round of monitoring or any time thereafter.
    h. Second round of monitoring. A more rigorous reassessment of the
source water occurs through a second round of monitoring that begins
six years after initial bin classification. If EPA does not develop and
finalize modifications to the LT2ESWTR prior to the date when PWSs must
begin the second round of monitoring, then this second round must
conform to the same requirements that applied to the initial round of
monitoring. PWSs may be classified in a different treatment bin,
depending on the results of the second round of monitoring.
    The Stage 2 M-DBP Advisory Committee recommended that EPA initiate
a stakeholder process several years prior to the second round of
monitoring to review new information and determine if today's rule
should be modified. If the Agency modifies the LT2ESWTR, the second
round of monitoring would potentially involve a new analytical method
and a different treatment bin structure.
3. Summary of Major Comments
    Public comment on the August 11, 2003, LT2ESWTR proposal generally
supported the use of source water monitoring to determine additional
treatment requirements. The following discussion summarizes major
comments and EPA's responses in regard to sampling parameters and
frequency, sampling location, sampling schedule, monitoring plants that
operate only part-year, failing to monitor, providing treatment instead
of monitoring, grandfathering previously collected data, ongoing source
water assessment, second round of monitoring, and new source
monitoring.
    a. Sampling parameters and frequency. Most commenters supported the
proposed requirements for large PWSs to sample monthly for
Cryptosporidium, as well as for E. coli and turbidity in filtered PWSs,
for 24 months. Alternatives recommended by some commenters included
ending monitoring after one year if no oocysts are detected, allowing
large PWSs to use an E. coli screening analysis to determine if
Cryptosporidium monitoring is necessary, and using watershed data to
determine treatment needs instead of source water monitoring.
    In response, EPA continues to believe that large PWSs should
complete 24 months of Cryptosporidium monitoring, regardless of the
first-year results, in order to capture a degree of annual variability
in Cryptosporidium occurrence. Moreover, for the reasons discussed
previously in this preamble, EPA continues to support the Advisory
Committee recommendation that all large PWSs should monitor for
Cryptosporidium, rather than use the E. coli screening analysis. EPA is
not aware of studies that support the use of other watershed data in
place of Cryptosporidium monitoring to determine treatment needs.
    Regarding requirements for small PWSs, most commenters supported
the E. coli screening analysis for small filtered PWSs. Several
commenters recommended more options for Cryptosporidium monitoring by
small PWSs, such as allowing monitoring to be spread over two years,
instead of the one year required in the proposal, or allowing fewer
samples. EPA agrees that budgeting for Cryptosporidium monitoring by
some small PWSs will be easier if it is spread over two years, and
today's rule allows this as an option.

However, based on the analysis of false negative and false positive
rates described previously, EPA continues to believe that at least 24
Cryptosporidium samples are necessary to determine the appropriate bin
classification for year-round plants.
    b. Sampling location. With respect to sampling location
requirements, several commenters recommended that PWSs be allowed to
collect samples either before or after pretreatment processes. These
commenters stated that the chemicals used in pretreatment processes are
unlikely to affect the analysis of Cryptosporidium oocysts at typical
concentrations. Further, where sampling is conducted prior to a
pretreatment process like presedimentation, commenters supported
allowing PWSs to receive additional treatment credit for the process.
    In response, EPA continues to believe that common pretreatment
chemicals like oxidants and coagulants have the potential to adversely
affect the performance of Cryptosporidium analytical methods.
Consequently, today's rule requires that in most cases, PWSs must
sample upstream of chemical addition. Where PWSs sample prior to
pretreatment processes like presedimentation with coagulation, they are
eligible to receive additional treatment credit for the process.
However, if sampling prior to chemical addition is not feasible for a
particular plant and the treatment chemical is present at a very low
level that is unlikely to interfere with sample analysis, the State may
approve sampling after chemical addition.
    Many commenters recommended that States approve sampling locations
for their PWSs. Commenters indicated that State review and approval of
monitoring plans will help to prevent confusion and PWSs potentially
sampling at an incorrect location. EPA agrees with these commenters and
has established a requirement in today's rule for PWSs to report a
description of the sampling location to the State. If a PWS does not
hear back from the State by the time it is scheduled to begin sampling,
it may assume that its monitoring location is acceptable.
    c. Sampling schedule. In regard to sampling schedule requirements,
several commenters requested that PWSs be given a time window larger
than 5 days around scheduled sampling dates to collect samples.
Recommended alternatives included a 7 or 9-day window, or only
requiring that PWSs collect a sample within a specified month. In
addition, commenters identified situations that interfere with sample
collection, such as plant interruptions and laboratory or
transportation problems, and noted that some of these are outside the
conditions under which the proposal allowed a PWS to collect a delayed
or replacement sample without penalty.
    In response, EPA continues to believe that for routine sample
collection, a 5-day window provides sufficient flexibility, given that
PWSs will pick the sampling days and can schedule around holidays,
weekends, and other times when sampling would be problematic. However,
today's rule allows PWSs to sample outside of this window without
penalty if necessary due to unforeseen conditions. Further, if a PWS
collects a sample but is unable to have it analyzed due to problems
with equipment, transportation or the laboratory, today's rule allows
the PWS to collect a replacement sample without penalty.
    In regard to the time frame for collecting missed or replacement
samples, commenters recommended a number of approaches. These include
adding extra sampling days to the original sampling schedule, which a
PWS could then use in the event of missed sampling dates, and allowing
PWSs to collect make-up samples either immediately after the scheduled
sampling date or at the end of the monitoring period.
    In general, EPA considers it preferable for PWSs to collect missed
or replacement samples as close as is feasible to scheduled sampling
dates. However, if there is a significant delay with respect to the
original sampling date, collecting make-up samples at an alternate time
may be appropriate to ensure that sampling results are seasonally
representative. Therefore, today's rule requires PWSs to collect a
missed sample as close as is feasible to the scheduled sampling date,
and to collect replacement samples within 21 days of receiving
information that one is needed, unless doing so within this time frame
is not feasible. However, the State can authorize alternative sampling
dates so that monitoring is not seasonally biased. This could include
sampling during the same time in the following year, if the missed
sample occurred during the first year of monitoring, or sampling after
the end of the scheduled monitoring period.
    d. Plants operating only part of the year. Commenters on monitoring
requirements for surface water plants that operate for only part of the
year generally recommended that sampling occur only during the period
of operation. However, several different options were put forward for
how the sampling be conducted. Some commenters recommended a minimum of
12 samples per year for two years distributed evenly over the period
that the plant operates. Others suggested allowing the PWS to collect
the required number of samples over a longer time period in order to
limit the frequency of required samples when the plant is operating.
Several commenters said that State input is critical to determining the
appropriate monitoring period since States may have historical
knowledge of plant operating practices.
    In response, EPA agrees that monitoring of plants that operate only
part-year under today's rule should be conducted only during months
when the plant is operating, unless the State determines that a longer
monitoring period is appropriate due to historical operating practices.
Further, plants that operate only part-year should maintain the same
sampling frequency as plants operating year-round, with the exception
that plants monitoring for Cryptosporidium must collect at least six
samples per year to allow for appropriate bin classification. EPA does
not believe extending monitoring over more years in plants that operate
only part-year is appropriate, as this would delay the installation of
additional treatment where needed.
    e. Failing to monitor. Most commenters opposed automatically
classifying PWSs in the highest treatment bin (Bin 4) if they fail to
complete required monitoring, as the proposed rule stipulated.
Commenters suggested alternative approaches, such as giving States the
flexibility to address missed samples using current enforcement
mechanisms, classifying a PWS only one level higher than the bin
determined by the collected data, allowing an additional year of
sampling, and allowing States to use other information (e.g., sanitary
surveys, other monitoring data) to aid in the classification. A few
commenters, however, supported Bin 4 classification for PWSs that fail
to monitor, on the basis that any other approach would create an
incentive for PWSs to stop testing if poor water quality is suspected.
    EPA agrees that States should have flexibility in dealing with PWSs
that fail to monitor. Further, providing the highest level of treatment
may not be in the best interests of consumers where a PWS has minor
problems in carrying out source water monitoring. However, EPA also
believes that violations for monitoring failures must reasonably ensure
that PWSs complete monitoring as required to determine a bin
classification within the compliance

date. Failure to do so would potentially compromise public health
protection.
    Based on these considerations, EPA has not established an automatic
Bin 4 classification for monitoring failures under today's rule.
Rather, if a PWS misses three or more Cryptosporidium samples, this
persistent violation requires a Tier 2 public notice (other violations
require a Tier 3 notice). Further, if a PWS is unable to determine a
bin classification by the compliance date due to failure to collect the
required number of Cryptosporidium samples, this is a treatment
technique violation with a required Tier 2 public notice (unless the
PWS has already issued a Tier 2 notice for missing 3 Cryptosporidium
samples and is monitoring on a State-approved schedule). These
violations last until the State determines that a PWS has begun
monitoring on a schedule that will lead to bin classification or the
PWS agrees to install treatment instead of monitoring.
    f. Providing treatment instead of monitoring. Commenters supported
the option for a PWS to provide the highest level of Cryptosporidium
treatment required under today's rule rather than conducting source
water monitoring. Several commenters recommended that a PWS should be
allowed to take this option after having initiated monitoring. EPA
agrees, and today's rule allows a PWS to stop monitoring at any time by
notifying the State that it will provide 5.5-log Cryptosporidium
treatment for filtered PWSs or 3-log Cryptosporidium inactivation for
unfiltered PWSs by the compliance deadline specified in section IV.G.
    g. Grandfathering previously collected data. With respect to
grandfathering previously collected data, many commenters expressed
concern with a proposed requirement that samples must have been
collected in equal time intervals. Commenters stated that although PWSs
may have sampled on a regular schedule, previously collected data sets
are likely to have gaps due to samples rejected for method QC
violations or periods when the PWS was unable to collect a sample. In
addition, there are instances where PWSs have changed the frequency of
sampling, such as from monthly to twice per month.
    EPA agrees that if a PWS has collected samples according to a
regular schedule and met other data quality standards, then rejecting a
large data set due to isolated gaps in the sampling frequency would be
inappropriate. Consequently, today's rule allows States to approve
grandfathering of previously collected data with omissions in the
sampling interval, provided the PWS conducts additional monitoring if
required by the State to ensure the data set is seasonally
representative. Further, PWSs may grandfather previously collected data
sets in which the sampling frequency varies, as long as samples were
collected at least monthly. In this situation, PWSs must use monthly
average concentrations, rather than individual sample concentrations,
for bin classification.
    With respect to data quality standards, such as meeting analytical
method QC criteria, sampling at the correct location, and analyzing the
minimum sample volume, several commenters stated that EPA should apply
the same acceptance standards to previously collected data as are
applied to data collected under today's rule. Other commenters, though,
suggested that States should have the flexibility to accept previously
collected data that deviate from the data quality standards for
monitoring under the rule. These commenters stated that such data sets
might include samples collected over a longer period of time and may
reflect more worst-case weather events.
    In response, EPA believes that data quality standards should be
uniformly applied under today's rule, so that previously collected data
should not be held to a lower standard than new data or evaluated
differently from State to State. The requirements in today's rule with
respect to Cryptosporidium analytical methods and minimum sample volume
reflect recommendations of the Advisory Committee, which also
recommended that the same data quality standards be applied for
grandfathering. Further, because today's rule allows PWSs to collect
make-up samples to address gaps in previously collected data sets, PWSs
will have the opportunity to collect make-up samples for results that
are rejected due to data quality standards without losing an entire
data set.
    In regard to notification of the acceptability of data for
grandfathering, commenters recommended that if previously collected
data submitted by a PWS are rejected, the PWS should have at least two
months between notification and the date new monitoring must be
initiated. These two months will give the PWS time to address rejection
of the data and prepare for sampling. EPA agrees with this
recommendation. Under today's rule, if a PWS properly submits a
complete data set for grandfathering and the PWS must conduct new
monitoring due to rejection of the data, the PWS has at least two
months following notification by the State to initiate sampling.
    h. Ongoing watershed assessment. Commenters asked for greater
flexibility in the requirement for States to determine whether there
have been significant changes in the watersheds of their PWSs that
could lead to increased contamination. The proposed rule specified that
States must make this determination during sanitary surveys. However,
several commenters noted that some States perform source water
protection assessments on the same frequency as sanitary surveys, and
these detailed assessments might be a better mechanism to monitor
changes in the watershed. EPA agrees and today's rule allows States to
determine whether significant changes have occurred in the watershed
through either a sanitary survey or an equivalent review of the source
water under another program.
    i. Second round of monitoring. Some commenters supported the
proposed requirement for a second round of source water monitoring, but
most opposed requiring it for all PWSs. These commenters recommended
that States should be authorized to use sanitary surveys, source water
assessments, ambient water quality data, treatment plant data, and
other information to determine if a second round of monitoring is
necessary for a PWS. Some commenters suggested that EPA fund research
to allow the use of finished water monitoring as the determinant for
treatment requirements in a second round of monitoring.
    In response, EPA continues to believe that PWSs should conduct a
second round of monitoring to determine if the level of treatment
required as a result of the first round of monitoring is still
appropriate. Consequently, today's rule requires this. However, EPA
agrees that prior to a second round of monitoring, the Agency should
evaluate the results of the first round of monitoring, along with
whatever new information is available on Cryptosporidium analytical
methods, risk, and other relevant issues. If EPA determines that there
should be changes to the requirements for a second round of monitoring
in today's rule, the Agency will issue a new rule establishing those
changes.
    j. New source monitoring. EPA requested comment in the proposal on
monitoring requirements for new plants and sources (USEPA 2003a). Most
commenters recommended that new plants and sources undergo monitoring
equivalent to that required for existing plants and sources, and
suggested that States should have discretion to determine when
monitoring should take place. EPA agrees with these recommendations and
today's rule requires PWS to conduct source water

monitoring for new plants and sources on a schedule approved by the
State. This schedule must include dates for the PWS to determine its
treatment bin classification and, if necessary, comply with additional
Cryptosporidium treatment requirements.

