JUN 2 0 1991
POSSIBLE REQUIREMENTS OF THE
GROUND-WATER DISINFECTION RULE
The purpose of this document is to present possible ground-
water disinfection requirements and to solicit feedback from the
public.
l
The document consists of two sections: 1) Ground-Water
Disinfection Draft Rule Criteria, and 2} Rationale for the
Ground-Water Disinfection Draft Rule Criteria. The Draft Rule
Criteria section (sometimes referred to as the Draft Rule
Criteria document) specifies a set of possible requirements for
the_Ground-Water Disinfection Rule (GWDR). In some cases,
variations are presented as alternate requirements. The
Rationale section describes the purpose and structure of the
rule, and provides a brief explanation of some of the outstanding
issues raised in the Draft Rule Criteria section.
EPA anticipates adhering to the following schedule in
developing this rule: i
Agency approval of intent
and scope of rule:
Distribute draft rule
to interested public:
Propose rule:
Promulgate rule:
December 1991
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February i.992
June 1993|
l
June 1995|
The information contained herein has not undergone formal
Agency review. It is meant to elicit thoughts and information
from the public to assist EPA in development of the rule. EPA
solicits comment on all the information and criteria, described
herein. All comments received by October 15, 1991 will be
considered in the development of the Draft Rule, iComments
received after November 15, 1991 will be considered in the
development of the Proposed Rule. Comments should be sent to:
Stig Regli - GWDR
OGWDW (WH-550D)
USEPA
401 M Street, SW
Washington, DC 20460
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JUN 6 1991
GROUND-WATER DISINFECTION
DRAFT RULE CRITERIA
Background
The 1986 SDWA amendments mandate EPA to promulgate
disinfection requirements including variance criteria
for all public water supplies. In June 1989, EPA
promulgated disinfection requirements for surface
supplies and ground water under the direct influence of
surface water. EPA must now propose and promulgate
disinfection requirements for ground water not under
the direct influence of surface water to fulfill the
statutory requirement. ,
i
A "strawman rule" with regulatory options was presented
at a public meeting on June 21, 1990.
Proposal is planned for 1993 and promulgation is
planned for 1995 (same schedule as Disinfectants and
Disinfection By-Products Rule).
II. General Requirements
Source Water Disinfection Requirements:
Community and Noncommunity Systems: A public water
system using ground water must disinfect the source
water of each of its wells unless: !
I
(a) one (or more) of the system's wells meets
"natural disinfection" criteria, in which case,
the system is not required to disinfect that well
or '
(b) the system qualifies for a variance under
Section 1415 (a)(l)(B) of the SDWA, in which case,
source water disinfection for the pertinent well
is not required.
Both of these conditions are intended to reflect those
situations where source water is not vulnerable to
viral contamination.
Distribution System Disinfection Requirements:
Community^Systems: Each system must disinfect the
distribution system continuously and maintain a
detectable disinfectant residual or an HPC
concentration of <500/ral in the water within the
distribution system unless the State determines that
the distribution system is not vulnerable to external
contamination or significant bacterial growth.
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Noncommunitv Systems: Each system is not required to
disinfect its distribution system unless the State
determines that the distribution system is vulnerable
to external contamination or significant bacterial
growth.
[Alternate: .
Community Systems, and Noncommunity Systems Having at
Least 15 Service Connections: Each system must
disinfect the distribution system continuously and
maintain a detectable disinfectant residual or an HPC
concentration of <500/ml in the water within the
distribution system unless the State determines that
the distribution system is not vulnerable to external
contamination or significant bacterial growth.
Noncommunitv Systems Having Fewer 'Than 15 Service
Connections: Each system is not required to disinfect.
its distribution system unless the State determines
that the distribution system is vulnerable to external;
contamination or significant bacterial growth.]
Qualified Operators:
All systems required to disinfect their source water
must be operated by qualified operators as determined
by the State.
