space, where people either reside, attend school or day care, or
work on a regular basis, or that were previously occupied but
vacated due to a site-related hazardous substance(s). This also
includes resource structures (e.g., library, church, tribal
structure).
* * * * *
    Screening concentration: Media-specific benchmark concentration
for a hazardous substance that is used in the HRS for comparison
with the concentration of that hazardous substance in a sample from
that media. The screening concentration for a specific hazardous
substance corresponds to its reference concentration for inhalation
exposures or reference dose for oral exposures, as appropriate, and,
if the substance is a human carcinogen with either a weight-of-
evidence classification of A, B, or C, or a weight-of-evidence
classification of carcinogenic to humans, likely to be carcinogenic
to humans or suggestive evidence of carcinogenic potential, to that
concentration that corresponds to its 10-6 individual
lifetime excess cancer risk for inhalation exposures or for oral
exposures, as appropriate.
    Shallow ground water: The uppermost saturated zone, typically
unconfined.
* * * * *
    Slope factor (also referred to as cancer potency factor):
Estimate of the probability of response (for example, cancer) per
unit intake of a substance over a lifetime. The slope factor is
typically used to estimate upper-bound probability of an individual
developing cancer as a result of exposure to a particular level of a
human carcinogen with either a weight-of-evidence classification of
A, B, or C, or a weight-of-evidence classification of carcinogenic
to humans, likely to be carcinogenic to humans or having suggestive
evidence of carcinogenic potential. [(mg/kg-day)-1 for
non-radioactive substances and (pCi)-1 for radioactive
substances].

    Soil gas: The gaseous elements and compounds in the small spaces
between particles of soil.
    Soil porosity: The degree to which the total volume of soil is
permeated with pores or cavities through which fluids (including air
or gas) can move. It is typically calculated as the ratio of the
pore spaces within the soil to the overall volume of the soil.
* * * * *
    Subslab: The area immediately beneath a regularly occupied
structure with a basement foundation or a slab-on-grade foundation.
Subslab samples are collected to determine the concentration of
hazardous substances in the soil gas beneath a home or building.
    Subsurface intrusion: The migration of hazardous substances from
the unsaturated zone and/or ground water into overlying structures.
* * * * *
    Unit risk: The upper-bound excess lifetime cancer risk estimated
to result from continuous exposure to an agent (i.e., hazardous
substance) at a concentration of 1 [mu]g/L in water, or 1 [mu]g/m\3\
in air.
    Unsaturated zone: The portion of subsurface between the land
surface and the zone of saturation. It extends from the ground
surface to the top of the shallowest ground water table (excluding
localized or perched water).
* * * * *
    Weight-of-evidence: EPA classification system for characterizing
the evidence supporting the designation of a substance as a human
carcinogen. The EPA weight-of-evidence, depending on the date EPA
updated the profile, includes either the groupings:
     Group A: Human carcinogen--sufficient evidence of
carcinogenicity in humans.
     Group B1: Probable human carcinogen--limited evidence
of carcinogenicity in humans.
     Group B2: Probable human carcinogen--sufficient
evidence of carcinogenicity in animals.
     Group C: Possible human carcinogen--limited evidence of
carcinogenicity in animals.
     Group D: Not classifiable as to human carcinogenicity--
applicable when there is no animal evidence, or when human or animal
evidence is inadequate.
     Group E: Evidence of noncarcinogenicity for humans.
    Or the descriptors:
     Carcinogenic to humans.
     Likely to be carcinogenic to humans.
     Suggestive evidence of carcinogenic potential.
     Inadequate information to assess carcinogenic
potential.
     Not likely to be carcinogenic to humans.

2.0 Evaluations Common to Multiple Pathways

    2.1 Overview. The HRS site score (S) is the result of an
evaluation of four pathways:
     Ground Water Migration (Sgw).
     Surface Water Migration (Ssw).
     Soil Exposure and Subsurface Intrusion
(Ssessi).
     Air Migration (Sa).
    The ground water and air migration pathways use single threat
evaluations, while the surface water migration and soil exposure and
subsurface intrusion pathways use multiple threat evaluations. Three
threats are evaluated for the surface water migration pathway:
Drinking water, human food chain, and environmental. These threats
are evaluated for two separate migration components--overland/flood
migration and ground water to surface water migration. Two
components are evaluated for the soil exposure and subsurface
intrusion pathway: Soil exposure and subsurface intrusion. The soil
exposure component evaluates two threats: Resident population and
nearby population, and the subsurface intrusion component is a
single threat evaluation.
    The HRS is structured to provide a parallel evaluation for each
of these pathways, components, and threats. This section focuses on
these parallel evaluations, starting with the calculation of the HRS
site score and the individual pathway scores.
    2.1.1 Calculation of HRS site score. Scores are first calculated
for the individual pathways as specified in sections 2 through 7 and
then are combined for the site using the following root-mean-square
equation to determine the overall HRS site score, which ranges from
0 to 100:
[GRAPHIC] [TIFF OMITTED] TR09JA17.062

    2.1.2 Calculation of pathway score. Table 2-1, which is based on
the air migration pathway, illustrates the basic parameters used to
calculate a pathway score. As Table 2-1 shows, each pathway
(component or threat) score is the product of three ``factor
categories'': Likelihood of release, waste characteristics, and
targets. (The soil exposure and subsurface intrusion pathway uses
likelihood of exposure rather than likelihood of release.) Each of
the three factor categories contains a set of factors that are
assigned numerical values and combined as specified in sections 2
through 7. The factor values are rounded to the nearest integer,
except where otherwise noted.
    2.1.3 Common evaluations. Evaluations common to all four HRS
pathways include:

 Characterizing sources.
    --Identifying sources (and, for the soil exposure and subsurface
intrusion pathway, areas of observed contamination, areas of
observed exposure and/or areas of subsurface contamination [see
sections 5.1.0 and 5.2.0]).
    --Identifying hazardous substances associated with each source
(or area of observed contamination, or observed exposure, or
subsurface contamination).
    --Identifying hazardous substances available to a pathway.

                  Table 2-1--Sample Pathway Scoresheet
------------------------------------------------------------------------
                                                               Value
             Factor category               Maximum value     assigned
------------------------------------------------------------------------
                          Likelihood of Release
------------------------------------------------------------------------
1. Observed Release.....................             550  ..............
2. Potential to Release.................             500  ..............
3. Likelihood of Release (higher of                  550  ..............
 lines 1 and 2).........................
------------------------------------------------------------------------
                          Waste Characteristics
------------------------------------------------------------------------
4. Toxicity/Mobility....................           (\a\)  ..............
5. Hazardous Waste Quantity.............           (\a\)  ..............
6. Waste Characteristics................             100  ..............
------------------------------------------------------------------------
                                 Targets
------------------------------------------------------------------------
7. Nearest Individual...................  ..............  ..............
    7a. Level I.........................              50  ..............
    7b. Level II........................              45  ..............
    7c. Potential Contamination.........              20  ..............
    7d. Nearest Individual (higher of                 50  ..............
     lines 7a, 7b, or 7c)...............
8. Population...........................           (\b\)  ..............
    8a. Level I.........................           (\b\)  ..............
    8b. Level II........................           (\b\)  ..............

    8c. Potential Contamination.........           (\b\)  ..............
    8d. Total Population (lines           ..............  ..............
     8a+8b+8c)..........................
9. Resources............................               5  ..............
10. Sensitive Environments..............           (\b\)  ..............
    10a. Actual Contamination...........           (\b\)  ..............
    10b. Potential Environments.........           (\b\)  ..............
    10c. Sensitive Environments (lines             (\b\)  ..............
     10a+10b)...........................
11. Targets (lines 7d+8d+9+10c).........           (\b\)  ..............
12. Pathway Score is the product of
 Likelihood of Release, Waste
 Characteristics, and Targets, divided
 by 82,500. Pathway scores are limited
 to a maximum of 100 points.............
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category. The product
  of lines 4 and 5 is used in Table 2-7 to derive the value for the
  waste characteristics factor category.
\b\ There is no limit to the human population or sensitive environments
  factor values. However, the pathway score based solely on sensitive
  environments is limited to a maximum of 60 points.

 Scoring likelihood of release (or likelihood of exposure)
factor category.
    --Scoring observed release (or observed exposure or observed
contamination).
    --Scoring potential to release when there is no observed
release.
 Scoring waste characteristics factor category.
    --Evaluating toxicity.
    [ssquf] Combining toxicity with mobility, persistence,
degradation and/or bioaccumulation (or ecosystem bioaccumulation)
potential, as appropriate to the pathway (component or threat).
    [ssquf] Evaluating hazardous waste quantity.
    --Combining hazardous waste quantity with the other waste
characteristics factors.
    [ssquf] Determining waste characteristics factor category value.
 Scoring targets factor category.
    --Determining level of contamination for targets.

    These evaluations are essentially identical for the three
migration pathways (ground water, surface water, and air). However,
the evaluations differ in certain respects for the soil exposure and
subsurface intrusion pathway.
    Section 7 specifies modifications that apply to each pathway
when evaluating sites containing radioactive substances.
    Section 2 focuses on evaluations common at the pathway,
component, and threat levels. Note that for the ground water and
surface water migration pathways, separate scores are calculated for
each aquifer (see section 3.0) and each watershed (see sections
<IP_ADDRESS> and <IP_ADDRESS>) when determining the pathway scores for a site.
Although the evaluations in section 2 do not vary when different
aquifers or watersheds are scored at a site, the specific factor
values (for example, observed release, hazardous waste quantity,
toxicity/mobility) that result from these evaluations can vary by
aquifer and by watershed at the site. This can occur through
differences both in the specific sources and targets eligible to be
evaluated for each aquifer and watershed and in whether observed
releases can be established for each aquifer and watershed. Such
differences in scoring at the aquifer and watershed level are
addressed in sections 3 and 4, not section 2.
    2.2 Characterize sources. Source characterization includes
identification of the following:
     Sources (and areas of observed contamination, areas of
observed exposure, or areas of subsurface contamination) at the
site.
     Hazardous substances associated with these sources (or
areas of observed contamination, areas of observed exposure, or
areas of subsurface contamination).
     Pathways potentially threatened by these hazardous
substances.
    Table 2-2 presents a sample worksheet for source
characterization.
    2.2.1 Identify sources. For the three migration pathways,
identify the sources at the site that contain hazardous substances.
Identify the migration pathway(s) to which each source applies. For
the soil exposure and subsurface intrusion pathway, identify areas
of observed contamination, areas of observed exposure, and/or areas
of subsurface contamination at the site (see sections 5.1.0 and
5.2.0).

Table 2-2--Sample Source Characterization Worksheet

Source: __
A. Source dimensions and hazardous waste quantity.
Hazardous constituent quantity: __
Hazardous wastestream quantity: __
Volume: __
Area: __
Area of observed contamination: __
Area of observed exposure: __
Area of subsurface contamination: __
B. Hazardous substances associated with the source.

