Office of Water EPA 811 -P-92-001
(4601) October 1992
£EPA DRAFT GROUND WATER
DISINFECTION RULE
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JUL 2 2 1992
DRAFT GROUND-WATER DISINFECTION RULE
The purpose of this document is to present possible ground-
water disinfection requirements and to solicit comment from the
public.
The document consists of five sections: I) Background, II)
Description of the Draft Ground-Water Disinfection Rule, III)
Basis for the Draft Ground-Water Disinfection Rule Criteria, IV)
State Implementation, and V) Relation to Other EPA Programs and
Policies. Sections I and II are found on pages 1-10. Sections
III-V are found on pages beginning with the respective Roman
numeral. The Draft Rule description (Section II) specifies a set
of possible requirements for the Ground-Water Disinfection Rule
(GWDR). In some cases, variations are presented as alternate
requirements. The Basis section (Section III) describes the
purpose and structure of the rule and provides a brief
explanation of some of the outstanding issues raised in the Draft
Rule description section.
The information contained herein has not undergone formal
Agency review. It is meant to elicit comment and information
from the public to assist EPA in development of the rule. EPA
solicits comment on all the information and criteria described
herein, but specifically on those issues in the text that include
alternates, assumptions, or questions. All comments received by
September 30, 1992 will be considered in the development of the
Proposed Rule. Comments received after September 30, 1992 will
be considered in the development of the Final Rule. Comments
should be sent to:
GWDR Comments Clerk
Office of Ground Water and Drinking Water (WH-550D) '
USEPA
401 M Street, SW
Washington, DC 20460
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I. BACKGROUND
The 1986 SDWA amendments require that EPA 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 intends to propose and promulgate
disinfection requirements for ground water not under
the direct influence of surface water to protect the
public health of persons served by those systems and to
fulfill the statutory requirement.
A "strawman rule" with regulatory options was presented
at a public meeting on June 21, 1990. Draft rule
criteria were made available on June 20, 1991.
Proposal is planned for 1993 and promulgation is
planned for 1995.
EPA has made the following changes from the June 1991
Draft Rule Criteria:
Increased recognition of the decentralized
nature of many ground-water systems,
resulting in changes in several requirements
(e.g., all systems, regardless of size, would
be required to monitor the disinfectant
residual concentration at the entrance to the
distribution system of each well or well
field only once a day).
Additional discussion of "natural
disinfection11 and variance criteria (see
Section III).
Extended compliance dates to allow States and
systems to gather data and make decisions
concerning the need for undisinfected systems
to disinfect.
II. DESCRIPTION OF THE DRAJT GROUND-WATER DZ8ZVTECTZON RULE
A. General Requirements
* Source Water Disinfection Requirements:
Coamuai'tv and M^B^^m/iunitY Svsteasi A public water
system using ground water must disinfect the source
1
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water from each of its wells (or well fields) unless:
(a) one (or more) of the system's wells meets
"natural disinfection" criteria, in which case the
system is not required to disinfect water from
that well; or
(b) the system qualifies for a variance under
Section 1415 (a) (1) (B) of the SDWA, in which case
source water disinfection for the pertinent well
is not required.
Both of these conditions are intended to address those
situations where source water is not vulnerable to
viral contamination.
Distribution System Disinfection Requirements:
systems t Each system must maintain a
disinfectant residual of at least 0.2 mg/1 at the
entrance to the distribution system at all times and
maintain a detectable disinfectant residual or a
heterotrophic plate count (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.
systems: There are no distribution system
disinfection requirements unless the State determines
that the distribution system is vulnerable to external
contamination or significant bacterial growth. If the
State determines that the distribution system is
vulnerable (due to design, construction, operation, or
maintenance) , the same requirements apply as for
community systems above.
/•Alternate:
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disinfection requirements unless the State determines
that the distribution system is vulnerable to external
contamination or significant bacterial growth. If the
. State determines that the distribution system is
vulnerable, the same requirements apply as for
community systems above.]
Qualified Operators:
Require all systems with a ground water source that
disinfect with disinfectants other than sodium
hypochlorite to be operated by qualified operators;
qualification will be determined by the State.
/"Alternate 1: All community water systems required to
disinfect their source water must be operated by
qualified operators; qualification trill be determined
by the State.]
[Alternate 2: All community water systems, regardless
of whether they disinfect, must be operated by
qualified operators; qualification trill be determined
by the State.)
Treatment technique requirements are established in
lieu of MCLs for viruses, HPC, and Legionella. [The
issue of whether to Include coverage for Legionella in
this rule is unresolved. See discussion in Section
III.]
Maximum Contaminant Level Goals:
MCLQ
Viruses 0
HPC no MCLG
Legionella [if included] 0
B. "Pr equal if y ing conditions'* to Be Met to Avoid Source
Water Disinfection and "Natural Disinfection1' criteria
l. "Preorualifvina Conditions** for Avoiding source
Water Disinfection
In addition -fee -eteetina one -of -the "natural
disinfection" criteria below for a variance
criterion described in section I.O). all of the
following conditions must be met for a well to
avoid source water disinfection!
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* 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 the cause of the violation
has been identified and corrected.
2. "Natural Disinfection" Criteria
A veil can qualify a« having "natural
disinfection" if at least one of the following .
criteria are met (in addition to all conditions
under "1" above). If required bv the State* the
system must afM&Bit * report to the State to assist
the State in making such determinations (see
Reporting Requirements). EPA vill provide
guidance for making the«e determinations. See
Section III for a discussion of BPA's current
thinking on this guidance.
* The nearest potential source pf 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,
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,
inactivation, 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.
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* A hydrogeologic feature such as a thick
unsaturated zone controls potential contaminant
flow to the well, and human activities do not
adversely affect the integrity of the feature.
C. Disinfection Requirements
(In this section, requirements for wells will apply also to
wellfields if the wellfield has a single entry point to the
distribution system.)
Source Water Disinfection Requirements
If source vater diainfeetien 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, but
current thinking is 99.99%. Our intention is to
Jbase the level of inactivation on virus study data
(to determine virus concentrations at vulnerable
veils; and risk analysis of contaminated supplies.
Level will 6e set to ensure high probabilities
that most systems will not exceed an acceptable
risJt level from drinking vater consumption fe.a.,
<1 infection per 10,000 people per year; . See
Section III.]
* Systems disinfecting their vell(s) with a chemical
disinfectant must, for each well, maintain a
disinfectant residual concentration of at least
0.2 mg/1 in the water entering the distribution
system. Systems may taXe grab samples at all
wells on an ongoing basis at the frequency of one
sample per day of operation per well. If at any
time the residual falls below 0.2 mg/1, the system
must conduct -cprab 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. continuous
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monitoring will also be allowed.
* Systems disinfecting with ultraviolet light (UV)
must use a sensor and recorder at each well to
indicate that the UV treatment applied is not less
than "y" mW-sec/cm2 for more than four hours. It
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 UV treatment applied 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
Coanunitv Systems
* Unless the State determines that the distribution
system is not vulnerable to external contamination
or significant bacterial growth (including the
presence of an active backflow prevention and
cross connection control program), each system
must maintain a disinfectant residual of at least
0.2 mg/1 at the entrance to the distribution
system at all times and maintain a detectable
disinfectant residual or a heterotrophic plate
count (HPC) concentration of <500/ml in the water
within the distribution system. A system is in
violation if disinfectant residuals in the
distribution system are undetectable [definition
of detectable residual to be determined] or HPC
levels are 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.
Nonc?mmupitv Systems
* There are no distribution system disinfection
•requirements unless the State determines that the
distribution system is vulnerable to external
contamination or significant bacterial growth
(including through backflow or cross connections).
If the State determines that the distribution
system is vulnerable, the sane requirements apply
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as for community systems above.
/•Alternate:
f*nmaunj £v Svs'tfttS- And Nonconununitv Svstfttff H&vino
at Least 15 Service Connectlong
Unless the State determines that the distribution
system is not vulnerable to external contamination
or significant bacterial grovth, each systea oust
Baintain a disinfectant residual of at least 0.2
mg/1 at the entrance to the distribution system at
all times and aaintain a detectable disinxectant
residual or a heterotrophic plate count (SPC)
concentration of <500/ml in the water within the
distribution system. A system is in violation if
disinfectant residuals in the distribution system
are undetectable [definition of detectable
residual to be determined] or SPC levels are
greater than 500/ml in more than five percent of
the samples each month for any two consecutive
months. Samples must be taJcen at least at the
saae time and at the saae points in the
distribution system as for total coliforms under
the Total Coliforms Rule.
Noneoaaunitv Systems Having Fever Than 25 Service
Connect!ons
There are no distribution system disinfection
requirements unless the State determines that the
distribution system is vulnerable to external
contamination or significant bacterial growth. If
the state determines that the distribution system
is vulnerable, the same requirements apply as for
community systems above.]
O. Analytical Requirements
Testing and sampling must be conducted in
accordance with standard Method*. 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 concentrations may
also be measured using automated methods
calibrated in reference to the results obtained by
the standard method (Indigo Method, not the
lodometric Method) if approved by the State.
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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,)
E. Reporting Requirements
Analytical results for monitoring 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 "prequalifying conditions" are no
longer being met. [Alternative: The system must
certify annually that it continues to meet
criteria for "natural disinfection" or variances.]
F. compliance
States will have 18 months from promulgation to
adopt this rule.
Within 54 months of promulgation, all community
systems that are not disinfecting at the time of
promulgation must install disinfection and meet
monitoring and performance requirements, unless
the State determines that the system is not
required to disinfect because it qualifies for
"natural disinfection" or a variance.
Within 78 months of promulgation, all noncommunity
systems that are not disinfecting at the time of
promulgation must install disinfection and meet
monitoring and performance requirements, unless
the State determines that the system is not
required to disinfect because it qualifies for
"natural disinfection" or a variance.
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All systems disinfecting at the time of
promulgation must meet monitoring and performance
requirements within 18 months and 30 months,
respectively, after promulgation of the rule.
6. 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. If required,
the system must submit a report to the State that
will assist the state in making this
determination. The site-specific information and
analysis required for a variance are more rigorous
than that required to qualify for "natural
disinfection."
A well may qualify for a variance if the Primacy
Agency determines that the following variance
criterion is met and that all of the
"prequalifying conditions" for avoiding source
water disinfection are met (see Section II.B.I).
[EPA is considering changing the tvo "natural
disinfection" travel-tie* criteria to be variance
criteria. See Section III.C.J
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 demonstrates that there
is at least "z"-log removal of viruses
between the nearest source of fecal
contamination and the wellhead, indicating
that the source water of the well is not
vulnerable to fecal contamination. This more
detailed analysis may require use of site-
specific determinations of particular
parameters (instead of conservative parameter
values from research literature) to show that
disinfection is not needed to protect public
health due to the nature of the raw water
source. [Frequency of sanitary survey-"
unresolved. The June 21, 1990 mstrairman*
variance criteria specified a sanitary survey
frequency of every five years, which was
consistent vith the frequency of sanitary
surveys required under the Total Coliforms
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Rule for ground-water systems collecting
fewer than five samples per month. While EPA
recognizes that this frequency is not
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 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.
B. Exemptions
Exemptions are allowed provided the following
criteria are met:
System is unable to comply with the rule due
to compelling factors (which may include
economic factors).
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. (EPA will
develop guidance.)
EPA will include guidance for making such
determinations in the GWDR guidance manual.
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III. BASIS FOR THE DRAFT GROUND-WATER DISINFECTION RULE CRITERIA
In this section, EPA has included more detailed information
on several of the criteria included in Section II. Section III.A
contains 'dose response estimates and a discussion of risk
assessment. In III.B, we have included a discussion of avoiding
disinfection through "natural disinfection." Section III.C
contains a discussion of variances. Section III.D concerns
whether Legionell* should be included as a regulated contaminant.
Section III-E contains information about how EPA is trying to
determine the appropriate level of microbial inactivation to
include in the rule. Section III.F contains information about
how EPA has tried to reduce small system impacts.
III-l
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A. Microbial Pathogen Dos«-R«sponse Estimates and Risk
Assessment
This Rule is concerned with potential health hazards from
microbial'ly-contaminated ground waters not under the direct
influence of surface water used for drinking water. [The Surface
Water Treatment Rule (SWTR) (USEPA, 1989) covers ground water
sources under the direct influence of surface water. EPA
distinguishes this category of ground water as that which is
vulnerable to contamination by protozoa.] A number of microbial
pathogens may be associated with ground waters. These include
more than 100 types of viruses (e.g., hepatitis A agent,
rotavirus, Norwalk and Norwalk-like agents, coxsackieviruses,
echoviruses) and several bacterial pathogens (e.g., Salmonella,
Shigella, Campylobact%r). Infections caused by these pathogens
frequently result in nonfatal gastrointestinal illness, but more
serious illnesses are known, some of which result in. death. EPA
is requesting comment on several unresolved issues having to do
with determining appropriate dose-response values for pathogenic
microorganisms and estimating human health risks from these
agents.
l. Illness Endpoints of Concern
The possible microbial illnesses, or "endpoints of concern,"
and their severity vary with the organism and individual host.
In EPA's previous drinking water regulations involving pathogenic
organisms, these endpoints have been taken together as a broadly
generalized "microbial illness" resulting from these organisms in
total, rather than as separately defined illnesses attributable
to specific organisms, such as hepatitis caused by the hepatitis
A virus. The intention of those regulations was to minimize all
microbial illnesses. The most common microbial illness,
gastrointestinal illness or diarrhea, is generally considered
non-life threatening in normally healthy adults. However, the
centers for Disease Control (CDC) have presented data that
indicate overall death rates from gastrointestinal illness from a
variety of organisms approach 0.1% (Bennett et al., 1987). In
addition, studies (Glass et al., 1991; Lew et al., 1991)
indicate that sensitive subpopulations, including infants and
those over 70 years old, have mortalities of 3-5% from diarrhea
requiring hospitalization. Additionally, specific pathogenic
organisms produce illness endpoints more serious than those for
gastrointestinal illness. Hepatitis A infections, for example,
may lead to jaundice .and liver.damage, as well as death. COC
calculates death rates from hepatitis A illnesses in the U.S. at
0.6% of those who are ill(1985). Incidence and mortality
information for a variety of waterborne disease agents are found
in Tables A and B. (Although the agents and diseases listed in
Tables A and B are all waterborne, they are not exclusively
waterborne. Incidence in Table A is from all waterborne sources,
III.A-1
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TABLE A: Estimated waterborne microbial infections, United States,
1985
Disease or agent
Incidence Fatality/case ratio (*)
Campy lobacteriosis
Escherichia coli
Miscellaneous enteric
Salmonellosis, -nontyphi
Shigella
Typhoid
Vibrio (excluding cholera)
Yersiniosis (excluding plague)
Norwa Ik /other 27 run particles
TOTAL
320,000
150,000
10,000
60,000
30,000
60
1,000
1,800
300,000
870,000
0.1
0.2
1.0
0.1
0.2
6.0
4.0
0.05
0.0001
0.1
Data calculated from Bennett et a.I. (1987)
TABLE B: Suspected Nonprotozoan Waterborne Diseases and Infections
Disease or agent
Fatality/case ratio (*)
Cholera 1.0
Legionellosis 15
Enteroviral disease (excluding polio) 0.001
Hepatitis A 0.3
Poliomyelitis 10
Rotavirus 0.01
Coxsackievirus no data
Echovirus no data
Reovirus no data
Data from Bennett et al. (1987)
III.A-2
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not only public vater systems using ground water not under the
influence of surface water. In Table B, EPA has not included
incidence attributable to water/ since Bennett did not include
such data.)
EPA is considering proposing gastrointestinal illness as the
endpoint of concern for microbial infections from drinking water
and requests comment on the use of this endpoint rather than an
endpoint or endpoints of more serious nature. Treatment of
drinking water to provide adequate protection of the population
from gastrointestinal illness would be expected to also provide
protection from more serious illnesses.
Because differences in organisms and illness endpoints
result in different dose-response curves, and because the
fatality/case ratio varies between organisms over several orders
of magnitude, should EPA consider developing risk assessments for
specific pathogens as is done for specific chemical contaminants?
