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-OWMay 2009 Draft EPA document. Do not cite or distribute. 1
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, 

May 2009 Draft EPA document. Do not cite or distribute. 2
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 

May 2009 Draft EPA document. Do not cite or distribute. 3
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

May 2009 Draft EPA document. Do not cite or distribute. 4
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 

May 2009 Draft EPA document. Do not cite or distribute. 5
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 

May 2009 Draft EPA document. Do not cite or distribute. 6
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 

May 2009 Draft EPA document. Do not cite or distribute. 7
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? 21 

58

1. Initial Review.....................................................................................................................21 

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

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

4. Occurrence and Exposure Analysis...................................................................................35 

5. Treatment Feasibility .........................................................................................................41 

6. Other Regulatory Revisions...............................................................................................42 

C. How Did EPA Factor Children’s Health Concerns Into the Review?...............................46 

VI. Results of EPA’s Review of NPDWRs.............................................................................47 

A. What are the Review Result Categories?...........................................................................47 

1. No Action at this Time and the NPDWR is Still Appropriate...........................................47 

2. Candidate for Revision. .....................................................................................................48 

B. What Are the Details of EPA’s Review of Each NPDWR? .............................................50 

1. Acrylamide...........................................................................................................................50 

2. Alachlor................................................................................................................................52 

3. Alpha Particle Emitters........................................................................................................56 

4. Antimony ............................................................................................................................. 

5. Arsenic .................................................................................................................................58 

May 2009 Draft EPA document. Do not cite or distribute. 8
6. Asbestos............................................................................................................................... 59

84

114

115

121

126

7. Atrazine................................................................................................................................60 

8. Barium..................................................................................................................................61 

9. Benzene................................................................................................................................64 

10. Benzo(a)pyrene..................................................................................................................68 

11. Beryllium ...........................................................................................................................70 

12. Beta Particle and Photon Emitters .....................................................................................71 

13. Cadmium............................................................................................................................73 

14. Carbofuran .........................................................................................................................73 

15. Carbon Tetrachloride .........................................................................................................75 

16. Chlordane...........................................................................................................................79 

17. Chromium ..........................................................................................................................82 

18. Cyanide .............................................................................................................................. 

19. 2,4-D (2,4-Dichlorophenoxyacetic acid) ...........................................................................85 

20. Dalapon (2,2-Dichloropropionic Acid)..............................................................................87 

21. Di(2-ethylhexyl)adipate (DEHA) ......................................................................................88 

22. Di(2-ethylhexyl)phthalate (DEHP)....................................................................................89 

23. 1,2-Dibromo-3-chloropropane (DBCP).............................................................................90 

24. 1,2-Dichlorobenzene (o-Dichlorobenzene)........................................................................94 

25. 1,4-Dichlorobenzene (p-Dichlorobenzene)........................................................................94 

26. 1,2-Dichloroethane (Ethylene Dichloride).........................................................................95 

27. 1,1-Dichloroethylene .........................................................................................................99 

28. cis-1,2-Dichloroethylene..................................................................................................102 

29. trans-1,2-Dichloroethylene ..............................................................................................103 

30. Dichloromethane (Methylene Chloride)..........................................................................103 

31. 1,2-Dichloropropane ........................................................................................................110 

32. Dinoseb ............................................................................................................................ 

33. Diquat............................................................................................................................... 

34. Endothall..........................................................................................................................118 

35. Endrin............................................................................................................................... 

36. Epichlorohydrin ...............................................................................................................122 

37. Ethylbenzene....................................................................................................................124 

38. Ethylene Dibromide (EDB; 1,2-Dibromoethane)............................................................125 

39. Fluoride............................................................................................................................ 

40. Glyphosate .......................................................................................................................129 

41. Heptachlor........................................................................................................................131 

42. Heptachlor Epoxide .........................................................................................................135 

43. Hexachlorobenzene..........................................................................................................138 

44. Hexachlorocyclopentadiene.............................................................................................142 

45. Lindane (gamma-Hexachlorocyclohexane).....................................................................145 

46. Mercury (Inorganic).........................................................................................................148 

47. Methoxychlor...................................................................................................................149 

48. Monochlorobenzene (Chlorobenzene).............................................................................150 

49. Nitrate (as N)....................................................................................................................150 

50. Nitrite (as N) ....................................................................................................................152 

51. Oxamyl (Vydate) .............................................................................................................154 

May 2009 Draft EPA document. Do not cite or distribute. 9
52. Pentachlorophenol............................................................................................................158 

53. Picloram...........................................................................................................................160 

54. Polychlorinated Biphenyls (PCBs) ..................................................................................163 

55. Combined Radiums (226 and 228) ..................................................................................164 

56. Selenium ..........................................................................................................................166 

57. Simazine...........................................................................................................................167 

58. Styrene ............................................................................................................................. 168

176

59. 2,3,7,8-TCDD (Dioxin)....................................................................................................169 

60. Tetrachloroethylene .........................................................................................................170 

61. Thallium...........................................................................................................................174 

62. Toluene ............................................................................................................................ 

63. Toxaphene........................................................................................................................179 

64. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid) .............................................182 

65. 1,2,4-Trichlorobenzene....................................................................................................183 

66. 1,1,1-Trichloroethane.......................................................................................................184 

67. 1,1,2-Trichloroethane.......................................................................................................186 

68. Trichloroethylene.............................................................................................................190 

69. Uranium ...........................................................................................................................194 

70. Vinyl chloride ..................................................................................................................195 

71. Xylenes (Total) ................................................................................................................199 

VII. EPA’s Request for Comments.......................................................................................201 

A. Request for Comment and/or Information on the Candidates for Revision ....................201 

B. Request for Information/Data on Other Review Topics..................................................202 

C. Requests for Information on the Impacts of Climate Change on Water Quality.............203 

VIII. EPA’s Next Steps.........................................................................................................203 

IX. References.......................................................................................................................204 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 10
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. 

May 2009 Draft EPA document. Do not cite or distribute. 11
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 

May 2009 Draft EPA document. Do not cite or distribute. 12
(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 

May 2009 Draft EPA document. Do not cite or distribute. 13
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)). 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 14
Table IV-1. Contaminants with NPDWRs Included in Six-Year Review 2 

Contaminants 

MCLG 

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

MCLG MCL 

(mg/L)1 (mg/L)1

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). 

May 2009 Draft EPA document. Do not cite or distribute. 15
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. 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 

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

contaminants.1

 

 

1

 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. 

May 2009 Draft EPA document. Do not cite or distribute. 16
• 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 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). 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 

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

justified by new public health risk information. 

May 2009 Draft EPA document. Do not cite or distribute. 17
• 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: 

• 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., especially 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. 

May 2009 Draft EPA document. Do not cite or distribute. 18
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 

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

May 2009 Draft EPA document. Do not cite or distribute. 19
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 

(Updated)” (USEPA, 2009a). 

May 2009 Draft EPA document. Do not cite or distribute. 20
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. 

May 2009 Draft EPA document. Do not cite or distribute. 21
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 

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 draft third Drinking Water Contaminant Candidate List or CCL3 (73 FR 9628, February 21, 2008 (USEPA, 

2008b) in order to capture health and treatment information that may not be addressed by the current regulations. 

May 2009 Draft EPA document. Do not cite or distribute. 22
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. 

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 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, 

May 2009 Draft EPA document. Do not cite or distribute. 23
including developmental and reproductive toxicity. This category has three subsets of 

contaminants. 

