consider revisions to the NPDWR for simazine at this time and has
placed simazine in the emerging information/data gap category because
of an impending re-evaluation of the Agency's risk assessment for
atrazine and the assessment for simazine is based on atrazine data. See
section VI.7 (atrazine) for additional information.

58. Styrene
    a. Background. EPA published the current NPDWR for styrene on
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an
MCLG and an MCL of 0.1 mg/L. EPA based the MCLG on a reference dose of
0.2 mg/kg-day and a cancer classification of C, possible human
carcinogen.
    b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to styrene. The revised health
effects assessment will consider relevant studies on the toxicity of
styrene, including its potential developmental and reproductive
toxicity. The new health effects assessment was not completed by March
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The
IRIS Substance Assessment Tracking System Web site (http://
cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information
on the status of the health effects assessment.
    c. Review Result. Since the MCL for styrene is set at its MCLG and
a reassessment of the health risks resulting from exposure to styrene
is in progress, the Agency does not believe a revision to the NPDWR is
appropriate at this time.
59. 2,3,7,8-TCDD (Dioxin)
    a. Background. EPA published the current NPDWR for dioxin on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of
zero based on a cancer classification of B2, probable human carcinogen.
The NPDWR also established an MCL of 3x10-8 mg/L, based on
analytical feasibility.
    b. Technical Reviews. In 2003, the Agency prepared a draft human
health reassessment for dioxin and its related compounds (USEPA, 2003c)
that underwent external review by the National Academy of Science. In
their peer review report (NAS, 2006), NAS recommended that EPA
reevaluate its conclusions regarding the carcinogenicity of dioxin
based on the criteria set out in the 2005 cancer guidelines; that EPA
should consider developing more information on the noncancer effects of
dioxin; and that EPA evaluate new dose-response data released by the
NTP. The Agency is currently considering the NAS recommendations. The
Agency does not expect any new health effects assessment to be
completed in the time frame of the current Six-Year Review cycle
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date
information on the status of the health effects assessment.
    Although a health effects assessment is in process for dioxin, the
existing MCLG is still zero and the current MCL is based on a PQL of
3x10-8 mg/L. Therefore, EPA reviewed whether there is
potential to revise the PQL. The PT data currently available for dioxin
are not sufficient to evaluate the potential for PQL revision (USEPA,
2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: Laboratory
MRLs in the Six-Year Review ICR dataset, and the MDL for the approved
method for the detection of dioxin (Method 1613). While EPA prefers to
use laboratory performance data to calculate the PQL, the MRL and MDL
information can be valuable for this review to indicate whether it is
possible to quantitate at levels below the current PQL. The Six-Year
Review ICR dataset contains dioxin data for fewer than 2,500 systems,
which is an insufficient sample size to derive an EQL based on MRL
data. The MDL of the approved method is 1x10-8 mg/L.
Applying a multiplier of 5 would yield an EQL of 5x10-8 mg/
L. The result is slightly higher than the current PQL and, therefore,
EPA did not estimate an EQL. Based on these varied and unrelated
approaches/sources of information, EPA believes that a PQL reduction
for dioxin is not appropriate at present. Since the MCL is constrained
by the PQL, and the PQL is unchanged, EPA does not believe it is
necessary to conduct an occurrence analysis at this time.
    c. Review Result. The Agency does not believe a revision to the
NPDWR for dioxin is appropriate at this time because a reassessment of
the health risks resulting from exposure to dioxin is in progress
(USEPA, 2009b). Furthermore, a review of analytical feasibility did not
identify a potential to revise the MCL, which is limited by
feasibility.
60. Tetrachloroethylene
    a. Background. EPA published the current NPDWR for
tetrachloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991c)).
The NPDWR established an MCLG of zero based on a cancer classification
of B2, probable human carcinogen. The NPDWR also established an MCL of
0.005 mg/L, based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to tetrachloroethylene. The
revised health effects assessment will consider relevant studies on the
toxicity of tetrachloroethylene, including its potential developmental
and reproductive toxicity. The new health effects assessment was not
completed by March 1, 2009, the review cutoff date for this notice
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date
information on the status of the health effects assessment and
indicates that tetrachloroethylene is currently undergoing review by
NAS.
    Although a risk assessment is in process for tetrachloroethylene,
the existing MCLG is zero and the current MCL of 0.005 mg/L is based on
the PQL. Therefore, EPA reviewed whether there is potential to revise
the PQL. EPA reviewed PE data from the first Six-Year Review cycle and
then analyzed more recent PT data to determine if the PQL could be
revised (i.e., analytical feasibility). Passing rates for PE data
available through late 1999 for tetrachloroethylene are above 95
percent at the lowest concentrations. However, the true concentrations
were all higher than the current PQL of 0.005 mg/L. More recent PT data
from late 1999 through 2004, supplied by a PT provider, also show
greater than 90 percent passing rates for studies around the current
PQL, including 13 with true values below the PQL. Because most of the
laboratory passing rates from PE and PT studies exceeded the 75 percent
criterion typically used to derive a PQL, including several with true
values below the PQL, a lowering of the PQL for tetrachloroethylene
might be possible. These results, however, are insufficient to
recalculate a revised PQL for tetrachloroethylene because not enough
data points are available below the current PQL to derive a value at
the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: Laboratory
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved
methods for the detection of tetrachloroethylene (Methods 502.2, 524.2,
and 551.1). While EPA prefers to use laboratory performance data to
calculate the PQL, the MRL and MDL information can be valuable for this
review to indicate whether it is possible to quantitate at levels below
the current PQL. EPA also noted that the State of New Jersey uses a PQL
of 0.001 mg/L, based on a 1987 study of laboratory performance at low
concentrations that used criteria similar to those in the PT data
(NJDWQI, 1987). The Six-Year Review ICR dataset contains MRL values for
138,348 samples. More than 80 percent of these values are less than

or equal the modal MRL: 117,033 (85 percent) equal the modal MRL of
0.0005 mg/L and an additional 15,848 (11 percent) are lower than 0.0005
mg/L. Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e).
The MDLs of approved method are 0.00005, 0.00014, and 0.000008 mg/L.
Applying a multiplier of 10 would give a possible PQL range from
0.00008 to 0.0014 mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of
information, EPA believes that there is potential to lower the PQL for
tetrachloroethylene. To determine whether any MCL revision is likely to
provide a meaningful opportunity to improve public health protection,
EPA evaluated the occurrence of tetrachloroethylene at the EQL of
0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L. Table
VI-24 shows the results of the occurrence and exposure analysis for the
current MCL and these thresholds. The occurrence and exposure analysis
shows that average concentrations exceed the current MCL for 23 to 25
out of 50,436 systems (0.046 to 0.050 percent) serving approximately
630, 000 to 1.1 million people (or 0.277 to 0.473 percent of 227
million people). Note that these results are based on the subset of
monitoring data provided in response to the Six-Year Review ICR and do
not necessarily reflect MCL violations, which are based on annual
average concentrations at entry points; SDWIS/FED indicates 174 MCL
violations for tetrachloroethylene between 1998 and 2005, with annual
violations ranging from 10 to 33 (USEPA, 2007g). Average concentrations
at 412 to 519 of 50,436 systems (0.817 to 1.029 percent), serving 12.4
to 14.6 million people (or 5.466 to 6.419 percent of 227 million
people), exceed the lowest EQL of 0.0005 mg/L. While these systems are
widely distributed and located in most of the States providing data, a
few large systems (serving 500,000 or more people) account for almost
half of the exposed population.