2. Infection vs. Illness
Microbial dose-response determinations try to relate
ingested levels of organisms to a given detection endpoint such
as demonstrable infection or symptomatic illness. EPA is
concerned about the quantitative relationship between infection
and illness. In the interest of protecting public health in a
diverse population, EPA assumes all infections result in
symptomatic gastrointestinal illness. For example, EPA's Surface
Water Treatment Rule (SWTR) (USEPA, 1989) was developed to
achieve risk reduction with respect to microbial infection.
s
EPA is aware that generally infection is not equal to
illness. As an example, in the Rendtorff (1954) study on the
infectious dose for Giardia, many healthy individuals became
infected (as shown by cysts in stool samples), but none became
ill. A survey of a waterborne outbreak of giardiasis in Berlin,
NH showed 76% of the infections were asymptomatic. Only 3% of
those infected required hospitalization (Lopez et al., 1980).
For Vibrio cholerae 01 (the toxigenic Latin American strain), 75%
of infections are asymptomatic. Some 20% of those infected
develop mild diarrhea and only 5% develop the severe, clinically
recognized form of the disease (CDC, 1991).
It is understood, however, that sensitivity to microbial
illness includes enhanced likelihood of. significant illness after
infection. Thus, EPA believes that regulating microbial
pathogens with respect to infection rather than illness provides
protection to all, including sensitive subpopulations. This
approach also would minimize further infection via person-to-
person spread and by not increasing the virus population added to
the waste stream.
III.A-3
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EPA also assumes that the susceptibility to infection of the
population studied by Rendtorff (male prisoners) is
representative of the U.S. population as a whole. However,
whether an individual becomes infected depends upon pathogen
virulence and dose, as well as the health and susceptability of
the individual. Since currently used dose-response curves
exclude the sensitive subpopulations discussed above, would it be
appropriate to factor in an additional margin of safety to
protect these populations? For risk assessment purposes, EPA
also assumes that a dose of one infectious unit can yield an
infection. Using the dose-response curve developed from the
Rendtorff data (Rose et al., 1991), this assumption yields about
a 2% chance for an individual to become infected if one cyst is
ingested. While an infectious unit may theoretically represent a
single virus particle (Katz and Plotkin, 1987) or Giardia cyst,
doses many orders of magnitude higher may be required to yield an
infection. For the purposes of this regulation, EPA considers an
infectious unit for viruses as that measured by an acceptable
viral infectivity assay.
3. Selection of Appropriate Pathogenic organism* for
Regulatory Development
In the development of the SWTR (USEPA, 1989), EPA evaluated
the microorganisms required to be regulated under the SOWA and
selected Giardia as the representative organism for risk
assessment, regulation, and treatment. Giardia was selected
because data were available for risk assessment and because it
was perceived that Giardia was more resistant to disinfection
than most other known microbial pathogens in water. It was
assumed that adequate disinfection of Giardia would yield
adequate disinfection for other microorganisms of concern.
Protozoan pathogens, such as Cryptosporidiua or Giardia, are
not normally found in ground waters not under the direct
influence of surface water. The pathogens of concern in ground
waters only include enteric viruses and bacteria. EPA considers
viruses as generally more resistant to disinfection than
bacteria. For the purposes of the GWDR, EPA solicits comment on
the selection of representative viruses for risk assessment and
regulatory purposes. At issue are both general and specific
problems in defining risk from waterborne viral infection. EPA
proposes to use a conceptual "synthetic virus" of combined
properties (e.g., infectivity, mobility, resistance to
disinfection, occurrence) for_regulatory-development, as
described by Regli et al. (1991). This would provide reasonable
worst-case threats from any given virus. EPA considered using a
single virus or virus group as the basis for determining risk,
but rejected this approach, because no one virus appeared
suitable. Complicating the selection of a single virus for
calculating risk is the fact that occurrence data for pathogenic
IJI.A-4
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viruses in water are scant and primarily from outbreak
investigations. Moreover, dose-response data are available for
only a few viruses and the relative occurrence in water for
different viruses may vary over time, depending on the prevalence
of a particular viral disease in nearby populations that
influence the source water quality. Additionally, sensitivities
to different disinfectants vary among viruses. Rotaviruses, for
example, are more sensitive to chlorine than hepatitis A, but
less sensitive than hepatitis A to chloramine.
Hepatitis A represents the greatest health threat in terms
of severity of waterborne illness and is more resistant to
disinfection than many other pathogens (Sobsey et al., 1991).
Unfortunately, no practical enumeration method for hepatitis A in
drinking water exists, and no dose-response data are available.
Thus, the Agency cannot conduct a quantitative risk assessment
based on this organism. In contrast, rotaviruses have a lower
infectious dose than most other waterborne viruses, and
dose-response data are available, but the disease is not as
severe as that caused by hepatitis A.
As a result of these complications, EPA is proposing to use
a "synthetic virus" for calculating risk. This concept would
combine the properties of several pathogenic waterborne viruses
to create a reasonable worst-case situation. The Agency would
use the enterovirus group (poliovirus, echovirus, coxsackievirus)
to determine waterborne occurrence, since relatively simple
quantitation methods exist and this measurement would represent
worst-case occurrence for any particular enteric virus;
rotaviruses for calculating dose-response; and hepatitis A to
estimate disinfection efficiency. -EPA requests comment on this
approach for calculating risk.
4. Acceptable Risk
EPA requests comment on acceptable levels of public health
risk from drinking water pathogens. The current approach in
developing this rule assumes a requirement for an acceptable
microbial risk. In the development and promulgation of the SWTR,
a risk of no more than one infection per 10,000 people per year
was taken as the desired health goal. Given a 70-year lifespan,
this risk level is equivalent to a 1% lifetime risk for microbial
infection .from drinking water. EPA proposes regulating ground-
water disinfection to achieve no more than one microbial
infection per 10,000 people per year. At. this-level of total
infection, the specific lifetime risk of death from waterborne
microbial illness can be calculated. Using the CDC ratio of
0.001 (Bennett et al., 1987) for the proportion of deaths
resulting from waterborne microbial illnesses and the
above-mentioned equivalence of infection with illness, then a
III.A-5
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conservative estimated mean lifetime risk would be 10'5. Although
there are significant differences in how risks are calculated and
interpreted for microorganisms relative to chemical contaminants
considered as known or probable human carcinogens, this microbial
risk can be compared to the cancer risk range in which EPA
drinking water Maximum Contaminant Levels (MCLs) for carcinogens
are set: about 10"* to 10"6 theoretical 95* upper-bound lifetime
cancer risk.
[When such information becomes available, a comparison of
noncancer chemical endpoints vith nonfatal microbial illnesses
will be added.]
References
Bennett, JV, SO Holmberg, MF Rogers and SL Solomon (1987).
Infectious and parasitic diseases. Am J Prev Med 3:102-114.
RW Amler and HB Dull (eds) , IN: Closing the cran: the burden
of unnecessary illness. Oxford University Press.
Centers for Disease Control (1991). Update: cholera- western
hemisphere, recommendations for treatment of cholera. MMWR
40: 562-565.
Glass, RI, JF Lew, RE Gangarosa, CW Lebaron and H-S Ho (1991).
Estimates of morbidity and mortality rates for diarrheal
diseases in American children. J. Pediatrics 118:27-33.
Grubbs, WD, BA Macler and S Regli (in press). Simulation of
microbial occurrence, exposure and health risks after
drinking water treatment processes. USEPA Publications.
Katz, M and SA Plotkin (1967). Minimal infective dose of
attenuated Polio virus for man. Am J Pub Health 37:1837.
Lew, JF, RI Glass, RE Gangarosa, IP Cohen, C Bern and CL Moe
(1991). Diarrheal deaths in the United States, 1979 through
1987. A special problem for the elderly. JAMA 265:3280-
3284.
Lopez et al. (1980). Waterborne giardiasis: a community-wide
outbreak of disease and a high rate of asymptomatic
infection. Amer. J. Epidem. 112:495-507.
Regli, S, JB Rose, CN Haas and CP Gerba (1991). Modeling the
risk from Giardia and viruses in drinking water. J AWWA 83:
76-84.
Rendtorff, RC (1954). The experimental transmission of human
intestinal protozoan parasites. II. Giardia lamblia cysts
III.A-6
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given in capsules. Am J Hyg 59: 209-220.
Rose, JB, CN Haas and S Regli (1991). Risk assessment and
control of waterborne giardiasis. Am J Pub Health 81:709-
713..
Sobsey, MD, T Fuji and RM Hall (1991). Inactivation of
cell-associated and dispersed Hepatitis A virus in water. J
AWWA 83: 64-67.
USEPA (1989). National Primary Drinking Water'Regulations:
Filtration and Disinfection; Turbidity, Giardia lamblia,
Viruses, Legionolla and Heterotrophic Bacteria. Final Rule,
40 CFR parts 141 and 142. Federal Register, June 29, 1989,
54: 27486-27541.
III.A-7
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B. "Natural Disinfection"
"Natural disinfection" is herein defined as source water
treatment, via virus attenuation by natural subsurface processes
such as virus inactivation, dispersion (dilution) and
irreversible sorption to aquifer framework solid surfaces.
Public water supply systems meeting "natural disinfection"
treatment requirements and associated conditions may be able to
avoid source water disinfection treatment.
^. Rationale for Supplementing Variance Criteria bv
Developing "Natural Disinfection" Criteria
EPA has estimated that there are approximately 180,000
community and noncommunity (public) water supply systems with
wells or well fields that rely upon ground water not under the
direct influence of surface water (as defined in the SWTR). An
unknown number of these systems are adding disinfectants or
otherwise reducing pathogen occurrence by treatment of the source
water. The remaining systems assume that the source water is of
acceptable quality because of the impracticality of monitoring
for viruses and the unsuitability of bacteria as an indicator for
the presence of viruses. The addition of disinfectants to
control bacterial growth in or resulting from infiltration into
distribution systems is not addressed by this section.
EPA chose viruses as the target microbial pathogen because
viruses are more mobile and more resistant to inactivation than
bacteria. EPA currently believes that protecting against viruses
will provide sufficient protection against fecal bacteria from
the same sources. Protozoa are immobilized by the filtering
action of the soil or aquifer media, so they are not expected to
reach source waters not under the direct influence of surface
water.
Under the GWDR, States with primacy will be responsible for
regulatory decisions concerning disinfection at these systems.
In order to minimize the increase in cost to the public and
burden to the regulated community, EPA intends to incorporate
into the nils a menu of methods that States can use (with
complementary guidance) to reach decisions on whether
disinfection by treatment is required. Each method has a dual
purpose: 1) to define a category of public wells or well fields
that are considered not vulnerable to viral contamination using
national criteria (and a process for evaluating those criteria),
and 2) to develop a regulatory mechanism that, through the
process of meeting the regulatory requirements, protects the
public health by increasing the public water system's knowledge
about site vulnerability to viral contamination and enabling the
system to take measures to minimize chances of contamination.
ZZZ.B-1
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EPA believes that wells or well fields identified under this
rule as not vulnerable to viral contamination should be
sufficiently well-defined so that there is a low probability that
vulnerable systems will be categorized incorrectly (i.e., as not
vulnerable) and thus allowed to avoid disinfection. EPA
considers wells or well fields not vulnerable if natural virus
attenuation processes are sufficiently active ("natural
disinfection") so as to restore the quality of the water. For
example, if the nearest possible contamination sources are so far
away that any release of viral contamination today would not
reach a community well for many years, then any viruses present
would become incapable of causing infection, and EPA would
consider that well not vulnerable. Depending on the site
hydrogeologic setting, it may be sufficient for the public water
system to demonstrate such nonvulnerability simply by measuring
the distance from the well to the nearest source of contamination
and reporting that measurement as required.
A well or well field that demonstrates nonvulnerability to
viral contamination according to the methods to be specified in
the rule is said to meet "natural disinfection1* criteria.
Assuming all other criteria are met (the "prequalifying
conditions'*) and the State approves, the well or well field may
avoid source water disinfection requirements under this rule. It
a well or well field does not meet the "natural disinfection"
criteria, the system may opt for a more detailed evaluation of
vulnerability so as to avoid disinfection through the variance
process.
2. Rationale tot Developing Multiple "Natural
Disinfection" Criteria
The National Drinking Water Advisory Council has recommended
that the GWDR be developed so that as the contamination source
gets closer to the well, requirements for site-specific
hydrogeologic data and analyses to show "natural disinfection"
become more precis*. EPA is using this statement of expanded
requirements for situations of increased apparent vulnerability
as a basis for creating the "natural disinfection" criteria.
Towards this end, EPA has developed multiple criteria to
accommodate a wide -range in apparent vulnerability to
contamination. The multiple criteria represent a "menu" of
methods, any one of which may be chosen by the regulated
community to demonstrate "natural disinfection" for any
particular well or wellfield.
Public water systems (or States) may choose one of four
"natural disinfection* criteria to demonstrate suitability for
avoiding disinfection requirements under the rule: 1) setback
distance, 2) hydrogeologic feature, 3) ground-water "particle"
travel time, and 4) contaminant (virus) travel time.
III.B-2
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Setback distance and hydrogeologic feature are the simplest
and least resource-intensive criteria to evaluate and are most
likely to be met by the least vulnerable systems. For more
vulnerable wells, systems may compile from existing sources
sufficient site-specific hydrogeologic data to meet the ground-
water or contaminant travel-time "natural disinfection" criteria.
If systems cannot meet any of the "natural disinfection"
criteria, they may choose to measure or otherwise obtain
additional and/or more precise and more accurate'site-specific
data (with accompanying documentation) to meet the variance
criteria. Public water supplies not meeting either "natural
disinfection" or variance criteria for one or more wells or
wellfields must meet source water treatment, performance and
monitoring requirements for those wells or wellfields.
To assist States and systems, the "natural disinfection"
criteria are structured for flexibility. To meet the
hydrogeologic feature criterion, the public water system may
propose to the State any EPA-approved component of the regional
or local hydrogeology as the feature which provides protection.
In meeting either of the two travel-time criteria, the public
water system may choose any ground-water flow or contaminant
transport model, as appropriate, that the state has approved.
3. The Scientific Basis for the Development of "Natural
Disinfection" Criteria
The "natural disinfection criteria" are based on the use of
models that incorporate some of the physical processes that
govern virus travel through the unsaturated and saturated zones.
A variety of processes have been described in the scientific
literature. Some, such as filtration and settling, are believed
applicable to bacteria but not viruses. Others, such as sorption
(both reversible and irreversible), are believed to be too
inadequately quantified to be applied in this analysis, even
though the "natural disinfection" model used in this analysis has
that capability. The most important processes in this analysis
are virus inactivation and dispersion. EPA is sponsoring research
and developing more sophisticated transport models to better
understand and quantify those processes such as sorption that may
be important yet insufficiently utilized.
The amount of virus inactivation depends on the time
available; viruses become Inactive at a rats that depends
primarily on temperature, but also on pH, organic matter content,
microbial activity, degree of water saturation, salt species
content and concentration, virus aggregation amount, virus type,
and other factors. The time available depends on the
hydrogeologic setting (ground water velocity field), pumping rate
III.B-3
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and the rate of sorption to and desorption from soil and aquifer
solids.
Dispersion is caused by mechanical mixing and diffusion. The
result of mixing of virus-contaminated water with otherwise clean
water is dilution of the virus plume. The amount of dilution
depends on the transport distance and the properties of the soil
or aquifer.
The contaminant transport model input parameters in
Appendix A list all the factors that govern virus transport in
this analysis. Many other parameters are needed to completely
describe all the physical processes that govern virus
inactivation and transport. EPA invites public comment on the
important processes affecting virus transport and inactivation in
ground water.
In addition to the physical processes governing the
transport of viruses, a complete solution to a virus fate and
transport problem requires specifying the initial virus
concentration at a source and defining the target final
concentration at a well. As discussed in Section S.c., the
initial concentration is assumed. The final concentration is
defined using risk analysis; the process is described in the next
section.
4. Waterborne Disease frosi Public Water supply Wells
The intent of this rule is not only to prevent waterborne
disease outbreaks, but to minimize endemic gastroenteric disease.
