DRAFT
  Guidance in Developing Health Criteria
                       for
Determining Unreasonable Risks to Health
                    October, 1990
                Office of Drinking Water
            U.S. Environmental Protection Agency
                 Washington, DC 20460
                                           Printed on Recycled Paper

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Purpose

     The purpose  of this guidance is to  provide  information  and
recommendations  on  the health  based  criteria that  should  be
considered in  determining  an unreasonable risk to  health (URTH)
for drinking water contaminants.   This guidance will assist States
having primacy in  the  issuance of a  variance or exemption from a
Maximum  Contaminant  Level  (MCL).    In  this guidance,  EPA  is
providing  several  ways that  an  URTH value might be  determined.
Actual values  are stated for various contaminants  with  an upper
bound URTH level that is recommended.

     This document provides EPA's guidance to States  on determining
URTH values.   It-does not establish or affect legal  rights or
obligations.   It  does  not establish a  binding norm and  is  not
finally determinative  of the  issues  addressed.   Agency decisions
in  any  particular  case  will  be  made applying  the  law  and
regulations on the basis of specific facts and actual action.

Background

     Under  Sections  1415  and  1416, respectively,  of  the  Safe
Drinking Water Act (SDWA) of 1974, as amended in 1986, States with
primacy may grant a variance or exemption to a public water supply
(PWS) from an MCL if the State finds that the variance or exemption
will not result in an unreasonable risk to health to  persons served
by the PWS.

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      In  1979, EPA developed a guidance document on the issuance of
variances or exemptions.  This document listed four criteria to be
considered in determining  the  *unreasonableness1 of risk:

      1.   The degree  to which  the MCL is or will be exceeded and
          the health  effects resulting therefrom;

      2.   The duration  of  the  requested variance or exemption;

      3.   Historical  data  (how long the problem has existed); and

      4.   The type of population  exposed.

      Utilizing  these  criteria,  an  URTH  level  was  generally
determined as any concentration of a  contaminant that was greater
than  two times the MCL.

      After the 1986 Amendments of the SDWA,  the 1979 URTH guidance
was reevaluated.  This document replaces the 1979 guidance and has
expanded on the above criteria  to better characterize the potential
health risks that may result with the exceedance of an MCL.

      Under SDWA section 1415,  a  variance may be issued to a PWS
only  after the system has applied the best technology or treatment
technique that  the Administrator finds available.  A variance  is
usually granted to a  system because the characteristics of  the raw

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water  supply  available to  the system are  such that the  system
cannot meet the requirements of the MCL(s)  despite application of
the best available technology.   At the time a variance is granted,
Section 1415(A)(i) provides that the primacy Stats shall prescribe
a schedule for compliance with the MCL(s).  The compliance schedule
may  include  increments  of  progress  and  the  implementation  of
additional control measures by the PWS to meet the MCL(s).

     Under SOW A section 1416, an exemption for a PWS may be granted
if the PWS is unable to comply with an MCL or treatment technique
for a drinking water contaminant.  The inability to comply may be
due  to compelling  factors  such  as  economic  constraints.    An
exemption  is  granted  for  one  year  with  an exten-sion for two
additional years, if necessary.   In  instances where a PWS serves
500 or less service connections,  an  exemption may be renewed for
one or more 2-year periods if  the system demonstrates that it is
taking all practicable steps for  compliance.

Approach for Developing Health  Criteria

     In developing the Health  Criteria for determining URTH, the
toxicity exhibited by  each contaminant is evaluated individually.
This is done^ in part, by considering any available risk assess-
ments conducted  for each  contaminant.   The various types of  risk
assessments that could be considered are discussed below.   In
evaluating the assessments,  carcinogenic risks  should be compared
with risks for non-cancer  health effects.  This comparison serves

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to  balance  the potential- risks.   Thus,  the  consideration  of one
type of risk such as cancer would not exclude the consideration of
another endpoint of toxicity such  as  reproductive effects.

Risk Aas<
     The Environmental Protection Agency (EPA) regulates contami-
nants  that may  pose an  adverse health  risk and  are  known  or
anticipated to occur in water.  Because of  the  chemical make up
and behavior  of  a given contaminant,  each contaminant may elicit
a  toxic response that differs  from  another contaminant.   The
toxicity for  a given contaminant is considered in developing the
Maximum Contaminant Level Goal  (MCLG), a  non-enforceable health
goal.  Under the SOW A, the MCL, or enforceable standard,  is set as
close to the  MCLG  as feasible.   Usually the  MCL will  equal the
MCLG.   In  some  cases  (e.g.,  carcinogens), however,  the MCL may
exceed  the MCLG  based on feasibility.   Although the MCL may be
somewhat higher  than the  health goal,  it represents a  level of
acceptable risk  that the  Agency  considers to be reasonable.

     Thus, MCLs  are determined  for each  contaminant considering
the  toxicity  exhibited  by   that  contaminant,   technological
capabilities, costs and residual risk.  Since  MCLs are determined
contaminant by contaminant, the level above an MCL that constitutes
an  unreasonable  risk  to  health  should   also  be   evaluated
           v         ,
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     The mechanism  for producing  a toxic  response  for a  given
contaminant may be considered as threshold or non-threshold.  For
a threshold response, exposure to a specific dose can result in a
toxic outcome, whereas for non-threshold response, exposure to any
level can  theoretically lead to a toxic outcome.   However,  the
hypothetical  risk  at low levels  can be  very small.   Most non-
cancer health effects are thought to result from a threshold level.
The biological mechanism for carcinogenesis is not well understood;
therefore,  a non-threshold mechanism is assumed.  EPA assesses the
health risks for threshold effects differently from non-threshold
effects.

