculate such comparisons. Such calculations show that 

infants and young children could be exposed to doses of perchlorate at 

levels as high as 5.5 times greater than the reference dose, supporting the 

concern that infants and young children may, in fact, be more vulnerable 

to perchlorate exposure. Moreover, while EPA stated in the notice that 

“for some [subpopulations], the modeled exposure exceeds the [reference 

dose],” the agency was not explicit about the extent to which the reference 

dose is exceeded—as calculated above—and did not explain the 

implications of this result on its conclusion that the health reference level 

of 15 parts per billion is protective of all subpopulations. In providing 

comments on the draft notice to the Office of Water, an Office of Research 

and Development scientist noted that the agency’s failure to present a 

comparison of the estimated daily exposure with the reference dose 

constituted a “serious omission,” and characterized the infants’ estimated 

exposure as “substantially higher” than the reference dose. 

 

152In its February 2011 final regulatory determination on perchlorate, EPA stated that iodide 

uptake inhibition may not reflect the relationship of the precursor event to adverse 

outcomes in newborns and infants, who may not have the iodide stores sufficient to offset 

the effects of reduced iodide uptake. 

Page 74 GAO-11-254 Safe Drinking Water Act
 

As previously mentioned, in addition to the modeling analysis discussed 

above, the Office of Research and Development had conducted numerous 

other sensitivity analyses with the PBPK model that were not presented or 

discussed in EPA’s October 2008 preliminary regulatory determination for 

perchlorate. Some of the analyses were subsequently presented in a May 

2009 EPA report on the sensitivity analyses following an independent peer 

review and public comment period of the analyses.153 One of the analyses 

included in the report was an explicit comparison between estimated 

perchlorate doses received by all population groups and the existing 

reference dose that a senior EPA scientist had identified in September 

2008 (a month before the preliminary determination was published) as 

“necessary for an adequate health risk characterization for perchlorate 

exposures from drinking water.” According to an Office of Research and 

Development official, another analysis included in the report that 

compared the model-predicted iodide uptake inhibition of sensitive 

subpopulations with the model-predicted iodide uptake inhibition of an 

average adult at the no-observed-effect level dose identified by the 

National Academies was more appropriate than the analysis presented in 

the Federal Register notice. In this comparison, the PBPK model 

estimated an iodide uptake inhibition rate for the age group with the 

highest inhibition rate—again the 7-day-old formula-fed infant—of 4.3 

percent, compared with a rate of 1.6 percent for an average adult. In 

contrast, the PBPK analysis EPA used for its preliminary regulatory 

determination predicted a 2.2 percent iodide uptake inhibition for a 7-dayold formula-fed infant that EPA concluded was “comparable” to the 1.8 

percent iodide uptake inhibition that the National Academies 

recommended as the point of departure for calculating the reference dose. 

This analysis showing a greater disparity between the iodide inhibition 

rates in adults and infants was available before EPA issued its preliminary 

determination. 

EPA’s limited presentation of the numerous PBPK analyses conducted by 

the Office of Research and Development in its preliminary regulatory 

determination notice validated the concern expressed at the time by Office 

of Research and Development scientists who conducted the analyses: that 

individual analyses could be used out of context in a way that could be 

misleading. Accordingly, Office of Research and Development scientists 

 

153EPA, “Inhibition of the Sodium-Iodide Symporter by Perchlorate: An Evaluation of Life 

Stage Sensitivity Using Physiologically-Based Pharmacokinetic (PBPK) Modeling,” 

EPA/699/R-08/106A (Washington, D.C., May 2009). 

Page 75 GAO-11-254 Safe Drinking Water Act
 

conducting the PBPK analyses said it was important to present the 

different analyses in the interest of informed and transparent decision 

making. An Office of Research and Development official articulated in 

September 2008 that while his office and the Office of Water had 

developed careful and sophisticated PBPK analyses to support the 

agency’s preliminary regulatory determination, “the use of these science 

results in [the] draft regulatory determination is seriously flawed and 

misleading.” The official further noted that the draft interpreted these 

analyses indicating the absence of a perchlorate health risk for infants, but 

that the results actually indicated that infants would receive a perchlorate 

dose “approximately an order of magnitude greater than the reference 

dose.” As a result, Office of Research and Development officials and 

scientists that conducted the analyses concluded that the PBPK analysis 

done by the office did not support the draft preliminary regulatory 

determination’s suggested health reference level of 15 parts per billion as 

being health protective for all sensitive subpopulations of concern to EPA. 

While these Office of Research and Development officials and scientists 

communicated their disagreement regarding the fundamental implications 

of, and the agency’s presentation of the PBPK modeling results in the draft 

preliminary regulatory determination to the Office of Water—which was 

managing revisions to the notice as it underwent OMB review—they were 

not given an opportunity to review the final draft of the preliminary 

determination notice, and some key changes that they suggested were not 

reflected in the notice that was published in October 2008. 

EPA stated in its preliminary determination notice that it planned to issue 

a final determination by December 2008. In August 2009, however, instead 

of finalizing its 2008 preliminary regulatory determination after evaluating 

public comments—which is the typical practice—EPA decided to seek a 

second round of public comments through a Federal Register notice, 

specifically requesting input on sensitive populations. In this notice, EPA 

indicated that it was reevaluating how to best incorporate PBPK modeling 

into its evaluation of perchlorate, if at all, and presented an alternative 

PBPK analysis discussed earlier that explored the relative sensitivity of the 

various life stages to a fixed dose (the no-observed-effect level dose)—an 

analysis that EPA scientists who conducted the PBPK modeling believed 

should have been included in the 2008 preliminary regulatory 

determination in order to present the science correctly. This analysis 

showed, for example, that the model-predicted iodide uptake inhibition is 

approximately one and one-half-fold higher for the formula-fed infant 

compared with the average adult. In addition, EPA reported in this notice 

that infants less than 6 months in age generally consume five to eight times 

more water than pregnant women or women of child bearing age on a per 

Page 76 GAO-11-254 Safe Drinking Water Act
 

body weight basis, and thus will receive a higher dose for any given 

drinking water concentration. EPA stated in its February 2011 final 

determination to regulate perchlorate that it is evaluating the alternative 

health reference levels it had developed in its August 2009 notice—based 

on exposure information for 14 life stages—and considers them to be 

levels of public health concern for purposes of its regulatory 

determination. 

EPA’s Independence in 

Developing and 

Communicating Its 

Scientific Findings Was 

Limited by Its Acceptance 

of External Input on the 

Preliminary Determination 

Notice 

Compounding scientists’ concerns about the mischaracterization and lack 

of transparency regarding relevant scientific analyses, key language in 

EPA’s preliminary regulatory determination notice appears to have been 

drafted by OMB rather than EPA. In working to finalize the preliminary 

regulatory determination notice, EPA’s Office of Water worked with OMB, 

whose clearance of the notice was required per EPA’s policy implementing 

Executive Order 12866 before the Office of Water could provide it to the 

EPA Administrator for review, approval, and publication in the Federal 

Register.

154 According to the Office of Water, in four iterations of review, 

OMB sent EPA a substantial number of comments on the notice; in 

response, EPA “clarified its description of the supporting analysis and 

strengthened the rationale for the determination.” The following example 

highlights OMB’s role in reviewing and approving the specific wording of 

EPA’s scientific analyses regarding perchlorate exposure in infants and 

children: 

Text EPA provided to OMB: “Because infants and children eat and drink more on a 

per body weight basis than adults, eating a normal diet and drinking water with 15 

[micrograms per liter] of perchlorate is likely to result in exposure that is greater 

than the reference dose in these groups.” 

Revised text provided to EPA by OMB: “Because infants and children eat and drink 

more on a per body weight basis than adults, eating a normal diet and drinking water 

with 15 [micrograms per liter] of perchlorate may result in exposure that is greater 

than the reference dose in these groups.” 

 

154The objectives of this executive order are to enhance planning and coordination with 

respect to both new and existing regulations; to reaffirm the primacy of federal agencies in 

the regulatory decision-making process; to restore the integrity and legitimacy of 

regulatory review and oversight; and to make the process more accessible and open to the 

public. 

Page 77 GAO-11-254 Safe Drinking Water Act
 

By changing three words, OMB downplayed EPA’s characterization of the 

health risks of perchlorate exposure. Importantly, the EPA scientist who 

wrote the text provided to OMB noted to EPA reviewers—before it was 

sent to OMB in August 2008—that the PBPK model actually showed 

exposures at levels “much higher” than the reference dose, but also said 

that he believed describing the exposure scenario as “likely” was the 

strongest characterization that might be retained through OMB review. In 

addition, in September 2008, during its review of the draft preliminary 

determination notice and before clearing it for publication, OMB reminded 

EPA that it expected the notice to “state a clear conclusion that the HRL 

[health reference level] is protective of all subpopulations, as agreed to in 

the August framework”—and accordingly, this conclusion appeared in the 

agency’s October 2008 preliminary determination notice.155

Overall, the changes EPA made in response to OMB’s extensive comments 

through the external review process downplayed the health risks of 

exposure to perchlorate and presented EPA’s conclusions with greater 

certainty than key EPA scientists stated they were comfortable supporting. 

In addition, it is difficult to identify the nature and extent of OMB’s 

changes to the 2008 preliminary regulatory determination notice on 

perchlorate because OMB provided four iterations of comments, resulting 

in substantial revisions; EPA did not make OMB’s actual comments on the 

regulatory determinations part of the public record. Rather, an Office of 

Water official developed a statement for the record briefly summarizing 

the nature and extent of the comments. EPA included a copy of this 

statement, the draft determination notice that was sent to OMB for 

clearance, and a copy of the final version of the draft determination notice 

for publication in the public record. We note that the approach used by the 

Office of Water to make OMB’s comments on regulatory determinations 

part of the public record is different from that used in other programs, 

such as the IRIS program, which makes actual comments on draft 

assessments provided by OMB and other federal agencies available to the 

public. This latter approach is more transparent and supports a clear 

understanding of the nature and extent of OMB’s proposed changes. 

Moreover, the practice of fully disclosing individual comments promotes 

transparency, which is one of EPA’s core values established in its strategic 

plan, and which the Administrator emphasized in a 2009 memorandum on 

 

155According to an EPA official, “August framework” refers to the agreement that was faxed 

to EPA from the Council on Environmental Quality that included this conclusion as a key 

component of the rationale EPA and other federal agencies agreed to in August 2008. 

Page 78 GAO-11-254 Safe Drinking Water Act
 

the importance of transparency sent to all EPA employees.156 The 

memorandum established transparency guidelines intended to maintain 

the fairness and openness of EPA operations and thus strengthen public 

confidence in EPA decisions.157

Enacted with the goal of assuring the safety of public drinking water, the 

Safe Drinking Water Act authorizes EPA to regulate contaminants in 

public drinking water systems. Since the enactment of the 1996 

amendments to the act, EPA had not recommended any new contaminants 

for regulation until February 2011, when it, among other things, reversed 

its 2008 preliminary decision to not regulate perchlorate. Systemic 

limitations in its implementation of the 1996 amendments’ requirements 

for determining whether additional contaminants in public drinking water 

warrant regulation have impeded EPA’s progress in helping assure the 

public of safe drinking water. Specifically, EPA lacks (1) criteria and a 

process for identifying those contaminants on its candidate list that pose 

the greatest public health concern and (2) a coordinated process to obtain 

occurrence and health effects information to support informed regulatory 

determinations, resulting in regulatory determinations on contaminants 

selected on the basis of available data rather than on the basis of public 

health concern. 

Conclusions 

In addition, while the unregulated contaminants testing program mandated 

by the 1996 amendments provided EPA with the authority and a structure 

to obtain consistent, high-quality occurrence data that could effectively 

support regulatory determinations on individual contaminants, the extent 

and utility of the occurrence data this program generates to support EPA’s 

drinking water program is reduced because the agency has not (1) taken 

full advantage of its statutory authority to require testing for the maximum 

 

156Lisa P. Jackson, Administrator, Memorandum “Transparency in EPA’s Operations,” (Apr. 

23, 2009). (Committing “to uphold the values of transparency and openness in conducting 

EPA operations” and asking employees to help “ensure EPA operates in full compliance 

with [the] principle” of transparency.) 

157Executive Order 12866 requires agencies to, among other things, “[i]dentify for the 

public, in a complete, clear, and simple manner, the substantive changes between the draft 

submitted to [OMB] for review and the action subsequently announced,” “[i]dentify for the 

public those changes in the regulatory action that were made at the suggestion or 

recommendation of [OMB],” and make available to the public the draft action as sent to 

OMB for review. To the extent EPA’s regulatory determinations are subject to this 

executive order, including individual agency comments in the public record could be better 

aligned with the executive order’s objectives. 

Page 79 GAO-11-254 Safe Drinking Water Act
 

number of contaminants allowed, 30, under each 5-year testing cycle, and 

(2) used sufficiently sensitive analytic tests in some cases. We recognize 

that EPA may not always know the health reference level for a 

contaminant at the time the analytic method is being selected because a 

health risk assessment may be in progress. However, until the agency 

resolves this timing challenge—such as by the use of the more sensitive 

tests USGS has used for many years—EPA may be unable to routinely 

develop occurrence data at appropriately low detection levels to support 

informed regulatory determinations. Also, EPA’s decision to use the more 

limited screening survey for a majority of the contaminants tested, which 

can provide national occurrence data with greater uncertainty than those 

provided by assessment monitoring, has to date limited the utility of some 

of the testing data obtained, and it remains unclear whether EPA will find 

these data sufficient for future determinations. 