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Available to pathway
                             ---------------------------------------------------------------------------------------------------------------------------
                                         Air                            Surface Water (SW)             Soil Exposure/Subsurface Intrusion (SESSI)
                             --------------------------             ------------------------------------------------------------------------------------
     Hazardous substance                                                                            Soil  exposure             Subsurface Intrusion
                                                           Ground                             ----------------------------------------------------------
                                  Gas      Particulate   Water (GW)   Overland/     GW to SW                                 Area of         Area of
                                                                        flood                    Resident      Nearby       observed        subsurface
                                                                                exposure      contamination
--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------

    2.2.2 Identify hazardous substances associated with a source.
For each of the three migration pathways, consider those hazardous
substances documented in a source (for example, by sampling, labels,
manifests, oral or written statements) to be

associated with that source when evaluating each pathway. In some
instances, a hazardous substance can be documented as being present
at a site (for example, by labels, manifests, oral or written
statements), but the specific source(s) containing that hazardous
substance cannot be documented. For the three migration pathways, in
those instances when the specific source(s) cannot be documented for
a hazardous substance, consider the hazardous substance to be
present in each source at the site, except sources for which
definitive information indicates that the hazardous substance was
not or could not be present.
    For an area of observed contamination in the soil exposure
component of the soil exposure and subsurface intrusion pathway,
consider only those hazardous substances that meet the criteria for
observed contamination for that area (see section 5.1.0) to be
associated with that area when evaluating the pathway.
    For an area of observed exposure or area of subsurface
contamination (see section 5.2.0) in the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway,
consider only those hazardous substances that:
     Meet the criteria for observed exposure, or
     Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol, or
     Meet the criteria for an observed release in a
structure within, or in a sample from below, an area of observed
exposure and have a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-\5\
atm-m\3\/mol.
    2.2.3 Identify hazardous substances available to a pathway. In
evaluating each migration pathway, consider the following hazardous
substances available to migrate from the sources at the site to the
pathway:

 Ground water migration.
    --Hazardous substances that meet the criteria for an observed
release (see section 2.3) to ground water.
    --All hazardous substances associated with a source with a
ground water containment factor value greater than 0 (see section
<IP_ADDRESS>).
 Surface water migration--overland/flood component.
    --Hazardous substances that meet the criteria for an observed
release to surface water in the watershed being evaluated.
    --All hazardous substances associated with a source with a
surface water containment factor value greater than 0 for the
watershed (see sections <IP_ADDRESS>.2.1.1 and <IP_ADDRESS>.2.2.1).
 Surface water migration--ground water to surface water
component.
    --Hazardous substances that meet the criteria for an observed
release to ground water.
    --All hazardous substances associated with a source with a
ground water containment factor value greater than 0 (see sections
<IP_ADDRESS>.2 and <IP_ADDRESS>).
 Air migration.
    --Hazardous substances that meet the criteria for an observed
release to the atmosphere.
    --All gaseous hazardous substances associated with a source with
a gas containment factor value greater than 0 (see section
<IP_ADDRESS>.1).
    --All particulate hazardous substances associated with a source
with a particulate containment factor value greater than 0 (see
section <IP_ADDRESS>.1).
 For each migration pathway, in those instances when the
specific source(s) containing the hazardous substance cannot be
documented, consider that hazardous substance to be available to
migrate to the pathway when it can be associated (see section 2.2.2)
with at least one source having a containment factor value greater
than 0 for that pathway.

    In evaluating the soil exposure and subsurface intrusion
pathway, consider the following hazardous substances available to
the pathway:

 Soil exposure component--resident population threat.
    --All hazardous substances that meet the criteria for observed
contamination at the site (see section 5.1.0).
 Soil exposure component--nearby population threat.
    --All hazardous substances that meet the criteria for observed
contamination at areas with an attractiveness/accessibility factor
value greater than 0 (see section <IP_ADDRESS>.1).
 Subsurface intrusion component.
    --All hazardous substances that meet the criteria for observed
exposure at the site (see section 5.2.0).
    --All hazardous substances with a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol that meet the criteria for an
observed release in an area of subsurface contamination (see section
5.2.0).
    --All hazardous substances that meet the criteria for an
observed release in a structure within, or in a sample from below,
an area of observed exposure (see section 5.2.0).

    2.3 Likelihood of release. Likelihood of release is a measure of
the likelihood that a waste has been or will be released to the
environment. The likelihood of release factor category is assigned
the maximum value of 550 for a migration pathway whenever the
criteria for an observed release are met for that pathway. If the
criteria for an observed release are met, do not evaluate potential
to release for that pathway. When the criteria for an observed
release are not met, evaluate potential to release for that pathway,
with a maximum value of 500. The evaluation of potential to release
varies by migration pathway (see sections 3, 4 and 6).
    Establish an observed release either by direct observation of
the release of a hazardous substance into the media being evaluated
(for example, surface water) or by chemical analysis of samples
appropriate to the pathway being evaluated (see sections 3, 4 and
6). The minimum standard to establish an observed release by
chemical analysis is analytical evidence of a hazardous substance in
the media significantly above the background level. Further, some
portion of the release must be attributable to the site. Use the
criteria in Table 2-3 as the standard for determining analytical
significance. (The criteria in Table 2-3 are also used in
establishing observed contamination for the soil exposure component
and for establishing areas of observed exposure and areas of
subsurface contamination in the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway, see section
5.1.0 and section 5.2.0). Separate criteria apply to radionuclides
(see section 7.1.1).

       Table 2-3--Observed Release Criteria for Chemical Analysis
------------------------------------------------------------------------

-------------------------------------------------------------------------
Sample Measurement < Sample Quantitation Limit.\a\
No observed release is established.
Sample Measurement >= Sample Quantitation Limit.\a\
An observed release is established as follows:
     If the background concentration is not detected (or is less
     than the detection limit), an observed release is established when
     the sample measurement equals or exceeds the sample quantitation
     limit.\a\
     If the background concentration equals or exceeds the
     detection limit, an observed release is established when the sample
     measurement is 3 times or more above the background concentration.
------------------------------------------------------------------------
\a\ If the sample quantitation limit (SQL) cannot be established,
  determine if there is an observed release as follows:
--If the sample analysis was performed under the EPA Contract Laboratory
  Program, use the EPA contract-required quantitation limit (CRQL) in
  place of the SQL.
--If the sample analysis is not performed under the EPA Contract
  Laboratory Program, use the detection limit (DL) in place of the SQL.

    2.4 Waste characteristics. The waste characteristics factor
category includes the following factors: Hazardous waste quantity,
toxicity, and as appropriate to the pathway or threat being
evaluated, mobility, persistence, degradation, and/or

bioaccumulation (or ecosystem bioaccumulation) potential.
    2.4.1 Selection of substance potentially posing greatest hazard.
For all pathways (components and threats), select the hazardous
substance potentially posing the greatest hazard for the pathway
(component or threat) and use that substance in evaluating the waste
characteristics category of the pathway (component or threat). For
the three migration pathways (and threats), base the selection of
this hazardous substance on the toxicity factor value for the
substance, combined with its mobility, persistence, and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor
values, as applicable to the migration pathway (or threat). For the
soil exposure component of the soil exposure and subsurface
intrusion pathway, base the selection on the toxicity factor alone.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, base the selection on the toxicity
factor value for the substance, combined with its degradation factor
value. Evaluation of the toxicity factor is specified in section
<IP_ADDRESS>. Use and evaluation of the mobility, persistence,
degradation, and/or bioaccumulation (or ecosystem bioaccumulation)
potential factors vary by pathway (component or threat) and are
specified under the appropriate pathway (component or threat)
section. Section <IP_ADDRESS> identifies the specific factors that are
combined with toxicity in evaluating each pathway (component or
threat).
    <IP_ADDRESS> Toxicity factor. Evaluate toxicity for those hazardous
substances at the site that are available to the pathway being
scored. For all pathways and threats, except the surface water
environmental threat, evaluate human toxicity as specified below.
For the surface water environmental threat, evaluate ecosystem
toxicity as specified in section <IP_ADDRESS>.1.1.
    Establish human toxicity factor values based on quantitative
dose-response parameters for the following three types of toxicity:
     Cancer--Use slope factors (also referred to as cancer
potency factors) combined with weight-of-evidence ratings for
carcinogenicity for all exposure routes except inhalation. Use
inhalation unit risk (IUR) for inhalation exposure. If an inhalation
unit risk or a slope factor is not available for a substance, use
its ED10 value to estimate a slope factor as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.063

     Noncancer toxicological responses of chronic exposure--
use reference dose (RfD) or reference concentration (RfC) values as
applicable.
     Noncancer toxicological responses of acute exposure--
use acute toxicity parameters, such as the LD50.
    Assign human toxicity factor values to a hazardous substance
using Table 2-4, as follows:
     If RfD/RfC and slope factor/inhalation unit risk values
are available for the hazardous substance, assign the substance a
value from Table 2-4 for each. Select the higher of the two values
assigned and use it as the overall toxicity factor value for the
hazardous substance.
     If either an RfD/RfC or slope factor/inhalation unit
risk value is available, but not both, assign the hazardous
substance an overall toxicity factor value from Table 2-4 based
solely on the available value (RfD/RfC or slope factor/inhalation
unit risk).
     If neither an RfD/RfC nor slope factor/inhalation unit
risk value is available, assign the hazardous substance an overall
toxicity factor value from Table 2-4 based solely on acute toxicity.
That is, consider acute toxicity in Table 2-4 only when both RfD/RfC
and slope factor/IUR values are not available.
     If neither an RfD/RfC, nor slope factor/inhalation unit
risk, nor acute toxicity value is available, assign the hazardous
substance an overall toxicity factor value of 0 and use other
hazardous substances for which information is available in
evaluating the pathway.

                  Table 2-4--Toxicity Factor Evaluation
------------------------------------------------------------------------
                                                          Assigned value
------------------------------------------------------------------------
                        Chronic Toxicity (Human)
------------------------------------------------------------------------
Reference dose (RfD) (mg/kg-day):
  RfD < 0.0005..........................................          10,000
  0.0005 <= RfD < 0.005.................................           1,000
  0.005 <= RfD < 0.05...................................             100
  0.05 <= RfD < 0.5.....................................              10
  0.5 <= RfD............................................               1
  RfD not available.....................................               0
Reference concentration (RfC) (mg/m\3\):
  RfC < 0.0001..........................................          10,000
  0.0001 <= RfC < 0.006.................................           1,000
  0.006 <= RfC < 0.2....................................             100
  0.2 <= RfC < 2.0......................................              10
  2.0 <= RfC............................................               1
  RfC not available.....................................               0
------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
                                             Carcinogenicity (human)
-----------------------------------------------------------------------------------------------------------------
                                               B or Likely to be       C or Suggestive evidence
       A or Carcinogenic to humans          carcinogenic to humans     of carcinogenic potential  Assigned value
----------------------------------------------------------------------------------------------------------------
                                 Weight-of-evidencea/Slope factor (mg/kg-day)-1
----------------------------------------------------------------------------------------------------------------
0.5 <= SF \b\...........................  5 <= SF...................  50 <= SF..................          10,000
0.05 <= SF < 0.5........................  0.5 <= SF < 5.............  5 <= SF < 50..............           1,000
SF < 0.05...............................  0.05 <= SF < 0.5..........  0.5 <= SF < 5.............             100
                                          SF < 0.05.................  SF < 0.5..................              10
Slope factor not available..............  Slope factor not available  Slope factor not available               0
----------------------------------------------------------------------------------------------------------------
                              Weight-of-evidence a/Inhalation unit risk ([mu]g/m3)
----------------------------------------------------------------------------------------------------------------
0.00004 <= IUR \c\......................  0.0004 <= IUR.............  0.004 <= IUR..............          10,000
0.00001 <= IUR < 0.00004................  0.0001 <= IUR < 0.0004....  0.001 <= IUR < 0.004......           1,000
IUR < 0.00001...........................  0.00001 <= IUR < 0.0001...  0.0001 <= IUR < 0.001.....             100
                                          < 0.00001.................  IUR < 0.0001..............              10
Inhalation unit risk not available......  Inhalation unit risk not    Inhalation unit risk not                 0
                                           available.                  available.
----------------------------------------------------------------------------------------------------------------
\a\ A, B, and C, as well as Carcinogenic to humans, Likely to be carcinogenic to humans, and Suggestive evidence
  of carcinogenic potential refer to weight-of-evidence categories. Assign substances with a weight-of-evidence
  category of D (inadequate evidence of carcinogenicity) or E (evidence of lack of carcinogenicity), as well as
  inadequate information to assess carcinogenic potential and not likely to be carcinogenic to humans a value of
  0 for carcinogenicity.
\b\ SF = Slope factor.
\c\ IUR = Inhalation Unit Risk.

