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ENVIRONMENTAL PROTECTION AGENCY 

[EPA-HQ-OW-2008-0747; FRL– ] 

RIN 2040-AE90

National Primary Drinking Water Regulations; Announcement of the Results of EPA’s 

Review of Existing Drinking Water Standards and Request for Public Comment and/or 

Information on Related Issues 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Notice; request for comments. 

SUMMARY: The Safe Drinking Water Act (SDWA) requires the United States 

Environmental Protection Agency (EPA) to conduct a periodic review of existing National 

Primary Drinking Water Regulations (NPDWRs) and determine which, if any, need to be 

revised. The purpose of the review, called the Six-Year Review, is to identify those 

NPDWRs for which current health effects assessments, changes in technology, and/or other 

factors provide a health or technical basis to support a regulatory revision that will improve 

or strengthen public health protection. EPA has completed its detailed review of 71 

NPDWRs and at this time believes that four NPDWRs are candidates for regulatory revision. 

These four NPDWRs are acrylamide, epichlorohydrin, tetrachloroethylene, and 

trichloroethylene. EPA requests public comment and/or relevant information that will assist 

the Agency as we move forward with regulatory action to revise these four NPDWRs. In 

addition to the 71 NPDWRs discussed in detail in today’s action, this review also includes 14 

other NPDWRs that need no detailed review because of recent or ongoing revision actions. 

DATES: Comments must be received on or before [INSERT DATE 60 DAYS AFTER 

THE DATE OF THE PUBLICATION IN THE FEDERAL REGISTER], 60 days after 

publication in the Federal Register. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OWDeleted: ¶

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2008-0747, by one of the following methods: 

• http://www.regulations.gov: Follow the online instructions for submitting comments. 

• Mail: Water Docket, Environmental Protection Agency, Mailcode: 2822T, 1200 

Pennsylvania Ave., NW, Washington, DC 20460. 

• Hand Delivery: EPA Docket Center Public Reading Room, EPA Headquarters West, 

Room 3334, 1301 Constitution Ave., NW, Washington, DC. Such deliveries are only 

accepted during the Docket's normal hours of operation, and special arrangements 

should be made for deliveries of boxed information. 

Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2008-0747. EPA's 

policy is that all comments received will be included in the public docket without change and 

may be made available online at http://www.regulations.gov, including any personal information 

provided, unless the comment includes information claimed to be Confidential Business 

Information (CBI) or other information whose disclosure is restricted by statute. Do not submit 

information that you consider to be CBI or otherwise protected using 

http://www.regulations.gov. Please contact EPA prior to submitting CBI. 

The http://www.regulations.gov web site is an “anonymous access” system, which means 

EPA will not know your identity or contact information unless you provide it in the body of your 

comment. If you send an e-mail comment directly to EPA without going through 

http://www.regulations.gov your e-mail address will be automatically captured and included as 

part of the comment that is placed in the public docket and made available on the Internet. If you 

submit an electronic comment, EPA recommends that you include your name and other contact 

information in the body of your comment and with any disk or CD-ROM you submit. If EPA 

cannot read your comment due to technical difficulties and cannot contact you for clarification, Deleted: ¶

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EPA may not be able to consider your comment. Electronic files should avoid the use of special 

characters, any form of encryption, and be free of any defects or viruses. For additional 

instructions on submitting comments, go to section I.B of this document. 

Docket: All documents in the docket are listed in the http://www.regulations.gov index. 

Although listed in the index, some information is not publicly available, e.g., CBI or other 

information whose disclosure is restricted by statute. Certain other material, such as copyrighted 

material, will be publicly available only in hard copy. Publicly available docket materials are 

available either electronically in http://www.regulations.gov or in hard copy at the Water Docket, 

EPA/ DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal 

holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the 

telephone number for the EPA Docket Center is (202) 566-2426. 

FOR FURTHER INFORMATION CONTACT: For technical inquiries contact: Rajiv 

Khera, (202) 564–4881, or Karen Wirth, (202) 564-5246, Office of Ground Water and Drinking 

Water, Environmental Protection Agency. For general information about, and copies of, this 

document or information about the existing NPDWRs discussed in this action, contact the Safe 

Drinking Water Hotline. Callers within the United States may reach the Hotline at (800) 426-

4791. The Hotline is open Monday through Friday, excluding Federal holidays, from 9 a.m. to 

5:30 p.m. Eastern Time.

ABBREVIATIONS AND ACRONYMS USED IN THIS ACTION

>—greater than 

2,4-D—2,4-dichlorophenoxyacetic acid 

μg/L—microgram per liter Deleted: ¶

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AMG—Alternative Monitoring Guidelines 

ASDWA—Association of State Drinking Water Administrators 

ATSDR—Agency for Toxic Substances and Disease Registry 

AWWA—American Water Works Association 

BAT—best available technology 

CARC—Cancer Assessment Review Committee 

CBI—Confidential Business Information 

CCL—Contaminant Candidate List 

CFR—Code of Federal Regulations

Cr III—trivalent chromium 

Cr VI—hexavalent chromium 

CWS—community water system 

DBPs—disinfection byproducts 

DBCP—1,2-dibromo-3-chloropropane 

DBPR—Disinfectants and Disinfection Byproducts Rule 

DEHA—di(2-ethylhexyl)adipate 

DEHP—di(2-ethylhexyl)phthalate 

DWEL—drinking water equivalent level 

EDB—ethylene dibromide 

EPA—U.S. Environmental Protection Agency 

EQL—estimated quantitation level 

ESA—ethanesulfonic acid 

FR—Federal Register Deleted: ¶

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FQPA—Food Quality Protection Act 

GAC—granular activated carbon 

GWR—Ground Water Rule 

HAA5—haloacetic acids 

IARC—International Agency for Research on Cancer 

ICR—Information Collection Request 

IRED—Interim Reregistration Eligibility Decision 

IRIS—Integrated Risk Information System 

LCR—Lead and Copper Rule 

LH—lutenizing hormone 

LOAEL—lowest-observed-adverse-effect level 

LT2ESWTR—Long-Term 2 Enhanced Surface Water Treatment Rule 

MCL—maximum contaminant level 

MCLG—maximum contaminant level goal 

MDL—method detection limit 

mg/kg-day—milligrams per kilogram of body weight per day 

mg/L—milligrams per liter 

MOA—mode of action 

MRL—minimum reporting level 

N—nitrogen 

NAS—National Academy of Sciences 

NAWQA—National Water Quality Assessment 

NCFAP—National Center for Food and Agricultural Policy Deleted: ¶

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NCOD—National Drinking Water Contaminant Occurrence Database 

NDWAC—National Drinking Water Advisory Council 

NELAC—National Environmental Laboratory Accreditation Conference 

NOAEL—no-observed-adverse-effect level 

NPDWR—National Primary Drinking Water Regulation 

NRC—National Research Council 

NTNCWS—non-transient, non-community water system 

NTP—National Toxicology Program 

OPP—Office of Pesticide Programs 

ORD—Office of Research and Development 

OW—Office of Water 

PCBs—polychlorinated biphenyls 

PCE—tetrachloroethylene 

PE—Performance Evaluation 

pCi/L—picoCurie per liter 

PN—public notification 

ppb—part per billion (e.g., microgram per liter) 

ppm—part per million (e.g., milligram per liter) 

PQL—practical quantitation limit 

PT—Performance Testing 

PTA—packed tower aeration 

PWS—public water system 

R2S2—Regulatory Review Support Spreadsheet Deleted: ¶

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RED—Reregistration Eligibility Decision 

RfD—reference dose 

RSC—relative source contribution 

SAB—Science Advisory Board 

SSCT—Small System Compliance Technology 

SDWA—Safe Drinking Water Act 

SDWIS/FED—Safe Drinking Water Information System/Federal version 

SMCL—secondary maximum contaminant level 

SOC—synthetic organic chemical 

STORET—STOrage and RETrieval data system 

SWTR—Surface Water Treatment Rule 

T3—triiodothyronine (thyroid hormone) 

T4—levothyroxine (thyroid hormone) 

TCDD—tetrachlorodibenzo-p-dioxin 

TCE—trichloroethylene 

TNCWS—transient, non-community water system 

TP—trichlorophenoxypropionic acid 

TRED—Interim Tolerance Reassessment and Risk Management Decisions 

TRI—Toxics Release Inventory 

TSC—Technical Support Center 

TT—treatment technique 

TTHM—total trihalomethanes 

USDA—U.S. Department of Agriculture Deleted: ¶

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UCMR 2—second Unregulated Contaminant Monitoring Rule 

USGS—U.S. Geological Survey 

VOC—volatile organic compound 

WS—water supply 

Table of Contents 

I. General Information .............................................................................................................10 

A. Does This Action Apply to My Public Water System? .....................................................10 

B. How Should I Submit Comments on This Action? ...........................................................11 

C. What Should I Consider as I Prepare My Comments for EPA?........................................11 

II. Statutory Requirements for the Six-Year Review ..............................................................12 

III. Stakeholder Involvement in the Six-Year Review Process...............................................12 

A. How Have Stakeholders Been Involved in the Review Process?......................................12 

B. How Did EPA Incorporate Feedback from the Science Advisory Board’s 2002 

Comments on the Six-Year Review Protocol? ..............................................................................13 

IV. Regulations Included in the Six-Year Review ..................................................................13 

V. EPA’s Protocol for Reviewing the NPDWRs Included in This Action..............................16 

A. What Was EPA’s Review Process? ...................................................................................16 

B. How Did EPA Conduct the Initial Review and Evaluate Key Technical Elements of the 

NPDWRs? 22 

1. Initial Review.....................................................................................................................22 

2. Health Effects.....................................................................................................................23 

3. Analytical Feasibility.........................................................................................................28 

4. Occurrence and Exposure Analysis ...................................................................................38 

5. Treatment Feasibility .........................................................................................................44 

6. Other Regulatory Revisions...............................................................................................46 

C. How Did EPA Factor Children’s Health Concerns Into the Review?...............................50 

VI. Results of EPA’s Review of NPDWRs.............................................................................50 

A. What are the Review Result Categories?...........................................................................50 

1. No Action at this Time and the NPDWR is Still Appropriate...........................................51 

2. Candidate for Revision. .....................................................................................................51 

B. What Are the Details of EPA’s Review of Each NPDWR? .............................................53 

1. Acrylamide...........................................................................................................................53 

2. Alachlor................................................................................................................................55 

3. Alpha Particle Emitters........................................................................................................59 

4. Antimony .............................................................................................................................61 

5. Arsenic .................................................................................................................................61 

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6. Asbestos ...............................................................................................................................62 

7. Atrazine................................................................................................................................63 

8. Barium..................................................................................................................................64 

9. Benzene................................................................................................................................67 

10. Benzo(a)pyrene..................................................................................................................71 

11. Beryllium ...........................................................................................................................73 

12. Beta Particle and Photon Emitters .....................................................................................74 

13. Cadmium............................................................................................................................76 

14. Carbofuran .........................................................................................................................76 

15. Carbon Tetrachloride .........................................................................................................79 

16. Chlordane...........................................................................................................................82 

17. Chromium ..........................................................................................................................86 

18. Cyanide ..............................................................................................................................88 

19. 2,4-D (2,4-Dichlorophenoxyacetic acid) ...........................................................................89 

20. Dalapon (2,2-Dichloropropionic Acid)..............................................................................91 

21. Di(2-ethylhexyl)adipate (DEHA) ......................................................................................92 

22. Di(2-ethylhexyl)phthalate (DEHP)....................................................................................92 

23. 1,2-Dibromo-3-chloropropane (DBCP).............................................................................94 

24. 1,2-Dichlorobenzene (o-Dichlorobenzene)........................................................................98 

25. 1,4-Dichlorobenzene (p-Dichlorobenzene)........................................................................98 

26. 1,2-Dichloroethane (Ethylene Dichloride).........................................................................99 

27. 1,1-Dichloroethylene .......................................................................................................103 

28. cis-1,2-Dichloroethylene..................................................................................................106 

29. trans-1,2-Dichloroethylene ..............................................................................................107

30. Dichloromethane (Methylene Chloride)..........................................................................107 

31. 1,2-Dichloropropane ........................................................................................................114 

32. Dinoseb ............................................................................................................................118 

33. Diquat...............................................................................................................................119 

34. Endothall..........................................................................................................................122 

35. Endrin...............................................................................................................................125 

36. Epichlorohydrin ...............................................................................................................126 

37. Ethylbenzene....................................................................................................................128 

38. Ethylene Dibromide (EDB; 1,2-Dibromoethane)............................................................129 

39. Fluoride............................................................................................................................130 

40. Glyphosate .......................................................................................................................133 

41. Heptachlor........................................................................................................................135 

42. Heptachlor Epoxide .........................................................................................................139 

43. Hexachlorobenzene..........................................................................................................142 

44. Hexachlorocyclopentadiene.............................................................................................146 

45. Lindane (gamma-Hexachlorocyclohexane).....................................................................149 

46. Mercury (Inorganic).........................................................................................................152 

47. Methoxychlor...................................................................................................................153 

48. Monochlorobenzene (Chlorobenzene).............................................................................154 

49. Nitrate (as N)....................................................................................................................154 

50. Nitrite (as N) ....................................................................................................................156 

51. Oxamyl (Vydate) .............................................................................................................158 

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52. Pentachlorophenol............................................................................................................162 

53. Picloram ...........................................................................................................................164 

54. Polychlorinated Biphenyls (PCBs) ..................................................................................167 

55. Combined Radiums (226 and 228) ..................................................................................168 

56. Selenium ..........................................................................................................................170 

57. Simazine...........................................................................................................................171 

58. Styrene .............................................................................................................................172 

59. 2,3,7,8-TCDD (Dioxin)....................................................................................................173 

60. Tetrachloroethylene .........................................................................................................174 

61. Thallium...........................................................................................................................178 

62. Toluene ............................................................................................................................180 

63. Toxaphene........................................................................................................................183 

64. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid) .............................................186 

65. 1,2,4-Trichlorobenzene....................................................................................................187 

66. 1,1,1-Trichloroethane.......................................................................................................188 

67. 1,1,2-Trichloroethane.......................................................................................................191 

68. Trichloroethylene.............................................................................................................194 

69. Uranium ...........................................................................................................................198 

70. Vinyl chloride ..................................................................................................................199 

71. Xylenes (Total) ................................................................................................................203 

VII. EPA’s Request for Comments .......................................................................................205 

A. Request for Comment and/or Information on the Candidates for Revision ....................205 

B. Request for Information/Data on Other Review Topics..................................................206 

C. Requests for Information on the Impacts of Climate Change on Water Quality.............207 

VIII. EPA’s Next Steps .........................................................................................................207 

IX. References .......................................................................................................................208 

SUPPLEMENTARY INFORMATION: 

I. General Information 

A. Does This Action Apply to My Public Water System? 

This action itself does not impose any requirements on anyone. Instead, it notifies interested 

parties of EPA’s review of existing NPDWRs and its conclusions about which of these warrants 

new regulatory action at this time. EPA requests public comment on the four NPDWRs 

identified as candidates for revision, with a specific focus on comments and/or relevant 

information that will inform the regulatory revisions. 

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B. How Should I Submit Comments on This Action? 

Please see Section VII for the issues related to this notice for which EPA requests comment 

and/or information. EPA will accept written or electronic comments (please do not send both). 

Instructions for submitting comments are in the preceding section. EPA prefers electronic 

comments. No facsimiles (faxes) will be accepted. Commenters who want EPA to acknowledge 

receipt of their comments should also send a self-addressed, stamped envelope. 

The Agency intends to address the comments received on the four NPDWRs identified as 

candidates for revision in subsequent Federal Register notices proposing and finalizing the 

regulatory revisions, and in documents that will be made available in the docket for those 

notices. 

C. What Should I Consider as I Prepare My Comments for EPA?

You may find the following suggestions helpful for preparing your comments: 

• Explain your views as clearly as possible. 

• Describe any assumptions that you used. 

• Provide any technical information and/or data you used that support your views. 

• If you estimate potential burden or costs, explain how you arrived at your estimate. 

• Provide specific examples to illustrate your concerns. 

• Offer alternatives. 

• Make sure to submit your comments by the comment period deadline. 

• To ensure proper receipt by EPA, identify the appropriate docket identification number in the 

subject line on the first page of your response. It would also be helpful if you provided the 

name, date, and Federal Register citation related to your comments. Deleted: ¶

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II. Statutory Requirements for the Six-Year Review

Under the SDWA, as amended in 1996, 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. 

Pursuant to the 1996 SDWA Amendments, EPA completed and published the results of its 

first Six-Year Review (Six-Year Review 1) July 18, 2003 (68 FR 42908, USEPA, 2003e) after 

developing a systematic approach, or protocol, for the review of NPDWRs. EPA has applied the 

same protocol with minor refinements (revised protocol) to the second Six-Year Review of 

NPDWRs (Six-Year Review 2). Section V of today’s action describes the protocol and the 

minor refinements used for the Six-Year Review 2 and section VI describes the review findings 

for each of the NPDWRs covered by the current effort (see Table IV-1). 

III. Stakeholder Involvement in the Six-Year Review Process 

A. How Have Stakeholders Been Involved in the Review Process? 

The Agency developed a Six-Year Review protocol during the first review cycle with 

extensive stakeholder inputs, including a stakeholder meeting, Agency presentations at a variety 

of meetings, and consultation with the National Drinking Water Advisory Council (NDWAC). 

NDWAC formed a working group to develop recommendations regarding the process the 

Agency should apply to conduct a periodic and systematic review of existing NPDWRs. The 

Working Group held two meetings and a conference call during June through September 2000 

(67 FR 19030, April 17, 2002, USEPA, 2002c). The NDWAC approved the Working Group’s 

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

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

key elements, as appropriate: health effects, analytical and treatment feasibility, implementationrelated issues, occurrence and exposure, and economic impacts. As discussed in more detail in 

section V of today’s action, EPA continues to follow the general protocol recommended by the 

NDWAC. 

B. How Did EPA Incorporate Feedback from the Science Advisory Board’s 2002 Comments on 

the Six-Year Review Protocol? 

In June 2002 and during the Six-Year Review 1, EPA consulted with the Science Advisory 

Board (SAB) Drinking Water Committee and requested their review and comment on whether 

the protocol that EPA developed based on the NDWAC’s recommendations was consistently 

applied and appropriately documented. The SAB provided verbal feedback regarding the 

transparency and clarity of EPA's criteria for making its Six-Year Review 1 decisions. At that 

time, EPA revised the protocol to better explain how the decision criteria were applied. For the 

Six-Year Review 2 and to increase transparency and clarity, EPA also developed a more detailed 

decision tree and an automated tool, called the Regulatory Review Support Spreadsheet (R2S2). 

The more detailed decision tree incorporates the sequential relationships between the various 

NPDWR review elements and R2S2 tracks each contaminant through the decision making 

process. The Agency has documented the decision tree and the automated tool in the document, 

“EPA Protocol for the Second Review of Existing National Primary Drinking Water Regulations 

(Updated)” (USEPA, 2009a). 

IV. Regulations Included in the Six-Year Review 

Table IV-1 lists all the NPDWRs established to date. The table also reports the maximum 

contaminant level goal (MCLG), which is “set at the level at which no known or anticipated Deleted: ¶

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adverse effects on the health of persons occur and which allows an adequate margin of safety” 

(SDWA section 1412(b)(4)), and the maximum contaminant level (MCL), which is the 

maximum permissible level of a contaminant in water delivered to any user of a public water 

system and “is as close to the maximum contaminant level goal as is feasible” (SDWA section 

1412(b)(4)(B)), except for contaminants that have a treatment technique (TT) in lieu of an MCL 

because it is not “economically or technically feasible” to set an MCL (SDWA section 

1412(b)(7)(A))1

. Of these 85 NPDWRs, EPA has reviewed 14 as part of recent or ongoing 

regulatory actions and, as a result, they are not subject to a detailed review in today’s notice. 

The review for the remaining 71 is discussed in detail in today’s action. 

Table IV-1. Contaminants with NPDWRs Included in Six-Year Review 2 

Contaminants 

MCLG 

(mg/L)1 MCL (mg/L)1 Contaminants 

MCLG 

(mg/L)1

MCL 

(mg/L)1

Acrylamide 0 TT Epichlorohydrin 0 TT 

Alachlor 0 0.002 Ethylbenzene 0.7 0.7 

Alpha particles 0 (pCi/L) 15 (pCi/L) Ethylene dibromide (EDB) 0 0.00005 

Antimony 0.006 0.006 Fluoride 4 4 

Arsenic 0 0.01 Giardia lamblia 0 TT 

Asbestos 7 (million 

fibers/L) 

7 (million 

fibers/L) Glyphosate 0.7 0.7 

Atrazine 0.003 0.003 Haloacetic acids (HAA5) n/a2 0.06 

Barium 2 2 Heptachlor 0 0.0004 

Benzene 0 0.005 Heptachlor Epoxide 0 0.0002 

Benzo(a)pyrene 0 0.0002 Hexachlorobenzene 0 0.001 

Beryllium 0.004 0.004 Hexachlorocyclopentadiene 0.05 0.05 

Beta particles 0 

(millirems/yr) 

4 

(millirems/yr) Lead 0 TT 

Bromate 0 0.01 Legionella 0 TT 

Cadmium 0.005 0.005 Lindane 0.0002 0.0002 

Carbofuran 0.04 0.04 Mercury (Inorganic) 0.002 0.002 

Carbon tetrachloride 0 0.005 Methoxychlor 0.04 0.04 

Chloramines 4 4 Monochlorobenzene 

(Chlorobenzene) 0.1 0.1 

Chlordane 0 0.002 Nitrate (as nitrogen, N) 10 10 

Chlorine 4 4 Nitrite (as N) 1 1 

 

1

 Under limited circumstances, SDWA Section 1412(b)(6)(A) also gives the Administrator the discretion to 

promulgate an MCL that is less stringent than the feasible level and that “maximizes health risk reduction benefits at 

a cost that is justified by the benefits.”

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Table IV-1. Contaminants with NPDWRs Included in Six-Year Review 2 

Contaminants 

MCLG 

(mg/L)1 MCL (mg/L)1 Contaminants 

MCLG 

(mg/L)1

MCL 

(mg/L)1

Chlorine dioxide 0.8 0.8 Oxamyl (Vydate) 0.2 0.2 

Chlorite 0.8 1 Pentachlorophenol 0 0.001 

Chromium (total) 0.1 0.1 Picloram 0.5 0.5 

Coliform 0%3 5%3 Polychlorinated biphenyls 

(PCBs) 0 0.0005 

Copper 1.3 TT Radium 0 (pCi/L) 5 (pCi/L) 

Cryptosporidium 0 TT Selenium 0.05 0.05 

Cyanide 0.2 0.2 Simazine 0.004 0.004 

2,4-

Dichlorophenoxyacetic 

acid (2,4-D) 

0.07 0.07 Styrene 0.1 0.1 

Dalapon 0.2 0.2 

2,3,7,8-Tetrachlorodibenzop-dioxin (2,3,7,8-TCDD or 

dioxin) 

0 3.00E-08 

Di(2-ethylhexyl)adipate 

(DEHA) 0.4 0.4 Tetrachloroethylene (PCE) 0 0.005 

Di(2-ethylhexyl)phthalate 

(DEHP) 0 0.006 Thallium 0.0005 0.002 

1,2-Dibromo-3-

chloropropane (DBCP) 0 0.0002 Toluene 1 1 

1,2-Dichlorobenzene (oDichlorobenzene) 0.6 0.6 Total trihalomethanes 

(TTHM) n/a4 0.08 

1,4-Dichlorobenzene (pDichlorobenzene) 0.075 0.075 Toxaphene 0 0.003 

1,2-Dichloroethane 

(Ethylene dichloride) 0 0.005 

2,4,5-Trichlorophenoxypropionic acid (2,4,5-TP or 

Silvex) 

0.05 0.05 

1,1-Dichloroethylene 0.007 0.007 1,2,4-Trichlorobenzene 0.07 0.07 

cis-1,2-Dichloroethylene 0.07 0.07 1,1,1-Trichloroethane 0.2 0.2 

trans-1,2-

Dichloroethylene 0.1 0.1 1,1,2-Trichloroethane 0.003 0.005 

Dichloromethane 

(Methylene chloride) 0 0.005 Trichloroethylene (TCE) 0 0.005 

1,2-Dichloropropane 0 0.005 Uranium 0 (μg/L) 30 (μg/L) 

Dinoseb 0.007 0.007 Vinyl chloride 0 0.002 

Diquat 0.02 0.02 Viruses 0 TT 

Endothall 0.1 0.1 

Endrin 0.002 0.002 Xylenes (total) 10 10 

1. Units are in milligrams per liter (mg/L) unless otherwise noted, e.g., micrograms per liter (μg/L) and picoCuries per liter (pCi/L). 

Milligrams per liter are equivalent to parts per million (ppm) and micrograms per liter are equivalent to parts per billion (ppb). 

2. There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: dichloroacetic acid (zero), 

trichloroacetic acid (0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated

with this group but have no MCLGs. 

3. No more than 5.0% samples total coliform-positive in a month. 

4. There is no MCLG for total trihalomethanes. MCLGs for some of the individual contaminants are: bromodichloromethane (zero),

bromoform (zero), dibromochloromethane (0.06 mg/L), and chloroform (0.07mg/L). 

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V. EPA’s Protocol for Reviewing the NPDWRs Included in This Action 

A. What Was EPA’s Review Process? 

The protocol document, “EPA Protocol for the Review of Existing National Primary 

Drinking Water Regulations (Updated)” (USEPA, 2009a), contains a detailed description of the 

process the Agency used to review the NPDWRs discussed in today’s action. EPA’s primary 

goal was to identify and prioritize candidates for regulatory revision to target those revisions that 

are most likely to result in an increased level of public health protection and/or result in 

substantial cost savings for systems and their customers while maintaining the level of public 

health protection.2

 This section provides an overview of the review process and section V.B 

provides a more detailed description of how EPA applied the process to the review of the 

NPDWRs discussed in today’s action. 

EPA applied the following basic principles to the review process: 

• The Agency sought to avoid redundant review efforts. Because EPA has reviewed 

information for 14 contaminants as part of recent or ongoing regulatory actions, they are not 

subject to the detailed review in today’s notice. 

• EPA evaluated the potential for new information to affect NPDWRs in a manner consistent 

with existing policies and procedures for developing NPDWRs. For example, in determining 

whether a possible change in analytical feasibility existed, the Agency considered the current 

 

2

 Note that the legislative history of the 1996 SDWA Amendments indicate 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 (see Senate Report Number 104-169, 104th Congress, 1st Session, 1995 at 38). 

In other words, an MCL could be relaxed (i.e., increased) in cases where a revised health risk assessment leads to a 

less stringent (higher) MCLG than the existing MCL so that the level of health protection is maintained. There have 

been several instances in which revised health assessments have suggested higher MCLGs and the Agency could 

have considered relaxing the MCLs. In these instances and because SDWA allows EPA to determine when 

revisions are appropriate, the Agency decided that there would be a negligible gain in public health protection and/or 

cost savings and any revision would be a low priority activity because of competing workload priorities, the 

administrative costs associated with rulemaking, and the burden on States and the regulated community to 

implement any regulatory changes

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policy and procedures for calculating the practical quantitation level for drinking water 

contaminants.3

 

• Because any possible change in an MCLG affects other NPDWR elements, EPA will not 

generally consider potential revisions to any contaminant with a health effects assessment in 

process that would not be completed during the review period, where either the 

contaminant’s MCL is equal to its MCLG or the MCL is based on the 1996 SDWA 

Amendments’ cost-benefit provision. The rationale for this outcome is that any new 

information from the health effects assessment could affect the MCL or the assessment of the 

benefits associated with the MCL for these contaminants. Therefore, the Agency does not 

believe it is appropriate to consider revisions to these NPDWRs while a health effects 

assessment is ongoing. 

• For those contaminants with ongoing health assessments that have MCLGs equal to or 

greater than zero and MCLs limited by analytical feasibility or the standard is based on a 

Treatment Technique, EPA conducted a further review of the potential to revise the MCL or 

TT. The rationale for this approach is that the MCL or TT is based on technology limitations 

and therefore, EPA should consider whether there have been improvements in technology 

and whether any revision might provide a meaningful opportunity to improve or at least 

maintain public health protection. If EPA found that there were no changes in technology 

(i.e., analytical feasibility or a TT) or if changes were possible but there was no meaningful 

opportunity to improve public health protection or reduce costs (while maintainng public 

 

3

 The following Federal Register notices describe the process the Agency has used to determine analytical 

feasibility for drinking water contaminants: 50 FR 46880, November 13, 1985 (USEPA, 1985); 52 FR 25690, July 

8, 1987 (USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA, 1989b). For this Six Year Review effort and to 

supplement the analytical feasibility evaluation, the Agency also reviewed extensive minimum reporting level 

(MRL) data obtained from States and primacy entities as part of the Six-Year Review information collection request 

(ICR) for SDWA compliance monitoring data. 

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health protection), these contaminants remained in the ongoing health effects assessment 

category. 

• For this review, EPA considered new information from health effects assessments that were 

completed by a March 1, 2009 cutoff date. If an updated assessment is completed after the 

March 1, 2009 information cutoff date, then EPA will review the update and any new 

conclusions or additional information associated with the contaminant during the next review 

cycle or during the revision of an NPDWR (e.g., acrylamide, PCE and TCE). If the health 

effects assessments are not completed in time for the regulatory revisions for acrylamide, 

PCE and TCE, EPA does not plan to change the existing MCLG of zero. EPA is currently 

considering how best to evaluate the benefits for these regulatory revisions if the EPA health 

effects assessments are not complete. One option would be to use the same health effects 

information that was used for promulgating the original regulation. Another option is to 

consider using other best available, peer-reviewed health risk assessments that are complete 

as the Agency is proceeding with the regulatory revisions. EPA requests comment on these 

options and any other options that the public considers appropriate to evaluate the benefits. 

• The Agency may consider accelerating a review and potential revision for a particular 

NPDWR before the next review cycle when justified by new public health risk information. 

• During the review, EPA identified areas where information is inadequate or unavailable (data 

gaps) or emerging and is needed to determine whether revision to an NPDWR is appropriate. 

When the Agency is able to fill such gaps or fully evaluate the emerging information, the 

Agency will consider it as part of the next review cycle. The Agency may consider 

accelerating a review and potential revision for a particular NPDWR if the information 

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becomes available before the next review cycle and if review and a potential revision are 

justified by new public health risk information. 

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

new analyses. 

During Six-Year Review 1, the Agency developed a systematic approach or protocol 

(USEPA, 2003b). The Agency based this protocol on the recommendations of the NDWAC, 

through internal Agency deliberations, and discussions with the diverse group of stakeholders 

involved in drinking water and its protection. The overview of the protocol in Figure V-1 shows 

the sequence of key decisions that led to EPA assigning each NPDWR to one of two major 

categories of outcomes in the Six-Year Review 2. The two major outcomes of the review are 

either: 1) the NPDWR is still appropriate and no action is necessary at this time, or 2) the 

NPDWR is a candidate for revision. The reasons for a Six-Year Review outcome of no further 

action at this time include at least one or more of the following reasons: 

• The NPDWR has been reviewed or is being reviewed in a recent or ongoing action; 

• The NPDWR has an ongoing health effects assessment (i.e., for those NPDWRs with an 

MCL set at the MCLG or the MCL is based on the SDWA cost benefit provision); 

• EPA is considering whether a new health effects assessment is needed; 

• EPA did not identify any new, relevant information that indicate changes to the NPDWR; 

• New information indicate a possible change to the MCLG and/or MCL but changes to the 

NPDWR are a low priority activity due to negligible gains in public health protection and/or 

cost savings; or 

• There are data gaps or emerging information that needs to be evaluated. 

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Figure V-1. Six-Year Review Protocol Overview and Major Categories of Revise/Take No Action Outcomes

Yes

No

New information to suggest possible changes (i.e., 

to an MCLG, MCL, Treatment Technique and/or 

other regulatory revisions)?

Meaningful opportunity for health risk reduction for 

persons served by PWS and/or cost savings while 

maintaining/improving public health protection?

Outcome:

No action 

at this time

Outcome:

Candidate 

for Revision

Data sufficient to support

regulatory revision?

No new information

Low priority - No meaningful 

opportunity

Data gaps/emerging 

information

Yes

No

Ongoing or planned HEA

Health effects assessment (HEA)

in process or planned? *

NPDWRs Under Review

Yes

No

Yes

No

NPDWR reviewed in recent or ongoing action? 

No

Yes Regulatory action ongoing

or recently completed

* Contaminants with an HEA in process that have an MCL based on practical 

quantitation limit and are greater than MCLG are passed to the next question to 

evaluate potential to revise the MCL. 

Uncertain – emerging

information

During the current Six-Year Review, the Agency assessed the protocol and determined it 

remained appropriate and suitable for the second review. The research requirements and 

decision-making process of the Six-Year Review 2 protocol are essentially the same as those 

implemented during Six-Year Review 1. The Agency made some minor refinements to enhance 

the Agency’s effectiveness in applying the protocol to the review of NPDWRs. The refinements 

that address SAB’s comments about the clarity and the transparency of the protocol’s decision 

making process are described in the next two paragraphs. Section V.B describes the key 

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technical elements and any refinements in the data and/or the analysis methods used during SixYear Review 2. 

The primary refinement to the protocol during Six-Year Review 2 is the implementation of a 

more detailed “decision tree” than either the one used during Six-Year Review 1 (USEPA, 

2003b) or the overview shown in Figure V-1. The protocol is broken down into a series of 

questions about whether there is new information for a contaminant that suggests potential to 

revise each of the NPDWR elements. These questions are logically ordered into a decision tree 

that incorporates the sequential relationships between the different NPDWR elements. For 

example, when EPA establishes an MCL, it must generally set the MCL as close to the MCLG as 

feasible. Consequently, for a contaminant that has an MCL equal to its MCLG, EPA must make 

decisions about the availability and adequacy of new information regarding the possibility to 

revise the MCLG before decisions regarding the possibility to revise the MCL. It also means 

that if there is no possibility to revise a contaminant’s MCLG and the MCL is already equal to 

the MCLG, then there is no basis for revising the MCL. In this instance, the MCL branch of the 

decision tree is not reached, and it is not necessary to make related decisions such as whether the 

practical quantitation limit (PQL) can be revised. This approach results in a more efficient 

review process. EPA also developed an automated tool called the R2S2 that tracks each 

contaminant’s movement through the decision tree, including the revise/take no action outcomes. 

This tool enhances transparency throughout the decision process. The automation also 

streamlines the decision process and facilitates the Agency’s reporting of its review results. The 

Agency has documented the decision tree and the automated tool in the document entitled, “EPA 

Protocol for the Second Review of Existing National Primary Drinking Water Regulations 

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B. How Did EPA Conduct the Initial Review and Evaluate Key Technical Elements of the 

NPDWRs? 

This section describes the specific technical reviews that EPA conducted, including the initial 

review, health effects, analytical methods, occurrence and exposure, treatment feasibility, and 

economic analysis. 

1. Initial Review 

EPA’s initial review of all the contaminants included in the Six-Year Review 2 involved a 

simple identification of the NPDWRs that were being reviewed under concurrent EPA actions or 

had been reviewed and revised in EPA actions completed since 2002. Table V-1 provides a list 

of the 14 contaminants that met one of these criteria and identifies the recent or ongoing action in 

which the contaminant has been reviewed or is undergoing review. While these 14 contaminants 

are part of the Six-Year Review 2, they were not subject to any detailed analysis given that new 

information on these contaminants has been recently reviewed under separate actions. However, 

EPA requests comments on these contaminants along with the other contaminants discussed in 

detail in this notice. 

The remaining 71 contaminants pass through this step to the review of the technical NPDWR 

elements, which are described in the following sections. 

Table V-1. NPDWRs That Have Been Reviewed or Are Being Reviewed Under Recent or Ongoing 

Actions 

Contaminant/Indicator Recent or Ongoing Action 

Disinfection Byproducts 

Bromate Stage 2 DBPR 

Chlorite1 Stage 2 DBPR 

HAA5: monochloroacetic acid, dichloroacetic acid 

trichloroacetic acid, monobromoacetic acid dibromoacetic acid Stage 2 DBPR 

TTHMs: chloroform, bromodichloromethane, 

dibromochloromethane, bromoform Stage 2 DBPR 

Disinfectant Residuals 

Chloramines1 Stage 2 DBPR 

Chlorine1 Stage 2 DBPR 

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Table V-1. NPDWRs That Have Been Reviewed or Are Being Reviewed Under Recent or Ongoing 

Actions 

Contaminant/Indicator Recent or Ongoing Action 

Chlorine dioxide Stage 2 DBPR 

Inorganics 

Copper Under consideration for long-term revisions 

Lead 

LCR Short-Term Revisions 

Under consideration for long-term revisions 

Microorganisms 

Coliform Total Coliform Rule-making currently underway 

Cryptosporidium LT2ESWTR 

Giardia lamblia LT2ESWTR 

Legionella2 LT2ESWTR 

CCL33

Viruses2

LT2ESWTR 

GWR 

CCL33

DBPR – Disinfectants and Disinfection Byproducts Rule 

LT2ESWTR – Long-Term 2 Enhanced Surface Water Treatment Rule 

LCR – Lead and Copper Rule 

GWR – Ground Water Rule 

 

Dates of promulgation are as follows: 

Stage 2 DBPR: 71 FR 388, January 4, 2006 (USEPA, 2006h) 

LT2ESWTR: 71 FR 654, January 5, 2006 (USEPA, 2006g) 

LCR Short-Term Regulatory Revisions: 72 FR 57782, October 10, 2007 (USEPA, 2007f) 

GWR: 71 FR 65574, November 8, 2006 (USEPA, 2006f) 

1. Although the standard for this disinfectant was not revised as part of the Stage 2 DBPR, regulatory revisions need to be 

considered in conjunction with other disinfectant residuals and disinfection byproducts. 

2. LT2ESWTR and GWR promulgated treatment techniques that built upon and enhanced the existing regulations (Surface 

Water Treatment Rule, Interim Enhanced Surface Water Treatment Rule, and Long-Term 1 Enhanced Surface Water 

Treatment Rule) that address broad categories of microorganisms in treated water. 

3. Listed on the third Drinking Water Contaminant Candidate List or CCL3 (74 FR 51850, October 8, 2009 (USEPA, 2009l) in 

order to capture health and treatment information that may not be addressed by the current regulations. 

2. Health Effects 

The document, “Six-Year Review 2 —Health Effects Assessment - Summary Report” 

(USEPA, 2009b), describes how EPA reviewed the contaminants discussed in today’s action and 

provides the results of the health effects technical review. The principal objectives of the health 

effects review are to identify: 1) contaminants for which a new health effects assessment 

indicates that a change in MCLG might be appropriate (e.g., because of a change in cancer 

classification or a reference dose (RfD)), and 2) contaminants for which the Agency identifies 

new health effects information suggesting a need to initiate a new health effects assessment. 

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To meet the first objective, the Agency reviewed the results of health effects assessments 

completed under the following programs and identified, where feasible, possible MCLG values. 

• EPA Integrated Risk Information System (IRIS) 

• EPA Office of Pesticide Programs (OPP) 

• National Academy of Sciences (NAS; when commissioned by EPA). 

To meet the second objective, the Agency first conducted an extensive literature review to 

identify peer-reviewed studies. Then the Agency reviewed the studies to determine whether 

there was new health effects information such as reproductive and developmental toxicity that 

potentially affects the MCLG of any of the remaining contaminants that do not have an ongoing 

health effects assessment, including those with recently completed health effects assessments. 

Table V-2 reflects the outcome of the health effects review for the NPDWRs discussed in 

today’s action. EPA placed each contaminant into one of the following 13 categories. 

• Agency health effects assessment in process and not completed as of March 1, 2009. The 

Agency currently is conducting a health effects assessment for the contaminant. That 

assessment will consider all available, relevant studies on the toxicology of the contaminant, 

including developmental and reproductive toxicity. This outcome contains three categories

of contaminants. 

• Category 1 contains 15 contaminants with MCLGs equal to or greater than zero and 

either MCLs that are limited by analytical feasibility or TT standards. For this category, 

EPA conducted further review of the potential for revisions to the MCL due to possible 

changes in analytical feasibility. The Agency’s review of new information that might 

affect the MCL for one of these contaminants is a refinement of the protocol. During 

Six-Year Review 1, EPA took no further action on any contaminants with ongoing health 

Deleted: category has three subsets

Deleted: The first subset

Deleted: 14

Deleted: subset

Deleted: the first subset is 

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effects assessments. EPA generally sets each MCL as close to the MCLG as is feasible, 

and a common limitation is the availability of analytical methods to reliably measure the 

contaminant. 

• Category 2 contains two contaminants (arsenic and uranium) that have MCLGs equal 

to zero and MCLs that are based on the costs and benefits balancing provision in SDWA 

1412(b)(6)(A). Any changes in the ongoing health effects assessment could impact the 

evaluation of benefits for these contaminants. Therefore, EPA has decided to take no 

further action to evaluate these two contaminants until completion of the health effects 

assessment. 

• Category 3 contains 13 contaminants with non-zero MCLGs and MCLs generally 

equal to their respective MCLGs. Because EPA cannot determine whether there is 

potential to revise either the MCLG or the MCL until after the health effects assessment 

is completed, EPA plans to take no further action on these contaminants at this time. 

• New health effects assessment completed since Six-Year Review 1. An IRIS or OPP 

assessment has been completed since 2002. EPA also conducted a follow-up literature 

search to confirm that no new information became available following the completion of the 

new health effects assessment. Table V-2 shows four categories of contaminants with new 

health effects assessments: four with results indicating potential for lower MCLG (Category 

4), five with results indicating potential for higher MCLG (Category 5), two with results 

indicating the MCLG remains appropriate (Category 6), and three contaminants for which 

emerging information following the completion of a health effects assessment or a pending 

pesticide cancellation decision may affect EPA’s review (Category 7). 

Deleted: The second subset

Deleted: , 

Deleted: . The MCLG for each of these 

contaminants is 

Deleted: the MCL was established

Deleted: The third subset

Deleted: 14

Deleted: The exception is thallium, 

which has an MCL limited by analytical 

feasibility. Consequently, EPA 

conducted further review of the potential 

for revisions to the MCL for thallium in 

the event of possible changes in 

analytical feasibility.

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• Literature review only conducted during Six-Year Review 2. For the contaminants that did 

not have an ongoing health effects assessment or a new one completed during the current 

review period, EPA conducted a review of the health effects literature to identify whether 

there was new information with potential to revise the MCLG. There are six categories of 

contaminants. 

• Three categories pertain to contaminants that had a health effects assessment 

completed during Six-Year Review 1, including two with possible lower MCLGs

(Category 8), three with possible higher MCLGs (Category 9), and three with no 

potential to revise their MCLGs (Category 10). During Six-Year Review 1, the Agency 

determined that possible changes to these contaminants’ NPDWRs were a low priority 

activity for the Agency because of: competing workload priorities, the administrative 

costs associated with rulemaking, and the burden on States and the regulated community 

to implement any regulatory changes. As part of Six-Year Review 2, EPA is assessing 

whether there is new information that affects this determination. 

• Category 11 contains five contaminants for which the Agency identified new 

information, described in section VI, that could impact the MCLG and, therefore, these 

contaminants are considered potential nominees for a new health assessment. 

• Category 12 contains carcinogens for which the literature review sought new 

information on whether there might be a nonlinear mode of action or other reproductive 

and developmental health effects. 

• Category 13 contains seven contaminants with non-zero MCLGs, for which EPA 

conducted a full literature search, including developmental and reproductive toxicity. 