[Alternate: Require all systems, regardless of whether
they disinfect, to be operated by qualified operators
as determined by the State.]
Treatment technique requirements are established in
lieu of MCLs for viruses, heterotrophic plate count
bacteria (HPC), and Legionella. [The issue of whether
to include coverage for Legionella in this rule is
unresolved.]
Maximum Contaminant Level Goals:
Contaminant
Viruses
HPC
Legionella [if included]
MCLG
0
none
0
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III. "Natural Disinfection" Criteria and Associated
Conditions to Be Met to Avoid Source Water Disinfection
A) Natural Disinfection Criteria
A well can qualify as having "natural disinfection" if
the Primacy Agency determines that at least one of the
following criteria are met (in addition to all
conditions under "B" below). The system
report to the State that will assist thg State in
making this determination (see Reporting Regu-i r^moni-c^
EPA will provide guidance for making thes.*
determinations .
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* The nearest potential source of fecal contamination
must be at least "a" meters from the well (surface
water must be considered as a potential contaminant
source), and flow through caves, large fractures, or
other similar features does not occur. '
* The travel time of a ground-water particle (not
considering the effects of retardation, I dispersion or
diffusion) taking the most direct path must be at least
x" days from the nearest potential source of fecal
contamination to the receptor well.
* The travel time of a microbial pathogen (including the
effects of retardation, dispersion, and! diffusion)
taking the most direct path must be at least "y" days
from the nearest potential source of fecal
contamination to the receptor well.
* A hydrogeologic feature such as a thick confining layer
or a thick unsaturated zone controls potential
contaminant flow to the well, and the integrity of the
feature is little affected by anthropogenic activities.
B) Associated Conditions
j
In addition to meeting one criterion above r all of the
following conditions must be met for a well to qualify
as having "natural disinfection"; -
* The well must not have been identified as a source of a
waterborne disease outbreak, or if so identified,
either the well must have been modified to prevent
another such occurrence as determined by the State, or
source water contamination must have been ruled out as
a cause of the outbreak. i
The well must meet State-approved well
codes.
construction
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The system must not have violated the Total Coliforms
Rule unless:
(a) the State determines the violation is not due
to negligence, and
(b) the cause of the violation has been
identified and alleviated.
IV. Disinfection Requirements
Source Water Disinfection Requirements
If source water disinfection is required;
* Disinfection treatment (or other process approved by
the State) of each well in the system must achieve at
least "x"% inactivation and/or removal of viruses.
Each well must meet design and operating conditions
specified by the State to ensure that this level of
inactivation is achieved. EPA will provide guidance to
States for specifying design and operating conditions
for each well. Applications of the CT concept will be
promoted. [Level of inactivation—unresolved. Our
intention is to base the level of inactivation on virus
survey data and risk analysis of contaminated supplies.
Level will be set to ensure high probabilities that
most systems will not exceed an acceptable risk level
from drinking water consumption (e.g., <1 infection per
10,000 people per year).]
[Alternate: Allow the State to set the levels of
inactivation and/or removal of viruses by disinfection
treatment (or other process approved by the State) on a
case-by-case basis.]
* Systems not disinfecting their well(s) with ultraviolet
light must, for each well, maintain a disinfectant
residual concentration of at least 0.2 mg/1 in the
water entering the distribution system. .Systems with
wells serving greater than 3,300 people must
demonstrate this by continuous monitoring at those
wells. If there is a failure in the continuous
monitoring, the system may substitute grab sample
monitoring every four hours for up to five days.
Systems with wells serving 3,300 people or less may
take grab samples in lieu of providing continuous
monitoring at those wells on an ongoing basis at the
frequency of one sample per day per well. If a system
uses grab sampling in lieu of continuous monitoring,
any time the residual falls below 0.2 mg/1, the system
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must conduct grab sample monitoring every four hours
until the residual is restored. If the disinfectant
residual falls below 0.2 mg/1 for more than four hours
at any well, the system must notify the State as soon
as possible but no later than the end of the next
business day.