     Threshold;   A  quantitative  risk  assessment for  threshold
contaminants can be derived through first determining a Reference
Dose (RfD).   The RfD can be  summarized  as an estimate of a daily
exposure to the human population,  including sensitive subpopula-
tions, that  is not likely to produce any adverse health effects
over a  lifetime.    The RfD  is  calculated  by dividing a  no- or
lowest-observed-adverse-effect   level   (NOAEL   or   LOAEL)   by
uncertainty  factors.   The NOAEL  or LOAEL  is  identified  from an
experimental  study of appropriate  exposure duration in humans or
animals reflecting  a sensitive endpoint  in a sensitive species.
The  uncertainty factors  may range from 1  to  10,000  or more,
depending  on the data base for  the chemical.   The uncertainty
factors are used to account for differences in response to toxicity
within and between species.   Additional factors may be used  when
a  NOAEL has  not been identified or to  account for  data  base

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quality.

     For  threshold  contaminants,  the RfD serves as  the  basis of
the  MCLG.   The  RfD is adjusted  for a 70-kg adult  consuming an
average of 2  liters of water per day over a lifetime (70 years).
The  resulting value is called a  Drinking Water Equivalent Level
(DWEL), and assumes that  all of  the exposure comes from drinking
water.  Since this  often is  not the case, the DWEL is adjusted by
an assumed or actual exposure (the relative source contribution;
RSC) from  drinking  water.   If  actual data  are  not  available,  a
range of 20 to 80%  may be used  for the RSC.  This final value is
the MCLG.

     In addition to the RfD, risk assessments are also conducted
for  less-than-lifetime exposures  to drinking water contaminants.
These are  expressed by EPA  in  non-enforceable  Health Advisories
(HAs).  The HAs are based  on non-cancer endpoints of toxicity and
are developed for exposures  of one day, ten days, longer-term (up
to seven years) , as well as  lifetime  (70 years)  .  They are calcu-
lated in a manner similar to the RfD with the exception that the
NOAELs and LOAELs are identified from studies where the exposure
duration is comparable to that which the HA represents in terms of
percentage of lifetime exposed.   In  addition,  less-than-lifetime
HAs are calculated for a 10 kg child consuming 1  liter of water per
day.  Other sources of exposure are generally not considered since
water is  assumed, to be the  major source o£ exposure for a short
period such as an accidental spill.  One-day HAs are based on acute

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exposure studies of 1 to. 7 days.  'The  Ten-day HA is derived from
human or animal studies with 30 days exposure or less.  The Longer-
term HA, calculated for both a  child and an adult, is derived from
subchronic  studies  based  on  exposure  periods  correlating  to
approximately 10 percent of an individual's lifetime.  Assuming a
70-year  lifetime,  the Longer-term  HA  correlates to  an exposure
period of up to 7 years.  The Lifetime HA is  determined in the same
way as the MCLG.

     Non-threshold:    The  EPA  assumes,  in  the absence  of  any
contrary data, that carcinogenicity is a toxic response that does
not have a threshold.  In other words, any exposure can lead to a
carcinogenic response.  The EPA evaluates contaminants that may be
carcinogenic  qualitatively as  well as quantitatively.    Table l
summarizes  the EPA cancer  classification  scheme.    This scheme
qualitatively ranks chemicals  as to their carcinogenic potential
in humans based on weight of evidence presented in the available
toxicological and epidemiological literature.

     If  toxicological  evidence leads to the  classification of a
contaminant as  a human  (Group  A),  probable human (Group B) or in
some instances  possible human  (Group C)  carcinogen,  mathematical
models can  be used to calculate  a theoretical upper-bound excess
cancer risk associated with the  ingestion  of the contaminant in
drinking water.  Using these models, risks  from oral  exposure  can
be estimated  for excess cancers  compared to the population (e.g.,
one in 10,000  [10*4] to one in  one million  [10**]).  The  10"* to 10"

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6 risk range is the target for setting MCLs for human or probable
human carcinogens.   Often data used in these estimates come from
lifetime exposure studies  in animals.

     MCLGs  for  non-threshold contaminants are set  at zero as an
aspirational goal.   The  MCL,  then, is  set as close  to zero as
feasible, generally falling in the excess cancer risk range of 10"
4 to 10"6.   MCLGs for Group C  contaminants are usually derived from
the RfD approach with an additional uncertainty factor of  1 to 10
to  account  for possible  carcinogenicity.    If  an RfD  is  not
available  for a Group C contaminant, the HCLG nay be set in the
range of 10"5 to 10"6.
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Group A;  Human carcinogen
Sufficient evidence  in epidemiologic or occupational  studies  to
support causal association between exposure and cancer in humans.
Group B;  Probable human carcinogen
Limited evidence  in human  studies  (Group Bl)  and/or sufficient
evidence from animal studies (Group B2)
Group Ct  Possible human carcinogen
Limited evidence from animal studies and inadequate or no data in
humans
Group D;  Not classifiable
Inadequate or non human and animal evidence of carcinogenicity
Group E;  No evidence of carcinogenicity for humans
No evidence  of carcinogenicity  in  at least two  adequate animal
tests in different species or in adequate human and animal studies
Source:  USEPA 1986.  Federal Register 51:33992-34003.  Sept. 24.

Risk Assessments for Determining URTH

     The above risk assessment methodologies used to develop HAs,
MCLGs and MCLs are used in determining the health criteria for URTH
levels.  As stated  earlier,  contaminants  classified as carcinogens
may  also  exhibit  noncancer  related  health  effects  such  as
reproductive texicity. Thus, the risk assessments for both cancer
and noncancer effects must be compared.

     Exposure  duration  should  also  be considered.  The  risk

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assessments  for  both  cancer  and  noncancer  effects  are  time
dependent. Cancer assessments usually assume a lifetime exposure,
while the risk assessments for noncancer effects cover less-than-
lifetime and lifetime exposures. Ideally, the variance or exemption
period  will  cover   a  less-than-lifetime  exposure  period.  In
addition, past exposure to a given contaminant may not be known.
Some of the values for URTH provided in  this document are based on
the Longer-term HA which assume exposures of seven years or less.
Therefore, EPA recommends that variances or exemptions not exceed
seven years when URTH is based on noncarcinogenic health effects.