• The first subset contains 14 contaminants with MCLGs equal to zero and either 

MCLs that are limited by analytical feasibility or TT standards. For this subset, 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 the first subset is a refinement of the protocol. During Six-Year 

Review 1, EPA took no further action on any contaminants with ongoing health 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. 

• The second subset contains two contaminants, arsenic and uranium. The MCLG for 

each of these contaminants is equal to zero and the MCL was established 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. 

• The third subset contains 14 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. The exception is thallium, which has an MCL limited by analytical feasibility. 

May 2009 Draft EPA document. Do not cite or distribute. 24
Consequently, EPA conducted further review of the potential for revisions to the MCL 

for thallium in the event of possible changes in analytical feasibility. 

• 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 subcategories of contaminants with 

new health effects assessments: four with results indicating potential for lower MCLG, five 

with results indicating potential for higher MCLG, two with results indicating the MCLG 

remains appropriate, 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. 

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

not have a new or ongoing health effects assessment 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. This category has four major subsets of 

contaminants. 

• The first subset contains contaminants that had a health effects assessment completed 

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

possible higher MCLGs, and three with no potential to revise their MCLGs. During SixYear 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 

May 2009 Draft EPA document. Do not cite or distribute. 25
Review 2, EPA is assessing whether there is new information that affects this 

determination. 

• The second subset 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 assessment. 

• The third subset of seven contaminants 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. 

• The fourth subset contains seven contaminants with non-zero MCLGs, for which 

EPA conducted a full literature search, including developmental and reproductive 

toxicity. 

May 2009 Draft EPA document. Do not cite or distribute. 26
Table V-2. Summary of the Outcome of the Six-Year Health Effects Review 

Health Effects Review Category Contaminants 

MCLG = 0 

and MCL based on Analytical Feasibility or 

standard is a TT 

14 Total - acrylamide; alpha particles; 

benzo(a)pyrene; beta particles; carbon tetrachloride; 

DEHP; 1,2-dichloroethane; dichloromethane; 

pentachlorophenol; PCBs; radium; dioxin; 

tetrachloroethylene; trichloroethylene 

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 MCLG > 0 

14 Total – antimony; asbestos; beryllium; cadmium; 

cyanide; DEHA; 1,2-dichlorobenzene; 1,4-

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

dichloroethylene; ethylbenzene; fluoride; styrene; 

thallium1

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) 

New health risk information could raise 

MCLG/MCL 

5 Total – alachlor (20062); barium (2005); diquat 

(20023); glyphosate (20024); 1,1,1-trichloroethane 

(2007, new data) 

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

Health 

Effects 

Assessment 

Completed 

Since SixYear 

Review 1 Awaiting the outcome of emerging health 

studies or cancellation decision 3 Total - atrazine5; simazine5; carbofuran6

New health risk information 

could lower MCLG/MCL 

2 Total – hexachlorocyclopentadiene (2001); oxamyl 

(2000) 

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 

No new health risk 

information 

3 Total – chlordane (1998), inorganic mercury 

(1997), vinyl chloride (2000) 

New Information Identified; Potential 

Nominee for a New Assessment 

5 Total – total chromium (hexavalent); nitrate; nitrite; 

selenium; 1,2,4-trichlorobenzene 

MCLG = 0 

No new health risk information 

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

epichlorohydrin; heptachlor; heptachlor epoxide; 

hexachlorobenzene; toxaphene 

Literature 

Review 

Only 

MCLG > 0 

No new health risk information 

7 Total – dalapon; dinoseb; endrin; methoxychlor; 

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

1. 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. 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). 

3. 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). 

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

differences only in RfD rounding. 

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

period, there are emerging health effects studies that the Agency is reviewing. 

6. 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. 

May 2009 Draft EPA document. Do not cite or distribute. 27
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 under this 

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 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 carcinogens 

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 possible changes in analytical feasibility and provides the results of the 

analytical feasibility analyses. The purpose of these analyses is to determine 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)). 

May 2009 Draft EPA document. Do not cite or distribute. 28
The review protocol for Six-Year Review 1 utilized data from WS 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 through late 1999 and 

laboratory passing rate PT data from late 1999 through 2004. One PT 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 window (see 54 FR 22062 at 22100, May 22, 1989 

(USEPA, 1989b)). For Six-Year Review 2, EPA did not have sufficient PT data to actually 

recalculate any PQL. Instead, EPA used the PT passing rate results (i.e., the percent of 

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

indicate potential for PQL revision. 

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 relied on 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 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. 

May 2009 Draft EPA document. Do not cite or distribute. 29
An MRL is the lowest level of a contaminant concentration that a laboratory can reliably 

achieve within specified limits of precision and accuracy under routine laboratory operating 

conditions using a given method (USEPA, 2009c). EPA evaluated the distribution of MRL 

values for each contaminant to identify the mode or value occurring most frequently for that 

contaminant (modal MRL). The use of modal MRLs is a refinement of the protocol, necessitated 

by limited availability of PT (formerly 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). 

The second source of information that EPA reviewed to evaluate possible changes in 

analytical feasibility (or the PQL) was the MDL approach. 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 

and/or ranges from individual analytical methods developed and approved by EPA for use on 

drinking water. Based on these MDL values, EPA used an MDL multiplier to estimate where the 

possible lower limit of quantitation may currently lie. The multiplier is 10 for most contaminants 

except dioxin, which has a multiplier of 5 in its original PQL. 

EPA also considered both the modal MRL and MDL-based estimates when it derived 

estimated quantitation levels (EQLs) (USEPA, 2009e) for the occurrence analysis (see section 

V.B.4) to help the Agency determine if there may be a meaningful opportunity to improve public 

health protection. The possible lower bound PQL value was derived using the alternative 

sources of information (MRL and MDL) is referred to as EQL. It should be noted, however, that 

May 2009 Draft EPA document. Do not cite or distribute. 30
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 three categories of NPDWRs. Table V-3

shows the three 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 is inconclusive. 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). 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 31
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 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.

• Contaminants with no ongoing health effects assessment and existing MCLs are based on 

analytical feasibility and greater than their MCLGs. For the 11 contaminants in this 

category, EPA evaluated available PT and WS 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 contaminants (benzene2, 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. 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-3. For the final contaminant, ethylene 

dibromide (EDB)3

, none of the data sources indicate potential to revise the PQL. 

 

2

 Although the new health effects assessment completed for benzene during Six-Year Review 2 indicated no 

potential to revise its MCLG, its MCL is still limited by its PQL and, therefore, it is included in this group of 

contaminants. 3

 Although the new health effects assessment completed for EDB during Six-Year Review 2 indicated no 

potential to revise its MCLG, its MCL is still limited by its PQL and, therefore, it is included in this group of 

contaminants. 

May 2009 Draft EPA document. Do not cite or distribute. 32
Table V-3 lists the type of data that indicate potential for a PQL reduction. The list includes 

“PT” when the PQL reassessment based on PT 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-3 shows the result “Data do not support PQL reduction.” The 

contaminant specific discussions in section VI of today’s action provide the results of the 

analytical feasibility review for all the contaminants in Table V-3. 

May 2009 Draft EPA document. Do not cite or distribute. 33
Table V-3. NPDWRs Included in the Analytical Feasibility 

Reassessment and the Result of that Assessment 

Contaminant Current PQL Analytical Feasibility Reassessment Result1

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 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) 

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 

May 2009 Draft EPA document. Do not cite or distribute. 34
4. Occurrence and Exposure Analysis 

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

voluntarily submit their SDWA compliance monitoring data. This request was for the submission o

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 regulate

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 

an Information Collection Request. Through this process EPA requested that all States and primacy entities 

f 

d 

quality dependable contaminant occurrence database consisting of data from 45 States (see map in 

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).