An outbreak is recognized by the number of oases of clinical
illness; in almost all cases, outbreaks are not identified
unless this number is sufficiently large so that at least one-
half of one percent of the consuming population is clinically ill
within one or a few months. Endemic gastroenteric diseases are
those likely caused by ingestion of waterborne pathogens but the
number of cases occur below outbreak level and generally cannot
be directly associated with drinking water or any other
particular source.
The lov number of reported outbreaks per year in untreated
public ground-water supplies (approximately 0.006% between 1981
and 1990) suggests that the vast majority of existing water
suppliers are, at present, protected against outbreaks (illness
rates from drinking water not exceeding 0.5% of the population
per month) using State-mandated setback distances between
pathogen source and wall. In fact, more outbreaks occur in water
supplies that add disinfectants; the outbreaks occur as a result
of one or more failures in the distribution systaa. EPA believes
that most of the reported outbreaks due to contaminated source
water occurred in localities with very vulnerable ground water,
k
"III.B-4
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such as karst regions or where rocks are highly fractured. Under
this rule, those sites will normally be required to disinfect.
As d'iscussed in Regli et al. (1991), when EPA promulgated
the SWTR, it suggested that water be treated for pathogen, removal
with the goal of ensuring high probability that the population
consuming the water would not be subject to a risk of greater
than one infection per 10,000 people per year. Both the SWTR and
this rule require water treatment in lieu of water testing
because the rule regulates contaminants which are difficult to
detect and pose acute health risks. The risk analysis used to
determine the allowable concentration at the veil in this rule is
based, like the SWTR, on the goal of ensuring that the consuming
population would not be subject to a risk of greater than one
infection per 10,000 people per year.
"Natural disinfection" is a treatment technique because it
seeks to minize disease by reducing the concentration of
contaminants as they are transported in ground water from the
source to the well. The calculation of the amount of
inactivation/removal and dilution during transport is the basis
for the "natural disinfection" criteria. As with any treatment
technique, the amount of treatment by "natural disinfection" can
be variable and must be specified by rule. In this rule, the
amount of treatment is specified as either a distance or time of
travel for ground water flow and/or contaminant transport from
source to well. The greater the distance or travel time, the
greater the amount of treatment by dilution and inactivation.
Thus, the "natural disinfection" criteria are specified distances
or travel times that are easily measurable surrogates for
predicting the actual decrease in virus concentrations.
To predict or evaluate the effectiveness of "natural
disinfection" as a treatment technique, EPA uses a model that
simulates (and simplifies) natural processes. The model predicts
the decrease in virus concentration as the viruses are
transported from a source to a pumping well. The model
calculations require assumptions about 1) an initial
concentration at or near a source and 2) a risk-based allowable
concentration at a pumping well. The next sections present more
details about the risk analyses that are used to determine
concentrations.
a. pga of liak AnalTeee to Determine
the AMQuat of Treatment bv "Maturel Piaiafeetion**
The risk analyses assume that: 1) an acceptable level of
risk of infection can be defined due to consumption of
contaminated ground water, and 2) this value can be used to
calculate an acceptable virus concentration in ground water used
as a source of drinking water.
III.B-5
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Two different analyses of risk are described herein. The
results of both analyses are presented in Table III. 8.1 as
alternative options ("50m-r" option and "ll-log" option). Both
analyses are based on an assumed initial concentration at or near
the source and a defined allowable concentration at the well. The
permissable concentration allowed at the well is the same in both
analyses. The only difference between the two analyses is that
they are subject to different initial concentrations at different
points along the path as ground water flows from-the contaminant
source to the well.
The first analysis ("50m+") assumes that current state
setback distances act to protect against waterborne disease
outbreaks, but additional distance is necessary to minimize
endemic disease. This analysis assumes a virus concentration in
the saturated zone at a distance 50 m downgradient from the
source along the flowpath from the souce to the well. The
analysis calculates how much additional setback distance (or
travel time) is needed to reduce virus concentrations to a level
sufficient to prevent endemic disease rates from exceeding one
illness per 10,000 people per year. This risk analysis is herein
termed the "50m+" analysis to indicate that some additional
distance beyond the 50 m point is required to attenuate the virus
concentrations to an acceptable level.
The second risk analysis ("11-log") uses an assumed virus
concentration at a source and determines total setback distance
(or travel time) necessary to attenuate the virus concentration
sufficient to prevent endemic disease rates from exceeding one
illness per 10,000 people per year.- This risk analysis is herein
referred to as the "ll-log" analysis because the decrease in
concentration between source and well is 11 orders of magnitude
(99.999999999% treatment) or "ll-log" on a logarithmic scale.
The concentrations of viruses at the source or at the 50 m
distance from the source were essential input parameters to the
analyses. However, neither concentration is easily measurable.
The concentration of viruses at potential sources such as septic
tanks is believed to be quite variable (due to the presence or
absence of infected people shedding viruses), and there are few
measured values available. EPA decided to follow a consensus in
the scientific community advising EPA that all calculations
involving septic tanks be based on a source concentration of
10,000 virus plaque forming units (PFU) per liter. There is no
consensus within the scientific community for the concentration
at the point 50 m downgradient from the source nor is there
consensus that the risk analysis should be based on the
concentration at the SO m point. EPA seeks comment on both
assumed concentrations. In all subsequent discussion of virus
concentrations, EPA uses units of viruses per liter and assumes
that PFU per liter is herein equivalent to viruses per liter.
III.B-6
-------
EPA conducted a survey of State-mandated setback distances.
Setback distances vary among States and within States. A State
may have several setback distances depending on whether the
source is a septic tank or a sewage treatment facility or whether
the well is a private or public water supply well. Some States
have varying setback distances depending on the pumping rate of a
public well. EPA chose 50 m as a representative value for State-
1 mandated setback distances for public water supply wells. EPA
" seeks comment on this determination.
1
•j Table III.B.I presents two alternative options ("50m+" and
| "11-log") for specifying the amount of required treatment by
! "natural disinfection" under this rule. Two options are presented
\ because there is insufficient data to determine the amount of
j required treatment by "natural disinfection". Each option is
based on a differing assumption about the initial virus
1
.
'!
i
concentrations. There is also significant uncertainty in
specifying the virus inactivation rate as the virus is
transported from the source to the well. Inactivation rates are
most dependent on ground water temperature which may vary
significantly (with season, with depth, and with geographic and
geologic setting) . To reflect the dependence of inactivation
rates on ground-water temperatures, low and high constant
inactivation rates were assumed based on low (10 degrees C.) and
high (15 degrees C.) average ground water temperatures. Each
differing assumption is discussed in greater detail in the
following sections.
III.B-7
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TABLE III.B.I
"NATURAL DISINFECTION" CRITERIA
Lov Inaet. Rate High Inact. Rata
criterion 50m* ll-log (8-log) 50a+ 11-log (8-lo
»•
Setback Distance 160m 325m 80m 160m
Hydrogeologic Feature:
Depth to Well
Screen 160m 325m 80m 160m
Thickness of
Unsaturated Zone NA 160m NA 50m
Ground-Water
Travel Tine TBD 24 mo (12 mo) TBD 9 mo (4 mo)
Virus Travel Time TBD 9 mo (7 mo) TBD 3 mo (2 mo)
[note: TBD » To Be Determined. "50m+" travel times can not be
determined using existing EPA models. An improved model is being
developed for determining these travel times and to recalculate
all other "natural disinfection" criteria using models that
better simulate important physical processes. 8-log values are
approximately equivalent to the TBD values. Parentheses indicate
that these values are placeholders until the "50m*" values are
determined.]
Table IZZ.B.l details the complete menu of "natural disinfection"
criteria options. Under each option, the setback distance, travel
times and hydrogeologic features provide equivalent protection.
"11-log" and "50*" are based on a specified initial concentration
and a final concentration at the well. High and low inactivation
is based on high and low average ground water temperatures which
act to vary virus inactivation rates.
IIZ.B-8
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a. Calculation of the Xaount of Treatment bv "Natural
Disinfection" ("50m+" or "ii-Locr" Treatment)
The -amount of treatment by "natural disinfection" is
determined by simulating the "natural" treatment process. The
"natural" treatment process occurs during flow of virus-
contaminated water from a source to a pumping well. Determining
the amount of treatment requires knowledge or assumptions about
initial virus concentrations at the source and allowable virus
concentrations at the pumping well.
veil. The
assumed initial concentrations and the defined allowable final
concentration* at the well in the "50m+" and "11-log" treatments
are determined using risk analysis. In the risk analysis, the
health effect goal, i.e. infection rate, is translated into a
virus concentration (for additional details, see Regli et al.,
1991, ''Modeling the risk from Giardia and viruses in drinking
water", J. AWWA 83:76-84). The first step in the translation from
risk level to concentration is to determine the best fit of a
probability distribution curve to virus dose/infection response
data. Regli et al. have determined that a Beta-Poisson
distribution best fits most of the virus dose-response data. .
The second step is to determine which set of virus dose-
response data should be used to determine the allowable target
concentration in a pumping well. Although more than 100 different
viruses have been identified in septage, there are sufficient
data to formulate infectious dose-response relationships for only
five of these viruses at present (rotavirus, echovirus and three
polio virions). Of those five data sets, the rotavirus dose-
response relationship yields the lowest allowable virus
concentrations in drinking water, approximately 2 viruses per
10,000,000 liters (2 x 10-71) of water (Rsgli «t al., 1991, Table
2). It should b« noted that the rang* of acceptable
concentrations in those five data sets varies from approximately
2 viruses per 1000 liters of water to approximately 2 viruses per
10,000,000 liters (2 x 10'7/1) of water.
Hepatitis A virus (KAV) is perhaps the best target virus for
conducting a risk analysis. According to Regli et al., it is the
virus most frequently implicated in waterborne disease, is among
the enteric viruses have, the most significant clinical
manifestations, and is among those more resistant to
disinfection. However, no HAV dose-response data is available.
In all model simulations to determine the amount of
treatment by "natural disinfection," the allowable virus
concentration at the pumping well is fixad at 2 viruses par
10,000,000 liters (2 x 10'7/1) of water as determined in Rsgli et
al. (1991) based on the rotavirus dose-response data.
III.B-9
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ii. x««um«d initial virus concentration at the aoure* -
"50m+" analvais. Although both the "50m*" and "11-log" treatment
criteria -are based on meeting the allowable virus concentration
at a pumping well, they differ in determining the initial virus
concentration at the source. The "50m*" analysis makes use of an
added assumption that is not used in the "11-log" analysis. The
"50m*" analysis assumes that present State setback distances are
effective in .preventing outbreaks of vaterborne disease from
consuming contaminated ground water. Because an outbreak can be
defined as an infection rate, this rate can be translated into a
virus concentration in a manner similar to the above calculation
of allowable virus concentration at the pumping well. The "50m*n
analysis uses the defined virus concentration for outbreaks and
the assumption that the 50 m distance acts to prevent virus
concentrations in water from exceeding the level defined for an
outbreak .
A conservative criterion for the rate of infection during- an
outbreak is one percent of the population infected within one
month. Stated in probabilistic terns, this infection rate
criterion is one infection per 100 people per month. Again using
Regli et al. (1991) this infection rate can be translated into a
virus concentration in water. This concentration is determined by
solving equation (10) in Regli et al. (1991) for the daily
probability of infection for a person consuming 2 liters of water
per day. The calculated daily probability of infection is
inserted into a rearranged equation (4) of Regli et al. (1991)
together with the rota virus dose-response curve parameters (alpha
•0.26 and beta * 0.46) to solve for the acceptable virus*
concentration in drinking water. This calculation indicates that
a concentration no greater than approximately 3 viruses per ten
thousand liters (3 x 10"*/1) of water will prevent public
awareness of an outbreak of disease, assuming that at least one
percent of the population would need to be infected within one
month for this awareness to occur.
Combining the concentration assumed to prevent disease
outbreaks with the assumption that a 50 m setback distance is
effective in preventing outbreaks yields an assumed concentration
at a point 50 • from a source. This specified concentration at
the 50 m point (assumed to be directly downgradient from the
source along the flowpath) is used as the initial concentration
at the source in the "50m*" analysis of the treatment achieved by
"natural disinfection."
iii. x««t««d initial virus concentration at the source -
latiYftii For the "11- log" treatment, there is
consensus among the scientific community that all calculations
should be based on a source initial concentration of 10,000
viruses per liter. The consensus is based on measurements of
III.B-10
-------
virus concentration in septic tanks and raw sewage which may
exfiltrate from leaky sewer lines.
iv. Calculation of the Amount of Treatment by "Natural
Disinfection" for both the "50m+" and "11-locr" ootiona. After
the acceptable concentration (2x 10'7/1)in the well water was
determined by using the risk analysis, EPA can determine the
amount of treatment by "natural disinfection" that is needed to
meet that defined concentration. The "50m+" analysis specifies a
concentration of approximately one virus per 10,000 liters of
water (10"*/1) at the 50 m point and a concentration of
approximately one virus per 10,000,000 liters (10'7/1) at the
well. Thus, the decrease in virus concentration is three orders
of magnitude ("3-log") (from 10"*/1 to 10'7/1) . No assumptions are
made about the decrease in virus concentration from the source to
the 50 m point.
EPA used a model to calculate the setback distances required
to achieve a "3-log" reduction. The distance required is added to
the 50m distance assumed in the analysis. The combined distance
is specified in Table III.B.I as the "natural disinfection1*
setback distance criterion for the "50m+" option.
[The travel-times for the "50m+M options are listed in Table
III.B.I as TBD (To Be Determined). "50m+" travel times can not be
determined using existing EPA models. An improved model is being
developed for determining these travel times.]
[Although travel times for the "50m* option are not '
available, EPA estimates that travel-times calculated using "8-
log" treatment may, albeit poorly, approximate the "50m*" travel
times. The "8-log" approximation is based on a very crude back-
calculation that attempts to estimate the initial virus
concentration at a source based on knowledge of the virus
concentration at the 50 m point. Until the "50m*" travel times
become available, the "8-log" travel times are presented (in
parentheses) in Table III.B.l.]
For the "11-log" option, EPA used the model to calculate the
distance and travel times required to achieve this w11-log"
treatment. Using art initial source concentration of 10,000
viruses per liter (104/!) and a veil water concentration of one
virus per 10,000,000 liters (10'7/1) "11-log" treatment of viruses
(from 104/1 to 10'7/1) is required to meet the infectious disease
risk goal. Table III.B.l. presents the distances and travel-times
(from source to well) required to achieve "11-log" treatment.
Each of the "natural disinfection" criteria listed in Table
III.B.l are addressed at length in the following text.
III.B-ll
-------
Surface water bodies are considered to be a potential source
of virus contamination. However, the virus concentration in
surface water is likely not more than 1 (10°/1) to 100 (10:/1)
viruses per liter. Thus, if surface water were the only source of
concern, then "7-log to 9-log" treatment would be sufficient. In
this draft, the treatment requirements are not based on the type
of source. This reasonable worst case analysis assumes that
septic tanks or sever lines are the primary sources of concern.
If consensus can be reached on the virus concentration in
each type of source, then EPA may consider modifying the "natural
disinfection" criteria to account for these differences. For
example, a septic tank may routinely (in the absence of an
outbreak) have higher concentrations of viruses than a sewer
line, so the setback distance for septic tanks would be larger
than for sewer lines. EPA requests comment on defining source-
specific initial virus concentrations so that "natural
disinfection" criteria would vary depending on the type of
source.
A second set of bounding assumptions governs the
inactivation rates of viruses during transport through the
unsaturated and saturated zones. As a result of inactivation,
the viruses lose their ability to infect the host although they
remain physically present in the source water. The rate of
inactivation has been experimentally measured for a large number
of environmental factors. It has been reported that ground water
temperature has a very significant effect on the rate of virus
inactivation. The experimental results indicate that at low
ground water temperatures, the number of viruses decreases by an
order of magnitude each month. At high ground water temperatures
the amount of removal can be as much or more than four orders of
magnitude each month. Because of the wide range in inactivation
rate, EPA used high and low ground water temperature values to
bound the natural disinfection calculations.
