oEPA
               United States
               Environmental Protection
               Agency
           Office of
           Solid Waste and
           Emergency Response
DIRECTIVE NUMBER: 9355.0-30

 • LE: Role of the Baseline Risk Assessment in Superfund
    Remedy Selection Decision
                APPROVAL DATE:   Aprii 1991

                EFFECTIVE DATE:   April 1991

                ORIGINATING OFFICE: OERR

                Q FINAL
                  »           »           »
                D DRAFT

                 CTATMC     [ ]  A~ Pendin8 OMB approval
                 dTATUS:      I  B- Pending AA-OSWER approval
                              C- For review &/or commenc
                           [ ]  D- In development or circular:-^

                REFERENCE (Other dOCUmentt):      headquarters
  OSWER      OSWER      OSWER
VE   DIRECTIVE    DIRECTIVE   Dl

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 i ~nvirOr!mSfii3t HT£
Wasnmgton. DC 20.460.
                  OSWER  Directive Initiation  Request
                                                                    1. Directive Numoer
                                                                      9355.0-30
                                   2. Originator Information
Name of Contact Parson
SF Document Center
Coordinator
Mail Code
OS-245
Office
OERR
Taeonone Cooe
202-260-9760
      3. "tie
            Role of the Baseline Risk Assessment  in Superfund Remedy Selection Decision
      4. Summary ot Directive {include onef statement of puocsei
       This memo provides further guidance on how to use the baseline risk assessment to make
       risk management decisions such as determinig whether remedial action under CERCLA Sectic
       104 or 106 is necessary. It clarifies the use of the baseline risk assessment in
       selecting appropriate remedies under CERCLA Section 121/ promotes consistency in per-
       paring site specific risk assessments and helps insure appropriate documentation is
      5. Keywords
                                                                             inciuuea
                        Risk Assessment
      6«. woes i his Directive Supersede Previous Girec'.ivetsj?
      b. Does It Supplement Previous Directive(s)''
                                              No
                                              No
                   Yes   What directive (numcer. title)
                   Yes   What directive (number, title)
      7 Draft Level
           A - Signed 5y AA'CAA    I  '  9 - Signed by Office Director
                    C - For Review 1 Comment
0 - In Development
8.
Document
to
be
distributed
to
States
by Headquarters?


Yes i ! No
      This Hequasl Ma«la OSWER p^ractlvaa SysUm Format Standards.
      9. Signature of Lead Cffice Directives Coordinator
                                 Date
      10 Name anc "-lie ol Approving Ctfical/ / //
        Don R. Clay, Assistant/Administrator
        Office of Solid Waste and Emergency Response
                                 Date
                                    April 1991
      EPA Form 13i$-t7 (R«v. S-87) Previous editions are oosolete.
   OSWER           Of'VER               OSWER               O
VE     DIRECTIVE          DIRECTIVE         DIRECTIVE

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,1\0 ~.~


tal)

~~( 1'fII01t<-
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. D.C. 20460
APR 2 2 1991
OFFICE OF
SOLID WASTE AND EMERGENCY RESPONSE
OSWER DIRECTIVE 9355.0-30
MEMORANDUM
FROM:
Role of the Baseline Risk Assessment in
Remedy selec~ De~iSions .

Don R. clay ~
Assistant Adm~nistr 0
Superfund
SUBJECT:
TO:
Directors, Waste Management Division
Regions I, IV, V, VII, VIII
Director, Emergency and Remedial Response Division
Region II
Directors, Hazardous Waste Management Division
Regions III, VI, IX
Director, Hazardous Waste Division,
Region X
Purpose
The purpose of this memorandum is to clarify the role of the
baseline risk assessment in developing Superfund remedial
alternatives and supporting risk management decisions.
specifically, the following points are made in the memorandum:
o
Where the cumulative carcinogenic site risk to an individual
based on reasonable maximum exposure for both current and
future land use is less than 10", and the non-carcinogenic
hazard quotient is less than 1, action generally is not
warranted unless there are adverse environmental impacts.
However, if MCLs or non-zero MCLGs are exceeded, action
generally is warranted.
o
Other chemical-specific ARARs .may also be used to determine
whether a site warrants remediation.
o
A risk manager may also decide that a baseline risk level
less than 10.' is unacceptable due to site specific reasons
and that remedial action is warranted.
,q;::;. p.,,.rl!C Jr Rec1lcled Paoe