----------------------------------------------------------------------------------------------------------------
                                             Acute Toxicity (human)
-----------------------------------------------------------------------------------------------------------------
                                   Dermal LD50 (mg/kg)   Dust or mist LC50    Gas or vapor LC50
        Oral LD50 (mg/kg)                                      (mg/l)               (ppm)         Assigned value
----------------------------------------------------------------------------------------------------------------
LD50 < 5.........................  LD50 < 2...........  LC50 < 0.2.........  LC50 < 20..........           1,000

5 <= LD50 < 50...................  2 <= LD50 < 20.....  0.2 <= LC50 < 2....  20 <= LC50 <200....             100
50 <= LD50 < 500.................  20 <= LD50 < 200...  2 <= LC50 <20......  200 <= LC50 <2,000.              10
500 <= LD50......................  200 <= LD50........  20 <= LC50.........  2,000 <= LC50......               1
LD50 not available...............  LD50 not available.  LC50 not available.  LC50 not available.               0
----------------------------------------------------------------------------------------------------------------

    If a toxicity factor value of 0 is assigned to all hazardous
substances available to a particular pathway (that is, insufficient
toxicity data are available for evaluating all the substances), use
a default value of 100 as the overall human toxicity factor value
for all hazardous substances available to the pathway. For hazardous
substances having usable toxicity data for multiple exposure routes
(for example, inhalation and ingestion), consider all exposure
routes and use the highest assigned value, regardless of exposure
route, as the toxicity factor value. For HRS purposes, assign both
asbestos and lead (and its compounds) a human toxicity factor value
of 10,000.
    Separate criteria apply for assigning factor values for human
toxicity and ecosystem toxicity for radionuclides (see sections
7.2.1 and 7.2.2).
    <IP_ADDRESS> Hazardous substance selection. For each hazardous
substance evaluated for a migration pathway (or threat), combine the
human toxicity factor value (or ecosystem toxicity factor value) for
the hazardous substance with a mobility, persistence, and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor
value as follows:

 Ground water migration.
    --Determine a combined human toxicity/mobility factor value for
the hazardous substance (see section 3.2.1).
 Surface water migration--overland/flood migration
component.
    --Determine a combined human toxicity/persistence factor value
for the hazardous substance for the drinking water threat (see
section <IP_ADDRESS>.1).
    --Determine a combined human toxicity/persistence/
bioaccumulation factor value for the hazardous substance for the
human food chain threat (see section <IP_ADDRESS>.1).
    --Determine a combined ecosystem toxicity/persistence/
bioaccumulation factor value for the hazardous substance for the
environmental threat (see section <IP_ADDRESS>.1).
 Surface water migration--ground water to surface water
migration component.
    --Determine a combined human toxicity/mobility/persistence
factor value for the hazardous substance for the drinking water
threat (see section <IP_ADDRESS>.1).
    --Determine a combined human toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the
human food chain threat (see section <IP_ADDRESS>.1).
    --Determine a combined ecosystem toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the
environmental threat (see section <IP_ADDRESS>.1).
 Air migration.
    --Determine a combined human toxicity/mobility factor value for
the hazardous substance (see section 6.2.1).

    Determine each combined factor value for a hazardous substance
by multiplying the individual factor values appropriate to the
pathway (or threat). For each migration pathway (or threat) being
evaluated, select the hazardous substance with the highest combined
factor value and use that substance in evaluating the waste
characteristics factor category of the pathway (or threat).
    For the soil exposure and subsurface intrusion pathway,
determine toxicity and toxicity/degradation factor values as
follows:

 Soil exposure and subsurface intrusion--soil exposure
component.
    --Select the hazardous substance with the highest human toxicity
factor value from among the substances that meet the criteria for
observed contamination for the threat evaluated and use that
substance in evaluating the waste characteristics factor category
(see section <IP_ADDRESS>.1).
 Soil exposure and subsurface intrusion--subsurface
intrusion component.
    --Determine a combined human toxicity/degradation factor value
for each hazardous substance being evaluated that:
    [ssquf] Meets the criteria for observed exposure, or
    [ssquf] Meets the criteria for observed release in an area of
subsurface contamination and has a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
    [ssquf] Meets the criteria for an observed release in a
structure within, or in a sample from below, an area of observed
exposure and has a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-5 atm-
m\3\/mol.
    --Select the hazardous substance with the highest combined
factor value and use that substance in evaluating the waste
characteristics factor category (see sections <IP_ADDRESS>.1 and
<IP_ADDRESS>).

    2.4.2 Hazardous waste quantity. Evaluate the hazardous waste
quantity factor by first assigning each source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination) a source hazardous waste quantity value as specified
below. Sum these values to obtain the hazardous waste quantity
factor value for the pathway being evaluated.
    In evaluating the hazardous waste quantity factor for the three
migration pathways, allocate hazardous substances and hazardous
wastestreams to specific sources in the manner specified in section
2.2.2, except: Consider hazardous substances and hazardous
wastestreams that cannot be allocated to any specific source to
constitute a separate ``unallocated source'' for purposes of
evaluating only this factor for the three migration pathways. Do
not, however, include a hazardous substance or hazardous wastestream
in the unallocated source for a migration pathway if there is
definitive information indicating that the substance or wastestream
could only have been placed in sources with a containment factor
value of 0 for that migration pathway.
    In evaluating the hazardous waste quantity factor for the soil
exposure component of the soil exposure and subsurface intrusion
pathway, allocate to each area of observed contamination only those
hazardous substances that meet the criteria for observed
contamination for that area of observed contamination and only those
hazardous wastestreams that contain hazardous substances that meet
the criteria for observed contamination for that area of observed
contamination. Do not consider other hazardous substances or
hazardous wastestreams at the site in evaluating this factor for the
soil exposure component of the soil exposure and subsurface
intrusion pathway.
    In evaluating the hazardous waste quantity factor for the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway, allocate to each area of observed exposure or
area of subsurface contamination only those hazardous substances and
hazardous wastestreams that contain hazardous substances that:

 Meet the criteria for observed exposure, or
 Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
 Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and
have a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-5 atm-m\3\/mol.

    Do not consider other hazardous substances or hazardous
wastestreams at the site in evaluating this factor for the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway. When determining the hazardous waste quantity for
multi-subunit structures, use the procedures identified in section
<IP_ADDRESS>.2.
    <IP_ADDRESS> Source hazardous waste quantity. For each of the three
migration pathways, assign a source hazardous waste quantity

value to each source (including the unallocated source) having a
containment factor value greater than 0 for the pathway being
evaluated. Consider the unallocated source to have a containment
factor value greater than 0 for each migration pathway.
    For the soil exposure component of the soil exposure and
subsurface intrusion pathway, assign a source hazardous waste
quantity value to each area of observed contamination, as applicable
to the threat being evaluated.
    For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, assign a source hazardous waste
quantity value to each regularly occupied structure within an area
of observed exposure or an area of subsurface contamination that has
a structure containment factor value greater than 0. If sufficient
data is available and state of the science shows there is no
unacceptable risk due to subsurface intrusion into a regularly
occupied structure located within an area of subsurface
contamination, that structure can be excluded from the area of
subsurface contamination.
    For determining all hazardous waste quantity calculations except
for an unallocated source or an area of subsurface contamination,
evaluate using the following four measures in the following
hierarchy:
     Hazardous constituent quantity.
     Hazardous wastestream quantity.
     Volume.
     Area.
    For the unallocated source, use only the first two measures. For
an area of subsurface contamination, evaluate non-radioactive
hazardous substances using only the last two measures and evaluate
radioactive hazardous substances using hazardous wastestream
quantity only. See also section 7.0 regarding the evaluation of
radioactive substances.
    Separate criteria apply for assigning a source hazardous waste
quantity value for radionuclides (see section 7.2.5).
    <IP_ADDRESS>.1 Hazardous constituent quantity. Evaluate hazardous
constituent quantity for the source (or area of observed
contamination) based solely on the mass of CERCLA hazardous
substances (as defined in CERCLA section 101(14), as amended)
allocated to the source (or area of observed contamination), except:
     For a hazardous waste listed pursuant to section 3001
of the Solid Waste Disposal Act, as amended by the Resource
Conservation and Recovery Act of 1976 (RCRA), 42 U.S.C. 6901 et
seq., determine its mass for the evaluation of this measure as
follows:

--If the hazardous waste is listed solely for Hazard Code T (toxic
waste), include only the mass of constituents in the hazardous waste
that are CERCLA hazardous substances and not the mass of the entire
hazardous waste.
--If the hazardous waste is listed for any other Hazard Code
(including T plus any other Hazard Code), include the mass of the
entire hazardous waste.

     For a RCRA hazardous waste that exhibits the
characteristics identified under section 3001 of RCRA, as amended,
determine its mass for the evaluation of this measure as follows:

--If the hazardous waste exhibits only the characteristic of
toxicity (or only the characteristic of EP toxicity), include only
the mass of constituents in the hazardous waste that are CERCLA
hazardous substances and not the mass of the entire hazardous waste.
--If the hazardous waste exhibits any other characteristic
identified under section 3001 (including any other characteristic
plus the characteristic of toxicity [or the characteristic of EP
toxicity]), include the mass of the entire hazardous waste.

    Based on this mass, designated as C, assign a value for
hazardous constituent quantity as follows:
     For the migration pathways, assign the source a value
for hazardous constituent quantity using the Tier A equation of
Table 2-5.
     For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value using the Tier A equation of Table 5-2
(section <IP_ADDRESS>.2).
     For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the area of observed
exposure a value using the Tier A equation of Table 5-19 (section
<IP_ADDRESS>.2).
    If the hazardous constituent quantity for the source (or area of
observed contamination or area of observed exposure) is adequately
determined (that is, the total mass of all CERCLA hazardous
substances in the source and releases from the source [or in the
area of observed contamination or area of observed exposure] is
known or is estimated with reasonable confidence), do not evaluate
the other three measures discussed below. Instead assign these other
three measures a value of 0 for the source (or area of observed
contamination or area of observed exposure) and proceed to section
<IP_ADDRESS>.5.
    If the hazardous constituent quantity is not adequately
determined, assign the source (or area of observed contamination or
area of observed exposure) a value for hazardous constituent
quantity based on the available data and proceed to section
<IP_ADDRESS>.2.

