Support Document for the Hazardous
Bui®: Rlek Aeteseinent
for Human snd
Volume I
Section 6
Prepared for
U.S. Environmental Proltctfon Agency
of Solid Waste
No.
August 1995
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VttWP-Soool-F
6.0 --TE /;NT> TRANSPORT MODELING 6.1 Conceptual Approach
SECTION 6.0
FATE AND TRANSPORT MODELING
In this analysis, exclusion levels in waste, soil, or groundwater were backcalculated
from a target individual lifetime risk of 10"* for carcinogens or hazard quotient of 1 for
noncarcinogens. Section 5 describes the exposure component of the analysis: how
concentrations in exposure media were backcalculated from risk or hazard quotient This
section describes the fate and transport component of the analysis: how emissions from the
waste management units (WMUs) are backcalculated from the exposure media concentrations.
Section 7 describes the WMU component of the analysis: how soil or waste concentrations
are backcalculated from emission rates. The only exception to this organization is that air
dispersion modeling, which models a transport process, is covered in Section 7 with the
WMU component because it is so intimately linked to the WMU.
Section 6 is divided into 7 subsections. Section 6.1 describes the conceptual approach
to the fate and transport modeling. Sections 6.2 through 6.6 describe the fate and transport
algorithms used for pathways associated with each exposure media: air, soil, groundwater,
surface water, and food chain (plant, animal, -nd fish). Section 6.7 describes the inputs for
the fate and transport modeling.
6.1 CONCEPTUAL APPROACH
6.1.1 Pathway Selection
In selecting environmental fate and transport pathways to include in this analysis,
previous rulemakings and Agency studies that implement multiple pathway analyses were
used as a guide. For example, the Agency has used multiple pathway risk assessment
methodologies in several recent rules including: Hazardous Waste Management System:
Identification and Listing of Hazardous Waste: Wastes from Wood Surface Protection: Final
Rule (59 FR 458, January 4, 1994); Standards for Use or Disposal of Sewage Sludge; Final
Rules (58 FR 32, February 19, 1993)fShd Corrective Action Management Units; Corrective
Action Provisions Under Subtitle C: Final Rule (58 FR 29, February 16, 1993). Other
rulemakings under development within the Office of Solid Waste also use multiple pathway
risk assessment methodologies including various hazardous waste listing determinations and
the dioxin emission rules for hazardous waste combustion units. Most of these analyses draw
on several Agency guidance documents issued in recent years. In January 1990 the Agency
issued an interim report Methodology for Assessing Health Risks Associated with Indirect
Exposure to Combustor Emissions .(EPA/600/6-90/003 and referred to as the Indirect
Exposure Document [U.S. EPA, 1990e]). This document served as the basis for further
August 1995 6-1
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
development of multiple pathway analyses by the Agency: in November 1993, the Agency
issued an Addendum to the Indirect Exposure Document and, in April 1994, draft
implementation guidance entitled Implementation Guidance for Conducting Indirect Exposure
Analysis at RCRA Combustion Units. In June 1994 the Agency released a review draft of
Estimating Exposure to Dioxin-Like Compounds: Volumes l-III (U.S. EPA, 1994a), which
presents an extensive and expanded version of the Agency's previous multipathway exposure
analyses. Finally on November 16, 1994, the Agency issued Draft Soil Screening Guidance
(59 FR 59225), which presents a multiple pathway analysis using air, groundwater, and soil
pathways for soil screening levels at Superfund sites.
Based on these previous efforts by the Agency in multiple pathway analyses, comments
by reviewers on previous versions of the draft HWIR analysis, and some screening analyses
to determine pathways that are either very similar or unimportant compared to other
pathways, 30 human exposure pathways and 22 ecological exposure pathways were selected
for inclusion in this analysis.
Hundreds of exposure pathways have been identified in various recent EPA risk
assessment activities. Increasingly, regulatory standards are established by considering a
number of direct and indirect exposure pathways relevant to both the constituents of concern
and the source of environmental release. As a starting point, the following types of pathways
were considered:
• All direct pathways (e.g., inhalation, direct ingestion of soil, direct ingestion of
drinking water, dermal contact with soil and water)
• Major indirect pathways demonstrated to be of concern for certain groups of
constituents (e.g., exposure to dioxins is frequently associated with fish and fcodchain
pathways)
• Pathways associated with foodchain exposure vehicles (e.g., crops and beef and
milk).
The following criteria were then established to select the most important exposure pathways
for analysis:
*
• Pathways were limited to six compartments (e.g., soil -» crops -> humans has two
compartments, soil and crops). This number of compartments was chosen because it
allowed some plausible pathways that would otherwise have been excluded; however,
it was felt that more compartments would add complexity without adding meaningful,
plausible pathways to the analysis.
• Duplicative pathways were omitted; where considering one pathway would clearly be
protective of another similar pathway, the less protective pathway was omitted.
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
The following specific types of pathway were eliminated from consideration:
• Indirect ingestion while bathing—The ingestion rate of water while bathing is 30
times smaller than the consumption rate of drinking water used in the drinking water
ingestion pathways; therefore, the drinking water ingestion pathways should ensure
protectiveness of the incidental water ingestion pathways.
• Inhalation of volatiles while bathing—No appropriate chemical-specific algorithms
could be found to address this pathway.
• Ingestion of airborne particulates—The ingestion rate of soil used in the direct soil
ingestion pathways is many times larger than the ingestion rate from airborne
particulates; therefore, the direct soil ingestion pathways should ensure protectiveness
of the ingestion of airborne particulates pathway. Also, given the way the soil
ingestion studies were conducted, ingestion of airborne particulates could be
considered to be accounted for in the soil ingestion pathway.
Breast milk exposure to infants could be associated with maternal exposure by any of
the pathways modeled. Such exposures were considered, but not as separate pathways.
Infant exposure via breast milk was calculated as a function of maternal exposure (see Section
5.2.8) and found to be approximately equal to maternal exposure. Therefore, use of the infant
receptor instead of the mother would not change the backcalculated exit criteria. Use of a
receptor exposed both in infancy and as an adult would lower the exit criteria by a factor of 2
for any pathway.
The human pathways modeled in this analysis are described briefly in Table 6-1. Some
pathways have been eliminated from the analysis since the previous version of this analysis,
due to difficulties in modeling or implausibility of the scenario. These include the following:
• Groundwater to surface water pathways—The methodology for grouhdwater to
surface water pathways was based on the assumption that lateral dispersion of the
contaminant plume in groundwater between the waste management unit and the
groundwater-surface water interface is negligible; however, this may not be the case,
and further research is needed to characterize the amount of lateral dispersion.
(Pathways 18, 22, 26, 30, 34, 40, and 46).
*T|r
• Dermal swimming pathways—These pathways were based on the assumption that
recreational and fitness swimming were occuring in a fairly small and swiftly flowing
stream, an implausible scenario. A more plausible scenario for these pathways would
use a lake instead of a flowing water system. Current sensitivity analysis indicates
that the dermal bathing pathways are protective of the swimming pathways.
(Pathways 43, 44, 46, 48)
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6.0 FATE AND TRANSPORT MODELING
6.1 Conceptual Approach
Table 6-1. Human Exposure Pathways
Exposure
BMdhun
Groundwater
Air
Air
Soil
Soil
Soil
Soil
Soil
Soil
Plant
(veg/root)
Route of
exposure
Ingestion
Inhalation
Inhalation
Ingestion
Ingestion
Ingestion
Dermal
Dermal
Dermal
Ingestion
Type of fete aad
traBsport
Groundwater
Direct air
Direct air
Direct soil
Overland
Air deposition
Direct soil
Overland
Air deposition
Air deposition
Pathway*
1
WMU -» groundwater -» humans
Ingestion of contaminated groundwater as a drinking water
source
2a (oa site or off site)
WMU -» air -» humans
Inhalation of volatile*
2k (OB site or off site)
WMU -» air -» humans
Inhalation of suspended paniculate*
3 (oa site)
WMU -» humans
Ingestion of contaminated soil
3 (off site)
WMU — » overland — » humans
Ingestion of contaminated soil
4
WMU -» air -» deposition to soil -» humans
Ingestion of contaminated soil
5 (OB site)
WMU -» humans
- .rmal contact with contaminated soil
5 (off site)
WMU -» overland -» humans
Dermal contact with contaminated soil
6
WMU -> air -* deposition to surface soil -» humans
Dermal contact with contaminated soil
9
WMU -» air -+ deposition to soil/garden crops -» garden crops
— » humans
Consumption of contaminated crops grown in home gardens
Plant (veg) Ingestion
Air diffusion
WMU -» air -» garden crops —» humans
Consumption of contaminated crops grown in home gardens
9 (on site)
WMU -» garden crops -» humans
Consumption of contaminated crops grown in home gardens
Plant (veg/root) Ingestion
Direct soil
Plant (veg/root) Ingestion
Overland
9 (off site)
WMU -» overland -4 garden crops -» humans
Consumption of contaminated crops grown in home gardens
(continued)
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6.0 FATE AND TRANSPORT MODELING
6.1 Conceptual Approach
Table 6-1 (continued)
Exposure
Route oT
exposure
Type of fate ud
trusport
Pathway*
Animal Ingestion Air deposition 10
(beef/milk) WMU -» sir -+ deposition to soil/feed crops -» feed crops/soil
-» cattle -» humans
Consumption of animal products with elevated levels of toxicant
caused by eating contaminated feed crept and soil
Animal Digestion Air diffusion 10a
(beef/milk) WMU -» air -» feed cropi -» cattle -» humans
Consumption of animal products with elevated levels of toxicant
caused by eating contaminated feed crops
Animal
(beef/milk)
Ingesnoo
Direct soil
11 (OB alto)
WMU -» feed crops -» cattle -» humans
Consumption of animal products with elevated levels of toxicant
caused by eating contaminated feed crops and soil
Animal Ingestion
(beetfmilk)
Overland
ll(offstte)
WMU -»overland -» feed crops/sod -» cattle -» humans
Consumption of animal products with elevated levels of toxicant
caused by eating contaminated feed crops and soil:
Groundwater Dermal
(bathing)
Groundwaier
14
WMU -» groundwater -
Dermal bathing contact with contt
I groundwater
Surface water Ingestion
Surface water Ingestion
Air diffusion 17
WMU -» air -» surface water
..igestion of contaminated surface water as a drinking water
source
Overland
WMU -» overland flow -» turface water -» humans
Ingestion of contaminated surface water as a drinking water
source
Surface water Ingestion
Fish
Ingestion
Ingestioa
Ingestion
Air deposition 20
WMU -» air -» deposition to soil -» overland flow -» surface
water -» humans
Ingestion of contaminated surface water as a drinking water
source
Air diffusion 21
WMU -» sir -» surface water -» fish -» humans
Consumption offish contaminated by toxicants in surface water
"Overland -*!«, 23
WMU -» overland flow -» surface water -» fish -» humans
Consumption offish contaminated by toxicants in surface water
Air deposition 24
WMU -» air -* deposition to surface soil -» overland flow -»•
surface water —> fish -+ humans
Consumption offish contaminated by toxicants in surface water
Fish
Fish
(continued)
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.1 Conceptual Approach
Table 6-1 (continued)
Exposure
BCdiUB
Animal
(beef/milk)
Animai
(beef/milk)
Animal
(beef/milk)
Surface water
Surface water
Surface water
Route of .
exponr*
Ingestion
Infection
Digestion
Dermal
(bathing)
Dermal
(bathing)
Dermal
(bathing)
Type of fate awl
transport
Air diffusion
Overland
Air deposition
Air diffusion
Air dftpiyfitiiMi
Overland
Pathway*
33
WMU -» air -» surface water -» cattle -» humans
Consumption of animal products with elevated levels of toxicant
canted by drinking contaminated surface water
35
WMU -» overland flow -» surface water -» cattk -» humans
Consumption of animal products with elevated levels of toxicant
caused by drinking contaminated surface water
M
WMU -» air -» deposition to soil -» overland Sow -> surface
water -» cask -» humans
Consumption of animal products with elevated levels of toxicant
caused by drinking contaminated surface water
37
WMU -» air -» surface water -» humans
Dermal bathing contact with contaminated surface water
38
WMU -> air -» deposition to toil -» overland flow -» surface
water -» humans
Dermal bathing contact with contaminated surface water
42
WMU -» overland flow -» surface water -» humans
^trmal bathing contact with contaminated surface water
Overland = Soil erosion.
Overland flow = Bom runoff and soil erosion; or, for surface impoundments, a spill directly to surface water.
Veg • Aboveground fruits and vegetables.
Root = Belowground (or root) vegetables.
* Some pathway numbers are missing, reflecting pathways that have been eliminated from the analysis or combined with
other pathways.
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
• Irrigation pathways—Many of these pathways were based on the assumption that
, forage pastures and home gardens were being irrigated, an implausible scenario.
(Pathways 25-32).
The ecological pathways are described in Table 6-2. Sections 6.2 through 6.6 describe the
pathways in greater detail.
The pathways modeled are divided into seven types of fate and transport (also shown in
Tables 6-1 and 6-2), as follows:
• Direct air pathways—Pathways beginning with emissions of volatiles and respirable
(PM10) particulates; vapor phase constituents may be inhaled directly or may diffuse
into plants.
• Direct soil pathways—Pathways involving on-site soil exposures.
• Groundwater pathways—Pathways beginning with release to groundwater.