May 2009 Draft EPA document. Do not cite or distribute. 35
Figure V-2. States with Compliance Monitoring Data Included in the Six-Year Review 2

The contaminant occurrence data from the 47 States and entities 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 chemicals, 7 

radiological contaminants, and 3 microbiological4 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. 

 

4

 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. 

May 2009 Draft EPA document. Do not cite or distribute. 36
EPA used a two-stage analytical approach to analyze these data and characterize the national 

occurrence of contaminants.5

 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.6 A typical stage 1 occurrence 

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

detection of a specific contaminant, or with at least one analytical detection with a concentration 

greater than a concentration threshold of interest, i.e., a possible MCLG or EQL. This approach 

generates a conservative (i.e., upwardly biased) estimate of the number of potential systems 

having contaminant occurrence at levels of interest. 

The stage 2 occurrence analysis estimates national contaminant occurrence by generating 

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

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). 

 

5

 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. 6

 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). 

May 2009 Draft EPA document. Do not cite or distribute. 37
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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 38
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-3 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 6 contaminants with health effects assessment 

changes that indicate potential to reduce the MCLG, and the 11 contaminants that do not have 

ongoing health effects assessments, but do have MCLs limited by PQLs and new data indicate 

potential to reduce the PQLs (see Table V-3). EPA used the results of the stage 2 occurrence 

analyses to identify which possible NPDWR revisions present a meaningful opportunity to 

improve the level of health protection or a meaningful opportunity for cost savings to drinking 

water systems and their customers while maintaining the same level of health protection. 

Section VI contains occurrence results and EPA’s review results for the contaminants in Table 

V-3 that have potential for MCL revisions. 

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

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

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

May 2009 Draft EPA document. Do not cite or distribute. 39
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 obtained publicly available source water quality data and conducted a qualitative 

assessment of treatment cost savings for systems that might be treating these contaminants with 

best available technologies (BATs) or small system compliance technologies (SSCTs) listed in 

the NPDWR for each contaminant (USEPA, 2009g). 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. 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 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 of monitoring locations with maximum 

contaminant levels above each contaminant’s current MCL and a possible MCLG based on the 

May 2009 Draft EPA document. Do not cite or distribute. 40
new information from the contaminant’s health effects assessment. 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 

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 to 

determine whether treatment feasibility would be a limiting factor if EPA were to lower the 

MCL for tetrachloroethylene and trichloroethylene. 

Based on this evaluation, the Agency believes that treatment capabilities would be adequate 

to support a lower MCL value for any of these contaminants for which a lower MCL may be 

May 2009 Draft EPA document. Do not cite or distribute. 41
appropriate (USEPA, 2009g). Treatment technologies specified as BAT within the current 

NPDWR, and small system compliance technologies, which were specified by EPA in 1998 

(USEPA, 1998b) for these contaminants are considered to be efficient and practical for 

implementation at a public water system (PWS). 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 42
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 SDWA7; 

• 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 

• 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 an NPDWR review, and EPA agreed that an information or fact sheet might be 

appropriate for the fourth item regarding public notification (PN) requirements for fluoride8

. 

 

7

 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. 8

 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 

May 2009 Draft EPA document. Do not cite or distribute. 43
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-4 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 

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. 

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 an NPDWR review. However the Agency agreed that a fact or information sheet may be 

useful to clarify any confusion. 

May 2009 Draft EPA document. Do not cite or distribute. 44
Table V-4. Issues Identified by the EPA/State Workgroup That Fall within the Scope of an 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 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 

the probability and 

magnitude of health 

threats, some monitoring 

requirements for these 

systems may be 

insufficient, and others 

may be excessive. 

• 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 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 45
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 

concerns related to SOC triggers. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 46
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. 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:

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

The NPDWR is appropriate and no action is necessary at this time due to one of the 

following reasons: 

a. A health effects assessment is in process or the Agency is considering whether to initiate 

an assessment. For those contaminants with a health effects assessment in process that will not 

be completed in time for the current review, 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. For several contaminants, 

EPA identified new health information that may warrant a new health effects assessment. 

May 2009 Draft EPA document. Do not cite or distribute. 47
b. NPDWR remains appropriate after data/information review. 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, 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. 

 

May 2009 Draft EPA document. Do not cite or distribute. 48
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 

Risk assessment in process or 

potential nominee for an 

assessment 

(32 NPDWRs) 

Alpha particles (or emitters) 

Antimony 

Arsenic 

Asbestos 

Benzo(a)pyrene 

Beryllium 

Beta particles and photon 

emitters 

Cadmium 

Carbon tetrachloride 

Chromium 

Cyanide 

1,2-Dichlorobenzene 

1,4-Dichlorobenzene 

1,2-Dichloroethane 

cis-1,2-Dichloroethylene 

trans-1,2-Dichloroethylene 

Dichloromethane 

Di(2-ethylhexyl)adipate 

Di(2-ethylhexyl)phthalate 

Ethylbenzene 

Fluoride 

Nitrate 

Nitrite 

Pentachlorophenol 

Polychlorinated biphenyls 

(PCBs) 

Radiums 

Selenium 

Styrene 

2,3,7,8-TCDD (dioxin) 

Thallium 

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: 

Information gaps 

(3 NPDWRs) 

Atrazine 

Carbofuran Simazine 

Candidate 

for Revision 

Based on new information 

(4 NPDWRs) 

Acrylamide 

Epichlorohydrin 

Tetrachloroethylene (PCE) 

Trichloroethylene (TCE) 

May 2009 Draft EPA document. Do not cite or distribute. 49
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 dosed (maximum) 

at 1 mg/L (ppm). Each water system is required to certify, in writing, to the State (using thirdparty 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. 

However, as the present draft reassessment does not change the cancer classification for 

acrylamide, its MCLG will continue to be zero. EPA therefore considered whether there was 

potential to revise the TT for acrylamide. EPA has identified information that suggests that the 

May 2009 Draft EPA document. Do not cite or distribute. 50
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%, and the 90th percentile acrylamide content was 0.025%, 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% 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% of ground water systems and 66% of 

surface water systems surveyed use a polymer for water treatment. Many of these are anionic 

and nonionic polymers, particularly for ground water systems; anionic and nonionic polymers 

used to treat drinking water are most likely polyacrylamides. 

May 2009 Draft EPA document. Do not cite or distribute. 51
 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 treatment technique, EPA believes that the costs of a revision would be minimal 

(USEPA, 2009g). 

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 monomer levels than required by the existing 

NPDWR. Hence, revisions to the acrylamide NPDWR will provide a meaningful opportunity 

for health risk reduction. EPA expects that the final health effects assessment will further 

support the public health benefits associated with any revision. 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 

classification of B2, probable human carcinogen. The NPDWR also established an MCL of 

0.002 mg/L, based on analytical feasibility. 

May 2009 Draft EPA document. Do not cite or distribute. 52
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% 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 53
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% of the NAWQA locations and less than 0.3% 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 2,691 (100.0%) 9,236 (100.0%) 

Nondetect 2,017 (75%) 8,571 (92.8%) 

Detected 674 (25%) 665 (7.2%) 

Exceeds current MCL of 0.002 mg/L 7 (0.26%) 35 (0.38%) 

Exceeds alternative value of 0.04 mg/L 1 (0.04%) 1 (0.01%) 

1. STORET database 1992-2008. 

2. NAWQA database 1992-2006. 

Source: USEPA, 2004c 

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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 54
there may be opportunities to achieve operational cost savings if these systems are able to reoptimize current treatment. 