        Table 2-5--Hazardous Waste Quantity Evaluation Equations
------------------------------------------------------------------------
                                                          Equation for
      Tier              Measure             Units       assigning value
                                                              \a\
------------------------------------------------------------------------
A..............  Hazardous constituent  lb...........  C
                  quantity (C).
B \b\..........  Hazardous wastestream  lb...........  W/5,000
                  quantity (W).
C \b\..........  Volume (V)...........                 .................
                 Landfill.............  yd\3\........  V/2,500
                 Surface impoundment..  yd\3\........  V/2.5
                 Surface impoundment    yd\3\........  V/2.5
                  (buried/backfilled).
                 Drums \c\............  gallon.......  V/2.5
                 Tanks and containers   yd\3\........  V/2.5
                  other than drums.
                 Contaminated soil....  yd\3\........  V/2,500
                 Pile.................  yd\3\........  V/2.5
                 Other................  yd\3\........  V/2.5
D \b\..........  Area (A).............
                 Landfill.............  ft\2\........  A/3,400
                 Surface impoundment..  ft\2\........  A/13
                 Surface impoundment    ft\2\........  A/13
                  (buried/backfilled).
                 Land treatment.......  ft\2\........  A/270
                 Pile \d\.............  ft\2\........  A/13
                 Contaminated soil....  ft\2\........  A/34,000
------------------------------------------------------------------------
\a\ Do not round to nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1
  cubic yard = 4 drums = 200 gallons.
\c\ If actual volume of drums is unavailable, assume 1 drum = 50
  gallons.
\d\ Use land surface area under pile, not surface area of pile.

    <IP_ADDRESS>.2 Hazardous wastestream quantity. Evaluate hazardous
wastestream quantity for the source (or area of observed
contamination or area of observed exposure) based on the mass of
hazardous wastestreams plus the mass of any additional CERCLA
pollutants and contaminants (as defined in CERCLA section 101[33],
as amended) that are allocated to the source (or area of

observed contamination or area of observed exposure). For a
wastestream that consists solely of a hazardous waste listed
pursuant to section 3001 of RCRA, as amended or that consists solely
of a RCRA hazardous waste that exhibits the characteristics
identified under section 3001 of RCRA, as amended, include the mass
of that entire hazardous waste in the evaluation of this measure.
    Based on this mass, designated as W, assign a value for
hazardous wastestream quantity as follows:
     For the migration pathways, assign the source a value
for hazardous wastestream quantity using the Tier B equation of
Table 2-5.
     For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value using the Tier B equation of Table 5-2
(section <IP_ADDRESS>.2).
     For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the area of observed
exposure a value using the Tier B equation of Table 5-19 (section
<IP_ADDRESS>.2).
    Do not evaluate the volume and area measures described below if
the source is the unallocated source or if the following condition
applies:
     The hazardous wastestream quantity for the source (or
area of observed contamination or area of observed exposure) is
adequately determined--that is, total mass of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source
and releases from the source (or for the area of observed
contamination) is known or is estimated with reasonable confidence.
    If the source is the unallocated source or if this condition
applies, assign the volume and area measures a value of 0 for the
source (or area of observed contamination) and proceed to section
<IP_ADDRESS>.5. Otherwise, assign the source (or area of observed
contamination) a value for hazardous wastestream quantity based on
the available data and proceed to section <IP_ADDRESS>.3.
    <IP_ADDRESS>.3 Volume. Evaluate the volume measure using the volume
of the source (or the volume of the area of observed contamination,
area of observed exposure, or area of subsurface contamination). For
the soil exposure and subsurface intrusion pathway, restrict the use
of the volume measure to those areas of observed contamination,
areas of observed exposure, or areas of subsurface contamination as
specified in sections <IP_ADDRESS>.2 and <IP_ADDRESS>.2.
    Based on the volume, designated as V, assign a value to the
volume measure as follows:
     For the migration pathways, assign the source a value
for volume using the appropriate Tier C equation of Table 2-5.
     For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value for volume using the appropriate Tier C
equation of Table 5-2 (section <IP_ADDRESS>.2).
     For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the value based on
the volume of the regularly occupied structures within the area of
observed exposure or area of subsurface contamination using the Tier
C equation of Table 5-19 (section <IP_ADDRESS>.2).
    If the volume of the source (or volume of the area of observed
contamination, area of observed exposure, or area of subsurface
contamination, if applicable) can be determined, do not evaluate the
area measure. Instead, assign the area measure a value of 0 and
proceed to section <IP_ADDRESS>.5. If the volume cannot be determined (or
is not applicable for the soil exposure and subsurface intrusion
pathway), assign the source (or area of observed contamination, area
of observed exposure, or area of subsurface contamination) a value
of 0 for the volume measure and proceed to section <IP_ADDRESS>.4.
    <IP_ADDRESS>.4 Area. Evaluate the area measure using the area of the
source (or the area of the area of observed contamination, area of
observed exposure, or area of subsurface contamination). Based on
this area, designated as A, assign a value to the area measure as
follows:
     For the migration pathways, assign the source a value
for area using the appropriate Tier D equation of Table 2-5.
     For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value for area using the appropriate Tier D equation
of Table 5-2 (section <IP_ADDRESS>.2).
     For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign a value based on the
area of regularly occupied structures within the area of observed
exposure or area of subsurface contamination using the Tier D
equation of Table 5-19 (section <IP_ADDRESS>.2).
    <IP_ADDRESS>.5 Calculation of source hazardous waste quantity value.
Select the highest of the values assigned to the source (or areas of
observed contamination, areas of observed exposure, or areas of
subsurface contamination) for the hazardous constituent quantity,
hazardous wastestream quantity, volume, and area measures. Assign
this value as the source hazardous waste quantity value. Do not
round to the nearest integer.
    <IP_ADDRESS> Calculation of hazardous waste quantity factor value.
Sum the source hazardous waste quantity values assigned to all
sources (including the unallocated source) or areas of observed
contamination, areas of observed exposure, or areas of subsurface
contamination for the pathway being evaluated and round this sum to
the nearest integer, except: If the sum is greater than 0, but less
than 1, round it to 1. Based on this value, select a hazardous waste
quantity factor value for the pathway from Table 2-6.

            Table 2-6--Hazardous Waste Quantity Factor Values
------------------------------------------------------------------------
             Hazardous waste quantity value               Assigned value
------------------------------------------------------------------------
0.......................................................               0
1 \a\ to 100............................................           \b\ 1
Greater than 100 to 10,000..............................             100
Greater than 10,000 to 1,000,000........................          10,000
Greater than 1,000,000..................................       1,000,000
------------------------------------------------------------------------
\a\ If the hazardous waste quantity value is greater than 0, but less
  than 1, round it to 1 as specified in text.
\b\ For the pathway, if hazardous constituent quantity is not adequately
  determined, assign a value as specified in the text; do not assign the
  value of 1.

    For a migration pathway, if the hazardous constituent quantity
is adequately determined (see section <IP_ADDRESS>.1) for all sources (or
all portions of sources and releases remaining after a removal
action), assign the value from Table 2-6 as the hazardous waste
quantity factor value for the pathway. If the hazardous constituent
quantity is not adequately determined for one or more sources (or
one or more portions of sources or releases remaining after a
removal action) assign a factor value as follows:
     If any target for that migration pathway is subject to
Level I or Level II concentrations (see section 2.5), assign either
the value from Table 2-6 or a value of 100, whichever is greater, as
the hazardous waste quantity factor value for that pathway.
     If none of the targets for that pathway is subject to
Level I or Level II concentrations, assign a factor value as
follows:

--If there has been no removal action, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value for that pathway.
--If there has been a removal action:
    [ssquf] Determine values from Table 2-6 with and without
consideration of the removal action.
    [ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be 100 or greater,
assign either the value from Table 2-6 with consideration of the
removal action or a value of 100, whichever is greater, as the
hazardous waste quantity factor value for the pathway.
    [ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be less than 100,
assign a value of 10 as the hazardous waste quantity factor value
for the pathway.

    For the soil exposure component of the soil exposure and
subsurface intrusion pathway, if the hazardous constituent quantity
is adequately determined for all areas of observed contamination,
assign the value from Table 2-6 as the hazardous waste quantity
factor value. If the hazardous constituent quantity is not
adequately determined for one or more areas of observed
contamination, assign either the value from Table 2-6 or a value of
10, whichever is greater, as the hazardous waste quantity factor
value.
    For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, if the hazardous constituent

quantity is adequately determined for all areas of observed
exposure, assign the value from Table 2-6 as the hazardous waste
quantity factor value. If the hazardous constituent quantity is not
adequately determined for one or more areas of observed exposure,
assign either the value from Table 2-6 or assign a factor value as
follows:
     If any target for the subsurface intrusion component is
subject to Level I or Level II concentrations (see section 2.5),
assign either the value from Table 2-6 or a value of 100, whichever
is greater, as the hazardous waste quantity factor value for this
component.
     If none of the targets for the subsurface intrusion
component is subject to Level I or Level II concentrations and if
there has been a removal or other temporary response action that
does not permanently interrupt target exposure form subsurface
intrusion, assign a factor value as follows:

--Determine the values from Table 2-6 with and without consideration
of the removal or other temporary response action.
--If the value that would be assigned from Table 2-6 without
consideration of the removal or other temporary response action
would be 100 or greater, assign either the value from Table 2-6 with
consideration of the removal action or a value of 100, whichever is
greater, as the hazardous waste quantity factor value for the
component.
--If the value that would be assigned from Table 2-6 without
consideration of the removal or other temporary response action
would be less than 100, assign a value of 10 as the hazardous waste
quantity factor value for the component.

     Otherwise, if none of the targets for the subsurface
intrusion component is subject to Level I or Level II concentrations
and there has not been a removal action, assign a value from Table
2-6 or a value of 10, whichever is greater.
    2.4.3 Waste characteristics factor category value. Determine the
waste characteristics factor category value as specified in section
<IP_ADDRESS> for all pathways and threats, except the surface water-human
food chain threat and the surface water-environmental threat.
Determine the waste characteristics factor category value for these
latter two threats as specified in section <IP_ADDRESS>.
    <IP_ADDRESS> Factor category value. For the pathway (component or
threat) being evaluated, multiply the toxicity or combined factor
value, as appropriate, from section <IP_ADDRESS> and the hazardous waste
quantity factor value from section <IP_ADDRESS>, subject to a maximum
product of 1x10\8\. Based on this waste characteristics product,
assign a waste characteristics factor category value to the pathway
(component or threat) from Table 2-7.

