National Primary Drinking Water Regulations: Interim Enhanced Surface Water Treatment Rule Notice of Data Availability
Federal RegisterNov 3, 1997
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SUMMARY: USEPA proposed in 1994 to amend the Surface Water Treatment
Rule to provide additional protection against disease-causing organisms
(pathogens) in drinking water (59 FR 38832: July 29, 1994). 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-Disinfectants/Disinfection 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. In addition, USEPA is hereby
providing notice that the Agency is re-opening the comment period for
the 1994 proposal for 90 days beginning on the date of publication of
today's Notice in the Federal Register. 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 Interim Enhanced Surface Water Treatment Rule (IESWTR) would
apply to surface water systems serving 10,000 or more people. USEPA
intends to promulgate the final rule in November 1998 as required by
the 1996 Amendments to the Safe Drinking Water Act. The Agency plans
subsequently to address surface water systems serving fewer than 10,000
people as part of a ``long-term'' Enhanced Surface Water Treatment Rule
which may also include additional refinements for larger systems.
Key issues related to the IESWTR that are addressed in this Notice
include the establishment of a Maximum Contaminant Level Goal for
Cryptosporidium; removal of Cryptosporidium by filtration; revised
turbidity provisions; disinfection benchmark provisions to assure
continued levels of microbial protection while facilities take the
necessary steps to comply with new disinfection byproduct standards;
sanitary surveys; inclusion of Cryptosporidium in the definition of
ground water under the direct influence of surface water; and inclusion
of Cryptosporidium in the watershed control requirements for unfiltered
public water systems. Other issues that are discussed include
inactivation of Cryptosporidium, viruses and Giardia lamblia; uncovered
finished water reservoirs; cross connection control; and recycling of
filter backwash water and filter-to-waste.
Today's Federal Register also contains a related Notice of Data
Availability for the Stage 1 Disinfectants/Disinfection Byproducts Rule
(DBPR). USEPA proposed this rule at the same time as the IESWTR and
plans to promulgate it along with the IESWTR 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 IESWTR 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 Elizabeth Corr or
Paul S. Berger, Ph.D.(Microbiology), Office of Ground Water and
Drinking Water (MC 4607), U.S. Environmental Protection Agency, 401 M
Street SW, Washington DC 20460; telephone (202) 260-8907 (Corr) or
(202) 260-3039 (Berger).
Regional Contacts
Region 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 IESWTR
are public water systems that use surface water and serve at least
10,000 people. Regulated categories and entities include:
------------------------------------------------------------------------
Category Examples of regulated entities
------------------------------------------------------------------------
Public Water System.................... PWSs that use surface water and
serve at least 10,000 people.
State Governments...................... State government offices that
regulate drinking water.
------------------------------------------------------------------------
[[Page 59487]]
This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by the
IESWTR. This table lists the types of entities that USEPA 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 outlined under Alternatives A and B in
Sec. 141.70 of the proposed rule (59 FR 38832, July 29, 1994).
If you have questions regarding the applicability of the IESWTR 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 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.
List of Abbreviations Used in This Document
ASCE--American Society of Civil Engineers
ASTM--American Society for Testing Materials
AWWA--American Water Works Association
C--the residual concentration of disinfectant, mg/L
CDC--Centers for Disease Control
CFE--Combined Filter Effluent
CFR--Code of Federal Regulations
CPE--Comprehensive Performance Evaluation
CT--the residual concentration of disinfectant multiplied by the
contact time
DOC--dissolved organic carbon
ESWTR--Enhanced Surface Water Treatment Rule
FACA--Federal Advisory Committee Act
gpm/sf--gallons per minute per square foot
HAA5--Haloacetic acids (monochloroacetic, dichloroacetic,
trichloroacetic, monobromoacetic, and dibromoacetic acids)
HAV--hepatitis A virus
hrs--hours
ICR--Information Collection Rule
IESWTR--Interim Enhanced Surface Water Treatment Rule
IFA--Individual Filter Assessment
IFE--Individual Filter Effluent
ISO--International Standards Organization
k--the pseudo first-order reaction rate constant
L--liter
Log Inactivation--logarithm of (No/NT)
Log--logarithm (common, base 10)
LTESWTR--Long Term Enhanced Surface Water Treatment Rule
MCL--Maximum Contaminant Level
MCLG--Maximum Contaminant Level Goal
M-DBP--Microbial and Disinfectants/Disinfection Byproducts
mg/L--milligram per liter
mg-min/L--milligram minutes per liter
MMWR--Morbidity and Mortality Weekly Report
mW-s/cm2--milliwatt seconds per square centimeter
No--the initial viable concentration of microorganisms
NPDWR--National Primary Drinking Water Regulation
NT--the concentration of surviving microorganisms at time T
NTU--nephelometric turbidity unit
deg.C--degrees centigrade
PE--Performance Evaluation
pH--negative logarithm of the effective hydrogen-ion concentration
PV1--poliovirus 1
PV3--poliovirus 3
PWS--Public Water System
RSD--Relative Standard Deviation
SAB--Science Advisory Board
SDWA--Safe Drinking Water Act
T--the contact time, second or minute
TOC--total organic carbon
TTHM--Total Trihalomethanes
TWG--Technical Work Group
UV--ultraviolet
x--log removal Reduction by 1/10**x
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 proposed IESWTR
1. Summary of major elements
2. Alternative treatment requirements
3. Possible supplemental treatment requirements
a. uncovered finished water reservoirs
b. cross connection control program
c. State notification of high turbidity levels
4. Other related issues
II. New Information and Key Issues To Be Addressed
A. MCLG for Cryptosporidium
1. Summary of 1994 proposal and public comments
2. New data and perspectives
3. Advisory Committee recommendations and related issues
B. Removal of Cryptosporidium by filtration
1. Summary of 1994 proposal and public comments
2. New data and perspectives
a. rapid granular filtration
b. other filtration technologies
c. multiple barrier approach
3. Advisory Committee recommendations and related issues
C. Turbidity control
1. Summary of 1994 proposal as it relates to turbidity issues
and public comments
2. New data and perspectives
a. 95th percentile and maximum turbidity levels of composite
filtered water
b. individual filter performance
c. turbidity measurement
3. Advisory Committee recommendations and related issues
D. Disinfection benchmark for Stage I DBP MCLs
1. Applicability
2. Developing the profile and benchmark
3. State review
4. Guidance
5. Request for public comment
E. Definition of ground water under direct influence of surface
water (GWUDI)--inclusion of Cryptosporidium in the definition
1. Summary of 1994 proposal and public comments
2. Overview of existing guidance
3. Summary of new data and perspectives
[[Page 59488]]
4. Request for public comment
F. Inclusion of Cryptosporidium in watershed control requirements
1. Summary of 1994 proposal and public comments
2. Overview of existing guidance
3. Summary of new data and perspectives
G. Sanitary survey requirements
1. Summary of 1994 proposal
2. Overview of existing regulations and guidance
3. New developments
4. Advisory Committee recommendations and related issues
H. Covered finished water reservoirs
1. Summary of 1994 proposal and public comments
2. Overview of existing information
3. Request for public comment
I. Cross connection control program
1. Summary of 1994 proposal and public comments
2. Overview of existing information
3. Request for public comment
J. Recycling filter backwash water and filtering to waste
1. Filter backwash recycle configuration
2. State drinking water regulations
3. Literature overview of standards of practice
4. Filter-to-waste
5. Request for public comment
K. Certification criteria for water plant operators
L. Regulatory compliance schedule and other compliance-related
issues
1. Regulatory compliance schedule
2. Compliance violations and State primacy obligations
3. Compliance with current regulations
M. Disinfection studies
1. New Giardia inactivation studies at high pH levels
2. Effectiveness of different disinfectants on Cryptosporidium
3. New virus inactivation studies
III. Economic Analysis of M-DBP Advisory Committee Recommendations
A. Overview of RIA for proposed rule
B. What's changed since proposed rule
C. Summary of cost analysis
1. Total national costs
2. Household costs
D. Cost of turbidity performance criteria & associated monitoring
1. System level impact analysis
2. National impact analysis
a. decision tree
b. utility costs
c. State costs
E. Disinfection benchmark
1. Decision tree
2. Utility costs
3. State costs
F. Sanitary surveys
G. Summary of benefits analysis
IV. National Technology Transfer and Advancement Act
I. Introduction and Background
A. Existing Regulations
1. Surface Water Treatment Rule
Under the Surface Water Treatment Rule (SWTR)(54 FR 27486, June 29,
1989), 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 (TTHM) of 0.10 mg/l as an annual average in November
1979 (44 FR 68624). 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 (54 FR 27544; June 29, 1989), revised in
June 1989 and effective on December 31, 1990 applies to all public
water systems (USEPA, 1989b). This regulation 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-positive; 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 (61 FR 24354)
(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 (SAB), an independent panel
of experts established by Congress, cited
[[Page 59489]]
drinking water contamination as one of the most important environmental
risks and indicated that disease-causing microbial contaminants (i.e.,
bacteria, protozoa and viruses) are probably the greatest remaining
health risk management challenge for drinking water suppliers (USEPA/
SAB 1990). This view was prompted by the SAB's concern about the number
of waterborne disease outbreaks in the U.S. Between 1980 and 1994, 379
waterborne disease outbreaks were reported, with over 500,000 cases of
disease. During this period, a number of agents were implicated as the
cause, including protozoa, viruses and bacteria, as well as several
chemicals. Most of the cases (but not outbreaks) were associated with
surface water, and specifically with a single outbreak of
cryptosporidiosis in Milwaukee (over 400,000 cases) (Craun, Pers. Comm.
1997a).
The number of waterborne disease outbreaks and cases is, however,
probably much greater than that recorded because the vast majority of
waterborne disease is probably not reported. Few States have an active
outbreak surveillance program and disease outbreaks are often not
recognized in a community or, if recognized, are not traced to the
drinking water source. This situation is complicated by the fact that
the vast majority of people experiencing gastrointestinal illness
(predominantly diarrhea) do not seek medical attention. For those who
do, physicians generally cannot attribute gastrointestinal illness to
any specific origin such as a drinking water source. An unknown but
probably significant portion of waterborne disease is endemic, i.e.,
not associated with an outbreak, and thus is even more difficult to
recognize.
One of the key regulations USEPA has developed and implemented to
counter pathogens in drinking water is the SWTR. Among its provisions,
the rule requires that a public water system have sufficient treatment
to reduce the source water concentration of Giardia and viruses by at
least 99.9% (3 logs) and 99.99% (4 logs), respectively.
The goal of the SWTR is to reduce risk to less than one infection
per year per 10,000 people (10-4). However, one of the
SWTR's shortcomings is that the source waters of some systems have high
pathogen concentrations that, when reduced by the levels required under
the rule, still may not meet a common health goal (e.g.,
10-4).
Another shortcoming of the SWTR is that the rule does not
specifically control for the protozoan Cryptosporidium. The first
report of a recognized outbreak caused by Cryptosporidium was published
during the development of the SWTR (D'Antonio et al., 1985). Other
outbreaks caused by this pathogen have since been reported both in the
United States and other countries (Smith et al.,1988; Hayes et al.,
1989; Levine and Craun, 1990; Moore et al., 1993; Craun, 1993). A
particular public health challenge is that simply increasing existing
disinfection levels above those most commonly practiced in the United
States today does not appear to be an effective strategy for
controlling Cryptosporidium.
In addition to these issues, there is another potentially counter-
balancing public health concern. The disinfectants used to control
microbial pathogens may produce toxic or carcinogenic disinfection
byproducts (DBPs) when they react with organic chemicals in the source
water. Thus, an important question facing water supply professionals is
how to minimize the risk from both microbial pathogens and DBPs
simultaneously.
At the time the SWTR was promulgated, USEPA had limited data
concerning Giardia and Cryptosporidium occurrence in source waters and
treatment efficiencies. The 3-log removal/inactivation of Giardia
lamblia and 4-log removal/inactivation of enteric viruses required by
the SWTR were developed to provide protection from most pathogens in
source waters. However, additional data has become available since
promulgation of the SWTR concerning source water occurrence and
treatment efficiencies for Giardia, as well as for Cryptosporidium
(LeChevallier et al. 1991 a,b). A major concern is that if systems
currently provide four or more logs of removal/inactivation for
Giardia, such systems might reduce existing levels of disinfection to
more easily meet new DBP regulations, and thus only marginally meet the
three-log removal/inactivation requirement for Giardia lamblia
specified in the current SWTR. Depending upon source water Giardia
concentrations, such treatment changes could lead to significant
increases in microbial risk (Regli et al., 1993; Grubbs et al., 1992;
USEPA, 1994b).
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
[[Page 59490]]
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)).
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 disinfectants/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) (USEPA, 1994a), an ``interim'' ESWTR (proposal:
59 FR 38832, July 29, 1994) (USEPA, 1994b), and an Information
Collection rule (proposal: 59 FR 6332, February 10, 1994) (USEPA,
1994c). 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
[[Page 59491]]
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 Stage 1 DBPR 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 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 IESWTR 1994 Proposal
1. Summary of Major Elements
As part of the IESWTR July 29, 1994, Federal Register notice (59 FR
38832), USEPA proposed to revise the SWTR to provide additional
protection against pathogens in drinking water. USEPA proposed to set
the MCLG for Cryptosporidium at zero based on animal studies and human
epidemiology studies of waterborne outbreaks of cryptosporidiosis. The
proposal also focused on treatment requirements for the waterborne
pathogens Giardia lamblia, Cryptosporidium, Legionella and viruses that
would apply to all public water systems that use surface water or
ground water under the influence of surface water and serve 10,000
people or more. Major features of the proposal included a stricter
watershed control requirement for systems using surface water that wish
to avoid filtration; a change in the definition of ground water under
the influence of surface water to include the presence of
Cryptosporidium; a periodic sanitary survey requirement for all systems
using surface water or ground water under the influence of surface
water; and several alternative requirements, described below, for
augmenting treatment control of Giardia lamblia, Cryptosporidium, and
viruses. USEPA also requested comment on several supplemental
provisions and on other related issues, described below.
