National Primary Drinking Water Regulations: Disinfectants and Disinfection Byproducts Notice of Data Availability
Federal RegisterNov 3, 1997
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SUMMARY: In 1994 USEPA proposed a Stage 1 Disinfectants/Disinfection
Byproducts Rule (DBPR) to reduce the level of exposure from
disinfectants and disinfection byproducts (DBPs) in drinking water
(USEPA, 1994b). This Notice of Data Availability summarizes the 1994
proposal; describes new data and information that the Agency has
obtained and analyses that have been developed since the proposal;
provides information concerning recommendations of the Microbial-
Disinfection/Disinfectants Byproducts (M-DBP) Advisory Committee
(chartered in February 1997 under the Federal Advisory Committee Act)
on key issues related to the proposal; and requests comment on these
recommendations as well as on other regulatory implications that flow
from the new data and information. USEPA solicits comment on all
aspects of this Notice and the supporting record. The Agency also
solicits additional data and information that may be relevant to the
issues discussed in the Notice. USEPA is particularly interested in
public comment on the Committee's recommendations and whether the
Agency should reflect these recommendations in the final rule. USEPA
also requests that any information, data or views submitted to the
Agency since the close of the comment period on the 1994 proposal that
members of the public would like the Agency to consider as part of the
final rule development process be resubmitted during this current 90-
day comment period unless already in the underlying record in the
Docket for this Notice.
The Stage 1 DBPR would apply to community water systems and
nontransient noncommunity water systems that treat their water with a
chemical disinfectant for either primary or residual treatment. In
addition, certain requirements for chlorine dioxide would apply to
transient noncommunity water systems because of the short-term health
effects from high levels of chlorine dioxide.
Key issues related to the Stage 1 DBPR that are addressed in this
Notice include the establishment of Maximum Contaminant Levels for
total trihalomethanes, five haloacetic acids, bromate and chlorite;
requirements for enhanced coagulation and enhanced softening;
disinfection credit; health effects information; and analytical
methods.
Today's Federal Register also contains a related Notice of Data
Availability for the Interim Enhanced Surface Water Treatment Rule
(IESWTR). USEPA proposed this rule at the same time as the Stage 1 DBPR
and plans to promulgate it along with the Stage 1 DBPR in November
1998.
DATES: Comments should be postmarked or delivered by hand on or before
February 3, 1998. Comments must be received or post-marked by midnight
February 3, 1998.
ADDRESSES: Send written comments to DBP NODA Docket Clerk, Water Docket
(MC-4101); U.S. Environmental Protection Agency; 401 M Street, SW;
Washington, DC 20460. Please submit an original and three copies of
your comments and enclosures (including references). If you wish to
hand-deliver your comments, please call the Docket between 9:00 a.m.
and 4 p.m., Monday through Friday, excluding legal holidays, to obtain
the room number for the Docket. Comments may be submitted
electronically to [email protected].
FOR FURTHER INFORMATION CONTACT: The Safe Drinking Water Hotline,
Telephone (800) 426-4791. The Safe Drinking Water Hotline is open
Monday through Friday, excluding Federal holidays, from 9:00 am to 5:30
pm Eastern Time. For technical inquiries, contact Thomas Grubbs or
William Hamele, Office of Ground Water and Drinking Water (MC 4607),
U.S. Environmental Protection Agency, 401 M Street SW, Washington DC
20460; telephone (202) 260-7270 (Grubbs) or (202) 260-2584 (Hamele).
Regional Contacts
I. Kevin Reilly, Water Supply Section, JFK Federal Bldg., Room 203,
Boston, MA 02203, (617) 565-3616
II. Michael Lowy, Water Supply Section, 290 Broadway, 24th Floor, New
York, NY 10007-1866, (212) 637-3830
III. Jason Gambatese, Drinking Water Section (3WM41), 841 Chestnut
Building, Philadelphia, PA 19107, (215) 566-5759
IV. David Parker, Water Supply Section, 345 Courtland Street, Atlanta,
GA 30365, (404) 562-9460
V. Kimberly Harris (micro), Miguel Del Toral (DBP), Water Supply
Section, 77 W. Jackson Blvd., Chicago, IL 60604, (312) 886-4239
(Harris), (312) 886-5253 (Del Toral)
VI. Blake L. Atkins, Team Leader, Water Supply Section, 1445 Ross
Avenue, Dallas, TX 75202, (214) 665-2297
VII. Stan Calow, State Programs Section, 726 Minnesota Ave., Kansas
City, KS 66101, (913) 551-7410
VIII. Bob Clement, Public Water Supply Section, (8WM-DW), 999 18th
Street, Suite 500, Denver, CO 80202-2466, (303) 312-6653
IX. Bruce Macler, Water Supply Section, 75 Hawthorne Street, San
Francisco, CA 94105, (415) 744-1884
X. Wendy Marshall, Drinking Water Unit, 1200 Sixth Avenue (OW-136),
Seattle, WA 98101, (206) 553-1890
SUPPLEMENTARY INFORMATION:
Regulated Entities
Entities potentially regulated by the Stage 1 DBPR are public water
systems that add a disinfectant or oxidant. Regulated categories and
entities include:
------------------------------------------------------------------------
Examples of regulated
Category entities
------------------------------------------------------------------------
Public Water System....................... Community water systems that
add disinfectant or
oxidant.
State Governments......................... State government offices
that regulate drinking
water.
------------------------------------------------------------------------
This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by the
Stage 1 DBPR. This table lists the types of entities that EPA is now
aware could potentially be regulated by the rule. Other types of
entities not listed in this table could also be regulated. To determine
whether your facility may be regulated by this action, you should
carefully examine the applicability criteria in Sec. 141.130 of the
proposed rule published on July 29, 1994 at 59 FR 38668 (USEPA, 1994b).
If you have questions regarding the applicability of this action to a
particular entity, contact one of the persons listed in the preceding
FOR FURTHER INFORMATION CONTACT section.
Additional Information for Commenters
The Agency requests that commenters follow the following format:
type or print comments in ink, and cite, where possible, the
paragraph(s) in this Notice to which each comment refers. Commenters
should use a separate paragraph for each method or issue discussed.
Electronic comments must be submitted as a WP5.1 or WP6.1 file or as an
ASCII file avoiding the use of special characters and any form of name
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or title of the Federal Register. Comments and data will also be
accepted on disks in WordPerfect in 5.1 or WP6.1 or ASCII file format.
Electronic comments on this Notice may be filed online at many Federal
Depository Libraries. Commenters who want EPA to acknowledge receipt of
their comments should include a self-addressed, stamped envelope. No
facsimiles (faxes) will be accepted.
Availability of Record
The record for this Notice, which includes supporting documentation
as well as printed, paper versions of electronic comments, is available
for inspection from 9 to 4 p.m., Monday through Friday, excluding legal
holidays at the Water Docket, U.S. EPA Headquarters, 401 M. St., S.W.
Washington, D.C. 20460. For access to docket materials, please call
202/260-3027 to schedule an appointment and obtain the room number.
Copyright Permission
Supporting documentation reprinted in this document from
copyrighted material may be reproduced or republished without
restriction in accordance with 1 CFR 2.6.
Abbreviations Used in This Notice
AOC: Assimilable organic carbon
ASDWA: Association of State Drinking Water Administrators
AWWA: American Water Works Association
AWWARF: AWWA Research Foundation
AWWSCo: American Water Works Service Company
BAC: Biologically active carbon
BAF: Biologically active filtration
BAT: Best Available Technology
BCAA: Bromochloroacetic acid
BDOC: Biodegradable organic carbon
CT: Contact time
CWS: Community Water System
DBP: Disinfection byproducts
D/DBP: Disinfectants and disinfection byproducts
DBPRAM: DBP Regulatory Analysis Model
DOC: Dissolved Organic Carbon
EPA: United States Environmental Protection Agency
ESWTR: Enhanced Surface Water Treatment Rule
FACA: Federal Advisory Committee Act
FY: Fiscal year
GAC: Granular Activated Carbon
GWDR: Ground Water Disinfection Rule
HAA5: Haloacetic acids (five)
IC: Ion chromotography
ICR: Information Collection Rule
ILSI: International Life Sciences Institute
IOC: Inorganic chemical
LOAEL: Lowest observed adverse effect level
MCL: Maximum Contaminant Level (expressed as mg/l, 1,000 micrograms
(g)=1 milligram (mg))
MCLG: Maximum Contaminant Level Goal
M-DBP: Microbial and Disinfectants/Disinfection Byproducts
MDL: Method Detection Limit
mg/dl: Milligrams per deciliter
mg/L: Milligrams per liter
MGD: Million Gallons per Day
MRDL: Maximum Residual Disinfectant Level (as mg/l)
MRDLG: Maximum Residual Disinfectant Level Goal
MWDSC: Metropolitan Water District of Southern California
NCI: National Cancer Institute
NIPDWR: National Interim Primary Drinking Water Regulation
NOAEL: No observed adverse effect level
NOM: Natural Organic Matter
NPDWR: National Primary Drinking Water Regulation
NTNCWS: Nontransient noncommunity water system
O&M: Operations and maintenance
PE: Performance evaluation
PODR: Point of Diminishing Returns
POE: Point-of-Entry Technologies
POU: Point-of-Use Technologies
ppb: Parts per billion
PQL: Practical Quantitation Level
PWS: Public Water System
RIA: Regulatory Impact Analysis
RMCL: Recommended Maximum Contaminant Level
SAB: Science Advisory board
SDWA: Safe Drinking Water Act, or the ``Act,'' as amended in 1986
SUVA: Specific ultraviolet absorbance at 254 nm
SWTR: Surface Water Treatment Rule
TOC: Total organic carbon
TTHM: Total trihalomethanes
TWG: Technical Working Group
UNC: University of North Carolina
VOC: Volatile Synthetic Organic Chemical
WIDB: Water Industry Data Base
WITAF: Water Industry Technical Action Fund
Table of Contents
I. Introduction and Background
A. Existing Regulations
1. Surface Water Treatment Rule
2. Total trihalomethane MCL
3. Total Coliform Rule
4. Information Collection Rule
B. Public Health Concerns to be Addressed
C. Statutory Provisions
1. SDWA and 1986 provisions
2. Changes to initial provisions and new mandates
D. Regulatory Negotiation Process
E. Information Collection Rule
F. Formation of 1997 Federal Advisory Committee
G. Overview of 1994 DBP Proposal
1. MCLGs/MCLs/MRDLGs/MRDLs
2. Best available technologies
3. Treatment technique
4. Preoxidation (predisinfection) credit
5. Analytical methods
6. New information
II. Health Effects
A. Cancer Epidemiology Studies
1. Expert panels recommendations on cancer epidemiology
2. Implementation of expert panel recommendations
a. Improve exposure assessments/geographic identification
studies/classes of DBPs other than THMs
b. Meta-analysis of existing cancer epidemiology data
B. Reproductive and Developmental Epidemiology Studies
1. Improving exposure assessments
2. New studies since proposal
C. Significant New Toxicological Information for Stage 1
Disinfectants and Disinfection Byproducts
1. Chlorite
2. Chlorine dioxide
3. Trihalomethanes
4. Haloacetic acids
5. Chloral hydrate
6. Bromate
D. Summary of Key Observations
E. Request for Public Comments
III. Enhanced Coagulation and Enhanced Softening
A. 1994 Enhanced Coagulation and Enhanced Softening Proposal
B. New Information on Enhanced Coagulation and Softening Since
1994 Proposal
1. New Data on enhanced coagulation
a. UNC Enhanced Coagulation Study
b. Metropolitan Water District of Southern California WDSC/
ColoradoUniversity Enhanced Coagulation Study
c. Malcolm Pirnie, Inc./Colorado University data collection and
analysis
d. Evaluation of current (baseline) TOC removals at full scale
e. Evaluation of ``optimized'' TOC removal
f. ``Case-by-case'' data analyses
2. New data on enhanced softening
a. AWWARF Studies--data on TOC removal
b. Shorney and Coworkers--data on the use of SUVA
c. Malcolm Pirnie, Inc. modeling
d. ICR mail survey
C. Summary of Key Enhanced Coagulation and Enhanced Softening
Observations
D. Request for Public Comment on Enhanced Coagulation and
Enhanced Softening Issues
IV. Predisinfection Credit
A. 1994 Proposal
B. New Information Since 1994 Proposal
1. ICR mail survey--predisinfection practices
2. Summers et al.--Impact of chlorination point on DBP
production
C. Summary of Key Observations
D. Request for Public Comments
V. Analytical Methods
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A. Chlorine Dioxide
B. Haloacetic Acids
C. Total Trihalomethanes (TTHMs)
D. Bromate
E. Chlorite
F. Total Organic Carbon (TOC)
G. Specific Ultraviolet Absorbance (SUVA)
H. Summary of Key Observations
I. Request for Public Comments
VI. MCLs for TTHMs, HAAs, Chlorite, and Bromate
A. 1994 Proposal
B. New Information Since 1994 Proposal
1. TTHM and HAA5 MCLs
2. Bromate
3. Chlorite
VII. Regulatory Compliance Schedule and Other Compliance-related
Issues
A. Regulatory Compliance Schedule
B. Compliance violations and State primacy obligations
C. Compliance with current regulations
VIII. Economic Analysis of the M-DBP Advisory Committee
Recommendations
A. Plant-level DBP Treatment Effectiveness and Cost
B. Decision Tree Analysis--Compliance Forecasts
C. National Cost Estimates
1. System level costs
2. Household costs
3. Monitoring and State implementation costs
D. DBP Exposure Estimates
E. National Benefits Analysis
F. Cost-Effectiveness
G. Summary of Key Observations
H. Request for Public Comments
IX. National Technology Transfer and Advancement Act
X. References
I. Introduction and Background
A. Existing Regulations
1. Surface Water Treatment Rule
Under the Surface Water Treatment Rule (SWTR)(USEPA, 1989a), USEPA
set maximum contaminant level goals of zero for Giardia lamblia,
viruses, and Legionella; and promulgated national primary drinking
water regulations for all public water systems (PWSs) using surface
water sources or ground water sources under the direct influence of
surface water. The SWTR includes treatment technique requirements for
filtered and unfiltered systems that are intended to protect against
the adverse health effects of exposure to Giardia lamblia, viruses, and
Legionella, as well as many other pathogenic organisms. Briefly, those
requirements include (1) removal or inactivation of 3 logs (99.9%) for
Giardia and 4 logs (99.99%) for viruses (2) combined filter effluent
performance of 5 NTU as a maximum and 0.5 NTU at 95th percentile
monthly, based on 4-hour monitoring for treatment plants using
conventional treatment or direct filtration (with separate standards
for other filtration technologies); and (3) watershed protection and
other requirements for unfiltered systems.
2. Total trihalomethane MCL
USEPA set an interim maximum contaminant level (MCL) for total
trihalomethanes (TTHMs) of 0.10 mg/l as an annual average in November
1979 (USEPA, 1979). This standard was based on the need to balance the
requirement for continued disinfection of water to reduce exposure to
pathogenic microorganisms while simultaneously lowering exposure to
disinfection byproducts which might be carcinogenic to humans.
The interim TTHM standard only applies to any PWSs (surface water
and/or ground water) serving at least 10,000 people that add a
disinfectant to the drinking water during any part of the treatment
process. At their discretion, States may extend coverage to smaller
PWSs. However, most States have not exercised this option. About 80
percent of the PWSs, serving populations of less than 10,000, are
served by ground water that is generally low in THM precursor content
(USEPA, 1979) and which would be expected to have low TTHM levels even
if they disinfect.
3. Total Coliform Rule
The Total Coliform Rule (USEPA, 1989b) was revised in June 1989,
and became effective on December 31, 1990. The rule, which applies to
all public water systems, sets compliance with the maximum contaminant
level (MCL) for total coliforms as follows. For systems that collect 40
or more samples per month, no more than 5.0% of the samples may be
total coliform-positives; for those that collect fewer than 40 samples,
only one sample may be total coliform-positive. If a system exceeds the
MCL for a month, it must notify the public using mandatory language
developed by the USEPA. The required monitoring frequency for a system
ranges from 480 samples per month for the largest systems to once
annually for certain of the smallest systems. All systems must have a
written plan identifying where samples are to be collected. In
addition, systems are required to conduct repeat sampling after a
positive sample.
The Total Coliform Rule also requires each system that collects
fewer than five samples per month to have the system inspected every 5
years (10 years for certain types of systems using only protected and
disinfected ground water.) This on-site inspection (referred to as a
sanitary survey) must be performed by the state or by an agent approved
by the state.