Deleted: a new or 

Deleted: This category has four major 

subsets

Deleted: The first subset contains 

Deleted: The second subset

Deleted: The third subset of seven 

contaminants 

Deleted: seven 

Deleted: ,

Deleted: 

Deleted: The fourth subset

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Table V-2. Summary of the Outcome of the Six-Year Health Effects Review 

Health Effects Review Category Contaminants 

Category 1: MCLG ≥ 0 

and MCL based on Analytical Feasibility or 

standard is a TT 

15 Total - acrylamide; alpha particles; 

benzo(a)pyrene; beta particles; carbon 

tetrachloride; DEHP; 1,2-dichloroethane; 

dichloromethane; pentachlorophenol; PCBs; 

radium; dioxin; tetrachloroethylene; thallium; 

trichloroethylene 

Category 2: MCLG = 0 

and MCL based on cost-benefit 2 Total – arsenic and uranium 

Health Effects 

Assessment in 

Process During 

Information 

Review 

Period for the 

Notice (and not 

available by the 

March 1, 2009 

cutoff date)

Category 3: MCLG > 0 

and the MCL is set at the MCLG

13 Total – antimony; asbestos; beryllium; 

cadmium; cyanide; DEHA; 1,2-dichlorobenzene; 

1,4-dichlorobenzene; cis-1,2-dichloroethylene; 

trans-1,2-dichloroethylene; ethylbenzene; fluoride; 

styrene 

Category 4: New health risk information 

could lower MCLG/MCL 

4 Total – 2,4-D (2005, new data); endothall (2005, 

new data); toluene (2005, uncertainty factor 

adjustment); total xylenes (2003, uncertainty factor 

adjustment) 

Category 5: New health risk information 

could raise MCLG/MCL 

5 Total – alachlor (20061); barium (2005); diquat 

(20022); glyphosate (20023); 1,1,1-trichloroethane 

(2007, new data) 

Category 6: No new health risk information 2 Total – benzene (2003); EDB (2004) 

Health Effects 

Assessment 

Completed 

Since Six-Year 

Review 1 

Category 7: Awaiting the outcome of 

emerging information or cancellation 

decision 

3 Total - atrazine4; simazine4; carbofuran5

Category 8: New health risk 

information could lower 

MCLG/MCL 

2 Total – hexachlorocyclopentadiene (2001); 

oxamyl (2000) 

Category 9: New health risk 

information could raise 

MCLG/MCL 

3 Total – 1,1-dichloroethylene (2002); lindane 

(2002); picloram (1995) 

Health 

Effects 

Assessment 

Completed 

During SixYear 

Review 1 Category 10: No new health 

risk information 

3 Total – chlordane (1998), inorganic mercury 

(1997), vinyl chloride (2000) 

Category 11: New Information Identified; 

Potential Nominee for a New Assessment 

5 Total – total chromium (hexavalent); nitrate; 

nitrite; selenium; 1,2,4-trichlorobenzene 

Category 12: MCLG = 0 

No new health risk information 

7 Total –- DBCP; 1,2-dichloropropane; 

epichlorohydrin; heptachlor; heptachlor epoxide; 

hexachlorobenzene; toxaphene 

Literature 

Review Only 

Category 13:MCLG > 0 

No new health risk information 

7 Total – dalapon; dinoseb; endrin; methoxychlor; 

monochlorobenzene; 2,4,5-TP; 1,1,2-

trichloroethane 

1. The 2006 cumulative risk document (USEPA, 2006a) does not present a new assessment; it uses the cancer assessment in 

the 1998 Reregistration Eligibility Decision (RED; USEPA, 1998a). 

2. The 2002 Interim Tolerance Reassessment and Risk Management Decisions (TRED; USEPA, 2002d) does not include a 

change in risk values, which are those reported in the 1995 RED (USEPA, 1995a). 

3. The 2002 TRED (USEPA, 2002a) uses risk values consistent with those reported in the 1993 RED (USEPA, 1993b), with 

differences only in RfD rounding. 

4. Although atrazine and simazine had new health effects assessments completed during the Six-Year Review 2 information 

period, on October 7, 2009 the Agency announced its intent to re-evaluate the risk assessment for atrazine. Because the 

simazine assessment is based on atrazine data, simazine was placed in this same category.

Formatted Table

Deleted: 14

Deleted: =

Deleted: 14

Deleted: ; thallium1

Deleted: 20062

Deleted: 20023

Deleted: 20024

Deleted: ¶

Deleted: health studies

Deleted: 3 Total - atrazine5; simazine5; 

carbofuran6

Deleted: Thallium is in this category 

because it has a non-zero MCLG. Its MCL, 

however, is limited by analytical feasibility. 

Therefore, EPA followed the protocol of 

reviewing new information that might affect 

MCL for all contaminants with MCLs greater 

than their MCLGs, most of which have 

MCLGs of zero.¶

2. 

Deleted: 3

Deleted: 4

Deleted: 5

Deleted: there are emerging health effects 

studies that

Deleted: is reviewing.

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5. Although carbofuran had a new health effects assessment completed during the Six-Year Review 2 information period, a 

recent pesticide cancellation decision could affect the MCLG. 

In addition to identifying for which contaminants there is information that potentially affects 

the MCLG, the health effects review indicates which contaminants proceed to other review steps 

under the protocol. Several contaminants proceed to the analytical methods review to determine 

whether improvements in analytical methods indicate potential to revise the practical 

quantitation limit (PQL) in the NPDWRs. As Table V-3 shows, 14 contaminants from Category 

1 proceed to the analytical methods review – despite an ongoing health effects assessment –

because their MCLs are limited by their respective PQLs. These 14 include alpha particles; 

benzo(a)pyrene; beta particles; carbon tetrachloride; DEHP; 1,2-dichloroethane; 

dichloromethane; pentachlorophenol; PCBs; radium; dioxin; tetrachloroethylene; thallium; 

trichloroethylene. In addition, two contaminants in Category 6 (benzene and EDB) and two in 

Category 10 (chlordane and vinyl chloride) have MCLs that are limited by PQLs and, therefore, 

these contaminants proceed to the analytical methods review even though their health effects 

assessments indicated no change to their respective MCLG values. Similarly, six contaminants 

in Category 12 (DBCP; 1,2-dichloropropane; heptachlor; heptachlor epoxide; 

hexachlorobenzene; toxaphene) and one in Category 13 (1,1,2-trichloroethane) have MCLs that 

are limited by their respective PQL and, therefore, proceed to the analytical methods review 

despite there being no new information on health effects. 

Among the contaminants having new health effects information during either Six-Year 

Review 2 or the previous review that potentially affects their respective MCLG values (i.e., 

potentially lower MCLGs), four in Category 4 (2,4-D; endothall; toluene; total xylenes) and two 

in Category 8 (hexachlorocyclopentadiene and oxamyl) proceed to the analytical methods 

review. For each of these contaminants, EPA evaluated whether analytical feasibility might 

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become a limiting factor if EPA were to consider a lower MCLG and whether new information 

indicates there is a potential to revise the PQL.

Two contaminants (acrylamide from Category 1 and epichlorohydrin from Category 12) 

bypass the analytical methods review because they have TT standards and PQLs are not a 

limiting factor for the standards. Five contaminants from Category 5 (alachlor; barium; diquat; 

glyphosate; 1,1,1-trichloroethane) and three from Category 9 (1,1-dichloroethylene; lindane;

picloram) bypass the analytical methods review because the new health effects information 

identified either during Six-Year Review 2 or Six-Year Review 1 indicated possible increases in 

their respective MCLGs. Each of these contaminants has a PQL that is lower than its MCLG 

and, therefore, a review of whether the PQL could be lower is inconsequential.

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Table V-3. Contaminants Proceeding to Analytical Feasibility Review from Health Effects Review

Health Effects Review 

Category1 Contaminants Proceeding to Analytical Feasibility Review

Category 1

14 of 15 proceeding because PQL limits MCL: alpha particles; benzo(a)pyrene; 

beta particles; carbon tetrachloride; DEHP; 1,2-dichloroethane; 

dichloromethane; pentachlorophenol; PCBs; radium; dioxin; 

tetrachloroethylene; thallium; trichloroethylene

acrylamide bypasses the analytical review because it does not have a PQL 

Category 2

0 of 2 proceeding because there is no potential to revise MCL unless 

completed health effects assessment indicates change to benefits analysis 

(arsenic and uranium)

Health Effects 

Assessment in 

Process During 

Information 

Review 

Period for the 

Notice (and not 

available by the 

March 1, 2009 

cutoff date) Category 3 0 of 13 did not proceed because MCL set at MCLG and 

health assessment still in process

Category 4 4 of 4 proceeding to evaluate whether PQL is or could be below possible 

MCLG: 2,4-D; endothall; toluene; total xylenes

Category 5 0 of 5 proceeding; all 5 bypass analytical review because PQL not a factor in 

review

Category 6 2 of 2 proceeding because PQL limits MCL: benzene and EDB

Health Effects 

Assessment 

Completed 

Since Six-Year 

Review 1 Category 7 0 of 3 proceeding because there is no potential to revise an MCL that is based 

on the MCLG under review

Category 8 2 of 2 proceeding to evaluate whether PQL is or could be below possible 

MCLG: hexachlorocyclopentadiene; oxamyl 

Category 9 0 of 3 proceeding; all 3 bypass analytical review because PQL not a factor in 

review

Category 10 2 of 3 proceeding because PQL limits MCL: chlordane and vinyl chloride

Category 11 0 of 3 proceeding because there is no potential to revise an MCL that is based 

on the MCLG that may be further reviewed

Category 12

6 of 7 proceeding because PQL limits MCL: DBCP; 1,2-dichloropropane; 

heptachlor; heptachlor epoxide; hexachlorobenzene; toxaphene

epichlorohydrin bypasses the analytical review because it does not have a PQL 

Literature 

Review Only

Category 13 1 of 7 proceeding because PQL limits MCL: 1,1,2-trichloroethane

1. These categories correspond to the categories in Table V-2.

3. Analytical Feasibility 

EPA has a process in place to approve new analytical methods for drinking water 

contaminants; therefore, the review and approval of potential new methods are outside the scope 

of the Six-Year Review protocol. EPA recognizes, however, that the approval and addition of 

new and/or improved analytical methods (since the promulgation of the NPDWRs considered 

under this section of the review) may enhance the ability of laboratories to quantify contaminants 

at lower levels. This ability of laboratories to measure a contaminant at lower levels could affect 

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its PQL, the value at which an MCL is set when it is limited by analytical feasibility. Therefore, 

the Six-Year Review process includes a review of whether there have been changes in analytical 

feasibility for the subset of the NPDWRs that reached this stage of the decision tree. These 

include contaminants with or without ongoing health effects assessments that have MCLs limited 

by analytical feasibility and contaminants with possible MCLGs that are lower than their current 

PQLs. 

The document, “Analytical Feasibility Support Document for the Second Six-Year Review of 

Existing National Primary Drinking Water Regulations” (USEPA, 2009c), describes the process 

EPA used to evaluate whether changes in PQL are possible in those instances where the MCL is 

limited, or might be limited, by analytical feasibility. EPA uses the PQL to estimate the level at 

which laboratories can routinely measure a chemical contaminant in drinking water. 

Historically, EPA has used two main approaches to determine a PQL for SDWA analytes: (1) 

Performance Evaluation (PE) data from Water Supply (WS) studies, which is the preferred 

alternative when sufficient data are available; or (2) a multiplier method, in which the PQL is 

calculated by multiplying the EPA-derived method detection limit (MDL) by a factor of 5 or 10 

(50 FR 46880, November 13,1985 (USEPA, 1985); 52 FR 25690 July 8, 1987 (USEPA, 1987); 

54 FR 22062 May 22, 1989 (USEPA, 1989b)). 

The review protocol for Six-Year Review 1 utilized data from PE studies, which were 

laboratory accreditation studies conducted under EPA oversight until 1999, when the program 

was privatized. Now, the National Environmental Laboratory Accreditation Conference 

(NELAC) conducts the accreditation program via Performance Testing (PT) studies. PQL 

reassessments discussed in this notice are based on the Six-Year 1 PE data collected through late 

1999 and laboratory passing rate PT data collected from late 1999 through 2004. One PT 

Deleted: carcinogens

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feasibility and provides the results of the 

analytical feasibility analyses. The 

purpose of these analyses is to determine 

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provider made pass/fail rates from PT studies available to EPA. This major provider accounts 

for a large portion of the PT results nationwide (USEPA, 2009c). 

Using PE or PT data to derive the PQL for chemical NPDWRs involves determining the 

concentration of an analyte at which 75 percent of EPA Regional and State laboratories achieve 

results within a specified acceptance range (see 54 FR 22062 at 22100, May 22, 1989 (USEPA, 

1989b)). For Six-Year Review 2, EPA did not have sufficient PT and PE data to recalculate any 

PQL values, in part because the spiked concentrations were rarely far enough below current 

PQLs. Instead, EPA used the PT and PE passing rate results (i.e., the percent of laboratories 

passing a performance test for a given study) at and below the current PQL to determine whether 

data may support a lower PQL. 

When PT results were not available below the PQL or when the results did not provide 

conclusive indications regarding a potential to revise a PQL, EPA used two alternate approaches 

to estimate possible PQLs: an approach based on the minimum reporting levels (MRLs) obtained 

as part of the Six-Year Review Information Collection Request (ICR) (see section V.B.4), and an 

approach based on method detection limits (MDL). While EPA prefers to use laboratory 

performance data to calculate a PQL, the MRL and MDL information can be valuable for this 

review to indicate whether it is possible to quantitate at levels below the current PQL. 

A laboratory reports an MRL when it does not detect a particular contaminant in a sample of 

water. The MRL is the lowest concentration level of a contaminant that a laboratory can reliably 

measure or quantitate within specified limits of precision and accuracy under routine laboratory 

operating conditions using a given method (USEPA, 2009c). MRL values were included with 

the data provided by the States in response to the Six-Year Review ICR. EPA evaluated the 

distribution of MRL values for each contaminant to identify the mode or value occurring most 

Deleted: window

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revision. 

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Deleted: An

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frequently for that contaminant (i.e., the modal MRL) and estimated the percentage of MRL 

values that are equal to or less than the modal MRL. When this percentage was at least 80

percent and the modal MRL was below the PQL, EPA chose to use this modal MRL value as an

estimated quantitation limit (also referred to as an EQL throughout this document). The use of 

modal MRLs is a refinement of the protocol, necessitated by limited availability of PT and PE 

data below the current PQL and made possible by the extensive amount of information included 

in the Six-Year Review ICR dataset (see section V.B.4). 

When the MRL data did not meet the 80 percent threshold used for deriving an EQL via this 

approach, EPA used an MDL approach to derive an EQL. As noted previously, this approach 

has been used in the past to derive PQLs for regulated contaminants. In addition, this same 

approach was used to identify possible analytical feasibility levels for Six-Year Review 1 

(USEPA, 2003a). In deriving these levels, the Agency used the MDLs associated with the 

analytical methods approved by EPA for drinking water analysis. EPA obtained MDL values 

from individual analytical methods developed and approved by EPA for use on drinking water. 

EPA applied a multiplier to these MDL values and based the EQL on the midpoint of the 

resulting range (i.e., the mean if there are two MDLs or a median if there are more than two 

MDLs). The multiplier is 10 for most contaminants except dioxin and EDB, which have PQLs 

that were historically based on an MDL multiplier of 54. EPA also used the MDL multiplier 

approach to confirm whether EQLs based on MRL data are consistent with the range of values 

based on an MDL multiplier approach.

EPA used the EQL thresholds derived via the modal MRL or MDL-multiplier approaches for 

the occurrence analysis (see section V.B.4) to help the Agency determine if there may be a 

 

4

 As noted in Table V-4 and sections VI.38 and VI.59, EPA found that there was no potential to lower the PQL 

for dioxin and EDB. Even if EPA had used a 10 x MDL multiplier for these two contaminant instead of the 5 x 

MDL multiplier, this would not have changed the outcome of the analytical feasibility assessments.

Deleted: (formerly

Deleted: )

Deleted: The second source of 

information that EPA reviewed to 

evaluate possible changes in analytical 

feasibility (or the PQL) was the 

Deleted: and/or ranges 

Deleted: Based on 

Deleted: , EPA used an MDL multiplier 

to estimate where the possible lower limit 

of quantitation may currently lie

Deleted: has a

Deleted: in its original PQL.¶

Deleted: considered both

Deleted: modal MRL and 

Deleted: -based estimates when it 

Deleted: estimated quantitation levels 

(EQLs) (USEPA, 2009e)

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meaningful opportunity to improve public health protection. It should be noted, however, that 

the EQL does not represent the Agency’s intent to promulgate new PQLs with this notice. Any 

revisions to PQLs will be part of future rule making efforts. 

EPA performed analytical feasibility analyses for the contaminants identified in Table V-3 as 

proceeding to this portion of the review. Table V-4.4 shows the contaminants gathered into three

more general categories and the outcomes of the Agency’s review. 

• A health effects assessment indicates potential for lower MCLG. This category includes the 

six contaminants identified in the health effects review as having information indicating the 

potential for a lower MCLG – four with new health effects assessments completed during 

Six-Year Review 2 and two with health effects assessments completed during Six-Year 

Review 1. Although their current MCLs are not limited by a PQL, EPA reviewed analytical 

feasibility to determine if analytical feasibility might limit the potential for MCL revisions. 

For two contaminants (endothall and oxamyl), the current PQL is higher than the possible 

MCLG identified in the health effects review. For these contaminants, the potential to lower 

their PQLs based on PE and PT data is inconclusive, but MRL and MDL data indicate the 

potential to revise the PQL. EPA thus proceeded to evaluate occurrence data to determine 

whether a lower PQL, and thus the MCL, may provide a meaningful opportunity to improve 

public health protection. The current PQL is not a limiting factor for the remaining four 

contaminants identified by the health effects review as having possible changes in their 

MCLG (i.e., 2,4-D, hexachlorocyclopentadiene, toluene, and xylenes).

• Contaminants with ongoing health effects assessments and existing MCLs are based on 

analytical feasibility. This category includes 14 contaminants with ongoing health 

assessments with existing MCLs that are greater than their MCLGs because they are limited 

Deleted: The possible lower bound 

PQL value was derived using the 

alternative sources of information (MRL 

and MDL) is referred to as EQL. 

Deleted: three categories of NPDWRs. 

Deleted: . Consequently, analytical 

feasibility might be a limiting factor for 

setting the MCL equal to the possible 

MCLG (see sections VI.B.34 and VI.B.51 

of today’s action for a more detailed 

discussion)

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by analytical feasibility. One contaminant has a non-zero MCLG (thallium) and the 

remaining 13 contaminants have MCLGs equal to zero. Although a risk assessment is in 

process for these contaminants, because SDWA requires the Agency to set the MCL as close 

to the MCLG as feasible, EPA evaluated whether the PQL is likely to be lower for these 

contaminants. For four of these contaminants (carbon tetrachloride, 1,2-dichloroethane, 

tetrachloroethylene, and trichloroethylene), EPA concluded that new information from PT 

studies, along with MRL and MDL data, indicate the potential to revise the PQL. For one 

contaminant (dichloromethane), data from PT studies are inconclusive, but MRL and MDL 

data indicate the potential to revise the PQL. For these five contaminants, EPA proceeded to 

evaluate occurrence data to determine whether lowering the PQL, and thus the MCL, may 

provide a meaningful opportunity to improve public health protection5. For the remaining 

nine contaminants, either EPA did not have sufficient new information to evaluate analytical 

feasibility or EPA concluded that new information does not indicate the potential for a PQL 

revision. Consequently, the outcome of the review for these nine contaminants is to take no 

action at this time.

• Contaminants without ongoing health effects assessments or for which no new health risk 

information was identified and for which existing MCLs are based on analytical feasibility 

and greater than their MCLGs. For the 11 contaminants in this category, EPA evaluated 

available PT and PE data as well as MRL and MDL data to determine whether there is 

potential to lower the PQL and thereby set the MCL closer to the MCLG. For five of these 

 

5

 If EPA found that there was no meaningful opportunity to revise the MCL (i.e., carbon tetrachloride, 1,2-

dichloroethane and dichloromethane), these contaminants remained in the health effects assessment in process 

category. 

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contaminants (benzene chlordane, 1,2-dichloropropane, hexachlorobenzene, and 1,1,2-

trichloroethane) EPA concluded that new information from PT studies, along with MRL and 

MDL data, indicates that while it might be possible to set a lower PQL, the data are 

insufficient to support an actual PQL recalculation at this time. Consequently, the outcome 

of the review for these contaminants is to take no action at this time. For five additional 

contaminants (DBCP, heptachlor, heptachlor epoxide, toxaphene, and vinyl chloride), the 

data from PT studies are inconclusive, but MRL and/or MDL data indicate potential for a 

lower PQL, as indicated in Table V-4. For these five contaminants, EPA proceeded to 

evaluate occurrence data to determine whether lowering the PQL, and thus the MCL, may 

provide a meaningful opportunity to improve public health protectionTable V-4.4. For the 

final contaminant, ethylene dibromide (EDB), none of the data sources indicate potential to 

revise and the outcome of the review for this contaminant is to take no action at this time. 

Table V-4Table V-4.4 lists the type of data that indicate potential for a PQL reduction. The 

list includes “PT” when the PQL reassessment based on PT and PE data (USEPA, 2009c) reports 

that a reduction is supported. The list also includes “MRL” and “MDL” when either of these 

approaches indicates potential for PQL reduction. A result of “PQL reduction supported” 

without a “PT” in the list indicate that the PQL reassessment outcome is uncertain, but other data 

(i.e., MRL and/or MDL) indicate potential for PQL reduction. When the PQL reassessment 

outcome is that the current PQL remains appropriate, Table V-4Table V-4.4 shows the result 

“Data do not support PQL reduction.” The contaminant specific discussions in section VI of 

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,

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today’s action provide the results of the analytical feasibility review for all the contaminants in 

Table V-4Table V-4.4. 

Table V-4.4. NPDWRs Included in the Analytical Feasibility 

Reassessment and the Result of that Assessment 

Contaminant Current PQL Analytical Feasibility Reassessment Result 

6 Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG 

2,4-D 

(possible MCLG: 0.04 mg/L) 0.005 mg/L PQL not limiting 

Endothall 

(possible MCLG: 0.05 mg/L) 0.09 mg/L PQL reduction supported (MRL, MDL) 

Hexachlorocyclopentadiene (possible 

MCLG: 0.04 mg/L) 0.001 mg/L PQL not limiting 

Oxamyl 

(possible MCLG: 0.002 mg/L) 0.02 mg/L PQL reduction supported (MRL, MDL) 

Toluene 

(possible MCLG: 0.6 mg/L) 0.005 mg/L PQL not limiting 

Total xylenes 

(possible MCLG: 1 mg/L) 0.005 mg/L PQL not limiting 

14 Contaminants with Ongoing Health Effects Assessments (as of March 1, 2009) and MCLs Are Based on 

Analytical Feasibility and Higher than MCLGs 

Alpha particles No PQL and no new information 

Benzo(a)pyrene 0.0002 mg/L Data do not support PQL reduction 

Beta particles No PQL and no new information 

Carbon Tetrachloride 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

DEHP 0.006 mg/L Data do not support PQL reduction 

1,2-dichloroethane 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

Dichloromethane 0.005 mg/L PQL reduction supported (MRL, MDL) 

Pentachlorophenol 0.001 mg/L Data do not support PQL reduction 

PCBs 0.0005 mg/L Data do not support PQL reduction 

Radium No PQL and no new information 

Dioxin 3E-08 mg/L Data do not support PQL reduction 

Tetrachloroethylene 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

Thallium 0.002 mg/L Data do not support PQL reduction 

Trichloroethylene 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

11 Contaminants without Ongoing Health Effects Assessments and MCLs Are Based on Analytical 

Feasibility and Higher than MCLGs 

Benzene 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

Chlordane 0.002 mg/L PQL reduction supported (PT, MRL, MDL) 

DBCP 0.0002 mg/L PQL reduction supported (MDL) 

1,2-dichloropropane 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

EDB 0.0005 mg/L Data do not support PQL reduction 

Heptachlor 0.0004 mg/L PQL reduction supported (MRL, MDL) 

Heptachlor epoxide 0.0002 mg/L PQL reduction supported (MRL, MDL) 

Hexachlorobenzene 0.001 mg/L PQL reduction supported (PT, MRL, MDL) 

Toxaphene 0.003 mg/L PQL reduction supported (MRL, MDL) 

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1,1,2-trichloroethane 0.005 mg/L PQL reduction supported (PT, MRL, MDL) 

Vinyl chloride 0.002 mg/L PQL reduction supported (MRL) 

mg/L – milligrams per liter 

EPA conducted occurrence and exposure analyses for the contaminants in Table V-4.4 for 

which a PQL reduction is supported or the PQL is not limiting. This includes the 6 contaminants 

with new health effects assessments that indicate potentially lower MCLGs, 5 of the 14 

contaminants with ongoing health effects assessments and MCLs limited by PQLs, and 10 of the 

11 contaminants without ongoing health effects assessments and MCLs limited by PQLs.

4. Occurrence and Exposure Analysis 

To support the national contaminant occurrence assessments under Six-Year Review 2, EPA 

conducted an Information Collection Request. Through this process EPA requested that all 

States and primacy entities voluntarily submit their SDWA compliance monitoring data. This 

request was for the submission of compliance monitoring data collected between January 1998 

and December 2005 for 79 regulated contaminants. A total of 51 States and entities provided 

compliance monitoring data that included all analytical detection and non-detection records. 

These data represent the national occurrence of regulated contaminants in public drinking water 

systems. Through extensive data management efforts, quality assurance evaluations, and 

communications with State data management staff, EPA established a high quality dependable 

contaminant occurrence database consisting of data from 45 States and two Indian Tribes (see 

map in

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Figure V-2). Details of the data management and data quality assurance evaluations are 

available in the support document entitled, “Analysis of Occurrence Data from the Second SixYear Review of Existing National Primary Drinking Water Regulations” (USEPA, 2009f). 

Figure V-2. States with Compliance Monitoring Data Included in the Six-Year Review 2

The contaminant occurrence data from the 45 States and two Indian Tribes comprise more 

than 15 million analytical records from approximately 132,000 public water systems. 

Approximately 254 million people are served by these public water systems nationally. Records 

were submitted for 16 inorganic chemicals, 32 synthetic organic chemicals, 21 volatile organic 

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chemicals, 7 radiological contaminants, and 3 microbiological8 contaminants. The number of 

States and public water systems represented in the dataset varies across contaminants because of 

variability in voluntary State data submissions and contaminant monitoring schedules. This is 

the largest, most comprehensive set of drinking water compliance monitoring data ever compiled 

and analyzed by EPA. 

EPA used a two-stage analytical approach to analyze these data and characterize the national 

occurrence of contaminants.9

 The first stage of analysis provides a straightforward evaluation of 

contaminant occurrence. This stage 1 occurrence analysis is a simple, non-parametric count of 

occurrence of regulated contaminants in public water systems.10 A typical stage 1 occurrence 

analysis generates a count of the number (or percentage) of systems with at least one analytical 

detection having a concentration greater than a concentration threshold of interest, i.e., a possible 

MCLG or EQL. It provides a health protective approach that may be more appropriate for 

contaminants that produce health effects after shorter than lifetime exposure periods (e.g., 

several months or less). This approach also generates a conservative (i.e., upwardly biased) 

estimate of the number of potential systems having contaminant occurrence at levels of interest

for contaminants having health risks that are only related to chronic or long-term exposure over 

many years. 

The stage 2 occurrence analysis estimates national contaminant occurrence by generating 

estimated long-term mean concentrations of a specific contaminant at systems nationally. This 

 

8

 The compliance monitoring data for the microbiological contaminants were collected to support ongoing rule 

development so these data have not been analyzed separately in this action. 9

 The use of the stage 1 and stage 2 terminology should not be confused with the Stage 1 and Stage 2 

Disinfectants and Disinfection By Products Rulemakings. Instead, this terminology has been used to describe the 

two stages of the occurrence analyses performed for Six-Year Review 2, as well as Six-Year Review 1. 10 These analyses are conservative in the sense that they are protective of human health (i.e., they are more 

likely to overestimate risks to human health than underestimate them). 

Deleted: of a specific contaminant, or 

with at least one analytical detection with

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provides occurrence analyses that are less conservative than the stage 1 occurrence analysis 

(because the stage 2 occurrence analysis is based on estimated mean concentrations rather than 

on single maximum concentrations), and also provides occurrence analyses that may be more 

reflective of potential chronic exposure. Generally, the stage 1 occurrence analysis reflects a 

rough approximation of peak occurrence while the stage 2 occurrence analysis is based on 

estimated average occurrence. A complete description of the two-stage analytical approach and 

a detailed presentation of occurrence estimates are available in the support document entitled, 

“Analysis of Occurrence Data from the Second Six-Year Review of Existing National Primary 

Drinking Water Regulations” (USEPA, 2009f). 

EPA calculated the system means for the stage 2 occurrence analysis using a simple 

arithmetic average of all detection and non-detection data for each public water system. Because 

the contaminant concentrations associated with the non-detection data are unknown, EPA 

assigned three different values to the non-detection results to estimate a range of system-level 

means, which then allowed EPA to estimate number and percent of systems with estimated 

means exceeding selected threshold values. Two of the three values are based on the MRL 

values that accompany the non-detection results in the Six-Year Review ICR dataset. The MRL 

is the lowest level that can be reliably achieved within specified limits of precision and accuracy 

under routine laboratory operating conditions using a given method. The three values that EPA 

substituted for non-detection results were MRL, 1/2 MRL, and zero. 

The most conservative approach was to assume that all non-detection results were equal to 

the MRL. This approach yields an upper-bound estimate of each system's level of exposure. 

EPA also explored the less conservative assumption that concentrations of the non-detection 

results were uniformly distributed between the MRL and zero, thereby substituting one-half the Deleted: ¶

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MRL for all non-detection results. Finally, EPA considered the assumption that the actual 

concentration for each non-detection result was typically much smaller than the MRL, 

supporting the use of zero to represent each non-detection. This method yielded a lower-bound 

estimate of the system’s mean. This simplified approach differs from the stage 2 occurrence 

analysis approach in the Six-Year Review 1, which used more sophisticated modeling methods 

to address the non-detection results. That analysis, however, was based on a substantially 

smaller dataset (i.e., data from 16 States instead of 45 States). (Note that many States substitute 

zero for all non-detections when determining compliance with the NPDWRs.) EPA uses each of 

the assumptions in the stage 2 occurrence analyses in order to obtain reasonable bounds on the 

actual system mean concentrations. Once the system means were calculated for each of the three 

substitution methods, the results means were then compared to the various thresholds of interest 

(e.g., the number and percent of systems with a mean concentration above a health threshold of 

concern). 

The two-stage analytical approach was previously developed for Six-Year Review 1. The 

data management and general occurrence analytical approach were peer-reviewed for use under 

the Six-Year Review 1. 

EPA conducted the stage 2 occurrence analysis for 5 of the 14 NPDWRs in Table V-4.4 with 

ongoing health effects assessment and MCLs that are limited by PQLs for which EPA identified 

analytical feasibility data supporting possible PQL revision: carbon tetrachloride; 

dichloromethane; 1,2-dichloroethane; tetrachloroethylene; and trichloroethylene. EPA also 

conducted the stage 2 occurrence analysis for the five contaminants with health effects 

assessment changes that indicate potential to reduce the MCLG and the ten contaminants that do 

not have ongoing health effects assessments, but do have MCLs limited by PQLs and new data 

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indicate potential to reduce the PQLs (see Table V-4.4). Note that EPA conducted the Stage 1 

analysis for one contaminant with health effects assessment changes that indicate a potential to 

reduce the MCLG (i.e., oxamyl) because the health endpoint is associated with acute exposure. 

EPA used the results of these analyses to identify which possible NPDWR revisions present a 

meaningful opportunity to improve the level of health protection. Section VI contains the 

occurrence estimates for each of the 21 contaminants (shown in Table V-4.4) having either new 

information suggesting potentially lower MCLGs or MCLs based on PQLs that might be lower 

based on new information. 

Because the Six-Year Review ICR data reflect water quality at entry points to the distribution 

system, the occurrence analysis method described above is not adequate to evaluate the cost 

savings potential for the nine contaminants that have health effects assessment changes that 

indicate potential for higher MCLG values (see Table V-2). EPA lacks the comprehensive 

information on source water quality and existing treatment needed to determine how many 

systems would be able to alter treatment practices were an MCLG to increase. To review the 

potential for cost savings, EPA conducted a qualitative assessment of the potential for treatment 

cost savings based on three factors: the magnitude of the difference between the current MCLG 

and the possible MCLG; available source water occurrence information; and the potential for 

systems having best available technologies (BATs) or small system compliance technologies 

(SSCTs) to realize operational cost savings (USEPA, 2009g). 

There is no comprehensive database of water quality in drinking water sources. Therefore, 

EPA used source water quality information from two national data sources, the National Water 

Quality Assessment (NAWQA) program conducted by the U.S. Geological Survey (USGS), and 

EPA’s STORET (short for STOrage and RETrieval) data system, which are part of EPA’s Office 

Deleted: the stage 2 occurrence 

Deleted: or a meaningful opportunity 

for cost savings to drinking water systems 

and their customers while maintaining the 

same level of health protection

Deleted: occurrence results and EPA’s 

review results for the 

Deleted: that have potential for MCL 

revisions.¶

Deleted: obtained publicly available 

source water quality data and 

Deleted: that might be treating these 

contaminants with 

Deleted: listed in the NPDWR for each 

contaminant 

Deleted: Source water quality data 

were needed to determine cost savings 

potential for the contaminants for which a 

health effects assessment indicates the 

potential for higher MCLG values. 

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of Ground Water and Drinking Water’s National Contaminant Occurrence Database (NCOD). 

The STORET data come from a variety of monitoring programs and the NAWQA data come 

from watershed or “study units” that USGS selected to reflect important hydrologic and 

ecological resources; critical sources of contaminants, including agricultural, urban, and natural 

sources; and a high percentage of population served by municipal water supply and irrigated 

agriculture. The original 51 study units account for more than 70 percent of total water use 

(excluding thermoelectric and hydropower) and more than 50 percent of the population’s supply 

of drinking water (Gilliom et al., 2006). For each dataset, EPA estimated the number and 

percent of monitoring locations with at least one sample result above each contaminant’s current 

MCL, and above a possible MCLG based on the new information from the contaminant’s health 

effects assessment. Although these results do not indicate how many systems may be treating for 

each contaminant, they provide the best available information regarding the frequency of 

contaminant occurrence at levels of interest. Section VI reports the results by contaminant. 

5. Treatment Feasibility 

An NPDWR either identifies the BATs for meeting an MCL, or establishes enforceable 

treatment technique requirements. For the NPDWRs addressed in section VI of today’s action, 

two have TT requirements and the rest have an MCL. All of the MCLs are set equal to the 

MCLG or the PQL or by benefit-cost analysis; none are currently limited by treatment 

feasibility. As a refinement for Six-Year Review 2, EPA considered treatment feasibility after 

identifying contaminants with potential to lower an MCL or change a TT that constituted a 

meaningful opportunity to improve the level of health protection. The EPA document, ‘‘Water 

Treatment Technology Feasibility Support Document for Chemical Contaminants for the Second 

Six-Year Review of National Primary Drinking Water Regulations’’ (USEPA, 2009g), describes 

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the process EPA used to evaluate treatment feasibility, where appropriate, and provides the 

results of these analyses. As a part of this review, EPA utilized the same sources that have been 

the primary resources in development of EPA regulations and guidance, including published 

EPA treatment reports, peer-reviewed journals, and other technology sources, as well as 

information received from EPA stakeholders. 

a. MCL-Type Rules. 

EPA evaluated existing treatment technology information for two MCL-type NPDWRs 

(tetrachloroethylene and trichloroethylene) where EPA determined that lowering the PQL and 

thus the MCL could lead to a meaningful opportunity to improve public health protection, to 

determine whether treatment feasibility would be a limiting factor. 

Based on this evaluation, the Agency believes that treatment capabilities would be adequate 

to support a lower MCL value for these contaminants for which a lower MCL may be 

appropriate (USEPA, 2009g). EPA’s assessment of the treatment technologies for these 

contaminants that are specified as BAT in the current NPDWR and some of the small system 

compliance technologies specified by EPA in 1998 (USEPA, 1998b), shows that they are 

effective enough to achieve concentrations as low as the EQL. If EPA were to determine that it 

is appropriate to revise these NPDWRs, it would undertake a more thorough review of treatment 

feasibility, including a consideration of costs, to determine whether treatment feasibility would 

be a constraint or not. 

b. Treatment Technique-Type Rules. 

EPA reviewed two chemical NPDWRs – acrylamide and epichlorohydrin (both classified B2 

carcinogens) – for which a TT is set in lieu of an MCL. The TT requirement limits the allowable 

acrylamide and epichlorohydrin monomer levels in polymeric coagulant aids and their dosages 

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MCL for tetrachloroethylene and 

trichloroethylene

Deleted: any of 

Deleted: Treatment

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Deleted: ,

Deleted: , which were

Deleted: ) for these contaminants are 

considered to be efficient and practical 

for implementation at a public water 

system (PWS)

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for drinking water treatment, storage, and distribution. Although a health effects assessment for 

acrylamide is ongoing, it is a carcinogen with an MCLG of zero and the draft health effects 

assessment indicates that the cancer classification remains the same. As a refinement in SixYear Review 2, EPA considered new information to determine if the TTs for these contaminants 

may need to be revised. This information indicates that improvements in manufacturing 

capabilities have reduced the residual monomer content in acrylamide and epichlorohydrin-based 

polymeric coagulants aids and these changes would support revisions to the TTs for acrylamide 

and epichlorohydrin. Sections VI.B.1 and VI.B.36 of today’s action summarize these issues for 

acrylamide and epichlorohydrin, respectively. 

6. Other Regulatory Revisions 

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

regulatory revisions are needed, such as monitoring and system reporting requirements, as a part 

of the Six-Year Review 2. EPA utilized the protocol established during the Six-Year Review 1 

to evaluate which implementation issues to consider (USEPA, 2003b). EPA’s protocol focused 

on items that were not already being addressed, or had not been addressed, through alternative 

mechanisms (e.g., as a part of a recent or ongoing rulemaking). EPA considered potential 

implementation-related revisions in these cases if the revisions: 

• Represented a change to an NPDWR, as defined under section 1401 of SDWA11; 

• Were "ready" for rulemaking – that is, the problem to be resolved had been clearly defined, 

and specific options to address the problem had been formulated; and 

 

11 The subject of the Six-Year-Review, as specified in section 1412(b)(9) of the SDWA, is "each national 

primary drinking water regulation," as defined under section 1401 of the SDWA. 

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• Would clearly improve the level of public health protection and/or provide a meaningful 

opportunity for cost savings (either monetary or burden reduction) while not lessening public 

health protection. 

a. Issues Identified by the EPA/State Workgroup 

To gather input regarding implementation-related concerns and help the Agency identify the 

top one or two issues for Six-Year Review 2 (USEPA, 2009h), EPA requested that the 

Association of State Drinking Water Administrators (ASDWA) form a workgroup of member 

States and primacy agencies. In the fall of 2007, ten member States agreed to participate and 

confer with EPA on a joint EPA/State workgroup. The State/EPA workgroup initially identified 

22 issues, but narrowed the list to 4 items. Of these four items, three appeared to be within the 

scope of this NPDWR review, and EPA agreed that an information or fact sheet might be 

appropriate for the fourth item regarding public notification (PN) requirements for fluoride12. 

The EPA/State workgroup agreed that public input via the Federal Register would provide 

additional insight on the national scope of these three issues (i.e., Are the issues isolated to a few 

States or more widespread?), the importance of these issues to other States as well as water 

systems, and ideas on potential resolutions. Table V-5.5 provides a brief description of the 

remaining three issues and some of the potential solutions discussed in the workgroup meetings. 

EPA is requesting public input and further information on these three implementation issues 

to better inform future State/EPA workgroup discussions. More specifically, EPA would like to 

 

12 Currently, PWSs that exceed the fluoride MCL of 4.0 mg/L are required to notify their customers within 30 

days of the exceedance. If a PWS exceeds the fluoride SMCL of 2.0 mg/L, they are required to notify their 

customers within 12 months of the exceedance. The States voiced concerns about (1) the confusion that occurs 

between the different PN requirements for the MCL and the SMCL, and (2) the timeliness of the PN requirement for 

the SMCL. The workgroup indicated that waiting 12 months to notify customers of an exceedance of the SMCL 

does not adequately protect young children from dental fluorosis during a critical stage of tooth enamel 

development. The participating States requested that EPA consider regulatory revisions to clarify the PN 

requirements and better reflect the health and aesthetic implications of each. EPA noted that PN requirements are 

not within the scope of this NPDWR review. However the Agency agreed that a fact or information sheet may be 

useful to clarify any confusion. 

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gauge how many States and/or public water utilities may be affected by these issues, and which 

one or two issues are most important to States. EPA also requests input and suggestions from 

commenters regarding any other potential solutions to the issues. As part of the public comment 

process, EPA also welcomes any data on the occurrence of nitrates and/or nitrites in the 

distribution system, especially as it may relate to nitrification associated with the use of 

chloramines for disinfection. 

Table V-5.5. Issues Identified by the EPA/State Workgroup That Fall within the Scope of this NPDWR 

Review 

Implementation Issue Examples of Potential Solutions discussed by the Workgroup 

Change the location of 

nitrate-nitrite monitoring 

to address possible 

nitrification within the 

distribution system for 

water systems using 

chloramines1

• Location of Monitoring 

- Move sampling location from the entry point to the distribution to within the 

distribution system 

- Or, maintain entry point sampling and also sample in the distribution system 

• Frequency of Monitoring 

- Consider sampling in conjunction with DBPs, TCR or some other scheme. 

• EPA notes that 40 Code of Federal Regulations (CFR) 141.23(a)(2) may allow 

surface water systems discretion to locate the sampling point in the distribution 

system if that is more representative of the source after treatment.2 

Reduce the monitoring 

for ground water systems 

with historically low levels 

of nitrate-nitrite 

• Consider revisions to change the frequency of monitoring, the trigger level and the 

duration of time for systems to qualify for reduced monitoring. Examples included: 

- A monitoring frequency of 3, 6, or 9 years (consistent with the existing 

standardized monitoring framework) or some other frequency. 

- A new trigger level set at either 1/2 the MCL (or some other fraction), the 

PQL/MDL (or some other level of detection), or another appropriate level. 

- As for the duration of how long a system would need to meet the trigger level in 

order to be allowed to begin reduced monitoring, some options included a 3-, 6-, 

or 9-year period (consistent with the standardized monitoring framework) or a 5-, 

10-, or 15-year period. 

• Or consider providing a waiver option to give States discretion to reduce monitoring.

• Or consider a non-regulatory option such as the Alternative Monitoring Guidelines 

(which some considered too burdensome). 

Revise the monitoring 

requirements for Non 

Community Water 

Systems (NCWS) to 

better target the potential 

health risks associated 

with chronic 

contaminants. In light of 

• Revise all contaminant rules to include additional monitoring requirements for 

Transient Non Community Water Systems (TNCWS), as well as radionuclide 

monitoring requirements for Non Transient Non Community Water Systems 

(NTNCWS) 

• Or review existing regulated contaminants and include TNCWS monitoring 

requirements based on the relative health risk from chronic exposure. 

• Or develop general language that would apply to all contaminant rules, giving States 

the discretion to require additional monitoring for contaminants that pose chronic 

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the probability and 

magnitude of health 

threats, some monitoring 

requirements for these 

systems may be 

insufficient, and others 

may be excessive. 

exposure risks and can have acute health effects at elevated levels potentially found 

at TNCWSs (the preferred option from States). 