2. Alternative Treatment Requirements
USEPA proposed five treatment alternatives for controlling Giardia
lamblia, Cryptosporidium, and viruses. Each alternative included
several options. Alternative A addressed enhanced treatment for Giardia
lamblia only. Alternatives B and C addressed treatment for
Cryptosporidium only. Alternative D addressed enhanced treatment for
viruses only. Alternative E would maintain existing levels of treatment
for Giardia lamblia and viruses.
a. Alternative A. Enhanced treatment for Giardia lamblia. The SWTR
currently requires a 99.9 percent (3-log) removal/inactivation of
Giardia lamblia for all surface waters, regardless of Giardia lamblia
cyst concentrations in the source water. Under Alternative A, the
minimum level of treatment a system would be required to provide (e.g.,
3, 4, 5 or 6 log removal/inactivation) would depend on the Giardia
lamblia density in the source water as determined by monitoring over
some specified interval of time. The level of prescribed treatment for
a particular system would correspond to providing water below an annual
risk level for Giardia lamblia infections (e.g. 10-4).
b. Alternative B. Specific Treatment for Cryptosporidium. USEPA
also proposed a treatment technique for Cryptosporidium similar to the
proposal for Giardia under Alternative A, such that the required level
of Cryptosporidium treatment for any particular system would depend on
the density of Cryptosporidium in the source water.
c. Alternative C. 99% (2-log) removal of Cryptosporidium. Under
this alternative, USEPA would require systems to achieve at least a 99%
(2-log) removal of Cryptosporidium by filtration (with pretreatment).
The 2-log level was based on the premise that a 3-log level (as
currently required for Giardia removal/inactivation) is not
economically or technologically possible, since data suggests that
Cryptosporidium is consistently more resistant to disinfection than is
Giardia. USEPA indicated that it would continue to assess new field and
laboratory data to control Cryptosporidium by physical removal and
disinfection for consideration in subsequent microbial regulations.
d. Alternative D. Specific disinfection treatment for viruses. The
SWTR required systems to achieve a four-log removal/inactivation of
viruses. This is to be achieved through a combination of filtration and
disinfection or, for systems not required to filter their source
waters, by disinfection alone. However, this level of treatment may not
be adequate to achieve a particular health risk (e.g., 10-4
infections/yr/person) for viruses. Viruses are of particular concern,
given that one or several virus particles may be infectious (Regli et
al.,1991) and that several enteric viruses are associated with
relatively high mortality rates (Bennett et al., 1987). Failure or
impairment of filtration performance could allow substantial pathogen
contamination of drinking water, particularly if the disinfection
barrier following filtration is minimal.
Alternative D would require that systems provide sufficient
disinfection such that disinfection alone would achieve at least a 0.5-
log inactivation of Giardia lamblia or, alternatively, a 4-log
inactivation of viruses. This proposed approach would be independent of
the level of physical removal or the source water density of viruses.
If the filtration process was able to remove three logs of Giardia
lamblia, a system would still have to provide at least an additional
0.5-log inactivation of Giardia lamblia or 4-log inactivation of
viruses by disinfection.
e. Alternative E. No change to existing SWTR treatment requirements
for Giardia lamblia and viruses. Alternative E maintains existing SWTR
levels of
[[Page 59492]]
treatment for Giardia lamblia and viruses. USEPA could regulate
Cryptosporidium directly (e.g., Alternative C above) or make a finding
that existing SWTR filtration and disinfection requirements are
adequate to control this organism.
3. Possible Supplemental Treatment Requirements
USEPA also requested comment on three supplemental requirements
regarding uncovered finished water reservoirs, cross connection control
and State notification of turbidity levels.
a. Uncovered Finished Water Reservoirs. As part of the 1994
proposal, USEPA requested comment on possible supplemental requirements
for uncovered finished water reservoirs. The Agency noted that USEPA
guidelines recommend that all finished water reservoirs be covered
(USEPA, 1991a) and that the American Water Works Association (AWWA)
also has issued a policy statement that strongly supports the covering
of such reservoirs (AWWA, 1993).
b. Cross Connection Control Program. USEPA requested comment on
whether to require States or public water systems to have cross
connection control programs. Plumbing cross-connections are actual or
potential connections between a potable and non-potable water supply
(USEPA, 1989a). According to Craun (1991), 24% of the waterborne
disease outbreaks that occurred during 1981-1990 were caused by water
contamination in the distribution system, primarily as the result of
cross-connections and main repairs.
c. State Notification of High Turbidity Levels. USEPA also
requested comment on whether to require systems to notify the State as
soon as possible for persistent turbidity levels above the performance
standards or for any other situation that is not now a violation of the
turbidity standards. Under the SWTR, any time the turbidity of a
treatment plant's combined filter effluent exceeds 5 NTU the system
must notify the State as soon as possible, but no later than the end of
the next business day. In addition, the system must notify the public
as soon as possible, but in no case later than 14 days after the
violation.
USEPA indicated in the proposal that it was considering broadening
the requirement for State notification. The Agency suggested it might,
for example, require systems to notify the State as soon as possible if
at any point during the month it becomes apparent that a system will
violate the monthly 95th percentile turbidity performance standard
specified in the SWTR, rather than wait to the end of the month.
USEPA outlined a number of public health reasons for requiring
swift State notification for persistent turbidity levels. Pathogens may
accompany the turbidity particles that exit the filters, especially
with poor quality source waters. High turbidity levels in the filtered
water, even for a limited time, may represent a significant risk to the
public. USEPA's proposed approach was intended to allow States to
respond in controlling a potentially serious problem more quickly.
4. Other related issues. The Agency also requested comments on
other issues related to possible IESWTR options. A number of these are
listed below.
(a) To what extent should the ESWTR address the issue of recycling
filter backwash, given its potential for increasing the densities of
Giardia lamblia and Cryptosporidium on the filter?
(b) Should the ESWTR define minimum certification criteria for
surface water treatment plant operators? Currently the SWTR (40 CFR
141.70) requires such systems to be operated by ``qualified personnel
who meet the requirements specified by the State.''
(c) What criteria, if any, should the ESWTR include to ensure that
systems optimize treatment plant performance?
(d) Should turbidity performance criteria be modified? Should
criteria pertain to individual filters?
(e) Should the rule include a performance standard for particle
removal?
(f) Should the rule include a requirement for an early warning for
high turbidity?
(g) Under what conditions could systems be allowed different log
removal credits than is currently recommended in the SWTR Guidance
Manual?
(h) How should USEPA decide, in developing a Notice of Data
Availability, what treatment approach(es) is most suitable for
additional public comment?
II. New Information and Key Issues to be Addressed
A. MCLG for Cryptosporidium
1. Summary of 1994 Proposal and Public Comments
The July 29, 1994, Federal Register notice proposed to set the MCLG
for Cryptosporidium at zero. The purpose of the MCLG is to protect
public health. The reasons for this determination were based upon
animal studies and human epidemiology studies of waterborne outbreaks
of cryptosporidiosis.
Most commenters supported an MCLG of zero for Cryptosporidium.
Those who provided reasons stated that (1) a single cell could infect,
and data do not support a threshold dose below which an outbreak or
disease will not occur, (2) the organism is present in water and has
caused major waterborne disease outbreaks, and (3) it is consistent
with the goals set under the SWTR and Total Coliform Rule. Commenters
who opposed the proposed MCLG stated that USEPA needed more health risk
and organism/disease transmission data and better analytical methods
before setting an MCLG and regulating Cryptosporidium.
2. New data and Perspectives
Since publication of the proposed rule, results of a human feeding
study have become available. Dupont et al. (1995) fed 29 healthy
volunteers single doses ranging from 30 to 1 million C. parvum oocysts
obtained from a calf. Of the 16 volunteers who received 300 or more
oocysts, 88% became infected. Of the five volunteers who received the
lowest dose (30 oocysts), one became infected. The median infective
dose was 132 oocysts. According to a mathematical model based upon the
Dupont et al. data, 0.5% of a population exposed to an average dose of
one oocyst, would be expected to become infected. (Haas et al., 1996).
An important concern is that certain populations are at greater
risk of waterborne disease infection than others. These vulnerable
populations include the immunocompromised; children, especially the
very young; the elderly; and pregnant women (Gerba et al. 1996; Fayer
and Ungar 1986). The most significant segment within these vulnerable
populations with regard to cryptosporidiosis is people who are
immunocompromised. In patients with severely weakened immune systems,
(e.g cancer, AIDS patients), cryptosporidiosis can be serious, long-
lasting and sometimes fatal. There is concern about cryptosporidiosis
in immunocompromised individuals because currently there is no cure for
the disease.
C. parvum is the only Cryptosporidium species known for certain to
infect humans. One controversial report (the only one of its kind)
found evidence that C. baileyi, which infects birds, was present in the
stools and other autopsied organs of an immunodeficient patient
(Ditrich et al., 1991). There was no indication that Cryptosporidium
had been responsible in this instance for any adverse health effects.
C. parvum also infects many other mammals. While C. parvum is a
[[Page 59493]]
well-documented human pathogen, strain variation may occur and one
strain may cause infection and/or disease at a higher or lower
concentration than other strains. USEPA is currently funding research
[Cryptosporidium virulence study using different strains, Herbert
Dupont] to examine this issue.
There is some question about the taxonomy (i.e., classification) of
species within the genus Cryptosporidium. Up until 1980, classification
was based on the assumption that a particular species only infected one
type of animal. This assumption appears to be incorrect; hence other
appropriate taxonomy schemes have been suggested.
An important issue not directly related to the MCLG involves the
measurement of C. parvum in water. With current technology, it is often
very difficult to distinguish between viable and non-viable oocysts.
When Cryptosporidium is identified it is often not clear whether it is
C. parvum or another species. Several Cryptosporidium species look
similar to C. parvum and react to ``specific'' C. parvum stains in a
like manner (cross-reactions). In addition, it can be difficult to
distinguish Cryptosporidium from alga and invertebrate eggs (Clancy et
al. 1994)
3. Advisory Committee Recommendations and Related Issues
The M-DBP Federal Advisory Committee supported the proposed
establishment of a Cryptosporidium MCLG at zero. However, a key issue
identified by the Committee and public commenters is whether the MCLG
should be set at the genus level (i.e., Cryptosporidium), as proposed,
or at the more specific species level (i.e., C. parvum). Setting the
MCLG at the genus level would automatically include any Cryptosporidium
species other than C. parvum that is later found to be pathogenic to
humans. In contrast, setting an MCLG at the species level would
indicate that only C. parvum infects humans, and would also be
consistent with the approach taken under the SWTR for Giardia where the
MCLG is set at the species level (i.e., G. lamblia). USEPA has not
decided which approach is most appropriate and seeks public comment on
this issue.
As indicated above, USEPA's intent in establishing this MCLG at
zero is to protect public health. The Agency believes there is adequate
research data to support this determination. However, as noted above,
the Agency recognizes that there is scientific uncertainty on the issue
of Cryptosporidium taxonomy and on the question of cross reactions
between species. USEPA expects further clarification on this issue as
research continues, Cryptosporidium analytical methods improve, and
more is learned about the circumstances under which cross-reactivity
between species occurs. The Agency also wishes to emphasize that the
scope or specificity of the MCLG may be modified in the future to
reflect new research and additional information about particular
species that represent a significant risk to human health.
As part of this notice, USEPA requests comment on whether to
establish a Cryptosporidium MCLG at the genus level as proposed or at
the species level (i.e., Cryptosporidium vs. Cryptosporidium parvum).
USEPA also requests copies of any additional research, data or other
information related to this issue.
B. Removal of Cryptosporidium by Filtration
1. Summary of 1994 Proposal and Public Comments Received
One of USEPA's proposed treatment Alternatives (Alternative C)
would require filtered systems to achieve at least a 2 log removal of
Cryptosporidium oocysts. USEPA recognized that the proposed removal
level was based on limited data and therefore solicited comment on
whether other minimum removal levels might be appropriate.
Most commenters addressing the issue of treatment alternatives
supported Alternative C. Some commenters opposed any treatment
requirement greater than a 2 log removal due to a lack of better
understanding of dose-response, effectiveness of treatment, and
analyses to justify the higher treatment costs involved.
Other commenters referred to specific studies (Nieminski 1995;
Patania et al., 1995) that provided additional information on
Cryptosporidium removal. One commenter cited a study (Parker and Smith,
1993), where oocyst damage was observed after agitation with sand. This
study postulated that oocysts may be damaged as they pass through the
filtration media. This commenter also pointed to the lack of data on
cyst removal by full-scale plants and recommended that additional
research be conducted. Some commenters recognized the need to regulate
Cryptosporidium, but opposed having the level of treatment based upon
source water pathogen density (alternative B). One commenter indicated
that further implementation and evaluation of the adequacy of the SWTR
needs to occur before modifying it.
2. New Data and Perspectives
a. Rapid Granular Filtration. Table 1 summarizes research pertinent
to Cryptosporidium and Giardia lamblia removal efficiencies by rapid
granular filtration. Brief descriptions of these studies and a summary
of key points follow.
Table 1.--Cryptosporidium and Giardia Lamblia Removal Efficiencies by Rapid Granular Filtration
----------------------------------------------------------------------------------------------------------------
Type of treatment plant Log removal Experimental design Researcher
----------------------------------------------------------------------------------------------------------------
Conventional filtration plants... Crypt 2.7-5.9....... Pilot Plants....... Patania et al. 95.
Do........................... Giardia 3.4-5.8..... ......do........... Do.
