EPA Protocol for the Review

of Existing National Primary

Drinking Water Regulations
 Printed on Recycled Paper

Office of Water

Office of Ground Water and Drinking Water (4607M)

EPA 815-R-03-002

www.epa.gov/safewater 

June 2003
Protocol for the Review of NPDWRs June 2003 ii

EPA 815-R-03-002

EPA Protocol for the Review of

Existing National Primary Drinking Water Regulations

June 2003

United States Environmental Protection Agency

Office of Water

Office of Ground Water and Drinking Water

Standards and Risk Management Division

Targeting and Analysis Branch

1200 Pennsylvania Avenue, NW (4607M)

Washington, DC 20460
Protocol for the Review of NPDWRs June 2003 iii

Acknowledgments

This document was prepared in support of the 1996-2002 Six-Year Review of Existing National

Primary Drinking Water Regulations (NPDWRs) for EPA's Office of Ground Water and

Drinking Water with James Taft as Targeting and Analysis Branch Chief during the course of the

review. Judy Lebowich served as EPA co-team lead for the Six-Year Review and as the Work

Assignment Manager for the development of this document. At different times throughout the

process, Marc Parrotta and Wynne Miller have also served as co-team leads for the project. The

Six-Year Review Work Group consists of representatives of the Office of Ground Water and

Drinking Water, the Office of Science and Technology, the Office of General Counsel, the

Office of Pesticide Programs, the Office of Research and Development, the Office of Policy,

Economics and Innovation, the Office of Solid Waste and Emergency Response, and EPA

Regions I, V, VII, IX, and X. Work Group members provided technical guidance throughout. 

The National Drinking Water Advisory Council (NDWAC) and many stakeholders provided

valuable advice to improve the review process and this document. The Cadmus Group, Inc.,

served as the prime contractor for developing this document.
Protocol for the Review of NPDWRs June 2003 iv

TABLE OF CONTENTS

List of Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

SECTION I: INTRODUCTION .............................................1

A. What Is the Purpose of the Six-Year Review? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

B. What Is the Purpose of This Protocol? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

C. What Information Will I Find In This Document? ............................... 2

SECTION II: OVERVIEW OF THE 

SIX-YEAR REVIEW PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

A. What Basic Principles Did EPA Follow During this Review? . . . . . . . . . . . . . . . . . . . . . 5

B. What Types of Analyses Did EPA Conduct? ...................................6

1. Initial Technical Review ................................................6

2. In-Depth Technical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

C. What Types of Regulatory Revisions Did EPA Consider? . . . . . . . . . . . . . . . . . . . . . . . 10

1. Changes to MCLGs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2. Changes to MCLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Changes to Treatment Technique Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Changes to Other Treatment Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Changes to Other Regulatory Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

SECTION III: DETAILED DISCUSSION OF 

THE SIX-YEAR REVIEW PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

A. Health risk assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1. What Were the Objectives of the Health Effects Review? . . . . . . . . . . . . . . . . . . . . . . 15

2. How Did EPA Review Health Effects Data for Chemical Contaminants? . . . . . . . . . 15

3. How Did EPA Review Health Effects Data for Microbiological NPDWRs? . . . . . . . 18

B. Technology Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1. What Were the Objectives of the Technology Assessments? . . . . . . . . . . . . . . . . . . . . 19

2. How Did EPA Review Analytical Methods? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3. How Did EPA Review Treatment Technologies? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

C. Other Regulatory Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1. What Was the Objective of the Review of Other Regulatory Revisions? . . . . . . . . . . 22

2. How Did EPA Consider Other Regulatory Revisions? . . . . . . . . . . . . . . . . . . . . . . . . 22

D. Occurrence and Exposure Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

1. What Were the Objectives of the Occurrence and Exposure Analysis? . . . . . . . . . . . 23

2. How Did EPA Conduct the Occurrence and Exposure Analysis? ............... 23

E. Consideration of Economic Factors ......................................... 24

1. What Were the Objectives of EPA's Evaluation of Economic Impacts? ........... 24

2. How Did EPA Consider Economic Impacts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Protocol for the Review of NPDWRs June 2003 v

TABLE OF CONTENTS, continued...

SECTION IV: STAKEHOLDER INVOLVEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

A. Who Were the Key Stakeholders in the Six-Year Review Process? . . . . . . . . . . . . . . . . 27

B. How Were Stakeholders Involved in the Six-Year Review Process? . . . . . . . . . . . . . . . . 27

C. How Did EPA Plan to Involve the Science Advisory Board? . . . . . . . . . . . . . . . . . . . . . 28

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Appendix A: List of Pre-1997 National Primary Drinking 

Water Regulations (NPDWRs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Appendix B: Differences between the National Drinking Water Advisory Committee's

(NDWAC's) Recommendations and this Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Appendix C: Overview of the IRIS Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

Appendix D: Overview of the OPP Process for Toxicity Assessments . . . . . . . . . . . . . . D-1

Appendix E: Overview of the Analytical Methods Review Process . . . . . . . . . . . . . . . . . E-1

LIST OF FIGURES

Figure 1: Overview of the Protocol and Making the Revise/Not Revise Decision . . . . . . . . . . . 9
Protocol for the Review of NPDWRs June 2003 vi

List of Acronyms and Abbreviations

ASTM American Society for Testing and Materials

ATP Alternate test procedure

ASDWA Association of State Drinking Water Administrators

ATSDR Agency for Toxic Substances and Disease Registry 

AWWA American Water Works Association

BAT Best available technology

BMP Best management practice

CFR Code of Federal Regulations

CMR Chemical Monitoring Reform

EPA U.S. Environmental Protection Agency

FACA Federal Advisory Committees Act

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act

FQPA Food Quality Protection Act

FR Federal Register

IRED Interim reregistration eligibility decision

IRIS Integrated Risk Information System

LOAEL Lowest-observed-adverse-effect level

MCL Maximum contaminant level

MCLG Maximum contaminant level goal

MDL Method detection limit

mL milliliters

MOE Margin of exposure

NAS National Academy of Sciences

NDWAC National Drinking Water Advisory Council

NERL National Exposure Research Laboratory
List of Acronyms and Abbreviations

Protocol for the Review of NPDWRs June 2003 vii

NIST National Institute of Standards and Technology

NOAEL No-observed-adverse-effect level

NPDWR National Primary Drinking Water Regulation

OGWDW Office of Ground Water and Drinking Water

OPP Office of Pesticide Programs

OW Office of Water

PAD Population adjusted dose (aPAD – acute; cPAD – chronic)

PE Performance evaluation

PQL Practical quantitation level

PT Proficiency testing 

PWS Public water system

RED Reregistration eligibility decision

RfD Reference dose (aRfD – acute RfD; cRfD – chronic RfD)

RSC Relative source contribution

SAB Science Advisory Board

SDWA Safe Drinking Water Act

SM Standard methods

TCR Total Coliform Rule

TT Treatment technique

WS Water supply
Protocol for the Review of NPDWRs June 2003 viii

EPA Protocol for the 

Review of Existing National Primary 

Drinking Water Regulations

EXECUTIVE SUMMARY

The Safe Drinking Water Act (SDWA), as amended in 1996, requires that the U.S.

Environmental Protection Agency (EPA) review existing National Primary Drinking Water

Regulations (NPDWRs) no less often than every six years and, if appropriate, revise them. This

document describes the systematic approach that EPA used to review 68 chemical NPDWRs and

the Total Coliform Rule (TCR) which were promulgated prior to the 1996 Amendments. The

statutory deadline for completing this review was August 2002. EPA developed this document

based on recommendations of the National Drinking Water Advisory Council (NDWAC),

through internal Agency deliberations, and discussions with the diverse stakeholders involved in

drinking water and its protection. 

As long as an NPDWR revision maintains or provides for the same or greater protection of

public health, the SDWA 1996 Amendments give the Administrator discretion to determine if

revision is appropriate. In order to determine that a revision is appropriate, EPA believes the

revision must continue to meet the basic statutory requirements of the SDWA and present

meaningful opportunities to improve the level of public health protection and/or to achieve costsavings while maintaining, or improving, the level of public health protection.

EPA applied the following basic principles to the review process:

• The Agency assumed health effects, analytical feasibility, treatment data, and analyses

underlying existing regulations remain adequate and relevant, except in those instances

where reliable, peer-reviewed, new data were available that indicated a need to reevaluate an NPDWR (e.g., where a change in health risk assessment has occurred).

• If new data were available, EPA determined whether changes in existing standards were

warranted. For example, in determining whether there was a change in analytical

feasibility, the Agency applied the current policy and procedures for calculating the

practical quantitation level for drinking water contaminants.

• EPA was unable to complete evaluation of certain new data within the time available for

the review. For example, if a new health risk assessment for a contaminant was not

completed during the review cycle, EPA generally made a "not revise" decision on the

rationale that it was not appropriate to revise the regulation while the assessment was

ongoing. When an updated assessment is completed, EPA will review the update and

any new conclusions or additional information associated with the contaminant during

the next review cycle. The Agency may make a determination to review a particular

NPDWR before August 2008 where a compelling reason exists to revisit the "not revise"

decision sooner.
Protocol for the Review of NPDWRs June 2003 ix

• During the review, EPA identified areas where information was inadequate or

unavailable ("data gaps") and is needed before an NPDWR may be considered as a

candidate for revision. If EPA was unable to fill such gaps during the review process, the

Agency provided information about the data gaps to the appropriate Agency group(s) for

consideration and prioritization. The results of further research or data gathering, if any,

will be considered as part of a subsequent review.

• During the review process, the Agency did not consider potential regulatory revisions

that were already the subject of other rulemaking activities.

• EPA applied the Agency's peer review policy (USEPA, 2000e), where appropriate, to any

new analyses.

To most efficiently utilize limited resources and assure continued public health protection,

the Agency conducted the review in two phases: (1) an initial technical review of all 69

NPDWRs (see Appendix A for a list); and (2) an in-depth technical evaluation of those

NPDWRs identified during the initial review as potential candidates for revision. The key

elements of the review included: health effects, technology assessment (i.e., analytical and

treatment feasibility), and consideration of other regulatory requirements (e.g., monitoring). If

the Agency identified a potential health or technological basis for a revision during the initial

screening, EPA also conducted occurrence and exposure analyses and evaluated available

economic information as a part of the in-depth review.

Based on the results of comprehensive analyses, EPA identified those NPDWRs that

remained appropriate at the completion of the 1996-2002 review cycle, and those NPDWRs that

may be appropriate for revision. The Agency published its preliminary determinations and its

protocol for the review in the April 17, 2002, Federal Register to seek comment from the public

(67 FR 19030 (USEPA, 2002d)). EPA received comments from 44 commenters on these

preliminary determinations. These comments, along with other new information received since

April 2002, have been considered as a part of the current revise/not revise decisions.
1

 Several NPDWRs promulgated prior to 1997 have been the subject of recent rulemaking or are the

subject of ongoing rulemaking activity. The review of these NPDWRs has been incorporated into those rulemaking

activities. Appendix A identifies each of the pre-1997 NPDWRs and indicates whether it is being reviewed in

accordance with this protocol or whether it has been or will be reviewed as a part of a separate rulemaking activity.

Protocol for the Review of NPDWRs June 2003 1

EPA Protocol for the 

Review of Existing National Primary 

Drinking Water Regulations

SECTION I: INTRODUCTION

A. What Is the Purpose of the Six-Year Review?

Under the Safe Drinking Water Act (SDWA), as amended in 1996, the U.S. Environmental

Protection Agency (EPA) must periodically review existing National Primary Drinking Water

Regulations (NPDWRs) and, if appropriate, revise them. Section 1412(b)(9) of SDWA, states:

The Administrator shall, not less often than every 6 years, review and revise, as

appropriate, each national primary drinking water regulation promulgated under

this title. Any revision of a national primary drinking water regulation shall be

promulgated in accordance with this section, except that each revision shall

maintain, or provide for greater, protection of the health of persons.

Prior to the 1996 Amendments, the SDWA required EPA to review NPDWRs at least every

three years to determine whether any changes in technology, treatment techniques (TTs) or other

means might provide better health protection. EPA was required to publish its findings in the

Federal Register and provide an explanation, after opportunity for public comment, of any

finding that such new technology, TT, or other means would not be feasible. Although the

Agency did revise existing NPDWRs on occasion when new data became available, EPA did not

have a systematic process for reviewing NPDWRs on a regular basis.

B. What Is the Purpose of This Protocol?

This protocol defines the systematic process EPA used to review most of the NPDWRs1

promulgated prior to the 1996 Amendments during the 1996-2002 review cycle. Although this

document is specific to the initial review under the 1996 SDWA Amendments, the Agency plans

to adopt a similar approach, modified as appropriate and with stakeholder involvement, for

subsequent review cycles.

EPA presented its initial ideas for the regulatory review protocol at a stakeholder meeting in

November 1999. Based on the comments made at that meeting, EPA revised the draft protocol. 

Among other changes, the revised draft clarified the role of research in the process and expanded

the discussion of the potential need to review/revise an NPDWR. The Agency provided its
2

 The NDWAC Working Group and the full NDWAC operate in accordance with the provisions of the

Federal Advisory Committees Act (FACA). All meetings are announced in the Federal Register and members of the

public are welcome to attend as observers.

Protocol for the Review of NPDWRs June 2003 2

revised draft to a National Drinking Water Advisory Council (NDWAC) Working Group2 that

met during the Summer of 2000 to develop recommendations regarding the protocol process. 