Given these challenges, 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 OA9

) 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 draft CCL3 (73 FR 9628, 

February 21, 2008 (USEPA, 2008b)). 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. 

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 

 

9

 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% of 

the samples by year), the alachlor ESA and OA degradates were commonly detected (i.e., 19% to 51% of the 

samples by year for the ESA degradate and 7% to 40% 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. 

May 2009 Draft EPA document. Do not cite or distribute. 55
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 emitting particles 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 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 56
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). However, EPA does not expect the 

health effects assessment to change the cancer classification for alpha particles, and the MCLG 

would remain at zero. 

As a part of the Six-Year Review, the Agency considered whether new information was 

available 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. 

May 2009 Draft EPA document. Do not cite or distribute. 57
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)). 

May 2009 Draft EPA document. Do not cite or distribute. 58
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 II10 contaminant (equivalent to Group C, possible human 

carcinogen) by the oral route of exposure. 

 

10 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; 

May 2009 Draft EPA document. Do not cite or distribute. 59
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 

 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 60
(CARC) classified atrazine as “not likely to be carcinogenic to humans” 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 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. 

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 

concluded that barium is not likely to be carcinogenic to humans (USEPA, 2005a). Based on the 

May 2009 Draft EPA document. Do not cite or distribute. 61
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%11 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 

less than 0.1% of the NAWQA locations and less than 0.3% of the STORET locations. 

 

11 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% for drinking water (the ceiling on RSC specified by the methodology).

May 2009 Draft EPA document. Do not cite or distribute. 62
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 2,294 (13.8 %) 43 (0.9%) 

Detected 14,301 (86.2%) 4,821 (99.1%) 

Exceeds current MCL/MCLG of 2.0 mg/L 60 (0.36%) 3 (0.1%) 

Exceeds alternative value of 6.0 mg/L 21 (0.13%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2005. 

Source: USEPA, 2004c 

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 challenges, 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 

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: 

May 2009 Draft EPA document. Do not cite or distribute. 63
• 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 

identified hematological effects in workers at levels below those previously reported. The 

Agency for Toxic Substances and Disease Registry (ATSDR) (2007) chronic MRL 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 MRL were used as the basis for a noncancer health reference level, the value would 

May 2009 Draft EPA document. Do not cite or distribute. 64
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 WS 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 WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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 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. Of these, 120,308 (86%) equal the modal MRL of 0.0005 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 65
An additional 17,964 (13%) are lower than 0.0005 mg/L. 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. 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 (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 thresholds of 0.0005, 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 

EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. 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%) serving 14,000 people (or 0.006% of 227 million people). Note that these 

results 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 95 to 123 of 50,435 systems (0.188% to 0.244%), serving 304,000 

to 485,000 people (or 0.134% to 0.214% of 227 million people), exceed the EQL of 0.0005 

mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 66
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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 67
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. 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. EPA reviewed WS 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 WS data available through late 1999 for benzo(a)pyrene are all 

May 2009 Draft EPA document. Do not cite or distribute. 68
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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 29,769 (54%) equal the modal MRL of 0.00002 mg/L. An 

additional 970 (2%) are lower than 0.00002 mg/L, and 21,198 (38%) are between 0.00002 mg/L 

and 0.0001 mg/L. The MDLs of approved methods are 0.000016, 0.000029, and 0.00023 mg/L. 

Because the MDL values fall across a wide range, EPA selected the intermediate value, applied a 

multiplier of 10, and rounded up. The resulting 10×MDL value is 0.0003 mg/L. Since the MRL 

values are widely dispersed, and the intermediate 10×MDL value is higher than the current PQL, 

these data do not support a PQL reduction. 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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 69
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 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 70
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 protective12. 

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 

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 

 

12 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)). 

May 2009 Draft EPA document. Do not cite or distribute. 71
for this notice (USEPA, 2009b). However, EPA does not expect the health effects assessment to 

change the cancer classification for beta particles, and the MCLG would remain at zero. 

As a part of the Six-Year Review, the Agency considered whether 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 twotiered 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 

particles is in progress (USEPA, 2009b). Furthermore, there is no new information regarding 

analytical or treatment feasibility that would warrant reconsideration of the MCL. 

May 2009 Draft EPA document. Do not cite or distribute. 72
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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 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%, a 

possible new MCLG would be 0.00012 mg/L. The default RSC value of 20% was selected 

because of the significant exposures resulting from actual food dietary exposure for children 

from 1 to 6 years old, which approaches 100% 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 had until July 14, 2009, to raise 

objections and/or request a hearing on the tolerance revocations. 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 on-going 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 74
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 with 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 on-going regulatory actions could affect the 

possible MCLG. Therefore, EPA is placing carbofuran in the information gap category due to 

the uncertainty of 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. 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 75
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. 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. EPA reviewed WS 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 WS 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 WS 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 

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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels in the Six-Year Review ICR 

May 2009 Draft EPA document. Do not cite or distribute. 76
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. Of these, 119,849 (86%) equal the modal MRL of 

0.0005 mg/L. An additional 16,195 (12%) are lower than 0.0005 mg/L. 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. 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 (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 thresholds of 0.0005, 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 EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. The 

occurrence and exposure analysis shows that average concentrations exceed the current MCL for 

five of 50,446 systems (0.010%), serving fewer than 2,000 people (or 0.001% of 227 million 

people). Note that these results do not necessarily reflect MCL violations, which are based on 

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% to 0.234%), serving 

368,000 to 750,000 people (or 0.162% to 0.330% of 227 million people), exceed the EQL of 

0.0005 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 77
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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 78
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. 

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 WS 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 WS 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. 

May 2009 Draft EPA document. Do not cite or distribute. 79
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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 26,893 (47%) equal the modal MRL of 0.0002 mg/L. An additional 

9,764 (17%) are lower than 0.0002 mg/L, and 20,844 (36%) are between 0.0002 mg/L and the 

MCL of 0.002 mg/L. The MDLs of approved methods range from 0.0000041 to 0.00014 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.000041 to 0.0014 mg/L. 

Because of the broad dispersion in MRL values, EPA averaged the 10×MDL values, rounded up 

to 0.001 mg/L, and used that value as the minimum threshold in the occurrence and exposure 

analysis. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 80
the occurrence of chlordane at an estimated quantitation level 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 set equal to 0.001 mg/L. The occurrence and exposure analysis shows that average 

concentrations exceed the current MCL for one of 31,841 systems (0.003%) serving 80 people 

(or 0.00004% of 182 million people). Note that these results 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% to 0.006%), still serving approximately 

80 to 120 people (or 0.00004 to 0.00007% of 182 million people), exceed the EQL of 0.001 

mg/L. 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 81
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 

• 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 

May 2009 Draft EPA document. Do not cite or distribute. 82
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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 83
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. 

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. 

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 may be 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). 

May 2009 Draft EPA document. Do not cite or distribute. 84
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 

(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 

health effects assessment13. 

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 

 

13 Note that cyanide is listed as hydrogen cyanide in the IRIS tracking system. 

May 2009 Draft EPA document. Do not cite or distribute. 85
DWEL could be 0.2 mg/L. An RSC of 20% 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 

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 consistent with the 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. 

May 2009 Draft EPA document. Do not cite or distribute. 86
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 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 

May 2009 Draft EPA document. Do not cite or distribute. 87
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. 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 88
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 

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. 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. EPA reviewed WS 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 WS 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). 