         Table 2-7--Waste Characteristics Factor Category Values
------------------------------------------------------------------------
              Waste characteristics product               Assigned value
------------------------------------------------------------------------
0.......................................................               0
Greater than 0 to less than 10..........................               1
10 to less than 1x10\2\.................................               2
1x10\2\ to less than 1x10\3\............................               3
1x10\3\ to less than 1x10\4\............................               6
1x10\4\ to less than 1x10\5\............................              10
1x10\5\ to less than 1x10\6\............................              18
1x10\6\ to less than 1x10\7\............................              32
1x10\7\ to less than 1x10\8\............................              56
1x10\8\ to less than 1x10\9\............................             100
1x10\9\ to less than 1x10\10\...........................             180
1x10\10\ to less than 1x10\11\..........................             320
1x10\11\ to less than 1x10\12\..........................             560
1x10\12\................................................           1,000
------------------------------------------------------------------------

    <IP_ADDRESS> Factor category value, considering bioaccumulation
potential. For the surface water-human food chain threat and the
surface water-environmental threat, multiply the toxicity or
combined factor value, as appropriate, from section <IP_ADDRESS> and the
hazardous waste quantity factor value from section <IP_ADDRESS>, subject
to:
     A maximum product of 1x10\12\, and
     A maximum product exclusive of the bioaccumulation (or
ecosystem bioaccumulation) potential factor of 1x10\8\.
    Based on the total waste characteristics product, assign a waste
characteristics factor category value to these threats from Table 2-
7.
    2.5 Targets. The types of targets evaluated include the
following:
     Individual (factor name varies by pathway, component,
and threat).
     Human population.
     Resources (these vary by pathway, component, and
threat).
     Sensitive environments (included for the surface water
migration pathway, air migration pathway, and soil exposure
component of the soil exposure and subsurface intrusion pathway).
    The factor values that may be assigned to each type of target
have the same range for each pathway for which that type of target
is evaluated. The factor value for most types of targets depends on
whether the target is subject to actual or potential contamination
for the pathway and whether the actual contamination is Level I or
Level II:
     Actual contamination: Target is associated either with
a sampling location that meets the criteria for an observed release
(or observed contamination or observed exposure) for the pathway or
with an observed release based on direct observation for the pathway
(additional criteria apply for establishing actual contamination for
the human food chain threat in the surface water migration pathway,
see sections <IP_ADDRESS> and <IP_ADDRESS>). Sections 3 through 6 specify how
to determine the targets associated with a sampling location or with
an observed release based on direct observation. Determine whether
the actual contamination is Level I or Level II as follows:

--Level I:
    [ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or
observed exposure) for the pathway and are at or above media-
specific benchmark values. These benchmark values (see section
2.5.2) include both screening concentrations and concentrations
specified in regulatory limits (such as Maximum Contaminant Level
(MCL) values), or
    [ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic
human food chain organisms are at or above benchmark values. Such
tissue samples may be used in addition to media-specific
concentrations only as specified in sections <IP_ADDRESS> and <IP_ADDRESS>.
--Level II:
    [ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or
observed exposure) for the pathway, but are less than media-specific
benchmarks. If none of the hazardous substances eligible to be
evaluated for the sampling location has an applicable benchmark,
assign Level II to the actual contamination at the sampling
location, or
    [ssquf] For observed releases or observed exposures based on
direct observation, assign Level II to targets as specified in
sections 3, 4, 5, and 6, or
    [ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic
human food chain organisms, when applicable, are below benchmark
values.
--If a target is subject to both Level I and Level II concentrations
for a pathway (component or threat), evaluate the target using Level
I concentrations for that pathway (component or threat).

     Potential contamination: Target is subject to a
potential release (that is, target is not associated with actual
contamination for that pathway or threat).
    Assign a factor value for individual risk as follows (select the
highest value that applies to the pathway, component or threat):
     50 points if any individual is exposed to Level I
concentrations.
     45 points if any individual is exposed to Level II
concentrations.
     Maximum of 20 points if any individual is subject to
potential contamination. The value assigned is 20 unless reduced by
a distance or dilution weight appropriate to the pathway. Assign
factor values for population and sensitive environments as follows:
     Sum Level I targets and multiply by 10. (Level I is not
used for sensitive environments in the soil exposure component of
the soil exposure and subsurface intrusion and air migration
pathways.)
     Sum Level II targets.
     Multiply potential targets in all but the soil exposure
and subsurface intrusion pathway by distance or dilution weights
appropriate to the pathway, sum, and divide by 10. Distance or
dilution weighting accounts for diminishing exposure with increasing
distance or dilution within the different pathways. For targets
within an area

of subsurface contamination in the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway, multiply by a
weighting factor as directed in section <IP_ADDRESS>.2.3.
     Sum the values for the three levels.
    In addition, resource value points are assigned within all
pathways for welfare-related impacts (for example, impacts to
agricultural land), but do not depend on whether there is actual or
potential contamination.
    2.5.1 Determination of level of actual contamination at a
sampling location. Determine whether Level I concentrations or Level
II concentrations apply at a sampling location (and thus to the
associated targets) as follows:
     Select the benchmarks applicable to the pathway
(component or threat) being evaluated.
     Compare the concentrations of hazardous substances in
the sample (or comparable samples) to their benchmark concentrations
for the pathway (component or threat), as specified in section
2.5.2.
     Determine which level applies based on this comparison.
     If none of the hazardous substances eligible to be
evaluated for the sampling location has an applicable benchmark,
assign Level II to the actual contamination at that sampling
location for the pathway (component or threat).
    In making the comparison, consider only those samples, and only
those hazardous substances in the sample, that meet the criteria for
an observed release (or observed contamination or observed exposure)
for the pathway, except: Tissue samples from aquatic human food
chain organisms may also be used as specified in sections <IP_ADDRESS>
and <IP_ADDRESS> of the surface water-human food chain threat. If any
hazardous substance is present in more than one comparable sample
for the sampling location, use the highest concentration of that
hazardous substance from any of the comparable samples in making the
comparisons.
    Treat sets of samples that are not comparable separately and
make a separate comparison for each such set.
    2.5.2 Comparison to benchmarks. Use the following media-specific
benchmarks for making the comparisons for the indicated pathway (or
threat):
     Maximum Contaminant Level Goals (MCLGs)--ground water
migration pathway and drinking water threat in surface water
migration pathway. Use only MCLG values greater than 0.
     Maximum Contaminant Levels (MCLs)--ground water
migration pathway and drinking water threat in surface water
migration pathway.
     Food and Drug Administration Action Level (FDAAL) for
fish or shellfish--human food chain threat in surface water
migration pathway.
     EPA Ambient Water Quality Criteria (AWQC/National
Recommended Water Quality Criteria) for protection of aquatic life--
environmental threat in surface water migration pathway.
     EPA Ambient Aquatic Life Advisory Concentrations
(AALAC)--environmental threat in surface water migration pathway.
     National Ambient Air Quality Standards (NAAQS)--air
migration pathway.
     National Emission Standards for Hazardous Air
Pollutants (NESHAPs)--air migration pathway. Use only those NESHAPs
promulgated in ambient concentration units.
     Screening concentration for cancer corresponding to
that concentration that corresponds to the 10-6
individual cancer risk for inhalation exposures (air migration
pathway or subsurface intrusion component of the soil exposure and
subsurface intrusion pathway) or for oral exposures (ground water
migration pathway; drinking water and human food chain threats in
surface water migration pathway; and soil exposure and subsurface
intrusion pathway).
     Screening concentration for noncancer toxicological
responses corresponding to the RfC for inhalation exposures (air
migration pathway and subsurface intrusion component of the soil
exposure and subsurface intrusion pathway) or RfD for oral exposures
(ground water migration pathway; drinking water and human food chain
threats in surface water migration pathway; and soil exposure and
subsurface intrusion pathway).
    Select the benchmark(s) applicable to the pathway (component or
threat) being evaluated as specified in sections 3 through 6.
Compare the concentration of each hazardous substance from the
sampling location to its benchmark concentration(s) for that pathway
(component or threat). Use only those samples and only those
hazardous substances in the sample that meet the criteria for an
observed release (or observed contamination or observed exposure)
for the pathway, except: Tissue samples from aquatic human food
chain organisms may be used as specified in sections <IP_ADDRESS> and
<IP_ADDRESS>. If the concentration of any applicable hazardous substance
from any sample equals or exceeds its benchmark concentration,
consider the sampling location to be subject to Level I
concentrations for that pathway (or threat). If more than one
benchmark applies to the hazardous substance, assign Level I if the
concentration of the hazardous substance equals or exceeds the
lowest applicable benchmark concentration.
    If no hazardous substance individually equals or exceeds its
benchmark concentration, but more than one hazardous substance
either meets the criteria for an observed release (or observed
contamination or observed exposure) for the sample (or comparable
samples) or is eligible to be evaluated for a tissue sample (see
sections <IP_ADDRESS> and <IP_ADDRESS>), calculate the indices I and J
specified below based on these hazardous substances.
    For those hazardous substances that are carcinogens (that is,
those having either a carcinogen weight-of-evidence classification
of A, B, or C or a weight-of-evidence classification of carcinogenic
to humans, likely to be carcinogenic to humans, or suggestive
evidence of carcinogenic potential), calculate an index I for the
sample location as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.064

Where:

Ci = Concentration of hazardous substance i in sample (or
highest concentration of hazardous substance i from among comparable
samples).
SCi = Screening concentration for cancer corresponding to
that concentration that corresponds to its 10-6
individual cancer risk for applicable exposure (inhalation or oral)
for hazardous substance i.
n = Number of applicable hazardous substances in sample (or
comparable samples) that are carcinogens and for which an
SCi is available.

    For those hazardous substances for which an RfD or RfC is
available, calculate an index J for the sample location as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.065

Where:

Cj = Concentration of hazardous substance j in sample (or
highest concentration of hazardous substance j from among comparable
samples).
CRj = Screening concentration for noncancer toxicological
responses corresponding to RfD or RfC for applicable exposure
(inhalation or oral) for hazardous substance j.
m = Number of applicable hazardous substances in sample (or
comparable samples) for which a CRj is available.
    If either I or J equals or exceeds 1, consider the sampling
location to be subject to Level I concentrations for that pathway
(component or threat). If both I and J are less than 1, consider the
sampling location to be subject to Level II concentrations for that
pathway (component or threat). If, for the sampling location, there
are sets of samples that are not comparable, calculate I and J
separately for each such set, and use the highest calculated values
of I and J to assign Level I and Level II.
    See sections 7.3.1 and 7.3.2 for criteria for determining the
level of contamination for radioactive substances.
* * * * *

5.0 Soil Exposure and Subsurface Intrusion Pathway

    5.0.1 Exposure components. Evaluate the soil exposure and
subsurface intrusion pathway based on two exposure components:
     Soil exposure component (see section 5.1).
     Subsurface intrusion component (see section 5.2).
    Score one or both components considering their relative
importance. If only one component is scored, assign its score as the
soil exposure and subsurface intrusion pathway score. If both
components are scored, sum the two scores and assign it as the soil
exposure and subsurface intrusion pathway score, subject to a
maximum of 100.

[GRAPHIC] [TIFF OMITTED] TR09JA17.066

    5.1 Soil exposure component. Evaluate the soil exposure
component based on two threats: Resident population threat and
nearby population threat. Evaluate both threats based on three
factor categories: Likelihood of exposure, waste characteristics,

and targets. Figure 5-1 indicates the factors included within each
factor category for each type of threat.
    Determine the soil exposure component score (Sse) in
terms of the factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.067

Where:

LEi = Likelihood of exposure factor category value for
threat i (that is, resident population threat or nearby population
threat).
WCi = Waste characteristics factor category value for
threat i.
Ti = Targets factor category value for threat i.
SF = Scaling factor.

    Table 5-1 outlines the specific calculation procedure.

              Table 5-1--Soil Exposure Component Scoresheet
------------------------------------------------------------------------
      Factor categories and factors        Maximum value  Value assigned
------------------------------------------------------------------------
                       Resident Population Threat
------------------------------------------------------------------------
Likelihood of Exposure:
    1. Likelihood of Exposure...........             550
Waste Characteristics:
    2. Toxicity.........................           (\a\)
    3. Hazardous Waste Quantity.........           (\a\)
    4. Waste Characteristics............             100
Targets:
    5. Resident Individual..............              50
    6. Resident Population:.............
        6a. Level I Concentrations......           (\b\)
        6b. Level II Concentrations.....           (\b\)
        6c. Resident Population (lines             (\b\)
         6a + 6b).......................
    7. Workers..........................              15
    8. Resources........................               5
    9. Terrestrial Sensitive                       (\c\)
     Environments.......................
    10. Targets (lines 5 + 6c + 7 + 8 +            (\b\)
     9).................................
Resident Population Threat Score:
    11. Resident Population Threat                 (\b\)
     (lines 1 x 4 x 10).................
------------------------------------------------------------------------
                        Nearby Population Threat
------------------------------------------------------------------------
Likelihood of Exposure:
    12. Attractiveness/Accessibility....             100
    13. Area of Contamination...........             100
    14. Likelihood of Exposure..........             500
Waste Characteristics:
    15. Toxicity........................           (\a\)
    16. Hazardous Waste Quantity........           (\a\)
    17. Waste Characteristics...........             100
Targets:
    18. Nearby Individual...............               1
    19. Population Within 1 Mile........           (\b\)
    20. Targets (lines 18 + 19).........           (\b\)
Nearby Population Threat Score:
    21. Nearby Population Threat (lines            (\b\)
     14 x 17 x 20)......................
Soil Exposure Component Score:
    22. Soil Exposure Component Score                100
     \d\ (Sse), (lines [11 + 21]/82,500,
     subject to a maximum of 100).......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ No specific maximum value applies to factor. However, pathway score
  based solely on terrestrial sensitive environments is limited to
  maximum of 60.
\d\ Do not round to nearest integer.