     The risk assessments  for URTH are  presented as a range from
the  MCL to  an upper-bound   (least  stringent)  level.   The EPA
recommends that the  upper-bound not be  exceeded when determining
URTH.   However,  the  State may determine  URTH to  lie  within or
outside the  range based on  site-specific  considerations.   These
considerations may include,  for example, site-specific exposures,
past exposure (if known), population sensitivity or volatility of
the contaminant.
     The types of risk, assessment values  used in developing the
range of health criteria are:

     1.   The MCLG and MCL.
     2.   The Longer-term Health Advisory  for  a  child.
     3.   DWEL.
     4.   Cancer classification.
     5.   The 10"* cancer  risk level.
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     6.   MCLG multiplied by  a  factor  of one to ten  for  Group  c
          contaminants.

     When determining the upper-bound  URTH  level,  EPA considered
that :

     for threshold contaminants where the MCL is based on

     0    Acute toxicity: the MCL is appropriate  to use for URTH
whenever the MCL  for a  contaminant is based on an acutely toxic
response and there is little margin of  safety above the MCL. Where
there is a  greater margin of safety,  some  exceedance of  the MCL
based on scientific judgment may be reasonable.

     0    Subchronic and chronic toxicity: the Longer-term HA for
a  child could be  used  for  URTH.  This  level  of  exposure  is
considered protective of  a  potentially sensitive  subgroup over a
seven year period.

     0    the DWEL may be used  for URTH when data to calculate a
Longer-term HA are not available.

     for nonthreshold contaminants

     0    where the MCL  is  set  at or above the 10"* excess cancer
risk, the MCL is appropriate  for URTH.
     0    where the  MCL is set at a concentration less than the
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10   risk  level,  the  10"  cancer risk level may be used for URTH if
this value does not exceed the DWEL or Longer-term HA for a child.
The  lower of these values would then be recommended as URTH.

     0    where  the  MCL  for a Group  C contaminant  includes an
additional safety  factor of 1 to  10,   the  removal  of the factor
could be used as URTH,  provided that the Longer-term HA for a child
or  DWEL is not exceeded.   The lower  of  these values  would be
recommended as URTH.

     Table 2 summarizes examples of how the above strategy can be
applied and  lists the recommended risk assessments that could be
considered   in   determining  URTH  levels   for  drinking  water
contaminants.  Following Table 2 is a more complete description of
those values  for each contaminant and EPA's recommendations for
which of these values  should be applied as the URTH level.
                        ISSUES TOR COKMBHT
     EPA  is   seeking  comment  on  the  proposed  approach  for
determining  URTH.  The  following  table  and  chemical  specific
discussions are provided as examples of how this approach could be
applied. Issues to  address  include:

     1. Is  it  appropriate to base URTH on the  Longer-term HA for
£ child fcr threshold contaminants?
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     2. Is it appropriate to base URTH on the 10"4 cancer risk for
nonthreshold contaminants?  Could a  higher risk  such  as  10"3 be
justified for a short period of  time if noncancer risks were not
exceeded?

     3. Is it reasonable to limit the URTH for noncarcinogens to
seven  years?   Should   the  same guidance  be  recommended  for
carcinogens?

     4. Should other types of risk assessments not mentioned here
be considered for determining URTH?
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                  Table 2. DEVELOPMENT OF URTH RANGE (MGIL)
Compound
INORGANICS
Asbestos
>10 (jm
Cadmium
Copper
Fluoride
Mercury
Nitrate
Nitrite
Nitrate/Nitrite
Selenium
MICROBIOLOGICAL
Total Coliforms
ORGANICS
Acrylamide
Alachlor
Atrazine
Benzene
MCLG
•
7 MFL
0.005
1.3
4
0.002
10
1
10
0.05

0

0
0
0.003
0
Longer-
Term
HA
MCL Child

7 MFL ~
0.005 0.005
1.3
4
0.002 ~
10 10
1 1
10
0.05

5%/1% -

TT 0.02
0.002 -
0.003 0.06
0.005 (10 day
Cancer t(T**»
DWEL Class Risk

A 700
0.02 B1
D
D
0.01 D
D
..
_
0.1

—

0.007 B2 0.001
0.4 B2 0.04
0.2 C
A 0.1
URTH Level
Group C Recommended
MCLGxW V EPA

70 7 MFL
0.005
1.3
5
0.01
10 child
1 child,
10 child
0.1

5%/1%

0.001
0.04
0.03 0.03
-0.01
Carbofuran
             = 0.2)
0.04    0.04    0.05
0.2
0.05
(Continued on next page)
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              Table 2.  DEVELOPMENT OF URfH RANGE fMG/L) (Continued]
Compound
                MCLG	MCL
Longer-
 Term
 HA
 Child    DWEL
      Cancer  1O***
       Class   Risk
                                                        URTH Level
                                               Group C  Recommended
                                               MCLGxIO   tiy EPA
Carbon Tetrachloride
Chlordane
2.4-D
DBCP
cis-1,2-DCE
trans-1,2-DCE
o-DCB
p-DCB
    ^ichloroethane
1,1-Dichloroethylene
1,2-Dichloropropane
                  0       0.005   0.07
                  0       0.002   »
                  0.07    0.07    0.1
                  0       0.0002  --
                  0.07    0.07    3
                  0.1      0.1      2
                  0.6     0.6      9
                  0.075   0.075  10
                  0       0.005   0.7
                   0.007  0.007   1
                  0       0.005   -
          0.03   B2
          0.002  B2
                  D
0.4

0.4
0.6
4
4

0.4
                 B2
                  D
                  D
                  D
                  C
                 B2
                  C
                 B2
                                        0.03
                                        0.003