Average ground-water temperatures in the continental United
States vary from 4 to 25»C. However, there is not a consensus
within the scientific community on the appropriate correction
factor needed in order to account for changes in ground-water
temperature throughout the United States. One reason for a lack
of consensus is that few data are available for human enteric
viruses. Another possible reason is that temperature could have
an indirect effect on virus inactivation. For example, at higher
temperatures, other microbes, antagonistic to a virus, may be
more active.
III.B-12
-------
Researchers have experimentally determined inactivation
rates at various temperatures and have developed an empirical
equation to calculate the correction factor. The empirical
equation can include results from experiments using a number of
different viruses, including bacteriophage. The equation EPA
uses in VIRALT includes results from experiments using MS-2
bacteriophage, echovirus, and poliovirus and assumes a linear
relationship between inactivation rate and ground water
temperature. Hepatitis A and rotavirus are the target viruses in
our analyses because they have either significant health effects
and/or infactivity at low doses. However, few data are available
to correct the viral inactivation rates of these two viruses for
the effects of temperature. EPA seeks comment on measured
inactivation rates and temperature corrections to those
inactivation rates.
Table III.B.I presents the "50m*" and "11-log" "natural
disinfection" criteria options based on low (10 degrees C.) and
high inactivation rates (15 degrees C.), each representing a
different average ground-water temperature using equation (14) of
Yates and Yates (1987) [Water Resources, v. 21, n. 9, p. 1119-
1125]. It should be noted that the average ground water
temperature is dependent, in large part, on seasonal distribution
of the data used to determine the average, on the depth of
measurement, the flowpath of the ground water and the geologic
setting. The effect of the temperature correction is so large
that the colder regions of the United States would require
setbacks almost twice as large as those in warmer regions. EPA
has no epidemiological data to show, however, that climate zones
govern waterborne disease outbreaks or low leVels of
gastroenteric illness despite the large temperature effect on
inactivation rat*.
The next sections discuss each of the "natural disinfection"
criteria in greater detail.
ft. "natural Die infect ion** Criteria
This section discusses the choice and calculation of each of
the four "natural disinfection" criteria. The four criteria are:
1) Setback distance, 2) hydrogeologic feature, 3) ground water
travel time and 4) contaminant travel time. EPA seeks comment on
each of the criteria, the reasonable worst case assumptions used
in establishing the criteria and the methodology and input data
used to determine values for each criterion.
Each natural disinfection criterion was calculated using a
model. For this draft, all calculations were performed using the
ground water flow and contaminant transport model VIRALT, Version
2.1 (Park et al., March 1992, VIRALT 2.1: A modular semi-
analytical and numerical model for simulating viral transport in
III.B-13
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ground water; unpublished manuscript). VIRALT was used to
simulate the change in virus concentration with distance from a
contaminant source as the ground water flows to a pumping well.
When the virus concentration at the well was reduced to an
acceptable value, a criterion could be defined.
a. Setback Distance
The setback distance is the horizontal distance from a
pumping well to the nearest potential source of virus
contamination. This criterion is based on the conservative
assumption that the direction of ground-water flow is not known
or is so highly variable that it must be assumed that the nearest
contaminant source is directly upgradient from the well. By
using this assumption, the source must be a relatively large
distance from the well in order to assure nonvulnerability. (if
the direction of ground-water flow is known sufficiently well so
as to determine that nearby sources are downgradient from the
well but within the allowable setback distance, then the well may
qualify for "natural disinfection11 based on one of the two
travel-time criteria.)
The setback distance is easily measured, is used by most
States in regulating State practices, and is also used in the
Wellhead Protection program. Because types of sources are few
and easily identified, compliance with this criterion will be
easy to determine. For example, the public water supply will
likely have access to maps shoving the locations of sewer lines,
and it may be safely assumed that, in unsewered areas, each house
has a nearby septic tank. Other sources such as landfills or
sewage treatment lagoons are prominent features and can be easily
identified. EPA believes that accidents by septage-transport
trucks are of such low probability that there is little potential
for a "short-circuit." Because this criterion requires no
knowledge of site hydrogeology, it is not a true vulnerability
assessment.
In many cases, existing State setback distances are based
more on empirical knowledge and professional practice than on
laboratory, theoretical, or field analysis of the governing
physical and chemical processes. It is likely that common sizes
of building lots have played a rols in determining the setback
distances between septic tanks and sewer lines. EPA requests
comment on how issues such as lot size or common practice should
be handled in determining a setback distance for use as a
national standard in determining whether disinfection is required
for public water supply wells.
The following setback distances were calculated:
III.B-14
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,
"50 m*-"
"11-log"
Low
inactivation
rat*
160 m
325 m
High
inactivation
rate
80 ra
160 m
b. Hvdroaeelooie Feature
The second "natural disinfection11 criteria option is based
on selected hydrogeologic features. Feature selection is based
on two aspects: 1) ease of documenting the presence, absence,
and/or integrity of a feature, and 2) the ease of documenting the
performance of the feature in attenuating viral contamination at
a well or well field. For example, some hydrogeologic features
such as confining layers may perform well in protecting against
microbial contamination, but it may be difficult to demonstrate
that the confining layer is intact (i.e, that the leakage
discharge through a cross-sectional area or flux from the layer
to the aquifer is small). Another hydrogeologic feature, small
values for the vertical gradient in hydraulic head, may act in
protecting against contamination. Although measurable, it may be
difficult to document the performance of this feature except
through the use of a sophisticated, three-dimensional, ground-
water flow model.
EPA assumes that, for any particular hydrogeologic setting,
existing and available hydrogeologic data about that site are
better suited to describing the horizontal rather than the
vertical component of ground-water flow. For example, the
difference in elevation of standing water in adjacent wells may,
for some hydrogeologic settings, provide estimates of the
potential for ground water to flow laterally. On the other hand,
in general, horizontal ground-water velocities are larger than
vertical ground-water velocities. Contaminants from distant
sources may reach shallow wells faster than contaminants from
more nearby source* can reach deeper wells.
EPA is currently considering two hydrogeologic features
suitable for demonstrating "natural disinfection": 1) depth of
the well screen (if present) measured from the ground surface,
and 2) unsaturated zone thickness. The distance from the ground
surface to the well screen is, in principle, similar to the
concept of measuring the distance from the well to the nearest
source of contamination; one is the horizontal setback distance,
and the other is the "vertical setback" distance. In this
analysis, EPA assumed that the potential contaminant source more
or less directly overlies the well. The two concepts are
similar, because each relies on an easily measured distance
criterion to prevent viral contamination. In weighing the
III.B-15
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relative risks associated with horizontal versus vertical
distances to potential contaminant sources, EPA believes that
there are no compelling reasons to require that the horizontal
and "vertical setback" distances have significantly differing
values, -wells pumping large ground water volumes may have high
induced vertical gradients. For these wells, it may be
inappropriate to allow "vertical setback" distances to equal
horizontal setback distances. EPA seeks comment on this issue.
Few localities have sources of contamination directly over
the well, so that any component of horizontal flow toward the
well adds to the flow distance to the well screen and provides
additional natural attenuation. This additional natural
attenuation is not explicitly accounted for in the rule, although
it provides additional conservatism to help err on the side of
allowing only nonvulnerable sites to avoid disinfection, i.e., -it
provides a larger "safety factor." In a similar manner, the rule
criteria for horizontal distance from the well to the nearest
source of contamination neglects the additional distance
travelled as the ground water flows vertically down to the well
screen, if the well is screened. Again, such additional natural
attenuation is not explicitly accounted for in the rule although
it provides an added safety factor. Both safety factors serve to
mitigate against the effects of error* resulting from high
uncertainty about the hydrogeology at any particular site.
The second hydrogeologic feature, unsaturated zone
thickness, may be evaluated directly or indirectly. The
thickness criteria may be evaluated directly by meeting the
thickness value in the rule or indirectly by, using VIRALT (or
other model) to demonstrate that the ground-water travel time or
contaminant transport time in the available unsaturated zone is
sufficient to attenuate contamination. Unsaturated thickness is
variable, depending on well discharge, recharge, and other
factors. A public water system choosing to claim "natural
disinfection" based on this thickness must be able to demonstrate
that the unsaturated thickness available meets the rule criteria
under all reasonably foreseeable circumstances.
A third hydrogeologic feature, thickness of a confining
layer, is under consideration for inclusion in the rule. In
general, the thicker the confining layer, the easier it is for
the State to identify both the presence of and the performance of
the feature. Hovever, a demonstration that the confining layer
acts to attenuate virus concentrations would require a
contaminant transport model more sophisticated than VZRALT 2.1.
EPA is currently developing additional contaminant transport
models that may be used to determine "natural disinfection*
criteria for other, more complex, hydrogeologic settings or
features.
III.B-16
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Another option under consideration for the hydrogeologic
feature criterion is to explicitly state the amount of log
reduction required by the rule (e.g., li-log reduction). To meet
this option, a State may choose any hydrogeologic feature
characteristic of all or part of that State and use any suitable
contaminant-transport model to demonstrate that the feature will
provide travel times suitably long enough to meet the virus
concentration reduction requirement. The intent of this
requirement is to allow the States to use a criterion which has
hydrogeologic utility in that State. This option would not be a
vulnerability assessment because no site-specific source location
data would be required.
EPA believes the States will likely wish to use both setback
distances and a variety of hydrogeologic features as screening
tools to more easily identify nonvulnerable wells. EPA seeks '
comment from each State on the hydrogeologic features most
applicable to that State's hydrogeologic settings. EPA curently
intends to develop numerical "natural disinfection" criteria for
each hydrogeologic feature proposed by the States and judged
suitable or feasible by EPA. EPA will add these newly developed
criteria to the proposed rule. EPA believes that each State will
be able to use previously developed or ongoing studies of aquifer
sensitivity, vulnerability mapping, hydrogeologic mapping, and
soils mapping, as well as State and U.S. Geological Survey
hydrogeologic expertise to suggest the appropriate criteria for
that State.
VIRALT was used to calculate the unsaturated thicknesses
that allow sufficiently low virus concentrations at the well so
as to meet the "11-log" treatment target. No values are presented
for the "50m+" bounding analysis because this analysis assumes a
concentration in the saturated zone at a distance 50 m .from a
source. This assumption is not applicable to the unsaturated
thickness values. The values for depth to well screen were
assumed to be equivalent to the setback distance values presented
in Section 6(a).
The following criteria for depth to well screen were
assumed:
"50 m*"
"ll-log"
Low
inactivation
rate
160 •
325 •
High
inactivation
rate
80 •
160 •
III.B-17
-------
The following criteria for thickness of unsaturated zone
were calculated:
"50 m+"
"11-log"
Low
inactivation
rat*
not applicable
160 m
High
inactivation
rate
not applicable
50 n
e. Ground-Water Travel Tim*
In developing "natural disinfection" criteria, EPA seeks to
identify parameters that are relatively easy to determine but
require some site-specific knowledge. EPA chose to build upon
the ongoing Wellhead Protection Program by using tools similar to
those used in the delineation of wellhead protection areas.
The Safe Drinking Water Act (SDWA) as amended (1986)
established the State Wellhead Protection Program. Under the
SDWA, States are required to have an approved wellhead protection
program in place to prevent pollution. The approved program
requires that each well have a defined zone surrounding it (a
delineation area) in which contaminant sources are differentially
managed. The zones are defined in the Act as "the surface and
subsurface area surrounding a water well or wellfield, supplying
a public water system, through which contaminants are reasonably
likely to move toward and reach such water well or wellfield."
In the Guidelines for Delineation of Wellhead Protection Areas
(EPA, 1987, office of Ground-Water Protection, EPA 440/6-87-010),
EPA listed six primary methods suitable for Wellhead Protection
Area delineation. Of these six methods, all but one method (the
arbitrary fixed radii) required the delineator to use some
specific knowledge about the site hydrogeology and the well or
well field. By the end of 1991, EPA had approved Wellhead
Protection Programs in 18 States.
Under the Wellhead Protection Program, there are few
specific requirements to determine the locations of possible
sources of contamination. The myriad types and sources of
chemical contaminants and the always possible occurrence of an
accident preclude any requirements based only on distance to
local sources. In contrast, this rule is concerned only with
microbiological contaminants. Potential sources/types of
microbiological contamination are few, primarily septic tanks and
sewer lines (although the number of such sources may be large),
and septage truck spills are not likely. Because the number of
possible source types is small, this rule allows the public water
III.B-18
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system to determine the locations of those that are nearest to
the well.
The "natural disinfection" criterion for ground-water travel
time is defined as the travel time of a ground-water "particle"
from the nearest contaminant source to the pumping well. In this
calculation, the nearest source is the one that is the shortest
travel time away from the well. A ground-water "particle" is
simulated by the center of mass of a conservative tracer plume
that does not undergo dispersion. Use of this criterion is a
true vulnerability assessment, because it requires knowledge of
both source location and site hydrogeology. since this criterion
is used in the Wellhead Protection Program, EPA believes that
States are already familiar with the concept or will be by the
time that this rule is promulgated.
To assist a community with the more complex methods of
wellhead protection area delineation, EPA developed computer
software that is designed specifically to perform the delineation
task easily and efficiently. This software, WHPA, Version 2.1
(Blandford and Huyafcorn, March 1991, WHPA: A modular semi-
analytical model for the delineation of wellhead protection
areas; unpublished manuscript) draws the boundaries of the
Wellhead Protection Area based on knowledge about the site
hydrogeology and pumping rates of the well or well field. EPA
believes that the input values that describe the site
hydrogeology are available from existing compilations by state or
Federal agencies; other necessary data will be normally
collected by the well operator.
In the Wellhead Protection Program, an approved plan
contains a decision on the scope of the wellhead protection
effort. For example, the plan may choose to define the Wellhead
Protection Area as the area encompassed by all ground water that
is less than two-yeers travel time to the well or well field.
The delineator mey choose to use the WHPA ground-water model as
the tool to identify those ground waters that meet the two-year
travel-time criterion. Because knowledge of ground-water travel
time is commonly used in wellhead protection, EPA is also
proposing it for use in this rule as "natural disinfection1*
criteria option three. For example, the system mey choose to
calculate the two-year ground-water travel time and demonstrate
that no microbial contaminant sources exist within that aree.
EPA intends that this rule require little additional evaluation
for wells or well fields that have been assessed using the WHPA
model or other methods of calculating ground-water travel time
for wellhead protection purposes. To meet the rule criterion,
each well or well field will need only to locate existing sources
of contamination to make additional use of such calculations.
The procedure to determine an acceptable ground-water travel
time was similar to the procedure used to determine the setback
III.B-19
-------
distance or hydrologic feature and is briefly summarized in
Section III.B.4. Given a viRALT model simulation that yields an
acceptable virus concentration at the well, values for the ground
water travel time are determined from the ground-water flow
module in VIRALT to establish the acceptable ground-water travel
time. This value was chosen as the "natural disinfection"
criterion for ground-water travel time. It should be noted that
WHPA is the ground-water flow model used in the .VIRALT transport
simulations..Thus, it is relatively easy to compare WHPA and
VIRALT simulations. However, any ground water flow model
acceptable by the State with guidance from EPA may be used to
demonstrate the ground-water travel time.
Each ground water flow model simulation (either WHPA or
VIRALT) required input parameter values that describe the ground-
water velocity field. These values had to be assumed. Some
assumptions were based on "reasonable worst-case" possibilities;
other assumptions were selected as common to many or most of the
hydrogeologic settings that can produce modest yields of ground
water to a well. Since EPA has no data base available to
determine mean or median values for the input parameters, input
values were based on values reported in standard compilations.
EPA chose fixed values for all input parameters that are
believed to be well-established for a typical, vulnerable
productive aquifer. For example, EPA believes that a typical,
vulnerable productive aquifer would be an unconsolidated coastal
plain, glacial, or alluvial sand deposit. The hydraulic
conductivity and porosity of such sands may vary widely but, in
general, most values occur within a moderate range. Thus', this
value is fixed in the simulations. Appendix A provides a complete
listing of all input parameters. The values given in that listing
were used in all simulations excepted as noted herein.