May 2009 Draft EPA document. Do not cite or distribute. 89
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 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. Of these, 22,980 (45%) equal the modal MRL of 0.001 mg/L. An additional 

15,842 (31%) are lower than 0.001 mg/L, and 11,659 (23%) are between 0.001 mg/L and the 

MCL of 0.006 mg/L. The MDLs of approved methods range from 0.0013 to 0.00225 mg/L. 

Applying a multiplier of 10 would give a possible PQL range from 0.013 to 0.0225 mg/L. Since 

nearly a quarter of samples do not achieve the modal MRL, and the 10×MDL values are higher 

than the current PQL, these data do not support a PQL reduction. 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. 

May 2009 Draft EPA document. Do not cite or distribute. 90
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. 

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 WS 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 WS 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 WS 

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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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 

May 2009 Draft EPA document. Do not cite or distribute. 91
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 possible PQL range from 0.00009 to 0.0001 mg/L. Because of the number of reported 

MRLs above the MCL, EPA averaged the 10×MDL values, rounded up to 0.0001 mg/L, and 

used that value as the minimum threshold for the occurrence and exposure analysis. 

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 an estimated quantitation level 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 

set equal to 0.0001 mg/L. The occurrence and exposure analysis shows that average 

concentrations exceed the current MCL for 42 of 37,618 systems (0.112%) serving 25,000 

people (or 0.013% of 194 million people). Note that these results 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%), serving 

approximately 1.2 to 1.4 million people (0.610% to 0.713% of 194 million people), exceed the 

EQL of 0.0001 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 92
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; 

May 2009 Draft EPA document. Do not cite or distribute. 93
• 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. 

May 2009 Draft EPA document. Do not cite or distribute. 94
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 assessment14. 

 

14 Note that 1,2-dichloroethane is listed as ethylene dichloride in the IRIS tracking system. 

May 2009 Draft EPA document. Do not cite or distribute. 95
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. 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. EPA reviewed WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 116,533 (84%) equal the modal MRL of 0.0005 mg/L. 

An additional 18,160 (13%) are lower than 0.0005 mg/L. The MDLs of approved methods range 

from 0.00003 to 0.00006 mg/L. Applying a multiplier of 10 would give a possible PQL range 

May 2009 Draft EPA document. Do not cite or distribute. 96
from 0.0003 to 0.0006 mg/L. 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 

(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 thresholds of 0.0005, 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 EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. The 

occurrence and exposure analysis shows that average concentrations exceed the current MCL for 

three of 50,442 systems (0..006%) serving 150 people (or 0.00007% of 227 million people). 

Note that these results 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%), serving 210,000 to 277,000 people (or 0.092% to 0.122% 

of 227 million people), exceed the EQL of 0.0005 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 97
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 

May 2009 Draft EPA document. Do not cite or distribute. 98
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 

May 2009 Draft EPA document. Do not cite or distribute. 99
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% 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% of the NAWQA locations and less than 5% of the STORET locations. 

May 2009 Draft EPA document. Do not cite or distribute. 100
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 58 (2.4%) 0 (0.0%) 

1. STORET database 2002-2007. 

2. NAWQA database 1992-2006. 

Source: USEPA, 2004c 

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 challenges, 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 

Agency considered whether any possible revision to the NPDWR for 1,1-dichloroethylene is 

May 2009 Draft EPA document. Do not cite or distribute. 101
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. 

May 2009 Draft EPA document. Do not cite or distribute. 102
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, 

May 2009 Draft EPA document. Do not cite or distribute. 103
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 assessment15. 

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. 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. EPA reviewed WS 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 WS 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 WS and PT data were higher than the current PQL of 0.005 mg/L. Given 

the lack of WS and PT study results below the current PQL to derive a value at the 75 percent 

passing rate, WS and PT data are insufficient to support a PQL reduction (USEPA, 2009c). 

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 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. Of these, 121,532 (88%) equal the modal MRL of 0.0005 mg/L. 

An additional 11,294 (8%) are lower than 0.0005 mg/L. The MDLs of approved methods range 

 

15 Note that dichloromethane is listed as methylene chloride in the IRIS tracking system. 

May 2009 Draft EPA document. Do not cite or distribute. 104
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. 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 

(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 WS 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 thresholds of 0.0005, 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 EQLs set 

equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. 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%) serving 11,000 to 12,000 people (or 0.005% of 227 million people). Note 

that these results 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%), serving approximately 1.8 

to 3.5 million people (or 0.813% to 1.542% of 227 million people), exceed the EQL of 0.0005 

mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 105
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 WS 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 WS 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 

May 2009 Draft EPA document. Do not cite or distribute. 106
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% 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) 

May 2009 Draft EPA document. Do not cite or distribute. 107
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. 

May 2009 Draft EPA document. Do not cite or distribute. 108
Table VI-13. Stage 2 Occurrence Summary for Dichloromethane 

Systems with Mean > 

0.0005 mg/L 

Nondetect = 1/2 MRL1

Total Reported TRI On-Site 

or Off-Site Disposal or 

Release of Dichloromethane 

– All Industries, 20062

Total Reported TRI On-Site or 

Off-Site Disposal or Release 

of Dichloromethane – All 

Industries, 20042

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: USEPA, 2009f 

2. 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 

May 2009 Draft EPA document. Do not cite or distribute. 109
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-

May 2009 Draft EPA document. Do not cite or distribute. 110
dichloropropane might lead to a lower MCL. EPA reviewed WS 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 WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 119,831 (86%) equal the modal MRL of 0.0005 mg/L. 

An additional 18,311 (13%) are lower than 0.0005 mg/L. The MDLs of approved methods range 

from 0.00003 to 0.00004 mg/L. Applying a multiplier of 10 would give a possible PQL range 

from 0.0003 to 0.0004 mg/L. Because of the preponderance of MRL values of 0.0005 mg/L, 

May 2009 Draft EPA document. Do not cite or distribute. 111
EPA selected that value as the minimum threshold for the occurrence and exposure analysis 

(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 thresholds of 0.0005, 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 EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 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 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%), serving 

296,000 to 494,000 people (0.130% to 0.218% of 227 million people), exceed the EQL of 0.0005 

mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 112
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 

May 2009 Draft EPA document. Do not cite or distribute. 113
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. 

May 2009 Draft EPA document. Do not cite or distribute. 114
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 2002 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% 

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 

May 2009 Draft EPA document. Do not cite or distribute. 115
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% 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 contaminant 

May 2009 Draft EPA document. Do not cite or distribute. 116
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 challenges, 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 

May 2009 Draft EPA document. Do not cite or distribute. 117
• 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% 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 WS 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 WS data available through late 1999 for endothall are generally 

above 80 percent, but there were no results for WS 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 

May 2009 Draft EPA document. Do not cite or distribute. 118
PQL. No PT studies had true values below the current PQL. Given the variable results from the 

PT studies and the lack of WS and PT study results below the current PQL, WS 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%) have an MRL value of 

0.05 mg/L or lower. 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. Because most 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. 

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 WS 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 

levels in the Six-Year Review ICR dataset. The occurrence and exposure analysis shows that 

May 2009 Draft EPA document. Do not cite or distribute. 119
average concentrations do not exceed the current MCL for any system in the analysis. Note that 

these results 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%), serving 10,000 people (or 0.008% 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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 120
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. 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 121
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 drinking 

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%. 

May 2009 Draft EPA document. Do not cite or distribute. 122
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% 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% of ground 

water systems and 66% 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 epcichlorohydrin. Because 

most epichlorohydrin-based polymers available today have a significantly lower residual 

monomer content than that specified in the treatment technique, EPA believes that the costs of a 

revision would be minimal (USEPA, 2009g). 