B. Filtered System Cryptosporidium Treatment Requirements

1. Today's Rule
    Today's rule requires filtered PWSs using surface water or GWUDI
sources to provide greater levels of treatment if their source waters
have higher concentrations of Cryptosporidium. Specifically, filtered
PWSs are classified in one of four treatment bins based on results from
the source water monitoring described in the previous section. PWSs
classified in the lowest concentration bin are subject to no additional
treatment requirements, while PWSs assigned to higher concentration
bins must reduce Cryptosporidium levels beyond IESWTR and LT1ESWTR
requirements. All PWSs must continue to comply with the requirements of
the SWTR, IESWTR, and LT1ESWTR, as applicable.
    This section addresses procedures for classifying filtered PWSs in
Cryptosporidium treatment bins and the treatment requirements
associated with each bin. Section IV.D presents the treatment and
control options, collectively termed the ``microbial toolbox,'' that
PWSs must use to meet additional Cryptosporidium treatment requirements
under today's rule.
    a. Bin classification. After completing initial source water
monitoring, filtered PWSs must calculate a Cryptosporidium bin
concentration for each treatment plant where Cryptosporidium monitoring
is required. This Cryptosporidium bin concentration is used to classify
filtration plants in one of the four treatment bins shown in Table
IV.B-1.

        Table IV.B-1.--Bin Classification Table for Filtered PWSs
------------------------------------------------------------------------
                                with a Cryptosporidium       The bin
      For PWSs that are:        bin concentration of .   classification
                                          . .               is . . .
------------------------------------------------------------------------
* * * required to monitor for   less than 0.075         Bin 1.
 Cryptosporidium.                oocysts/L.
                                0.075 oocysts/L or      Bin 2.
                                 higher, but less than
                                 1.0 oocysts/L.
                                1.0 oocysts/L or        Bin 3.
                                 higher, but less than
                                 3.0 oocysts/L.
                                3.0 oocysts/L or        Bin 4.
                                 higher.
* * * serving fewer than        NA....................  Bin 1.
 10,000 people and NOT
 required to monitor for
 Cryptosporidium \1\.
------------------------------------------------------------------------
\1\ Filtered PWSs serving fewer than 10,000 people are not required to
  monitor for Cryptosporidium if they monitor for E. coli and
  demonstrate a mean concentration of E. coli less than or equal to 10/
  100 mL for lake/reservoir sources or 50/100 mL for flowing stream
  sources or do not exceed an alternative State-approved indicator
  trigger (see section IV.A.1).

    In general, the Cryptosporidium bin concentration is calculated by
averaging individual sample results from one or more years of
monitoring. Specific procedures vary, however, depending on the
frequency and duration of monitoring. These procedures are as follows:
    (1) For PWSs that collect a total of at least 24 but not more than
47 Cryptosporidium samples over two or more years, the Cryptosporidium
bin concentration is equal to the highest arithmetic mean of all sample
concentrations in any 12 consecutive months of Cryptosporidium
monitoring.
    (2) For PWSs that collect a total of at least 48 samples, the
Cryptosporidium bin concentration is equal to the arithmetic mean of
all sample concentrations.
    (3) For PWSs that serve fewer than 10,000 people and monitor for
Cryptosporidium for only one year (i.e., collect 24 samples in 12
months), the Cryptosporidium bin concentration is equal to the
arithmetic mean of all sample concentrations.
    (4) For PWSs with plants that operate only part-year that monitor
for less than 12 months per year, the Cryptosporidium bin concentration
is equal to the highest arithmetic mean of all sample concentrations
during any year of Cryptosporidium monitoring.
    In data sets with variable sampling frequency, PWSs must first
calculate an arithmetic mean for each month of sampling and then apply
one of these four procedures using the monthly mean concentrations. As
described in section IV.A, PWSs may grandfather previously collected
Cryptosporidium data where the sampling frequency varies (e.g., one
year of monthly sampling and one year of twice-per-month sampling).
    Filtered PWSs serving fewer than 10,000 people are not required to
monitor for Cryptosporidium if they demonstrate a mean E. coli
concentration less than or equal to 10/100 mL for lake/reservoir
sources or 50/100 mL for flowing stream sources or do not exceed an
alternative State-approved indicator trigger. PWSs that meet this
criterion are classified in Bin 1 as shown in Table IV.B-1.
    When determining the Cryptosporidium bin concentration, PWSs must
calculate individual sample concentrations as the total number of
oocysts counted, divided by the volume assayed (see section V.K for
details). In samples where no oocysts are detected, the result is
assigned a value of zero for the purpose of calculating the bin
concentration. Sample analysis results are not adjusted for analytical
method recovery or the percent of Cryptosporidium oocysts that are
infectious.
    PWSs must report their treatment bin classification to the State
for approval following initial source water monitoring (see section
IV.G for specific compliance dates). The report must include a summary
of the data and calculation procedure used to determine the bin
concentration. If EPA does not amend today's rule before the second
round of monitoring described in section IV.A, PWSs must recalculate
their bin classification after completing the second round of
monitoring and report the results to the State for approval. If the
State does not respond to a PWS regarding its bin classification after
either report, the PWS must comply with the Cryptosporidium treatment
requirements of today's rule based on the reported bin classification.
    b. Bin treatment requirements. Table IV.B-2 shows the additional
Cryptosporidium treatment requirements associated with the four
treatment bins for filtered PWSs under today's rule. All filtered PWSs
must comply with these treatment requirements based on their bin
classification, which must be determined using the procedures just
described.

                     Table IV.B-2.--Treatment Requirements for LT2ESWTR Bin Classifications
----------------------------------------------------------------------------------------------------------------
                                         And you use the following filtration treatment in full compliance with
                                          the SWTR, IESWTR, and LT1ESWTR (as applicable), then your additional
                                                            treatment requirements are . . .
                                      --------------------------------------------------------------------------
 If your bin classification  is . . .  Conventional filtration
                                            treatment \1\,
                                          diatomaceous earth       Direct filtration      Alternative filtration
                                         filtration, or slow                                   technologies
                                           sand filtration
----------------------------------------------------------------------------------------------------------------
Bin 1................................  No additional treatment  No additional treatment  No additional
                                                                                treatment.
Bin 2................................  1-log treatment \2\....  1.5-log treatment \2\..  As determined by the
                                                                                State 2 4
Bin 3................................  2-log treatment \3\....  2.5-log treatment \3\..  As determined by the
                                                                                State 3 5
Bin 4................................  2.5-log treatment \3\..  3-log treatment \3\....  As determined by the
                                                                                State 3 6
----------------------------------------------------------------------------------------------------------------
\1\ Applies to a treatment train using separate, sequential, unit processes for coagulation/flocculation,
  clarification, and granular media filtration. Clarification includes any solid/liquid separation process
  following coagulation where accumulated solids are removed during this separate component of the treatment
  system.
\2\ PWSs may use any technology or combination of technologies from the microbial toolbox in section IV.D.
\3\ PWSs must achieve at least 1-log of the required treatment using ozone, chlorine dioxide, UV, membranes, bag
  filtration, cartridge filtration, or bank filtration.
\4\ Total Cryptosporidium removal and inactivation must be at least 4.0 log.
\5\ Total Cryptosporidium removal and inactivation must be at least 5.0 log.
\6\ Total Cryptosporidium removal and inactivation must be at least 5.5 log.

    The total Cryptosporidium treatment required for plants in Bins 2,
3, and 4 is 4.0-log, 5.0-log, and 5.5-log, respectively. Conventional
treatment (including softening), slow sand, and diatomaceous earth
filtration plants in compliance with the IESWTR or LT1ESWTR, as
applicable, receive a prescribed 3.0-log Cryptosporidium treatment
credit toward these total bin treatment requirements. Accordingly,
these plant types must provide 1.0- to 2.5-log of additional treatment
when classified in Bins 2-4, respectively. Direct filtration plants in
compliance with existing regulations receive a prescribed 2.5-log
treatment credit and, consequently, must achieve 0.5-log greater
treatment to comply with Bins 2-4. Section IV.D describes how States
may award a level of treatment credit that differs from the prescribed
credit based on a demonstration of performance by the PWS.
    For PWSs using alternative filtration technologies, such as
membranes, bag filters, or cartridge filters, no prescribed treatment
credit is available because the performance of these processes is
specific to individual products. Consequently, when PWSs using these
processes are classified in Bins 2-4, the State must determine
additional treatment requirements based on the credit the State awards
to a particular technology. The additional treatment requirements must
ensure that plants classified in Bins 2-4 achieve total Cryptosporidium
reductions of 4.0- to 5.5-log, respectively. Section IV.D describes
challenge testing procedures to determine treatment credit for
membranes, bag filters, and cartridge filters.
    PWSs can achieve additional Cryptosporidium treatment credit
through implementing pretreatment processes like presedimentation or
bank filtration, by developing a watershed control program, and by
applying additional treatment steps like ozone, chlorine dioxide, UV,
and membranes. In addition, PWSs can receive a higher level of credit
for existing treatment processes through achieving very low filter
effluent turbidity or through a demonstration of performance. Section
IV.D presents criteria for awarding Cryptosporidium treatment credit to
these and other treatment and control options, which collectively
comprise the microbial toolbox.
    PWSs in Bin 2 can meet additional Cryptosporidium treatment
requirements by using any option or combination of options from the
microbial toolbox. For Bins 3 and 4, PWSs must achieve at least 1-log
of the additional treatment requirement by using ozone, chlorine
dioxide, UV, membranes, bag filtration, cartridge filtration, or bank
filtration.
2. Background and Analysis
    Today's rule will increase protection against Cryptosporidium and
other pathogens in PWSs with the highest source water contamination
levels. This targeted approach builds upon existing regulations under
which all filtered PWSs must provide the same level of treatment
regardless of source water quality. EPA's intent with today's rule is
to ensure that PWSs with higher risk source waters achieve public
health protection commensurate with PWSs with less contaminated
sources.
    The Cryptosporidium treatment requirements for filtered PWSs in
today's rule are unchanged from the August 11, 2003 proposal (USEPA
2003a) and reflect consensus recommendations by the Stage 2 M-DBP
Advisory Committee (USEPA 2000a). The following discussion summarizes
the Agency's basis for establishing risk-targeted Cryptosporidium
treatment requirements and for setting the specific bin concentration
ranges and treatment requirements that apply to filtered PWSs in
today's rule.
    a. Basis for targeted treatment requirements. In developing today's
rule, EPA evaluated the degree to which new information on
Cryptosporidium warranted moving beyond existing regulations. As
discussed in section III, the IESWTR established a Cryptosporidium MCLG
of zero and requires large filtered PWSs to achieve 2-log
Cryptosporidium removal. The LT1ESWTR extended this requirement to
small PWSs. After these rules were promulgated, advances were made in
analytical methods and treatment for Cryptosporidium, and EPA collected
new information on Cryptosporidium occurrence and infectivity.
Consequently, EPA assessed the implications of these developments for
further controlling Cryptosporidium to approach the zero MCLG.
    The risk-targeted approach for filtered PWSs in today's final rule
stems from four general findings based on new information on
Cryptosporidium:
    (1) New data on Cryptosporidium infectivity suggest that the risk
associated with a particular level of Cryptosporidium is most likely
higher than EPA estimated at the time of earlier rules;
    (2) New data on Cryptosporidium occurrence indicate that levels are
relatively low in most water sources, but a subset of sources has
substantially higher concentrations;
    (3) The finding that UV light can readily inactivate
Cryptosporidium, as well as other technology developments, makes
achieving high levels of