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2
o
comp~iance with a chemical-specific ARAR generally wil~ =e
consldeted-protective even if it is outside the risk ra~ge
(unless there are extenuating circumstances such as expos~=e
to multiple contaminants or pathways of exposure) .
o
The upper boundary of the risk range is not a discre~e li~e
at 1 x 10'1., although EPA generally uses 1 x 10'. in ::"akir:g
risk management decisions. A specific risk estimate aro~r:i
10'1. may be considered acceptable if justified based C~
site-specific conditions.
o
The ROD should clearly justify the use of any non-standarj
exposure factors and the need for remedial action if
baseline risks are within the generally acceptable risk
range. The ROD should also include a table listing the
final remediation goals and the corresponding risk level ~--
each chemical of concern. .
Backqround
The 1990 National Contingency Plan (NCP) (55 Fed. Reg. 866:-
8865 (Mar. 8, 1990») calls for a site-specific baseline risk
assessment to be conducted, as appropriate, as part of the
remedial investigation (Section 300.430(d) (1»). Specifically,
the NCP states that the baseline risk assessment should
"characterize the current and potential threats to human ~ea~t~
and the environment that may be posed by contaminants migratir:~
to ground water or surface water, releasing to air, leaching
through soil, remaining in the soil, and bioaccumulating in the
food chain" (Section 300.430(d) (4). The primary purpose of t~e
baseline risk assess~ent is to provide risk managers wit~ an
understanding of the actual and potential risks to human health
and the environment posed by the site and any uncertainties
associated with the assessment. This information may be useful
in determining whether a current or potential threat to hu~an
health or the environment exists that warrants remedial action.
The "Risk Assessment Guidance for Superfund: Volume I,
Human Health Evaluation Manual - Part A" (HHEM) (EPA/540/1-
89/002) provides guidance on how to conduct the human health
portion o( the baseline risk assessment. Volume II of the "Risk
Assessment Guidance for Superfund" the "Environmental Evaluation
Manual" (EPA/540/1-89/001) and the companion manual, "Ecological
Assessm@.nt of Hazardous Waste Sites: A Field and Laboratory
Reference" (EPA/600/3-89/013) provide guidance on conducting the
environmental portion of the baseline risk assessment. Other
pertinent guidance includes the "Guidance for Conducting Remedia:
Investigations and Feasibility Studies Under CERCLA" (RI/FS
guidance, EPA/540/G-89/004), which describes how the baseline,
risk assessment fits into the overall RI/FS process. "Gu ~janc€;' ,
on Preparing Superfund Decision Documents" (ROD guidance)

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3
(EPA/624/1-87/001) provides information on how to document t~e
results of the baseline risk assessment in the ROD.
Obiective
The objective of this memorandum is to provide f~r~~er
guidance on how to use the baseline risk assess~ent to ~ake ris~:
management decisions such as determining whether re~edial act:~~
under CERCLA Sections 104 or 106 is necessary. This ~e~orand~~
also clarifies the use of the baseline risk assesswent in
selecting appropriate remedies under CERCLA Section 121, p~~~ctes
consistency in preparing site-specific risk assessments, and
helps ensure that appropriate documentation from the basel:ne
risk assessment is included in Superfund remedy selection
documents.
Implementation
RISKS WARRANTING REMEDIAL ACTION
Whenever there is a release or substantial threat of release
of a hazardous substance into the environment (or a release or
threat of release into the environment of a pollutant or
contaminant "which may present an imminent and substantial dar.ge~
to public health or welfare") I section 104(a) (1) of CERCLA
provides EPA with the authority to take any response action
consistent with the National Contingency Plan it deems necessar1"
to protect public health or welfare or the environment. Sectic~
106 of CERCLA grants EPA the authority to require potentially
responsible parties (or others) to perform removal or remedial
actions "when the President determines that there may be an
imminent and substantial endangerment to the public health or
welfare or ~he environment because of an actual or threatened
release cf a i1~zardous substance from a facility."
As a general policy and in order to operate a unified
Superfund program, EPA generally uses the results of the baseli~e
risk assessment to establish the basis for taking a remedial
action using either Section 104 or 106 authority. EPA may use
the results of the baseline risk assessments to determine whether
a release or threatened release poses an unacceptable risk to
human health or the environment that warrants remedial action ar.i
to determine if a site presents an imminent and substantial
endangerment. The risk assessment methodology for all sites
should be the same regardless of whether the RI/FS or remedial
design and remedial action is performed by EPA or potentially
responsible parties.
Generally, where the baseline risk assessment indicates that
a cumulative site risk to an individual using reasonable maxi~~~
exposure assumptions for either current or future land use
exceeds the lO'~ lifetime excess cancer risk end of the risk