* Systems disinfecting with ultraviolet light must use a
sensor and recorder at each well to indicate that the
dosage is not less than "y" mW-sec/cm2 for more than
four hours. If there is a failure in the monitoring
equipment, the system must stop the delivery of water
from the well(s) to the distribution system until the
monitoring equipment is again operative. Any time the
ultraviolet dosage is less than "y" mW-sec/cm2 for more
than four hours at a well, the system must notify the
State as soon as possible but no later .than the end of
the next business day.
Distribution System Disinfection Requirements
Community Systems
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* Unless the State determines that the distribution
system is not vulnerable to external contamination or
significant bacterial growth, disinfection of the
distribution system must be continuous, and
disinfectant residuals in the distribution system
cannot be undetectable [definition of detectable
residual to be determined] or HPC levels cannot be
greater than 500/ml in more than five percent of the
samples each month for any two consecutive months
Samples must be taken at least at the same time and at
the same points in the distribution system as for total
coliforms under the Total Coliforms Rule.
Noncommunity Systems j
'
* Unless the State determines that the disstribution
system is vulnerable to significant bacterial growth or
external contamination, noncommunity systems are not
required to disinfect their distribution 'systems. If
the State determines that the distribution system is
vulnerable to such contamination, then the disinfection
requirements for the distribution system are the same
as for community systems.
[Alternate:
Community Systems, and Noncommunitv System* rrxvir,~ at
Least 15 Service Connections \
* Unless the State determines that the distribution
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system is not vulnerable to external contamination or
significant bacterial growth, 'disinfection of the
distribution system must be continuous, and
disinfectant residuals in the distribution system
cannot be undetectable [definition of detectable
residual to be determined] or HPC levels cannot be
greater than 500/ml in more than five percent of the
samples each month for any two consecutive months.
Samples must be taken at least at the same time and at
the same points in the distribution system as for total
coliforms under the Total Coliforms Rule.
Noncommunitv Systems Having Fewer Than 15 Service
Connections
Unless the State determines that the distribution
system is vulnerable to significant bacterial growth or
external contamination, these systems are not required
to disinfect their distribution systems. If the .State
determines that the distribution system is vulnerable
to such contamination, then the disinfection
requirements for the distribution system are the same
as for community systems, and noncommunity systems
having at least 15 service connections.]
V. Analytical Requirements
Testing and sampling must be conducted in accordance :
with Standard Methods, 17th edition, or methods
approved by EPA, for HPC and residual disinfectant
concentration. Residuals of free chlorine and combined
chlorine may also be measured by using DPD colorimetric
test kits if approved by the State. Ozone residuals
may also be measured using .automated methods calibrated
in reference to the results obtained by the standard
method if approved by the State. Methods for measuring ,
UV dosage must be approved by the State (EPA will
provide guidelines for UV measurement). [Guidance for .
UV methods being developed.]
Measurements for residual disinfectant concentration
and UV dosage must be conducted by a party approved by
the State. Measurements for HPC must be conducted by a
laboratory certified by the State or EPA to do such
analysis. (Until laboratory certification criteria are
developed for the analysis of HPC, any laboratory
certified by EPA for total coliforms analysis is deemed
certified for HPC.)
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VI. Reporting Requirements
All parameters required in the rule must be reported
monthly to the State. '
Systems meeting criteria for variances or "natural
disinfection" must notify the State when any of the
criteria or associated conditions are no longer being
met.
Within 18 months after promulgation of the rule, all
systems seeking avoidance of source water disinfection
must submit a report to the State that specifies the
process and criteria by which the system proposes to
avoid source water disinfection. The report must:
(a) propose that the system qualifies for either
natural disinfection" or a variance, and
(b) include site-specific information that
supports the proposal in (a). [Which parameters
would be required to be reported for each of the
four "natural disinfection" criteria is under
development.]