The NDWAC Working Group submitted their recommendations to the full NDWAC in

November 2000, which approved the recommended guidance and presented it to the Agency

(NDWAC, 2000). EPA incorporated the majority of the NDWAC's recommendations into this

document. In a few cases, however, EPA either decided not to incorporate a NDWAC

recommendation, or to revise it, because of practical considerations and/or resource constraints. 

Appendix B contains a summary of those NDWAC recommendations that were not incorporated

or that were substantially revised.

The systematic planning process used to develop this protocol satisfies the Agency's quality

assurance requirements (USEPA, 2002b). The process described in this protocol addresses

critical aspects of health protection and the setting of standards under the SDWA. In addition,

this protocol allows for the fact that numerous types of regulatory changes may be considered

and therefore, contains an element of flexibility to allow EPA the opportunity to consider a range

of possible issues. The review process described in this protocol document culminated with

decisions of whether or not to revise each of the reviewed NPDWRs. 

EPA requested public comments on its protocol in the April 17, 2002, Federal Register. In

response to these protocol-related comments, the Agency has revised this document to better

explain how occurrence and exposure, and economic considerations have been factored into the

decision process.

The publication of a decision to revise pursuant to a section 1412(b)(9) review is not the end

of the regulatory process, but is the beginning of one. A decision to revise starts a regulatory

process for a contaminant that involves more detailed analyses concerning health effects, costs,

benefits, occurrence, and other matters relevant to deciding whether and how an NPDWR should

be revised. At any point in this process, EPA may find that regulatory revisions are no longer

appropriate and may discontinue regulatory revision efforts at that time. Review of that

NPDWR would continue in future Six-Year Reviews.

Similarly, a decision "not to revise at this time" means only that EPA does not believe that

regulatory changes to a particular NPDWR are appropriate due to: a lack of new data, ongoing

scientific reviews, low priority, or other reasons discussed in this document. Reviews of these

contaminants continue and future Six-Year Reviews may lead to a decision that regulatory

changes are appropriate.

C. What Information Will I Find In This Document?

This protocol is divided into three remaining sections as follows:

• Section II: Overview of the Six-Year Review Process provides a summary of the

review process. It discusses how potential candidates for regulatory revision were
Protocol for the Review of NPDWRs June 2003 3

identified; how this list was refined to nominate NPDWR(s) for revision; and the

potential types of regulatory decisions that EPA considered.

• Section III: Detailed Discussion of the Review Process provides an in-depth

discussion of each of the analyses that were conducted (i.e., health effects, analytical and

technology assessments, consideration of other regulatory revisions, occurrence and

exposure, and evaluation of available economic information), and how these analyses

interrelate.

• Section IV: Stakeholder Involvement discusses how EPA involved the public during

the Six-Year Review process.

This protocol also contains five appendices as described below: 

• Appendix A: List of pre-1997 National Primary Drinking Water Regulations

(NPDWRs) identifies each of pre-1997 NPDWRs and indicates whether it was being

reviewed in accordance with this protocol or whether it has been/will be reviewed as a

part of a separate rulemaking activity.

• Appendix B: Differences between the National Drinking Water Advisory Council's

(NDWAC's) Recommendations and this Protocol summarizes the NDWAC

recommendations that EPA either modified or did not include in this protocol.

• Appendix C: Overview of the IRIS Assessments provides a discussion of how EPA

conducts its Integrated Risk Information System (IRIS) health assessments.

• Appendix D: Overview of the OPP Process for Toxicity Assessments contains a 

discussion of the Office of Pesticide Programs (OPP) process for conducting toxicity

assessments.

• Appendix E: Overview of the Analytical Methods Review Process describes EPA's

process for approving new analytical methods for chemical drinking water contaminants

and how the Agency has derived practical quantitation levels in the past.
Protocol for the Review of NPDWRs June 2003 4
3

 "Peer review" is a documented critical review of a specific major scientific and/or technical work product. 

The peer review is conducted by qualified individuals (or organizations) who are independent of those who

performed the work, but who are collectively equivalent in technical expertise (i.e., peers) to those who performed

the original work. The peer review is conducted to ensure that activities are technically adequate, competently

performed, properly documented, and satisfy established quality requirements. The peer review is an in-depth

assessment of the assumptions, calculation, extrapolations, alternate interpretations, methodology, acceptance

criteria, and conclusions pertaining to the specific major scientific and/or technical work product and of the

documentation that supports them.

4

 EPA establishes a practical quantitation level to estimate the level at which laboratories can routinely

measure a chemical contaminant in drinking water. See: 50 FR 46902, November 13, 1985 (USEPA, 1985); 52 FR

25690, July 8, 1987 (USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA, 1989a). 

Protocol for the Review of NPDWRs June 2003 5

SECTION II: OVERVIEW OF THE 

SIX-YEAR REVIEW PROCESS

This section provides an overview of the review process. It contains a discussion of the basic

principles that EPA followed during the review, the types of analyses that EPA conducted, and

the types of regulatory revisions that EPA considered. Figure 1 in this section provides a

graphical overview of the review process. A more detailed discussion of each of the analyses,

that were conducted under the review, is provided in section III.

A. What Basic Principles Did EPA Follow During this Review?

EPA's primary goal was to identify and prioritize candidates for regulatory revision in order

to target those revisions that are most likely to result in a meaningful opportunity for health risk

reduction and/or result in a meaningful opportunity for cost-savings while maintaining the level

of public health protection. In conducting the review, EPA applied the following basic

principles:

• The Agency assumed that health effects, occurrence, analytical feasibility, treatment data,

and analyses underlying existing regulations remain adequate and relevant, except in

those instances where reliable, peer-reviewed3

, new data were available that indicated a

need to re-evaluate an NPDWR (e.g., where a change in health risk assessment has

occurred).

• If new data were available, EPA determined whether changes in existing standards were

warranted. For example, in determining whether there was a change in analytical

feasibility, the Agency applied the current policy and procedures for calculating the

practical quantitation level for drinking water contaminants.4

• EPA generally made a "not revise at this time" decision for those NPDWRs whenever

evaluation of certain new data could not be completed within the time available for the

review. For example, if a new health risk assessment for a contaminant was not

completed during the review cycle, EPA made a "not revise at this time" decision on the

rationale that it was not appropriate to revise the regulation while the assessment was

ongoing. When an updated assessment is completed, EPA will review the update and
Protocol for the Review of NPDWRs June 2003 6

any new conclusions or additional information associated with the contaminant during

the next review cycle. The Agency may make a determination to review a particular

NPDWR before August 2008 where a compelling reason exists to revisit the "not revise"

decision sooner.

• During the review, EPA identified areas where information was inadequate or

unavailable ("data gaps") and is needed before an NPDWR may be considered as a

candidate for revision. Where EPA was unable to fill such gaps during the review

process, the Agency has provided information about the data gaps to the appropriate

Agency group(s) for consideration and prioritization so that further research and data

collection can be considered as part of a subsequent review cycle. 

• During the review process, the Agency did not consider potential regulatory revisions

that were already the subject of other periodic rulemaking activities.

• EPA applied the Agency's peer review policy, where appropriate, to any new analyses

(USEPA, 2000e).

B. What Types of Analyses Did EPA Conduct?

To most efficiently utilize limited resources and assure continued public health protection,

the Agency conducted the review in two phases: (1) an initial technical review of all 69

NPDWRs included in this Six-Year Review (see Appendix A for a list); and (2) an in-depth

technical evaluation of those NPDWRs identified during the initial review as potential

candidates for revision. Figure 1, at the end of this section, illustrates the Six-Year Review

process.

1. Initial Technical Review 

The initial review phase included these three screening and general evaluation steps: 

• Health effects review. The purpose of the health effects review was to identify NPDWRs

for which the Agency has revised health risk assessments that indicate possible changes

to the maximum contaminant level goal (MCLG) and perhaps to the maximum

contaminant level (MCL); 

• Current technology review. The purpose of the current technology review was to identify

NPDWRs where improvements in analytical or treatment feasibility might allow the

MCL to be established closer to the MCLG, or where adjustments in TT requirements

might be appropriate; and/or

• Other regulatory revisions review. The purpose of the other regulatory revisions review

was to identify where adjustments to implementation aspects of NPDWRs (e.g., system

monitoring and reporting requirements) might be appropriate, and where such changes

were not already being addressed, or had not been addressed, through alternative

mechanisms such as a recent or ongoing rulemaking. 

EPA primarily performed these reviews independently. Once the results of the individual

reviews were available, the Agency integrated the results to determine whether a potential health

or technological basis existed to support a regulatory revision. For the purposes of the Six-Year
Protocol for the Review of NPDWRs June 2003 7

Review, EPA considered a potential health basis to exist if the results of the health effects review

indicated that a possible basis existed for revising the MCLG and, if appropriate, the MCL. EPA

considered a potential technological basis to exist if the results of the current technology review

and/or the results of the other regulatory revisions review provided a possible basis for revising

the MCL, TT, and/or other regulatory requirements. 

EPA generally determined after the initial review that an NPDWR was not a candidate for

revision at that time, if a health risk assessment was in process or had been initiated as a result of

the review. The Agency made this determination because EPA does not believe it is appropriate

to revise an NPDWR while a health risk assessment is underway. EPA also determined, after the

initial review, that an NPDWR was not a candidate for revision at that time if none of the initial

screening analyses identified a basis for a potential regulatory revision.

2. In-Depth Technical Analysis

The Agency subjected the remaining NPDWRs to more in-depth technical analyses. If the

results of the initial review indicated a possible revision to the MCLG/MCL, EPA further

considered health and technology factors that might affect the development of a revised standard

(e.g., revisions to the MCLG, MCL, or TT requirements, and/or revisions to other regulatory

revisions such as system monitoring and reporting requirements). 

For the chemical NPDWRs, if the outcome of these analyses indicated that a regulatory

revision might be appropriate, the Agency also estimated potential occurrence and exposure at

public water systems (PWSs). The Agency used the results of the other analyses to determine

the contaminant concentrations that would be used in the occurrence and exposure analyses (i.e.,

the levels of regulatory interest). EPA also conducted a qualitative economic evaluation, which

was primarily based on available occurrence and exposure data. The Agency used the results of

these analyses to determine whether, in the Agency's judgement, an opportunity existed for

meaningful health risk reduction and/or meaningful cost savings to PWSs and their customers

without lessening the level of public health protection.

If EPA identified data gaps that could not be filled during the current review cycle, the

Agency did not conduct some or all of the remaining analyses. Although, Figure 1, on page 8

shows the identification of data gaps as the final step in the review; in some instances, data gaps

were identified during earlier steps in the process. If the Agency identified data gaps, EPA

determined that a revision to the NPDWR was not appropriate during the current review.

Based on the results of comprehensive analyses, EPA identified those NPDWRs that

remained appropriate at the completion of the 1996-2002 review cycle, and those NPDWRs that

may be appropriate for revision. If the Agency decided that it was not appropriate to revise an

NPDWR during the 1996-2002 review cycle, that decision was based on one of the following

reasons. 

• Health risk assessment in process: At the time the review was completed, the Agency

was conducting, or had scheduled, a detailed review of current health effects information. 

Because the results of the assessment were not available at the time the review was

completed, the Agency did not believe it was appropriate to revise the NPDWR at that

time. In these cases, EPA will consider the results of the updated health risk assessment

during the 2002-2008 review cycle. However, if the results of the health risk assessment
5

 EPA conducted occurrence and exposure analyses to help in determining whether a revision was a

priority for the Agency. For example, the Agency estimated occurrence and exposure to a contaminant at

concentrations between the current MCL and any possible MCL to help determine whether there was likely to be a

meaningful opportunity for health risk reduction or cost-savings to PWSs and their customers, if EPA were to revise

the MCL. 

Protocol for the Review of NPDWRs June 2003 8

indicate a compelling reason to reconsider the MCLG, EPA may decide to accelerate the

review schedule for that contaminant's NPDWR.

• NPDWR remained appropriate after data/information review: The outcome of the

review indicated that the current regulatory requirements remained appropriate and,

therefore, no regulatory revisions were warranted. Any new information available to the

Agency either supported the current regulatory requirements or did not justify a revision.

• New information but no revision appropriate at the completion of the review because:

- Low priority: In EPA's judgment, any resulting revisions to the NPDWR would not

provide a meaningful opportunity for health risk reduction or result in meaningful

cost-savings to PWSs and their customers.5

 EPA considers these revisions to be a

low priority activity for the Agency and, thus, "not appropriate" for revision "at this

time" because of one or more of the following considerations: competing workload

priorities; the administrative costs associated with rulemaking; and the burden on

States and the regulated community to implement any regulatory change that resulted.

- Information gaps: Although results of the review support consideration of a possible

revision, the available data were insufficient to support a definitive regulatory

decision. 

EPA published its preliminary determinations and its protocol for the review in the April 17,

2002, Federal Register in order to seek comment from the public. EPA received comments from

44 commenters on these preliminary determinations. These comments, along with other new

information received since April 2002, have been considered as a part of the current revise/not

revise decisions.
Protocol for the Review of NPDWRs June 2003 9

Yes

No

Does the review suggest possible changes 

in MCLG/MCL/TT and/or other 

regulatory revisions?

Is a meaningful opportunity for health risk 

reduction or meaningful opportunity for 

cost savings likely to occur?

No Revision 

at this time

Candidate 

for Revision

Are the data sufficient to support

regulatory revision?