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4
range, action under CERCLA is generally warranted at the site.
For sites where the cumulative site risk to an individual based
on reasonable maximum exposure for both current and future land
use is less than 10", action generally is not warranted, but ~ay
be warranted if a chemical specific standard that defines
acceptable risk is violated or unless there are noncarcinogenic
effects or an adverse environmental impact that warrants actior..
A risk manager may also decide that a lower level of risk to
human health is unacceptable and that remedial action is
warranted where, for example, there are uncertainties in the r:s::
assessment results. Records of Decision for remedial actions
taken at sites posing risks within the 10'(, to 10'6 risk range
must explain why remedial action is warranted.
The cumulative site baseline risk should include all media
that the reasonable maximum exposure scenario indicates are
appropriate to combine and should not assume that institutional
controls or fences will account for risk reduction. For
noncarcinogenic effects of toxicants, unacceptable risk occurs
when exposures exceed levels which represent concentrations to
which the human population, including sensitive subgroups, may =1
exposed without adverse effect during a lifetime or part of a .
lifetime, as appropriate to address teratogenic and developrnenta~
effects.
Chemical specific standards that define acceptable risk
levels (e.g., non-zero MCLGs, MCts) also may be used to dete~,:~~
whether an exposure is associated with an unacceptable risk to
human health or the environment and whether remedial action under
Section 104 or 106 is warranted. For ground water actions, MCLs
and non-zero MCLGs will generally be used to gauge whether
remedial action is warranted.

EPA uses the general 10't. to 10'6 risk range as a "target
range" within which the Agency strives to manage risks as part of
a Superfund cleanup. Once a decision has been made to take an
action, the Agency has expressed a preference for cleanups
achieving the more protective end of the range (i.e., 10'6) /
although waste management strategies achieving reductions in si~~
risks anywhere within the risk range may be deemed acceptable by
the EPA risk manager. Furthermore, the upper boundary of the
risk range is not a discrete line at 1 x 10", although EPA
generally uses 1 x 10" in making risk management decisions. A
specific risk estimate around 10't. may be considered acceptable
if justified based on site-specific conditions, including any
remaining uncertainties on the nature and extent of contaminati~
and associated risks. Therefore, in certain cases EPA may
consider risk estimates slightly greater than 1 x 10'(, to be
protective.
When an ARAR for a specific chemical (or in some cases a
group of chemicals) defines an acceptable level of exposure,

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5
compliance with the ARAR will generally be considered protect~';e
even if it is outside the risk range (unless there are
extenuating circumstances such as exposure to multiple
contaminants or pathways of exposure). Conversely, in certain
situations EPA may determine that risks less than
." . .
1 x 10 are not sufflclently protective and warrant remedial
action.
Where current conditions have not resulted in a release
posing risks that warrant action but there is a significant
possibility that a release will occur that is likely to resul~ .~
an unacceptable risk, remedial action may also be taken. The
significance of the potential future release may be evaluated ,-
part based on the quantities of material at the site and the
environmental setting.
RISKS CONSIDERED IN RISK MANAGEMENT DECISION
As noted above, both current and reasonably likely future
risks need to be considered in order to demonstrate that a site
does not present an unacceptable risk to human health and the
environment. An adequate consideration of future risk may
necessitate the assessment of risks assuming a land use differen~
from that which currently exists at the site. The potential ~a~i
use associated with the highest level of exposure and risk tha~
can reasonably be expected to occur should be addressed i~ the
baseline risk assessment. Further, this land use and these
exposure assumptions should be used in developing remediation
goals.