The following ground-water travel times have been calculated
as "natural disinfection" criteria:
«50 m+" ("8-log")
"ll-log"
Low
inactivation
rate
12 mo
24 mo
High
inactivation
rate
4 mo
9 mo
Travel Tlmi
Unlike wellhead protection, this rule offers the option of
determining contaminant travel time (as a supplement to ground
water travel time) from source to well. EPA has chosen
III.B-20
-------
contaminant travel tin* as a criteria option because this is the
most accurate and precise measure of well vulnerability. Use of
this criterion relies upon calculation of the ground-water travel
time. It is well-suited for evaluating wells and well fields for
which WHPA or some other method has been used to determine
ground-water travel times, but where nearby sources of
contamination prevent use of the ground-water travel-time
criterion to avoid the disinfection requirements.
In this draft, VIRALT is used to determine the contaminant
travel time. The mathematical description of virus transport used
in VIRALT, like the mathematical description of ground-water flow
used in WHPA, is based on assumptions; some assumptions have
more validity than others. A more detailed discussion of some of
the model assumptions is presented in the documentation available
with the software. Others are described in Section 7. The
applicability of either VIRALT or WHPA to a particular site is
best determined on a site-by-site basis by the State. EPA
guidance will suggest methods to determine the suitability of
using either model at a particular site.
VIRALT is designed for dual use; l) to develop numerical
values for the "natural disinfection" criteria and 2) as one tool
to demonstrate that a well or wellfield meets the "natural
disinfection" criteria. EPA and the States will make VIRALT
available to systems that choose to demonstrate suitability for
avoiding disinfection under this rule based on the contaminant
travel-time criterion. VIRALT was modified to respond to some of
the concerns of the EPA Science Advisory Board. EPA is developing
a more sophisticated contaminant transport model for use.in
devleoping "natural disinfection" criteria. It is anticipated
that both VIRALT and any newer models will be provided to the
States and regulated community as tools to deaonstrtate "natural
disinfection."
EPA encourages use of VIRALT, because it allows assessment
of both absolute and relative vulnerability to contamination
based on site-specific data, source concentrations, and knowledge
of the physics of ground-water flow and contaminant transport.
However, EPA and the States may accept a demonstration of
"natural disinfection" using any ground-water flow and/or
contaminant transport model determined to be acceptable by the
state with guidanc* from EPA.
The calculation of ground water or virus travel time using
WHPA or VIRALT is similar. The two are similar because VIRALT
uses the ground-water travel times calculated by WHPA and because
VIRALT contains a built-in data base that automatically provides
default values for transport parameters once the user has
identified the type of soil and some aquifer characteristics.
EPA guidance provides additional discussion on the proper use of
VIRALT, the appropriateness of overriding the default values, and
III.B-21
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suggestions for using VIRALT to demonstrate or evaluate
suitability for avoiding the source water disinfection
requirements. Both VIRALT and WHPA are designed to be as easy to
use as possible with a minimum of training. For example, both are
menu-driven with context-sensitive help screens.
Each VIRALT simulation will yield a maximum virus
concentration at the well. If the maximum virus concentration
exceeds the acceptable limit, then the time at which that maximum
concentration is reached is noted. EPA chose the "natural
disinfection" criterion for contaminant travel time based on that
distribution of maximum concentration arrival times.
As a result of longitudinal dispersion and no retardation,
VIRALT-calculated virus travel times are "fast" as compared with
the calculated ground water travel time for the "plug" flow (no
dispersion) of a water mass. As a result of mixing, longitudinal
dispersion acts to spread out the virus plume along the
pathlines. The water "plug" and the virus plume have differing
centers of mass due to the effects of virus inactivation. In
general, the center of mass of the virus plume arrives before the
center of mass of the water "plug."
Each VIRALT simulation required input parameter values that
describe the both the ground-water velocity field and the
transport of viruses within that flow field (e.g., virus
inactivation rate, rate of virus partitioning between aquifer
solids and water, and the capability of the aquifer to transport
contaminants through connected pores). The values describing the
veleocity field are discussed in the previous section on the
ground water flow model. This discussion addresses only the
additional parameters required to describe the transport of
viruses within that flow field. Most values had to be assumed.
Since EPA has no data base available to determine mean or median
values for the input parameters, input values were based on
values reported in standard compilations. The longitudinal
dispersivity is scale-dependent; VIRALT provides a default value
for the longitudinal dispersivity based on the distance from the
source to the well using the compilation of Neuman (1990).
VIRALT is designed to simulate transport from an areal
source, such as a septic tank drainage field, or a line source,
such as a sewer line. Since multiple sources are a potential
problem for a public water system, VIRALT can be used to specify
an area that represents either a single source or a multiple
source within which there exists a defined constant or pulse
contamination release. The contamination pulse can be described
using 10 points on a plot of concentration versus time.
In determining the "natural disinfection" criteria, the
initial virus concentration is assumed to be either 1) a
continuing release of virus-contaminated water at a constant flow
III.8-22
-------
rate (steady-state) and concentration or 2) a one-time release of
a pulse of water of constant concentration.
Multiple sources must be simulated as if the virus
concentrations are uniform at any time throughout the source
area. This assumption will overestimate the contaminant
concentrations from, for example, a simulated housing
development. EPA has no results available from a model that can
explicitly simulate multiple sources to estimate' the uncertainty
arising from this assumption.
The following virus travel times were calculated as
"natural disinfection" criteria:
"50 m+"
"11-log"
Low
inactivation
rate
7 mo
9 mo
High
inactivation
rate
2 mo
3 mo
7. Effects of ieientifie Uncertainty
The determination of "natural disinfection" criteria using a
contaminant transport model for a reasonable worst case shows
that the criteria are most sensitive to five contaminant
transport parameters: initial virus concentration at the source,
final virus concentration at the well, virus inactivation rate,
site hydraulic gradient, and retardation coefficient. EPA
believes that choice of worst-case values for each of these five
important parameters will result in development of overly strict
"natural disinfection" criteria. Few sites would qualify as
having adequate "natural disinfection." In order to make
"natural disinfection" applicable to more sites without any
significant compromise in health protection, EPA chose to use
reasonable worst-case values rather than worst-case values for
four of the five important input parameters listed above. (EPA
chose reasonable worst-case values for less important input
parameters as wall; these are not discussed here for the sake of
simplicity.) Tha following text discusses each of these five
parameters and the rationale for choosing input values for each.
i. initial Tims concentration afe the tftujfMi Tha initial
source concentration is always variable and depends on the number
of infected people shedding viruses and the amount of dilution
based on the ratio of "grey" water to "black" watar entering the
system. A wida range of virus concentrations in saptic tanks and
raw sewage has been measured but the number of measurements are
III.B-23
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few and not definitive. EPA believes that 10,000 viruses per
liter is a reasonable worst-case value for initial virus
concentration at the source. Virus concentrations in raw sewage
may be higher, especially in areas (and countries) where endemic
disease rates may be high.
ii. Final virus concentration at the veil.. The final virus
concentration is based on the infectious dose-response
relationship for rotavirus. As discussed earlier, there are
sufficient data to calculate such a relationship for only five of
more than 100 potential viruses. Of the five calculated
relationships, the rotavirus dose-response relationship
represents a worst-case scenario. EPA believes that the final
virus concentration at the well based on this dose-response
relationship is a worst-case value. It should be noted that the
dose-response relationship for rotavirus might not oe the worst-
case scenario if similar calculations were available for a
greater number of viruses.
iii. Virus iaaetivation r^te. The inactivation rate of
viruses is probably the single most important parameter governing
virus fate and transport in ground water. Use of a worst-case
inactivation rate would require using values for hepatitis A
virus (HAV), since an HAV infection is the worst-case known
health risk from consuming virus-contaminated ground water.
However, there are few available data for HAV inactivation rates,
as compared with data for other viruses. The HAV data that are
available were collected at temperatures lower than and higher
than most ambient ground-water temperatures (5 and 25 °C.) and
were not used in the existing compilations of virus inactivation
rates.
EPA believes that the large differences in the virus
inactivation rat* due to temperature variation reflect
imprecision in our scientific understanding of the process. EPA
has chosen to use the variation in inactivation rates as a
measure of uncertainty in our abilities to predict virus
transport from source to well. As a result of these large
uncertainties, EPA believes that any of the setback distances
calculated by VIRALT for the reasonable worst-case (rather than
worst-case) hydrogeologic setting are appropriate. Selection of
a shorter setback distance will allow many more wells and
wellfields to meet: "natural disinfection* criteria without
compromising health protection. All setback distances in this
draft are larger than State standards presently in use for septic
tanks and sever lines.
iv. aite hTdraulio gradient. Regional hydraulic gradients
are important in governing the velocity of ground water flow.
Higher gradients may result in higher velocities and higher
velocities may increase the number of viruses reaching the well.
IIZ.B-24
-------
A worst case assumption would be that the hydraulic gradient is
high. EPA believes that a large number of public water supplies
are situated in hydrogeologic settings where the regional
gradient'is small (e.g. on or adjacent to alluvial flood plains).
In calculating the "natural disinfection" criteria, EPA makes the
"best case" assumption that regional hydraulic gradients are very
small.
The setback distances developed in the rule assume that the
source is located directly uoaradient from the veil, in general,
good engineering practice requires that the well be located so
that potential contamination sources are downaradient; from the
well. In hydrogeologic settings where the local gradient is
stable and well characterized, wells can potentially be sited
very close to a dovngradient source. EPA believes that those
sites with measured, stable hydraulic gradients will easily be
able to demonstrate suitability for avoiding disinfection using
the ground-water flow criterion. In general, EPA proposes to
base the setback distance criterion on the worst-case assumption
that the source is directly upgradient from the well, because
many sites have very low gradients such that seasonal change or
surface water stage can generate large variations in regional
flow direction.
The combination of a worst case directional variable and a
"best case" magnitude for the hydraulic gradient yields a
reasonable worst case value for the determination of the "natural
disinfection" criteria.
v. Retardation coefficient, in developing the "natural
disinfection" criteria, EPA assumed that the arrival of viruses
at the well is not retarded as compared with the calculated
travel time of ground water. EPA considers this to be a
reasonable worst-case assumption, because viruses may actually
travel "faster" or "slower" than the calculated average water
velocity. If, during transport, viruses attach themselves to and
are subsequently released from the solid framework of the
aquifer, then the virus travel-time may be "slow." If, during
transport, viruses act as do some reported colloidal particles,
then they may take a direct path through the larger pores where
the velocities are .larger (pore-size exclusion), thereby
accomplishing a "fast" travel time.
Research on colloidal particle transport shows that the
probability of a particle attaching to the framework of the
porous media depends on the chemistry of the fluid. This is an
active area of research. While there is consensus that the
process is important, there may not be consensus on the best way
to incorporate the process into contaminant transport models. A
better understanding of the processes governing attachment and
release of particles could result in decreased required setback
III.B-25
-------
distances and fewer instances of mandated disinfection within the
regulated community.
vi. Other issues. One method under consideration for
reducing uncertainty is to use transport parameters describing a
synthetic, worst-case virus, i.e., one that combines the features
of several viruses including the most mobile viruses and those
implicated in the most injurious waterborne disease. For
example, if sufficient data were available, EPA could use a
hepatitis inactivation rate combined with values that describe
poliovirus attachment to and release from the aquifer matrix. At
present, EPA uses inactivation values derived from statistical
analysis of combined bacteriophage (MS-2), echovirus, and
poliovirus data. Contaminant travel times for the synthetic virus
would err towards the shortest travel times. Sites that
qualified for "natural disinfection" using the synthetic virus
would be not vulnerable with reduced uncertainty. EPA seeks
comment on the suitability of using a synthetic virus in the
model simulations.
At present, EPA is unable to access any data base that
describes the hydrogeology of public water system wells currently
not disinfecting their source waters. EPA believes that access
to such information would enable the Agency to better evaluate
the impact of the "natural disinfection" criteria and to revise
the criteria where data justified such revision. The data base
would allow EPA to reduce some of the uncertainties associated
with use of the VIRALT model. For example, rather than selecting
model input values using professional judgement, EPA could
determine those values using Monte Carlo sampling of the data
base. The data base could also be used to determine the
prevalence of low-cost "natural disinfection" criteria, such as
well screen depth information. Transaction costs associated with
the rule could b« evaluated by showing the availability of
information in-hand or any new information requirements. States
could use the data base to supplement their existing evaluations
of aquifer sensitivity to contamination, thereby potentially
reducing implementation costs. EPA seeks comment on the need for
or role of a data base that contains hydrogeologic information on
public water system* not currently disinfecting.
EPA is using deterministic rather than probabilistic models
of virus transport. A deterministic model requires an independent
value for each input parameter at each site. A probabalistic
model requires a method to determine the covariance among
selected parameters and a description of the spatial and/or
temporal variability of each input parameter. EPA requests
comment on the suitability of each type of model for developing
"natural disinfection" criteria and for determining suitability
for avoiding additional disinfection treatment.
ft 7?lP*nt Response - Natural Disinfection Criteria
III.B-26
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On June 6, 1991, EPA released the GWDR Draft Rule Criteria
dealing with the concept of Natural Disinfection and asked for
public comment. At least 23 members of the public submitted
comments on the Natural Disinfection Criteria provisions. These
comments "were carefully considered during development of the
Draft GWDR. In the following, EPA addresses the most significant
comments and indicates how the comments shaped development of the
Rule.
In general, most comments support disinfection requirements
and the development of variance and other criteria to meet Rule
requirements. Most public health authorities suggest that the
first priority for protecting public health is meeting existing
State water well construction codes, bacteriological monitoring
and safe and proper operating requirements. In response to these
comments, EPA developed "Prequalifying Conditions." PWSSs must.
meet all of these conditions before receiving any consideration
as to whether the System meets Natural Disinfection or Variance
criteria. Another commenter asked EPA to recognize that
disinfection is a remediation procedure that, in general, is less
effective than contamination prevention. EPA agrees and has
structured the Rule so that a PWSS will benefit from preventing
source water contamination by conducting a vulnerability
assessment, i.e., locating nearby sources of contamination and
collecting site-specific hydrogeologic data. EPA believes that
the incidence of waterborne endemic disease justifies the need
for regulations that are more stringent than existing State
requirements.
A commenter representing many PWSSs suggests that the Rule
specify a level of treatment. EPA agrees with the concept and has
based the "11-log" option on meeting a specified level of
treatment. EPA believes that the PWSSs require additional
regulatory language designed to help a PWSS show that it meets
the treatment requirements. For example, EPA has structured the
Rule so that a PWSS that meets a Natural Disinfection criterion,
such as setback distance, will automatically meet the treatment
requirement. EPA agrees that the basic treatment requirement
should be stated in the Preamble. In addition, EPA explicitly
states the treatment level as a Variance Criterion, as suggested
by the organization.
Two comments expressed concerns that regional variations,
such as hydrogeologic settings with high source densities or
highly variable travel times, have characteristics that will
impede implementation of the Rule. EPA agrees with these
comments. States and localities that have the resources to
demonstrate natural disinfection in the presence of multiple
sources or heteroge'nous ground water velocity are encouraged to
do so. In general, EPA believes that regions with high density
of sources should have adequate resources to demonstrate "natural
disinfection." Other localities, faced with complex hydrogeology
III.B-27
-------
and limited resources, may require additional technical
assistance. EPA guidance will seek to address this problem. EPA
has no evidence that supports the contention of one commenter
that a single septic system within a microbial pathogen
protection zone will not cause the well to exceed the MCLG. The
commenter suggests that EPA develop criteria for determining the
critical density of pathogen sources. Recent research on
colloidal particle collision efficiency shows that it is a
function of solution electrolyte concentration. The probability
of a charged virus attaching to the aquifer framework increases
with increasing solute concentration. EPA believes that there
may be instances when increasing septic density increases virus
attachment, up to some critical density. However, EPA believes
that there are insufficient data, at present, to support
incorporation of this information into virus transport models.
One commenter noted that the variance criteria were not
sufficiently different from the Natural Disinfection criteria so
as to justify issuing a variance. Another commenter noted that
the variance criteria stringency effectively discouraged systems
from seeking variances. EPA believes that that variances should
be issued only to PWSSs that are clearly not vulnerable .to virus
contamination. Determination of vulnerability requires site
hydrogeologic information as does some, but not all, of the
Natural Disinfection criteria. The differences in the two
procedures is the amount and quality of the hydrogeologic data.