• Air deposition pathways—Pathways beginning with air emissions of particulates that
deposit on soil or plant surfaces.
• Air diffusion pathways—Pathways beginning with emissions of volatiles that, while
in the vapor phase, diffuse directly into surface water.
• Overland pathways—Pathways beginning with overland transport (surface runoff
and soil erosion) to surface water or transport by soil erosion to off-site fields.
Not all pathways were or will be evaluated for all WMUs. Constituents may be
released from each WMU by a variety of mechanisms, as described in Section 7. Each
release mechanism may be associated with one (or sometimes two) of the pathway types
described above. By examining the release mechanisms assumed for each WMU and
identifying the pathway types associated with those release mechanisms, the appropriate
pathways to be modeled for each WMU were identified.
6.12 Sources of Algorithms
Wherever appropriate, the algontflms used in the backcalculation were taken from
Methodology for Assessing Health Risks Associated with Indirect Exposure to Combust or
Emissions (U.S. EPA, 1990e; hereafter, the Indirect Exposure document, or IED) as modified
by the November 10, 1993, draft of Addendum: Methodology for Assessing Health Risks
Associated with Indirect Exposure to Combustor Emissions, Working Group Recommendations
(U.S. EPA, 1993a; hereafter, the Addendum). For convenience, the methodology presented in
the IED as modified by the Addendum will be referred to as the Indirect Exposure Method-
ology, or IEM. Discussion of those algorithms in the following sections is adapted from
August 1995 6-7
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6.0 FATE AND TRANSPORT MODELING
6.1 Conceptual Approach
Table 6-2. Ecological Exposure Pathways
Pathway
Group
Terr I
Exposure
medium
Sod
Soil
Plant
Soil fauna
Route of
exposure
Ingestion
Direct
contact
Ingestion
Ingestion
Type of fate
and transport
Direct soil
Direct soil
Direct soil
Direct soil
Pathway*
3 (on site)
WMU -+ mammals, birds, soil fauna
Ingestion of contaminated soil
5 (Mate)
WMU -» plants, soil fauna
Direct contact with contaminated soil
9 (on site)
WMU — » vegetation — » "iTyit'f. birds
Consumption of contaminated vegetation (ej.
Ha (on site)
WMU ** toil fauna -» mammals, birds
Consumption of soil fauna (e^., earthworms,
elevated levels of toxicant
„ forage grasses)
insects) with
Animals
Infection Direct soil
lib (on site)
WMU -» soil fauna/vegetation -» animals -» predaiory
Consumption of animals with elevated levels of toxicant
TerrD Soil
Ingestion Overland
3 (off site)
WMU -» overland -» mammals, birds, soil fauna
Ingestion of contaminated soil
Soil Direct Overland
contact
5 (off site)
WMU -» overland -» plants, soil fauna
Direct contact with contaminated soil
Plant
Infection Overland
9 (off site)
WMU -» overland -» vegetation -» mammals, birds
Consumption of contaminated vegetation (e$^ forage grasses)
Soil fauna Infection Overland
lie (off site)
WMU -» overland -» soil fauna -» ma
als. birds
Animals
Infection Overland
Consumption of soft fauna (e.g., earthworms, insects) with
elevated levels of toxicant
iid (off sits) " " "•' '
WMU -»overland -» soil fauna/vegetation -» animals -»
predatory mammals, birds
Consumption of animals with elevated levels of toxicant
Ten-IE Soil
Infection Air deposition
WMU -» air -» deposition to soil -» ma
fauna
Ingest ion of 'contaminated soil
als, birds, soil
Soil Direct Air deposition
contact
WMU -> air -» depositioa to surface soil -» pianls, soil fauna
Direct contact with contaminated soil
"s ..... ..... ' ................... ' ..................................... ~ ..... " .......................
WMU -» air -» deposition to sod -» vegetation -» mammals,
birds
Consumption of contaminated vegetation (e.g., forage grasses)
TerrlV Plant
Infection Air deposition
(continued)
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6.0 FATE AND TRANSPORT MODELING
6.1 Conceptual Approach
Table 6-2 (continued)
Pathway
Group
TerrV
Aql
Aqn
AqOI
Exposure
mediuB
Flint
Surface
water
Fuh
Surface
water
Surface
water
Fuh
Surface
water
Surface
water
Fish
Surface
water
Route or
exposure
Ingestion
Ingestion
Infection
Direct
contact
Ingestion
Ingestion
Direct
contact
Ingectioa
Ingestioa
Direct
contact
Type of fate
and transport
Air diffusion
Air diffusion
Air diffusion
Air diffusion
Air deposition
Air deposition
Air deposition
Overland
Overland
Overland
••*».
Pathway*
8a
WMU -> air -» vegetation -» mammals, birds
Consumption of contaminated vegetation (ej.. forage grasses)
17
WMU — nir -» surface water -» mammals, birds
Ingestion of contaminated surface water at a drinking water
source
21
WMU -> air -» mface water — > fish — » mammals, birds, fish
Consumption offish contaminated by toxicants in surface water •
yj
WMU -» air -» surface water -» fish, daphiuds. benthos
Direct contact with contaminated surface water, sediments
20
WMU —t air — t flrpftsifioft to soil — f overland flow — f surface
water -+ mammals, birds
Ingestion of contaminated surface water as a drinking water
source
24
WMU -» air -» deposition to surface toil -» overland flow -»
lurfacc water — f fish — t mammalSi birds, fish
Consumption offish contaminated by toxicants in surface water
~ ^ ' ,
j
WMU -» air -» deposition to soil -» overland Sow -» surface
water -» fish, rtaphnids, benthos
Direct contact with contaminated surface water, sediments
19
WMU — » overland flow — » surface water -4 mammals, birds
Ingestien of contaminated surface water as a drinking water .
source
23
WMU -» overland flow -» surface water -» fish -» mammals,
birds, fish
Consumption offish contaminated by toxicants in surface water
42
WMU -» overland flow -» surface water -» fish, daphnids,
h^nlty^
Direct contact with contaminated surface water, sediments
Overland = Soil erosion.
Overland flow = Both runoff and soil erosion; or, for surface tmpoundmeats, a spill directly to surface water.
' Some pathway numbers are missing, reflecting pathways that have been eliminated from the analysis.
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
those sources; however, parameter names and units have been altered in some cases to
achieve consistency within this document
Where algorithms were not available from the IBM, other appropriate sources were
used. The following algorithms were not covered by the IEM:
• Soil erosion to off-site field—The algorithms used to estimate soil concentration in
an. off-site field as a result of soil erosion were derived by analogy to the soil
• concentration due to deposition equation in the DEM; calculation of soil erosion was
based on the Universal Soil Loss Equation as presented in the IBM.
Certain modifications to the algorithms were made for dioxin-like compounds to reflect
the different behavior of these constituents in the environment These modifications were
based on Estimating Exposure to Dioxin-like Compounds, Volume 111: Site-Specific
Assessment Procedures (U.S. EPA, 1994a, hereafter, the Dioxin document). The Dioxin
document defines dioxin-like compounds as follows:
. . . compounds with nonzero Toxicity Equivalency Factor (TEF) values as
defined in the 1989 International scheme . . . [which] assigns nonzero values to
all chlorinated dibenzodioxins (CDDs) and chlorinated dibenzofurans (CDFs) with
chlorines substituted in the 2,3,7,8 positions. Additionally, the analogous
brominated compounds (BDDs and BDFs) and certain polychlorinated biphenyls
(PCBs) have recently been identified as having dioxin-like toxicity . . . and thus
are also included in the definition of dioxin-like compounds.
Although the methodology presented in the Dioxin document may be applicable to other
highly lipophilic compounds, in keeping with this definition, the modifications for dioxin-like
compounds were made only for 2,3,7,8-TCDDioxin Toxicity Equivalents (TEQs), and PCBs.
Other dioxin congeners are addressed through the 2,3,7,8-TCDDioxin TEQ.
6.1.3 Back calculation
All of the algorithms used in this analysis are presented in the source documents as
forward calculations, mimicking how transport actually occurs (e.g., constituent is present in
waste at a particular concentration, constituent is released, transported to a receptor, and the
receptor is exposed, resulting in risk^This analysis reverses this usual flow of calculation,
backcalculating from risk to waste concentration. Figure 6-1 shows an example pathway both
as it actually occurs (forward) and as it is calculated in this analysis (backward).
In the forward version, this pathway starts with a waste concentration and calculates
mass of contaminant eroded from the WMU and ending up as a loading to surface water.
The loading to surface water is used to calculate the concentration in surface water, which is
then used to calculate the concentration in fish. Finally, the concentration in fish is used to
calculate exposure and risk to humans consuming the fish.
August 1995 .6-10
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
Pathway 23
Forward: WMU -» overland flow -> surface water -* fish -> humans
Backward: humans -» fish -> surface water -» overland flow -> WMU
Figure 6-1. Example of backcalculation vs. forward calculation.
In the backward version, the target risk is used to backcalculate the exposure that would
result in the target risk This exposure is then used to backcalculate the concentration in fish
that would lead to this exposure via fish consumption. This concentration in fish is used to
backcalculate the concentration in surface water that would result in this fish concentration.
The surface water concentration is used to backcalculate the loading that would result in the
surface water concentration. Finally, the loading is used to backcalculate the waste
concentration that would result in that loading via soil erosion, given the WMU
characteristics.
To do backcalculations, all of the fate ' .d transport models must be reversed, so that
what is normally calculated is an input, and what is normally the primary input is calculated.
For example, one component of the example pathway above relates water concentration to
fish concentration, using a chemical-specific bioconcentration factor (BCF). In the usual,
forward, formulation, that equation is:
BCF .
Here, surface water concentration is an input (along with the BCF), and fish concentration is
calculated. In the backcalculation formulation, the equation is:
Here, the equation has been solved for surface water concentration, so that fish concentration
is an input (along with the BCF) and surface water concentration is calculated.
6.1.4 High-End Parameters •
The approach taken to addressing uncertainty in the model calculations was to develop
a central tendency and high-end value for as many variables and parameters used in the
analysis as possible. In conducting the actual computations for a central tendency run, all
August 1995 6-11
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6.0 FATE AND TRANSPORT MODELING 6.1 Conceptual Approach
central tendency values are used for all inputs. In conducting the high-end runs, two
exposure parameters were set at high end and two other parameters were set at high end
while all other parameters were set at central tendency values. Iterations were done until all
combinations of parameters set at high end and central tendency were completed for all
pathway/WMUsAeceptors. This type of sensitivity analysis provides information on which
parameters have the greatest effects on the results and how certain we are of the values for
those parameters. For example, high-end WMU characteristics may be the driving parameters
for several pathways for the surface impoundments. One can then evaluate the quality of the
data on surface impoundment characteristics to determine their reasonableness for the
analysis. As indicated previously, the quality of the data used in this analysis varied greatly.
August 1995 6-12
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6.0 FATE AND TRANSPORT MODELING
6J Air Pathways
6.2 Affi PATHWAYS
Figure 6-2 provides an overview of the fate and transport for air pathways. The
dispersion component may be dispersion to either an on-site or off-site location. Table 6-3
summarizes the receptors modeled for the air pathways.
&2.1 Scenarios
6.2.1.1 Human '
Human scenarios for air pathways include the inhalation of both vapor-phase and
paniculate-phase contaminants emitted from the WMU and carried in the air to the receptor's
location. Inhaled particulates are assumed to be PM10 (i.e., paniculate matter with a particle
diameter of 10 urn or less), as this is the typical definition of respirabie particles.
Receptors selected for the air pathways are adult residents and workers. Adult residents
living at the fenceline of a WMU may be exposed by direct inhalation of either vapors or
particulates. For closed WMUs where residential development occurs on site, adult residents
may also be exposed on site. Workers may also be exposed by direct inhalation of vapors
and particulates while working on site at active (open) WMUs. Although the exposure
frequency and duration for workers is typically somewhat lower than for residents, worker;
are far more likely to be exposed on site, at higher air concentrations, than residents. Since
neither receptor would clearly be protective of the other in all situations, both were included
in the analysis. •
Air Concentration at Receptor
Volatiles
Particulates I
Dispersion
Dispersion
Volatile
Emissions
P articulate
Emissions
Waste Concentration
J
Figure 6-2. Fate and transport for air pathways.
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6.0 FATE AND TRANSPORT MODELING 6.2 Air Pathways
Table 6-3. Summary of Receptors for Air Pathways
Receptor
Adult Child Subsistence Home Subsistence Ffefe
Pathway resident resident fanner gardener fisher consumer Worker
2a: Direct air-inhalation /• /
of volatile* (on site)
2a: Direct air-inhalation
of volatile* (off site)
2b: Direct air-inhalation
of particulates
(on site)
2b: Direct air-inhalation
of particulates
(off site)
' Closed land application unit only.
Child residents were not selected as receptors for the air pathways because the adult
resident scenario is protective of children. There is no indication that children inhale a
greater amount of air per unit of body weigh, uian adults; therefore, average daily exposure
normalized to body weight would be the same for adults and children. However, the
exposure duration for children would be shorter, reducing lifetime exposure for children.
An additional air scenario would be the inhalation of contaminants volatilizing from
shower water. Contaminants could reach ground or surface water used for showering by a
variety of fate and transport pathways. The receptors for such pathways would be adult or
child residents. However, no adequate chemical-specific model for modeling the
volatilization of constituents from shower water has been found. Therefore, these pathways
have not been included in the analysis.