NPDWR remains appropriate

after data/information review

No meaningful opportunity

for health risk reduction

and/or cost savings

Data gaps - determine

research needs

Yes

No

Pending health

risk assessment

Is a health risk assessment

in process/planned?

Yes

No

Yes

No

In-depth Technical Analysis

New risk assessment, methods feasibility, 

treatment effectiveness, occurrence and exposure

and economic implications.

1. Publish FR notice with preliminary revise/not decisions.

2. Review Public Comments and consider revising decisions 

in context of new information.

3. Publish FR notice with list of NPDWRs to be revised

NPDWRs under review

Initial Technical Review

Health Effects, Methods and Treatment 

Feasibility, and Other Regulatory 

Revisions

Figure 1: Overview of the Protocol and Making the Revise/Not Revise Decision
Protocol for the Review of NPDWRs June 2003 10

C. What Types of Regulatory Revisions Did EPA Consider?

As a part of the review, EPA considered regulatory revisions, with the primary goal of

improving or maintaining public health protection. The types of revisions considered were based

on the various components of each NPDWR. Some NPDWRs set enforceable MCLs for

particular contaminants in drinking water. Others impose TTs to remove chemical contaminants

or microbiological pathogens from drinking water. Most standards also include requirements for

water systems to test for contaminants in the water to make sure standards are achieved. 

NPDWRs also specify recordkeeping and reporting requirements, define what constitutes

compliance, and specify language and delivery requirements for public notification. 

Some regulatory revisions that are not listed below (e.g., revisions to approved analytical

methods) are already addressed through periodic rulemaking activities of SDWA, and thus, were

not included in the Six-Year Review.

1. Changes to MCLGs

SDWA requires EPA to establish non-enforceable health-based MCLGs. As a part of the

Six-Year Review, EPA considered MCLG changes only in those instances where a new health

risk assessment had been completed since the MCLG was promulgated or last revised, and where

the most current assessment resulted in a revised reference dose (RfD) and/or cancer

classification which justified calculating a revised MCLG. 

A revision to an MCLG may result in a more or less stringent standard. The legislative

history of the SDWA Amendments of 1996 makes clear that Congress envisioned the possibility

that a relaxed standard might be appropriate under circumstances that would not result in a

lessening of the level of public health protection. In its discussion of potential revisions to an

existing drinking water standard, Senate Report Number 104-169 (available electronically at

http://thomas.loc.gov/) states:

Amendments made by the bill require that any future standard issued for a

contaminant already regulated must maintain or provide for greater protection of

the health of persons. Generally, this will preclude the promulgation of a revised

standard for a contaminant that is less stringent than the standard already in

place. However, there are circumstances under which a standard may be

relaxed. The maximum contaminant level goal for a contaminant is set at a level

at which there is no adverse effect on the health of persons with an adequate

margin of safety. New scientific information may cause the MCLG to be revised

and in some cases these revisions may be to less stringent levels. This may lead

to a revision of the maximum contaminant level since it need be no more stringent

than the MCLG. New information may also allow for a smaller margin of safety

because it narrows the range of uncertainty for estimates of health risks. Finally,

some substances which have been regulated as carcinogens for ingestion in

drinking water may be reclassified (as asbestos has been in the most recent

revision) or assigned a threshold for the effect based on new scientific

information. In each of these cases, EPA may issue a revised standard for a

contaminant that is less stringent than the one it replaces.

(S. Rep. 104-169, 104th Cong., 1st Sess. (1995) at 38)
6

 Although the 1996 Amendments to SDWA allow EPA to set the MCL at higher than the feasible level if

the benefits do not justify the costs, SDWA also precludes the Agency from making an existing standard less

stringent solely on economic considerations. Therefore, EPA does not believe it is appropriate to revise a pre-1997

MCL unless a health or technical basis exists for the revision.

7

 Potential changes to MCLs may be appropriate in circumstances where the potentially revised MCLG is

more or less stringent than the current MCL (refer back to section II.C.1 for further discussion).

Protocol for the Review of NPDWRs June 2003 11

EPA also believes it is reasonable to consider the extent of potential cost-savings for PWSs

and their customers when determining whether revisions that potentially would result in a

relaxed standard (i.e., where a health basis exists for a less stringent standard) or streamlined

implementation are appropriate. These considerations allow the Administrator to better

prioritize efforts that are most likely to result in a meaningful opportunity for health risk

reduction or cost-savings to PWSs and their customers. Revisions that do not satisfy at least one

of these criteria are a low priority activity for the Agency, and, thus not appropriate "at this time"

because of one or more of the following considerations:

• Competing workload priorities; 

• The administrative costs associated with rulemaking; and 

• The burden on States and the regulated community to implement any regulatory change

that resulted.

Further, because section 1412(b)(9) of SDWA requires that any revision to an existing

NPDWR maintain or improve the level of public health protection, EPA believes that a clear,

technically-based demonstration regarding the absence of potential risk is necessary to

deregulate a contaminant.

2. Changes to MCLs

An MCL is an enforceable standard for a contaminant. SDWA generally requires the MCL

to be set as close to the MCLG as is feasible. As a part of the Six-Year Review, EPA 

considered MCL revisions under the following circumstances6

: 

• The health effects review indicated a change to the MCLG that also indicated a change to

the MCL was appropriate7

; and/or

• The current MCL was limited by analytical or treatment feasibility and the review of

these capabilities indicated it might now be feasible to set the MCL closer to the MCLG.

3. Changes to Treatment Technique Requirements

When it is not economically or technically feasible to set an MCL, or when there is no

reliable or economically feasible method to detect contaminants in the water, EPA sets a TT

requirement in lieu of an MCL. A TT specifies a type of treatment (e.g., filtration, disinfection,

other methods of control to limit contamination in drinking water, etc.) and means for ensuring

adequate treatment performance (e.g., monitoring of water quality to ensure treatment

performance, etc.).

Water TTs may improve to the point where more protective drinking water standards may be

considered. Before EPA would consider a revision to TT requirements, the potential methods
8

 The 1996 SDWA Amendments identify two classes of technologies for systems serving 10,000 and fewer

persons: compliance technologies and variance technologies. A compliance technology is defined in

§1412(b)(4)(E)(ii) as a technology or other means that is affordable and achieves compliance with an MCL or

satisfies a TT requirement. EPA listed compliance technologies in the EPA publication entitled Small System

Compliance Technology List for the Non-Microbial Contaminants Regulated Before 1996 (USEPA, 1998a). 

Variance technologies, defined in §1412(b)(15)(A), are specified for those system size category/source water quality

combinations for which there are no listed compliance technologies. Variance technologies, where they are

permitted, may not achieve compliance with a particular MCL or TT requirement; however, they must achieve the

maximum reduction or inactivation efficiency that is affordable, taking into consideration system size and source

water quality. Variance technologies must also achieve a level of contaminant reduction that is protective of public

health.

Protocol for the Review of NPDWRs June 2003 12

must be generally available and must have demonstrated consistent control of the subject

contaminant in drinking water. As a part of the Six-Year Review, EPA reviewed available

information on TTs for those chemical NPDWRs for which: (1) a TT is set in lieu of an MCL;

and (2) no health risk assessment was in process to determine if changes to TT requirements

might be warranted.

4. Changes to Other Treatment Technology

When EPA sets an MCL, the NPDWR also contains Best Available Technology (BAT)

recommendations that address drinking water treatment processes. Although not required for

compliance purposes, EPA sets BATs that have the capability to meet MCLs.

As part of the Six-Year Review, the Agency limited its review of BATs to those NPDWRs

for which EPA was considering possible revisions to the MCL based on the health effects or

analytical feasibility reviews. To revise a BAT, the treatment technology must be generally

available and must have demonstrated consistent removal of the subject contaminant under field

conditions. 

EPA has a separate program in place to periodically review specific treatment technology

issues, such as compliance and variance technology for small systems (i.e., systems serving up to

10,000 people) for both the MCL-type and the TT-type rules (however, for microbiological

contaminant regulations, no variances are allowed).8

 As a part of its periodic review of small

system compliance and variance technology, the Agency also plans to include the identification

of: (1) BATs for larger systems for future regulations, and (2) new and emerging technologies as

potential compliance and variance technologies for all system sizes for existing and future

regulations. EPA believes that this separate review of treatment technologies is appropriate

because it maintains the focus of technology assessment within one program function (USEPA,

1998a).

5. Changes to Other Regulatory Revisions

In addition to possible revisions to MCLGs, MCLs, and TTs, EPA considered other

regulatory revisions, such as monitoring and system reporting requirements, as a part of the SixYear Review process. EPA focused this review on issues that were not already being addressed,

or had not been addressed, through alternative mechanisms (e.g., as part of a recent or ongoing

rulemaking). Where appropriate alternative mechanisms did not exist, EPA considered these

implementation-related concerns if the potential revision met the following criteria:
Protocol for the Review of NPDWRs June 2003 13

• It indicated a potential change to an NPDWR, as defined under section 1401 of SDWA;

• It was "ready" for rulemaking – that is, the problem to be resolved has been clearly

identified and specific option(s) have been formulated to address the problem; and

• It met at least one of the following conditions:

– clearly improved the level of public health protection; and/or

– represented a meaningful opportunity for cost savings while not lessening public

health protection.
Protocol for the Review of NPDWRs June 2003 14
9

 The health effects for these contaminants are reassessed no less frequently than every 15 years. Within

EPA, health risk assessments for pesticides are conducted by the OPP under authority of the Federal Insecticide,

Fungicide, and Rodenticide Act (FIFRA), and the Food Quality Protection Act (FQPA) of 1996. A goal of FIFRA is

that EPA reviews each pesticide's registration every 15 years. Under some circumstances, a pesticide's health effects

may be reassessed more frequently.

Protocol for the Review of NPDWRs June 2003 15

SECTION III: DETAILED DISCUSSION OF 

THE SIX-YEAR REVIEW PROCESS

 This section provides a detailed discussion of how EPA conducted its review of health risk

assessments, technology assessments, other regulatory revisions, and, where appropriate,

occurrence and exposure analyses, and economic factors. 

A. Health risk assessments

1. What Were the Objectives of the Health Effects Review?

The objectives for the examination of health effects under the Six-Year Review were to: 

• Identify new health risk assessments for individual contaminants that could change the

MCLG for the contaminant in question and affirm or change the MCL, thus, affording

the same or greater protection of human health provided by the present MCLG;

• Use existing Agency health risk assessments in accomplishing the health effects data

review;

• Ensure that the health effects data for each contaminant is the subject of a detailed review

at least once in every two, Six-Year Review cycles (with the exception of pesticides that

are still in active use, because they are subject to a detailed review that is conducted on a

different schedule9

); and

• Accomplish the review within the limitations imposed by Agency resources.

The procedure for review of health effects data differed depending on whether the substance

to be controlled is a chemical contaminant or a microbiological pathogen/indicator, as discussed

in detail below. The health risk assessment identified a list of NPDWRs that were possible

candidates for regulatory revisions based on changes in health considerations. This list of

NPDWRs was combined with those identified by other key elements of the review to develop a

list of NPDWRs that were candidates for additional evaluation.

2. How Did EPA Review Health Effects Data for Chemical Contaminants?

EPA used a systematic approach in reviewing the health effects data for chemical

contaminants. This approach considered the risk assessment policies that link the MCLG and

MCL as well as the data that have become available since the time of regulation. The document,

Six-Year Review - Chemical Contaminants - Health Effects Technical Support Document
10 For purposes of the Six-Year Review protocol, EPA considered a risk assessment final when an Interim

Reregistration Eligibility Decision (IRED), Reregistration Eligibility Decision (RED), and/or IRIS assessments was

complete. The IRED is an intermediate decision for an individual pesticide that does not take into account

cumulative risk issues for pesticides with a common mode of action. The RED does include cumulative risk. If an

IRIS assessment was also in process when the IRED or RED was signed, EPA made a case-by-case decision on

whether to wait for the IRIS assessment before considering possible revisions to the NPDWR.

11 See footnote 10.

Protocol for the Review of NPDWRs June 2003 16

(USEPA, 2003e), describes how EPA reviewed the chemical contaminants and provides the

results of the health effects technical review.

If there is evidence that a chemical may cause cancer, and if the cancer mode of action is

linear, there is no dose below which the chemical is considered safe, and thus the MCLG is set at

zero. In these instances, the MCL is based on feasible technology (analytical

methods/treatment). If a chemical is carcinogenic and acts by a well-documented, nonlinear

mode of action, the MCLG may be set at a level above zero. As the health risks of nonlinear

carcinogens undergo reassessment, this may provide regulatory options for MCLGs for

carcinogens that are greater than zero.

For non-carcinogenic chemicals, the MCLG is based on an oral RfD. The RfD is an estimate

(with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human

population (including sensitive subgroups) that is likely to be without an appreciable risk of

deleterious non-cancer effects during a lifetime. A change in an Agency RfD for a chemical

could accordingly lead to a change in an MCLG and MCL. In deriving the MCLG for a

non-carcinogen, the Agency applies a Relative Source Contribution (RSC) factor to allocate a

portion of the total allowable exposure to drinking water. The RSC is one factor which will

determine whether or not a change in RfD will lead to a change in the MCLG/MCL.

In the past, it was Agency policy to apply a risk management factor to the RfD for chemicals

with equivocal data on carcinogenicity. This policy is a second factor that must be evaluated to

determine the impact of a change in RfD on the MCLG/MCL for these chemicals.