Requests for variances should be accompanied by more and better
data than requests for Natural Disinfection avoidance. It is
likely that PWSSs having a lot of high quality data will choose
to meet the Natural Disinfection criteria; few will choose to
seek a variance. One PWSS commented that all public water supply
systems should disinfect their source waters. This system
suggested that the natural disinfection process needs, to be
accepted as a viable concept by the scientific community. EPA's
National Drinking Water Advisory Council recommends that the
scientific basis behind the GWDR precede Rule development. EPA
agrees with these comments.
commenters have expressed reservations about requiring PWSSs
to use VIRALT or any other ground water flow and contaminant fate
and transport models to determine vulnerability. EPA believes
that this section adequately addresses the issue.
III.B-28
-------
APPENDIX A
This appendix contains the input data summaries and output
displays .for a single VIRALT 2.1 simulation. The VIRALT user's
manual provides a detailed description of each input parameter
and output display. The first page gives the input data summary
for the unsaturated zone. The second page gives the input data
summary for the saturated zone. Note that the First Order Decay
Rate is given in terms of the natural logarithm. The third page
gives the input data summary for the pumping well'. The fourth
page gives the output calculation result for the virus
concentration at the top of the saturated zone after analysis of
transport in the unsaturated zone. The fifth page provides a map
view showing: 1) geometry of the source paralleling the y-axis,
2) the location of the pumping well, and 3) the calculated
pathlines representing ground water flow to the well. The sixth
page is a graph showing the calculated change in contaminant
concentration at the well with time. The input data in this
appendix were used to develop the "natural disinfection" criteria
values. Any changes from the parameters shown in this appendix
are discussed in the main text section on "natural
disinfection." The final page provides information about the
availability of VIRALT.
III.B-A1
-------
Unsaturated Zone Summary
Default Soil Type:
Thickness of Soil Layer:
Saturated Hydraulic Conductivity:
Saturated water Content:
Residual Water Content:
Empirical Parameter Alpha:
Empirical Parameter Beta:
Time Limit for Virus
Transport Simulation:
Leakage Rate:
Initial Concentration:
virus Source Configuration:
Type of Viral Transport Analysis:
Longitudinal Dispersivity:
Molecular Diffusion Coefficient:
Ground-Water Temperature:
First order Decay (die-off) Rate:
Bulk Density of Aquifer Material:
Distribution Coefficient, Kd:
Retardation Factor, R:
Boundary Condition Type:
Number of time periods with
variable leakage rates and/or
viral concentrations:
sandy loam
3.0 m
1.06000 m/d
0.41 dimensionless
0.06 dimensionless
7.5000 1/m
1.89 dimensionless
90. days
.05 m/day
10,000 PFU/liter
open source
transient
0.100 m
0.000 m**2/d
15.00 Centigrade
0.290 1/d
1.56 g/cc
0.00 ml/g
1.00 dimensionless
prescribed
concentration
transient
XXX.B-A2
-------
Saturated Zone Summarv
Number of Pumping wells:
Number of Recharge Wells:
Transmissivity (L**2/T):
Hydraulic Gradient (dimensionless):
Angle of Ambient Flow (degrees):
Aquifer Porosity (dimensionless):
Aquifer Thickness (L):
Boundary Type and Location:
Time Limit for
Pathline Computation:
Time Limit for Virus
Transport simulation:
virus Source Configuration:
Initial Virus Concentration
in Aquifer:
Type of viral Transport Analysis:
Longitudinal Dispersivity:
Molecular Diffusion Coefficient:
Ambient Ground-Water Temperature:
First Order Decay (die-off) Rate:
Bulk Density of Aquifer Material:
Distribution Coefficient, Kd:
Retardation Factor, R:
Boundary Condition Type:
l
0
4000. m**2/d
0.000100 m/m
0.00 degrees
0.25 dimensionless
35. m
no boundary
270. days
90. days
open source
0.000 PFU/liter
transient
36. m
0. m**2/d
15.00 Centigrade
0.290 1/d
1.99 g/cc
0.00 ml/g
1.00 dimensionless
prescribed
concentration
read from UZMODL
IIX.B-A3
-------
Wall Summarv
Pumping well fl
X Coordinate: 160. m
Y Coordinate: 250. m
well Discharge Rate: 2500. m**3/d
Delineate Capture Zone: Yes
Number of Pathlines: 20 •'
III.B-A4
-------
Output (Aftar Analysis of Transport in the Pna«turated 2on«i
Maximum concentration of viruses
at water table: m PFU/liter
at 38.8 days
III.B-A5
-------
92
194
296
398
500
-------
29E-06
90
-------
FACT SHEET: VIRALT 2.1
GROUND-WATER PROTECTION DIVISION
OFFICE OF GROUND WATER AND DRINKING
WATER
U.S. ENVIRONMENTAL PROTECTION AGENCY
YIRALT 2.1
A Modular Semi-Analytical and Numerical Model for Simulating Viral Transport in Ground
Water, Version 2.1. Cost S50.00.
This user's guide and computer software (one high density disk) is a ground water flow
and contaminant transport model designed to assist with the task of determining whether
public water supply wells are vulnerable to virus or other contamination.
The model includes a one-dimensional, unsaturated flow and transport module that
provides contaminant concentrations at the water table directly beneath the source. These
concentration values are automatically used as input for two-dimensional saturated flow
and one-dimensional transport along each pathline to one or more pumping wells. The
transport module can handle either line or areal sources, steady-state or transient
transport, taking into account longitudinal dispersion, adsorption and linear
inactivation/decay in both the unsaturated and saturated zones.
The flow module includes solutions for various types of simple boundary conditions e.g.
streams and barriers. Operation of the code is similar to WHPA 2.1.
Available From: International Ground Water Modeling Center
Institute for Ground Water Research and Education
Colorado School of Mines
Golden, CO 80401-1887
(303) 273-3103
-------
c.
All variance criteria are based on meeting the 50 m+ or 11-
log treatment goals that are the basic requirements of the rule.
The "natural disinfection" criteria serve as easily measurable
surrogates for the treatment goal. Two variance criteria are
under consideration in this rule. One criterion simply states
the treatment goal and requires a demonstration that the goal is
met using sufficient site-specific data so as to minimize but not
eliminate uncertainty. The other criterion is based on meeting
one of two travel-time criteria.
There are two elements of a site vulnerability assessment.
One element is the location of the source of contamination; the
other element is the hydrogeologic setting. The two travel-time
"natural disinfection1* criteria use both elements of the
vulnerability assessment. The setback distance uses only the
source location element; the hydrogeologic feature uses only the
hydrogeologic setting element. EPA prefers that "natural
disinfection" decisions be made based on both elements. However/
public water systems that use both elements (perhaps at high
cost) yet still do not qualify for "natural disinfection" would
have little recourse under the more formal variance procedure.
For this reason, EPA proposes and seeks comment on two options
for variance criteria. The first option is to require public
water systems seeking variances to collect new or additional
site-specific data in the hope that the better data will show
nonvulnerability with less uncertainty. The second option is to
move the two travel-time criteria (i.e. ground water and virus)
out of the "natural disinfection" criteria and provide these two
criteria as options for those systems seeking variances. In this
case, all "natural disinfection" decisions would be made based on
just one of the two vulnerability elements, either source
location (setback distance) or hydrogeologic setting
(hydrogeologic feature).
Both options propose increased site-specific data
requirements for utilities seeking variances. The difference
between the tvo options is primarily a result of the data
collection requirements. EPA believes that VIRALT and WHPA model
analyses can be conducted with sufficient accuracy and
reliability under this rule using available compilations of site-
specific data; no'new data collection would be required. In
contrast, any efforts to reduce uncertainty with higher quality
data under a variance procedure will likely require additional
data collection at the site. Thus, under the first option, a
public water supply system seeking a variance will have the
flexibility to choose to collect any data it thinks it needs to
meet any.of the four "natural disinfection" criteria. Under the
second option, the system will not be able to collect data to
bring to bear on the setback distance or hydrogeologic feature
"natural disinfection" criteria.
III.C-l
-------
*, -5 ^- *! 6S that e smallest utilities will have the mos*
flexibility if all four "natural disinfection" criteria remain in
place; th« variance criteria would be based on reducina
Fi^v. ^
uncertainty
III.C-2
-------
D. Legionella
1. Background
Ever since the 1976 outbreak of Legionnaires disease in
Philadelphia, caused by the bacterium Legrionella pneuaophila,
there has been concern as to the extent drinking water
constitutes a hazard for infection with this organism and more
than thirty other species of Legio/iella (plural, -legionellae) .
At least 16 species are pathogenic for humans. The pneumonia
(Legionnaires disease) resulting from legionellae infection is
acute and severe, with a case fatality rate of about 15%
(Mangione and Broome, 1985). The attack rate is low, ranging
from 0.1 to 4% of persons exposed, and is highest in persons who
are immunosuppressed, or whose underlying host defenses have been
damaged.
A second distinct form of the disease, known as Pontiac
fever, causes fever, aching muscles and headache, and has an .
attack rate close to 100%, but is nonfatal. Both diseases are
collectively termed legionellosis. Legionellosis is most often
caused by the species L. pneujnopAila. Why Legionnaires disease
develops in some cases and Pontiac fever in others is not known,
but viable legionellae may not be needed for Pontiac fever
(Dowling et al., 1992) or, alternatively, strains causing Pontiac
fever may be unable to multiply in human cells (Fields et al.,
1990).
2. Incidence
The actual incidence of legionellosis is not known, but
based on an attack rate of about 1.2 cases of legionellosis per
10,000 persons per year (Foy et al., 1979), it can be estimated
that more than 25,000 cases of this disease occur annually within
the United States. Bennett et al. (1987) estimate that the
incidence in the United States is 75,000 cases annually. The
number of cases reported to the Centers for Disease Control,
however, is much smaller than these estimates, about 1,000 per
year, but this number is steadily increasing (CDC, 1991). This
difference may reflect the fact that most States have a passive
surveillance system, and that the vast majority of hospitals do
not attempt to identify the causative agent in patients with
pneumonia. .Many cases .of hospital-racquired. infections have been
reported. Most cases, both sporadic and outbreaks, have occurred
when water containing virulent legionellae was aerosolized and
inhaled by susceptible persons. Foodborne outbreaks and person-
to-person spread have not been reported. However, person-to-
person spread has been suggested (Love et al., 1978) but not
confirmed either by a prospective clinical and serologic study
iii.o-i
-------
(Yu et al., 1983) or by observations during outbreaks.
Legionellae are widespread in natural surface waters, such
as lakes, ponds, and streams, and are able to multiply in that
environment if conditions are conducive, e.g., if ambient water
temperature is high. The organism appears to be ubiquitous in
surface water and part of the natural aquatic environment
(Fliermans et al., 1981). A study from Puerto Rico (Ortiz-Roque
and Hazen, 1987) revealed I. pneuaoph.ila to be abundant in water
from the leaves of rain forest plants high above the ground and
in coastal marine waters.
Data, however, are sparse concerning the presence of
legionellae in ground water that is not under the direct
influence of surface water. Spino et al. (1984) could not find
legionellae in raw ground water or aerated ground-water samples
for two New England aeration towers. The ground water was not
characterized in the Spino et al. study. In contrast, Seidel et
al. (1986a) found the organism, albeit infrequently, in ground
water. In their investigation, Seidel et al. (1986a) examined
between 316-363 untreated ground water samples from four
locations in Germany, and detected only two samples positive for
Lecrionella pneumophila. Sample volume was between 2 and 11.5
liters, and analysis was by buffered charcoal yeast extract agar
with alpha-ketoglutarate, or an antibiotic modification. Thus,
this study suggests that ground water is not an important source
of Leaionella. The investigators also found no Leaionella
pneumophila-positive samples in bank filtrates (24 samples) and
in pre-treated reservoir water (19 samples). In contrast, 8% of
318 cold drinking water samples (5-26*0) from public buildings
were Leaionella oneumophila-positive (per 0.1-1 liter), as were
49% of 1097 warm water samples (per 0.1 ml to 1 liter). All
buildings in which positive samples were found were served by
ground water. Disinfection levels of the building water samples
were not given.
In an additional report, Seidel et al. (1986b) found
L* pneumophila in 0.6 and 3.2% of raw and treated ground water
samples, respectively, in further studies carried out in Germany.
It is also noteworthy that the authors were able to detect
L. pneumophila in water containng 0.6 mg free chlorine/liter.
In reports from England, Colbourne et al. (1986, 1988),
using conventional culture methods, failed to recover Lealo/iella
from public water supplies of nine regions, including both ground
and surface water sources, except for a-£ew distribution systems.
However, when they employed a serological technique (indirect
immunofluorescent assay (IFA)), they detected legionellae in both
underground (14% of 118 samples) and treated surface water
sources (11% of 64 samples), and in distribution systems (12%)
(Colbourne et al., 1988). These investigators state that all
systems had been chlorinated in accordance with World Health
ni.D-2
-------
Organization guidelines (Anon, 1984), but no data were presented
on chlorine residuals within the distribution system. After heat
treating some of the samples at 45aC for 10-20 minutes/ five of
seven IFA-positive distribution system samples that had
previously been negative on culture yielded low numbers of L.
pneumophila in a culture medium. The investigators suggested the
possibility that low temperatures induce "resting" forms of
legionellae as a survival mechanism; these do not reproduce until
heat treatment. Exposure of water samples to pH 2.2 for five
minutes has a similar enhancing effect (Bopp et al., 1981).
Another possible explanation for such enhancement is that
legionellae were protected inside protozoan cysts and only grew
after the cysts were destroyed by heat. Barbaree et al. (1986)
has found that legionellae not only reside, but also multiply, in
some free-living protozoa. The ability of protozoa to protect
this organism may explain resistance of legionellae to
disinfectants. Perhaps the inability to find Legionella by Spino
et al. (1984) was due to the fact that they did not use heat
treatment or low pH in their detection methodology.
other organisms may influence legionellae growth. It has
been shown that green algae and various bacteria are able to
support the growth of L. pneumophila. It is probable that this
effect is due to the production of the amino acid, L-cysteine,
which legionellae need for growth. This presumption is supported
by States et al. (1987), who only observed legionellae in certain
locations in the distribution system where the water was pooled
and nutrients could accumulate.
Once legionellae infiltrate the distribution system, even at
very low densities, they may enter plumbing systems and lodge in
hot water heaters, shower heads, aerators, faucet spouts, hot
water valve seats and other locations in contact with hot water
in hospitals, public buildings, and homes (Stout et al., 1992).
Hot water tanks maintained between 30 and 54*C provide conditions
conducive for multiplication of the organism (State* et al.,
1987). If the hot water temperature does not exceed about 50°c,
then L*gion»lla may grow to high densities, posing a health
threat, especially to immunocompromised populations in health
care institutions. L. pneumophila has been reported found in
water in private homes and apartments (Arnow et al., 1985; Stout
et al., 1987; Tobin et al., 1981), in motels/hotels (Bartlett et
al., 1983), as well as in hospitals. In the Stout et al. study,
the drinking water sources were wells, one of which was shallow.
In the Arnow et al. (1985) study, the hot water system of
32% of 95 apartments and houses in one area of Chicago were
contaminated by L. pneuaophila in concentrations of 1 to 10,000
organisms per liter. No cases of legionellosis, however, were
reported. Temperatures of the hot water systems that contained
Legionella were significantly lower than those that did not (42%
of systems below 60*C were Legionella-positive vs. 7% of systems
III.D-3
-------
60°C or higher). The free chlorine concentration of the hotter
water ranged from 0 to 0.4 mg/1, whereas the cooler water ranged
from 0.1 to 0.6 mg/1.
Legionellae have also been associated with biofilms in
pipes. Colbourne et al. (1984) cultured these organisms from
water after disturbing pipe deposits and from surfaces of water-
fitting components. In 1987, as a result of an outbreak of
Legionnaires disease, Colbourne and Dennis (1987)' surveyed the
drinking water system on a passenger ship for legionellae. Water
on the ship contained 1-2 mg/1 free residual chlorine, and hot
water temperature was held at 60°c. No legionellae were found in
the water, but some were found in the biofilm on the inner wall
of a drinking water storage tank and deposits in the base of a
water heater. These investigators also surveyed the pipework of
two cooling towers and found legionellae in the biofiln, even
though the pipes were periodically cleaned with chlorine or other
biocides. They concluded that legionellae could survive and
perhaps grow in biofilms in drinking water systems and cooling
water pipes.