May 2009 Draft EPA document. Do not cite or distribute. 123
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 polyacrylamides are widely available with lower monomer 

levels than required by the existing NPDWR. Hence, revisions to the epichlorohydrin NPDWR 

will provide a meaningful opportunity for health risk reduction. 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. 

May 2009 Draft EPA document. Do not cite or distribute. 124
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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels in the Six-Year Review ICR 

May 2009 Draft EPA document. Do not cite or distribute. 125
dataset, and 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. Of these, 26,926 (32%) equal the modal MRL of 0.00001 mg/L. An 

additional 454 (0.5%) are lower than 0.00001 mg/L, and 8,416 (10%) are between 0.00001 mg/L 

and the MCL of 0.00005 mg/L. 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. Since most MRLs do not achieve the modal value, 

and the current PQL is at the low end of the range of 5×MDL values, EPA believes that there is 

no potential to lower the PQL for EDB. 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 126
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 

dental fluorosis and skeletal fractures in combination with data on the relative contribution of 

May 2009 Draft EPA document. Do not cite or distribute. 127
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 necessary16. 

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. 

 

16 At this time, the results of the osteosarcoma cancer study recommended by NAS have not been published. 

May 2009 Draft EPA document. Do not cite or distribute. 128
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% 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. 

May 2009 Draft EPA document. Do not cite or distribute. 129
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, 2004c 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 130
Given these challenges, 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 

May 2009 Draft EPA document. Do not cite or distribute. 131
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 WS 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 WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 24,918 (42%) equal the modal MRL of 

May 2009 Draft EPA document. Do not cite or distribute. 132
0.00004 mg/L. An additional 7,966 (14%) are lower than 0.00004 mg/L, and 24,752 (42%) are 

between 0.00004 mg/L and 0.0001 mg/L. 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. Because of the broad dispersion in MRL 

values, EPA used the 10×MDL values to develop thresholds in the occurrence and exposure 

analysis. EPA took the median 10×MDL value of 0.00005 mg/L and rounded up to 0.0001 mg/L 

to establish a minimum threshold for the occurrence and exposure analysis. 

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 thresholds of 0.0001 and 0.0002 mg/L (USEPA, 

2009f). Table VI-17 shows the results of the occurrence and exposure analysis for the current 

MCL and EQLs set equal to 0.0002 mg/L and 0.0001 mg/L. The occurrence and exposure 

analysis shows that average concentrations exceed the current MCL for one of 33,020 systems 

(0.003%) serving 325 people (or 0.0002% of 184 million people). Note that these results 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%), serving 31,500 

people (or 0.017% of 184 million people), exceed the EQL of 0.0001 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 133
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 

low priority activity for the Agency, and, thus, is not appropriate to revise at this time because of: 

May 2009 Draft EPA document. Do not cite or distribute. 134
• 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 WS 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 WS 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 WS 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 

May 2009 Draft EPA document. Do not cite or distribute. 135
the PQL. There are two PT studies with passing rates below 75 percent. Despite this variability, 

most of the laboratory passing rates from WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 26,424 (45%) equal the modal MRL 

of 0.00002 mg/L. An additional 5,969 (10%) are lower than 0.00002 mg/L, and 25,888 (44%) 

are between 0.00002 mg/L and 0.0001 mg/L. 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. Because of the broad dispersion in MRL 

values, EPA used the 10×MDL values to develop thresholds in the occurrence and exposure 

analysis. EPA took the median 10×MDL value of 0.000059 mg/L and rounded up to 0.0001 

mg/L to establish a minimum threshold for the occurrence and exposure analysis. 

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 estimated quantitation level of 0.0001 

May 2009 Draft EPA document. Do not cite or distribute. 136
mg/L (USEPA, 2009f). Table VI-18 shows the results of the occurrence and exposure analysis 

for the current MCL and an EQL set equal to 0.0001 mg/L. The occurrence and exposure 

analysis shows that average concentrations exceed the current MCL for one of 33,015 systems 

(0.003%) serving 325 people (or 0.0002% of 184 million people). Note that these results 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%), serving 

14,400 people (or 0.008% 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. 

May 2009 Draft EPA document. Do not cite or distribute. 137
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. 

May 2009 Draft EPA document. Do not cite or distribute. 138
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 WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 40,791 (69%) equal the modal MRL 

of 0.0001 mg/L. An additional 7,380 (13%) are lower than 0.0001 mg/L. The MDLs of 

May 2009 Draft EPA document. Do not cite or distribute. 139
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; however, the 

median 10×MDL value is 0.00003 mg/L, which 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. 

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 thresholds of 0.0001 and 0.0005 mg/L 

(USEPA, 2009f). Table VI-19 shows the results of the occurrence and exposure analysis for the 

current MCL and EQLs set equal to 0.0005 mg/L and 0.0001 mg/L. The occurrence and 

exposure analysis shows that average concentrations exceed the current MCL for three of 32,826 

systems (0.009%) serving 2,000 people (or 0.001% of 184 million people). Note that these 

results 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%), serving approximately 9,000 to 94,000 people (or 

0.005% to 0.051% of 184 million people), exceed the EQL of 0.0001 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 140
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 

May 2009 Draft EPA document. Do not cite or distribute. 141
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% results in a possible 

MCLG of 0.04 mg/L (USEPA, 2009b). 

May 2009 Draft EPA document. Do not cite or distribute. 142
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 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). 

May 2009 Draft EPA document. Do not cite or distribute. 143
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: 

May 2009 Draft EPA document. Do not cite or distribute. 144
• 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 

May 2009 Draft EPA document. Do not cite or distribute. 145
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%. 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% 

of the NAWQA locations and less than 0.3% of the STORET locations. Any MCLG/MCL 

May 2009 Draft EPA document. Do not cite or distribute. 146
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, 2004c 

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 challenges, 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 

May 2009 Draft EPA document. Do not cite or distribute. 147
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/L17 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. 

 

17 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). 

May 2009 Draft EPA document. Do not cite or distribute. 148
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. 

May 2009 Draft EPA document. Do not cite or distribute. 149
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 

May 2009 Draft EPA document. Do not cite or distribute. 150
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. 

May 2009 Draft EPA document. Do not cite or distribute. 151
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% of nitratenitrogen 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 

May 2009 Draft EPA document. Do not cite or distribute. 152
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, 

May 2009 Draft EPA document. Do not cite or distribute. 153
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 

mg/L. An RSC of 20% was selected based on the actual food dietary exposure (81%) for 

May 2009 Draft EPA document. Do not cite or distribute. 154
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 WS 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 WS 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 WS and PT studies, and the lack of PT data 

below the current PQL, WS 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 revise the PQL: 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 information can be valuable for this 

review to indicate whether it is possible to quantitate at levels below the current PQL. The SixYear Review ICR dataset contains MRL values for 52,201 samples. Of these, 45,290 (87%) 

have an MRL value of 0.002 mg/L or lower. Method 531.1 has an MDL of 0.00086 mg/L, and 

May 2009 Draft EPA document. Do not cite or distribute. 155
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. Because most 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. 

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 WS 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 exposure. 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%) serving 200 people (or 0.000% of 167 million people). Note that these results 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 1998 and 2005 

(USEPA, 2007g). Individual sample concentrations at 18 of 30,876 systems (0.058%), serving 

fewer than 0.3 million people (0.177%), exceeded the possible MCLG of 0.002 mg/L at least one 

time between 1998 and 2005. 