The report will be used by the State, along with any
additional data provided by the system,jto evaluate
whether the system meets "natural disinfection" or
variance criteria. Other available information about
the site, region, and/or aquifer may be'used by the
State in making the determination. [The* specific
methods utilized by the State and the data required to
make these determinations is under development.]
VII. Compliance
All community systems must meet monitoring and
performance requirements within 18 months and 36
months, respectively, after promulgation of the rule.
All noncommunity systems must meet monitoring and
performance requirements within 36 months' and 72
months, respectively, after promulgation of the rule
VIII. Variances
Variances from source water disinfection requirements
are allowed for each well. A well that does not
qualify for "natural disinfection" may still qualify
for a variance. The system must submit a report to the
State that will assist the State in making this
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determination (see Reporting Requirements). The site-
specific information and analysis required for a
variance are more rigorous than that required to
qualify for "natural disinfection."
The State must provide notice and opportunity for
public hearing on each proposed variance. A notice and
public hearing may cover the granting of more than one
variance at a time.
Variance criteria to be met to avoid source water
disinfection:
A sanitary survey that includes a more specific
analysis of site hydrogeology than is required to
meet the "natural disinfection" criteria is ;
conducted (guidance to be developed) and the
results indicate that the source water of the well
is not vulnerable to fecal contamination.
[Frequency of sanitary survey—unresolved. The
June 21, 1990 "strawman" variance criteria
specified a sanitary survey frequency of every
five years, which was consistent with the
frequency of sanitary surveys required under the
Total Coliforms Rule for ground-water systems
collecting fewer than five samples per month. EPA
is considering amending the Total Coliforms Rule
to require a sanitary survey frequency that is
consistent with the 3-6-9 cycle of the
Standardized Monitoring Framework. EPA intends to
require a sanitary survey frequency that would be
consistent with the Total Coliforms Rule.]
The well must not have been identified as a source
of a waterborne disease outbreak, or if so
identified, either the well must have been
modified to prevent another such occurrence as
determined by the State, or source water
contamination must have been ruled out as a cause
of the outbreak.
The well must meet State-approved well
construction codes.
The system must not have violated the Total
Coliforms Rule unless:
(a) the State determines the violation is
not due to negligence, and
(b) the cause of the violation has been
identified and alleviated.
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IX. Exemptions
*
Exemptions are allowed provided the following criteria
ave> meif- •
are met:
System is unable to comply with the rule due to
compelling factors (which may include economic
factors).
i
System is in operation on the effective date of
the rule, or if not, no alternative source of
drinking water is available.
Granting of the exemption will not result in an
unreasonable risk to health. '
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SOURCE WATER DISINFECTION
REQUIREMENTS
"Natural disinfection"
criteria met?
1
Yes
No
Variance criteria
met?
I
Yes
INU
'
Disinfection not
required
Disinfection required:
-minimum inactivation level
- disinfectant residual > 0.2
mg/l or UV dosage at POE
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DISTRIBUTION SYSTEM DISINFECTION
REQUIREMENTS
Community
Systems
State determined
distribution
system not
vulnerable?
Yes
No
Detectable
disinfectant
residual or HPC <
500/ml
Ft
Disinfection not
required
Yes
Noncommunity
Systems
State determined
distribution
system
vulnerable?
No
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Rationale for the
Ground-Water Disinfection Draft Rule Criteria
Introduction and Purpose; The purpose of the Draft Rule Criteria
is to present EPA's current thinking on possible ground-water
disinfection requirements and to solicit feedback from the
public. The Draft Rule Criteria document is a brief description
of the evolving criteria under consideration for publication in
the Federal Register in June 1993 as the proposed Ground-Water
Disinfection Rule (GWDR).