• Note: For some of these options, EPA would need to evaluate whether sufficient 

occurrence and exposure information is available for TNCWS and NTNCWS to 

assess the need for revised monitoring strategies. 

1. The health effects technical review identified new information on developmental effects of nitrate and nitrite, as well as data 

regarding its carcinogenicity, that may indicate the need to update the Agency’s risk assessment (see section VI.B.49 and 

VI.B.50 of today’s action). In light of this information, EPA is considering nitrate and nitrite as potential candidates for new health 

effects assessments. If new assessments are initiated and completed, EPA will be able to determine the potential impacts on 

the MCLG, MCL, and/or monitoring requirements, and what future actions may or may not be appropriate. 

2. 40 CFR 141.23(a)(2) states: Surface water systems shall take a minimum of one sample at every entry point to the 

distribution system after any application of treatment or in the distribution system at a point which is representative of each

source after treatment (hereafter called a sampling point) beginning in the initial compliance period. The system shall take each 

sample at the same sampling point unless conditions make another sampling point more representative of each source or 

treatment plant. 

b. Other Issues (Synthetic Organic Chemicals Trigger Levels) 

40 CFR 141.24(h)18 of the national primary drinking water regulations lists detection limits 

for the synthetic organic chemicals (SOCs), including pesticides. These detection limits serve as 

triggers for determining whether the compliance monitoring frequency for SOCs may be 

reduced; public water systems detecting SOCs at or below trigger concentration can qualify for 

reduced monitoring. Several Regions and States have requested guidance and clarification on 

the use of detection limits in monitoring of drinking water samples for SOCs. The primary 

concern is that some laboratories have reported difficulty in achieving the detection limits for 

some SOCs on a regular basis and, in those cases, the water systems that they support are not 

able to qualify for reduced monitoring. 

 EPA is seeking information about the extent and magnitude of any issues related to the 

ability of laboratories to achieve the SOC trigger levels specified in section 141.24(h)(18). EPA 

wishes to determine if this issue is widespread or limited to specific SOCs and/or specific 

laboratories. EPA is requesting that stakeholders provide information/data to support their 

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C. How Did EPA Factor Children’s Health Concerns Into the Review? 

The 1996 amendments to SDWA require special consideration of all sensitive populations 

(e.g., infants, children, pregnant women, elderly, and individuals with a history of serious illness) 

in the development of drinking water regulations (section 1412(b)(3)(C)(V) of SDWA, as 

amended in 1996). As a part of the Six-Year Review 2, EPA completed a literature search 

covering developmental and reproductive endpoints (e.g., fertility, embryo survival, 

developmental delays, birth defects, and endocrine effects) for regulated chemicals that have not 

been the subject of a health effects assessment during this review period (see section V.B.1 of 

today’s action). EPA reviewed the output from the literature searches to identify any studies that 

might have an influence on the present MCLG. Three chemicals were identified with potential 

developmental/reproductive endpoints of concern that might not be addressed by the current 

NPDWR: nitrate, nitrite, and selenium. In each case, where the literature search indicated a need 

to consider recent studies of developmental or reproductive toxicity, EPA is considering whether 

to nominate the contaminant for a new health effects assessment. 

VI. Results of EPA’s Review of NPDWRs 

Table VI-1 lists EPA’s review results for each of the 71 NPDWRs discussed in this section of 

today’s action along with the principal rationale for the review outcomes. Table VI-1 also 

includes a list of the 14 NPDWRs that have been or are being reviewed/revised by recent or 

ongoing regulatory actions. 

A. What are the Review Result Categories? 

For each of the 71 NPDWRs discussed in detail in the following sections of today’s action, 

the review results in one of the following outcomes:

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1. No Action at this Time and the NPDWR is Still Appropriate. 

The NPDWR is appropriate and no action is necessary at this time for one of the following 

reasons: 

a. A health effects assessment is in process or the Agency is considering whether to initiate 

an assessment. The MCL remains appropriate because either, (1) it is equal to the MCLG, (2) 

the MCL is based on SDWA’s cost-benefit provision, (3) there is no potential to change the 

MCL based on changes in analytical feasibility, or (4) there may be a potential change to the 

MCL based on analytical feasibility, but any such change is unlikely to provide a meaningful 

opportunity to improve public health protection. This group includes both contaminants where 

an assessment is in process, and contaminants where EPA identified new health information that 

may warrant a new health effects assessment. 

b. NPDWR remains appropriate after data/information review. There is no ongoing health 

assessment and the outcome of the review indicates that the current regulatory requirements 

remain appropriate and, therefore, no regulatory revisions are warranted at this time. Any new 

information available to the Agency either supports the current regulatory requirements or does 

not justify a revision. 

c. New information is available that indicates potential for a regulatory revision, but no 

revision recommended because: 

• Negligible gain in public health protection and/or cost savings: Any resulting changes 

to the NPDWR would not significantly improve the level of public health protection 

or result in a major cost savings for public water systems and their customers. 

• Information Gaps or Emerging Information: Either new information is emerging that 

could affect EPA’s evaluation of the NPDWR or the available data are insufficient to 

support a definitive regulatory recommendation at this time. 

2. Candidate for Revision. 

The NPDWR is a candidate for revision based on the review of new information. 

 

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health effects assessment in process that 

will not be completed in time for the 

current review, the

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Table VI-1. Summary of Six-Year Review 2 Results 

Recent or Ongoing Action 

(14 NPDWRs) 

Bromate 

Chloramines 

Chlorine 

Chlorine dioxide 

Chlorite 

Coliform 

Copper 

Cryptosporidium 

Giardia lamblia 

HAA5 

Lead 

Legionella 

TTHMs 

Viruses 

 Health effects assessment in 

process (as of March 1, 2009) or 

potential nominee for an 

assessment 

(32 NPDWRs)

Alpha particles (or emitters) 1

Antimony 

Arsenic 

Asbestos 

Benzo(a)pyrene1

Beryllium 

Beta particles and photon 

emitters1

Cadmium 

Carbon tetrachloride1

Chromium 

Cyanide 

1,2-Dichlorobenzene 

1,4-Dichlorobenzene 

1,2-Dichloroethane1

cis-1,2-Dichloroethylene 

trans-1,2-Dichloroethylene 

Dichloromethane1

Di(2-ethylhexyl)adipate1

Di(2-ethylhexyl)phthalate 1

Ethylbenzene 

Fluoride 

Nitrate 

Nitrite 

Pentachlorophenol1

Polychlorinated biphenyls 

(PCBs) 1

Radiums1

Selenium 

Styrene 

2,3,7,8-TCDD (dioxin) 1

Thallium1

1,2,4-Trichlorobenzene 

Uranium 

NPDWR remains appropriate 

after data/information review 

(8 NPDWRs) 

Dalapon 

Dinoseb 

Endrin 

Ethylene Dibromide (EDB) 

Mercury (inorganic) 

Methoxychlor 

Monochlorobenzene 

(chlorobenzene) 

2,4,5-Trichorophenoxy-propionic 

acid (2,4,5-TP) 

Low priority 

(24 NPDWRs) 

Alachlor 

Barium 

Benzene 

Chlordane 

1,2-Dibromo-3-chloropropane 

(DBCP) 

1,1-Dichloroethylene 

1,2-Dichloropropane 

2,4-Dichlorophenoxyacetic acid 

(2,4-D) 

Diquat 

Endothall 

Glyphosate 

Heptachlor 

Heptachlor epoxide 

Hexachlorobenzene 

Hexachlorocyclopentadiene 

Lindane 

Oxamyl 

Picloram 

Toluene 

Toxaphene 

1,1,1-Trichloroethane 

1,1,2-Trichloroethane 

Xylenes 

Vinyl chloride 

Not 

Appropriate for

Revision at this

Time 

New 

information, 

but no 

revision 

recommended 

because: 

Emerging 

information or data

gaps 

(3 NPDWRs) 

Atrazine 

Carbofuran Simazine 

Candidate 

for Revision 

Based on new information 

(4 NPDWRs) 

Acrylamide2

Epichlorohydrin 

Tetrachloroethylene (PCE) 2

Trichloroethylene (TCE) 2

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1. For these compounds, there is no potential to change the MCL based on changes in analytical feasibility or there may be a 

potential change to the MCL based on analytical feasibility but any such change is unlikely to provide a meaningful opportunity to 

improve public health protection. Therefore, EPA chose to leave these in the ongoing health assessment category.

2. Note that a health assessment is in process but new analytical feasibility and TT information may justify a revision.

B. What Are the Details of EPA’s Review of Each NPDWR? 

1. Acrylamide 

a. Background. EPA published the current NPDWR for acrylamide on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR imposes a TT requirement that 

limits the allowable monomer levels in products used during drinking water treatment, storage, 

and distribution to 0.05 percent acrylamide in polyacrylamide coagulant aids, and limits the 

dosage of such products to a maximum of 1 mg/L (ppm). Each water system is required to 

certify, in writing, to the State (using third-party or manufacturer’s certification) that the product 

used meets these residual monomers and use-level specifications. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to acrylamide. The revised health effects assessment is considering relevant studies on 

the toxicity of acrylamide, including its potential developmental and reproductive toxicity. The 

draft assessment was published in the Federal Register on December 28, 2007 (72 FR 73813 

(USEPA, 2007b)). The Science Advisory Board (SAB) conducted a peer review of the 

document, which also included a review of public comments received on the draft assessment. 

The SAB panel concurred with the Agency’s rationale and justification for acrylamide being a 

“likely human carcinogen” via mutagenic mechanism. At the present time, acrylamide is still 

under evaluation by the Agency, and the IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

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Although there is an ongoing health effects assessment, the MCLG is zero and the current TT 

standard allows exposure at levels above the MCLG. Therefore, EPA reviewed whether there is 

potential to revise the TT for acrylamide. EPA has identified information that suggests that the 

residual acrylamide content in water treatment polymers has decreased significantly, likely due 

to improvements in manufacturing processes and technologies (USEPA, 2009g). NSF 

International analyses conducted between January 2005 and June 2007 found that, in 66 

polyacrylamide products submitted for certification under NSF Standard 60, the median residual 

acrylamide content was 0.006 percent, and the 90th percentile acrylamide content was 0.025

percent, half of the limit set in the treatment technique. 

Acrylamide standards in Europe and Australia are also stricter than the NPDWR. Based on 

the maximum allowable dosage and monomer level in the NPDWR, finished water could contain 

up to 0.5 μg/L (ppb) of acrylamide. By contrast, the European Union requires that finished water 

contain less than 0.1 μg/L (parts per billion or ppb) acrylamide, and Australia requires that the 

concentration in finished water be less than 0.2 μg/L (ppb). The United Kingdom requires that 

polyacrylamides used in drinking water contain less than 0.02 percent residual acrylamide, and 

that the polyacrylamide dose be less than 0.5 mg/L (parts per million or ppm) at all times, for a 

maximum finished water concentration of 0.1 μg/L (ppb).

To assess the occurrence of acrylamide in drinking water, EPA sought data on current usage 

practices for polyacrylamide coagulant aids. The Agency is not presently aware of any recent, 

large-scale studies of polymer usage in drinking water facilities, and therefore cannot fully 

characterize the occurrence of acrylamide in drinking water. However, the 1996 

WATER:\STATS database (described in Levine et al., 2004), based on an American Water 

Works Association (AWWA) survey, indicates that 13 percent of ground water systems and 66

percent of surface water systems surveyed use a polymer for water treatment. Many of these are 

Deleted: However, as

Deleted: present draft reassessment 

does not change

Deleted: cancer classification for 

acrylamide, its MCLG will continue to be 

zero. 

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anionic and nonionic polymers, particularly for ground water systems; anionic and nonionic 

polymers used to treat drinking water are most likely polyacrylamides. 

 Additional information on the extent of use of polyacrylamide in drinking water and the 

impending health effects assessment will further assist the Agency in determining the potential 

public health benefits associated with a revision to the treatment technique for acrylamide. 

Because most polyacrylamides available today have a lower residual monomer content than that 

specified in the current treatment technique (2009g), EPA believes that the costs of a revision 

would be minimal and recognizes that the benefits may also be small. 

c. Review Result. The Agency believes it is appropriate to revise the NPDWR for acrylamide 

although a health effects assessment is currently in progress. The existing MCLG is still zero 

(based on the current B2 cancer classification) and NSF International data indicate that 

polyacrylamides are widely available with lower residual monomer levels than required by the 

existing NPDWR. Hence, revisions to the acrylamide NPDWR will provide a meaningful 

opportunity to maintain the health risk reductions achieved by technological advances in 

manufacturing. If the updated health effects assessment is completed in time to consider for the 

regulatory revision of acrylamide, the Agency will consider this final assessment in its evaluation 

of health benefits. As discussed in Section VII, the Agency solicits information from public on 

the extent of use of polyacrylamide in drinking water facilities (since this may provide additional 

information on the occurrence of acrylamide in drinking water) to help inform the regulatory 

revision. EPA notes that any changes to the NPDWR for acrylamide may also include revisions 

to the closely related NPDWR for epichlorohydrin. 

2. Alachlor 

a. Background. EPA published the current NPDWR for alachlor on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

Deleted: (USEPA, 2009g)

Deleted: for 

Deleted: . EPA expects that the final 

health effects assessment will further 

support the public 

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classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.002 mg/L, based on analytical feasibility. 

b. Technical Reviews. In 2006, the Agency updated its health effects assessment of alachlor 

(USEPA, 2006a). The Agency identified a change in this assessment that could lead to a change 

in the MCLG. This assessment considered relevant studies on the toxicity of alachlor including 

developmental and reproductive toxicity. For noncancer effects, the assessment confirmed the 

RfD of 0.01 mg/kg-day (milligrams per kilogram of body weight per day). The assessment also 

concluded that alachlor is likely to be a human carcinogen at high doses; not likely to be a human 

carcinogen at low doses, and that a linear dose-response extrapolation is no longer appropriate. 

It established a health reference value of 0.005 mg/kg-day for the nonlinear cancer assessment 

(USEPA, 2006a). Since the health reference value of 0.005 mg/kg-day is lower than the RfD of 

0.01 mg/kg-day, the Agency used this value to calculate a possible MCLG. Based on the health 

reference value of 0.005 mg/kg-day, and assuming a 70-kg adult body weight and 2 liters water 

intake per day, the drinking water equivalent level (DWEL) could be 0.2 mg/L. A relative 

source contribution (RSC) of 20 percent results in a possible MCLG of 0.04 mg/L (USEPA, 

2009b). 

Since the health review for alachlor indicates that the MCLG could possibly increase to 0.04 

mg/L (from its current MCLG of zero) and because the current MCL is based on a PQL of 0.002 

mg/L, neither analytical nor treatment feasibility would be a limiting factor for a possible higher 

level of 0.04 mg/L. 

 EPA evaluated the results of the occurrence and exposure analyses for alachlor to determine 

whether a revised MCLG/MCL would be likely to result in a meaningful opportunity for cost 

savings to PWSs and their customers while maintaining or improving the level of public health 

protection (USEPA, 2009f). Review of health information for alachlor indicated that the MCLG 

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could be increased to 0.04 mg/L from its current MCLG of zero. Consequently, the MCL of 

alachlor possibly can also increase to 0.04 mg/L. Although the Agency obtained and evaluated 

the finished water occurrence data for alachlor, its usefulness is limited for determining potential 

cost savings to PWSs and their customers because the Agency does not know which systems are 

treating for this contaminant. As an alternative, the Agency evaluated available data on source 

water quality and conducted a qualitative assessment of treatment cost savings. 

Table VI-2 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at threshold levels of interest. This information 

indicates that any resulting NPDWR change would affect systems that rely on source water at 

less than 0.4 percent of the NAWQA locations and less than 1.8 percent of the STORET 

locations. 

Table VI-2. Ambient Water Quality Monitoring Occurrence Summary for Alachlor 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 2,252 (100.0%) 9,236 (100.0%) 

Nondetect 1,669 (74.1%) 8,571 (92.8%) 

Detected 583 (25.9%) 665 (7.2%) 

Exceeds current MCL of 0.002 mg/L 40 (1.8%) 35 (0.38%) 

Exceeds alternative value of 0.04 mg/L 0 (0.0%) 1 (0.01%) 

1. STORET database 2002-2006. 

2. NAWQA database 1992-2008. 

Source: USEPA, 2009c

The BATs and small system compliance technologies for alachlor have other beneficial 

effects, e.g., reduction of other co-occurring contaminants, precursors for disinfection byproducts 

(DBPs) or other common impurities. Therefore, if EPA were to consider a higher level, the 

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Deleted: 0.3%

Deleted: 691

Deleted: 2,017 (75%)

Deleted: 674

Deleted: 7 (0.26%)

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Agency does not know how many PWSs that are currently treating to comply with the existing 

MCL of 0.002 mg/L would be likely to discontinue treatment that is already in place (USEPA, 

2009d). Also, the Agency does not know to what extent affected systems might be able to 

reduce costs given that capital costs are not recoverable. However, the Agency recognizes that 

there may be opportunities to achieve operational cost savings if these systems are able to reoptimize current treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

The Agency notes that alachlor and two of its unregulated acid degradates (alachlor 

ethanesulfonic acid or ESA and alachlor oxanilic acid or OA13) are currently listed on the second 

Unregulated Contaminants Monitoring Rule (UCMR 2) (72 FR 367, January 4, 2007 (USEPA, 

2007e)). The Agency also listed alachlor ESA and OA on the CCL3 (74 FR 51850, October 8, 

2009 (USEPA, 2009l)). Once the UCMR 2 monitoring results are available for alachlor and its 

degradates, the Agency will be able to more fully evaluate alachlor along with its degradates in 

determining how this information might impact the current regulation for alachlor and/or the 

need for any revised or new regulation to capture the impact from the ESA and OA degradates. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

 

13 Between 2004 and 2006, the United States Department Agriculture’s Pesticide Data Program (USDA PDP) 

collected data for alachlor and its ESA and OA degradates from finished and untreated water samples for a limited 

number of water systems (USDA, 2004, 2005, and 2006). While alachlor was rarely detected (i.e., 0 to 0.8 percent

of the samples by year), the alachlor ESA and OA degradates were commonly detected (i.e., 19 to 51 percent of the 

samples by year for the ESA degradate and 7 percent to 40 percent of the samples by year for the OA degradate). 

The detected values for the ESA and OA degradates ranged from 0.0028 to 0.357 μg/L and 0.001 to 0.102 μg/L, 

respectively. The detected values for alachlor ranged from 0.0163 to 0.043 μg/L. 

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c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for alachlor, EPA does not believe a revision to the NPDWR for alachlor 

is appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for alachlor is likely to provide a meaningful opportunity for cost 

savings to public water systems and their customers. Taking into consideration the low 

occurrence of this contaminant in source waters, EPA has decided that any revision to the 

NPDWR would be a low priority activity for the Agency, and, thus, is not appropriate to revise at 

this time because of: 

• 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. 

In addition, the Agency considers it premature to make any decision to revise the alachlor 

NPDWR pending the final UCMR 2 monitoring results. 

3. Alpha Particle Emitters 

a. Background. EPA published an interim NPDWR and set an MCL of 15 pCi/L for gross 

alpha particle activity on July 9, 1976 (41 FR 28402 (USEPA, 1976)). As noted in the August 

14, 1975 proposal (40 FR 34324 (USEPA, 1975)) and a subsequent September 30, 1986 FR 

notice (51 FR 34836 (USEPA, 1986a), EPA considered the feasibility of treatment techniques, 

analytical methods and monitoring when establishing the MCL of 15 pCi/L. EPA also 

considered the risks associated with other alpha particle emitters relative to radium-226, which 

generally fell within the Agency’s acceptable risk range of 10-4 to 10-6 at the MCL of 15 pCi/L. 

On December 7, 2000 (65 FR 76708 (USEPA, 2000c)), EPA established an MCLG of zero based 

on a cancer classification of A (known human carcinogen) and finalized the NPDWR by 

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retaining the MCL of 15 pCi/L. EPA noted in the December 7, 2000, FR notice that new risk 

estimates from Federal Guidance Report 13 reaffirmed that the 15 pCi/L gross alpha particle 

MCL (including radium 226 but excluding uranium and radon) was appropriate and protective. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to alpha particle emitters. The revised health effects assessment will consider relevant 

studies on the toxicity of alpha particle emitters, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). 

Although there is an ongoing health effects assessment, the MCLG is zero and the current 

MCL is higher than the MCLG. Therefore, EPA reviewed whether there is potential to revise the 

MCL based on new information regarding analytical and treatment feasibility for gross alpha 

particles. EPA promulgated a detection limit of 3 pCi/L in 1976 (41 FR 28402 (USEPA, 1976)) 

and retained the use of a detection limit as the required measure of sensitivity for radiochemical 

analysis in lieu of an MDL or PQL in the final rule (65 FR 76708 (USEPA, 2000c)). EPA did 

not identify new analytical methods during the current review that would feasibly lower the 

detection limit. In addition, since the December 7, 2000, regulation, there is no new information 

regarding treatment feasibility. Since there is no new information regarding analytical or 

treatment feasibility that suggests changes to the MCL, EPA does not believe it is necessary to 

conduct an occurrence analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for gross alpha 

particles is appropriate at this time because a reassessment of the health risks resulting from 

exposure to alpha particles is in progress (USEPA, 2009b). Furthermore, there is no new 

information regarding analytical or treatment feasibility that would warrant reconsideration of 

the MCL. 

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expect the 

Deleted: to change the cancer 

classification for alpha particles,

Deleted: MCLG would remain at zero.¶

As a part of the Six-Year Review, the 

Agency considered

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4. Antimony 

a. Background. EPA published the current NPDWR for antimony on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.006 mg/L. EPA 

based the MCLG on a reference dose of 0.0004 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to antimony. The revised health effects assessment will consider relevant studies on 

the toxicity of antimony, including its potential developmental and reproductive toxicity. The 

Agency does not expect the new health effects assessment to be completed in the time frame of 

the current Six-Year Review cycle (USEPA, 2009b). On December 21, 2007 (72 FR 72715 

(USEPA, 2007c)), the Agency noted that the health effects assessment for antimony is in 

process. 

c. Review Result. Since the MCL for antimony is set at its MCLG and a reassessment of the 

health risks resulting from exposure to antimony is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

5. Arsenic 

a. Background. EPA published the current NPDWR for arsenic on January 22, 2001 (66 FR 

6976 (USEPA, 2001c)). The NPDWR established an MCLG of zero based on a cancer 

classification of A, known human carcinogen. The NPDWR also established an MCL of 0.010 

mg/L, which is higher than the feasible analytical level of 0.003 mg/L. EPA exercised its 

discretionary authority to set an MCL at a level higher than feasible (SDWA Section 

1412(b)(6)), based on the finding that a final MCL of 0.010 mg/L represents the level that best 

maximizes health risk reduction benefits at a cost that is justified by the benefits (66 FR 6976 at 

7020 (USEPA, 2001c)). 

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b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to arsenic. In June 2007, EPA’s Science Advisory Board (SAB) issued its evaluation 

of the Agency’s 2005 draft toxicological review for inorganic arsenic (USEPA, 2007a). In its 

2007 report, SAB supports the continued use of a linear cancer risk model for inorganic arsenic, 

noting that the available data do not describe the shape of the dose-response curve at low doses. 

The new health effects assessment (both cancer and noncancer) were not completed by March 1, 

2009, the review cutoff date for this notice. The revised health effects assessments will consider 

relevant studies on the toxicity of arsenic, including its potential developmental and reproductive 

toxicity. The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessments. 

c. Review Result. The Agency does not believe a revision to the NPDWR for arsenic is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

arsenic is ongoing (USEPA, 2009b). As noted previously, the arsenic MCL is based on the 

SDWA cost benefit provision (Section 1412(b)(6)) and the health effects assessment is important 

for reviewing the benefits associated with the basis of the MCL. 

6. Asbestos 

a. Background. EPA published the current NPDWR for asbestos on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 7 million fibers/L. 

EPA evaluated asbestos as a Category II14 contaminant (equivalent to Group C, possible human 

carcinogen) by the oral route of exposure. 

 

14 Category II contaminants include those contaminants for which EPA has determined there is limited evidence 

of carcinogenicity from drinking water considering weight of evidence, pharmacokinetics, potency, and exposure. 

For Category II contaminants, EPA has used two approaches to set the MCLG: Either (1) setting the MCLG based 

upon noncarcinogenic endpoints of toxicity (the RfD) then applying an additional risk management factor of 1 to 10; 

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b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to asbestos. The revised health effects assessment will consider relevant studies on the 

toxicity of asbestos, including its potential developmental and reproductive toxicity. The 

Agency does not expect the new health effects assessment to be completed in the time frame of 

the current Six-Year Review cycle (USEPA, 2009b). The IRIS Substance Assessment Tracking 

System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on 

the status of the health effects assessment. 

c. Review Result. Since the MCL for asbestos is set at its MCLG and a reassessment of the 

health risks resulting from exposure to asbestos is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

7. Atrazine 

a. Background. EPA published the current NPDWR for atrazine on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.003 mg/L. EPA 

based the MCLG on a reference dose of 0.005 mg/kg-day and a cancer classification of C, 

possible human carcinogen. 

b. Technical Reviews. In 2006, the Agency finalized a health effects assessment for the 

reregistration of atrazine as a pesticide (USEPA, 2006c). This assessment examined an 

extensive toxicology database and included investigation of atrazine’s neuroendocrine mode of 

action and related reproductive and developmental effects. The assessment established a new 

RfD of 0.018 mg/kg-day, based on attenuation of pre-ovulatory luteinizing hormone (LH) surge, 

a key event indicative of hypothalamic function disruption. In accordance with the 1999 Interim 

Guidelines for Carcinogen Risk Assessment, EPA’s Cancer Assessment Review Committee 

(CARC) classified atrazine as “not likely to be carcinogenic to humans” because the tumor 

 

or (2) setting the MCLG based upon a theoretical lifetime excess cancer risk range of 10-5 to 10-6 using a 

conservative mathematical extrapolation model. 

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response in the Sprague-Dawley rats was determined to be a strain specific mechanism which is 

not relevant to humans. 

c. Review Result. The Agency believes it is not appropriate to consider revisions to the 

NPDWR for atrazine at this time and has place atrazine in the emerging information/data gap 

category because of an impending re-evaluation of the Agency’s risk assessment for atrazine. 

On October 7, 200915, the Agency announced its intent to launch a comprehensive new 

evaluation of the atrazine to determine its effects on humans. At the end of this process, the 

Agency will decide whether to revise its current risk assessment for atrazine and whether new 

restrictions are necessary to better protect public health. EPA will evaluate the pesticide’s 

potential cancer and non-cancer effects on humans. Included in this new evaluation will be the 

most recent studies on atrazine and its potential association with birth defects, low birth weight, 

and premature births. Our examination of atrazine will be based on transparency and sound 

science, including independent scientific peer review and will help determine whether a change 

in EPA’s regulatory position on this pesticide is appropriate. 

8. Barium 

a. Background. EPA published the current NPDWR for barium on July 1, 1991 (56 FR 

30266 (USEPA, 1991b)). The NPDWR established an MCLG and an MCL of 2 mg/L. EPA 

based the MCLG on a reference dose of 0.07 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity via the oral route. 

b. Technical Reviews. In 2005, the Agency updated the health effects assessment of barium 

and revised the RfD from 0.07 mg/kg-day to 0.2 mg/kg-day (USEPA, 2005a). The change in the 

RfD could lead to a change in the MCLG. This assessment considered relevant studies on the 

toxicity of barium including developmental and reproductive toxicity. The assessment 

 

15 Additional information is available at www.epa.gov/pesticides/reregistration/atrazine/atrazine_update.htm.

Deleted: c. Review Result. The Agency 

believes it is not appropriate to consider 

revisions to the NPDWR for atrazine at 

this time because there are some 

forthcoming studies on atrazine and its 

metabolites from the Agency’s Office of 

Research and Development (ORD). 

While the LH effect remains a 

biologically plausible and sensitive 

endpoint for the atrazine human health 

effects assessment, EPA will continue to 

analyze any relevant information 

regarding the adverse health effects of 

atrazine. The Agency does not anticipate 

that the ORD research will significantly 

change the atrazine health effects 

assessment conclusions supporting the 

Food Quality Protection Act (FQPA) 

reregistration decision published in 2006 

(USEPA, 2006c). However, it is unclear 

whether the new data would impact the 

Agency’s determination on whether any 

revisions to the current MCLG/NPDWR 

for atrazine are appropriate (USEPA, 

2009b). The Agency expects to publish 

the ORD studies in 2009.¶

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concluded that barium is not likely to be carcinogenic to humans (USEPA, 2005a). Based on the 

new IRIS assessment and RfD of 0.2 mg/kg-day, and assuming 70 kg body weight and 2 liters 

water intake per day, the DWEL could be 7.0 mg/L. An RSC of 80 percent16 results in a 

possible MCLG of 6.0 mg/L. 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for barium to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to achieve cost savings for PWSs and their customers while 

maintaining, or improving, the level of public health protection (USEPA, 2009f). Although the 

Agency obtained and evaluated the finished water occurrence data for barium, its usefulness is 

limited for determining potential cost savings to PWSs and their customers because the Agency 

does not know which systems are treating for this contaminant. As an alternative, the Agency 

evaluated available data on source water quality and conducted a qualitative assessment of 

treatment cost savings. 

Table VI-3 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at threshold levels of interest. This information 

indicates that any resulting NPDWR change would affect systems that rely on source water at 

 

16 The present MCLG for barium does not include an RSC because the dose used in the calculation applied to 

only the dose from the drinking water. If a new MCLG were to be developed from the animal data that support the 

2005 IRIS RfD, an RSC would be required. Regulations or guidelines pertaining to barium from media other than 

water were not identified. Barium metaborate is a registered pesticide but it does not have any food uses and does 

not have a human health ambient water quality guideline value. EPA used the subtraction calculation method to 

determine the possible RSC of 80 percent for drinking water (the ceiling on RSC specified by the methodology).

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less than 0.1 percent of the NAWQA locations and less than 1.4 percent of the STORET 

locations. 

Table VI-3. Ambient Water Quality Monitoring Occurrence Summary for Barium 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 16,595 (100.0%) 4,864 (100.0%) 

Nondetect 2,299 (13.9 %) 43 (0.9%) 

Detected 14,296 (86.1%) 4,821 (99.1%) 

Exceeds current MCL/MCLG of 2.0 mg/L 234 (1.4%) 3 (0.1%) 

Exceeds alternative value of 6.0 mg/L 163 (1.0%) 0 (0.0%) 

1. STORET database 2002-2006. 

2. NAWQA database 1992-2008. 

Source: USEPA, 2009c

The BATs and small system compliance technologies for barium have other beneficial 

effects, e.g., reduction of other co-occurring contaminants or other common impurities. 

Therefore, if EPA were to consider a higher level, the Agency does not know how many PWSs 

that are currently treating to comply with the existing MCL of 2 mg/L would be likely to 

discontinue treatment that is already in place (USEPA, 2009d). Also, the Agency does not know 

to what extent affected systems might be able to reduce costs given that capital costs are not 

recoverable. However, the Agency recognizes that there may be opportunities to achieve 

operational cost savings if these systems are able to re-optimize current treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for barium, EPA does not believe a revision to the NPDWR for barium 

is appropriate at this time. In making this decision, the Agency considered whether any possible 

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revision to the NPDWR for barium is likely to provide a meaningful opportunity for cost savings 

to public water systems and their customers. Taking into consideration the low occurrence of 

this contaminant in source waters, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

9. Benzene 

a. Background. EPA published the current NPDWR for benzene on July 8, 1987 (52 FR 

25690 (USEPA, 1987)). The NPDWR established an MCLG of zero based on a cancer 

classification of A, known human carcinogen. The NPDWR also established an MCL of 0.005 

mg/L, based on analytical feasibility. 

b. Technical Reviews. In 2000 and 2003, the Agency updated the IRIS assessment of 

benzene. The cancer assessment was completed first and characterized benzene as a known 

human carcinogen by all routes of exposure; the one-in-a million risk estimates for cancer by the 

oral route of exposure ranged from 1 μg/L to 10 μg/L (USEPA, 2000b). This cancer assessment 

was also noted in the first Six-Year Review (67 FR 19030, April 17, 2002 (USEPA, 2002c)). As 

part of the Six-Year Review process, the Agency’s Office of Water (OW) conducted a literature 

search through June 2007 for relevant data on the carcinogenicity of benzene as well as its 

potential developmental and reproductive toxicity (USEPA, 2009b). While the literature search 

did identify several new studies that evaluated the cancer and noncancer effects of benzene, none 

of the new studies would affect the cancer classification, which serves as the basis for the MCLG 

of zero. A recent occupational study (Lan et al., 2004) of the noncancer effects of benzene 

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identified hematological effects in workers at levels below those previously reported. The 

Agency for Toxic Substances and Disease Registry (ATSDR) (2007) chronic minimum risk level 

based on the Lan et al. (2004) data of 0.0005 mg/kg/day is lower than the IRIS RfD of 0.004 

mg/kg/day. If the ATSDR minimum risk level were used as the basis for a noncancer health 

reference level, the value would be 0.004 mg/l, a value that is slightly below the current MCL. 

Because the MCLG remains at zero, the Agency believes that a further review of the health 

effects of benzene is not warranted at this time. 

The current MCL for benzene is based on a PQL of 0.005 mg/L. For the Six-Year Review, 

the Agency considered whether changes in the analytical feasibility of benzene might lead to a 

lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then analyzed 

more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). Passing 

rates for PE data available through late 1999 for benzene are above 95 percent around the current 

PQL of 0.005 mg/L, including two studies with true values below the current PQL. All passing 

rates in the PE data exceeded 75 percent. More recent PT data from late 1999 through 2004, 

supplied by a PT provider, also show greater than 90 percent passing rates for studies around the 

PQL, including eight with true values below the current PQL. Because most of the laboratory 

passing rates from PE and PT studies exceeded the 75 percent criterion typically used to derive a 

PQL, a lowering of the PQL for benzene might be possible. These results, however, are 

insufficient to recalculate a revised PQL for benzene because not enough data points are 

available below the current PQL to derive a value at the 75 percent passing rate (USEPA, 

2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of benzene (Methods 502.2 and 524.2). While 

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EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

139,190 samples. More than 80 percent of these values are less than or equal the modal MRL:

120,308 (86 percent) equal the modal MRL of 0.0005 mg/L, and an additional 17,964 (13

percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the EQL 

(USEPA, 2009e). The MDLs of approved methods range from 0.00001 to 0.0004 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.0001 to 0.004 mg/L, which 

contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for benzene. To determine whether any MCL revision is 

likely to provide a meaningful opportunity to improve public health protection, EPA evaluated 

the occurrence of benzene at of the EQL of 0.0005 mg/L and additional thresholds of 0.001, and 

0.0025 mg/L (USEPA, 2009f). Table VI-4 shows the results of the occurrence and exposure 

analysis for the current MCL and these thresholds. The Six-Year Review ICR occurrence data 

have a modal MRL of 0.0005 mg/L, which limits reliable contaminant detection to 0.0005 mg/L. 

As indicated, average concentrations exceed the current MCL for 10 of 50,435 systems (0.020

percent) serving 14,000 people (or 0.006 percent of 227 million people). Note that these results 

are based on the subset of monitoring data provided in response to the Six-Year Review ICR and 

do not necessarily reflect MCL violations, which are based on annual average concentrations at 

entry points; Safe Drinking Water Information System/Federal version (SDWIS/FED) indicates 

41 MCL violations for benzene between 1998 and 2005, with annual violations ranging from 1 to 

12 (USEPA, 2007g). The occurrence and exposure analysis shows that average concentrations at 

Deleted: Of

Deleted: ,

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Deleted: . An

Deleted: %

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

Deleted: 0005, 0.

Deleted: EQLs set equal to 0.0025 

mg/L, 0.001 mg/L, and 0.0005 mg/L. 

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95 to 123 of 50,435 systems (0.188 percent to 0.244 percent), serving 304,000 to 485,000 people 

(or 0.134 percent to 0.214 percent of 227 million people), exceed the EQL of 0.0005 mg/L. 

Table VI-4. Number and Percent of Systems with Mean Concentrations Exceeding Benzene 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,435 systems with benzene data in the SixRegulatory or Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 10 (0.020%) 10 (0.020%) 10 (0.020%) 

1/2 MCL (0.0025 mg/L) 16 (0.032%) 14 (0.028%) 14 (0.028%) 

2xEQL (0.001 mg/L) 70 (0.139%) 58 (0.115%) 52 (0.103%) 

EQL (0.0005 mg/L) not applicable 123 (0.244%) 95 (0.188%) 

Corresponding Population Served 

(Percentages based on 226,947,000 people served by the systems with 

Regulatory or benzene data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 14,000 (0.006%) 14,000 (0.006%) 14,000 (0.006%) 

1/2 MCL (0.0025 mg/L) 111,000 (0.049%) 110,000 (0.048%) 110,000 (0.048%) 

2xEQL (0.001 mg/L) 180,000 (0.079%) 159,000 (0.070%) 158,000 (0.070%) 

EQL (0.0005 mg/L) not applicable 485,000(0.214%) 304,000 (0.134%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

benzene is appropriate at this time. The occurrence and exposure analysis based on possible 

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changes in analytical feasibility indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve public health protection. Taking into consideration the low 

occurrence of this contaminant, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

10. Benzo(a)pyrene 

a. Background. EPA published the current NPDWR for benzo(a)pyrene on July 17, 1992 (57 

FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.0002 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to benzo(a)pyrene. The revised health effects assessment will consider relevant studies 

on the toxicity of benzo(a)pyrene, including its potential developmental and reproductive 

toxicity. The new health effects assessment was not completed by March 1, 2009, the review 

cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System 

website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the 

status of the health effects assessment. 

Although a risk assessment is in process for benzo(a)pyrene, the existing MCLG is zero and 

the current MCL of 0.0002 mg/L is based on the PQL. Therefore, EPA reviewed whether there 

is potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

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Deleted: For the Six-Year Review, the 

Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

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feasibility). Passing rates for PE data available through late 1999 for benzo(a)pyrene are all 

above 75 percent. However, the true concentrations were all higher than the current PQL of 

0.0002 mg/L. More recent PT data from late 1999 through 2004, supplied by a PT provider, 

show several true concentrations with passing rates less than the 75 percent criterion typically 

used to derive a PQL. All of the true concentrations in the PT data were higher than the current 

PQL. Given the variability in passing rates and the lack of data points below the current PQL, a 

lowering of the PQL for benzo(a)pyrene is not appropriate at this time (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of benzo(a)pyrene (Methods 550, 550.1, and 

525.2). While EPA prefers to use laboratory performance data to calculate the PQL, the MRL 

and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 55,487 samples. Fewer than 80 percent of these values are less than or equal the 

modal MRL: 29,769 (54 percent) equal the modal MRL of 0.00002 mg/Land an additional 970 

(2 percent) are lower than 0.00002 mg/L. Therefore, EPA did not set the EQL equal to the 

modal MRL (USEPA, 2009e). The MDLs of approved methods are 0.000016, 0.000029, and 

0.00023 mg/L. EPA selected the median value, applied a multiplier of 10, and rounded up to 

0.0003 mg/L. The result is higher than the current PQL and, therefore, EPA did not estimate an 

EQL (USEPA, 2009e). Based on these varied and unrelated approaches/sources of information, 

EPA believes that there is no potential to lower the PQL for benzo(a)pyrene. Since the MCL is 

constrained by the PQL, and the PQL is unchanged, EPA does not believe it is necessary to 

conduct an occurrence analysis at this time. 

Deleted: WS

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels 

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

Deleted: , and 21,198 (38%) are 

between 0.00002 mg/L and 0.0001 mg/L. 

The 

Deleted: Because the MDL values fall 

across a wide range, 

Deleted: intermediate

Deleted: . The resulting 10×MDL 

value is 

Deleted: Since the MRL values are 

widely dispersed, and the intermediate 

10×MDL value

Deleted: , these data do not support a 

PQL

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c. Review Result. The Agency does not believe a revision to the NPDWR for benzo(a)pyrene 

is appropriate at this time because a reassessment of the health risks resulting from exposure to 

benzo(a)pyrene is in progress (USEPA, 2009b). Furthermore, a review of analytical feasibility 

did not identify a potential to revise the MCL, which is limited by feasibility. 

11. Beryllium 

a. Background. EPA published the current NPDWR for beryllium on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.004 mg/L. EPA 

classified beryllium in Group B2, probable human carcinogen, based on clear evidence of its 

carcinogenicity via inhalation or injection in several animal species. However, EPA also placed 

beryllium in drinking water Category II for regulation, based on the weight of evidence for 

carcinogenicity via ingestion, and the potency, exposure and pharmacokinetics of this chemical. 

EPA derived the MCLG by applying an additional risk management factor of 10 to the RfD of 

0.005 mg/kg-day (57 FR 31776 at 31785, July 17, 1992 (USEPA, 1992)). 

b. Technical Reviews. As noted in Six Year Review 1 (68 FR 42908, USEPA, 2003e), EPA 

updated its assessment of the health risks resulting from exposure to beryllium in 1998 (USEPA, 

1998c). The 1998 IRIS assessment uses the 1986 EPA cancer guidelines (USEPA, 1986b) and 

classifies beryllium as Group B1, probable human carcinogen, via inhalation route. However, 

the 1998 IRIS assessment states that the database is inadequate for assessing the carcinogenicity 

of ingested beryllium and concluded that the human carcinogenic potential of ingested beryllium 

cannot be determined. The Agency considered the 1998 assessessment in Six Year Review 1 

and decided that it was not appropriate to revise the NPDWR at that time. EPA has initiated a 

reassessment of the health risks resulting from exposure to beryllium. The new assessment was 

not completed by March 1, 2009, the review cutoff date for this notice (USEPA, 2009b). The 

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IRIS Substance Assessment Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) 

has the most up-to-date information on the status of the health effects assessment. 

c. Review Result. Since the MCL for beryllium is set at its MCLG and a reassessment of the 

health risks resulting from exposure to beryllium is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

12. Beta Particle and Photon Emitters 

a. Background. EPA published an interim NPDWR and set an MCL of 4 millirems/yr 

(mrem/yr) for beta particle and photon emitters on July 9, 1976 (41 FR 28402 (USEPA, 1976)). 

As noted in the August 14, 1975 proposal (40 FR 34324 (USEPA, 1975)) and a subsequent 

September 30, 1986 FR (51 FR 34836 (USEPA, 1986a) advanced notice of proposed 

rulemaking, EPA considered the feasibility of treatment techniques, analytical methods and 

monitoring when establishing the MCL of 4 mrem/yr. EPA also considered the risks associated 

with beta particle and photon emitters, which generally fell within the Agency’s acceptable risk 

range of 10-4 to 10-6 at the MCL of 4 mrem/yr. On December 7, 2000 (65 FR 76708 (USEPA, 

2000c)), EPA established an MCLG of zero based on a cancer classification of A (known human 

carcinogen) and finalized the NPDWR by retaining the MCL of 4 mrem/yr. EPA noted in the 

December 7, 2000, FR notice that new risk estimates from Federal Guidance Report 13 

reaffirmed that the 4 mrem/yr MCL was appropriate and protective17. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to beta particles. The revised health effects assessment will consider relevant studies 

 

17 After the December 7, 2000, final regulation, two trade associations and several municipal water systems 

challenged EPA’s standard for the beta photon emitters by claiming that the Agency did not use the best available 

science when finalizing the standard. In February of 2003, the District of Columbia (DC) Circuit Court of Appeals 

upheld EPA’s regulation for beta and photon emitters (as well as radium 226 and 228 and uranium). In July, 2004, 

the DC Circuit Court of Appeals also upheld the policy and scientific basis of EPA’s application of the beta particle 

and photon (man-made) drinking water standards to the ground water protection standards used for Yucca Mountain 

under 40 CFR part 197 (66 FR 32073, June 13, 2001 (USEPA, 2001d)). 