The preamble to the NCP states that EPA will consider fut~=e
land use as residential in many cases. In general, residential
areas should be assumed to remain residential: and undeveloped
areas can be assumed to be residential in the future unless sites
are in areas where residential land use is unreasonable. Often
the exposure scenarios based on potential future residential lanj
use provide the greatest risk estimates (e.g., reasonable maxi~~~
exposure scenario) and are important considerations in decidi~g
whether to take action (55 Fed. Reg. at 8710) .
However, the NCP also states that "the assumption of future
residential land use may not be justifiable if the probability
that the site will support residential use in the future is
~w.all." sites that are surrounded by operating industrial
facilities can be assumed to remain as industrial areas unless
there is an indication that this is not appropriate. Other land
uses, such as recreational or agricultural, may be used, if
appropriate. When exposures based on reasonable future land use
are used to estimate risk, the NCP preamble states that the ROD
"should include a qualitative assessment of the likelihood that
the assumed future land use will occur" (55 Fed. Reg. at 8710) .

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6
Unacceptable environmental risks also may prompt re~edial
action and may occur where there is no significant risk to hU~3~
health. Threats or potential threats to sensitive habitats, s~c~
as wetlands, and critical habitats of species protected under ~~e
Endangered Species Act are especially important to consider ~he~
determining whether to take an action under CERCLA Section 104 cr
106. Ambient Water Quality criteria for aquatic organis~s are
chemical-specific standards that will generally be considered
when determining whether to take an action based on the
environmental risk of releases to surface waters.
NO-ACTION DECISIONS
If the baseline risk assessment and the comparison of
exposure concentrations to chemical-specific standards indicates
that there is no unacceptable risk to human health or the
environment and that no remedial action is warranted, then the
CERCLA Section 121 cleanup standards for selection of a Superf~~j
remedy, including the requirement to meet applicable or relevan:
and appropriate requirements (ARARs), are not triggered. CERCLA
section 121 (a) requires only that those remedial actions that
are "determined to be necessary... under section 104 or ... 1C
... be selected in accordance with section 121." If EPA '
determines that an action is necessary, the remedial acticn ~~s:
attain ARARs, unless a waiver is invoked. Of course, sites t~3:
do not warrant action under CERCLA sections 104 or 106 ~ay
warrant action under another state or Federal statute, such as
RCRA subtitle D requirements for the appropriate closure of a
solid waste landfill.
The decision not to take action at an NPL site under sectio~
104 and 106 should also be documented in a ROD. The decision
documentation process should include the preparation of a
proposed plan for public comment, ROD and eventually a closeout
report and Federal Register deletion notice.
POINT OF DEPARTURE WHEN ACTION 'WARRANTED
Once remedial action has been determined to be warranted,
the result's of the baseline risk assessment may be used to modi f'.,:
preliminary remediation goals. These preliminary goals are
developed at scoping based on ARARs and the 10.6 cancer risk
point of departure pursuant to NCP section 300.430(e) (2) (i).
USE OF BASELINE RISK ASSESSMENT TO MODIFY PRELIMINARY REMEDIATI:::
GOALS
Remediation goals developed under CERCLA Section 121 are
generally medium-specific chemical concentrations that will pose-
no unacceptable threat to human health and the environment.
Preliminary remediation goals are developed early in the RI/FS
process based on ARARs and other readily available infor~ation,