For most of the 68 chemical NPDWRs included in the Six-Year Review, the MCLG is

derived from the cancer classification and/or the RfD. Therefore, the health effects technical

review focused on whether there has been a change to these values. The Agency reviewed the

results of health risk assessments completed under the following programs to determine if there

has been a change in critical effect or dose-response pattern that indicates the possible need for

an MCLG revision.

• EPA's IRIS (see Appendix C)10

• OPP (see Appendix D)11

• Agency for Toxic Substances and Disease Registry (ATSDR)

• National Academy of Sciences (NAS).

Where possible, an oral RfD or comparable value is derived and an assessment of

carcinogenicity from oral exposure is conducted under each of these programs. 
12 For the 1996-2002 review, EPA considered a zero MCLG to be protective of public health and that new

information on developmental and reproductive effects would not affect the MCLG. However, for those NPDWRs

with a zero MCLG, EPA reviewed available information to inquire whether data show a non-linearity of the doseresponse; EPA did not find any data to support such a mode of action (USEPA, 2003e). EPA recognizes that

information on potential reproductive and developmental effects for chemicals with MCLGs of zero may have an

impact on risk management strategies, such as monitoring frequency, to control peak occurrence. This aspect of the

assessment will be considered during subsequent Six-Year Review cycles, in conjunction with available occurrence

data, to determine whether changes in risk management strategies might provide for better public health protection.

Protocol for the Review of NPDWRs June 2003 17

As a result of the health effects review, EPA placed each of the 68 chemical NPDWRs into

one of the following categories:

(1) New risk assessment 1997 or later. An IRIS, OPP, ATSDR, and/or NAS assessment has

been completed in 1997 or later. These assessments have considered developmental and

reproductive toxicity as a part of the assessment. The Agency considered these

assessments to be recent enough that it was not necessary to conduct a literature search to

identify any additional relevant studies that have become available on the toxicological

effects of these contaminants. In cases where the health risk assessment resulted in a

change in the critical effect, or the dose-response pattern for a regulated contaminant, and

where that change could result in a change in the MCLG, EPA subjected the NPDWR to

a more in-depth analysis as a part of the review process. Where recent assessments were

conducted by an agency other than EPA and new developmental and reproductive data

were identified, EPA initiated an update of its assessment.

(2) New risk assessment since promulgation, but prior to 1997. An IRIS, OPP, ATSDR,

and/or NAS assessment has been completed since the NPDWR was promulgated, but

prior to 1997. None of these assessments reflected a change in RfD or cancer

classification. However, since these assessments may not have specifically considered

developmental and reproductive health effects, EPA conducted a full literature search,

including developmental and reproductive toxicity, for those NPDWRs with non-zero

MCLGs to identify any relevant studies that might affect the MCLGs of these

contaminants.12 In a few instances, the results of the literature search indicated that it

might be appropriate to revise the RfD and/or cancer classification. EPA initiated

updates to risk assessments for these chemicals, and established a schedule for their

completion. EPA did not consider these NPDWRs appropriate candidates for revision

during the 1996-2002 review cycle.

(3) Agency risk assessment in progress during the Six-Year health effects review. The

Agency was conducting a health risk assessment for the contaminant but the assessment

was not completed in time for consideration during the 1996-2002 review cycle. When

completed, the assessment will consider all relevant studies that have become available

on the toxicology of the contaminant, including developmental and reproductive toxicity. 

EPA generally did not consider these NPDWRs appropriate candidates for revision

during the 1996-2002 review cycle.

(4) Original NPDWR risk assessment. No health risk assessment has been conducted since

promulgation of the NPDWR. The Agency conducted a full toxicological literature

search, including developmental and reproductive toxicity, for each of these

contaminants with non-zero MCLGs to identify new toxicological studies that might
Protocol for the Review of NPDWRs June 2003 18

have an impact on the MCLGs. In a few instances, the results of the literature search

indicated that it might be appropriate to revise the RfD and/or cancer classification. EPA

initiated updates to risk assessments for these chemicals, and established a schedule for

their completion. EPA did not consider these NPDWRs appropriate candidates for

revision during the 1996-2002 review cycle.

Thus, only contaminants in the first category were considered to be potential candidates for an

MCLG revision during the 1996-2002 review cycle. If the revised health risk assessment

indicated changes to the MCLG/MCL, the Agency conducted a detailed occurrence and

exposure assessment. See section III.D for more discussion of how EPA conducted the

occurrence and exposure analyses.

The document, Six-Year Review - Chemical Contaminants - Health Effects Technical

Support Document, (USEPA, 2003e) describes the process that EPA used to address the health

effects aspect of the current review for the chemical contaminants.

3. How Did EPA Review Health Effects Data for Microbiological NPDWRs?

The Total Coliform Rule (TCR) is one of several EPA regulations that protect the public

from pathogens in drinking water. The TCR requires all PWSs to monitor for the presence of

total coliforms in the distribution system. Total coliforms are a group of closely related bacteria

that are (with few exceptions) not harmful to humans. They are natural and common inhabitants

of the soil and ambient waters (e.g., lakes, rivers and estuaries), as well as in the gastrointestinal

tract of animals. A few of these coliforms (fecal coliforms, including Escherichia coli or E. coli)

only grow within the intestinal tract of humans and other warm-blooded animals. Total

coliforms may be injured by environmental stresses (e.g., lack of nutrients) and water treatment

(e.g., chlorine disinfection) in a manner similar to most bacterial pathogens and many virus

pathogens. Therefore, EPA considers them a useful indicator of bacterial and many viral

waterborne enteric pathogens. More specifically, for drinking water, total coliforms are used to

determine the adequacy of water treatment and the integrity of the distribution system. The

absence of total coliforms in the distribution system minimizes the likelihood that fecal

pathogens are present. Thus, total coliforms are used to determine the vulnerability of a system

to fecal contamination.

The 1989 TCR set an MCLG of zero for total coliforms because EPA was not aware of any

data in the scientific literature supporting a particular value for the concentration of coliforms

below which no known or anticipated adverse health effects occur, with an adequate margin of

safety. 

The memorandum, Six-Year Review of the Total Coliform Rule - Comments Received

(USEPA, 2002c), describes the process EPA applied to the review of the TCR. Where

appropriate, EPA applied the same approach to reviewing the TCR as it did to the review of the

68 chemical NPDWRs. However, because of the nature of the TCR, the pathogens it controls,

the Agency focused its review on the implementation-related requirements.
Protocol for the Review of NPDWRs June 2003 19

B. Technology Assessments

1. What Were the Objectives of the Technology Assessments?

SDWA generally requires that MCLs be set as close to the MCLG as is feasible. When

determining feasibility, the Agency considers cost and capability of the analytical and treatment

methods to respectively measure and remove/reduce drinking water contaminants, and the

availability of these technologies. In some cases, particularly when the Agency sets a zero

MCLG, EPA establishes a higher MCL based on the limitations of analytical or treatment

feasibility. 

Where these constraints apply to the current MCL, the objectives of the technology

assessments were to determine whether there have been improvements in analytical methods or

treatment technologies that may allow EPA to lower the MCL.

2. How Did EPA Review Analytical Methods?

As described in Appendix E, EPA's Office of Ground Water and Drinking Water (OGWDW)

has a process in place to approve new and/or improved analytical methods for drinking water

contaminants. The review and approval of new methods, updates to §§141.23, 141.24, or

141.25, and the approval of methods through §141.27 (alternate analytical techniques - also

known as alternate test procedures or ATP) is generally performed through periodic method

update rules. The review and approval of new methods and/or updates to the methods is also

performed through the rulemaking process to regulate a contaminant or revise the standard for a

contaminant, when appropriate (e.g., the January 22, 2001 final rule for arsenic, (66 FR 6975

(USEPA, 2001b)). More recent methods update rules include 62 FR 10167, March 5, 1997

(USEPA, 1997a), 64 FR 67449, December 1, 1999 (USEPA, 1999d), and 66 FR 3526, a

proposed rule published January 16, 2001 (USEPA, 2001a).

The Six-Year Review did not duplicate those efforts, but used the information from these

method updates in the review process. In those instances where the MCL has been established

based on the limitations of analytical method capabilities and/or where the health effects analysis

suggests that the MCLG/MCL should be lowered, EPA reviewed the existing approved methods

in the context of potential changes in analytical feasibility. The goal of this part of the review

was for EPA to determine whether the currently approved methods provide sufficient analytical

capability to reliably measure the contaminant at levels lower than the current MCL. If the

currently approved method capabilities (i.e., a method detection limit (MDL)) and the practical

quantitation level (PQL) remain limiting factors for revising an MCL, and if the occurrence and

exposure analyses suggest that a meaningful opportunity for health risk reduction could occur

with a more stringent standard, then EPA may determine that the revision may be appropriate. 

Under these circumstance, EPA will consider including a request in the Federal Register for

potential new and/or improved methods that are technologically and economically feasible. 

However, once a more sensitive method is approved for a contaminant, there may be a time lag

between the time of promulgation and the ability of laboratories to begin using the new method. 

Any time lag in the usage of more sensitive methods may therefore result in the delay of any

noticeable change in the feasible level of quantitation.

The remainder of this section generally describes how EPA determines the feasible level of

measurement for chemical and microbiological contaminants for SDWA purposes. It also

discusses how EPA evaluated available, new data to determine if any changes in analytical
13 Because the WS program has been externalized, the Agency is currently deciding how it should assess

the multiple laboratory data that are used to determine the PQL for chemical contaminants. Appendix E briefly

discusses the externalization of the Performance Evaluation program.

Protocol for the Review of NPDWRs June 2003 20

feasibility for the chemical contaminants have occurred since promulgation of the NPDWR. The

document, Analytical Feasibility Support Document for the Six-Year Review of Existing National

Primary Drinking Water Regulations: Reassessment of Feasibility for Chemical Contaminants,

(USEPA, 2003a) describes the process that EPA used to address the analytical feasibility aspect

of the current review for specific chemical contaminants.

Chemical Contaminants

OGWDW establishes a PQL to estimate the level at which laboratories can routinely measure

a chemical contaminant in drinking water. Historically, OGWDW has typically used two main

approaches to determine a PQL for SDWA analytes. The preferred approach used data from

Water Supply (WS) studies (which were predominantly used to certify drinking water

laboratories).13 In most cases, OGWDW used the WS method when sufficient WS data were

available to calculate a PQL. In the absence of sufficient WS data, OGWDW used a multiplier

method, in which the PQL was calculated by multiplying the EPA-derived MDL by a factor of 5

or 10. 

Although there are several approaches that could have been used for the reassessment or

re-evaluation of the PQLs, to be consistent with the historical process, only the "WS data

method" and the "MDL Multiplier method" were considered for this Six-Year Review process. 

Of these two approaches, the Agency preferred to use the WS data approach since it relies on

actual data from a number of EPA Regional and State laboratories. In cases where the WS data

were indicative of a change in the PQL, the MDL multiplier method was only used to estimate

what the potentially new PQL could be. 

EPA reviewed analytical capabilities for contaminants under two circumstances: (1) for those

NPDWRs where the current MCL is set at the PQL and there is no indication that the MCLG

would change; and (2) for those NPDWRs that have undergone a health effects review and there

was a potentially more stringent MCLG. For each of these chemical NPDWRs, EPA used the

following steps to evaluate whether changes in analytical feasibility have occurred:

(1) a methods comparison step to identify whether the ability to detect (and therefore

quantify) these contaminants at lower levels has increased; 

(2) a methods usage over time step to identify the analytical methods that appear to be the

most widely used for the analysis of particular contaminants.

(3) a WS data analysis step to determine if a PQL could be recalculated (if sufficient WS

information were available) or if there was an indication that a PQL might be lower using

the available information.

The results of these three steps aided in assessing whether a PQL might change for a specific

contaminant and, if so, an estimate of what the new PQL might be. Ultimately, the purpose of

this analysis was to determine whether the analytical method capabilities would support a lower

MCL.
Protocol for the Review of NPDWRs June 2003 21

Microbiological Contaminants

For microbes, EPA does not have, or currently envision, a routine pathogen monitoring

requirement, but rather employs indicators of water quality (e.g., total coliforms, E. coli). PQLs

have not been used for microbial indicators because, for approval, the method must be able to

detect a single cell (i.e., MDL and PQL must both be one cell) in a 100 milliliter (mL) water

sample (40 CFR 141.21(f)). In addition, the false-positive and false-negative (i.e., recovery)

rates must be reasonable. EPA is considering whether to define "reasonable" in numerical terms. 

In some cases, EPA may require systems to determine the density of a particular pathogen or

indicator in either their source waters or drinking waters. For example, under the future Long

Term 2-Enhanced Surface Water Treatment Rule (LT2-ESWTR), EPA may require surface

water systems to determine the density of Cryptosporidium in the source water to determine the

level of water treatment the system would need. In this case, the accuracy and precision of the

method at low levels of pathogen density would have to be determined using interlaboratory

studies. The method would have to be sufficiently sensitive to detect a single oocyst. Therefore,

the PQLs and MDLs are not meaningful. In addition, it may be appropriate to determine an

MDL and PQL for some required non-microbial measurements associated with microbial water

quality such as turbidity, disinfectant residual, and algal microcystins. Currently, accurate

measurement of microbiological density is problematic. Moreover, regulation of most

microbiological contaminants are currently treatment-technique based. Therefore, for the

purposes of making a revise/not revise decision, the Agency primarily focused the review on the

treatment-technique (if appropriate) and "other regulatory revisions" aspects of the NPDWRs for

microbiological contaminants. The TCR is the only microbiological NPDWR reviewed under

this protocol as a part of the 1996-2002 review cycle. The TCR is a monitoring rule. Rather

than specify TT requirements, the TCR provides PWSs with a list of recommended best

management practices (BMPs). The review of the "other regulatory revisions" for the TCR

considered whether revisions to the BMPs might be appropriate.