treatment for Cryptosporidium feasible for PWSs of all sizes; and
    (4) EPA Methods 1622 and 1623 are capable of assessing annual mean
levels of Cryptosporidium in drinking water sources.
    These findings led EPA to conclude that most filtered PWSs
currently provide sufficient treatment for Cryptosporidium, but
additional treatment is needed in those PWSs with the highest source
water Cryptosporidium levels to protect public health. Further, PWSs
can characterize Cryptosporidium levels in their source waters with
available analytical methods and can provide higher levels of treatment
with available technologies. Consequently, risk-targeted treatment
requirements for Cryptosporidium based on source water contamination
levels are appropriate and feasible to implement.
    b. Basis for bin concentration ranges and treatment requirements.
To establish the risk-targeted treatment requirements in today's rule,
EPA had to determine the degree of treatment that should be required
for different source water Cryptosporidium levels to protect public
health. This determination involved addressing several questions:
     What is the risk associated with Cryptosporidium in a
drinking water source?
     How much Cryptosporidium removal do filtration plants
achieve?
     What is the appropriate statistical measure for
classifying PWSs into treatment bins?
     What degree of additional treatment is needed for higher
source water Cryptosporidium levels?
     How should PWSs calculate their treatment bin
classification?
    This section summarizes how EPA evaluated these questions in
developing today's rule. See the proposed LT2ESWTR for further details
(USEPA 2003a).

What is the Risk Associated With Cryptosporidium in a Drinking Water
Source?

    The risk of infection from Cryptosporidium in drinking water is a
function of exposure (i.e., the dose of oocysts ingested) and
infectivity (i.e., likelihood of infection as a function of ingested
dose). Primary (i.e., direct) exposure to Cryptosporidium depends on
the concentration of oocysts in the source water, the fraction removed
by the treatment plant, and the volume of water consumed (secondary
exposure occurs through interactions with infected individuals). Thus,
the daily risk of infection (DR) is as follows:

DR = (oocysts/L in source water) x (fraction remaining after treatment)
x (liters consumed per day) x (likelihood of infection per oocyst
dose).

    Assuming 350 days of consumption per year for people served by
community water systems (CWSs), the annual risk (AR) of infection is as
follows:

AR = 1 - (1 - DR) \350\.

    As discussed in section III.E, EPA has estimated the mean
likelihood of infection from ingesting one Cryptosporidium oocyst to
range from 4 to 16 percent. Median individual daily water consumption
is estimated as 1.07 L/day. Figure IV.B-1 illustrates ranges for the
annual risk of infection by Cryptosporidium in CWSs based on these
values for different source water infectious oocyst concentrations and
treatment plant removal efficiencies. The dashed lines represent the
uncertainty associated with Cryptosporidium infectivity for each log-
removal curve. See Chapter 5 of the LT2ESWTR Economic Analysis for
details (USEPA 2005a).
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[GRAPHIC] [TIFF OMITTED] TR05JA06.000

BILLING CODE 6560-50-C
    The results in Figure IV.B-1 show, for example, that if a treatment
plant had a concentration of infectious Cryptosporidium in the source
water of 0.1 oocysts/L and the plant achieved 3-log removal, the mean
annual risk of

Cryptosporidium infection would range from 0.0017 to 0.0060 (17 to 60
infections per 10,000 consumers). In comparison, if the same plant had
a source water infectious Cryptosporidium level of 0.01 oocysts/L, the
annual infection risk would range from 1.7 to 6 per 10,000 consumers.

How much Cryptosporidium removal do filtration plants achieve?

    The amount of Cryptosporidium removal that filtration plants
achieve was a key factor in assessing the additional treatment that
plants with higher source water Cryptosporidium levels should provide.
To evaluate this factor, EPA reviewed studies of Cryptosporidium
removal by common treatment processes. As described in the proposal for
today's rule, these processes were conventional treatment, direct, slow
sand, and diatomaceous earth filtration, as well as membrane, bag, and
cartridge filtration (USEPA 2003a).
    The majority of plants treating surface water use conventional
treatment, which is defined in 40 CFR 141.2 as coagulation,
flocculation, sedimentation, and filtration. In the proposal, EPA
reviewed studies of conventional treatment by Dugan et al. (2001),
Nieminski and Bellamy (2000), McTigue et al. (1998), Patania et al.
(1999), Huck et al. (2000), Emelko et al. (2000), and Harrington et al.
(2001). Based on these studies, EPA estimated that conventional
treatment plants in compliance with the IESWTR or LT1ESWTR typically
achieve a Cryptosporidium removal efficiency of approximately 3-log.
Consequently, conventional treatment plants receive 3-log credit toward
Cryptosporidium treatment requirements under today's rule.
    This 3-log credit for conventional treatment is consistent with the
Stage 2 M-DBP Agreement in Principle (USEPA 2000a), which states as
follows:

    ``The additional treatment requirements in the bin requirement
table are based, in part, on the assumption that conventional
treatment plants in compliance with the IESWTR achieve an average of
3 logs removal of Cryptosporidium.''

    The M-DBP Advisory Committee did not recommend a level of
Cryptosporidium treatment credit for other types of filtration plants.
    EPA also reviewed studies of the performance of clarification
processes like dissolved air flotation, which can be used in place of
sedimentation in a conventional treatment train (Gregory and Zabel
1990, Plummer et al. 1995, Edzwald and Kelley 1998). These studies
indicate that plants using clarification processes other than
sedimentation that are located after coagulation and prior to
filtration can achieve performance equivalent to conventional treatment
plants. As a result, any treatment train that includes coagulation/
flocculation, clarification, and granular media filtration is regarded
as conventional treatment for purposes of awarding treatment credit
under today's rule. The clarification step must be a solid/liquid
separation process where accumulated solids are removed during this
separate component of the treatment system.
    Direct filtration plants use coagulation, flocculation, and
filtration processes just as conventional treatment plants do, but they
lack a sedimentation basin or equivalent clarification process. In the
proposal, EPA reviewed studies of sedimentation by Dugan et al. (2001),
States et al. (1997), Edzwald and Kelly (1998), Payment and Franco
(1993), Kelly et al. (1995), and Patania et al. (1995). Results from
these studies demonstrate that sedimentation basins can achieve 0.5-log
or greater Cryptosporidium removal. In addition, some studies have
observed that direct filtration achieves less Cryptosporidium removal
than conventional treatment (Patania et al. 1995) and the incidence of
Cryptosporidium in the treated water is higher (McTigue et al. 1998).
Given these findings, EPA has awarded direct filtration plants a 2.5-
log credit towards Cryptosporidium treatment requirements under today's
rule (i.e., 0.5-log less credit than for conventional treatment).
    Slow sand filtration involves passing raw water through a bed of
sand at low velocity and without prior coagulation. Diatomaceous earth
filtration is a process by which a filtration medium is initially
deposited onto a support membrane and medium is added throughout the
operation to keep the filter from clogging. In the proposal, EPA
reviewed slow sand filtration studies by Fogel et al. (1993), Hall et
al. (1994), Schuler and Ghosh (1991), and Timms et al. (1995) and
diatomaceous earth filtration studies by Schuler and Gosh (1990) and
Ongerth and Hutton (1997, 2001). For both processes, these studies
indicate that a well-designed and properly operated filter can achieve
Cryptosporidium removal efficiencies similar to those observed for
conventional treatment plants. Slow sand and diatomaceous earth
filtration plants, therefore, receive a 3-log credit towards
Cryptosporidium treatment requirements under today's rule.
    Estimating a typical Cryptosporidium removal efficiency for
filtration technologies like membranes, bag filters, and cartridge
filters is not possible because the performance of such filters is
specific to a particular product. As a result, credit for these devices
must be determined by the State based on product-specific testing using
the procedures described in section IV.D or other criteria approved by
the State.
    Table IV.B-3 summarizes the credits various types of filtration
plants receive toward Cryptosporidium treatment requirements under
today's rule. This credit determines the degree of additional treatment
that plants classified in Bins 2-4 must apply, as shown in Table IV.B-
2.

                Table IV.B-3.--Cryptosporidium Treatment Credit Towards LT2ESWTR Requirements \1\
----------------------------------------------------------------------------------------------------------------
                                     Conventional
                                       treatment                             Slow sand or         Alternative
           Plant type                  (includes       Direct filtration  diatomaceous earth      filtration
                                      softening)                              filtration         technologies
----------------------------------------------------------------------------------------------------------------
Treatment credit................  3.0-log...........  2.5-log...........  3.0-log...........  Determined by
                                                                                State. \2\
----------------------------------------------------------------------------------------------------------------
\1\ Applies to plants in full compliance with the IESWTR or LT1ESWTR as applicable.
\2\ Credit must be determined through product or site-specific assessment.

    As discussed previously, studies indicate that conventional
treatment plants producing very low filtered water turbidity can
achieve a higher level of Cryptosporidium removal than 3-log, and
today's rule allows such plants to receive additional treatment credit.
Further, States can award a higher or lower level of credit to an
individual plant based on a site-specific demonstration of performance.
Section IV.D provides details on both of these topics.
    The Cryptosporidium removal credits for filtration plants in
today's rule differ from the amount of credit awarded under the IESWTR
and LT1ESWTR. As

discussed in section III, those rules require all filtered PWSs to
achieve 2-log removal of Cryptosporidium. PWSs using conventional
treatment, or direct, slow sand, or diatomaceous earth filtration are
in compliance with this requirement if they meet specified filtered
water turbidity standards. These regulatory criteria were based on
consideration of the minimum level of removal that all these filtration
processes will achieve (USEPA 1998a). However, in the risk assessments
that supported these regulations, EPA estimated that most filtration
plants will achieve significantly more removal, with median
Cryptosporidium reductions near 3-log.
    Today's rule will supplement IESWTR and LT1ESWTR requirements by
mandating additional treatment at certain PWSs based on source-water
Cryptosporidium levels. When assessing the need for additional
treatment at potentially higher risk PWSs, EPA believes that
considering the full removal efficiency achieved by different types of
treatment plants is appropriate. Because making a site-specific
assessment of removal efficiency at all treatment plants individually
is not feasible, establishing prescribed treatment credits based on
available data is necessary. Accordingly, EPA has concluded that
available data support the higher levels of prescribed credit towards
Cryptosporidium treatment requirements for filtration plants
established by today's rule.

What is the appropriate statistical measure for classifying PWSs into
treatment bins?

    EPA and the Advisory Committee evaluated different statistical
measures for characterizing Cryptosporidium monitoring results to
determine if additional treatment should be required. These measures
included the arithmetic mean, median, 90th percentile, and maximum.
    EPA concluded, consistent with Advisory Committee recommendations,
that Cryptosporidium levels should be characterized by an arithmetic
mean. This conclusion is based on two factors: (1) Available data
suggest that the mean concentration directly relates to the average
risk of the exposed population (i.e., drinking water consumers); and
(2) with a limited number of samples, the mean can be estimated more
accurately than other statistical measures, such as a 90th percentile
estimate.

What degree of additional treatment is needed for higher source water
Cryptosporidium levels?