Importantly, EPA’s Office of Water has not developed policies and 

guidance that can help agency staff interpret and apply the 1996 

amendments’ broad statutory criteria, or developed a protocol to follow in 

making regulatory determinations that can both guide staff and 

incorporate accountability into the process. Without such policies and 

guidance, the basis for EPA’s regulatory determinations—and the quality 

of the documentation the agency uses to support them—can fluctuate over 

time with changes in agency leadership and staff. Also, without guidance, 

EPA lacks thresholds or parameters for applying the broad statutory 

criteria to ensure their consistent application. For example, EPA is 

informally applying an unspecified national occurrence requirement for 

contaminants to meet the statutory criterion of occurring “with a 

frequency and at levels of public health concern.” This national occurrence 

requirement has not been defined or vetted internally or externally, yet its 

use represents a critical interpretation of the Safe Drinking Water Act that 

has important implications for the safety of public drinking water in the 

United States. Moreover, without guidance on such things as the 

characteristics of occurrence data and health effects information that are 

adequate to support regulatory determinations, methods and analyses to 

evaluate the health effects on sensitive subpopulations, and a process to 

ensure that the presentation of occurrence data and health effects 

information in regulatory determination notices and support documents is 

comprehensive, consistent, informative, and understandable, EPA’s 

support for its regulatory determinations will continue to lack 

transparency, clarity, and consistency—affecting their credibility. For 

example, such information cannot be comprehensive without clear 

explanations of key information, such as whether and how EPA used 

various data, the relative source contribution method the agency used to 

Page 80 GAO-11-254 Safe Drinking Water Act
 

calculate the health reference level, instances in which the minimum 

reporting levels for data used in assessing contaminants’ occurrence in 

drinking water were not sufficiently sensitive to detect occurrence at the 

level of public health concern, and any exceptions to existing guidance 

reflected in the agency’s support for its regulatory determinations. In 

addition, as illustrated by EPA’s preliminary determination on perchlorate, 

information on the relative source contribution method the agency uses to 

calculate the health reference level is also key to providing a 

comprehensive understanding of regulatory determinations. Moreover, in 

light of the importance of the regulatory determinations to ensure the 

safety of public drinking water and protect public health, the lack of 

guidance hampers EPA’s ability to consistently apply and document (1) 

the statutory requirement to consider sensitive subpopulations—such as 

infants and children, those with kidney and liver disease, those with 

compromised immune systems, and the elderly—when selecting 

contaminants for regulatory determination, and (2) EPA’s children’s health 

policy, which specifies how health risks to infants and children should be 

analyzed when the agency is developing a policy, regulatory action, or 

decision. As demonstrated by the preliminary determination for 

perchlorate, EPA also had not determined how to use the expertise of 

officials and scientists in relevant offices, including the Office of 

Children’s Health Protection, in making decisions regarding drinking water 

contaminants, such as by ensuring that, to the extent possible, such offices 

consistently participate in regulatory determination work groups. 

In the absence of guidance defining the circumstances and process under 

which EPA may want to reconsider final determinations to not regulate, it 

is unclear whether and to what extent EPA would consistently do so. In 

addition, in issuing policies and guidance, EPA could be better assured 

that the guidance would address identified shortcomings by having an 

independent review of any proposed guidance by an entity with scientific 

and technical credibility, such as either of EPA’s two standing drinking 

water advisory committees. Importantly, guidance alone may not ensure 

that EPA conducts future regulatory determinations in a consistent 

manner without an internal review mechanism to ensure the application of 

any guidance. Such a mechanism could be instrumental in preventing the 

use of an atypical process such as the one used for the preliminary 

determination on perchlorate—which lacked transparency and limited the 

agency’s independence in developing and communicating its scientific 

findings. 

EPA has posted health advisories on its Web site to inform states, 

localities, and public water systems that action on their parts may be 

Page 81 GAO-11-254 Safe Drinking Water Act
 

required to protect public health from exposure in public drinking water to 

9 of the 20 contaminants the agency has decided not to regulate. However, 

because EPA does not require public water systems to monitor for these 

unregulated contaminants, current data on the occurrence of these 

contaminants in the nation’s public water systems are generally not 

available. The lack of actual comprehensive data on the occurrence of 

these contaminants in public water systems, widespread state and local 

government budget constraints, and, in some cases, limitations in states’ 

ability to require systems to conduct testing, are factors that could hamper 

efforts by states and localities to use the health advisories in a timely and 

effective manner to protect public health. Further, while not directed to 

consumers, the health advisories in some cases contain warnings about 

using public water to prepare formula and food for infants and children 

containing the contaminants at certain levels. Because many consumers 

would have to find and pay a laboratory to have their water tested to be 

informed of the occurrence of these contaminants in their drinking water, 

it would also be difficult for them to effectively use the advisories to 

protect their health and that of their families. 

Finally, EPA currently submits its regulatory determinations to OMB for 

review and clearance pursuant to executive order and OMB policy, but for 

the 2008 preliminary regulatory determination on perchlorate—and for the 

prior 20 determinations—OMB’s individual comments and direction are 

not transparently identified in the public record. This information is key to 

understanding the degree to which EPA is maintaining its independence in 

developing and communicating the results of its scientific analyses. 

Moreover, the lack of transparency of OMB’s overall review and clearance 

is important because, for example, in discussing complex scientific 

analyses and conclusions, changes that appear to be minor can actually 

significantly alter the conclusions presented in the determinations—

conclusions can be made to appear more certain than they actually are or, 

conversely, can be made to appear less important than EPA scientists 

assess them to be. 

To increase EPA’s consistency, transparency, and clarity in implementing 

the Safe Drinking Water Act in a way that better assures the public of safe 

drinking water, we recommend that the Administrator of EPA take the 

following 17 actions. 

Recommendations for 

Executive Action 

To systematically implement the statutory requirement to consider for 

regulation the contaminants that present the greatest public health 

Page 82 GAO-11-254 Safe Drinking Water Act
 

concern, we recommend that the EPA Administrator require that the 

Office of Water 

• develop criteria and a process for identifying those contaminants on its 

candidate list that present the greatest public health concern, and 

• develop a coordinated process for obtaining both the occurrence and 

health effects data that may be needed for the agency to make 

informed regulatory determinations on these priority contaminants. 

To take full advantage of the opportunities provided by the testing 

program mandated by the statute and thereby obtain high-quality 

occurrence data on the authorized number of unregulated contaminants, 

we recommend that the EPA Administrator require the Office of Water to 

take the following steps: 

• Use its full statutory authority to test for the 30 contaminants allowed 

under each 5-year testing cycle. 

• Conduct testing for most or all of the selected contaminants using the 

assessment monitoring program, rather than the more limited 

screening surveys, to obtain robust occurrence data, from which 

national estimates with high confidence levels can be derived. 

• Select minimum reporting levels for testing selected unregulated 

contaminants that are sufficiently sensitive to reliably (1) detect the 

known and likely occurrence of contaminants in public water systems 

at levels of public health concern and (2) provide useful and credible 

information on the occurrence of the contaminants in public drinking 

water systems. 

To support the development of regulatory determinations that are 

transparent, clear, and consistent and that follow applicable agency policy, 

we recommend that the EPA Administrator require the Office of Water to 

expeditiously develop, and make available to the public, policies or 

guidance that clearly articulates the agency’s interpretation of the act’s 

broad statutory criteria for making regulatory determinations and provides 

a protocol for making such determinations. 

In particular, the guidance should 

• specify any thresholds or parameters that the agency requires to be met 

to support a positive finding for each criterion to ensure their 

consistent application. 

Page 83 GAO-11-254 Safe Drinking Water Act
 

• include factors for determining when the occurrence and health effects 

data the agency identifies are adequate to support a regulatory 

determination. 

• establish a process to ensure that the presentation of health effects and 

occurrence information in regulatory determination notices and 

support documents is comprehensive, consistent, informative, and 

understandable and that it includes clear explanations of key 

information, such as 

• whether and how EPA used various data, 

• the relative source contribution method the agency used to 

calculate the health reference level, 

• instances in which the minimum reporting levels for data used in 

assessing contaminants’ occurrence in drinking water are above the 

health reference level (e.g., are not sufficiently sensitive to detect 

occurrence at the level of public health concern) and the limitations 

of using such occurrence data to support regulatory determinations, 

and 

• any exceptions to existing guidance reflected in the agency’s 

support for its regulatory determinations. 

• establish the approaches, such as methods and analyses, as 

appropriate, to evaluate the health effects on sensitive subpopulations, 

including such groups as infants and children, those with kidney and 

liver disease, those with compromised immune systems, and the 

elderly, and to comply with applicable agency policy and guidance for 

assessing children’s health risks. 

• specify that appropriate stakeholders—that is, EPA offices with 

relevant expertise such as the Office of Children’s Health Protection 

and regional offices that have known or likely occurrence of the 

contaminants being evaluated in public water systems within their 

areas of jurisdiction—be encouraged and have the opportunity to 

participate in the regulatory determination work groups. 

• define the circumstances under which, and the process EPA will use, to 

reconsider whether to regulate a contaminant for which it previously 

issued a determination not to regulate and, in the context of the 

recommended guidance, consider whether the agency needs to reevaluate any of its past determinations to not regulate. 

Page 84 GAO-11-254 Safe Drinking Water Act
 

We further recommend that a draft of the guidance we are recommending 

EPA develop be reviewed by the Science Advisory Board’s Drinking Water 

Committee or the National Drinking Water Advisory Council and that EPA 

consider the committee’s comments before finalizing the guidance. In 

addition, we recommend that the EPA Administrator develop and 

implement an internal review mechanism to help ensure that EPA’s 

regulatory determinations are consistent with the guidance. 

In light of EPA’s decisions to issue health advisories in conjunction with 

determinations to not regulate certain contaminants that have been 

detected in some public water systems at levels of public health concern, 

we recommend that the EPA Administrator (1) determine whether the 

Office of Water’s use of health advisories provides sufficient information on 

these unregulated contaminants to support timely and effective actions by 

states, localities, public water systems, and the public to ensure the safety of 

public drinking water, and (2) if not, direct the Office of Water to develop a 

plan to more effectively communicate such information to these entities. 

To improve transparency and help EPA ensure that it maintains the 

fairness and openness of its operations and thus strengthens public 

confidence in its decisions, we recommend that the EPA Administrator 

require the Office of Water to include in the public record OMB’s and other 

federal agencies’ comments on and revisions to regulatory determination 

notices and support documents. 

We provided a draft of this report to the Administrator of EPA for review 

and comment. In commenting on the draft report, EPA did not say 

whether it agreed or disagreed with our findings. EPA agreed with two of 

our recommendations regarding its drinking water health advisories, 

stating that it would evaluate their utility and determine whether and how 

to revise the advisories to better serve states, localities, public water 

systems, and the public. However, EPA did not agree to adopt the 

remaining 15 recommendations we made to improve EPA’s 

implementation of the Safe Drinking Water Act’s requirements for 

determining whether additional drinking water contaminants warrant 

regulation. These recommendations are largely aimed at developing basic 

guidance to support clear and consistent agency actions to help assure the 

public of safe drinking water. 

Agency Comments 

and Our Evaluation 

Regarding our recommendation to develop criteria and a process for 

identifying those drinking water contaminants on its candidate lists that 

present the greatest public health concern, EPA took the position that no 

Page 85 GAO-11-254 Safe Drinking Water Act
 

action is needed, as the agency’s candidate list itself represents the 

contaminants of greatest public health concern. We acknowledge in our 

report that the candidate list represents one level of prioritization, but we 

also identify the need for EPA to further prioritize the 116 contaminants 

on its current candidate list to obtain coordinated and timely health effects 

and occurrence data and make regulatory determinations on contaminants 

of greatest public health concern. We also report that in 2009, EPA’s 

Science Advisory Board concluded that the candidate list is too large to 

effectively prioritize contaminants for the purpose of making regulatory 

determinations. Especially in light of increased fiscal constraints and 

programmatic demands, we believe it is of utmost importance for EPA to 

prioritize the contaminants on its candidate list to identify those of 

greatest public health concern so that the agency can effectively target its 

limited resources to obtain the data it needs to support regulatory 

determinations on priority contaminants. EPA noted that the agency “is 

prioritizing” contaminants from the candidate list for the next cycle of 

regulatory determinations. The implication of this statement is that EPA 

will, in fact, prioritize contaminants, but without having established 

criteria and a process for so doing. We continue to believe that 

establishing criteria and a process for identifying contaminants on the 

candidate lists that present the greatest public health concern is important 

to provide transparency and credibility to EPA’s implementation of the 

statutory requirement for prioritizing. 

Regarding our recommendation to develop a coordinated process for 

obtaining the occurrence and health effects data needed to make informed 

regulatory determinations on the contaminants of greatest public health 

concern, EPA’s response describes its current efforts for obtaining these 

data—such as engaging in “internal and external discussions about data 

gaps that need to be filled” and participating in the Office of Research and 

Development’s planning process to prioritize health effects research for 

the next 5 years—and does not acknowledge that any further steps are 

needed. As we reported, the approaches EPA has used, and advocates 

continued reliance on, have resulted in the agency’s making limited 

progress in filling data gaps since the 1996 amendments. Moreover, the 

data gaps for contaminants on its current candidate list are substantial—

EPA identified a lack of sufficient occurrence or health effects data, or 

both, for at least 100 of the 116 contaminants on the list. Therefore, we 

continue to believe that the Office of Water needs to develop a 

coordinated process for obtaining both occurrence and health effects data 

for those contaminants on its candidate list that present the greatest 

public health concern. 

Page 86 GAO-11-254 Safe Drinking Water Act
 

EPA did not agree to implement our recommendations that the EPA 

Administrator require the Office of Water to fully and effectively utilize the 

testing program by (1) using EPA’s full statutory authority to test for the 

30 contaminants allowed under each 5-year testing cycle; (2) conducting 

testing for most or all of the selected contaminants using the assessment 

monitoring program; and (3) selecting minimum reporting levels that are 

sufficiently sensitive to, for example, reliably detect the occurrence of 

contaminants in public water systems at levels of public health concern. 

While we understand from its response that EPA currently supports fully 

utilizing this important program, EPA has not done so in the past; we 

believe it is important for EPA to implement our recommendations and 

thereby institutionalize the agency’s commitment to fully and effectively 

using the unregulated contaminants testing program going forward. 

To support the development of regulatory determinations that are 

transparent, clear, and consistent and that follow applicable agency policy, 

we made an overarching recommendation that EPA develop policies or 

guidance that clearly articulate the agency’s interpretation of the Safe 

Drinking Water Act’s broad statutory criteria, as well as eight additional 

recommendations identifying specific components of this guidance and 

calling for review of the draft guidance by one of EPA’s independent 

advisory committees and the establishment of an internal review 

mechanism to help ensure the determinations are consistent with the 

guidance. EPA did not agree to implement these nine recommendations. 

Specifically, EPA said it believed that establishing policies or guidance for 

regulatory determinations was not “practicable” because of the many 

combinations of health effects factors and potential ranges of frequencies 

and levels of contaminants measured in drinking water. We do not believe 

that the existence of variables or complexities is a basis for not developing 

guidance for EPA staff to implement the statutory requirements for 

regulatory determinations. In fact, the complexities cited would argue for, 

rather than against, the need to develop guidance for staff on applying the 

criteria. EPA also did not agree with these recommendations on the basis 

that policies or guidance could “inhibit its ability to continually improve its 

actions.” This perspective suggests that guidance per se lacks flexibility. 

We do not agree that guidance and flexibility are incompatible or that 

developing guidance would inhibit EPA’s ability to improve its actions. 

Rather, flexibility can and should be incorporated into guidance by 

establishing parameters or options for areas in which flexibility is deemed 

appropriate. Moreover, consistency and accountability are lacking in this 

important program because EPA has not developed guidance on the 

application of the broad statutory criteria, which are susceptible to varying 

interpretations. As stated in our report, the statutory criteria are so 

Page 87 GAO-11-254 Safe Drinking Water Act
 

broadly stated that they could potentially be interpreted so as to lead to 

regulating all the contaminants on the candidate list, some of them, or 

none of them. In its comments, EPA highlighted that, under these criteria, 

ultimately it is the Administrator’s judgment as to whether regulation of a 

contaminant in drinking water presents a meaningful opportunity for 

health risk reduction, after considering the information presented by 

agency staff. It is precisely for this reason that we believe it is essential for 

the staff to have sufficient guidance on applying the broad criteria 

consistently and transparently so that the Administrator’s judgment can be 

based on sound and consistent information. Without such guidance, the 

basis for EPA’s determinations and the quality of the documentation the 

staff use to support them can fluctuate over time as a result of, among 

other reasons, changes in agency leadership and staff. 