6J.1J Ecological
Currently, no air pathways are assessed for ecological receptors.
6.2.2 Pathway Algorithms
The following sections describe the air pathways and present the fate and transport
equations for them. These pathways are:
• Pathway 2a: inhalation (volatiles) -> air -> WMU (Section 6,2.2.1)
• Pathway 2b: inhalation (particulates) -> air -» WMU (Section 6.2.2.2).
August 1995 6-14
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6.0 FATE AND TRANSPORT MODELING 63 Air Pathways
6.2J.1 Pathway 2a: Inhalation (Volatiles) -» Air -> WMU
Constituents may volatilize from contaminated soils or wastes or be directly released to
air from storage tanks, treatment and disposal facilities, etc. Residents living in die proximity
of a WMU and workers at such facilities may inhale vapor-phase constituents.
/
The only fate and transport process involved in this pathway is air dispersion of
contaminants from the WMU to the receptor location. As discussed in Section 6.1, air
dispersion modeling is covered in Section 7, because it is so closely linked to WMU
characteristics. No other fate and transport processes occur with this pathway; therefore, no
fate and transport equations are used or presented for this pathway.
6JJ.2 Pathway 2b: Inhalation (Particulates) -> Air -> WMU
Constituents sorbed to particles in the surface soil or waste matrix may be entrained
into the air from contaminated surface soils or wastes. Paniculate-constituent complexes that
are of respirable size (i.e., PM10 or below) may be inhaled. Residents living in the proximity
of a WMU and workers at such facilities may inhale constituents sorbed to airborne
particulates.
The only fate and transport process involved in this pathway is air dispersion of
contaminants from the WMU to the receptor location. As discussed in Section 6.1, air
dispersion modeling is covered in Section 7, because it is so closely linked to WMU
characteristics. No other fate and transport p-xesses occur with this pathway; therefore, no
fate and transport equations are used or presented for this pathway.
August 1995 . 6-15
-------
6.0 FATE AND TRANSPORT MODELING
6-3 Soil Pathways
6.3 SOIL PATHWAYS
Figure 6-3 provides an overview of the fate and transport for soil pathways.
63.1 Scenarios
6J.1.1 Human
Human exposure scenarios for soil pathways include ingestion of soil and direct contact
(dermal exposure) with soiL Receptors selected for soil pathways include adult residents,
child residents, and workers. Table 6-4 summarizes the receptors modeled for the soil
pathways.
/
Fpr ingestion of soil, the receptor is a resident living at the fenceline (for active sites)
or on site (for closed sites) who ingests soil from childhood through adulthood. Young
children (i.e., 1 to 6 years old) typically ingest a greater quantity of soil than adults; at the
same time, they have a much smaller average body weight than an adult This results in a
significantly greater average daily exposure for children than for adults (the difference is
about a factor of 10). However, the exposure duration for such a child is limited to the 6
years an individual would fall into the appropriate age range, thus lowering lifetime average
exposure for carcinogens (exposure duration is not generally considered for noncarcinogens,
beyond it being long enough to consider the exposure chronic.) Therefore, OSW policy for
assessing exposure via soil ingestion to carcinogenic constituents is to consider exposure to a
Soil Concentration at Receptor
i
Onsite Exposure
Offsite Exposure
Soil
Erosion
Deposition
from Air
| Waste
>
r
Concentration
Partculate
Emissions
^
Figure 6-3. Fate and transport for soil pathways.
August 1995
6-16
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
Table 6-4. Summary of Receptors for Soil Pathways
Receptor
Adult Child Subsistence Home SubsfeteKe Fish
Pathway resident resident farmer gardener fisher Consumer Worker
3: Direct soil-soil /* /•
ingestion (on site)
3: Overland-soil
ingestion (off site)
4: Air deposition-soil
ingestion
5: Direct soil-dermal
soil (on site)
5: Overland-dermal
soil (off site)
6: Air deposition-dermal
soil
* Closed land application unit only.
single individual through childhood and adulthood for soil ingestion exposures, thus
accounting for both the greater average daily dose of childhood and the longer exposure
duration of adulthood. For noncarcinogens, only childhood exposure is considered.
For dermal contact with soil, both child and adult residents were considered. Both
child and adult residents live at the fenceline (for active sites) or on site (for closed sites) and
are dermally exposed to contaminated soil while working or playing outdoors. Children
typically have a slightly greater skin surface area to body weight ratio than adults, resulting in
a slightly larger average daily exposure for children than for adults (the child's exposure is
about 60 percent greater than the adult exposure). However, as with soil ingestion, the
exposure duration for such a child is limited to 6 years, thus lowering lifetime average
exposure for carcinogens. The difference in exposure between the child and adult is much
less pronounced for dermal exposure man for the ingestion exposures discussed above.
Therefore, the child and adult scenarios have not been combined as they are for soil ingestion
for carcinogens. Instead, both child and adult scenarios are calculated. Typically, the adult
scenario will be protective for carcinogens (due to the longer exposure duration) and the child
scenario will be more protective for noncarcinogens (due to the greater surface area to body
weight ratio). • •
In addition to the child and adult resident receptors considered for dermal contact with
soil, workers on site at active sites were also considered. These receptors typically have
i
August 1995 6-17
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
shorter exposure durations and lower exposure frequencies than residential receptors; however,
they may be exposed to higher levels of soil contamination due to their presence on site at
active sites.
6.3.1.2 Ecological
For ecological receptors, exposure scenarios for soil pathways include direct ingestion
of soil by birds and mammals in the generic terrestrial ecosystem as well as exposures to
plants and soil fauna as a result of direct contact with contaminated soil. In addition, the soil
pathways include food chain exposures representing a variety of dietary habits of terrestrial
birds and mammals. As described in Section 3.3, ecological receptors were selected to
represent major trophic elements of ecosystems such as carnivores, herbivores, and
omnivores. Because wildlife is closely linked to the environment, the soil pathways for
ecological receptors consider both direct ingestion of contaminated soil and ingestion of
contaminated food items assumed to originate from the contaminated area. As a result, the
exposure pathways described for humans were combined for ecological receptors. For
example, pathway 3 (off-site) for human exposure describes the ingestion of contaminated soil
following overland transport from the WMU to a field. Pathway 9 (off-site) considers the
ingestion of contaminated plants following overland transport from WMU to field and
subsequent soil-to-plant uptake. For ecological receptors that ingest plants (e.g., meadow
vole), these exposures were, considered to occur concurrently and backcalculations were
performed based on soil and plant ingestion as described in Section 5.3.43.* For birds and
mammals that consume vertebrates and/or soil fauna, exposure calculations were performed
for ingestion of contaminated soil and prey i1" ns. Where bioaccumulation data were
unavailable for prey items, the protective exposure concentration was based exclusively on
direct soil ingestion.
For ingestion of soil and, where data permitted, ingestion of contaminated food items,
mammals and birds were assumed to live on a closed contaminated site or near an active site.
Exposures were assumed to occur during sensitive life stages (e.g., gestation) or over the
course of their life cycle for areas that represent "favorite" feeding or hunting grounds. It was
implicitly assumed that the contaminated areas could support sufficient biomass to sustain at
least one reproducing couple of each of the representative species. For smaller animals, the
size of the contaminated area (e.g., 2 x 106 nr for land application unit) would have a
significantly larger carrying capacity than a single reproducing pair. However, for larger
animals such as deer and the red-tailed hawk, the contaminated area would not be likely to
support more than a few mating pairs.**Contaminated field sizes were selected to incorporate
the full home range of the larger terrestrial animals so that: (1) it could reasonably be
assumed that the area could support the biomass necessary to sustain at least one reproducing
*It should be noted that, for plant ingestion by strict herbivores (see Section 6.6.1.12), uptake via air-to-plant
and direct deposition were also considered. For omnivores such as the raccoon that consume significant amounts
of all four food categories (worms, invertebrates, vertebrates, plants), only soil-to-plant uptake was considered.
August 1995 6-18
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
pair, and (2) the fraction assumed to originate from the contaminated area could
conservatively be set at 1.
For direct contact with soil, vascular terrestrial plants and soil fauna were considered
that represent important components of the soil community (see Table 3-3 on soil fauna).
These receptors were assumed to be located near the fenceline (off-site), adjacent to active
sites or closed sites. Although ingestion of soil and other contaminated soil species is likely
to contribute to exposure, the primary route of exposure for soil fauna was assumed to be
through direct contact The route of plant uptake for the soil pathways was assumed to be
through soil-to-route transfer from the soil. Plant receptors included a variety of macrophytcs
including forage grasses, trees, and other vascular plants.
The terrestrial pathways shown in Section 6.3.2 include food chain and direct exposures
to birds and mammals as well as ecological receptors in intimate contact with contaminated
soil (i.e., plants and soil fauna). As described in Section 3.3, the receptors for the generic
terrestial ecosystem included:
• Short tailed shrew • Red-tailed hawk • Soil fauna
• Deer mouse • American kestrel • Plants
• Meadow vole • Northern bobwhite
• Eastern cottontail • American robin
• Red fox • American woodcock
• Raccoon
• White-tailed deer
6J.2 Pathway Algorithms
The following sections describe the soil pathways and present the fate and transport
equations for them. These pathways are:
• Pathway 3 (on site): ingestion -» WMU(Section 6.3.2.1)
• Pathway 3 (off site): ingestion -» overland -» WMU (Section 6.3.2.2)
• Pathway 4: ingestion -» deposition -» air -» WMU (Section 6.3.2.3)
• Pathway 5 (on site): dermal -» WMU (Section 6.3.2.1)
• Pathway 5 (off site): dermal -» overland -» WMU (Section 6.3.2.2)
• Pathway 6: dermal -» deposition -> air -» WMU (Section 6.3.2.3)
• Pathway Terr I (on site): ingetfcon/direct contact-» WMU (Section 6.3.2.1)
• Pathway Terr n (off site): ingestion/direct contact -» overland -» WMU
(Section 6.3.2.2)
• Pathway Terr ffl: ingestion/direct contact -> deposition -» air -* WMU
(Section 6.3.2.3).
August 1995 6-19
-------
•91
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
6.3J.I Pathways 3, 5, and Terr I (On Site): Ingestion (3, Terr D/Dermal (SVDirect
Contact (Terr I) -> WMU
Constituents sorbed to particles in the surface soil matrix may be directly ingested with
surface soil or absorbed via dermal contact with soil For example, children playing in
contaminated areas may ingest or dermally absorb contaminants present in the surface soil;
similarly, adults working with soil (e.g., gardening, landscaping) may absorb contaminants
present in the surface soil and may accidentally ingest small amounts of soil contaminants
sorbed to hands by normal hand-to-mouth behavior. Mammals, birds, plants, and soil fauna
may also be exposed.
There is no fate and transport involved in these pathways, as exposure is assumed to
occur on site. The partitioning model is presented in Section 7.
6.3.2.2 Pathways 3, 5, and Terr H (Off Site): Ingestion (3 and Terr ID/Dermal
(SyOirect Contact (Terr U) -* Overland -> WMU
Constituents sorbed to particles in the surface soil matrix may be transported over the
ground to other locations via soil erosion. Constituents may then be directly ingested with
surface soil. For example, children playing in contaminated areas may ingest contaminants
present in the surface soil; similarly, adults working with soil (e.g., gardening, landscaping)
may accidentally ingest small amounts of soil contaminants sorbed to hands by normal hand-
to-mouth behavior. Mammals, birds, plants, and soil fauna may also be exposed.
The only fate and transport involved in this pathway is soil erosion from the WMU to
the off-site exposure area at the fenceline. Because this depends on the area of the WMU,
the calculations are WMU-specific and are presented in Section 7; however, it is also
discussed here.
6.3.2.2.1 SoU Erosion
Contaminants sorbed to surface soil particles may be transported off site through the
process of soil erosion. The amount of contaminant transported to an off-site field depends
on the amount of soil loss from the site (a function of area and unit soil loss), which
quantifies the amount of soil eroded from the site; the sediment delivery ratio, which accounts
for soil that is redeposited before reaching the off-site field; and an enrichment ratio, which
refers to the fact that erosion favors the*lighter soil particles, which have higher surface area
to volume ratios and are higher in organic matter content Therefore, concentrations of
organic contaminants, which are a function of organic carbon content of sorting media, would
be expected to be higher in eroded soil as compared to in situ soil.
Soil erosion from a WMU to an off-site field is not covered in the Indirect Exposure
Methodology because the IBM was developed for combustors. However, the process is
essentially similar to deposition from air, except that contaminants plus soil are deposited by
soil erosion. The amount of soil eroded is negligible compared to the mass of soil already in
August 1995 6-20
-------
6.0 FATE AND TRANSPORT MODELING 6 J Soil Pathways
the field. The deposition rate from soil erosion may be backcalculated in the same manner as
deposition from air, and the concentration at the WMU may then be backcalculated from the
deposition rate of pollutant and the amount of soil eroded. These two steps were combined
into a single equation.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms. The rainfall factor, R, represents the influence of precipitation on erosion,
and is derived from data on the frequency and intensity of storms. The credibility factor, K,
reflects the influence of soil properties on erosion. The length-slope factor, LS, reflects the
influence of slope steepness and length of the field in the direction of the erosion. The
erosion control practice factor, P, reflects the use of surface conditioning, dikes, or other
methods to control runoff/erosion. The cover factor, C primarily reflects how vegetative
cover and cropping practices, such as planting across slope rather than up and down slope,
influences erosion.