    Development of the risk-based treatment requirements in today's
rule involved first determining the threshold source-water
Cryptosporidium level at which filtered PWSs should provide additional
treatment to protect public health. The key factors in making this
determination were the estimations of Cryptosporidium risk and
treatment plant removal efficiency discussed previously, along with the
performance of analytical methods for classifying PWSs in different
treatment bins.
    EPA and Advisory Committee deliberations focused on mean source-
water Cryptosporidium concentrations in the range of 0.01 to 0.1
oocysts/L as threshold levels for requiring additional treatment. Based
on the type of risk information shown in Figure IV.B-1, these levels
are estimated to result in an annual infection risk in the range of 1.7
x 10-4 to 6.0 x 10-3 (or 1.7 to 60 infections per
10,000 consumers) for a treatment plant achieving 3-log Cryptosporidium
removal (the treatment efficiency estimated for conventional plants
under existing regulations).
    A shortcoming with establishing the threshold for additional
treatment at 0.01 oocysts/L, however, is that a PWS would exceed this
concentration with only a very few oocysts being detected. For a PWS
collecting monthly 10-L samples and bin classification based on the
maximum running annual average, as required under today's rule,
detecting two oocysts during one year of monitoring would exceed a mean
of 0.01 oocysts/L. Given the uncertainty associated with
Cryptosporidium monitoring, EPA and the Advisory Committee did not
support requiring additional treatment for filtered PWSs based on so
few counts. Although this shortcoming could theoretically be addressed
by a higher sampling frequency, the feasibility of increased sampling
is limited by the capacity of laboratories and the cost of sample
analysis.
    A related concern in establishing the threshold concentration for
requiring additional treatment was bin misclassification. If the
threshold concentration was set at 0.1 oocysts/L, for example, some
PWSs with actual mean source-water concentrations greater than this
level would measure a concentration less than this level and would be
misclassified in the bin that requires no additional treatment.
Consequently, they would not provide sufficient public health
protection. As discussed previously, this type of error is due to the
limited number and volume of samples that can be analyzed, imperfect
method recovery, and variability in Cryptosporidium occurrence.
    Based on these considerations, the Advisory Committee recommended
and today's rule establishes that filtered PWSs must provide additional
treatment for Cryptosporidium when their mean source-water
concentration exceeds 0.075 oocysts/L. At this concentration, PWSs
collecting monthly 10-L samples must count at least nine oocysts in one
year (9 oocysts per 120 L total sample volume) before additional
treatment is required. Further, any PWS with a mean source-water
infectious Cryptosporidium level above 0.1 oocysts/L, which corresponds
to an estimated infection risk range of 1.7 to 6.0 x 10-3,
is highly likely to be appropriately classified in a bin requiring
additional treatment.
    After identifying this first threshold for requiring additional
treatment, determining the Cryptosporidium concentrations that should
bound higher treatment bins was necessary. In making these
determinations, EPA concurred with Advisory Committee recommendations
that sought to balance the possibility of bin misclassification against
equitable risk reduction and public health protection.
    Treatment bins that span a wider concentration range result in
lower bin misclassification rates. The analysis summarized in section
IV.A shows that the monitoring required under today's rule can
accurately characterize a PWS's mean Cryptosporidium level within a
0.5-log margin, but error rates increase for smaller margins (USEPA
2005a). Conversely, treatment bins that span a narrower concentration
range provide more equitable protection from risk among different PWSs.
This is due to identical treatment requirements applying to all PWSs in
the same bin. In consideration of these issues, today's rule
establishes two higher treatment bins at Cryptosporidium concentrations
of 1.0 oocysts/L and 3.0 oocysts/L. These values result in the four
bins shown in Table IV.B-1. Available occurrence data indicate that few
PWSs will measure mean Cryptosporidium concentrations greater than 3.0
oocysts/L, so there is no need to establish a treatment bin above this
level.
    With respect to the degree of additional Cryptosporidium treatment
that PWSs in Bins 2-4 must provide, EPA and the Advisory Committee
considered values of 0.5-log and greater. Today's rule establishes a 1-
log additional treatment requirement for conventional plants in Bin 2.
Because

the concentration range of Bin 2 spans approximately one order of
magnitude, this degree of treatment ensures that plants classified in
Bin 2 will achieve treated water Cryptosporidium levels comparable to
plants in Bin 1. Conventional plants in Bins 3 and 4 must provide 2.0-
and 2.5-log of additional treatment, respectively. As recommended by
the Advisory Committee, these higher additional treatment levels are
required based on the recognition that plants in Bins 3 and 4 have a
much greater potential vulnerability to Cryptosporidium. Consequently,
significantly higher treatment is appropriate to protect public health.
    These additional treatment requirements for conventional treatment
plants in Bins 2-4 are based on a prescribed 3-log Cryptosporidium
treatment credit for compliance with the IESWTR or LT1ESWTR, as
discussed previously. They translate to total Cryptosporidium treatment
requirements of 4.0-, 5.0-, and 5.5-log for Bins 2, 3, and 4,
respectively. Plants receiving higher or lower levels of prescribed
treatment credit are required to provide less or more additional
treatment if classified in Bins 2-4.
    Plants using slow sand or diatomaceous earth filtration, which also
receive a 3-log treatment credit, incur the same additional treatment
requirements as conventional plants if classified in Bins 2-4. Direct
filtration plants, however, must provide 0.5-log greater additional
treatment if classified in Bins 2-4 because they receive a 2.5-log
prescribed credit. EPA expects, though, that most direct filtration
plants will be classified in Bin 1 because direct filtration is
typically applied only to higher quality source waters.
    Because EPA is unable to establish a prescribed treatment credit
for other types of filtration technologies like membranes, bag filters,
and cartridge filters, today's rule requires that States assign a
treatment credit to a particular filtration product. This credit then
determines the amount of additional treatment that a plant using this
product must provide if classified in Bins 2-4 in order to achieve the
required total treatment level. Section IV.D provides criteria for
assigning Cryptosporidium treatment credit to membranes, bag filters,
and cartridge filters.
    As described in Section IV.D, today's rule establishes a wide range
of treatment and control options through the microbial toolbox for PWSs
to meet additional Cryptosporidium treatment requirements. PWSs may
choose any option or combination of options from the microbial toolbox
to meet the treatment requirements of plants in Bin 2. For plants in
Bins 3 or 4, though, PWSs must achieve at least 1-log of the additional
treatment requirement using UV, ozone, chlorine dioxide, membranes, bag
filters, cartridge filters, or bank filtration. EPA is establishing
this provision in today's rule as recommended by the Advisory Committee
because these processes will serve as significant additional treatment
barriers for PWSs with the highest levels of pathogens in their
sources.

How should PWSs calculate their treatment bin classification?

    The specific calculations that PWSs use to determine their bin
classification are based on analyses of misclassification rates and
bias. As described in section IV.A, today's rule requires PWSs to
collect at least 24 samples (except for plants that operate only part-
year) when they monitor for Cryptosporidium. Most PWSs will collect
these 24 samples over two years, but PWSs may sample at a higher
frequency and small PWSs may complete this monitoring in one year.
These differences affect the bin classification calculation.
    PWSs that sample monthly over two years (24 samples total) must use
the maximum running annual average (Max-RAA) for bin classification
because this achieves a low false negative rate (the likelihood a PWS
will be incorrectly classified in a lower bin). In comparison, if such
PWSs used the mean of all samples over two years for bin
classification, the false negative rate would be almost four times
higher (see Table IV.B.4).
    PWSs that choose to sample at least twice per month over two years
(48 samples total) must use the mean of all 48 samples for their bin
classification. This approach achieves a low false negative rate
similar to the Max-RAA for 24 samples and, in addition, reduces the
false positive rate (the likelihood a PWS will be incorrectly
classified in higher bin--see Table IV.B.4). Due to the lower false
positive rate associated with 48 samples, EPA expects that some PWSs
will choose to sample for Cryptosporidium twice per month.
    Small PWSs (serving fewer than 10,000 people) that complete their
Cryptosporidium monitoring over one year must use the mean of all 24
samples for bin classification. This approach has a higher false
negative rate than the approaches allowed for PWSs that monitor over
two years. However, it is the only feasible option for PWSs that
conduct just one year of Cryptosporidium sampling. Averaging sample
concentrations over less than one year is not appropriate (except in
the case of plants that operate only part-year that monitor for less
than one year) as this would bias the bin classification due to
seasonal variation in water quality.

  Table IV.B-4.--False Positive and False Negative Rates for Monitoring
           and Binning Strategies Considered for the LT2ESWTR
------------------------------------------------------------------------
                                                   False        False
                   Strategy                      positive 1   negative 2
------------------------------------------------------------------------
48 sample arithmetic mean.....................         1.7%         1.4%
24 sample Max-RAA.............................         5.3%         1.7%
24 sample arithmetic mean.....................         2.8%        6.2%
------------------------------------------------------------------------
1 False positive rates calculated for systems with Cryptosporidium
  concentrations 0.5 log below the Bin 1 boundary of 0.075 oocysts/L.
2 False negative rates calculated for systems with Cryptosporidium
  concentrations 0.5 log above the Bin 1 boundary of 0.075 oocysts/L.

    Two additional considerations that relate to characterizing
Cryptosporidium monitoring results to determine treatment requirements
are (1) fewer than 100 percent of oocysts in a sample are recovered and
counted by the analyst and (2) not all the oocysts measured with
Methods 1622 or 1623 are capable of causing infection. These two
factors are offsetting, in that oocyst counts not adjusted for recovery
tend to underestimate the true concentration, while the total oocyst
count typically overestimates the infectious concentration that
presents a health risk.
    As described in section III, matrix spike data indicate that
average recovery of Cryptosporidium oocysts with Methods 1622 or 1623
in a national monitoring program will be approximately 40 percent.
Regarding the fraction of oocysts that are infectious, LeChevallier et
al. (2003) tested natural waters for Cryptosporidium using both Method
1623 and a method (cell culture-PCR) to test for infectivity. Results
suggested that 37 percent of the Cryptosporidium oocysts detected by
Method 1623 were infectious. This finding is consistent with the
observation that 37 percent of the oocysts counted during the ICRSS
using Methods 1622 or 1623 had internal structures, which indicate a
higher likelihood of infectivity (among the remaining oocysts, 47
percent had amorphous structures and 16 percent were empty).
    While it is not possible to establish a precise value for method
recovery or the fraction of oocysts that are infectious,

available data suggest that these parameters may be of similar
magnitude. Consequently, the Advisory Committee recommended that
monitoring results should not be adjusted to account for either
recovery or the fraction infectious. EPA concurs with this
recommendation and today's rule requires that PWSs be classified in
treatment bins using the total number of Cryptosporidium oocysts
counted, without further adjustment. The LT2ESWTR treatment bins in
today's rule are constructed to reflect this approach.
3. Summary of Major Comments
    For filtered PWS treatment requirements in the LT2ESWTR proposal,
EPA received significant public comment on the risk-based approach to
requiring additional treatment, the role of States in determining bin
classification, and the treatment credit for filtration plants. The
following discussion summarizes comments in these areas and EPA's
responses.
    Most commenters supported the risk-based approach of the LT2ESWTR
in which filtered PWSs monitor for microbial contaminants and only
those PWSs finding higher levels of contamination are required to
provide additional treatment for Cryptosporidium. Among these comments,
many stated support for the four treatment bins for filtered PWSs, with
some noting that future research will indicate whether the bins should
be restructured in a later rulemaking. Several commenters expressed
support for EPA's combination of the Stage 2 DBPR and LT2ESWTR as
essential to creating a balanced approach between DBP control and
microbial risk.
    A few commenters opposed the expenditure of funds to reduce risk
from Cryptosporidium on the basis that epidemiological evidence
suggests this risk is low and most communities have not experienced
cryptosporidiosis outbreaks. EPA agrees that additional treatment for
Cryptosporidium in drinking water is not warranted in all communities.
Under today's rule, most PWSs are expected to be classified in the
lowest bin, which requires no additional treatment. However, based on
risk information presented in USEPA (2005a) and summarized in this
preamble, EPA believes that additional treatment is necessary to
protect public health in PWSs with the highest Cryptosporidium levels.
Further, as described in USEPA (2005a), EPA's assessment of
Cryptosporidium risk in drinking water is consistent with the limited
available epidemiological data on disease incidence.
    With respect to the role of States in bin classification, most
commenters recommended that States assign or approve the bin
classification for their PWSs. Commenters maintained that State
approval of bin classification is an inherent governmental function and
will avoid confusion as to the level of treatment each PWS must
provide. Further, the approval process will provide an opportunity for
dialog between States and PWSs. EPA agrees with these comments and
today's rule requires PWSs to submit their calculation of bin
classification to the State for review. If the PWS does not hear back
from the State, it must proceed to apply the level of treatment
appropriate for its calculated bin classification in accordance with
its applicable compliance schedule.
    In regard to the Cryptosporidium treatment credit that should be
awarded to filtration plants, many commenters supported the 3-log
Cryptosporidium removal credit for conventional treatment and slow sand
filtration. Some comments included data showing that conventional
treatment can achieve greater than 4-log removal of Cryptosporidium,
and several commenters stated concerns that EPA has underestimated the
level of treatment achievable through conventional treatment.
Commenters supported the inclusion of plants using softening and
dissolved air flotation for conventional treatment credit and requested
that EPA extend this credit to similar treatment trains using other
types of clarification processes.
    EPA recognizes that studies show conventional treatment can achieve
more than 3-log Cryptosporidium removal under optimal conditions.
However, studies also demonstrate that removal efficiencies can be
significantly less for suboptimal plant set-up and operation. EPA does
not expect that all plants will operate under optimal conditions at all
times. Consequently, today's rule awards a prescribed 3-log credit to
conventional plants complying with the IESWTR or LT1ESWTR and allows
plants to receive higher credit through demonstrating low finished
water turbidity or through an alternative demonstration of performance,
as describe in section IV.D. EPA agrees that plants using alternative
clarification process that involves solids removal between coagulation
and filtration should qualify for 3-log credit and today's rule
provides for this.