4. Information Collection Rule
The Information Collection Rule (ICR) is a monitoring and data
reporting rule that was promulgated on May 14, 1996 (USEPA, 1996b). The
purpose of the ICR is to collect occurrence and treatment information
to evaluate the need for possible changes to the current Surface Water
Treatment Rule and existing microbial treatment practices and to
evaluate the need for future regulation for disinfectants and DBPs. The
ICR will provide USEPA with additional information on the national
occurrence in drinking water of (1) chemical byproducts that form when
disinfectants used for microbial control react with compounds already
present in source water and (2) disease-causing microorganisms,
including Cryptosporidium, Giardia, and viruses. The ICR will also
collect engineering data on how PWSs currently control such
contaminants. This information is being collected because the
regulatory negotiation on disinfectants and DBPs concluded that
additional information was needed to assess the potential health
problem created by the presence of DBPs and pathogens in drinking water
and to assess the extent and severity of risk in order to make sound
regulatory and public health decisions. The ICR will also provide
information to support regulatory impact analyses for various
regulatory options, and to help develop monitoring strategies for cost
effectively implementing regulations.
B. Public Health Concerns To Be Addressed
In 1990, USEPA's Science Advisory Board, an independent panel
established by Congress, cited drinking water contamination as one of
the highest ranking environmental risks. The Science Advisory board
reported that microbiological contaminants (e.g. bacteria, protozoa,
viruses) are likely the greatest remaining health risk management
challenge for drinking water suppliers. The control of microbiological
contaminants is further complicated because commonly-used disinfection
processes themselves may pose health risks. Conventional practices
require the addition of disinfectant chemicals to the water that, while
effective in controlling many harmful microorganisms, combine with
organic matter in the water and form compounds known as disinfection
byproducts (DBPs). One of the most complex questions facing water
supply professionals is how to minimize the risks from these DBPs and
still control microbial contaminants.
Chemical disinfectants (e.g., chlorine, chloramines, chlorine
dioxide) are
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added to drinking water to provide continuous disinfection throughout
the distribution system. There is generally little health concern over
exposure to the levels of the disinfectant residuals commonly found in
finished drinking water. A number of organic DBPs, including some
trihalomethanes (chloroform, bromoform, and bromodichloromethane) and
some haloacetic acids (e.g., dichloroacetic acid) cause cancer in
laboratory animals. Other DBPs cause reproductive or developmental
effects in laboratory animals (e.g., chlorite). Bromate, a byproduct of
ozonation, causes cancer in laboratory animals.
Several epidemiology studies have evaluated the association of
chlorination and chloramination with several adverse outcomes including
cancer, cardiovascular disease, and adverse reproductive outcomes.
Several studies have reported small increases in bladder, colon, and
rectal cancers. In some cases, these effects appeared to be associated
with the duration of exposure and volume of water consumed. Data on
DBPs and cardiovascular disease are inconclusive. Animal studies in the
mid 1980's indicated a potential increase in the serum lipid levels in
animals exposed to chlorinated water. However, in a cross-sectional
epidemiology study in humans, comparing chlorinated and unchlorinated
water supplies with varying water hardness, no adverse effects on serum
lipid levels were found. Recent epidemiology studies have reported
increased incidence of decreased birth weight, premature births,
intrauterine growth retardation, and neural tube defects with
chlorinated water. As with the other reported adverse outcomes from the
epidemiology studies, there is considerable debate in the scientific
community on the significance of these findings (USEPA, 1994a). A
discussion of new health effects information that has become available
since the 1994 proposal appears in Section VI of this Notice.
In order to accurately assess risk from DBPs, it is important to
have information on human exposure to DBPs, information on the toxicity
of the DBPs and an understanding of the mode of action of toxicity. The
preamble to the 1994 proposed DBP rule presented information on the
occurrence and exposure to the Stage 1 DBPs. The information presented
in that preamble was summarized from the document ``Occurrence
Assessment for Disinfectants and Disinfection By-products (Phase 6a) in
Drinking Water'' (USEPA, 1992a) and from information presented as a
part of the 1992 and 1993 Regulatory Negotiation process that led to
the 1994 Stage 1 DBP proposal (see section D below). Since the
proposal, USEPA has updated the document cited above with new
occurrence and exposure information. Copies of the revised document,
entitled ``Occurrence Assessment for Disinfectants and Disinfection
Byproducts in Public Drinking Water Supplies'' (USEPA, 1997a) can be
obtained from the Docket for this Notice. The Information Collection
Rule (ICR) (USEPA, 1996b) will supply additional information on the
occurrence of DBPs for the Stage 2 DBP rule; however, this ICR
information will not be available in time for the Stage 1 DBP rule.
C. Statutory Provisions
1. SDWA and 1986 Provisions
The Safe Drinking Water Act (SDWA or the Act), as amended in 1986,
requires USEPA to publish a ``maximum contaminant level goal'' (MCLG)
for each contaminant which, in the judgement of the USEPA
Administrator, ``may have any adverse effect on the health of persons
and which are known or anticipated to occur in public water systems''
(Section 1412(b)(3)(A)). MCLGs are to be set at a level at which ``no
known or anticipated adverse effect on the health of persons occur and
which allows an adequate margin of safety'' (Section 1412(b)(4)).
The Act also requires that at the same time USEPA publishes an
MCLG, which is a non-enforceable health goal, it also must publish a
National Primary Drinking Water Regulation (NPDWR) that specifies
either a maximum contaminant level (MCL) or treatment technique
(Sections 1401(1) and 1412(a)(3)). USEPA is authorized to promulgate a
NPDWR ``that requires the use of a treatment technique in lieu of
establishing a MCL,'' if the Agency finds that ``it is not economically
or technologically feasible to ascertain the level of the
contaminant''.
Section 1414(c) of the Act requires each owner or operator of a
public water system to give notice to the persons served by the system
of any failure to comply with an MCL or treatment technique requirement
of, or testing procedure prescribed by, a NPDWR and any failure to
perform monitoring required by section 1445 of the Act.
Section 1412(b)(7)(C) of the SDWA requires the USEPA Administrator
to publish a NPDWR ``specifying criteria under which filtration
(including coagulation and sedimentation, as appropriate) is required
as a treatment technique for public water systems supplied by surface
water sources''. In establishing these criteria, USEPA is required to
consider ``the quality of source waters, protection afforded by
watershed management, treatment practices (such as disinfection and
length of water storage) and other factors relevant to protection of
health''. This section of the Act also requires USEPA to promulgate a
NPDWR requiring disinfection as a treatment technique for all public
water systems and a rule specifying criteria by which variances to this
requirement may be granted.
2. Changes to Initial Provisions and New Mandates
In 1996, Congress reauthorized the Safe Drinking Water Act. Several
of the 1986 provisions discussed above were renumbered and augmented
with additional language, while other sections mandate new drinking
water requirements. These modifications, as well as new provisions, are
detailed below.
As part of the 1996 amendments to the Safe Drinking Water Act (the
Amendments), USEPA's general authority to set a MCLG and NPDWR was
modified to apply to contaminants that may ``have an adverse effect on
the health of persons'', that are ``known to occur or there is a
substantial likelihood that the contaminant will occur in public water
systems with a frequency and at levels of public health concern'', and
for which ``in the sole judgement of the Administrator, regulation of
such contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems' (1986 SDWA
Section 1412 (b)(3)(A) stricken and amended with 1412(b)(1)(A)).
The Amendments also require that USEPA, when proposing a NPDWR that
includes an MCL or treatment technique, publish and seek public comment
on health risk reduction and cost analyses. The Amendments also require
USEPA to take into consideration the effects of contaminants upon
sensitive subpopulations (i.e. infants, children, pregnant women, the
elderly, and individuals with a history of serious illness), and other
relevant factors. (Section 1412 (b)(3)(C)).
The 1996 Amendments also newly require USEPA to promulgate an
Interim Enhanced SWTR and a Stage I Disinfectants and Disinfection
Byproducts Rule by November 1998. In addition, the 1996 Amendments
require USEPA to promulgate a Final Enhanced SWTR and a Stage 2
Disinfection Byproducts Rule by November 2000 and May 2002,
respectively (Section 1412(b)(2)(C)).
[[Page 59392]]
Under the Amendments of 1996, recordkeeping requirements were
modified to apply to ``every person who is subject to a requirement of
this title or who is a grantee'' (Section 1445 (a)(1)(A)). Such persons
are required to ``establish and maintain such records, make such
reports, conduct such monitoring, and provide such information as the
Administrator may reasonably require by regulation * * *''.
D. Regulatory Negotiation Process
In 1992 USEPA initiated a negotiated rulemaking to develop a
disinfectants/disinfection byproducts rule. The negotiators included
representatives of State and local health and regulatory agencies,
public water systems, elected officials, consumer groups and
environmental groups. The Committee met from November 1992 through June
1993.
Early in the process, the negotiators agreed that large amounts of
information necessary to understand how to optimize the use of
disinfectants to concurrently minimize microbial and DBP risk on a
plant-specific basis were unavailable. Nevertheless, the Committee
agreed that USEPA propose a Disinfectant/Disinfection Byproducts rule
to extend coverage to all community and nontransient noncommunity water
systems that use disinfectants. This rule proposed to reduce the
current TTHM MCL, regulate additional disinfection byproducts, set
limits for the use of disinfectants, and reduce the level of organic
compounds in the source water that may react with disinfectants to form
byproducts.
One of the major goals addressed by the Committee was to develop an
approach that would reduce the level of exposure from disinfectants and
DBPs without undermining the control of microbial pathogens. The
intention was to ensure that drinking water is microbiologically safe
at the limits set for disinfectants and DBPs and that these chemicals
do not pose an unacceptable risk at these limits.
Following months of intensive discussions and technical analysis,
the Committee recommended the development of three sets of rules: a
two-staged Disinfectants/Disinfection Byproduct Rule (proposal: 59 FR
38668, July 29, 1994), an ``interim'' ESWTR (proposal: 59 FR 38832,
July 29, 1994), and an Information Collection rule (proposal: 59 FR
6332, February 10, 1994). The IESWTR would only apply to systems
serving 10,000 people or more. The Committee agreed that a ``long-
term'' ESWTR (LTESWTR) would be needed for systems serving fewer than
10,000 people when the results of more research and water quality
monitoring became available. The LTESWTR could also include additional
refinements for larger systems.
The approach in developing these proposals considered the
constraints of simultaneously treating water to control for both
microbial contaminants and DBPs. As part of this effort, the
Negotiating Committee concluded that the SWTR may need to be revised to
address health risk from high densities of pathogens in poorer quality
source waters and from the protozoan, Cryptosporidium. The Committee
also agreed that the schedules for IESWTR and LTESWTR should be
``linked'' to the schedule for the Stage 1 DBP Rule to assure
simultaneous compliance and a balanced risk-risk based implementation.
The Committee agreed that additional information on health risk,
occurrence, treatment technologies, and analytical methods needed to be
developed in order to better understand the risk-risk tradeoff, and how
to accomplish an overall reduction in risk.
Finally the Negotiating Committee agreed that to develop a
reasonable set of rules and to understand more fully the limitations of
the current SWTR, additional field data were critical. Thus, a key
component of the regulation negotiation agreement was the promulgation
of the Information Collection Rule (ICR) noted above and described in
more detail below.
E. Information Collection Rule
As stated above, the ICR established monitoring and data reporting
requirements for large public water systems serving populations over
100,000. About 350 PWSs operating 500 treatment plants are involved in
the data collection effort. Under the ICR, these PWSs monitor their
source water for bacteria, viruses, and protozoa (surface water sources
only); water quality factors affecting DBP formation; and DBPs within
the treatment plant and in the distribution system. In addition, PWSs
must provide operating data and a description of their treatment plan
design. Finally, a subset of PWSs perform treatment studies, using
either granular activated carbon or membrane processes, to evaluate DBP
precursor removal. Monitoring for treatment study applicability began
in September 1996. The remaining occurrence monitoring began in July
1997.
The initial intent of the ICR was to collect monitoring data and
other information for use in developing the Stage 2 DBPR and IESWTR and
to estimate national costs for various treatment options. However,
because of delays in promulgating the ICR and technical difficulties
associated with laboratory approval and review of facility sampling
plans, most ICR monitoring did not begin until July 1, 1997. As a
result of this delay and the new Stage 1 DBPR and IESWTR deadlines
specified in the 1996 SDWA amendments, ICR data will not be available
for analysis in connection with these rules. In place of the ICR data,
the Agency has worked with stakeholders to identify additional data
developed since 1994 that can be used in components of these rules.
USEPA intends to continue to work with stakeholders in analyzing and
using the comprehensive ICR data and research for developing subsequent
revisions to the SWTR and the Stage 2 DBP Rule.
F. Formation of 1997 Federal Advisory Committee
In May 1996, the Agency initiated a series of public informational
meetings to exchange information on issues related to microbial and
disinfectants/disinfection byproducts regulations. To help meet the
deadlines for the IESWTR and Stage 1 DBPR established by Congress in
the 1996 SDWA Amendments and to maximize stakeholder participation, the
Agency established the Microbial and Disinfectants/Disinfection
Byproducts (M-DBP) Advisory Committee under the Federal Advisory
Committee Act (FACA) on February 12, 1997, to collect, share, and
analyze new information and data, as well as to build consensus on the
regulatory implications of this new information. The Committee consists
of 17 members representing USEPA, State and local public health and
regulatory agencies, local elected officials, drinking water suppliers,
chemical and equipment manufacturers, and public interest groups.
The Committee met five times, in March through July 1997, to
discuss issues related to the IESWTR and Stage 1 DBPR. Technical
support for these discussions was provided by a Technical Work Group
(TWG) established by the Committee at its first meeting in March 1997.
The Committee's activities resulted in the collection, development,
evaluation, and presentation of substantial new data and information
related to key elements of both proposed rules. The Committee reached
agreement on the following major issues discussed in this Notice and
the Notice for the IESWTR published elsewhere in today's Federal
Register: (1) MCLs for TTHMs, HAA5 and bromate; (2) requirements for
enhanced coagulation and enhanced softening (as part of DBP control);
(3) microbial benchmarking/profiling to
[[Page 59393]]
provide a methodology and process by which a PWS and the State, working
together, assure that there will be no significant reduction in
microbial protection as the result of modifying disinfection practices
in order to meet MCLs for TTHM and HAA5; (4) disinfection credit; (5)
turbidity; (6) Cryptosporidium MCLG; (7) removal of Cryptosporidium;
(8) role of Cryptosporidium inactivation as part of a multiple barrier
concept and (9) sanitary surveys. The Committee's recommendations to
USEPA on these issues were set forth in an Agreement In Principle
document dated July 15, 1997. This document is included with this
Notice as Appendix 1.
G. Overview of 1994 DBP Proposal
The proposed Disinfectants and Disinfection Byproducts Stage I Rule
(DBPI) addressed a number of complex and interrelated drinking water
issues. The proposal attempted to balance the control of health risks
from compounds formed during drinking water disinfection against the
risks from microbial organisms (such as Giardia lamblia,
Cryptosporidium, bacteria, and viruses) to be controlled by the IESWTR.
The proposed Stage 1 DBP rule applied to all community water
systems (CWSs) and nontransient noncommunity water systems (NTNCWSs)
that treat their water with a chemical disinfectant for either primary
or residual treatment. In addition, certain requirements for chlorine
dioxide would apply to transient noncommunity water systems because of
the short-term health effects from high levels of chlorine dioxide.
Following is a summary of key components of the 1994 Stage 1 DBPR
proposal.
1. MCLGs/MCLs/MRDLGs/MRDLs
EPA proposed MCLGs of zero for chloroform, bromodichloromethane,
bromoform, bromate, and dichloroacetic acid and MCLGs of 0.06 mg/L for
dibromochloromethane, 0.3 mg/L for trichloroacetic acid, 0.04 mg/L for
chloral hydrate, and 0.08 mg/L for chlorite. In addition, EPA proposed
to lower the MCL for TTHMs from 0.10 to 0.080 mg/L and added an MCL for
five haloacetic acids (i.e., the sum of the concentrations of mono-,
di-, and trichloroacetic acids and mono-and dibromoacetic acids) of
0.060 mg/L. EPA also, for the first time, proposed MCLs for two
inorganic DBPs: 0.010 mg/L for bromate and 1.0 mg/L for chlorite.
In addition to proposing MCLGs and MCLs for several DBPs, EPA
proposed maximum residual disinfectant level goals (MRDLGs) of 4 mg/L
for chlorine and chloramines and 0.3 mg/L for chlorine dioxide. The
Agency also proposed maximum residual disinfectant levels (MRDLs) for
chlorine and chloramines of 4.0 mg/L, and 0.8 mg/L for chlorine
dioxide. MRDLs protect public health by setting limits on the level of
residual disinfectants in the distribution system. MRDLs are similar in
concept to MCLs--MCLs set limits on contaminants and MRDLs set limits
on residual disinfectants in the distribution system. MRDLs, like MCLs,
are enforceable, while MRDLGs, like MCLGs, are not enforceable.