Table VI-24--Number and Percent of Systems With Mean Concentrations Exceeding Tetrachloroethylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (Percentages based on 50,436 systems with
 Regulatory or feasibility-based      tetrachloroethylene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                                              Nondetect values = \1/2\
                                   Nondetect values = MRL\1\           MRL\2\            Nondetect values = 0\3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  25 (0.050%)..............  23 (0.046%).............  23 (0.046%)
1/2 MCL (0.0025 mg/L)............  75 (0.149%)..............  71 (0.141%).............  68 (0.135%)
2xEQL (0.001 mg/L)...............  286 (0.568%).............  251 (0.498%)............  220 (0.437%)
EQL (0.0005 mg/L)................  not applicable...........  519 (1.030%)............  412 (0.818%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (Percentages based on 227,009,000 people
                                     served by the systems with tetrachloroethylene data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based   Nondetect values = MRL\1\  Nondetect values = \1/2\   Nondetect values = 0\3\
            threshold                                                   MRL\2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  1,074,000 (0.473%).......  628,000 (0.277%)........  628,000 (0.277%)
\1/2\ MCL (0.0025 mg/L)..........  1,706,000 (0.752%).......  1,692,000 (0.745%)......  1,647,000 (0.726%)
2xEQL (0.001 mg/L)...............  10,706,000 (4.716%)......  10,177,000 (4.483%).....  9,625,000 (4.240%)
EQL (0.0005 mg/L)................  not applicable...........  14,572,000 (6.419%).....  12,408,000 (5.466%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that a revision to the MCL
may provide a meaningful opportunity to improve the level of public
health protection, EPA considered whether treatment feasibility is
likely to pose any limitations if the MCL were lowered (USEPA, 2009g).
The current BATs for tetrachloroethylene are packed tower aeration
(PTA) and granular activated carbon (GAC). Small system compliance
technologies (SSCTs) for tetrachloroethylene include GAC and several
aeration technologies. EPA's assessment shows that PTA and GAC are
effective enough to achieve concentrations as low as the EQL.
    EPA is not currently able to assess the potential health benefits
from a revised MCL for tetrachloroethylene, because the revised health
effects assessment is not yet available. However, based on its B2
cancer classification (MCLG of zero) and the occurrence and exposure
analysis at possible MCL values, the Agency believes that a revision to
the MCL may provide a meaningful opportunity to reduce public health
risks.
    c. Review Result. The Agency believes it is appropriate to revise
the NPDWR for tetrachloroethylene although a health effects assessment
is currently in progress. The existing MCLG is zero (based on the
current B2 cancer classification) and the current MCL is based on a PQL
(i.e., analytical feasibility) of 0.005 mg/L. The Agency's review
indicates that analytical feasibility could be as much as 10 times
lower (~ 0.0005 mg/L) and occurrence at this level appears to be
relatively widespread. Hence, revisions to the tetrachloroethylene
NPDWR may provide a meaningful opportunity for health risk reduction.
If the updated health effects assessment is completed in time to
consider for the regulatory revision of tetrachloroethylene, the Agency
will consider this assessment in its evaluation of public health
benefits associated with any revision. As discussed in Section VII, the
Agency solicits public comment and/or relevant information that may
inform the regulatory revision for tetrachloroethylene. EPA is also
requesting that stakeholders provide information/data about the lowest
level of quantitation (including the analytical method used) that
laboratories can reliably and consistently achieve.

61. Thallium
    a. Background. EPA published the current NPDWR for thallium on July
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of
0.0005 mg/L. EPA based the MCLG on a reference dose of 0.00007 mg/kg-
day and a cancer classification of D, not classifiable as to human
carcinogenicity. The NPDWR also established an MCL of 0.002 mg/L, based
on analytical feasibility.
    b. Technical Reviews. EPA completed the risk reassessment for
thallium in September of 2009 (USEPA, 2009k). Because the new health
effects assessment was not completed by March 1, 2009, the review
cutoff date for this notice (USEPA, 2009b), the outcome of this
assessment has not been included in the current review effort. EPA will
consider the updated assessment in the next review cycle.
    The current MCL is based on a PQL of 0.002 mg/L. Therefore, EPA
reviewed whether there is potential to revise the PQL. EPA reviewed PE
data from the first Six-Year Review cycle and then analyzed more recent
PT data to determine if the PQL can be revised (i.e., analytical
feasibility). Passing rates for PE data available through late 1999 for
thallium are above 80 percent around the current PQL of 0.002 mg/L,
including one study with a true concentration less than the current
PQL. More recent PT data from late 1999 through 2004, supplied by a PT
provider, show passing rates at or above 75 percent, but tending to
fall below 80 percent as the true concentration approaches the current
PQL. No studies had true concentrations below the current PQL. Given
the lack of data points below the current PQL and the low PT passing
rates close to the PQL, a lowering of the PQL for thallium is not
appropriate at this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: laboratory
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved
methods for the detection of thallium (Methods 200.8 and 200.9). While
EPA prefers to use laboratory performance data to calculate the PQL,
the MRL and MDL information can be valuable for this review to indicate
whether it is possible to quantitate at levels below the current PQL.
The Six-Year Review ICR dataset contains MRL values for 73,409 samples.
Fewer than 80 percent of these values are less than or equal the modal
MRL: 46,273 (63 percent) equal the modal MRL of 0.001 mg/L and an
additional 11,032 (15 percent) are lower than 0.001 mg/L. Therefore,
EPA did not set the EQL equal to the modal MRL (USEPA, 2009e). The MDLs
of approved methods range from 0.0003 to 0.0007 mg/L. Applying a
multiplier of 10 would give a possible PQL range from 0.003 to 0.007
mg/L. The result is higher than the current PQL and, therefore, EPA did
not estimate an EQL (USEPA, 2009e). Based on these varied and unrelated
approaches/sources of information, EPA believes that there is no
potential to lower the PQL for thallium. Since the MCL is constrained
by the PQL, and the PQL is unchanged, EPA does not believe it is
necessary to conduct an occurrence analysis at this time.
    c. Review Result. The Agency does not believe a revision to the
NPDWR for thallium is appropriate at this time because a reassessment
of the health risks resulting from exposure to thallium was in progress
(USEPA, 2009k) and did not meet the March 1, 2009 cutoff date for this
review. Furthermore, a review of analytical feasibility did not
identify a potential to revise the MCL, which is limited by
feasibility.
62. Toluene
    a. Background. EPA published the current NPDWR for toluene on
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an
MCLG and an MCL of 1 mg/L. EPA based the MCLG on a reference dose of
0.2 mg/kg-day and a cancer classification of D, not classifiable as to
human carcinogenicity.
    b. Technical Reviews. In 2005, the Agency updated its health
effects assessment of toluene (USEPA, 2005b). The change in this
assessment could lead to a change in the MCLG. This assessment
considered relevant studies on the toxicity of toluene including
developmental and reproductive toxicity. The assessment revised the RfD
from 0.2 mg/kg-day to 0.08 mg/kg-day and concluded that there is
inadequate information to assess the carcinogenic potential of toluene
(USEPA, 2005b). Although there were no changes in the critical study or
effect, there were changes in the toxicity database that increase
concern for immunotoxicity and neurotoxicity via the oral exposure
route and justified the higher uncertainty factor for the revised RfD
(USEPA, 2005b). Based on the new IRIS assessment and RfD of 0.08 mg/kg-
day, and assuming a 70-kg adult body weight and 2 liters water intake
per day, the DWEL could be 2.8 mg/L. An RSC of 20 percent results in a
possible MCLG of 0.6 mg/L.
    Analytical feasibility does not pose any limitations for the
current MCL and would not be a limiting factor for the possible MCLG
decrease under consideration. EPA evaluated the results of the
occurrence and exposure analyses for toluene to determine whether a
revised MCLG/MCL would be likely to result in a meaningful opportunity
to improve the level of public health protection (USEPA, 2009f). Table
VI-25 shows the results of the occurrence and exposure analysis for the
current MCL and the possible MCLG set equal to 0.6 mg/L based on the
new health effects information. The occurrence and exposure analysis
shows that average concentrations exceed the current MCL for one system
out of 50,451 (0.002 percent) serving approximately 500 people (0.0002
percent of 227 million people). Note that these results are based on
the subset of monitoring data provided in response to the Six-Year
Review ICR and do not necessarily reflect MCL violations, which are
based on annual average concentrations at entry points; SDWIS/FED
indicates MCL violations for toluene at only one system in one year
between 1998 and 2005 (USEPA, 2007g). Average concentrations at two of
50,451 systems (0.004 percent), serving 800 people (or 0.0004 percent
of 227 million people), exceed the possible MCLG based on new health
effects information (0.06 mg/L).