C. Unfiltered System Cryptosporidium Treatment Requirements

1. Today's Rule
    Today's rule requires all PWSs that use a surface water or GWUDI
source and are unfiltered to provide treatment for Cryptosporidium. The
degree of required treatment depends on the level of Cryptosporidium in
the source water, as determined through required monitoring. Further,
unfiltered PWSs must meet overall treatment requirements using at least
two disinfectants and must continue to meet all applicable filtration
avoidance criteria. Details of these requirements follow.
    a. Determination of mean Cryptosporidium level. Following
completion of the required initial source water monitoring described in
section IV.A, each unfiltered PWS must determine the arithmetic mean of
all its Cryptosporidium sample results generated during the monitoring
period. As required for filtered PWSs, individual sample results must
be calculated as the total number of oocysts counted, divided by the
volume assayed (see section V.K for details). Samples are not adjusted
for method recovery and, in samples where no oocysts are detected, the
result is treated as zero.
    Unfiltered PWSs must report their mean Cryptosporidium level to the
State for approval (see section IV.G for specific reporting dates). The
report must include a summary of the data used to determine the mean
concentration. If the State does not respond to a PWS regarding its
mean Cryptosporidium level, the PWS must comply with the
Cryptosporidium treatment requirements of today's rule, as described
next, based on the reported level.
    If EPA does not amend today's rule before the second round of
monitoring described in section IV.A, unfiltered PWSs must recalculate
their mean Cryptosporidium level using results from the second round of
monitoring. Unfiltered PWSs must report this level to the State as
described for the initial round of monitoring.
    b. Cryptosporidium treatment requirements. Unfiltered PWSs must
comply with the following treatment requirements based on their mean
source-water Cryptosporidium level: if the level is less than or equal
to 0.01 oocysts/L then at least 2-log Cryptosporidium inactivation is
required; if the level is greater than 0.01 oocysts/L, or if the
unfiltered PWS chooses not to monitor for Cryptosporidium, then at
least 3-log Cryptosporidium inactivation is

required. See section IV.G for treatment compliance dates.
    EPA has developed criteria, described in section IV.D, to award
Cryptosporidium inactivation credit for treatment with chlorine
dioxide, ozone, or UV light. Unfiltered PWSs may use any of these
disinfectants to meet their Cryptosporidium inactivation requirements
under today's rule. Further, unfiltered PWSs must achieve the following
with respect to disinfection treatment:
    (1) A PWS that uses chlorine dioxide or ozone and fails to achieve
the required level of Cryptosporidium inactivation on more than one day
in the calendar month is in violation of the treatment technique
requirement.
    (2) A PWS that uses UV light and fails to achieve the required
level of Cryptosporidium inactivation in at least 95 percent of the
water delivered to the public every month is in violation of the
treatment technique requirement.
    c. Use of two disinfectants. Unfiltered PWSs must use at least two
different disinfectants to provide 4-log virus, 3-log Giardia lamblia,
and 2- or 3-log Cryptosporidium inactivation as required under 40 CFR
141.72(a) and today's rule. Further, each of two disinfectants must
achieve by itself the total inactivation required for one of these
target pathogens. This requirement does not modify the existing
requirement under 40 CFR 141.72(a) for PWSs to provide a disinfectant
residual in the distribution system.
2. Background and Analysis
    The intent of the Cryptosporidium treatment requirements for
unfiltered PWSs in today's final rule is to ensure that they achieve
public health protection equivalent to that achieved by filtered PWSs.
These requirements are unchanged from the August 11, 2003 proposal
(USEPA 2003a), and they reflect consensus recommendations by the Stage
2 M-DBP Advisory Committee (USEPA 2000a). The following discussion
summarizes the Agency's basis for establishing risk-targeted
Cryptosporidium treatment requirements for unfiltered PWSs in today's
rule and for requiring the use of two disinfectants.
    a. Basis for Cryptosporidium treatment requirements. As described
in section III, available data suggest that unfiltered PWSs must take
additional steps to achieve public health protection against
Cryptosporidium equivalent to that provided by filtered PWSs.
    In occurrence data from the ICR, the median Cryptosporidium level
in unfiltered PWS sources was 0.0079 oocysts/L, which is approximately
10 times less than the median level of 0.052 oocysts/L in filtered PWS
sources. In translating these source water levels to finished water
concentrations, EPA and the Advisory Committee assumed that
conventional filtration treatment plants in compliance with the IESWTR
or LT1ESWTR achieve an average of 3-log (99.9 percent) removal of
Cryptosporidium. Existing regulations do not require unfiltered PWSs to
provide any treatment for Cryptosporidium.
    If the median source water Cryptosporidium level in filtered PWSs
is approximately 10 times higher than in unfiltered PWSs, and filtered
PWSs achieve 3-log Cryptosporidium removal, then the median finished
water Cryptosporidium level in filtered PWSs is approximately 100 times
lower than in unfiltered PWSs. Thus, these data suggest that most
unfiltered PWSs must provide 2-log Cryptosporidium treatment to ensure
equivalent public health protection.
    Some unfiltered PWSs must provide greater than 2-log
Cryptosporidium treatment to ensure equitable protection, depending on
their source water level. Under today's rule, the Cryptosporidium
treatment requirements for filtered PWSs, as described in section
IV.B.1, will achieve mean finished water Cryptosporidium levels of less
than 1 oocyst/10,000 L. An unfiltered PWS with a mean source water
Cryptosporidium concentration above 0.01 oocysts/L would have to
provide at least 3-log inactivation to achieve an equivalent finished
water Cryptosporidium level.
    As stated earlier, EPA has determined that UV light is a feasible
technology for PWSs of all sizes, including unfiltered PWSs, to
inactivate Cryptosporidium. In addition, treating for Cryptosporidium
using ozone is feasible for some unfiltered PWSs. Inactivating
Cryptosporidium with chlorine dioxide, while allowed under today's
rule, does not appear to be feasible for most unfiltered PWSs due to
regulatory limits on chlorite--a chlorine dioxide byproduct.
    Based on these findings, today's rule requires all unfiltered PWSs
to provide at least 2-log Cryptosporidium inactivation, and to provide
at least 3-log inactivation if the mean source water level exceeds 0.01
oocysts/L. These treatment requirements will ensure that unfiltered
PWSs achieve public health protection against Cryptosporidium that is
comparable to filtered PWSs in the finished water that is distributed
to consumers.
    Available data indicate that no unfiltered PWSs will show measured
mean source water Cryptosporidium levels of 0.075 oocysts/L or higher--
the level at which a filtered PWS must provide at least 4-log
Cryptosporidium under today's rule. Consequently, EPA is not
establishing treatment requirements in today's rule to address
Cryptosporidium at this higher level. Under existing regulations (40
CFR 141.171 and 141.521), unfiltered PWSs must maintain a watershed
control program that minimizes the potential for contamination by
Cryptosporidium oocysts in the source water. If the measured mean
Cryptosporidium level in an unfiltered PWS is 0.075 oocysts/L or
higher, EPA believes the State should critically evaluate the adequacy
of the watershed control program.
    Under today's rule, unfiltered PWSs using ozone or chlorine dioxide
to treat for Cryptosporidium must demonstrate the required 2- or 3-log
inactivation every day the PWS serves water to the public, except any
one day each month. Existing regulations (40 CFR 141.72(a)(1)) require
unfiltered PWSs to ensure inactivation of 3-log Giardia lamblia and 4-
log viruses every day except any one day per month. Consequently,
today's rule extends this compliance standard to Cryptosporidium
inactivation.
    For unfiltered PWSs that use UV to treat for Cryptosporidium,
today's rule requires demonstration of the required 2- or 3-log
inactivation in at least 95 percent of the water delivered to the
public every month. EPA intends this standard to be comparable to the
``every day except any one day per month'' standard established for
ozone and chlorine dioxide. Because UV disinfection systems will
typically consist of multiple reactors that will be monitored
continuously, EPA believes that a compliance standard based on the
percentage of water disinfected to the required level is more
appropriate than a single daily measurement. Section IV.D describes an
equivalent standard for filtered PWSs.
    b. Basis for requiring the use of two disinfectants. Unfiltered
PWSs must use at least two different disinfectants to meet the
inactivation requirements for Cryptosporidium (2- or 3-log), Giardia
lamblia (3-log) and viruses (4-log), and each of two disinfectants must
achieve by itself the total inactivation required for one of these
target pathogens. For example, a PWS could use UV light to achieve 3-
log inactivation of Giardia lamblia and Cryptosporidium and use
chlorine to provide 4-log virus inactivation. The use of two
disinfectants protects public health by creating multiple barriers
against microbial pathogens. This has two