2. Best Available Technologies
EPA identified the best available (BAT) technology for achieving
compliance with the MCLs for both TTHMs and HAA5 as enhanced
coagulation or treatment with granular activated carbon with a ten
minute empty bed contact time and 180 day reactivation frequency
(GAC10), with chlorine as the primary and residual disinfectant. The
BAT for achieving compliance with the MCL for bromate was control of
ozone treatment process to reduce formation of bromate. The BAT for
achieving compliance with the chlorite MCL was control of precursor
removal treatment processes to reduce disinfectant demand, and control
of chlorine dioxide treatment processes to reduce disinfectant levels.
EPA identified BAT for achieving compliance with the MRDL for chlorine,
chloramine, and chlorine dioxide as control of precursor removal
treatment processes to reduce disinfectant demand, and control of
disinfection treatment processes to reduce disinfectant levels.
3. Treatment Technique
EPA proposed a treatment technique that would require surface water
systems and groundwater systems under the direct influence of surface
water that use conventional treatment or precipitative softening to
remove DBP precursors by enhanced coagulation or enhanced softening. A
system would have been required to remove a certain percentage of TOC
(based on raw water quality) prior to the point of continuous
disinfection. EPA also proposed a procedure to be used by a PWS not
able to meet the percent reduction, to allow them to comply with an
alternative minimum TOC removal level. Compliance for systems required
to operate with enhanced coagulation or enhanced softening was based on
a running annual average, computed quarterly, of normalized monthly TOC
percent reductions. A complete discussion of the proposed requirements
is in Section III.A.
4. Preoxidation (Predisinfection) Credit
The proposed rule did not allow PWSs required to use enhanced
coagulation or enhanced softening to take credit for compliance with
disinfection requirements in the SWTR/IESWTR prior to removing required
levels of precursors unless they met specified criteria. These criteria
are explained in Section IV.A.
5. Analytical Methods
EPA proposed nine analytical methods (some of which can be used for
multiple analytes) to ensure compliance with proposed MRDLs for
chlorine, chloramines, and chlorine dioxide. The three disinfectant
residuals were measured and reported as: chlorine as free chlorine
(four methods) or total chlorine (five methods); chloramines as
combined chlorine (three methods) or total chlorine (five methods); and
chlorine dioxide as chlorine dioxide (3 methods). EPA proposed methods
for the analysis of two classes of organic DBPs: TTHMs (three methods)
and HAA5 (2 methods). In addition, EPA proposed one method for
measuring both inorganic DBPs (chlorite and bromate) and two methods
for total organic carbon (TOC).
6. New Information
Since July, 1994, new information has become available in several
key areas related to issues put forth in the DBP Stage 1 proposal. The
key issues where new information has become available since the
proposal include the following: (1) MCLs; (2) Enhanced Coagulation and
Enhanced Softening; (3) Predisinfection Credit; (4) Health Effects
Information; (5) Analytical Methods; and (6) the Regulatory Impact
Analysis (DBP and TOC occurrence, compliance decision tree). This
information and its implications are discussed in more detail below.
II. Health Effects
The preamble to the 1994 proposed rule provided a summary of the
health criteria documents for bromate; chloramines; haloacetic acids
and chloral hydrate; chlorine; chlorine dioxide, chlorite, and
chlorate; and trihalomethanes. The information presented in the
proposal was used to establish MCLGs and MRDLGs for the disinfectants
and DBPs listed above. Since the 1994 proposal, several epidemiology
and toxicology studies have been completed. The study results need to
be considered for the final Stage 1 DBPR. The following section briefly
[[Page 59394]]
discusses the new epidemiological and laboratory toxicology studies. In
addition, USEPA has developed summaries of this new information and
included these documents in the Docket for this action as ``Summaries
of New Health Effects Data'' (USEPA, 1997b).
A. Cancer Epidemiology Studies
The preamble to the proposed rule discussed several cancer
epidemiology studies that had been conducted over the past 20 years on
chlorinated drinking water (see USEPA, 1994b). At the time of the
proposed rule, there was disagreement among the members of the
Negotiating Committee on the conclusions to be drawn from the cancer
epidemiology studies. Some members of the Committee felt that the
cancer epidemiology data, taken in conjunction with the results from
toxicological studies, provide an ample and sufficient weight of
evidence to conclude that exposure to DBPs in drinking water could
result in an increased cancer risk at levels encountered in some public
water supplies. Other members of the Committee concluded that the
degree of resolution in cancer epidemiology studies on the consumption
of chlorinated drinking water to date was insufficient to provide
definitive information for the regulation. USEPA, therefore, agreed to
pursue additional research to reduce the uncertainties associated with
these epidemiology data and to better characterize and project the
potential human cancer risks associated with the consumption of
chlorinated drinking water. To implement this commitment, USEPA
sponsored two expert panel reviews on the state of cancer epidemiology.
Each of these panels recommended short and long-term research for
improving the assessment of risks using cancer epidemiology.
1. Expert Panels Recommendations on Cancer Epidemiology
USEPA conducted an expert panel workshop in July 1994 on the
scientific considerations for conducting cancer epidemiologic studies
for DBPs (USEPA, 1994a). The expert panel presented the following
conclusions.
(A)lthough ecological and analytic epidemiologic studies have
reported associations between chlorinated water and cancer at
various sites, many of the studies have methodologic problems or
systematic biases that limit the interpretation of results.
Moreover, the studies vary according to the amount of information
available on exposure to chlorinated water or DBPs. The panel agrees
that existing epidemiologic data are insufficient to conclude that
the reported associations are causal or provide an accurate estimate
of the magnitude of risk.
This cancer workshop panel also provided several recommendations
for conducting additional research. These included: (1) improving
exposure assessments; (2) conducting a reanalysis of previously
conducted interview-based case control studies using improved exposure
estimates and analytical methods to determine the validity of these
risks and to address confounding factors and bias not adequately
excluded in previous reports such as the meta-analysis completed by
Morris, et al. (1992) discussed in the 1994 proposed rule (USEPA,
1994b, page 38689); (3) conducting feasibility studies to identify
geographic locations with adequate exposure data and appropriate
cohorts for study (including the possibility of using existing cohorts
that are being studied for other potential exposures); and (4)
consideration of several possible designs for full scale studies (i.e.,
cohort, case-control, and case-control nested within a cohort).
In October 1995, the International Life Sciences Institute (ILSI)
sponsored a workshop on ``Disinfection by-products in Drinking Water:
Critical Issues in Health Effects Research'' (ILSI, 1995). One of the
panels at the workshop provided a brief summary of the findings from
cancer epidemiology studies and made recommendations for further
research in this area. The panel concluded that the epidemiological
studies of bladder and colorectal cancer have generally shown an
increased risk associated with the consumption of chlorinated surface
water, although a causal association has not been conclusively
established. The panel made several recommendations for future research
including the need to conduct hypothesis driven cancer epidemiological
studies to examine the risk of classes of DBPs other than THMs and to
support these studies with improved exposure assessments.
2. Implementation of Expert Panel Recommendations
a. Improve Exposure Assessments/Geographic Identification Studies/
Classes of DBPs Other Than THMs. USEPA, in conjunction with other
parties, has begun research to provide the tools needed to improve
exposure assessments for epidemiology studies. USEPA is supporting
studies in Colorado, North Carolina, and New Jersey that will provide
improved tools for conducting exposure assessments for epidemiology
studies. While the results from these studies will not be available for
the final Stage 1 DBP rule, they will be very useful in designing
future epidemiology studies.
In addition to USEPA's research, the Microbial/DBP Research Council
(M/DBP Council) is funding a study on ``Identification of Geographic
Areas for Possible Epidemiological Studies'' and is evaluating several
proposals for a project on ``Development of Methods for Predicting THM
and HAA Concentrations in Exposure Assessment Studies.'' The M/DBP
Council was formed as a joint USEPA and American Water Works
Association Research Foundation (AWWARF) project to identify and fund
critical research. This research, in conjunction with the USEPA
research discussed above, will improve the understanding of risks
associated with the consumption of chlorinated surface water. However,
as with USEPA's work, this research will not be completed in time to
impact the Stage 1 DBPR.
b. Meta-analysis of Existing Cancer Epidemiology Data. The 1994
proposal includes results of a meta-analysis that pooled the relative
risks from 10 cancer epidemiology studies in which there was a presumed
exposure to chlorinated water and its byproducts (Morris et al., 1992).
This meta-analysis estimated that approximately 10,000 cancer cases
each year could be attributed to the consumption of chlorinated
drinking water and its byproducts. As discussed in the preamble to the
proposed rule, this study generated considerable debate among the
members of the Negotiation Committee. An evaluation of the Morris et
al. meta-analysis has been recently completed for USEPA. USEPA is
currently evaluating this report and will provide an opportunity to
comment on EPA's assessment and implications for the regulatory
provisions for the final Stage 1 DBPR.
In addition to the meta-analysis, USEPA has summarized several new
cancer epidemiology studies and included them as part of the
``Summaries of New Health Effects Data'' (USEPA, 1997b) that is
included in the Docket for this Notice. USEPA will be evaluating the
data from the new epidemiology studies and will provide an opportunity
to comment on the potential implications of these new studies for the
regulatory provisions for the final Stage 1 DBPR.
B. Reproductive and Developmental Epidemiology Studies
The preamble to the 1994 proposal discussed several reproductive
epidemiology studies that had been conducted (see USEPA, 1994b, page
38690). It also included a discussion of an USEPA and ILSI expert panel
that reviewed the published epidemiologic and experimental data on
reproductive
[[Page 59395]]
and developmental effects and a strategy developed by the panel for
related short-term and long-term research (USEPA, 1993b). The panel
concluded that the currently available data on the effects of
chlorination byproducts provide an inadequate basis for identifying
DBPs as a reproductive or developmental hazard. Recommendations were
made for refining studies using existing data bases, strengthening
studies designed to collect new data, improving exposure assessments,
investigating selected health endpoints, and developing a stronger link
between animal research and epidemiology studies.
The results from the ILSI expert panel, and additional information
provided since the 1994 proposal, are summarized in Reif et al. (1996).
This paper reviewed the available epidemiological data on the reported
association between the consumption of chlorinated drinking water and
reproductive and developmental effects. The panel reached the following
conclusions. ``The currently available human studies on effects of
chlorination by-products provide an inadequate basis for identifying
DBPs as a reproductive or developmental hazard. Nevertheless,
additional laboratory animal and epidemiological research should be
conducted, employing a coordinated multi disciplinary approach.'' They
also provided recommendations for short-and longer-term research.
1. Improving Exposure Assessments
Many of the exposure assessment projects identified above for
cancer epidemiology are also relevant to improving exposure assessments
for evaluating reproductive and developmental effects. As discussed in
the cancer epidemiology section, while the results from these studies
will not be available for the final Stage 1 DBPR, they will be very
useful in designing future reproductive epidemiology studies.
2. New Studies Since Proposal
Since the proposal, several new reproductive and developmental
epidemiology studies have been published. Additionally, studies in
California and Colorado are nearing completion, but results will not be
available for this NODA. Savitz et al. (1995) used data from a
population-based case-control study to evaluate the potential risk of
miscarriage, preterm delivery and low birth weight in North Carolina
based on water source, amount of water consumed, and TTHM concentration
in water. The authors concluded, ``These data do not indicate a strong
association between chlorinated byproducts and adverse pregnancy
outcome, but given the limited quality of the exposure assessment and
the increased miscarriage risk in the higher exposure group, more
refined evaluation is warranted.''
Kanitz et al. (1996) conducted an epidemiology study in Italy on
the association between somatic parameters (e.g., birthweight, body
length, cranial circumference, and neonatal jaundice) and drinking
water disinfection with chlorine dioxide and/or sodium hypochlorite.
The authors concluded, ``The study provides some new information on the
possible association between some drinking water disinfection
treatments and somatic parameters of infants at birth. Further
investigations will be needed to verify the results of the present
study by rigorous exposure assessments.''
The 1994 proposed rule reported the results of a New Jersey
Department of Health report on the results of a cross-sectional study
evaluating the association between drinking water contaminants with low
birth weight and selected birth defects (Bove et al., 1992a, 1992b).
Since the proposal, an article summarizing the cross-sectional study
has been published by Bove et al. (1995). The results are consistent
with those reported in the proposed Stage 1 DBPR. The authors
concluded, ``By itself, this study cannot resolve whether the drinking
water contaminants caused the adverse birth outcomes; therefore, these
findings should be followed up utilizing available drinking water
contamination databases.''
While the new epidemiology studies add to the database on the
potential reproductive and developmental effects from DBPs, USEPA
believes that the results are inconclusive. A more complete discussion
of the new reproductive and development epidemiology studies can be
found in the ``Summaries of New Health Effects Data'' (USEPA, 1997b).
C. Significant New Toxicological Information for the Stage 1
Disinfectants and Disinfection Byproducts
Since the proposal, new toxicological information has become
available for several of the disinfectants and DBPs. The information
presented below is a summary of the significant new information for
several disinfectants and DBPs. For a more complete discussion of the
new information see the ``Summaries of New Health Effects Data''
(USEPA, 1997b) in the Docket (a summary of the new information for
chlorine and chloramines is not included below, but is included in the
document cited above.)
1. Chlorite
The 1994 proposal included an MCLG of 0.08 mg/L and an MCL of 1.0
mg/L for chlorite. In order to fill an important data gap, the Chemical
Manufacturers Association (CMA) agreed to conduct a two-generation
reproductive effects study of chlorite. The Negotiating Committee
agreed that if the studies indicated that a level of 1.0 mg/L of
chlorite is safe, the MCL would remain at 1.0 mg/L. If the studies
indicate that a level of 1.0 mg/L of chlorite is not safe or, if such a
study is not conducted, the MCL would be re-evaluated.
After the Negotiating Committee agreed to support a proposed MCL of
1.0 mg/L, USEPA selected developmental neurotoxicity hazard as the
critical effect for chlorite (Mobley et al., 1990). Based on this 1990
rat developmental study, an MCLG of 0.08 mg/L was derived for chlorite.
USEPA believed that the MCL of 1.0 mg/L agreed to by the Committee was
not adequate to protect the public from the acute developmental health
effects of chlorite. USEPA decided to propose an MCL of 1.0 mg/L to
honor the agreement of the Committee and requested comment on several
possible approaches for promulgating the final rule.
Since the proposal, a study on the subchronic toxicity of sodium
chlorite in rats (Harrington et al., 1995a) and a developmental
toxicity study in rabbits (Harrington, et al., 1995b) have been
published. Both of these studies reported no adverse toxicological
effects. Other than the two-generation reproductive study cited above,
which USEPA recently received, relevant new literature has not been
found that would alter the assessment for chlorite from the 1994
proposal. USEPA is conducting an external peer review of the CMA two-
generation reproductive study. These peer review comments will be
included in the Docket for this NODA when they become available. USEPA
will evaluate the data from the CMA study, including the peer review,
and will provide an opportunity to comment on the potential
implications for the regulatory provisions for chlorite prior to the
final Stage 1 DBP rule. The CMA study is included in the Docket for
this action (CMA, 1997).
2. Chlorine Dioxide
The proposed Stage 1 DBPR included a MRDLG of 0.3 mg/L and a MRDL
of 0.8 mg/L for chlorine dioxide. The proposed MRDLG for chlorine
dioxide was based on developmental neurotoxicity as the critical effect
(Orme et al., 1985). The Negotiating Committee agreed to the MRDL of
0.8 mg/L for
[[Page 59396]]
chlorine dioxide with certain qualifications and reservations. As cited
above, the Committee agreed that a two-generation reproductive study on
chlorite would be completed for consideration in the final Stage 1
DBPR. Toxicity information on chlorite is considered relevant for
characterizing the toxicity of chlorine dioxide. If the chlorite study
indicated no concern from reproductive effects at 0.8 mg/L, then the
proposed MRDL for chlorine dioxide would remain the same as proposed.
If these new data indicate reproductive or developmental effects, then
the MRDL will need to be re-examined comparing the tradeoffs and
regulatory impacts of a lower chlorine dioxide MRDL and the positive
aspects of using chlorine dioxide as a disinfectant.
Other than the two-generation reproductive study conducted by CMA
for chlorite, there is no new literature that would alter the
assessment for chlorine dioxide from the 1994 proposal. As stated
above, USEPA believes that the results from the chlorite study are
applicable for addressing the toxicity data gaps for chlorine dioxide.
USEPA will evaluate the data from the CMA study, including the peer
review, and will provide an opportunity to comment on the potential
implications for the regulatory provisions for chlorine dioxide prior
to the final Stage 1 DBP rule.