August 1995 6-21
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways (4,6,Terr HI)
6.3J.3 Pathways 4, 6, and Terr IH: Ingestion (4 and Terr HD/Dermal (6)/Direct
Contact (Terr HI) -» Deposition -* Air -» WMU
Constituents sorbed to particles in the surface soil matrix may be entrained into the air
from contaminated surface soils. Airborne particulates may deposit on surface soils via
deposition mechanisms (e.g., settling, dry deposition). Constituents deposited on soils may
then be directly ingested with surface soil. For example, children playing in contaminated
areas may ingest or dermally absorb contaminants present in the surface soil; similarly, adults
working with soil (e.g., gardening, landscaping) may absorb contaminants present in the
surface soil and may accidentally ingest small amounts of soil contaminants sorbed to hands
by normal hand-to-mouth behavior. Mammals, birds, plants, and soil fauna may also be
exposed.
The fate and transport components of Pathways 4 and 6 are air dispersion and
deposition onto soil. Contaminant may be lost from the location of deposition by several loss
processes. Air dispersion modeling is covered in Section 7 by WMU.
The cumulative soil concentration of a pollutant is derived from the dry deposition rate
over the time period of deposition and the contaminant loss rate from the soil. The cumula-
tive soil concentration represents the concentration increment due to accumulation of contam-
inant deposited onto soil from one of the WMUs. The cumulative soil concentration does not
take into account background concentrations of the contaminant that may already be present,
.whether natural or from other pollution sources.
Contaminants may be lost from soils as a result of numerous factors, including leach-
ing, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall soil
loss rate, k,, is the sum of the loss rates for each of these processes.
Losses due to degradation (k,g) are empirically determined from field studies.
Degradation rates vary greatly, depentShg on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k,,, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
August 1995 6-22
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways (4,6,Terr ffl)
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants, rather than vapor-phase contaminants). If such redeposi-
tion occurred, the soil concentration would be higher than if such redeposition did not occur.
As a result, the algorithm as used (without redeposition) may underestimate soil concentra-
tions for compounds that would volatilize then dissolve in rainwater and be redeposited;
however, the revolatilization of semivolatile organic contaminants such as dioxin that have
been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (Le., a farm where exposures
occur) is matched by an equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a yard or garden, a small
area within a watershed; therefore, the soil loss constant used does not include a surface
runoff loss constant or a soil erosion loss constant
The most common means to estimate unit erosion loss is with the Universal Soil Loss
Equation, or USLE. The USLE uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis. ,.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
Equation 6-1 shows the backcaftfilation for deposition rate from soil concentration.
Equations 6-2 through 6-10 present the equations for calculating the soil loss constant, k,,
which is used in Equation 6-1.
August 1995 6-23
-------
6.0 FATE AND TRANSPORT MODELING
6J Soil Pathways (4,6,Terr DT)
Deposition to Soil: Combined Deposition Rate
t,»104cm2/m:
-e "*•']• itfmg/g
Parameter
Definition
Central
tendoicy
valae
High-end
value
Refer to
Average annual combined deposition rate
(g/n^/yt)
Calculatfd
Concentration in soil at deposition location
(mg/g)
Source: IBM (U.S. EPA, 1990e; 1993a).
From Equations 5-5, 5-6. 5-12,
5-22 .
z
BD
k.
t
Mixing depth (cm)
Soil bulk density (g/cm3)
Soil loss constant (yfl)
Time period of deposition (yr)
2 J (unfilled) 1 (unfilled)
U 12
See Equation 6-2
9 30
6.7.3J
6.7.3.1
6.7.3.3
August 1995
6-24
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways (4ATerr
Soil Loss Constant
Parameter
k, Soil to
Definition
ss constant (yrl)
Central
tendency
value
Higfa^nd
value
Refer to
CatculatH
SoU ton constant due to leaching (yfl) See Equation 6-3
Soil loss constant due to degradation (yr'1) 0 6.7.6.1
SoU loss constant due to volatilization (yr'1) See Equation 6-5
Source: IBM (1LS. EPA. 1990e; 1993a).
August 1995 6-25
-------
6.0 FATE AND TRANSPORT MODELING
6J SoU Pathways (4,6,Terr UTi
Soil Loss Constant Due to Leaching
"st ' /
6»Z» 1 * BD
Parameter
k* .
q
e
z
BD
Definition
Soil loss constant due to leaching (yr*1)
Average annual recharge rate
Soil volumetric water content
(cm/yr)
(mL/cm3)
Soil depth from which leaching occurs (cm)
Soil bulk density (g/cm3)
Kd Soil-water partition coefficient (mL/g)
Source: IBM
(U.S. EPA, 1990e; 1993a).
^^^^^^^B
*"r]
' Central
tendency High-end
value value
Calculated
WMU-specific
See Equation 64
2_5 (unfilled) 1 (unfilled)
U 1'2
Chemical-specific
(6-3)
Refer to
6.7.2.2
6.7.3.3
6.7.3.1
6.7.6.1
August 1995
6-26
-------
6.0 FATE AND TRANSPORT MODELING
6J Soil Pathways (4,6Yrerr HI)
Soil Volumetric Water Content
e-e
(6-4)
. Parameter
e
e,
q
*,
b
DefluitkM
Soil volumetric water content (mL/cm3)
Soil saruratrd volumetric water content
(mL/cm3)
Average annual recharge rate (cm/yr)
Saturated hydraulic conductivity (cm/yr)
Soil-specific exponent representing water
retention (unitless)
Central
teadeacy
value
CalcuL
0.43
High-cod
value
ated
0.55
WMU-specific
3.600
5.4 ,
20.000
3.0
Refer to
6.7.3.1
6.7.2.2
6.7.3.1
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995
6-27
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways (4,6,Terr
Soil Loss Constant Due to Volatilization
Central
tendency High-end
Parameter Definition valve value Refer to
kgy Soil loss constant due to volatilization (yr*1) Calculated
Kg Equilibrium coefficient (s/cm-yr) See Equation 6-6
K, Gas-phase mass transfer coefficient (cm/s) See Equation 6-7
Source: EM (U.S. EPA, 1990c: 1993a).
August 1995 6-28
-------
6.0 FATE AND TRANSPORT MODELING
6J SoU Pathways (4^Terr HI)
1
Volatilization Equilibrium Coefficient
3.1536*
(6-6)
Parameter
DcflaitiM
Central
tendency High-cad
value value
Source: IBM (U.S. EPA. 1990e; 1993a).
Refer to
K
*S
H
Z
Kd
R
T
BD
P/iirilihriiifn
-------
6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways (4,6,Terr IH)
Gas-Phase Mass Transfer Coefficient
-0."
(6-7)
Central
tendency High-end
Parameter Definition value value Refer to
K, Gas-phase mass transfer coefficient (cm/a) Calculated
u Windspced (m/s) WMU-specific 6.1.22
SCQ Schmidt number on gas side (unitless) See Equation 6-8
dj Effective diameter of contaminated area (m) See Equation 6-9
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-30
-------
6.0 FATE AND TRANSPORT MODELING
Soil Pathways (4,6,Teir OD
Parameter
SCn
""•Q
u.
p.
D»
Source: EM
Schmidt Number on Gas Side
ScG* Pa (6-8)
Q Pa-»a
Central
tendency High-end
Definition value vahie Refer to
Schmidt number on gas swte (witless) ~ Calculated
Viscosity of air (g/cm-s) Ule-4 6.7.7
Density of air (g/cm3) 1.2e-3 6.7.7
.
Diffusivity in air (crnvs) Chemical-specific 6.7.6.1
(U^. EPA. 1990e: 1993a).
August 1995
6-31
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6.0 FATE AND TRANSPORT MODELING
63 Soil Pathways (4,6,Terr HI)
Effective Diameter
4M
K
(6-9)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Effective diameter of
contaminated area (m)
Area of contaminated area
(m2)
5,100 (garden) 2,024 (garden) 6.7.33
Source: IBM (U.S. EPA, 1990e; 1993a).
August 1995
6-32
-------
6.0 FATE AND TRANSPORT MODELING
6J Soil Pathways (4,6,Terr
Universal Soil
Loss Equation
Xe =R 'K'LS'C'P ^907. 18 kg/ton '245.1 acre/km 2 • HT6 Aw 2/m 2
Paraaae
x.
R
K
LS
C
P
tor DefloitioB
Unit soil loss (kgAnJ/yr)
USLE rainfall factor (yf1)
USLE erodftffity factor (ton/acre)
USLE length-slope factor (unitless)
USLE cover factor (unities)
USLE erosion control practice factor
(unitless)
Central
tendency High-end .
vaJm value
faf^llatfrt
WMU-specific
025
1 3
0.1 0^
1
(6-10)
Refer to
6.7.32
6.7.32
6.7.32
6.7.32
6.7.32
Source: IBM (U.S. EPA. 1990e: 1993a).
August 1995
6-33
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6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
6.3 J Uncertainty for Soil Pathways
6.3J.I Universal Soil Loss Equation
Uncertainty arises out of the use of the Universal Soil Loss Equation. This is an
empirical, though widely used, model. It was intended for use in site-specific situations,
where highly specific input data can be used, and for relatively small fields. How well it
predicts soil erosion in a generic application, as here, and for fairly large WMUs, is uncertain.
It is most likely that it overestimates quantity of soil eroded.
6.3.3.2 Soil Loss Constant Term
The overall soil loss constant term, k,, is uncertain in several ways. This term is the
sum of loss rates for leaching, degradation, and volatilization. One uncertainty arises from
the assumption that all of these loss terms are first order and can therefore be added together.
This is a common assumption, but some of the processes may, in fact, be zero order. A first
order loss process may be characterized by a half-life, the time it takes half of the remaining
contaminant to be lost Therefore, the mass lost per unit of time varies with the
concentration. A zero order loss process is characterized by a constant mass loss per unit of
time. Neither of these processes can be said to be more conservative than the other, because
the first order rate depends on the starting concentration and the zero order rate does not, at
any given time, which one results in a higher concentration will depend on the starting
concentration. Therefore, it cannot be said whether incorrectly assuming that loss constant
that is actually zero order is first order will overestimate or underestimate soil concentration.
Another source of uncertainty regarding the soil loss constant is that the various loss
processes are calculated independently when, in fact, they occur simultaneously. As a result,
losses could be overpredicted because the amount of contaminant available to each process is
overestimated by not accounting for the other loss processes. This would result in an
underestimate of soil concentration.
Finally, degradation losses were set to zero. Degradation rates are highly dependent on
site-specific factors that cannot be accounted for in a generic analysis of this nature and may
often be zero. To the extent that constituents do degrade into constituents of less concern, the
omission of degradation from the soil loss constant will underestimate losses and therefore
overestimate soil concentration. •**.
The overall effect of all of the above uncertainties on the soil loss constant is not clear.
One of the factors would tend to underestimate soil concentration, one would tend to over-
estimate soil concentration, and the effect of one could be either an over- or underestimate of
soil concentration.
August 1995 6-34
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6.0 FATE AND TRANSPORT MODELING 6J Soil Pathways
6.3.3.3 Soil Water Content Equation
The equation from the Superfund Exposure Assessment Manual (U.S. EPA, 1988a) used
to calculate soil water content based on recharge and soil properties was developed for site-
specific application. Its application in a generic analysis raises uncertainty as to how well it
predicts soil water content A distribution of this value would have been preferred; however,
it was not available and so had to be calculated. However, some of the input parameters are
highly generalized (such as recharge) and others (such as the soil moisture retention exponent
b) are drawn from estimates rather than measured values. It is not clear in which direction
this uncertainty would affect the results.
August 1995 6-35
-------
6.0 FATE AND TRANSPORT MODELING
6.4 Groundwater Pathways
6.4 GROUNDWATER PATHWAYS
Figure 6-4 provides an overview of the fate and transport for groundwater pathways.
The leaching and fate and transport of groundwater contaminants between the waste
management unit and the point of withdrawal, represented in the figure by dashed lines, are
being modeled separately by EPA and are presented in a separate document. The results of
the groundwater modeling will be incorporated with the results of this analysis in setting exit
levels.
6.4.1 Scenarios
6.4.L1 Human
Human exposure scenarios for groundwater include ingestion of groundwater and
dermal exposure to groundwater while bathing. The receptors selected for the groundwater
pathways are adult and child residents.
Table 6-5 summarizes the receptors modeled for the groundwater pathways. For
drinking water ingestion, the receptor selected is an adult resident who uses contaminated
groundwater as a drinking water supply. Child residents were not selected as receptors for
the groundwater ingestion pathways because the adult resident scenario is protective of
children. There is no indication that children consume a greater quantity of drinking water
per unit of body weight than adults; therefore, average daily exposure normalized to body
Water Concentration at Receptor
Groundwater
Concentration
Waste Concentration
Figure 6-4. Fate and transport for groundwater pathways.
August 1995
6-36
-------
6.0 FATE AND TRANSPORT MODELING 6.4 Groundwatcr Pathways
Table 6-5. Summary of Receptors for Groundwater Pathways
Receptor
Adult Child Sulttfateoce Home SubefcttKe Fbfc
Pathway resident resident farmer gardener fisher COMOBMT Worker
1: Groundwater-ingestion
14: Groundwater-dennal
(battling)
weight would be the same for adults and children. However, the exposure duration for
children would be shorter, reducing lifetime exposure for children.