    5.1.0 General considerations. Evaluate the soil exposure
component based on areas of observed contamination:
     Consider observed contamination to be present at
sampling locations where analytic evidence indicates that:

--A hazardous substance attributable to the site is present at a
concentration significantly above background levels for the site
(see Table 2-3 in section 2.3 for the criteria for determining
analytical significance), and
--This hazardous substance, if not present at the surface, is
covered by 2 feet or less of cover material (for example, soil).

     Establish areas of observed contamination based on
sampling locations at which there is observed contamination as
follows:

--For all sources except contaminated soil, if observed
contamination from the site is present at any sampling location
within the source, consider that entire source to be an area of
observed contamination.
--For contaminated soil, consider both the sampling location(s) with
observed contamination from the site and the area lying between such
locations to be an area of observed contamination, unless available
information indicates otherwise.

     If an area of observed contamination (or portion of
such an area) is covered by a permanent, or otherwise maintained,
essentially impenetrable material (for example, asphalt) that is not
more than 2 feet thick, exclude that area (or portion of the area)
in evaluating the soil exposure component.
     For an area of observed contamination, consider only
those hazardous substances that meet the criteria for observed
contamination for that area to be associated with that area in
evaluating the soil exposure component (see section 2.2.2).

    If there is observed contamination, assign scores for the
resident population threat and the nearby population threat, as
specified in sections 5.1.1 and 5.1.2. If there is no observed
contamination, assign the soil exposure component of the soil
exposure and subsurface intrusion pathway a score of 0.
    5.1.1 Resident population threat. Evaluate the resident
population threat only if there is an area of observed contamination
in one or more of the following locations:
     Within the property boundary of a residence, school, or
day care center and within 200 feet of the respective residence,
school, or day care center, or
     Within a workplace property boundary and within 200
feet of a workplace area, or
     Within the boundaries of a resource specified in
section <IP_ADDRESS>.4, or
     Within the boundaries of a terrestrial sensitive
environment specified in section <IP_ADDRESS>.5.
    If not, assign the resident population threat a value of 0,
enter this value in Table 5-1, and proceed to the nearby population
threat (section 5.1.2).
    <IP_ADDRESS> Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the resident population
threat if there is an area of observed contamination in one or more
locations listed in section 5.1.1. Enter this value in Table 5-1.
    <IP_ADDRESS> Waste characteristics. Evaluate waste characteristics
based on two factors: toxicity and hazardous waste quantity.
Evaluate only those hazardous substances that meet the criteria for
observed contamination at the site (see section 5.1.0).
    <IP_ADDRESS>.1 Toxicity. Assign a toxicity factor value to each
hazardous substance as specified in section <IP_ADDRESS>. Use the
hazardous substance with the highest toxicity factor value to assign
the value to the toxicity factor for the resident population threat.
Enter this value in Table 5-1.
    <IP_ADDRESS>.2 Hazardous waste quantity. Assign a hazardous waste
quantity factor value as specified in section 2.4.2. In estimating
the hazardous waste quantity, use Table 5-2 and:
     Consider only the first 2 feet of depth of an area of
observed contamination, except as specified for the volume measure.
     Use the volume measure (see section <IP_ADDRESS>.3) only for
those types of areas of observed contamination listed in Tier C of
Table 5-2. In evaluating the volume measure for these listed areas
of observed contamination, use the full volume, not just the volume
within the top 2 feet.
     Use the area measure (see section <IP_ADDRESS>.4), not the
volume measure, for all other types of areas of observed
contamination, even if their volume is known.
    Enter the value assigned in Table 5-1.

              Table 5-2--Hazardous Waste Quantity Evaluation Equations for Soil Exposure Component
----------------------------------------------------------------------------------------------------------------
                                                                                Equation for assigning
               Tier                           Measure                   Units                  value \a\
----------------------------------------------------------------------------------------------------------------
A.................................  Hazardous Constituent       lb...................  C.
                                     Quantity (C).
 B\b\.............................  Hazardous Wastestream       lb...................  W/5,000.
                                     Quantity (W).
C \b\.............................  Volume (V)................
                                    Surface Impoundment \c\...  yd\3\................  V/2.5.
                                    Drums \d\.................  gallon...............  V/500.
                                    Tanks and Containers Other  yd \3\...............  V/2.5.
                                     Than Drums.
D \b\.............................  Area (A)..................
                                    Landfill..................  ft \2\...............  A/34,000.
                                    Surface Impoundment.......  ft \2\...............  A/13.
                                    Surface Impoundment         ft \2\...............  A/13.
                                     (Buried/backfilled).
                                    Land treatment............  ft \2\...............  A/270.
                                    Pile \e\..................  ft \2\...............  A/34.
                                    Contaminated Soil.........  ft \2\...............  A/34,000.
----------------------------------------------------------------------------------------------------------------
\a\ Do not round nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1 cubic yard = 4 drums = 200 gallons.
\c\ Use volume measure only for surface impoundments containing hazardous substances present as liquids. Use
  area measures in Tier D for dry surface impoundments and for buried/backfilled surface impoundments.
\d\ If actual volume of drums is unavailable, assume 1 drum = 50 gallons.
\e\ Use land surface area under pile, not surface area of pile.

    <IP_ADDRESS>.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10 \8\. Based on this
product, assign a value from Table 2-7 (section <IP_ADDRESS>) to the
waste characteristics factor category. Enter this value in Table 5-
1.
    <IP_ADDRESS> Targets. Evaluate the targets factor category for the
resident population threat based on five factors: Resident
individual, resident population, workers, resources, and terrestrial
sensitive environments.
    In evaluating the targets factor category for the resident
population threat, count only the following as targets:
     Resident individual--a person living or attending
school or day care on a property with an area of observed
contamination and whose residence, school, or day care center,
respectively, is on or within 200 feet of the area of observed
contamination.
     Worker--a person working on a property with an area of
observed contamination and whose workplace area is on or within 200
feet of the area of observed contamination.
     Resources located on an area of observed contamination,
as specified in section 5.1.1.
     Terrestrial sensitive environments located on an area
of observed contamination, as specified in section 5.1.1.
    <IP_ADDRESS>.1 Resident individual. Evaluate this factor based on
whether there is a resident individual, as specified in section
<IP_ADDRESS>, who is subject to Level I or Level II concentrations.
    First, determine those areas of observed contamination subject
to Level I concentrations and those subject to Level II
concentrations as specified in sections 2.5.1 and 2.5.2. Use the
health-based benchmarks from Table 5-3 in determining the level of
contamination. Then assign a value to the resident individual factor
as follows:
     Assign a value of 50 if there is at least one resident
individual for one or more areas subject to Level I concentrations.
     Assign a value of 45 if there is no such resident
individuals, but there is at least one resident individual for one
or more areas subject to Level II concentrations.
     Assign a value of 0 if there is no resident individual.

Enter the value assigned in Table 5-1.
    <IP_ADDRESS>.2 Resident population. Evaluate resident population
based on two factors: Level I concentrations and Level II
concentrations. Determine which factor applies as specified in
sections 2.5.1 and 2.5.2, using the health-based benchmarks from
Table 5-3. Evaluate populations subject to Level I concentrations as
specified in section <IP_ADDRESS>.2.1 and populations subject to Level II
concentrations as specified in section <IP_ADDRESS>.2.2.

  Table 5-3--Health-Based Benchmarks for Hazardous Substances in Soils
------------------------------------------------------------------------

-------------------------------------------------------------------------
Screening concentration for cancer corresponding to that concentration
 that corresponds to the 10 -6 individual cancer risk for oral
 exposures.
Screening concentration for noncancer toxicological responses
 corresponding to the Reference Dose (RfD) for oral exposures.
------------------------------------------------------------------------

    Count only those persons meeting the criteria for resident
individual as specified in section <IP_ADDRESS>. In estimating the number
of people living on property with an area of observed contamination,
when the estimate is based on the number of residences, multiply
each residence by the average number of persons per residence for
the county in which the residence is located.
    <IP_ADDRESS>.2.1 Level I concentrations. Sum the number of resident
individuals subject to Level I concentrations and multiply this sum
by 10. Assign the resulting product as the value for this factor.
Enter this value in Table 5-1.
    <IP_ADDRESS>.2.2 Level II concentrations. Sum the number of resident
individuals subject to Level II concentrations. Do not include those
people already counted under the Level I concentrations factor.
Assign this sum as the value for this factor. Enter this value in
Table 5-1.
    <IP_ADDRESS>.2.3 Calculation of resident population factor value. Sum
the factor values for Level I concentrations and Level II
concentrations. Assign this sum as the resident population factor
value. Enter this value in Table 5-1.
    <IP_ADDRESS>.3 Workers. Evaluate this factor based on the number of
workers that meet the section <IP_ADDRESS> criteria. Assign a value for
these workers using Table 5-4. Enter this value in Table 5-1.

                  Table 5-4--Factor Values for Workers
------------------------------------------------------------------------
                                                               Assigned
                     Number of workers                          value
------------------------------------------------------------------------
0..........................................................            0
1 to 100...................................................            5
101 to 1,000...............................................           10
Greater than 1,000.........................................           15
------------------------------------------------------------------------

    <IP_ADDRESS>.4 Resources. Evaluate the resources factor as follows:
     Assign a value of 5 to the resources factor if one or
more of the following is present on an area of observed
contamination at the site:
--Commercial agriculture.
--Commercial silviculture.
--Commercial livestock production or commercial livestock grazing.

     Assign a value of 0 if none of the above are present.
    Enter the value assigned in Table 5-1.
    <IP_ADDRESS>.5 Terrestrial sensitive environments. Assign value(s)
from Table 5-5 to each terrestrial sensitive environment that meets
the eligibility criteria of section <IP_ADDRESS>.
    Calculate a value (ES) for terrestrial sensitive environments as
follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.068

Where:

Si = Value(s) assigned from Table 5-5 to terrestrial
sensitive environment i.
n = Number of terrestrial sensitive environments meeting section
<IP_ADDRESS> criteria.

    Because the pathway score based solely on terrestrial sensitive
environments is limited to a maximum of 60, determine the value for
the terrestrial sensitive environments factor as follows:

       Table 5-5--Terrestrial Sensitive Environments Rating Values
------------------------------------------------------------------------
                                                             Assigned
           Terrestrial sensitive environments                  value
------------------------------------------------------------------------
Terrestrial critical habitat \a\ for Federal designated              100
 endangered or threatened species.......................
    National Park
    Designated Federal Wilderness Area..................
    National Monument...................................
Terrestrial habitat known to be used by Federal                       75
 designated or proposed threatened or endangered species
    National Preserve (terrestrial)
     National or State Terrestrial Wildlife Refuge......
    Federal land designated for protection of natural
     ecosystems.........................................
     Administratively proposed Federal Wilderness Area..
    Terrestrial areas utilized for breeding by large or
     dense aggregations of animals \b\..................
Terrestrial habitat known to be used by State designated              50
 endangered or threatened species.......................
    Terrestrial habitat known to be used by species
     under review as to its Federal designated
     endangered or threatened status
State lands designated for wildlife or game management..              25
    State designated Natural Areas
    Particular areas, relatively small in size,
     important to maintenance of unique biotic
     communities........................................
------------------------------------------------------------------------
\a\ Critical habitat as defined in 50 CFR 424.02.
\b\ Limit to vertebrate species.