Regarding our recommendation that EPA develop guidance that would 

specify any thresholds or parameters that the agency requires to be met, 

EPA stated that there is not a “one size fits all” model for evaluating 

contaminants for drinking water regulation. We agree, but we do not 

believe that this precludes the development of useful and important 

guidance, particularly with regard to interpreting contaminant occurrence 

“with a frequency and at levels of public health concern” that would 

provide “a meaningful opportunity for health risk reduction.” We believe 

EPA should be able to conceptualize the key scenarios that could 

reasonably meet these criteria, as well as anticipate, for various situations, 

the types of analyses appropriate to the evaluation. In our report, we cited 

a 1993 EPA report that provides some potential scenarios for regulating 

drinking water contaminants. As we said, this report could serve as a 

starting point in developing this important guidance. Moreover, if in fact 

EPA does not believe any thresholds or parameters are applicable to its 

regulatory determinations, the agency should expressly state this in 

guidance. The Safe Drinking Water Act does not require that contaminants 

be found in public water systems on a national basis for an Administrator 

to find a meaningful opportunity for health risk reduction; it also provides 

for relief from monitoring and for flexibilities for instances in which a 

contaminant occurs in certain areas but not in others. As we reported, 

EPA’s informal use of a national occurrence requirement has significant 

implications for the safety of public drinking water, but EPA has not 

defined or vetted this critical interpretation of the statutory criterion 

internally or externally. 

Regarding our recommendations for EPA to (1) develop guidance that 

includes factors for determining when the occurrence and health effects 

data the agency identifies are adequate to support a regulatory 

Page 88 GAO-11-254 Safe Drinking Water Act
 

determination and (2) establish a process to ensure that the presentation 

of health effects and occurrence information is comprehensive, consistent, 

informative, and understandable, and that it includes clear explanations of 

key information we outlined, EPA stated that it will strive to improve the 

clarity and transparency of its support documents and Federal Register

notices so that the public better understands the information and data 

being considered, any potential limitations or exceptions, how it uses this 

information to make decisions, and the rationale for its decisions. 

However, we continue to believe that the guidance we recommend is 

integral to EPA’s accomplishing and sustaining the improvements it 

recognizes are needed. 

Regarding our recommendation to establish approaches, such as methods 

and analyses, to evaluate the health effects on sensitive populations—

including such groups as infants and children, those with kidney and liver 

disease, those with compromised immune systems, and the elderly—and 

to comply with applicable agency policy and guidance for assessing 

children’s health risks, EPA states it will consider how to incorporate the 

elderly into its evaluations and to continue to coordinate with the Office of 

Children’s Health Protection to improve the methods it uses to assess 

health effects for regulatory determinations. These actions are not 

responsive to our recommendation and provide no assurance that EPA 

will not continue to assess sensitive populations in a manner that lacks 

transparency and internal consistency. 

In response to our recommendation that additional guidance is needed to 

specify that appropriate stakeholders be encouraged to, and have the 

opportunity to, participate in the regulatory determination work groups, 

EPA stated it did not believe additional guidance is needed, opting to 

continue to rely on its existing administrative process (the Action 

Development Process) to fill this role. However, we believe that in some 

cases a more proactive approach is needed to ensure that appropriate 

stakeholders—EPA offices with relevant expertise and regional offices in 

areas with known or likely occurrence of the contaminants being 

evaluated—participate in the regulatory determination work groups. As 

we reported, officials from the Office of Children’s Health Protection said 

they were involved only informally and intermittently in the first two 

regulatory determination work groups largely as a result of staff and 

resource limitations. As a result, in some cases, the Office of Water may 

need to augment the voluntary approach of the administrative process by 

identifying relevant stakeholders and working with their management, if 

need be, to encourage their participation. 

Page 89 GAO-11-254 Safe Drinking Water Act
 

Furthermore, EPA stated that it does not believe guidance is needed to 

define the circumstances under which it will reconsider whether to 

regulate a contaminant it has determined not to regulate, and the process 

EPA will use to do so, because its candidate list process allows for reevaluation of contaminants for which EPA has previously made negative 

regulatory determinations if new health effects or occurrence information 

becomes available. We believe good management necessitates specific 

guidance on how and when the agency will reconsider determinations to 

ensure that this is done consistently and in a timely manner. Also, we 

continue to believe that EPA should consider, in the context of the 

guidance we recommended that EPA develop, whether it needs to reevaluate any of its past determinations to not regulate in light of the 

systemic and individual shortcomings we have identified in this report. 

In response to our recommendation regarding the independent review of 

the recommended guidance—which EPA has said is not “practicable” to 

develop—EPA states that it will “plan to seek input” from its National 

Drinking Water Advisory Council on how to improve transparency and 

clarity of its regulatory determinations “at an appropriate stage of the 

process during the agency’s (next or future) regulatory determinations 

effort.” We continue to believe it is essential for EPA to develop the 

guidance we recommend and that the most efficient and effective way to 

obtain input from one of EPA’s drinking water advisory committees is to 

have it review EPA’s draft guidance. Regarding the recommendation for 

EPA to develop and implement an internal review mechanism to help 

ensure that EPA’s regulatory determinations are consistent with the 

guidance we recommend, EPA states that it will continue to use its Action 

Development Process and agency work group to ensure that 

determinations are clear, transparent, and “as consistent as possible.” Our 

report shows that these mechanisms have not been effective to date. 

Consequently, we continue to believe that EPA needs to develop and 

implement an internal review mechanism to help ensure that the agency’s 

regulatory determinations are consistent with the guidance we 

recommend. 

Finally, in response to our recommendation that the EPA Administrator 

require the Office of Water to include in the public record communications 

with OMB and other federal agencies during the development of 

regulatory determinations and associated notices and scientific analyses, 

EPA states that Executive Order 12866 does not require that every 

communication with OMB or other federal agencies be included in the 

public record. EPA also states that unless otherwise required by law, it 

does not believe that including these documents in the docket is a good 

Page 90 GAO-11-254 Safe Drinking Water Act
 

policy because the predecisional documents may be confusing to the 

public, undermine the ultimate policy choice, and inhibit deliberations. We 

continue to believe that to improve transparency of these determinations, 

which are by law committed to the Administrator’s judgment, EPA should 

consistently provide in the public record documentation of OMB’s and 

other federal agencies’ comments on and revisions to EPA regulatory 

determination documents, regardless of whether there is a specific legal 

requirement for disclosure. As a result of EPA’s comments on the scope of 

our recommendation, we have revised it to focus on the transparency of 

OMB’s and other federal agencies’ comments on and revisions to EPA’s 

regulatory determination notices and support documents. EPA also 

provided technical comments, which we incorporated as appropriate. 

Appendix X contains the full text of the agency’s comments. 

As agreed with your offices, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies to the appropriate 

congressional committees, Administrator of EPA, Office of Management 

and Budget, and other interested parties. In addition, the report will be 

available at no charge on the GAO Web site at http://www.gao.gov. 

If you or your staffs have any questions about this report, please contact 

me at (202) 512-3841 or trimbled@gao.gov. Contact points for our Offices 

of Congressional Relations and Public Affairs may be found on the last 

page of this report. GAO staff who made major contributions to this report 

David C. Trimble 

are listed in appendix XI. 

Acting Director 

Natural Resources and Environment 

Page 91 GAO-11-254 Safe Drinking Water Act
Appendix I: Objectives, Scope, and 

Methodology 

Page 92 GAO-11-254 

Appendix I: Objectives, Scope, and 

Methodology 

Our objectives were to (1) evaluate the extent to which the Environmental 

Protection Agency’s (EPA) implementation of the 1996 amendments’ 

requirement to determine which potentially harmful contaminants to 

regulate has helped assure the public of safe drinking water and (2) review 

the process and scientific analyses EPA used to develop its 2008 

preliminary regulatory determination on perchlorate. 

To assess EPA’s implementation of the 1996 amendments’ requirement to 

determine which potentially harmful drinking water contaminants to 

regulate, we reviewed the statute, legislative history, and relevant 

amendments and analyzed relevant documentation, such as Federal 

Register notices announcing EPA’s regulatory determinations, 

contaminant candidate lists, and unregulated contaminant monitoring 

rules; EPA regulatory determination work group documents; regulatory 

determination support documents1

; and relevant policy and guidance 

documents such as EPA’s policy regarding the estimation of relative 

source contributions, as well as the agency’s guidance for considering 

children’s health when developing EPA actions. We reviewed the primary 

support documents for the 20 contaminants with final regulatory 

determinations from the 2003 and 2008 cycles and related drinking water 

health advisories; reports by the Department of Health and Human 

Services’ (HHS) Agency for Toxic Substances and Disease Registry 

(ATSDR) and the National Academies; and Integrated Risk Information 

System (IRIS) assessments, as applicable. We reviewed EPA’s information 

on the potential adverse health effects of, and extent to which the public 

may be exposed to, individual contaminants in public drinking water 

systems, as well as public comments on EPA’s determinations. We 

judgmentally selected 6 of the 20 contaminants with completed regulatory 

determinations (boron; dieldrin; 2,4-dinitrotoluene; 2,6-dinitrotoluene; 

manganese; and 1,1,2,2-tetrachloroethane) to review how EPA presented 

its rationale and support for its determinations in its regulatory 

determination notices and key support documents. We selected 

contaminants that, taken together, provided coverage for the following 

five variables: (1) contaminants from each of the regulatory determination 

 

1

In this report, we refer to Federal Register notices regarding EPA’s regulatory 

determinations (notices) and EPA’s regulatory determination support documents 

individually and collectively, as appropriate. When referring to these documents 

collectively, we use the term “regulatory determination documents.” The support 

documents varied under the two regulatory determination cycles, with several support 

documents for each contaminant considered under the first cycle and a consolidated 

support document for each contaminant under the second cycle. 

 Safe Drinking Water Act 
Appendix I: Objectives, Scope, and 

Methodology 

cycles; (2) contaminants whose occurrence data came from one of the 

three primary data sources (National Inorganic and Radionuclide Survey, 

Unregulated Contaminant Monitoring Rounds 1 and 2, and EPA’s first 

Unregulated Contaminants Monitoring Rule); (3) contaminants with 

cancer adverse health effects as well as contaminants with noncancer 

adverse health effects; (4) contaminants whose occurrence data had 

minimum reporting levels higher than the health reference levels, as well 

as those whose occurrence data had minimum reporting levels lower than 

the health reference levels; and (5) contaminants detected at levels in 

excess of the health reference level at 1 percent or more of public water 

systems sampled, as well as contaminants with fewer such detections. 

In addition, we reviewed health effects information and public drinking 

and source water occurrence data from other entities, such as ATSDR, 

California’s Office of Environmental Health Hazard Assessment, and the 

U.S. Geological Survey (USGS). We interviewed officials from EPA’s Office 

of Water, Office of Research and Development, and Office of Children’s 

Health Protection to obtain their perspectives on, among other things, the 

regulatory determination process and the health effects and contaminant 

occurrence research used to support determinations. We interviewed 

officials at the Association of State Drinking Water Administrators and the 

American Water Works Association to obtain their perspectives on EPA’s 

regulatory determinations process and decisions. Overall, the focus of this 

review has been on EPA’s regulatory determination process. While this 

work included reviewing information developed under two other 

processes integral to the regulatory determination process—the 

development of contaminant candidate lists and implementation of the 

unregulated contaminants monitoring rule—we did not evaluate EPA’s 

implementation of these processes. 

To review the process and scientific analyses EPA used to develop its 2008 

preliminary regulatory determination on perchlorate, we analyzed the 2008 

Federal Register notice announcing EPA’s preliminary determination and 

the 2009 Federal Register notice—EPA’s supplemental request for 

comments. We reviewed the process EPA used in adopting the National 

Academies’ risk assessment of perchlorate in its IRIS database, as well as 

other key scientific analyses EPA relied on in making its preliminary 

determination: its analysis of exposure to perchlorate from food and water 

and its sensitivity analysis of various age groups to perchlorate exposure. 

We analyzed the related peer reviews on these analyses and public 

comments on EPA’s preliminary regulatory determination. In addition, we 

reviewed relevant documentation of communications among EPA officials 

and between EPA officials and officials from other federal agencies related 

Page 93 GAO-11-254 Safe Drinking Water Act
Appendix I: Objectives, Scope, and 

Methodology 

to perchlorate. Further, we interviewed key officials in EPA’s Office of 

Water and Office of Research and Development who were involved in the 

development of EPA’s preliminary determination. In addition, we 

interviewed officials from EPA’s Office of Water, Office of Research and 

Development, and Office of Children’s Health Protection to obtain 

information on EPA’s decision making, support documents, and analyses 

regarding the perchlorate decision, as well as to obtain their perspectives 

on the determination. 

In addition, to provide supplemental information on EPA’s implementation 

of the Safe Drinking Water Act of interest to the requesters, we reviewed 

EPA’s regulatory actions from 1974 to 2010 that occurred in response to 

the major amendments and provide this information in the background 

section of the report, with additional details provided in appendix II. We 

also reviewed a key EPA Report to Congress from 1993, which discussed 

the implementation of the act under the first two legislative frameworks, 

as well as the conditions preceding the 1996 amendments to the act. We 

visited a drinking water treatment facility and laboratory to obtain a 

contextual understanding of public drinking water systems and 

contaminant occurrence testing, as well as the system operators’ 

perspectives on emerging contaminants and EPA’s regulatory 

determinations process. In addition, we attended the Association of State 

Drinking Water Administrators’ Annual Conference in October 2009 and 

the American Water Works Association’s Water Quality Technology 

Conference in November 2009 to obtain perspectives on drinking water 

treatment and regulations, as well as to familiarize ourselves with 

emerging contaminants of concern and other water quality issues. We 

conducted this performance audit from March 2009 to May 2011, in 

accordance with generally accepted government auditing standards. Those 

standards require that we plan and perform the audit to obtain sufficient, 

appropriate evidence to provide a reasonable basis for our findings and 

conclusions based on our audit objectives. We believe that the evidence 

obtained provides a reasonable basis for our findings and conclusions 

based on our audit objectives. 

Page 94 GAO-11-254 Safe Drinking Water Act
Appendix II: Information o

Actions

Ac

n EPA’s Regulatory

 under the 1974 Safe Drinking Water 

t 

Page 95 GAO-11-254 

Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

EPA’s regulatory actions under the Safe Drinking Water Act have varied 

over time as the agency’s legal authority to determine which drinking 

water contaminants to regulate, if any, has changed from discretionary to 

prescriptive and back to largely discretionary. 