The receptors selected for the dermal bathing groundwater pathway are an adult and
young child resident (1 to 6 years old) who use contaminated groundwater as a source of
water for bathing. Children typically have a slightly greater skin surface area to body weight
ratio than adults, resulting in a slightly larger average daily exposure for children than for
adults (the child's exposure is about 60 percent greater than the adult exposure). However,
the exposure duration for such a child is limited to 6 years, thus lowering lifetime average
exposure for carcinogens. Therefore, both child and adult scenarios are calculated. Typically,
the adult scenario will be protective for carcinogens (due to the longer exposure duration) and
the child scenario will be more protective for noncarcinogens (due to the greater surface area
to body weight ratio).
6.4.1.2 Ecological
There are no ecological scenarios for groundwater pathways.
6.4.2 Pathway Algorithms
The following sections describe the soil pathways and present the fate and transport
equations for them. These pathways are:
'•*te
• Pathway 1: ingestion -» groundwater -» WMU (Section 6.4.2.1)
• Pathway 14: dermal (bathing) -* groundwater -» WMU (Section 6.4.2.2).
6.4.2.1 Pathway 1: Ingestion -» Groundwater -» WMU
Constituents in land application units, monofills, wastepiles, or surface impoundments
may percolate down into underlying groundwater aquifers. Residents using contaminated
aquifers may ingest contaminated groundwater.
August 1995 6-37
-------
&0 FATE AND TRANSPORT MODELING 6.4 Groundwatcr Pathways
The fate and transport components of this pathway are presented in a separate document
describing the groundwater modeling.
6.4JJ Pathway 14: Dermal (Bathing) -> Groundwater -> WMU
Constituents in contaminated soils, monofills, wastepiles, or surface impoundments may
percolate down into underlying groundwater aquifers. Residents using contaminated aquifers
may absorb constituents through the skin while bathing.
The fate and transport components of this pathway are presented in a separate document
describing the groundwater modeling.
August 1995 6-38
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6.0 FATE AND TRANSPORT MODELING
63 Surface Water Pathways
6.5 SURFACE WATER PATHWAYS
Figure 6-5 provides an overview of the fate and transport for surface water pathways.
6.5.1 Scenarios
i
6.5.1.1 Human
Human exposure scenarios for surface water include ingestion of surface water used as
drinking water and dermal exposure to surface water while bathing. The surface water system
modeled is a 5- to 28-mile reach of a flowing system, such as a river. See Section 6.7.5.1 for
more details on the characterization of the surface water system. The receptors selected for
the surface water pathways are adult and child residents. Table 6-6 summarizes the receptors
modeled for the surface water pathways. . •
For drinking water ingestion, the receptor selected is an adult resident who uses
contaminated surface water as a drinking water supply. Child residents were not selected as
receptors for the surface water ingesn'on pathways because the adult resident scenario is
protective of children. There is no indication that children consume a greater quantity of
drinking water per unit of body weight than adults; therefore, average daily exposure
Water Concentration at Receptor]
* •*>
Surface Water
Concentration
Diffusion
from Air
Overland Flow/
Soil Erosion
Dispersionj
Deposition to
Watershed
Volatile
Emissions
Dispersion
Paniculate
Emissions
V
Waste Concentration j
Figure 6*5. Fate and transport for surface water pathways.
August 1995
6-39
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6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways
Table 6-6. Summary of Receptors for Surface Water Pathways
Receptor
Adult Child Subsistence Home Subsistence Ftah
resident resident fanner gardener fisher consumer Worker
Pathway
17: Air diffusion- /
drinking water
ingestion ' ^___
19: Overland-drinking J
water ingestion
20: Air deposition-
drinking water
ingestion
37: Air diffusion (SW>
dermal bathing
38: Air deposition
(OF/SW)-dennal
bathing
42: Overland (SW>
dermal bathing
normalized to body weight would be the same for adults and children. However, the
exposure duration for children would be shorter, reducing lifetime exposure for children.
For dermal bathing exposure, the receptors selected are an adult and a young child (1 to
6 years old) resident who use contaminated surface water as a source of water for bathing.
Children typically have a slightly greater skin surface area to body weight ratio than adults,
resulting in a slightly larger average daily exposure for children than for adults (the child's
exposure is about 60 percent greater than the adult exposure). However, the exposure
duration for such a child is limited to 6 years, thus lowering lifetime average exposure for
carcinogens. Therefore, both child and adult scenarios are calculated. Typically, the adult
scenario will be protective for carcinogens (due to the longer exposure duration) and the child
scenario will be more protective for noncarcinogens (due to the greater surface area to body
weight ratio). • -•*»
6.5.1.2 Ecological
For ecological receptors, exposure scenarios for surface water pathways include direct
ingestion of contaminated water by mammals and birds in the generic aquatic ecosystem (i.e.,
the littoral freshwater ecosystem described in Section 5.3.2.2) as well as exposures to aquatic
plants and fish/aquatic invertebrates as a result of direct contact with contaminated water. As
with the soil pathways, the surface water pathways include food chain exposures representing
the dietary habits of birds and mammals associated with freshwater ecosystems. The
August 1995 6-W
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6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways
ecological receptors were selected to represent species that feed on small (-trophic level 3)
and large (-trophic level 4) fish and species that feed on aquatic macroinvertebrates (-trophic
level 2). However, species that feed primarily on aquatic vegetation (e.g., muskrat) were not
included due to the paucity of data on aquatic plant uptake and concentration of contaminants.
Because wildlife is closely linked to the environment, the surface water pathways for
ecological receptors consider both direct ingestion of contaminated water and ingestion of
prey assumed to originate from contaminated stream reach. As a result, the exposure
pathways described for humans were combined for ecological receptors. For example,
pathway 17 for human exposure describes the. ingestion of contaminated surface water
following air deposition from the WMU to the stream. Pathway 21 considers the ingestion of
contaminated fish following air deposition from WMU to stream and subsequent
bioconcentration in the fish. For ecological receptors that consume fish (e.g., mink), these
exposures were considered to occur concurrently and backcalculations were performed based
on surface water and fish ingestion as described in Sections 5.32.1.3 and 5.3.2.2.3.* Where
bioaccumulation or bioconcentration data were unavailable for fish, the protective exposure
concentration was based exclusively on direct water ingestion for birds and mammals
For ingestion of contaminated fish and surface water, piscivorous fish, mammals, and
birds were assumed to live in or along the contaminated stream reach. Exposures were
assumed to occur during sensitive life stages (e.g., gestation) or over the course of their life
cycle in areas that represent "favorite" feeding or hunting waters. It was implicitly assumed
that the contaminated areas could support a sufficient fish population (or populations of
aquatic invertebrates) to sustain at least one reproducing pair of each of the representative
species of mammals and birds. Similarly, it ~as implicitly assumed that the stream reach
could support a viable population of large piscivorous fish as well as smaller planktivorous
fish and forage fish (see Figure 5-4). The size of the contaminated stream reach (- 5 miles)
was selected to incorporate the majority of the hunting ranges of the birds and mammals
associated with the aquatic ecosystem so that: (1) it could reasonably be assumed that the area
could support enough fish necessary to sustain at least one reproducing pair, and (2) the
fraction assumed to originate from the contaminated stream could conservatively be set at 1.
For direct contact with surface water, freshwater species identified by the Ambient
Water Quality Criteria (AWQC) guidelines (U.S. EPA, 1985i) were identified, including fish
and invertebrates representative of the aquatic community (see Table 4-1). These receptors
were evaluated based on the Final Chronic Value (FCV) calculated for the AWQC or
estimated using methods described infection 4.3.5. The FCVs, whether taken from the
AWQC or estimated using the Tier I or Tier n methods developed for the Great Lakes
System (60 FR 15366), include toxicity data on eight taxonomic families. Although data on
aquatic plants is required by the AWQC guidelines to calculate a Final Plant Value (FPV), the
*For chemicals that bioaccumulate appreciably, the contribution to exposure from drinking contaminated
surface water was shown to be insignificant However, for chemicals that bioconcentrate weakly (BCF < 100).
the contribution of contaminated drinking water was included in the calculation of protective surface water
concentrations.
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways
development of a Criterion is not contingent on the availability of aquatic plant data; a
Criterion may be proposed in the absence of a Final Plant Value. The calculation guidelines
for the FPV were made more stringent by the 1985 AWQC guidelines, primarily because the
procedures for conducting and interpreting the results of toxicity tests on aquatic plants are
not well developed. However, although the AWQC guidelines suggest that criteria protective
of aquatic animals are also protective of aquatic plants, this does not appear to be supported
technically (e.g., Benenati, 1990). In addition, the Tier I and Tier n guidelines for the
calculation of chronic water quality criteria for aquatic life state that, while desirable, toxicity
data on aquatic plants are not required (60 FR 15395). In short, the FCV calculated for the
protection of aquatic life does not include toxkity data on aquatic plants.* Consequently,
aquatic plants were considered as a separate group of receptors from fish and aquatic
invertebrates in the aquatic community. As discussed in Section 4.3.7, both aquatic
microphytes (i.e., algae) and macrophytes (e.g., duckweed) were included as ecological
receptors.
Exposure to contaminated sediments was also considered with the surface water
pathways since some fraction of contaminant partitions to sediments when introduced into the
surface waterbody. Ecological receptors were evaluated that ingest a high volume of
sediment in the diet or live in intimate contact with the sediment Only one species—the
spotted sandpiper—was selected to evaluate exposures from sediment ingestion because this
species ingests a high percentage of sediment in the diet (7 to 30 percent); other species of
mammals and birds considered in this analysis ingest a relatively insignificant amount of
sediment As described in Section 4.3.6, freshwater species used in the development of Final
Chronic Values for fish and aquatic invertebr ;s were presumed to be roughly equivalent in
terms of toxicologic sensitivity as benthic species (U.S. EPA, 19931). As a result the FCVs
were used to estimate sediment benchmarks for the protection of the benthic community. It
should be noted that the food web model used to estimate bioaccumulation factors for fish
and aquatic invertebrates in the littoral ecosystem includes ingestion and uptake of
contaminants from the sediment
The aquatic pathways shown in Section 6.5.2 include food chain and direct exposures to
birds and mammals as well as ecological receptors in intimate contact with contaminated
surface water (i.e., fish, aquatic invertebrates, and plants) and sediments. As described in
Section 3.3, the receptors for the generic freshwater ecosystem included:
"Recently proposed AWQC for phenanthrene and tributyltin did not include a Final Plant Value. Although
toxicity data on aquatic plants were presented, they were deemed insufficient to derive an FPV.
August 1995 6-42
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6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways
• Mink • Bald eagle • Fish/aquatic invertebrates
• River otter • Osprey • Aquatic plants
• Great blue heron • Benthic dwellers
• Mallard
• Lesser scaup
• Kingfisher
• Spotted sandpiper
• Herring gull
Pathway Algorithms
The framework for estimating surface water impacts presented in the Addendum
estimates water column as well as benthic sediment concentrations. Water column
concentrations include dissolved, sorbed to suspended sediments, and total (sorbed plus
dissolved, or total contaminant divided by total water volume). This framework also provides
three concentrations for the benthic sediments: dissolved in pore water, sorbed to benthic
sediments, and totaL The model accounts for four routes of contaminant entry into the
waterbody:
• Sorbed to soils eroding into the waterbody
• Dissolved in runoff water
• Direct deposition of particle-bound contaminant
• Direct diffusion of vapor phase contaminants into the waterbody.
• •*>
For this analysis, all of these routes were used except direct deposition to the
waterbody; early results indicated that this route of entry was negligible compared to the soil
erosion/runoff component In addition, spills from surface impoundments directly into surface
water were included in this analysis.
The surface water model found in the Combustor Indirect Exposure methodology also
accounts for three dissipation processes that remove contaminants from the water column
and/or bed sediment reservoirs:
• Decay of total contaminants (sorbed and dissolved) within the water column
• Volatilization of dissolved phase out of the water column
• Removal of total contaminan^via "burial" into the benthic sediment layer.
For flowing systems, such as the river modeled in this analysis, the model also accounts
for advective losses from the reach modeled.
The current construct of the model does not consider decay of contaminants within the
benthic sediment, although such considerations could be folded into the burial rate constant
This burial rate constant is a function of the deposition of sediments from the water column
to the bed; it accounts for the fact that much of the soil eroding into a waterbody annually
becomes bottom sediment rather than suspended sediment
August 1995
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6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways
For this analysis, decay of contaminants in the water column was not included Losses
due to decay are typically empirically determined from field studies. Decay rates vary
greatly, depending on site-specific conditions, and may be zero. Because the purpose of this
analysis was to calculate waste exclusion levels that would not pose significant risk under the
wide variety of conditions that might occur in the United States, it was not considered
appropriate to use a nonzero decay rate, as this would not be protective in all areas.
Volatilization of dissolved contaminants and removal via burial in bed sediments were
considered. .
Key assumptions in the surface water impact algorithm are:
• The impacted waterbody was assumed to be a river sufficiently large to support
aquatic life. The surface waterbody characteristics are described more fully in
Section 6.7.5.1.
• The impact to the waterbody is assumed to be uniform. This tends to be more
realistic for smaller waterbodies as compared to large river systems.