                                        0.003
                                        0.2      0.75
                                        0.04
                                        0.02    0.07
                                        0.06
                   0.03
                   0.003
                   0.1
                   0.003
                   0.4
                   2
                   9
                   0.75
                   0.04
                   0.07
                   0.06
Epfchlorohydrin
Ethylbenzene
EDB
Heptachlor
Heptachlor Epoxide
LJndane
Methoxychlor
Monochlorobenzene
PCBs
                         TT       0.07
                          0.7     1
                          0.00005 -
                          0.0004  0.005
          0.07
          3
        B2
        D
        B2
0.02    B2
0
0.7
0
0
0       0.0002  0.0001   0.0004  B2
0.0002  0.0002  0.03     0.01     C
0.4     0.4     0.5      2        D
0.1     0.1      2       0.7      D
0       0.0005  0.001    -       B2
  fnti.
inued on next page)
0.4

0.00004 -
0.0008  -
0.0004  ~
0.003   0.002
                                                          0.0005   -
0.07
1
 0.00005
0.0008
0.0004
0.002
0.5
2
0.0005
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           Table 2.  DEVELOPMENT OF URTH RANGE (MGIL) (Continued!
Compound
Tetrachloroethylene
Toxaphene
2.4.5-TP
1,1,1 -Trichloroethane
Trichloroethylene
Vinyl Chloride
Xylenes
MCLG
0
0
0.05
0.2
0
0
10
MCL
0.005
0.003
0.05
0.2
0.005
0.002
10
Longer-
Term
HA
Child
1
~
0.07
40
—
0.01
40
DWEL
0.5
0.003
.0.3
1
0.3
—
60
Cancer
Class
B2
B2
D
D
B2
A
D
TO4*" Group C
Risk MCLGxIO
0.07
0.003
—
..
0.3
0.0015 -
..
URTH Level
Recommended
toy EPA
0.07
0.003
0.07
1
0.3
0.002
40
TT = Treatment technique
TBD = To be determined
** = 10^ Lifetime Risk
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INORGANICS

Asbestos
     The EPA proposed an MCLG of 7 and an MCL of 7 million fibers
per liter  (MFL)  for  asbestos  fibers  greater than 10 /m in length
based  on  equivocal  evidence  of  carcinogenicity  in male  rats
following ingestion of chrysotile fibers.  There are insufficient
data to determine  a  Longer-term  Health Advisory for a child or a
drinking water equivalent level.  Asbestos is classified in Group
A:     Human  carcinogen  for  inhalation,   according  to  EPA's
classification scheme.  The 10"4  excess cancer risk estimated for
asbestos is 700 MFL.  There is limited evidence that asbestos may
be carcinogenic  by ingestion.   It is  unlikely  that asbestos, if
found  in  the  water,  would  exceed 7 MFL;  thus,  URTH may  be
considered any concentration above the MCL.

Cadmium
     The EPA proposed  an MCLG of 0.005 and  an  MCL of 0.005 mg/L
for cadmium based on renal dysfunction.   The Longer-term Health
Advisory for a  child is also 0.005  mg/L,  and the drinking water
equivalent level is 0.02 mg/L.  cadmium is  classified in Group Bl:
probable  human  carcinogen by   inhalation  with  no  evidence of
carcinogenicity by ingestion according to the EPA's classification
scheme.    Based  on  this  information  and  the  bioaccumulative
potential for cadmium, an upper-bound  unreasonable risk to health
level of 0.005 mg/L  based on the MCLG and the  Longer-term Health
Advisory is recommended for a period of up to 7 years.
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Copper
     The  EPA  proposed an MCLG of 1.3 and an  MCL  of  1.3  mg/L for
copper  based  on  acute  gastrointestinal   effects   in  humans.
A Longer-term Health  Advisory for a child and the drinking water
equivalent level has not been determined.  Copper  is classified in
Group D:  not classifiable for human carcinogenicity according to
the EPA's classification scheme.   Based  on this  information,  an
upper-bound  unreasonable risk  to  health  level  of  1.3 mg/L  is
recommended based on  acute toxicity.

Fluoride
     The  EPA  promulgated an MCLG of  4  and an MCL of  4  mg/L for
fluoride  based  on crippling skeletal fluorosis in humans.   Only
two cases of  crippling skeletal  fluorosis  have been observed in
this country  associated with the consumption of drinking water
containing fluoride levels of 8 mg/L or more.

     It is generally believed that the consumption  of approximately
20 mg of  fluoride per person per day over at least a twenty year
period  will   increase  the  risk of  crippling  skeletal fluorosis.
Thus, persons who chronically consume inordinately large amounts
of water, i.e., 4 liters/day, (perhaps 1%  of the population) would
be at risk of crippling skeletal fluorosis at a level greater than
5 mg/L.   Based on this  information,  an upper bound unreasonable
risk to health  level  of  5 mg/L  is recommended.
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Marcurv

     The EPA proposed  an  MCLG of 0.002 and an  MCL of 0.002 mg/L
for  mercury based  on  absence  of  toxicity  in  rats  following
subchronic exposure to mercury.   The Longer-term Health Advisory
for  a child has not  been  determined,  but  the drinking  water
equivalent level is 0.01.   Mercury is classified in Group D:  not
classifiable as  to  human  carcinogenicity according to  the  EPA's
classification scheme.  Based on this information, an upper-bound
unreasonable risk to  health level of 0.01 based  on the drinking
water  equivalent level  is  recommended  for  a  period  of  up  to
7 years.

Nitrate as M. Nitrate and Nitrate + Nitrite (measured as Nl

     Nitrate
     The EPA proposed an MCLG of 10 and an MCL of 10 mg/L (N) for
nitrate based on acute toxicity in infants following ingestion of
water with nitrate.

     Infants and particularly those with gastrointestinal disease
(e.g., diarrhea) are considered the most sensitive members  of the
population.  The consumption of  biologically contaminated water
(e.g.,  £.   coin  may  contribute  to the  problem,  resulting in
diarrhea which may render an infant much more  sensitive  to nitrate
and/or nitrite toxicity.
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     Nitrate  in drinking"water at levels in excess of the current
 10 mg/L MCL has been responsible  for serious methemoglobinemia and
 mortality  in  some  infants  under  the  age  of  approximately  six
 months.