3. Trihalomethanes
The proposed rule includes an MCL for total trihalomethanes (TTHM)
of 0.080 mg/L. MCLGs of zero for chloroform, bromodichloromethane
(BDCM), and bromoform were based on sufficient evidence of
carcinogenicity in animals. The MCLG of 0.060 mg/L for
dibromochloromethane (DBCM) was based on observed liver toxicity from a
subchronic study and possible carcinogenicity. Since the 1994 proposal,
several new studies have been published on the metabolism for BDCM and
chloroform (Testai et al., 1995; Gemma et al., 1996a, 1996b; Gao et
al., 1996; Nakajima et al., 1995). In addition, several new studies
were found concerning the genotoxicity of chloroform, BDCM, and
bromoform (Roldan-Arjona and Pueyo, 1993; LeCurieux et al., 1995;
Pegram et al., 1997; Larson et al., 1994c; Fujie et al., 1993; Shelby
and Witt, 1995; Hayashi et al., 1992; Sofuni et al., 1996; Matsuoka et
al., 1996; Miyagawa et al., 1995; Banerji and Fernandes, 1996; and
Potter et al., 1996). There are considerable new data on cytotoxicity
and regenerative cell proliferation in the liver and kidney of rats and
mice under various conditions (Larson et al., 1993, 1994a, 1994b,
1994c, 1995a, 1995b, 1996; Templin et al., 1996a, 1996b). Many other
studies also examined the mechanism of chloroform carcinogenicity,
including studying the effects on methylation and expression of growth
control genes (Fox et al., 1990, Vorce and Goodman, 1991, Dees and
Travis, 1994, Testai et al., 1995, Sprankle et al., 1996, Chiu et al.,
1996, Gemma et al., 1996a, 1996b). Short-term toxicity studies
(Thorton-Manning et al., 1994; Lilly et al., 1994 and 1996) and chronic
toxicity studies which included reproductive evaluations (Klinefelter
et al., 1995) were found for BDCM.
The new studies on THMs contribute to the weight-of-evidence
conclusions reached in the 1994 proposal. Based on the available new
studies noted above, the proposed MCLGs for BDCM, DBCM, and bromoform
are not anticipated to change.
The International Life Science Institute (ILSI) convened an expert
panel in 1996 to explore the application of the USEPA's 1996 Proposed
Guidelines for Carcinogen Risk Assessment (USEPA, 1996a) to the
available data on the potential carcinogenicity of chloroform and
dichloroacetic acid (DCA); these data include chronic bioassay data and
information on mutagenicity, metabolism, toxicokinetics and mode of
carcinogenic action. USEPA will be evaluating the data from the ILSI
expert panel for chloroform and will provide an opportunity to comment
on the potential implications for the regulatory provisions for
chloroform and the trihalomethanes prior to the final Stage 1 DBP rule.
4. Haloacetic Acids
The proposed rule included an MCL of 0.060 mg/L for the haloacetic
acids (five HAAs-monobromoacetic acid, dibromoacetic acid,
monochloroacetic acid, dichloroacetic acid, and trichloroacetic acid)
with an MCLG of zero for dichloroacetic acid (DCA) based on sufficient
evidence of carcinogenicity in animals, and a MCLG of 0.3 mg/L for
trichloroacetic acid (TCA) based on developmental toxicity and possible
carcinogenicity.
There has been cancer research completed for other HAAs since the
1994 proposal. The 1994 proposal did not include an MCLG for
monochloroacetic acid (MCA) because there were inadequate occurrence
data for MCA. Since the proposal, a few toxicological studies on MCA
have been identified. A recent 2-year carcinogenicity study on MCA and
trichloroacetic acid (TCA) (DeAngelo et al., 1997) demonstrated that
MCA and TCA were not carcinogenic in male rats. This confirms the
results of the NTP (1990) cancer rodent bioassays of MCA. There have
been several recent studies examining the mode of carcinogenic action
for both DCA and TCA (Pereira and Phelps 1996; and Pereira 1996)
including mutagenicity studies (Austin et al., 1996; Mackay et al.,
1995; Fox et al., 1996; Fuscoe et al., 1996; Tao et al., 1996; and
Parrish et al., 1996). As discussed above USEPA will evaluate the
significance of the ILSI panel's report on the risk assessment for DCA
and provide an opportunity to comment on the potential implications for
the regulatory provisions for DCA and the other haloacetic acids prior
to the final Stage 1 DBP rule.
Screening studies have shown the potential of different haloacetic
acids, including DCA and brominated haloacetic acids, to produce
reproductive and developmental effects (Linder et al., 1997c; Hunter et
al., 1996; Richard and Hunter, 1996; Linder et al. 1994, 1995, 1997a,
1997b). At this time, these new studies are not expected to alter the
MCLGs for DCA or TCA in the proposed rule. USEPA continues to believe
that there are inadequate occurrence data to establish MCLGs for MCA,
monobromoacetic acid and dibromoacetic acid.
5. Chloral Hydrate
The proposed rule included an MCLG of 0.04 mg/L for chloral
hydrate. USEPA did not set an MCL for chloral hydrate because it
believed the MCLs for TTHM and HAA5, and the treatment technique
requirements would provide adequate control for chloral hydrate. In the
1994 proposal, chloral hydrate was considered a group C, possible human
carcinogen. Since the 1994 proposal, several new studies have been
published which contribute to the weight of evidence conclusion for the
potential carcinogenicity of chloral hydrate. These include in vitro
cell transformation and genotoxicity studies (Gibson et al., 1995;
Adler, 1996; Allen et al., 1994; Parry et al., 1996; and Ni et al.,
1996). Some screening studies were found concerning the potential of
chloral hydrate to cause reproductive and developmental toxicity
(Klinefelter et al., 1995 and Saillenfait et al., 1995). The available
new studies mentioned above do not indicate a change in the MCLG for
chloral hydrate.
6. Bromate
The proposed rule included an MCL of 0.010 mg/L and an MCLG of zero
for bromate. A major issue in the proposal was that setting an MCL at
0.010 mg/L
[[Page 59397]]
would exceed the theoretical 1 x 10-4 lifetime excess cancer
risk level for bromate of 5 ug/L. Since the proposal, several
toxicology studies have been completed on bromate, including assays for
reproductive and developmental effects (Wolfe and Kaiser, 1996).
USEPA has recently completed a chronic cancer study in male rats
and male mice for bromate. USEPA is evaluating this data and will
provide an opportunity for public comment on the potential implications
for the regulatory provisions for bromate prior to the final rule.
D. Summary of Key Observations
Since the proposal, several epidemiology and toxicology studies
have been completed on the potential health effects associated with
exposure to DBPs. USEPA currently believes the new published data will
not impact the MCLGs for BDCM, CDBM, bromoform, chloral hydrate, or
trichloroacetic acid. However, USEPA is currently evaluating the
results from new toxicology studies for chlorite and bromate and will
evaluate the report from the ILSI expert panel on chloroform and DCA
when it becomes available. USEPA will provide an opportunity to comment
on the potential implications for the regulatory provisions for these
DBPs prior to the final rule.
E. Request for Public Comments
USEPA requests comment on all the new information outlined above
and its potential impacts on the regulatory provisions for the final
Stage 1 DBPR and any additional data on the health effects from DBPs
that need to be considered for the final Stage 1 DBPR.
III. Enhanced Coagulation and Enhanced Softening
A. 1994 Enhanced Coagulation and Enhanced Softening Proposal
As discussed above, the 1994 proposed rule for D/DBPs included
enhanced coagulation/enhanced softening requirements in addition to
maximum contaminant levels (MCLs) for total trihalomethanes (TTHMs) and
the sum of five haloacetic acids (HAA5) (USEPA, 1994b). In that
proposal, Subpart H systems (utilities treating either surface water or
groundwater under the direct influence of surface water) that use
conventional treatment (i.e., coagulation, sedimentation, and
filtration) or precipitative softening would be required to remove DBP
precursors by enhanced coagulation or enhanced softening. The removal
of total organic carbon (TOC) would be used as a performance indicator
for DBP precursor control. The 1994 proposed rule (in ``Step 1'' of the
treatment technique) provided for 20-50 percent TOC removal, depending
on influent water quality (Table III-1).
Table III-1.--1994 Proposed Required Removal of TOC by Enhanced
Coagulation/Enhanced Softening for Surface-Water Systems a Using
Conventional Treatment b
------------------------------------------------------------------------
Source-water alkalinity, mg/L as
CaCO3
Source-water TOC, mg/L --------------------------------------
0-60 >60-120 >120 c
(percent) (percent) (percent)
------------------------------------------------------------------------
>2.0-4.0......................... 40.0 30.0 20.0
>4.0-8.0......................... 45.0 35.0 25.0
>8.0............................. 50.0 40.0 30.0
------------------------------------------------------------------------
a Also applies to utilities that treat groundwater under the influence
of surface water.
b Systems meeting at least one of the conditions in Section
141.135(a)(1)(i)-(iv) of the proposed rule are not required to operate
with enhanced coagulation.
c Systems practicing precipitative softening must meet the TOC removal
requirements in this column.
The 1994 Stage I Federal Register notice proposed that systems
achieve a percent TOC removal based on their influent TOC concentration
and alkalinity. The proposed rule provided for a number of exceptions
to the enhanced coagulation and enhanced softening requirements,
namely: (a) When the system's treated water TOC concentration, prior to
the point of continuous disinfection, is 2.0 mg/L (b) when
the PWS's source water TOC level, prior to any treatment, is 60 mg/L; and these systems are achieving TTHMs
3), except those
that use ion exchange, are not subject to performance criteria for the
removal of TOC.
As part of the enhanced coagulation requirements, the proposed rule
indicated that if a PWS could not meet the prescribed TOC removal
criteria, it must perform a series of jar or pilot-scale tests (``Step
2'') to determine how much TOC removal they can reasonably and
practically achieve. This Step 2 requirement was created to handle the
10 percent of the waters that were not expected to meet the Step 1
criteria, and considerations as to what was practical to achieve
involved a consensus-based balancing of policy and scientific
perspectives.
The proposed jar-testing protocol involves adding regular-grade
alum in 10 mg/L increments (or an equivalent amount of iron coagulant)
until specific depressed pH goals are achieved (this was referred to as
``maximum pH'' in the proposal), which depends on influent alkalinity
and what is practical to achieve. For the alkalinity ranges 0-60, >60-
120, >120-240, and >240 mg/L as calcium carbonate (CaCO3),
the maximum pH values are 5.5, 6.3, 7.0, and 7.5, respectively. The
maximum pH is a target pH goal for step 2 testing. The maximum pH is
the pH value the tested water must be at or below before incremental
coagulant addition is discontinued. The protocol was based on alum, as
more data were available on the use of this coagulant in a wide variety
of waters. However, the proposed rule allows for the use of iron
coagulants in the step 2 jar testing.
The TOC of each jar-treated water is measured, and then the
residual TOC is plotted versus alum dosage. The ``point of diminishing
returns'' (PODR) is determined to be when 10 mg/L of additional alum
(or an equivalent amount of iron coagulant) does not decrease residual
TOC by 0.3 mg/L (i.e., slope of TOC versus alum dosage curve
[0.3 mg/L TOC]/[10 mg/L alum]). These data would be used by
a utility
[[Page 59398]]
to request alternative TOC removal performance criteria from the
primacy agency. However, one of the intents in setting the step 1 TOC
removal percentages at the values chosen was to provide that 90 percent
of the systems would not need to do step 2 testing. This would minimize
transactional costs for the primacy agencies.
If the TOC removal curve never met the slope criterion at any
coagulant dose, such a water would be considered unamenable to enhanced
coagulation and no TOC removal would be required for such a water.
Waters with low TOC and moderate-to-high alkalinity were expected to be
some of the more difficult to treat with enhanced coagulation, so
systems treating such waters were encouraged to explore alternative
technologies (e.g., ozone/chloramines) that could reduce DBP levels
significantly below the proposed Stage 1 MCLs (i.e., 3?
(2) Use of ferrous salts: Can ferrous salts be used at softening pH
levels to further enhance TOC removals?
(3) Step 2: Whether data are available on the use of ferrous salts
in the softening process which can help define a step 2 for softening?
What is the definition of Step 2?
B. New Information on Enhanced Coagulation and Enhanced Softening since
1994 Proposal
Since the 1994 proposal, there has been considerable research on a
number of enhanced coagulation and enhanced softening issues
highlighted above in a wide variety of waters nationwide. A summary of
the results of some of the studies and surveys are included below.
Studies of enhanced coagulation are covered first, followed by
discussion of enhanced softening studies. Note that a number of the
softening studies looked at TOC removal in essentially the same
framework as is used for enhanced coagulation, with emphasis on the
coagulant and lime dose and geared toward finding a similar format for
step 2 enhanced softening as was defined for enhanced coagulation. A
number of these studies focused on the benefits of increased lime or
coagulant doses in removing TOC in softening systems. Results of these
studies generally showed that percent TOC removal is dependent on the
raw water.
1. New Data on Enhanced Coagulation
a. UNC Enhanced Coagulation Study. To address many of the
aforementioned issues, the University of North Carolina (UNC) at Chapel
Hill, with funding from the Water Industry Technical Action Fund
(WITAF), performed an enhanced coagulation study (Singer et al., 1995).
The UNC research team evaluated a wide range of waters nationwide,
which included at least three waters in each box of the 3 x 3 matrix in
Table III-1. Each water was jartested in order to determine the
feasibility of achieving the proposed step 1 TOC percent removal
requirement for each water, as well as to assess the PODR criteria.
In addition, recognizing that coagulation primarily removes the
humic fraction of the natural organic matter (NOM) in water (Owen et
al., 1993), a determination of the percent humic content was made for
each of the waters studied in order to better characterize the
treatability of each water. NOM fractionation was performed on samples
of each raw water and on select coagulated waters using an XAD-8 resin
adsorption procedure (Thurman & Malcolm, 1981). In this procedure, the
hydrophobic fraction of the water, which includes humic substances, was
determined.
Furthermore, Edzwald and Van Benschoten (1990) have found the
specific ultraviolet absorbance (SUVA) of a water to be a good
indicator of the humic content of that water, so SUVA was also
determined in the UNC study. SUVA is defined as the UV (measured in
m-1) divided by the dissolved organic carbon (DOC)
concentration (measured as mg/L). Typically, SUVA values 40 mg/L).
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In the jar tests of the Raleigh water, an alum dose of
35 mg/L resulted in the removal of 47 percent
of the TOC, where the proposed step 1 TOC removal for this water was
predicted to be 45 percent. The PODR, based on the slope criterion of
0.3 mg/L TOC/10 mg/L of alum, was realized at a jar-test alum dose of
39 mg/L, in which 51 percent of the TOC was removed. In order to comply
with a 45-percent TOC removal requirement with a 15-percent safety
factor (Krasner et al, 1996), a system would need to design for a 52-
percent TOC removal.
The results using the Raleigh water appear to address several of
the outstanding issues: namely, that the step 1 TOC removal
requirements for this water is appropriate, the slope criterion did
identify the PODR, and evaluation of the PODR required an examination
of points beyond the threshold coagulant dose. Figure III-3 shows jar
test results for a low-TOC (2.9 mg/L), high-alkalinity (239 mg/L) water
from Indianapolis, IN, from the UNC study (White et al., 1997). The TOC
removal curve never exceeded the 0.3/10 slope criterion, which means
that this water would be exempt from the enhanced coagulation
requirements in the 1994 proposed rule. The step 1 TOC removal
requirement of 20 percent can be achieved, with an alum dose of
65 mg/L required in the jar tests. However, the slope of
the TOC removal curve shows that this water is not very amenable to
enhanced coagulation.
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A summary of the controlling criterion for each of the 31 waters
tested by UNC, based on the 1994 proposed rule criteria, is shown in
Table III-2 (adapted from White et al., 1997). Only 14 of the 31 waters
met the proposed step 1 percent TOC removal requirements or achieved a
settled water TOC concentration 3
Source-water TOC, mg/L -------------------------------------------------------------------------
0-60 >60-120 >120
----------------------------------------------------------------------------------------------------------------
>2.0-4.0.............................. a PODR b N/A c
PODR PODR PODR
PODR STEP 1 d N/A
PODR PODR
PODR
>4.0-8.0.............................. STEP 1 PODR STEP 1
STEP 1 PODR STEP 1
STEP 1 STEP 1 PODR
STEP 1
>8.0.................................. STEP 1 STEP 1 STEP 1
STEP 1 PODR PODR
PDOR STEP 1 PODR
----------------------------------------------------------------------------------------------------------------
a Settled water TOC less than 2.0 mg/L.
b Point of diminishing returns.
c Not amenable to enhanced coagulation.
d Step 1 required percent removal of TOC.