     Multiply the values assigned to the resident population
threat for likelihood of exposure (LE), waste characteristics (WC),
and ES. Divide the product by 82,500.
--If the result is 60 or less, assign the value ES as the
terrestrial sensitive environments factor value.
--If the result exceeds 60, calculate a value EC as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.069

    Assign the value EC as the terrestrial sensitive environments
factor value. Do not round this value to the nearest integer.
    Enter the value assigned for the terrestrial sensitive
environments factor in Table 5-1.
    <IP_ADDRESS>.6 Calculation of resident population targets factor
category value. Sum the values for the resident individual, resident
population, workers, resources, and terrestrial sensitive
environments factors. Do not round to the nearest integer. Assign
this sum as the targets factor category value for the resident
population threat. Enter this value in Table 5-1.
    <IP_ADDRESS> Calculation of resident population threat score.
Multiply the values for likelihood of exposure, waste
characteristics, and targets for the resident population threat, and
round the product to the nearest integer. Assign this product as the
resident population threat score. Enter this score in Table 5-1.
    5.1.2 Nearby population threat. Include in the nearby population
only those individuals who live or attend school within a 1-mile
travel distance of an area of observed contamination at the site and
who do not meet the criteria for resident individual as specified in
section <IP_ADDRESS>.
    Do not consider areas of observed contamination that have an
attractiveness/accessibility factor value of 0 (see section

<IP_ADDRESS>.1) in evaluating the nearby population threat.
    <IP_ADDRESS> Likelihood of exposure. Evaluate two factors for the
likelihood of exposure factor category for the nearby population
threat: attractiveness/accessibility and area of contamination.
    <IP_ADDRESS>.1 Attractiveness/accessibility. Assign a value for
attractiveness/accessibility from Table 5-6 to each area of observed
contamination, excluding any land used for residences. Select the
highest value assigned to the areas evaluated and use it as the
value for the attractiveness/accessibility factor. Enter this value
in Table 5-1.
    <IP_ADDRESS>.2 Area of contamination. Evaluate area of contamination
based on the total area of the areas of observed contamination at
the site. Count only the area(s) that meet the criteria in section
5.1.0 and that receive an attractiveness/accessibility value greater
than 0. Assign a value to this factor from Table 5-7. Enter this
value in Table 5-1.

             Table 5-6--Attractiveness/Accessibility Values
------------------------------------------------------------------------
             Area of observed contamination               Assigned value
------------------------------------------------------------------------
Designated recreational area............................             100
Regularly used for public recreation (for example,                    75
 fishing, hiking, softball).............................
Accessible and unique recreational area (for example,                 75
 vacant lots in urban area).............................
Moderately accessible (may have some access                           50
 improvements, for example, gravel road), with some
 public recreation use..................................
Slightly accessible (for example, extremely rural area                25
 with no road improvement), with some public recreation
 use....................................................
Accessible, with no public recreation use...............              10
Surrounded by maintained fence or combination of                       5
 maintained fence and natural barriers..................
Physically inaccessible to public, with no evidence of                 0
 public recreation use..................................
------------------------------------------------------------------------

             Table 5-7--Area of Contamination Factor Values
------------------------------------------------------------------------
    Total area of the areas of observed contamination
                      (square feet)                       Assigned value
------------------------------------------------------------------------
Less than or equal to 5,000.............................               5
Greater than 5,000 to 125,000...........................              20
Greater than 125,000 to 250,000.........................              40
Greater than 250,000 to 375,000.........................              60
Greater than 375,000 to 500,000.........................              80
Greater than 500,000....................................             100
------------------------------------------------------------------------

    <IP_ADDRESS>.3 Likelihood of exposure factor category value. Assign a
value from Table 5-8 to the likelihood of exposure factor category,
based on the values assigned to the attractiveness/accessibility and
area of contamination factors. Enter this value in Table 5-1.

                                            Table 5-8--Nearby Population Likelihood of Exposure Factor Values
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                             Attractiveness/accessibility factor value
   Area of contamination factor value    ---------------------------------------------------------------------------------------------------------------
                                                100             75              50              25              10               5               0
--------------------------------------------------------------------------------------------------------------------------------------------------------
100.....................................             500             500             375             250             125              50               0
80......................................             500             375             250             125              50              25               0
60......................................             375             250             125              50              25               5               0
40......................................             250             125              50              25               5               5               0
20......................................             125              50              25               5               5               5               0
5.......................................              50              25               5               5               5               5               0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    <IP_ADDRESS> Waste characteristics. Evaluate waste characteristics
based on two factors: toxicity and hazardous waste quantity.
Evaluate only those hazardous substances that meet the criteria for
observed contamination (see section 5.1.0) at areas that can be
assigned an attractiveness/accessibility factor value greater than
0.
    <IP_ADDRESS>.1 Toxicity. Assign a toxicity factor value as specified
in section <IP_ADDRESS> to each hazardous substance meeting the criteria
in section <IP_ADDRESS>. Use the hazardous substance with the highest
toxicity factor value to assign the value to the toxicity factor for
the nearby population threat. Enter this value in Table 5-1.
    <IP_ADDRESS>.2 Hazardous waste quantity. Assign a value to the
hazardous waste quantity factor as specified in section <IP_ADDRESS>.2,
except: consider only those areas of observed contamination that can
be assigned an attractiveness/accessibility factor value greater
than 0. Enter the value assigned in Table 5-1.
    <IP_ADDRESS>.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10\8\. Based on this
product, assign a value from Table 2-7 (section <IP_ADDRESS>) to the
waste characteristics factor category. Enter this value in Table 5-
1.
    <IP_ADDRESS> Targets. Evaluate the targets factory category for the
nearby population threat based on two factors: nearby individual and
population within a 1-mile travel distance from the site.
    <IP_ADDRESS>.1 Nearby individual. If one or more persons meet the
section <IP_ADDRESS> criteria for a resident individual, assign this
factor a value of 0. Enter this value in Table 5-1.
    If no person meets the criteria for a resident individual,
determine the shortest travel distance from the site to any
residence or school. In determining the travel distance, measure the
shortest overland distance an individual would travel from a
residence or school to the nearest area of observed contamination
for the site with an attractiveness/accessibility factor value
greater than 0. If there are no natural barriers to travel, measure
the travel distance as the shortest straight-line distance from the
residence or school to the area of observed contamination. If
natural barriers exist (for example, a river), measure the travel
distance as the shortest straight-line distance from the residence
or school to the nearest crossing point and from there as the
shortest straight-

line distance to the area of observed contamination. Based on the
shortest travel distance, assign a value from Table 5-9 to the
nearest individual factor. Enter this value in Table 5-1.

               Table 5-9--Nearby Individual Factor Values
------------------------------------------------------------------------
                                                                Assigned
        Travel distance for nearby individual (miles)            value
------------------------------------------------------------------------
Greater than 0 to \1/4\......................................      \a\ 1
Greater than \1/4\ to 1......................................          0
------------------------------------------------------------------------
\a\ Assign a value of 0 if one or more persons meet the section <IP_ADDRESS>
  criteria for resident individual.

    <IP_ADDRESS>.2 Population within 1 mile. Determine the population
within each travel distance category of Table 5-10. Count residents
and students who attend school within this travel distance. Do not
include those people already counted in the resident population
threat. Determine travel distances as specified in section
<IP_ADDRESS>.1.
    In estimating residential population, when the estimate is based
on the number of residences, multiply each residence by the average
number of persons per residence for the county in which the
residence is located.
    Based on the number of people included within a travel distance
category, assign a distance-weighted population value for that
travel distance from Table 5-10.
    Calculate the value for the population within 1 mile factor (PN)
as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.070

Where:

Wi=Distance-weighted population value from Table 5-10 for
travel distance category i.

    If PN is less than 1, do not round it to the nearest integer; if
PN is 1 or more, round to the nearest integer. Enter this value in
Table 5-1.
    <IP_ADDRESS>.3 Calculation of nearby population targets factor
category value. Sum the values for the nearby individual factor and
the population within 1 mile factor. Do not round this sum to the
nearest integer. Assign this sum as the targets factor category
value for the nearby population threat. Enter this value in Table 5-
1.

                                     Table 5-10--Distance Weighted Population Values for Nearby Population Threat a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                          Number of people within the travel distance category
                                               ---------------------------------------------------------------------------------------------------------
       Travel distance category (miles)                                                          1,001   3,001    10,001   30,001    100,001
                                                   0     1 to    11 to   31 to  101 to  301 to    to       to       to       to        to     300,001 to
                                                          10      30      100     300    1,000   3,000   10,000   30,000   100,000   300,000   1,000,000
--------------------------------------------------------------------------------------------------------------------------------------------------------
Greater than 0 to \1/4\.......................       0     0.1     0.4     1.0       4      13      41      130      408     1,303     4,081      13,034
Greater than \1/4\ to \1/2\...................       0    0.05     0.2     0.7       2       7      20       65      204       652     2,041       6,517
Greater than \1/2\ to 1.......................       0    0.02     0.1     0.3       1       3      10       33      102       326     1,020       3,258
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Round the number of people present within a travel distance category to nearest integer. Do not round the assigned distance-weighted population
  value to nearest integer.

    <IP_ADDRESS> Calculation of nearby population threat score. Multiply
the values for likelihood of exposure, waste characteristics, and
targets for the nearby population threat, and round the product to
the nearest integer. Assign this product as the nearby population
threat score. Enter this score in Table 5-1.
    5.1.3 Calculation of soil exposure component score. Sum the
resident population threat score and the nearby population threat
score, and divide the sum by 82,500. Assign the resulting value,
subject to a maximum of 100, as the soil exposure component score
(Sse). Enter this score in Table 5-1.
    5.2 Subsurface intrusion component. Evaluate the subsurface
intrusion component based on three factor categories: likelihood of
exposure, waste characteristics, and targets. Figure 5-1 indicates
the factors included within each factor category for the subsurface
intrusion component.
    Determine the component score (Sssi) in terms of the
factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.071

Where:

LE=Likelihood of exposure factor category value.
WC=Waste characteristics factor category value.
T=Targets factor category value.
SF=Scaling factor.

    Table 5-11 outlines the specific calculation procedure.

          Table 5-11--Subsurface Intrusion Component Scoresheet
------------------------------------------------------------------------
      Factor categories and factors        Maximum value  Value assigned
------------------------------------------------------------------------
Subsurface Intrusion Component:
Likelihood of Exposure:
    1. Observed Exposure................             550
    2. Potential for Exposure...........
        2a. Structure Containment.......              10
        2b. Depth to contamination......              10
        2c. Vertical Migration..........              15
        2d. Vapor Migration Potential...              25
    3. Potential for Exposure (lines 2a              500
     * (2b + 2c + 2d), subject to a
     maximum of 500)....................
    4. Likelihood of Exposure (higher of             550
     lines 1 or 3)......................
Waste Characteristics:
    5. Toxicity/Degradation.............           (\a\)
    6. Hazardous Waste Quantity.........           (\a\)
    7. Waste Characteristics (subject to             100
     a maximum of 100)..................
Targets:
    8. Exposed Individual...............              50
    9. Population:......................
        9a. Level I Concentrations......           (\b\)
        9b. Level II Concentrations.....           (\b\)
        9c. Population within an Area of           (\b\)
         Subsurface Contamination.......
        9d. Total Population (lines 9a +           (\b\)
         9b + 9c).......................