     Based on this  information the URTH value  for  infants  up to
 6 months of  age is 10  mg/L  nitrate (as N) .   Based on available
 epidemiology  data, the  URTH value for nitrate for all individuals
 except  infants up  to 6 months  of age  is  20  mg/L (as N) .   In
 addition, biological  water quality  standards  must be met in both
 cases.

     Nitrite
     Nitrate  is toxic because it is metabolized within the human
body to  yield nitrite,  which in turn  reacts  with  hemoglobin to
yield  methemoglobin  (i.e.,  nitrate per se  does not  react with
hemoglobin).   Nitrite may also occur in drinking water.  The URTH
level  for  nitrite  should  not  exceed 1  mg/L  as  N  based  on
methemoglobin formation following short-term exposure.

     Nitrate  and Nitrite
     As both  nitrate  and nitrite may occur in drinking water and
as  exposure  to  either may lead  to  methemoglobinemia,   it is
reasonable to conclude that  the toxicity  of  nitrate and nitrite
                                   •j
may be additive.   As a consequence,  the URTH level for combined
 levels of nitrate and nitrite should not exceed 10 mg/L (i.e., the
 sun of nitrate and nitrite, as nitrogen, shall not exceed 10  mg/L).
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Selenium
     The EPA proposed an MCLG of  0.05 mg/L and an MCL of 0.05 mg/L
for selenium based on a human study evaluating selenium deficiency.
The Longer-term Health Advisory for a child is not established, but
the drinking water equivalent  level is  0.1 mg/L.    Selenium is
classified   in   Group D:     not  classifiable   as  to   human
carcinogenicity  according to  the  EPA's  classification  scheme.
Based on  this  information,  an  upper-bound unreasonable risk to
health level  of 0.1 mg/L based on the  drinking water equivalent
level is recommended for a period of up to 7 years.

MICROORGANISMS

Total Coliforms
     The  EPA  promulgated an  MCLG  of  0  and  an  MCL of  5%/l%
detections  for total col i forms  based on  acute gastrointestinal
disorders.    Based  on  the  acute pathogenicity  implied by  the
presence of  total col i forms,  an  upper-bound unreasonable risk to
health level  is any exceedance of the criteria specified for the
MCL.

ORGXKICS
     The EPA  proposed an MCLG of  zero and a treatment technique
for acrylamide  based on carcinogenicity.  The Longer-term Health
Advisory  for  a  child  is 0.02  mg/L,  and  the  drinking  water
                               -21-

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equivalent level.is  O.OQ7.  Acrylamide is classified in Group B2:
probable  human carcinogen according to  the  EPA's classification
scheme.   The 10~*. excess  cancer  risk estimated  for aery 1 amide is
0.001 mg/L.  Based on this information,  &n upper-bound unreasonable
risk to health level of 0.001 mg/L based on the 10'4 excess cancer
risk is recommended.

Alaehlor
     The EPA proposed an MCLG of zero and an MCL of 0.002 mg/L for
alachlor  based  on  feasibility  based  on  carcinogenicity.   The
Longer-term Health Advisory  for a child has  not been calculated,
but the drinking  water equivalent level  is 0.4 mg/L.  Alachlor is
classified in  Group B2:   probable human carcinogen according to
the  EPA's classification scheme.   The 10"4  excess  cancer risk
estimated for  alachlor  is 0.04  mg/L.   Based  on this information,
an upper-bound unreasonable risk to health level of 0.04 mg/L based
on the 10"* excess cancer  risk is recommended.

Atratine
     The  EPA proposed an MCLG of 0.003  and  an MCL of 0.003 mg/L
for atrazine based on cardiac effects in dogs  fed  atrazine  for one
year.  The Longer-term Health Advisory for a child is 0.05 mg/L,
and the drinking water equivalent level is  0.2 mg/L.   Atrazine is
classified in Group C:  possible human carcinogen  according to the
EPA's classification scheme.   EPA  applied an additional  10-fold
uncertainty f*etrvr in calculating the MCLG for atrazine  to  account
for possible carcinogenicity; without  ttiis additions! factor, the
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MCLG  would  have been 0.03 mg/L.  • Based on  this  information,  an
upper-bound unreasonable  risk  to  health level  of 0.03 mg/L based
on the removal of.the extra 10-fold UF and the Longer-term Health
Advisory for a child is  recommended for  a period of up to 7 years.

Benzene
     The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for benzene based on feasibility.  There are insufficient data to
calculate a Longer-term Health Advisory  for a child or a drinking
water equivalent level for non-cancer health effects.  However, a
Ten-day Health Advisory of 0.2 mg/L has been estimated.  Benzene
is classified in Group A:  human carcinogen according  to the EPA's
classification scheme.  The  10*4 excess  cancer risk estimated for
benzene is 0.1 mg/L.  Ordinarily,  the 10"4 excess cancer risk would
be recommended for the upper  bound URTH.  However, the 10~* risk of
0.1 mg/L is virtually the same as the Ten-day Health Advisory of
0.2 mg/L.   Also,  taking into  consideration  that  benzene is also
classified in Group A,  the upper bound  urth for this compound is
recommended at the  10"5  cancer  risk of 0.01 mg/L.

Carbofuraii
     The EPA proposed an MCLG  of  0.04 and an MCL of 0.04 mg/L for
carbofuran  based on  absence  of cholinesterase  or  reproductive
effects in dogs  fed carbofuran one year.  The Longer-term Health
Advisory  for  a  child  is  0.05 mg/L,   and the drinking  water
equivalent level is 0.2  mg/L.   Carbofuran is classified in Group E:
no  evidence  of  human  carcinogenicity according  to  the EPA's
                               -23-

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classification scheme.  .Based on this information, an upper-bound
unreasonable risk to health level of 0.05 mg/L based on the Longer-
term Health Advisory is recommended for  a  period of up to 7 years.