May 2009 Draft EPA document. Do not cite or distribute. 156
Table VI-22. Number and Percent of Systems with Mean 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: 

• Competing workload priorities; 

• The administrative costs associated with rulemaking; and 

May 2009 Draft EPA document. Do not cite or distribute. 157
• 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. 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. EPA reviewed WS 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 WS 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 WS studies with passing rates equal to or less than the 75 percent criterion, and 

only one of 16 true values in the WS data is 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 

May 2009 Draft EPA document. Do not cite or distribute. 158
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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 26,666 (45%) equal the modal MRL of 

0.00004 mg/L. An additional 2,399 (4%) are lower than 0.00004 mg/L. Above the modal MRL, 

13,419 (23%) are between 0.00004 and 0.0001 mg/L, and 17,095 (29%) are between 0.0002 

mg/L and the MCL of 0.001 mg/L. The MDLs of approved methods are 0.000032, 0.00016, and 

0.001 mg/L. Because the MDL values fall across a wide range, EPA selected the intermediate 

value, applied a multiplier of 10, and rounded up. The resulting 10×MDL value is 0.002 mg/L. 

Since the MRL values are widely dispersed, and the intermediate 10×MDL value is higher than 

the current PQL, these data do not support a PQL reduction. 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 

May 2009 Draft EPA document. Do not cite or distribute. 159
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% results in a possible MCLG of 1 mg/L (USEPA, 

2009b). 

May 2009 Draft EPA document. Do not cite or distribute. 160
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, 2004c 

May 2009 Draft EPA document. Do not cite or distribute. 161
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 challenges, 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. 

May 2009 Draft EPA document. Do not cite or distribute. 162
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. 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. EPA reviewed WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels in the Six-Year Review ICR 

May 2009 Draft EPA document. Do not cite or distribute. 163
dataset, and the MDL for the approved method for the detection of PCBs (Method 508A). 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 

35,178 samples. Of these, 23,785 (68%) equal the modal MRL of 0.0001 mg/L. An additional 

2,355 (7%) are lower than 0.0001 mg/L, and 7,489 (21%) are between 0.0001 mg/L and the 

MCL of 0.0005 mg/L. 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. Since more than 20% of samples do not 

achieve the modal MRL, and the 10×MDL value is higher than the current PQL, these data do 

not support a PQL reduction. 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-

May 2009 Draft EPA document. Do not cite or distribute. 164
6

 at the MCL of 5 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 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 protective18. 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). However, EPA does not expect the health effects assessment to change 

the cancer classification for radiums, and the MCLG would remain at zero. 

As a part of the Six-Year Review, the Agency considered whether new information was 

available 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. 

 

18 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). 

May 2009 Draft EPA document. Do not cite or distribute. 165
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 intake19 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 

 

19 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. 

May 2009 Draft EPA document. Do not cite or distribute. 166
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 

May 2009 Draft EPA document. Do not cite or distribute. 167
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 because there are some forthcoming studies of atrazine and its 

metabolites from the Agency’s ORD. The Agency does not anticipate that the ORD research 

will significantly change the atrazine 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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 168
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 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, as a part of the Six-Year 

May 2009 Draft EPA document. Do not cite or distribute. 169
Review, the Agency considered whether changes in analytical feasibility might lead to a lower 

MCL. The PT data currently available for dioxin are not sufficient to evaluate the potential for 

PQL revision (USEPA, 2009c). 

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 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 MRL values for 1,278 

samples. Of these, 964 (75%) equal the modal MRL of 5×10-9 mg/L. An additional 191 (15%) 

are lower than 5×10-9 mg/L. The MDL of the approved method is 1×10-8 mg/L. Applying a 

multiplier of 5 would give a possible PQL of 5×10-8 mg/L, which is only slightly higher than the 

current PQL. 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 

approaches are inconclusive. EPA therefore 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 

May 2009 Draft EPA document. Do not cite or distribute. 170
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 

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. 

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. 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. EPA reviewed WS 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 WS 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 WS 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). 

May 2009 Draft EPA document. Do not cite or distribute. 171
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 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 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. Of these, 117,033 (85%) equal 

the modal MRL of 0.0005 mg/L. An additional 15,848 (11%) are lower than 0.0005 mg/L. The 

MDLs of approved methods range 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. 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 (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 thresholds of 0.0005, 0.001, and 0.0025 mg/L. 

Table VI-24 shows the results of the occurrence and exposure analysis for the current MCL and 

EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. 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%) serving approximately 630, 000 to 1.1 million people (or 0.277% to 

0.473% of 227 million people). Note that these results do not necessarily reflect MCL 

violations, which are based on annual average concentrations at entry points; SDWIS/FED 

May 2009 Draft EPA document. Do not cite or distribute. 172
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%), serving 12.4 to 14.6 million people (or 5.466% to 6.419% 

of 227 million people), exceed the lowest EQL of 0.0005 mg/L. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 173
carbon (GAC). Small system compliance technologies (SSCTs) for tetrachloroethylene include 

GAC and several aeration technologies. EPA believes these BATs and SSCTs are still practical 

and would not pose any limitations if EPA were to revise the MCL. 

 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 to 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 will 

provide a meaningful opportunity for health risk reduction. EPA expects that the final health 

effects assessment for tetrachloroethylene will further support the 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 

May 2009 Draft EPA document. Do not cite or distribute. 174
MCLG on a reference dose of 0.00007 mg/kg-day and a cancer classification of D, not 

classifiable as to human carcinogenicity. The NPDWR also established an MCL of 0.002 mg/L, 

based on analytical feasibility. 

b. Technical Reviews. EPA 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 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 health effects assessment is in process for thallium, the current MCL is based on 

a PQL of 0.002 mg/L. Therefore, 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. EPA reviewed WS 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 WS 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% 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels in the Six-Year Review ICR 

May 2009 Draft EPA document. Do not cite or distribute. 175
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 73,409 samples. Of these, 46,273 (63%) equal the modal MRL of 0.001 mg/L. An 

additional 11,032 (15%) are lower than 0.001 mg/L. Finally, 15,953 (22%) equal the MCL of 

0.002 mg/L, and 151 samples exceed the MCL. 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. Although the majority of MRL values are below the current PQL, the 

10×MDL values are higher than the current PQL, and do not support a PQL reduction. 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 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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 176
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 

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% 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%) serving 

approximately 500 people (0.0002% of 227 million people). Note that these results 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%), serving 800 people (or 0.0004% of 227 million people), exceed the possible MCLG 

based on new health effects information (0.06 mg/L). 

May 2009 Draft EPA document. Do not cite or distribute. 177
Table VI-25. Number and Percent of Systems with Mean Concentrations Exceeding Toluene 

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 

May 2009 Draft EPA document. Do not cite or distribute. 178
• 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 WS 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 WS 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 WS 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 WS and PT 

May 2009 Draft EPA document. Do not cite or distribute. 179
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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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. Of these, 36,763 (67%) equal the modal MRL of 0.001 mg/L. An 

additional 8,525 (16%) are lower than 0.001 mg/L. 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. 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. 

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 thresholds of 0.0015 and 0.001 mg/L (USEPA, 2009f). 

Table VI-26 shows the results of the occurrence and exposure analysis for the current MCL and 

EQLs set equal to 0.0015 mg/L and 0.001 mg/L. The occurrence and exposure analysis shows 

that average concentrations exceed the current MCL for three to four of 30,387 systems (0.010% 

to 0.013%) serving 23,000 people (or 0.014% of 160 million people). Note that these results do 

May 2009 Draft EPA document. Do not cite or distribute. 180
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%), serving 23,000 

people (or 0.015% 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. 

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 

May 2009 Draft EPA document. Do not cite or distribute. 181
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 

the RfD or the cancer classification (USEPA, 2009b). 

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. 