Do........................... Crypt 2.3-3.0....... Pilot scale plant.. Nieminski/Ongerth 95.
Do........................... Giardia 3.3-3.4..... +full scale plant Do.
with seeded cysts/
oocysts.
Do........................... Crypt 2.7-3.1....... Pilot Plants....... Ongerth/Pecaroro 95.
Do........................... Giardia 3.1-3.5..... ......do........... Do.
Do........................... Crypt 2-2.5......... Full scale plants.. LeChevallier et al. 91b.
Do........................... Giardia 2-2.5....... Full scale plants.. LeChevallier et al. 91b.
Do........................... Crypt 2.3-2.5....... Full scale plants.. LeChevallier/Norton 92.
Do........................... Giardia 2.2-2.8..... ......do........... Do.
Do........................... Crypt 2-3........... Pilot scale plant.. Foundation for Water.
Research 94.
Do........................... Giardia and......... Full scale plant... Kelley et al. 95.
DoCrypt 1.5-2................ operation considered
ot optimized).
Direct filtration plants......... Crypt 1.5-4.0....... Pilot Plants....... Patania et al. 1995.
Do........................... Giardia 1.5-4.8..... ......do........... Do.
[[Page 59494]]
Do........................... Crypt 2.8-3.0....... ......do........... Nieminski/Ongerth 95.
Do........................... Giardia 3.3-3.9..... ......do........... Do.
Do........................... Crypt 2-3........... ......do........... West et al. 1994.
----------------------------------------------------------------------------------------------------------------
Patania, Nancy L; et al. 1995
Raw water turbidities were between 0.2 and 13. When treatment
conditions were optimized for turbidity and particle removal at four
different sites, Cryptosporidium removal ranged from 2.7 to 5.9 log and
Giardia removal ranged from 3.4 to 5.1 log during stable filter
operation. The median turbidity removal was 1.4 log, whereas the median
particle removal was 2 log. Median oocyst and cyst removal was 4.2 log.
A filter effluent turbidity of 0.1 NTU or less resulted in the most
effective cyst removal, by up to l log greater than when filter
effluent turbidities were greater than 0.1 NTU (within the 0.1 to 0.3
NTU range) (see Figures 1 and 2 below). Cryptosporidium removal rates
of less than 2.0 log (indicated in Figures 1 and 2) occurred at the end
of the filtration cycle.
Blackened data points in these figures represent data in which
oocysts were not detected in the filtered water. The log removal values
shown would be greater than indicated had the influent oocyst
concentration been sufficiently high to show oocyst detection in the
filtered water. The researchers also noted that removal of
Cryptosporidium was 0.4 to 0.9 log lower during filter ripening than
during stable filter operation; Giardia removal was generally 0.4 to
0.5 log lower during ripening. Cryptosporidium removal was 1.4 to 1.8
log higher for conventional treatment (including sedimentation) as
compared to direct filtration. Similarly, Giardia removal was 0.2 to
1.8 log higher. Figures 1 and 2 below show the log removal rates
discussed above.
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Nieminski, Eva C. and Ongerth, Jerry E. 1995
This study evaluated performance in a pilot plant and in a full
scale plant (not in operation during the time of the study) and
considered two treatment modes: direct filtration and conventional
treatment. The source water of the full scale plant had turbidities
typically between 2.5 and 11 NTU with a peak level of 28 NTU. The
source water of the pilot plant typically had turbidities of 4 NTU with
a maximum of 23 NTU. For the pilot plant, achieving filtered water
turbidities between 0.1-0.2 NTU, Cryptosporidium removals averaged 3.0
log for conventional treatment and 3.0 log for direct filtration, while
the respective Giardia removals averaged 3.4 log and 3.3 log. For the
full scale plant, achieving similar filtered water turbidities,
Cryptosporidium removal averaged 2.25 log for conventional treatment
and 2.8 log for direct filtration, while the respective Giardia
removals averaged 3.3 log for conventional treatment and 3.9 log for
direct filtration. Differences in performance between direct filtration
and conventional treatment by the full scale plant were attributed to
different source water quality during the filter runs.
Ongerth, Jerry E. and Pecoraro, J.P. 1995
This project used very low turbidity source waters (0.35 to 0.58
NTU). With optimal coagulation, 3 log removal for both cysts were
obtained. In one test run, where coagulation was intentionally
suboptimal, the removals were only 1.5 log for Cryptosporidium and 1.3
log for Giardia. This emphasized the importance of proper coagulation
for cyst removal even though the effluent turbidity was less than 0.5
NTU.
LeChevallier, Mark W. and Norton, William D. 1992
Source water turbidities ranged from less than 1 to 120 NTU.
Removals of Giardia and Cryptosporidium (2.2-2.8 log) were slightly
less than those reported by other researchers, possibly because full
scale plants were studied, under less ideal conditions than the pilot
plants. The participating treatment plants were in varying stages of
treatment optimization. Removal achieved a median of 2.5 log for
Cryptosporidium and Giardia.
LeChevallier, Mark W.; Norton, William D.; and Lee, Raymond G. 1991b
This study evaluated removal efficiencies for Giardia and
Cryptosporidium in 66 surface water treatment plants in 14 States and 1
Canadian province. Most of the utilities achieved between 2 and 2.5 log
removals for both Giardia and Cryptosporidium. When no cysts were
detected on the finished water below detection protozoan levels were
set at the detection limit for calculating removal efficiencies.
Foundation for Water Research 1994
Raw water turbidity ranged from 1 to 30 NTU. Cryptosporidium oocyst
removal was between 2 and 3 log. Investigators concluded that any
measure which reduced filter effluent
[[Page 59497]]
turbidity should reduce risk from Cryptosporidium. The importance in
selecting coagulants, dosages, and pH should not be overlooked. Apart
from turbidity, indicators of possible reduced efficiency for oocyst
removal would be increased color and dissolved metal ion coagulant
concentration in the effluent, for these are indications of reduced
efficiency of coagulation/ flocculation.
Kelley, M.B. et al. 1995
Protozoa removal was between 1.5 and 2 log. The authors speculated
that this low Cryptosporidium removal occurred because the coagulation
process was not optimized, though the finished water turbidity was less
than 0.5 NTU. Also, when cysts were not detected in the finished water
below detection values were assumed as filtered water concentration
levels.
West, Thomas; et al. 1994
Pilot scale direct filtration was used with anthracite mono-media
at filtration rates of 6 and 14 gpm/sq ft. Raw water turbidity was 0.3
to 0.7 NTU. Removal efficiencies for Cryptosporidium at both filtration
rates were 2 log during filter ripening (despite turbidity exceeding
0.2 NTU), and 2 to 3 log for the stable filter run, declining
significantly during particle breakthrough. When effluent turbidity was
less than 0.1 NTU, removal typically exceeded 2 log. Log removal of
Cryptosporidium generally exceeded that for particle removal.
Summary of Studies
The studies described above indicate that rapid granular
filtration, when operated under appropriate coagulation conditions and
optimized to achieve a filtered water turbidity level of less than 0.3
NTU, should achieve at least 2 log of Cryptosporidium removal. Removal
rates vary widely, up to almost 6 log, depending upon water matrix
conditions, filtered water turbidity effluent levels, and where and
when removal efficiencies are measured within the filtration cycle. The
highest log pathogen removal rates occurred in those pilot plants and
systems which achieved very low finished water turbidities (less than
0.1 NTU).
Members of the M-DBP Advisory Committee discussed that tighter
turbidity performance criteria would increase the likelihood of systems
achieving higher oocyst removal rates. As a general principle, members
of the M-DBP Advisory Committee indicated that if a utility were
required to achieve less than 0.3 NTU 95% of the time, it would target
substantially lower turbidity levels in order to have confidence that
it will not exceed the 0.3 level. This principle was also recognized by
the M-DBP Advisory Committee's Technical Work Group and served as a
technical basis for much of the Committee's discussion of turbidity
(i.e., that if the performance standard is 0.3 NTU systems would target
achieving less than 0.2 NTU 95 percent of the time).
The Patania and Nieminski/Ongerth studies as they relate to
finished water turbidity levels and log removal are particularly
relevant to this point. These particular studies involve finished water
turbidity at low levels in the same range as the finished water target
identified by the Committee. The associated removal of Cryptosporidium
at these turbidity levels was reliably in the range of 2 log or
greater.
Other key points discussed during the Advisory Committee's
deliberations related to the studies include:
As turbidity performance improves for treatment of a
particular water, there tends to be greater removal of Cryptosporidium.
Pilot plant study data in particular indicate high
likelihood of achieving at least 2 log removal when plant operation is
optimized to achieve low turbidity levels. Moreover, pilot studies
represented in the table tend to be for low-turbidity waters, which are
considered to be the most difficult to treat regarding particulate
removal and associated protozoan removal. Since high removal rates have
been demonstrated in pilot studies using lower-turbidity source waters,
it is likely that similar or higher removal rates would be achieved for
higher-turbidity source waters.
The evaluation of Cryptosporidium removal in full-scale
plants can be difficult in that this data includes many non-detects in
the finished water. In these cases, values assigned at the detection
limit will likely result in over-estimation of oocysts in the finished
water. This in turn means that removal levels will tend to be under-
estimated.
Another factor that contributes to differences among the
data is that some of the full-scale plant data comes from plants that
are not optimized, but that still meet existing SWTR requirements. In
such cases, oocyst removal may be less than 2 log. In those studies
that indicate that full-scale plants are achieving greater than 2 log
removal (LeChevallier studies in particular), the following
characteristics pertain:
--Substantial numbers of filtered water measurements resulted in oocyst
detections;
--Source water turbidity tended to be relatively high compared to some
of the other studies;
--A significant percentage of these systems were also achieving low
filtered water turbidities, substantially less than 0.5 NTU.
Removal of Cryptosporidium can vary significantly in the
course of the filtration cycle (i.e., at the start-up and end of filter
operations versus the stable period of operation, which is the
predominant period).
b. Other Filtration Technologies. Other filtration technologies
include slow sand and diatomaceous earth filtration. ``Technologies and
Costs for the Treatment of Microbial Contaminants in Potable Water
Supplies, October 1988'' by USEPA (1988) listed research studies
indicating that a well designed and operated plant using these
technologies is capable of 3-to 4-log removal of Giardia and viruses.
Recent findings appear in Table 2 below.
Table 2.--Cryptosporidium and Giardia Lamblia Removal Efficiencies
----------------------------------------------------------------------------------------------------------------
Type of treatment plant Log removal Experimental design Researcher
----------------------------------------------------------------------------------------------------------------
Slow Sand........................ Giardia >3.......... Pilot plant at 4.5 Schuller and Ghosh, 91.
to.
Crypt >3............ 16.5 degrees C.....
Crypt 4.5........... Full scale plant... Timms et al., 1995
Diatomaceous Earth............... Giardia >3.......... Pilot plant, Schuler and Ghosh, 90.
addition of.
Crypt >3............ coagulant increased
.................. removal beyond.....
.................. values shown.......
----------------------------------------------------------------------------------------------------------------
[[Page 59498]]
c. Multiple Barrier Approach.
The M-DBP Advisory Committee engaged in extensive discussion
regarding the adequacy of relying solely on physical removal to control
Cryptosporidium in drinking water supplies and on the need for
inactivation. There was a substantial absence of technical consensus on
how to or whether it is currently possible to adequately measure
Cryptosporidium inactivation efficiencies for various disinfection
technologies. This issue emerged as a significant impediment to
addressing inactivation in the IESWTR.
As part of the original 1994 proposal, USEPA included control
strategies that would entail the development of a map of inactivation
efficiencies for Cryptosporidium. As discussed later in Section M. of
this Notice, adequate information to develop such a map is not
available at this time. The Advisory Committee discussion recognized,
however, that inactivation requirements may be appropriate and
necessary under future regulatory scenarios and that physical removal
by filtration may not be sufficient under all circumstances or for all
source waters.
As part of the development process for the long term ESWTR, the
Advisory Committee recommended that USEPA request comment on a risk-
based proposal for Cryptosporidium embodying the multiple barrier
approach (e.g., source water protection, physical removal,
inactivation, etc.), including, where risks suggest appropriate,
inactivation requirements. In establishing the LTESWTR, the Committee
recommended that the following issues be evaluated:
--Data and research needs and limitations (e.g., occurrence, treatment,
viability, active disease surveillance, etc.);
--Technology and methods capabilities and limitations;
--Removal and inactivation effectiveness;
--Risk tradeoffs including risks of significant shifts in disinfection
practices;
--Cost considerations consistent with the SDWA;
--Reliability and redundancy of systems; and
--Consistency with the requirements of the Act.
3. Advisory Committee Recommendations and Related Issues
USEPA reiterates its request for comment on the following
recommendations of the M-DBP Advisory Committee.
All surface water systems that serve more than 10,000 people and
are required to filter must achieve at least a 2-log removal of
Cryptosporidium. Systems which use rapid granular filtration (direct
filtration or conventional filtration treatment-as currently defined
in the SWTR), and meet the turbidity requirements described in
section II.C. are assumed to achieve at least a 2-log removal of
Cryptosporidium. Systems which use slow sand filtration and
diatomaceous earth filtration and meet existing turbidity
performance requirements under the SWTR (less than 1 NTU for the
95th percentile or alternative criteria as approved by the State)
are assumed to achieve at least 2-logs removal of Cryptosporidium.
Systems may demonstrate that they achieve higher levels of
physical removal.
C. Turbidity Control
1. Summary of 1994 Proposal as it Relates to Turbidity Issues and
Public Comments
Finished water turbidity levels are currently regulated by USEPA
under the SWTR as a treatment technique to ensure removal of Giardia
and viruses. The SWTR requires systems to monitor the turbidity of the
combined filter effluent every four hours at each treatment plant.