The Act’s Original 

Framework Gave EPA 

Broad Discretion in 

Deciding Whether to 

Regulate Specific 

Contaminants 

In light of increased awareness of widespread water quality problems and 

health risks, Congress passed the Safe Drinking Water Act in 1974. The act 

directed the EPA Administrator to develop regulations for drinking water 

contaminants that “in his judgment” may have adverse human health 

effects and provided substantial discretionary authority to carry out this 

mission by not legally mandating the regulation of any specific 

contaminants or class of contaminants. EPA interpreted the law as 

providing the agency with discretion to select contaminants for regulation 

on the basis of their potential for causing an adverse health effect.1

 In 

contrast to current statutory requirements, the original act did not require 

EPA to demonstrate the presence of contaminants with potential adverse 

health effects in public drinking water systems or evaluate public 

exposure to them. From 1974 to 1986, the act outlined a three-step 

framework for developing regulations, starting with quickly promulgating 

interim regulations that would be subject to future revision as national 

primary drinking water regulations. In addition, EPA was to arrange for a 

study by the National Academies2

 to assess the health effects of 

contaminants in drinking water and to develop proposals for maximum 

contaminant level goals3

—levels at which there are no known or 

anticipated adverse human health effects—for those contaminants that 

may cause adverse health effects. Finally, on the basis of the National 

Academies’ study, EPA was to propose and promulgate maximum 

contaminant level goals and enforceable maximum contaminant levels that 

were to be set as close as feasible to the goals for the contaminants that 

EPA determined may have adverse health effects. 

 

1

EPA, Technical and Economic Capacity of States and Public Water Systems to 

Implement Drinking Water Regulations: Report to Congress, EPA 810/R-93-001 

(Washington, D.C., 1993). 

2

The National Academies consist of four private, nonprofit organizations that advise the 

federal government on scientific and technical matters: the National Academy of Sciences, 

National Academy of Engineering, Institute of Medicine, and National Research Council. 

3

Originally, maximum contaminant level goals were known as “recommended maximum 

contaminant levels.” 

 Safe Drinking Water Act 
Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

Under this original framework, from 1974 until the 1986 amendments to 

the act, EPA established interim regulations for 23 contaminants, most of 

which stemmed from previously established Public Health Service 

standards.4

 EPA did not, however, propose or promulgate national primary 

drinking water regulations, referred to as revised regulations, before 

Congress amended the act in 1986. The National Academies issued reports 

in 1977, 1980, and 1982 addressing drinking water contaminants of 

concern; however, the reports did not provide the required maximum 

contaminant level goals for these contaminants, noting that the 

development of such goals represented a regulatory function more 

appropriate for EPA. In 1982 and 1983, EPA issued two Advanced Notices 

of Proposed Rulemaking based on the National Academies’ reports and 

other scientific sources that together identified 83 contaminants the 

agency planned to evaluate for regulation; the 83 contaminants included 22 

contaminants for which EPA had set interim regulations and 61 additional 

contaminants.5

 EPA requested public comments on the appropriateness of 

regulating the identified contaminants, as well as on the agency’s proposed 

regulatory approach. By 1986, when the act was amended, EPA had not 

completed evaluating the 83 contaminants. 

The 1986 Amendments 

Mandated the Regulation 

of 83 Specific 

Contaminants, Most of 

Which EPA Accomplished, 

but Not within the 

Prescribed Time Frames 

According to a key EPA report, Congress enacted major amendments to 

the Safe Drinking Water Act in 1986 because of continuing concerns about 

drinking water quality and frustration with the pace at which the agency 

was working to develop drinking water regulations.6

 Importantly, the 

amendments mandated that by June 1989 EPA regulate the 83 

contaminants the agency had previously identified. The amendments also 

required EPA to regulate a minimum of 25 additional contaminants every 3 

years after 1989, known as the “25 in 3” requirement. By directing EPA to 

 

4

In 1914, the Public Health Service—now part of the U.S. Department of Health and Human 

Services—set the first federal drinking water standards. These standards addressed only 

bacteriological contaminants capable of causing contagious disease and applied only to 

water systems providing drinking water to interstate carriers, such as ships and trains. The 

Public Health Service revised and expanded its standards in 1925, 1946, and 1962. The 1962 

standards—regulating about 30 contaminants including arsenic, lead, and turbidity—were 

the most comprehensive federal drinking water standards in existence before the Safe 

Drinking Water Act of 1974. 

5

Trihalomethanes, the other contaminant subject to interim regulation, was not on the list 

of 83 because EPA said insufficient time had elapsed since its interim regulation was issued 

to support revision. 

6

EPA 810/R-93-001 

Page 96 GAO-11-254 Safe Drinking Water Act
Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

regulate 83 specific contaminants and requiring a minimum number of 

additional regulations every 3 years, Congress curtailed the broad 

discretion that the 1974 act had initially provided to EPA. 

EPA struggled to promulgate the regulations mandated by the 1986 

amendments within the prescribed time frames. While EPA did not meet 

the 1989 deadline, by 1996 the agency had regulated 77 of the mandated 

contaminants.7

 EPA regulated 6 more of the mandated contaminants by 

2001; EPA has not regulated 2 of the 83—radon and sulfate.8

 Further, by 

1996, EPA had not regulated any additional contaminants as part of the “25 

in 3” requirement but had regulated 1 additional contaminant not 

statutorily required9

 and had initiated regulations for 8 additional 

contaminants, which were finalized in 1998 and 2000. 

In addition to the requirements to regulate certain contaminants, the 1986 

amendments directed EPA to establish a program to test for unregulated 

contaminants. Specifically, pursuant to the amendments, EPA was 

required to promulgate regulations requiring every public water system to 

conduct testing for unregulated contaminants at least once every 5 years.10

The regulations were to list the unregulated contaminants for which public 

water systems may be required to test and include criteria by which states 

could show cause for addition or deletion of contaminants from the list 

based on an assessment of the contaminants’ potential to be found in the 

system. Accordingly, EPA required two cycles of public water system 

testing from 1988 to 1992 and from 1993 to 1997. Through this testing, EPA 

obtained occurrence data—information about where, how frequently, and 

at what concentrations contaminants are found—on 62 unregulated 

 

7

By 1993, the list of 83 had expanded to 85 as a result of the splitting of dichlorobenzene 

and radium into ortho-dichlorobenzene and para-dichlorobenzene and radium 226 and 

radium 228, respectively. In addition, EPA had substituted seven of the compounds on the 

original list. 

8

EPA promulgated national primary drinking water regulations for 5 radionuclides in 2000 

and for arsenic in 2001. EPA considered sulfate as part of regulatory determination Cycle 1 

and determined not to regulate it in 2003. 

9

In 1992, EPA issued a final regulation for hexachlorobenzene, which was not on the 

statutorily mandated list of contaminants, explaining that the contaminant was being 

regulated “because it has been found in drinking water and may cause adverse health 

effects.” See 57 Fed. Reg. 31776, 31783 (1992). 

10The amendments provided the EPA Administrator with discretion to require public water 

systems to test more frequently. 

Page 97 GAO-11-254 Safe Drinking Water Act
Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

contaminants from 40 states in the first round and on 48 unregulated 

contaminants from 35 states in the second round. 

By the early 1990s, EPA, states, and drinking water officials had become 

concerned that continuing the rapid regulatory pace required by the 1986 

amendments might overburden drinking water systems and states and 

hinder effective implementation of the regulations. Consequently, EPA and 

others called for reforms to better enable the agency to focus on 

contaminants of greatest public health concern. 

The 1996 Amendments 

Largely Restored EPA’s 

Discretion in Deciding 

Whether to Regulate 

Specific Contaminants, 

and EPA Selected No 

Contaminants for 

Regulation until February 

2011, When It Determined 

It Will Regulate 

Perchlorate 

In 1996, in the midst of concerns about the number and pace of regulations 

required under the 1986 amendments and the need to better focus limited 

resources on contaminants of greatest public health concern, Congress 

again enacted significant amendments to the Safe Drinking Water Act, 

largely restoring EPA’s regulatory discretion. In the 1996 amendments, 

Congress removed the statutory requirement that EPA regulate 25 new 

contaminants every 3 years; rather, the agency is now required only to 

decide whether or not to regulate at least 5 contaminants every 5 years—

called the regulatory determination process. In making regulatory 

determinations, EPA is to consider contaminants that present “the greatest 

public health concern,” taking into account sensitive populations, among 

other factors. EPA’s regulatory determinations are to be based on three 

broad statutory criteria, all of which must be met for EPA to decide that a 

regulation is needed: 

• the contaminant may have an adverse effect on the health of persons; 

• 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 

• 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. 

While the 1996 amendments largely restored discretion in EPA’s regulatory 

authority, they also specified two other requirements related to 

identification and evaluation of contaminants that present the greatest 

public health concern. First, the act established a new requirement for 

EPA to identify and publish every 5 years a list of unregulated 

contaminants that may pose risks through drinking water, called the 

contaminant candidate list, from which EPA is to select contaminants for 

Page 98 GAO-11-254 Safe Drinking Water Act
Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

regulatory determinations.11 Second, the amendments modified the 

authority EPA had under the 1986 amendments to require public water 

systems to test for unregulated contaminants. Specifically, the 1996 

amendments limited both the number of small public water systems that 

EPA could require to conduct testing and the number of unregulated 

contaminants for which systems must test. While EPA retained its 

authority to require that all large public water systems (those serving more 

than 10,000 people) test for certain unregulated contaminants, it may now 

only require a representative sample of small public water systems (those 

serving 10,000 or fewer people) to test for those contaminants. In addition, 

whereas the 1986 amendments placed no limit on the number of 

unregulated contaminants that EPA could require public water systems to 

test, the 1996 amendments limited EPA to requiring testing for a maximum 

of 30 unregulated contaminants every 5 years. EPA has implemented these 

requirements through its testing program for unregulated contaminants. In 

contrast to the testing previously required by EPA and conducted by 

public water systems pursuant to the 1986 amendments, which relied on 

varying protocols, EPA’s implementation of the testing requirements under 

the 1996 amendments uses standardized testing protocols it has developed 

to help ensure more consistent data quality and comparability. 

Under the 1996 amendments, if EPA decides through its regulatory 

determination process that a drinking water regulation is warranted, the 

agency has 24 months to publish a proposed rule and an additional 18 to 

27 months to issue a final drinking water rule setting an enforceable limit 

for the contaminant—the maximum contaminant level. With regard to 

developing maximum contaminant levels, the 1996 amendments added a 

requirement that EPA conduct a cost-benefit analysis as part of the 

standard-setting process. The amendments further require that in carrying 

out the provisions concerning listing, selecting, and regulating 

contaminants, to the degree that an action is based on science, EPA use 

the best available, peer-reviewed science and data collected by accepted 

or best available methods. EPA is also to ensure that the presentation of 

information on public health effects is comprehensive, informative, and 

understandable. 

In addressing the requirement to make decisions on whether to regulate at 

least 5 contaminants every 5 years, EPA made regulatory determinations 

 

11EPA can also make a regulatory determination for a contaminant that is not on the 

contaminant candidate list but to date has not done so. 

Page 99 GAO-11-254 Safe Drinking Water Act
Appendix II: Information on EPA’s Regulatory 

Actions under the 1974 Safe Drinking Water 

Act 

on 20 contaminants in 2003 and 2008, deciding in each case not to regulate. 

EPA had not decided to regulate any additional contaminants since the 

enactment of the 1996 amendments12 until February 2011 when the EPA 

Administrator announced that the agency made a determination to 

regulate perchlorate as well as a group of carcinogenic volatile organic 

compounds (VOC), which include chemicals such as certain industrial 

solvents. This planned regulatory action stems from EPA’s effort to revise 

the existing drinking water regulations for trichloroethylene (TCE) and 

tetrachloroethylene (PCE), and the Administrator’s plan to address 

contaminants as groups rather than one at a time to enhance drinking 

water protection in a timely and cost-effective manner. According to EPA, 

the agency plans to include 8 regulated contaminants, as well as 8 

unregulated VOCs that are on its current candidate list. 

Regarding the requirement to develop, every 5 years, a contaminant 

candidate list, EPA issued such lists in 1998, 2005, and 2009. Pursuant to 

its authority to require testing of unregulated contaminants, EPA 

mandated one cycle of testing, which was completed in 2005; a second 

cycle is expected to be completed in mid-2011, according to EPA officials. 

 

12Since the 1996 amendments, EPA has finalized national primary drinking water 

regulations that it had previously proposed; these address several previously unregulated 

contaminants. 

Page 100 GAO-11-254 Safe Drinking Water Act
Appendix III: Information on U.S. Public Appendix III: Information on U.S. Public Drinking Water Systems 

Drinking Water Systems 

The following tables provide detailed information from the U.S. 

Environmental Protection Agency (EPA) on public drinking water systems 

in the United States. EPA’s Office of Water Web site defines three types of 

public water systems: 

• Community Water System: a public water system that supplies water to 

the same population year-round. 

• Non-Transient Non-Community Water System: a public water system 

that regularly supplies water to at least 25 of the same people at least 6 

months per year, but not year-round. Some examples are schools, 

factories, office buildings, and hospitals that have their own water 

systems. 

• Transient Non-Community Water System: a public water system that 

provides water in a place such as a gas station or campground where 

people do not remain for long periods of time and is open at least 60 

days a year. 

Table 6 provides information on the number of systems and population 

served, including percentages, by system type and size. Table 7 provides 

information on the number of systems and population served, including 

percentages, by system type and source water. 

Page 101 GAO-11-254 Safe Drinking Water Act 
Appendix III: Information on U.S. Public 

Drinking Water Systems 

Table 6: U.S. Public Drinking Water Systems by Size 

Category of system 

Number of 

systems

Percentage of 

systems

Population 

served 

Percentage of 

population served

Community water systems 

Very small systemsa 28,804 56 4,820,949 2

Small systemsb 13,820 27 19,806,741 7

Medium systemsc4,871 9 28,402,697 10

Large systemsd3,746 7 106,856,965 36

Very large systemse410 1 134,452,529 46

Total 51,651 100 294,339,881 100

Non-transient non-community water systems 

Very small systems 15,619 85 2,195,162 35

Small systems 2,625 14 2,704,116 43

Medium systems 132 1 699,947 11

Large systems 18 <1 440,980 7

Very large systems 1 <1 203,000 3

Total 18,395 100 6,243,205 100

Transient non-community water systems 

Very small systems 80,703 97 7,147,163 54

Small systems 2,681 3 2,598,895 20

Medium systems 87 <1 471,533 4

Large systems 11 <1 360,715 3

Very large systems 2 <1 2,725,000 20

Total 83,484 100 13,303,306 100

All public water systems 

Very small systems 125,126 82 N/Af N/Af

Small systems 19,126 12 N/Af N/Af

Medium systems 5,090 3 N/AfN/Af

Large systems 3,775 2 N/AfN/Af

Very large systems 413 >1 N/AfN/Af

Total 153,530 100 N/AfN/Af

Source: EPA. 

a

Very small water systems serve 25–500 people. 

b

Small water systems serve 501–3,300 people. 

c

Medium water systems serve 3,301–10,000 people. 

d

Large water systems serve 10,001–100,000 people. 

e

Very large water systems serve more than 100,000 people. 

f

Populations are not summed because some people are served by multiple systems and counted 

more than once. 