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on the toxicity of beta particles, including its potential developmental and reproductive toxicity. 

The new health effects assessment was not completed by March 1, 2009, the review cutoff date 

for this notice (USEPA, 2009b). 

Although there is an ongoing health effects assessment, the MCLG is zero and the current 

MCL is higher than the MCLG. Therefore, EPA reviewed whether there is potential to revise the 

MCL based on new information was available regarding the analytical and treatment feasibility 

for beta particle and photon emitters. EPA promulgated the MCL of 4 mrem/yr for man-made 

beta particle and photon emitters (present in any combination) in 1976 (41 FR 28402 (USEPA, 

1976)) and retained the use of the detection limit as the required measure of sensitivity in the 

December 2000 final rule (65 FR 76708 (USEPA, 2000c)). The original rule estimated a risk 

ceiling of 5.6×10-5 for whole body doses. Limits were set in picoCurie units for each nuclide 

equivalent to a 4 mrem dose. The newer dosimetry found in Federal Guidance13 and reported in 

the December 2000 final rule reveals more exact risks that are still within the Agency’s 

acceptable limits. While individual dose estimates changed over time, the overall limit of 4 

mrem was retained along with a two-tiered screening level to avoid analyzing each possible 

nuclide below the screen, and still be protective. EPA did not identify new analytical methods 

during the current review that would feasibly lower the detection limits for beta particle and 

photon emitters. In addition, since the December 7, 2000 regulation, there is no new information 

regarding treatment feasibility. Since there is no new information regarding analytical or 

treatment feasibility that suggests changes to the MCL, EPA does not believe it is necessary to 

conduct an occurrence analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for beta particles is 

appropriate at this time because a reassessment of the health risks resulting from exposure to beta 

Deleted: However, EPA does not 

expect the 

Deleted: to change the cancer 

classification for beta particles,

Deleted: MCLG would remain at zero.¶

As a part of the Six-Year Review, the 

Agency considered

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particles is in progress (USEPA, 2009b). Furthermore, there is no new information regarding 

analytical or treatment feasibility that would warrant reconsideration of the MCL. 

13. Cadmium 

a. Background. EPA published the current NPDWR for cadmium on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.005 mg/L. 

Because of inadequate dose-response data to characterize the presence or lack of a carcinogenic 

hazard from oral exposure, the Agency classified cadmium as a Group D carcinogen, not 

classifiable as to human carcinogenicity by the oral route of exposure. Therefore, EPA 

developed the MCLG for cadmium based on the RfD of 0.0005 mg/kg-day. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to cadmium. The revised health effects assessment will consider relevant studies on 

the toxicity of cadmium, including its potential developmental and reproductive toxicity. The 

new health effects assessment was not completed by March 1, 2009, the review cutoff date for 

this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

c. Review Result. Since the MCL for cadmium is set at its MCLG and a reassessment of the 

health risks resulting from exposure to cadmium is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

14. Carbofuran 

a. Background. EPA published the current NPDWR for carbofuran on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.04 mg/L. 

EPA based the MCLG on a reference dose of 0.005 mg/kg-day and a cancer classification of E, 

evidence of non-carcinogenicity for humans. 

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b. Technical Reviews. In 2006, the Agency updated health effects assessment of carbofuran. 

The Agency identified a change in this assessment that could lead to a change in the MCLG (73 

FR 44864, July 31, 2008 (USEPA, 2008a)). This assessment considered relevant studies on the 

toxicity of carbofuran including developmental and reproductive toxicity. The assessment 

revised the RfD from 0.005 mg/kg-day to an acute RfD of 0.00006 mg/kg-day and concluded 

that carbofuran is not likely to be carcinogenic to humans (USEPA, 2006d). Based on the 

revised acute RfD of 0.00006 mg/kg-day, and assuming 10 kg body weight and 1 liter water 

intake per day for a child, the resulting DWEL would be 0.0006 mg/L. Using an RSC of 20

percent, a possible new MCLG would be 0.00012 mg/L. The default RSC value of 20 percent

was selected because of the significant exposures resulting from actual food dietary exposure for 

children from 1 to 6 years old, which approaches 100 percent of the updated RfD (USEPA, 

2006d). 

Two recent Agency actions may affect carbofuran presence in food and water sources. In 

May 2009, EPA revoked all tolerances (maximum residue limits) for carbofuran, which could 

prohibit all carbofuran residues on food, effective December 31, 2009 (74 FR 23046, May 15, 

2009 (USEPA, 2009i)). The registrant and interested parties have raised objections and

requested a hearing on the tolerance revocations. EPA is reviewing the submissions to determine 

whether a hearing is warranted. Revoking carbofuran tolerances is part of a broader series of 

Agency actions to cancel all uses of carbofuran in the United States due to dietary, occupational, 

and ecological risks of concern. Following resolution of the current ongoing administrative 

process for resolving the safety of the tolerances, EPA will proceed to cancel the remaining uses 

of carbofuran. 

In addition, prior to the tolerance revocation, the registrant, FMC Corporation, voluntarily 

cancelled 22 uses of carbofuran (74 FR 11551, March 18, 2009 (USEPA, 2009j)). Existing 

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Deleted: %

Deleted: %

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raise

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stocks of carbofuran can be applied to food crops until December 31, 2009, and to non-food 

crops according to the label until supplies are depleted. These decisions are expected to reduce 

exposure to carbofuran and its metabolite (3-hydroxycarbofuran) in food products and in water, 

which would affect the RSC used to derive a possible MCLG. Therefore, EPA believes that it 

should factor in the effect of these actions, once completed, before the Agency determines the 

potential for an NPDWR revision. 

The occurrence of carbofuran in drinking water is an additional source of uncertainty in the 

review process that is compounded by the recent voluntary cancellations and tolerance 

revocations. The Six-Year Review ICR occurrence data are based on the Standardized 

Monitoring Framework for synthetic organic compounds, which is designed to evaluate longterm exposure to contaminants with chronic exposure health endpoints. As a result, short-term 

seasonal peaks, which correspond to carbofuran application as a pesticide, cannot be readily 

detected in this dataset. The cancellation will reduce carbofuran application and the potential for 

seasonal peaks to occur. Reductions in overall carbofuran use is expected to reduce the potential 

occurrence of carbofuran in drinking water sources. 

c. Review Result. Although there are new health data that support consideration of whether 

to revise the MCLG/MCL for carbofuran, the ongoing regulatory actions could affect the 

possible MCLG. Therefore, EPA is placing carbofuran in the information gap category due to 

the uncertainty of how the cancellation impacts the MCLG. In addition, EPA notes that the 

decision to cancel the reregistration of carbofuran would reduce the presence of this compound 

in the environment and the likelihood of exposure to carbofuran in food and drinking water 

sources. Consequently, EPA believes it is not appropriate to consider any revisions to the 

NPDWR for carbofuran at this time. 

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15. Carbon Tetrachloride 

a. Background. EPA published the current NPDWR for carbon tetrachloride on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to carbon tetrachloride. The revised health effects assessment will consider relevant 

studies on the toxicity of carbon tetrachloride, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

Although a risk assessment is in process for carbon tetrachloride, the existing MCLG is zero 

and the current MCL of 0.005 mg/L is based on the PQL. Therefore, EPA reviewed whether 

there is potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle 

and then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for carbon tetrachloride are at 

or above 95 percent around the current PQL of 0.005 mg/L, including one study with a true value 

below the current PQL. More recent PT data from late 1999 through 2004, supplied by a PT 

provider, also show greater than 90 percent passing rates for studies around the PQL, except for 

one study with a passing rate of 85 percent. Nine PT studies had true values below the current 

PQL. Because most of the laboratory passing rates from PE and PT studies exceeded the 75 

percent criterion typically used to derive a PQL, a lowering of the PQL for carbon tetrachloride 

might be possible. These results, however, are insufficient to recalculate a revised PQL for 

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Deleted: For the Six-Year Review, the 

Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

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carbon tetrachloride because not enough data points are available below the current PQL to 

derive a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of carbon tetrachloride (Methods 502.2, 524.2, 

and 551.1). While EPA prefers to use laboratory performance data to calculate the PQL, the 

MRL and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 139,221 samples. More than 80 percent of these values are less than or equal the 

modal MRL: 119,849 (86 percent) equal the modal MRL of 0.0005 mg/L and an additional 

16,195 (12 percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the 

EQL (USEPA, 2009e). The MDLs of approved methods range from 0.000002 to 0.00021 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.00002 to 0.0021 mg/L, 

which contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for carbon tetrachloride. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of carbon tetrachloride at the EQL of 0.0005 mg/L and additional 

thresholds of 0.001 and 0.0025 mg/L (USEPA, 2009f). Table VI-5 shows the results of the 

occurrence and exposure analysis for the current MCL and these thresholds. The occurrence and 

exposure analysis shows that average concentrations exceed the current MCL for five of 50,446 

systems (0.010 percent), serving fewer than 2,000 people (or 0.001 percent of 227 million 

people). Note that these results are based on the subset of monitoring data provided in response 

to the Six-Year Review ICR and do not necessarily reflect MCL violations, which are based on 

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

Deleted: 0.0005,

Deleted: ,

Deleted: EQLs set equal to 0.0025 

mg/L, 0.001 mg/L, and 0.0005 mg/L

Deleted: %

Deleted: %

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annual average concentrations at entry points; SDWIS/FED indicates 19 MCL violations for 

carbon tetrachloride between 1998 and 2005 with annual violations ranging from 1 to 4 (USEPA, 

2007g). Average concentrations for 84 to 118 of 50,446 systems (0.167 percent to 0.234

percent), serving 368,000 to 750,000 people (or 0.162 percent to 0.330 percent of 227 million 

people), exceed the EQL of 0.0005 mg/L. 

Table VI-5. Number and Percent of Systems with Mean Concentrations Exceeding Carbon 

Tetrachloride Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,446 systems with carbon tetrachloride data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 5 (0.010%) 5 (0.010%) 5 (0.010%) 

1/2 MCL (0.0025 mg/L) 13 (0.026%) 12 (0.024%) 12 (0.024%) 

2xEQL (0.001 mg/L) 59 (0.117%) 50 (0.099%) 40 (0.079%) 

EQL (0.0005 mg/L) not applicable 118 (0.234%) 84 (0.167%) 

Corresponding Population Served 

(Percentages based on 226,935,000 people served by the systems with 

carbon tetrachloride data in the Six-Year Review ICR occurrence 

Regulatory or dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 1,800 (0.001%) 1,700 (0.001%) 1,700 (0.001%) 

1/2 MCL (0.0025 mg/L) 5,800 (0.003%) 5,500 (0.002%) 5,500 (0.002%) 

2xEQL (0.001 mg/L) 265,000 (0.117%) 212,000 (0.093%) 190,000 (0.084%) 

EQL (0.0005 mg/L) not applicable 750,000 (0.330%) 368,000(0.162%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

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c. Review Result. The Agency does not believe a revision to the NPDWR for carbon 

tetrachloride is appropriate at this time because a reassessment of the health risks resulting from 

exposure to carbon tetrachloride is in progress (USEPA, 2009b). Furthermore, the occurrence 

and exposure analysis based on possible changes in analytical feasibility indicates that any 

revision to the MCL is unlikely to provide a meaningful opportunity to improve public health 

protection. After consideration of the low occurrence of this contaminant, EPA has decided that 

any revision to the NPDWR would be a low priority activity for the Agency, and, thus, is not 

appropriate to revise at this time because of: 

• 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. 

16. Chlordane 

a. Background. EPA published the current NPDWR for chlordane on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.002 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of chlordane as well as its potential developmental 

and reproductive toxicity. EPA has not identified any new information that indicates that it is 

appropriate to consider revisions to the cancer classification for chlordane at this time (USEPA, 

2009b). Because the MCLG remains at zero, the Agency believes that a further review of the 

health effects of chlordane is not warranted at this time. Deleted: ¶

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The current MCL for chlordane is based on a PQL of 0.002 mg/L. For the Six-Year Review, 

the Agency considered whether changes in the analytical feasibility of chlordane might lead to a 

lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then analyzed 

more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). Passing 

rates for PE data available through late 1999 for chlordane are above 80 percent around the 

current PQL of 0.002 mg/L, including three studies with true values below the current PQL. 

More recent PT data from late 1999 through 2004, supplied by a PT provider, also show greater 

than 80 percent passing rates, except for two studies with passing rates equal to or below 75 

percent. There are no PT studies with true values below the PQL. Because most of the 

laboratory passing rates from PE and PT studies – including three below the PQL – exceeded the 

75 percent criterion typically used to derive a PQL, a lowering of the PQL for chlordane might 

be possible. These results, however, are insufficient to recalculate a revised PQL for chlordane 

because not enough data points are available below the current PQL to derive a value at the 75 

percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of chlordane (Methods 505 and 508). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

57,506 samples. Fewer than 80 percent of these values are less than or equal the modal MRL:

26,893 (47 percent) equal the modal MRL of 0.0002 mg/L and an additional 9,764 (17 percent) 

are lower than 0.0002 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL 

(USEPA, 2009e). The MDLs of approved methods are 0.0000041 and 0.00014 mg/L. Applying 

Deleted: WS

Deleted: WS

Deleted: WS

Deleted: they indicate any potential to 

revise

Deleted: minimum reporting levels 

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

Deleted: , and 20,844 (36%) are 

between 0.0002 mg/L and the MCL of 

0.002 mg/L. 

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a multiplier of 10 would give possible PQLs of 0.000041 and 0.0014 mg/L. EPA took the mean 

of the two values and , rounded up to 0.001 mg/L for the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for chlordane. To determine whether any MCL revision is 

likely to provide a meaningful opportunity to improve public health protection, EPA evaluated 

the occurrence of chlordane at the EQL of 0.001 mg/L (USEPA, 2009f). Table VI-6 shows the 

results of the occurrence and exposure analysis for the current MCL and an EQL. The 

occurrence and exposure analysis shows that average concentrations exceed the current MCL for 

one of 31,841 systems (0.003 percent) serving 80 people (or 0.00004 percent of 182 million 

people). Note that these results are based on the subset of monitoring data provided in response 

to the Six-Year Review ICR do not necessarily reflect MCL violations, which are based on 

annual average concentrations at entry points; SDWIS/FED indicates no MCL violations for 

chlordane between 1998 and 2005 (USEPA, 2007g). Average concentrations at one to two of 

31,841 systems (0.003 percent to 0.006 percent), still serving approximately 80 to 120 people (or 

0.00004 to 0.00007 percent of 182 million people), exceed the EQL of 0.001 mg/L. 

Deleted: a 

Deleted: PQL range from

Deleted: to 

Deleted: Because of the broad 

dispersion in MRL values, EPA averaged 

the 10×MDL

Deleted: , and used that value as the 

minimum threshold in the occurrence and 

exposure analysis

Deleted: an estimated quantitation level

Deleted: set equal to 0.001 mg/L

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Deleted: %

Deleted: %

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Table VI-6. Number and Percent of Systems with Mean Concentrations Exceeding Chlordane 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 31,841 systems with chlordane data in the SixRegulatory or Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.002 mg/L) 1 (0.003%) 1 (0.003%) 1 (0.003%) 

EQL (0.001 mg/L) 2 (0.006%) 2 (0.006%) 1 (0.003%) 

Corresponding Population Served 

(Percentages based on 182,037,000 people served by the systems with 

Regulatory or chlordane data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.002 mg/L) 80 (0.00004%) 80 (0.00004%) 80 (0.00004%) 

EQL (0.001 mg/L) 120 (0.00007%) 120 (0.00007%) 80 (0.00004%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

chlordane is appropriate at this time. The occurrence and exposure analysis based on possible 

changes in analytical feasibility indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve public health protection. Taking into consideration the low 

occurrence of this contaminant, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• Competing workload priorities; 

• The administrative costs associated with rulemaking; and Deleted: ¶

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

resulted. 

17. Chromium 

a. Background. EPA published the current NPDWR for total chromium on January 30, 1991 

(56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.1 mg/L. 

Although the NPDWR regulates total chromium, the adverse health effects associated with 

hexavalent chromium (Cr VI) are the basis of the current MCLG because that is the more toxic 

species (56 FR 3526, January 31, 1991 (USEPA, 1991a)). EPA based the MCLG on an RfD of 

0.005 mg/kg-day and an assumed RSC from water of 70 percent for total chromium. EPA 

regulated chromium as a Group D carcinogen, not classifiable as to human carcinogenicity by 

the oral route of exposure. 

b. Technical Reviews. The health effects technical review identified some information 

regarding the carcinogenicity of chromium that may indicate the need to update the Agency’s 

health effects assessment (USEPA, 2009b). In 1998, the Agency (USEPA, 1998d) updated the 

IRIS assessment for Cr VI, which revised the RfD from 0.0048 mg/kg-day (rounded to 0.005) to 

0.003 mg/kg-day. While both RfDs are based on the same one-year drinking water rat study 

(MacKenzie et al., 1958), the change in the RfD in 1998 was due to the following factors: (a) a 

slight change in the no-observed-adverse-effect level (NOAEL), (b) a modification to the 

original uncertainty factor, and (c) the addition of a modifying factor of three because of data on 

the potential for gastrointestinal effects in humans as a result of oral exposure. There is no 

current RfD for soluble trivalent chromium (soluble Cr III); the Cr III RfD of 1.5 mg/kg-day on 

IRIS (USEPA, 1998e) is for insoluble Cr III salts. 

In 2002 and as part of the first Six Year Review (67 FR 19030 (USEPA, 2002c)), EPA noted 

that the National Toxicology Program (NTP) had agreed to study the chronic toxicity and 

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carcinogenicity of oral exposure to Cr VI. The NTP study, conducted with sodium dichromate 

dehydrate (i.e., Cr VI) in rats and mice, is now available (NTP, 2008), as is a pre-peer review 

draft of a similar study with chromium picolinate (Cr III) (NTP, 2007). The Cr VI study found 

clear evidence of carcinogenic activity of sodium dichromate dihydrate in male and female F344 

rats based on increased incidences of squamous cell neoplasms of the oral cavity, specifically the 

squamous epithelium that lines the oral mucosa and tongue (NTP, 2008). NTP also concluded 

that there was clear evidence of carcinogenic activity of sodium dichromate dihydrate in male 

and female B6C3F1 mice based on increased incidences of neoplasms in the small intestine 

(adenomas and/or carcinomas of the duodenum, jejunum, or ileum). The observed noncancer 

effects in the Cr VI study included histiocytic cellular infiltration in the liver, small intestine, and 

pancreatic and mesenteric lymph nodes of rats and mice, and diffuse epithelial hyperplasia in the 

small intestine of male and female mice. A peer-reviewed report for the study of chromium 

picolinate (Cr III) is not yet available. Zhang and Li (1987) evaluated the effects of human 

exposure to Cr VI in drinking water in Chinese villages. In a recent analysis of the human data 

originally reported in these Chinese villages, Sedman et al. (2006) further support a statistically 

significant increase in stomach cancer in the population exposed to Cr VI in their drinking water, 

thus suggesting a potential for carcinogenicity of Cr VI in drinking water. 

An assessment for chromium VI currently exists on IRIS but does not include an evaluation 

of carcinogenicity via oral ingestion. As a result, on December 21, 2007 (72 FR 72715 (USEPA, 

2007c)), the Agency nominated and included Cr VI on its 2008 IRIS agenda. The Agency is 

currently working with California EPA, New Jersey Department of Environmental Protection, 

and the Centers for Disease Control ATSDR (since they have recently developed draft 

assessments for chromium VI) and has posted a schedule for compltion and the most up-to-date 

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information on the status of the health effects assessment on the IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm).

A review of analytical or treatment feasibility is not necessary for total chromium because 

changes to the MCLG are not warranted at this time and the current MCL is set at the MCLG. 

Since EPA did not identify a health or technology basis for revising the total chromium 

NPDWR, the Agency did not conduct a detailed occurrence and exposure analysis. 

c. Review Result. The Agency does not believe a revision to the NPDWR for total chromium 

is appropriate at this time. A reassessment of the health risks associated with chromium 

exposure is being initiated and the Agency does not believe it is appropriate to revise the 

NPDWR while that effort is in process. 

18. Cyanide 

a. Background. EPA published the current NPDWR for cyanide on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.2 mg/L. EPA 

based the MCLG on a reference dose of 0.02 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. During the first Six-Year Review cycle, EPA 

recommended a revision to the BATs for cyanide to clarify that “chlorine” should be “alkaline 

chlorine” to avoid potential for the formation of harmful cyanogen chloride. EPA promulgated 

that revision in 69 FR 38850, June 29, 2004 (USEPA, 2004b). 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to cyanide. The revised health effects assessment will consider relevant studies on the 

toxicity of cyanide, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

Deleted: On December 21, 2007 (72 

FR 72715 (USEPA, 2007c)), the Agency 

nominated and included Cr VI on its 2008 

IRIS agenda. The Agency is currently 

conducting additional literature searches 

for Cr VI along with 19 other chemicals. 

Based on the results of the literature 

searches and as resources allow, the 

Agency may begin assessments on these 

chemicals to support the development of 

toxicity values or re-evaluate cancer 

designations. ¶

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(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment18. 

c. Review Result. Since the MCL for cyanide is set at its MCLG and a reassessment of the 

health risks resulting from exposure to cyanide is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

19. 2,4-D (2,4-Dichlorophenoxyacetic acid) 

a. Background. EPA published the current NPDWR for 2,4-D on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.07 mg/L. EPA 

based the MCLG on a reference dose of 0.01 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2005, the Agency updated its health effects assessment of 2,4-D 

(USEPA, 2005c). The Agency identified a change in this assessment that could lead to a change 

in the MCLG. This assessment considered relevant studies on the toxicity of 2,4-D including 

developmental and reproductive toxicity. The assessment revised the RfD from 0.01 mg/kg-day 

to 0.005 mg/kg-day and concluded that 2,4-D is not classifiable as to its carcinogenicity 

(USEPA, 2005c). Based on the new Office of Pesticide Programs (OPP) assessment and RfD of 

0.005 mg/kg-day, and assuming a 70-kg adult body weight and 2 liters water intake per day, the 

DWEL could be 0.2 mg/L. An RSC of 20 percent results in a possible MCLG of 0.04 mg/L 

(USEPA, 2009b). 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor for the possible MCLG decrease under consideration. EPA evaluated the results 

of the occurrence and exposure analyses for 2,4-D to determine whether a revised MCLG/MCL 

would be likely to result in a meaningful opportunity to improve the level of public health 

 

18 Note that cyanide is listed as hydrogen cyanide in the IRIS tracking system. 

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protection (USEPA, 2009f). Table VI-7 shows the results of the occurrence and exposure 

analysis for the current MCL and the possible MCLG set equal to 0.04 mg/L based on the new 

health effects information. The occurrence and exposure analysis shows that average 

concentrations do not exceed the current MCL for any system in the analysis. Note that these 

results are based on the subset of monitoring data provided in response to the Six-Year Review 

ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates no MCL violations for 2,4-D between 

1998 and 2005 (USEPA, 2007g). The occurrence and exposure analysis shows that average 

concentrations do not exceed the possible MCLG based on new health effects information (0.04 

mg/L). 

Table VI-7. Number and Percent of Systems with Mean Concentrations Exceeding 2,4-D Thresholds 

and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 33,187 systems with 2,4-D data in the Six-Year 

Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.07 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.04 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Corresponding Population Served 

(Percentages based on 187,451,200 people served by the systems with 

2,4-D data in the Six-Year Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.07 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.04 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

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c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for 2,4-D, EPA does not believe a revision to the NPDWR for 2,4-D is 

appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for 2,4-D is likely to provide a meaningful opportunity for health risk 

reductions. Taking into consideration the low occurrence of this contaminant, EPA has decided 

that any revision to the NPDWR would be a low priority activity for the Agency, and, thus, is not 

appropriate to revise at this time because of: 

• 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. 

20. Dalapon (2,2-Dichloropropionic Acid) 

a. Background. EPA published the current NPDWR for dalapon on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.2 mg/L. EPA 

based the MCLG on a reference dose of 0.03 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of dalapon, including its potential developmental and 

reproductive toxicity. The literature search did not identify any studies that warrant a review of 

the RfD or the cancer classification (USEPA, 2009b). 

A review of analytical or treatment feasibility is not necessary for dalapon because changes 

to the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the dalapon NPDWR, the Agency did 

not conduct a detailed occurrence and exposure analysis. 

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c. Review Result. EPA’s review shows that there are no data supporting a change to the 

dalapon NPDWR. As a result, a revision to the NPDWR would not be appropriate at this time. 

21. Di(2-ethylhexyl)adipate (DEHA) 

a. Background. EPA published the current NPDWR for DEHA on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.4 mg/L. EPA 

based the MCLG on a reference dose of 0.6 mg/kg-day and a cancer classification of C, possible 

human carcinogen. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to DEHA. The revised health effects assessment will consider relevant studies on the 

toxicity of DEHA, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

c. Review Result. Since the MCL for DEHA is set at its MCLG and a reassessment of the 

health risks resulting from exposure to DEHA is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

22. Di(2-ethylhexyl)phthalate (DEHP) 

a. Background. EPA published the current NPDWR for DEHP on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.006 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to DEHP. The revised health effects assessment will consider relevant studies on the 

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toxicity of DEHP, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

Although a risk assessment is in process for DEHP, the existing MCLG is zero and the 

current MCL of 0.006 mg/L is based on the PQL. Therefore, EPA reviewed whether there is 

potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for DEHP are below 75 

percent for several concentrations around the current PQL, including two studies with true values 

below the current PQL. More recent PT data from late 1999 through 2004, supplied by a PT 

provider, show passing rates below the 75 percent criterion for three studies, and all of the true 

concentrations in the PT data were higher than the current PQL. Given the passing rates around 

the current PQL, a lowering of the PQL for DEHP is not appropriate at this time (USEPA, 

2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of DEHP (Methods 525.2 and 506). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

50,490 samples. Fewer than 80 percent of these values are less than or equal the modal MRL: 

22,980 (45 percent) equal the modal MRL of 0.001 mg/L and an additional 15,842 (31 percent) 

Formatted: Font:

Deleted: For the Six-Year Review, the 

Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

Deleted: WS

Deleted: WS

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels 

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

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are lower than 0.001 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL 

(USEPA, 2009e). The MDLs of approved methods are 0.0013 and 0.00225 mg/L. Applying a 

multiplier of 10 would give a possible PQL range from 0.013 to 0.0225 mg/L. The range is 

higher than the current PQL and, therefore, EPA did not estimate an EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that there 

is no potential to lower the PQL for DEHP. Since the MCL is constrained by the PQL, and the 

PQL is unchanged, EPA does not believe it is necessary to conduct an occurrence analysis at this 

time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for DEHP is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

DEHP is in progress (USEPA, 2009b). Furthermore, a review of analytical feasibility did not 

identify a potential to revise the MCL, which is limited by feasibility. 

23. 1,2-Dibromo-3-chloropropane (DBCP) 

a. Background. EPA published the current NPDWR for DBCP on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.0002 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of DBCP as well as its potential developmental 

and reproductive toxicity. EPA has not identified any new information that indicates that it is 

appropriate to consider revisions to the cancer classification for DBCP at this time (USEPA, 

2009b). Because the MCLG remains at zero, the Agency believes that a further review of the 

health effects of DBCP is not warranted at this time. 

Deleted: , and 11,659 (23%) are 

between 0.001 mg/L and the MCL of 

0.006 mg/L. The 

Deleted: range from

Deleted: to

Deleted: Since nearly a quarter of 

samples do not achieve the modal MRL, 

and the 10×MDL values are 

Deleted: , these data do

Deleted: support a PQL reduction

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The current MCL for DBCP is based on a PQL of 0.0002 mg/L. For the Six-Year Review, 

the Agency considered whether changes in the analytical feasibility of DBCP might lead to a 

lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then analyzed 

more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). Passing 

rates for PE data available through late 1999 for DBCP are above 85 percent, including one 

study with a true value below the current PQL. More recent PT data from late 1999 through 

2004, supplied by a PT provider, also show greater than 75 percent passing rates, including three 

with a true value below the current PQL. Because all of the laboratory passing rates from PE

and PT studies, including four with true values slightly below the PQL, exceeded the 75 percent 

criterion typically used to derive a PQL, a lowering of the PQL for DBCP might be possible. 

These results, however, are insufficient to recalculate a revised PQL for DBCP because not 

enough data points are available below the current PQL to derive a value at the 75 percent 

passing rate (USEPA, 2009c). 

EPA examined two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of DBCP (Methods 504.1 and 551.1). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. However, there are substantial uncertainties in interpreting the 

MRLs (USEPA, 2009e). For example, some States have reported modal MRLs that are higher 

than the MCL. EPA therefore considered only MDL data to verify the potential to revise the 

PQL, and to establish a threshold for the occurrence and exposure analysis. The MDLs of 

approved methods are 0.000009 and 0.00001 mg/L. Applying a multiplier of 10 would give a 

Deleted: WS

Deleted: WS

Deleted: WS

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels 

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possible PQLs of 0.00009 and 0.0001 mg/L. EPA took the mean and rounded up to 0.0001 mg/L 

for the EQL (USEPA, 2009e). 

Based on the PT data and the MDLs for approved methods, EPA believes that there may be 

potential to lower the PQL for DBCP. To determine whether any MCL revision is likely to 

provide a meaningful opportunity to improve public health protection, EPA evaluated the 

occurrence of DBCP at the EQL of 0.0001 mg/L (USEPA, 2009f). Table VI-8 shows the results 

of the occurrence and exposure analysis for the current MCL and an EQL. The occurrence and 

exposure analysis shows that average concentrations exceed the current MCL for 42 of 37,618 

systems (0.112 percent) serving 25,000 people (or 0.013 percent of 194 million people). Note 

that these results are based on the subset of monitoring data provided in response to the Six-Year 

Review ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates only nine MCL violations for DBCP 

between 1998 and 2005 (USEPA, 2007g). Average concentrations at 92 to 97 of 37,618 systems 

(0.245 to 0.258 percent), serving approximately 1.2 to 1.4 million people (0.610 to 0.713 percent

of 194 million people), exceed the EQL of 0.0001 mg/L. 

Deleted: PQL range from 

Deleted: to 

Deleted: Because of the number of 

reported MRLs above the MCL, 

Deleted: averaged the 10×MDL values,

Deleted: , and used that value as the 

minimum threshold

Deleted: occurrence and exposure 

analysis

Deleted: an estimated quantitation level

Deleted: set equal to 0.0001 mg/L

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: %

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Table VI-8. Number and Percent of Systems with Mean Concentrations Exceeding DBCP Thresholds 

and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 37,618 systems with DBCP data in the Six-Year 

Regulatory or Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0002 mg/L) 42 (0.112%) 42 (0.112%) 42 (0.112%) 

EQL (0.0001 mg/L) 97 (0.258%) 93 (0.247%) 92 (0.245%) 

Corresponding Population Served 

(Percentages based on 193,749,000 people served by the systems with 

Regulatory or DBCP data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0002 mg/L) 25,000 (0.013%) 25,000 (0.013%) 25,000 (0.013%) 

EQL (0.0001 mg/L) 1,382,000 (0.713%) 1,371,000 (0.707%) 1,181,000 (0.610%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

DBCP is appropriate at this time. The occurrence and exposure analysis based on possible 

changes in analytical feasibility indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve public health protection. Taking into consideration the low 

occurrence of this contaminant, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• Competing workload priorities; 

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• The administrative costs associated with rulemaking; and 

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

resulted. 

24. 1,2-Dichlorobenzene (o-Dichlorobenzene) 

a. Background. EPA published the current NPDWR for 1,2-dichlorobenzene on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.6 

mg/L. EPA based the MCLG on a reference dose of 0.09 mg/kg-day and a cancer classification 

of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to 1,2-dichlorobenzene. The revised health effects assessment will consider relevant 

studies on the toxicity of 1,2-dichlorobenzene, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

c. Review Result. Since the MCL for 1,2-dichlorobenzene is set at its MCLG and a 

reassessment of the health risks resulting from exposure to 1,2-dichlorobenzene is in progress, 

the Agency does not believe a revision to the NPDWR is appropriate at this time. 

25. 1,4-Dichlorobenzene (p-Dichlorobenzene) 

a. Background. EPA published the current NPDWR for 1,4-dichlorobenzene on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG and an MCL of 0.075 

mg/L. EPA based the MCLG on a reference dose of 0.1 mg/kg-day and a cancer classification of 

C, possible human carcinogen. 

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b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to 1,4-dichlorobenzene. The revised health effects assessment will consider relevant 

studies on the toxicity of 1,4-dichlorobenzene, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

c. Review Result. Since the MCL for 1,4-dichlorobenzene is set at its MCLG and a 

reassessment of the health risks resulting from exposure to 1,4-dichlorobenzene is in progress, 

the Agency does not believe a revision to the NPDWR is appropriate at this time. 

26. 1,2-Dichloroethane (Ethylene Dichloride) 

a. Background. EPA published the current NPDWR for 1,2-dichloroethane on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to 1,2-dichloroethane. The revised health effects assessment will consider relevant 

studies on the toxicity of 1,2-dichloroethane, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment19. 

 

19 Note that 1,2-dichloroethane is listed as ethylene dichloride in the IRIS tracking system. 

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Although a risk assessment is in process for 1,2-dichloroethane, the existing MCLG is zero 

and the current MCL of 0.005 mg/L is based on the PQL. Therefore, EPA reviewed whether 

there is potential to revise the PQL EPA reviewed PE data from the first Six-Year Review cycle 

and then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for 1,2-dichloroethane are 

above 95 percent around the current PQL of 0.005 mg/L, including one study with a true value 

below the current PQL. More recent PT data from late 1999 through 2004, supplied by a PT 

provider, also show greater than 90 percent passing rates for studies around the current PQL, 

including seven with true values below the current PQL. Because all of the laboratory passing 

rates from PE and PT studies – including several with true concentrations below the PQL – 

exceeded the 75 percent criterion typically used to derive a PQL, a lowering of the PQL for 1,2-

dichloroethane might be possible. These results, however, are insufficient to recalculate a 

revised PQL for 1,2-dichloroethane because not enough data points are available below the 

current PQL to derive a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and the 

MDLs for approved methods for the detection of 1,2-dichloroethane (Methods 502.2 and 524.2). 

While EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

139,085 samples. More than 80 percent of these values are less than or equal the modal MRL:

116,533 (84 percent) equal the modal MRL of 0.0005 mg/L and an additional 18,160 (13

percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the EQL 

(USEPA, 2009e). The MDLs of approved methods range from 0.00003 to 0.00006 mg/L. 

Formatted: Font:

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Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

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revise the PQL

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Applying a multiplier of 10 would give a possible PQL range from 0.0003 to 0.0006 mg/L, 

which contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for 1,2-dichloroethane. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of 1,2-dichloroethane at the EQL of 0.0005 mg/L and additional 

thresholds of 0.001 and 0.0025 mg/L (USEPA, 2009f). Table VI-9 shows the results of the 

occurrence and exposure analysis for the current MCL and these thresholds. The occurrence and 

exposure analysis shows that average concentrations exceed the current MCL for three of 50,442 

systems (0.006 percent) serving 150 people (or 0.00007 percent of 227 million people). Note 

that these results are based on the subset of monitoring data provided in response to the Six-Year 

Review ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates 27 MCL violations for 1,2-dichloroethane 

between 1998 and 2005 (USEPA, 2007g). Average concentrations at 63 to 82 of 50,442 systems 

(0.125 to 0.163 percent), serving 210,000 to 277,000 people (or 0.092 to 0.122 percent of 227 

million people), exceed the EQL of 0.0005 mg/L. 

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

Deleted: 0.0005,

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Deleted: EQLs set equal to 0.0025 

mg/L, 0.001 mg/L, and 0.0005 mg/L

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Table VI-9. Number and Percent of Systems with Mean Concentrations Exceeding 1,2-Dichloroethane 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,442 systems with 1,2-dichloroethane data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 3 (0.006%) 3 (0.006%) 3 (0.006%) 

1/2 MCL (0.0025 mg/L) 9 (0.018%) 9 (0.018%) 8 (0.016%) 

2xEQL (0.001 mg/L) 46 (0.091%) 37 (0.073%) 30 (0.059%) 

EQL (0.0005 mg/L) not applicable 82 (0.163%) 63 (0.125%) 

Corresponding Population Served 

(Percentages based on 226,934,000 people served by the systems with 

Regulatory or 1,2-dichloroethane data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 150 (0.00007%) 150 (0.00007%) 150 (0.00007%) 

1/2 MCL (0.0025 mg/L) 870 (0.0004%) 870 (0.0004%) 830 (0.0004%) 

2xEQL (0.001 mg/L) 190,000 (0.084%) 145,200 (0.064%) 87,150 (0.038%) 

EQL (0.0005 mg/L) not applicable 277,000 (0.122%) 210,000 (0.092%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. The Agency does not believe a revision to the NPDWR for 1,2-

dichloroethane is appropriate at this time because a reassessment of the health risks resulting 

from exposure to 1,2-dichloroethane is in progress (USEPA, 2009b). Furthermore, the 

occurrence and exposure analysis based on possible changes in analytical feasibility indicates 

that any revision to the MCL is unlikely to provide a meaningful opportunity to improve public 

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health protection. After consideration of the low occurrence of this contaminant, EPA has 

decided that any revision to the NPDWR would be a low priority activity for the Agency, and, 

thus, is not appropriate to revise at this time because of: 

• 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. 

27. 1,1-Dichloroethylene 

a. Background. EPA published the current NPDWR for 1,1-dichloroethylene on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG and an MCL of 0.007 

mg/L. EPA based the MCLG on a reference dose of 0.01 mg/kg-day and a cancer classification 

of C, possible human carcinogen. 

b. Technical Reviews. In the first Six-Year Review cycle, EPA evaluated new information 

from a health effects assessment completed in 2002 (USEPA, 2002b). At that time, the Agency 

could not determine that a revision to the NPDWR would provide a meaningful opportunity for 

cost savings to public water systems or their customers, and decided that any revision would be a 

low priority activity for the Agency because of competing workload priorities, the administrative 

costs associated with rulemaking, and the burden on States and the regulated community to 

implement any regulatory change (68 FR 42908 (USEPA, 2003e)). The 2002 assessment 

considered relevant studies on the toxicity of 1,1-dichloroethylene including developmental and 

reproductive toxicity. The assessment revised the RfD from 0.01 mg/kg-day to 0.05 mg/kg-day 

and concluded that there is inadequate information to assess carcinogenic potential via the oral 

route (USEPA, 2002b). In the current review cycle, EPA conducted a literature search through 

June 2007 for relevant data on the toxicology of 1,1-dichloroethylene, including its potential 

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developmental and reproductive toxicity. The literature search did not identify any additional 

new data that would affect the RfD or cancer classification (USEPA, 2009b). Based on the 2002 

IRIS assessment and RfD of 0.05 mg/kg-day, and assuming a 70-kg adult body weight and 2 

liters water intake per day, the DWEL could be 1.75 mg/L. The 2002 cancer assessment 

indicates that the risk management factor of 10, applied to the current MCLG, may no longer be 

needed. An RSC of 20 percent results in a possible MCLG of 0.35 mg/L (USEPA, 2009b). 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for 1,1-dichloroethylene to determine whether a revised MCLG/MCL would 

be likely to result in a meaningful opportunity to achieve cost savings for PWSs and their 

customers while maintaining, or improving, the level of public health protection (USEPA, 

2009f). Although the Agency obtained and evaluated the finished water occurrence data for 1,1-

dichloroethylene, its usefulness is limited for potential cost savings to PWSs and their customers 

because the Agency does not know which systems are treating for this contaminant. As an 

alternative, the Agency evaluated available data on source water quality and conducted a 

qualitative assessment of treatment cost savings. 

Table VI-10 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at threshold levels of interest. This information 

indicates that any resulting NPDWR change would affect systems that rely on source water at 

less than 0.02 percent of the NAWQA locations. The STORET results are driven by the 157 

sampling locations in Phoenix, Arizona, that have a maximum sample above the MCL of 0.007 

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mg/L. Five of these locations also account for those having a maximum sample that exceeds 

0.35 mg/L. 

Table VI-10. Ambient Water Quality Monitoring Occurrence Summary for 1,1-Dichloroethylene 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 2,448 (100.0%) 5,788 (100.0%) 

Nondetect 1,498 (61.2%) 5,636 (97.37%) 

Detected 950 (38.8%) 152 (2.63%) 

Exceeds current MCLG of 0.007 mg/L 165 (6.7%) 1 (0.02%) 

Exceeds alternative value of 0.35 mg/L 5 (0.2%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2008. 

Source: USEPA, 2009c

The BATs and small system compliance technologies for 1,1-dichloroethylene have other 

beneficial effects, e.g., reduction of other co-occurring contaminants, precursors for DBPs, or 

other common impurities. Therefore, if EPA were to consider a higher level, the Agency does 

not know how many PWSs that are currently treating to comply with the existing MCL of 0.007 

mg/L would be likely to discontinue treatment that is already in place (USEPA, 2009d). Also, 

the Agency does not know to what extent affected systems might be able to reduce costs given 

that capital costs are not recoverable. However, the Agency recognizes that there may be 

opportunities to achieve operational cost savings if these systems are able to re-optimize current 

treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for 1,1-dichloroethylene, EPA does not believe a revision to the 

NPDWR for 1,1-dichloroethylene is appropriate at this time. In making this decision, the 

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Agency considered whether any possible revision to the NPDWR for 1,1-dichloroethylene is 

likely to provide a meaningful opportunity for cost savings to public water systems and their 

customers. Taking into consideration the low occurrence of this contaminant in source waters, 

EPA has decided that any revision to the NPDWR would be a low priority activity for the 

Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

28. cis-1,2-Dichloroethylene 

a. Background. EPA published the current NPDWR for cis-1,2-dichloroethylene on January 

30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 

0.07 mg/L. EPA based the MCLG on a reference dose of 0.01 mg/kg-day and a cancer 

classification of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to cis-1,2-dichloroethylene. The revised health effects assessment will consider 

relevant studies on the toxicity of cis-1,2-dichloroethylene, including its potential developmental 

and reproductive toxicity. The new health effects assessment was not completed by March 1, 

2009, the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

c. Review Result. Since the MCL for cis-1,2-dichloroethylene is set at its MCLG and a 

reassessment of the health risks resulting from exposure to cis-1,2-dichloroethylene is in 

progress, the Agency does not believe a revision to the NPDWR is appropriate at this time. 

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29. trans-1,2-Dichloroethylene 

a. Background. EPA published the current NPDWR for trans-1,2-dichloroethylene on 

January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an 

MCL of 0.1 mg/L. EPA based the MCLG on a reference dose of 0.02 mg/kg-day and a cancer 

classification of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to trans-1,2-dichloroethylene. The revised health effects assessment will consider 

relevant studies on the toxicity of trans-1,2-dichloroethylene, including its potential 

developmental and reproductive toxicity. The new health effects assessment was not completed 

by March 1, 2009, the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance 

Assessment Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most upto-date information on the status of the health effects assessment. 

c. Review Result. Since the MCL for trans-1,2-dichloroethylene is set at its MCLG and a 

reassessment of the health risks resulting from exposure to trans-1,2-dichloroethylene is in 

progress, the Agency does not believe a revision to the NPDWR is appropriate at this time. 

30. Dichloromethane (Methylene Chloride) 

a. Background. EPA published the current NPDWR for dichloromethane on July 17, 1992 

(57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to dichloromethane. The revised health effects assessment will consider relevant 

studies on the toxicity of dichloromethane, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

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the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment20. 