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such as concentrations associated with 10'6 cancer risk or a
hazard quotient equal to one for noncarcinogens calculated fro~
EPA toxicity information. These preliminary goals may be
modified based on results of the baseline risk assessment, whic~
clarifies exposure pathways and may identify situations where
cumulative risk of multiple contaminants or multiple exposure
pathways at the site indicate the need for more or less stringe~~
cleanup levels than those initially developed as preliminary
remediation goals. In addition to being modified based on the
baseline risk assessment, preliminary remediation goals and the
corresponding cleanup levels may also be modified based on the
given waste management strategy selected at the time of remedy
selection that is based on the balancing of the nine criteria
used for remedy selection (55 Fed.Reg. at 8717 and 8718).
EARLY AND INTERIM ACTIONS
Early operable unit actions (e.g., hot spot removal and
treatment) and interim actions (e.g., temporary storage or gro~~i
water plume containment) may be taken to respond to an immediate
site threat or to take advantage of an opportunity to
significantly reduce risk quickly (55 Fed. Reg. at 8705). For
example, an interim containment action may be particularly usefu~
early in the process for complicated ground water remedial
actions, where concentrations greater than MCLs provide a good
indication that remediation of a potential drinking water sou~=e
is necessary; such quick remedial action is important to preve;.~
further spread of the contaminant plume while a final ground
water remedy is being developed.
Early and interim action RODs do not require a completed
baseline risk assessment, although enough information must be
available to demonstrate the potential for risk and the need to
take action. Data sufficient to support the interim action
decision can be extracted from the ongoing RI/FS for the site and
set out in a focused feasibility study or other appropriate
document that includes a short analysis of a limited number of
alternatives (55 Fed. Reg. at 8704). These data should include a
summary of contaminants of concern, concentrations and relevant
exposure information. A discussion should accompany these data
explaininq the need for immediate remedial action based on the
presence of contamination that, if left unaddressed in the short-
term, either contributes immediate risk or is likely to
contribute to increased site risk or degradation of the
environment/natural resources. The early and interim action R08s
should note that some exposure pathways at the site may not be
addressed by the action.
An interim action ROD eventually must be followed by a
subsequent ROD for that operable unit based on the complete
RI/FS, that includes the baseline risk assessment, in order to
document lonq-term protection of human health and the envi~on~en:

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8
at that portion ~f the site. The interim action ROD, however,
should demo~strate qualitatively (and quantitatively if possible)
that there 1S a risk or potential for risk and explain how the
temporary measures selected will address a portion of this risk.
DOCUMENTATION OF BASELINE RISK ASSESSMENT RESULTS IN ~HE ROD
The Summary of site Risks section of the ROD should include
a discussion of the risks associated with current and fut~re la~i
use and a table presenting these risk levels for each exposure
medium (e.g., direct contact with soil by potential future
residents exposed via incidental soil ingestion and dermal
contact). In some situations, risks from exposure via more t~an
one medium (e.g., soil and drinking water) will affect the same
potentially exposed individual at the same time. It is
appropriate in these situations to combine the risks from the
different media to give an indication of total risk that an
individual may be exposed to from a site.
In addition to summarizing the baseline risk assessment
information, the ROD (except no-action RODs) should include how
remedial alternatives will reduce risks by achieving cleanup
levels through treatment or by eliminating exposures through
engineering controls for each contaminant of concern in each
appropriate medium.
The Comparative Analysis should include a discussion of ea~~
of the nine criteria; consideration of risk is part of the
discussion of several of the criteria. The discussion of overal~
protection of human health and the environment should include a
discussion of how the remedy will eliminate, reduce, or control
risks identified in the baseline risk assessment posed through
each pathw~y and whether exposure levels will be reduced to
acceptable lev&ls. For example, if direct human contact with
contaminated soil is identified as a significant risk at a site,
the ROD (except no-action RODs) should indicate how the selected
remedy will eliminate or control exposures to ensure protection
of human health. The discussion of long-term effectiveness and
permanence should include, where appropriate, an assessment of
the residual risk from untreated residual waste remaining at the
site. The short-term effectiveness discussion should address
risks during remedial action to those on-site and nearby.
Finally, that part of the Decision Summary in the ROD that
focuses on the selected remedy should show:
o
the chemical-specific remediation level and
corresponding chemical-specific risk level(s) to be
attained at the conclusion of the response action an~
the points (or area) of compliance for the media being
addressed; and