White and co-workers (1997) examined the relationship between the
percent humic (hydrophobic) content of the raw waters in the UNC study
and the maximum percent removal of DOC achieved at the high alum doses
where little additional TOC removal was observed. Figure III-4 shows
that waters with relatively high levels of humic material tended to
exhibit higher degrees of DOC removal than those with low humic
content. Figure III-5 shows that waters that contained high initial
nonhumic (hydrophilic) DOC concentrations tended to have high residual
DOC concentrations following coagulation.
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In the UNC study, the humic carbon content of the raw waters was
reasonably correlated (r\2\=0.74) with their SUVA values (White et al.,
1997). Figure III-6 shows that waters with high initial SUVA values
(i.e., 3.4-5.7 L/mg-m) exhibited significant reductions in SUVA as a
result of coagulation, reflecting substantial removal of the humic (and
other UV-absorbing) components of the overall organic matter, whereas
waters with low initial SUVA values (i.e., 1.5-2.0 L/mg-m) exhibited
relatively low reductions in SUVA. For all of the waters examined, the
residual SUVA (i.e., 2.4 L/mg-m) tended to plateau at high
alum doses, reflecting that the residual DOC was primarily nonhumic
organic matter.
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In the UNC study, for the 14 waters in which the step 1 TOC removal
requirements were met before the PODR was reached, the average raw-
water SUVA was 3.9 L/mg-m, whereas the average raw-water SUVA of the
other 17 waters was 2.6 L/mg-m (White et al., 1997). For most of the 31
waters examined, the PODR was found to occur at alum doses where SUVA
had already reached its plateau. These findings suggested that raw-
water SUVA values might be utilized in redefining the step 1 TOC
removal requirements and that residual SUVA values might be utilized in
defining the PODR. Unlike NOM characterizations with XAD resins in a
research laboratory, SUVA is an easy parameter that can be determined
by laboratories that measure DOC concentrations and UV absorbance.
b. Metropolitan Water District of Southern California/Colorado
University Enhanced Coagulation Study. As noted in the UNC study,
waters with low TOC and high alkalinity were expected to be the more
difficult to treat with enhanced coagulation. Metropolitan Water
District of Southern California (MWDSC) and Colorado University at
Boulder did detailed studies on two low-TOC waters, one with moderate
alkalinity (California State Project Water) and the other with high
alkalinity (Colorado River water). In addition to using an XAD-8 resin
fractionation to quantify the humic (hydrophobic) versus nonhumic
(hydrophilic) content of the NOM, a 1000-dalton (1K) ultrafilter was
used to determine what fraction of the bulk or coagulated water was of
a lower versus higher molecular weight (Amy et al., 1987).
California State Project Water (with 80 mg/L alkalinity) was jar-
treated with incremental alum doses of 622 mg/L (up to a
total of 111 mg/L). Figures III-7 and III-8 show that addition of alum
at 47 mg/L reduced the raw-water bulk DOC concentration from 4.3 mg/L
to 2.6 mg/L (a 39-percent bulk DOC removal); subsequent alum addition
resulted in a plateauing of the DOC removal rate (Krasner et al.,
1995). Throughout the entire range of alum doses evaluated, little of
the low-MW and nonhumic DOC was removed. The high-MW and humic
fractions, however, were well removed with increasing alum dosages,
demonstrating preferential removal of these fractions. The residual DOC
remaining after enhanced coagulation was primarily made up of low-MW
and nonhumic material. The latter NOM fractions represent the part of
the bulk DOC that is not readily amenable to removal by coagulation.
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For this sample of California State Project Water, 52 percent of
the DOC was humic NOM and the SUVA value was 2.5 L/mg-m (Krasner et
al., 1995). Figure III-9 shows that increasing doses of alum reduced
the fraction of humic DOC in the residual DOC to 26 percent. In
addition, the reduction in SUVA closely paralleled the reduction in the
humic content of the residual DOC. SUVA was reduced to 1.7 L/mg-m with
47 mg/L of alum, whereas the addition of 111 mg/L of alum only reduced
the value of SUVA to 1.5 L/mg-m.
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Colorado River water has a greater amount of low-molecular weight
DOC and somewhat more nonhumic DOC than California State Project Water
(Krasner et al., 1995). Nonetheless, increased doses of alum did remove
DOC in Colorado River water, although not to the same extent as in
California State Project Water. Although the alkalinity of Colorado
River water (135 mg/L) is higher than that of California State Project
Water, the difference in treatability was more likely related to the
differences in the NOM characteristics of the two waters. As with
California State Project Water, the residual DOC in the coagulated
Colorado River water was primarily low-molecular weight and nonhumic
NOM (Figures III-10 and III-11). The raw-water Colorado River water had
a SUVA value of 1.1 L/mg-m and 44 percent of the DOC was humic NOM.
After the addition of 114 mg/L of alum, the humic content of the
residual DOC was only reduced to 38 percent and the SUVA value was only
reduced to 1.0 L/mg-m (Figure III-12).
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Cheng and co-workers (1995) studied enhanced coagulation of
California State Project Water and Colorado River water, as well as the
effects of seasonal changes on TOC removal. Several water blends were
tested, including 100-percent California State Project Water and
Colorado River water, as well as 90-, 80-, 70-, 60-, and 50-percent
Colorado River water blends. These blends represent the range of waters
that are treated at MWDSC's plants and may be subject to enhanced
coagulation treatment. The SUVA values for California State Project
Water during this study ranged from 2.8 to 3.8 L/m-mg, whereas the SUVA
values for Colorado River water varied from 1.0 to 1.7 L/m-mg (the
blends of California State Project Water and Colorado River water
contained SUVA values of 8 mg/L)/low alkalinity
(120 mg/L) waters had low-SUVA (median = 1.7).
For the entire 3 x 3 matrix, the cumulative probability distribution
(10th, 50th, and 90th percentile) of SUVA values typically increased
with either increasing TOC or decreasing alkalinity. Because SUVA is an
indication of humic NOM content, and it is the humic fraction that is
most amenable to enhanced coagulation, this SUVA distribution supports
the earlier observation of the UNC research team that step 1 TOC
removals were most readily met in high-TOC waters with low alkalinity.
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From this database, the Colorado University research team (Edwards,
1997; Tseng & Edwards, 1997) developed a model for predicting organic
carbon removal during enhanced coagulation, using as input the
coagulant dose, coagulation pH, raw-water UV absorbance, and raw-water
DOC concentration. The model assumes that all DOC can be divided into
two distinct fractions (Figure III-13): DOC that strongly complexes
hydroxide surfaces formed during coagulation and DOC that does not
(Edwards et al., 1996). Edwards defined these fractions as sorbing and
nonsorbing DOC, respectively. In the model, the relative fraction of
sorbing and nonsorbing NOM is calculated using an empirical relation
based on the value of SUVA (Edwards, 1997).
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In the Colorado University modeling effort (Edwards, 1997), the
best predictive capability was provided by a site-specific approach
using a best-fit sorption constant and nonsorbing DOC fraction for each
water quality and coagulant type (Figure III-14). Assuming a typical
DOC analytical error of either 0.25 mg/L or 5
percent, 81 percent of the model predictions were accurately predicted
within analytical precision.
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The Colorado University DOC/SUVA model was subsequently used to
determine the ``maximum'' TOC removal that can be achieved with
enhanced coagulation. All nine boxes in the 3 x 3 matrix (Table III-3)
were evaluated using the 10th, 50th, and 90th percentile water
qualities. The model was used to determine the amount of sorbable TOC
and to examine removal of 100, 90, 80, 70, 60, and 50 percent of the
sorbable TOC.
Table III-4 summarizes the results from the maximum TOC removal
task. A 10th percentile SUVA value corresponds to a water that is
difficult to treat (relative to other waters in that same box), whereas
a 50th and 90th percentile SUVA value corresponds to waters that are
average and easy to treat, respectively, in that box. The sorbable
amount of TOC represents the maximum amount of TOC that can be removed
using coagulants with no limit on coagulant dosage. Therefore, these
values may not be practical or realistic to achieve. In Table III-4,
the 1994 proposed Step 1 TOC removal requirements are listed, along
with a 15 percent safety factor. For example, in the low-TOC, low
alkalinity box, the current Step 1 TOC removal requirement (40 percent)
with a safety factor is 46 percent. In this box, for an easy to treat
water (90th percentile SUVA of 3.97), 62 percent of the sorbable TOC
would need to be removed to ensure compliance with the proposed
requirement; whereas for a difficult to treat water (10th percentile
SUVA of 2.84), 71 percent of the sorbable TOC would need to be removed.
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The next analyses evaluated what TOC removal is ``practical'' to
achieve in order to better define the 3 x 3 matrix. The data analyses
were aimed at developing an alternative set of percent TOC removal
numbers for step 1 requirements, recognizing that the goal was to
select values that could be ``reasonably'' met by 90 percent of the
systems implementing enhanced coagulation. Using the database compiled
through the Malcolm Pirnie, Inc./AWWA project and summarized in Table
III-3, the following nine equations were developed to predict ``90th-
percentile'' TOC for a given coagulant dose. Figure III-15 illustrates
the shape of the curves for the low-alkalinity waters.
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The significance of the 90th-percentile data point is that 90
percent of systems (represented by the database) will have a lower
residual TOC compared to what is predicted by the equations for a given
coagulant dose.
1. TOC=1.42+2.04 e -7.15
Dose (moles/L) [for low-TOC, low-alkalinity box]
2. TOC=1.37+2.10 e -3.92
Dose (moles/L) [for low-TOC, medium-alkalinity box]
3. TOC=2.10+1.27 e -2.73
Dose (moles/L) [for low-TOC, high-alkalinity box]
4. TOC=1.60+5.38 e -6.29
Dose (moles/L) [for medium-TOC, low-alkalinity box]
5. TOC=2.11+4.41 e -3.47
Dose (moles/L) [for medium-TOC, medium-alkalinity box]
6. TOC=2.64+3.30 e -4.83
Dose (moles/L) [for medium-TOC, high-alkalinity box]
7. TOC=3.22+23.1 e -2.99
Dose (moles/L) [for high-TOC, low-alkalinity box]
8. TOC=4.88+13.8 e -3.33
Dose (moles/L) [for high-TOC, medium-alkalinity box]
9. TOC=6.61+6.44 e -3.57
Dose (moles/L) [for high-TOC, high-alkalinity box]
Based upon the above equations, the coagulant dosages for achieving
the proposed percent TOC removals and the proposed PODR slope criterion
(i.e., 0.3 mg/L TOC per 10 mg/L of alum) were calculated. These
calculations indicated that the low-TOC boxes will be at the proposed
slope criterion at coagulant dosages lower than what would be required
for achieving the proposed step 1 percent TOC removals. The opposite
was true for the high-TOC boxes. For the medium-TOC boxes, the
calculated coagulant dosages were approximately equal for both
criteria. The trends for the different boxes in the matrix are similar
to that observed by the UNC research team (Table III-2). Table III-5
summarizes the controlling criteria.
Table III-5.--Controlling Criterion for Enhanced Coagulation for Waters
Evaluated in Malcolm Pirnie, Inc. Study, Based on Modeling Approach
------------------------------------------------------------------------
Alkalinity mg/L
TOC (mg/L) -----------------------------------------
0-60 >260-120 >120
------------------------------------------------------------------------
>2.0-4.0...................... PODR........ PODR......... PODR
>4.0-8.0...................... Step 1...... PODR......... Step 1
>8.0.......................... Step 1...... Step 1....... Step 1
------------------------------------------------------------------------
Malcolm Pirnie, Inc. next examined SUVA removal curves (Figure III-
16), similar to what was examined by the UNC research team (Figure III-
6).
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The 90th-percentile SUVA curves were observed to reach asymptotic
values with increasing coagulant Dose (Figure III-16 illustrates the
shape of the curves for the low-TOC waters). The following seven
equations were developed to predict the 90th-percentile SUVA for a
given coagulant Dose. The three alkalinity ranges for the high-TOC
waters were collapsed into one group due to lack of sufficient data.
Similar to the TOC equations, the significance of the 90th-percentile
data point is that 90 percent of systems (represented by the database)
will have a lower residual SUVA compared to what is predicted by the
equations for a given coagulant Dose.
a. SUVA=1.8+2.1 e -11.1
Dose (moles/L) [for low-TOC, low-alkalinity box]
b. SUVA=1.8+1. 2 e -7.9
Dose (moles/L) [for low-TOC, medium-alkalinity box]
c. SUVA=1.4+2.2 e -9.5
Dose (moles/L) [for low-TOC, high-alkalinity box]
d. SUVA=1.9+2.8 e -17.5
Dose (moles/L) [for medium-TOC, low-alkalinity box]
e. SUVA=1.8+2.0 e -5.2
Dose (moles/L) [for medium-TOC, medium-alkalinity box]
f. SUVA=2.1+0.95 e -6.0
Dose (moles/L) [for medium-TOC, high-alkalinity box]
g. SUVA=2.5+2.8 e -3.8
Dose (moles/L) [for high-TOC boxes]
From a theoretical viewpoint, the asymptote of the above equations
represents the minimum SUVA that could be achieved for a given data set
(box) of the 3x3 matrix. The dosages for the minimum SUVA are related
to certain maximum percent TOC removals. However, from a practical
standpoint, achieving the minimum SUVA could be extremely difficult. An
alternative approach could be to attempt to reach SUVA values which are
20 or 25 percent above minimum SUVA indicated by the above equations.
Equations 1 through 9 and equations a. through g. were combined to
determine the practical percent TOC removal values that could be
achieved. The results for ``minimum SUVA+25%'' are shown in Table III-
6.
Table III-6.--TOC Removals (%) at ``Minimum SUVA+25%,'' Based on Malcolm
Pirnie, Inc. Modeling Effort
------------------------------------------------------------------------
Alkalinity (mg/L)
TOC (mg/L) ---------------------------
0-60 >60-120 >120
------------------------------------------------------------------------
>2.0-4.0.................................... 35 25 15
>4.0-8.0.................................... 35 45 20
>8.0........................................ 60 55 35
------------------------------------------------------------------------
One limitation of a step 2 based on a settled-water SUVA approach
would be that the utilities would have to determine these SUVA values
in the absence of any oxidant (such as chlorine, permanganate, or
ozone). Addition of oxidant changes the characteristics of the NOM in a
manner that disproportionately affects the UV absorbance compared to
TOC, thus changing the SUVA values without any actual removal of TOC.
d. Evaluation of current (baseline) TOC removals at full-scale.
Full-scale TOC removal data were obtained from 76 treatment plants
(Table III-7). These data were obtained from plants in the American
Water Works Service Company (AWWSCo) system, plants studied by Randtke
et al. (1994), and plants in North Carolina studied by Singer et al.
(1995). Note that these data represent a one-time sampling at each
plant and no specific attempt was made to meet the proposed TOC removal
percentages. Also, the proposed compliance requirements were based on
an annual average. Based on current treatment, 83 percent of the
systems treating moderate-TOC, low-alkalinity water removed an amount
of TOC greater than the proposed step 1 requirement, whereas only 14
percent of the systems treating water with low TOC and high alkalinity
met the proposed step 1 requirement. For the other systems treating
low- or moderate-TOC water, 29-38 percent met the proposed step 1
requirements with existing treatment. Although all of the high-TOC
systems met the proposed TOC removal requirements with current
treatment, the number of systems in this database were insignificant
(1-2 per box).
Table III-7.--TOC Removal at Full-Scale Treatment Plants
----------------------------------------------------------------------------------------------------------------
TOC >2.0-4.0 mg/L Percent of plants that achieve specified TOC removal
----------------------------------------------------------------------------------------------------------------
No. of Step 1 0-10% 10-20% 20-30% 30-40% >40%
Alkalinity (mg/L) Plants TOC% removal removal removal removal removal
----------------------------------------------------------------------------------------------------------------
0-60................................. 14 40 14 14 14 29 *29
>60-120.............................. 11 30 36 0 27 18 18
>120................................. 7 20 57 29 14 0 0
----------------------------------------------------------------------------------------------------------------
TOC >4.0-8.0 mg/L
(4)Percent of plants that achieve
specified TOC removal
--------------------------------------------------------------------------
0-15%
removal 15-25%
removal 25-35%
removal 35-45%
removal >45%
removal
----------------------------------------------------------------------------------------------------------------
0-60................................. 18 45 0 0 11 6 83
>60-120.............................. 8 35 12 25 25 38 0
>120................................. 13 25 31 31 23 15 0
----------------------------------------------------------------------------------------------------------------
TOC >8.0 mg/L
(4)Percent of plants that achieve
specified TOC removal
--------------------------------------------------------------------------
0-20 20-30 30-40 40-50 >50
----------------------------------------------------------------------------------------------------------------
0-60................................. 2 50 0 0 0 0 100
>60-120.............................. 2 40 0 0 0 0 100
>120................................. 1 30 NA NA 100 NA NA
----------------------------------------------------------------------------------------------------------------
*Values in bold represent the percentage of systems that achieved full-scale TOC removal that is greater than
the proposed step 1 requirements.