Although a risk assessment is in process for dichloromethane, the existing MCLG is zero and 

the current MCL of 0.005 mg/L is based on the PQL. Therefore, EPA reviewed whether there is 

potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for dichloromethane are all 

above 90 percent for studies near the PQL. More recent PT data from late 1999 through 2004, 

supplied by a PT provider, also show greater than 85 percent passing rates for studies around the 

PQL, except for one study with a passing rate of 76 percent. However, all of the true 

concentrations in the PE and PT data were higher than the current PQL of 0.005 mg/L. Given 

the lack of PE and PT study results below the current PQL to derive a value at the 75 percent 

passing rate, PE and PT data are insufficient to support a PQL reduction (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of dichloromethane (Methods 502.2 and 

524.2). While EPA prefers to use laboratory performance data to calculate the PQL, the MRL 

and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 138,445 samples. More than 80 percent of these values are less than or equal the 

modal MRL: 121,532 (88 percent) equal the modal MRL of 0.0005 mg/L and an additional 

11,294 (8 percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the 

 

20 Note that dichloromethane is listed as methylene chloride in the IRIS tracking system. 

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Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

Deleted: WS

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Deleted: WS

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Deleted: WS

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revise the PQL

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EQL (USEPA, 2009e). The MDLs of approved methods range from 0.00002 to 0.00009 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.0002 to 0.0009 mg/L, 

which includes the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, there is evidence of a 

potential to lower the PQL for dichloromethane even though the PE and PT data are insufficient 

to support a PQL reduction. To determine whether any MCL revision is likely to provide a 

meaningful opportunity to improve public health protection, EPA evaluated the occurrence of 

dichloromethane at the EQL of 0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L 

(USEPA, 2009f). Table VI-11 shows the results of the occurrence and exposure analysis for the 

current MCL and these thresholds. The occurrence and exposure analysis shows that average 

concentrations exceed the current MCL for 13 to 17 of 50,169 systems (0.026 to 0.034 percent) 

serving 11,000 to 12,000 people (or 0.005 percent of 227 million people). Note that these results 

are based on the subset of monitoring data provided in response to the Six-Year Review ICR and 

do not necessarily reflect MCL violations, which are based on annual average concentrations at 

entry points; SDWIS/FED indicates 67 MCL violations for dichloromethane between 1998 and 

2005 with annual violations ranging from 4 to 14 (USEPA, 2007g). Average concentrations at 

383 to 579 of 50,169 systems (0.763 to 1.154 percent), serving approximately 1.8 to 3.5 million 

people (or 0.813 to 1.542 percent of 227 million people), exceed the EQL of 0.0005 mg/L. 

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

Deleted: WS

Deleted: .

Deleted: 0005, 0.

Deleted: ,

Deleted: EQLs set equal to 0.0025 

mg/L, 0.001 mg/L, and 0.0005 mg/L

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Table VI-11. Number and Percent of Systems with Mean Concentrations Exceeding Dichloromethane 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,169 systems with dichloromethane data in the 

Regulatory or Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 17 (0.034%) 16 (0.032%) 13 (0.026%) 

EQL (0.0025 mg/L) 53 (0.106%) 51 (0.102%) 46 (0.092%) 

EQL (0.001 mg/L) 276 (0.550%) 208 (0.415%) 169 (0.337%) 

EQL (0.0005 mg/L) not applicable 579 (1.154%) 383 (0.763%) 

Corresponding Population Served 

(Percentages based on 226,844,000people served by the systems with 

Regulatory or dichloromethane data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 12,000 (0.005%) 12,000 (0.005%) 11,000 (0.005%) 

EQL (0.0025 mg/L) 44,000 (0.019%) 40,000 (0.018%) 39,000 (0.017%) 

EQL (0.001 mg/L) 1,517,000 (0.669%) 1,386,000 (0.611%) 946,000 (0.417%) 

EQL (0.0005 mg/L) not applicable 3,497,000 (1.542%) 1,844,000 (0.813%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

During Six-Year Review 1, a stakeholder questioned the feasibility of lowering the PQL for 

dichloromethane below 0.001 mg/L because its use in EPA analytical methods makes it a 

common laboratory contaminant (68 FR 42908 (USEPA, 2003e)). EPA responded that the high 

passing rates among PE studies at concentrations close to the current PQL of 0.005 mg/L would 

not be expected if this were the case and that EPA had no data to suggest that the occurrence 

estimates reflected monitoring sample contamination (68 FR 42908 (USEPA, 2003e)). For SixYear Review 2, EPA notes that it does not have PE or PT study results at either 0.001 mg/L or 

0.0005 mg/L and, therefore, cannot assess the potential for laboratory contamination of 

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dichloromethane to affect passing rates at this level. A USGS study of volatile organic 

compound (VOC) occurrence (Moran, 2006) indicates this potential exists at low concentrations. 

The study presented dichloromethane laboratory reporting levels for newer low-level analytical 

methods (i.e., defined as the level that limits the frequency of false positives and false negatives 

to 1 percent of test results) that ranged from 0.00006 mg/L to 0.00757 mg/L, with a median value 

of 0.00038 mg/L. The report noted that the laboratory reporting levels for dichloromethane tend 

to be higher than levels for other VOCs such as PCE (levels ranging from 0.000027 mg/L to 

0.0005 mg/L with a median of 0.0001 mg/L) and TCE (ranging from 0.000038 mg/L to 0.0005 

mg/L with a median of 0.000038 mg/L) because it was a frequent laboratory contaminant. 

A USGS study of ground water, source water, and drinking water quality indicated 

consistently lower dichloromethane (methylene chloride) occurrence frequencies compared to 

either PCE or TCE, which are among the most frequently occurring VOCs included in the study 

(Moran, 2006). Table VI-12 provides a summary of the occurrence results reported in the USGS 

study. This study also determined that population density was the strongest predictor of 

dichloromethane occurrence. 

Table VI-12. Summary of USGS VOC Occurrence Study Findings for Dichloromethane (Methylene 

Chloride) 

 Ground Water Samples Source Water Samples Drinking Water Samples 

Number 5,054 577 1,680 

Type 3,877 NAWQA 

1,177 Other sources

Ground water sources for 

community water systems 

Ground water community water 

systems 

Location National National New England and Mid-Atlantic 

States 

Dichloro

methane 

Results 

• 3% exceed 0.00002 mg/L 

• <1% exceed 0.0002 mg/L 

• Ranked 30th of 55 VOCs 

based on median 

concentration (0.00005 

mg/L) 

• 0.2% (1 sample) exceed 

0.0002 mg/L 

• Ranked 8th of 52 VOCs 

based on median 

concentration (0.0017 

mg/L – 1 sample) 

• 3% exceed 0.0002 mg/L 

• Ranked 11th of 51 VOCs in 

detection frequency 

• Ranked 31st of 55 solvents in 

median concentration (0.001 

mg/L) 

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PCE 

• 11% exceed 0.00002 

mg/L 

• 4% exceed 0.0002 mg/L 

• Ranked 12th of 55 VOCs 

based on median 

concentration (0.00007 

mg/L) 

• 4% exceed 0.0002 mg/L 

• Ranked 16th of 52 VOCs 

based on median 

concentration (0.0009 

mg/L) 

• 4% exceed 0.0002 mg/L 

• Ranked 7th of 51 VOCs in 

detection frequency 

• Ranked 11th of 55 solvents in 

median concentration (0.0014 

mg/L) 

TCE 

• 5% exceed 0.00002 mg/L 

• 2.5% exceed 0.0002 mg/L 

• Ranked 20th of 55 VOCs 

based on median 

concentration (0.00012 

mg/L) 

• 3% exceed 0.0002 mg/L 

• Ranked 10th of 52 VOCs 

based on median 

concentration (0.0015 

mg/L) 

• 4% exceed 0.0002 mg/L 

• Ranked 8th of 51 VOCs in 

detection frequency 

• Ranked 8th of 55 solvents in 

median concentration (0.0015 

mg/L) 

Source: Moran, 2006 

EPA compared Six-Year Review ICR occurrence patterns for dichloromethane with 

contaminant release information to determine if drinking water occurrence corresponds with 

potential contaminant sources reported in the Toxics Release Inventory (TRI) and found that the 

states with the majority of systems with mean concentrations that exceed 0.0005 mg/L did not 

tend to be the States with the highest dichloromethane releases (Moran, 2006). Table VI-13 

provides summary information from that comparison. In particular, the numbers of system 

means exceeding 0.0005 mg/L in Montana and Alaska seem inconsistent with TRI release 

information and the USGS study finding that population density is the strongest predictor of 

dichloromethane occurrence. 

Because of data gaps regarding the feasibility of PQL reduction and potential occurrence data 

accuracy at the lowest EQL, EPA concluded that revising the MCL may not constitute a 

meaningful opportunity to improve the level of public health protection. 

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Table VI-13. Stage 2 Occurrence Summary for Dichloromethane 

Systems with Mean > 

0.0005 mg/L 

Nondetect = 1/2 MRL 

Total Reported TRI On-Site 

or Off-Site Disposal or 

Release of Dichloromethane 

– All Industries, 20061

Total Reported TRI On-Site or 

Off-Site Disposal or Release 

of Dichloromethane – All 

Industries, 20041

State Number 

Percent of 

579 Total 

Systems Pounds 

Percent of 6.8 

Million Total 

Pounds Pounds 

Percent of 7.9 

Million Total 

Pounds 

MT 67 12% 22,700 0% 30,600 0% 

TX 45 8% 314,120 5% 410,103 5% 

FL 40 7% 31,451 0% 246,775 3% 

AK 37 6% No data 0% No data 0% 

IN 29 5% 509,303 7% 699,783 9% 

WI 28 5% 111,403 2% 98,113 1% 

MO 27 5% 51,002 1% 32,860 0% 

CA 26 4% 149,423 2% 86,554 1% 

OH 24 4% 192,237 3% 203,269 3% 

NM 21 4% No data 0% No data 0% 

IL 19 3% 279,024 4% 285,101 4% 

AL 18 3% 319,529 5% 375,650 5% 

MN 17 3% 39,851 1% 81,309 1% 

CO 15 3% 18,475 0% 17,003 0% 

MI 13 2% 75,141 1% 129,959 2% 

WY 13 2% No data 0% No data 0% 

IA 12 2% 2,348 0% 1,657 0% 

MD 12 2% 36,990 1% 31,347 0% 

NC 12 2% 49,800 1% 600,032 8% 

NY 11 2% 322,382 5% 712,197 9% 

1. Source: TRI Explorer Chemical Report Summary on-line state summaries for 2006 and 2004. 

c. Review Result. The Agency does not believe a revision to the NPDWR for 

dichloromethane is appropriate at this time because a reassessment of the health risks resulting 

from exposure to dichloromethane is in progress (USEPA, 2009b). In view of the fact that 

dichloromethane is a common laboratory contaminant, there is uncertainty regarding the extent 

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to which a PQL revision is feasible or whether the Six-Year Review ICR data are reliable at 

concentrations well below the current PQL. Furthermore, the occurrence and exposure analysis 

based on possible changes in analytical feasibility indicates that any revision to the MCL is 

unlikely to provide a meaningful opportunity to improve public health protection. After 

consideration of these factors, EPA has decided that any revision to the NPDWR would be a low 

priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

31. 1,2-Dichloropropane 

a. Background. EPA published the current NPDWR for 1,2-dichloropropane on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a 

cancer classification of B2, probable human carcinogen. The NPDWR also established an MCL 

of 0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of 1,2-dichloropropane as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for 1,2-

dichloropropane at this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency 

believes that a further review of the health effects of 1,2-dichloropropane is not warranted at this 

time. 

The current MCL for 1,2-dichloropropane is based on a PQL of 0.005 mg/L. For the SixYear Review, the Agency considered whether changes in the analytical feasibility of 1,2-

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dichloropropane might lead to a lower MCL. EPA reviewed PE data from the first Six-Year 

Review cycle and then analyzed more recent PT data to determine if the PQL can be revised (i.e., 

analytical feasibility). Passing rates for PE data available through late 1999 for 1,2-

dichloropropane are above 90 percent near the current PQL of 0.005 mg/L, but there were no 

results for PE studies with true values below the current PQL. More recent PT data from late 

1999 through 2004, supplied by a PT provider, also show greater than 90 percent passing rates 

around the PQL, including nine studies with true values below the current PQL. Because most 

of the laboratory passing rates from PE and PT studies – including several with true 

concentrations below the PQL – exceeded the 75 percent criterion typically used to derive a 

PQL, a lowering of the PQL for 1,2-dichloropropane might be possible. These results, however, 

are insufficient to recalculate a revised PQL for 1,2-dichloropropane because not enough data 

points are available below the current PQL to derive a value at the 75 percent passing rate 

(USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of 1,2-dichloropropane (Methods 502.2 and 

524.2). While EPA prefers to use laboratory performance data to calculate the PQL, the MRL 

and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 139,237 samples. More than 80 percent of these values are less than or equal the 

modal MRL: 119,831 (86 percent) equal the modal MRL of 0.0005 mg/L and an additional 

18,311 (13 percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the 

EQL (USEPA, 2009e). The MDLs of approved methods range from 0.00003 to 0.00004 mg/L. 

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revise

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Applying a multiplier of 10 would give a possible PQL range from 0.0003 to 0.0004 mg/Lwhich 

supports the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for 1,2-dichloropropane. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of 1,2-dichloropropane at the EQL of 0.0005 mg/L and additional 

thresholds of 0.001 and 0.0025 mg/L (USEPA, 2009f). Table VI-14 shows the results of the 

occurrence and exposure analysis for the current MCL and these thresholds. The occurrence and 

exposure analysis shows that average concentrations do not exceed the current MCL for any 

system in the analysis. Note that these results are based on the subset of monitoring data 

provided in response to the Six-Year Review ICR and do not necessarily reflect MCL violations, 

which are based on annual average concentrations at entry points; SDWIS/FED indicates three 

MCL violations for 1,2-dichloropropane between 1998 and 2005 (USEPA, 2007g). Average 

concentrations at 47 to 61 of 50,437 systems (0.093 to 0.121 percent), serving 296,000 to 

494,000 people (0.130 to 0.218 percent of 227 million people), exceed the EQL of 0.0005 mg/L. 

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

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mg/L, 0.001 mg/L, and 0.0005 mg/L

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Table VI-14. Number and Percent of Systems with Mean Concentrations Exceeding 1,2-

Dichloropropane Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,437 systems with 1,2-dichloropropane data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

1/2 MCL (0.0025 mg/L) 2 (0.004%) 2 (0.004%) 2 (0.004%) 

2xEQL (0.001 mg/L) 27 (0.054%) 24 (0.048%) 21 (0.042%) 

EQL (0.0005 mg/L) not applicable 61 (0.121%) 47 (0.093%) 

Corresponding Population Served 

(Percentages based on 226,912,000 people served by the systems with 

1,2-dichloropropane data in the Six-Year Review ICR occurrence 

Regulatory or dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

1/2 MCL (0.0025 mg/L) 120 (0.00005%) 120 (0.00005%) 120 (0.00005%) 

2xEQL (0.001 mg/L) 286,000 (0.126%) 286,000 (0.126%) 284,000 (0.125%) 

EQL (0.0005 mg/L) not applicable 494,000 (0.218%) 296,000 (0.130%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

1,2-dichloropropane is appropriate at this time. The occurrence and exposure analysis based on 

possible changes in analytical feasibility indicates that any revision to the MCL is unlikely to 

provide a meaningful opportunity to improve public health protection. Taking into consideration 

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the low occurrence of this contaminant, EPA has decided that any revision to the NPDWR would 

be a low priority activity for the Agency, and, thus, is not appropriate to revise at this time 

because of: 

• 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. 

32. Dinoseb 

a. Background. EPA published the current NPDWR for dinoseb on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.007 mg/L. EPA 

based the MCLG on a reference dose of 0.001 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of dinoseb, including its potential developmental and 

reproductive toxicity. The literature search did not identify any studies that warrant a review of 

the RfD or the cancer classification (USEPA, 2009b). 

A review of analytical or treatment feasibility is not necessary for dinoseb because changes 

to the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the dinoseb NPDWR, the Agency did 

not conduct a detailed occurrence and exposure analysis. 

c. Review Result. EPA’s review shows that there are no data supporting a change to the 

dinoseb NPDWR. As a result, a revision to the NPDWR would not be appropriate at this time. 

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33. Diquat 

a. Background. EPA published the current NPDWR for diquat on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.02 mg/L. EPA 

based the MCLG on a reference dose of 0.0022 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2001, the Agency updated its health effects assessment of diquat 

(USEPA, 2001a). A subsequent reassessment of tolerances for residues in or on raw agricultural 

products (USEPA, 2002d) did not identify any new health effects information and based the 

updated tolerances on health effects information in the 2001 assessment (USEPA, 2001a). The 

Agency identified a change in this assessment that could lead to a change in the MCLG. This 

assessment considered relevant studies on the toxicity of diquat including developmental and 

reproductive toxicity. The assessment revised the RfD from 0.002 mg/kg-day to 0.005 mg/kgday and developed a cancer classification of E, evidence of noncarcinogenicity (USEPA, 2001a). 

Based on the new OPP assessment and RfD of 0.005 mg/kg-day, and assuming a 70-kg adult 

body weight and 2 liters water intake per day, the DWEL could be 0.175 mg/L. An RSC of 20

percent results in a possible MCLG of 0.035 mg/L, rounded to 0.04 mg/L. 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the available occurrence and 

exposure information for diquat to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to achieve cost savings for PWSs and their customers while 

maintaining, or improving, the level of public health protection (USEPA, 2009f). Although the 

Agency obtained and evaluated the finished water occurrence data for diquat, its usefulness is 

limited for determining potential cost savings to PWS and their customers because the Agency 

does not know which systems are treating for this contaminant. As an alternative, the Agency 

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evaluated available data on source water quality and conducted a qualitative assessment of 

treatment cost savings. Because the primary informations sources used to evaluate potential 

source water occurrence—STORET and NAWQA—do not report monitoring results for diquat, 

the Agency obtained available information on diquat use and fate and transport. 

Diquat’s primary uses are as an algaecide, defoliant, desiccant, and herbicide (USEPA, 

1995a). The most recent pesticide application estimates in the Pesticide Use Database developed 

by the National Center for Food and Agricultural Policy (NCFAP) indicate overall cropland 

application of almost 270,000 pounds in 1997, primarily on potato and alfalfa crops (NCFAP, 

2000). The NCFAP based these estimates on State-level pesticide usage patterns for the period 

1994-1998 and State-level crop acreage for 1997. These estimates reflect several limitations: 

they do not include noncropland applications, the data sources vary in quality, and State-level 

pesticide use data gaps are filled using data for nearby states. The USGS estimated county-level 

pesticide usage for 2002 based on crop acreage estimates in the 2002 Census of Agriculture and 

State-level application rates for the period 1999-2004 developed by the CropLife Foundation 

(USGS, no date), which implemented the NCFAP method for estimating pesticide usage 

(Gianessi and Regner, 2006) and, therefore, has similar limitations. The USGS estimates total 

diquat application to crops of approximately 200,000 pounds per year, with potatoes accounting 

for almost 90 percent of these applications (USGS, no date). Diquat use on crops occurred 

primarily in regions of New England, the Great Lakes, North Dakota, the Pacific Northwest, 

California, and Florida. In comparison to other commonly used pesticides, diquat has the lowest 

national estimate for use on crops (Gianessi and Regner, 2006). 

The Reregistration Eligibility Decision (RED) for Diquat Dibromide (USEPA, 1995a) notes 

that although diquat is persistent (i.e., it does not hydrolyze and is resistant to degradation), it 

becomes immobile when it adsorbs to soil particles and, therefore, is not expected to contaminate

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ground water. Furthermore, diquat dissipates quickly from surface water because it adsorbs to 

soil sediments, vegetation, and organic matter; the estimated half-life is 1 to 2 days for diquat in 

surface water based on a study of two ponds in Florida (USEPA, 1995a). These factors indicate 

the possibility of low occurrence in drinking water sources. 

The BAT and small system compliance technologies for diquat have other beneficial effects, 

e.g., removing other co-occurring contaminants. Therefore, if EPA were to consider a higher 

level, the Agency does not know how many PWSs that are currently treating to comply with the 

existing MCL of 0.02 mg/L would be likely to discontinue treatment that is already in place 

(USEPA, 2009d). Also, the Agency does not know to what extent affected systems might be 

able to reduce costs given that capital costs are not recoverable. However, the Agency 

recognizes that there may be opportunities to achieve operational cost savings if these systems 

are able to re-optimize current treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for diquat, EPA does not believe a revision to the NPDWR for diquat is 

appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for diquat is likely to provide a meaningful opportunity for cost savings 

to public water systems and their customers. After consideration of this factor, EPA has decided 

that any revision to the NPDWR would be a low priority activity for the Agency, and, thus, is not 

appropriate to revise at this time because of: 

• Competing workload priorities; 

• The administrative costs associated with rulemaking; and 

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

resulted. 

34. Endothall 

a. Background. EPA published the current NPDWR for endothall on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.1 mg/L. EPA 

based the MCLG on a reference dose of 0.02 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2005, the Agency updated its health effects assessment of endothall 

(USEPA, 2005d). The Agency identified a change in this assessment that could lead to a change 

in the MCLG. This assessment considered relevant studies on the toxicity of endothall including 

developmental and reproductive toxicity. The assessment revised the RfD from 0.02 mg/kg-day 

to 0.007 mg/kg-day and concluded that endothall is unlikely to be carcinogenic to humans 

(USEPA, 2005d). Based on the new OPP assessment and RfD of 0.007 mg/kg-day, and 

assuming a 70-kg adult body weight and 2 liters water intake per day, the DWEL could be 0.245 

mg/L. An RSC of 20 percent results in a possible MCLG of 0.05 mg/L. 

Because of a possible change in the MCLG for endothall, EPA considered whether analytical 

feasibility is likely to be a limitation if the Agency were to consider lowering the MCL to 0.05 

mg/L (the possible MCLG). EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for endothall are generally 

above 80 percent, but there were no results for PE studies with true values below the current 

PQL of 0.09 mg/L. More recent PT data from late 1999 through 2004, supplied by a PT 

provider, show passing rates above 75 percent for most studies, but there are four studies with 

passing rates equal to or less than the 75 percent criterion, including two close to the current 

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PQL. No PT studies had true values below the current PQL. Given the variable results from the 

PT studies and the lack of PE and PT study results below the current PQL, PE and PT data are 

insufficient to support a PQL reduction (USEPA, 2009c). 

While the PT data are not sufficient to support a lowering of the PQL for endothall at this 

time, the current PQL of 0.09 mg/L is greater than the possible MCLG. It would therefore limit 

a possible revision to the MCL. EPA evaluated two alternative sources of information to 

determine whether they indicate any potential to revise the PQL: laboratory minimum reporting 

levels in the Six-Year Review ICR dataset, and the MDLs for the approved method for the 

detection of endothall (Method 548.1). While EPA prefers to use laboratory performance data to 

calculate the PQL, the MRL and MDL information can be valuable for this review to indicate 

whether it is possible to quantitate at levels below the current PQL. The Six-Year Review ICR 

dataset contains MRL values for 21,792 samples. Of these, 21,445 (98 percent) have an MRL 

value of 0.05 mg/L or lower. Because more than 80 percent of the MRL values are at or below 

the possible MCLG of 0.05 mg/L, EPA selected that value as the minimum threshold for the 

occurrence and exposure analysis (USEPA, 2009e). The MDL of the approved method is 

0.00179 mg/L. Applying a multiplier of 10 would give a possible PQL of 0.0179 mg/L,which is 

below the possible MCLG (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, there is evidence of a 

potential to lower the PQL for endothall even though the PE and PT data are insufficient to 

support a PQL reduction. To determine whether any MCL revision is likely to provide a 

meaningful opportunity to improve public health protection, EPA evaluated the occurrence of 

endothall at the possible MCLG of 0.05 mg/L (USEPA, 2009f). Table VI-15 shows the results 

of the occurrence and exposure analysis for the current MCL and the possible MCLG set equal to 

0.05 mg/L based on the new health effects information and the laboratory minimum reporting 

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method is 0.00179 mg/L. Applying a 

multiplier of 10 would give a possible 

PQL of 0.0179 mg/L. Because most

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levels in the Six-Year Review ICR dataset. The occurrence and exposure analysis shows that 

average concentrations do not exceed the current MCL for any system in the analysis. Note that 

these results are based on the subset of monitoring data provided in response to the Six-Year 

Review ICR and do not necessarily reflect MCL violations, which are based on running annual 

average concentrations at entry points; nevertheless, SDWIS/FED indicates no MCL violations 

for endothall between 1998 and 2005 (USEPA, 2007g). The average concentration at one of the 

14,156 systems (0.007 percent), serving 10,000 people (or 0.008 percent of 119 million people), 

exceeds the possible MCLG based on new health effects information (0.05 mg/L). 

Table VI-15. Number and Percent of Systems with Mean Concentrations Exceeding Endothall 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 14,156 systems with endothall data in the SixYear Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.1 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.05 mg/L) 1 (0.007%) 1 (0.007%) 1 (0.007%) 

Corresponding Population Served 

(Percentages based on 118,536,800 people served by the systems with 

endothall data in the Six-Year Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.1 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.05 mg/L) 10,000 (0.008%) 10,000 (0.008%) 10,000 (0.008%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

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c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for endothall, EPA does not believe a revision to the NPDWR for 

endothall is appropriate at this time. In making this decision, the Agency considered whether 

any possible revision to the NPDWR for endothall is likely to provide a meaningful opportunity 

for health risk reductions. Taking into consideration the low occurrence of this contaminant, 

EPA has decided that any revision to the NPDWR would be a low priority activity for the 

Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

35. Endrin 

a. Background. EPA published the current NPDWR for endrin on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.002 mg/L. EPA 

based the MCLG on a reference dose of 0.0003 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of endrin, including its potential developmental and 

reproductive toxicity. The literature search did not identify any studies that warrant a review of 

the RfD or the cancer classification (USEPA, 2009b). 

A review of analytical or treatment feasibility is not necessary for endrin because changes to 

the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the endrin NPDWR, the Agency did not 

conduct a detailed occurrence and exposure analysis. 

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c. Review Result. EPA’s review shows that there are no data supporting a change to the 

endrin NPDWR. As a result, a revision to the NPDWR would not be appropriate at this time. 

36. Epichlorohydrin 

a. Background. EPA published the current NPDWR for epichlorohydrin on January 30, 1991 

(56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR imposes a TT requirement that 

limits the allowable level of epichlorohydrin monomer in the polymer that is added to water as a 

flocculent to remove particulates. Each water system is required to certify, in writing, to the 

State (using third-party or manufacturer’s certification) that the combination (or product) of dose 

and monomer level does not exceed the following level: 0.01 percent residual epichlorohydrin 

monomer in polymer products used during water treatment and dosed at 20 mg/L (ppm). 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of epichlorohydrin as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for 

epichlorohydrin at this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency 

believes that a further review of the health effects of epichlorohydrin is not warranted at this 

time. 

EPA has identified information that suggests that the residual epichlorohydrin content in 

water treatment polymers has decreased significantly, likely due to improvements in 

manufacturing processes and technologies (USEPA, 2009g). NSF International analyses 

conducted between January 2005 and June 2007 found that, in 84 epichlorohydrin-based 

polymers/co-polymers submitted for certification under NSF Standard 60, the residual 

epichlorohydrin content was always below the detection limit of 0.002 percent. 

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Epichlorohydrin standards in Europe and Australia are also stricter than the NPDWR. Based 

on the concentration of dose and monomer level in the NPDWR, finished water could contain up 

to 2 μg/L (ppb) of epichlorohydrin. By contrast, the European Union requires that finished water 

contain less than 0.1 μg/L (ppb) epichlorohydrin, and Australia requires that the concentration in 

finished water be less than 0.5 μg/L (ppb). The United Kingdom requires that polymers used in 

drinking water contain less than 0.002 percent residual epichlorohydrin, and the dose of these 

polymers be less than 5 mg/L (ppm) at all times, for a maximum finished water concentration of 

0.1 μg/L (ppb). 

To assess the occurrence of epichlorohydrin in drinking water, EPA sought data on current 

usage practices for polymers containing it. The Agency is not presently aware of any recent, 

large-scale studies of polymer usage in drinking water facilities, and therefore cannot fully 

characterize the occurrence of epichlorohydrin in drinking water. However, cationic polymers 

used in water treatment often contain epichlorohydrin. The 1996 WATER:\STATS database 

(described in Levine et al., 2004), based on an AWWA survey, indicates that 13 percent of 

ground water systems and 66 percent of surface water systems surveyed use a polymer for water 

treatment. Many of these are cationic polymers, particularly for surface water systems; cationic 

polymers used to treat drinking water often use epichlorohydrin monomer. 

 Additional information on the extent of use of epichlorohydrin based polymers/co-polymers 

in drinking water would further assist the Agency in evaluating the potential public health 

benefits associated with a revision to the treatment technique for epichlorohydrin. Because most 

epichlorohydrin-based polymers available today have a significantly lower residual monomer 

content than that specified in the treatment technique (2009g), EPA believes that the costs of a 

revision would be minimal and recognizes that benefits may also be small. 

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c. Review Result. The Agency believes it is appropriate to revise the NPDWR for 

epichlorohydrin. The existing MCLG is zero (based on the current B2 cancer classification) and 

NSF International data indicate that epichlorohydrin based polymers/copolymers are widely 

available with lower monomer levels than required by the existing NPDWR. Hence, revisions to 

the epichlorohydrin NPDWR will provide a meaningful opportunity to maintain the health risk 

reductions achieved by technological advances in manufacturing. As discussed in Section VII, 

the Agency solicits public comment on the use of epichlorohydrin-based polymers/co-polymers 

in drinking water facilities (since this may provide additional information on the occurrence of 

epichlorohydrin in drinking water) to help inform the regulatory revisions. EPA notes that any 

changes to the NPDWR for epichlorohydin may also include revisions to the closely related 

NPDWR for acrylamide. 

37. Ethylbenzene 

a. Background. EPA published the current NPDWR for ethylbenzene on January 30, 1991 

(56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.7 mg/L. 

EPA based the MCLG on a reference dose of 0.1 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to ethylbenzene. The revised health effects assessment will consider relevant studies 

on the toxicity of ethylbenzene, including its potential developmental and reproductive toxicity. 

The new health effects assessment was not completed by March 1, 2009, the review cutoff date 

for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

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c. Review Result. Since the MCL for ethylbenzene is set at its MCLG and a reassessment of 

the health risks resulting from exposure to ethylbenzene is in progress, the Agency does not 

believe a revision to the NPDWR is appropriate at this time. 

38. Ethylene Dibromide (EDB; 1,2-Dibromoethane) 

a. Background. EPA published the current NPDWR for EDB on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.00005 mg/L, based on analytical feasibility. 

b. Technical Reviews. The Agency updated the health effects assessment for EDB in 2004 

and retained the cancer classification on which the 1991 MCLG is based (USEPA, 2004a). As a 

part of the 2004 assessment, EPA considered relevant studies on the toxicity of EDB, including 

its potential developmental and reproductive toxicity. 

The current MCL for EDB is based on a PQL of 0.00005 mg/L. For the Six-Year Review, 

the Agency considered whether changes in the analytical feasibility of EDB might lead to a 

lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then analyzed 

more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). Passing 

rates for PE data available through late 1999 for EDB are all 75 percent or higher. However, the 

true concentrations were all higher than the current PQL of 0.00005 mg/L. More recent PT data 

from late 1999 through 2004, supplied by a PT provider, likewise show passing rates of 75 

percent or higher, but again, all of the true concentrations in the PT data were higher than the 

current PQL. Because of the lack of data below the PQL, a lowering of the PQL for EDB is not 

appropriate at this time (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQ L could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

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the MDLs for approved methods for the detection of EDB (Methods 504.1 and 551.1). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

83,063 samples. Fewer than 80 percent of these values are less than or equal the modal MRL:

26,926 (32 percent) equal the modal MRL of 0.00001 mg/L and an additional 454 (0.5 percent) 

are lower than 0.00001 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL 

(USEPA, 2009e). The MDLs of approved methods are 0.00001 and 0.000032 mg/L. Applying a 

multiplier of 5, which was used to establish the PQL, would give a possible PQL range from 

0.00005 to 0.00016 mg/L. The result is higher than or equal to the current PQL and, therefore, 

EPA did not estimate an EQL (USEPA, 2009e). Based on these varied and unrelated

approaches/sources of information, EPA believes that there is no potential to lower the PQL. 

Since the MCL is constrained by the PQL, and the PQL is unchanged, EPA does not believe it is 

necessary to conduct an occurrence analysis at this time. 

c. Review Result. EPA did not identify new data that support consideration of a possibly 

lower PQL (and therefore a possibly lower MCL). Therefore, EPA does not believe a revision to 

the NPDWR for EDB is appropriate at this time. 

39. Fluoride 

a. Background. EPA published the current NPDWR for fluoride on April 2, 1986 (51 FR 

11396 (USEPA, 1986c)). The NPDWR established an MCLG and an MCL of 4.0 mg/L. The 

MCLG was developed from a lowest effect level for crippling skeletal fluorosis of 20 mg/day 

with continuous exposures over a 20-year or longer period. The lowest-observed-adverse-effect 

level (LOAEL) was divided by an uncertainty factor of 2.5 and a drinking water intake of 2 

liters/day (L/day) to obtain the MCLG. Drinking water was considered to be the only source of 

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Deleted: , and 8,416 (10%) are between 

0.00001 mg/L and the MCL of 0.00005 

mg/L. The 

Deleted: Since most MRLs do not 

achieve the modal value,

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end

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exposure for the calculation. At the same time, EPA published a secondary maximum 

contaminant level (SMCL) for fluoride of 2.0 mg/L to protect against dental fluorosis, which was 

considered to be an adverse cosmetic effect. PWSs exceeding the fluoride SMCL must provide 

public notification to their customers. 

Fluoride is unique because of its beneficial effects at low level exposures, and because it is 

voluntarily added to some drinking water systems as a public health measure for reducing the 

incidence of cavities among the treated population. The amount of fluoride added to drinking 

water for fluoridation ranges from 0.7 to 1.2 mg/L, depending on ambient air temperatures. The 

decision to fluoridate a water supply is made by the State or local municipality, and is not 

mandated by EPA or any other Federal entity. 

b. Technical Reviews. As a result of the first Six-Year Review of the fluoride NPDWR (67 

FR 19030 (USEPA, 2002c) (preliminary); 68 FR 42908 (USEPA, 2003e) (final)), EPA requested 

that the National Research Council (NRC) of the National Academies of Science (NAS) conduct 

a review of the recent health and exposure data on orally ingested fluoride. In 2006, the NRC 

published the results of their evaluation in a report entitled, Fluoride in Drinking Water: A 

Scientific Review of EPA’s Standards. Based on its review, NRC concluded that severe dental 

fluorosis is an adverse health effect when it causes confluent thinning and pitting of the enamel, 

a situation that compromises the function of the enamel in protecting the dentin and eventually 

the pulp from decay and infection. There was consensus among the committee that severe dental 

fluorosis is an effect that should be avoided and that “exposure at the MCLG clearly puts 

children at risk of developing severe enamel fluorosis.” In addition, the committee examined the 

scientific data on the impact of fluoride on the strength and structure of bone and the majority 

concluded that the MCLG “is not likely to be protective against bone fractures.” NRC 

recommended that EPA use the available dose-response data for the effects of fluoride on severe 

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dental fluorosis and skeletal fractures in combination with data on the relative contribution of 

drinking water to total fluoride exposure to identify an MCLG that would be protective against 

these effects. 

The NRC also evaluated the impact of fluoride on reproduction and development, 

neurotoxicity and behavior, the endocrine system, genotoxicity, cancer and other effects. They 

concluded that the available data were inadequate to determine if a risk for effects on these 

endpoints exists at an MCLG of 4 mg/L and made recommendations for additional research. 

After considering the genotoxicity data, cancer studies in humans and animals, and studies of 

mode of action in cell systems, NRC determined that the evidence on the potential of fluoride to 

initiate or promote cancers, particularly of the bone, is tentative and mixed. They recommended 

that EPA await the results and publication of an in-process hospital-based, case-control study of 

osteosarcoma and fluoride exposure from the Harvard School of Dental Medicine before 

determining if an Agency update of the cancer risk assessment for fluoride is necessary21. 

c. Review Result. The Agency does not believe a revision to the NPDWR for fluoride is 

appropriate at this time because the Agency’s Office of Water (OW) is in the process of 

developing its dose-response assessment of the noncancer impacts of fluoride on severe dental 

fluorosis and the skeletal system. In addition, the OW is updating its evaluation of the relative 

contribution of drinking water to total fluoride exposure considering the contributions from 

dental products, foods, pesticide residues, and other sources such as ambient air and medications. 

Once the Agency completes and publishes peer reviewed versions of these in-process 

assessments, it will be able to determine the potential impacts on the MCLG, MCL, and/or the 

SMCL and whether any revisions to these would be appropriate. 

 

21 At this time, the results of the osteosarcoma cancer study recommended by NAS have not been published. 

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40. Glyphosate 

a. Background. EPA published the current NPDWR for glyphosate on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.7 mg/L. EPA 

based the MCLG on a reference dose of 0.1 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2002, the Agency updated its health effects assessment of 

glyphosate (USEPA, 2002a). The Agency identified a change in this assessment that could lead 

to a change in the MCLG. This assessment considered relevant studies on the toxicity of 

glyphosate including developmental and reproductive toxicity. The assessment revised the RfD 

from 0.1 mg/kg-day to 2 mg/kg-day and concluded that glyphosate has evidence of noncarcinogenicity in humans (USEPA, 2002a). Based on the new OPP assessment and RfD of 2 

mg/kg-day, and assuming a 70-kg adult body weight and 2 liters water intake per day, the DWEL 

could be 70 mg/L. An RSC of 20 percent results in a possible MCLG of 14 mg/L, (USEPA, 

2009b). 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for glyphosate to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to achieve cost savings for PWSs and their customers while 

maintaining, or improving, the level of public health protection (USEPA, 2009f). Although the 

Agency obtained and evaluated the finished water occurrence data for glyphosate, its usefulness 

is limited for determining potential cost savings to PWSs and their customers because the 

Agency does not know which systems are treating for this contaminant. As an alternative, the 

Agency evaluated available data on source water quality and conducted a qualitative assessment 

of treatment cost savings. 

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Table VI-16 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at thresholds levels of interest. This information 

indicates that any resulting NPDWR change would not affect systems that rely on source water 

at any of the NAWQA or STORET locations. 

Table VI-16. Ambient Water Quality Monitoring Occurrence Summary for Glyphosate 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 241 (100.0%) 41 (100.0%) 

Nondetect 180 (74.7%) 37 (90.2%) 

Detected 61 (25.3%) 4 (9.8%) 

Exceeds current MCLG of 0.7 mg/L 0 (0.0%) 0 (0.0%) 

Exceeds alternative value of 14.0 mg/L 0 (0.0%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2005. 

Source: USEPA, 2009c

The BAT and small system compliance technologies for glyphosate have other beneficial 

effects, e.g., pretreatment for other co-occurring contaminants or disinfection. Therefore, if EPA 

were to consider a higher level, the Agency does not know how many PWSs that are currently 

treating to comply with the existing MCL of 0.7 mg/L would be likely to discontinue treatment 

that is already in place (USEPA, 2009d). Also, the Agency does not know to what extent 

affected systems might be able to reduce costs given that capital costs are not recoverable. 

However, the Agency recognizes that there may be opportunities to achieve operational cost 

savings if these systems are able to re-optimize current treatment. 

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Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for glyphosate, EPA does not believe a revision to the NPDWR for 

glyphosate is appropriate at this time. In making this decision, the Agency considered whether 

any possible revision to the NPDWR for glyphosate is likely to provide a meaningful opportunity 

for cost savings to public water systems and their customers. Taking into consideration the low 

occurrence of this contaminant in source waters, EPA has decided that any revision to the 

NPDWR would be a low priority activity for the Agency, and, thus, is not appropriate to revise at 

this time because of: 

• 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. 

41. Heptachlor 

a. Background. EPA published the current NPDWR for heptachlor on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.0004 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of heptachlor as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for heptachlor at 

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this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency believes that a 

further review of the health effects of heptachlor is not warranted at this time. 

The current MCL for heptachlor is based on a PQL of 0.0004 mg/L. For the Six-Year 

Review, the Agency considered whether changes in the analytical feasibility of heptachlor might 

lead to a lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then 

analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). 

Passing rates for PE data available through late 1999 for heptachlor are above 90 percent around 

the current PQL of 0.0004 mg/L, including three studies with true values below the current PQL. 

All passing rates in the PE data exceeded 80 percent. More recent PT data from late 1999 

through 2004, supplied by a PT provider, show greater than 75 percent passing rates for a 

majority of studies, but there are no studies with true values below the current PQL. There are 

three PT studies with passing rates below 75 percent. Despite this variability, most of the 

laboratory passing rates from PE and PT studies, including three with true values below the PQL, 

exceeded the 75 percent criterion typically used to derive a PQL. Therefore, a lowering of the 

PQL for heptachlor might be possible. These results, however, are insufficient to recalculate a 

revised PQL for heptachlor because not enough data points are available below the current PQL 

to derive a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of heptachlor (Methods 505, 508, 508.1, 

525.2, and 551.1). While EPA prefers to use laboratory performance data to calculate the PQL, 

the MRL and MDL information can be valuable for this review to indicate whether it is possible 

to quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 58,758 samples. Fewer than 80 percent of these values are less than or equal the 

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revise

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modal MRL: 24,918 (42 percent) equal the modal MRL of 0.00004 mg/L and an additional 7,966 

(14 percent) are lower than 0.00004 mg/L. Therefore, EPA did not set the EQL equal to the 

modal MRL (USEPA, 2009e). The MDLs of approved methods are 0.000003, 0.0000015, 

0.000005, 0.00015, and 0.000081 mg/L. Applying a multiplier of 10 would give a possible PQL 

range from 0.000015 to 0.0015 mg/L. EPA used the median 10×MDL value of 0.00005 mg/L 

and rounded up to 0.0001 mg/L for the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there may be potential to lower the PQL for heptachlor. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of heptachlor at the EQL of 0.0001 mg/L and additional threshold of 

0.0002 mg/L (USEPA, 2009f). Table VI-17 shows the results of the occurrence and exposure 

analysis for the current MCL and these thresholds. The occurrence and exposure analysis shows 

that average concentrations exceed the current MCL for one of 33,020 systems (0.003 percent) 

serving 325 people (or 0.0002 percent of 184 million people). Note that these results are based 

on the subset of monitoring data provided in response to the Six-Year Review ICR and do not 

necessarily reflect MCL violations, which are based on annual average concentrations at entry 

points; SDWIS/FED indicates no MCL violations for heptachlor between 1998 and 2005 

(USEPA, 2007g). Average concentrations at 42 of 33,020 systems (0.127 percent), serving 

31,500 people (or 0.017 percent of 184 million people), exceed the EQL of 0.0001 mg/L. 