• The partitioning of the contaminant within the soil/water matrices—surface soils,
suspended solids in the waterbody, and bed sediments of the waterbody—can be
described by a partition coefficient
• For the surface water solution algoriC^n, it is assumed that equilibrium is established
between contaminants within the water column and contaminants in bed sediments.
This equilibrium is modeled by a key assumption that the dissolved phase
concentration in the water column is equal to the dissolved phase concentration
within the bed sediments.
The following sections describe the surface water pathways and present the fate and
transport equations for them. These pathways are:
• Pathway 17: ingestion -» surface water -» air -> WMU (Section 6.5.2.1)
• Pathway 19: ingestion -» surface water -> overland -> WMU (Section 6.5.2.2)
• Pathway 20: ingestion -» surface water -» overland -> deposition -> air -» WMU
(Section 6.5.2.3) ** .
• Pathway 37: dermal bathing -* surface water -> air.-» WMU (Section 6.5.2.1)
• Pathway 38: dermal bathing -* surface water"-> overland -> deposition -» air
-» WMU (Section 6.5.2.3)
• Pathway 42: dermal bathing -^ surface water -» overland -> WMU (Section 6.5.2.2)
• Pathway Aq I: ingestion/direct contact -» sediment/surface water -> air -> WMU
(Section 6.5.2.1)
• Pathway Aq II: ingestion/direct contact -»sediment/surface water -> overland -»
deposition -> air -> WMU (Section 6.5.2.3)
August 1995 6-44
-------
6.0 FATE AND TRANSPORT MODELING &5 Surface Water Pathways
• Pathway Aq ffl: ingestion/direct contact -> sediment/surface water -> overland -»
WMU (Section 6.5.2.2).
All of these pathways backcalculate from a surface water concentration. As described
above, the surface water modeling framework can use either dissolved or total water column
concentration. Since all regulated (i.e., public) drinking water sources are required to filter
surface water to be used as drinking water to remove suspended solids, and since most private
drinking water sources are likely to be groundwater wells rather than surface water, all the
surface water pathways use the dissolved concentration.
August 1995
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (l-7,37,Aq I)
6.5.2.1 Pathways 17, 37, and Aq I: Digestion (17 and Aq D/Dermal Bathing (37)/Direct
Contact (Aq I) -> Surface Water -» Air -> WMU
Constituents may volatilize from many of the WMUs. These vapor-phase constituents
may diffuse into surface water from air. Residents.who rely on the contaminated surface
waters as a source of drinking water may ingest constituents dissolved in the surface water or
absorb constituents through the skin while bathing. Fish, aquatic organisms, aquatic plants,
and birds and mammals that rely on the aquatic food chain may be exposed to contaminated
surface water.
The fate and transport component of these pathways is diffusion of vapor-phase
contaminant into surface water. The dissolved concentration in the waterbody was assumed
to reach equilibrium with a vapor phase concentration above the waterbody. At equilibrium,
gaseous diffusion into the waterbody is matched by volatilization out of the waterbody.
Gaseous diffusion is estimated with a transfer rate and a vapor phase air concentration.
Equations 6-11 through 6-20 present the equi.-ons for backcalculating air concentration over
the waterbody from dissolved surface water concentration.
August 1995
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (17,37,Aq I)
Air Concentration: from Dissolved Water Concentration
C*
,2: (6-n)
Central
tendeacy High-«od
Parameter
c
•IT
c~
H
Vf,
f~
*"
V
"*•
TSS
KV
R
T
WA,
d.
A
DefiaitfcM
Concentration in air (ug/m3)
Dissolved water concentration (mg/L)
Henry's law constant (atnvm3/mo!)
Waterbody flow volume (L/yr)
Fraction of total waterbody
contamination in water column (unitless) •
Overall total water concentration
dissipation rate (yf1)
Flow-independent mixing volume (L)
Suspended sediment/surface water
partition coefficient (L/kg)
Total suspended solids (mg/L)
Overall transfer rate (m/yr)
Universal gas constant (atm-m3/mol-K)
Waterbody temperature (K)
Waterbody surface area (m2)
Depth of water column (m)
Total depth of waterbody (water column
and sediment) (m)
value value
Tabulated
From Equations 5-39, 5-44.
5-45.5-46,5-51,5-52,5-53
Chemical-specific
3e+ll IJe+lO
See Equation 6-20
See Equation 6-13
i
6.7e+8 8.3e+6
Chemical-specifk
10 80
See Equation 6-17
8.21e-5
298
le+6 4.6e+4
0.64 0.15
0.67 0.18
Refer to
6.7.6.1
6.7.5.1
6.7.5.1
6.7.6.1
6.7.52
6.7.7
6.7.5.2
6.7.5.1
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-47
-------
6.0 FATE AND TRANSPORT MODELING
6J Surface Water Pathways (17,37,Aq I)
Air Concentration: from Bottom Sediment Concentration
w
^ '
Parameter DefinitioB
C^ Concentration in air (ug/m3)
Ch, Contaminant concentration in bed
sediments (mg/kg)
H Henry's law constant (atm-mVmol)
Vf, Waterbody flow volume (L/yr)
f,^. Fraction of total waterbody
contamination in water column (unitless)
k,, Overall total water concentration
dissipation rate (yr'1)
V Flow-independent mixing volume (L)
Kdlw Suspended sediment/surface water
partition coefficient (L/kg)
TSS Total suspended solids (mg/L)
Kdfc, Bed sediment/sediment pore water
partition coefficient (Ukg)
Ky Overall transfer rale (m/yr)
R Universal gas constant (atnvm3/mol-K)
T Waierbody temperature (K)
WA, Waterbody surface area (m2)
dw Depth of water column (m^
dt • Total depth of waterbody (water column
and sediment) (m)
Vo-Vte
Central
tendeacy High-end
value value
Oi^utafriJ
From Equations 5-140 and
5-141
Chemical-specific
3e+ll IJe^lO
See Equation 6-20
See Equation 6-13
6.7e+8 83e-MS
Chemical-specifk
10 80
Chemical-specific
See Equation 6- 17
821e-5
298
le+6 4.6e+4
0.64 0.15
0.67 0.18
Refer to
6.7.6.1
6.7.5.1
6.7.5.1
6.7.6.1
6.7.52
6.7.6.1
6.7.7
6.7.52
6.7.5.1
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-48
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (17,37,Aq I)
Water Concentration Dissipation Rate with Volatilization
St* ** "v
kg/mg
D D
Paraaieter Definition
Central
tendency
value
High-end
value
Refer to
Overall total water concentration
Calculated
k>
k.
«b.
BS
Burial rate (yf*1) • Calculated
Volatilization rate (yr*1) Calculated
Bed sediment porosity (unitless) 0.6
Bed sediment concentration (mg 106
sediment/L)
6.7.52
6.7.52
Bed sediment/sediment pore water
partition coefficient (LAg)
Chemical-specific
6.7.6.1
Suspended sedunent/surface water
partition coefficient (L/kg)
Chemical-specific
6.7.6.1
TSS
Total suspended solids (mg/L)
Rate of burial (m/yr)
10
80
See Equation 6-14
6.7.52
Watertaody depth (m)
0.67
0.18
6.7.5.1
Overall transfer rate (m/yr)
Dissolved fraction (unities*)
See Equation 6-17
See Equation 6-19
Source: EM (US. EPA, 1990e; 1993a).
-*«.
August 1995
6^9
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (17,37,Aq I)
Rate of Burial
W,.
Xe • WAL •££>• itfg/kg - VFX*TSS
WA *TSS* 103 Urn 3 • lO'
Parameter
Wb
DeflnitkM
Rate of burial (m/yr)
Central
. tendeacy High-end
value value
Calculated
Refer to
Unit sod loss (kgAn2/yr)
See Equation 6-15
SD
Watershed area (m2)
lJe+9
6e+7
Watershed sediment delivery ratio (unitless)
See Equation 6-16
6.7.5.1
Waterbody flow volume (m3/yr)
3e+8
lJe+7
6.7.5.1
TSS
Total suspended solids (mg/L)
10
80
6.7.52
Waterbody surface area (m2)
le-HS
4.0644
6.7.5.1
BS
Bed sediment concentration (kg sediment/L)
6.7.52
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-50
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (17J7,Aq I)
Universal, Soil Lossl
Xe *R •A>LS«C«/»«907. 18 kg/ton «245
Parameter DeflnitkM
Xe Unit soil loss (kgAn2/yr)
R USLE rainfall factor (yr1)
K USLE credibility factor (ton/acre)
LS USLE length-slope factor (unitless)
C USLE cover factor (unitkss)
P USLE erosion control practice factor
(unitkss)
Equation
.7 acre/km2 •\Q-6km2/m2 -
Central
tendeacy High-end
value value
Cakulafed
WMU-specific
025
1 3
0.1 OJ
1
(6-15)
Refer to
6.7.32
6.7.32
6.7.32
6.7.32
6.7.32
Source: EM (UJS. EPA, 1990e; 1993a).
August 1995
6-51
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6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (17,37,Aq I)
Watershed: Sediment Delivery Ratio
-0.125
(6-16)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
SD
Sediment delivery ratio (unitless)
Calculated
Empirical intercept coefficient (unitless)
0.6
Area of watenhed (m2)
lJe+9
6.7.5.1
Source: IBM (U.S. EPA, 1990e; 1993a).
-**.
August 1995
6-52
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6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (17,37,Aq I)
Diffusion Transfer Rate
Parameter
K,
KL
KO
If
Kv KL
DeflaitiOB
Overall transfer rate (m/yr)
Liquid phase transfer coefficient (m/yr)
Gas-phase transfer coefficient (m/yr)
Unitless Henry's law constant
y U/
KG'"
Central
tendency
vane
Calculate
See Equation
36,500
Hfeb-end
value Refer to
d
6-18
6.7.5.2
Chemical-specific 6.7.6.1
Source: IBM (US. EPA. 1990c; 1993a).
August 1995 6-53
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (17,37,Aq I)
Liquid Phase Transfer Coefficient
: Parameter
V
DW
U
b
Source: EM (US.
t_j \\t * ff * A^/ /W -ICff\
H 0
Definitioa
Liquid phase transfer coefficient (m/yr)
Diffusivity in water (cm2/s)
Current velocity (m/s)
Waterbody depth (m)
EPA, 1990e; 1993a).
- »3 15»107j/yr
Central
tendency High-end
value value
Cak'ulat'yl
Chemical-specific
0.7 0.5
0.67 0.18
(6-18)
Refer to
6.7.6.1
6.7.5.1
6.7.5.1
August 1995 6-54
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6.0 FATE AND TRANSPORT MODELING
Surface Water Pathways (17,37,Aq I)
Dissolved Fraction
(6-19)
Parameter
Deflnitkw
Ceatrai
teodeacy High-ead
value value
Refer to
Dissolved fraction (unities)
Calculated
Suspended sediment/surface water
partition coefficient (L/kg)
Chemical-spec ific
6.7.6.1
TSS
Total suspended solids (mg/L)
10
80
6.7.52
Source: EM (U^. EPA, 1990e: 1993a).
August 1995
6-55
-------
6.0 FATE AND TRANSPORT MODELING
63 Surface Water Pathways (17,37,Aq I)
Fraction of Contaminant in Water Column
Parameter
f
"*•
TSS
dw
d,
«L
Kd*
BS
db
d
( 1 + Aurf-.. • TSS • 10 kg/ntg ] • ___
i **» " " / j
^J
.
t
DefinitioB
Fraction of total waterbody contaminantion
in water column (unitkss)
Suspended sediment/surface water partition
coefficient (IAg)
Total suspended solids (mg/L)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Bed sediment porosity (unitless)
Bed sediment/sediment pore water partition
coefficient (Meg)
Bed sediment concentration (sediment/L)
Depth of bed sediments (m)
dz
Central
eodency High-cod
value value Refer to
CalculaM
Chemical-specific 6.7.6.1
10 80 6.7.52
0.64 0.15 6.7.5.1
0.67 0.18 6.7.5.1
0.6 6.7.52
Chemical-specific 6.7.6.1
1 6.7.52
0.03 6.7.5.1
Source: EM.
August 1995
6-56
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (19,42^q HI)
6.5.2.2 Pathways 19,42, and Aq III: Ingestion (19 and Aq ni)/Dennai Bathing
(42)/Direcf Contact (Aq m) -» Surface Water -> Overland -> WMU
Constituents sorbed to panicles in the surface soil or waste matrix may be transported
over the ground to surface water via soil erosion and runoff. Contaminants in surface
impoundments may spill to nearby surface waters. Residents using contaminated surface
water as a source of drinking water may ingest constituents dissolved in the surface water or
may absorb constituents through the skin while bathing. Fish, aquatic organisms, aquatic
plants, and birds and mammals that rely on the aquatic food chain may be exposed to
contaminated surface water.
The fate and transport component of these pathways is overland transport by soil
erosion and runoff from the WMU to surface water. Contaminant dissolved in annual surface
runoff was estimated as a function of the contaminant dissolved in soil water and annual
water runoff. For soil erosion, a sorbed concentration of contaminant in soil, together with an
annual soil erosion estimate, a sediment deliv^.y ratio, and an enrichment ratio, were used to
describe the delivery of contaminant to the waterbody via soil erosion.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
•. Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
August 1995 6-57
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (19,42,Aq HI)
A sediment delivery ratio serves to reduce the total potential amount of soil erosion
(i.e., the total potential equals a unit erosion rate as in kg/m2 times a watershed area, in m2)
reaching the waterbody,. recognizing that most of the erosion from a watershed during a year
deposits prior to reaching the waterbody. The enrichment ratio recognizes the fact that soils
that erode tend to be lighter in texture, more abundant in surface area, and have higher
organic carbon. Ail of these characteristics lead to concentrations in eroded soils that tend to
be higher in concentration as compared to in situ soils for many constituents.