Systems using direct filtration or conventional treatment must achieve
a combined filter effluent turbidity level of no more than 0.5 NTU in
95% of the measurements in each month and never exceed 5 NTU. Failure
of individual filters may allow pathogens to enter the distribution
system. However, the SWTR does not presently require systems to monitor
the effluent of individual filters.
As a treatment technique, turbidity is an indicator of filtration
performance. Treatment plants are, as noted above, required to meet
certain turbidity levels to meet the removal requirements for Giardia.
Although turbidity is not a direct indicator of health risk, a very low
turbidity level of the treated water is in general a good indicator of
effective Cryptosporidium and Giardia oocyst and cyst removal by rapid
granular filtration. USEPA continues to believe that turbidity is the
most readily measurable parameter to indicate filtration treatment
effectiveness.
A primary focus of the 1994 proposal was the establishment of
treatment requirements that would address public health risks from high
densities of pathogens in poor quality source waters and from the
waterborne pathogen Cryptosporidium. As discussed earlier in this
Notice, waterborne pathogens have caused significant disease outbreaks
in the United States. Approaches outlined in the 1994 proposal included
treatment requirements based on site-specific concentrations of
pathogens in source water and a proposed 2-log removal requirement for
Cryptosporidium by filtration.
USEPA also specifically requested comment on what criteria, if any,
should be included to ensure that systems optimize treatment plant
performance and on whether any of the existing turbidity performance
criteria should be modified (e.g., should systems be required to base
compliance with the turbidity standards on individual filter effluent
monitoring in lieu of or in addition to monitoring the confluence of
all filters; and should any performance standard value be changed). In
addition, the Agency requested comment in the 1994 proposal on possible
supplemental requirements for State notification of persistent high
turbidity levels (e.g., broadening the requirements for State
notification of turbidity exceedances).
Some comments suggested and supported a revised approach to the
IESWTR that would focus on optimizing existing water treatment
processes to provide insurance against microbial disease outbreak in
the absence of source water occurrence data. Another comment suggested
that current levels of treatment, including filtration, have a
sufficient degree of effectiveness in preventing transmission of
Cryptosporidium in drinking water.
One commenter suggested that turbidity performance standards should
not be modified until the SWTR has been further implemented. One
commenter suggested that decreases in turbidity standards or monitoring
after each filter should be voluntary unless scientific data
demonstrate otherwise. Another commenter suggested that individual
filters can be evaluated during sanitary surveys. Several commenters
supported tighter turbidity standards and monitoring of individual
filters. Suggested turbidity performance levels included 0.1 or less,
or 0.2 NTU as revised standards. Several commenters supported
monitoring of individual filters, with one suggesting backwashing of
filters when turbidity levels increase.
2. New Data and Perspectives
As presented in detail below, the M-DBP Advisory Committee's
recommendations to the Agency included tighter turbidity performance
criteria and individual filter monitoring requirements as part of the
IESWTR. These revised performance criteria, along with the individual
filter monitoring requirements, would better enable systems to
demonstrate that they meet a 2 log removal requirement for
Cryptosporidium. Because Cryptosporidium is exceptionally
[[Page 59499]]
resistant to inactivation using chlorine, physical removal by
filtration is extremely important in controlling this organism. Data
presented in the previous section of this Notice support modifications
to the existing turbidity requirements under the SWTR to enable systems
to demonstrate that they meet the proposed 2 log requirement.
The revised turbidity performance criteria would also contribute to
another of the IESWTR's key objectives, which is to establish a
microbial backstop to prevent significant increases in microbial risk
when systems implement new disinfection byproduct standards under the
Stage 1 DBPR. As indicated by data presented below, tighter turbidity
performance criteria would reflect actual current performance for a
substantial percentage of systems nationally. Revising the turbidity
criteria would effectively ensure that these systems continue to
perform at these levels (in addition to resulting in improved
performance by systems that currently meet the existing criteria but
that operate at levels higher than those suggested in the Advisory
Committee's recommendations). The other major component of a microbial
backstop would be provisions for disinfection profiling and
benchmarking, which are discussed in Section D. of this Notice.
The revisions to the turbidity provisions (including the individual
filter provisions) recommended by the Committee would also contribute
to the microbial backstop objective in direct relationship to the
treatment process itself. The reliability of the disinfection barrier
as a means for preventing waterborne disease should increase
substantially as a result of these tighter turbidity provisions
because:
--There would be fewer and shorter periods of elevated turbidity during
which the disinfection barrier could be compromised; and
--The removal of particulate matter achieved by the filtration process
will both be higher on average and more consistent throughout the
treatment cycle, thus putting less burden on the disinfection barrier.
a. 95th Percentile and Maximum Turbidity Levels of Composite
Filtered Water.
Three data sets, summarizing the historical turbidity performance
of various filtration plants, were evaluated to assess the national
impact of modifying existing turbidity requirements. This included
turbidity information from the American Water Works Service Company
(AWWSC, 1997), a multi-State data set (which was analyzed in two sets)
(SAIC, 1997), and information from plants participating in the
Partnership for Safe Water program (Bissonette, 1997). Only turbidity
data from plants serving populations greater than 10,000 persons were
used. The analyses also included only plants that met the current 95th
percentile turbidity standard, 0.5 NTU, and the current maximum
turbidity standard, 5 NTU, in all months. Each of the data sets was
analyzed to assess the current performance of plants with respect to
the number of months in which selected 95th percentile and maximum
turbidity levels were exceeded.
The AWWSC is a privately-held company that owns and operates for
profit about 70 water treatment facilities located across the country.
For this analysis, the AWWSC data set (AWWSC, 1997) included one year's
data for 45 plants in 10 States. The States, with number of plants in
each state listed in parentheses, are as follows: California (1),
Connecticut (3), Iowa (2), Indiana (6), Maryland (1), Missouri (2),
Pennsylvania (24), Tennessee (1), Virginia (2), and West Virginia (3).
USEPA analyzed the composite filtered effluent turbidity data obtained
from the AWWSC plants measured every 4-hours.
The analyses examined two variations of turbidity data obtained
from the multi-State data set (SAIC, 1997). The multi-State data set
included 86 plants in 11 states. The States, with number of plants in
each state listed in parentheses, are as follows: California (10),
Georgia (5), Kansas (9), New Jersey (5), Ohio (12), Oregon (10), Rhode
Island (6), Texas (9), Wisconsin (8), West Virginia (6), Wyoming (6).
The State data was analyzed as two data sets, denoted as State 1 and
State 2. The State 1 data set included only plant information with
measurements every 4 hours, comprising slightly more than half of the
State data (47 plants in CA (10), OR (10), TX (9), WI (6), WY (6), WV
(6)). The State 2 data set was comprised of both the State 1 data and
other data including plant information consisting of daily maximum
turbidity values only, altogether 86 plants.
The State 1 data set was expected to provide a more accurate
picture of typical plant performance among the plants in the entire
State data set because there were more data points per plant. However,
the State 2 data set increased regional coverage by incorporating data
from five additional States (GA, KS, NJ, OH, RI) to reflect additional
geographic variation that may not have been captured in the State 1
data set.
In order to determine how many of the systems met lower 95th
percentile turbidity levels based on turbidity measurements every four
hours, the data from those States in which systems only report maximum
daily values had to be statistically adjusted. The adjustment is
necessary to take into account the difference in the number of reported
measurements in a month that can exceed a particular level (e.g., 0.3
NTU) without exceeding the monthly 95th percentile for that level.
(Systems that report measurements every four hours can have up to 9 of
180 measurements (5%) that exceed the level in a month; however, there
is no way to directly calculate an equivalent value for systems that
only report daily maximum values without making some adjustment.) No
adjustment was necessary for assessing monthly maximum turbidity
levels.
The State 2 analyses adjusted the monthly 95th percentile turbidity
levels for plants with only daily maximum data. This was done because
the 95th percentile based on 31 daily turbidity maximums a month will
overestimate the 95th percentile based on 186 daily measures (or
measurements every 4 hours). To assess the magnitude of the bias, the
State 1 data were used to examine the relationship between the 95th
percentile of the daily maximums and the 95th percentile of the daily
measurements.
The State 2 monthly 95th percentile analyses were obtained by
dividing the estimated monthly 95th percentiles of those systems
reporting only daily maximums by a factor of 1.2 to account for bias.
This factor was derived as follows. The daily maximum was determined
for each day in the State 1 data set and a monthly 95th percentile (of
the 30 or 31 daily maximums) was determined, i.e., the second largest
daily maximum. The corresponding monthly 95th percentile based on the
daily data was also determined. The ratio of these two values was then
calculated and summarized across months. The median ratio across all
months was 1.2, with 90 percent of the ratios ranging between 1.0 and
1.9. The analysis used to derive the adjustment factor examined only
plants that reported six values per day.
The remaining data set included in the turbidity analysis was of
plants participating in the Partnership for Safe Water. The Partnership
for Safe Water is a joint venture of several organizations, including
the American Water Works Association, the Association of State Drinking
Water Administrators, the Association of Metropolitan Water Agencies,
the National Association of Water Companies, the American Water Works
Association Research Foundation and USEPA. These organizations
[[Page 59500]]
entered into a voluntary ``partnership'' with the nation's drinking
water filtration plants treating surface water to tighten treatment
practices and operational controls to reduce the risk from
Cryptosporidium and other waterborne pathogens. The Partnership
approach, described in the ``Partnership for Safe Water Voluntary Water
Treatment Plant Performance Improvement Program Self-Assessment
Procedures'' (USEPA et al. 1995), is based on USEPA's Composite
Correction Program (CCP). The CCP is a voluntary program which is
described in detail in the handbook Optimizing Water Treatment Plant
Performance Using the Composite Correction Program--USEPA/625/6-91/027.
The Partnership for Safe Water utility membership consists of 199
utilities representing almost 280 water treatment plants. These plants
serve approximately 80 million persons. The Partnership consists of
four phases with each phase providing tools and methodologies to assist
utilities in progressing toward a higher quality finished water. The
following data summarizes turbidity performance based on 4-hour
measurements reported by the Partnership utilities for 12 months
overlapping 1995 and 1996. The data represents a composite of
Partnership utilities that have completed varying phases of Partnership
activities, ranging from having just joined to having progressed well
into the self-assessment phase (phase 3). All data were derived from
the 1997 Partnership for Safe Water Annual report (Bissonette, 1997).
The results of the analyses of all of the data sets are shown in
Tables 3 and 4.
Tables 3 and 4 indicate the extent to which plants, as currently
operated, are meeting different turbidity levels. Conversely the data
indicate the portion of utilities which might need to alter existing
practice in order to meet lower turbidity limits, if such limits were
required through regulation.
Table 3 is organized to reflect the extent to which utilities are
currently meeting monthly 95th percentile turbidity limits, assuming
that compliance with such limits is determined as currently done under
the existing monthly 95th percentile standard of 10,000. State 1 (4-hour daily data from 47 plants): 10 CA, 10 OR, 9 TX, 6 WI, 6 WV,
6 WY. State 2 (86 plants including State 1 data and daily maximums * from additional plants) : 10 CA, 5 GA, 9
KS, 5 NJ, 12 OH, 10 OR, 6 RI, 9 TX, 8 WI, 6 WV, 6 WY. AWWSC: 45 plants: 1 CA, 3 CT, 2 IA, 6 IN, 1 MD, 2 MO, 24
PA, 1 TN, 2 VA, 3 WV. Partnership for Safe Water 235 plants. *For plants with only daily maximums, the monthly
95th percentile was estimated as the 95th percentile of the daily maximums divided by 1.2. The adjustment was
done to account for the potential bias of taking the 95th percentile of daily maximums, and was based on the
relationship observed in the State 1 data between the 95th percentile of the daily maximums and the 95th
percentile of the 4-hour data.
Table 4.--Number and Percent of Plants That Exceeded Monthly Maximum Turbidity Limits in at Least N Months out
of 12
----------------------------------------------------------------------------------------------------------------
At least 1 month At least 3 months At least 6 months
Maximum turbidity limit Data source -----------------------------------------------------------------
Num Pct Num Pct Num Pct
----------------------------------------------------------------------------------------------------------------
0.3.......................... State 1........ 36 76.6 15 31.9 6 12.8
State 2 69............. 80.2 36 41.9 15 7.4
AWWSC 24............. 53.3 10 22.2 4 8.9
Partnership 129............ 54.9 72 30.6 37 15.7
0.5.......................... State 1........ 18 38.3 3 6.4 1 2.1
State 2 35............. 40.7 7 8.1 1 1.2
AWWSC 12............. 26.7 3 6.7 0 0.0
Partnership 65............. 27.7 20 8.5 5 2.1
1.0.......................... State 1........ 1 2.1 0 0.0 0 0.0
State 2 6.............. 7.0 0 0.0 0 0.0
AWWSC 4.............. 8.9 0 0.0 0 0.0
Partnership 16............. 6.8 4 1.7 2 0.9
2.0.......................... State 1........ 1 2.1 0 0.0 0 0.0
State 2 2.............. 2.3 0 0.0 0 0.0
AWWSC 0.............. 0.0 0 0.0 0 0.0
Partnership 7.............. 3.0 2 0.9 1 0.4
----------------------------------------------------------------------------------------------------------------
b. Individual Filter Performance.
During a turbidity spike, significant amounts of particulate matter
(including oocysts, if present) may pass through the filter. Figure 3
presents the turbidity levels over time of a typical filter. The
greatest potential for a peak (and thus, pathogen break-through) is
near the beginning of the filter run after filtered backwash or start
up of operation (Amirtharajah 1988; Bucklin et al. 1988; Cleasby 1990;
and Hall and Croll 1996).
Various factors effect the duration and amplitude of filter spikes,
including sudden changes to the flow rate through the filter, treatment
of the filter backwash water, filter to waste capability, and site-
specific water quality conditions. The M-DBP Advisory Committee also
discussed the need to control turbidity spikes in order to limit the
number of oocysts passing through the filter.