In developing the Draft Rule Criteria, EPA considered public
comments on draft regulatory options presented to the public in
mid-1990 (the "strawman" rule). Since EPA continues to gather
information and solicit public comments for use in development of
the GWDR, the criteria may significantly change t;y the time the
rule is proposed. i
Format; Outstanding issues considered unresolved at this time
have been highlighted with italics and brackets in the Draft Rule
Criteria document. Several of the problematic issues are briefly
explained in this Rationale. i
Purpose of the GWDR: The purpose of the disinfection
requirements will be to: . I
(1) Fulfill the Safe Drinking Water Act (SDWA) requirement that
EPA promulgate disinfection requirements for all public water
systems, and
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(2) Correct deficiencies in water treatment by ptiblic water
systems using ground water not under the direct influence of
surface water believed to be responsible for waterborne disease
outbreaks and waterborne endemic disease. Three microorganisms
required to be regulated under the SDWA would be controlled:
viruses, heterotrophic plate count bacteria (HPC)> and Legionella
(if it is shown to occur in the ground waters subject to this
rule). Potential deficiencies in water treatment include no
disinfection treatment when a system is vulnerable to
contamination, inadequate disinfection, interrupted disinfection
and distribution system defects. ; '
EPA promulgated disinfection requirements for public water
systems using surface water or ground water under the direct
influence of surface water on June 19, 1989. Those requirements
are sometimes referred to as the Surface Water Treatment Rule
(SWTR). The GWDR will apply to public water systems using ground
water not under the direct influence of surface water and will
complete the statutory requirements that all public water systems
be required to disinfect.
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Each component of the disinfection requirements presented is
meant to correspond to a possible treatment deficiency within a
public water system. As explained below under "Structure of the
Rule," unless certain conditions are met, many systems using
ground water will be required to apply disinfection treatment if
they have not done so already. The minimum level of disinfection
(not yet determined) is to ensure adequate inactivation of iany
viruses or bacteria in the source waters of systems considered
vulnerable to such contamination. The requirement to maintain
either a certain amount of disinfectant residual or a certain
ultraviolet (UV) dosage at the entry point to the distribution
system is to ensure continuity of disinfection (i.e., prevent
interruptions of disinfection treatment) for the water entering
the distribution system. The requirement to maintain a
detectable disinfectant residual or a certain level of HPC in the
distribution system is to ensure continuity of disinfection
throughout the distribution system, high probability that there
are no failures in the distribution system, and to minimize
bacterial growth.
Structure of the Rule: The disinfection requirements are divided
into source water requirements and distribution system
requirements and are independent of one another. The main reason
for this rule structure is to allow the requirements for
disinfection to be more accurately matched to the need for
disinfection. This rule structure should also prevent a
significant number of systems from unnecessarily going through
the variance process. For example, a system vulnerable to-source
water contamination but not vulnerable to distribution system
contamination could avoid distribution system requirements based
on State discretion rather than the variance process.
States consider the formal process of granting variances
burdensome and would prefer use of different terminology, i.e.,
"criteria for avoiding disinfection," to circumvent this process;
however, the definition of "variance" criteria for disinfection
is a statutory requirement. The rule structure presented^in the
Draft Rule Criteria document is meant to lessen the State's
burden, as it would allow certain classes of systems to avoid
disinfection without going through the variance process.
Variances would be allowed only from source water
disinfection. This is consistent with the SDWA requirements
(Section 1415 (a)(1)(B)) that treatment technique variances can
be based on "the nature of the raw water source" of the system.
Obtaining a variance would be one of two ways a system could
avoid source water disinfection. The other possibility would be
meeting "natural disinfection" criteria and associated
conditions. '.
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Avoidance of distribution system disinfection requirements
would also be possible. The Draft Rule Criteria document
presents two possible distribution system requirements:
(1) All community systems would have to disinfect unless the
State determined that the distribution system is :not vulnerable
to external contamination or significant bacterial growth. The
reverse would be true for noncommunity systems: inoncommunity
systems would not have to disinfect unless the State found the
distribution system to be vulnerable to such contamination.