Page 102 GAO-11-254 Safe Drinking Water Act
Appendix III: Information on U.S. Public 

Drinking Water Systems 

Table 7: U.S. Public Drinking Water Systems by Source Water 

Category of system Number of systems Percentage of systems Population served

Percentage

of population

Community water systems 

Groundwatera40,025 78 88,032,021 30

Surface waterb11,617 22 206,264,490 70

Total 51,642 100 294,296,511 100

Non-transient non-community water systems 

Groundwater 17,688 96 5,415,937 87

Surface water 702 4 820,476 13

Total 18,390 100 6,236,413 100

Transient non-community water systems 

Groundwater 81,492 98 10,754,201 81

Surface water 1,978 2 2,548,200 19

Total 83,470 100 13,302,401 100

All categories of systems 

Groundwater 139,205 91 N/AcN/Ac

Surface water 14,297 9 N/AcN/Ac

Total 153,502 100 N/Ac N/Ac

Source: EPA. 

a

Groundwater: Groundwater comes from natural underground formations, often consisting of sand or 

gravel, that contain water. These formations are called aquifers. 

b

Surface water: Surface water sources include lakes, streams, rivers, and reservoirs. Groundwater 

sources under the direct influence of surface water are also included in this category. 

c

Populations are not summed because some people are served by multiple systems and counted 

more than once. 

Page 103 GAO-11-254 Safe Drinking Water Act
A

Develop 

Water Contaminants Be

Reg

ppendix IV: Calculations EPA Uses to 

Health Reference Levels for Drinking

ing Considered for 

ulation 

Page 104 GAO-11-254 

Appendix IV: Calculations EPA Uses to 

Develop Health Reference Levels for Drinking 

Water Contaminants Being Considered for 

Regulation 

This appendix provides information on the method EPA generally has 

used to compute the health reference level for drinking water 

contaminants that are carcinogenic and the method it uses for 

contaminants with noncarcinogenic adverse health effects, such as 

neurological disorders. 

Figure 1: Health Reference Level Equation for Contaminants with Carcinogenic 

Health Effects 

(Riska x body weightb)

(Slope factorc x drinking 

water intaked)

Health reference 

level 

= =

equivalent to one-in-a-million (10-6) 

cancer risk

Concentration in drinking water 

Source: EPA.

a

Expression of increased cancer risk from a lifetime of exposure: 1 person in a million = 10-6 = 

0.000001. 

b

Adult body weight, assumed to be 70 kilograms. 

c

Slope factors result from EPA modeling of linear low-dose extrapolations. A slope factor is an upper 

bound, approximating a 95 percent confidence limit, on the increased cancer risk from a lifetime 

exposure to an agent by ingestion. This estimate is usually expressed in units of proportion (of a 

population) affected per milligram of substance per kilogram of body weight per day (mg/kg/day). 

d

Amount of water consumed by an adult per day, assumed to be 2 liters. 

Figure 2: Health Reference Level Equation for Contaminants with Noncarcinogenic 

Adverse Health Effects 

Relative source 

contributione

Health reference 

level 

 =X

Drinking water equivalent leveld

(Reference dosea x body weightb)

drinking water intakec 

Source: EPA.

a

An estimate of a daily exposure to the human population (including sensitive subpopulations) that is 

likely to be without an appreciable risk of deleterious effects during a lifetime, generally expressed in 

units of milligrams per kilogram of body weight per day (mg/kg/day). 

b

Adult body weight, assumed to be 70 kilograms. 

c

Amount of water consumed by an adult per day, assumed to be 2 liters. 

d

Estimated exposure to a contaminant that is assumed to be protective for noncarcinogenic health 

effects during a lifetime of exposure, generally expressed in units of milligrams per liter (mg/L). It is 

calculated by multiplying the reference dose times body weight and dividing that result by drinking 

water intake. 

e

The estimate of the exposure to a contaminant from drinking water relative to overall exposure from 

other sources (e.g., food and ambient air), expressed as a percentage. 

 Safe Drinking Water Act 
Appendix V: Calculations of Relative Source 

Contribution Using the Percentage and Appendix V: Calculations of Relative Source Subtraction Methods 

Contribution Using the Percentage and 

Subtraction Methods 

As discussed in the report, to determine a health reference level for a 

contaminant with adverse noncarcinogenic health effects for use in its 

regulatory determinations, EPA typically applies a relative source 

contribution factor—the allocation of the oral exposure to the 

contaminant from drinking water alone—in its equation (see fig. 3). 

Figure 3: Health Reference Level Equation 

Relative source 

contributione

Health reference 

level 

 =X

Drinking water equivalent leveld

(Reference dosea x body weightb)

drinking water intakec 

Source: EPA.

a

An estimate of a daily exposure to the human population (including sensitive subpopulations) that is 

likely to be without an appreciable risk of deleterious effects during a lifetime, generally expressed in 

units of milligrams per kilogram of body weight per day (mg/kg/day). 

b

Adult body weight, assumed to be 70 kilograms. 

c

Amount of water consumed by an adult per day, assumed to be 2 liters. 

d

Estimated exposure to a contaminant that is assumed to be protective for noncarcinogenic health 

effects during a lifetime of exposure, generally expressed in units of milligrams per liter (mg/L). It is 

calculated by multiplying the reference dose times body weight and dividing that result by drinking 

water intake. 

e

The estimate of the exposure to a contaminant from drinking water relative to overall exposure from 

other sources (e.g., food and ambient air), expressed as a percentage. 

According to EPA policy, if the agency determines that it has adequate 

data to estimate the relative source contribution—instead of applying a 

default assumption—to calculate a health reference level, it may use one 

of two methods—the percentage or subtraction method.1

 Tables 9 and 10 

illustrate the differences in the health reference levels that result when 

each of these methods is applied using the hypothetical exposure data and 

reference dose in table 8. 

 

1

According to EPA’s guidance document, the subtraction method can only be used when 

other exposure standards (criteria), such as Clean Air Act or Clean Water Act standards, 

are not relevant. In addition, adequate data to characterize the likelihood of exposure to 

relevant sources is required. See EPA, Office of Science Technology and Office of Water, 

Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human 

Health, EPA-822-B-00-004 (Washington, D.C., October 2000). 

Page 105 GAO-11-254 Safe Drinking Water Act
Appendix V: Calculations of Relative Source 

Contribution Using the Percentage and 

Subtraction Methods 

Table 8: Hypothetical Data Used in Examples 

Estimated exposure from water (EW) = 0.15 μg/kg/day 

Estimated exposure from food (EF) = 0.15 μg/kg/day 

Total estimated exposure from 

water and food (EW+EF=ETOT) = 

0.3 μg/kg/day 

Reference dose (RfD) = 0.5 μg/kg/day 

Source: GAO. 

The percentage method is a comparison of multiple sources of exposure 

with one another to estimate their relative contribution to the total. It is 

intended to reflect the exposure to a contaminant from drinking water 

relative to other sources of exposure, as well as the likelihood for everchanging levels in each of the sources of exposure (due to ever-changing 

sources of emissions and discharges). Importantly, it is based on an 

assumption that there may be enough relative variability in exposure such 

that an apportionment (relating that percentage to the RfD) is a reasonable 

way of accounting for the uncertainty regarding that variability. Using the 

percentage method, the relative source contribution is determined by 

(1) calculating the relative proportion of exposure from water as a percent 

of the total observed exposure and then (2) applying that percentage as 

the relative source contribution in the health reference level equation. See 

example in table 9. 

Example 1: 

Percentage Method 

Table 9: Example of How the Relative Source Contribution Is Determined Using the Percentage Method 

Step 1: Calculate the relative proportion of exposure from water as a percent of the total observed exposure. 

Estimated exposure from water (EW) ÷ Total estimated exposure (ETOT) = Relative source contribution 

0.15 μg/kg/day ÷ 0.3 μg/kg/day = 0.5 (50 percent) 

Step 2: Apply relative source contribution percentage in health reference level equation. 

Health reference level 

(parts per billion) = 

[(Reference dose 

(μg/kg/day) x 

Body weight) 

(kilograms) ÷ 

Drinking water intake] 

(liters per day) x 

Relative source 

contribution 

(expressed as a 

percentage) 

8.8 = [(0.5 x 70) ÷ 2] x 50 

Source: GAO. 

Page 106 GAO-11-254 Safe Drinking Water Act
Appendix V: Calculations of Relative Source 

Contribution Using the Percentage and 

Subtraction Methods 

The subtraction method allocates the entire reference dose to the known 

sources of exposure by subtracting the known nontarget sources of 

exposure and allocating the remainder of the reference dose to the 

target—in this case, drinking water—even in cases (such as this example) 

where the total estimated exposure is less than the reference dose. This 

method has the effect of removing any cushion between the existing 

exposure levels and the reference dose. Therefore, using this method may 

allow drinking water exposures in excess of levels currently found in 

public water systems. To calculate the relative source contribution using 

the subtraction method: (1) subtract all non-drinking-water exposures 

from the reference dose to determine the amount of the reference dose 

“available” for exposure through drinking water, (2) determine what 

percentage of the reference dose that remainder represents, and (3) apply 

the resulting percentage as the relative source contribution in the health 

reference level equation. See example in table 10. 

Example 2: 

Subtraction Method 

Table 10: Example of How the Relative Source Contribution Is Determined Using the Subtraction Method 

Step 1: Subtract nonwater exposures from reference dose. 

Reference dose (RfD) – Estimated exposure from food (EF) = Remainder of reference dose “available” for water 

0.5 μg/kg/day – 0.15 μg/kg/day = 0.35 μg/kg/day 

Step 2: Determine the amount of the reference dose “available” for exposure from drinking water by dividing the result from 

Step 1 by the reference dose and multiplying by 100 to convert to a percentage. 

Remainder “available” for water ÷ Reference dose (RfD) = Relative source contribution 

0.35 μg/kg/day ÷ 0.5 μg/kg/day = 0.7 (70 percent) 

Step 3: Apply the relative source contribution percentage in the health reference level equation. 

Health reference level 

(parts per billion) = 

[(Reference dose 

(μg/kg/day) x 

Body weight) 

(kilograms) ÷ 

Drinking water intake] 

(liters per day) x 

Relative source 

contribution 

(expressed as a 

percentage) 

12.3 = [(0.5 x 70) ÷ 2] x 70 

Source: GAO. 

Page 107 GAO-11-254 Safe Drinking Water Act
upplemental Information on

PA’s 2003 Regulatory Determination for 

nese and Its 2008 Determination for 

Page 108 GAO-11-254 

Appendix VI: S

E

Manga

Boron 

Appendix VI: Supplemental Information on EPA’s 

2003 Regulatory Determination for Manganese and 

Its 2008 Determination for Boron 

This appendix provides supplemental information on the agency’s use of 

outdated and limited occurrence data and inconsistent consideration and 

presentation of potential health risks in its regulatory determination 

notices and support documents for manganese and boron. 

EPA’s 2003 Regulatory 

Determination to Not 

Regulate Manganese 

A ubiquitous, naturally occurring element found in certain rocks and 

sediments, manganese is also produced and used in a wide variety of 

industrial processes and consumer products, resulting in widespread 

manmade releases of manganese and manganese compounds into the 

environment.1

 EPA made its decision in 2003 to not regulate manganese 

using data on the occurrence and likely occurrence of manganese in 

drinking water that the agency acknowledged was outdated and limited. 

Specifically, EPA relied primarily on older (1980s), but nationally 

representative, data from its National Inorganic and Radionuclide Survey 

to assess manganese occurrence in public water systems fed by 

groundwater sources.2

 In its regulatory determination support document 

for manganese, EPA reported that 3.2 percent of groundwater public 

drinking water systems exceeded EPA’s health reference level for 

manganese—affecting an estimated 2.3 million people. In addition, EPA 

reported that 4.6 percent of groundwater systems exceeded one-half the 

health reference level—affecting an estimated 3.9 million people. In its 

Health Effects Support Document for Manganese, EPA stated that it 

“should be noted that these estimates are based on very limited and 

outdated data. The possibility exists that the number of people served by 

groundwater with manganese levels that are above the health reference 

level could be higher than these estimates; however, the data are lacking at 

Occurrence Data 

 1

Manganese ore is smelted to produce an alloy used to improve the stiffness, hardness, and 

strength of steel; a number of manganese compounds are used in such products and 

applications as unleaded gasoline, water and wastewater treatment, matches, dry-cell 

batteries, fireworks, fertilizer, fungicides, varnish, and livestock food supplements. 

2

According to EPA, about 30 percent of community water system customers are served by 

groundwater systems. 

 Safe Drinking Water Act 
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

this time to develop a more timely assessment.”3 Moreover, the use of 

older data is problematic because of significant increases in releases of 

manganese and manganese compounds to the environment; according to 

EPA’s 2003 regulatory determination support documentation, the 

increases since the 1990s have been dramatic in some years. Despite EPA’s 

acknowledgement of significant deficiencies in the underlying data, and its 

decision not to update these data through its testing program, EPA’s notice 

did not explain why it nonetheless proceeded with a regulatory 

determination for manganese. Further, as discussed in the body of this 

report, EPA has not issued guidance on what threshold levels of 

occurrence would satisfy the second statutory criterion for a decision to 

regulate. In this case, EPA decided that levels of manganese in excess of 

the health reference level in at least 3.2 percent of groundwater drinking 

water systems did not warrant regulation.4

Moreover, EPA did not have national data on manganese occurrence in 

public water systems that use surface water—according to EPA, surface 

water systems serve about 70 percent of community water system 

customers. While EPA limited its occurrence estimates to groundwater 

systems in its 2003 manganese regulatory determination notice, its support 

document for manganese discusses some USGS data on ground and 

surface source water and manganese occurrence data from five states, but 

in a manner that does not explain the determination in light of this 

 

3

EPA stated in its regulatory determination support document providing the nationally 

ted 

er 

In 1993, in discussing strategies the agency might use under the 1986 statutory framework 

to select 

extrapolated occurrence estimates for manganese that these estimates were not presen

in the regulatory determination notice because national extrapolations for some of the 

contaminants considered for regulation “can be problematic” and that the National 

Inorganic and Radionuclide Survey data for manganese only represented groundwat

public water systems. Thus, instead of reporting the nationally extrapolated occurrence

estimates, EPA presented in the notice the unweighted sampling data for groundwater 

public water systems, highlighting exposure to 39,000 people. 