Deleted: ,

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Deleted: . An

Deleted: %

Deleted: , and 24,752 (42%) are 

between 0.00004 mg/L and 0.0001 mg/L

Deleted: Because of the broad 

dispersion in MRL values, 

Deleted: 10×MDL values to develop 

thresholds in the occurrence and exposure 

analysis. EPA took the 

Deleted: to establish a minimum 

threshold for the occurrence and exposure 

analysis

Deleted: thresholds

Deleted: EQLs set equal to 0.0002 

mg/L and 0.0001 mg/L

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Table VI-17. Number and Percent of Systems with Mean Concentrations Exceeding Heptachlor 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 33,020 systems with heptachlor data in the SixRegulatory or Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0004 mg/L) 1 (0.003%) 1 (0.003%) 1 (0.003%) 

1/2 MCL (0.0002 mg/L) 1 (0.003%) 1 (0.003%) 1 (0.003%) 

EQL (0.0001 mg/L) 42 (0.127%) 42 (0.127%) 42 (0.127%) 

Corresponding Population Served 

(Percentages based on 184,444,000 people served by the systems with 

Regulatory or heptachlor data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0004 mg/L) 325 (0.0002%) 325 (0.0002%) 325 (0.0002%) 

1/2 MCL (0.0002 mg/L) 325 (0.0002%) 325 (0.0002%) 325 (0.0002%) 

EQL (0.0001 mg/L) 31,500 (0.017%) 31,500 (0.017%) 31,500 (0.019%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

heptachlor is appropriate at this time. The occurrence and exposure analysis based on possible 

changes in analytical feasibility indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve public health protection. Taking into consideration the low 

occurrence of this contaminant, EPA has decided that any revision to the NPDWR would be a 

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• 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. 

42. Heptachlor Epoxide 

a. Background. EPA published the current NPDWR for heptachlor epoxide on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a 

cancer classification of B2, probable human carcinogen. The NPDWR also established an MCL 

of 0.0002 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of heptachlor epoxide as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for heptachlor 

epoxide at this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency believes 

that a further review of the health effects of heptachlor epoxide is not warranted at this time. 

The current MCL for heptachlor epoxide is based on a PQL of 0.0002 mg/L. For the SixYear Review, the Agency considered whether changes in the analytical feasibility of heptachlor 

epoxide might lead to a lower MCL. EPA reviewed PE data from the first Six-Year Review 

cycle and then analyzed more recent PT data to determine if the PQL can be revised (i.e., 

analytical feasibility). Passing rates for PE data available through late 1999 for heptachlor 

epoxide are above 85 percent around the current PQL of 0.0002 mg/L, including two studies 

with true values below the current PQL. All passing rates in the PE data exceeded 80 percent. 

More recent PT data from late 1999 through 2004, supplied by a PT provider, show greater than 

75 percent passing rates for a majority of studies, but there are no studies with true values below 

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the PQL. There are two PT studies with passing rates below 75 percent. Despite this variability, 

most of the laboratory passing rates from PE and PT studies exceeded the 75 percent criterion 

typically used to derive a PQL. Therefore, a lowering of the PQL for heptachlor epoxide might 

be possible. These results, however, are insufficient to recalculate a revised PQL for heptachlor 

epoxide because not enough data points are available below the current PQL to derive a value at 

the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of heptachlor epoxide (Methods 505, 508, 

508.1, 525.2, and 551.1). While EPA prefers to use laboratory performance data to calculate the 

PQL, the MRL and MDL information can be valuable for this review to indicate whether it is 

possible to quantitate at levels below the current PQL. The Six-Year Review ICR dataset 

contains MRL values for 58,731 samples. Fewer than 80 percent of these values are less than or 

equal the modal MRL: 26,424 (45 percent) equal the modal MRL of 0.00002 mg/L and an

additional 5,969 (10 percent) are lower than 0.00002 mg/L. Therefore, EPA did not set the EQL 

equal to the modal MRL (USEPA, 2009e). The MDLs of approved methods are 0.000004, 

0.0000059, 0.000001, 0.00013, and 0.000202 mg/L. Applying a multiplier of 10 would give a 

possible PQL range from 0.00001 to 0.00202 mg/L. EPA used the median 10×MDL value of 

0.000059 mg/L and rounded up to 0.0001 mg/L for the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there may be potential to lower the PQL for heptachlor epoxide. To determine whether any 

MCL revision is likely to provide a meaningful opportunity to improve public health protection, 

EPA evaluated the occurrence of heptachlor epoxide at an EQL of 0.0001 mg/L (USEPA, 

2009f). Table VI-18 shows the results of the occurrence and exposure analysis for the current 

Deleted: WS

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revise

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between 0.00002 mg/L and 0.0001 mg/L

Deleted: Because of the broad 

dispersion in MRL values, 

Deleted: 10×MDL values to develop 

thresholds in the occurrence and exposure 

analysis. EPA took the 

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threshold 

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analysis

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MCL and an EQL. The occurrence and exposure analysis shows that average concentrations 

exceed the current MCL for one of 33,015 systems (0.003 percent) serving 325 people (or 0.0002

percent of 184 million people). Note that these results are based on the subset of monitoring data 

provided in response to the Six-Year Review ICR and do not necessarily reflect MCL violations, 

which are based on annual average concentrations at entry points; SDWIS/FED indicates two 

MCL violations for heptachlor epoxide between 1998 and 2005 (USEPA, 2007g). Average 

concentrations at three of 33,015 systems (0.009 percent), serving 14,400 people (or 0.008

percent of 184 million people), exceed the EQL of 0.0001 mg/L. 

Table VI-18. Number and Percent of Systems with Mean Concentrations Exceeding Heptachlor 

Epoxide Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 33,015 systems with heptachlor epoxide data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0002 mg/L) 1 (0.003%) 1 (0.003%) 1 (0.003%) 

EQL (0.0001 mg/L) 3 (0.009%) 3 (0.009%) 3 (0.009%) 

Corresponding Population Served 

(Percentages based on 184,478,000 people served by the systems with 

Regulatory or heptachlor epoxide data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.0002 mg/L) 325 (0.0002%) 325 (0.0002%) 325 (0.002%) 

EQL (0.0001 mg/L) 14,400 (0.008%) 14,400 (0.008%) 14,400 (0.008%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

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c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

heptachlor epoxide is appropriate at this time. The occurrence and exposure analysis based on 

possible changes in analytical feasibility indicates that any revision to the MCL is unlikely to 

provide a meaningful opportunity to improve public health protection. Taking into consideration 

the low occurrence of this contaminant, EPA has decided that any revision to the NPDWR would 

be a low priority activity for the Agency, and, thus, is not appropriate to revise at this time 

because of: 

• 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. 

43. Hexachlorobenzene 

a. Background. EPA published the current NPDWR for hexachlorobenzene on July 17, 1992 

(57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.001 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of hexachlorobenzene as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for 

hexachlorobenzene at this time (USEPA, 2009b). Because the MCLG remains at zero, the 

Agency believes that a further review of the health effects of hexachlorobenzene is not warranted 

at this time. 

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The current MCL for hexachlorobenzene is based on a PQL of 0.001 mg/L. For the Six-Year 

Review, the Agency considered whether changes in the analytical feasibility of 

hexachlorobenzene might lead to a lower MCL. EPA reviewed PE data from the first Six-Year 

Review cycle and then analyzed more recent PT data to determine if the PQL can be revised (i.e., 

analytical feasibility). Passing rates for PE data available through late 1999 for 

hexachlorobenzene are above 80 percent around the current PQL of 0.001 mg/L, including eight 

studies with true values below the current PQL. More recent PT data from late 1999 through 

2004, supplied by a PT provider, also show greater than 75 percent passing rates for a majority 

of studies, including eight out of nine studies with true values below the current PQL. There are 

two PT studies with passing rates equal to or less than 75 percent, including one with a true value 

below the PQL. Despite this variability, most of the laboratory passing rates from PE and PT 

studies – including several with true concentrations below the PQL – exceeded the 75 percent 

criterion typically used to derive a PQL. Therefore, a lowering of the PQL for 

hexachlorobenzene might be possible. These results, however, are insufficient to recalculate a 

revised PQL for hexachlorobenzene because not enough data points are available below the 

current PQL to derive a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of hexachlorobenzene (Methods 505, 508, 

508.1, 525.2, and 551.1). While EPA prefers to use laboratory performance data to calculate the 

PQL, the MRL and MDL information can be valuable for this review to indicate whether it is 

possible to quantitate at levels below the current PQL. The Six-Year Review ICR dataset 

contains MRL values for 58,713 samples. More than 80 percent of these values are less than or 

equal the modal MRL: 40,791 (69 percent) equal the modal MRL of 0.0001 mg/L and an

Deleted: WS

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revise

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additional 7,380 (13 percent) are lower than 0.0001 mg/L. Therefore, EPA selected the modal 

MRL as the EQL (USEPA, 2009e). The MDLs of approved methods are 0.000002, 0.0000077, 

0.000001, 0.00013, and 0.000003 mg/L. Applying a multiplier of 10 would give a possible PQL 

range from 0.00001 to 0.0013 mg/L, which contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for hexachlorobenzene. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of hexachlorobenzene at the EQL of 0.0001 mg/L and an additional 

threshold of 0.0005 mg/L (USEPA, 2009f). Table VI-19 shows the results of the occurrence and 

exposure analysis for the current MCLand these thresholds. The occurrence and exposure 

analysis shows that average concentrations exceed the current MCL for three of 32,826 systems 

(0.009 percent) serving 2,000 people (or 0.001 percent of 184 million people). Note that these 

results are based on the subset of monitoring data provided in response to the Six-Year Review 

ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates two MCL violations for 

hexachlorobenzene between 1998 and 2005 (USEPA, 2007g). Average concentrations at 9 to 16 

of 32,826 systems (0.027 to 0.049 percent), serving approximately 9,000 to 94,000 people (or 

0.005 to 0.051 percent of 184 million people), exceed the EQL of 0.0001 mg/L. 

Deleted: %

Deleted: ; however, the median 

10×MDL value is 0.00003 mg/L

Deleted: is less than the modal MRL. 

Because of the preponderance of MRL 

values of 0.0001 mg/L, EPA selected that 

value as the minimum threshold for the 

occurrence and exposure analysis

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Deleted: MCL and EQLs set equal to 

0.0005 mg/L and 0.0001 mg/L

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Table VI-19. Number and Percent of Systems with Mean Concentrations Exceeding 

Hexachlorobenzene Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 32,826 systems with hexachlorobenzene data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.001 mg/L) 3 (0.009%) 3 (0.009%) 3 (0.009%) 

1/2 MCL (0.0005 mg/L) 4 (0.012%) 4 (0.012%) 4 (0.012%) 

EQL (0.0001 mg/L) not applicable 16 (0.049%) 9 (0.027%) 

Corresponding Population Served 

(Percentages based on 184,124,800 people served by the systems with 

Regulatory or hexachlorobenzene data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.001 mg/L) 2,000 (0.001%) 2,000 (0.001%) 2,000 (0.001%) 

1/2 MCL (0.0005 mg/L) 5,000 (0.003%) 5,000 (0.003%) 5,000 (0.003%) 

EQL (0.0001 mg/L) not applicable 94,000(0.051%) 9,000 (0.005%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.001 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

hexachlorobenzene is appropriate at this time. The occurrence and exposure analysis based on 

possible changes in analytical feasibility indicates that any revision to the MCL is unlikely to 

provide a meaningful opportunity to improve public health protection. Taking into consideration 

the low occurrence of this contaminant, EPA has decided that any revision to the NPDWR would 

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be a low priority activity for the Agency, and, thus, is not appropriate to revise at this time 

because of: 

• 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. 

44. Hexachlorocyclopentadiene 

a. Background. EPA published the current NPDWR for hexachlorocyclopentadiene on July 

17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 

0.05 mg/L. EPA based the MCLG on a reference dose of 0.007 mg/kg-day and a cancer 

classification of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. In the first Six-Year Review cycle, EPA evaluated new information 

from a health effects assessment completed in 2001 (USEPA, 2001b). At that time, the Agency 

could not determine that a revision to the NPDWR would provide a meaningful opportunity for 

public health protection (67 FR 19030 (USEPA, 2002c)). The 2001 assessment considered 

relevant studies on the toxicity of hexachlorocyclopentadiene including developmental and 

reproductive toxicity. The assessment revised the RfD from 0.007 mg/kg-day to 0.006 mg/kgday (USEPA, 2001b). In the current review cycle, EPA conducted a literature search through 

June 2007 for relevant data on the toxicology of hexachlorocyclopentadiene, including its 

potential developmental and reproductive toxicity. The literature search did not identify any new 

data that would affect the RfD or cancer classification (USEPA, 2009b). Based on the 2001 IRIS 

assessment and RfD of 0.006 mg/kg-day, and assuming a 70-kg adult body weight and 2 liters 

water intake per day, the DWEL could be 0.21 mg/L. An RSC of 20 percent results in a possible 

MCLG of 0.04 mg/L (USEPA, 2009b). 

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Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor for the possible MCLG decrease under consideration. 

 EPA evaluated the results of the occurrence and exposure analyses for 

hexachlorocyclopentadiene to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to improve the level of public health protection (USEPA, 

2009f). Table VI-20 shows the results of the occurrence and exposure analysis for the current 

MCL and the possible MCLG. The occurrence and exposure analysis shows that average 

concentrations do not exceed the current MCL for any systems in the analysis. Note that these 

results are based on the subset of monitoring data provided in response to the Six-Year Review 

ICR and do not necessarily reflect MCL violations, which are based on running annual average 

concentrations at entry points; SDWIS/FED indicates no MCL violations for 

hexachlorocyclopentadiene between 1998 and 2005 (USEPA, 2007g). The occurrence and 

exposure analysis shows that average concentration do not exceed the possible MCLG based on 

health effects information (0.04 mg/L). 

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Table VI-20. Number and Percent of Systems with Mean Concentrations Exceeding 

Hexachlorocyclopentadiene Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 32,801 systems with 

hexachlorocyclopentadiene data in the Six-Year Review ICR 

occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.05 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.04 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Corresponding Population Served 

(Percentages based on 184,738,000 people served by the systems with 

hexachlorocyclopentadiene data in the Six-Year Review ICR 

occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.05 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (0.04 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for hexachlorocyclopentadiene, EPA does not believe a revision to the 

NPDWR for hexachlorocyclopentadiene is appropriate at this time. In making this decision, the 

Agency considered whether any possible revision to the NPDWR for hexachlorocyclopentadiene 

is likely to provide a meaningful opportunity for health risk reductions. Taking into 

consideration the low occurrence of this contaminant, EPA has decided that any revision to the 

NPDWR would be a low priority activity for the Agency, and, thus, is not appropriate to revise at 

this time because of: 

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• 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. 

45. Lindane (gamma-Hexachlorocyclohexane) 

a. Background. EPA published the current NPDWR for lindane on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.0002 mg/L. EPA 

based the MCLG on a reference dose of 0.0003 mg/kg-day and a cancer classification of C, 

possible human carcinogen. 

b. Technical Reviews. In the first Six-Year Review cycle, EPA evaluated new information 

from a health effects assessment completed in 2002 (USEPA, 2006b). At that time, the Agency 

could not determine that a revision to the NPDWR would provide a meaningful opportunity for 

cost savings to public water systems or their customers, and decided that any revision would be a 

low priority activity for the Agency because of competing workload priorities, the administrative 

costs associated with rulemaking, and the burden on States and the regulated community to 

implement any regulatory change (68 FR 42908, July 18, 2003 (USEPA, 2003e)). The 2002 

assessment considered relevant studies on the toxicity of lindane including developmental and 

reproductive toxicity. The assessment revised the RfD from 0.0003 mg/kg-day to 0.0047 mg/kgday and classified it as “Suggestive evidence of carcinogenicity, but not sufficient to assess 

human carcinogenic potential” (USEPA, 2006b). During the current review cycle, all uses of 

lindane were cancelled voluntarily (71 FR 74905, December 13, 2006 (USEPA, 2006e)), 

effective July 1, 2007. However, lindane is a persistent and bioaccumulative pesticide. 

Accordingly, EPA conducted a literature search for relevant data on the toxicology of lindane, 

including its potential developmental and reproductive toxicity. The literature search did not 

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identify any additional new data that would affect the RfD or cancer classification (USEPA, 

2009b).The possible revised MCLG is based on the 2002 OPP assessment and RfD of 0.0047 

mg/kg-day, a body weight of 70 kg, water intake of 2 L/day, and an RSC of 20 percent. 

Uncertainty factors related to reproductive and developmental effects, and/or a possible risk 

management factor based on the suggested evidence of carcinogenicity, could be used in 

developing a possible revised MCLG. Depending on the choice of uncertainty factors, the 

MCLG could range between 0.001 mg/L and 0.03 mg/L. 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for lindane to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to achieve cost savings for PWSs and their customers while 

maintaining, or improving, the level of public health protection (USEPA, 2009f). Although the 

Agency obtained and evaluated the finished water occurrence data for lindane, its usefulness is 

limited for determining potential cost savings to PWSs and their customers because the Agency 

does not know which systems are treating for this contaminant. As an alternative, the Agency 

evaluated available data on source water quality and conducted a qualitative assessment of 

treatment cost savings. 

Table VI-21 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA. Although the degree to which 

these occurrence rates represent national drinking water source occurrence is uncertain, the 

information shows no to low occurrence at threshold levels of interest. In the upper bound 

analysis, an NPDWR change would affect systems that rely on source water at less than 0.01

percent of the NAWQA locations and less than 0.3 percent of the STORET locations. Any 

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MCLG/MCL revision to a potentially higher level of 0.001 mg/L (the lower bound) or 0.03 mg/L 

(the upper bound) would likely affect fewer systems. 

Table VI-21. Ambient Water Quality Monitoring Occurrence Summary for Lindane 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 2,691 (100.0%) 8,195 (100.0%) 

Nondetect 2,017 (75%) 8,058 (98.3%) 

Detected 674 (25%) 137 (1.7%) 

Exceeds current MCLG of 0.0002 mg/L 7 (0.26%) 1 (0.01%) 

Exceeds upper bound alternative value of 

0.03 mg/L 1 (0.04%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2005. 

Source: USEPA, 2009c

The BATs and small system compliance technologies for lindane have other beneficial 

effects, e.g., reduction of other co-occurring contaminants, precursors for DBPs, or other 

common impurities. Therefore, if EPA were to consider a higher level, the Agency does not 

know how many PWSs that are currently treating to comply with the existing MCL of 0.0002 

mg/L would be likely to discontinue treatment that is already in place (USEPA, 2009d). Also, 

the Agency does not know to what extent affected systems might be able to reduce costs given 

that capital costs are not recoverable. However, the Agency recognizes that there may be 

opportunities to achieve operational cost savings if these systems are able to re-optimize current 

treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for lindane, EPA does not believe a revision to the NPDWR for lindane 

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is appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for lindane is likely to provide a meaningful opportunity for cost savings 

to public water systems and their customers. Taking into consideration the low occurrence of 

this contaminant in source waters, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

46. Mercury (Inorganic) 

a. Background. EPA published the current NPDWR for inorganic mercury on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.002 

mg/L. The Agency based the MCLG on a DWEL of 0.01 mg/L22 and a cancer classification of 

D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of inorganic mercury, including its potential 

developmental and reproductive toxicity. The literature search did not identify any studies that 

warrant a review of the RfD or the cancer classification (USEPA, 2009b). 

A review of analytical or treatment feasibility is not necessary for inorganic mercury because 

changes to the MCLG are not warranted at this time and the current MCL is set at the MCLG. 

Since EPA did not identify a health or technology basis for revising the inorganic mercury 

NPDWR, the Agency did not conduct a detailed occurrence and exposure analysis. 

 

22 The DWEL was recommended by a panel of experts on mercury, and was derived using the weight of 

evidence from the entire inorganic mercury database. The DWEL was later back-calculated to an RfD of 0.0003 

mg/kg-day (USEPA, 1995). 

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c. Review Result. EPA’s review shows that there are no data supporting a change to the 

inorganic mercury NPDWR. As a result, a revision to the NPDWR would not be appropriate at 

this time. 

47. Methoxychlor 

a. Background. EPA published the current NPDWR for methoxychlor on January 30, 1991 

(56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.04 mg/L. 

EPA based the MCLG on a reference dose of 0.005 mg/kg-day and a cancer classification of D, 

not classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of methoxychlor, including its potential developmental 

and reproductive toxicity. The literature search did not identify any studies that warrant a review 

of the RfD or the cancer classification (USEPA, 2009b). The Six-Year Review 1 stated that the 

Agency had initiated a reassessment of the health risks posed by exposure to methoxychlor (67 

FR 19030 (USEPA, 2002c)). Since 2002, the Agency has cancelled all product uses and 

concluded that the database to complete the health effects assessment for methoxychlor was 

inadequate (USEPA, 2004c). In its Reregistration Eligibility Decision, OPP noted substantive 

data gaps for methoxychlor, including lack of Guideline studies for chronic systemic toxicity as 

well as reproductive and developmental toxicity (USEPA, 2004c). 

A review of analytical or treatment feasibility is not necessary for methoxychlor because 

changes to the MCLG are not warranted at this time and the current MCL is set at the MCLG. 

Since EPA did not identify a health or technology basis for revising the methoxychlor NPDWR, 

the Agency did not conduct a detailed occurrence and exposure analysis. 

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c. Review Result. EPA’s review shows that there are no data supporting a change to the 

methoxychlor NPDWR. As a result, a revision to the NPDWR would not be appropriate at this 

time. 

48. Monochlorobenzene (Chlorobenzene) 

a. Background. EPA published the current NPDWR for monochlorobenzene on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.1 

mg/L. EPA based the MCLG on a reference dose of 0.02 mg/kg-day and a cancer classification 

of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of monochlorobenzene, including its potential 

developmental and reproductive toxicity. The literature search did not identify any studies that 

warrant a review of the RfD or the cancer classification (USEPA, 2009b). 

A review of analytical or treatment feasibility is not necessary for monochlorobenzene 

because changes to the MCLG are not warranted at this time and the current MCL is set at the 

MCLG. Since EPA did not identify a health or technology basis for revising the 

monochlorobenzene NPDWR, the Agency did not conduct a detailed occurrence and exposure 

analysis. 

c. Review Result. EPA’s review shows that there are no data supporting a change to the 

monochlorobenzene NPDWR. As a result, a revision to the NPDWR would not be appropriate 

at this time. 

49. Nitrate (as N) 

a. Background. EPA published the current NPDWR for nitrate on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 10 mg/L (as N). 

EPA based the MCLG on a survey of epidemiologic studies of infant methemoglobinemia in 

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populations exposed to nitrate contaminated water. No cancer classification is currently 

available for nitrate (USEPA, 2009b). 

b. Technical Reviews. The health effects technical review identified new information on 

developmental effects of nitrate, as well as data regarding its carcinogenicity, that may indicate 

the need to update the Agency’s health effects assessment (USEPA, 2009b). Several studies 

suggest that nitrate in drinking water can have adverse effects on the thyroid (Mukhopadhyay et 

al., 2005; Tajtakova et al., 2006; Zaki et al., 2004). Nitrate has long been known as a 

competitive inhibitor of iodide uptake in the thyroid (Wolff and Maury, 1963). Inhibition of 

iodide uptake can lead to alteration in thyroid hormone levels including decreases in 

levothyroxine (T4) levels. NAS (1995) stated that it is likely that the motor changes reported by 

Markel et al. (1989) when the animals were young were not a direct effect of nitrate, but were 

secondary to effects on learning behavior. Based on these considerations, a new assessment of 

the noncancer effects of nitrate may be warranted, including consideration of whether 

methemoglobinemia in infants, which is an acute effect, is still the most appropriate basis for the 

chronic exposure limit for nitrate. In addition, recent information may suggest the consideration 

of separate acute and chronic values for nitrate. 

The health effects review identified a number of relevant new studies that may warrant a 

review of the cancer classification for nitrate. These studies include a number of new 

epidemiology studies (Cocco et al., 2003; Coss et al., 2004; de Roos et al., 2003; Mueller et al., 

2004; Volkmer et al., 2005; Ward et al., 2003; Ward et al., 2005a; Ward et al., 2005b; Ward et 

al., 2006; Yang et al., 2007; Zeegers et al., 2006), as well as a recent report from an International 

Agency for Research on Cancer (IARC) Working group (Grosse et al., 2006). This latter report 

concluded that, under conditions that result in endogenous nitrosation, ingested nitrate or nitrite 

is probably carcinogenic to humans. 

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In light of this information, EPA considers nitrate as a potential candidate for a new health 

effects assessment. The Agency solicits feedback on its plans to reassess health risks resulting 

from exposure to nitrate. The Agency also welcomes any scientific information related to nitrate 

health risks from the public. Because EPA considers nitrate as a candidate for a new assessment, 

EPA does not believe it is appropriate to consider any possible revisions to the MCLG (as well 

as the MCL) at this time. 

A review of analytical or treatment feasibility is not necessary for nitrate because changes to 

the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the nitrate NPDWR, the Agency did not 

conduct a detailed occurrence and exposure analysis. 

c. Review Result. The Agency is considering whether to initiate a new health assessment for 

nitrate and therefore does not believe a revision to the NPDWR is appropriate at this time. 

As discussed in Section VII, the Agency is asking for input and information about several 

implementation issues related to nitrate (see section V.B.6). 

50. Nitrite (as N) 

a. Background. EPA published the current NPDWR for nitrite on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 1 mg/L (as N). 

EPA based the MCLG on extrapolation from nitrate, assuming the conversion of 10 percent of 

nitrate-nitrogen to nitrite-nitrogen. No cancer classification is currently available for nitrite 

(USEPA, 2009b). 

b. Technical Reviews. The health effects technical review identified new information on 

developmental effects of nitrite, as well as data regarding its carcinogenicity, that may indicate 

the need to update the Agency’s health effects assessment (USEPA, 2009b). Several studies 

suggest that nitrate in drinking water can have adverse effects on the thyroid (Mukhopadhyay et 

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al., 2005; Tajtakova et al., 2006; Zaki et al., 2004). Since nitrite is formed from nitrate, and the 

current nitrite RfD is based on nitrate data, the impact of these new data on a nitrite noncancer 

assessment should be evaluated. Nitrite has long been known as a competitive inhibitor of iodide 

uptake in the thyroid; although it is a weaker inhibitor than nitrate (Wolff and Maury, 1963). 

Inhibition of iodide uptake can lead to alteration in thyroid hormone levels including decreases in 

T4. A developmental toxicity study in rats (Vorhees et al., 1984) observed statistically 

significant delays in swimming development in addition to pup mortality and body weight 

changes. Based on these considerations, a new assessment of the noncancer effects of nitrite 

may be warranted, including consideration of whether methemoglobinemia in infants, which is 

an acute effect, is still the most appropriate basis for the chronic exposure limit for nitrite. In 

addition, recent information may suggest the consideration of separate acute and chronic values 

for nitrite. 

The health effects review identified a number of relevant new studies that may warrant a 

review of the cancer classification for nitrate. These studies include a number of new 

epidemiology studies (Cocco et al., 2003; Coss et al., 2004; de Roos et al., 2003; Mueller et al., 

2004; Volkmer et al., 2005; Ward et al., 2003; Ward et al., 2005a; Ward et al., 2005b; Ward et 

al., 2006; Yang et al., 2007; Zeegers et al., 2006). In addition, a recent report from an 

International Agency for Research on Cancer (IARC) Working group (Grosse et al., 2006) 

concluded that, under conditions that result in endogenous nitrosation, ingested nitrate or nitrite 

is probably carcinogenic to humans. 

In light of this information, EPA considers nitrite as a potential candidate for a new health 

effects assessment. The Agency solicits feedback on its plans to reassess health risks resulting 

from exposure to nitrite. The Agency also welcomes any scientific information related to nitrite 

health risks from the public. Because EPA considers nitrite as a candidate for a new assessment, 

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EPA does not believe it is appropriate to consider any possible revisions to the MCLG (as well 

as the MCL) at this time. 

A review of analytical or treatment feasibility is not necessary for nitrite because changes to 

the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the nitrite NPDWR, the Agency did not 

conduct a detailed occurrence and exposure analysis. 

c. Review Result. The Agency is considering whether to initiate a new health assessment for 

nitrite and therefore does not believe a revision to the NPDWR is appropriate at this time. 

As discussed in Section VII, the Agency is requesting input and informationon about several 

implementation issues related to nitrite (see section V.B.6). 

51. Oxamyl (Vydate) 

a. Background. EPA published the current NPDWR for oxamyl on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.2 mg/L. EPA 

based the MCLG on a reference dose of 0.025 mg/kg-day and a cancer classification of E, 

evidence of non-carcinogenicity for humans. 

b. Technical Reviews. In 2000, the Agency updated its health effects assessment of oxamyl 

(USEPA, 2000a). The Agency identified a change in this assessment that could lead to a change 

in the MCLG. This assessment considered relevant studies on the toxicity of oxamyl including 

developmental and reproductive toxicity. The assessment revised the RfD from 0.025 mg/kgday to 0.001 mg/kg-day and concluded that there is evidence that oxamyl is noncarcinogenic to 

humans (USEPA, 2000a). Based on the new OPP assessment and RfD of 0.001 mg/kg-day, and 

assuming a 10-kg child body weight and 1 liter water intake per day, the DWEL could be 0.01 

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mg/L23. An RSC of 20 percent was selected based on the actual food dietary exposure (81

percent) for children who are 1 to 6 years old (USEPA, 2000a); this RSC results in a possible 

MCLG of 0.002 mg/L (USEPA, 2009b). 

Because of a possible change in the MCLG for oxamyl, EPA considered whether analytical 

feasibility is likely to be a limitation if the Agency were to consider lowering the MCL to 0.002 

mg/L (the possible MCLG). EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if it might be possible to recalculate the PQL, 

which is 0.02 mg/L and might be a limit to a possible MCLG of 0.002 mg/L (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for oxamyl are below 75 

percent for most studies with true concentrations below the current PQL of 0.02 mg/L. More 

recent PT data from late 1999 through 2004, supplied by a PT provider, show no results below 

the current PQL but had most passing rates above 75 percent with true values at or above the 

current PQL. Given the variable results from the PE and PT studies, and the lack of PT data 

below the current PQL, PE and PT data are insufficient to support a PQL reduction (USEPA, 

2009c). 

While the PT data are not sufficient to support a lowering of the PQL for oxamyl at this time, 

the present PQL of 0.02 mg/L is greater than the possible MCLG. It would therefore limit a 

possible revision to the MCL. EPA evaluated two alternative sources of information to 

determine whether they indicate any potential to quantitate at levels as low as the possible 

MCLG: laboratory minimum reporting levels in the Six-Year Review ICR dataset, and the 

MDLs for approved methods for the detection of oxamyl (Methods 531.1 and 531.2). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

 

23 A child’s body weight and drinking water intake were used to calculate the DWEL because children are the 

population with the highest risk from dietary exposure.

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information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

52,201 samples. Of these, 45,290 (87 percent) have an MRL value of 0.002 mg/L or lower. 

Because more than 80 percent of the MRL values are at or below the possible MCLG of 0.002 

mg/L, EPA selected that value as the minimum threshold for the occurrence and exposure 

analysis (USEPA, 2009e). Method 531.1 has an MDL of 0.00086 mg/L, and Method 532.2 has a 

detection limit (DL) of 0.000065 mg/L. Applying a multiplier of 10 would give a possible PQL 

range from 0.00065 to 0.0086 mg/L, which contains the possible MCLG (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, there is evidence of a 

potential to lower the PQL for oxamyl even though the PE and PT data are insufficient to support 

a PQL reduction. To determine whether any MCL revision is likely to provide a meaningful 

opportunity to improve public health protection, EPA evaluated the occurrence of oxamyl at the 

possible MCLG of 0.002 mg/L (USEPA, 2009f). Table VI-22 shows the results of the 

occurrence and exposure analysis for the current MCL and the possible MCLG. The analysis 

uses single sample or peak results instead of system average results because the health endpoint 

is associated with acute exposure24. The occurrence and exposure analysis shows that individual 

sample concentrations exceed the current MCL of 0.2 mg/L for one of 30,876 systems (0.003

percent) serving 200 people (or 0.000 percent of 167 million people). Note that these results are 

based on the subset of monitoring data provided in response to the Six-Year Review ICR and do 

not necessarily reflect MCL violations, which are based on running annual average 

concentrations at entry points; SDWIS/FED indicates no MCL violations for oxamyl between 

 

24 The Six-Year Review ICR occurrence data are based on the Standardized Monitoring Framework for 

synthetic organic compounds, which is designed to evaluate long-term exposure to contaminants with chronic 

exposure health endpoints. As a result, EPA recognizes that short-term seasonal peaks, which correspond to oxamyl 

application as a pesticide, cannot be readily detected in this dataset. Nonetheless and as noted, EPA used the peak 

concentrations to evaluate occurrence for oxamyl because the health endpoint is associated with acute exposure.

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1998 and 2005 (USEPA, 2007g). Individual sample concentrations at 18 of 30,876 systems 

(0.058 percent), serving fewer than 0.3 million people (0.177 percent), exceeded the possible 

MCLG of 0.002 mg/L at least one time between 1998 and 2005. 

Table VI-22. Number and Percent of Systems with Peak Concentrations Exceeding Oxamyl 

Thresholds and Corresponding Estimates of Population Served 

Regulatory or Health-based 

Threshold 

Systems with Any Sample that is Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 30,876 systems with oxamyl data in 

the Six-Year Review ICR occurrence dataset) 

MCL (0.2 mg/L) 1 (0.003%) 

Possible MCLG (0.002 mg/L) 18 (0.058%) 

Regulatory or Health-based 

Threshold 

Corresponding Population Served 

(Percentages based on 167,378,400 people served by the 

systems with oxamyl data in the Six-Year Review ICR 

occurrence dataset) 

MCL (0.2 mg/L) 200 (0.0001%) 

Possible MCLG (0.002 mg/L) 297,000 (0.177%) 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for oxamyl, EPA does not believe a revision to the NPDWR for oxamyl 

is appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for oxamyl is likely to provide a meaningful opportunity for health risk 

reductions. Taking into consideration the low occurrence of this contaminant, EPA has decided 

that any revision to the NPDWR would be a low priority activity for the Agency, and, thus, is not 

appropriate to revise at this time because of: 

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• 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. 

52. Pentachlorophenol 

a. Background. EPA published the current NPDWR for pentachlorophenol on July 1, 1991 

(56 FR 30266 (USEPA, 1991b)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.001 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to pentachlorophenol. The revised health effects assessment will consider relevant 

studies on the toxicity of pentachlorophenol, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

Although a risk assessment is in process for pentachlorophenol, the existing MCLG is zero 

and the current MCL of 0.001 mg/L is based on the PQL. Therefore, EPA reviewed whether 

there is potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle 

and then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Several passing rates in the PE data for pentachlorophenol available through late 

1999 are below 75 percent, and none of the true concentrations were below the current PQL. 

There are six PE studies with passing rates equal to or less than the 75 percent criterion, and only 

one of 16 true values in the PE data is below the current PQL. More recent PT data from late 

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information to determine whether 

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lead to a lower MCL. 

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1999 through 2004, supplied by a PT provider, show passing rates below the 75 percent criterion 

for eight studies, and all of the true concentrations in the PT data were higher than the current 

PQL. Because of the variability in passing rates and the lack of data points below the current 

PQL, a lowering of the PQL for pentachlorophenol is not appropriate at this time (USEPA, 

2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of pentachlorophenol (Methods 515.1, 515.2, 

and 525.2). While EPA prefers to use laboratory performance data to calculate the PQL, the 

MRL and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 59,594 samples. Fewer than 80 percent of these values are less than or equal the 

modal MRL: 26,666 (45 percent) equal the modal MRL of 0.00004 mg/L and an additional 2,399 

(4 percent) are lower than 0.00004 mg/L. Therefore, EPA did not set the EQL equal to the 

modal MRL (USEPA, 2009e). The MDLs of approved methods are 0.000032, 0.00016, and 

0.001 mg/L. EPA selected the median value, applied a multiplier of 10, and rounded up to 0.002 

mg/L. The result is higher than the current PQL and, therefore, EPA did not estimate an EQL 

(USEPA, 2009e). Based on these varied and unrelated approaches/sources of information, EPA 

believes that there is no potential to lower the PQL for pentachlorophenol. Since the MCL is 

constrained by the PQL, and the PQL is unchanged, EPA does not believe it is necessary to 

conduct an occurrence analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for 

pentachlorophenol is appropriate at this time because a reassessment of the health risks resulting 

from exposure to pentachlorophenol is in progress (USEPA, 2009b). Furthermore, a review of 

Deleted: they indicate any potential to 

revise the PQL

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13,419 (23%) are between 0.00004 and 

0.0001 mg/L, and 17,095 (29%) are 

between 0.0002 mg/L and 

Deleted: MCL of 0.001 mg/L. 

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across a wide range, 

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value is 

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widely dispersed, and the intermediate 

10×MDL value

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analytical feasibility did not identify a potential to revise the MCL, which is limited by 

feasibility. 

53. Picloram 

a. Background. EPA published the current NPDWR for picloram on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.5 mg/L. EPA 

based the MCLG on a reference dose of 0.07 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In the first Six-Year Review cycle, EPA evaluated new information 

from a health effects assessment completed in 1995 (USEPA, 1995b). At that time, the Agency 

could not determine that a revision to the NPDWR would provide a meaningful opportunity for 

cost savings to public water systems or their customers, and decided that any revision would be a 

low priority activity for the Agency because of competing workload priorities, the administrative 

costs associated with rulemaking, and the burden on States and the regulated community to 

implement any regulatory change (67 FR 19030 (USEPA, 2002c); 68 FR 42908 (USEPA, 

2003e)). The 1995 assessment considered relevant studies on the toxicity of picloram including 

developmental and reproductive toxicity. The assessment revised the RfD from 0.07 mg/kg-day 

to 0.2 mg/kg-day and classified picloram as Group E, evidence of noncarcinogenicity (USEPA, 

1995b). In the current review cycle, EPA conducted a literature search through June 2007 for 

relevant data on the toxicology of picloram, including its potential developmental and 

reproductive toxicity. The literature search did not identify any new data that would affect the 

RfD or cancer classification (USEPA, 2009b). Based on the 1995 OPP assessment and RfD of 

0.2 mg/kg-day, and assuming a 70-kg adult body weight and 2 liters water intake per day, the 

DWEL could be 7 mg/L. An RSC of 20 percent results in a possible MCLG of 1 mg/L (USEPA, 

2009b). 

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Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for picloram to determine whether a revised MCLG/MCL would be likely to 

result in a meaningful opportunity to achieve cost savings for PWSs and their customers while 

maintaining, or improving, the level of public health protection (USEPA, 2009f). Although the 

Agency obtained and evaluated the finished water occurrence data for picloram, its usefulness is 

limited for determining potential cost savings to PWSs and their customers because the Agency 

does not know which systems are treating for this contaminant. As an alternative, the Agency 

evaluated available data on source water quality and conducted a qualitative assessment of 

treatment cost savings. 

Table VI-23 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at threshold levels of interest. This information 

indicates that any resulting NPDWR change would not affect systems that rely on source water 

at any of the NAWQA or STORET locations. 

Table VI-23. Ambient Water Quality Monitoring Occurrence Summary for Picloram 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 870 (100%) 5,772 (100.0%) 

Nondetect 745 (85.6%) 5,733 (99.3%) 

Detected 125 (14.4%) 39 (0.7%) 

Exceeds current MCLG of 0.5 mg/L 0 (0%) 0 (0.0%) 

Exceeds alternative value of 1.0 mg/L 0 (0%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2005. 

Source: USEPA, 2009c

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The BATs and small system compliance technologies for picloram have other beneficial 

effects, e.g., reduction of other co-occurring contaminants, precursors for DBPs, or other 

common impurities. Therefore, if EPA were to consider a higher level, the Agency does not 

know how many PWSs that are currently treating to comply with the existing MCL of 0.5 mg/L 

would be likely to discontinue treatment that is already in place (USEPA, 2009d). Also, the 

Agency does not know to what extent affected systems might be able to reduce costs given that 

capital costs are not recoverable. However, the Agency recognizes that there may be 

opportunities to achieve operational cost savings if these systems are able to re-optimize current 

treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for picloram, EPA does not believe a revision to the NPDWR for 

picloram is appropriate at this time. In making this decision, the Agency considered whether any 

possible revision to the NPDWR for picloram is likely to provide a meaningful opportunity for 

cost savings to public water systems and their customers. Taking into consideration the low 

occurrence of this contaminant in source waters, EPA has decided that any revision to the 

NPDWR would be a low priority activity for the Agency, and, thus, is not appropriate to revise at 

this time because of: 

• 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. 

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54. Polychlorinated Biphenyls (PCBs) 

a. Background. EPA published the current NPDWR for PCBs on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.0005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the cancer health risks resulting 

from exposure to PCBs. The revised health effects assessment will consider relevant studies on 

the toxicity of PCBs, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). On December 21, 2007 (72 FR 72715 (USEPA, 2007c)), the Agency 

noted that the health effects assessment for PCBs is in process. 

Although a risk assessment is in process for PCBs, the existing MCLG is zero and the current 

MCL of 0.0005 mg/L is based on the PQL. Therefore, EPA reviewed whether there is potential 

to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and then 

analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). 

The PE data for PCBs available through late 1999 includes only one true concentration below the 

current PQL, and the passing rate for that concentration is below 75 percent. The passing rates 

for studies above the PQL are above 75 percent. More recent PT data from late 1999 through 

2004, supplied by a PT provider, show passing rates above 75 percent for all studies, but 

includes no studies below the current PQL. Because of the lack of data points below the current 

PQL, a lowering of the PQL for PCBs is not appropriate at this time (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDL for the approved method for the detection of PCBs (Method 508A). While EPA 

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prefers to use laboratory performance data to calculate the PQL, the MRL and MDL information 

can be valuable for this review to indicate whether it is possible to quantitate at levels below the 

current PQL. The Six-Year Review ICR dataset contains MRL values for 35,178 samples. 

Fewer than 80 percent of these values are less than or equal the modal MRL: 23,785 (68

percent) equal the modal MRL of 0.0001 mg/L and an additional 2,355 (7 percent) are lower 

than 0.0001 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL (USEPA, 

2009e). The MDL of approved method is 0.00008 mg/L. Applying a multiplier of 10 would 

give a possible PQL of 0.0008 mg/L. The result is higher than the current PQL, and therefore, 

EPA did not estimate an EQL (USEPA, 2009e). Based on these varied and unrelated 

approaches/sources of information, EPA believes that there is no potential to lower the PQL for 

PCBs. Since the MCL is constrained by the PQL, and the PQL is unchanged, EPA does not 

believe it is necessary to conduct an occurrence analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for PCBs is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

PCBs is in progress (USEPA, 2009b). Furthermore, a review of analytical feasibility did not 

identify a potential to revise the MCL, which is limited by feasibility. 

55. Combined Radiums (226 and 228) 

a. Background. EPA published an interim NPDWR and set an MCL of 5 pCi/L for combined 

radium 226 and 228 on July 9, 1976 (41 FR 28402 (USEPA, 1976)). As noted in the August 14, 

1975 proposal (40 FR 34324 (USEPA, 1975)) and a subsequent September 30, 1986 FR notice, 

EPA considered the feasibility of treatment techniques, analytical methods and monitoring when 

establishing the MCL of 5 pCi/L. EPA also considered the risks associated with exposure to 

radium 226 and 228, which generally fell within the Agency’s acceptable risk range of 10-4 to 10-

6

 at the MCL of 5 pCi/L. On December 7, 2000 (65 FR 76708 (USEPA, 2000c)), EPA 

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

Deleted: , and 7,489 (21%) are between 

0.0001 mg/L and 

Deleted: MCL of 0.0005 mg/L. The 

Deleted: Since more than 20% of 

samples do not achieve the modal MRL, 

and the 10×MDL value

Deleted: these data do

Deleted: support a PQL reduction

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established an MCLG of zero based on a cancer classification of A (known human carcinogen) 

and finalized the NPDWR by retaining the MCL of 5 pCi/L. EPA noted in the December 7, 

2000 FR notice that new risk estimates from Federal Guidance Report 13 reaffirmed that the 5 

pCi/L MCL was appropriate and protective25. EPA also tightened the monitoring requirements 

for combined radiums by requiring that systems monitor for radium 226 and 228 separately. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to radiums. The revised health effects assessment will consider relevant studies on the 

toxicity of radiums, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). 