Carbon tetrachloride
     The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for carbon  tetrachloride based on carcinogenicity.   The Longer-
term Health Advisory for a child  is  0.07 mg/L,  and  the drinking
water  equivalent level  is 0.03 mg/L.   Carbon  tetrachloride  is
classified in Group B2:  probable human carcinogen according to the
EPA's classification scheme.  The  10"4 excess cancer risk estimated
for carbon tetrachloride is 0.03 mg/L.  Based on this information,
an upper-bound unreasonable risk to health level of 0.03 mg/L based
on the drinking water equivalent level  is recommended.

Chiordan•
     The EPA proposed an MCLG of zero and  an MCL of 0.002 mg/L for
chlordane based on carcinogenicity and  technological feasibility.
The  Longer-term  Health  Advisory  for a  child  has  not  been
calculated, but the drinking water equivalent level is 0.002 mg/L.
Chlordane is  classified in Group B2:   probable  human carcinogen
according to  the  EPA's classification scheme.   The  10"* excess
cancer risk estimated for chlordane is  0.003 mg/L.  Based on this
information, an  upper-bound unreasonable  risk to health level of
0.003 mg/L based on  the 10"* cancer risk is recommended.
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     The EPA proposed an MCLG of 0.07 and an MCL of 0.07 mg/L for
2,4-D based on liver and kidney  effects  in  animals.   The Longer-
term Health Advisory  for a  child  is 0.1 -ng/L, and  the drinking
water  equivalent level  is  0.4  mg/L.    2,4-D  is classified  in
Group D:  not classifiable as  to human carcinogenicity according
to the EPA's classification scheme.   Based on this information, an
upper-bound unreasonable risk to  health level of 0.1 mg/L based on
the Longer-term Health Advisory is recommended for a period of up
to 7 years.

DBCP
     The EPA proposed  an MCLG  of zero and  an  MCL of 0.0002 mg/L
for DBCP based on carcinogenicity.  The Longer-term Health Advisory
for a child and  the drinking water equivalent level has not been
calculated.   DBCP  is classified  in  Group B2:   probable human
carcinogen according to the EPA's classification scheme.  The 10*4
excess cancer risk estimated  for DBCP is 0.003 mg/L.   Based  on this
information, an  upper-bound  unreasonable risk to health level of
0.003 mg/L based on the 10*4  cancer  risk  is  recommended.
ei«-l. 2-Diehloroetlivlene
     The EPA proposed an MCLG of 0.07 and an MCL of 0.07 mg/L for
cis-l,2-DCE based on  absence of effects in a subchronic study in
animals.  The  Longer-term  Health Advisory for a child is  3 mg/L,
and the drinking water equivalent level  is  0.4 mg/L.  cis-l,2-DCE
                               -25-

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is  classified   in   Group  D:     not  classifiable  as  to  human
carcinogenicity  according  to  the  EPA's  classification  scheme.
Based  on  this information,  an upper-bound unreasonable  risk  to
health  level  of  0.4 mg/L based on  the  drinking water equivalent
level is recommended for a period of up to 7 years.

trans—l,2—Dlchloroethvlene
     The EPA  proposed  an MCLG of 0.1 and  an  MCL of 0.1 mg/L for
trans-l,2-DCE based on absence of effects in a subchronic study in
animals.  The Longer-term  Health Advisory for a child is 2 mg/L,
and the drinking water equivalent level is 0.6 mg/L.  trans-1,2-
DCE  is classified  in  Group D:    not  classifiable as to  human
carcinogenicity  according  to  the  EPA's  classification  scheme.
Based  on  this information,  an upper-bound unreasonable  risk  to
health level of 2 mg/L based on the Longer-term  Health Advisory is
recommended for  a period of up to 7 years.