BILLING CODE 6560-50-P
[[Page 59502]]
[GRAPHIC] [TIFF OMITTED] TP03NO97.045
BILLING CODE 6560-50-C
c. Turbidity Measurement.
Turbidity is a measure of light scatter that is affected by the
size distribution and shape of suspended particles in the water. Four
methods are commonly used to measure turbidity and all are approved for
use under the SWTR. They include the Nephelometric Method listed in
2130B of the Standard Methods for the Examination of Water and
Wastewater, Standard Test Method for Turbidity of Water ASTM (1990)
D1889-94, the Nephelometric Method in 180.1 of USEPA-600/R-93-100 and
the Great Lakes Instruments Method 2 (see section 141.74(a)(1)).
Turbidimeters which measure turbidity commonly consist of the
following components: (1) a light source and lenses and other optical
devices to project the light beam at the sample container and to direct
the scattered light to the detector; (2) a transparent cell that
contains the water to be measured; (3) light traps within the sample
chamber that minimize the amount of stray light that reaches the
detector; and (4) a meter that indicates the intensity of the light
reaching the detector. While turbidity measurement has long been
recognized as a means for evaluating treatment performance for removal
of particulate matter (which include microorganisms), issues remain
pertinent to the accuracy and precision of the measurement (Hart et al.
1992; Sethi et al. 1997).
Large tolerances in instrument design criteria, intended to promote
competition among instrument manufacturers, have lead to turbidimeters
with significantly different design features being available on the
market. Turbidimeters with different designs (but within the design
specifications of Standard Methods), calibrated according to
manufacturer's recommendations, have been shown to provide different
turbidity readings for a given suspension (Hart et al. 1992). The
significance of this phenomenon as it might pertain to the same water
with changing turbidities over time or different waters in the U.S. is
not known. Therefore, narrowing instrument design criteria could reduce
variation of turbidity measurement but the best direction that such
change should take is not yet apparent.
Calibration procedures also affect turbidity measurements.
Calibration typically involves placing a quantity of a standard
suspension in the turbidimeter and then adjusting the response so that
the meter gives a reading equal to the turbidity value assigned to the
standard. Instruments that are calibrated with currently approved
different standard suspensions can yield different turbidity
measurements on the same water (Hart et al. 1992). The significance of
this phenomenon as it might pertain to the same water with changing
turbidities over time or different waters in the U.S. is also not
known. While narrowing specifications for current calibration
procedures could reduce variation of turbidity measurements, the best
direction that such change should take is not yet apparent.
Other factors that may affect turbidity measurement include
procedures used to prepare and wipe the sample cell and use of sample
degassing procedures. The extent to which all of the above factors,
collectively, affect turbidity measurement is not known. However, past
performance evaluation (PE) studies conducted by USEPA provide some
indication of accuracy and precision of turbidity measurements among
different laboratories for a common synthetically prepared water. In PE
studies, PE samples with known turbidity levels are sent to
participating laboratories (who are not informed of the turbidity
level). Laboratories participating in these studies used turbidimeters
from various manufacturers and conducted their analysis in accordance
with calibration and analytical procedures they are familiar with.
Thus, the variability of the results reflect differences resulting from
using different turbidimeter models and methods and the effects of
different laboratory procedures. Table 5 summarizes results from PE
studies conducted at turbidity levels close to the SWTR turbidity
performance limit of 0.5 NTU. The Relative Standard Deviation (RSD) is
the Standard Deviation divided by the mean. It appears that the RSD at
turbidity levels considered in these PE studies are slightly below 20%.
(A RSD of 20% implies that 95% of one-time turbidity measurements made
by different laboratories would fall within 40% of the mean. The RSD
for an individual laboratory, making numerous measurements on a given
sample water would be expected to be significantly less than that
achieved among different laboratories (using a variety of turbidimeters
as indicated in Table 5).
[[Page 59503]]
Table 5.--USEPA Performance Evaluation Results of Turbidity Measurements (USEPA 1997d)
[Turbidity readings are expressed in NTU, and Relative Standard Deviation in %]
----------------------------------------------------------------------------------------------------------------
No. of Relative S
Study No. True Turb. samples Mean D
----------------------------------------------------------------------------------------------------------------
34 USEPA/State............................................. .720 54 .752 16.0
34 All Lab................................................. .720 1503 .744 15.8
23 USEPA/State............................................. .650 24 .659 10.1
25 USEPA/State............................................. .600 28 .585 13.8
25 All Lab................................................. .600 708 .597 16.0
25 USEPA/State............................................. .450 29 .463 20.5
25 All Lab................................................. .450 707 .481 19.5
22 USEPA/State............................................. .350 52 .406 16.1
----------------------------------------------------------------------------------------------------------------
No data is yet available on measurement performance from PE studies
at levels less than 0.3 NTU. A major concern expressed by participants
among the Advisory Committee is the ability to reliably measure low
turbidity levels. The TWG assumed that if systems operated to achieve a
turbidity limit of less than 0.2 NTU 95 percent of the time, this would
provide an adequate margin of safety from variability in treatment
performance and turbidity measurement error, to consistently meet a
turbidity limit of 0.3 NTU.
USEPA intends to conduct two PE studies with true turbidities
ranging from 0.1 to 0.3 NTU. One study is planned to begin no later
than the end of January 1998 and the other study within 6 months
thereafter. These new studies will provide an indication of accuracy
and precision of turbidity measurements at lower levels than previously
examined. Measurements by on-line turbidimeters will also be evaluated.
On-line monitoring issues: For expedience, on-line turbidimeters
are often calibrated against a bench instrument that has been
accurately calibrated by comparing the turbidity level in a water
sample. However, at regular intervals they need to be taken off line
and calibrated, as for bench instruments, by pouring the prepared
standard suspension into the chamber of the instrument. On-line
instruments must be inspected regularly to remove air bubbles and
accumulated debris. Fluctuations in continuous measurements do not
necessarily signify a decrease in water treatment performance.
Fluctuations in continuous measurements should be investigated since
they may be due to air bubbles, debris or a temporary disturbance due
to a change in the flow rate of sample water flow through the
turbidimeter. To address the contingency of such phenomenon, the
Advisory Committee recommended, based on advice from the Technical Work
Group, that turbidity spikes should be defined on the basis of at least
2 consecutive measurements taken over some interval of time (e.g., 15
minutes).
There is no standard design specification for on-line turbidimeters
regarding chamber size and recommended flow rate. Thus, turbidity
spikes of the treated water will be reflected with a delay of a few
seconds to a few minutes, depending on chamber volume and flow rate of
the turbidimeter. A turbidity peak measured by a turbidimeter with a
large chamber volume and small flow rate will result in slightly
reduced peak.
3. Advisory Committee Recommendations and Related Issues
USEPA reiterates its request for comment on the following
recommendations of the M-DBP Advisory Committee.
1. Turbidity Performance Requirements. For all surface water
systems that use conventional treatment or direct filtration, serve
more than 10,000 people, and are required to filter: (a) the
turbidity level of a system's combined filtered water at each plant
must be less than or equal to 0.3 NTU in at least 95 percent of the
measurements taken each month and, (b) the turbidity level of a
system's combined filtered water at each plant must at no time
exceed 1 NTU. For both the maximum and the 95th percentile
requirements, compliance shall be determined based on measurements
of the combined filter effluent at four-hour intervals.
2. Individual Filter Requirements. All surface water systems
that use rapid granular filtration, serve more than 10,000 people,
and are required to filter shall conduct continuous monitoring of
turbidity for each individual filter and shall provide an exceptions
report to the State on a monthly basis. Exceptions reporting shall
include the following: (1) any individual filter with a turbidity
level greater than 1.0 NTU based on 2 consecutive measurements
fifteen minutes apart; and (2) any individual filter with a
turbidity level greater than 0.5 NTU at the end of the first 4 hours
of filter operation based on 2 consecutive measurements fifteen
minutes apart. A filter profile will be produced if no obvious
reason for the abnormal filter performance can be identified.
If an individual filter has turbidity levels greater than 1.0
NTU based on 2 consecutive measurements fifteen minutes apart at any
time in each of 3 consecutive months, the system shall conduct a
self-assessment of the filter utilizing as guidance relevant
portions of guidance issued by the Environmental Protection Agency
for Comprehensive Performance Evaluation (CPE). If an individual
filter has turbidity levels greater than 2.0 NTU based on 2
consecutive measurements fifteen minutes apart at any time in each
of two consecutive months, the system will arrange for the conduct
of a CPE by the State or a third party approved by the State.
3. State Authority: States must have rules or other authority to
require systems to conduct a Composite Correction Program (CCP) and
to assure that systems implement any follow-up recommendations that
result as part of the CCP.
In reference to the above recommendations, EPA also requests
comment on what would or would not constitute an obvious reason for
abnormal filter performance. The Agency also requests comment on how
much time a system should have to conduct a self-assessment of the
filter and how much time a system should have to arrange for the
conduct of a CPE under circumstances such as described in the
recommendations.
USEPA also requests comment on whether there are particular filters
currently in operation in the United States for which specific guidance
may be needed with regard to individual filter monitoring. For example,
some members of the M-DBP Advisory Committee suggested that special
guidance be developed for unique filtration devices made by Infilco
Degremeont (previously made by Aldridge). These devices consist of
multi-celled filters with a traveling bridge-automated back washing
unit that are not conducive to individual cell monitoring.
USEPA also requests comment regarding existing SWTR provisions for
lime softening plants that have very low
[[Page 59504]]
turbidity in source waters. The existing SWTR allows States to set
numerically higher standards up to 1 NTU in 95 percent of samples taken
per month for conventional treatment and direct filtration plants if
the State determines that on-site studies demonstrate at least 99.9
percent overall removal and/or inactivation of Giardia cysts. (54 FR
27503). In the SWTR (54 FR 27486), the Agency notes that actual
demonstrations ``(e.g. with pilot plant study results)'' are not
required for the State to determine when minimum performance
requirements at the higher turbidity level might be appropriate for a
particular system. The SWTR states:
Instead, the State's determination may be based upon an analysis
of existing design and operating conditions (e.g. adequacy of
treatment prior to filtration, percent turbidity removal across the
entire treatment train, stringency of disinfection) and/or
performance relative to certain water quality characteristics (e.g.
microbiological analysis of the filtered water, particle size counts
in water before and after filtration). The State may wish to
consider such factors as source water quality and system size in
determining the extent of analysis necessary. (54 FR 27503).
Committee members raised situations where filtration plants have
been designed for specific source water quality characteristics such as
high alkalinity and extremely low turbidity water (e.g. 0.1 to 0.5
NTU). In systems with such source waters, turbidity levels from the
filters may actually be higher than in the source waters due to
reactions from chemicals added mainly for purposes other than source
water particle removal. Lime softening plants operating under certain
conditions, depending upon process configuration and raw water
characteristics or when flocculation conditions change, may
periodically experience a carry over of extremely fine calcium
carbonate or magnesium hydroxide particles. These fine particles may
pass through filters thereby resulting in artificially elevated
effluent turbidity levels. If turbidity performance criteria are
tightened under the IESWTR some plants may have difficulty meeting
these criteria but still achieve substantial removal of Giardia
lamblia, Cryptosporidium parvum, and viruses. As reflected in the 1989
SWTR, USEPA believes that in cases where lime softening is practiced
and source water turbidity levels are low, provisions for alternative
treatment performance criteria (i.e., in lieu of turbidity) may be
appropriate.
As in the present SWTR, USEPA believes that demonstrations of
equivalent protection need not be based on actual demonstrations (e.g.
pilot plant study results). Instead the State's determination can be
based on the factors cited at 54 FR 27503 as quoted above. Other
factors related to source water microbial quality (e.g. pristine source
water, source water protection programs, microbial monitoring results,
bank filtration) may be appropriate for such determinations.
USEPA requests comment on the appropriateness of continuing
existing provisions that provide States the flexibility of approving
higher turbidity levels up to 1 NTU in 95 percent of samples per month
and up to 2 NTU maximum turbidity for such plants, and additionally
seeks comments on:
What types of plants might fall in this category (e.g.
softening plants designed for color and hardness removal with very
low turbidity source waters);
What demonstrations of equivalent protection from
Giardia lamblia, Cryptosporidium parvum, and viruses are appropriate
(e.g. microbiological analysis of the filtered water, monitoring
results for protozoans, watershed control, wellhead protection
programs);
What additional or alternative requirements States
might place on such systems to insure the objective of equivalent
protection from Giardia lamblia, Cryptosporidium parvum, and viruses
(e.g. regular monitoring for protozoans in source and or filtered
water, or for other water quality parameters, watershed control,
well head protection programs);
Allowing systems to acidify turbidity samples when
calcium carbonate carry-over exists to obtain true turbidity
readings; and
The appropriateness of including source water microbial
quality measurements or surrogates as part of a State determination
of equivalent protection when considering whether to authorize
higher operating turbidity levels.
D. Disinfection Benchmark for Stage 1 DBP MCLS
A fundamental principle of the 1992-93 regulatory negotiation which
was reflected in the 1994 proposal for the IESWTR was that new
standards for control of byproducts must not result in significant
increases in microbial risk. This principle was also one of the
underlying premises of the M-DBP Advisory Committee's deliberations,
i.e., that existing microbial protection must not be significantly
reduced or undercut as a result of systems taking the necessary steps
to comply with the Stage 1 DBPR. The Advisory Committee's
recommendations to meet this key objective are discussed in this
section.
The approach outlined below represents the recommendation of the
Advisory Committee to develop a mechanism that is designed to assure
that pathogen control is maintained while the Stage 1 DBPR provisions
are implemented. Briefly, the disinfection benchmark addresses the
three issues of who must gather the necessary information to evaluate
current practices, how the benchmark operates, and finally, how the
system and the State work together to assure that microbial control is
maintained.