      Table VI-25--Number and Percent of Systems With Mean Concentrations Exceeding Toluene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                   health-based threshold (percentages based on 50,451 systems with toluene data
    Regulatory or health-based                     in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (1 mg/L).....................  1 (0.002%)...............  1 (0.002%)..............  1 (0.002%)
Possible MCLG (0.6 mg/L).........  2 (0.004%)...............  2 (0.004%)..............  2 (0.004%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,955,000 people
                                         served by the systems with toluene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
    Regulatory or health-based       Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (1 mg/L).....................  500 (0.0002%)............  500 (0.0002%)...........  500 (0.0002%)
Possible MCLG (0.6 mg/L).........  800 (0.0004%)............  800 (0.0004%)...........  800 (0.0004%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the
MCL is unlikely to provide a meaningful opportunity to improve the
level of public health protection, it was not necessary to perform any
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support
consideration of whether to revise the MCLG/MCL for toluene, EPA does
not believe a revision to the NPDWR for toluene is appropriate at this
time. In making this decision, the Agency considered whether any
possible revision to the NPDWR for toluene is likely to provide a
meaningful opportunity for health risk reductions. Taking into
consideration the low occurrence of this contaminant, EPA has decided
that any revision to the NPDWR would be a low priority activity for the
Agency, and, thus, is not appropriate to revise at this time because
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to
implement any regulatory change that resulted.
63. Toxaphene
    a. Background. EPA published the current NPDWR for toxaphene on
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an
MCLG of zero based on a cancer classification of B2, probable human
carcinogen. The NPDWR also established an MCL of 0.003 mg/L, based on
analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA
conducted a literature search for relevant data on the carcinogenicity
of toxaphene as well as its potential developmental and reproductive
toxicity. EPA has not identified any new information that indicates
that it is appropriate to consider revisions to the cancer
classification for toxaphene at this time (USEPA, 2009b). Because the
MCLG remains at zero, the Agency believes that a further review of the
health effects of toxaphene is not warranted at this time.
    The current MCL for toxaphene is based on a PQL of 0.003 mg/L. For
the Six-Year Review, the Agency considered whether changes in the
analytical feasibility of toxaphene might lead to a lower MCL. EPA
reviewed PE data from the first Six-Year Review cycle and then analyzed
more recent PT data to determine if the PQL can be revised (i.e.,
analytical feasibility). Passing rates for PE data available through
late 1999 for toxaphene are generally above 90 percent around the
current PQL of 0.003 mg/L, including three studies with true values
below the current PQL. All passing rates in the PE data exceeded 80
percent. More recent PT data from late 1999 through 2004, supplied by a
PT provider, show greater than 80 percent passing rates for a majority
of studies, but there are no studies with true values below the current
PQL. There are two PT studies with passing rates equal to or below 75
percent, at true values well above the current PQL. Despite this
variability, most of the laboratory passing rates from PE and PT
studies exceeded the 75 percent criterion typically used to derive a
PQL, including three with true values below the PQL. Therefore, a
lowering of the PQL for toxaphene might be possible. These results,
however, are insufficient to recalculate a revised PQL for toxaphene
because not enough data points are available below the current PQL to
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: laboratory
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved
methods for the detection of toxaphene (Methods 505, 508.1, and 525.2).
While EPA prefers to use laboratory performance data to calculate the
PQL, the MRL and MDL information can be valuable for this review to
indicate whether it is possible to quantitate at levels below the
current PQL. The Six-Year Review ICR dataset contains MRL values for
54,529 samples. More than 80 percent of these values are less than or
equal the modal MRL: 36,763 (67 percent) equal the modal MRL of 0.001
mg/L and an additional 8,525 (16 percent) are lower than 0.001 mg/L.
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The
MDLs of approved methods are 0.0017, 0.001, and 0.00013 mg/L. Applying
a multiplier of 10 would give a possible PQL range from 0.0013 to 0.017
mg/L, which is above the EQL, but includes values below the PQL (USEPA,
2009e).
    Based on these varied and unrelated approaches/sources of
information, EPA believes that there may be potential to lower the PQL
for toxaphene. To determine whether any MCL revision is likely to
provide a meaningful opportunity to improve public health protection,
EPA evaluated the occurrence of toxaphene at the EQL of 0.001 mg/L and
an additional threshold of 0.0015 mg/L (USEPA, 2009f). Table VI-26
shows the results of the occurrence and exposure analysis for the
current MCL and these thresholds. The occurrence and exposure analysis

shows that average concentrations exceed the current MCL for three to
four of 30,387 systems (0.010 to 0.013 percent) serving 23,000 people
(or 0.014 percent of 160 million people). Note that these results are
based on the subset of monitoring data provided in response to the Six-
Year Review ICR and do not necessarily reflect MCL violations, which
are based on annual average concentrations at entry points; SDWIS/FED
indicates three MCL violations for toxaphene between 1998 and 2005
(USEPA, 2007g). Average concentrations at five of 30,387 systems (0.016
percent), serving 23,000 people (or 0.015 percent of 160 million
people), exceed the EQL of 0.001 mg/L.

     Table VI-26--Number and Percent of Systems with Mean Concentrations Exceeding Toxaphene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 30,387 systems with
 Regulatory or feasibility-based           toxaphene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.003 mg/L).................  4 (0.013%)...............  3 (0.010%)..............  3 (0.010%)
\1/2\ MCL (0.0015 mg/L)..........  5 (0.016%)...............  5 (0.016%)..............  5 (0.016%)
EQL (0.001 mg/L).................  not applicable...........  5 (0.016%)..............  5 (0.016%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 160,012,000 people
                                        served by the systems with toxaphene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.003 mg/L).................  23,000 (0.014%)..........  23,000 (0.014%).........  23,000 (0.014%)
\1/2\ MCL (0.0015 mg/L)..........  23,000 (0.014%)..........  23,000 (0.014%).........  23,000 (0.014%)
EQL (0.001 mg/L).................  not applicable...........  23,000 (0.014%).........  23,000 (0.014%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.001 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the
MCL is unlikely to provide a meaningful opportunity to improve the
level of public health protection, it was not necessary to perform any
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for toxaphene is
appropriate at this time. The occurrence and exposure analysis based on
possible changes in analytical feasibility indicates that any revision
to the MCL is unlikely to provide a meaningful opportunity to improve
public health protection. Taking into consideration the low occurrence
of this contaminant, EPA has decided that any revision to the NPDWR
would be a low priority activity for the Agency, and, thus, is not
appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to
implement any regulatory change that resulted.
64. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
    a. Background. EPA published the current NPDWR for 2,4,5-TP on
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an
MCLG and an MCL of 0.05 mg/L. EPA based the MCLG on a reference dose of
0.008 mg/kg-day and a cancer classification of D, not classifiable as
to human carcinogenicity.
    b. Technical Reviews. As part of the Six-Year Review process, EPA
conducted a literature search for relevant data on the toxicology of
2,4,5-TP, including its potential developmental and reproductive
toxicity. The literature search did not identify any studies that
warrant a review of the RfD or the cancer classification (USEPA,
2009b).
    A review of analytical or treatment feasibility is not necessary
for 2,4,5-TP because changes to the MCLG are not warranted at this time
and the current MCL is set at the MCLG. Since EPA did not identify a
health or technology basis for revising the 2,4,5-TP NPDWR, the Agency
did not conduct a detailed occurrence and exposure analysis.
    c. Review Result. EPA's review shows that there are no data
supporting a change to the 2,4,5-TP NPDWR. As a result, a revision to
the NPDWR would not be appropriate at this time.
65. 1,2,4-Trichlorobenzene
    a. Background. EPA published the current NPDWR for 1,2,4-
trichlorobenzene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an MCL of 0.07 mg/L. EPA based the MCLG
on a reference dose of 0.01 mg/kg-day and a cancer classification of D,
not classifiable as to human carcinogenicity.
    b. Technical Reviews. The health effects technical review
identified information regarding the carcinogenicity of 1,2,4-
trichlorobenzene, as well as its noncancer effects, that may indicate
the need to update the Agency's health effects assessment (USEPA,
2009b). Two chronic carcinogenicity studies of 1,2,4-trichlorobenzene,
one in mice (Moore, 1994a) and one in rats (Moore, 1994b), reported
liver effects in both mice and rats, as well as kidney effects in rats.
Mice appeared more sensitive than rats for noncancer effects, and mice
also demonstrated a significant treatment-related increase in the
incidence of hepatocellular carcinomas. No increased incidence of any
tumor type was observed in rats. These health effect data could have
implications for the 1,2,4-trichlorobenzene MCLG because they identify
effect levels for noncancer effects in the liver and kidney, as well as
evidence of carcinogenicity in mice.