o-Dichloroben«ene
     The EPA proposed an MCLG of 0.6 and an MCL  of 0.6 mg/L for o-
dichlorobenzene  (DCS)  based on absence  of  effects in a subchronic
study in rodents.  The Longer-term  Health  Advisory for a child is
9 mg/L, and the  drinking water equivalent level is   3 mg/L.  o-
DCB  is classified  in  Group D:    not  classifiable as  to human
carcinogenicity  according  to the  EPA's  classification scheme.
Based  on  this information,  an upper-bound unreasonable  risk to
haalth  level of  3 sg/L based cr. the Longer-term Health Advisory is
recommended for  a period of up to 7 years.
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p-Dichlorobenaene
     The EPA promulgated an MCLG of 0.075 and an MCL of 0.075 rag/L
for p-dichlorobenzene (p-DCB) based on kidney effects observed in
rats  exposed to  p-DCB  for  two years.   The  Longer-term Health
Advisory for a child is  10  mg/L,  and the drinking water equivalent
level is 3 mg/L.  p-DCB is classified in Group C:  possible human
carcinogen  according to the EPA's classification scheme.   EPA
applied an additional 10-fold uncertainty  factor to the MCLG for
p-DCB  to  account  for  possible  carcinogenicity;  without  this
additional uncertainty factor,  the MCLG would have  been 0.75 mg/L.
Based on  this information,  an  upper-bound unreasonable  risk to
health level of 0.75 mg/L based on removal  of the extra 10-fold UF
is recommended for a period of up to 7 years.
     The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for 1,2-dichloroethane based on carcinogenicity.  The Longer-term
Health Advisory  for  a child is 0.7 mg/L,  and  the drinking water
equivalent level has  not  been calculated.   1,2-Dichloroethane is
classified in  Group  B2:   probable human carcinogen according to
the  EPA's  classification  scheme.    The 10*4  excess  cancer risk
estimated for 1,2-DCE is 0.04 mg/L.   Based  on this information, an
upper-bound unreasonable  risk to  health level of 0.04 mg/L based
on the 10*4 excess cancer  risk is recommended.
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1.i-Dichloroethvlena
     The EPA promulgated an MCLG of 0.007  and an MCL of 0.007 mg/L
for 1,1-dichloroethylene based on mild liver effects and possible
carcinogenicity.  The  Longer-term  Health  Advisory for a child is
1 mg/L, and the drinking water equivalent  level is 0.4 mg/L.  1,1-
DCE is classified in Group C:   possible human carcinogen according
to the EPA's classification scheme.  EPA applied an additional 10-
fold uncertainty factor  to the MCLG  for 1,1-DCE;  without this
additional  factor,  the MCLG would  have been 0.07 mg/L.   Based on
this information, an upper-bound unreasonable risk to health level
of  0.07 mg/L  based  on  removal  of the extra  10-fold  UF  is
recommended for a period of up to 7 years.
1.2-DiehloroproDan*
     The EPA proposed an MCLG of zero and an MCL of 0.005 mg/L for
1,2-dichloropropane  (DCP)  based on carcinogenicity.   The Longer-
term Health Advisory for a child and the drinking water equivalent
level have not been calculated*  1,2-DCP is classified in Group B2:
probable human carcinogen according  to the EPA's classification
scheme.   The  10"* excess  cancer  risk  estimated for 1,2-DCP is
0.06 mg/L.  Based on this information, an upper-bound unreasonable
risk to health level of 0.06 mg/L based on the 104  excess cancer
risk is recommended.
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Epichlorohvdrin
     The EPA proposed  an MCLG of zero and  a  treatment technique
for  epichlorohydrin based  on carcinogenicity  and  technological
feasibility.   The  Longer-term Health  Advisory for  a  child  is
0.07 mg/L,   and  the drinking water  equivalent  level  is  also
0.07 mg/L.   Epichlorohydrin is classified  in  Group B2:  probable
human carcinogen according  to the EPA's  classification scheme.
The  10"4 excess  cancer  risk  estimated for  epichlorohydrin  is
0.4 mg/L.  Based on this information,  an upper-bound unreasonable
risk to health level of 0.07 mg/L based on the Longer-term Health
Advisory is recommended for a period of up to 7 years.

Ethvlbenaene
     The EPA proposed  an MCLG of 0.7 and  an  MCL  of 0.7 mg/L for
ethylbenzene based  on  kidney and liver effects in  animals.   The
Longer-term Health Advisory for a child is 1 mg/L, and the drinking
water equivalent  level is  3 mg/L.   Ethylbenzene is classified in
Group D:  not  classifiable as to human carcinogenicity  according
to the EPA's classification scheme.  Based  on  this information, an
upper-bound unreasonable' risk to  health level of  1 mg/L based on
the Longer-term Health Advisory is recommended for a period of up
to 7 years.

Bthvlene dibreaide  (BDBi
     The EPA proposed  an MCLG of zero and an MCL of 0.00005 mg/L
for EDB based on carcinogenicity.   The Longer-term Health Advisory
for a child and the drinking water equivalent level have not been
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calculated.    EDB  is  classified -in Group B2:   probable  human
carcinogen according to the EPA's classification scheme.  The 10"'
excess  cancer  risk estimated for EOB is  0.00004  mg/L.   Based on
this information and considering that the  MCL for EDB is at the 10"
4  risk level, an upper-bound unreasonable risk to health level of
0.00005 mg/L is recommended.

Heptachlor
     The EPA proposed  an MCLG of zero and  an  MCL of 0.0004 mg/L
for heptachlor  based on carcinogenicity.   The Longer-term Health
Advisory  for  a  child  is  0.005 mg/L,   and the  drinking  water
equivalent level  is 0.02 mg/L.  Heptachlor  is classified in Group
B2:     probable   human  carcinogen  according  to   the  EPA's
classification  scheme.   The 10"* excess  cancer risk estimated for
heptachlor is  0.0008 mg/L.   Based on this information, an upper-
bound unreasonable risk to health  level  of 0.0008  mg/L based on
the 10"4 excess cancer  risk  is  recommended.

Heptachlor epoxide
     The EPA proposed  an MCLG of zero and  an MCL of 0.0002 mg/L
for heptachlor epoxide based on carcinogenicity.  The Longer-term
Health Advisory for a child is 0.0001 mg/L,  and the  drinking water
equivalent level  is o.ooo4 mg/L.  Heptachlor epoxide is  classified
in Group  B2:   probable human carcinogen according to the EPA's
classification scheme.  The 10*4 excess cancer  risk estimated for
heptachlor epoxide is  0.0004 mg/L.   Based on this information, an
upper~tour.d  unreasonable risk t© health level of 0.0004 mg/L based
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on the 10"* excess cancer" risk is recommended.
Lindan*
     The EPA proposed an MCLG of 0.0002 and an MCL of 0.0002 mg/L
for lindane  based on liver and  kidney effects in  rodents.   The
Longer-term  Health  Advisory for  a child  is 0.03 mg/L,  and the
drinking  water  equivalent  level  is  0.01 mg/L.    Lindane  is
classified in Group C:   possible human  carcinogen according to the
EPA's  classification scheme.    EPA applied an addition 10-fold
uncertainty   factor   to  the  MCLG   to  account   for  possible
carcinogenicity; without this additional factor, the MCLG would be
0.002 mg/L.   Based on this information,  an upper-bound unreasonable
risk to health level of 0.002 mg/L based on  removal  of the 10-fold
UF is recommended for a period of up to 7 years.