3. How Did EPA Review Treatment Technologies?

As discussed previously, an NPDWR either identifies the BAT for meeting the MCL (even

though BATs are not required for compliance purposes), or establishes enforceable TT

requirements. Currently, for all the pre-1997 chemical NPDWRs reviewed in accordance with

this protocol that include an MCL, the MCL is set equal to the MCLG or the PQL. None of

these MCLs are currently limited by treatment feasibility. Thus, although EPA generally

reviews treatment technologies through alternative mechanisms, there were a few scenarios for

which EPA reviewed treatment feasibility as a part of the Six-Year Review process:

• The health effects technical review identified a potential change to the MCLG/MCL; or

• A health risk assessment was not in process for the contaminant and one of the following

two conditions applied:

(1) the analytical feasibility review identified a possible change to the MCL; or

(2) the NPDWR is a TT-type rule.

EPA also considered revisions that clarify or modify BAT or TT requirements where existing

requirements were not clear or were incorrectly specified. In addition, and where appropriate,

EPA evaluated the likelihood that systems would discontinue existing treatment if EPA were to

raise the MCL. See section III.E for further discussion of how EPA considered economic

factors, as they relate to treatment.
Protocol for the Review of NPDWRs June 2003 22

Treatment capabilities of existing BATs and TTs are well documented by EPA and other

organizations. Likewise, small system compliance and variance technologies are well

documented and periodically reviewed by the Agency. During the development of NPDWRs,

EPA provides state-of-the-science and feasibility of treatment information primarily through its

technical support documents (e.g., EPA technologies and costs reports, and guidance materials

published to assist in regulatory implementation). As part of the Six-Year Review process, EPA

used these same resources, in addition to newer treatment and cost reports, peer-reviewed data,

and other available treatment technology information including that received by EPA from

stakeholders.

The evaluation of treatment technologies supported the regulatory review process by

identifying any known water treatment limitations that might affect a revision of an MCL. In the

case of TT-type rules, this effort supported consideration of whether changes to TT requirements

were warranted. For example, consideration was given to any new treatment processes that are

available and appropriate. If the Agency identified treatment technology-related research needs

as a part of the Six-Year Review process, those research needs were forwarded to the appropriate

Agency group(s) for consideration and prioritization as a part of the overall drinking water

research strategy.

The document, Water Treatment Technology Feasibility Support Document for Chemical

Contaminants; In Support of EPA Six-Year Review of National Primary Drinking Water

Regulations, (USEPA, 2003f) describes the process that EPA used to address the treatment

feasibility aspect of the current review for specific chemical contaminants.

C. Other Regulatory Revisions

1. What Was the Objective of the Review of Other Regulatory Revisions?

In addition to possible revisions to MCLGs, MCLs, and TTs, EPA considered other

regulatory revisions, such as monitoring and system reporting requirements, as a part of the SixYear Review process. The objective of the review of other regulatory revisions was to identify 

potential revisions related to the implementation of the rules that may result in improved public

health protection, and/or present the opportunity for meaningful cost-savings while maintaining,

or improving, the level of public health protection.

2. How Did EPA Consider Other Regulatory Revisions? 

 EPA focused its review on issues that were not already being addressed, or had not been

addressed, through alternative mechanisms (e.g., as part of a recent or ongoing rulemaking).

Where appropriate alternative mechanisms did not exist, EPA considered these implementationrelated concerns if the potential revision met the following criteria:

• It indicated a potential change to an NPDWR, as defined under section 1401 of SDWA;

• It was "ready" for rulemaking – that is, the problem to be resolved has been clearly

identified and specific option(s) have been formulated to address the problem; and

• It met at least one of the following conditions:

– clearly improved the level of public health protection; and/or

– represented a meaningful opportunity for cost-savings while maintaining or

improving the public health protection.
14 While occurrence and exposure estimates factor into the derivation of an RSC, a much more important

factor is exposure information for other media (air, food, etc.) relative to that for water. Exposure information for

other media will be assessed as a part of the health risk assessment described in section III.A of this document, and

not as a part of the occurrence and exposure assessment described in this section. 

Protocol for the Review of NPDWRs June 2003 23

The document, Consideration of Other Regulatory Revisions for Chemical Contaminants in

Support of the Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2003b) summarizes the specific issues identified during the review process. Some of these

issues (e.g., the need to specifically define new system/new source monitoring requirements for

chemical contaminants) have already been addressed in the recently published arsenic and

radionuclides NPDWRs (66 FR 6975, January 22, 2001 (USEPA, 2001b); 65 FR 76707,

December 7, 2000 (USEPA, 2000d)).

D. Occurrence and Exposure Analysis

1. What Were the Objectives of the Occurrence and Exposure Analysis?

The objectives of the occurrence and exposure analysis components of the review process

were to estimate the numbers of PWSs at which contaminants occur at levels of regulatory

interest in drinking water, and to evaluate the number of people exposed to these levels. This

analysis was not necessary for the TCR, since national data were not available and were not

needed. If an organism is known to be transmitted by the fecal-oral route, and has caused at least

one waterborne disease outbreak in this country, that is sufficient reason to control the organism

nationally. The number of systems affected by an organism depends on the characteristics of the

waterborne organism and the type of water source. Therefore, the remaining discussion of the

occurrence and exposure analysis pertains only to the chemical NPDWRs under review.

Combined with results of the other technical analyses described in section III (e.g., health

effects), the results of the occurrence and exposure analysis were used to help determine which

revisions are most likely to provide the greatest public benefit. In some cases, these results may

also be used as a factor when recalculating RSCs.14 EPA plans to perform further, in-depth,

occurrence and exposure analysis prior to any proposed revision to an NPDWR.

2. How Did EPA Conduct the Occurrence and Exposure Analysis?

During the 1996-2002 review cycle, EPA used data voluntarily provided by eight States as a

part of the Agency's occurrence analyses for its Chemical Monitoring Reform (CMR) evaluation

(USEPA, 1999b). EPA augmented this information with other data that were voluntarily

submitted by an additional eight States, based on the same geographic diversity and agricultural

and industrial pollution potential analyses utilized in the CMR analyses. 

The Agency does not believe it is appropriate to revise a pre-1997 NPDWR solely on the

basis that a contaminant is low-occurring or high-occurring at PWSs. However, in assessing

whether to revise the MCL and/or other regulatory revisions, EPA considered the estimated

occurrence and exposure to a contaminant at PWSs at concentrations between the current MCL

and any possible MCL. More specifically, this assessment helped the Agency to determine

whether such revisions were likely to provide a meaningful opportunity for health risk reduction

or cost-savings to PWSs and their customers. Therefore, EPA conducted a detailed occurrence
Protocol for the Review of NPDWRs June 2003 24

and exposure analysis if a regulated chemical contaminant was identified as a potential candidate

for revision by the health effects, technology, and/or other regulatory revisions reviews.

As a part of a "Stage 1" analysis, EPA estimated the percent of PWSs (and the total

population served by those PWSs) with at least one analytical result exceeding the following

thresholds: the lowest level of detection reported by the States; one-half the current MCL, and

the current MCL. Of the chemicals reviewed under this first regulatory review cycle, all were

analyzed in this way, except for contaminants for which: (1) not enough data were available; (2)

the NPDWR specifies a TT-type requirement instead of an MCL; and (3) EPA did not request

data, since the Agency determined there was no health or technological basis for revising, and

because these data would have required extra burden for States to transmit.

Based on the outcome of the health effects, technology, and other regulatory revision

reviews, EPA determined the level(s) of regulatory interest and performed a more detailed,

"Stage 2" statistical analysis. The "Stage 2" analysis estimated the numbers of systems (and the

corresponding affected populations) with mean contaminant concentrations above the levels of

regulatory interest. For example, where WS data in the analytical feasibility review indicated a

possibly lower PQL, EPA estimated a value and used this as a threshold in the occurrence and

exposure analysis. If this analysis indicated that a contaminant was unlikely to occur at

concentrations above those of regulatory interest, EPA determined that a revision was not

warranted during the 1996-2002 review cycle.

The document, Occurrence Estimation Methodology and Occurrence Findings Report for the

Six-Year Review of Existing National Primary Drinking Water Regulations, (USEPA, 2003c)

describes the process that EPA used to address the occurrence and exposure aspect of the current

review for specific chemical contaminants

E. Consideration of Economic Factors

1. What Were the Objectives of EPA's Evaluation of Economic Impacts? 

While section 1412(b)(9) of SDWA provides the Agency broad discretion to consider

economic impacts in the context of the Six-Year Review, the statute precludes EPA from using

economic impacts as the sole basis for a revision that would provide less health protection than

the current standard (anti-backsliding). However, if new peer-reviewed scientific health effects

research indicates that an MCLG could be raised while maintaining public health protection,

then such a change is permitted. For NPDWRs published prior to the 1996 SDWA

Amendments, consideration of economic factors was of limited use when determining whether

revisions were appropriate, except in those situations where a health or technical basis existed

for a potential regulatory revision. Therefore, EPA qualitatively evaluated available economic

information for those NPDWRs identified as potential candidates for revision by the health and

technology reviews. The purpose of this analysis was to determine whether a potential revision

is likely to provide a meaningful opportunity for health risk reduction and/or cost-savings that at

least maintain the current level of public health protection.
Protocol for the Review of NPDWRs June 2003 25

2. How Did EPA Consider Economic Impacts?

EPA did not quantify likely costs and benefits as a part of the review, since many of the

factors that are needed for such calculations depend on specific regulatory options that will not

be definitive until EPA begins the actual rulemaking process. EPA therefore conducted a

qualitative assessment based on the extent of occurrence of a contaminant at the MCL, as well as

at alternative levels, to help determine whether possible changes to an MCL offered a

meaningful opportunity for health risk reduction and/or cost-savings to PWSs and their

customers. For example, in those instances where the health effects and/or technology reviews

indicated that a more stringent MCL might be appropriate, EPA considered the difference

between the levels of occurrence and exposure at the current MCL and the occurrence and

exposure at potentially revised regulatory level(s) indicated by those reviews. On the other

hand, if the health effects review indicated it might be appropriate to establish a less stringent

MCLG/MCL, EPA considered whether such a revision would be likely to offer a meaningful

opportunity for cost-savings. In making this assessment, EPA considered the number of PWSs

with concentrations above the current MCL that may avoid the need to install treatment.

For any NPDWR for which the Agency made a revise decision, the Agency will conduct

detailed cost and benefit analyses, as required, prior to proposing specific regulatory revisions.
Protocol for the Review of NPDWRs June 2003 26
Protocol for the Review of NPDWRs June 2003 27

SECTION IV: STAKEHOLDER INVOLVEMENT

Section IV discusses how the Agency involved the public during the Six-Year Review

process. More specifically, it lists those organizations with which EPA coordinated during the

Six-Year Review process (i.e., key stakeholders), describes the mechanisms EPA used to keep

these stakeholders involved, and discusses the Science Advisory Board's (SAB's) role in the

review process.

A. Who Were the Key Stakeholders in the Six-Year Review Process?

The key stakeholders for the 1996-2002 review cycle included members of the following:

• The general public

• Congress

• Other Federal agencies

• State, Tribal, and local officials

• Public health/health care providers

• Public interest groups

• Public water suppliers

• National trade associations

• Environmental groups

• Manufacturers

• Agricultural producers. 

B. How Were Stakeholders Involved in the Six-Year Review Process?

EPA involved stakeholders by: holding periodic stakeholder meetings; participating in

national meetings, workshops, and technical forums; meeting informally with associations and

technical experts; posting information on the OGWDW web page (www.epa.gov/safewater/);

and publishing Federal Register notices on the Six-Year Review. 

EPA invited representatives from State and Tribal communities, PWSs, public health

organizations, academia, environmental and public interest groups, engineering firms, and other

stakeholders to a stakeholder meeting in Washington, DC, in November 1999 (64 FR 55711,

October 14, 1999 (USEPA, 1999a)). Approximately 50 participants attended, including

representatives from the invited groups. EPA discussed its preliminary strategy for the Six-Year

Review and invited stakeholder comment. Stakeholders generally agreed that EPA had

identified the appropriate key elements for the review; however, in some cases, stakeholders

suggested that EPA needed to be more proactive in seeking out new information that might

affect the regulatory decision (USEPA, 1999c). The executive meeting summary is available on

EPA's drinking water web page, http://www.epa.gov/safewater/ccl/novmtg.html. 

In the Spring of 2000, the NDWAC formed a working group to develop recommendations

regarding the process the Agency should apply to conducting a periodic and systematic review of

existing NPDWRs. The Working Group held two meetings and a conference call from June

through September 2000 (USEPA, 2000a-2000c). The NDWAC approved the Working Group's

recommendations in November 2000 and formally provided them to EPA in December 2000

(NDWAC, 2000). The NDWAC recommended that EPA's review include consideration of five

key elements, as appropriate: health effects, analytical and treatment feasibility,

implementation-related issues, occurrence and exposure, and economic impacts. The NDWAC
Protocol for the Review of NPDWRs June 2003 28

suggested that the Agency conduct a preliminary screening review of each NPDWR to identify

potential candidates for an in-depth analysis. Except where noted in Appendix B, EPA has

followed the protocol recommended by the NDWAC.