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e. Evaluation of ``optimized'' TOC removal. An ``optimized''
coagulation database was assembled, utilizing experiments performed by
AWWSCo and by Randtke et al. (1994) (Table III-8). This database
included experiments in which a combination of coagulant and acid was
evaluated. The National Sanitation Foundation (NSF) limit on sulfuric
acid addition (to minimize the introduction of trace impurities present
in the acid) is 50 mg/L. In examining the database, an attempt was made
to limit coagulant doses to 10-20 times the TOC level.
Thus, a water with 3 mg/L TOC might use up to 30-60 mg/L of coagulant
(with or without acid), but would not use 100 mg/L of coagulant full-
scale. However, a water with 10 mg/L TOC could use 100 mg/L or more of
coagulant given the aforementioned 10-20 multiplier for
coagulant dose and TOC. A dose of this magnitude is discouraged because
the NSF limits on aluminum sulfate and ferric chloride are 150 mg/L and
250 mg/L, respectively. Because these experiments were performed
without these acid and coagulant dose limits as constraints, some
waters were evaluated with more realistic chemical doses in the PODR
experiments. A judgment was made in deciding which set of conditions
was the most realistic for each water evaluated. With these elements in
mind, an assessment was made as to which experiment was the most
appropriate (controlling criteria) for each water. In some cases, a
source water was tested more than once. If the identical sample of
water (same TOC, SUVA, alkalinity) was coagulated with different
coagulants, with or without acid, the highest TOC removal for that
water was chosen, as many systems enhancing their coagulation process
are also evaluating switching the type of coagulant.
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f. ``Case-by-case'' data analyses. A decision was made by the TWG,
based on the Malcolm Pirnie, Inc. modeling effort and examination of
the case-by-case data, to segment out raw waters with SUVA
(SUVAr) 120 mg/L) waters in the low
(>2-4 mg/L) and moderate (>4-8 mg/L) TOC boxes have SUVA 2.0 L/mg-m, the
minimum, 25th percentile, 50th percentile, 75th percentile, and maximum
TOC removal for each of the boxes in the 3 x 3 matrix were determined.
This analysis allowed for an analysis of the cumulative probability
distribution of TOC removal for waters that are amenable to enhanced
coagulation.
(3) For example, the high-TOC (>8 mg/L)/low alkalinity (0-60 mg/L)
box had a range of TOC removals from 56 to 76 percent. In order to
comply with a 50 percent TOC removal (the proposed step 1 value for
that box) with a safety factor of 15 percent, a 57 percent TOC removal
would be required. The minimum and 25th percentile TOC removal for that
box is 56 percent. Thus, it is expected that essentially all of the
waters in this box (based on this limited data set and data from other
sources) could comply with the proposed step 1 requirement.
(4) If the step 1 requirement for the high-TOC/low-alkalinity box
was raised, for example, to 60 percent, then systems would need a 69
percent TOC removal to safely meet such a requirement. The 75th
percentile of TOC removal for this box is 69 percent. Thus, raising the
step 1 requirement to 60 percent could potentially drive half or more
of the systems in this box to need to do step 2 testing for possible
alternative performance criteria. Thus, these data suggest that for
this and a number of other boxes (all of the high-TOC boxes and
probably most of the moderate-TOC boxes), the currently proposed step 1
TOC removals are appropriate. Systems that can achieve higher TOC
removals in these boxes will consider doing so in order to more
effectively meet the DBP MCLs that have been proposed.
(5) For the low-TOC boxes, even after excluding the low-SUVA
waters, the proposed step 1 TOC removal levels still appear too high.
In Malcolm Pirnie, Inc.''s modeling of TOC removal at minimum SUVA + 25
percent, it was predicted that the required TOC removals in the low-TOC
boxes would be 35, 25, and 15 percent for low-, moderate-, and high-
alkalinity, respectively. These predicted TOC removal values are in the
range for which the majority of low-TOC waters with SUVA values >2.0 L/
mg-m can achieve. Thus, the TWG recommended to the FACA Negotiating
Committee-based on Malcolm Pirnie, Inc.''s modeling effort and this
case-by-case analysis--a revised set of TOC removal numbers for the
low-TOC boxes, keeping in mind that low-SUVA waters would be excluded
from the requirement.
(6) The TWG also recommended to the FACA Negotiating Committee an
alternative step 2 point of diminishing return (PODR) of settled-water
SUVA 2.0 L/mg-m. This action will also reduce transactional
costs, as presentation of a settled-water SUVA value will be easier
than presenting jar-test data. Nonetheless, the jar-test protocol and
slope criterion will still be needed for evaluating alternative
performance criterion for other waters.
2. New Data on Enhanced Softening
a. AWWARF studies--data on TOC removal. Several studies examined
the relationship between increased coagulant dose and TOC removal
(Shorney and Randtke, 1996; Clark et al. 1994). These studies indicate
that the benefit from increased coagulant dose in TOC removal was
dependent on the raw water. In a study funded by AWWARF, Shorney and
Randtke (1994) indicated that utilities treating source water
relatively low in TOC (i.e., 2.5 to 4 mg/L) and low in turbidity will
have the greatest difficulty in removing TOC (Figure III-17 and III-
18).
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The authors indicate some improved TOC removal from small doses of
iron salts (5 mg/L ferric sulfate), but no additional TOC removal
during softening occurred with increased coagulant addition (up to 25
mg/L dose) as shown in Figures III-17 and III-18.
In limited jar testing and in pilot testing, the City of Austin (a
softening plant) has observed no significant difference in TOC removal
with increasing doses of ferric sulfate beyond a low dose. Table III-9
shows the impact of increasing ferric sulfate doses on the turbidity
and TOC concentration for jar tests in the City of Austin. The results
indicate no significant difference in TOC removal with increasing doses
of ferric coagulants, but did show that varying the coagulant dose did
impact the turbidity removal as measured by NTU.
Table III-9.--Impact of Varying Ferric Coagulant Dose on TOC Removal,
Austin, Texas, 4/9/93, 110 mg/L Lime Dose, Jar Tests
------------------------------------------------------------------------
Treated
water Treated
Ferric sulfate addition (mg/L) turbidity, water TOC
NTU (mg/L)
------------------------------------------------------------------------
3................................................ 16 2.45
6................................................ 15 2.30
9................................................ 12 2.46
12............................................... 12 2.23
18............................................... 5.5 2.31
------------------------------------------------------------------------
Pilot testing confirmed the jar test results by showing that
increasing ferric sulfate doses beyond that required for turbidity
removal proved to have no advantage in additional TOC removal (see
Figure III-19).
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Full-scale plant data from St. Louis County Water Company and
Kansas City, MO Water Services show that water temperature, turbidity,
and raw water TOC levels have direct impact upon the efficiency of lime
softening with iron salt coagulants to improve TOC removal.
Multiple jar tests on various waters done by Singer et al. (1996)
focused on the relationship between use of lime and soda ash and TOC
removal. Using only lime and soda ash (no coagulants), Singer et al.
defined the dosages required to meet TOC removal percentages in the
matrix. He also defined the dosages required to remove 10 mg/L of
magnesium for nine waters that met the alkalinity levels in the right
hand column of the matrix (i.e., >120 mg/L). Results of these jar tests
are shown in Table III-10. Impacts of the proposed rule would be
significant to softening plants if the TOC removal requirements were
required to be met by all plants because the requisite lime and soda
ash doses were higher than existing doses in the plants. Singer et al.
(1996) found the removal of 10 mg/L of magnesium hardness to have less
impact, although using the magnesium criteria would make TOC removal
levels variable and less significant than meeting the removal levels in
the matrix.
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b. Shorney and coworkers--data on use of SUVA. As discussed
previously, SUVA may be a practical method for determining which PWSs
would be required to perform enhanced coagulation and enhanced
softening. SUVA has been found to be a good indicator of humic content
and it is the humic material that is best removed by coagulation.
Shorney et al. (1996) report raw water SUVA values -1) divided by the DOC concentration (mg/L). Typically,
SUVA values 2-4............................................ 11 8
>4-8............................................ 20 17
>8.............................................. 4 3
------------------------------------------------------------------------
The data were analyzed with two goals in mind: to find the
appropriate TOC removal levels for the rule matrix for softening plants
and to determine what would define an appropriate step 2 for softening
systems. To address the first question, the average TOC percent
removals for each TOC group were plotted on a percentile basis and are
shown in Figure III-21 (Clark et al., 1997) for the 2-4 mg/L TOC, and
Figure III-22 for the 4-8 mg/L TOC (Clark et al., 1997).
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To examine the percentage of plants that would meet the proposed
requirements, the survey data were analyzed and the results are shown
in Table III-12. The results in Table III-12 indicate that the relative
impact of meeting the TOC removal requirement in the proposed rule
would be greatest in the low TOC group (>2-4 mg/L) .
Table III-12.--Percentage of Softening Plants Meeting Current Proposed
Requirements
------------------------------------------------------------------------
Proposed
1994 Percentage
Raw TOC (mg/L) required of plants
percent that met
removals requirements
------------------------------------------------------------------------
>2-4........................................... 20 60
>4-8........................................... 25 80
>8............................................. 30 66
------------------------------------------------------------------------
To address the second question regarding Step 2 criteria, the
survey results for percent removal TOC and lime dose were plotted to
examine the relationship between them (see Figure III-23) and to
determine whether a point of diminishing returns can be identified for
lime addition. Figure III-23 indicates that no correlation can be
discerned, the data are highly variable, and no point of diminishing
returns corresponding to a specific lime dose addition can be
identified. The wide variation in water quality (e.g., pH, alkalinity,
type of TOC), as well as the differences in coagulant usage, probably
contributed to data variability.
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Another important issue for softening systems is the pH level used
in the softening process. As the lime dose is increased, the pH of the
softening process increases and the character of the precipitate
changes; as the pH rises above 10, the major precipitate formed changes
from calcium carbonate to magnesium hydroxide. The TOC percent removal
in the survey data was plotted versus the pH of softening and is shown
in Figure III-24 . The data show that at higher softening pH levels,
generally greater percentages of TOC are removed. Also as the lime dose
is increased alkalinity is consumed and if the lime dose is high enough
to deplete the raw water alkalinity, soda ash must be added to maintain
the precipitation process. Crossing either one of these thresholds
(either changing the dominant precipitate from calcium carbonate to
magnesium hydroxide or changing from a lime softening system to a lime/
soda softening system) constitutes a major change in the treatment
process. Magnesium hydroxide floc do not act the same as calcium
carbonate floc either in settling or in sludge treatment and the plant
design for the two precipitates would be significantly different.
Forcing a plant to increase pH to the point of having to add soda ash
would also be a significant treatment change due to pH adjustment
problems and because the precipitate would likely be changing at the
same time. Most softening plants are normally operated without soda ash
addition because of the high cost of soda ash, the additional sludge
production, the increased chemical addition to stabilize the water and
the increased sodium levels in the finished water (Randtke et al., 1994
and Shorney et al., 1996).
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Raising the pH by adding lime can have other impacts such as
depleting alkalinity and potentially causing corrosion problems. To
determine what finished water alkalinity most softening plants produce,
the survey data was plotted for finished water alkalinity and TOC
percent removal (see Figure III-25 (Clark et al., 1997)). With only a
few outliers and regardless of the percent TOC removal, most plants
produce finished water with alkalinity between 30 and 60 mg/L as
CaCO3.
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The survey obtained basic information on disinfection practices in
softening plants. Forty percent of the plants responding predisinfect.
Softening plants predisinfect for the same reasons that conventional
coagulation plants do, that is, to comply with Surface Water Treatment
Rule Disinfection requirements, to oxidize iron and manganese, to
control zebra mussels and Asiatic clams, and to control taste and odor
problems. Disinfectants in use in softening plants are as follows:
28% of plants use free chlorine for both primary and
secondary disinfection.
50% of plants use free chlorine/chloramine.
10% of plants use chloramine.
7% of plants use chlorine dioxide/chloramine.
5% of plants use ozone/chloramine.
In spite of the fact that some 78% of softening plants are using
free chlorine for at least a portion of their disinfection, the
reported yearly average THMs indicate that 90 percent of plants are
currently meeting an 80 g/L level for THMs (see Figure III-26
(Clark et al., 1997)). All reporting softening plants have average HAA5
levels below 60
g/L (see Figure III-27 (Clark et al., 1997)). For the majority
of softening plants, minor adjustments to disinfection practices may
bring them into compliance with the proposed total THM and HAA5 MCLs,
as long as predisinfection credit is allowed. Without predisinfection
credit, these plants could face the major impact of having to provide
disinfection time after sedimentation, and for at least one of the
reporting utilities, that could mean significantly increasing the free
chlorine contact time to get the maximum CT credit by making up for a
shortened detention time. The end result for that system will likely be
an increase in finished water total THMs over what are being produced
using predisinfection credit. However, these site-specific issues will
need to be addressed individually, as removing the precursors by
enhanced softening will also remove some of the chlorine demand
resulting in less disinfectant addition to obtain the necessary
residual.
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C. Summary of Key Enhanced Coagulation and Enhanced Softening
Observations
Based on the data and analysis outlined above, the M/DBP Advisory
Committee has recommended the following revisions to the proposed
enhanced coagulation and softening requirements to address the
outstanding issues on the use of this technology to control DBP
precursors (see Table III-13). The top row has been modified from the
proposal by lowering the values by 5%. Enhanced softening systems are
required to comply with the column for alkalinity > 120 mg/L as
CaCO3.
Table III-13.--1997 Proposed Required Removal of TOC by Enhanced Coagulation/Enhanced Softening for Surface-
Water Systems Using Conventional Treatment
----------------------------------------------------------------------------------------------------------------
Source water alkalinity, mg/L as CaCO3
-----------------------------------------------
Source water TOC, mg/L 0-60a >60-120 a >120 a b
(percent) (percent) (percent)
----------------------------------------------------------------------------------------------------------------
>2.0-4.0........................................................ 35.0 25.0 15.0
>4.0-8.0........................................................ 45.0 35.0 25.0
>8.0............................................................ 50.0 40.0 30.0
----------------------------------------------------------------------------------------------------------------
a Not applicable to waters with raw-water SUVA 2.0 L/mg-m.
b Systems practicing precipitative softening must meet the TOC removal requirements in this column.
For waters with TOC >4.0 mg/L (6 of the 9 boxes in the 3 x 3
matrix), the TWG felt that 90 percent of these waters can meet the 1994
proposed step 1 TOC removal requirements. For waters with TOC >2.0-4.0
mg/L, the Committee recommended that the TOC removal requirements be
35, 25, and 15 percent for low-, moderate-, and high-alkalinity waters,
respectively. For low-TOC waters with raw-water SUVA >2 L/mg-m, the TWG
felt that 90 percent of the systems treating such waters will be able
to comply with the revised step 1 TOC removal levels.
The Committee recommended that waters with raw-water SUVA
2.0 L/mg-m be given an exemption to enhanced coagulation and
enhanced softening. SUVA is an indicator of the humic content of a
water. Coagulation removes humic matter, so waters with low-SUVA values
contain primarily nonhumic matter, which is not amenable to enhanced
coagulation. The use of a raw water SUVA 2.0 L/mg-m. At this point, the
residual TOC is mainly composed of nonhumic matter that is not amenable
to enhanced coagulation; therefore, it is not productive to add
additional coagulant. Because oxidants can destroy UV, but not TOC,
SUVA must be determined on water that has not been exposed to oxidants.
Thus, using a settled-water SUVA 2.0 L/mg-m as a PODR should
be done on jar-tested water (as the slope criterion is done) unless the
full-scale plant is not using preoxidation/predisinfection. The TWG
believes that these revised requirements will result in a limited
amount of transactional costs for the PWSs and their primacy agencies.
The Committee recommended this option to EPA.
Enhanced softening systems that cannot meet the removal percentages
specified in the TOC removal matrix must demonstrate that they have met
alternative performance criteria, e.g., depressed the alkalinity to a
minimum level or lowered settled water SUVA 2.0 L/mg-m.
Also, systems that remove a minimum of 10 mg/L of magnesium hardness
(as CaCO3) from their raw water are exempt for enhanced
softening requirements. Lime softening plants would not be required to
perform lime-soda ash softening, and no softening plant will be
required to lower treated effluent alkalinity below 40 mg/L (as
CaCO3), as part of any Step 2 procedure.