Mathoxvchlor
     The EPA proposed an MCLG of 0.04 and an MCL of 0.04 mg/L for
methoxychlor based on reproductive effects in rodents.  The Longer-
term Health  Advisory for a child is  0.5 mg/L, and the drinking
water equivalent  level  is 2 mg/L.       is  classified in Group D:
not classifiable as to human carcinogenicity according to the EPA's
classification scheme.   Based  on this  information,  an upper-bound
unreasonable risk to health level of  0.5 mg/L based  on the Longer-
term Health Advisory is recommended for a period of  up to 7 years.
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Monochlorob«nz«n<
     The EPA  proposed an MCLG of 0.1 and an  MCL  of  0.1 mg/L for '
monochlorobenzene based on liver and kidney effects in a subchronic
study with  rodents.   The Longer-term Health Advisory for a child
is 2 mg/L,  and the drinking water equivalent level  is 0.7 mg/L.
Monochlorobenzene  is  classified  in Group D:   not classifiable as
to human  carcinogenicity  according  to the  EPA's classification
scheme.   Based on this  information,  an upper-bound  unreasonable
risk to  health level  of 2 mg/L  based  on the Longer-term Health
Advisory is recommended  for a period of up to 7 years.

Polychlorinated biphenvls  (PCBs)
     The EPA  proposed an MCLG of zero  and  an MCL of 0.0005 mg/L
for PCBs based on carcinogenicity.  The Longer-term Health Advisory
for a child is 0.001 mg/L, and the drinking water  equivalent level
has  not  been  calculated.   PCBs  are  classified in  Group B2:
probable human carcinogen according to the EPA's classification
scheme.    The  10"4  excess cancer  risk  estimated  for  PCBs  is
0.0005 mg/L.     Based  on  this  information,   an   upper-bound
unreasonable  risk to  health level of 0.0005 mg/L based on the 10"4
risk is recommended.

Tetracaicroernvi«n«
     The EPA  proposed an MCLG of zero and an MCL of 0.005  mg/L for
tetrachloroethylene  based  on carcinogenicity.   The  Longer-term
Health  Advisory for  a  child  is 1 mg/L, and the drinking  water
equivalent  level  is Or5 mg/L.  Tetrachloroethylene  is classified
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in  Group  B2:   probable human  carcinogen according to  the  EPA's
classification scheme.  The  10~4  excess cancer risk estimated for
tetrachloroethylene is 0.07  mg/L.   Based on this information,  an
upper-bound unreasonable risk  to health level of 0.07 mg/L based
on the 10"4 excess cancer risk  is  recommended.

Toxaphene
     The EPA proposed an MCLG of  zero and an MCL of 0.003 mg/L for
toxaphene  based  on  carcinogenicity.    The  Longer-term  Health
Advisory  for  a child has  not  been calculated,  but  the drinking
water equivalent level is 0.003 mg/L.  Toxaphene is classified in
Group B2:   probable  human  carcinogen  according to  the  EPA's
classification scheme.  The  10**  excess cancer risk estimated for
toxaphene is  0.003  mg/L.   Based on this  information,  an upper-
bound unreasonable risk to health level of 0.003 mg/L based on the
10"* excess cancer risk is  recommended.

2.4.5-TP
     The EPA proposed an MCLG  of  0.05 and an MCL of 0.05 mg/L for
2,4,5-TP based on absence of effects  in a dog study.  The Longer-
term Health Advisory  for a  child  is  0.07 mg/L,  and the drinking
water equivalent  level is 0.3 mg/L.   2,4,5-TP  is classified in
Group D:  not classifiable as  to  carcinogenicity according to the
EPA's classification scheme.   Based on this information, an upper-
bound unreasonable risk to health level  of  0.07 mg/L based on the
Longer-term Health Advisory  is recommended for a period of up to
7 years.
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1.1,l-Trichloro«thane
     The EPA promulgated an MCLG of 0.2  and an MCL of 0.2 mg/L for
1,1,1-trichloroethane based on liver and kidney effects in animals.
The Longer-term  Health  Advisory for a  child  is  40  mg/L,  and the
drinking water equivalent level is 1 mg/L.  1,1,1-Trichloroethane
is classified in Group D:  not classifiable as to carcinogenicity
according  to the  EPA's classification scheme.    Based  on  this
information, an  upper-bound  unreasonable  risk to health level of
1 mg/L based on the drinking water equivalent  level is recommended
for a period of up to 7 years.

Trichleroethvlene
     The EPA promulgated an MCLG  of zero and an MCL of 0.005 mg/L
for trichloroethylene based on  carcinogenicity.   The Longer-term
Health  Advisory for  a  child has not  been calculated,  but the
drinking water equivalent level  is 0.3 mg/L.   Trichloroethylene is
classified in Group B2:  probable  human carcinogen according to the
EPA's classification scheme.  The 10"4 excess cancer  risk estimated
for trichloroethylene is 0.3  mg/L.  Based on  this information, an
upper-bound  unreasonable  risk to health level of  0.3 mg/L  based
on the  10*4 excess  cancer risk is recommended.

Vinvl Chloride
     The EPA promulgated  an MCLG of zero  and an  MCL of  0.002 mg/L
for  vinyl  chloride based  on carcinogenicity.   The Longer-term
Health  Advisory for  a  child   is 0.01 mg/L;  a  drinking  water
equivalent level  has  not  been  calculated.   Vinyl chloride  is
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classified  in  Group A:   .human car'cinogen according  to the EPA's
classification scheme.   The  10"4  excess cancer risk estimated for
vinyl  chloride is  0.0015  mg/L.   Based  on  this  information,  an
upper-bound unreasonable risk to health level of 0.002 mg/L based
on the MCL, which  slightly exceeds  the 10"4  excess cancer risk is
recommended.
     The EPA  prbposed an  MCLG of 10  and an MCL  of 10 mg/L for
xylenes based on body weight  effects in rats.   The Longer-term
Health Advisory  for a child  is 40 mg/L, and  the drinking water
equivalent level  is  60 mg/L.   Xylenes are classified in Group D:
not classifiable as to human carcinogenicity according to the EPA's
classification scheme.  Based  on this  information, an upper-bound
unreasonable  risk to health level of 40 mg/L based on the  Longer-
term Health Advisory is recommended for a period of up to 7 years.
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