In addition to the November 1999 stakeholder meeting and consultation with the NDWAC,

EPA representatives delivered presentations at a variety of meetings held by other organizations,

including: American Water Works Association (AWWA) Technical Advisory Workgroup

meetings, held in February 2001 in Washington, DC and in February 2002 in San Diego, CA; a

meeting held by the Association of State Drinking Water Administrators (ASDWA) in March

2001 in Alexandria, VA; and the annual AWWA meeting held in Washington, DC in June 2001. 

At each of these meetings, stakeholders were given the opportunity to comment on the protocol

by which EPA was planning to perform the review of existing NPDWRs. EPA received valuable

input from stakeholders on the proposed protocol to reviewing existing NPDWRs. 

In December of 2000, EPA Headquarters circulated a memorandum to its Regional offices

requesting feedback on issues relating to the implementation of its drinking water regulations. 

Although the memorandum specified a "potential set of issues" for consideration, Regions were

asked to identify any other known issues related to regulatory implementation. In addition,

ASDWA was asked to confer with the States regarding implementation issues that they felt

needed to be reviewed or addressed. In response to the memorandum and the request to

ASDWA, EPA received comments from four EPA Regions (3, 6, 7, and 8), five States (Iowa,

Michigan, Minnesota, Pennsylvania, and Texas), and ASDWA.

In the April 17, 2002, Federal Register, EPA published its protocol and its preliminary

revise/not revise decisions for the 69 NPDWRs, and requested public comment. The Agency

received and reviewed comments from 44 commenters. EPA discussed the major public

comments and the Agency's response to these comments in the document entitled, Public

Comment and Response Summary for the Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2003d). Based on these public comments, EPA revised this protocol

document to better explain how the Agency integrated the separate analyses and where it applied

judgment in the decisionmaking. EPA also revised several of its technical support documents to

clarify how the Agency conducted the specific analyses that support its revise/not revise

decisions.

C. How Did EPA Plan to Involve the Science Advisory Board?

In June 2002, EPA consulted with the SAB Drinking Water Committee and requested their

review and comment on whether the protocol EPA developed based on the NDWAC

recommendations was consistently applied and appropriately documented. The SAB provided

verbal feedback regarding the transparency and clarity of EPA's decision criteria for making its

revise/not revise decisions under the 1996-2002 review cycle. EPA revised this protocol

document to better explain how the decision criteria were applied and will also take the SAB

comments into consideration when planning for the next review cycle.
Protocol for the Review of NPDWRs June 2003 29

REFERENCES

NDWAC. 2000. Recommended Guidance for Review of Existing National Primary Drinking

Water Regulations. November 2000. Available on the Internet at:

http://www.epa.gov/safewater/ndwac/guidfnl.pdf.

Senate Report. 1995. COMMITTEE OF ENVIRONMENT AND PUBLIC WORKS, SAFE DRINKING

WATER ACT AMENDMENTS OF 1995, S. DOC. NO. 169, 104th Cong., 1st Sess. 38 (1995).

USEPA. 1975. Water Programs: National Interim Primary Drinking Water Regulations. 

Federal Register. Vol. 40, No. 248, p. 59566. December 24, 1975.

USEPA. 1976. Interim Primary Drinking Water Regulations; Promulgation of Regulations on

Radionuclides. Federal Register. Vol. 41, No. 133. p. 28401, July 9, 1976. 

USEPA. 1979. National Interim Primary Drinking Water Regulations; Control of

Trihalomethanes in Drinking Water. Federal Register. Vol. 44, No. 231. p. 68624,

November 29, 1979. 

USEPA. 1985. National Primary Drinking Water Regulations; Volatile Synthetic Organic

Chemicals; Final Rule and Proposed Rule. Federal Register. Vol. 50, No. 219. p. 46902,

November 13, 1985.

USEPA. 1986. National Primary and Secondary Drinking Water Regulations; Fluoride; Final

Rule. Federal Register. Vol. 51, No. 63. p. 11396, April 2, 1986.

USEPA. 1987. National Primary Drinking Water Regulations – Synthetic Organic Chemicals;

Monitoring for Unregulated Contaminants; Final Rule. Federal Register. Vol. 52, No. 130. 

p. 25690, July 8, 1987.

USEPA. 1989a. National Primary and Secondary Drinking Water Regulations; Proposed Rule. 

Federal Register. Vol. 54, No. 97. p. 22062, May 22, 1989.

USEPA. 1989b. National Primary Drinking Water Regulations; Filtration, Disinfection;

Turbidity, Giardia Lamblia, Viruses, Legionella, and Heterotrophic Bacteria; Final Rule. 

Part 2. Federal Register. Vol. 54, No. 124. p. 27486, June 29, 1989.

USEPA. 1991a. National Primary Drinking Water Regulations – Synthetic Organic Chemicals

and Inorganic Chemicals; Monitoring for Unregulated Contaminants; National Primary

Drinking Water Regulations Implementation; National Secondary Drinking Water

Regulations; Final Rule. Federal Register. Vol. 56, No. 30. p. 3526, January 30, 1991. 

USEPA. 1991b. Drinking Water Regulations – Maximum Contaminant Level Goals and

National Primary Drinking Water Regulations for Lead and Copper; Final Rule. Federal

Register. Vol. 56, No. 110. p. 26460, June 7, 1991.

USEPA. 1991c. Drinking Water; National Primary Drinking Water Regulations; Monitoring for

Volatile Organic Chemicals; MCLGs and MCLs for Aldicarb, Aldicarb Sulfoxide, Aldicarb
Protocol for the Review of NPDWRs June 2003 30

Sulfone, Pentachlorophenol, and Barium; Final Rule. Federal Register. Vol. 56, No. 126. 

p. 30266, July 1, 1991. 

USEPA. 1992. Drinking Water; National Primary Drinking Water Regulations – Synthetic

Organic Chemicals and Inorganic Chemicals; National Primary Drinking Water Regulations

Implementation; Final Rule. Federal Register. Vol. 57, No. 138. p. 31776, July 17, 1992.

USEPA. 1996. Performance Evaluation Studies Supporting Administration of the Clean Water

Act and the Safe Drinking Water Act. Federal Register. Vol. 61, No. 139. p. 37464, July

18, 1996.

USEPA. 1997a. National Primary Drinking Water Regulations: Analytical Methods for

Radionuclides; Final Rule and Proposed Rule. Federal Register. Vol. 62, No. 43. p. 10167,

March 5, 1997.

USEPA. 1997b. National Drinking Water Advisory Council, Occurrence and Contaminant

Selection Working Group; Notice of Open Meeting. Federal Register. Vol. 62, No. 113. p.

32113, June 12, 1997.

USEPA. 1998a. Small System Compliance Technology List for the Non-Microbial

Contaminants Regulated Before 1996. EPA 815-R-98-002 (September 1998)

USEPA. 1998b. National Primary Drinking Water Regulations: Disinfectants and Disinfection

Byproducts; Final Rule. Federal Register. Vol. 63, No. 241. p. 69389, December 16, 1998.

USEPA. 1998c. National Primary Drinking Water Regulations: Interim Enhanced Surface

Water Treatment; Final Rule. Federal Register. Vol. 63, No. 241. p. 69478, December 16,

1998.

USEPA. 1999a. Announcement of Stakeholders Meeting on the Drinking Water Contaminant

Identification and Selection Process, and the 6-Year Review of All Existing National

Primary Drinking Water Regulations, as Required by the Safe Drinking Water Act, as

Amended in 1996; Notice of Stakeholders Meeting. Federal Register. Vol. 64, No. 198. p.

55711, October 14, 1999.

USEPA. 1999b. A Review of Contaminant Occurrence in Public Water Systems. EPA Report

816-R-99-006. November 1999. Available on the Internet at: 

http://www.epa.gov/safewater/occur/nov99_lo.pdf. 

USEPA. 1999c. Stakeholder Meeting on the Contaminant Candidate List and the 6-Year

Review of Existing National Primary Drinking Water Regulations. November 1999. 

Available on the Internet at: http://www.epa.gov/safewater/ccl/novmtg.html.

USEPA. 1999d. National Primary and Secondary Drinking Water Regulations - Chemical and

Microbiological Contaminants, Analytical Methods; and Laboratory Certification

Requirements Revisions. Federal Register. Vol. 64, No. 230. p. 67449, December 1, 1999.

USEPA. 2000a. Working Group Meeting on Contaminant Candidate List Regulatory

Determinations and the 6-Year Review of Existing Regulations. Office of Water. June 2000.

Available on the Internet at: http://www.epa.gov/safewater/ccl/junemtg.html.
Protocol for the Review of NPDWRs June 2003 31

USEPA. 2000b. Working Group Meeting on Contaminant Candidate List Regulatory

Determinations and the 6-Year Review of Existing Regulations. Office of Water. July 2000. 

Available on the Internet at: http://www.epa.gov/safewater/ccl/julymtg.html.

USEPA. 2000c. NDWAC Working Group Meeting on Contaminant Candidate List Regulatory

Determinations and the 6-Year Review of Existing Regulations. Office of Water. September

2000. Available on the Internet at: http://www.epa.gov/safewater/ccl/25septmtg.html.

USEPA. 2000d. National Primary Drinking Water Regulations; Radionuclides; Final Rule. 

Federal Register. Vol. 65, No. 236. p. 76707, December 7, 2000.

USEPA. 2000e. Science Policy Council Handbook: Peer Review, 2nd Edition. EPA Report 100-

B-00-001. Office of Science Policy, Office of Research and Development. December 2000.

USEPA. 2001a. National Primary and Secondary Drinking Water Regulations - Pollutants

Analysis; Test Procedures; Guidelines Establishment. Federal Register. Vol. 66, No. 10.

p.3526, January 16, 2001.

USEPA. 2001b. National Primary Drinking Water Regulation; Arsenic and Clarifications to

Compliance and New Source Contaminants Monitoring; Final Rule. Federal Register. Vol.

66, No. 14. p. 6975, January 22, 2001.

USEPA. 2002a. National Primary Drinking Water Regulations: Long-Term 1 Enhanced Surface

Water Treatment Rule; Final Rule. Federal Register. Vol. 67, No. 9. p. 1811, January 14,

2002.

USEPA, 2002b. Quality Assurance for the Six-Year Review of National Primary Drinking

Water Regulations. Memo from Judy Lebowich and Wynne Miller, Targeting and Analysis

Branch. Office of Ground Water and Drinking Water. March 2002.

USEPA. 2002c. Six-Year Review of the Total Coliform Rule – Comments Received. Memo

from Kenneth H. Rotert, Standards and Risk Reduction Branch, Office of Ground Water and

Drinking Water. March 2002.

USEPA. 2002d. National Primary Drinking Water Regulations – Announcement of the Results

of EPA's Review of Existing Drinking Water Standards and Request for Public Comment;

Proposed Rule. Federal Register. Vol. 67, No. 74. p. 19030, April 17, 2002. 

USEPA. 2003a. Analytical Feasibility Support Document for the Six-Year Review of Existing

National Primary Drinking Water Regulations (Reassessment of Feasibility for Chemical

Contaminants). EPA 815-R-03-003. Final. March 2003.

USEPA. 2003b. Consideration of Other Regulatory Revisions for Chemical Contaminants in

Support of the Six-Year Review of National Primary Drinking Water Regulations. EPA

815-R-03-005. Final. June 2003.

USEPA. 2003c. Occurrence Estimation Methodology and Occurrence Findings Report for the

Six-Year Review of Existing National Primary Drinking Water Regulations. EPA

815-R-03-006. Final. June 2003.
Protocol for the Review of NPDWRs June 2003 32

USEPA. 2003d. Public Comment and Response Summary for the Six-Year Review of National

Primary Drinking Water Regulations. EPA 815-R-03-001. Final. June 2003.

USEPA. 2003e. Six-Year Review - Chemical Contaminants - Health Effects Technical Support

Document. EPA 822-R-03-008. Final. June 2003.

USEPA. 2003f. Water Treatment Technology Feasibility Support Document for Chemical

Contaminants; In Support of EPA Six-Year Review of National Primary Drinking Water

Regulations. EPA 815-R-03-004. Final. June 2003.
Protocol for the Review of NPDWRs June 2003

APPENDICES

Appendix A: Pre-1997 National Primary Drinking Water

Regulations (NPDWRs)

Appendix B: Differences between the National Drinking Water

Advisory Council's (NDWAC's) Recommendations

and the Protocol

Appendix C: Overview of the IRIS Assessments

Appendix D: Overview of the OPP Process for Toxicity

Assessments

Appendix E: Overview of Analytical Methods Review Process
Protocol for the Review of NPDWRs June 2003 34
Protocol for the Review of NPDWRs June 2003 A-1

Appendix A: List of Pre-1997 National Primary Drinking 

Water Regulations (NPDWRs)

Table A-1 identifies the NPDWRs promulgated prior to the 1996 SDWA Amendments

(pre-1997 NPDWRs) and the rulemaking by which they were originally promulgated. EPA

reviewed these NPDWRs by 2002 in accordance with the review protocol described in this

document. Table A-2 identifies the remaining pre-1997 NPDWRs which are being or have

already been reviewed in separate actions and the NPDWRs promulgated after the 1996 SDWA

Amendments. The NPDWRs listed in Table A-2 will be reviewed as a part of the 2002-2008

review cycle.