    In light of this information, EPA considers 1,2,4-trichlorobenzene
as a potential candidate for a new health effects assessment. The
Agency solicits general feedback on its plans to reassess health risks
resulting from exposure to 1,2,4-trichlorobenzene. The Agency also
welcomes any scientific information related to 1,2,4-trichlorobenzene
health risks from the public. Because EPA considers 1,2,4-
trichlorobenzene as a candidate for a new assessment, EPA does not
believe it is appropriate to consider revisions to the MCLG (as well as
the MCL) at this time.
    A review of analytical or treatment feasibility is not necessary
for 1,2,4-trichlorobenzene because changes to the MCLG are not
warranted at this time and the current MCL is set at the MCLG. Since
EPA did not identify a health or technology basis for revising the
1,2,4-trichlorobenzene NPDWR, the Agency did not conduct a detailed
occurrence and exposure analysis.
    c. Review Result. The Agency is considering whether to initiate a
new health assessment for 1,2,4-trichlorobenzene and therefore does not
believe a revision to the NPDWR is appropriate at this time.
66. 1,1,1-Trichloroethane
    a. Background. EPA published the current NPDWR for 1,1,1-
trichloroethane on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of 0.20 mg/L. EPA based the MCLG on a
reference dose of 0.035 mg/kg-day and a cancer classification of D, not
classifiable as to human carcinogenicity.
    b. Technical Reviews. In 2007, the Agency updated its health
effects assessment of 1,1,1-trichloroethane (USEPA, 2007d). The Agency
identified a change in this assessment that could lead to a change in
the MCLG. This assessment considered relevant studies on the toxicity
of 1,1,1-trichloroethane including developmental and reproductive
toxicity. The assessment revised the RfD from 0.035 mg/kg-day to 2 mg/
kg-day and concluded that there is inadequate information to assess the
carcinogenic potential of 1,1,1-trichloroethane (USEPA, 2007d). Based
on the new IRIS assessment and RfD of 2 mg/kg-day, and assuming a 70-kg
adult body weight and 2 liters water intake per day, the DWEL could be
70 mg/L. An RSC of 20 percent results in a possible MCLG of 14 mg/L
(USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the
current MCL and would not be a limiting factor if EPA were to raise the
MCLG. EPA evaluated the results of the occurrence and exposure analyses
for 1,1,1-trichloroethane to determine whether a revised MCLG/MCL would
be likely to result in a meaningful opportunity to achieve cost savings
for PWSs and their customers while maintaining, or improving, the level
of public health protection (USEPA, 2009f). Although the Agency
obtained and evaluated the finished water occurrence data for 1,1,1-
trichloroethane, its usefulness is limited for determining potential
cost savings to PWSs and their customers because the Agency does not
know which systems are treating for this contaminant. As an
alternative, the Agency evaluated available data on source water
quality and conducted a qualitative assessment of treatment cost
savings.
    Table VI-27 provides summary data for contaminant occurrence based
on maximum sample values for the locations included in the STORET and
NAWQA data. Although the degree to which these occurrence rates
represent national drinking water source occurrence is uncertain, the
information shows no to low occurrence at threshold levels of interest.
This information indicates that any resulting NPDWR change would affect
systems that rely on source water at none of the NAWQA locations and at
less than 0.1 percent of the STORET locations.

  Table VI-27--Ambient Water Quality Monitoring Occurrence Summary for
                          1,1,1-Trichloroethane
------------------------------------------------------------------------
                                 Number of locations  (% of locations)
    Maximum concentration    -------------------------------------------
                                   STORET \1\             NAWQA \2\
------------------------------------------------------------------------
Total.......................  3,429 (100.0%)......  5,788 (100.0%)
Nondetect...................  2,304 (67.2%).......  5,290 (91.4%)
Detected....................  1,125 (32.8%).......  498 (8.6%)
Exceeds current MCLG of 0.2   5 (0.1%)............  0 (0.0%)
 mg/L.
Exceeds alternative value of  0 (0.0%)............  0 (0.0%)
 14 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2008.
\2\ NAWQA database 1992-2008.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for 1,1,1-
trichloroethane have other beneficial effects, e.g., reduction of other
co-occurring contaminants, precursors for DBPs, or other common
impurities. Therefore, if EPA were to consider a higher level, the
Agency does not know how many PWSs that are currently treating to
comply with the existing MCL of 0.2 mg/L would be likely to discontinue
treatment that is already in place (USEPA, 2009d). Also, the Agency
does not know to what extent affected systems might be able to reduce
costs given that capital costs are not recoverable. However, the Agency
recognizes that there may be opportunities to achieve operational cost
savings if these systems are able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting
revision is not likely to provide a meaningful opportunity for cost
savings. In view of this, any revision would be a low priority activity
and not appropriate at this time.
    c. Review Result. Although there are new data that support
consideration of whether to revise the MCLG/MCL for 1,1,1-
trichloroethane, EPA does not believe a revision to the NPDWR for
1,1,1-trichloroethane is appropriate at this time. In making this
decision, the Agency considered whether any possible revision to the
NPDWR for 1,1,1-trichloroethane is likely to provide a meaningful
opportunity for cost savings to public water systems and their
customers. Taking into consideration the low occurrence of this
contaminant in source waters, EPA has decided that any revision to the
NPDWR would be a low priority activity for the Agency, and, thus, is
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and

     The burden on States and the regulated community to
implement any regulatory change that resulted.
67. 1,1,2-Trichloroethane
    a. Background. EPA published the current NPDWR for 1,1,2-
trichloroethane on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR
established an MCLG of 0.003 mg/L. EPA based the MCLG on a reference
dose of 0.004 mg/kg-day and a cancer classification of C, possible
human carcinogen. The NPDWR also established an MCL of 0.005 mg/L,
based on analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA
conducted a literature search for relevant data on the toxicology of
1,1,2-trichloroethane, including its potential developmental and
reproductive toxicity. The literature search did not identify any
studies that warrant a review of the RfD or the cancer classification
(USEPA, 2009b).
    The current MCL for 1,1,2-trichloroethane is based on a PQL of
0.005 mg/L. For the Six-Year Review, the Agency considered whether
changes in the analytical feasibility of 1,1,2-trichloroethane might
lead to a lower MCL. EPA reviewed PE data from the first Six-Year
Review cycle and then analyzed more recent PT data to determine if the
PQL can be revised (i.e., analytical feasibility). Passing rates for PE
data available through late 1999 for 1,1,2-trichloroethane are above 95
percent near the current PQL of 0.005 mg/L, but there were no PE
studies with true values below the current PQL. More recent PT data
from late 1999 through 2004, supplied by a PT provider, show greater
than 90 percent passing rates around the current PQL, including twelve
studies with true values below the PQL. Because most of the laboratory
passing rates from PT studies--including several with true
concentrations below the PQL--exceeded the 75 percent criterion
typically used to derive a PQL, a lowering of the PQL for 1,1,2-
trichloroethane might be possible. These results, however, are
insufficient to recalculate a revised PQL for 1,1,2-trichloroethane
because not enough data points are available below the current PQL to
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether they indicate any potential to quantitate at levels as low as
the current MCLG: laboratory MRLs in the Six-Year Review ICR dataset,
and the MDLs for approved methods for the detection of 1,1,2-
trichloroethane (Methods 502.2 and 524.2). While EPA prefers to use
laboratory performance data to calculate the PQL, the MRL and MDL
information can be valuable for this review to indicate whether it is
possible to quantitate at levels below the current PQL. The Six-Year
Review ICR dataset contains MRL values for 139,672 samples. Of these,
117,788 (84 percent) equal the modal MRL of 0.0005 mg/L. An additional
17,142 (12 percent) are lower than 0.0005 mg/L. Because more than 80
percent of the of MRLs are equal to or less than the current MCLG of
0.003 mg/L, EPA selected that value as the minimum threshold for the
occurrence and exposure analysis (USEPA, 2009e). The MDLs of approved
methods range from 0.00004 to 0.0001 mg/L. Applying a multiplier of 10
would give a possible PQL range from 0.0004 to 0.001 mg/L, which is
below the current MCLG (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of
information, EPA believes that there is potential to lower the PQL for
1,1,2-trichloroethane. To determine whether any MCL revision is likely
to provide a meaningful opportunity to improve public health
protection, EPA evaluated the occurrence of 1,1,2-trichloroethane at
the current MCLG of 0.003 mg/L (USEPA, 2009f). Table VI-28 shows the
results of the occurrence and exposure analysis for the current MCL and
the current MCLG of 0.003 mg/L. The occurrence and exposure analysis
shows that average concentrations do not exceed the current MCL for any
system in the analysis. Note that these results are based on the subset
of monitoring data provided in response to the Six-Year Review ICR and
do not necessarily reflect MCL violations, which are based on annual
average concentrations at entry points; SDWIS/FED indicates six MCL
violations for 1,1,2-trichloroethane between 1998 and 2005 (USEPA,
2007g). The average concentration at one out of 50,195 systems (0.002
percent), serving approximately 700 people (or 0.0003 percent of 227
million people), exceeds the current MCLG of 0.003 mg/L.