Equations 6-21 through 6-29 present the backcalculations for backcalculating soil
concentration from dissolved surface water concentration for overland transport
August 1995 6-58
-------
•if
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (19,42,Aq
Soil Concentration: from Dissolved Water Concentration
~tt>l/ —
PanuBeter
C«i
clO-3m3/L+Rf»lQ-2m/cm) d*
Central
tendency High-etd
value value Refer to
Calculated
From Equations 5 39, 5-44.
5-45,5-46,5-51,5-52,5-53
3e+ll 1.3e+lO 6.7.5.1
Fraction of total watexbody contamination in
water column (uhiuess)
See Equation 6-29
k*, Overall total water concentration dissipation
rate (yr'1)
V Flow-independent mixing volume (L)
8, Soil volumetric water content (unitiess)
Kd, Soil-water partition coefficient (cm3/gj
BD Soil bulk density (g/cm3)
Kdlw Suspended sediment/surface water partition
coefficient (IVkg)
TSS Total suspended solids (mg/L)
A Site area (m2)
Xe Unit soil loss (IcgV/yr)
SD Site sediment deh'very ratio (unitiess)
. .
ER Sou enrichment ratio (unitiess)
Rf Average annual runoff (cm/yr) •
d. Depth of water column (m)
dz . Total depth of waterbody (water column and
sediment) (m)
See Equation 6-23
A Tf^Ji fl IA^A
W. /V^O OfcJv^V
See Equation 6-27
Chemical-specific
13 12
Chemical-specifk
10 80
WMU-spccific
See Equation 6-25
See Equation 6-28
3 organics
1 metals
25 (Portland) 22 (Atlanta)
0.64 • 0.15
0.67 0.18
6.7.5.1
6.7.6.1
6.7.3.1
6.7.6.1
6.7.52
6.7.32
6.7.22
6.7.5.1
6.7.5.1
Source: IBM (U^. EPA, 1990e; 1993a).
August 1995
6-59
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (19,42,Aq m)
Soil Concentration: from Bottom Sediment Concentration
•l<
2;n/cm)
>_I (6-22)
Parameter
C«u
c
Hi
. vf,
f~
*-
V
e.
If A
Kd,
BD
K
-------
6.0 FATE AND TRANSPORT MODELING
63 Surface Water Pathways (19,42y\q
Water Concentration Dissipation Rate
... ,
„ %..«$.«,
\
Parameter Defuiitfaw
k., Overall total water concentration dissipatk
rate(yr-1)
Iq, Burial rate (yr1)
8^ Bed sediment porosity (unitless)
BS Bed sediment concentration (mg
sediment/L)
9*lO*kg/mg ^ Wb (6.23)
S*\Q~*kglmg &m
)
Central
tendeacjr High-cad
value valae Refer to
xi Calculated
r^vu^M
i
0.6 6.7.52
106 6.7.52
Kdfc Bed sediment/sedifnent pore water partition Chemical-specific 6.7.6.1
coefficient (lAg)
Kd^ Suspended sediment/surface water partition Chemical-specific 6.7.6.1
coefficient (lAg)
TSS Total suspended solids (mg/L)
Wb Rate of burial (m/yr)
Da Waterbody depth (m)
10 80 6.7.52
See Equation 6-24
0.67 . 0.18 6.7.5.1
Source: EM (U.S. EPA, 1990e; 19?3a).
August 1995
6-61
-------
6.0 FATE AND TRANSPORT MODELING 6J Surface Water Pathways (19,42,Aq IU)
Rate of Burial
10*L/m 3 • \0~3g/mg
Parameter
wb
DefioltkM
Rate of burial (m/yr)
Central
tendency
value
Caku
High-end
value-
Refer to
Unit soil loss (kg/m2/yr)
See Equation 6-25
SD
Watershed area (m2)
lJe+9
6e+7
6.7.5!l
Watershed sediment delivery ratio (unittess)
See Equation 6-26
Waterbody flow volume (m3/yr)
1.3e+7
67.5.1
TSS
Total suspended solids (mg/L)
10
80
6.7.52
Waterbody surface area (m2)
1646
6.7.5.1
BS
Bed sediment concentration (kg sediment/L)
6.7.52
Source: EM (US. EPA. 1990e; 1993a).
August 1995
6-62
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (19,42,Aq HI)
Universal Soil Loss Equation
Xe *R *K *LS • C *P • 907. 1 8 kg/ton • 245.7 acre/km 2 • 10* Am2/in 2 (6-25)
Parameter
*e
R
K
LS
C
P
Definition
Unit soil loss (kgAn2/yr)
USLE ramfall factor Cyr'1)
USLE erodibility factor (ton/acre)
USLE length-slope factor (uniUess)
USLE cover factor (uniUess)
USLE erosion control practice factor
(uniUess)
Central
teadeacy High-end
value value
Calculated
1 10 (Portland) 300 (Atlanta)
025
1 3
0.1 0.5
1
Refer to
6.7.32
6.7.32
6.7.32
6.7.32
6.7.32
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-63
-------
6,0 FATE AND TRANSPORT MODELING
6J Surface Water Pathways (19,42,Aq m)
Watershed: Sediment Delivery Ratio
SD*a • (WAL)
-0.125
(6-26)
Parameter
Definition
Central
tendency High-end
value . value
Refer to
SD
Sediment delivery ratio (unidess)
Palrnlnt^l
Empirical intercept coefficient (unidess)
0.6
12
Area of watershed (m2)
lJe+9
6.7.3.2
6.7.5.1
Source: EM (U^. EPA. 1990e; 1993a).
August 1995
6-64
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (19,42,Aq 01)
1
Soil Volumetric Water Content
6*6.
i
(6-27)
Parameter
e
e.
q
K,
b
Definition
Soil volumetric water content (mL/cm3)
Soil saturated volumetric water content
(rriL/cm3)
Average annual recharge rate (cm/yr) ,
Saturated hydraulic conductivity (cm/yr)
Soil-specific exponent representing water
retention (unities)
Central
tendency
value
Calcu
0.43
28 (Portland)
3,600
5,4
High-end
value
lated
0.55
15 (Atlanta)
20,000
3.0
Refer to
6.7.3.1
6.7.2.2
6.7.3.1
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995
6-65
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (19,42,Aq m)
Site Sediment Delivery Ratio
SD « a • 64,rai25 (6-28)
Central
tendency High-end
Parameter Definition value value Refer to
SD Sediment delivery ratio (unitless)
a Empirical intercept coefficient (unitless) WMU-specific
AS Area of WMU (m2) WMU-specific
Source: IBM (US. EPA. 1990e; 1993a).
August 1995 6-66
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (19,42,Aq
Fraction of Contaminant in Water Column
fwater*-, < f (6-29)
Parameter
f~
H.
TSS
d.
**
«b.
Kd.
BS
d>
Defiaitioa
Fraction of total waterbody contaminantion
in water column (uniuess)
Suspended sediment/surface water partition
coefficient (Meg)
Total suspended solids (mg/L)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Bed sediment porosity (unitless)
Bed sediment/sediment pore water partition
coefficient (Meg)
Bed sediment concentration (sediment/L) .
Depth of bed sediments (m)
Central
tendency
value
Calci
High-end
value
Chemical-specific
10
0.64
0.67
0.6
80
0.15
0.18
Chemical-specific
1
0.03
Refer to
6.7.6.1
6.7.52
6.7.5.1
6.7.5.1
6.7.52
6.7.6.1
6.7.52
6.7.5.1
Source: BEM.
August 1995 6-67
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (20^Aq II)
6.5.2.3 Pathways 20, 38, and Aq II: Ingestion (20 and Aq ID/Dermal Bathing
(38)/Direct Contact (Aq IT) -> Surface Water -> Overland -» Deposition •-> Air
->WMU
•r '• ••
-> *•. • t
Constituents sorbed to particles in the surface soil or waste matrix may be entrained
into the air. Airborne particulates may deposit on surface soils via deposition mechanisms
(e.g., settling, dry deposition). Constituents deposited on soils may then be transported over
the ground to surface water via soil erosion and runoff. Residents who rely on the contami-
nated surface waters as a source of drinking water may ingest constituents dissolved in the
surface water or may absorb constituents through the skin while bathing. Fish, aquatic
organisms, aquatic plants, and birds and mammals that rely on the aquatic food chain may be
exposed to contaminated surface water.
These pathways include two fate and transport components: deposition of contaminant
onto the watershed followed by soil erosion and runoff into the surface waterbody.
6.5.2.3.1 Soil Erosion and Runoff
Contaminant dissolved in annual surface runoff was estimated as a function of the
contaminant dissolved in soil water and annual water runoff. For soil erosion, a sorbed con-
centration of contaminant in soil together with an annual soil erosion estimate, a sediment
delivery ratio, and an enrichment ratio were used to describe the delivery of contaminant to
the waterbody via soil erosion.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
August 1995 6-68
-------
6.0 FATE AND TRANSPORT MODELING 6J Surface Water Pathways (20^Aq
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
A sediment delivery ratio serves to reduce the total potential amount of soil erosion
(i.e., the total potential equals a unit erosion rate as in kg/m2 times a watershed area, in m2)
reaching the waterbody recognizing that most of the erosion from a watershed during a year
deposits prior to reaching the waterbody. The enrichment ratio recognizes the fact that soils
that erode tend to be lighter in texture, more abundant in surface area, and have higher
organic carbon. All these characteristics lead to concentrations in eroded soils that tend to be
higher in concentration as compared to in situ soils for many constituents.
Equations 6-30 through' 6-36 present the backcalculations for backcalculating soil
concentration from dissolved surface water concentration for soil erosion and runoff.
6.5J.3.2 Deposition to Soil
The cumulative soil concentration of a pollutant as a result of deposition is derived
from the dry deposition rate over the time period of deposition and the contaminant loss rate
from the soil. The cumulative soil concentration represents the concentration increment due
to accumulation of contaminant deposited onto soil from one of the WMUs. The cumulative
soil concentration does not take into account' xkground concentrations of the contaminant
that may already be present, whether natural or from other pollution sources.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, k,, is the sum of the loss rates for each of these processes.
Losses due to degradation (k,g) .are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k,,, includes water balance terms to
account for precipitation, evapotranspirShon, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants rather than vapor-phase contaminants). If such redeposi-
tion occurred, the soil concentration would be higher than if such redeposition did not occur.
As a result, the algorithm as used (without redeposition) may underestimate soil concentra-
tions for compounds that would volatilize then dissolve in rainwater and be redeposited;
August 1995 6-69
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (20,38wVq O)
however, the revolatilization of semivolatile organic contaminants such as dioxin that have
been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by an equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a watershed; therefore the
sou loss constant used includes both a surface runoff loss constant and a soil erosion loss
constant The USLE is used to estimate unit erosion loss.
Equation 6-37 .shows the backcalculation for deposition rate from soil concentration.
Equations 6-38 through 6-47 present the equations for calculating the soil loss constant, k,,
which is used in Equation 6-37.
August 1995 6-70
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (20,38wVq ED
SoU Concentration: from Dissolved Water Concentration
•ER*Kd •10'3m:
»_JI (6-30)
Paraaieter
CM
DcflnitkM
Concentration in soil (mg/kg)
Central
vatae
High^ad
value
Refer to
Calculated
Dissolved water concentration (mg/L)
From Equations 5-39. 5-44.
5-45, 5-46, 5-51, 5-52, 5-53
Waterbody flow volume (L/yr) __
Fraction of total waterbody contaminantion
in water column (unitless)
3e+ll
IJe+lO
See Equation 6-36
6.7.5.1
"-
V
e.
Kd,
BD
v.
TSS
WA,.
*e
SD
ER
Rf
d»
d,
Overall total water concentration dissipation
rate (yr"1)
Flow-independent mixing volume (L)
Soil volumetric water content (unitless)
Soil-water partition coefficient (cm3/g> •
Soil bulk density (g/cm3)
Suspended sediment/surface water partition
coefficient (Meg)
Total suspended solids (mg/L)
Watershed area (m2)
Unit soil loss (kg/mVyr)
Watershed sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yirf*
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
See Equation 6-32
fL *T.— * Q O 1^ t £
\fm I WTW O»«^F^V
See Equation 6-40
Chemical-specifk
U 12
Chemical-specifk
10 80
] *>^ « ft f,m i ^
lOCTTr VRiT/
See Equation 6-34
See Equation 6-35
3 organics
1 metals
WMU-specific
0.64 0.15
0.67 0.18
6.7.5.1
6.7.6.1
6.7.3.1
6.7.6.1
6.7.52
6.7.5.1
6.7.32
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-71
-------
6.0 FATE AND TRANSPORT MODELING
Surface Water Pathways (2
-------
6.0 FATE AND TRANSPORT MODELING
Surface Water Pathways (20,3Mq II)
Water Concentration Dissipation Rate
(6-32)
ParwBetcr
Defloittoa
Central
tendency High-cod
value value
Refer to
Overall total water concentration dissipation
Palriilnlmrf
Burial rate (yf')
Bed sediment porosity (unitless)
0.6
6.7.52
BS
Bed sediment concentration (mg
sediment/L)
10*
6.7.52 .