Based on data provided by systems and reviewed by the TWG, the
baseline of microbial inactivation (expressed as logs of Giardia
lamblia inactivation) demonstrated high variability. Inactivation
varied by several logs on a day-to-day basis at any particular
treatment plant and by as much as tens of logs over a year due to
changes in water temperature, flow rate (and consequently contact
time), seasonal changes in residual disinfectant, pH, and disinfectant
demand (and consequently disinfectant residual). There were also
differences between years at individual plants.
To address these variations, the TWG developed an approach for a
system to use to characterize disinfection practice; the procedure is
called profiling. In essence, this approach allows a plant to chart or
plot its daily levels of Giardia inactivation on a graph which, when
viewed on a seasonal or annual basis, represents a ``profile'' of the
plant's inactivation performance. The system can use the profile to
develop a baseline or benchmark of inactivation against which to
measure possible changes in disinfection practice. This approach makes
it possible for a plant that may need to change practice to meet DBP
MCLs to assure no significant increase in microbial risk. It provides
the necessary tool to allow plants to project or measure the possible
impacts of potential changes in disinfection. Only certain systems
would be required to develop a profile and keep it on file for State
review during sanitary surveys, and only a subset of those required to
develop a profile would be required to submit it to the State as part
of a package submitted when the system is making significant changes to
its disinfection practice.
USEPA reiterates its request for comment on the following
recommendations of the M-DBP Advisory Committee that address the three
questions outlined above: (1) who should develop a profile, (2) how a
profile is actually generated, and (3) how the profile will be used.
1. Applicability
Systems would be required to prepare a disinfection profile, if at
least one of the following criteria are met:
[[Page 59505]]
(1) TTHM levels are at least 80% of the MCL (0.064 mg/l) as an
annual average for the most recent 12 month compliance period for
which compliance data are available prior to November 1998 (or some
other period designated by the State). Monitoring would be in
accordance with current TTHM requirements.
(2) Haloacetic acid (HAA5) levels are at least 80% of the MCL
(0.048 mg/l) as an annual average for the most recent 12 month
period for which data are available (or some other period designated
by the State). In connection with HAA5 monitoring, the following
provisions apply:
(a) Systems that have collected HAA5 data under the ICR must use
those data to determine the HAA5 level, unless the State determines
that there is a more representative annual data set.
(b) If the system does not have four quarters of HAA5 data by
the end of 90 days following the IESWTR promulgation date, the PWS
must conduct HAA5 monitoring for four quarters. This monitoring must
comply with the monitoring requirements included in the DBP Stage 1
rule.
(The Advisory Committee recommended a value of 80% of the MCL
because available data indicated that DBP levels varied from year to
year due to many factors (e.g., changes in source water quality,
changes in water demand). The Committee believed that targeting a level
20% below the MCL would include most systems that would be expected to
make changes to comply with the TTHM and HAA5 MCLs on a continuing
basis. Also, USEPA previously considered this target level at the
recommendation of the 1992 reg-neg committee, to evaluate DBP Stage 1
compliance forecasts and costs, based upon the judgement that most
facilities will take additional steps to ensure continuing MCL
compliance if they are at or above these levels.)
2. Developing the Profile and Benchmark
As outlined above, profiling is the characterization of a system's
disinfection practice over a period of time. The system can create the
profile by conducting new daily monitoring or by using
``grandfathered'' data (as explained below). A disinfection profile
consists of a compilation of daily Giardia lamblia log inactivations
(or virus inactivations under conditions to be specified in the final
rule), computed over the period of a year, based on daily measurements
of operational data (disinfectant residual concentration(s), contact
time(s), temperature(s), and where necessary, pH(s)).
Grandfathered data are those operational data that a system
previously collected at a treatment plant during the course of normal
operation. These data may or may not have been used previously for
compliance determinations with the SWTR. Those systems that have all
necessary data to determine profiles, using operational data collected
prior to promulgation of the IESWTR, would be able to use up to three
years of operational data in developing profiles. Grandfathered
operational data should be substantially equivalent to operational data
that would be collected under this rule.
Those systems that do not have three years of operational data to
develop profiles would have to conduct monitoring to develop the
profile for one year beginning no later than 15 months after IESWTR
promulgation. If the PWS has existing operational data to develop
profiles, it would have to use those data to develop profiles for the
years prior to the IESWTR promulgation.
In order to develop the profile, a system would have to:
--Measure disinfectant residual concentration (C, in mg/l) prior to
entrance into distribution system and just prior to each additional
point of disinfectant addition, whether with the same or a different
disinfectant.
--Determine contact time (T, in minutes) during peak flow conditions. T
can be based on either a tracer study or assumptions based on contactor
geometry and baffling. However, systems would have to use the same
method for both grandfathered data and new data.
--Measure water temperature ( deg. C).
--Measure pH (for chlorine only).
The system would then have to convert operational data to log
inactivation values for Giardia (and viruses when chloramines or ozone
used as primary disinfectant).
--Determine CTactual for each disinfection segment.
--Determine CT99.9 (i.e., 3-logs inactivation) from tables
in the SWTR/IESWTR using temperature (and pH for chlorine) for each
disinfection segment. [NOTE: USEPA may redesign the tables so that no
conversion is necessary (i.e., the tables will reflect a
CT90 (1-log) value.]
--For each segment, log inactivation = (CTact/
CT99.9) x 3.0.
A log inactivation benchmark would then be calculated as follows:
1. Calculate the average log inactivation for each calendar month.
2. Determine the calendar month with the lowest average log
inactivation.
3. The lowest average month becomes the critical period for that
year.
4. If data from multiple years are available, the average of
critical periods for each year becomes the benchmark.
5. If only one year of data is available, the critical period for
that year is the benchmark.
3. State Review
The State would review disinfection profiles as part of its
periodic sanitary survey. If a system that is required to develop a
disinfection profile subsequently decides to make a significant change
in disinfection practice, it would have to consult with the State
before implementing such a change. Significant changes would be defined
as: (1) moving the point of disinfection, (2) changing the type of
disinfectant, (3) changing the disinfection process, or (4) making any
other change designated as significant by the State. Supporting
materials for such consultation would have to include a description of
the proposed change, the disinfection profile, and an analysis of how
the proposed change will affect the current disinfection benchmark.
4. Guidance
USEPA, in consultation with interested stakeholders, will develop
guidance for States and systems on how to develop and evaluate
disinfection profiles, how to identify and evaluate significant changes
in disinfection practices, and guidance on moving the point of
disinfection from before the point of coagulant addition to after the
point of coagulant addition. USEPA will also develop guidance for
systems that would be required to develop a profile based on virus
inactivation instead of Giardia lamblia inactivation. Guidance will be
available when the IESWTR is promulgated.
5. Request for Public Comment
USEPA requests comment on all aspects of the recommendation
outlined above and any alternative suggestions that stakeholders or
other interested parties may have. Commenters may want to focus
particular attention on the following issues:
--Applicability requirements,
--Characterization of disinfection practices and components (e.g.,
monitoring, analysis),
--Use of TTHM and HAA5 data from the same time period instead of TTHM
data from one year and HAA5 data from another,
--Definition of significant changes to disinfection practice,
--Different approaches to evaluating possible changes in disinfection
practice against a disinfection profile, and
--Whether the use of grandfathered data, if available, should be
[[Page 59506]]
mandatory for profiling and benchmarking.
E. Definition of Ground Water Under the Direct Influence of Surface
Water (GWUDI)--Inclusion of Cryptosporidium in the Definition
1. Summary of 1994 Proposal and Public Comments
The July 29, 1994, Federal Register notice proposed to amend the
SWTR by including Cryptosporidium in the definition of a GWUDI system.
Under the rule, a system using ground water considered vulnerable to
Cryptosporidium contamination would be subject to the provisions of the
SWTR. USEPA proposed that this determination be made by the State for
individual sources using State-established criteria.
The 1994 proposed IESWTR also requested comment on revisions to
USEPA's guidance on this issue. Cryptosporidium oocysts are smaller
than Giardia cysts and may have substantially different hydrodynamic
behavior in ground water due to their smaller size and perhaps also due
to a difference in charge distribution on the outer surface of the
oocyst. USEPA guidance for the determination of GWUDI suggests methods
that may be insensitive to this differing hydrodynamic behavior in
ground water.
Almost all commenters agreed that Cryptosporidium should be added
to the definition. Only one commenter clearly opposed the addition
without caveat, maintaining that problems with the analytical methods
for the recovery and enumeration of viable organisms and uncertainties
associated with risk assessment should preclude its addition. One
commenter contended that Cryptosporidium should be included only if
USEPA addresses the amount of natural disinfection at each site and
defines treatment effectiveness, especially coagulant use, for GWUDI
systems. One commenter believed that the definition of Cryptosporidium
should be made at the species level, e.g. Cryptosporidium parvum,
because other species were not pathogenic to humans.
One commenter was concerned about the Microscopic Particulate
Analysis (MPA), one of the methods that USEPA identifies in guidance as
being suitable for making GWUDI determinations. As part of this method,
a microscopic examination is made of the ground water to determine
whether insect parts, plant debris, rotifers, nematodes, Giardia
lamblia, and other material associated with the surface or near surface
environment are present. The commenter claimed that the MPA has
analytical method problems similar to those associated with the
recovery of cysts and oocysts from environmental samples and suggested
that the method should undergo additional testing with positive and
negative controls and with performance evaluation samples.
2. Overview of Existing Guidance
USEPA issued guidance on the MPA in October 1992 as the Consensus
Method for Determining Groundwater Under the Direct Influence of
Surface Water Using Microscopic Particulate Analysis. Additional
guidance for making GWUDI determinations is also available (USEPA,
1994e,f). Since 1990, States have acquired substantial experience in
making GWUDI determinations and have documented their approaches
(Massachusetts Department of Environmental Protection, 1993; Maryland,
1993; Sonoma County Water Agency, 1991). Guidance on existing practices
undertaken by States in response to the SWTR may also be found in the
State Sanitary Survey Resource Directory, jointly published in December
1995 by USEPA and the Association of State Drinking Water
Administrators. AWWARF has also published guidance (Wilson et al.,
1996).
3. Summary of New Data and Perspectives
Most recently, Hancock et al. (1997) used the MPA test to study the
occurrence of Giardia and Cryptosporidium in the subsurface. They found
that, in a study of 383 ground water samples, the presence of Giardia
correlated with the presence of Cryptosporidium. The presence of both
pathogens correlated with the amount of sample examined but not with
the month of sampling. There was a correlation between source depth and
occurrence of Giardia but not Cryptosporidium. The investigators also
found no correlation between the distance of the ground water source
from adjacent surface water and the occurrence of either Giardia or
Cryptosporidium. However, they did find a correlation between distance
from a surface water source and generalized MPA risk ratings of high
(high represents an MPA score of 20 or greater), medium or low, but no
correlation was found with the specific numerical values that are
calculated by the MPA scoring system.
USEPA is interested in an expanded discussion of MPA performance.
The work cited here is preliminary information and represents the only
data provided to USEPA so far. USEPA is considering several analytical
activities to address possible changes in the GWUDI determination
guidance. These changes are as follows:
Change the MPA methodology to include a score for
Cryptosporidium oocysts in the risk rating method.
Conduct additional comparison of MPA scores with cyst and
oocyst recovery to evaluate the performance of MPA as an indicator
method (e.g., Schulmeyer, 1995).
Conduct additional MPA performance evaluation testing
(with both positive and negative controls).
Compare MPA scores and cyst/oocyst recovery in horizontal
collector wells and vertical wells to determine if additional guidance
for horizontal collector wells is needed.
4. Request for Public Comment
USEPA is continuing to consider inclusion of Cryptosporidium in the
definition of GWUDI. USEPA requests further comment on this issue as
well as on issues outlined above pertaining to guidance for GWUDI
determinations.
F. Inclusion of Cryptosporidium in Watershed Control Requirements
1. Summary of 1994 Proposal and Public Comments
USEPA proposed to extend the existing watershed control
requirements for unfiltered systems to include the control of
Cryptosporidium. This would be analogous to and build upon the existing
requirements for Giardia lamblia and viruses; Cryptosporidium would be
included in the watershed control provisions wherever Giardia lamblia
is mentioned. USEPA also proposed requiring a State, as a condition of
primacy, to describe how it would judge the adequacy of watershed
control programs for Cryptosporidium as well as Giardia lamblia and
viruses in the source water.
Several commenters to the proposed rule specifically supported
inclusion of Cryptosporidium in watershed control. Others supported
watershed control programs in general without specifically articulating
an opinion on Cryptosporidium. One commenter specifically opposed the
inclusion of Cryptosporidium in watershed control program, maintaining
that other avenues of watershed control could be promoted without
including this organism in the control plan. Another commenter opposed
including Cryptosporidium because environmental sources of Giardia and
Cryptosporidium were not sufficiently understood. This commenter also
opposed the requirement to include Cryptosporidium
[[Page 59507]]
in State watershed control program protocols as a condition of primacy.
Other comments included: (1) Systems need to be informed of the
nature of upstream pathogen sources and changes in upstream water
quality in a timely manner, (2) watershed characteristics should not be
the sole basis for determining water treatment strategies, (3) upstream
sewage discharges should be prohibited and cattle farming and feedlots
prohibited or substantially limited in a watershed, and (4) watershed
control programs should be scientifically based, educational, and
voluntary. One commenter contended that the burden of contamination on
the watershed should not fall to the drinking water systems, and that
better coordination on regulations is needed between the USEPA's
drinking water and wastewater programs.