 Table VI-28--Number and Percent of Systems With Mean Concentrations Exceeding 1,1,2-Trichloroethane Thresholds
                                and Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                        Systems with mean concentrations that are greater than the regulatory or
                                        health-based threshold (percentages based on 50,195 systems with 1,1,2-
                                          trichloroethane data in the Six-Year Review ICR occurrence dataset)
 Regulatory or health-based threshold --------------------------------------------------------------------------
                                                                                Nondetect
                                         Nondetect values = MRL \1\    Nondetect values = \1/2\ MRL   values = 0
                                                                                \2\                   \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).....................  0 (0.000%)...................  0 (0.000%)...................   0 (0.000%)
Current MCLG (0.003 mg/L)............  1 (0.002%)...................  1 (0.002%)...................   1 (0.002%)
----------------------------------------------------------------------------------------------------------------
                                        Corresponding population served (Percentages based on 226,852,000 people
                                          served by the systems with 1,1,2-trichloroethane data in the Six-Year
                                                             Review ICR occurrence dataset)
                                      --------------------------------------------------------------------------
 Regulatory or health-based threshold    Nondetect values = MRL \1\    Nondetect values = \1/2\ MRL   Nondetect
                                                                                \2\               values = 0
                                                                                \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).....................  0 (0.000%)...................  0 (0.000%)...................   0 (0.000%)
Current MCLG (0.003 mg/L)............  700 (0.0003%)................  700 (0.0003%)................          700
                                                                                (0.0003%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the
MCL is unlikely to provide a meaningful opportunity to improve the
level of public health protection, it was not necessary to perform any
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for 1,1,2-
trichloroethane is appropriate at this time. The occurrence and
exposure analysis based on possible changes in analytical feasibility
indicates that any revision to the MCL is unlikely to provide a
meaningful opportunity to improve public health protection. Taking into
consideration the low occurrence of this contaminant, EPA has decided
that any revision to the NPDWR would be a low priority activity for the
Agency, and, thus, is not appropriate to revise at this time because
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to
implement any regulatory change that resulted.
68. Trichloroethylene
    a. Background. EPA published the current NPDWR for
trichloroethylene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The
NPDWR established an MCLG of zero based on a cancer classification of
B2, probable human carcinogen. The NPDWR also established an MCL of
0.005 mg/L, based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to trichloroethylene. The revised
health effects assessment will consider relevant studies on the
toxicity of trichloroethylene, including its potential developmental
and reproductive toxicity. The new health effects assessment was not
completed by March 1, 2009, the review cutoff date for this notice
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date
information on the status of the health effects assessment.
    Although a risk assessment is in process for trichloroethylene, the
existing MCLG is zero and the current MCL of 0.005 mg/L is based on the
PQL. Therefore, EPA reviewed whether there is potential to revise the
PQL. EPA reviewed PE data from the first Six-Year Review cycle and then
analyzed more recent PT data to determine if the PQL can be revised
(i.e., analytical feasibility). Passing rates for PE data available
through late 1999 for trichloroethylene are above 95 percent at the
lowest concentrations. However, the true concentrations were all higher
than the current PQL of 0.005 mg/L. More recent PT data from 1999 to
2004, supplied by a PT provider, also show greater than 95 percent
passing rates for studies around the current PQL, including 6 with true
values below the PQL. Because most of the laboratory passing rates from
PE and PT studies exceeded the 75 percent criterion typically used to
derive a PQL, including several with true values below the PQL, a
lowering of the PQL for trichloroethylene might be possible. These
results, however, are insufficient to recalculate a revised PQL for
trichloroethylene because not enough data points are available below
the current PQL to derive a value at the 75 percent passing rate
(USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: laboratory
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved
methods for the detection of trichloroethylene (Methods 502.2, 524.2,
and 551.1). While EPA prefers to use laboratory performance data to
calculate the PQL, the MRL and MDL information can be valuable for this
review to indicate whether it is possible to quantitate at levels below
the current PQL. EPA also noted that the State of New Jersey uses a PQL
of 0.001 mg/L, based on a 1987 study of laboratory performance at low
concentrations that used criteria similar to those in the PT data
(NJDWQI, 1987). The Six-Year Review ICR dataset contains MRLs for
138,439 samples. More than 80 percent of these values are less than or
equal the modal MRL: 118,193 (85 percent) equal the modal MRL of 0.0005
mg/L and an additional 17,057 (12 percent) are lower than 0.0005 mg/L.
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The
MDLs of approved methods range are 0.00006, 0.00019, and 0.000042 mg/L.
Applying a multiplier of 10 would give a possible PQL range from
0.00042 to 0.0019 mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of
information, EPA believes that there is potential to lower the PQL for
trichloroethylene. To determine whether any MCL revision is likely to
provide a meaningful opportunity to improve public health protection,
EPA evaluated the occurrence of trichloroethylene at the EQL of 0.0005
mg/L and additional thresholds of 0.0010 and 0.0025 mg/L (USEPA,
2009f). Table VI-29 shows the results of the occurrence and exposure
analysis for the current MCL and these thresholds. The occurrence and
exposure analysis shows that average concentrations exceed the current
MCL for 25 out of 50,432 systems (0.050 percent) serving approximately
410,000 people (or 0.181 percent of 227 million people). Note that
these results are based on the subset of monitoring data provided in
response to the Six-Year Review ICR and do not necessarily reflect MCL
violations, which are based on annual average concentrations at entry
points; SDWIS/FED indicates 191 MCL violations for trichloroethylene
between 1998 and 2005 (USEPA, 2007g), with annual violations ranging
from 12 to 31. Average concentrations at 310 to 388 of 50,432 systems
(0.615 to 0.769 percent), serving approximately 12.0 to 13.0 million
people (or 5.237 to 5.670 percent of 227 million people), exceed the
EQL of 0.0005 mg/L. While these systems are widely distributed and
located in most of the States providing data, a few large systems
(serving 500,000 or more people) account for almost half of the exposed
population.

 Table VI-29--Number and Percent of Systems With Mean Concentrations Exceeding Trichloroethylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 50,432 systems with
 Regulatory or feasibility-based       trichloroethylene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  25 (0.050%)..............  25 (0.050%).............  25 (0.050%)
\1/2\ MCL (0.0025 mg/L)..........  70 (0.139%)..............  68 (0.135%).............  64 (0.127%)
2xEQL (0.001 mg/L)...............  239 (0.474%).............  208 (0.412%)............  182 (0.361%)
EQL (0.0005 mg/L)................  not applicable...........  388 (0.769%)............  310 (0.615%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,908,000 people
                                    served by the systems with trichloroethylene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect Values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  410,000 (0.181%).........  410,000 (0.181%)........  410,000 (0.181%)
\1/2\ MCL (0.0025 mg/L)..........  4,765,000 (2.100%).......  4,691,000 (2.067%)......  4,598,000 (2.026%)
2xEQL (0.001 mg/L)...............  10,367,000 (4.569%)......  8,282,000 (3.650%)......  7,399,000 (3.261%)
EQL (0.0005 mg/L)................  not applicable...........  12,866,000 (5.670%).....  11,884,000 (5.237%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that a revision to the MCL
may provide a meaningful opportunity to improve the level of public
health protection, EPA considered whether treatment feasibility is
likely to pose any limitations if the MCL were lowered (USEPA, 2009g).
The current BATs for trichloroethylene are packed tower aeration (PTA)
and granular activated carbon (GAC). Small system compliance
technologies for trichloroethylene include GAC and several aeration
technologies. EPA's assessment shows that PTA and GAC are effective
enough to achieve concentrations as low as the EQL.
    EPA is not currently able to assess the potential health benefits
from a revised MCL for trichloroethylene, because the revised health
effects assessment is not yet available. However, based on its B2
cancer classification (MCLG of zero) and the occurrence and exposure
analysis at possible MCL values, the Agency believes that a revision to
the MCL may provide a meaningful opportunity to reduce public health
risks.
    c. Review Result. The Agency believes it is appropriate to revise
the NPDWR for trichloroethylene although a health effects assessment is
currently in progress. The existing MCLG is zero (based on the current
B2 cancer classification) and the current MCL is based on a PQL (i.e.,
analytical feasibility) of 0.005 mg/L. The Agency's review indicates
that analytical feasibility could be as much as 10 times lower (~
0.0005 mg/L) and occurrence at this level appears to be relatively
widespread. Hence, revisions to the trichloroethylene NPDWR may provide
a meaningful opportunity for health risk reduction. If the updated
health effects assessment is completed in time to consider for the
regulatory revision of trichloroethylene, the Agency will consider this
assessment in its evaluation of public health benefits associated with
any revision. As discussed in Section VII, the Agency solicits public
comment and/or relevant information that may inform the regulatory
revision for trichloroethylene. EPA is also requesting that
stakeholders provide information/data about the lowest level of
quantitation (including the analytical method used) that laboratories
can reliably and consistently achieve.
69. Uranium
    a. Background. EPA published the current NPDWR for uranium on
December 7, 2000 (65 FR 76708 (USEPA, 2000c)). The NPDWR established an
MCLG of zero based on a cancer classification of A, known human
carcinogen. As noted in the December 2000 FR, uranium has also been
identified as a nephrotoxic metal (kidney toxicant) and EPA derived a
drinking water equivalent level of 20 [mu]g/L as a noncancer health
endpoint for kidney toxicity. The NPDWR also established an MCL of 30
[mu]g/L, which is higher than the feasible level of 20 [mu]g/L and the
level associated with kidney toxicity. In December 2000, EPA exercised
its discretionary authority to set an MCL at a level higher than
feasible (SDWA Section 1412(b)(6)), based on the finding that
``benefits do not justify the costs at the feasible level (20 [mu]g/L)
and that the net benefits are maximized at a level (30 [mu]g/L) that is
still protective of health with an adequate margin of safety'' (65 FR
76708 (USEPA, 2000c)) \25\.
---------------------------------------------------------------------------