general advantages over a single barrier: improved reliability and a
broader spectrum of efficacy.
    Because unfiltered PWSs rely solely on inactivation for microbial
treatment, an unfiltered PWS using only one disinfectant would provide
no primary microbial treatment if that disinfection process were to
fail. While disinfection processes should be designed for a high level
of reliability, they are not generally 100 percent reliable. Existing
regulations and today's rule recognize this limitation by allowing
unfiltered PWSs to fail to achieve required disinfection levels one day
per month. Consequently, EPA believes that for effective public health
protection, unfiltered PWSs should use at least two primary
disinfection processes. If one process fails, a second process will
provide some degree of protection against pathogens.
    A second advantage of a PWS using multiple disinfectants is that
this approach will typically be more effective against a broad spectrum
of pathogens. The efficacy of different disinfectants against different
types of pathogens varies widely. For example, UV light appears to be
very effective for inactivating protozoa like Cryptosporidium and
Giardia lamblia, but is less effective against certain enteric viruses
like adenovirus. Chlorine, however, is highly effective against enteric
viruses but less effective against protozoa. As a result, multiple
disinfectants will generally provide more effective inactivation of a
wide range of pathogens than a single disinfectant.
    c. Filtration avoidance. Today's rule does not withdraw or modify
any existing criteria for avoiding filtration under 40 CFR 141.71.
Accordingly, unfiltered PWSs must continue to comply with all existing
filtration avoidance criteria. EPA believes these criteria help to
ensure that watershed protection provides a microbial barrier in those
PWSs that do not filter.
    Further, today's rule does not establish any new criteria for
filtration avoidance. In the proposed LT2ESWTR, EPA indicated that
compliance with DBP standards under the Stage 2 DBPR would be
incorporated into the criteria for filtration avoidance. However, EPA
has not done this in today's final rule in order to give States more
flexibility in working with unfiltered PWSs to comply with the Stage 2
DBPR.
3. Summary of Major Comments
    EPA received significant public comment on the following treatment
requirements for unfiltered PWSs in the LT2ESWTR proposal: the
requirement for all unfiltered PWSs to provide at least 2-log
Cryptosporidium inactivation, treatment requirements for unfiltered
PWSs with high Cryptosporidium levels, and the requirement for
unfiltered PWSs to use at least two disinfectants. A summary of these
comments and EPA's responses follows.
    Several commenters supported the requirement that all unfiltered
PWSs achieve at least 2-log inactivation of Cryptosporidium, noting
that this was part of the Agreement in Principle (USEPA 2000a). Some
commenters, however, requested that EPA not establish a minimum
Cryptosporidium treatment level due to the following factors:
monitoring of unfiltered PWS sources has shown very low levels of
Cryptosporidium, and some sources may have no Cryptosporidium; the
Cryptosporidium in an unfiltered PWS source are likely to be of non-
human origin and are less likely to infect humans; and disease
incidence data have not established a link between unfiltered PWSs and
cryptosporidiosis in consumers.
    In response, EPA continues to believe that all unfiltered PWSs
should provide treatment for Cryptosporidium to protect public health.
Monitoring has shown that unfiltered PWS sources are contaminated with
Cryptosporidium, and no source is likely to be entirely free of
Cryptosporidium due to the ubiquity of Cryptosporidium in both human
and many animal populations. Studies, such as those cited in section
III, have established that Cryptosporidium from animals can infect
humans. EPA does not regard the absence of cryptosporidiosis cases
attributed to drinking water in a particular community as evidence that
no treatment for Cryptosporidium is needed. As described in section
III, cryptosporidiosis incidence data generally do not indicate overall
disease burden because most cases are undetected, unreported, and not
traced to a particular source.
    Some commenters recommended that EPA require only 1-log
Cryptosporidium inactivation for unfiltered PWSs that demonstrate
source water levels below 0.001 oocysts/L. EPA does not support this
approach, though, due to concerns with the reliability of monitoring to
establish such an extremely low level of Cryptosporidium. In addition,
UV light is a feasible technology for unfiltered PWSs of all sizes to
achieve at least 2-log Cryptosporidium inactivation. For these reasons,
EPA has concluded that the minimum Cryptosporidium treatment level
should be 2-log, as recommended by the Advisory Committee.
    In the proposed LT2ESWTR, EPA requested comment on the treatment
that should be required if an unfiltered PWS measured a Cryptosporidium
level of 0.075 oocysts/L or higher--the concentration at which a
filtered PWS must provide at least 4-log treatment. Several commenters
supported equivalent treatment requirements (i.e., at least 4-log
reduction) for unfiltered and filtered PWSs with Cryptosporidium at
this level. Other commenters stated that available data indicate no
unfiltered PWSs are likely to measure Cryptosporidium at such a high
level.
    EPA agrees that available data on Cryptosporidium occurrence
suggest that no unfiltered PWSs will measure a mean level of 0.075
oocysts/L or higher. Moreover, establishing a 4-log treatment
requirement on the precautionary basis that an unfiltered PWS might
measure a high level of Cryptosporidium has a significant cost--it
would require any unfiltered PWS to provide 4-log, rather than 3-log,
inactivation to avoid Cryptosporidium monitoring. EPA expects that many
small unfiltered PWSs will choose to provide 3-log Cryptosporidium
inactivation rather than monitor for Cryptosporidium. Accordingly, EPA
has concluded that establishing a 4-log Cryptosporidium treatment
requirement for unfiltered PWSs that measure a Cryptosporidium level of
0.075 oocysts/L or higher is unnecessary and inappropriate at this
time. In the event that an unfiltered PWS does measure Cryptosporidium
at this level, the State can require the PWS to take steps to reduce
the contamination under existing watershed control program requirements
for unfiltered PWSs.
    Some commenters supported the requirement for unfiltered PWSs to
use at least two disinfectants to meet overall inactivation
requirements for Cryptosporidium, Giardia lamblia, and viruses and for
each disinfectant to achieve the total inactivation required for one
target pathogen. These commenters stated that this requirement will
improve inactivation against a wide variety of pathogens and increase
treatment reliability. Other commenters, though, opposed this
requirement for a number of reasons: it will unnecessarily limit the
ability of PWSs to minimize DBPs, there is no similar requirement for
filtered PWSs, the requirement for each disinfectant to achieve the
total inactivation for one pathogen goes beyond the Agreement in
Principle, and EPA has not provided a risk analysis to justify the
requirement.

    In response, EPA believes that the benefits of both redundancy and
a broad spectrum of microbial protection justify requiring the use of
two disinfectants. Further, requiring each disinfectant to achieve the
full inactivation of one target pathogen establishes a minimal
performance level so that each disinfectant will serve as a substantive
barrier. In most cases, PWSs will comply with this requirement by using
UV or ozone to inactivate Giardia lamblia and Cryptosporidium and using
chlorine to inactivate viruses.

D. Options for Systems To Meet Cryptosporidium Treatment Requirements

1. Microbial Toolbox Overview
    Today's rule includes a variety of treatment and control options,
collectively termed the ``microbial toolbox,'' that PWSs can implement
to comply with additional Cryptosporidium treatment requirements.
Options in the microbial toolbox include source protection and
management programs, prefiltration processes, treatment performance
programs, additional filtration components, and inactivation
technologies. The Stage 2 M-DBP Advisory Committee recommended the
microbial toolbox to provide PWSs with broad flexibility in selecting
cost-effective LT2ESWTR compliance strategies.
    Most options in the microbial toolbox carry prescribed credits
toward Cryptosporidium treatment requirements. PWSs receive these
credits by demonstrating compliance with required design and
operational criteria, which are described in the sections that follow.
In addition, States may award treatment credits other than the
prescribed credit through a ``demonstration of performance,'' which
involves site-specific testing by a PWS with a State-approved protocol.
Under a demonstration of performance, a State may award credit to a
treatment plant or to a unit process of a treatment plant that is
higher or lower than the prescribed credit. This option also allows
States to award credit to a unit process that does not meet the design
and operational criteria in the microbial toolbox for prescribed
credit.
    To be eligible for treatment credit for a microbial toolbox option,
PWSs must initially report compliance with design criteria, where
required, to the State (some options do not require design criteria).
Thereafter, for most options, PWSs must report compliance with required
operational criteria to the State each month (the watershed control
program option requires yearly reporting). Failure by a PWS in any
month to demonstrate treatment credit equal to or greater than its
Cryptosporidium treatment requirements under today's rule is a
treatment technique violation. This violation lasts until the PWS
demonstrates that it is meeting criteria for sufficient treatment
credit to satisfy its Cryptosporidium treatment requirements.
    As described in section IV.B, filtered PWSs may use any option or
combination of options from the microbial toolbox to comply with the
additional Cryptosporidium treatment requirements of Bin 2. PWSs in
Bins 3 or 4 must achieve at least 1-log of the additional
Cryptosporidium treatment requirement by using ozone, chlorine dioxide,
UV, membranes, bag filtration, cartridge filtration, or bank
filtration.
    If allowed by the State, PWSs may use different microbial toolbox
options in different months to comply with Cryptosporidium treatment
requirements under today's rule. For example, a PWS in Bin 2, which
requires 1-log additional Cryptosporidium treatment, could comply with
this requirement in one month using ``individual filter performance,''
which carries a 1-log credit; in a subsequent month, this PWS could use
``combined filter performance'' and ``presedimentation basin with
coagulation,'' which each carry 0.5-log credit. This approach is
intended to provide greater operational flexibility to PWSs. It allows
a PWS to receive treatment credit for a microbial toolbox option in any
month the PWS is able to meet required operational criteria, even if
the PWS does not meet these criteria during all months of the year.
    Table IV.D-1 summarizes prescribed treatment credits and associated
design and operational criteria for microbial toolbox options. The
sections that follow describe each toolbox option in detail. In
addition, EPA has developed three guidance documents to assist PWSs
with selecting and implementing microbial toolbox options: Toolbox
Guidance Manual, UV Disinfection Guidance Manual, and Membrane
Filtration Guidance Manual. Each may be acquired from EPA's Safe
Drinking Water Hotline, which can be contacted as described under FOR
FURTHER INFORMATION CONTACT at the beginning of this notice.

     Table IV.D-1.--Microbial Toolbox: Options, Credits and Criteria
------------------------------------------------------------------------
                                      Cryptosporidium treatment credit
          Toolbox option            with design and operational criteria
                                                     \1\
------------------------------------------------------------------------
            Source Protection and Management Toolbox Options
------------------------------------------------------------------------
Watershed control program.........  0.5-log credit for State-approved
                                     program comprising required
                                     elements, annual program status
                                     report to State, and regular
                                     watershed survey. Unfiltered PWSs
                                     are not eligible for credit.
Alternative source/intake           No prescribed credit. PWSs may
 management.                         conduct simultaneous monitoring for
                                     treatment bin classification at
                                     alternative intake locations or
                                     under alternative intake management
                                     strategies.
-----------------------------------
                      Prefiltration Toolbox Options
------------------------------------------------------------------------
Presedimentation basin with         0.5-log credit during any month that
 coagulation.                        presedimentation basins achieve a
                                     monthly mean reduction of 0.5-log
                                     or greater in turbidity or
                                     alternative State-approved
                                     performance criteria. To be
                                     eligible, basins must be operated
                                     continuously with coagulant
                                     addition and all plant flow must
                                     pass through basins.
Two-stage lime softening..........  0.5-log credit for two-stage
                                     softening where chemical addition
                                     and hardness precipitation occur in
                                     both stages. All plant flow must
                                     pass through both stages. Single-
                                     stage softening is credited as
                                     equivalent to conventional
                                     treatment.
Bank filtration...................  0.5-log credit for 25-foot setback;
                                     1.0-log credit for 50-foot setback;
                                     horizontal and vertical wells only;
                                     aquifer must be unconsolidated sand
                                     containing at least 10 percent
                                     fines (as defined in rule); average
                                     turbidity in wells must be less
                                     than 1 NTU. PWSs using existing
                                     wells followed by filtration must
                                     monitor the well effluent to
                                     determine bin classification and
                                     are not eligible for additional
                                     credit.
-----------------------------------

                  Treatment Performance Toolbox Options
------------------------------------------------------------------------
Combined filter performance.......  0.5-log credit for combined filter
                                     effluent turbidity less than or
                                     equal to 0.15 NTU in at least 95
                                     percent of measurements each month.
Individual filter performance.....  0.5-log credit (in addition to 0.5-
                                     log combined filter performance
                                     credit) if individual filter
                                     effluent turbidity is less than or
                                     equal to 0.15 NTU in at least 95
                                     percent of samples each month in
                                     each filter and is never greater
                                     than 0.3 NTU in two consecutive
                                     measurements in any filter.
Demonstration of performance......  Credit awarded to unit process or
                                     treatment train based on a
                                     demonstration to the State with a
                                     State-approved protocol.
-----------------------------------
                  Additional Filtration Toolbox Options
------------------------------------------------------------------------
Bag and cartridge filters.........  Up to 2-log credit with
                                     demonstration of at least 1-log
                                     greater removal in a challenge test
                                     when used singly. Up to 2.5-log
                                     credit with demonstration of at
                                     least 0.5-log greater removal in a
                                     challenge test when used in series.
Membrane filtration...............  Log credit equivalent to removal
                                     efficiency demonstrated in
                                     challenge test for device if
                                     supported by direct integrity
                                     testing.
Second stage filtration...........  0.5-log credit for second separate
                                     granular media filtration stage if
                                     treatment train includes
                                     coagulation prior to first filter.
Slow sand filters.................  2.5-log credit as a secondary
                                     filtration step; 3.0-log credit as
                                     a primary filtration process. No
                                     prior chlorination.
-----------------------------------
                      Inactivation Toolbox Options
------------------------------------------------------------------------
Chlorine dioxide..................  Log credit based on measured CT in
                                     relation to CT table.
Ozone.............................  Log credit based on measured CT in
                                     relation to CT table.
UV................................  Log credit based on validated UV
                                     dose in relation to UV dose table;
                                     reactor validation testing required
                                     to establish UV dose and associated
                                     operating conditions.
------------------------------------------------------------------------
\1\ Table provides summary information only; refer to following preamble
  and regulatory language for detailed requirements.