2. Overview of Existing Guidance
The SWTR specifies the conditions under which a system can avoid
filtration (40 CFR 141.71). These conditions include good source water
quality, as measured by concentrations of coliforms and turbidity,
disinfection requirements; watershed control; periodic on-site
inspections; the absence of waterborne disease outbreaks; and
compliance with the Total Coliform Rule and the MCL for TTHMs.
The watershed control program under the SWTR must minimize the
potential for source water contamination by Giardia lamblia and
viruses. This program must include a characterization of the watershed
hydrology characteristics, land ownership and activities which may have
an adverse effect on source water quality. The SWTR Guidance Manual
(USEPA, 1991a) identifies both natural and human-caused sources of
contamination to be controlled. These sources include wild animal
populations, wastewater treatment plants, grazing animals, feedlots,
and recreational activities. The Guidance Manual recommends that
grazing and sewage discharges not be permitted within the watershed of
unfiltered systems, but indicates that these activities may be
permissible on a case-by-case basis where there is a long detention
time and a high degree of dilution between the point of activity and
the water intake.
3. Summary of New Data and Perspectives
Since proposal of the IESWTR in July 1994, several new outbreaks of
waterborne cryptosporidiosis have occurred in the United States. A
recent summary of these outbreaks (Solo-Gabriele and Neumeister, 1996)
identified raw sewage, surface runoff from livestock grazing areas,
septic tank effluent, cattle wastes, treated wastewater, and backflow
of contaminated water in the distribution system as the suspected
sources of Cryptosporidium contamination of the water supplies in these
outbreaks. Cattle grazing, feedstocks and in particular, calves and
other young livestock, appear to be of greater concern for
Cryptosporidium contamination than for Giardia. Some outbreaks of
cryptosporidiosis have been related to upsets in the treatment process
of filtered water systems or have occurred on occasions when spikes in
turbidity have occurred in those systems. However, little information
is available for unfiltered water systems as to whether spikes in raw
water turbidity increase the likelihood that elevated levels of
Cryptosporidium are present in the source water. Because
Cryptosporidium cannot easily be controlled with conventional
disinfection practices, there is particular concern about the presence
of this organism in the source waters of systems that do not filter.
Data from the ICR may be useful in providing information on the
relative Giardia and Cryptosporidium levels in the raw water sources of
unfiltered and filtered water systems. In one comprehensive study on
Giardia and Cryptosporidium densities in ambient water and drinking
water, investigators (LeChevallier and Norton, 1995) found
Cryptosporidium oocyst levels in ambient water ranging from 0.065/L to
65.1/L, with a geometric mean of 2.4 oocysts/L. In drinking water, the
level of Cryptosporidium oocysts ranged from 0.29-57 oocysts/100L, with
a mean of 3.3 oocysts/100L.
The Seattle Water Department summarized the Giardia and
Cryptosporidium monitoring results from several unfiltered water
systems (Montgomery Watson, 1995). The central tendency of this data is
about 1 oocyst/100L. Thus, depending upon what removal efficiencies are
achieved by filtration for Cryptosporidium (for example, 2 logs), it
appears that unfiltered water systems that comply with the source water
requirements of the SWTR may have a risk of cryptosporidiosis
equivalent to that of a water system with a well-operated filter plant
using a water source of average quality.
Although there are no specific monitoring requirements in the
watershed protection program, the non-filtering utility is required to
develop state-approved techniques to eliminate or minimize the impact
of identified point and non-point sources of pathogenic contamination.
USEPA is considering adding specific monitoring requirements to the
IESWTR for the unfiltered supplies serving 10,000 or more people to
ensure the continued effectiveness of the watershed control program.
The monitoring would be similar to the requirements under the ICR for
Giardia and Cryptosporidium although the sampling frequency may be
modified. As with the ICR, a USEPA-approved method and laboratory for
Giardia and Cryptosporidium analyses would be required.
At a minimum, such a monitoring program might require some level of
routine sampling (e.g., on a weekly, biweekly or monthly basis). The
program may also include ``event'' sampling. An ``event'' would
constitute an occasion when the raw water turbidity and/or fecal/total
coliform concentration exceeded a specific value or possibly exceeded a
site-specific 90th percentile value. At least one sample during an
event might be required in addition to routine sampling. Results of all
protozoa and related analyses would be made available to the State at a
minimum as part of the annual on-site inspection required under the
SWTR for non-filtering supplies.
USEPA is continuing to consider extending the existing watershed
control requirements for unfiltered systems to include the control of
Cryptosporidium. USEPA requests further comment on this issue. The
Agency also requests comment on issues pertaining to monitoring for
unfiltered systems serving 10,000 or more people, including comment on
the following approaches:
Routine Source Water Giardia and Cryptosporidium Monitoring:
Option 1. Weekly Giardia and Cryptosporidium Monitoring
Option 2. Bi-Weekly Giardia and Cryptosporidium Monitoring
Option 3. Monthly Giardia and Cryptosporidium Monitoring
The Agency also requests comments on whether the frequency of
monitoring should depend on system size, e.g., should requirements
differ for systems serving between 10-100,000 people versus those
serving more than 100,000 people.
``Event'' Source Water Giardia and Cryptosporidium Monitoring:
Option 1. No event sampling required.
Option 2. Collect sample(s) for Giardia and Cryptosporidium when
source water turbidity exceeds 1.0 NTU or some alternative value such
as a site-
[[Page 59508]]
specific 90th percentile which might be lower than 1.0 NTU.
Option 3. Collect sample(s) for Giardia and Cryptosporidium when
source water fecal coliform concentration exceeds 20 per 100 mL or
total coliform level exceeds 100 per 100 mL, depending on which class
of coliforms is used under the individual systems filtration avoidance
agreement. Alternatively, the trigger could be some other coliform or
fecal coliform value.
Option 4. Individual utility develops turbidity frequency
distribution (e.g., based on previous 1 to 3 years of daily historical
data) and collects sample(s) for Giardia and Cryptosporidium when
turbidity exceeds 90th percentile level.
Option 5. Some combination of Options 2, 3, or 4.
The Agency also requests comment on whether any of the above
options should depend on system size.
G. Sanitary Survey Requirements
1. Summary of 1994 Proposal and Public Comments
The July 29, 1994, Federal Register proposed to amend the SWTR to
require periodic sanitary surveys for all public water systems that use
surface water, or ground water under the direct influence of surface
water, regardless of whether they filter or not. States would be
required to review the results of each sanitary survey to determine
whether the existing monitoring and treatment practices for that system
are adequate, and if not, what corrective measures are needed to
provide adequate drinking water quality.
The July 1994 notice proposed that only the State or an agent
approved by the State would be able to conduct the required sanitary
survey, except in the unusual case where a State has not yet
implemented this requirement, i.e., the State had neither performed the
required sanitary survey nor generated a list of approved agents. The
proposal suggested that under exceptional circumstances the sanitary
survey could be conducted by the public water system with a report
submitted to the State within 90 days. USEPA also requested comment on
whether sanitary surveys should be required every three or every five
years.
Most commenters on this issue voiced support for requiring a
periodic sanitary survey for all systems. One commenter suggested that
USEPA develop sanitary survey guidance for administration by the
States, while another commenter suggested that sanitary surveys by the
private sector be certified by States or national associations using
USEPA-defined criteria. Commenters recommended that surveys be
conducted either by the State or a private independent party/
contractor. One respondent contended that sanitary surveys, as
presently conducted, were insufficient to assess operational
effectiveness in surface water systems.
With regard to sanitary survey frequency, commenters were nearly
evenly divided between every three years and every five years. Some
commenters argued that the frequency should depend on: (1) whether a
system's control is effective or marginal, (2) system size (less
frequent for small systems), (3) source water quality, (4) whether the
State believes a system's water quality is likely to change over time,
(5) results of the previous survey, and (6) population density on the
watershed. One commenter suggested an annual sanitary survey.
Regarding criteria for sanitary survey inspectors, some commenters
suggested that the State should decide what requirements to use. Others
suggested some combination of education and working experience related
to water plant operations, including (1) professional engineering
certificate and water plant operator license for at least five years,
(2) knowledge of surface water contaminants, source and fate of
contaminants, and both removal capabilities of existing treatment
technologies and ability to evaluate their performance, (3) a BS degree
(preferably MS degree) in sanitary or environmental engineering with
two years experience in evaluating water treatment plants and valid
plant operator's license, (4) five years experience in water system
operation, evaluation, and/or design, and a BS in engineering or
environmental science, (5) a BS degree in science or engineering and
five years experience in the drinking water field.
2. Overview of Existing Regulations and Guidance
Sanitary surveys have historically been conducted by state drinking
water programs as a preventive tool to identify water system
deficiencies that could pose a threat to public health. The first
regulatory requirement for systems to have a periodic on-site sanitary
survey appeared in the final TCR (54 FR 27544-27568). This rule
requires all systems that collect less than 5 total coliform samples
each month to undergo such surveys. These sanitary surveys must be
conducted by the State or an agent approved by the State. Community
water systems were to have had the first sanitary survey conducted by
June 29, 1994, and every five years thereafter while non-community
water systems are to have the first sanitary survey conducted by June
29, 1999, and every five years thereafter unless the system is served
by a protected and disinfected ground water supply, in which case, a
survey must be conducted every 10 years.
The SWTR did not specifically require water systems to undergo a
sanitary survey. Instead, it required that unfiltered water systems, as
one criterion to remain unfiltered, have an annual on-site inspection
to assess the system's watershed control program and disinfection
treatment process. The on-site survey must be conducted by the State or
a party approved by the state. This on-site survey is not a substitute
for a more comprehensive sanitary survey, but the information can be
used to supplement a full sanitary survey.
USEPA's SWTR Guidance Manual (USEPA, 1991a), Appendix K, suggests
that, in addition to the annual on-site inspection, a sanitary survey
be conducted every three to five years by both filtered and unfiltered
systems. This time period is suggested ``since the time and effort
needed to conduct the comprehensive survey makes it impractical for it
to be conducted annually.''
3. New Developments
Since the publication of the proposed ESWTR in 1994, USEPA and the
States (through the Association of State Drinking Water Authorities)
have issued a joint guidance on sanitary surveys entitled USEPA/State
Joint Guidance on Sanitary Surveys (1995). The Guidance outlines the
following elements as integral components of a comprehensive sanitary
survey:
Source
--Protection
--Physical Components and Condition
Treatment
Distribution System
Finished Water Storage
Pumps/Pump Facilities and Controls
Monitoring/Reporting/Data Verification
Water System Management/Operations
Operator Compliance with State Requirements
The guidance also addresses the qualifications for sanitary survey
inspectors, the development of assessment criteria, documentation,
follow-up after the survey, tracking and enforcement.
USEPA is aware that a number of States have independently developed
their own sanitary survey criteria. For instance, the American Water
Works Association California-Nevada Section,
[[Page 59509]]
Source Water Quality Committee in conjunction with the California
Department of Health Services, Division of Drinking Water and
Environmental Management (DHS) have published a document entitled
Watershed Sanitary Survey Guidance Manual (AWWA California -Nevada
Section 1993) to assist domestic water suppliers in defining the scope
of their watershed sanitary surveys and to provide information on the
methods and sources of information for conducting sanitary surveys.
4. Advisory Committee Recommendations and Related Issues
USEPA reiterates its request for comment on the following
recommendations of the M-DBP Advisory Committee.
A sanitary survey would be defined as an onsite review of the
water source (identifying sources of contamination using results of
source water assessments where available), facilities, equipment,
operation, maintenance, and monitoring compliance of a system to
evaluate the adequacy of the system, its sources and operations and
the distribution of safe drinking water. Included in this definition
is the concept that components of a sanitary survey may be completed
as part of a staged or phased State review process within the
established frequency interval set forth below. Finally, for a
sanitary survey to fall within this definition, it must address each
of the eight elements in the December 1995 USEPA/State Guidance on
Sanitary Surveys.
In terms of frequency, this approach would provide that sanitary
surveys must be conducted for all surface water systems (including
ground water under the influence) no less frequently than every
three years for community systems and no less frequently than every
five years for noncommunity systems. Any sanitary survey conducted
after December 1995, that addresses the eight sanitary survey
components of the 1995 EPA/State guidance, may be counted or
``grandfathered'' for purposes of completing the round of surveys.
This approach would also provide that for community systems
determined by the State to have outstanding performance based on
prior sanitary surveys, successive sanitary surveys may be conducted
no less than every five years.
Finally, under this approach, as part of follow-up activity for
sanitary surveys, systems must respond to deficiencies outlined in
the State's sanitary survey report within 45 days, indicating how
and on what schedule the system will address significant
deficiencies noted in the survey. In addition, States must have the
appropriate rules or other authority to assure that facilities take
the steps necessary to address significant deficiencies identified
in the survey report that are within the control of the PWS and its
governing body.
USEPA also requests comment on whether systems should be required
to respond in writing to a State's sanitary survey report discussed in
the paragraph above. USEPA also requests comment on (1) what would
constitute ``outstanding performance'' for purposes of allowing
sanitary surveys for a community water system to be conducted every
five years and (2) how to define ``significant deficiencies.''
H. Covered Finished Water Reservoirs
1. Summary of the 1994 Proposal and Public Comments Received
The July 29, 1994, Federal Register indicated that USEPA was
considering whether to issue regulations requiring systems to cover
finished water reservoirs and storage tanks, and requested public
comment. The rationale for this position was given in the proposed
rule.
Most commenters supported either federal or State requirements.
Some commenters suggested that regulations apply only to new
reservoirs. Some commenters opposed any requirement, citing high cost,
the notion that ``one size does not fit all'', and aesthetic benefits
of an open reservoir.