3. Control
The control of legionellae in the distribution system, once
they have been established, may be difficult, since they are able
to survive long periods in tap water (364-369 days in a study by
Skaliy and McEachern, 1979) and are relatively resistant to
disinfectants. In one study, 40 minutes were needed for 0.1 mg/1
of free chlorine residual to kill 99% 'of L. pnmumophila (21*C,
pH 7.6) (Kuchta et al., 1983). In contrast, 99% of coliforms are
killed by that amount of chlorine in less than one minute. Data
are conflicting as to whether the disinfection levels that will
remove 99.99 percent viruses will remove Legionmlla as well
(USEPA, 1991).
EPA's strategy is to minimize the occurrence of legionellae
in source water via mandatory treatment techniques, and to
provide guidance to control these organisms at the institutional
level. EPA's Surface Water Treatment Requirements, published on
June 29, 1989, regulated legionellae in surface water and in
ground water under the direct influence of surface water. The
Agency has also published guidance on the control of legionellae
in plumbing systems (USEPA, 1988). The Agency is now attempting
to determine whether legionellae should also be regulated in
systems using ground water that is not under the direct influence
of surface water.
Since it is not known whether legionellae occur in ground
water in the United States and, if so, to what extent, EPA and
the American Water Works Association Research Foundation are co-
sponsoring a study to collect occurrence data for viruses and
III.D-4
-------
Legionella in ground water. Study results will be used as an
additional (but not primary) source in the determination of the
necessity for EPA to take regulatory action to control these
organisms under this rule. If the data suggest otherwise, EPA
must then decide whether the minimal level of disinfection
required for viral inactivation and required as a residual in the
distribution system will also adequately control legionellae.
The Agency requests data on whether legionellae are found in
ground water not under the direct influence of surface water and,
if so, their density. If legionellae are found in ground water,
EPA may consider developing an MCL or treatment technique
requirement for this organism. The Agency solicits comment on
whether an MCL or treatment requirement is appropriate and, if
not, what other action EPA should take to control legionellae.
-III.D-5
-------
References
Anon, 1984. Guidelines for drinking water quality. World Health
Organization, Geneva.
Arnow, P.M., D. Weil, and M.F. Pava. 1985. Prevalence and
significance of Legionella pneumophila contamination of
residential hot-tap water systems. Jour. Inf. Dis. 152:
145-151.
Barbaree, J.M., B.S. Fields, J.C. Feeley, G.W. Gorman, and W.T.
Martin. 1986. Isolation of protozoa from water associated
with a legionellosis outbreak and demonstration of
intracellular multiplication of Legionella pneumophila.
Appl. Environ. Microbiol. 51:422-424.
Bartlett, C.L.R., J;B. Kurtz, J.G.P. Hutchison, G.C. Turner, and
A.E. Wright. 1983. Legionella in hospital and hotel water
supplies. Lancet ii:1315.
Bennett, J.V., S.D. Holmberg, M.F. Rogers and S.L. Solomon.
1987. Infectious and parasitic diseases, pp. 102-113. In;
Closing the Gap: The Burden of Unnecessary Illness, R.W.
Amler and H.B. Dull (Eds.), Oxford University Press, New
York.
Bopp, C.A., J.W. Sumner, G.K. Morris, and J.G. Wells. 1981.
Isolation of Legionella spp. from environmental water
samples of low pH treatment and use of a selective medium.
J. Clin. Microbiol. 13:714-719.
CDC. Centers for Disease Control. 1991. Summary of notifiable
diseases, United States, 1990. Morbidity and Mortality
Weekly Report, Vol 39, No. 53. Atlanta, Georgia.
Colbourne, J.S., D.J. Pratt, M.J. Smith, and S.P. Fisher-Hoch.
1984. The role of water fittings as sources of Legionella
pneumophila in a hospital plumbing system. Lancet i:210-
213.
Colbourne, J.S. and P.J. Dennis. 1987. Legionella: a biofilm
organism in engineered water systems? Presented at meeting
of Biodeterioration Society; Cambridge Univ., September
1987..
Colbourne, J.S. and R.M. Trew. 1986. Presence of Legionella in
London's water supplies. -Israel Jour. -Med. Sciences
22:633- 639.
Colbourne, J.S.,P.J. Dennis, R.M. Trew, C. Berry and G. Vesey.
1988. Legionella and public water supplies, pp. 31-36.
In; Proc. Internet. Conf. on Water and Wastewater
Microbiol., Newport Beach, California.
III.D-6
-------
Dowling, J.N., A.K. Saha, and R.H. Glew. 1992. Virulence
factors of the family Legionellaceae. Microbiol. Reviews
56:32-60.
Fields, B.S., J.M. Barbaree, G.N. Sanden, and W.E. Morrill.
1990. virulence of a Legionella anisa strain associated
with Pontiac fever: an evaluation using protozoan, cell
culture, and guinea pig models. Infect. Imnun. 58:3139-
3142.
/
Fliermans, C.B., W.B. Cherry, L.H. Orrison, S.J. Smith, D.L.
Tison and O.H. Pope. 1981. Ecological distribution of
Legionella pneumophila. Appl. Environ. Microbiol. 41:9-16.
Foy, H.M., P.S. Hayes, M.K. Cooney, C.V. Broome, I. Allan and R.
Tobe. 1979. Legionnaire's disease in a prepaid medical-care
group in Seattle, 1963-75. Lancet 1:767-770.
Kuchta, J.M., S.J. States, A.M. McNamera, R.M. Wadowsky and R.B.
Yee. 1983. Susceptibility of legrionella pnmumophila to
chlorine in tap water. Appl. Environ. Microbiol. 46:1134-
1139.
Love, W.C., A.K.R. Chaudhuri, K.C. Chin and R. Fallen. 1978.
Possible case-to-case transmission of Legionnaires' disease
(letter). Lancet ii:1249.
Mangione, E.J., and C.V. Broome. 1985. Legionellosis:
Epidemiology (Chapter 5). In: Legionellosis, Vol. II, S.M.
Katz (Ed), CRC Press, Inc., Boca Raton, FL.
Ortiz-Roque, C.M., and T.C. Hazen. 1987. Abundance and
distribution of Legionellaceae in Puerto Rican waters.
Appl. Environ. Microbiol. 53:2231-2236.
Seidel, K. W. Boernert, G. Baez, A. Blankenburg, I. Alexander.
1986a. Vorkommen von Leqionella pneumophila in grundwasser
sowie kalten und warmen trinkv&ssern (Translation: Presence
of Leaionella pneumophila in ground water, cold and warm
drinking waters). Vom Wasser 67:39-48.
Seidel, K., G. Baez, W. Bartocha, and W. Boernert. 1986b. Zum
vorkommen und zur bewertung von legionellen in der umwelt
unter besonderer beruecksichtigung von Leaionella
pneumophila [TRANSLATION: The presence and evaluation of
legionellae in the environment -with special consideration of
Leaionella pneumophilal. Bundesgesundhbl. 29(12)399-403.
Skaliy, P. and H.V. McEachern. 1979. Survival of the
Legionnaires' disease bacterium in water. Ann. Internal
Med. 90:662-663.
III.D-7
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Spino, D.F., E.W. Rice and E.E. Geldreich. 1984 Occurrence of
Legionella sp. and other aquatic bacteria in chemically
contaminated groundwater treated by aeration. In;
Legionella — Proceedings of the 2nd International
Symposium. C. Thornsberry, A. Balows, J.c. Feeley and W,
Jakubowski, (Eds). American Society for Microbiology.
States, S.J., L.E. Conley, J.M. Kutchta, B.M. Oleck, M.J.
Lipovich, R.S. Wolford, R.M. Wadowsky, A.M. McNamara, A.M.
Sykova, G. Keleti and R.B. Yee. 1987. Survival and
multiplication of Legionell* pneumophila in municipal
drinking water systems. Appl. Environ. Microbiol. 53:979-
986.
Stout, J.E., V.L. Yu, and P. Muraca. 1987. Legionnaires*
disease acquired within the homes of two patients. J. Amer.
Med. Assoc. 257(9):1215-1217.
Stout, J.E., V.L. Yu, P. Muraca, J. Joly, N. Troup, and L.S.
Tompkins. 1992. Potable water as a cause of sporadic cases
of community-acquired Legionnaires' disease. New England J.
Med. 326:151-155.
Tobin, H. O'H., R.A. Swann, and C.L.R. Bartlett. 1981.
Isolation of Legionella pneumophila from water systems:
methods and preliminary results. Brit. Med. J. 282:515-517.
USEPA. U.S. Environmental Protection Agency. 1985. National
Primary drinking water regulations; volatile synthetic
organic chemicals; final rule and proposed rule, Federal
Register 50:46880-47025.
USEPA. U.S. Environmental Protection Agency. 1988. Control of
Legionella in plumbing systems. Ini Reviews of
Environmental Contamination and Toxicology 107:79-92.
Springer-Verlag, New York.
USEPA. U.S. Environmental Protection Agency. 1991. Guidance
manual for compliance with the filtration and disinfection
requirements for public water systems using surface water
sources.
Yu, V.L., J.J. Zuravleff, L. Gavlik, M.H. Magnussen. 1983. Lack
of evidence for person-to-person transmission of
Legionnaires' disease. J. Infect. Diseases 147:362.
III.D-8
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E. Required Levels of Microbial Inactivation
EPA believes that targeting viruses for disinfection will
also provide control for other pathogens. Generally, viruses are
both more resistant to disinfection and cause infection at lower
doses than bacteria.
i. Virus Study
a. atudv Design. A comment to the Strawman Rule
expressed concern that EPA lacks the virus occurrence data
necessary to support a requirement for public ground-water
systems to provide a specified minimum level of
disinfection. In response, the occurrence of enteric
viruses in public ground-water supplies will be assessed in
a cooperative effort between EPA and the American Water
Works Association Research Foundation (AWWARF). The study
is designed to target public ground-water supplies which are
vulnerable to viral contamination, and which are not under
the direct influence of a surface water. Public water
systems with vulnerable ground-water supplies will be
identified by EPA Regions, Primacy Agencies, public health
officials, and recognized experts-. Vulnerability of a
ground-water supply will be estimated from knowledge of
source water quality, existence of potential sources of
human fecal contamination and their proximity to the well,
and hydrogeologic characteristics of the site. A relative
rank of vulnerability will be assigned to the list of
candidate ground-water supplies identified. Approximately
twenty-five systems will then be nominated for their
participation in this study. ' Participation by water systems
in this study will be voluntary.
fri Stapling and Analysis. Raw water will be collected
at 25 sites and sent to EPA's Cincinnati laboratory for
characterization. All 25 sites will be sampled monthly over
a period of one year. Extra samples may be added during the
course of the study to provide flexibility to respond to
occurrence of disease outbreaks or intensify the sampling at
some sites. Sampling efforts will involve passing a
measured volume of 200-300 gallons of raw water (100 gallons
minimum) through a positively charged cartridge filter to
concentrate enteric viruses present in the sample, viruses
adsorbed onto the cartridge filters during sampling will be
eluted from the filters in the laboratory. Conventional
tissue-culture methodologies will. be.utilized for general
enteric viruses (including polioviruses, coxsackieviruses,
and echoviruses), following the general methods outlined in
the "USEPA Manual of Methods for Virology," EPA/600/4-
84/013. RNA-polymerase chain reaction/gene probe techniques
will be utilized for detection of general enterovirus,
hepatitis A virus, Norwalk virus, and rotavirus. Additional
III.E-1
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assays will be conducted on raw water for an overall
assessment of water quality conditions during the course of
the study. They will include physicochemical measurements
such as pH, temperature, turbidity, and bacterial
measurements such as total coliforms, Escherichia cola,
enterococci, Clostridium perfringens, and Legionella.
c. Use of Data. The viruses to be assayed in this
study are known waterborne disease-causing viruses. Their
occurrence in ground waters is largely unknown and therefore
is the focus of this study. Viral concentrations per unit
of water sampled will be determined for the ground-water
supplies included in this study. This information will be
used in the development of the requirements for minimum
levels of disinfection for systems utilizing vulnerable
ground-water sources. In addition, the data obtained will
be useful for efforts to further define the characteristics
of vulnerability. The results of this study will not be
used to determine disinfection requirements of systems
utilizing ground-water sources which are not vulnerable to
virus contamination.
2. CT Values
In the proposed rule (scheduled for June 1993), EPA will
include some method(s) for PWSs to show that disinfection is
meeting treatment technique performance standards. One method
EPA is planning to propose is the CT method used previously in
the Surface Water Treatment Rule. EPA will use CT values as a
key parameter in determining the adequacy of the treatment
technique for viruses, in lieu of a maximum contaminant level.
There is, however, a problem in deciding which set of.CT values
to use, since these values can vary greatly depending on such
factors as the target organism, pH, and physical makeup of the
water. EPA has discussed its choice of a target organism
elsewhere in this document (see Section III.A for the discussion
of the "synthetic" virus and the choice of a virus - hepatitis A
virus - resistant to disinfection and thus suitable for worst-
case CT values) and will include CT values for various pHs
normally found in drinking water sources in the proposed GWDR.
Nowhere else, though, has EPA discussed the decision of what
physical makeup of the water was chosen to determine appropriate
CT values. Sobsey et al. (J AWWA, Nov., 1991) conducted studies
which showed that cell-associated hepatitus A viruses (HAV) were
inactivated at a slower rate than dispersed (non-cell-associated)
HAV by both free chlorine and by chloramines. This result was
not unexpected, as Sobsey pointed out, since there is
considerable evidence that disinfection is less effective for
viruses embedded in or associated with suspended solids (cell-
associated viruses) than for dispersed viruses. Given this
III.E-2
-------
situation, EPA must determine which set of CT values to include
in the proposed rule.
This, decision will have a considerable practical effect in
the final rule when it is promulgated. For free chlorine at
residuals of about 0.4 mg/1, Sobsey (1991) conducted inactivation
studies at 5 °C and reported that CTs required for 99.99 percent
(4-log) reduction were over 10 times greater for cell-associated
HAV than for dispersed HAV at pH 6 and 8 and over 5 times greater
at pH 10. For chloramines at pH 8, the CT required for 4-log
reduction of HAV was 40 percent higher for cell-associated
viruses at a chloramine residual of about 10 mg/1. In order to
meet the higher CT values, systems would be required to greatly
increase the disinfectant residual, contact time, or both, in
order to comply with treatment technique requirements, if the CTs
for cell-associated HAV are used.
The SWTR Guidance Manual included dispersed HAV CTs in
Appendix E; currently, EPA plans to propose these same values.
(Sobsey's limited data for dispersed HAV CT data for free
chlorine are relatively equal to EPA's SWTR values after
multiplying Sobsey's CT values by a safety factor of three, as
was done with the SWTR values. For monochloramine, with no
safety factor, Sobsey*s CT values were about 60% of the SWTR '
values.) EPA believes that the filtering effect of the soil will
reduce the number of cell-associated viruses and make a choice of
dispersed HAV CTs (rather than cell-associated CTs) appropriate.
Commenters should remember that this rule will apply only to
ground-water systems which are not under the direct influence of
surface water. Systems using ground water under the direct
influence of surface water must comply with the filtration and
disinfection treatment technique requirements contained in the
SWTR. EPA is soliciting comment on the following:
• Are CT values for dispersed (rather than cell-
associated) HAV appropriate?
• If CT values for dispersed HAV are generally adequate
and appropriate, under what conditions might the cell-
associated CT values be more appropriate (e.g.,
turbidity > 5 NTU)? will such conditions occur in
ground water not under the direct influence of surface
water? How often?
• Are there cell-associated CT or other inactivation data
available for free chlorine at pHs other than 6, 8, or
10? At residual concentrations other than 0.4 mg/1?