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9
o
The lead agency's basis for the remediation levels
(e.g., risk calculation, ARARs).
The attached table, "Remediation Levels and Corresponding Risks, 11
provides a direct means of displaying this info~ation for heal:~
risks and, where appropriate, environmental protection (Table 1).
The table should be completed for all media for which the ROD
selects final cleanup levels. The table should serve as a
summary of text in the selected remedy section of the ROD
Decision Summary. For interim action RODs, only qualitative
statements may be possible.
Additional guidance on the baseline risk assess~ent and i:s
role in remedy selection is available from several sources. For
guidance on the baseline risk assessment contact:
David Bennett, Chief
Toxics Integration Branch (05-230)
Hazardous Site Evaluation Division
Office of Emergency and Remedial Response
phone: (FTS) or (202) 475-9486.
For additional guidance on the interaction of the baseline risk
assessment and Superfund remedy selection, contact:
David Cooper
Remedial operations and Guidance Branch (OS-220W)
Hazardous Site Control Division
Office of Emergency and Remedial Response
phone: (FTS) 398-8361
(commercial phone: (703) 308-8361)
For guidance on enforcement-lead sites contact:
Stephen Ells
Guidance and Evaluation Branch (OS-510)
CERCLA Enforcement Division
Office of Waste Programs Enforcement
phon.: (FTS) or (202) 475-9803.
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NOTICE: The policies set out in this memorandum are intended
solely as guidance. They are not intended, nor can they be
relied upon, to create any rights enforceable by any party in
litigation with the United States. EPA officials may decide to
follow the guidance provided in this memorandum, or to act at
variance with the guidance, based on an analysis of specific site
circumstances. Remedy selection decisions are made and justified
on a case-specific basis. The Agency also reserves the right tc
change this quidance at any time without public notice.

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~LEI
Remediation Goals and Corresponding Risks a
It
Final Remediation Level.
Medium
Chemical
Remediation
Levele
SOIL
A
B
C
2.0 ppm
17.0 ppm
5.0 ppm
GROUND
WATER
B
C
F
G
0.1 ppm
4.0 ppm
7.0 ppm
15.0 ppm
SEDIMENf
Q
100.0 ppm
Point of
CompUance f
All facHtty
grounds
Waste
Management
Unlt
Boundary
Downstream
from point A
.,
Corresponding Risk Level.
8881.
of Goal
,

.,

1~
~
0.5 II
N/A ;1'
N/A >,1~

N/A I
N/A .m~
. .~:~:~~
-----_~:~_-I
.:~t~
N/A .::::~:,
I

. ~:~~~~:. .?:..';~: it.fiil
Chemical-Specific RME RIsk.
Cancer Non-Cancer
-------
HI
Risk
GW Risk
N/A
1.0 x 10-5
N/A
._--- - ----
Risk
MCL
MCLG
MCL
1.0 x 10-5
LOx 10-5
N/A
6.0 x 10 -6
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Ecological
Effects
N/A
~~t: . ..:-~v .,:- -:-: ~~'
. .'.. :.-.X :" ~Wt~%n@i¥Mt~~. <: :.:. .:: -.~~.wlti%*W..~ .>0: .: ~ .... ..: ~
a. Prepare summary sh~ts for selected remedy.

b. F1naI Remediation Levels are based on preliminary remediation goals
developed In the Feasibility Study (FS) (RIfFS Guidance 4.2.1) as modified
through the nine criteria evaluation and engineering design. In the process of
achieving remediation levels for each chemical. some chemicals wlU be
reduced to concentraUons below their remediation levels.
c. Chemical-specific risks co~pond to associated remediation levels. Risks
do not consider effects of exposures to other chemicals or media. If
appropriate. risks may be summed to calculate medla.speclfic risks.
Short-term effectiveness Is not considered.
d. Cancer risks are measu~ as indlvlduallncrementalUfetbne: non-cancer.
as Hazard Quotients.
e. Bases for values should be explained in the earlier Record Of Decision
(ROD) table.
r. Bases for location and method for determlnln~ attainment (e.g.. maximum
value detected over area XYZ) should be explained In the description of the
selected remedy.
Nt A - Not applicable

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