Table A-1: Pre-1997 NPDWRs Reviewed in Accordance with this Protocol

Contaminant Corresponding NPDWR Contaminant Corresponding NPDWR

Chemical Contaminants Chemical Contaminants (continued)

Acrylamide Phase II Rule cis-1,2-Dichloroethylene Phase II Rule

Alachlor Phase II Rule trans-1,2-

Dichloroethylene

Phase II Rule

Antimony Phase V Rule Dichloromethane

(Methylene chloride)

Phase V Rule

Asbestos Phase II Rule 1,2-Dichloropropane Phase II Rule

Atrazine Phase II Rule Di(2-ethylhexyl)adipate

(DEHA)

Phase V Rule

Barium Phase IIB Rule Di(2-ethylhexyl)

phthalate (DEHP)

Phase V Rule

Benzene Phase I Rule Dinoseb Phase V Rule

Benzo[a]pyrene Phase V Rule Diquat Phase V Rule

Beryllium Phase V Rule Endothall Phase V Rule

Cadmium Phase II Rule Endrin Phase V Rule

Carbofuran Phase II Rule Epichlorohydrin Phase II Rule

Carbon tetrachloride Phase I Rule Ethylbenzene Phase II Rule

Chlordane Phase II Rule Ethylene dibromide

(EDB)

Phase II Rule

Chromium (total) Phase II Rule Fluoride Fluoride Rule; Phase II Rule

revised monitoring requirements

Copper Lead and Copper Rule (LCR) Glyphosate Phase V Rule

Cyanide Phase V Rule Heptachlor Phase II Rule

2,4-D Phase II Rule Heptachlor epoxide Phase II Rule

Dalapon Phase V Rule Hexachlorobenzene Phase V Rule

1,2-Dibromo-3-

chloropropane (DBCP) 

Phase II Rule HexachlorocyclopentadienePhase V Rule

1,2-Dichlorobenzene (oDichlorobenzene)Phase II Rule Lead LCR

1,4-Dichlorobenzene (pDichlorobenzene) Phase I Rule Lindane Phase II Rule

1,2-Dichloroethane

(Ethylene dichloride)

Phase I Rule Mercury (Inorganic) Phase II Rule

1,1-Dichloroethylene Phase I Rule Methoxychlor Phase II Rule

Monochlorobenzene

(Chlorobenzene)

Phase II Rule Thallium Phase V Rule
Table A-1: Pre-1997 NPDWRs Reviewed in Accordance with this Protocol

Contaminant Corresponding NPDWR Contaminant Corresponding NPDWR

Protocol for the Review of NPDWRs June 2003 A-2

Nitrate (as N) Phase II Rule Toluene Phase II Rule

Nitrite (as N) Phase II Rule Toxaphene Phase II Rule

Oxamyl (Vydate) Phase V Rule 2,4,5-TP (Silvex) Phase II Rule

Pentachlorophenol Phase IIB Rule 1,2,4-Trichlorobenzene Phase V Rule

Picloram Phase V Rule 1,1,1-Trichloroethane Phase I Rule

Polychlorinated biphenyls

(PCBs)

Phase II Rule 1,1,2-Trichloroethane Phase V Rule

Selenium Phase II Rule Trichloroethylene Phase I Rule

Simazine Phase V Rule Vinyl chloride Phase I Rule

Styrene Phase II Rule Xylenes (total) Phase II Rule

2,3,7,8-TCDD (Dioxin ) Phase V Rule Microorganisms

Tetrachloroethylene Phase II Rule Total coliforms

(including fecal coliform

and E. coli)

Total Coliform Rule (TCR)

Dates of original promulgation are as follows:

- Phase II Rule: 56 FR 3526, January 30, 1991 (USEPA, 1991a)

- Phase V Rule: 57 FR 31776, July 17, 1992 (USEPA, 1992)

- Phase IIB Rule: 56 FR 30266, July 1, 1991 (USEPA, 1991c)

- Phase I Rule: 52 FR 25690, July 8, 1987 (USEPA, 1987)

- LCR: 56 FR 26460, June 7, 1991 (USEPA, 1991b)

- Fluoride Rule: 51 FR 11396, April 2, 1986 (USEPA, 1986)

- TCR: 54 FR 27562, June 29, 1989 (USEPA, 1989b)
Protocol for the Review of NPDWRs June 2003 A-3

Table A-2: NPDWRs Not Covered by this Protocol

Contaminant/Indicator Corresponding NPDWR1 Reason Not Included

Chemical Contaminants

Arsenic Pre-1986 National Interim Primary

Drinking Water Regulation (NIPDWR)

Reviewed/revised under January 22,

2001 Arsenic Rule2,3

Radionuclides

Beta particles and photon emitters

Pre-1986 NIPDWR Reviewed/revised under December 7,

2000 Radionuclides Rule Gross alpha particle activity 2

Radium-226/228 (combined)

Uranium 2000 Radionuclides Rule

Promulgated after 1996. NPDWR

established in the December 7, 2000

Radionuclides Rule2

Microorganisms

Cryptosporidium

Interim Enhanced Surface Water

Treatment Rule (IESWTR)

Long-Term 1 Enhanced Surface Water

Treatment Rule (LT1ESWTR)

Subject of ongoing rulemaking activity -

Long-Term 2 ESWTR (LT2ESWTR)

(November 2003 to mid 2004)4

Giardia lambia Surface Water Treatment Rule (SWTR);

IESWTR; LT1ESWTR

Heterotrophic plate count (HPC) SWTR

Legionella SWTR

Turbidity SWTR; IESWTR; LT1ESWTR

Viruses SWTR; IESWTR; LT1ESWTR

Disinfection Byproducts

Bromate ion

Disinfectants and Disinfection

Byproducts Rule Stage 1 (DBPR)

Revised rule promulgated after 1996 and

additional revisions to be considered

under Stage 2 DBPR (July 2003 to mid

2004)4

Chlorite ion

Haloacetic acids: Monobromoacetic

acid; Dibromoacetic acid;

Monochloroacetic acid;

Dichloroacetic acid; and

Trichloroacetic acid

Total Trihalomethanes (TTHMs):

Chloroform; Bromodichloromethane; Dibromochloromethane;

and Bromoform

TTHM Rule; Requirements revised

under Stage 1 DBPR

Revised rule promulgated after 1996 and

additional revisions to be considered

under Stage 2 DBPR (July 2003 to mid

2004)4

Disinfectant Residuals

Chlorine

Chloramines Stage 1 DBPR Revised rule promulgated after 1996

Chlorine dioxide
Table A-2: NPDWRs Not Covered by this Protocol

Protocol for the Review of NPDWRs June 2003 A-4

1 Dates of original promulgation are as follows:

– Arsenic Rule: 40 FR 59566, December 24, 1975 (USEPA, 1975)

– Radionuclides Rule: 41 FR 28402, July 9, 1976 (USEPA, 1976)

– IESWTR: 63 FR 69478, December 16, 1998 (USEPA, 1998c)

– LT1ESWTR: 67 FR 1811, January 14, 2002 (USEPA, 2002a)

– SWTR: 54 FR 27486, June 29, 1989 (USEPA, 1989b)

– Stage 1 DBPR Rule: 63 FR 69389, December 16, 1998 (USEPA, 1998b)

– TTHM Rule: 44 FR 68624, November 29, 1979 (USEPA, 1979)

2 Indicates date of rule revision.

– Arsenic Rule: 66 FR 6976, January 22, 2001 (USEPA, 2001b)

– Radionuclides Rule: 65 FR 76707, December 7, 2000 (USEPA, 2000d)

3 After promulgation of the revised arsenic NPDWR on January 22, 2001, EPA initiated a review of the new MCL, and

postponed the effective date of the rule until February 22, 2002. EPA requested independent expert panel reviews of the

science, cost and benefits analyses for the January 2001 rule, and in July 2001, sought additional public comment on a range

of MCLs. Following receipt of the final expert panel reports in the Fall of 2001, EPA requested comment on the reports. 

EPA will continue to evaluate the expert panel reports, the voluminous comments received during these comment periods,

and other relevant information and comments as they become available as part of the next Six-Year Review; EPA expects to

make a final decision on whether to revise the January 2001 rule as part of that Six-Year Review, which is due in August

2008. In the meantime, as announced by the Administrator on October 31, 2001, EPA will not further postpone the January

2001 rule, and EPA also does not expect to take any other additional action relative to the July 2001 proposal in the interim. 

The revised arsenic MCL became effective on February 22, 2002. The date for compliance with the MCL remains January

23, 2006.

4 Indicates anticipated date of promulgation.
Protocol for the Review of NPDWRs June 2003 B-1

Appendix B: Differences between the National Drinking Water Advisory Committee's

(NDWAC's) Recommendations and this Protocol 

This table indicates those NDWAC recommendations that EPA either did not incorporate or that

EPA changed substantially in this protocol document. Overall, EPA incorporated the majority of

the NDWAC's recommendations

NDWAC Recommendation EPA Response

EPA should review the basis of all existing

NPDWRs during the first review round (i.e., the

review round ending August 2002)

EPA does not believe that such a review is

practical in light of resource constraints and has

not incorporated it into the protocol. EPA will

review the basis of existing regulations only if

new data suggest the need for regulatory

revision(s).

Effective with review rounds starting after August

2002, EPA should complete both the review and

the revision within the Six-Year window.

This recommendation does not apply to the 1996-

2002 review round.

EPA should fully consider "other regulatory

revisions" (e.g., monitoring requirements system

data reporting requirements, etc.) as a part of the

Six-Year Review process.

EPA believes that many of these issues are best

addressed through mechanisms other than the SixYear Review process. Where appropriate

alternative mechanisms to consider these issues

are not available, EPA may consider them as a

part of the Six-Year Review if they meet the

following criteria:

 • they indicated a potential change to an

NPDWR, as defined under section 1401;

 • they are "ready" for rulemaking – that is, the

problem to be resolved has been clearly

identified and specific option(s) have been

formulated to address the problem; and

 • they represented a meaningful opportunity

for cost-savings while maintaining or

improving the level of public health

protection.

EPA should consider non-regulatory options, in

addition to regulatory changes, if the costs of

other regulatory compliance are considered to be

too high or interim measures are needed pending

promulgation of a rule.

EPA agrees that this suggestion has merit but

believes it is outside the scope of the Six-Year

Review effort and should be addressed through

alternative mechanisms. The recommendation

has not been incorporated into the protocol

document.

EPA should consider changes in State datareporting requirements, as well as changes to

system data-reporting requirements, as a part of

the Six-Year Review process.

EPA believes that revisions to State datareporting requirements are best considered

through other mechanisms outside the scope of

the Six-Year Review effort. The recommendation

has not been incorporated into the protocol

document.
NDWAC Recommendation EPA Response

Protocol for the Review of NPDWRs June 2003 B-2

EPA should consider multi-media mitigation

options as a part of the Six-Year Review process.

Efforts to pursue multi-media mitigation for

contaminants are outside the scope of the SixYear process, except in those instances where the

SDWA specifically authorizes EPA to consider a

multi-media approach as a part of the NPDWR. 

Therefore, consideration of multi-media

mitigation is outside the scope of the 1996-2002

Six-Year Review.

EPA should quantify, to the maximum extent

practicable, costs and benefits associated with

possible regulatory revisions.

EPA does not believe it is practicable to quantify

costs and benefits during the review phase. This

is best done as a part of the rulemaking phase

before EPA proposes actual revisions. Instead,

EPA will conduct a qualitative assessment of

economic considerations for those NPDWRs

where a health or technical basis exists for a

possible regulatory revision.
15 IRIS contains chemical specific health effects information. Information on synergistic effects of chemical

mixtures is scarce and is seldom available for inclusion in IRIS. 

Protocol for the Review of NPDWRs June 2003 C-1

Appendix C: Overview of the IRIS Assessments

The Integrated Risk Information System (IRIS) is an EPA database containing Agency

consensus scientific positions on potential adverse human health effects that may result from

chronic exposure to chemical substances found in the environment.15 Assessments by IRIS

undergo internal and external peer reviews by health scientists.

The main reasons for including a chemical in the IRIS program are (1) Agency statutory,

regulatory, or program implementation needs; and (2) availability of new scientific information

or new methodology that might significantly change current IRIS assessment.

IRIS assessments are based solely on scientifically valid studies. Evaluations of original

toxicological and epidemiological studies conducted by the National Toxicology Program,

National Cancer Institute, National Institute of Environmental Health Sciences, EPA's National

Center for Environmental Assessment, industry, universities, etc., are all used in risk assessment. 

These studies are individually evaluated for their soundness, methodological strength and

weaknesses, and whether or not they have been conducted according to current quality standards.

IRIS reviews are not based on secondary sources such as reviews conducted by other

national or international organizations (e.g., State of California, World Health Organization or

the International Agency for Research on Cancer), although such assessments are often

examined as part of the IRIS review.