At temperatures other than 5 *C.? For chloramines at
other than pH 8, 10 mg/1, and 5 *C.? For ozone,
chlorine dioxide, or UV at any pH, concentration, or
temperature?
rii.E-3
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Should distribution system residual requirements be
higher to account for the possiblity of post-treatment
contamination (e.g., from a cross-connection), which
may be more likely to be composed of cell-associated
viruses?
III.E-4
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F. Small System impacts
EPA has recognized that this rule will have an impact on
both a large number of small systems and on the States required
to exercise primacy over such systems. Also, many ground-water
systems that serve relatively large populations are decentralized
(drawing from many wells or well fields distributed over a large
area) and will face compliance and monitoring problems similar to
small systems. Following are discussions of areas in which EPA
has attempted to minimize the burden associated with rule
compliance.
1. Monitoring and Performance
EPA has modified the requirement for monitoring for
disinfectant residual concentration at the entrance to the
distribution system so that all systems, regardless of size, will
only have to monitor once per day at each entrance point. While
there will still be an effort required to sample at each entrance
point for decentralized systems on a daily basis, there no longer
will be a requirement to operate and maintain continuous monitors
at each entrance point.
One issue that EPA is still addressing is the requirement to
show that the disinfection treatment applied is achieving the
required reduction in virus concentration (EPA's current value
for planning purposes is 99.99% or 4-log reduction). While the
CT concept used in the SWTR should be practical from both a
compliance achievement and monitoring standpoint for larger,
centralized systems, EPA recognizes that small or decentralized
systems may have difficulty in complying with CT requirements.
Both decentralized and small systems may find it difficult to
meet CT levels because of limited contact times available between
the wellhead and the first customer. Such systems could
construct tanks to provide the necessary contact time, but site-
specific costs may be affected by the need to purchase property
on which to build the structure. (Quantification of this effect
is made even more difficult since land costs vary greatly and
land is not depreciated and may actually increase in value.)
Also, for small systems, the monitoring and reporting required to
show compliance with CT performance criteria may be too
complicated.
Because of these concerns, EPA is soliciting comments on how
to measure disinfection effectiveness other than by use of CT
values.
1I1.F-1
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2. Da* of Ultraviolet light for Disinfection
Treatment
Under the provisions of the Surface Water Treatment Rule,
EPA approved four disinfection processes as treatment techniques
and included disinfection efficiencies (CTs) for each: chlorine,
chlorine dioxide, ozone, and chloramines. Because of the
ineffectiveness against the target organism (Giardia lamblia) and
because typical raw surface water characteristics /would make
consistently adequate disinfection difficult, ultraviolet (UV)
disinfection was not included as an approved treatment technique
for surface waters. However, UV disinfection has been effective
against viruses under certain conditions, and many ground-water
sources will have raw water characteristics that will not reduce
its efficacy. Therefore, EPA is requesting comment on whether UV
disinfection should be proposed as a treatment technique
disinfection process for ground water, in addition to proposing
the four specified for surface water disinfection.
The use of chlorine, chlorine dioxide, chloramines, and
ozone as drinking water disinfectants has been studied and
results are widely available. However, only limited data are
available for UV disinfection. Following is a summary of the
technology, equipment, and design and operating conditions for UV
disinfection.
Technology. UV technology has been used for industrial
disinfection and sterilization for over 60 years. The process
involves exposur* of a thin film of water to on* or more quartz
mercury-vapor arc lamps emitting UV radiation at a wavelength
between 250 and 270 nm. In particular, UV radiation at 254 ran is
absorbed by the cell's nucleic acid, causing damage to the cell's
DNA. This damage prevents or inhibits further replication of the
DMA molecule. With the exception of viruses and fecal
streptococcus, most living organisms have the ability to repair
cells damaged by UV radiation through a process known as
photoreactivation.
Equipment. EPA expects that UV systems will b* installed in
small- and medium-sized systems. Therefore, most units will be
of a standard design, manufactured and installed by a vendor
rather than the water system. The three basic system designs and
their advantages and disadvantages are listed below. Quartz
sleeves are used in the first two designs to insulate lamps from
direct fluid contact for electrical safety, to facilitate
replacement, and to maintain the optimal operating temperature.
Closed shell quartz reactor; This design has the lamps
enclosed by a quartz sleeve fixed within a pressurized shell
of steel or PVC. Flow is along the long axis of the lamps.
Open channel system: The quartz-sheathed lamp(s) are placed
III.F-2
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in a long rectangular open channel. The lamps, either fixed
in place or as modules, are usually parallel to the flow,
but can be perpendicular. This design allows for good
hydraulics and ease of maintenance. Because it is an open
channel, disadvantages may include the need for repumping
(since the unit is not pressurized) and the possibility of
contamination (since the unit is open to the air).
Non-contact reactor; Water passes through the reactor in
teflon pipes. These pipes are surrounded by UV lamps.
Since the lamps are not submerged, quartz sleeves are not
required and the unit is not subjected to variations in bulb
temperature; therefore, this type of unit is more
efficient. Hydraulics are also good. Disadvantages include
the fact that teflon pipes become dirty and also degrade
over time.
Design and operating conditions. The rate of inactivation
or destruction of microrganisms is a direct function of the UV
intensity at the specified wavelength and is an inverse function
of the (water) layer thickness. This inactivation can be
expressed as a product of intensity, I (mH/cm3), and contact
time, T (sec), and is analogous to CT products for chemical
disinfectants. For the target organism (hepatitis A virus or
HAV) of this rule, IT values for 2- and 3-log inactivation are
presented in Table III.F.I. (EPA still lacks data on 4-log HAV
inactivation; these values will be incorporated in the future.)
To achieve compliance, systems using UV disinfection must show by
monitoring that these IT values are met.
Systems planning to use UV disinfection to meet the viral
inactivation requirements must ensure that the water to be
treated can be treated effectively. Figure III.F.I contains a
list of factors which must be considered when evaluating the
suitablity of UV for a particular site.
As with other disinfection processes, systems must determine
whether the required level of inactivation is achieved on a
continuing basis. Because of their design, vendors will be able
to show that nearly plug flow exists through the unit, and
systems will be able to calculate contact times on that basis.
Plug flow is based on the following design assumptions: long
length relative to the unit's cross-sectional dimension,
turbulent flow within the reactor, and approach and exit
conditions -which provide straight flow lines and thereby maintain
plug flow. More detailed design information will be contained in
the draft Guidance Manual for the GWDR.
To determine intensity, units will have an intensity probe
incorporated into the unit. The probe is comprised of two
III.F-3
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TABLE III.F.I
IT Values for Inactivation of viruses by
Ultraviolet Light (UV) (1,2)
Log Inactivation IT CmW-see/cm2) (3)
2.0 21
3.0 36
NOTES
1. Data adopted from Sobsey (1988) for UV inactivation of
Hepatitis A Virus (HAV). Values include safety factor of 3.
2. Table from USEPA "Guidance Manual for Compliance with the
Filtration and Disinfection Requirements for Public Water.
Systems using Surface Water Sources11. (October, 1989)
3. IT is the product of the intensity (I) of the UV light
applied (in mW/cm}) multiplied by the time of application
(T) (in seconds).
III.F-4
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FIGURE III.P.I
Factors Affecting the Choice of UV Disinfection
FACTOR SIGNIFICANCE
Hardness
Iron
Inorganic
suspended solids
Turbidity
Color
Nitrites,
sulfites,
manganese
HPC
Aromatic organics
UV transmittance
No residual
Location
Levels above 100 mg/1 (as CaCO}) may cause
plating or scale.
Levels above 0.2 mg/1 may cause fouling.
Particles >S Mm may have a shielding effect
on UV transmission.
Levels above 10 NTU may have a shielding
effect.
Levels above 15 TCU may include organic
substances that can absorb UV light (254 run)
and reduce disinfection efficiency.
Certain levels may cause plating. Should be
evaluated on a case-by-case basis.
Levels >500/ml may cause inactivation of
viruses to fall below the required/expected
level.
Certain levels may cause plating.
evaluated on a case-by-case basis.
Should be
Levels <75% may prevent adequate kill.
UV does not provide a disinfectant residual.
For systems which must provide a distribution
system residual, a secondary disinfectant
(e.g., chlorine or chloramines) must be
applied just prior to the entrance to the
distribution system and appropriate costs
considered.
UV equipment should be located downstream of
treatment processes, such as filters,
softeners, and GAC units. May be installed
ahead of membrane treatment processes to
protect membranes from microbial degradation.
-III.F-5
-------
primary components (a photo sensor and an intensity monitor) and
will usually be located on the wall located furthest from the
lamps. This placement is necessary to approximate the worst-case
conditions. Also, monitors must be connected to a shutoff system
to stop flow if the intensity of the UV reaching the monitor
drops below a level which ensures adequately disinfected water.
To prevent the need for shutting off the system, EPA
recommends that a minimum of two units be provided/ with each
unit capable of handling peak daily flow. Two units allow for
cleaning/ bulb replacement, repairs, and other required
maintenance. Also, a time- or flow-delay mechanism should be
incorporated to permit a warm-up period for tubes to ensure
continuous disinfection. If a system decides tc use automatic
shutoff instead of redundant backup units, the system must ensure
that adequate pressure remains in the distribution system to
prevent infiltration and provide for fire protection.
When operating a UV unit, cleanliness is a paramount
consideration. Any surface through which the UV radiation must
pass must be visually checked for surface fouling and cleaned on
a regular basis. Also, while reduction of intensity measured by
in-line probes may indicate fouling and should be tracked, more
checking is needed, other factors affecting UV lamp performance
include bulb age, electrode failure, and operating temperature.
Finally/ since UV disinfection does not extend beyond the
immediate area of the UV unit and does not provide a residual,
community systems using UV must provide a secondary disinfectant
(e.g., chlorine or chloramines) for the distribution system
unless the Primacy Agency determines that it is not required.
Noncommunity systems must provide a secondary residual if the
distribution system is determined to be vulnerable.
EPA requests comment on any specific UV requirement. In
particular, we request comment on the following:
• Are there inactivation data available for greater than
3-log inactivation of viruses?
• Should EPA ban or restrict the use of open channel UV
reactors because of the possibility of recontamination
from the air?
• How should approved units be designated? Will States
accept third party.testing and.approval of UV units?
• Are there particular monitoring requirements needed for
UV?
• Are the assumptions that plug flow and turbulent flow
exist in UV reactors good assumptions? Are they
III.F-6
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necessary assumptions?
• How should failure of the sensor unit be handled?
Should backup treatment units be required? Should
. there be a required delay before the backup unit goes
on-line to allow that unit to warm up? What other
requirements are suitable to ensure that pressure is
maintained in the distribution system?
3. "Natural Disinfection"
As explained earlier in Section III.B., EPA is developing
criteria that, if met, would provide equivalent health protection
from microbial contaminants to consumers as chemical (or UV)
disinfection of source water without requiring systems to install
and operate such equipment. In developing several of these
"natural disinfection" criteria, the data collection and analysis
requirements will be minimized and simplified to the greatest
extent possible without compromising health protection afforded
by the criteria. EPA is developing guidance for PWSs to gather
data and for states to evaluate data. EPA's intent is to qualify
systems for "natural disinfection" through the use of simply-
defined criteria that can be evaluated in a short time by
individuals without any specialized training using EPA's guidance
and a checklist.
III.F-7
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IV. Imp1•mentation Schedule for the GWDR
EPA has worked to make the implementation schedule for the
GWDR as simple as possible while providing timely health
protection. Figure IV-1 is the proposed implementation schedule,
based on a promulgation date of June 1995. Figure IV-2 shows how
the effective dates of the regulation result in coverage of water
systems and population by percentage.
A. Summary of Schedule
Based on a June 1995 promulgation date, the rule will be
effective in December 1996. On this date, systems already
disinfecting will be required to begin monitoring but will be
given until December 1997 to meet performance criteria. The year
between the requirement to begin monitoring and to meet the
performance criteria is allowed so that systems can modify
treatment practices to comply with federal requirements or State
regulations that are more stringent than federal regulations.
State requirements may not be clear until December, 1996 or
later, because the Safe Drinking Water Act allows states 18
months after promulgation of Federal regulations (until December,
1996) to adopt such regulations.
For water systems not disinfecting at the time of
promulgation of the Federal rule, monitoring and performance
requirements for the GWDR will be effective in December 1999 for
CWSs and in December 2001 for NCWSs. The dates are staggered to
allow States time to process requests for "natural disinfection"
status and variances from disinfecting. Also, the Surface Water
Treatment Rule requires that ground water that is under the
direct influence of surface water be identified by June 1999 for
NCWSs. EPA believes it was appropriate to allow all NCWSs in
this category to b« identified before disinfection was required
under the GWDR. Ground water that is under the direct influence
of surface water will be governed by the SWTR, not the GWDR.
B. EPA Proposed Approach
EPA proposes to promulgate this regulation with the schedule
in Figure IV-1. This approach has the advantages of simplifying
the Federal Regulation, making the State adoption process less
burdensome,, and making the rule easier to understand. Of course,
if the schedule in Figure iv-i is used, the States will have to
identify, as a special primacy condition, the intterim deadline
they will us* to_determine which systems will receive variances
and which systems will receive "natural disinfection" status.
Another advantage of the proposed approach is that it would
allow the States to make use of elements of their existing
program in granting variances and "natural disinfection" status.
States with effective sanitary survey programs could craft their
. iv-i
-------
implementation schedule around already planned sanitary surveys,
minimizing disruption of existing State procedures. The
disadvantage of this approach is that the rule will not become
Federally enforceable for PWSs not currently disinfecting until
1999 and 2001 for CWSs and NCWSs.
EPA has developed possible interim deadlines for
consideration. These are shown in italics at the bottom of
Figure IV-1. These deadlines would require systems to decide on
a course of action by a date certain and would establish a latest
possible date for systems to apply for variances or "natural
disinfection11 status. One advantage of this interim deadline is
that systems in all States would be on the same schedule.
without such a federal deadline, systems would b« able to submit
applications in accordance with the compliance schedule
established by each State. Another advantage is that compliance
with the interim deadline is federally enforceable. The
requirement for a system to submit either an application for a
variance or "natural disinfection" status or inform the State
that it intends to disinfect would be enforceable for PWSs not
currently disinfecting in 1997 and 1999 for CWSs and NCWSs,
respectively.
C. Solicitation of comments
EPA solicits comments on the schedule as a whole. In
particular, EPA would like comment, especially from the EPA
Regions and States, on whether the interim deadlines would aid in
rule implementation and enforcement. We would also like to get
an appreciation of how these additional interim deadlines.would
affect the cost of implementing this rule.
IV-2
-------
GWDR IMPLEMENTATION DATES
Figure IV-1
(Based on June 1995 Promulgation)
12/96 Regulations effective.
12/96 All systems disinfecting at the time of promulgation of the Federal rule
must meet monitoring requirements.
12/97 All systems disinfecting at the time of promulgation of the Federal rule
must meet performance requirements.
6/99 States must determine whether NCWS groundwater systems are
under the direct influence of surface water. (SWTR Requirement)
12/99 CWSs must disinfect. (CWSs may disinfect through chemical
disinfection or "natural disinfection" (if approved by the State) or be
granted a variance from disinfection by the State.)
12/01 NCWSs must disinfect. {NCWSs may disinfect through chemical
disinfection or "natural disinfection" (if approved by the State) or be
granted a variance from disinfection by the State.}
Note: EPA solicits comment, especially from the EPA Regions and States, on
whether the interim deadlines below would aid in rule implementation and
enforcement. We would also like to get an appreciation of how these
additional interim deadlines would affect the cost of implementing this rule.
12/97 CWSs must either submit an application requesting a variance or
"natural disinfection" status or inform the State in writing that they do
not intend to apply and wilt disinfect.
12/99 NCWSs must either submit an application requesting a variance or
"natural disinfection " status or inform the State in writing that they do
not intend to apply and will disinfect.
IV-3
-------
GWDR COVERAGE CHART
Figure IV-2
(Population and Systems Fully Covered)
.n.r ofomuta.tM.nh Percent Systems Percent
12/97(30) 27 67
12/99(54) 40 79
12/01 (78) 100 100
IV-4
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