The alternate requirement specifies 15 service connections in
noncommunity systems as the criterion for dividing systems into
two categories:
? I
(2) Community systems, and noncommunity systems having at least
15 service connections, would have to disinfect unless the State
determined the distribution system is not vulnerable to external
contamination or significant bacterial growth. Noncommunity
systems,with fewer than 15 service connections would not be
required to disinfect unless the State found the distribution
system to be vulnerable to such contamination. !
EPA believes that most noncommunity distribution systems are very
small and are unlikely to be determined vulnerable to external
contamination or significant bacterial growth. Structuring the
State decision making differently for noncommunity systems versus
community systems would minimize transactional costs to States
while also ensuring adequate protection in the distribution
system. The alternate requirement would be more protective of
the larger noncommunity systems.
"Natural Disinfection" Criteria; The specific aquifer and well
characteristics that would allow a system to avoid source water
disinfection without applying for a variance have not yet been
fully developed. The criteria given in the Draft Rule Criteria
document are preliminary and may change significantly in the
process of rule development.
The rationale for introducing another method of estimating
vulnerability (i.e., "natural disinfection" criteria) separate
from variance criteria is to minimize transactional costs to
States that must make decisions on whether systems can avoid
disinfection.
One assumption underlying these criteria is that a system
determined to be not vulnerable to enteric virus contamination in
the source water will also be not vulnerable to enteric bacterial
contamination. Survivability of enteric bacteria tends to be low
as a result of sensitivity to environmental stress, and bacterial
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transport through most aquifers is much more restricted than for
enteric viruses.
Another assumption underlying these criteria is that the
more a system knows about its configuration and proximity to
potential contaminant sources, the more deserving the system is
of meeting the criteria.
Many ground-water systems will have aquifer characteristics
that clearly indicate the systems are not vulnerable to virus
contamination at the wellhead. Examples include systems located
far from contaminant sources, situations where travel times are
long for water or viruses between the nearest contamination
site(s) and the wellhead, and systems located in confined
aquifers or in aquifers having thick overlying unsaturated zones.
Other ground-water systems will have aquifer characteristics that
less clearly indicate whether the systems are vulnerable to virus
contamination. These systems will either apply for a variance or
disinfect their source water.
The intent of introducing "natural disinfection" criteria is
to establish conditions, which if met, would presume that the
wellhead is not vulnerable to virus contamination. The proposed
conceptual "natural disinfection" criteria (numerical boundaries
are now being developed) allow several different methods for
establishing nonvulnerability. The choice of method would depend
upon the information available to the State.
The determination based on distance from contaminant source
to well would be the most conservative choice due to the high
uncertainty in the information on which the vulnerability
judgment would be made. The determination of nonvulnerability
based on travel time of water between the closest contamination
site(s) and the wellhead would require more specific information
(which should be readily available to most systems and/or
States), represent a more accurate analysis, and therefore would
be less conservative. The determination of nonvulnerability
based on viral travel time would require still more specific
information (which should be available to many systems and/or
States) than that based on water travel time, represent a still
more accurate analysis, and therefore would be even less
conservative. EPA will recommend in guidance how these
nonvulnerability determinations could be made.
If the system could not qualify by meeting any of the
"natural disinfection" criteria, the system could still apply for
a variance. But this would involve providing very site-specif.ic
information to the State to demonstrate that it is not vulnerable
to virus contamination. For example, a comprehensive sanitary
survey that includes an analysis of the hydrogeological
characteristics would be required. This might include monitoring
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of indicators for viruses such as coliphage or use of more
sophisticated ground-water models than those generally provided
by EPA.
Guidance for determining compliance with both "natural
disinfection" criteria and variance criteria is now being
developed by EPA and will be made available for public comment.
Variance Criteria: Since variances would apply only to source
water disinfection, the variance criteria presented in the Draft
Rule Criteria document relate only to source water
vulnerabilities to contamination. Criteria that' States might use
to assess vulnerability of distribution systems iwould be placed
in guidance, e.g., a cross-connection control program, and system
design that would ensure a high probability that positive
pressure is maintained throughout the distribution system.