    \25\ After the December 7, 2000 final regulation, two trade
associations and several municipal water systems challenged EPA's
standard for uranium by claiming that the Agency did not use the
best available science when finalizing the standard. In February of
2003, the DC Circuit Court of Appeals upheld EPA's regulation for
uranium (as well as combined radiums, and beta particle and photon
emitters).
---------------------------------------------------------------------------

    b. Technical Reviews. EPA has initiated a reassessment of the
health risks resulting from exposure to uranium. The revised health
effects assessment will consider relevant studies on the toxicity of
uranium, including its potential developmental and reproductive
toxicity. The new health effects assessment was not completed by March
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The
IRIS Substance Assessment Tracking System Web site (http://
cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information
on the status of the health effects assessment.
    c. Review Result. The Agency does not believe a revision to the
NPDWR for uranium is appropriate at this time because a reassessment of
the health risks resulting from exposure to

uranium is ongoing (USEPA, 2009b). As noted previously, the uranium MCL
is based on the SDWA cost benefit provision (Section 1412(b)(6)) and
the health effects assessment is important for reviewing the benefits
associated with the basis of the MCL.
70. Vinyl Chloride
    a. Background. EPA published the current NPDWR for vinyl chloride
on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR established an
MCLG of zero based on a cancer classification of A, known human
carcinogen. The NPDWR also established an MCL of 0.002 mg/L, based on
analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA
conducted a literature search for relevant data on the carcinogenicity
of vinyl chloride as well as its potential developmental and
reproductive toxicity. EPA has not identified any new information that
indicates that it is appropriate to consider revisions to the cancer
classification for vinyl chloride at this time (USEPA, 2009b). Because
the MCLG remains at zero, the Agency believes that a further review of
the health effects of vinyl chloride is not warranted at this time.
    The current MCL for vinyl chloride is based on a PQL of 0.002 mg/L.
For the Six-Year Review, the Agency considered whether changes in the
analytical feasibility of vinyl chloride might lead to a lower MCL. EPA
reviewed PE data from the first Six-Year Review cycle and then analyzed
more recent PT data to determine if the PQL can be revised (i.e.,
analytical feasibility). Passing rates for PE data available through
late 1999 for vinyl chloride are generally in the 75 to 80 percent
range near the current PQL of 0.002 mg/L, but there were no results for
PE studies with true values below the current PQL. More recent PT data
from late 1999 through 2004, supplied by a PT provider, also show
greater than 80 percent passing rates for studies around the current
PQL, including two studies with true values below the PQL. Despite the
limited data below the PQL, most of the laboratory passing rates from
PE and PT studies--including two with true concentrations below the
PQL--exceeded the 75 percent criterion usually used to derive a PQL.
Therefore, a lowering of the PQL for vinyl chloride might be possible
(USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine
whether an EQL below the current PQL could be estimated: laboratory
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved
methods for the detection of vinyl chloride (Methods 502.2 and 524.2).
While EPA prefers to use laboratory performance data to calculate the
PQL, the MRL and MDL information can be valuable for this review to
indicate whether it is possible to quantitate at levels below the
current PQL. The Six-Year Review ICR dataset contains MRL values for
139,494 samples. More than 80 percent of these values are less than or
equal the modal MRL: 105,410 (76 percent) equal the modal MRL of 0.0005
mg/L and an additional 25,723 (18 percent) are lower than 0.0005 mg/L.
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The
MDLs of approved methods range from 0.00017 to 0.00018 mg/L. Applying a
multiplier of 10 would give a possible PQL range from 0.0017 to 0.0018
mg/L, which is higher than the EQL, but below the current PQL (USEPA,
2009e).
    Based on these varied and unrelated approaches/sources of
information, EPA believes that there may be potential to lower the PQL
for vinyl chloride. To determine whether any MCL revision is likely to
provide a meaningful opportunity to improve public health protection,
EPA evaluated the occurrence of vinyl chloride at the EQL of 0.0005 mg/
L and an additional threshold of 0.001 mg/L (USEPA, 2009f). Table VI-30
shows the results of the occurrence and exposure analysis for the
current MCL and these thresholds. The occurrence and exposure analysis
shows that average concentrations exceed the current MCL for 8 to 11 of
50,411 systems (0.016 to 0.022 percent) serving fewer than 14,000
people (or 0.003 to 0.006 percent of 226 million people). Note that
these results are based on the subset of monitoring data provided in
response to the Six-Year Review ICR and do not necessarily reflect MCL
violations, which are based on annual average concentrations at entry
points; SDWIS/FED indicates 25 MCL violations for vinyl chloride
between 1998 and 2005 (USEPA, 2007g). Average concentrations at 32 to
49 of 50,411 systems (0.063 to 0.097 percent), serving 483,000 to
766,000 people (or 0.213 to 0.338 percent of 226 million people),
exceed the EQL of 0.0005 mg/L.

   Table VI-30--Number and Percent of Systems With Mean Concentrations Exceeding Vinyl Chloride Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                    feasibility-based threshold (percentages based on 50,411 systems with vinyl
 Regulatory or feasibility-based            chloride data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).................  11 (0.022%)..............  10 (0.020%).............  8 (0.016%)
\1/2\ MCL (0.001 mg/L)...........  21 (0.042%)..............  18 (0.037%).............  15 (0.030%)
EQL (0.0005 mg/L)................  not applicable...........  49 (0.097%).............  32 (0.063%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding Population Served (Percentages based on 226,464,000 people
                                      served by the systems with vinyl chloride data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).................  14,000 (0.006%)..........  12,000 (0.005%).........  6,000 (0.003%)
\1/2\ MCL (0.001 mg/L)...........  56,000 (0.025%)..........  23,000 (0.010%).........  18,000 (0.008%)
EQL (0.0005 mg/L)................  not applicable...........  766,000 (0.338%)........  483,000 (0.213%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the
MCL is unlikely to provide a meaningful opportunity to improve the
level of public health protection, it was not necessary to perform any
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support
consideration of a possibly lower PQL (and therefore a possibly lower
MCL), EPA does not believe a revision to the NPDWR for vinyl chloride
is appropriate at this time. The occurrence and exposure analysis based
on possible changes in analytical feasibility indicates that any
revision to the MCL is unlikely to provide a meaningful opportunity to
improve public health protection. Taking into consideration the low
occurrence of this contaminant, EPA has decided that any revision to
the NPDWR would be a low priority activity for the Agency, and, thus,
is not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to
implement any regulatory change that resulted.
71. Xylenes (Total)
    a. Background. EPA published the current NPDWR for total xylenes on
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an
MCLG and an MCL of 10 mg/L. EPA based the MCLG on a reference dose of 2
mg/kg-day and a cancer classification of D, not classifiable as to
human carcinogenicity.
    b. Technical Reviews. In 2003, the Agency updated its health
effects assessment of xylenes (USEPA, 2003d). The change in this
assessment could lead to a change in the MCLG. This assessment
considered relevant studies on the toxicity of xylenes including
developmental and reproductive toxicity. The assessment revised the RfD
from 2 mg/kg-day to 0.2 mg/kg-day and concluded that there is
inadequate information to assess the carcinogenic potential of xylenes
(USEPA, 2003d). Based on the new IRIS assessment and RfD of 0.2 mg/kg-
day, and assuming a 70-kg adult body weight and 2 liters water intake
per day, the DWEL could be 7 mg/L. An RSC of 20 percent results in a
possible MCLG of 1 mg/L.
    Analytical feasibility does not pose any limitations for the
current MCL and would not be a limiting factor for the possible MCLG
decrease under consideration. EPA evaluated the results of the
occurrence and exposure analyses for total xylenes to determine whether
a revised MCLG/MCL would be likely to result in a meaningful
opportunity to improve the level of public health protection (USEPA,
2009f). Table VI-31 shows the results of the occurrence and exposure
analysis for the current MCL and the possible MCLG set equal to 1 mg/L
based on the new health effects information. The occurrence and
exposure analysis shows that average concentrations do not exceed the
current MCL for any system in the analysis. Note that these results are
based on the subset of monitoring data provided in response to the Six-
Year Review ICR and do not necessarily reflect MCL violations, which
are based on annual average concentrations at entry points; SDWIS/FED
indicates two MCL violations for xylene between 1998 and 2005 (USEPA,
2007g). The occurrence and exposure analysis shows that average
concentrations do not exceed the possible MCLG based on new health
effects information (1 mg/L).