4

in determining whether to regulate chemicals, EPA stated that if nationally representative 

data showed stable occurrence levels at around 1/10th the maximum contaminant level 

goal with no indication of occurrence at higher levels, regulation may not be warranted. 

EPA, Technical and Economic Capacity of States and Public Water Systems to 

Implement Drinking Water Regulations, Report to Congress, EPA 810-R-93-001 

(Washington, D.C., 1993). EPA identified strategies for a new proposed approach 

contaminants for regulation as EPA had nearly completed regulating the contaminants 

mandated under the 1986 amendments and was moving toward regulating contaminants

selected by EPA. 

Page 109 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

potentially inconsistent data.5, 6 For example, the agency characterized 

drinking water occurrence data on manganese from five states as showing 

“substantial low-level manganese occurrence,” but did not reconcile this 

assessment with the occurrence data it presented for these five states that 

show the following percentages of state populations served by public 

water systems with levels of manganese that exceed the health reference 

level: 2.4 percent, 3.2 percent, 9.1 percent, 14.7 percent, and 27.2 percent.7

In addition, EPA described USGS detections in excess of its health 

reference level at groundwater sites (14 percent of samples) and surface 

water sites (10 percent of samples) as “modest” occurrence and “relatively 

low” occurrence, respectively. 

Further, EPA did not include information about the large number of 

Superfund sites known to be contaminated with manganese in its 

regulatory determination documents. According to ATSDR, manganese 

has been found in at least 51 percent of EPA’s 1,699 Superfund (National 

Priorities List) sites, which include some of the most seriously 

contaminated hazardous waste sites in the nation.8

 ATSDR’s Public Health 

Statement for Manganese notes that this information is important because 

the manganese at these sites may be harmful to the public. Moreover, 

EPA’s regulatory determination documents do not mention that DOD’s 

emerging contaminants program has been monitoring manganese. Under 

 

5

The USGS National Water-Quality Assessment program was initiated in 1991 as a longterm study of 59 significant watersheds and aquifers representing approximately two-thirds 

of the overall water use in the United States in a similar proportion to the population 

served by public water systems. In its regulatory determination documents, EPA reported 

the manganese results for 36 of the 59 watersheds and aquifers tested in the 1990s that had 

undergone USGS quality assurance checks. 

6

USGS detections in source water exceeding the human health benchmark indicate levels 

of the contaminant that are a potential human health concern; however, these detections 

do not necessarily indicate a contaminant would be found in finished drinking water at that 

level because of the possibility of blending with other source water or treatment prior to 

consumption. 

7

The five states, listed in order of the size of populations served by public water systems 

with manganese levels in excess of the health reference level, are Alabama, Oregon, New 

Jersey, Illinois, and California. 

8

Superfund sites on EPA’s National Priorities List represent those the agency has identified 

as among the most seriously contaminated sites, posing relatively high risks to human 

health or the environment for releases of hazardous substances. ATSDR states that 

although the total number of sites evaluated for manganese is not known, the possibility 

exists that the number of sites at which manganese is found may increase in the future as 

more sites are evaluated. ATSDR is the lead agency for conducting health assessments for 

Superfund sites and Resource Conservation and Recovery Act facilities. 

Page 110 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

this program, a DOD team on “materials of evolving regulatory interest” is 

focusing on a number of contaminants, including manganese, to develop 

actions to respond to such potential factors as health impacts, cleanup 

costs, compliance costs, readiness impacts, and facilities life-cycle costs.9

Relying on the third statutory criterion of presenting a meaningful 

opportunity for health risk reduction for this determination, EPA 

concluded that because manganese is generally not considered to be very 

toxic when ingested with the diet (i.e., food), and since drinking water 

accounts for a relatively small proportion of manganese intake, regulation 

would not likely present a meaningful opportunity for health risk 

reduction for persons served by public drinking water systems. However, 

EPA does not explain how this determination relates to information EPA 

had indicating that manganese in drinking water could have significant 

adverse health effects on sensitive populations, including children. 

Specifically, EPA’s 1996 IRIS assessment identified children, pregnant 

women, elderly people, iron- or calcium-deficient individuals, and 

individuals with liver impairment as potentially sensitive populations. 

Individuals in these populations may have an increased potential for 

excessive amounts of manganese in the body because of increased 

absorption or altered clearance mechanisms. 

Health Effects Data 

EPA’s 1996 IRIS assessment notes that differences in absorption and 

clearance mechanisms may be of particular importance for those exposed 

to manganese by multiple routes. Regarding oral exposure, the IRIS 

assessment states that there is some evidence that infants absorb more 

manganese from the gastrointestinal tract than adults, that newborns are 

less able to excrete absorbed manganese, and that the absorbed 

manganese more easily passes the blood-brain barrier in infants.10 EPA’s 

IRIS assessment also states that there is a concern for infants fed formula 

because it typically has a much higher concentration of manganese than 

human milk, and if powdered formula is made with drinking water, any 

 

9

Manganese is on DOD’s emerging contaminants watch list, along with other contaminants 

including dioxin, lead, cadmium, and cobalt. 

10According to the National Academies, the lack of the development of the blood-brain 

barrier in infants and children results in higher uptake of manganese by the brain. EPA’s 

IRIS assessment explains that when manganese is transported through the blood stream 

directly to the brain, it bypasses the liver and the opportunity for first-pass hepatic 

clearance, increasing manganese toxicity. 

Page 111 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

manganese in the water would represent an additional source of intake.11

The IRIS assessment states that these considerations concerning increased 

exposure in an important population group “warrant caution until more 

definitive data are available,” noting in addition the likelihood that any 

adverse neurological effects of manganese are likely to be irreversible and 

not manifested for many years after exposure. 

The 1996 IRIS assessment cites scientific literature up to 1994; since then, 

additional studies have identified health risks for children, particularly 

infants, from manganese-contaminated water. For example, a recent risk 

assessment journal article on the health risks to children from exposure to 

manganese in drinking water highlighted four epidemiological studies and 

two case reports published between 1994 and 2007 that demonstrate a 

plausible association between elevated manganese concentrations in 

drinking water and altered neurological function in children.12 Effects that 

were identified include reduced intellectual function and lower 

performance scores on behavioral tests.13 In addition, a 2006 report by the 

National Academies, Spacecraft Water Exposure Guidelines for Selected 

 

11In developing its oral reference dose for manganese, the Office of Water used the 

modifying factor of three that the IRIS assessment recommended for assessing exposure 

from drinking water to address these concerns associated with infants as well as to address 

the following risk issues: (1) individuals drinking water on an empty stomach, such as early 

in the morning, absorb more manganese; and (2) adverse health effects associated with a 

lifetime consumption of drinking water containing about 2 milligrams of manganese per 

liter were reported in a 1989 study. Use of the modifying factor had the effect of changing 

the reference dose from 0.14 milligrams per kilogram per body weight to 0.047 milligrams 

per kilogram per body weight. 

12M. T. Brown and B. Foos, “Assessing Children's Exposures and Risks to Drinking Water 

Contaminants: A Manganese Case Study,” Human and Ecological Risk Assessment: An 

International Journal, vol. 15, no. 5 (2009). 

13Similarly, ATSDR’s toxicological profile on manganese states that many reports indicate 

that oral exposure to manganese, especially from contaminated water sources, can 

produce significant health effects that have been most prominently observed in children 

and are similar to those observed from inhalation exposure. (Regarding inhalation 

exposure, ATSDR states that inhaled manganese is often transported directly to the brain 

before it is metabolized by the liver and can lead to such adverse neurological effects as 

mental disorders and manganism, whose symptoms include tremors, difficulty walking, and 

facial muscle spasms.) According to ATSDR, while an actual threshold at which manganese 

exposure produces neurological effects in humans has not been established, children 

consuming the same concentration of manganese in water as adults are ultimately exposed 

to a higher milligram-per-kilogram body weight ratio of manganese because of their lower 

body weight, higher consumption volume, and greater retention of manganese; children are 

also potentially more sensitive to manganese toxicity than adults. ATSDR concluded that, 

collectively, studies suggest that ingestion of water or food contaminated with manganese 

may result in adverse neurological effects. 

Page 112 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

Contaminants, stated that a survey of the literature on manganese toxicity 

strongly indicates, among other things, “hypersusceptibility” of infants and 

newborns and the elderly. Moreover, on the basis of information obtained 

from literature reviews conducted between 2001 and 2003 on chemicals 

with existing assessments to determine if new scientific information might 

change a current IRIS assessment, the IRIS program decided that 

manganese should be reassessed.14 Studies continue to identify children as 

particularly sensitive to manganese contamination in drinking water.15

Although the IRIS assessment had identified newborns as a potential 

sensitive subpopulation that warranted caution until more definitive data 

became available—and new data continued to identify concerns for 

infants and children—the Office of Water did not develop a specific health 

reference level for infants or children and did not make other adjustments 

to its health reference level to assess the sensitivity of children to 

manganese in drinking water. For example, Office of Water officials told 

us that one way it can assess sensitive populations is by adjusting the 

health reference level downward to account for increased sensitivity or by 

developing a separate risk assessment for the sensitive population. 

However, the Office of Water derived its drinking water health reference 

level—0.3 milligrams of manganese per liter of water—from the IRIS 

reference dose without any additional adjustment for sensitive 

populations beyond those factored into the reference dose. Specifically, 

the health reference level was calculated using EPA’s 1996 reference dose16

in its standard formula to develop a drinking water equivalent level, using 

the average weight and daily water consumption of a healthy adult.17

 

14While the IRIS program initiated an update assessment for manganese in 2008, it has been 

temporarily suspended as the program focuses on assessments it has considered to be of 

high priority. As of May 2011, manganese is not reported in IRIS Track as an ongoing 

assessment. 

15A 2010 study reported that low-level, chronic exposure to manganese from drinking water 

is associated with significant intellectual impairments in children. Its authors support 

revisiting the national and international guidelines for safe manganese in water, such as 

EPA’s health advisory of 0.3 milligrams per liter. M. F. Bouchard et al., “Intellectual 

Impairment in School-Age Children Exposed to Manganese from Drinking Water,” 

Environmental Health Perspectives (2010). 

16The Office of Water applied the modifying factor the 1996 IRIS assessment recommended 

for assessing exposure from drinking water. See footnote 11. 

17EPA has developed health assessment levels specifically for children routinely for many 

years for drinking water health advisories and has also, on occasion, developed them in 

assessing risks to children for primary drinking water regulations for other contaminants. 

Page 113 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

Moreover, EPA discussed the health risks to infants in an inconsistent and, 

at times, incomplete manner in its regulatory determination documents. 

For example, EPA’s 2003 regulatory determination support document for 

manganese states unequivocally that there are “no data to indicate 

children are more sensitive to manganese than adults.” However, EPA’s 

2003 health effects support document for manganese discusses studies 

that identify an association between exposure to manganese in drinking 

water and learning disabilities in children and concludes that additional 

studies are needed to investigate the possibility that children are more 

sensitive than adults. In addition, while EPA’s regulatory determination 

support document for manganese notes that infants and newborns may be 

potentially susceptible to manganese toxicity, this key document does not 

disclose that newborns may be exposed to high levels of manganese from 

infant formula or that these high levels of manganese in formula can be 

magnified when it is reconstituted with manganese-contaminated water. 

The support document contains only the following statement on 

manganese in breast milk and infant formula: “Although the manganese 

content in a soy-based formula is higher than the manganese content in 

human milk, the actual absorption of manganese from the formula may not 

be substantially greater, since soy milk is high in phytate18 and vegetable 

protein.” Importantly, EPA’s health effects support document also 

contains the prior statement but then specifically cites the results of 

several studies that “argue against this possibility”—that is, the cited 

studies contradict the hypothesis presented in the regulatory 

determination support document. Further, while EPA’s health effects 

document discloses that infant formula typically contains a much higher 

concentration of manganese than human or cows’ milk and that powdered 

formula reconstituted with drinking water represents an additional source 

of manganese intake for a potentially sensitive population, its regulatory 

determination support document omits this important exposure 

information. 

Overall, EPA presented the health risks of exposure to manganese in a 

manner that downplayed the potential risks in part by highlighting a 

concern about manganese deficiency. Specifically, EPA states multiple 

times in its regulatory determination and support documents that because 

manganese is an essential nutrient, concern over potentially toxic effects 

 

18Phytate, also called phytic acid, is the principal storage form of phosphorus in many 

plants, especially in wheat, rice, rye, barley, and beans. Phosphorus in this form is generally 

not bioavailable to humans because humans lack the digestive enzyme, phytase, required to 

separate phosphorus from the phytate molecule. 

Page 114 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

from high oral exposure must be balanced against concern for adverse 

effects from manganese deficiency. However, according to a National 

Academies’ report,19 there is no recommended daily allowance for 

manganese because it is available in numerous food sources to various 

degrees and “no natural deficiency of manganese in humans has been 

encountered.” Moreover, in the context of deciding whether manganese in 

drinking water should be regulated, EPA’s concern about the potential for 

adverse effects from manganese deficiency seems to be inconsistent with 

the fact that EPA already has established a secondary drinking water 

standard for manganese that addresses aesthetic problems—largely 

discoloration—of 0.05 milligrams per liter.20 This recommended standard is 

6 times more stringent than the health reference level of 0.3 milligrams per 

liter that EPA used in its regulatory determination. Thus, the basis for 

EPA’s concern about manganese deficiency stemming from a possible 

health-based national primary drinking water standard is not clear. 

Although EPA concluded that dietary intake of manganese was not very 

toxic, the agency determined that there was a need to issue a health 

advisory in conjunction with the regulatory determination on manganese. 

According to the advisory, it is to provide “guidance to communities that 

may be exposed to drinking water contaminated with high manganese 

(Mn) concentrations” and also “provides guidance on the concentrations 

below which potential health and organoleptic21 problems would unlikely 

occur.” The advisory provides a 10-day health advisory of 1 milligram of 

manganese per liter of water for acute exposure for children. However, 

EPA recommends that manganese exposure for infants younger than 6 

months should be limited to the agency’s lifetime (chronic) health 

advisory level of 0.3 milligrams per liter of water—even for acute 

exposure—“because of the concerns for differences in manganese content 

in human milk and formula and the possibility of a higher absorption and 

lower excretion in young infants.” As discussed, manganese levels in 

excess of the health reference level of 0.3 milligrams per liter of water 

have been detected in a number of public water systems. However, EPA’s 

health advisories do not provide information on which public water 

 

19National Academies, Spacecraft Water Exposure Guidelines for Selected Contaminants

(Washington, D.C., 2006). 

20In addition to setting health-based primary drinking water standards, under the Safe 

Drinking Water Act, EPA establishes secondary drinking water standards to address 

aesthetic problems, such as taste or odor. These standards are non-enforceable guidelines. 