Because the determination of SUVA requires measurement of DOC, the
TWG believed that guidance on this determination is necessary. DOC is
determined on filtered samples, but it is important that the filter
paper does not leach DOC. Protocols and quality assurance measures to
ensure that SUVA is properly measured are discussed in the analytical
methods section.
Another exception to enhanced coagulation in the proposed 1994 rule
was for systems that treated water with 60 mg/L
alkalinity that achieved TTHMs 2/chloramine addition in order to lead to reduction of
DBPs. Four investigators tested the validity of this assumption.
Summers (Summers et al., 1997) summarized the findings of the four
investigators concerning the impact of moving the point of chlorination
during coagulation, flocculation and sedimentation on DBP formation for
a representative range of waters and treatment conditions. In addition,
studies were carried out at the University of Cincinnati under the
sponsorship of EPA, the American Water Works Association (Water Utility
Council-Water Industry Technical Action Fund) and the Chlorine
Chemistry Council (Solarik et al., 1997). The results of these studies
are summarized here.
Sixteen source waters have been evaluated to date. The waters were
selected to proportionately represent the national source water
distribution in the enhanced coagulation 3 x 3 (TOC--alkalinity) matrix
as estimated from AWWA water industry database (WIDB). Waters were
chosen to represent the >2.0-4.0 mg/L and >4.0-8.0 mg/L TOC ranges. For
TOC >8.0 mg/L, prechlorination would generally not be a suitable
option, as experience and computer modeling have shown that
prechlorination of these waters under the conditions of this study is
likely to yield TTHM and HAA5 values that exceed the 0.080 mg/L and
0.060 mg/L proposed MCLs, respectively. WIDB TOC data indicate that
less than 10 percent of the surface waters have TOC concentrations
greater than 8.0 mg/L.
The study was conducted using a bench-scale batch jar testing
procedure with chlorine added at different times to simulate full-scale
continuous flow conditions with chlorine added at different points.
Alum
(Al2(SO4)318H2O)
was used as the coagulant for all waters and two alum doses were
examined for 14 of the 16 waters evaluated. The baseline dose was set
at the level required for turbidity control, while a second increased
dose was set at the level necessary to meet the required percent TOC
removal in the 3 X 3 enhanced coagulation matrix. In three cases, the
required TOC removal was achieved by baseline coagulation. The jar
tests were carried out at ambient laboratory temperature, (22 deg.C).
Chlorine was added to four parallel jars at four different times
during the coagulation, flocculation and sedimentation process for both
the baseline coagulant dose and the increased coagulant dose: 1) 3
minutes before rapid mixing (Pre-RM), (2) at the end of rapid mixing
(Post-RM), (3) in the middle of flocculation (Mid-Floc), and (4) at the
end of sedimentation (Post-Sed). Additionally, the raw uncoagulated
water was adjusted to the settled water pH and chlorinated. The DBP
results from the raw uncoagulated water served as a basis for
comparison. The chlorine doses were chosen to yield a free chlorine
residual of 0.6 0.4 mg/L after 3 hours of total contact
time at ambient pH (6.1-8.1) and laboratory temperature (22 deg.C). The
3 hour reaction time is representative of that of a typical
coagulation, flocculation and sedimentation process train. At the end
of the 3 hour incubation time, the reaction was quenched and DBPs were
assessed. Settled water was also chlorinated under uniform formation
conditions (UFC) (Summers et al., 1996) to represent distribution
system DBP formation. A more detailed experimental approach is
presented elsewhere (Solarik et al., 1997, Summers et al., 1997).
Impact of Point of Chlorination
The impact of moving the point of chlorination downstream for both
baseline and increased dose coagulation is shown in Figures IV.1, IV.2,
and IV.3 for TOX, TTHM, and HAA5 concentrations, respectively. The
distribution of data is shown as box and whisker plots indicating the
mean and median, the 10th, 25th, 75th, and 90th percentiles, and any
data that lies outside the 10th and 90th percentiles. Moving the point
of chlorination further downstream decreased the concentration of DBPs
formed after three hours of contact time with free chlorine. The DBP
concentrations shown in these three figures are not intended to
represent occurrence levels of DBPs in the distribution system, only
those which were formed under the conditions of this study. Figures
IV.4, IV.5, and IV.6 show the percent decrease in DBP formation
relative to that formed in the raw uncoagulated water.
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The decrease in DBP formation was calculated by subtracting the DBP
concentration formed upon chlorination at a given point in the jar test
from that formed upon chlorination of the raw waters. Chlorinating 3
minutes prior to rapid mixing (Pre-RM) led to a median 32, 26 and 17
percent decrease in TOX, TTHM, and HAA5 concentrations, respectively,
relative to those formed upon chlorination of the raw uncoagulated
water. Prechlorinating more than 3 minutes prior to rapid mixing was
shown to increase the DBP formation relative to Pre-RM.
For TOX, TTHM, and HAA5, moving the point of chlorination
downstream in the coagulation, flocculation, and sedimentation process
decreased DBP formation and the chlorine demand by providing additional
time for NOM removal before chlorine could react with the NOM to form
DBPs. While having only a small impact on average for TOX, TTHM, and
HAA5 formation, moving the point of chlorination from Pre-RM to Post-RM
was very beneficial for some waters. As expected, the largest benefit
for all parameters investigated was observed by moving the point of
chlorination to after sedimentation, which resulted in the lowest DBP
formation. On average, the benefit of moving the point of chlorination
downstream was greater for HAA5 than for TOX and TTHM.
The median, 10th and 90th percentile (shown in brackets) decrease
in TOX formation as a result of moving the point of chlorination from
Pre-RM to (1) post-RM was -5.4 percent (-17 and 16 percent); (2) mid-
Floc was 6.1 percent (-6.8 and 19 percent); and (3) post-Sed was 17
percent (4.5 and 34 percent).
The median, 10th and 90th percentile (shown in brackets) decrease
in TTHM formation as a result of moving the point of chlorination from
Pre-RM to (1) post-RM was 1.9 percent (-5.9 and 18 percent); (2) mid-
Floc was 13 percent (0.4 and 28 percent); and (3) post-Sed was 25
percent (6.5 and 43 percent).
The median, 10th and 90th percentile (shown in brackets) decrease
in HAA5 formation as a result of moving the point of chlorination from
Pre-RM to (1) post-RM was 5.3 percent (-11 and 23 percent); (2) mid-
Floc was 19 percent (-5.7 and 53 percent); and (3) post-Sed was 40
percent (26 and 67 percent).
The impact of percent TOC removal and point of chlorination on TOX,
TTHM, and HAA5 formation are shown in Figures IV.7, IV.8, and IV.9,
respectively. Increased TOC removal resulted in decreased DBP
formation. In general, moving the point of chlorination from raw water
to Mid-Floc and Post-Sed resulted in a percent decrease in DBP
formation that was equivalent to or greater than the percent TOC
removal achieved. Thus, in this study, precursor removal was a more
effective DBP control strategy when used in conjunction with delaying
the point of chlorination until Mid-Floc or later.
Impact of Alum Dose
Coagulation conditions of the waters at baseline conditions were
determined based on turbidity control. The median alum dose used for
baseline coagulation conditions was 30 mg/L (10th and 90th percentile
were 15 and 48 mg/L, respectively). Under these conditions, the median
TOC removal was 24 percent (10th and 90th percentiles were 6.5 and 38
percent, respectively). For this study, the alum dose was increased
from the baseline case by a median value of 22 mg/L (the 10th and 90th
percentiles were 15 and 35 mg/L, respectively). Increasing the alum
dose resulted in a median increase in TOC removal to 33 percent (10th
and 90th percentile were 18 and 48 percent, respectively). Thus, at the
higher alum doses, DBP formation was decreased. For nine of the waters
studied, increasing the alum dose from baseline coagulation conditions
resulted in TOC removal equivalent to or greater than those required by
the 3 x 3 enhanced coagulation matrix. This yielded a median increase
in the percent TOC removal of 14 percent. Table IV.1 summarizes the
median benefit associated with moving the point of chlorination
downstream under baseline coagulation and with increasing the alum dose
to achieve enhanced coagulation on DBP formation. DBP formation
resulting from chlorine addition at Pre-RM under baseline coagulation
conditions was used as a point of reference. The data in the table
indicates that even when prechlorination is practiced, TOX, TTHM, and
HAA5 formation can be reduced by moving from conventional to enhanced
coagulation. For TOX and TTHM, the benefits of moving to enhanced
coagulation are greatest when Post-Sed chlorination is used.
Furthermore, the benefits are greater for the control of HAA5 formation
than for the control of TOX and TTHM formation.
Table IV.1.--Impact of Point of Chlorination and Enhanced Coagulation on DBP Formation Using Pre-RM DBP
Formation Under Baseline Coagulation Conditions as Basis for Comparison
----------------------------------------------------------------------------------------------------------------
Median benefit (%)
-----------------------------------------------------------------------------
TOX (n=7) TTHM (n=9) HAA5 (n=6)
-----------------------------------------------------------------------------
Baseline Enhanced Baseline Enhanced Baseline Enhanced
coagulation coagulation coagulation coagulation coagulation coagulation
----------------------------------------------------------------------------------------------------------------
Pre-RM............................ ........... 11 ........... 17 ........... 4.7
Post-RM........................... 0.3 10 1.6 21 5.3 21
Mid-Floc.......................... 3.9 23 8.7 36 14 36
Post-Sed.......................... 11 40 21 48 35 61
----------------------------------------------------------------------------------------------------------------
3-Hour DBP Formation Relative to Distribution System DBP Formation
Chlorination with a 3-hour holding time before quenching the
reaction resulted in a significant formation of DBPs. The 3-hour period
was chosen as it is typical of reaction times in conventional treatment
plants. To get a general sense of short-term DBP formation kinetics,
DBP formation for chlorinated settled water held for 3 hours was
compared to DBP formation of settled water chlorinated under UFC (24
hour holding time). The data indicate that 3-hour chlorination resulted
in a high percentage of DBP formation that would normally be measured
in the distribution system. The median DBP concentrations formed in 3
hours were 61, 44, and 46 percent of distribution system formation for
TOX, TTHM, and HAA5, respectively. This can be thought of as in-plant
DBP formation relative to distribution system formation for systems
with 3-hour post sedimentation contact.
[[Page 59462]]
Summary
The results of this study indicate that enhancing the coagulation
process, while maintaining prechlorination, can result in decreased DBP
formation (especially for TOX and TTHM) with greater benefits being
realized by moving the point of chlorination to post rapid mixing or
further downstream for HAA5 and to mid flocculation or post
sedimentation for TOX and TTHM. Compared to prechlorinating three
minutes before rapid mixing, the greatest DBP reduction was realized by
moving the point of chlorination to post-sedimentation, with a median
decrease of 17, 25, and 40 percent in TOX, TTHM, and HAA5 formation,
respectively. However, operational and regulatory constraints may limit
the extent to which the point of chlorination can be moved downstream
in the process train, since one requirement in the IESWTR may be a
disinfection benchmark; which would require some plants making
significant changes in disinfection practice (including moving the
point of disinfection) to design the change to maintain their level of
Giardia inactivation at or above a site-specific level. This may limit
the degree to which some plants can delay the point of chlorination
without seeking State approval and potentially modifying their
treatment train to make up lost Giardia inactivation later in the
plant.
C. Summary of Key Observations
TWG analyses indicated that most PWSs, using enhanced coagulation
or enhanced softening as required, would be able to meet MCLs of 0.080
mg/L and 0.060 mg/L for TTHM and HAA5, respectively, while maintaining
existing disinfection practice. This analysis also indicated that
significant precursor removal and DBP reduction can still be achieved
with predisinfection left in place. Although in most cases the
reduction in DBP formation is not as great as would be accomplished in
moving the point of disinfection to after enhanced coagulation, the
Advisory Committee recommended balancing the need to maximize precursor
removal against the need to substantially maintain existing levels of
microbial protection that is provided by many plants through
predisinfection. However, as noted above, another key implication of
Summers' work is that some PWSs that only add disinfectant just prior
to coagulant addition (e.g., rapid mix), could achieve significant
additional DBP reduction without sacrificing meaningful disinfection
credit by moving the point of disinfectant addition from just before to
just after the point of coagulant addition.
The Advisory Committee recommended that PWSs continue to receive
credit for compliance with applicable disinfection requirements for
disinfectants applied at any point prior to the first customer
consistent with the existing provisions of the 1989 Surface Water
Treatment Rule.
EPA will develop guidance on the uses and costs of oxidants that
control water quality problems (e.g., Asiatic clams, zebra mussels,
iron, manganese, algae, taste and odor) and whose use will reduce or
eliminate the formation of DBPs of public health concern.
D. Request for Public Comments
EPA requests comment on continued disinfection credit for all
disinfectant use prior to the first customer.
V. Analytical Methods
EPA is requesting comment on the addition, and in one case the
deletion, of analytical methods for the disinfectants and DBPs listed
below. These potential changes are based on information received during
the public comment period or on new information that has become
available since the July 1994 proposed rule.
A. Chlorine Dioxide
The proposed DBP rule included the same three methods for analyzing
chlorine dioxide (ClO2) that are approved under the SWTR and
ICR regulations. Two of these methods, Standard Methods
4500.ClO2 C (APHA 1992) and 4500.ClO2 E (APHA
1992), are amperometric methods. The third method proposed was Standard
Method 4500.ClO2 D (APHA 1992), a colorimetric method using
the color indicator N,N-diethyl-p-phenylenediamine (DPD).
EPA received several comments stating that these methods to
calculate ClO2 concentration are intrinsically inaccurate
because free chlorine, chloramines and chlorite are subtracted from the
measurement, causing a propagation of errors. However, they stated that
the DPD method is sufficiently accurate for monitoring ClO2
residuals in drinking water and is relatively easy to perform.
Method 4500.ClO2 C was cited as an outdated, inaccurate
and time consuming method, subject to interferences from oxidants
commonly found in drinking water (Dietrich, 1992). Significant,
positive interferences have been described by Gates (1988), and
attributed to mono-and dichloramines by Haller and Listek (1948).
Method 4500.ClO2 E is a better method because it utilizes
differences in the physical properties of ClO2, as opposed
to chemical detection of anionic oxychlorocompounds (Aieta et al.,
1984). Therefore, EPA requests comments on omitting Method
4500.ClO2 C from the list of approved methods for the
analysis of chlorine dioxide for compliance with the MRDL for chlorine
dioxide. Comments on omitting it from 40 CFR 141.74 (SWTR analytical
methods) are also requested.
B. Haloacetic Acids
In 1994, EPA proposed two methods for the analysis of five
haloacetic acids--Method 552.1 (USEPA, 1992b) and Standard Method 6233B
(APHA 1992). Both methods use capillary column gas chromatographs
equipped with electron capture detectors. The two methods differ in the
sample preparation steps. Method 552.1 uses solid phase extraction
disks followed by an acidic methanol derivitization. Method 6233B is a
small volume liquid-liquid (micro) extraction with methyl-t-butyl
ether, followed by a diazomethane derivitization. Standard Method 6233B
was revised (and renumbered 6251B (APHA 1995)) to include
bromochloroacetic acid, for which a standard was not commercially
available in 1994. Recognizing these improvements, EPA approved Method
6251B for analysis under the 1996 Information Collection Rule (40 CFR
Part 141 or USEPA, 1996b). Several commenters requested that the
revised and renumbered method, Method 6251B, also be approved for the
analysis of haloacetic acids under the Stage 1 DBP regulations.
In 1995 EPA published a third method for HAAs, Method 552.2 (EPA
1995), and subsequently approved it for HAA analysis under the 1996
Information Collection Rule (40 CFR Part 141 or USEPA, 1996b). Method
552.2 is an improved method, combining the micro extraction procedure
of Standard Method 6233B with the acidic methanol derivitization
procedure of Method 552.1. It is capable of analyzing nine HAAs. EPA
received comments requesting approval of Method 552.2 for HAA5 analyses
required under this section.
EPA requests comment on the technical adequacy of using Methods
552.2 and 6251B (formerly 6233B) for analyzing haloacetic acids. Method
552.1 would continue to be approved for the analysis of haloacetic
acids.
C. Total Trihalomethanes (TTHMs)
Three methods are approved for the analysis of total
trihalomethanes
[[Page 59463]]
(TTHMs) under 40 CFR 141.24(e). These same methods were proposed under
the 1994 Stage I DBP proposal. One of the three methods, EPA Method
551, was revised to Method 551.1, rev. 1.0 (EPA 1995). Method 551.1 is
approved for ICR monitoring under 40 CFR 141.142.