Although there is an ongoing health effects assessment, the MCLG is zero and the current 

MCL is higher than the MCLG. Therefore, EPA reviewed whether there is potential to revise the 

MCL based on new information regarding analytical and treatment feasibility for radiums. EPA 

promulgated detection limits of 1 pCi/L for both radium 226 and radium 228 in 1976 (41 FR 

28402 (USEPA, 1976)) and retained the use of a detection limit as the required measure of 

sensitivity for radiochemical analysis in lieu of an MDL or PQL in the final rule (65 FR 76708, 

December 7, 2000 (USEPA, 2000c)). EPA did not identify new analytical methods during the 

current review that would feasibly lower the detection limits. In addition, since the December 7, 

2000, regulation, there is no new information regarding treatment feasibility. Since there is no 

new information regarding analytical or treatment feasibility that suggests changes to the MCL, 

EPA does not believe it is necessary to conduct an occurrence analysis at this time. 

 

25 After the December 7, 2000 final regulation, two trade associations and several municipal water systems 

challenged EPA’s standard for combined radiums by claiming that the Agency did not use the best available science 

when finalizing the standard. In February of 2003, the DC Circuit Court of Appeals upheld EPA’s regulation for 

combined radiums (as well as beta and photon emitters and uranium). 

Deleted: However, EPA does not 

expect the 

Deleted: to change the cancer 

classification for radiums,

Deleted: MCLG would remain at zero.¶

As a part of the Six-Year Review, the 

Agency considered

Deleted: was available 

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c. Review Result. The Agency does not believe a revision to the NPDWR for combined 

radiums is appropriate at this time because a reassessment of the health risks resulting from 

exposure to radium is in progress (USEPA, 2009b). Furthermore, there is no new information 

regarding analytical or treatment feasibility that would warrant reconsideration of the MCL. 

56. Selenium 

a. Background. EPA published the current NPDWR for selenium on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.05 mg/L. 

EPA based the MCLG on a maximum safe intake26 of 0.4 mg/person/day and a cancer 

classification of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. The health effects technical review identified new data that relate to 

the biological properties of selenium in mammalian species, as well as data regarding its cancer 

and anticancer properties, that may indicate the need to update the Agency’s health effects 

assessment (USEPA, 2009b). Hawkes and Keim (2003) reported thyroid hormone and related 

metabolism changes in subjects treated with deficient, sufficient, and excess dietary selenium. 

The excess selenium dose was associated with a slight decrease in triiodothyronine (T3) levels, a 

thyrotropin increase, and an increase in body weight compared to the selenium-sufficient 

subjects. The opposite responses occurred in the selenium-deficient subjects. Several studies 

identified changes in sperm parameters and fertility in mice fed either selenium-deficient or 

excess-selenium diets compared to diets with adequate selenium. In addition, new information 

about the metabolism of selenium since the IRIS review (USEPA, 1991a, 1993a) suggests that it 

may be appropriate to differentiate between inorganic selenium and organic selenium in the form 

 

26 The 0.4 mg/day safe level was based on data (Yang et al., 1989a, 1989b) that extrapolated from blood 

selenium levels to estimated dietary intake in the studied population. As described in the January 30, 1991 FR (56 

FR 3526 (USEPA, 1991c)), the Agency partially considered selenium’s status as a nutrient and did not use the 

typical procedure for deriving the MCLG. Hence, there is no specific reference to an RfD for selenium in the 1991 

FR notice. After the publication of the regulation, IRIS (USEPA, 1991a) posted an RfD of 0.005 mg/kg-day for 

selenium using the same data that are the basis of the regulation. 

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of selenoproteins and selenoaminoacids for an assessment that applies to drinking water. 

Although selenium is not a candidate for an MCLG of zero because of its status as a 

micronutrient, new data relevant to the cancer assessment are now available (e.g., DuffieldLillico et al., 2003; Su et al., 2005) and may need further evaluation. 

In light of this information, EPA considers selenium as a potential candidate for a new health 

effects assessment. The Agency solicits general feedback on its plans to reassess health risks 

resulting from exposure to selenium. The Agency also welcomes any scientific information 

related to selenium health risks from the public. Because EPA considers selenium as a candidate 

for a new assessment, EPA does not believe it is appropriate to consider any revisions to the 

MCLG (as well as the MCL) at this time. 

A review of analytical or treatment feasibility is not necessary for selenium because changes 

to the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the selenium NPDWR, the Agency did 

not conduct a detailed occurrence and exposure analysis. 

c. Review Result. The Agency is considering whether to initiate a new health assessment for 

selenium and therefore does not believe a revision to the NPDWR is appropriate at this time. 

57. Simazine 

a. Background. EPA published the current NPDWR for simazine on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.004 mg/L. EPA 

based the MCLG on a reference dose of 0.005 mg/kg-day and a cancer classification of C, 

possible human carcinogen. 

b. Technical Reviews. In 2006, the Agency finalized a health effects assessment for the 

reregistration of simazine as a pesticide (USEPA, 2006i). Because the database for simazine’s 

potential neuroendocrine effects is less robust than the atrazine database, and because simazine 

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and atrazine share a common neuroendocrine mechanism of toxicity, the atrazine data were used 

as bridging data for simazine. Thus, the 2006 assessment established a new RfD of 0.018 

mg/kg-day for simazine, based on the attenuation of pre-ovulatory LH surge from atrazine 

exposure. Similarly, simazine was reclassified in 2006 as “not likely to be carcinogenic to 

humans” based on weight-of-evidence that it is not genotoxic and because the tumor response in 

the Sprague-Dawley rats was determined to be a strain specific mechanism which is not relevant 

to humans. 

c. Review Result. The Agency believes it is not appropriate to consider revisions to the 

NPDWR for simazine at this time and has placed simazine in the emerging information/data gap 

category because of an impending re-evaluation of the Agency’s risk assessment for atrazine and 

the assessment for simazine is based on atrazine data. See section VI.7 (atrazine) for additional 

information. 

58. Styrene 

a. Background. EPA published the current NPDWR for styrene on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.1 mg/L. EPA 

based the MCLG on a reference dose of 0.2 mg/kg-day and a cancer classification of C, possible 

human carcinogen. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to styrene. The revised health effects assessment will consider relevant studies on the 

toxicity of styrene, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

Deleted: there are some forthcoming 

studies 

Deleted: atrazine and its metabolites 

from

Deleted: ORD. The Agency does not 

anticipate that the ORD research will 

significantly change 

Deleted: health effects assessment 

conclusions supporting the FQPA 

reregistration decision published in 2006 

(USEPA, 2006c). However, it is unclear 

whether the new data would impact the 

Agency’s determination on whether any 

revisions to the current MCLG/NPDWR 

for simazine are appropriate (USEPA, 

2009b). The Agency expects to publish 

the ORD studies in 2009

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c. Review Result. Since the MCL for styrene is set at its MCLG and a reassessment of the 

health risks resulting from exposure to styrene is in progress, the Agency does not believe a 

revision to the NPDWR is appropriate at this time. 

59. 2,3,7,8-TCDD (Dioxin) 

a. Background. EPA published the current NPDWR for dioxin on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

3×10-8 mg/L, based on analytical feasibility. 

b. Technical Reviews. In 2003, the Agency prepared a draft human health reassessment for 

dioxin and its related compounds (USEPA, 2003c) that underwent external review by the 

National Academy of Science. In their peer review report (NAS, 2006), NAS recommended that 

EPA reevaluate its conclusions regarding the carcinogenicity of dioxin based on the criteria set 

out in the 2005 cancer guidelines; that EPA should consider developing more information on the 

noncancer effects of dioxin; and that EPA evaluate new dose-response data released by the NTP. 

The Agency is currently considering the NAS recommendations. The Agency does not expect 

any new health effects assessment to be completed in the time frame of the current Six-Year 

Review cycle (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

Although a health effects assessment is in process for dioxin, the existing MCLG is still zero 

and the current MCL is based on a PQL of 3×10-8 mg/L. Therefore, EPA reviewed whether 

there is potential to revise the PQL. The PT data currently available for dioxin are not sufficient 

to evaluate the potential for PQL revision (USEPA, 2009c). 

Deleted: as a part of the Six-Year 

Review, the Agency considered

Deleted: changes in analytical 

feasibility might lead to a lower MCL

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EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDL for the approved method for the detection of dioxin (Method 1613). While EPA 

prefers to use laboratory performance data to calculate the PQL, the MRL and MDL information 

can be valuable for this review to indicate whether it is possible to quantitate at levels below the 

current PQL. The Six-Year Review ICR dataset contains dioxin data for fewer than 2,500 

systems, which is an insufficient sample size to derive an EQL based on MRL data. The MDL 

of the approved method is 1×10-8 mg/L. Applying a multiplier of 5 would yield an EQL of 5×10-

8

 mg/L. The result is slightly higher than the current PQL and, therefore, EPA did not estimate 

an EQL. Based on these varied and unrelated approaches/sources of information. EPA believes 

that a PQL reduction for dioxin is not appropriate at present. Since the MCL is constrained by 

the PQL, and the PQL is unchanged, EPA does not believe it is necessary to conduct an 

occurrence analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for dioxin is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

dioxin is in progress (USEPA, 2009b). Furthermore, a review of analytical feasibility did not 

identify a potential to revise the MCL, which is limited by feasibility. 

60. Tetrachloroethylene 

a. Background. EPA published the current NPDWR for tetrachloroethylene on January 30, 

1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a 

cancer classification of B2, probable human carcinogen. The NPDWR also established an MCL 

of 0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to tetrachloroethylene. The revised health effects assessment will consider relevant 

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels

Deleted: MRL values 

Deleted: 1,278 samples. Of these, 964 

(75%) equal the modal MRL of 5×10-9

mg/L. An additional 191 (15%) are 

lower

Deleted: 5×10-9 mg/L

Deleted: give a possible PQL

Deleted: , which is only

Deleted: . There are too few samples in 

the MRL data to provide a definitive 

result, but the samples that are available 

do suggest that the PQL might be 

lowered. Taken together, these

Deleted: are inconclusive. EPA 

therefore

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studies on the toxicity of tetrachloroethylene, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment and indicates that tetrachloroethylene is 

currently undergoing review by NAS. 

Although a risk assessment is in process for tetrachloroethylene, the existing MCLG is zero 

and the current MCL of 0.005 mg/L is based on the PQL. Therefore, EPA reviewed whether 

there is potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle 

and then analyzed more recent PT data to determine if the PQL could be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for tetrachloroethylene are 

above 95 percent at the lowest concentrations. However, the true concentrations were all higher 

than the current PQL of 0.005 mg/L. More recent PT data from late 1999 through 2004, supplied 

by a PT provider, also show greater than 90 percent passing rates for studies around the current 

PQL, including 13 with true values below the PQL. Because most of the laboratory passing rates 

from PE and PT studies exceeded the 75 percent criterion typically used to derive a PQL, 

including several with true values below the PQL, a lowering of the PQL for tetrachloroethylene 

might be possible. These results, however, are insufficient to recalculate a revised PQL for 

tetrachloroethylene because not enough data points are available below the current PQL to derive 

a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of tetrachloroethylene (Methods 502.2, 524.2, 

and 551.1). While EPA prefers to use laboratory performance data to calculate the PQL, the 

Formatted: Font:

Deleted: For the Six-Year Review, the 

Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

Deleted: WS

Deleted: WS

Deleted: WS

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels

Deleted: ¶

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MRL and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. EPA also noted that the State of New Jersey uses a 

PQL of 0.001 mg/L, based on a 1987 study of laboratory performance at low concentrations that 

used criteria similar to those in the PT data (NJDWQI, 1987). The Six-Year Review ICR dataset 

contains MRL values for 138,348 samples. More than 80 percent of these values are less than or 

equal the modal MRL: 117,033 (85 percent) equal the modal MRL of 0.0005 mg/L and an

additional 15,848 (11 percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal 

MRL as the EQL (USEPA, 2009e). The MDLs of approved method are 0.00005, 0.00014, and 

0.000008 mg/L. Applying a multiplier of 10 would give a possible PQL range from 0.00008 to 

0.0014 mg/L, which contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for tetrachloroethylene. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of tetrachloroethylene at the EQL of 0.0005 mg/L and additional 

thresholds of 0.001 and 0.0025 mg/L. Table VI-24 shows the results of the occurrence and 

exposure analysis for the current MCL and these thresholds. The occurrence and exposure 

analysis shows that average concentrations exceed the current MCL for 23 to 25 out of 50,436 

systems (0.046 to 0.050 percent) serving approximately 630, 000 to 1.1 million people (or 0.277 

to 0.473 percent of 227 million people). Note that these results are based on the subset of 

monitoring data provided in response to the Six-Year Review ICR and do not necessarily reflect 

MCL violations, which are based on annual average concentrations at entry points; SDWIS/FED 

indicates 174 MCL violations for tetrachloroethylene between 1998 and 2005, with annual 

violations ranging from 10 to 33 (USEPA, 2007g). Average concentrations at 412 to 519 of 

50,436 systems (0.817 to 1.029 percent), serving 12.4 to 14.6 million people (or 5.466 to 6.419

Deleted: Of

Deleted: ,

Deleted: %

Deleted: . An

Deleted: %

Deleted: methods range 

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis 

Deleted: 0005, 0.

Deleted: ,

Deleted: EQLs set equal to 0.0025 

mg/L, 0.001 mg/L, and 0.0005 mg/L

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: %

Deleted: ¶

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percent of 227 million people), exceed the lowest EQL of 0.0005 mg/L. While these systems are 

widely distributed and located in most of the States providing data, a few large systems (serving 

500,000 or more people) account for almost half of the exposed population. 

Table VI-24. Number and Percent of Systems with Mean Concentrations Exceeding 

Tetrachloroethylene Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,436 systems with tetrachloroethylene data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 25 (0.050%) 23 (0.046%) 23 (0.046%) 

1/2 MCL (0.0025 mg/L) 75 (0.149%) 71 (0.141%) 68 (0.135%) 

2xEQL (0.001 mg/L) 286 (0.568%) 251 (0.498%) 220 (0.437%) 

EQL (0.0005 mg/L) not applicable 519 (1.030%) 412 (0.818%) 

Corresponding Population Served 

(Percentages based on 227,009,000 people served by the systems with 

Regulatory or tetrachloroethylene data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 1,074,000 (0.473%) 628,000 (0.277%) 628,000 (0.277%) 

1/2 MCL (0.0025 mg/L) 1,706,000 (0.752%) 1,692,000 (0.745%) 1,647,000 (0.726%) 

2xEQL (0.001 mg/L) 10,706,000 (4.716%) 10,177,000 (4.483%) 9,625,000 (4.240%) 

EQL (0.0005 mg/L) not applicable 14,572,000 (6.419%) 12,408,000 (5.466%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that a revision to the MCL may provide a meaningful 

opportunity to improve the level of public health protection, EPA considered whether treatment 

feasibility is likely to pose any limitations if the MCL were lowered (USEPA, 2009g). The 

current BATs for tetrachloroethylene are packed tower aeration (PTA) and granular activated 

carbon (GAC). Small system compliance technologies (SSCTs) for tetrachloroethylene include 

Deleted: %

Deleted: ¶

Deleted: ¶

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GAC and several aeration technologies. EPA’s assessment shows that PTA and GAC are 

effective enough to achieve concentrations as low as the EQL. 

 EPA is not currently able to assess the potential health benefits from a revised MCL for 

tetrachloroethylene, because the revised health effects assessment is not yet available. However, 

based on its B2 cancer classification (MCLG of zero) and the occurrence and exposure analysis 

at possible MCL values, the Agency believes that a revision to the MCL may provide a 

meaningful opportunity to reduce public health risks. 

c. Review Result. The Agency believes it is appropriate to revise the NPDWR for 

tetrachloroethylene although a health effects assessment is currently in progress. The existing 

MCLG is zero (based on the current B2 cancer classification) and the current MCL is based on a 

PQL (i.e., analytical feasibility) of 0.005 mg/L. The Agency’s review indicates that analytical 

feasibility could be as much as 10 times lower (~ 0.0005 mg/L) and occurrence at this level 

appears to be relatively widespread. Hence, revisions to the tetrachloroethylene NPDWR may 

provide a meaningful opportunity for health risk reduction. If the updated health effects 

assessment is completed in time to consider for the regulatory revision of tetrachloroethylene, the 

Agency will consider this assessment in its evaluation of public health benefits associated with 

any revision. As discussed in Section VII, the Agency solicits public comment and/or relevant 

information that may inform the regulatory revision for tetrachloroethylene. EPA is also 

requesting that stakeholders provide information/data about the lowest level of quantitation 

(including the analytical method used) that laboratories can reliably and consistently achieve. 

61. Thallium 

a. Background. EPA published the current NPDWR for thallium on July 17, 1992 (57 FR 

31776 (USEPA, 1992)). The NPDWR established an MCLG of 0.0005 mg/L. EPA based the 

MCLG on a reference dose of 0.00007 mg/kg-day and a cancer classification of D, not 

Formatted: Check spelling and

grammar

Formatted: Check spelling and

grammar

Formatted: Check spelling and

grammar

Deleted: EPA believes these BATs

Deleted: SSCTs

Deleted: still practical and would not 

pose any limitations if EPA were

Deleted: revise

Deleted: MCL

Deleted: to 

Deleted: will 

Deleted: EPA expects that 

Deleted: final

Deleted: will further support the 

Deleted: ¶

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classifiable as to human carcinogenicity. The NPDWR also established an MCL of 0.002 mg/L, 

based on analytical feasibility. 

b. Technical Reviews. EPA completed the risk reassessment for thallium in September of 

2009 (USEPA, 2009k). Because the new health effects assessment was not completed by March 

1, 2009, the review cutoff date for this notice (USEPA, 2009b), the outcome of this assessment 

has not been included in the current review effort. EPA will consider the updated assessment in 

the next review cycle. 

The current MCL is based on a PQL of 0.002 mg/L. Therefore, EPA reviewed whether there 

is potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for thallium are above 80 

percent around the current PQL of 0.002 mg/L, including one study with a true concentration 

less than the current PQL. More recent PT data from late 1999 through 2004, supplied by a PT 

provider, show passing rates at or above 75 percent, but tending to fall below 80 percent as the 

true concentration approaches the current PQL. No studies had true concentrations below the 

current PQL. Given the lack of data points below the current PQL and the low PT passing rates 

close to the PQL, a lowering of the PQL for thallium is not appropriate at this time (USEPA, 

2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of thallium (Methods 200.8 and 200.9). While 

EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

Deleted: has initiated a reassessment of 

the health risks resulting from exposure 

to thallium. The revised health effects 

assessment will consider relevant studies 

on the toxicity of thallium, including its 

potential developmental and reproductive 

toxicity. The 

Deleted: ). The IRIS Substance 

Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) 

has the most up-to-date information on 

the status of the health effects assessment

Deleted: Although a health effects 

assessment is in process for thallium, the

Deleted: as a part of the Six-Year 

Review, the Agency evaluated several 

sources of information to determine 

whether changes in analytical feasibility 

might lead to a lower MCL. 

Deleted: WS

Deleted: WS

Deleted: %

Deleted: they indicate any potential to 

revise the PQL

Deleted: minimum reporting levels 

Deleted: ¶

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73,409 samples. Fewer than 80 percent of these values are less than or equal the modal MRL: 

46,273 (63 percent) equal the modal MRL of 0.001 mg/L and an additional 11,032 (15 percent) 

are lower than 0.001 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL 

(USEPA, 2009e). The MDLs of approved methods range from 0.0003 to 0.0007 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.003 to 0.007 mg/L. The 

result is higher than the current PQL and, therefore, EPA did not estimate an EQL (USEPA, 

2009e). Based on these varied and unrelated approaches/sources of information, EPA believes 

that there is no potential to lower the PQL for thallium. Since the MCL is constrained by the 

PQL, and the PQL is unchanged, EPA does not believe it is necessary to conduct an occurrence 

analysis at this time. 

c. Review Result. The Agency does not believe a revision to the NPDWR for thallium is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

thallium was in progress and did not meet the March 1, 2009 cutoff date for this review (USEPA, 

2009). Furthermore, a review of analytical feasibility did not identify a potential to revise the 

MCL, which is limited by feasibility. 

62. Toluene 

a. Background. EPA published the current NPDWR for toluene on January 30, 1991 (56 FR 

3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 1 mg/L. EPA 

based the MCLG on a reference dose of 0.2 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2005, the Agency updated its health effects assessment of toluene 

(USEPA, 2005b). The change in this assessment could lead to a change in the MCLG. This 

assessment considered relevant studies on the toxicity of toluene including developmental and 

reproductive toxicity. The assessment revised the RfD from 0.2 mg/kg-day to 0.08 mg/kg-day 

Deleted: Of

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Deleted: Finally, 15,953 (22%) equal 

the MCL of 0.002 mg/L, and 151 samples 

exceed

Deleted: MCL

Deleted: Although the majority of 

MRL values are below the current PQL, 

the 10×MDL values are

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reduction

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and concluded that there is inadequate information to assess the carcinogenic potential of toluene 

(USEPA, 2005b). Although there were no changes in the critical study or effect, there were 

changes in the toxicity database that increase concern for immunotoxicity and neurotoxicity via 

the oral exposure route and justified the higher uncertainty factor for the revised RfD (USEPA, 

2005b). Based on the new IRIS assessment and RfD of 0.08 mg/kg-day, and assuming a 70-kg 

adult body weight and 2 liters water intake per day, the DWEL could be 2.8 mg/L. An RSC of 

20 percent results in a possible MCLG of 0.6 mg/L. 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor for the possible MCLG decrease under consideration. EPA evaluated the results 

of the occurrence and exposure analyses for toluene to determine whether a revised MCLG/MCL 

would be likely to result in a meaningful opportunity to improve the level of public health 

protection (USEPA, 2009f). Table VI-25 shows the results of the occurrence and exposure 

analysis for the current MCL and the possible MCLG set equal to 0.6 mg/L based on the new 

health effects information. The occurrence and exposure analysis shows that average 

concentrations exceed the current MCL for one system out of 50,451 (0.002 percent) serving 

approximately 500 people (0.0002 percent of 227 million people). Note that these results are 

based on the subset of monitoring data provided in response to the Six-Year Review ICR and do 

not necessarily reflect MCL violations, which are based on annual average concentrations at 

entry points; SDWIS/FED indicates MCL violations for toluene at only one system in one year 

between 1998 and 2005 (USEPA, 2007g). Average concentrations at two of 50,451 systems 

(0.004 percent), serving 800 people (or 0.0004 percent of 227 million people), exceed the 

possible MCLG based on new health effects information (0.06 mg/L). 

Table VI-25. Number and Percent of Systems with Mean Concentrations Exceeding Toluene 

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Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 50,451 systems with toluene data in the SixYear Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (1 mg/L) 1 (0.002%) 1 (0.002%) 1 (0.002%) 

Possible MCLG (0.6 mg/L) 2 (0.004%) 2 (0.004%) 2 (0.004%) 

Corresponding Population Served 

(Percentages based on 226,955,000 people served by the systems with 

toluene data in the Six-Year Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (1 mg/L) 500 (0.0002%) 500 (0.0002%) 500 (0.0002%) 

Possible MCLG (0.6 mg/L) 800 (0.0004%) 800 (0.0004%) 800 (0.0004%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for toluene, EPA does not believe a revision to the NPDWR for toluene 

is appropriate at this time. In making this decision, the Agency considered whether any possible 

revision to the NPDWR for toluene is likely to provide a meaningful opportunity for health risk 

reductions. Taking into consideration the low occurrence of this contaminant, EPA has decided 

that any revision to the NPDWR would be a low priority activity for the Agency, and, thus, is not 

appropriate to revise at this time because of: 

• Competing workload priorities; 

• The administrative costs associated with rulemaking; and Deleted: ¶

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

resulted. 

63. Toxaphene 

a. Background. EPA published the current NPDWR for toxaphene on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.003 mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of toxaphene as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for toxaphene at 

this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency believes that a 

further review of the health effects of toxaphene is not warranted at this time. 

The current MCL for toxaphene is based on a PQL of 0.003 mg/L. For the Six-Year Review, 

the Agency considered whether changes in the analytical feasibility of toxaphene might lead to a 

lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and then analyzed 

more recent PT data to determine if the PQL can be revised (i.e., analytical feasibility). Passing 

rates for PE data available through late 1999 for toxaphene are generally above 90 percent 

around the current PQL of 0.003 mg/L, including three studies with true values below the current 

PQL. All passing rates in the PE data exceeded 80 percent. More recent PT data from late 1999 

through 2004, supplied by a PT provider, show greater than 80 percent passing rates for a 

majority of studies, but there are no studies with true values below the current PQL. There are 

two PT studies with passing rates equal to or below 75 percent, at true values well above the 

current PQL. Despite this variability, most of the laboratory passing rates from PE and PT 

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studies exceeded the 75 percent criterion typically used to derive a PQL, including three with 

true values below the PQL. Therefore, a lowering of the PQL for toxaphene might be possible. 

These results, however, are insufficient to recalculate a revised PQL for toxaphene because not 

enough data points are available below the current PQL to derive a value at the 75 percent 

passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of toxaphene (Methods 505, 508.1, and 525.2). 

While EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

54,529 samples. More than 80 percent of these values are less than or equal the modal MRL:

36,763 (67 percent) equal the modal MRL of 0.001 mg/L and an additional 8,525 (16 percent) 

are lower than 0.001 mg/L. Therefore, EPA selected the modal MRL as the EQL (USEPA, 

2009e). The MDLs of approved methods are 0.0017, 0.001, and 0.00013 mg/L. Applying a 

multiplier of 10 would give a possible PQL range from 0.0013 to 0.017 mg/L, which is above the 

EQL, but includes values below the PQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there may be potential to lower the PQL for toxaphene. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of toxaphene at the EQL of 0.001 mg/L and an additional threshold of 

0.0015 mg/L (USEPA, 2009f). Table VI-26 shows the results of the occurrence and exposure 

analysis for the current MCL and these thresholds. The occurrence and exposure analysis shows 

that average concentrations exceed the current MCL for three to four of 30,387 systems (0.010 to 

Deleted: they indicate any potential to 

revise

Deleted: minimum reporting levels 

Deleted: Of

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Deleted: . An

Deleted: %

Deleted: . Because of the 

preponderance of MRL values of 0.001 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis

Deleted: thresholds 

Deleted: and 0.001 

Deleted: EQLs set equal to 0.0015 

mg/L and 0.001 mg/L

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0.013 percent) serving 23,000 people (or 0.014 percent of 160 million people). Note that these 

results are based on the subset of monitoring data provided in response to the Six-Year Review 

ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates three MCL violations for toxaphene 

between 1998 and 2005 (USEPA, 2007g). Average concentrations at five of 30,387 systems 

(0.016 percent), serving 23,000 people (or 0.015 percent of 160 million people), exceed the EQL 

of 0.001 mg/L. 

Table VI-26. Number and Percent of Systems with Mean Concentrations Exceeding Toxaphene 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 30,387 systems with toxaphene data in the SixRegulatory or Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.003 mg/L) 4 (0.013%) 3 (0.010%) 3 (0.010%) 

1/2 MCL (0.0015 mg/L) 5 (0.016%) 5 (0.016%) 5 (0.016%) 

EQL (0.001 mg/L) not applicable 5 (0.016%) 5 (0.016%) 

Corresponding Population Served 

(Percentages based on 160,012,000 people served by the systems with 

Regulatory or toxaphene data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.003 mg/L) 23,000 (0.014%) 23,000 (0.014%) 23,000 (0.014%) 

1/2 MCL (0.0015 mg/L) 23,000 (0.014%) 23,000 (0.014%) 23,000(0.014%) 

EQL (0.001 mg/L) not applicable 23,000 (0.014%) 23,000(0.014%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.001 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

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Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

toxaphene is appropriate at this time. The occurrence and exposure analysis based on possible 

changes in analytical feasibility indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve public health protection. Taking into consideration the low 

occurrence of this contaminant, EPA has decided that any revision to the NPDWR would be a 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

64. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid) 

a. Background. EPA published the current NPDWR for 2,4,5-TP on January 30, 1991 (56 

FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 0.05 mg/L. 

EPA based the MCLG on a reference dose of 0.008 mg/kg-day and a cancer classification of D, 

not classifiable as to human carcinogenicity. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of 2,4,5-TP, including its potential developmental and 

reproductive toxicity. The literature search did not identify any studies that warrant a review of 

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A review of analytical or treatment feasibility is not necessary for 2,4,5-TP because changes 

to the MCLG are not warranted at this time and the current MCL is set at the MCLG. Since EPA 

did not identify a health or technology basis for revising the 2,4,5-TP NPDWR, the Agency did 

not conduct a detailed occurrence and exposure analysis. 

c. Review Result. EPA’s review shows that there are no data supporting a change to the 

2,4,5-TP NPDWR. As a result, a revision to the NPDWR would not be appropriate at this time. 

65. 1,2,4-Trichlorobenzene 

a. Background. EPA published the current NPDWR for 1,2,4-trichlorobenzene on July 17, 

1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL of 0.07 

mg/L. EPA based the MCLG on a reference dose of 0.01 mg/kg-day and a cancer classification 

of D, not classifiable as to human carcinogenicity. 

b. Technical Reviews. The health effects technical review identified information regarding 

the carcinogenicity of 1,2,4-trichlorobenzene, as well as its noncancer effects, that may indicate 

the need to update the Agency’s health effects assessment (USEPA, 2009b). Two chronic 

carcinogenicity studies of 1,2,4-trichlorobenzene, one in mice (Moore et al., 1994a) and one in 

rats (Moore et al., 1994b), reported liver effects in both mice and rats, as well as kidney effects in 

rats. Mice appeared more sensitive than rats for noncancer effects, and mice also demonstrated a 

significant treatment-related increase in the incidence of hepatocellular carcinomas. No 

increased incidence of any tumor type was observed in rats. These health effect data could have 

implications for the 1,2,4-trichlorobenzene MCLG because they identify effect levels for 

noncancer effects in the liver and kidney, as well as evidence of carcinogenicity in mice. 

In light of this information, EPA considers 1,2,4-trichlorobenzene as a potential candidate for 

a new health effects assessment. The Agency solicits general feedback on its plans to reassess 

health risks resulting from exposure to 1,2,4-trichlorobenzene. The Agency also welcomes any 

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scientific information related to 1,2,4-trichlorobenzene health risks from the public. Because 

EPA considers 1,2,4-trichlorobenzene as a candidate for a new assessment, EPA does not believe 

it is appropriate to consider revisions to the MCLG (as well as the MCL) at this time. 

A review of analytical or treatment feasibility is not necessary for 1,2,4-trichlorobenzene 

because changes to the MCLG are not warranted at this time and the current MCL is set at the 

MCLG. Since EPA did not identify a health or technology basis for revising the 1,2,4-

trichlorobenzene NPDWR, the Agency did not conduct a detailed occurrence and exposure 

analysis. 

c. Review Result. The Agency is considering whether to initiate a new health assessment for 

1,2,4-trichlorobenzene and therefore does not believe a revision to the NPDWR is appropriate at 

this time. 

66. 1,1,1-Trichloroethane 

a. Background. EPA published the current NPDWR for 1,1,1-trichloroethane on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG and an MCL of 0.20 mg/L. 

EPA based the MCLG on a reference dose of 0.035 mg/kg-day and a cancer classification of D, 

not classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2007, the Agency updated its health effects assessment of 1,1,1-

trichloroethane (USEPA, 2007d). The Agency identified a change in this assessment that could 

lead to a change in the MCLG. This assessment considered relevant studies on the toxicity of 

1,1,1-trichloroethane including developmental and reproductive toxicity. The assessment revised 

the RfD from 0.035 mg/kg-day to 2 mg/kg-day and concluded that there is inadequate 

information to assess the carcinogenic potential of 1,1,1-trichloroethane (USEPA, 2007d). 

Based on the new IRIS assessment and RfD of 2 mg/kg-day, and assuming a 70-kg adult body 

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weight and 2 liters water intake per day, the DWEL could be 70 mg/L. An RSC of 20 percent

results in a possible MCLG of 14 mg/L (USEPA, 2009b). 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor if EPA were to raise the MCLG. EPA evaluated the results of the occurrence and 

exposure analyses for 1,1,1-trichloroethane to determine whether a revised MCLG/MCL would 

be likely to result in a meaningful opportunity to achieve cost savings for PWSs and their 

customers while maintaining, or improving, the level of public health protection (USEPA, 

2009f). Although the Agency obtained and evaluated the finished water occurrence data for 

1,1,1-trichloroethane, its usefulness is limited for determining potential cost savings to PWSs 

and their customers because the Agency does not know which systems are treating for this 

contaminant. As an alternative, the Agency evaluated available data on source water quality and 

conducted a qualitative assessment of treatment cost savings. 

Table VI-27 provides summary data for contaminant occurrence based on maximum sample 

values for the locations included in the STORET and NAWQA data. Although the degree to 

which these occurrence rates represent national drinking water source occurrence is uncertain, 

the information shows no to low occurrence at threshold levels of interest. This information 

indicates that any resulting NPDWR change would affect systems that rely on source water at 

none of the NAWQA locations and at less than 0.1 percent of the STORET locations. 

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Table VI-27. Ambient Water Quality Monitoring Occurrence Summary for 1,1,1-Trichloroethane 

Number of Locations (% of locations) 

Maximum Concentration STORET1 NAWQA2

Total 3,429 (100.0%) 5,788 (100.0%) 

Nondetect 2,304 (67.2%) 5,290 (91.4%) 

Detected 1,125 (32.8%) 498 (8.6%) 

Exceeds current MCLG of 0.2 mg/L 5 (0.1%) 0 (0.0%) 

Exceeds alternative value of 14 mg/L 0 (0.0%) 0 (0.0%) 

1. STORET database 2002-2008. 

2. NAWQA database 1992-2008. 

Source: USEPA, 2009c

The BATs and small system compliance technologies for 1,1,1-trichloroethane have other 

beneficial effects, e.g., reduction of other co-occurring contaminants, precursors for DBPs, or 

other common impurities. Therefore, if EPA were to consider a higher level, the Agency does 

not know how many PWSs that are currently treating to comply with the existing MCL of 0.2 

mg/L would be likely to discontinue treatment that is already in place (USEPA, 2009d). Also, 

the Agency does not know to what extent affected systems might be able to reduce costs given 

that capital costs are not recoverable. However, the Agency recognizes that there may be 

opportunities to achieve operational cost savings if these systems are able to re-optimize current 

treatment. 

Given these considerations, the Agency believes that any resulting revision is not likely to 

provide a meaningful opportunity for cost savings. In view of this, any revision would be a low 

priority activity and not appropriate at this time. 

c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for 1,1,1-trichloroethane, EPA does not believe a revision to the 

NPDWR for 1,1,1-trichloroethane is appropriate at this time. In making this decision, the 

Agency considered whether any possible revision to the NPDWR for 1,1,1-trichloroethane is 

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likely to provide a meaningful opportunity for cost savings to public water systems and their 

customers. Taking into consideration the low occurrence of this contaminant in source waters, 

EPA has decided that any revision to the NPDWR would be a low priority activity for the 

Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

67. 1,1,2-Trichloroethane 

a. Background. EPA published the current NPDWR for 1,1,2-trichloroethane on July 17, 

1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of 0.003 mg/L. EPA 

based the MCLG on a reference dose of 0.004 mg/kg-day and a cancer classification of C, 

possible human carcinogen. The NPDWR also established an MCL of 0.005 mg/L, based on 

analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the toxicology of 1,1,2-trichloroethane, including its potential 

developmental and reproductive toxicity. The literature search did not identify any studies that 

warrant a review of the RfD or the cancer classification (USEPA, 2009b). 

The current MCL for 1,1,2-trichloroethane is based on a PQL of 0.005 mg/L. For the SixYear Review, the Agency considered whether changes in the analytical feasibility of 1,1,2-

trichloroethane might lead to a lower MCL. EPA reviewed PE data from the first Six-Year 

Review cycle and then analyzed more recent PT data to determine if the PQL can be revised (i.e., 

analytical feasibility). Passing rates for PE data available through late 1999 for 1,1,2-

trichloroethane are above 95 percent near the current PQL of 0.005 mg/L, but there were no PE

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studies with true values below the current PQL. More recent PT data from late 1999 through 

2004, supplied by a PT provider, show greater than 90 percent passing rates around the current 

PQL, including twelve studies with true values below the PQL. Because most of the laboratory 

passing rates from PT studies – including several with true concentrations below the PQL – 

exceeded the 75 percent criterion typically used to derive a PQL, a lowering of the PQL for 

1,1,2-trichloroethane might be possible. These results, however, are insufficient to recalculate a 

revised PQL for 1,1,2-trichloroethane because not enough data points are available below the 

current PQL to derive a value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether they indicate any 

potential to quantitate at levels as low as the current MCLG: laboratory MRLs in the Six-Year 

Review ICR dataset, and the MDLs for approved methods for the detection of 1,1,2-

trichloroethane (Methods 502.2 and 524.2). While EPA prefers to use laboratory performance 

data to calculate the PQL, the MRL and MDL information can be valuable for this review to 

indicate whether it is possible to quantitate at levels below the current PQL. The Six-Year 

Review ICR dataset contains MRL values for 139,672 samples. Of these, 117,788 (84 percent) 

equal the modal MRL of 0.0005 mg/L. An additional 17,142 (12 percent) are lower than 0.0005 

mg/L. Because more than 80 percent of the of MRLs are equal to or less than the current MCLG 

of 0.003 mg/L, EPA selected that value as the minimum threshold for the occurrence and 

exposure analysis (USEPA, 2009e). The MDLs of approved methods range from 0.00004 to 

0.0001 mg/L. Applying a multiplier of 10 would give a possible PQL range from 0.0004 to 

0.001 mg/L, which is below the current MCLG (USEPA, 2009e).

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for 1,1,2-trichloroethane. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

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Deleted: %

Deleted: . Because the preponderance 

of MRLs are at 0.0005 mg/L, below the 

MCLG for 1,1,2-trichloroethane, EPA 

believes that there is potential to revise 

the PQL to a level that would not limit 

the MCL.

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evaluated the occurrence of 1,1,2-trichloroethane at the current MCLG of 0.003 mg/L (USEPA, 

2009f). Table VI-28 shows the results of the occurrence and exposure analysis for the current 

MCL and the current MCLG of 0.003 mg/L. The occurrence and exposure analysis shows that 

average concentrations do not exceed the current MCL for any system in the analysis. Note that 

these results are based on the subset of monitoring data provided in response to the Six-Year 

Review ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates six MCL violations for 1,1,2-

trichloroethane between 1998 and 2005 (USEPA, 2007g). The average concentration at one out 

of 50,195 systems (0.002 percent), serving approximately 700 people (or 0.0003 percent of 227 

million people), exceeds the current MCLG of 0.003 mg/L. 

Table VI-28. Number and Percent of Systems with Mean Concentrations Exceeding 1,1,2-

Trichloroethane Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 50,195 systems with 1,1,2-trichloroethane data 

in the Six-Year Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Current MCLG (0.003 mg/L) 1 (0.002%) 1 (0.002%) 1 (0.002%) 

Corresponding Population Served 

(Percentages based on 226,852,000 people served by the systems with 

1,1,2-trichloroethane data in the Six-Year Review ICR occurrence 

dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Current MCLG (0.003 mg/L) 700 (0.0003%) 700 (0.0003%) 700 (0.0003%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

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Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

1,1,2-trichloroethane is appropriate at this time. The occurrence and exposure analysis based on 

possible changes in analytical feasibility indicates that any revision to the MCL is unlikely to 

provide a meaningful opportunity to improve public health protection. Taking into consideration 

the low occurrence of this contaminant, EPA has decided that any revision to the NPDWR would 

be a low priority activity for the Agency, and, thus, is not appropriate to revise at this time 

because of: 

• 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. 

68. Trichloroethylene 

a. Background. EPA published the current NPDWR for trichloroethylene on July 8, 1987 

(52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of zero based on a cancer 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.005 mg/L, based on analytical feasibility. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to trichloroethylene. The revised health effects assessment will consider relevant 

studies on the toxicity of trichloroethylene, including its potential developmental and 

reproductive toxicity. The new health effects assessment was not completed by March 1, 2009, 

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the review cutoff date for this notice (USEPA, 2009b). The IRIS Substance Assessment 

Tracking System website (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 

information on the status of the health effects assessment. 

Although a risk assessment is in process for trichloroethylene, the existing MCLG is zero and 

the current MCL of 0.005 mg/L is based on the PQL. Therefore, EPA reviewed whether there is 

potential to revise the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for trichloroethylene are above 

95 percent at the lowest concentrations. However, the true concentrations were all higher than 

the current PQL of 0.005 mg/L. More recent PT data from 1999 to 2004, supplied by a PT 

provider, also show greater than 95 percent passing rates for studies around the current PQL, 

including 6 with true values below the PQL. Because most of the laboratory passing rates from 

PE and PT studies exceeded the 75 percent criterion typically used to derive a PQL, including 

several with true values below the PQL, a lowering of the PQL for trichloroethylene might be 

possible. These results, however, are insufficient to recalculate a revised PQL for 

trichloroethylene because not enough data points are available below the current PQL to derive a 

value at the 75 percent passing rate (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below 

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of trichloroethylene (Methods 502.2, 524.2, 

and 551.1). While EPA prefers to use laboratory performance data to calculate the PQL, the 

MRL and MDL information can be valuable for this review to indicate whether it is possible to 

quantitate at levels below the current PQL. EPA also noted that the State of New Jersey uses a 

PQL of 0.001 mg/L, based on a 1987 study of laboratory performance at low concentrations that 

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Agency evaluated several sources of 

information to determine whether 

changes in analytical feasibility might 

lead to a lower MCL. 

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used criteria similar to those in the PT data (NJDWQI, 1987). The Six-Year Review ICR dataset 

contains MRLs for 138,439 samples. More than 80 percent of these values are less than or equal 

the modal MRL: 118,193 (85 percent) equal the modal MRL of 0.0005 mg/L and an additional 

17,057 (12 percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the 

EQL (USEPA, 2009e). The MDLs of approved methods range are 0.00006, 0.00019, and 

0.000042 mg/L. Applying a multiplier of 10 would give a possible PQL range from 0.00042 to 

0.0019 mg/L, which contains the EQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there is potential to lower the PQL for trichloroethylene. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of trichloroethylene at the EQL of 0.0005 mg/L and additional 

thresholds of 0.0010 and 0.0025 mg/L (USEPA, 2009f). Table VI-29 shows the results of the 

occurrence and exposure analysis for the current MCL and these thresholds. The occurrence and 

exposure analysis shows that average concentrations exceed the current MCL for 25 out of 

50,432 systems (0.050 percent) serving approximately 410,000 people (or 0.181 percent of 227 

million people). Note that these results are based on the subset of monitoring data provided in 

response to the Six-Year Review ICR and do not necessarily reflect MCL violations, which are 

based on annual average concentrations at entry points; SDWIS/FED indicates 191 MCL 

violations for trichloroethylene between 1998 and 2005 (USEPA, 2007g), with annual violations 

ranging from 12 to 31. Average concentrations at 310 to 388 of 50,432 systems (0.615 to 0.769

percent), serving approximately 12.0 to 13.0 million people (or 5.237 to 5.670 percent of 227 

million people), exceed the EQL of 0.0005 mg/L. While these systems are widely distributed 

and located in most of the States providing data, a few large systems (serving 500,000 or more 

people) account for almost half of the exposed population.

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preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis

Deleted: 0005, 0.

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mg/L, 0.001 mg/L, and 0.0005 mg/L.