A full list of chemicals assessed in IRIS and those for which assessments are planned can

be found on IRIS web site (http://www.epa.gov/iris). A large number of these IRIS assessments

are of direct relevance to the regulatory function of Office of Water (OW) and more specifically

to the six-year review. Some of the reviews are being conducted by OW. Others were

nominated for review by OW.
Protocol for the Review of NPDWRs June 2003 C-2
Protocol for the Review of NPDWRs June 2003 D-1

Appendix D: Overview of the OPP Process for Toxicity Assessments

Under the requirements of the Federal Insecticide, Fungicide, and Rodenticide Act

(FIFRA), a registrant (manufacturer) is required to submit animal toxicity data on the potential

human health effects that may be posed by pesticide chemicals. Toxicity data are provided

during the initial registration of a pesticide as well as during the periodic re-registration review

of the pesticide as required by FIFRA. The schedule priority, for when an existing pesticide

enters a re-review is set in part by regulatory requirements which include provisions to give

priority to certain active ingredients. The Office of Pesticides Programs (OPP) will establish the

review schedule taking into account the procedures outlined in the Act. A more complete

discussion of the re-registration process can be found in section 4(a)-(f) of FIFRA.

In 1998, The Office of Water's (OW's) OGWDW and the OPP established major areas of

coordination on cross-cutting scientific issues. Included in the major efforts was the

harmonization of the human health hazard assessments and dose-response relationships for

pesticides. The two offices have agreed to share health effects data and coordinate activities on

the issues such as endpoint selection, dose-response information, and quantifying risks. 

Therefore, the OW and OPP are working closely on establishing consistency in health effects

endpoints through resource and information sharing.

The OPP receives health effects data that are generated under specific scientific

guidelines established by the Agency and conducted under the requirements of Good Laboratory

Practices. These guidelines are available on the EPA's Internet site at the following location: 

http://www.epa.gov/opptsfrs/OPPTS_Harmonized/870_Health_Effects_Test_Guidelines/indexx.

html.

In addition to the required guideline studies, the OPP will obtain and review open

literature data on adverse effects to test species. Although these studies are not used in

establishing health end-points (RfDs) and cancer potency or threshold values, they are used in

establishing the "weight of evidence" for an adverse effect. Data sources include, but are not

limited to, published, peer-reviewed journal articles in the open literature and toxicity data

submitted to other U.S. federal or international agencies that do not conform to the OPP's test

guidelines.

Below is a brief overview of end-point selection. 

Toxicity Assessment

Non-Cancer Effects: 

Reference Dose. For non-cancer effects, toxicity is represented by an RfD; it may be

calculated for acute effects (acute RfD (aRfD)) and chronic effects (chronic RfD (cRfD)). RfDs

are calculated by determining the No-Observed-Adverse-Effect Level (NOAEL) or bench-mark

dose point of departure from either acute or chronic toxicity studies (the choice of study depends

on which type of RfD is being calculated - aRfD or cRfD) and dividing it by the appropriate

uncertainty factors. Typically, an uncertainty factor is applied to account for: variation within

the human population (i.e., intraspecies); the differences between humans and animals as the

animal data are extrapolated to humans (i.e., interspecies); the duration of the study; the end
Protocol for the Review of NPDWRs June 2003 D-2

point used in the calculation (NOAEL or Lowest-Observed-Adverse-Effect Level (LOAEL));

and the completeness of the database. 

If the RfD will be used in dietary risk assessment, then it is adjusted to take into account

the Food Quality Protection Act (FQPA) Safety Factor for infants and children. Such an

adjusted RfD is called a Population Adjusted Dose (PAD). Like the RfD, it may be acute

(aPAD) or chronic (cPAD). In making the decision regarding the FQPA Safety Factor, the

Agency takes into account both information on the toxicity of the pesticide and the completeness

of the toxicity and exposure databases. For more information on how the Agency applies the

FQPA Factor, see the document "Standard Operating Procedures for use of FQPA Safety

Factor," April 26, 1999 at http://www.epa.gov/pesticides/trac/science/. However, these standard

operating procedures are currently under revision; and notification of the release of these

revisions is posted at: http://www.epa.gov/oppfead1/trac/science.

Cancer Effects: 

Linear Effect - Cancer Potency Factor (q1*). The cancer potency factor, which is

commonly known as a q1*, is the relative strength of a carcinogen. The bigger the q1*, the more

potent the carcinogen. It is calculated using a computer model that assumes linearity at doses

below which the effect occurred in the studies.

Non-Linear Effect - Margin of Exposure. For some carcinogenic pesticides, it is not

considered appropriate to calculate a potency factor. In these cases, the cancer effect is assumed

to have a threshold, as for non-cancer effects, and as such, a Margin of Exposure (MOE) is

derived. The MOE is a ratio calculated by dividing the toxicity Point of Departure (such as a

NOAEL or benchmark dose) by the estimated or calculated exposure level. EPA has not yet

established a policy on the level of risk that is of no concern for non-linear cancer risk

assessment.

During the review of the toxicity data and the dose-response assessment, the pesticide

being evaluated undergoes review by several in-house peer review committees. 
Protocol for the Review of NPDWRs June 2003 E-1

Appendix E: Overview of the Analytical Methods Review Process

A. What Section of SDWA Requires the Agency to Specify Analytical Methods?

SDWA directs EPA to promulgate NPDWRs which specify either MCLs or TTs for

drinking water contaminants (SDWA section 1412; 42 U.S.C. § 300g-1). According to SDWA

(section 1401(1)(D)), NPDWRs include "criteria and procedures to assure a supply of drinking

water which dependably complies with such maximum contaminant levels; including accepted

methods for quality control and testing procedures to insure compliance with such levels." (42

U.S.C. § 300f(1)(D)) Moreover, EPA is to set an MCL for such NPDWRs "if, in the judgement

of the Administrator, it is economically and technologically feasible to ascertain the level of a

contaminant in water in public water systems." (SDWA section 1401(1)(C)(i); 42 U.S.C. §

300f(1)(C)(i)). Alternatively, if it is not economically or technologically feasible to so ascertain

the level of a contaminant, the Administrator may identify known TTs, which sufficiently reduce

the contaminant in drinking water, in lieu of an MCL (SDWA section 1401(1)(C)(ii)). 

B. What is the Typical Process for Approving Methods for SDWA Analytes?

Methods are initially approved as a part of an MCL or monitoring requirement

rulemaking. Thereafter, as revisions to the approved methods are published or as new

technologies are developed, the Agency, from time-to-time, will group a set of methods for

proposal in a methods update rule. It generally takes 18 to 24 months to promulgate a methods

update rule. This can increase significantly if there is adverse public comment on a proposed

method. 

The revised or new methods included in a methods update rule may be from EPA, other

Federal or State agencies, or standards organizations (e.g., American Society for Testing and

Materials (ASTM) or Standard Methods (SM)). These non-EPA entities have independent

review and/or collaborative testing requirements. In addition, under 40 CFR 141.27 (alternate

analytical techniques, also known as alternate test procedures or ATP) methods may also be

developed by private laboratories, vendors or groups. Independent review and collaborative

testing of these privately developed methods is accomplished by requiring submission of the

method to the Agency under the alternate test procedure (ATP) program. An alternate technique

is accepted "only if it is substantially equivalent to the prescribed test in both precision and

accuracy as it relates to the determination of compliance with the MCL." (40 CFR 141.27(a)) 

Initially, many ATP applications are missing data. Once a completed ATP application is

recorded by the Agency, the ATP pass/fail decision generally takes three to four months. For

successful ATPs, this period is followed by the formal rulemaking process, which was described

above as taking 18-24 months.

C. What Factors Does the Agency Consider in Approving Analytical Methods and in

Determining Feasible Limits?

In deciding whether an analytical method is economically and technologically feasible to

determine the level of a contaminant in drinking water, the Agency generally considers the

following (50 FR 46902, November 13, 1985 (USEPA, 1985); 52 FR 25690, July 8, 1987

(USEPA, 1987); 54 FR 22062, May 22, 1989a):

• Is the method sensitive enough to address the level of concern (i.e., is quantitation

sufficient to meet the MCL)?
Protocol for the Review of NPDWRs June 2003 E-2

• Does the method give reliable analytical results at the MCL? What is the precision

(or reproducibility) and the bias (accuracy or recovery)?

• Is the method specific? Does the method identify the contaminant of concern in the

presence of potential interferences?

• Is the availability of certified laboratories, equipment and trained personnel sufficient

to conduct compliance monitoring?

• Is the method rapid enough to permit routine use in compliance monitoring?

• What is the cost of the analysis to Water Supply systems?

Regarding the first criteria (i.e., sensitivity), the method detection limit (MDL) and the

practical quantitation level (PQL) are two performance measures used by EPA to estimate the

limits of performance of analytic chemistry methods for measuring contaminants in drinking

water. For SDWA analytes, EPA defines the MDL as "the minimum concentration of a

substance that can be measured and reported with 99% confidence that the analyte concentration

is greater than zero"(40 CFR Part 136 Appendix B). MDLs can be operator, method, laboratory,

and matrix specific. MDLs are not necessarily reproducible within a laboratory or between

laboratories on a daily basis due to the day-to-day analytical variability that can occur and the

difficulty of measuring an analyte at very low concentrations. In an effort to integrate this

analytical chemistry data into regulation development, the Agency uses the PQL to estimate or

evaluate the minimum, reliable quantitation level that most laboratories can be expected to meet

during day-to-day operations. EPA's Drinking Water program generally defines the PQL as "the

lowest level that can be reliably achieved within specified limits of precision and accuracy

during routine laboratory operating conditions" (50 FR 46902, November 13, 1985 (USEPA,

1985)) For several SDWA analytes, EPA has set the MCL at the PQL. 

D. How Are PQLs Typically Determined for SDWA Contaminants?

Historically, EPA's OGWDW has used two main approaches to determine a PQL for

SDWA analytes. The preferred approach, the WS method, uses data from WS studies to

calculate the lower limit of quantitation. The WS method was used in most cases when

sufficient WS data are available to calculate a PQL. In the absence of WS data, the second

approach that EPA used was the MDL multiplier method. In this approach, the PQL was

calculated by multiplying the EPA-derived MDL by a factor of 5 or 10. The 5 or 10 multiplier

was used to account for the variability and uncertainty that can occur at the MDL. 

1. How Were Water Supply Studies Conducted?

Water supply laboratory performance evaluation (PE) studies have been an integral part

of EPA's certification program for drinking water laboratories for over 20 years. Historically,

EPA's National Exposure Research Laboratory (NERL) in Cincinnati, Ohio conducted WS

studies for all current and proposed drinking water contaminants. Although EPA conducted the

WS studies semi-annually, for certification purposes, laboratories were only required to

demonstrate acceptable performance once a year (141.23(k)(3) and 141.24(f)(17)). 

Each WS study included WS samples (or sample concentrates) that were analyzed for

both SDWA analytes and analytes being considered for regulation under the SDWA. During

these WS studies, EPA-NERL sent participating laboratories a set of the stable WS sample

concentrates in sealed glass ampules, a data reporting form, and appropriate instructions. 

EPA-NERL sent WS samples to all laboratories that conducted drinking water analyses,
Protocol for the Review of NPDWRs June 2003 E-3

including utility laboratories, commercial laboratories, and State and EPA Regional laboratories. 

With appropriate dilution, the laboratory then analyzed the WS samples using the specified

procedures. Afterwards, the laboratory sent the completed reporting form to EPA for evaluation. 

After evaluation, EPA returned a fully detailed report to each participating laboratory. 

At this point in time, WS PE studies are no longer performed by EPA. On July 18, 1996

(61 FR 37464 (USEPA, 1996)), EPA proposed options for the externalization of the PE studies

program (now referred to as the Proficiency Testing or PT program). After evaluating public

comment, in the June 12, 1997 final notice EPA stated that the Agency has decided (62 FR

32113 (USEPA, 1997b)):

...on a program where EPA would issue standards for the operation of the program, the

National Institute of Standards and Technology (NIST) would develop standards for

private sector PE (PT) suppliers and would evaluate and accredit PE suppliers, and the

private sector would develop and manufacture PE (PT) materials and conduct PE (PT)

studies. In addition, as part of the program, the PE (PT) providers would report the

results of the studies to the study participants and to those organizations that have

responsibility for administering programs supported by the studies.

2. PQL Determinations - How Are WS Studies Evaluated and What Criteria Are

Used?

The derivation of the PQL involves determining the concentration of an analyte at which

a set percentage of the laboratories achieve results within a specified range of the spiked value. 

Historically, the percentage of laboratories was set at 75 percent, while a range of acceptance

limits around the spiked value were used. In many cases, EPA derived PQLs only from the data

submitted by the EPA Regional and State laboratories that participate in the WS studies. 

A PQL derived from WS data in such a manner is considered a stringent target for

routine laboratory performance because:

• WS samples are prepared in reagent water and therefore do not contain the matrix

interferences that may occur in field samples.

• Laboratories analyze only a small number of samples for the study and are aware that

the samples are for the purposes of PE (i.e., they are not "blind" samples).

In deriving a PQL from WS study data, the Agency typically sets a fixed percentage or 2

sigma (2 standard deviation) acceptance window around the known concentration (or spike

value) of the WS samples. Then percentage of laboratories achieving results within the specified

acceptance window (y-axis) is plotted against the known spike concentration of the WS study

samples (x-axis). While the acceptance limits for inorganics typically range from 15 to 30

percent, the acceptance limits for organics generally range from 40 to 50 percent. Several

SDWA analytes have acceptance limits of 2 sigma (2 standard deviation). Linear regression or

graphical analysis is performed on the WS data to determine the concentration at which 75

percent of EPA Regional and State laboratories achieve acceptable results.
Protocol for the Review of NPDWRs June 2003 E-4

EPA_815-R-03-002

EPA_Protocol_for_the_Review_of

Existing_National_Primary_Drinking_Water_Regulations