       Table VI-31--Number and Percent of Systems With Mean Concentrations Exceeding Xylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                    health-based threshold (percentages based on 47,698 systems with xylene data
    Regulatory or health-based                     in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (10 mg/L)....................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (1 mg/L)...........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population Served (percentages based on 218,072,000 people
                                    served by the systems with xylene data in the Six-Year Review ICR occurrence
                                                                      dataset)
                                  ------------------------------------------------------------------------------
Regulatory or health-based           Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
 threshold.......................              \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (10 mg/L)....................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (1 mg/L)...........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the
MCL is unlikely to provide a meaningful opportunity to improve the
level of public health protection, it was not necessary to perform any
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support
consideration of whether to revise the MCLG/MCL for total xylenes, EPA
does not believe a revision to the NPDWR for total xylenes is
appropriate at this time. In making this decision, the Agency
considered whether any possible revision to the NPDWR for total xylenes
is likely to provide a meaningful opportunity for health risk
reductions. Taking into consideration the low occurrence of this
contaminant, EPA has decided that any revision to the NPDWR would be a
low priority activity for the Agency, and, thus, is not appropriate to
revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to
implement any regulatory change that resulted.

VII. EPA's Request for Comments

A. Request for Comment and/or Information on the Candidates for
Revision

    EPA invites commenters to submit any new, relevant peer-reviewed
data or information pertaining to the four

NPDWRs identified in today's action as candidates for revision (i.e.,
acrylamide, epichlorohydrin, tetrechloroethylene and
trichloroethylene). This information will inform EPA's evaluation as
the Agency moves forward with the regulatory revisions for these four
NPDWRs. Peer reviewed data are studies/analyses that have been reviewed
by qualified individuals (or organizations) who are independent of
those who performed the work, but who are collectively equivalent in
technical expertise (i.e., peers) to those who performed the original
work. A peer review is an in-depth assessment of the assumptions,
calculations, extrapolations, alternate interpretations, methodology,
acceptance criteria, and conclusions pertaining to the specific major
scientific and/or technical work products and of the documentation that
supports them (USEPA, 2000d). Relevant data include studies/analyses
pertaining to analytical feasibility, treatment feasibility, and
occurrence/exposure related to the four NPDWRs candidates for revision
listed in today's action.\26\ Table VII-1 provides a list of the
specific items for which EPA is requesting comment and/or information
for the four candidates for revision. It also provides a cross-
reference to the section addressing the issue.

      Table VII-1--Items for Which EPA Is Requesting Comment and/or
            Information for the Four Candidates for Revision
------------------------------------------------------------------------
                 Issue                           Notice section
------------------------------------------------------------------------
Any new, relevant peer-reviewed data    Section VI.B.1.
 or information that would inform the
 revision of the NPDWR for acrylamide,
 including information pertaining to
 extent of use of polyacrylamide in
 drinking water facilities.
Any new, relevant peer-reviewed data    Section VI.B.36.
 or information that would inform the
 revision of the NPDWR for
 epichlorohydrin, including
 information pertaining to extent of
 use of epichlorohydrin-based polymers/
 co-polymers in drinking water
 facilities.
Any new, relevant peer-reviewed data    Section VI.B.60.
 or information that would inform the
 revision of the NPDWR for
 tetrachloroethylene, including
 information/data about the lowest
 level of quantitation (and analytical
 method used) that laboratories can
 reliably and consistently achieve.
Any new, relevant peer-reviewed data    Sections VI.B.65.
 or information that would inform the
 revision of the NPDWR for
 trichloroethylene, including
 information/data about the lowest
 level of quantitation (and the
 analytical method used) that
 laboratories can reliably and
 consistently achieve.
------------------------------------------------------------------------

B. Request for Information/Data on Other Review Topics

    EPA also invites commenters to submit new, relevant information on
several other review topics referenced in this notice and listed in
Table VII-2.

   Table VII-2--Issues for Which EPA Is Requesting Public Input and/or
                               Information
------------------------------------------------------------------------
              Issue                           Notice section
------------------------------------------------------------------------
Location for nitrate and nitrite  Section V.B.6.
 monitoring.
Monitoring frequency for ground   Section V.B.6.
 water systems with low nitrate
 and nitrite concentrations.
Monitoring requirements for non-  Section V.B.6.
 community water systems.
Detection limits that serve as    Section V.B.6.
 triggers to determine
 compliance monitoring frequency
 for SOCs.
New, relevant health effects      Section VI.B.17.
 information that will help the
 Agency decide whether to
 initiate a new health effects
 assessment for chromium.
New, relevant health effects      Sections VI.B.49 and VI.B.50.
 information that will help the
 Agency decide whether to
 initiate or nominate nitrate
 and nitrite for a new health
 effects assessment.
New, relevant health effects      Sections VI.B.56.
 information that will help the
 Agency decide whether to
 initiate or nominate selenium
 for a new health effects
 assessment.
New, relevant health effects      Sections VI.B.65.
 information that will help the
 Agency decide whether to
 initiate or nominate 1,2,4-
 trichlorobenzene for a new
 health effects assessment.
------------------------------------------------------------------------

C. Requests for Information on the Impacts of Climate Change on Water
Quality

    The Agency recognizes that changes in global climate can impact
temperature, rainfall patterns, and snow and ice cover. Changes in
these climate indicators can impact water quantity and water quality.
In an effort to assess the impacts of climate change on water quality,
EPA is asking if public water systems and/or States have any
information or data that illustrates the impact of climate change
(e.g., changes in rainfall, drought, temperature, and snow/ice cover)
on the occurrence of contaminants in drinking water, both in source
water and in finished water. EPA also requests data on changes in the
variability of occurrence and impacts on drinking water treatment to
address occurrence or variability changes.
---------------------------------------------------------------------------

    \26\ Note that new health effects studies/information for
acrylamide, PCE and TCE are being considered as part of the IRIS
update to these health assessments.
---------------------------------------------------------------------------

VIII. EPA's Next Steps

    EPA will consider the public comments and/or any new, relevant,
peer-reviewed data submitted for the four NPDWRs listed as candidates
for revision as the Agency proceeds with the regulatory revisions for
these regulations. The announcement that the Agency intends to revise
an NPDWR (pursuant to SDWA section 1412(b)(9)) is not a regulatory
decision. Instead, it initiates a regulatory process that will involve
more detailed analyses of health effects, analytical and treatment
feasibility, occurrence, benefits, costs, and other regulatory matters
relevant to deciding whether an NPDWR should be revised. The Six-Year
Review results do not obligate the Agency to revise an NPDWR in the
event that EPA determines during the regulatory process that revisions
are no longer

appropriate and discontinues further efforts to revise an NPDWR.
Similarly, the fact that an NPDWR has not been selected for revision
means only that EPA believes that regulatory changes to a particular
NPDWR are not appropriate at this time for the reasons given in today's
action; future reviews may identify information that leads to an
initiation of the revision process.