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Table VI-29. Number and Percent of Systems with Mean Concentrations Exceeding Trichloroethylene 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,432 systems with trichloroethylene data in 

Regulatory or the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 25 (0.050%) 25 (0.050%) 25 (0.050%) 

1/2 MCL (0.0025 mg/L) 70 (0.139%) 68 (0.135%) 64 (0.127%) 

2xEQL (0.001 mg/L) 239 (0.474%) 208 (0.412%) 182 (0.361%) 

EQL (0.0005 mg/L) not applicable 388 (0.769%) 310 (0.615%) 

Corresponding Population Served 

(Percentages based on 226,908,000 people served by the systems with 

Regulatory or trichloroethylene data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.005 mg/L) 410,000 (0.181%) 410,000 (0.181%) 410,000 (0.181%) 

1/2 MCL (0.0025 mg/L) 4,765,000 (2.100%) 4,691,000 (2.067%) 4,598,000 (2.026%) 

2xEQL (0.001 mg/L) 10,367,000 (4.569%) 8,282,000 (3.650%) 7,399,000 (3.261%) 

EQL (0.0005 mg/L) not applicable 12,866,000 (5.670%) 11,884,000 (5.237%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that a revision to the MCL may provide a meaningful 

opportunity to improve the level of public health protection, EPA considered whether treatment 

feasibility is likely to pose any limitations if the MCL were lowered (USEPA, 2009g). The 

current BATs for trichloroethylene are packed tower aeration (PTA) and granular activated 

carbon (GAC). Small system compliance technologies for trichloroethylene include GAC and 

several aeration technologies. EPA’s assessment shows that PTA and GAC are effective enough 

to achieve concentrations as low as the EQL.

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SSCTs are still practical and would not 

pose any limitations if EPA were to 

revise the MCL.

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EPA is not currently able to assess the potential health benefits from a revised MCL for 

trichloroethylene, because the revised health effects assessment is not yet available. However, 

based on its B2 cancer classification (MCLG of zero) and the occurrence and exposure analysis 

at possible MCL values, the Agency believes that a revision to the MCL may provide a 

meaningful opportunity to reduce public health risks. 

c. Review Result. The Agency believes it is appropriate to revise the NPDWR for 

trichloroethylene although a health effects assessment is currently in progress. The existing 

MCLG is zero (based on the current B2 cancer classification) and the current MCL is based on a 

PQL (i.e., analytical feasibility) of 0.005 mg/L. The Agency’s review indicates that analytical 

feasibility could be as much as 10 times lower (~ 0.0005 mg/L) and occurrence at this level 

appears to be relatively widespread. Hence, revisions to the trichloroethylene NPDWR may 

provide a meaningful opportunity for health risk reduction. If the updated health effects 

assessment is completed in time to consider for the regulatory revision of trichloroethylene, the 

Agency will consider this assessment in its evaluation of public health benefits associated with 

any revision. As discussed in Section VII, the Agency solicits public comment and/or relevant 

information that may inform the regulatory revision for trichloroethylene. EPA is also 

requesting that stakeholders provide information/data about the lowest level of quantitation 

(including the analytical method used) that laboratories can reliably and consistently achieve. 

69. Uranium 

a. Background. EPA published the current NPDWR for uranium on December 7, 2000 (65 

FR 76708 (USEPA, 2000c)). The NPDWR established an MCLG of zero based on a cancer 

classification of A, known human carcinogen. As noted in the December 2000 FR, uranium has 

also been identified as a nephrotoxic metal (kidney toxicant) and EPA derived a drinking water 

equivalent level of 20 μg/L as a noncancer health endpoint for kidney toxicity. The NPDWR 

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also established an MCL of 30 μg/L, which is higher than the feasible level of 20 μg/L and the 

level associated with kidney toxicity. In December 2000, EPA exercised its discretionary 

authority to set an MCL at a level higher than feasible (SDWA Section 1412(b)(6)), based on the 

finding that “benefits do not justify the costs at the feasible level (20 μg/L) and that the net 

benefits are maximized at a level (30 μg/L) that is still protective of health with an adequate 

margin of safety” (65 FR 76708 (USEPA, 2000c))27. 

b. Technical Reviews. EPA has initiated a reassessment of the health risks resulting from 

exposure to uranium. The revised health effects assessment will consider relevant studies on the 

toxicity of uranium, including its potential developmental and reproductive toxicity. The new 

health effects assessment was not completed by March 1, 2009, the review cutoff date for this 

notice (USEPA, 2009b). The IRIS Substance Assessment Tracking System website 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment. 

c. Review Result. The Agency does not believe a revision to the NPDWR for uranium is 

appropriate at this time because a reassessment of the health risks resulting from exposure to 

uranium is ongoing (USEPA, 2009b). As noted previously, the uranium MCL is based on the 

SDWA cost benefit provision (Section 1412(b)(6)) and the health effects assessment is important 

for reviewing the benefits associated with the basis of the MCL. 

70. Vinyl chloride 

a. Background. EPA published the current NPDWR for vinyl chloride on July 8, 1987 (52 

FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of zero based on a cancer 

 

27 After the December 7, 2000 final regulation, two trade associations and several municipal water systems 

challenged EPA’s standard for uranium by claiming that the Agency did not use the best available science when 

finalizing the standard. In February of 2003, the DC Circuit Court of Appeals upheld EPA's regulation for uranium 

(as well as combined radiums, and beta particle and photon emitters) 

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classification of A, known human carcinogen. The NPDWR also established an MCL of 0.002 

mg/L, based on analytical feasibility. 

b. Technical Reviews. As part of the Six-Year Review process, EPA conducted a literature 

search for relevant data on the carcinogenicity of vinyl chloride as well as its potential 

developmental and reproductive toxicity. EPA has not identified any new information that 

indicates that it is appropriate to consider revisions to the cancer classification for vinyl chloride 

at this time (USEPA, 2009b). Because the MCLG remains at zero, the Agency believes that a 

further review of the health effects of vinyl chloride is not warranted at this time. 

The current MCL for vinyl chloride is based on a PQL of 0.002 mg/L. For the Six-Year 

Review, the Agency considered whether changes in the analytical feasibility of vinyl chloride 

might lead to a lower MCL. EPA reviewed PE data from the first Six-Year Review cycle and 

then analyzed more recent PT data to determine if the PQL can be revised (i.e., analytical 

feasibility). Passing rates for PE data available through late 1999 for vinyl chloride are generally 

in the 75 to 80 percent range near the current PQL of 0.002 mg/L, but there were no results for 

PE studies with true values below the current PQL. More recent PT data from late 1999 through 

2004, supplied by a PT provider, also show greater than 80 percent passing rates for studies 

around the current PQL, including two studies with true values below the PQL. Despite the 

limited data below the PQL, most of the laboratory passing rates from PE and PT studies – 

including two with true concentrations below the PQL – exceeded the 75 percent criterion 

usually used to derive a PQL. Therefore, a lowering of the PQL for vinyl chloride might be 

possible (USEPA, 2009c). 

EPA evaluated two alternative sources of information to determine whether an EQL below

the current PQL could be estimated: laboratory MRLs in the Six-Year Review ICR dataset, and 

the MDLs for approved methods for the detection of vinyl chloride (Methods 502.2 and 524.2). 

Deleted: WS

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revise

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While EPA prefers to use laboratory performance data to calculate the PQL, the MRL and MDL 

information can be valuable for this review to indicate whether it is possible to quantitate at 

levels below the current PQL. The Six-Year Review ICR dataset contains MRL values for 

139,494 samples. More than 80 percent of these values are less than or equal the modal MRL: 

105,410 (76 percent) equal the modal MRL of 0.0005 mg/L and an additional 25,723 (18

percent) are lower than 0.0005 mg/L. Therefore, EPA selected the modal MRL as the EQL 

(USEPA, 2009e). The MDLs of approved methods range from 0.00017 to 0.00018 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.0017 to 0.0018 mg/L, 

which is higher than the EQL, but below the current PQL (USEPA, 2009e). 

Based on these varied and unrelated approaches/sources of information, EPA believes that 

there may be potential to lower the PQL for vinyl chloride. To determine whether any MCL 

revision is likely to provide a meaningful opportunity to improve public health protection, EPA 

evaluated the occurrence of vinyl chloride at the EQL of 0.0005 mg/L and an additional 

threshold of 0.001 mg/L (USEPA, 2009f). Table VI-30 shows the results of the occurrence and 

exposure analysis for the current MCL and these thresholds. The occurrence and exposure 

analysis shows that average concentrations exceed the current MCL for 8 to 11 of 50,411 

systems (0.016 to 0.022 percent) serving fewer than 14,000 people (or 0.003 to 0.006 percent of 

226 million people). Note that these results are based on the subset of monitoring data provided 

in response to the Six-Year Review ICR and do not necessarily reflect MCL violations, which 

are based on annual average concentrations at entry points; SDWIS/FED indicates 25 MCL 

violations for vinyl chloride between 1998 and 2005 (USEPA, 2007g). Average concentrations 

at 32 to 49 of 50,411 systems (0.063 to 0.097 percent), serving 483,000 to 766,000 people (or 

0.213 to 0.338 percent of 226 million people), exceed the EQL of 0.0005 mg/L. 

Deleted: Of

Deleted: ,

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Deleted: . An

Deleted: %

Deleted: . Because of the 

preponderance of MRL values of 0.0005 

mg/L, EPA selected that value as the 

minimum threshold for the occurrence 

and exposure analysis

Deleted: thresholds of 0.001 and 

0.0005 mg/L

Deleted: EQLs set equal to 0.001 mg/L 

and 0.0005 mg/L.

Deleted: %

Deleted: %

Deleted: %

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Table VI-30. Number and Percent of Systems with Mean Concentrations Exceeding Vinyl Chloride 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the Regulatory 

or Feasibility-based Threshold 

(Percentages based on 50,411 systems with vinyl chloride data in the 

Regulatory or Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.002 mg/L) 11 (0.022%) 10 (0.020%) 8 (0.016%) 

1/2 MCL (0.001 mg/L) 21 (0.042%) 18 (0.037%) 15 (0.030%) 

EQL (0.0005 mg/L) not applicable 49 (0.097%) 32 (0.063%) 

Corresponding Population Served 

(Percentages based on 226,464,000 people served by the systems with 

Regulatory or vinyl chloride data in the Six-Year Review ICR occurrence dataset) 

Feasibility-based 

Threshold 

Nondetect Values = 

MRL1 

Nondetect Values = 

1/2 MRL2 

Nondetect Values= 

03

MCL (0.002 mg/L) 14,000 (0.006%) 12,000 (0.005%) 6,000 (0.003%) 

1/2 MCL (0.001 mg/L) 56,000 (0.025%) 23,000 (0.010%) 18,000 (0.008%) 

EQL (0.0005 mg/L) not applicable 766,000 (0.338%) 483,000 (0.213%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset. 

Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the 

results equal to this value results in an upwardly biased estimate of the number of systems with mean 

concentrations that exceed this value. 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

c. Review Result. Although there are new data that support consideration of a possibly lower 

PQL (and therefore a possibly lower MCL), EPA does not believe a revision to the NPDWR for 

vinyl chloride is appropriate at this time. The occurrence and exposure analysis based on 

possible changes in analytical feasibility indicates that any revision to the MCL is unlikely to 

provide a meaningful opportunity to improve public health protection. Taking into consideration 

the low occurrence of this contaminant, EPA has decided that any revision to the NPDWR would 

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be a low priority activity for the Agency, and, thus, is not appropriate to revise at this time 

because of: 

• 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. 

71. Xylenes (Total) 

a. Background. EPA published the current NPDWR for total xylenes on January 30, 1991 

(56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and an MCL of 10 mg/L. 

EPA based the MCLG on a reference dose of 2 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. 

b. Technical Reviews. In 2003, the Agency updated its health effects assessment of xylenes 

(USEPA, 2003d). The change in this assessment could lead to a change in the MCLG. This 

assessment considered relevant studies on the toxicity of xylenes including developmental and 

reproductive toxicity. The assessment revised the RfD from 2 mg/kg-day to 0.2 mg/kg-day and 

concluded that there is inadequate information to assess the carcinogenic potential of xylenes 

(USEPA, 2003d). Based on the new IRIS assessment and RfD of 0.2 mg/kg-day, and assuming a 

70-kg adult body weight and 2 liters water intake per day, the DWEL could be 7 mg/L. An RSC 

of 20 percent results in a possible MCLG of 1 mg/L. 

Analytical feasibility does not pose any limitations for the current MCL and would not be a 

limiting factor for the possible MCLG decrease under consideration. EPA evaluated the results 

of the occurrence and exposure analyses for total xylenes to determine whether a revised 

MCLG/MCL would be likely to result in a meaningful opportunity to improve the level of public 

health protection (USEPA, 2009f). Table VI-31 shows the results of the occurrence and 

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exposure analysis for the current MCL and the possible MCLG set equal to 1 mg/L based on the 

new health effects information. The occurrence and exposure analysis shows that average 

concentrations do not exceed the current MCL for any system in the analysis. Note that these 

results are based on the subset of monitoring data provided in response to the Six-Year Review 

ICR and do not necessarily reflect MCL violations, which are based on annual average 

concentrations at entry points; SDWIS/FED indicates two MCL violations for xylene between 

1998 and 2005 (USEPA, 2007g). The occurrence and exposure analysis shows that average 

concentrations do not exceed the possible MCLG based on new health effects information (1 

mg/L). 

Table VI-31. Number and Percent of Systems with Mean Concentrations Exceeding Xylene 

Thresholds and Corresponding Estimates of Population Served 

Systems with Mean Concentrations that are Greater than the 

Regulatory or Health-based Threshold 

(Percentages based on 47,698 systems with xylene data in the SixYear Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (10 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (1 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Corresponding Population Served 

(Percentages based on 218,072,000 people served by the systems with 

xylene data in the Six-Year Review ICR occurrence dataset) 

Regulatory or Healthbased Threshold 

Nondetect Values = 

MRL1 

Nondetect Values= 

1/2 MRL2 

Nondetect Values= 

03

MCL (10 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

Possible MCLG (1 mg/L) 0 (0.000%) 0 (0.000%) 0 (0.000%) 

1. Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset 

2. Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR dataset. 

3. Results are based on setting all nondetect results equal to zero. 

Source: USEPA, 2009f. 

Since the occurrence analysis indicates that any revision to the MCL is unlikely to provide a 

meaningful opportunity to improve the level of public health protection, it was not necessary to 

perform any additional reviews on treatment feasibility or economic considerations. 

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c. Review Result. Although there are new data that support consideration of whether to 

revise the MCLG/MCL for total xylenes, EPA does not believe a revision to the NPDWR for 

total xylenes is appropriate at this time. In making this decision, the Agency considered whether 

any possible revision to the NPDWR for total xylenes is likely to provide a meaningful 

opportunity for health risk reductions. Taking into consideration the low occurrence of this 

contaminant, EPA has decided that any revision to the NPDWR would be a low priority activity 

for the Agency, and, thus, is not appropriate to revise at this time because of: 

• 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. 

VII. EPA’s Request for Comments 

A. Request for Comment and/or Information on the Candidates for Revision 

EPA invites commenters to submit any new, relevant peer-reviewed data or information 

pertaining to the four NPDWRs identified in today’s action as candidates for revision (i.e.

acrylamide, epichlorohydrin, tetrechloroethylene and trichloroethylene). This information will 

inform EPA’s evaluation as the Agency moves forward with the regulatory revisions for these 

four NPDWRs. Peer reviewed data are studies/analyses that have been reviewed 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. A peer review is an in-depth assessment of the assumptions, calculations, extrapolations, 

alternate interpretations, methodology, acceptance criteria, and conclusions pertaining to the 

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them (USEPA, 2000d). Relevant data include studies/analyses pertaining to analytical 

feasibility, treatment feasibility, and occurrence/exposure related to the four NPDWRs 

candidates for revision listed in today’s action28. Table VII-1 provides a list of the specific items 

for which EPA is requesting comment and/or information for the four candidates for revision. It 

also provides a cross-reference to the section addressing the issue. 

Table VII-1. Items for Which EPA is Requesting Comment and/or Information 

for the Four Candidates for Revision 

Issue Notice Section 

Any new, relevant peer-reviewed data or information that would 

inform the revision of the NPDWR for acrylamide, including 

information pertaining to extent of use of polyacrylamide in drinking 

water facilities 

Section VI.B.1 

Any new, relevant peer-reviewed data or information that would 

inform the revision of the NPDWR for epichlorohydrin, including 

information pertaining to extent of use of epichlorohydrin-based 

polymers/co-polymers in drinking water facilities 

Section VI.B.36 

Any new, relevant peer-reviewed data or information that would 

inform the revision of the NPDWR for tetrachloroethylene, including 

information/data about the lowest level of quantitation (and analytical 

method used) that laboratories can reliably and consistently achieve 

Section VI.B.60 

Any new, relevant peer-reviewed data or information that would 

inform the revision of the NPDWR for trichloroethylene, including 

information/data about the lowest level of quantitation (and the 

analytical method used) that laboratories can reliably and consistently 

achieve 

Sections VI.B.65 

B. Request for Information/Data on Other Review Topics 

EPA also invites commenters to submit new, relevant information on several other review 

topics referenced in this notice and listed in Table VII-2. 

Table VII-2. Issues for Which EPA is Requesting Public Input and/or Information 

Issue Notice Section 

Location for nitrate and nitrite monitoring Section V.B.6 

Monitoring frequency for ground water systems with low nitrate and 

nitrite concentrations 

Section V.B.6 

 

28 Note that new health effects studies/information for acrylamide, PCE and TCE are being considered as part of 

the IRIS update to these health assessments. 

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Monitoring requirements for non-community water systems Section V.B.6 

Detection limits that serve as triggers to determine compliance 

monitoring frequency for SOCs 

Section V.B.6 

New, relevant health effects information that will help the Agency 

decide whether to initiate a new health effects assessment for 

chromium 

Section VI.B.17 

New, relevant health effects information that will help the Agency 

decide whether to initiate or nominate nitrate and nitrite for a new 

health effects assessment 

Sections VI.B.49 and 

VI.B.50 

New, relevant health effects information that will help the Agency 

decide whether to initiate or nominate selenium for a new health 

effects assessment 

Sections VI.B.56 

New, relevant health effects information that will help the Agency 

decide whether to initiate or nominate 1,2,4-trichlorobenzene for a 

new health effects assessment 

Sections VI.B.65 

C. Requests for Information on the Impacts of Climate Change on Water Quality 

The Agency recognizes that changes in global climate can impact temperature, rainfall 

patterns, and snow and ice cover. Changes in these climate indicators can impact water quantity 

and water quality. In an effort to assess the impacts of climate change on water quality, EPA is 

asking if public water systems and/or States have any information or data that illustrates the 

impact of climate change (e.g., changes in rainfall, drought, temperature, and snow/ice cover) on 

the occurrence of contaminants in drinking water, both in source water and in finished water. 

EPA also requests data on changes in the variability of occurrence and impacts on drinking water 

treatment to address occurrence or variability changes. 

VIII. EPA’s Next Steps 

EPA will consider the public comments and/or any new, relevant, peer-reviewed data 

submitted for the four NPDWRs listed as candidates for revision as the Agency proceeds with 

the regulatory revisions for these regulations. The announcement that the Agency intends to 

revise an NPDWR (pursuant to SDWA section 1412(b)(9)) is not a regulatory decision. Instead, 

it initiates a regulatory process that will involve more detailed analyses of health effects, 

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analytical and treatment feasibility, occurrence, benefits, costs, and other regulatory matters 

relevant to deciding whether an NPDWR should be revised. The Six-Year Review results do not 

obligate the Agency to revise an NPDWR in the event that EPA determines during the regulatory 

process that revisions are no longer appropriate and discontinues further efforts to revise an 

NPDWR. Similarly, the fact that an NPDWR has not been selected for revision means only that 

EPA believes that regulatory changes to a particular NPDWR are not appropriate at this time for 

the reasons given in today’s action; future reviews may identify information that leads to an 

initiation of the revision process. 

IX. References 

ATSDR (Agency for Toxic Substances and Disease Registry). 2007. Toxicological profile for 

benzene. Atlanta, GA: Agency for Toxic Substances and Disease Registry, Public Health 

Service, U.S. Department of Health and Human Services. Available on the Internet at: 

http://www.atsdr.cdc.gov/toxprofiles/tp3.html. 

Cocco, P, G. Broccia, et al. 2003. Nitrate in community water supplies and incidence of nonHodgkin's lymphoma in Sardinia, Italy. Journal of Epidemiology and Community Health. v. 

57, pp. 510-511. 

Coss, A., K.P. Cantor, et al. 2004. Pancreatic cancer and drinking water and dietary sources of 

nitrate and nitrite. American Journal of Epidemiology. v. 159, pp. 693-701. 

de Roos, A.J., M.H. Ward, et al. 2003. Nitrate in public water supplies and the risk of colon and 

rectum cancers. Epidemiology. v. 14, pp. 640-649. 

Duffield-Lillico, A.J., E.H. Slate, et al. 2003. Selenium supplementation and secondary 

prevention of nonmelanoma skin cancer in a randomized trial. Journal of the National 

Cancer Institute. v. 95, pp. 1477-1481. Deleted: ¶

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Gianessi, L. and N. Reigner. 2006. Pesticide Use in U.S. Crop Production: 2002 With 

Comparison to 1992 and 1997 – Fungicides & Herbicides. Washington, D.C.: CropLife 

Foundation. 

Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, J.D. Martin, N. Nakagaki, L.H. 

Nowell, J.C. Scott, P.E. Stackelberg, G.P. Thelin, and David M. Wolock. 2006. The Quality 

of Our Nation's Waters: Pesticides in the Nation's Streams and Ground Water, 1992-2001. 

U.S. Geological Survey Circular 1291. 

Grosse, Y., R. Baan, et al. 2006. Carcinogenicity of nitrate, nitrite, and cyanobacterial peptide 

toxins. The Lancet Oncology. v. 7, pp. 628-629. 

Hawkes, W.C., and N.L. Keim. 2003. Dietary selenium intake modulates thyroid hormone and 

energy metabolism in men. Journal of Nutrition. v. 133, pp. 3443-3448. 

Lan, Q., L. Zhang, et al. 2004. Hematotoxicity in workers exposed to low levels of benzene. 

Science. v. 306, pp. 1774-1776. 

Levine, Audrey D., Brian A. Bolto, and David R. Dixon. 2004. Reactions of Polyelectrolytes 

With Other Water Treatment Chemicals. AwwaRF Report #2509. 

MacKenzie, R.D., R.U. Byerrum, C.F. Decker, et al. 1958. Chronic toxicity studies. II. 

Hexavalent and trivalent chromium administered in drinking water to rats. American 

Medical Association Archives of Industrial Health. v. 18, pp. 232-234. 

Markel, E, C. Nyakas, and S. Ormai. 1989. Nitrate induced changes in sensorimotor 

development and learning behavior in rats. Acta Physiologica Hungarica. v. 74, pp. 69-75. 

Moore, M. 1994a. 104-week dietary carcinogenicity study with 1,2,4-trichlorobenzene in mice. 

Hazleton Washington, Inc. Rockville, Maryland. HWA 2603-102. EPA/OTS Doc #88-

930000429. 

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Moore, M. 1994b. Final report- 104-week dietary carcinogenicity study with 1,2,4-

trichlorobenzene in rats. Hazleton Washington, Inc. Rockville, Maryland. HWA 2603-103. 

OTS0558832. OPPTS-44612. 

Moran, M.J. 2006. Occurrence And Implications Of Selected Chlorinated Solvents In Ground 

Water And Source Water In The United States And In Drinking Water In 12 Northeast And 

Mid-Atlantic States, 1993–2002. U.S. Geological Survey Scientific Investigations Report 

2005–5268. Reston, VA: U.S. Geological Survey. 

Mueller, B.A., S.S. Nielsen, et al. 2004. Household water source and the risk of childhood brain 

tumours: results of the SEARCH International Brain Tumor Study. International Journal of 

Epidemiology. v. 33, pp. 1209-1216. 

Mukhopadhyay, S., D. Ghosh, et al. 2005. Evaluation of possible goitrogenic and anti-thyroidal 

effect of nitrate, a potential environmental pollutant. Indian Journal of Physiology & 

Pharmacology. v. 49, pp. 284-288. 

NAS (National Academy of Sciences). 1995. Nitrate and nitrite in drinking water. Committee 

on Toxicology, Subcommittee on Nitrate and Nitrite in Drinking Water. National Academy 

Press, Washington, DC. 

NAS. 2006. Health Risks from Dioxin and Related Compounds: Evaluation of the EPA 

Reassessment. Committee on EPA's Exposure and Human Health Reassessment of TCDD 

and Related Compounds, National Research Council. 

NCFAP (National Center for Food and Agricultural Policy). 2000. Pesticide Use in U.S. Crop 

Production: 1997. National Summary Report. Washington, D.C.: NCFAP. 

NDWAC (National Drinking Water Advisory Council). 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. 

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NTP (National Toxicology Program). 2007. Draft Report. Toxicology and carcinogenesis 

studies of chromium picolinate monohydrate (CAS # 27882-76-4) in F344 rats and B6C3F1 

mice (feed studies). TR-556. 

NTP. 2008. Technical report on the toxicology and carcinogenesis studies of sodium 

dichromate dihydrate (CAS # 7789-12-0) in F344 rats and B6C3F1 mice (drinking water 

studies). TR-546. July 2008. 

Sedman, R.M., J. Beaumont, et al. 2006. Review of the evidence regarding the carcinogenicity 

of hexavalent chromium in drinking water. Journal of Environmental Science and Health, 

Part C, Environmental Carcinogenesis and Ecotoxicology Reviews. v. 24, pp. 155-182. 

Su, Y.P., J.M. Tang, et al. 2005. Histological and ultrastructural changes induced by selenium 

in early experimental gastric carcinogenesis. World Journal of Gastroenterology. v. 11, pp. 

4457-4460. 

Tajtakova, M., Z. Semanova, et al. 2006. Increased thyroid volume and frequency of thyroid 

disorders signs in schoolchildren from nitrate polluted area. Chemosphere. v. 62, pp. 559-

564. 

USDA (U.S. Department of Agriculture). 2004. Pesticide Data Program Annual Summary 

Calendar Year 2004. Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=PDP2004Summary. 

USDA. 2005. Pesticide Data Program Annual Summary Calendar Year 2005. Available on the 

Internet at: http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5049946. 

USDA. 2006. Pesticide Data Program Annual Summary Calendar Year 2006. Available on the 

Internet at: http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5064786. 

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USEPA (U.S. Environmental Protection Agency). 1975. Interim Primary Drinking water 

Regulations; Radionuclides; Proposed Rule. Federal Register. Vol. 40. No. 158. p. 34324, 

August 14, 1975. 

USEPA. 1976. Interim Primary Drinking Water Regulations; Radionuclides; Final Rule. 

Federal Register. Vol. 41. No. 133. p. 28402, July 9, 1976. 

USEPA. 1985. National Primary Drinking Water Regulations: Volatile Synthetic Organic 

Chemicals; Final Rule and Proposed Rule. Federal Register. Vol. 50, No. 219. p. 46880, 

November 13, 1985. 

USEPA. 1986a. National Primary Drinking Water Regulations; Radionuclides. Federal 

Register. Vol. 51, No. 189. p. 34836, September 30, 1986. 

USEPA 1986b. Guidelines for carcinogen risk assessment. Federal Register Vol. 51, No.185. p. 

33992, September 24, 1986. 

USEPA. 1986c. 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 Water Regulations, Filtration, Disinfection, Turbidity, 

Giardia Lamblia, Viruses, Legionella, Helterotrophic Bacteria Final Rule. Federal Register. 

Vol. 54, No.124. p. 27485, June 29, 1989 

USEPA. 1989b. National Primary and Secondary Drinking Water Regulations: Proposed Rule. 

Federal Register. Vol. 54, No. 97. p. 22062, May 22, 1989. 

USEPA. 1991a. IRIS, Selenium. Oral RfD. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0472.htm#reforal. 

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USEPA. 1991b. Drinking Water; National Primary Drinking Water Regulations; Monitoring for 

Volatile Organic Chemicals; MCLGs and MCLs for Aldicarb, Aldicarb Sulfoxide, Aldicarb 

Sulfone, Pentachlorophenol, and Barium; Final Rule. Federal Register. Vol. 56, No. 126. p. 

30266, July 1, 1991. 

USEPA. 1991c. 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. 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. 1993a. IRIS, Selenium. Cancer assessment. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0472.htm#carc. 

USEPA. 1993b. Reregistration Eligibility Decision (RED): Glyphosate. EPA 738-R-93-014. 

September. 

USEPA. 1995a. Reregistration Eligibility Decision (RED)--Diquat Dibromide. EPA Report 

738-R-95-016. Washington, D.C.: Office of Prevention, Pesticides and Toxic Substances. 

July 1995. Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/0288.pdf. 

USEPA. 1995b. Reregistration Eligibility Decision (RED)--Picloram. EPA Report 738-R95-

019. Washington, DC: Office of Prevention, Pesticides, and Toxic Substances. August 

1995. Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/0096.pdf. 

USEPA. 1998a. Reregistration Eligibility Decision: Alachlor. Office of Prevention, Pesticides, 

and Toxic Substances. EPA 738-R-98-020. December. 

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USEPA. 1998b. Small System Compliance Technology List for the Non-Microbial 

Contaminants Regulated before 1996. Office of Water. EPA 815-R-98-002. September. 

USEPA 1998c. IRIS: Beryllium and Compounds. Available on the Internet at: 

http://www.epa.gov/iris/subst/0012.htm. 

USEPA. 1998d. Toxicological review of Hexavalent Chromium in support of summary 

information on the Integrated Risk Information System (IRIS). Washington, DC: Office of 

Research and Development, National Center for Environmental Assessment. August 1998. 

Available on the Internet at: http://www.epa.gov/ncea/iris/toxreviews/0144-tr.pdf. 

USEPA. 1998e. Toxicological review of Trivalent Chromium in support of summary 

information on the Integrated Risk Information System (IRIS). Washington, DC: Office of 

Research and Development, National Center for Environmental Assessment. August 1998. 

Available on the Internet at: http://www.epa.gov/ncea/iris/toxreviews/0028-tr.pdf. 

USEPA. 2000a. Interim reregistration eligibility decision (IRED)--Oxamyl. EPA Report 738-

R-00-015. Washington, DC: Office of Prevention, Pesticides and Toxic Substances. October 

2000. Available on the Internet at: 

http://www.epa.gov/pesticides/reregistration/REDs/0253ired.pdf. 

USEPA. 2000b. IRIS, Benzene. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0276.htm. 

USEPA. 2000c. National Primary Drinking Water Regulations; Radionuclides; Final Rule. 

Federal Register. Vol. 65, No. 236. p. 76707, December 7, 2000. 

USEPA. 2000d. Science Policy Council Handbook: Peer Review, 2nd Edition. EPA Report 

100-B-00-001. Washington, DC: Office of Science Policy, Office of Research and 

Development. December 2000. Available on the Internet at: 

http://www.epa.gov/OSA/spc/pdfs/prhandbk.pdf. 

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USEPA. 2001a. HED Toxicology Chapter for Diquat Dibromide. Washington, DC: Office of 

Prevention, Pesticides and Toxic Substances. 

USEPA. 2001b. IRIS, Hexachlorocyclopentadiene. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0059.htm. 

USEPA. 2001c. 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. 2001d. Public Health and Environmental Radiation Protection Standards for Yucca 

Mountain, NV; Final Rule. Federal Register. Volume 66, Number 114. p. 32073, June 13, 

2001. 

USEPA. 2002a. Glyphosate in/on pasture and rangeland grasses, Roundup Ready® wheat, and 

non-grass animal feeds. Health Effects Division (HED) Risk Assessment. PP#s 0F06130, 

0F06195, and 0F06273. Barcode D280831. PC Codes 103601 & 417300. Case 292955. 

Submission S579658. Washington, DC: Office of Prevention, Pesticides, and Toxic 

Substances. 

USEPA. 2002b. IRIS, 1,1-Dichloroethylene. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0039.htm. 

USEPA. 2002c. 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. 2002d. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment 

Progress and Risk Management Decision (TRED): Diquat Dibromide. Washington, D.C.: 

Office of Prevention, Pesticides and Toxic Substances. April 2002. Available on the 

Internet at: http://www.epa.gov/oppsrrd1/REDs/diquat_tred.pdf. 

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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. March 2003. 

USEPA. 2003b. EPA Protocol for Review of Existing National Primary Drinking Water 

Regulations. EPA Report 815-R-03-002. Washington, DC: Office of Ground Water and 

Drinking Water. June 2003. Available on the Internet at: 

http://www.epa.gov/safewater/standard/review/pdfs/support_6yr_protocal_final.pdf. 

USEPA. 2003c. Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-pDioxin (TCDD) and Related Compounds. Preliminary Review Draft. National Center for 

Environmental Assessment, Research and Development. 

USEPA. 2003d. IRIS, Xylenes. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0270.htm. 

USEPA. 2003e. National Primary Drinking Water Regulations; Announcement of Completion 

of EPA’s Review of Existing Drinking Water Standards; Notice. Federal Register. Vol. 68, 

No. 138. p. 42908, July 18, 2003. 

USEPA. 2004a. IRIS, 1,2-Dibromoethane. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0361.htm. 

USEPA. 2004b. National Primary Drinking Water Regulations: Minor Corrections and 

Clarification to Drinking Water Regulations; National Primary Drinking Water Regulations 

for Lead and Copper. Federal Register. Volume 69, Number 124. p. 38850, June 29, 2004. 

USEPA. 2004c. Reregistration Eligibility Decision (RED)--Methoxychlor. EPA Report 738-R04-010. Washington, DC: Office of Prevention, Pesticides, and Toxic Substances. June 

2004. Available on the Internet at: 

http://www.epa.gov/oppsrrd1/REDs/methoxychlor_red.htm. 

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USEPA. 2005a. IRIS, Barium. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0010.htm. 

USEPA. 2005b. IRIS, Toluene. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0118.htm. 

USEPA. 2005c. Reregistration Eligibility Decision (RED)--2,4-D. EPA Report 738-R-05-002. 

Office of Prevention, Pesticides, and Toxic Substances. June 2005. Available on the Internet 

at: http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf. 

USEPA. 2005d. Reregistration Eligibility Decision (RED) for Endothall. EPA Report 738-R05-008. Office of Prevention, Pesticides and Toxic Substances. September 2005. Available 

on the Internet at: http://www.epa.gov/oppsrrd1/reregistration/REDs/endothall_red.pdf. 

USEPA. 2006a. Acetochlor/Alachlor: Cumulative Risk Assessment for the Chloroacetanilides. 

Washington, DC: Office of Pesticide Programs. March 8, 2006. Available on the Internet at: 

http://www.epa.gov/oppsrrd1/cumulative/chloro_cumulative_risk.pdf. 

USEPA. 2006b. Addendum to the 2002 Lindane Reregistration Eligibility Decision (RED). 

EPA Report 738-R-06-028. Washington, DC: Office of Prevention, Pesticides, and Toxic 

Substances. July 2006. Available on the Internet at: 

http://www.epa.gov/oppsrrd1/REDs/lindane_red_addendum.pdf. 

USEPA. 2006c. Finalization of Atrazine IRED, and Completion of Tolerance Reassessment and 

Reregistration Eligibility Process. Washington, DC: Office of Prevention, Pesticides, and 

Toxic Substances. April 2006. Available on the Internet at: 

http://www.epa.gov/oppsrrd1/REDs/atrazine_combined_docs.pdf. 

USEPA. 2006d. Interim Reregistration Eligibility Decision (IRED)--Carbofuran. EPA Report 

738-R-06-031. Office of Prevention, Pesticides, and Toxic Substances. August 2006. 

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Available on the Internet at: 

http://www.epa.gov/oppsrrd1/reregistration/REDs/carbofuran_ired.pdf. 

USEPA. 2006e. Lindane; Cancellation Order. Federal Register. Vol. 71, No. 239. p. 74905, 

December 13, 2006. 

USEPA. 2006f. National Primary Drinking Water Regulations: Ground Water Rule; Final Rule. 

Federal Register. Vol. 71, No. 216. p. 65574, November 8, 2006. 

USEPA. 2006g. National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface 

Water Treatment Rule; Final Rule. Federal Register. Vol. 71, No. 3. p. 654, January 5, 

2006. 

USEPA. 2006h. National Primary Drinking Water Regulations: Stage 2 Disinfectants and 

Disinfection Byproducts Rule; Final Rule. Federal Register. Vol. 71, No. 2. p. 388, January 

4, 2006. 

USEPA. 2006i. Reregistration Eligibility Decision (RED)--Simazine. EPA Report 738-R-06-

008. Washington, DC: Office of Prevention, Pesticides, and Toxic Substances. April 2006. 

Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/simazine_red.pdf. 

USEPA. 2007a. Advisory on EPA’s Assessments of Carcinogenic Effects of Organic and 

Inorganic Arsenic: A Report of the US EPA Science Advisory Board (SAB). EPA-SAB-07-

008. June 2007. Available on the Internet at: 

http://yosemite.epa.gov/sab/sabproduct.nsf/EADABBF40DED2A0885257308006741EF/$Fil

e/sab-07-008.pdf. 

USEPA. 2007b. Draft Toxicological Review of Acrylamide: In Support of Summary 

Information on the Integrated Risk Information System (IRIS). Federal Register. Vol. 72, 

No. 248. p. 73813, December 28, 2007. 

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USEPA. 2007c. Integrated Risk Information System (IRIS); Announcement of 2008 Program; 

Notice. Federal Register. Vol. 72, No. 245. p. 72715, December 21, 2007. 

USEPA. 2007d. IRIS, 1,1,1-Trichloroethane. Available on the Internet at: 

http://www.epa.gov/ncea/iris/subst/0197.htm. 

USEPA. 2007e. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems; Revisions; Final Rule. Federal Register. Vol. 72, No, 2. p. 367, January 4, 2007. 

USEPA. 2007f. National Primary Drinking Water Regulations for Lead and Copper: ShortTerm Regulatory Revisions and Clarifications; Final Rule. Federal Register. Vol. 72, No. 

195. p. 57782, October 10, 2007. 

USEPA. 2007g. Safe Drinking Water Information System/Federal version (SDWIS/FED) 

FY2006 Inventory Data. Available online at 

http://www.epa.gov/ogwdw000/databases/pivottables.html. 

USEPA. 2008a. Carbofuran; Proposed Tolerance Revocations; Proposed Rule. Federal 

Register. Vol. 73, No. 87. p. 44864, July 31, 2008. 

USEPA. 2009a. EPA Protocol for the Second Review of Existing National Primary Drinking 

Water Regulations (Updated). EPA Report 815-B-09-002. October 2009. 

USEPA. 2009b. Six-Year Review 2– Health Effects Assessment - Summary Report. EPA 

Report 822-R-09-006. October 2009. 

USEPA. 2009c. Analytical Feasibility Support Document for the Second Six-Year Review of 

Existing National Primary Drinking Water Regulations. EPA Report 815-B-09-003. October

2009. 

Deleted: USEPA. 2008b. Drinking 

Water Contaminant Candidate List 3—

Draft; Notice. Federal Register. Vol. 73, 

No. 35. p. 9628, February 21, 2008.

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USEPA. 2009d. Occurrence Analysis for Potential Source Waters for the Second Six-Year 

Review of National Primary Drinking Water Regulations. EPA Report 815-B-09-004. 

October 2009. 

USEPA. 2009e. Development of Estimated Quantitation Levels for the Second Six-Year 

Review of National Primary Drinking Water Regulations. EPA Report 815-B-09-005. 

October 2009. 

USEPA. 2009f. Analysis of Occurrence Data from the Second Six-Year Review of Existing 

National Primary Drinking Water Regulations. EPA Report 815-B-09-006. October 2009. 

USEPA. 2009g. Water Treatment Technology Feasibility Support Document for Chemical 

Contaminants for the Second Six-Year Review of National Primary Drinking Water 

Regulations. EPA Report 815-B-09-007. October 2009. 

USEPA. 2009h. Consideration of Other Regulatory Revisions in Support of the Second SixYear Review of the National Primary Drinking Water Regulations. EPA Report 815-B-09-

008. October 2009. 

USEPA. 2009i. Carbofuran; Final Tolerance Revocations; Final Rule. Federal Register. Vol.74, 

No. 93. p. 23046, May 15, 2009. 

USEPA. 2009j. Carbofuran; Product Cancellation Order; Notice. Federal Register. Vol. 74, No. 

51. p. 11551, March 18, 2009. 

USEPA. 2009k. Toxicological Review of Thallium and Compounds. In Support of Summary 

Information on the Integrated Risk Information System (IRIS). September 30, 2009. 

Available at http://www.epa.gov/ncea/iris/toxreviews/1012-tr.pdf. 

USEPA. 2009l. Drinking Water Contaminant Candidate List 3— Notice. Federal Register. 

Vol. 74, No. 194. p. 51850, October 8, 2009.

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USGS (U.S. Geological Survey). No date. Pesticide National Synthesis Project: 2002 Pesticide 

Use Map – Diquat. Available on the Internet at: 

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m1950. 

Accessed March 2008. 

Volkmer, B.G., B. Ernst, et al. 2005. Influence of nitrate levels in drinking water on urological 

malignancies: a community-based cohort study. BJU International. v. 95, pp. 972-976. 

Vorhees, C.V., R.E. Butcher, R.L. Bnunner, and V. Wootlen. 1984. Developmental toxicity and 

psychotoxicity of sodium nitrite in rats. Food and Chemical Toxicology. v. 22, p. 116. 

Ward, M.H., E.F. Heineman, et al. 2005a. Drinking water and dietary sources of nitrate and 

nitrite and risk of glioma. Journal of Occupational and Environmental Medicine. v. 47, pp. 

1260-1267. 

Ward, M.H., J.R. Cerhan, et al. 2006. Risk of non-Hodgkin lymphoma and nitrate and nitrite 

from drinking water and diet. Epidemiology. v. 17, pp. 375-382. 

Ward, M.H., K.P. Cantor, et al. 2003. Nitrate in public water supplies and risk of bladder 

cancer. Epidemiology. v. 14, pp. 183-190. 

Ward, M.H., T.M. de Kok, et al. 2005b. Workgroup report: Drinking-water nitrate and health--

recent findings and research needs. Environmental Health Perspectives. v. 113, pp. 1607-

1614. 

Wolff, J. and J.R. Maury. 1963. Thyroidal iodide transport. IV. The role of ion size. 

Biochimica et Biophysica Acta. v. 69, pp. 58-67. 

Yang, C.Y., D.C. Wu, et al. 2007. Nitrate in drinking water and risk of death from colon cancer 

in Taiwan. Environment International. v. 33, pp. 649-653. 

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Yang, G., et al. 1989a. Studies of safe maximal daily selenium intake in a seleniferous area in 

China. Part I. Journal of Trace Elements and Electrolytes in Health and Disease. v. 3, pp. 

77-87. 

Yang, G.Q., et al. 1989b. Studies of safe maximal daily selenium intake in a seleniferous area in 

China. Part II. Journal of Trace Elements and Electrolytes in Health and Disease. v. 3, pp. 

123-130. 

Zaki, A., A. Ait Chaoui, et al. 2004. Impact of nitrate intake in drinking water on the thyroid 

gland activity in male rat. Toxicology Letters. v. 147, pp. 27-33. 

Zeegers, M.P., R.F. Selen, et al. 2006. Nitrate intake does not influence bladder cancer risk: the 

Netherlands cohort study. Environmental Health Perspectives. v. 114, pp. 1527-1531. 

Zhang, J. and X. Li. 1987. Chromium pollution of soil and water in Jinzhou. Journal of Chinese 

Preventive Medicine. v. 21, pp. 262-264.

Dated: [INSERT SIGNATURE DATE] 

Lisa P. Jackson 

Administrator. 

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Do not cite or distribute.

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Formatted: English (U.S.)

Formatted: English (U.S.)