    10. Resources.......................               5
    11. Targets (lines 8 + 9d + 10).....           (\b\)
Subsurface Intrusion Component Score:
    12. Subsurface Intrusion Component               100
     (lines 4 x 7 x 11)/82,500 \c\
     (subject to a maximum of 100)......
Soil Exposure and Subsurface Intrusion
 Pathway Score:
    13. Soil Exposure Component +                    100
     Subsurface Intrusion Component
     (subject to a maximum of 100)......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ Do not round to the nearest integer.

    5.2.0 General considerations. The subsurface intrusion component
evaluates the threats from hazardous substances that have or could
intrude into regularly occupied structures from the subsurface.
Evaluate the subsurface intrusion component based on the actual or
potential intrusion of hazardous substances into all regularly
occupied structures that have structure containment values greater
than zero and meet the criteria identified in the section below as
being either in an area of observed exposure or in an area of
subsurface contamination. These structures may or may not have
subunits. Subunits are partitioned areas within a structure with
separate heating, ventilating, and air conditioning (HVAC) systems
or distinctly different air exchange rates. Subunits include
regularly occupied partitioned tenant spaces such as office suites,
apartments, condos, common or shared areas, and portions of
residential, commercial or industrial structures with separate
heating, ventilating, and air conditioning (HVAC) systems.
    In evaluating the subsurface intrusion component, consider the
following:
     Area(s) of observed exposure: An area of observed
exposure is delineated by regularly occupied structures with
documented contamination meeting observed exposure criteria; an area
of observed exposure includes regularly occupied structures with
samples meeting observed exposure criteria or inferred to be within
an area of observed exposure based on samples meeting observed
exposure criteria (see section <IP_ADDRESS>.1 Observed exposure).
Establish areas of observed exposure as follows:

--For regularly occupied structures that have no subunits, consider
both the regularly occupied structures containing sampling
location(s) meeting observed exposure criteria for the site and the
regularly occupied structure(s) in the area lying between such
locations to be an area of observed exposure (i.e., inferred to be
in an area of observed exposure), unless available information
indicates otherwise.
--In multi-story, multi-subunit, regularly occupied structures,
consider all subunits on a level with sampling locations meeting
observed exposure criteria from the site and all levels below, if
any, to be within an area of observed exposure, unless available
information indicates otherwise.
--In multi-tenant structures, that do not have a documented observed
exposure, but are located in an area lying between locations where
observed exposures have been documented, consider only those
regularly occupied subunits, if any, on the lowest level of the
structure, to be within an area of observed exposure (i.e., inferred
to be in an area of observed exposure, unless available information
indicates otherwise.

     Area(s) of subsurface contamination: An area of
subsurface contamination is delineated by sampling locations meeting
observed release criteria for subsurface intrusion, excluding areas
of observed exposure (see Table 2-3 in section 2.3). The area within
an area of subsurface contamination includes potentially exposed
populations. If the significant increase in hazardous substance
levels cannot be attributed at least in part to the site, and cannot
be attributed to other sites, attribution can be established based
on the presence of hazardous substances in the area of subsurface
contamination. Establish areas of subsurface contamination as
follows:

--Exclude those areas that contain structures meeting the criteria
defined as an area of observed exposure.
--Consider both the sampling location(s) with subsurface
contamination meeting observed release criteria from the site and
the area lying between such locations to be an area of subsurface
contamination (i.e., inferred to be in an area of subsurface
contamination). If sufficient data is available and state of the
science shows there is no unacceptable risk due to subsurface
intrusion into a regularly occupied structure located within an area
of subsurface contamination, that structure can be excluded from the
area of subsurface contamination.
Evaluate an area of subsurface contamination based on hazardous
substances that:
    [ssquf] Meet the criteria for observed exposure of a chemical
that has a vapor pressure greater than or equal to one torr or a
Henry's constant greater than or equal to 10-\5\ atm-
m\3\/mol, or
    [ssquf] Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol, or
    [ssquf] Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and
have a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-\5\ atm-m\3\/mol.
    --Evaluate all structures with no subunits that have containment
factor values greater than zero, and not documented to meet observed
exposure criteria to be in an area of subsurface contamination if
they are lying between locations of subsurface intrusion samples
meeting observed release criteria.
    --Evaluate multi-subunit structures as follows:
    [ssquf] If an observed exposure has been documented based on a
gaseous indoor air sample, consider all regularly occupied
subunit(s), if any, on the level immediately above the level where
an observed exposure has been documented (or has been inferred to be
within an area of observed exposure), to be within an area of
subsurface contamination. If sufficient data is available and state
of the science shows there is no unacceptable risk due to subsurface
intrusion on the level immediately above the level where an observed
exposure has been documented (or has been inferred to be within an
area of observed exposure) that level can be excluded from the area
of subsurface contamination.
    [ssquf] If observed release criteria have been met based on a
gaseous indoor air sample collected from a level not regularly
occupied, consider all regularly occupied subunit(s), if any, on the
level immediately above the level where the observed release
criteria has been documented, to be within an area of subsurface
contamination. If sufficient data is available and state of the
science shows there is no unacceptable risk due to subsurface
intrusion on the level immediately above the level where the
observed release criteria has been documented that level can be
excluded from the area of subsurface contamination.
    [ssquf] If any regularly occupied multi-subunit structure is
inferred to be in an area of subsurface contamination, consider only
those regularly occupied subunit(s), if any, on the lowest level, to
be within an area of subsurface contamination. If sufficient data is
available and state of the science shows there is no unacceptable
risk due to subsurface intrusion on the lowest level, that structure
can be excluded from the area of subsurface contamination.

    See Section 7.0 for establishing an area of subsurface
contamination based on the

presence of radioactive hazardous substances.
    If there is no area of observed exposure and no area of
subsurface contamination, assign a score of 0 for the subsurface
intrusion component.
    5.2.1 Subsurface intrusion component. Evaluate this component
only if there is an area of observed exposure or area of subsurface
contamination:
     Within or underlying a residence, school, day care
center, workplace, or
     Within or underlying a resource specified in section
<IP_ADDRESS>.3.
    <IP_ADDRESS> Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the subsurface intrusion
component if there is an area of observed exposure in one or more
locations listed in section 5.2.1. Enter this value in Table 5-11.
    <IP_ADDRESS>.1 Observed exposure. Establish observed exposure in a
regularly occupied structure by demonstrating that a hazardous
substance has been released into a regularly occupied structure via
the subsurface. Base this demonstration on either of the following
criteria:
     Direct observation:

--A solid, liquid, or gaseous material that contains one or more
hazardous substances attributable to the site has been observed
entering a regularly occupied structure through migration via the
subsurface or is known to have entered a regularly occupied
structure via the subsurface, or
--When evidence supports the inference of subsurface intrusion of a
material that contains one or more hazardous substances associated
with the site into a regularly occupied structure, demonstrated
adverse effects associated with that release may be used to
establish observed exposure.

     Chemical analysis:

--Analysis of indoor samples indicates that the concentration of
hazardous substance(s) is significantly above the background
concentration for the site for that type of sample (see section
2.3).
--Some portion of the significant increase above background must be
attributable to the site to establish the observed exposure.
Documentation of this attribution should account for possible
concentrations of the hazardous substance(s) in outdoor air or from
materials found in the regularly occupied structure, and should
provide a rationale for the increase being from subsurface
intrusion.

    If observed exposure can be established in a regularly occupied
structure, assign an observed exposure factor value of 550, enter
this value in Table 5-11, and proceed to section <IP_ADDRESS>.3. If no
observed exposure can be established, assign an observed exposure
factor value of 0, enter this value in Table 5-11, and proceed to
section <IP_ADDRESS>.2.
    <IP_ADDRESS>.2 Potential for exposure. Evaluate potential for
exposure only if an observed exposure cannot be established, but an
area of subsurface contamination has been delineated. Evaluate
potential for exposure based only on the presence of hazardous
substances with a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-\5\
atm-m\3\/mol. Evaluate potential for exposure for each area of
subsurface contamination based on four factors: Structure
containment (see section <IP_ADDRESS>.2.1), depth to contamination (see
section <IP_ADDRESS>.2.2), vertical migration (see section <IP_ADDRESS>.2.3)
and vapor migration potential (see section <IP_ADDRESS>.2.4). For each
area of subsurface contamination, assign the highest value for each
factor. If information is insufficient to calculate any single
factor value used to calculate the potential for exposure factor
values at an identified area of subsurface contamination,
information collected for another area of subsurface contamination
at the site may be used when evaluating potential for exposure.
Calculate the potential for exposure value for the site as specified
in section <IP_ADDRESS>.2.5.
    <IP_ADDRESS>.2.1 Structure containment. Calculate containment for
eligible hazardous substances within this component as directed in
Table 5-12 and enter this value into Table 5-11. Assign each
regularly occupied structure within an area of subsurface
contamination the highest appropriate structure containment value
from Table 5-12 and use the regularly occupied structure at the site
with the highest structure containment value in performing the
potential for exposure calculation. For all regularly occupied
structures with unknown containment features assign a structure
containment value of greater than zero for the purposes of
evaluating targets (see section <IP_ADDRESS>).

                    Table 5-12--Structure Containment
------------------------------------------------------------------------
                                Evidence of structure
            No.                      containment          Assigned value
------------------------------------------------------------------------
1.........................  Regularly occupied structure              10
                             with evidence of subsurface
                             intrusion, including
                             documented observed
                             exposure or sampling of bio
                             or inert gases, such as
                             methane and radon.
2.........................  Regularly occupied structure              10
                             with open preferential
                             subsurface intrusion
                             pathways (e.g., sumps,
                             foundation cracks, unsealed
                             utility lines).
3.........................  Regularly occupied structure               7
                             with an engineered vapor
                             migration barrier system
                             that does not address all
                             preferential subsurface
                             intrusion pathways.
4.........................  Regularly occupied structure               6
                             with an engineered passive
                             vapor mitigation system
                             without documented
                             institutional controls
                             (e.g., deed restrictions)
                             or evidence of regular
                             maintenance and inspection.
5.........................  Regularly occupied structure               4
                             with no visible open
                             preferential subsurface
                             intrusion pathways from the
                             subsurface (e.g., sumps,
                             foundation cracks, unsealed
                             utility lines).
6.........................  Regularly occupied structure               3
                             with an engineered passive
                             vapor mitigation system
                             (e.g., passive venting)
                             with documented
                             institutional controls
                             (e.g., deed restrictions)
                             or evidence of regular
                             maintenance and inspection.
7.........................  Regularly occupied structure               2
                             with an engineered, active
                             vapor mitigation system
                             (e.g., active venting)
                             without documented
                             institutional controls
                             (e.g., deed restrictions)
                             and funding in place for on-
                             going operation, inspection
                             and maintenance.
8.........................  Regularly occupied structure               1
                             with a permanent
                             engineered, active vapor
                             mitigation system (e.g.,
                             active venting) with
                             documented institutional
                             controls (e.g., deed
                             restrictions) and funding
                             in place for on-going
                             operation, inspection and
                             maintenance.
9.........................  Regularly occupied structure               0
                             with a foundation raised