21This term refers to aesthetic problems, such as taste, color, or odor. 

Page 115 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

systems may contain levels in excess of these standards. While some 

systems may test manganese voluntarily or to meet state requirements, 

current manganese levels may not be available for many systems. The 

potential lack of monitoring data for a particular system, along with the 

lack of public notification of health advisories by EPA’s Office of Water, 

may make it difficult for consumers to become aware of any related risks. 

EPA’s 2008 Regulatory 

Determination to Not 

Regulate Boron 

Boron is a naturally occurring element, and both naturally occurring and 

manmade borate compounds are used in many products, such as glass, 

ceramics, soaps, fire retardants, pesticides, cosmetics, photographic 

materials, and high-energy fuels. According to EPA’s regulatory 

determination documents, the potential adverse health affects that may be 

associated with exposure to boron in drinking water include adverse 

effects on male reproductive systems.22

Occurrence Data 

As it had for manganese 5 years year earlier, for its 2008 regulatory 

determination for boron, EPA used nationally representative occurrence 

data from its National Inorganic and Radionuclide Survey (NIRS) of 

drinking water systems fed by groundwater sources—data that EPA 

described in 2003 as “outdated and limited.”23 Importantly, EPA had limited 

data on occurrence in systems that use surface water, which serve about 

70 percent of the population served by community water systems. That is, 

EPA’s conclusions on the occurrence of boron in public water systems 

that use surface water relied on a 2004 voluntary, industry-sponsored 

survey by the American Water Works Research Foundation that provided 

data on 113 samples of untreated surface water analyzed for boron.24, 25

 

22In its regulatory determination notice and support document, EPA stated that the primary 

adverse effects seen in animals after chronic exposure to low doses of boron generally 

involve the testes and developing fetus. EPA also states that reproductive effects in males 

were noted in the chronic and subchronic animal studies discussed in the notice. 

23As mentioned earlier, EPA data show that about 30 percent of public water system 

customers are served by groundwater systems. 

24The American Water Works Research Foundation is now known as the Water Research 

Foundation. 

Page 116 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

While none of the 113 samples had levels of boron in excess of one-half of 

EPA’s health reference level, EPA acknowledged the survey was not 

statistically representative. As a result, these data may not correctly 

represent the extent or magnitude of boron in surface water. Along these 

lines, we note that while the 189 utilities participating in the study were 

located in 41 states, 41 percent of them were located in 3 states—

California, Illinois, and Indiana. Also, unlike EPA’s testing program for 

unregulated contaminants, which requires all public water systems serving 

more than 10,000 people and a randomly selected sample of public water 

systems serving 10,000 or fewer people to conduct either two or four tests 

during a period of 12 consecutive months, water utilities responding to 

this survey conducted one test per source. According to EPA’s unregulated 

contaminants testing program documentation, multiple samples during a 

year are necessary to capture the annual variability in contaminant 

occurrence to approach an adequate characterization of potential 

exposure. Further, results were not provided for 16 percent of the 

samples, and data were not provided on the number of public water 

systems associated with the 113 tests. 

In addition, EPA did not address whether and how anthropogenic 

(manmade) releases of boron might affect the uncertainty associated with 

the surface water occurrence data. For example, while EPA’s regulatory 

determination acknowledges that the manufacture and use of products 

containing boron compounds add to the release of boron into the 

environment, and presents information about environmental releases of 

boron identified in EPA’s Toxics Release Inventory, EPA does not explain 

in its regulatory determination documents whether these manmade 

releases are relevant to its regulatory determination. Further, EPA’s 

regulatory determination support document for boron does not 

acknowledge that, according to ATSDR, boron contamination is present at 

10 percent or more of the nation’s current or former Superfund sites, some 

of which could be contaminating actual or potential drinking water sites.26

ATSDR data also show that the average surface water boron concentration 

in the United States is lower than EPA’s health reference level—0.1 

milligrams per liter and 1.4 milligrams per liter, respectively—but that 

 

25In this study, the foundation reported that with few exceptions, boron levels in untreated 

surface water represent a reasonable estimate of boron levels in treated water provided to 

customers of public water systems. 

26ATSDR also stated that although the total number of National Priorities List sites 

evaluated for this substance is not known, the possibility exists that the number of sites at 

which boron is found may increase in the future as more sites are evaluated. 

Page 117 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

surface water concentrations vary greatly depending on boron content of 

local geologic formations as well as manmade sources. 

On the basis of the dated but nationally representative groundwater data, 

EPA reported in support documents that approximately 1.7 percent of 

groundwater public water systems serving about 400,000 people had 

detections of boron above the health reference level, and approximately 

4.3 percent of water systems serving about 2.5 million people had 

detections in excess of one-half the health reference level. In its regulatory 

determination notice, however, EPA reported the unweighted sampling 

data in NIRS, identifying exposure to about 6,400 people above the health 

reference level and about 42,700 above one-half the health reference level. 

Considering the data on groundwater sources and the industry research 

foundation’s finding that boron was not detected above one-half the 

reference level in surface water, EPA provided the following rationale for 

not regulating boron: 

“Taking this surface water information into account, the agency believes the overall 

occurrence and exposure from both surface and groundwater systems together is 

likely to be lower than the values observed for the NIRS groundwater data. Because 

boron is not likely to occur at levels of concern when considering both surface and 

groundwater systems, the agency believes that a national public drinking water 

regulation does not present a meaningful opportunity for health risk reduction.” 

This rationale appears to downplay the potential health risk to those 

served by systems with groundwater sources and suggests that the agency 

uses a national threshold for occurrence at levels of health concern in 

making its regulatory determinations. Moreover, it is not clear why EPA 

did not take advantage of its testing program to obtain more current and 

complete occurrence data before making its regulatory determination. 

EPA’s presentation of the health risks of exposure to boron in its 

regulatory determination support documents and the health advisory it 

developed concurrent with its regulatory determination differ both in 

terms of the potential for adverse health effects and the levels in drinking 

water identified as generally safe. Regarding the potential health risks, in 

its regulatory support document, EPA stated that animal studies identify 

the developing fetus as potentially sensitive to boron and concluded that 

boron concentrations greater than the health reference level of 1.4 

milligrams of boron per liter of water “might” have an effect on prenatal 

Health Effects Data 

Page 118 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

development.27 In this document, the Office of Water also states that the 

primary adverse effects identified from studies of animals after chronic 

exposure to low doses of boron generally involve the testes and the 

developing fetus. The Office of Water’s May 2008 Drinking Water Health 

Advisory for Boron (published just 2 months before the regulatory 

determination for boron) provides this same information, but states more 

strongly that there is “compelling evidence” to suggest that the “testicular 

morphological effects” reported in studies of animals are applicable to 

children and concluded that exposure to boron between birth and puberty 

may result in adverse cellular effects that would “affect testicular 

function.” In addition, a third related document—EPA’s Summary 

Document from the Health Advisory for Boron and Compounds—

provides an important warning regarding infants’ exposure to boron in 

drinking water that is not included in either EPA’s drinking water advisory 

for boron or its regulatory determination support document. Specifically, 

the summary document states that water containing boron “at levels above 

the HA [health advisory]” should not be used to prepare food or formula 

for infants. EPA does not identify which of the exposure duration health 

advisories it is referring to in this warning.28

Despite considering children to be a sensitive population and EPA’s 

children’s health policy suggesting that assessments for infants and children 

be conducted or—if not conducted, an explanation be provided as to why 

assessments are not warranted—the Office of Water did not include an 

assessment for children exposed to boron at the health reference level as 

part of its regulatory determination. Further, as discussed earlier, during the 

2000s, EPA developed technical guidance that can assist the Office of Water 

in assessing the sensitivity of children to drinking water contaminants. EPA 

officials told us that the Office of Water had not decided how to include the 

Office of Children’s Health Protection guidance in its assessments at the 

time of the regulatory determination on boron. 

In addition, the health reference level that the Office of Water used to assess 

an adult’s risk of daily, chronic exposure to boron in drinking water for its 

 

27The regulatory determination support document also states that individuals with severely 

impaired kidney function might also be sensitive to boron exposure. 

28In its boron health advisory, for a child weighing 10 kilograms, EPA presented a 10-day 

(acute) health advisory level of 3 milligrams of boron per liter of drinking water; a “longerterm” health advisory level for children of 2 milligrams per liter; a “longer-term” health 

advisory level for an adult of 5 milligrams per liter; and a lifetime health advisory level for 

an adult of 5 milligrams per liter. 

Page 119 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

regulatory determination process—1.4 milligrams of boron per liter of 

water—is widely divergent from the level that the office concurrently 

developed for the health advisory it prepared in conjunction with its 

regulatory determination. Specifically, the health advisory’s chronic risk 

level for adults was 5 milligrams of boron per liter of water.29 The 

assessments differ primarily because EPA used the percentage method and 

the standard default assumption in developing the health reference level, 

whereas it used the subtraction method in developing the health advisory. In 

discussing these different assessments with us, EPA officials said the health 

advisory and health effects support document for the regulatory 

determination were “out of sync” because of lengthy administrative 

processes. The officials said new information was identified and included in 

the health advisory that was not available at the time the regulatory 

determination on boron was made. As a basis for using the subtraction 

method for its health advisory, EPA’s advisory cited its 2000 Methodology 

for Deriving Ambient Water Quality Criteria for the Protection of Human 

Health. This document cautions that the subtraction method generally 

results in health exposure levels that are significantly higher than those that 

would be derived using the percentage method. Further, on the basis of the 

exposure data EPA presented in its regulatory determination documents, it 

is not clear that the agency had the adequate exposure data from all sources 

that the guidance specifies is a prerequisite for using the subtraction method 

instead of the more conservative default value. 

Moreover, EPA’s health advisory does not explain why the agency used 

the subtraction method for the advisory at the same time the agency was 

using the percentage method for the regulatory determination. The effect 

of using the subtraction method is significant because EPA’s regulatory 

determination document stated that the highest observed concentration of 

boron in groundwater was approximately 3.3 milligrams per liter—a level 

below the health advisory level of 5 milligrams per liter but above the 

health reference level of 1.4 milligrams. 

Further, because boron is not regulated by EPA, and EPA does not 

currently require public water systems to test for boron, it would be 

difficult for most people to determine how much boron is present in their 

 

29The health reference level of 1.4 milligrams EPA developed for its regulatory 

determination is closer to drinking water standards or guidelines for boron that, according 

to EPA’s Health Advisory, have been set by six states and the World Health Organization 

and that range from 0.6 milligrams to 1 milligram of boron per liter of drinking water than 

to the 5 milligrams per liter EPA developed for the related health advisory. 

Page 120 GAO-11-254 Safe Drinking Water Act
Appendix VI: Supplemental Information on 

EPA’s 2003 Regulatory Determination for 

Manganese and Its 2008 Determination for 

Boron 

drinking water—requisite information for heeding EPA’s warning to not 

use drinking water from some public water systems to prepare infant food 

or formula. Except in the states that have issued drinking water guidelines 

for boron, such as the six identified by EPA, individuals would generally 

have to have their water tested by a laboratory for the presence of boron. 

Page 121 GAO-11-254 Safe Drinking Water Act
Appendix VII: EPA’s Evaluation of 

Perchlorate Occurrence at Two Levels—5 

Parts and 15 Parts per Billion of Perchlorate 

in Water 

Appendix VII: EPA’s Evaluation of Perchlorate 

Occurrence at Two Levels—5 Parts and 15 

Parts per Billion of Perchlorate in Water 

As discussed earlier, before EPA made its preliminary regulatory 

determination for perchlorate on the basis of the health reference level of 

15 parts per billion of perchlorate in drinking water (calculated using a 

relative source contribution of 62 percent), the Office of Water had 

calculated a health reference level of 5 parts per billion using the 20 

percent default relative source contribution. Table 11 shows the impact of 

various relative source contribution factors and their related health 

reference levels on EPA’s characterization of the exposure to perchlorate 

in drinking water at levels of public health concern, based on a similar 

table the agency included in its preliminary regulatory determination 

notice. In particular, the table includes the exposure estimates related to 

the two health reference levels discussed above—the health reference 

level of 5 parts per billion that EPA initially developed using the 20 percent 

default relative source contribution and the health reference level of 15 

parts per billion that EPA subsequently developed for its preliminary 

regulatory determination using data from its novel exposure analysis and 

the subtraction method. 

At a health reference level of 5 parts per billion, EPA found that 3.2 

percent of public water systems had at least one detection in excess of 

that level, which EPA estimated could expose 14.6 million people to 

perchlorate at the level of public health concern. According to some EPA 

officials, this amount of public exposure to perchlorate at levels above the 

health reference level would suggest that a regulation was warranted. In 

contrast, the amount of public exposure to perchlorate at levels above the 

15 parts per billion health reference level was significantly lower. 

Specifically, at a health reference level of 15 parts per billion, less than 1 

percent of public water systems had at least one detection above the 

health reference level, which EPA estimated could expose about 2 million 

people to perchlorate in drinking water at the level of public health 

concern. 

Page 122 GAO-11-254 Safe Drinking Water Act 
Appendix VII: EPA’s Evaluation of 

Perchlorate Occurrence at Two Levels—5 

Parts and 15 Parts per Billion of Perchlorate 

in Water 

Table 11: Perchlorate Occurrence and Population Exposure Estimates at Various Potential Health Reference Levels Reported 

in EPA’s Preliminary Regulatory Determination for Perchlorate 

Potential health reference level 

(parts per billion) 

Relative source 

contributiona

 (percentage)

Public water systems with at 

least one detection greater 

than the health reference 

level (percentage) 

Population served by public 

water systems with at least 

one detection greater than 

the health reference level 

(millions of people)

4 16 4.0 16.6

5 20 3.2 14.6b

7 29 2.1 7.2

10 41 1.4 5.0

12 49 1.1 3.6

15 62c0.8 2.0d

17 69 0.7 1.9

20 82 0.5 1.5

25e100 0.4 1.0

Source: GAO analysis of EPA data. 

a

We calculated the relative source contribution factors using EPA’s equation for calculating health 

reference levels, using EPA’s default assumptions for body weight and drinking water intake. 

b

Exposure to perchlorate that EPA estimated at a health reference level of 5 parts per billion that EPA 

developed using the 20 percent default relative source contribution. 

c

Using EPA’s default assumptions for body weight and drinking water intake to calculate the relative 

source contribution that corresponds with a perchlorate concentration in drinking water of 15 

micrograms per liter results in a relative source contribution of 61.2 percent. We report 62 percent 

because that is the relative source contribution EPA derived based on the agency’s exposure 

analysis. 

d

Exposure to perchlorate that EPA estimated at a health reference level of 15 parts per billion that 

EPA developed using data from its novel exposure analysis and the subtraction method to calculate 

the relative source contribution. 

e

This value reported by EPA represents the drinking water equivalent level of 24.5 parts per billion 

rounded to the nearest whole number. A health reference level equal to the drinking water equivalent 

level assumes that all exposure to the contaminant is from drinking water—hence a relative source 

contribution of 100 percent. 