2. Watershed Control Program

a. Today's Rule
    Filtered PWSs can receive 0.5-log credit toward Cryptosporidium
treatment requirements under today's rule for implementing a State-
approved watershed control program designed to reduce the level of
Cryptosporidium. To be eligible to receive this credit initially, PWSs
must perform the following steps:
     Notify the State of the intent to develop a new or
continue an existing watershed control program for Cryptosporidium
treatment credit no later than two years prior to the date the PWS must
comply with additional Cryptosporidium treatment requirements under
today's rule.
     Submit a proposed watershed control plan to the State for
approval no later than one year prior to the date the PWS must comply
with additional Cryptosporidium treatment requirements under today's
rule. The watershed control plan must contain these elements:
    (1) The designation of an ``area of influence'' in the watershed,
which is defined as the area outside of which the likelihood of
Cryptosporidium contamination affecting the treatment plant intake is
not significant;
    (2) The identification of both potential and actual sources of
Cryptosporidium contamination, including a qualitative assessment of
the relative impact of these contamination sources on water quality at
the treatment plant intake;
    (3) An analysis of control measures that could mitigate the sources
of Cryptosporidium contamination, including the relative effectiveness
of control measures in reducing Cryptosporidium loading to the source
water and their feasibility; and
    (4) A statement of goals and specific actions the PWS will
undertake to reduce source water Cryptosporidium levels, including a
description of how the actions will contribute to specific goals,
watershed partners and their roles, resource requirements and
commitments, and a schedule for plan implementation.
    If the State approves the watershed control plan for
Cryptosporidium treatment credit, PWSs must perform the following steps
to be eligible to maintain the credit:
     Submit an annual watershed control program status report
to the State no later than a date specified by the State. The status
report must describe the following: (1) how the PWS is implementing the
approved watershed control plan; (2) the adequacy of the plan to meet
its goals; (3) how the PWS is addressing any shortcomings in plan
implementation; and (4) any significant changes that have occurred in
the watershed since the last watershed sanitary survey.
     Notify the State prior to making any significant changes
to the approved watershed control plan. If any change is likely to
reduce the planned level of source water protection, the PWS must
include in this notification a statement of actions that will be taken
to mitigate this effect.
     Perform a watershed sanitary survey no less frequently
than the PWS must undergo a sanitary survey under 40 CFR
142.16(b)(3)(i), which is every three to five years, and submit the
survey report to the State for approval. The State may require a PWS to
perform a watershed sanitary survey at an earlier date if the State
determines that significant changes may have occurred in the watershed
since the previous sanitary survey. A person approved by the State must
conduct the watershed sanitary survey and the survey must meet
applicable State guidelines. The watershed sanitary survey must
encompass the area of influence as identified in the State-approved
watershed control plan, assess the implementation of actions to reduce
source water Cryptosporidium levels, and identify any significant new
sources of Cryptosporidium.
    PWSs are eligible to receive Cryptosporidium treatment credit under
today's rule for preexisting watershed control programs (e.g., programs
in place at the time of rule promulgation).

To be eligible for credit, such programs must meet the requirements
stated in this section and the watershed control plan must address
future actions that will further reduce source water Cryptosporidium
levels.
    If the State determines that a PWS is not implementing the approved
watershed control plan (i.e., the PWS is not carrying out the actions
on the schedule in the approved plan), the State may revoke the
Cryptosporidium treatment credit for the watershed control program.
Failure by a PWS to demonstrate treatment credit at least equal to its
Cryptosporidium treatment requirement under today's rule due to such a
revocation of credit is a treatment technique violation. The violation
lasts until the State determines that the PWS is implementing an
approved watershed control plan or is otherwise achieving the required
level of Cryptosporidium treatment credit.
    PWSs must make the approved watershed control plan, annual status
reports, and watershed sanitary surveys available to the public upon
request. These documents must be in a plain language style and include
criteria by which to evaluate the success of the program in achieving
plan goals. If approved by the State, the PWS may withhold portions of
these documents based on security considerations.
    Unfiltered PWSs are not eligible to receive Cryptosporidium
treatment credit for a watershed control program under today's rule.
Under existing regulations (40 CFR 141.71), unfiltered PWSs must
maintain a watershed control program that minimizes the potential for
contamination by Cryptosporidium as a condition for avoiding
filtration.

b. Background and Analysis

    Cryptosporidium enters drinking water through fecal contamination
of PWS source waters. Implementing a watershed control program that
reduces or treats sources of fecal contamination in PWS sources will
benefit public health by lowering the exposure of drinking water
consumers to Cryptosporidium and other pathogenic microorganisms. In
addition, a watershed control program may enhance treatment plant
management practices through generating knowledge of the sources, fate,
and transport of pathogens.
    The Stage 2 M-DBP Advisory Committee recommended 0.5-log
Cryptosporidium treatment credit for a watershed control program (USEPA
2000a), and the August 11, 2003 proposal included criteria for PWSs to
receive this credit (USEPA 2003a). The following discussion summarizes
the basis for this credit and for differences in associated
requirements between the proposal and today's final rule.
    The efficacy of a watershed control program in reducing levels of
Cryptosporidium and other microbial pathogens depends on the ability of
a PWS to identify and control sources of fecal contamination. The fecal
sources that are significant in a particular watershed and the control
measures that will be effective in mitigating these sources are site
specific. Consequently, EPA believes that States should determine
whether a watershed control program developed by a PWS to reduce
Cryptosporidium contamination warrants 0.5-log treatment credit.
Accordingly, today's rule requires State approval of watershed control
programs for PWSs to receive credit.
    If a PWS intends to implement a watershed control program to comply
with Cryptosporidium treatment requirements under today's rule, EPA
believes the PWS should notify the State at least two years prior to
the required treatment compliance date. This notification will give the
State an opportunity to communicate with the PWS regarding site-
specific considerations for a watershed control program. Further, the
PWS should submit the proposed watershed control plan to the State for
approval at least one year prior to the treatment compliance date. This
schedule will give the State time to evaluate the program for approval
and, if necessary, allow the PWS to make modifications necessary for
approval. Thus, today's rule establishes these reporting deadlines.
    The required elements for a watershed control plan in today's rule
are the minimum necessary for a program that will be effective in
reducing levels of Cryptosporidium and other pathogens in a treatment
plant intake. These elements include defining the area of the watershed
where contamination can affect the intake water quality, identifying
sources of contamination within this area, evaluating control measures
to reduce contamination, and developing an action plan to implement
specific control measures.
    EPA encourages PWSs to leverage other Federal, State, and local
programs in developing the elements of their watershed control plans.
For example, SDWA section 1453 requires States to carry out a source
water assessment program (SWAP) for PWSs. Depending on how a State
implements this program, the SWAP may be used to define the area of
influence in the watershed and identify actual and potential
contamination sources. In 2002, EPA launched the Watershed Initiative
(67 FR 36172, May 23, 2002) (USEPA 2002b), which will provide grants to
support watershed-based approaches to preventing, reducing, and
eliminating water pollution. In addition, EPA recently promulgated
regulations for Concentrated Animal Feeding Operations that will limit
discharges that contribute microbial pathogens to watersheds.
    Many PWSs do not control the watersheds of their sources of supply.
Their watershed control plans should involve partnerships with
watershed landowners and government agencies that have authority over
activities in the watershed that may contribute Cryptosporidium to the
water supply. Stakeholders that control activities that could
contribute to Cryptosporidium contamination include municipal
government and private operators of wastewater treatment plants,
livestock farmers and persons who spread manure, individuals with
failing septic systems, logging operations, and other government and
commercial organizations.
    After a State approves a watershed control plan for a PWS and
initially awards 0.5-log Cryptosporidium treatment credit, the PWS must
submit a watershed control program status report to the State each
year. These reports are required for States to exercise oversight and
ensure that PWSs implement the approved watershed control plan. They
also provide a mechanism for PWSs to work with the States to address
any shortcomings or necessary modifications in watershed control plans
that are identified after plan approval.
    In addition, PWSs must undergo watershed sanitary surveys every
three to five years by a State-approved party. These surveys will
provide information to PWSs and States regarding significant changes in
the watershed that may warrant modification of the approved watershed
control plan. Also, they allow for an assessment of watershed control
plan implementation.
    The proposed rule required watershed sanitary surveys annually, but
EPA has reduced the frequency to every three to five years in today's
final rule. This frequency is consistent with existing requirements for
PWS sanitary surveys. EPA is establishing this longer frequency on the
basis that most watersheds will not undergo significant changes over
the course of a single year. If significant changes in the watershed do
occur, however, PWSs must identify these changes in their annual
program status reports. In addition, States have

the authority to require that a watershed sanitary survey be conducted
at an earlier date if the State determines that significant changes may
have occurred in the watershed since the previous survey.
    In the proposed rule, approval of a watershed control program
expired after a PWS completed the second round of source water
monitoring, and the PWS had to reapply for program approval. Today's
final rule, however, does not include this requirement. Instead,
today's rule gives States authority to revoke Cryptosporidium treatment
credit for a watershed control program at any point if a State
determines that a PWS is not implementing the approved watershed
control plan. EPA believes this approach is preferable to the automatic
expiration of credit in the proposed rule for two reasons: (1) It
assures PWSs that if they implement the approved watershed control
plan, they will maintain the treatment credit; and (2) it gives States
the authority to ensure PWSs implement watershed control programs for
which they receive treatment credit and to take action at any time if a
PWS does not.
    EPA believes that PWSs should be eligible to receive
Cryptosporidium treatment credit for watershed control programs that
are in place prior to the treatment compliance date. The same
requirements for watershed control program treatment credit apply
regardless of whether the program is new or existing at the time the
PWS submits the watershed control plan for approval. In the case of
existing programs, the watershed control plan must list future
activities the PWS will undertake that will reduce source water
contamination.
    The Toolbox Guidance Manual lists programmatic resources and
guidance available to assist PWSs in building partnerships and
implementing watershed protection activities. It also incorporates
information on the effectiveness of different control measures to
reduce Cryptosporidium levels and provides case studies of watershed
control programs. This guidance is intended to assist both PWSs in
developing watershed control programs and States in assessing and
approving these programs.
    In addition to this guidance and other technical resources, EPA
provides funding for watershed and source water protection through the
Drinking Water State Revolving Fund (DWSRF) and Clean Water State
Revolving Fund (DWSRF). Under the DWSRF program, States may fund source
water protection activities by PWSs, including watershed management and
pathogen source reduction plans. CWSRF funds can be used for
agricultural best management practices to reduce pathogen loading in
receiving waters and for the replacement of failing septic systems.

c. Summary of Major Comments

    Public comments on the August 11, 2003, LT2ESWTR proposal supported
the concept of awarding credit towards Cryptosporidium treatment
requirements for an effective watershed control program. Commenters
expressed concerns, however, with specific criteria for awarding this
credit, including annual watershed sanitary surveys, re-approval of
watershed control programs, standards for existing watershed control
programs, and public availability of documents related to the watershed
control program. A summary of these comments and EPA's responses
follows.
    Regarding the proposed requirement for annual watershed sanitary
surveys, commenters stated that this frequency is too high because
activities to reduce Cryptosporidium contamination in the watershed
will often take many years to implement. These commenters recommended
that watershed sanitary surveys be performed every three to five years
in conjunction with PWSs sanitary surveys or longer. In contrast, other
commenters supported annual watershed sanitary surveys as being
necessary to allow proper responses to new sources of contamination
that can occur quickly in watersheds. Such sources can occur through
development, new recreation programs, fires, unauthorized activities,
and other factors.
    While EPA believes that regular watershed sanitary surveys are
necessary to identify new sources of contamination and allow States to
properly oversee watershed control programs, EPA agrees that
significant changes typically will not occur over one year. Therefore,
today's final rule requires PWSs that receive Cryptosporidium treatment
credit for a watershed control program to undergo watershed sanitary
surveys every three to five years, rather than every year. To address
the concern that new sources of watershed contamination can arise
quickly, today's rule requires PWSs to identify any significant changes
that have occurred in their watersheds in their annual program status
reports. States can then require a watershed sanitary survey at an
earlier date if significant changes have occurred since the previous
survey.
    Many commenters opposed the proposed requirement for PWSs to
reapply for approval of their watershed control programs after
completing the second round of source water monitoring. The concern was
that this requirement would discourage PWSs from pursuing watershed
control programs because they would be uncertain about whether they
would continue to receive treatment credit for their programs in the
future. As an alternative, commenters recommended that States monitor
the progress of PWSs in implementing watershed control programs through
the watershed sanitary surveys and annual status reports. A State could
then deny treatment credit to a PWS if it failed to demonstrate
adequate commitment to its approved watershed control plan.
    EPA agrees with these comments and today's final rule does not
include a requirement for re-approval of the watershed control program
after the second round of monitoring. Instead, PWSs must submit annual
program status reports to the State and undergo regular watershed
sanitary surveys. If the State determines that a PWS is not
implementing its approved watershed control plan on the basis of these
measures, it can withdraw the treatment credit associated with the
program. PWSs that implement their approved watershed control plans,
however, can maintain the associated treatment credit indefinitely
under today's rule.
    Several commenters stated that PWSs with existing watershed control
programs should be eligible for Cryptosporidium treatment credit under
the same standards that apply to new programs. EPA agrees that both
existing and new watershed control programs should be eligible for
Cryptosporidium treatment credit under the same standards, and today's
rule allows this. As is required for new programs, PWSs with existing
watershed control programs must submit a watershed control plan that
details future activities the PWS will implement to reduce source water
contamination. As with new programs, States will have the discretion to
approve the proposed watershed control plan for 0.5-log Cryptosporidium
treatment credit.
    With respect to a proposed requirement that the watershed control
plan, annual status reports, and watershed sanitary surveys be made
available to the public, commenters stated that homeland security
concerns are associated with these documents. Homeland security
concerns apply to information on the location of treatment plant
intakes and other structures. EPA agrees that there are security
concerns associated with watershed control program documents. EPA also
believes, though, that the public should be allowed to learn about the
actions PWSs