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USEPA. 2000c. National Primary Drinking Water Regulations;
Radionuclides; Final Rule. Federal Register. Vol. 65, No. 236. p.
76707, December 7, 2000.
USEPA. 2000d. Science Policy Council Handbook: Peer Review, 2nd
Edition. EPA Report 100-B-00-001. Washington, DC: Office of Science
Policy, Office of Research and Development. December 2000. Available
on the Internet at: http://www.epa.gov/OSA/spc/pdfs/prhandbk.pdf.
USEPA. 2001a. HED Toxicology Chapter for Diquat Dibromide.
Washington, DC: Office of Prevention, Pesticides and Toxic
Substances.
USEPA. 2001b. IRIS, Hexachlorocyclopentadiene. Available on the
Internet at: http://www.epa.gov/ncea/iris/subst/0059.htm.
USEPA. 2001c. National Primary Drinking Water Regulation; Arsenic
and Clarifications to Compliance and New Source Contaminants
Monitoring; Final Rule. Federal Register. Vol. 66, No. 14. p. 6975,
January 22, 2001.
USEPA. 2001d. Public Health and Environmental Radiation Protection
Standards for Yucca Mountain, NV; Final Rule. Federal Register.
Volume 66, Number 114. p. 32073, June 13, 2001.
USEPA. 2002a. Glyphosate in/on pasture and rangeland grasses,
Roundup Ready[reg] wheat, and non-grass animal feeds. Health Effects
Division (HED) Risk Assessment. PPs 0F06130, 0F06195, and
0F06273. Barcode D280831. PC Codes 103601 & 417300. Case 292955.
Submission S579658. Washington, DC: Office of Prevention,
Pesticides, and Toxic Substances.
USEPA. 2002b. IRIS, 1,1-Dichloroethylene. Available on the Internet
at: http://www.epa.gov/ncea/iris/subst/0039.htm.
USEPA. 2002c. National Primary Drinking Water Regulations--
Announcement of the Results of EPA's Review of Existing Drinking
Water Standards and Request for Public Comment; Proposed Rule.
Federal Register. Vol. 67, No. 74. p. 19030, April 17, 2002.
USEPA. 2002d. Report of the Food Quality Protection Act (FQPA)
Tolerance Reassessment Progress and Risk Management Decision (TRED):
Diquat Dibromide. Washington, DC: Office of Prevention, Pesticides
and Toxic Substances. April 2002. Available on the Internet at:
http://www.epa.gov/oppsrrd1/REDs/diquat_tred.pdf.
USEPA. 2003a. Analytical Feasibility Support Document for the Six-
Year Review of Existing National Primary Drinking Water Regulations
(Reassessment of Feasibility for Chemical Contaminants). EPA 815-R-
03-003. March 2003.
USEPA. 2003b. EPA Protocol for Review of Existing National Primary
Drinking Water Regulations. EPA Report 815-R-03-002. Washington, DC:
Office of Ground Water and Drinking Water. June 2003. Available on
the Internet at: http://www.epa.gov/safewater/standard/review/pdfs/
support_6yr_protocal_final.pdf.
USEPA. 2003c. Exposure and Human Health Reassessment of 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds.
Preliminary Review Draft. National Center for Environmental
Assessment, Research and Development.
USEPA. 2003d. IRIS, Xylenes. Available on the Internet at: http://
www.epa.gov/ncea/iris/subst/0270.htm.
USEPA. 2003e. National Primary Drinking Water Regulations;
Announcement of Completion of EPA's Review of Existing Drinking
Water Standards; Notice. Federal Register. Vol. 68, No. 138. p.
42908, July 18, 2003.
USEPA. 2004a. IRIS, 1,2-Dibromoethane. Available on the Internet at:
http://www.epa.gov/ncea/iris/subst/0361.htm.
USEPA. 2004b. National Primary Drinking Water Regulations: Minor
Corrections and Clarification to Drinking Water Regulations;
National Primary Drinking Water Regulations for Lead and Copper.
Federal Register. Volume 69, Number 124. p. 38850, June 29, 2004.
USEPA. 2004c. Reregistration Eligibility Decision (RED)--
Methoxychlor. EPA Report 738-R-04-010. Washington, DC: Office of
Prevention, Pesticides, and Toxic Substances. June 2004. Available
on the Internet at: http://www.epa.gov/oppsrrd1/REDs/methoxychlor_
red.htm.
USEPA. 2005a. IRIS, Barium. Available on the Internet at: http://
www.epa.gov/ncea/iris/subst/0010.htm.
USEPA. 2005b. IRIS, Toluene. Available on the Internet at: http://
www.epa.gov/ncea/iris/subst/0118.htm.
USEPA. 2005c. Reregistration Eligibility Decision (RED)--2,4-D. EPA
Report 738-R-05-002. Office of Prevention, Pesticides, and Toxic
Substances. June 2005. Available on the Internet at: http://
www.epa.gov/oppsrrd1/REDs/24d_red.pdf.
USEPA. 2005d. Reregistration Eligibility Decision (RED) for
Endothall. EPA Report 738-R-05-008. Office of Prevention, Pesticides
and Toxic Substances. September 2005. Available on the Internet at:
http://www.epa.gov/oppsrrd1/reregistration/REDs/

endothall_red.pdf.
USEPA. 2006a. Acetochlor/Alachlor: Cumulative Risk Assessment for
the Chloroacetanilides. Washington, DC: Office of Pesticide
Programs. March 8, 2006. Available on the Internet at: http://
www.epa.gov/oppsrrd1/cumulative/chloro_cumulative_risk.pdf.
USEPA. 2006b. Addendum to the 2002 Lindane Reregistration
Eligibility Decision (RED). EPA Report 738-R-06-028. Washington, DC:
Office of Prevention, Pesticides, and Toxic Substances. July 2006.
Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/
lindane_red_addendum.pdf.
USEPA. 2006c. Finalization of Atrazine IRED, and Completion of
Tolerance Reassessment and Reregistration Eligibility Process.
Washington, DC: Office of Prevention, Pesticides, and Toxic
Substances. April 2006. Available on the Internet at: http://
www.epa.gov/oppsrrd1/REDs/atrazine_combined_docs.pdf.
USEPA. 2006d. Interim Reregistration Eligibility Decision (IRED)--
Carbofuran. EPA Report 738-R-06-031. Office of Prevention,
Pesticides, and Toxic Substances. August 2006. Available on the
Internet at: http://www.epa.gov/oppsrrd1/reregistration/REDs/
carbofuran_ired.pdf.
USEPA. 2006e. Lindane; Cancellation Order. Federal Register. Vol.
71, No. 239. p. 74905, December 13, 2006.
USEPA. 2006f. National Primary Drinking Water Regulations: Ground
Water Rule; Final Rule. Federal Register. Vol. 71, No. 216. p.
65574, November 8, 2006.
USEPA. 2006g. National Primary Drinking Water Regulations: Long Term
2 Enhanced Surface Water Treatment Rule; Final Rule. Federal
Register. Vol. 71, No. 3. p. 654, January 5, 2006.
USEPA. 2006h. National Primary Drinking Water Regulations: Stage 2
Disinfectants and Disinfection Byproducts Rule; Final Rule. Federal
Register. Vol. 71, No. 2. p. 388, January 4, 2006.
USEPA. 2006i. Reregistration Eligibility Decision (RED)--Simazine.
EPA Report 738-R-06-008. Washington, DC: Office of Prevention,
Pesticides, and Toxic Substances. April 2006. Available on the
Internet at: http://www.epa.gov/oppsrrd1/REDs/simazine_red.pdf.
USEPA. 2007a. Advisory on EPA's Assessments of Carcinogenic Effects
of Organic and Inorganic Arsenic: A Report of the U.S. EPA Science
Advisory Board (SAB). EPA-SAB-07-008. June 2007. Available on the
Internet at: http://yosemite.epa.gov/sab/sabproduct.nsf/
EADABBF40DED2A0885257308006741EF/$File/sab-07-008.pdf.
USEPA. 2007b. Draft Toxicological Review of Acrylamide: In Support
of Summary Information on the Integrated Risk Information System
(IRIS). Federal Register. Vol. 72, No. 248. p. 73813, December 28,
2007.
USEPA. 2007c. Integrated Risk Information System (IRIS);
Announcement of 2008 Program; Notice. Federal Register. Vol. 72, No.
245. p. 72715, December 21, 2007.
USEPA. 2007d. IRIS, 1,1,1-Trichloroethane. Available on the Internet
at: http://www.epa.gov/ncea/iris/subst/0197.htm.
USEPA. 2007e. Unregulated Contaminant Monitoring Regulation (UCMR)
for Public Water Systems; Revisions; Final Rule. Federal Register.
Vol. 72, No, 2. p. 367, January 4, 2007.
USEPA. 2007f. National Primary Drinking Water Regulations for Lead
and Copper: Short-Term Regulatory Revisions and Clarifications;
Final Rule. Federal Register. Vol. 72, No. 195. p. 57782, October
10, 2007.
USEPA. 2007g. Safe Drinking Water Information System/Federal version
(SDWIS/FED) FY2006 Inventory Data. Available online at http://
www.epa.gov/ogwdw000/databases/pivottables.html.
USEPA. 2008a. Carbofuran; Proposed Tolerance Revocations; Proposed
Rule. Federal Register. Vol. 73, No. 87. p. 44864, July 31, 2008.
USEPA. 2009a. EPA Protocol for the Second Review of Existing
National Primary Drinking Water Regulations (Updated). EPA Report
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USEPA. 2009b. Six-Year Review 2- Health Effects Assessment--Summary
Report. EPA Report 822-R-09-006. October 2009.
USEPA. 2009c. Analytical Feasibility Support Document for the Second
Six-Year Review of Existing National Primary Drinking Water
Regulations. EPA Report 815-B-09-003. October 2009.
USEPA. 2009d. Occurrence Analysis for Potential Source Waters for
the Second Six-Year Review of National Primary Drinking Water
Regulations. EPA Report 815-B-09-004. October 2009.
USEPA. 2009e. Development of Estimated Quantitation Levels for the
Second Six-Year Review of National Primary Drinking Water
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USEPA. 2009g. Water Treatment Technology Feasibility Support
Document for Chemical Contaminants for the Second Six-Year Review of
National Primary Drinking Water Regulations. EPA Report 815-B-09-
007. October 2009.
USEPA. 2009h. Consideration of Other Regulatory Revisions in Support
of the Second Six-Year Review of the National Primary Drinking Water
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USEPA. 2009j. Carbofuran; Product Cancellation Order; Notice.
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ncea/iris/toxreviews/1012-tr.pdf.
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Journal of Chinese Preventive Medicine. v. 21, pp. 262-264.

    Dated: December 17, 2009.
Lisa P. Jackson,
Administrator.
[FR Doc. 2010-6624 Filed 3-26-10; 8:45 am]
BILLING CODE 6560-50-P