I
Inclusion of Legionella: EPA is in the process of gathering
information on the occurrence of Legionella in ground waters.
Since it has not yet been clearly established that this organism
occurs in ground water not under the direct influence of surface
water, it may not be necessary to include covera-.ge for this
organism in the rule. '
Level of Inactivation: The appropriate level of inactivation, to
be specified either in the rule or in guidance, 'has not yet been
determined. The Draft Rule Criteria document presents two
possible requirements to reflect those possibilities: (1)
meeting a specific level of "x"% inactivation and/or removal of
viruses as determined by the State; or, (2) the State would
'determine what level would be adequate to ensures protection
against viral contamination. Whether or not specific
requirements such as the level of inactivation sire given in the
rule has a direct bearing on enforceability of the requirements.
Any criteria left to State discretion would not [be federally
enforceable, but enforceable only by the State. ' If EPA decides
to allow State discretion on this requirement, it will be because
of (1) a belief by EPA that dramatic risks to waiter systems will
not be an effect of State discretion and (2) a concern that many
systems might otherwise be required to excessively disinfect.
The results of the virus survey now under way will influence
which option is selected. '
Continuity of Disinfection: Requirements to maintain a 0.2 mg/1
disinfectant residual or an ultraviolet (UV) dossage of "y" mW-
sec/cm2 at the entry point to the distribution system would be
very similar to requirements in the SWTR. EPA believes that
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specifying the monitoring and enforceable criteria in the rule as
opposed to leaving this to State discretion has several
advantages: transactional and administrative costs to States
would be minimized, and federally enforceable, uniform criteria
for all systems considered vulnerable to contamination could be
applied.
Detectable Residual in the Distribution System: EPA will
probably propose the maintenance of a detectable disinfectant
residual in the distribution system, as opposed to a certain :
concentration of disinfectant residual, for the same reasons
behind the SWTR distribution system requirements: (1) the
absence of a distribution system residual in the distribution
system, rather than the presence of a residual below some
specific level, can serve as an indicator of potential
contamination at a site; (2) the relationship between a specific
concentration of disinfectant in the distribution system and the
consequent level of protection provided is not well defined at
this time; and (3) requiring systems to meet a specific residual
(e.g., at least 0.2 mg/1) throughout the distribution system
might result in systems having to augment their disinfection
practices unnecessarily and, at the same time, increase the
amount of disinfection by-products.
EPA recognizes that the absence of a disinfectant residual
at a distribution system site does not necessarily indicate
microbiological contamination; such contaminants simply may not
be present, even in the absence of a disinfectant residual. In
other words, if microbial populations are low, the lack of a
disinfectant residual is not a concern. Therefore, sites with
HPC populations of 500/ml or less would be considered equivalent
to sites with detectable disinfectant residuals for purposes of
determining compliance.
A definition of "detectable" disinfectant residual would be
placed either in the rule or in guidance since the term could be
interpreted in many different ways. For the SWTR, it was defined
to mean concentrations £ the detection limits for each analytical
method in Standard Methods. 16th Edition. A definition of
"detectable" residual needs to take into account the problem of
matrix interference (i.e., it should be applicable under field
conditions) and the skill level of operators at water treatment
plants conducting the analysis.
New Technologies: In response to public comments, allowance is
made for emerging technologies such as UV disinfection and
membrane processes in the source water disinfection requirements.
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Analytical Methods: Analytical methods for measuring UV dosage
at the entry point to the distribution system have not yet been
developed. No UV methods are given in Standard Methods, 17th
Edition.
Compliance: Considering the deadlines for determination of
whether ground water is under the direct influence of surface
water for community systems (June 29, 1994) and noncommunity
systems (June 29, 1999) and the estimated date of rule
promulgation (June 1995), EPA believes the proposed compliance
dates for community and noncommunity systems in this rule are
reasonable.
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