Page 123 GAO-11-254 Safe Drinking Water Act
Appendix VIII: 

Limitati

Perchlorate Exposure 

Supplemental Information on 

ons and Uncertainties of EPA’s 

Analysis

Page 124 GAO-11-254 

Appendix VIII: Supplemental Information on 

Limitations and Uncertainties of EPA’s 

Perchlorate Exposure Analysis 

To support its preliminary regulatory determination, EPA developed 

perchlorate exposure estimates using a novel methodology that merged 

biomonitoring data from CDC’s National Health and Nutrition 

Examination Survey (CDC biomonitoring data) with perchlorate 

occurrence data from EPA’s testing program. Using this methodology, 

EPA developed exposure estimates of daily perchlorate exposure from 

drinking water for various age and gender groups,1

 focusing largely on the 

perchlorate exposure of pregnant females because, EPA stated, the 

National Academies and EPA considered pregnant women and their 

fetuses to be the most sensitive population. In addition to the three 

limitations discussed in this report, reviewers noted additional limitations 

related to (1) the way in which participants were placed into groups that 

represented their potential for exposure to perchlorate from drinking 

water and food and (2) the adjustment—called a creatinine adjustment—

that EPA had to make to estimate daily exposure to perchlorate from a 

single urine sample. 

Limitations and 

Uncertainties Related to 

Grouping Participants 

According to Their 

Potential Exposure to 

Perchlorate from Drinking 

Water and Food 

After merging the data sets, EPA separated study participants into three 

groups, according to their potential for exposure to perchlorate through 

drinking water and food: participants whose exposure to perchlorate most 

likely comes from food and water, participants whose exposure most 

likely comes only from food, and participants whose exposure is unknown 

because occurrence data were not available. Study participants residing in 

the same counties as public water systems that had at least one detection 

of perchlorate during the sample period were considered to be most likely 

exposed to perchlorate in both food and water. Study participants were 

placed in the group most likely exposed to perchlorate from food alone on 

the basis of meeting one or more of the following criteria: (1) they resided 

in counties where there were no quantified detections of perchlorate in 

public drinking water systems sampled under EPA’s occurrence testing 

program, (2) they self-reported that they had not consumed public 

drinking water in the past 24 hours, or (3) they reported using a reverse 

osmosis filter at home (which can reduce perchlorate in drinking water). 

By placing participants into these two groups, EPA could estimate the 

relative contributions of food and water to perchlorate exposure. The 

remaining study participants were excluded from the analysis because 

EPA lacked data on perchlorate occurrence in drinking water to which 

they could be linked. However, as can be seen in the following examples, 

 

1

The study includes only children 6 years of age and older. 

 Safe Drinking Water Act 
Appendix VIII: Supplemental Information on 

Limitations and Uncertainties of EPA’s 

Perchlorate Exposure Analysis 

the data EPA had available to determine the group in which each study 

participant should be placed—exposure from food only or from food and 

water—and some criteria EPA applied in making these placements, 

introduce uncertainties into the exposure assessment that were not 

transparently acknowledged and explained in the agency’s 2008 

preliminary regulatory determination notice for perchlorate. 

• EPA’s testing program used a relatively insensitive minimum reporting 

level of 4 micrograms of perchlorate per liter of water.2

 As a result, 

EPA’s analysis of perchlorate exposure of CDC biomonitoring study 

participants placed in the group assumed to be exposed to perchlorate 

from food only—characterized by the study’s authors as the “most 

important category” for the purpose of investigating the dose of 

perchlorate in food—could overstate the number of participants who 

met the criterion to be placed into this group because the group could 

include people exposed to perchlorate at concentrations up to 4 

micrograms of perchlorate per liter of water. Further, to the extent 

participants in the food-only group were exposed to perchlorate in 

drinking water at levels below the minimum reporting level, the 

estimates of exposure from food alone are overstated. According to 

one reviewer, the minimum reporting level of 4 micrograms per liter 

introduces an uncertainty into the analysis that needs to be 

appropriately characterized, indicating that its use would 

underestimate perchlorate exposure for participants in the food and 

water group and inappropriately place individuals in the food-only 

group who should have been placed in the food and water group. 

• EPA’s perchlorate exposure estimates for participants placed in the 

food-only and food and water groups may also be subject to error 

because data limitations did not enable EPA to link participants to the 

perchlorate occurrence test results for their public water systems; 

rather, the data enabled each participant to be matched only to 

perchlorate occurrence test results for a public water system in the 

county in which the participant resides.3

 As a result, some participants 

 

2

In 2002, Massachusetts’s tests for perchlorate were sensitive enough to detect 

concentrations of perchlorate of less than 1 part per billion. Tests by the Departments of 

Defense and Energy have also detected concentrations of perchlorate in drinking water 

and groundwater of less than 1 part per billion. 

3

The CDC biomonitoring data and EPA occurrence data could be merged only at the county 

level because more specific location data, such as home addresses—which might have 

been useful for more accurately assigning individuals residing in counties served by 

multiple water systems to the correct group—could not be used because of privacy 

concerns. 

Page 125 GAO-11-254 Safe Drinking Water Act
Appendix VIII: Supplemental Information on 

Limitations and Uncertainties of EPA’s 

Perchlorate Exposure Analysis 

who were not actually exposed to perchlorate from their public water 

system may have been erroneously placed in the group exposed to 

perchlorate in food and water. 

• As noted by some reviewers, EPA’s criterion for placing participants in 

the group exposed to perchlorate from food alone if they reported they 

had not consumed tap water in the past 24 hours may have caused 

some participants to be erroneously placed in this group because these 

individuals may have nonetheless been exposed to perchlorate in 

drinking water that was used in the preparation of food, such as juice, 

soup, or coffee. 

• Another source of uncertainty that reviewers raised is the extent to 

which the analysis of the merged data is nationally representative. If 

the results of the analysis are weighted toward areas with known high 

or low perchlorate concentration in drinking water rather than being 

nationally representative, this limitation and its effects should be 

identified. However, EPA’s preliminary regulatory determination and 

the journal article on this analysis provide no information on the 

geographic coverage of the merged data, such as the number of states 

and the number of public water systems4

 represented by the merged 

CDC biomonitoring and EPA occurrence data. 

Limitations and 

Uncertainties Related to 

the Creatinine Adjustment 

To estimate each participant’s daily exposure to perchlorate from a single 

urine sample, EPA performed a creatinine adjustment on each sample. 

Making this adjustment required the following information for each 

participant: age, sex, weight, height, race, and lean body mass. As can be 

seen in the following examples, some of the assumptions that EPA applied 

in making these adjustments introduce uncertainties into the exposure 

assessment that were not transparently acknowledged and explained in 

the agency’s 2008 preliminary regulatory determination notice for 

perchlorate. 

• A key assumption EPA used in making the creatinine adjustment was 

that 100 percent of ingested perchlorate is eliminated in urine within a 

24-hour period. However, this is not a settled issue in the scientific 

community. The 2010 journal article detailing the methodology EPA 

used identifies several studies that report lower percentages of 

 

4

Some study participants may obtain their drinking water from private wells. In the 

exposure analysis, these individuals would be linked with the perchlorate test for a public 

water system in their county. 

Page 126 GAO-11-254 Safe Drinking Water Act
Appendix VIII: Supplemental Information on 

Limitations and Uncertainties of EPA’s 

Perchlorate Exposure Analysis 

perchlorate excreted in urine within 24 hours of exposure.5 For 

example, the journal article states that “several recent” perchlorate 

exposure studies report that approximately 70 percent of a perchlorate 

dose is excreted in urine. The estimates in the studies cited range from 

50 percent to 100 percent. The cited studies were published between 

2000 and 2007 and, consequently, were available at the time EPA was 

developing its relative source contribution factor for its preliminary 

regulatory determination on perchlorate. 

• Other limitations related to the creatinine adjustment that introduce 

uncertainty into the exposure estimates stem from differences among 

individuals in the timing of urine sample collections relative to when 

they most recently consumed food and water, as well as the expected 

variability among individuals’ intake and excretion related to their 

dietary and water consumption patterns (e.g., some individuals may 

excrete more or less of what they eat or drink). 

 

5

D. R. Huber et al., “Estimating perchlorate exposure from food and tap water based on 

U.S. biomonitoring and occurrence data,” Journal of Exposure Science and 

Environmental Epidemiology (2010). 

Page 127 GAO-11-254 Safe Drinking Water Act
Appendix IX: Calculations for the Perchlorate 

Health Reference Level in EPA’s 2008 

Preliminary Regulatory Determination and 

the Related 2010 Journal Article on EPA’s 

Exposure Analysis Methodology 

Appendix IX: Calculations for the Perchlorate Health 

Reference Level in EPA’s 2008 Preliminary Regulatory 

Determination and the Related 2010 Journal Article 

on EPA’s Exposure Analysis Methodology 

The exposure estimates for pregnant women that EPA presented in its 2008 

preliminary determination for perchlorate differed from those presented in 

the 2010 journal article that presented the exposure analysis methodology 

EPA used to support its preliminary determination.1

 This difference 

occurred because, in response to reviewers’ comments, the authors of the 

2010 journal article removed four data points that were determined to be 

outliers—two of which were data points that corresponded to women. As a 

result, in the article they reported pregnant women’s exposure to 

perchlorate from food alone at 0.198 micrograms per kilogram per day—

compared with EPA’s 0.263 estimate. This downward adjustment in the 

exposure estimate for pregnant women in 2010 resulted in a change in the 

relative source contribution estimate for perchlorate from 62 percent to 72 

percent.2

 Nonetheless, the 2008 and 2010 exposure analyses both support 

the same health reference level of 15 parts per billion—the level EPA and 

other federal agencies agreed to. As shown in table 12, this consistency in 

the health reference level was maintained because key assumptions were 

changed in calculating the health reference level. 

 

1

D. R. Huber et al., “Estimating perchlorate exposure from food and tap water based on 

U.S. biomonitoring and occurrence data,” Journal of Exposure Science and 

Environmental Epidemiology (2010). 

2

The 72 percent relative source contribution is calculated using the adjusted exposure 

number for pregnant women that was reported in the journal article. 

Page 128 GAO-11-254 Safe Drinking Water Act 
Appendix IX: Calculations for the Perchlorate 

Health Reference Level in EPA’s 2008 

Preliminary Regulatory Determination and 

the Related 2010 Journal Article on EPA’s 

Exposure Analysis Methodology 

Table 12: Comparison of the Health Reference Level Calculations Used in EPA’s Preliminary Perchlorate Regulatory 

Determination and Its Subsequent Article on the Perchlorate Exposure Methodology the Agency Used in Its Preliminary 

Regulatory Determination, Based on a Reference Dose of 0.7 Micrograms per Kilogram per Day 

Health 

reference level 

(parts per 

billion, 

rounded) = 

[(Reference 

dose 

(micrograms 

per kilogram 

per day) x 

Body weight) 

(kilograms) ÷ 

Drinking water 

intake] 

(liters per day) x 

Relative source 

contributiona

(expressed as a 

percentage) Source and date 

15 = [(0.7 x 70) ÷ 2] x 62 

EPA’s preliminary 

regulatory 

determination, 2008 

15 = [(0.7 x 66) ÷ 2.21] x 72 

Journal of Exposure 

Science and 

Environmental 

Epidemiology article, 

2010 

Source: GAO. 

Notes: If EPA’s 2008 calculation of the health reference level had retained the 62 percent relative 

source contribution factor but used the body weight and drinking water intake assumptions reflected 

in the journal article, the health reference level would have been 13 parts per billion. Conversely, 

using the 72 percent relative source contribution factor from the results reported in 2010 and the 

default estimates for body weight and drinking water intake that EPA used in 2008, the health 

reference level would be 18 parts per billion. 

a

EPA calculated the relative source contribution using the subtraction method. 

As shown in the table, in its preliminary regulatory determination, EPA 

derived a relative source contribution of 62 percent on the basis of 

pregnant women’s exposure to perchlorate from drinking water and used 

the agency’s default assumptions for weight (70 kilograms) and drinking 

water intake (2 liters per day) to calculate the health reference level of 15 

parts per billion. In the 2010 journal article, the authors support a health 

reference level of 15 parts per billion, but in this case, it is derived on the 

basis of a 72 percent relative source contribution that reflects both the 

data corrections the authors made in the exposure analysis and alternate 

assumptions for weight (66 kilograms) and drinking water intake (2.21 

liters per day.) These calculations illustrate how sensitive the outcomes of 

risk assessment methodologies can be to sometimes minor changes in 

basic assumptions. The sensitivity of the outcome—which then drives 

policy decisions—to these changes in assumptions, underscores the need 

for transparency and consistency in EPA’s selection of assumptions for a 

given risk assessment. 

Page 129 GAO-11-254 Safe Drinking Water Act
Appendix X: Comments from the Appendix X: Comments from the Environmental Protection Agency 

Environmental Protection Agency 

Page 130 GAO-11-254 Safe Drinking Water Act 
Appendix X: Comments from the 

Environmental Protection Agency 

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Appendix X: Comments from the 

Environmental Protection Agency 

Page 132 GAO-11-254 Safe Drinking Water Act
Appendix X: Comments from the 

Environmental Protection Agency 

Page 133 GAO-11-254 Safe Drinking Water Act
Appendix X: Comments from the 

Environmental Protection Agency 

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Appendix X: Comments from the 

Environmental Protection Agency 

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Appendix X: Comments from the 

Environmental Protection Agency 

Page 136 GAO-11-254 Safe Drinking Water Act
Appendix X: Comments from the 

Environmental Protection Agency 

Page 137 GAO-11-254 Safe Drinking Water Act
Appendix X: Comments from the 

Environmental Protection Agency 

Page 138 GAO-11-254 Safe Drinking Water Act
Appendix XI: 

A

GAO Contact and Staff 

cknowledgments 

Page 139 GAO-11-254 

Appendix XI: GAO Contact and Staff 

Acknowledgments 

David C. Trimble, (202) 512-3841 or trimbled@gao.gov

In addition to the contact named above, Christine Fishkin, Assistant 

Director; Jamie Meuwissen; Ryan Gottschall; Elizabeth Beardsley; Mark 

Braza; Nancy Crothers; Richard Johnson; John B. Stephenson; and Kiki 

Theodoropoulos made key contributions to this report. Also contributing 

to this report were Usman Ahmad, Archie Cowan, Michael Derr, Justin 

Fisher, Laura Gatz, Gary Guggolz, Ioan Ifrim, Michael Kniss, Carol Kolarik, 

Summer Lingard, Perry Lusk, Robert S. Wilson, and Eugene Wisnoski. 

 Safe Drinking Water Act 

GAO Contact 

Staff 

Acknowledgments 

(361065) 
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