plan to take to address Cryptosporidium contamination and the progress
of PWSs in implementing these actions. Consequently, today's rule
requires PWSs to make the approved watershed control plan, annual
status reports, and watershed sanitary surveys available to the public.
However, PWSs may withhold portions of these documents that raise
security concerns with State approval.
3. Alternative Source
a. Today's Rule
    If approved by the State, a PWS may determine its Cryptosporidium
treatment requirements under today's rule using additional source water
monitoring results for an alternative treatment plant intake location
or an alternative intake operational strategy. By meeting the
requirements of this option, which are described as follows, a PWS may
reduce its Cryptosporidium treatment requirements under today's rule.
     Monitoring for an alternative intake location or
operational strategy, termed ``alternative source monitoring,'' may
only be performed in addition to monitoring the existing plant
intake(s) (i.e., the intake(s) the PWS uses when it must begin
monitoring under today's rule).
     Alternative source monitoring must meet the sample number,
sample frequency, and data quality requirements that apply to source
water monitoring for bin classification, as described in section IV.A.
     PWSs that perform alternative source monitoring must
complete this monitoring by the applicable deadline for treatment bin
classification under today's rule, as described in section IV.G. Unless
a PWS grandfathers monitoring data for the existing plant intake,
alternative source monitoring must be performed concurrently with
monitoring the existing intake.
     PWSs must submit the results of alternative source
monitoring to the State, along with supporting information documenting
the location and/or operating conditions under which the alternative
source monitoring was conducted. If a PWS fulfills these requirements,
the PWS may request that the State classify the PWS in a treatment bin
under today's rule using the alternative source monitoring results.
     If the State approves bin classification for a PWS using
alternative source monitoring results, the PWS must relocate the plant
intake or implement the intake operational strategy to reflect the
alternative source monitoring. The PWS must complete these actions no
later than the applicable date for the PWS to comply with
Cryptosporidium treatment requirements under today's rule. The State
may specify reporting requirements to verify operational practices.
    Failure by a PWS that is classified in a treatment bin using
alternative source monitoring to relocate the intake or implement the
new intake operational strategy, as required, by the applicable
treatment compliance deadline is a treatment technique violation. This
violation lasts until the State determines that the PWS has carried out
required changes to the intake location or operation or is providing
the level of Cryptosporidium treatment required for the existing intake
location and operation.
b. Background and Analysis
    Plant intake refers to the works or structures at the head of a
conduit through which water is diverted from a source (e.g., river or
lake) into a treatment plant. Plants may be able to reduce influent
Cryptosporidium levels by changing the intake placement (either within
the same source or to an alternate source) or managing the timing or
level of withdrawal.
    The Stage 2 M-DBP Advisory Committee recommended that PWSs be
allowed to modify their plant intakes to comply with today's rule, and
the August 11, 2003 proposal included this option (USEPA 2000a). The
requirements for this option in today's final rule are unchanged from
the proposal. The following discussion summarizes the basis for these
requirements.
    The effect of changing the location or operation of a plant intake
on influent Cryptosporidium levels can only be ascertained through
monitoring. Consequently, EPA is not establishing a prescriptive credit
for this option. Rather, if a PWS expects that Cryptosporidium levels
from a current plant intake will result in a bin classification
requiring additional treatment under today's rule, the PWS may conduct
additional Cryptosporidium monitoring reflecting a different intake
location or operational strategy (alternative source monitoring). The
PWS may then request that the State approve bin classification for the
plant based on alternative source monitoring results, provided the PWS
will implement the corresponding changes to the intake location or
operation.
    PWSs that conduct alternative source monitoring must also monitor
their existing plant intakes. Monitoring the existing intake is
required for the State to determine a treatment bin classification for
a plant in the event the PWS does not modify the intake (to reflect
alternative source monitoring) prior to the treatment compliance
deadline under today's rule.
    Further, PWSs must conduct alternative source monitoring within the
applicable time frame for source water monitoring under today's rule.
This approach is required for the State to determine a bin
classification for the plant based on alternative source monitoring by
the bin classification deadline. In addition, this timing will allow
the PWS to modify the intake or implement additional treatment, if
necessary, by the treatment compliance deadline. This requirement
means, however, that unless a PWS meets the requirement for monitoring
its existing intake through grandfathering, the PWS must perform
alternative source monitoring concurrently with existing intake
monitoring, although it does not have to be on exactly the same
schedule.
    Because alternative source monitoring will be used for bin
classification, this monitoring must comply with all applicable
requirements for source water monitoring that are described in section
IV.A. Further, the PWS must provide the State with supporting
information documenting the conditions, such as the source location,
under which the alternative source monitoring was conducted. This
documentation is required so that if bin classification is based on
alternative source monitoring results, the State can ensure the PWS
implements the corresponding modifications to the intake.
c. Summary of Major Comments
    Public comments on the August 11, 2003, LT2ESWTR proposal supported
allowing PWSs to determine treatment bin classification by monitoring
for an alternative intake location or operational strategy. Several
commenters stated they were unsure if this option would be widely used
due to the burden of performing Cryptosporidium monitoring at both the
current intake and the alternative source. Commenters also recommended
that PWSs first conduct source water assessments or watershed sanitary
surveys to evaluate intake management strategies to reduce
Cryptosporidium levels in the plant influent.
    In response, EPA believes that PWSs who choose alternative source
monitoring must also monitor their current intake so that the State can
determine the appropriate bin classification if the PWS does not

subsequently modify its intake. While few PWSs may choose to pursue
alternative source monitoring, EPA believes this option should be
available for PWSs that elect to do so. EPA agrees that it is
appropriate for PWSs to assess contamination sources in the watershed
when considering whether to relocate or change the operation of their
intakes. The Toolbox Guidance Manual provides direction to PWSs on
conducting these assessments.
    EPA requested comment on whether representative Cryptosporidium
monitoring can be performed prior to implementation of a new intake
strategy (e.g., monitoring a new source prior to constructing a new
intake structure). Commenters stated that there may be situations where
allowing Cryptosporidium monitoring to demonstrate a reduction in
oocyst levels prior to implementation of a new intake strategy is
appropriate. Incurring costs for constructing a new intake before
determining whether the strategy will reduce oocyst levels is not cost
effective. EPA agrees with this comment and today's rule allows PWSs to
conduct alternative source monitoring prior to constructing a new
intake and to base their bin classification on these monitoring results
with State approval.
4. Pre-Sedimentation With Coagulant
a. Today's Rule
    Presedimentation is a preliminary treatment process used to remove
gravel, sand and other particulate material from the source water
through settling before the water enters the primary clarification and
filtration processes in a treatment plant. PWSs receive 0.5-log credit
towards Cryptosporidium treatment requirements under today's rule for a
presedimentation process that meets the following conditions:
     Treats all flow reaching the treatment plant;
     Continuously adds a coagulant to the presedimentation
basin;
     Achieves one of the following two performance criteria:
    (1) Demonstrates at least 0.5-log mean reduction of influent
turbidity. This reduction must be determined using daily turbidity
measurements in the presedimentation process influent and effluent and
must be calculated as follows: log10 (monthly mean of daily
influent turbidity)--log10 (monthly mean of daily effluent
turbidity).
    (2) Complies with State-approved performance criteria that
demonstrate at least 0.5-log mean removal of micron-sized particulate
material, such as aerobic spores, through the presedimentation process.
    PWSs may receive treatment credit for a presedimentation process
during any month the process meets these conditions. To be eligible for
credit, PWSs must report compliance with these conditions to the State
each month. PWSs may earn presedimentation treatment credit for only
part of the year if the process does not meet these conditions year-
round. In this situation, PWSs must fully meet their Cryptosporidium
treatment requirements under today's rule using other microbial toolbox
options during those months when the PWS does not receive treatment
credit for presedimentation.
    Alternatively, PWSs may apply to the State for Cryptosporidium
treatment credit for presedimentation processes using a demonstration
of performance, as described in section IV.D.9. Demonstration of
performance provides an option for PWSs with presedimentation processes
that do not meet these prescribed conditions for treatment credit and
for PWSs who seek greater than 0.5-log Cryptosporidium treatment credit
for their presedimentation processes.
    PWSs are not eligible for Cryptosporidium treatment credit for a
presedimentation process if their sampling point for the source water
Cryptosporidium monitoring used for bin classification was after (i.e.,
downstream of) the presedimentation process. In this case, the removal
achieved by the presedimentation process will be reflected in the
monitoring results and bin classification.
b. Background and Analysis
    Presedimentation involves passing raw water through retention
basins in which particulate material is removed through settling. PWSs
use presedimentation to reduce and stabilize particle concentrations
prior to the primary clarification and filtration processes in a
treatment plant. Presedimentation is often operated at higher hydraulic
overflow rates than conventional sedimentation (the sedimentation
process that directly precedes filtration in a conventional treatment
plant) and may not involve coagulant addition. PWSs may operate a
presedimentation process only during periods of high raw water
turbidity.
    As a process for removing particles, presedimentation can reduce
Cryptosporidium levels to some degree. In addition, presedimentation
can improve the performance of subsequent treatment processes by
dampening variability in raw water quality. The efficacy of
presedimentation in removing particles, including Cryptosporidium, is
influenced by the use of coagulant, the hydraulic loading rate, water
quality parameters like temperature and turbidity, and physical
characteristics of the sedimentation basin.
    The Stage 2 M-DBP Advisory Committee recommended 0.5-log
Cryptosporidium treatment credit for presedimentation with coagulation
(USEPA 2000a). The August 11, 2003 proposal included criteria, which
were similar to those in today's final rule, for PWSs to receive this
credit (USEPA 2003a). The following discussion summarizes the basis for
this credit and for differences in associated requirements between the
proposal and today's final rule.
    In the proposal, EPA reviewed published studies of Cryptosporidium
removal through conventional sedimentation processes by Payment and
Franco (1993), Kelly et al. (1995), Patania et al. (1995), States et
al. (1997), Edzwald and Kelly (1998), and Dugan et al. (2001). These
studies included bench-, pilot-, and full-scale processes, and the
reported levels of Cryptosporidium removal varied widely, ranging from
0.4- to 3.8-log. In addition, these studies also supported two other
significant findings:

    (1) Proper coagulation significantly improves Cryptosporidium
removal through sedimentation. In Dugan et al. (2001), for example,
average Cryptosporidium removal across a sedimentation basin was
1.3-log with optimal coagulation and decreased to 0.2-log when the
coagulant dose was insufficient.
    (2) The removal of aerobic spores correlates well with the
removal of Cryptosporidium when a coagulant is present. This
indicates that aerobic spores, which are naturally present in
surface waters, may be used as an indicator of Cryptosporidium
removal in coagulated full-scale sedimentation processes.

    Cryptosporidium removal efficiencies in conventional sedimentation
may be higher than in presedimentation due to differences in hydraulic
loading rates, coagulant doses, and other factors. EPA identified no
published studies of Cryptosporidium removal through presedimentation
processes. In the proposal, however, EPA evaluated data on the removal
of aerobic spores in the presedimentation processes of three PWSs as an
indicator of Cryptosporidium removal (USEPA 2003a). All three PWSs
added a coagulant (polymer, metal salts, or recycled sludge) to the
presedimentation process. The mean removal of aerobic spores through
presedimentation in the three PWSs ranged from 0.5- to 1.1-log over
time

spans ranging from several months to several years.
    These data support the finding that full-scale presedimentation
processes can achieve Cryptosporidium removals of 0.5-log and greater
under routine operating conditions and over an extended time period.
Accordingly, EPA concluded that 0.5-log Cryptosporidium treatment
credit for presedimentation processes is appropriate under certain
conditions. Today's rule establishes three conditions for PWSs to
receive this credit.
    The first condition for presedimentation to receive 0.5-log
Cryptosporidium treatment credit is that the process must treat all