Some commenters suggested elements for such regulations or
guidance, including (1) applying the same criteria to finished water
reservoirs as exists for unfiltered surface water systems, (2) using
engineering measures to minimize contamination, (3) disinfecting the
effluent to maintain residual in distribution system, (4) monitoring
reservoirs routinely for water quality indicators, (5) covering all
storage tanks, (6) fencing reservoirs with signs warning against
swimming, trespassing, and tampering, and (7) adding notices in the
annual water quality report that the reservoir is not in compliance
with current waterworks standards. A few commenters suggested a number
of other elements.
2. Overview of Existing Information
Possible Health Concerns: When a finished water reservoir is open
to the atmosphere it may be subject to some of the environmental
factors that surface water is subject to, depending upon site-specific
characteristics and the extent of protection provided. It may be
subject to contamination by persons tossing items into the reservoir or
illegal swimming (Pluntze 1974; Erb, 1989).
Microscopic and other organisms may proliferate in open finished
water reservoirs. Increases in algal cells, heterotrophic plate count
(HPC) bacteria, turbidity, color, particle counts, biomass and
decreases in chlorine residuals have been reported (Pluntze, 1974, AWWA
Committee Report, 1983, Silverman et al., 1983, LeChevallier et al.
1997a).
Small mammals, birds, fish, and the growth of algae may contribute
to the microbial degradation of an open finished water reservoir
(Graczyk et al., 1996; Geldreich, 1990; Fayer and Ungar, 1986; Current,
1986). Mammals, birds and fish and their carcasses seed the water and
the sediment with total and fecal coliforms, E. coli and pathogens. In
one study, sea gulls contaminated a 10 million gallon reservoir and
increased bacteriological growth and in another study waterfowl were
found to elevate coliform levels in small recreational lakes by twenty
times their normal levels (Morra, 1979). Seagulls are a source of
numerous coliforms and can also be a source for several human
pathogens, (Geldreich and Shaw, 1993). Algal growth increases the
biomass in the reservoir, which reduces dissolved oxygen and thereby
increases the release of iron, manganese, and nutrients from the
sediments. This, in turn, supports more growth (Cooke and Carlson,
1989). Plants, macrophytes and organic debris will add to the biomass
and nutrient supply.
State Regulations: In order to assess regulatory requirements at
the State level, it is necessary to contact individual drinking water
programs and collect and evaluate specific regulatory language obtained
from those programs. A survey of nine States was conducted in the
summer of 1996 (Montgomery Watson, 1996). The States which were
surveyed included several in the West (Oregon, Washington, California,
Idaho, Arizona, and Utah), two States in the East known to have water
systems with open reservoirs (New York and New Jersey), and one
midwestern state (Wisconsin). Seven of the nine States which were
surveyed require by direct rule that all new finished water reservoirs
and tanks be covered.
Survey of Ten Utilities: There is no comprehensive information
available on the number or size of open finished water reservoirs in
water systems around the country; however, there is one recent survey
of ten utilities which either have open finished water reservoirs or
which had them in the past and covered or replaced them (E&S
Environmental Chemistry, 1997). The existing open reservoirs which were
operated by these systems varied greatly in size, from 5.5 million
gallons (MG) to 900 MG. The systems with open finished reservoirs also
had closed reservoirs within their service area, but for some of the
systems the open reservoirs represent the largest component of total
storage volume in the systems.
[[Page 59510]]
Most of the reservoirs in the systems in this survey were excavated
and lined, but several of the larger ones were formed by dams or
natural lakes that had been converted to water supply use. Many of
these reservoirs have irregular geometry and configurations which make
covering very difficult or impossible. Others are so large that
covering them would be impractical. For some of these reservoirs, it is
impractical to find locations for replacement with the proper hydraulic
characteristics and size. To partially solve this problem in some
cases, systems have chosen to leave large existing open reservoirs off-
line, except for emergency supply purposes.
None of the systems had comprehensive evidence about the effect of
open reservoirs on water quality. These water systems had instituted a
number of measures at open reservoirs to control potential sources of
contamination; these measures included fencing setbacks, security
cameras, on-site surveillance, rechlorination, wire canopies to control
bird activity, and other measures.
3. Request for Public Comment
USEPA is considering as part of the IESWTR a requirement that
systems cover all new reservoirs, holding tanks or other storage
facilities for finished water for which construction begins after the
effective date of the rule. The Agency intends to further consider this
issue, including whether there should be a requirement that all
finished water reservoirs, holding tanks and other storage facilities
be covered, as part of the development of the Long-Term ESWTR. The
Agency requests further comment on this issue and whether provisions
should be established to require all new reservoirs, holding tanks, or
other storage facilities to be covered.
I. Cross Connection Control Program
1. Summary of 1994 Proposal and Public Comments
The July 29, 1994, Federal Register requested public comment on
whether the Agency should require States and/or systems to have a
cross-connection control program. In addition, the Agency solicited
comment on a number of associated issues, including (1) what specific
criteria, if any, should be included in such a requirement, (2) how
often such a program should be evaluated, (3) whether USEPA should
limit any requirement to only those connections identified as a cross
connection by the public water system or the State, and (4) conditions
under which a waiver from this requirement would be appropriate. The
Agency also requested commenters to identify other regulatory measures
USEPA should consider to prevent contamination of drinking water in the
distribution system (e.g., minimum pressure requirements in the
distribution system).
Most commenters supported either a federal or State cross
connection control program. Various commenters recommended that such a
program include a backflow prevention program with approved backflow
preventer lists, categorization of all service connections with respect
to potential risk of backflow, requirement for periodic testing and
maintenance of backflow prevention devices, periodic review of program
by State, establishment of an annual backflow device testing program,
establishment of a backflow device inspector certification program,
enforcement authority, and other suggestions. Commenters also
recommended national disinfection procedures for repair of water lines
and for placing new lines into service, a provision for at least one
person trained in cross-connection control to carry out the program,
and other suggestions.
Commenters opposed to a cross connection control program indicated
that (1) a federally-mandated program would be impractical, burdensome,
and would fail, (2) a State program would be more appropriate than an
USEPA-mandated program, (3) most States already have a comprehensive
program, thus negating need for federal regulations, (4) USEPA should
publish general guidelines only, and (5) there should be a separate
regulation because a cross connection control program would affect both
surface water and ground water.
2. Overview of Existing Information
Historically, a significant portion of waterborne disease outbreaks
reported by CDC are caused by distribution system deficiencies.
Distribution system deficiencies are defined in CDC's publication
Morbidity and Mortality Weekly Report as cross connections,
contamination of water mains during construction or repair, and
contamination of a storage facility. Between 1971-1994, approximately
53 waterborne disease outbreaks were associated with cross connections
or backsiphonage. Fifty-six outbreaks were associated with other
distribution system deficiencies (Craun, Pers. Comm. 1997b). Some
outbreaks have resulted from water main breaks or repairs.
There is no centralized repository where backflow incidents are
reported or recorded. The vast majority of backflow incidents are
probably not reported. Specific backflow incidents are described in
detail in USEPA's Cross-Connection Control Manual (USEPA, 1989a).
Where cross connections exist, some protection is still afforded to
the distribution system by the maintenance of a positive water pressure
in the system. Adequate maintenance of pressure provides a net movement
of water out through breaks in the distribution pipes and prevents
contaminated water outside of the pipes from entering the drinking
water supply. The loss of pressure in the distribution system, less
than 20 psi, can cause a net movement of water from outside the pipe to
the inside, possibly allowing the introduction of fecal contamination
into the system. This problem is of special concern where wastewater
piping is laid in the same street as the water pipes, creating a
potential threat to public health whenever there is low or no pressure.
Many States have cross connection control programs. A Florida
Department of Environmental Protection survey evaluated cross-
connection control regulations in the 50 states (Florida DEP 1996). The
survey results showed that 29 of the 40 states that responded to the
survey request have programs. The rigor of the programs and the extent
to which they are enforced was not addressed by the survey. An USEPA
report suggests that the responsibility for administration and
enforcement of the State programs is generally at the local level
(USEPA, 1995a).
3. Request for Public Comment
USEPA does not plan to address cross connection control in the
IESWTR. As noted above, many States currently have programs, although
the extent to which these vary is unclear. The Agency does plan to
consider cross connection control issues during the development of the
Long-Term ESWTR, in the context of a broad range of issues related to
distribution systems. USEPA continues to request comments or additional
information related to cross connection control or other distribution
system issues.
J. Recycling Filter Backwash Water and Filtering to Waste
The July 29, 1994, notice requested comment on the extent to which
the ESWTR should address the issue of recycling filter backwash water,
given its potential for increasing the densities of Giardia and
Cryptosporidium on the filters. The 1996 Amendments to the SDWA require
USEPA to promulgate a
[[Page 59511]]
regulation for filter backwash recycling not later than August 2000,
(SDWA 1412(b)(14)).
Most commenters who addressed this issue contended that backwash
water should not be recycled or that, if it is recycled, it should be
treated first. One commenter suggested that this decision should be
based on the pathogen density in the backwash water. Another commenter
suggested that the rule should include criteria for assessing the
extent of backwash recycling, depending on raw water quality, size of
filters, and water volume. Another commenter maintained that this issue
should be left to the State and system. One commenter suggested that
the impacts of recycling needed additional research and that any rule
addressing this issue needed to incorporate the results of the latest
research.
1. Filter Backwash Recycle Configurations
Treatment plants can be configured into several general categories
but the variation within each category is significant.
One aspect of this treatment variation is how recycling of waste
streams from plant processes are handled. Figure 4 shows a general
schematic of a conventional treatment plant and how recycle streams may
be developed and treated. Note that backwash water treatment is carried
out in a miniature coagulation-flocculation-sedimentation treatment
facility. Some utilities are considering microfiltration to replace
these unit processes.
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Figure 5 shows an alternate view for some water treatment
facilities that do not practice treatment of their recycled waste
streams. There is an almost infinite variety between these two
examples. In addition, waste streams can be recycled to many different
points in the treatment train. The most common recycle points are at
the plant influent or rapid mix. However, there are several known
examples of recycle streams being introduced into the treatment process
as late as the filter influent.
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Figure 6 shows a typical plot of turbidity over time from a filter
from reintroduction into service after backwash to breakthrough of
turbidity at the end of the filter run. Some plants have installed
filter-to-waste facilities which allow the discharge of the first
minutes of a filter's operation after backwashing usually into the
backwash reclamation system. In California, the State drinking water
regulations define filter-to-waste as: ` ``Filter-to-waste'' means a
provision in a filtration process to allow the first filtered water,
after backwashing a filter, to be wasted or reclaimed.' (McGuire, 1994)
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Figure 7 shows a general schematic of a filter-to-waste operation.
After the backwash process is complete and the filter influent water is
allowed to enter the filter, Valve A is operated so that all of the
filter effluent water is sent to waste. After a specified period of
time or when it is determined that the ripening spike is largely over,
Valve A is operated so that the filtered water becomes part of the
product water of the treatment plant.
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2. State Drinking Water Regulations
California has specific regulations that deal with backwash recycle
and filter-to-waste. Treatment of backwash recycle flows is covered in
the design of treatment facilities section. For new construction,
utilities are required to install solids removal treatment for recycled
filter backwash water. Also, treated backwash water must be returned to
the ``headworks'' (i.e., the plant influent) of the treatment plant.
Solids removal treatment unit processes are not specified in the
regulation, but new construction must be approved by the California
Department of Health Services (California Health and Safety Code,
Sections 646658 & 64660).
To minimize the filter ripening spike, the California Department of
Health specifies operational requirements such that filtration rates
are increased gradually when filters are placed back into service
following backwashing or any other interruption in the operation of the
filter. When any individual filter is placed back into service
following backwashing or other interruption event, the filtered water
turbidity from that filter cannot exceed any of the following criteria:
2.0 NTU.
1.0 NTU in at least 90 percent of the interruption events
during any consecutive 12-month period.
0.5 NTU after the filter has been in operation for 4
hours.
For new construction, utilities are required to provide filter-to-
waste or add additional coagulant chemicals to backwash water.
3. Literature Overview of Standard of Practice
a. Treatment Reference Texts. The joint ASCE/AWWA (1990) water
treatment plant design book includes one section on page 182 dealing
with washwater disposal and recovery. The section lists several
possibilities including recycling without treatment, equalization and
treatment, and lagoons to provide for both equalization and
sedimentation. On page 188, the backwash recycle facility at the
Duluth, Minnesota plant is described. Chemical addition, flocculation
and clarification comprise the backwash treatment system.
The fourth edition of Water Quality and Treatment contains one
section on pages 988-989 dealing with filter backwash residuals. The
section notes that recovery of ``dirty'' backwash water is becoming
increasingly common and that the volume of backwash water is typically
one to five percent of total plant production. Flow equalization is
listed as the most common approach to dealing with recycling of
backwash water. The section states that ``For conventional plants,
solid separation before return is not common, and some holding tanks
are mixed to keep solids in suspension.'' Direct filtration plants are
noted for needing solids separation
[[Page 59516]]
treatment of backwash water, because there is no sedimentation facility
in a direct filtration plant. Concerns are expressed in the section
about increasing the concentrations of Giardia cysts in the plant
influent with the recycle of untreated backwash water.
A handbook of practice was published in 1987 dealing with water
treatment plant waste management. Backwash water was described as a
major waste stream on page 5 and flow equalization was listed as an
important requirement. The handbook gives specific examples of the size
of backwash basins needed based on the number of filters backwashed and
the backwash frequency. The example discusses tankage volumes that
would allow a maximum 10 percent recycle rate of the backwash water to
the plant influent. Neither clarification nor polymer addition were
mentioned in this early reference (Cornwell et al., 1987).
b. ICR Treatment Plants. Of the 523 treatment plants subject to the
ICR, 282 use conventional treatment. Of the conventional treatment
plants, 146 (or 52%) practice recycling of their backwash water.
Additionally, 15 direct filtration plants and 3 in-line filter plants
recycle their backwash water. These data show that
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