Method 551.1 has several improvements upon Method 551. The use of
sodium sulfate is strongly recommended over sodium chloride for the
MTBE extraction of DBPs. This change was in response to a report
indicating elevated recoveries of some brominated DBPs due bromide
impurities in the sodium chloride (Xie, 1995). EPA's NERL laboratories
confirmed this finding in samples that were not extracted immediately
after the sodium chloride was added.
Other changes to Method 551.1 include a buffer addition to
stabilize chloral hydrate, elimination of the preservative ascorbic
acid, and modification of the extraction procedure to minimize the loss
of volatile analytes. The revised method requires the use of surrogate
and other quality control standards to improve the precision and
accuracy of the method.
D. Bromate
The proposed rule required systems that use ozone to monitor for
bromate ion. EPA proposed Method 300.0 (Determination of Inorganic
Anions by Ion Chromatography)(USEPA, 1993a) for the analysis of bromate
and chlorite ions. Method 300.0 is used in many laboratories because it
can analyze bromide, chloride, fluoride, nitrate, nitrite,
orthophosphate, sulfate, bromate, chlorite and chlorate ions. The cost
of bromate ion analysis was estimated to range from $50 to $100 per
sample.
At the time of the proposal, EPA was aware that Method 300.0 was
not sensitive enough to measure bromate ion concentration at the
proposed MCL of 0.010 mg/L (10 g/L). EPA recognized that
modifications to the method would be necessary to increase the method
sensitivity. Studies at that time indicated that changes to the
injection volume and the eluent chemistry would decrease the detection
limit below the MCL. There was also an issue concerning whether bromate
formation could be reliably controlled to levels below 10 g/L
when ozone is used as part of the treatment process. Most commenters
agreed that Method 300.0 was not sensitive enough to determine
compliance with a MCL of 10 g/L bromate ion, given that MCLs
are set no less than 5 times the MDLs. One commenter did achieve a MDL
for bromate ion in the 1-2 g /L range under research
laboratory conditions.
Since the proposal, EPA has improved Method 300.0 and renumbered it
as Method 300.1. EPA intends to approve this method for use in the
final rule; it is available for review in the Docket. Method 300.1
specifies a new, high capacity ion chromatography (IC) column that is
used for the analysis of all anions listed in method instead of
requiring two different columns as specified in Method 300.0. The new
column has a higher ion exchange capacity that improves chromatographic
resolution and minimizes the potential for chromatographic
interferences from common anions at concentrations typically 10,000
times greater than bromate ion. For example, quantification of 5.0
g/L bromate is feasible in a matrix containing 50 mg/L
chloride. Minimizing the interferences permits the introduction of a
larger sample volume to yield a method detection limit of 2 g/
L. Sample analysis time is approximately 30 minutes per sample.
An IC column's capacity is directly proportional to its operating
back pressure at a given flow rate and the older IC systems may not be
able to tolerate the higher back pressures required when using these
new IC columns. Consequently, in order to perform this analysis, some
laboratories with IC systems over 15 years old may need to upgrade
their instrumentation to current technology. Newer instruments can
easily be operated under these conditions.
As in Method 300.0, Part A of the revised method contains
procedures for measuring the common anions of bromide, nitrate,
nitrite, fluoride, chloride, sulfate and phosphate. Part B contains
procedures for measuring the disinfection byproduct anions of bromate,
chlorite and chlorate. Bromide ion is also included in Part B to
determine its potential presence as a disinfection byproduct precursor.
The anions are split into two distinct parts due to the disparity
in the relative concentrations expected in drinking water. Method 300.1
analyzes mg/L levels of the Part A common anions and g/L
levels of the Part B inorganic disinfection byproducts and bromide ion.
To accommodate this, the recommended sample volume injected for Part A
is 10 L and for Part B is 50 L, when using a 2 mm
diameter column. The lower injected sample volume for Part A is
required to compensate for their higher (mg/L) concentrations. If this
injected volume is not reduced, poor analyte response characteristics
are observed and the integrity of the data is compromised. The higher
injected sample volume for Part B is required to yield low detection
limits for the inorganic disinfection byproducts, specifically bromate.
Analysis for Part A and Part B cannot be concurrent without sacrificing
analytical integrity and therefore a separate 30 minute analysis must
be done for each concentration range.
To preserve samples for chlorite, chlorate, and bromate analyses,
the method requires the addition of ethylenediamine (EDA) at a final
sample concentration of 50 mg/L. EDA is primarily used as a
preservative for chlorite. Chlorite is susceptible to degradation both
through catalytic reactions with dissolved iron salts and reactivity
towards free chlorine which exists as hypochlorous acid/hypochlorite
ion in most drinking water as a residual disinfectant. EDA serves a
dual purpose as a preservative for chlorite by chelating iron as well
as any other catalytically destructive metal cations and removing
hypochlorous acid/hypochlorite ion by forming an organochloramine. EDA
also preserves the integrity of bromate concentrations by binding with
hypobromous acid/hypobromite which is an intermediate formed as a
byproduct of the reaction of ozone or free chlorine with bromide ion.
If hypobromous acid/hypobromite is not removed from the matrix, further
reactions may form bromate ion.
Method 300.1 was validated for the inorganic DBPs and bromide by
conducting nine replicate analyses at two different fortified levels of
seven water matrices including reagent water, simulated high ionic
strength water, untreated surface water, untreated ground water,
chlorinated drinking water, chlorine dioxide treated drinking water,
and ozonated drinking water. Holding time studies have been
incorporated into these validation studies with aliquots of each
fortified matrix currently being stored as unpreserved and EDA
preserved at 4 deg.C. These stored sample matrices will be monitored
out to 30 days to determine appropriate holding times. MDL
determinations have been completed in both reagent water and high ionic
strength water. Results of these validation studies are included in the
method.
With Method 300.1, EPA projects that more laboratories will achieve
lower detection limits for bromate and report data having better
precision and accuracy. Compliance monitoring for low levels of bromate
ion will require an appropriate certification process to ensure that
the measurements are accurate. Although there may be a
[[Page 59464]]
limited number of laboratories that will be qualified to do such
analyses, there should be adequate laboratory capacity for bromate ion
compliance monitoring. EPA estimates that 250 treatment plants
utilizing ozone will be monitored for bromate once per month, for a
total of 3,000 samples per year.
E. Chlorite
The proposed rule required monitoring for the chlorite ion for
those systems using chlorine dioxide for disinfection. The proposed
rule included Method 300.0 (ion chromatography) for chlorite analysis.
Other methods using amperometric and potentiometric techniques were
considered, but EPA decided that only the ion chromatography method
(300.0) would produce results with the precision needed for compliance
determinations. Several commenters suggested that EPA permit other
methods for chlorite.
Since the proposed rule, Method 300.1, which uses ion
chromatography, was developed for bromate ion (as discussed above).
Since Method 300.1 can also be used to analyze for chlorite ion, EPA
requests comment on allowing both Methods 300.0 and 300.1 as approved
methods for the analysis of chlorite ion.
F. Total Organic Carbon (TOC)
The proposed rule included two methods for analyzing TOC: Standard
Method 5310 C and 5310 D (APHA 1992). These methods were selected
because they cite a detection limit 0.5 mg/L and a precision
of 0.1 mg/L TOC. Standard Method 5310 B (18th edition) was
considered, but not proposed because the method had a detection limit
of 1 mg/L. The proposal stated that if planned improvements to the
instrumentation in 5310 B were successful, the next version would be
considered for promulgation.
Improvements were made to method 5310B and were included in a
revised method in the 19th edition of Standard Methods (APHA 1995).
Based on these improvements, method 5310B (19th edition) was approved
for TOC analyses under the Information Collection Rule. Several
commenters requested that Standard Methods 5310B also be approved for
TOC analysis under this rule because the newer instrumentation achieves
a detection limit of 0.5 mg/L TOC.
Since the ICR was promulgated, another revision of 5310 B was
published in the supplement to the Standard Methods 19th Edition (APHA
1996). EPA intends to approve this method for the analysis of TOC. EPA
requests comments on the technical equivalency of Methods 5310 B, C,
and D in the Supplement to Standard Methods 19th Edition and those same
methods in the 19th Edition.
G. Specific Ultraviolet Absorbance (SUVA)
Specific Ultraviolet Absorbance at 254 nm (SUVA) is an indicator of
the humic content of a water. Waters with low SUVA values contain
primarily non-humic matter and are not amenable to enhanced
coagulation. As discussed in section III, systems may demonstrate that
enhanced coagulation or enhanced softening is unnecessary if the raw
water after being filtered through a 0.45 m filter has a SUVA
below 2 L/mg-m.
SUVA is a calculated parameter obtained by dividing a sample's
ultraviolet light absorbance at a wavelength of 254 nm
(UV254), by the dissolved organic carbon (DOC), and
multiplying by 100:
SUVA = 100 (cm/m) [ UV254 (cm-1)/DOC (mg/L)]
Two separate analytical methods are necessary to make this
measurement: 1) UV254 and 2) DOC.
1. UV254. EPA approved Standard Methods 5910 (APHA 1995)
for measuring UV254 under the Information Collection Rule
and intends to approve its use under the disinfection byproducts rule.
EPA requests comments on this and other methods for measuring
UV254.
2. DOC. Standard Methods (19th Edition-Supplement)(APHA 1996)
defines DOC as the fraction of TOC that passes through a 0.45
m-pore-diameter filter. DOC is measured by performing an
analysis for TOC on the sample filtrate. Filtration eliminates
particulate organic matter but may contaminate the sample if carbon-
containing compounds leach from the filter. Standard Methods 5310 B,
5310 C and 5310 D require that filters be rinsed before use and checked
for their contribution to DOC by analyzing a filtered blank. Contact
with organic material such as plastic containers, rubber tubing, etc.
must be kept to a minimum to prevent contamination. EPA requests
comments on the approval of Standard Methods 5310 B, 5310 C and 5310 D
for measuring DOC for the SUVA calculation.
EPA is aware of several issues relating to the measurement of SUVA
that are not addressed in the methods above. In determining SUVA, DOC
and UV254 are both to be measured from the same sample
filtrate, which is prepared by filtering a raw water sample through a
pre-washed 0.45 m filter paper. Standard Methods 5910 (UV)
recommends to wash the filter with 50 mL of organic-free water to avoid
contamination, however, more rinsate may be necessary to eliminate the
DOC.
Because disinfectants/oxidants (chlorine, ozone, chlorine dioxide,
potassium permanganate) can destroy UV but not DOC, SUVA needs to be
determined on water prior to the application of disinfectants/oxidants.
In the raw water, this is usually not a problem. If disinfectants/
oxidants are applied in raw-water transmission lines upstream of the
plant, then raw-water SUVA should be based on a sample collected
upstream of the point of disinfectant/oxidant addition.
For determining settled-water SUVA, if the plant applies
disinfectants/oxidants prior to the settled water sample tap, then
settled-water SUVA should be determined in jar testing. Finally, the
use of iron-base coagulants can interfere with UV measurements, as
dissolved iron can penetrate the filter paper.
To address these issues in more detail, EPA intends to provide
guidance on SUVA measurements in the Guidance Manual for Enhanced
Coagulation (USEPA, 1997d). The manual will include guidance on
sampling, sample preparation, filter type, pH, interferences to UV,
high turbidity waters, quality control, etc. EPA requests comment on
other issues that should be addressed in the guidance, as well as any
recommendations on how the above issues should be addressed.
H. Summary of Key Observations
Since the 1994 proposal, improvements have been made to the
analytical methods for trihalomethanes, haloacetic acids, total organic
carbon, bromate ion and chlorite ion. EPA received comments to include
Method 552.2 and 6251B for HAAs, and Method 5310B for TOC. Commenters
made a general suggestion to approve methods promulgated under the ICR
rule in the Stage 1 DBP rule. EPA intends to approve these methods and
if appropriate, promulgate their most recent versions. EPA also intends
to approve Method 300.1, the revised method for bromate ion, and permit
its use for chlorite ion.
I. Request for Public Comments
1. EPA requests additional comments on omitting Method
4500.ClO2 C from the list of approved methods for the
analysis of chlorine dioxide.
2. EPA requests additional comments on the approval of EPA Method
552.2
[[Page 59465]]
and Standard Method 6251B for analyzing haloacetic acids.
3. EPA requests comment on replacing Method 300.0 with Method 300.1
for the analysis of bromate ion.
4. EPA requests comment on allowing both Method 300.0 and 300.1 as
approved methods for the analysis of chlorite ion.
5. EPA requests comments on the technical equivalency of Methods
5310 B, C and D in the Supplement to Standard Methods, 19th edition and
those same methods in the 19th edition of Standard Methods for
measuring TOC and DOC.
6. EPA requests comments on the methods and filtration procedures
for measuring SUVA.
VI. MCLs for TTHM, HAAs, Chlorite and Bromate
A. 1994 Proposal
The 1994 proposal for Stage 1 of the DBPR included MCLs for total
trihalomethanes (TTHMs), the sum of five haloacetic acids (HAA5),
bromate and chlorite at 0.080, 0.060, 0.010 and 1.0 mg/L, respectively
(EPA, 1994b). In addition to the proposed MCLs, Subpart H systems--
utilities treating either surface water or groundwater under the direct
influence of surface water--that use conventional treatment (i.e.,
coagulation, sedimentation, and filtration) or precipitative softening
would be required to remove DBP precursors by enhanced coagulation or
enhanced softening. The removal of total organic carbon (TOC) would be
used as a performance indicator for DBP precursor control.
As part of the proposed rule, EPA estimated that 17% of PWSs would
need to change their treatment process to alternative disinfectants
(ozone or chlorine dioxide) or advanced precursor removal (GAC or
membranes) in order to comply with the Stage 1 requirements. This
evaluation was important to assist in determining whether the proposed
MCLs were achievable and at what cost. This evaluation required an
understanding of the baseline occurrence for the DBPs and TOC being
considered in the Stage 1 DBPR, an understanding of the baseline
treatment in-place, and an estimation of what treatment technologies
systems would use to comply with the Stage 1 DBPR requirements.
For systems switching to ozone or chlorine dioxide, separate MCLs
were proposed for inorganic DBPs associated with their usage: bromate
and chlorite, respectively. Although the theoretical 10-4
risk level for bromate is 5 g/L, an MCL of 0.010 mg/L (10
g/L) was proposed (because available analytical detection
methods for bromate were reliable only to the projected practical
quantification limit (PQL) of 10 g/L (USEPA, 1994b). For
chlorite, the MCL goal (MCLG) was 0.08 mg/L, due (in part) to data gaps
that required higher uncertainty factors in the MCLG determination. The
Chemical Manufacturer's Association (CMA) agreed to fund new health
effects research on chlorine dioxide and chlorite--with EPA approval of
the experimental plan--to resolve these data gaps.
In the preamble to the proposed rule, EPA requested comment on
several issues related to the MCLs and requested any new information
that may influence the MCLs. For bromate, EPA requested comment on
whether there were ways to set (or achieve) a lower MCL (i.e., 0.005
mg/L [5 g/L]) and whether the PQL for bromate could be lowered
to 5 g/L in order to allow compliance determinations for a
lower MCL in Stage 1 of the proposed rule.
For chlorite, EPA requested comment on the appropriate MCL (i.e.,
at the MCLG, at the proposed MCL, or above the MCLG but below the
proposed MCL), the feasibility of achieving a particular MCL, and
whether there were other benefits to chlorine dioxide disinfection that
should be considered when balancing the health risks associated with
chlorite.
B. New Information Since 1994 Proposal
1. TTHM and HAA5 MCLs
At the direction of the Advisory Committee, the Technologies
Working Group (TWG) reviewed MCL compliance predictions developed for
the 1994 proposal because of concern by several Committee members that
modifications to the rule would result in more PWSs not being able to
meet the TTHM and HAA MCLs without installation of higher cost
technologies such as ozone or GAC. The members were particularly
concerned that allowing disinfection inactivation credit prior to
precursor removal (by enhanced coagulation or enhanced softening) in
order to prevent significant reductions in microbial protection would
result in higher DBP formation and force systems to install alternative
disinfectants, or advanced precursor removal to meet TTHM and HAA5
MCLs. As discussed earlier in today's Notice in Section IV.
(Disinfection Credit), PWSs can achieve significant reduction in DBP
formation through the combination of enhanced coagulation (or enhanced
softening) and moving the point of disinfection downstream from
coagulant addition, while preventing significant reduction in microbial
protection. The TWG's analysis of the cumulative effect of these
changes was that there would be no significant increase in the
percentage of PWSs that would need to install higher cost technologies
to meet TTHM and HAA5 MCLs and no significant reduction in microbial
protection. The TWG estimated that 6.4% (based on WIDB data) to 15%
(bas
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