May 2009 Draft EPA document. Do not cite or distribute. 182
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., 2004a) and one in 

rats (Moore et al., 2004b), 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 

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-

May 2009 Draft EPA document. Do not cite or distribute. 183
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 

weight and 2 liters water intake per day, the DWEL could be 70 mg/L. An RSC of 20% 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, 

May 2009 Draft EPA document. Do not cite or distribute. 184
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 0.4% of the STORET locations. 

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 2,825 (82.84%) 5,290 (91.4%) 

Detected 604 (17.16%) 498 (8.6%) 

Exceeds current MCLG of 0.2 mg/L 11 (0.32%) 0 (0.0%) 

Exceeds alternative value of 14 mg/L 0 (0.0%) 0 (0.0%) 

1. STORET database 1992-2008. 

2. NAWQA database 1992-2006. 

Source: USEPA, 2004c 

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, 

May 2009 Draft EPA document. Do not cite or distribute. 185
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 challenges, 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 

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, 

May 2009 Draft EPA document. Do not cite or distribute. 186
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 WS 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 WS 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 WS 

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 revise the PQL: laboratory minimum reporting levels 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, 

May 2009 Draft EPA document. Do not cite or distribute. 187
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%) equal the modal MRL of 0.0005 mg/L. 

An additional 17,142 (12%) are lower than 0.0005 mg/L. 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. 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. 

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 

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 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%), serving approximately 700 people (or 0.0003% of 227 million 

people), exceeds the current MCLG of 0.003 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 188
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. 

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; 

May 2009 Draft EPA document. Do not cite or distribute. 189
• 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, 

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. 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. EPA reviewed WS 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 WS 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, 

May 2009 Draft EPA document. Do not cite or distribute. 190
including 6 with true values below the PQL. Because most of the laboratory passing rates from 

WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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 used criteria similar to those in the PT data (NJDWQI, 1987). The Six-Year 

Review ICR dataset contains MRLs for 138,439 samples. Of these, 118,193 (85%) equal the 

modal MRL of 0.0005 mg/L. An additional 17,057 (12%) are lower than 0.0005 mg/L. 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. 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 (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 thresholds of 0.0005, 0.0010, and 0.0025 mg/L 

May 2009 Draft EPA document. Do not cite or distribute. 191
(USEPA, 2009f). Table VI-29 shows the results of the occurrence and exposure analysis for the 

current MCL and EQLs set equal to 0.0025 mg/L, 0.001 mg/L, and 0.0005 mg/L. The 

occurrence and exposure analysis shows that average concentrations exceed the current MCL for 

25 out of 50,432 systems (0.050%) serving approximately 410,000 people (or 0.181% of 227 

million people). Note that these results 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%), serving approximately 12.0 to 13.0 million people (or 5.237% to 5.670% of 227 

million people), exceed the EQL of 0.0005 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 192
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 believes these BATs and SSCTs are still practical and would 

not pose any limitations if EPA were to revise the MCL. 

 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, 

May 2009 Draft EPA document. Do not cite or distribute. 193
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. EPA expects that the final health 

effects assessment for trichloroethylene will further support the 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 

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 

May 2009 Draft EPA document. Do not cite or distribute. 194
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))20. 

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 

classification of A, known human carcinogen. The NPDWR also established an MCL of 0.002 

mg/L, based on analytical feasibility. 

 

20 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) 

May 2009 Draft EPA document. Do not cite or distribute. 195
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 WS 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 WS 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 WS 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 WS 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 they indicate any 

potential to revise the PQL: laboratory minimum reporting levels 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). 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 

May 2009 Draft EPA document. Do not cite or distribute. 196
quantitate at levels below the current PQL. The Six-Year Review ICR dataset contains MRL 

values for 139,494 samples. Of these, 105,410 (76%) equal the modal MRL of 0.0005 mg/L. 

An additional 25,723 (18%) are lower than 0.0005 mg/L. 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. 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 

(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 thresholds of 0.001 and 0.0005 mg/L (USEPA, 

2009f). Table VI-30 shows the results of the occurrence and exposure analysis for the current 

MCL and EQLs set equal to 0.001 mg/L and 0.0005 mg/L. 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%) serving fewer than 14,000 people (or 0.003% to 0.006% of 226 

million people). Note that these results 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%), serving 483,000 to 766,000 people (or 

0.213% to 0.338% of 226 million people), exceed the EQL of 0.0005 mg/L. 

May 2009 Draft EPA document. Do not cite or distribute. 197
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 

May 2009 Draft EPA document. Do not cite or distribute. 198
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% 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 

May 2009 Draft EPA document. Do not cite or distribute. 199
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 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. 

May 2009 Draft EPA document. Do not cite or distribute. 200
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 

specific major scientific and/or technical work products and of the documentation that supports 

May 2009 Draft EPA document. Do not cite or distribute. 201
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 as in today’s action21. Table VII- 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 

 

21 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. 

May 2009 Draft EPA document. Do not cite or distribute. 202
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, 

May 2009 Draft EPA document. Do not cite or distribute. 203
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 

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Comparison to 1992 and 1997 – Fungicides & Herbicides. Washington, D.C.: CropLife 

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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. 

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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: 

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May 2009 Draft EPA document. Do not cite or distribute. 208
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. 

May 2009 Draft EPA document. Do not cite or distribute. 209
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. 

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Federal Register. Vol. 65, No. 236. p. 76707, December 7, 2000. 

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Development. December 2000. Available on the Internet at: 

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Prevention, Pesticides and Toxic Substances. 

USEPA. 2001b. IRIS, Hexachlorocyclopentadiene. Available on the Internet at: 

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Compliance and New Source Contaminants Monitoring; Final Rule. Federal Register. Vol. 

66, No. 14. p. 6975, January 22, 2001. 

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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. 

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http://www.epa.gov/ncea/iris/subst/0039.htm. 

USEPA. 2002c. National Primary Drinking Water Regulations—Announcement of the Results 

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USEPA. 2003b. EPA Protocol for Review of Existing National Primary Drinking Water 

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USEPA. 2003e. National Primary Drinking Water Regulations; Announcement of Completion 

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USEPA. 2004b. National Primary Drinking Water Regulations: Minor Corrections and 

Clarification to Drinking Water Regulations; National Primary Drinking Water Regulations 

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http://www.epa.gov/ncea/iris/subst/0010.htm. 

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May 2009 Draft EPA document. Do not cite or distribute. 213
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Water Treatment Rule; Final Rule. Federal Register. Vol. 71, No. 3. p. 654, January 5, 

2006. 

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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. 

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Inorganic Arsenic: A Report of the US EPA Science Advisory Board (SAB). EPA-SAB-07-

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May 2009 Draft EPA document. Do not cite or distribute. 214
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195. p. 57782, October 10, 2007. 

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Register. Vol. 73, No. 87. p. 44864, July 31, 2008. 

USEPA. 2008b. Drinking Water Contaminant Candidate List 3—Draft; Notice. Federal 

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USEPA. 2009c. Analytical Feasibility Support Document for the Second Six-Year Review of 

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May 2009 Draft EPA document. Do not cite or distribute. 215
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Review of National Primary Drinking Water Regulations. EPA Report 815-B-09-004. July 

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. July 

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. July 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. July 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-

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No. 93. p. 23046, May 15, 2009. 

USEPA. 2009j. Carbofuran; Product Cancellation Order; Notice. Federal Register. Vol. 74, No. 

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Dated: [INSERT SIGNATURE DATE] 

Lisa P. Jackson 

Administrator. 

May 2009 Draft EPA document. Do not cite or distribute. 218