Kd,,, Bed sediment/sediment pore water partition
coefficient (Ukg)
Chemical-specific
Source: ffiM (U.S. EPA, 1990e; 1993a).
6.7.6.1
«*•
TSS
-^L_-
Suspended sediment/surface water partition
coefficient (L/kg)
Total suspended solids (mg/L)
Rate of burial (m/yr)
Waterbody depth (m)
Chemical-specific
. 10 80
See Equation 6-33
0.67 0.18
6.7.6.1
i
6.7.52
6.7.5.1
August 1995
6-73
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (2
Parameter
W
D .
x.
WAt
SD
Vf,
TSS
WA.
BS
Definition
Rate of burial (m/yr)
Unit soil loss (kg/m2/yr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Total suspended solids (mg/L)
Waterbody surface area (m2)
Bed sediment concentration (kg sedirnent/L)
Central
tendency
value
Calculate
See Equation
1 *^f i O
A*^v*7
See Equation
3e*8
10
1C46
1
HigB-end
value
d
6-34
6e*7
6-35
lJe+7
80
4.6C+4
Refer to
6.7.5.1
6.7.5.1
6.7.52
6.7.5.1
6.7.5.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-74
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (2
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (2
-------
6.0 FATE AND TRANSPORT MODELING 6.5 Surface Water Pathways (20^Aq O)
Fraction of Contaminant in Water Column
r«^-y < — (6-36)
(l+Kd^.TSS.lO-'kg/mg).^ v „ .... __,
Panaact
f—
**•
TSS
^^^
^1
«„.
IvUBu
BS
d,
er DeftaWoa
Fraction of total waterbody contaminantion
in water cohunn (unitfea)
Suspended nediment/surface water partition
coefficient (Ut|)
Total smwnded y^Mff (mi/L)
§" Oi
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Bed sediment porosity (unidess)
coefficient (Ukf)
Depth of bed sediments (m)
Ceafraft
tesMlcaKjr Hia>«Ml
vatat vahM
Calculated
Chemical-specifk
10 80
0.64 0.15
0.67 0.18
0.6
Chemical-specifk
1
0.03
Refer to
6.7.6.1
6.7.52
6.7.5.1
6.7.5.1
6.7.52
6.7.6.1
6.7.52
6.7.5.1
Source: IBM.
6-77
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (2(UMq O)
•
Deposition to Sod:
c«tf*2
°'. [•
ParaaMter Deflaitte
D \vmtf •mml r/m>Mfi«wl (imrxiHi
(i/hrVyr)
(mg/g)
Z Mixing depth (cm)
BD Soil bulk density (g/cm3)
k, Soil loss constant (yf ')
Combined Deposition Rate
r.iD.vio»«^«
-« "*•']• lO'inf/g
Central
teBdexy Hiffc^ewl
vahM vafeM
on nuc Oalculalcd
location From Equations 5-5. 5-6, 5-12.
5-22, 5-32
2.5 (untilled) 1 (unfilled)
1.5 12
See Equation 6-38
9 30
(6-37)
Refer to
6.7.33
6.7.3.1
6.7.3J
Source: EM (U^. EPA, 1990e: 1993a).
August 1995 6-78
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (20J8>Aq H)
Soil Loss Constant
(6-38)
Paraauter
Oefioitioa
Central
tendency High-end
value value
Refer to
Sod km constant (yfl)
Soil Ion constant due to leaching (yr'1)
See Equation 6-39
Soil loss constant due to degradation (yr"')
6.7.6.1
Soil loss constant doe to volatilization (yr'1)
See Equation 6-41
Soil loss constant due to surface runoff
See Equation 6-45
Soil loss constant due to soil erosion (yr*1)
See Equation 6-47
Source: IBM (US. EPA. 1990e; 1993a).
August 1995
6-79
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways
II)
Soil Loss Constant Due to Leaching
e»z«
i*
f ^\
Kd
BD'-l
e
V f*
(6-39)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Soil loss constant due to leaching (yr"1)
Average annual recharge (cm/yr)
WMU-spccific
Soil volumetric water content (mL/cm3)
See Equation 6-40
BD
Soil depth from whkh leaching occurs (cm) 2J (untilled) 1 (unfilled)
Soil bulk density (g/cm3)
\2
6.7.3J
6.7.3.1
Soil-water partition coefficient (mL/g)
Chemical-specific
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-80
-------
6.0 FATE AND TRANSPORT MODELING
Surface Water Pathways (20J8^q U)
Soil Volumetric Water Content
e-e.
(6-40)
Panuaeter
Central
tendency
vatae
High-cad
vahie
Refer to
Soil volumetric water content (mUcrn3)
Soil saturated voiumetric water content
(mL/cm3)
0.43
6.7.3.1
q Average annual recharge rate (cm/yr)
K, Saturated hydraulic conductivity (cm/yr)
WMU-specific
3.600-
20.000
6.7.3.1
Soil-specific exponent representing water
retention (unitless)
5.4
3.0
6.7.3.1
Source: SEAM (U.S. EPA. 1988a).
August 1995
6-81
-------
6.0 FATE AND TRANSPORT MODELING 6-5 Surface Water Pathways (2
-------
6.0 FATE AND TRANSPORT MODELING
&5 Surface Water Pathways (20^Aq II)
Volatilization Equilibrium Coefficient
=3.1536»107j/yr«
(6-42)
Parameter
*e
H
Z
V
R
T
BD
Source: DEM
DefWtiM
Equilibrium coefficient (s&nvyr)
Henry's law constant (atnvmVmol)
Soil depth from which volatilization occurs
(cm)
Soil water partition coefficient (mL/g)
Ideal gas constant (atm-L/mol-K)
Temperature (K)
Sod bulk density (g/cm3)
(U.S. EPA, 1990e; 1993a).
Central
tendency
vabM
CiUClllfl
Hfea-ead
value
ted
Chemical-specifk
2.3 (unfilled)
I (unfilled)
Chemical-specific
921 x 1(T3 '
298
1.3
1.2
Refer to
6.7.6.1
6/7.3.3
6.7.6.1
6.7.7
6.1.22
6.7.3.1
August 1995
6-83
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (20,38wVq U)
Gas-Phase Mass Transfer Coefficient
Parameter
K,
u
Definition
Gas-phase mass transfer coefficient (cm/s)
Windspeed (m/s)
Central
tendency High-end
vahie value
Calculated
WMU-specific
Refer to
Schmidt number on gas side (unitless) See Equation 6-44
Effective diameter of contaminated area (m) See Equation 6-46
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-84
-------
6.0 FATE AND TRANSPORT MODELING
6J Surface Water Pathways (2038^q II)
Schmidt Number on Gas Side
(6-44)
DefUtte
Central
tendency
value
High-end
value
Refer to
Schmidt number an gas side (unittess)
Calculated
P.
Viscosity of air (g/cm-s)
l.Slc-4
Density of air (g/cm3)
1.2e-3
6.7.7
6.7.7
Diffusmty in air (cm2/s)
Chemical-specific
6.7.6.1
Source: EM (US. EPA, 1990e; 1993a).
August 1995
6-85
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (20T3Mq ID
Soil Loss Constant Due to Runoff
X \
(6-45)
Parameter
Central
tendency
DefbdtfcM value
High-end
value
Refer to
Soil loss constant due to surface runoff
(yr-1)
Calculated
Average annual runoff (cm/yr)
WMU-specific
e
z
BD
Kd,
Soil volumetric water content (mL/cm3)
Soil mixing depth (cm)
Soil bulk density (a/cm3)
Soil-water partition coefficient (mL/g)
From Equation 6-40
2.5 (unfilled) 1 (unfilled)
IJ 12
Chemical-specific
6.7.3J
6.7.3.1
6.7.6.1
Source: DEM (U.S. EPA, 1990c: 1993a).
August 1995
6-86
-------
6.0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways (20^Aq ID
Effective Diameter
\
4M (6-46)
Central
teadeacy High-end
ParaaMter Deflnitioa . value valae Refer to
d. Effective diameier of OilmlMed
contaminaiBd area (m)
A Area of contaminated area 1 J4e+9 (watershed) 6e+7 (watershed) 6.7.5.1
(mj) •
Source: IBM (US. EPA, 1990e; 1993a).
August 1995 6-87
-------
6.0 FATE AND TRANSPORT MODELING
6.5 Surface Water Pathways (KU8,Aq H)
Soil Loss Constant Due to Erosion
Parameter
*.
Xe
6
Z
BD
Kd,
ffl.l-A
fr - „ ,.
" £0-2
\
Dcfbutioa
Soil toss constant due to soil erosion
Unit soil loss (kgAn2/yr)
:."]( *<*,•*£> "|
J %+KdjBD
) \ /
Central
tendeacy High-end
value value
(yr"1) Palrnlalxf
From Equation 6-34
(6-47)
Refer to
Soil volumetric water content (mL/cm3) From Equation 6-40
Soil mixing depth (cm)
Soil bulk density (a/cm3)
2J(untilled) l(untilled)
U U
Soil-water partition coefficient (mL/g) Chemical-specific
6.7.3J
6.7.3.1
6.7.6.1
Source: EM (US. EPA, 1990e; 1993a).
August 1995
6-88
-------
&0 FATE AND TRANSPORT MODELING 63 Surface Water Pathways
6.5J Uncertainty for Surface Water Pathways
6.5J.1 Surface Water Modeling Framework
The surface water modeling framework presented in the Addendum (U.S. EPA, 1993a)
and used here is a new model that has not been peer-reviewed. Therefore, there is
uncertainty as to how well it represents actual surface water fate and transport processes.
Most of the existing peer-reviewed surface water models in use at EPA, such as WASP and
EXAMS, are so highly site-specific that they could not be feasibly adapted to a generic
analysis such as this. It is uncertain whether use of this model would overestimate or
underestimate risk.
Although the surface water model framework is designed to accommodate chemical
transformations within the waterbody, these were omitted from this analysis. These processes
are highly chemical- and site-specific. Assessing the potential for transformation of all 200
chemicals considered would be an extensive research project However, chemicals were
screened to eliminate chemicals that hydrolyze completely in water, forming other
compounds. The effect of omitting such transformations could be either an overestimate or
underestimate of the risk, depending on whether a chemical transforms into a more or less
toxic or mobile form.
6.5.3.2 Universal Soil Loss Equation
Uncertainty arises out of the use of the Universal Soil Loss Equation. This is an
empirical, though widely used, model. It was intended for use in site-specific situations,
where highly specific input data can be used, and for relatively small fields. How well it
predicts soil erosion in a generic application, as here, and for fairly large sources of eroded
soil, is uncertain. It is most likely that it overestimates quantity of soil eroded.
6.5 JJ Soil Loss Constant Term
The overall soil loss constant term, k,, is uncertain in several ways. This term is the
sum of loss rates for leaching, erosion, runoff, degradation, and volatilization. One
uncertainty arises from the assumption that all of these loss terms are first order and can
therefore be added together. This is a common assumption, but some of the processes may,
in fact, be zero order. A first-order loss process may be characterized by a half-life, the time
it takes half of the remaining contaminant to be lost Therefore, the mass lost per unit of
time varies with the concentration. A zero-order loss process is characterized by a constant
mass loss per unit of time. Neither of these processes can be said to be more conservative
than the other; because the first-order rate depends on the starting concentration and the zero-
order rate does not, at any given time, which one results in a higher concentration will depend
on the starting concentration. Therefore, it cannot be said whether incorrectly assuming that
loss constant that is actually zero order is first order will overestimate or underestimate soil
concentration.
August 1995 6-89
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6.0 FATE AND TRANSPORT MODELING 6-5 Surface Water Pathways
Another source of uncertainty regarding the soil loss constant is that the various loss
processes are calculated independently when, in fact, they occur simultaneously. As a result,
losses could be overpredicted because the amount of contaminant available to each process is
overestimated by not-accounting for the other loss processes. This would result in an
underestimate of soil concentration.
The inclusion of losses due to soil erosion and runoff in the soil loss rate may also
overstate the net loss of contaminant from soil, thus underestimating soil concentration. For
small areas, such as the home garden or yard used in soil ingestion and dermal soil pathways,
it could be argued that soil loss due to these mechanisms is offset by erosion and runon onto
the garden or yard. However, for large areas, sucha s the watersheds used in the surface
water pathways, such offsetting runon and soil erosion is less likely to occur, since any soil
erosion or runon will occur from within the watershed. It is the Addendum's current
recommendation to include these losses.
Finally, degradation losses were set to zero. Degradation rates are highly dependent on
site-specific factors that cannot be accounted for in a generic analysis of this nature and may
be zero. To the extent that constituents do degrade into constituents of less concern, the
omission of degradation from the soil loss constant will underestimate losses and therefore
overestimate soil concentration.
The overall effect of all of the above uncertainties ~on the soil loss constant is not clear.
Two of the factors would tend to underestimate soil concentration, one would tend to
overestimate soil concentration, and the effect of one could be either an over- or under-
estimate of soil concentration.
6.5J.4 Soil Water Content Equation
The equation from the Superfund Exposure Assessment Manual (U.S. EPA, 1988a) used
to calculate soil water content based on recharge and soil properties was developed for site-
specific application. Its application in a generic analysis raises uncertainty as to how well it
predicts soil water content A distribution of this value would have been preferred; however,
it was not available and so had to be calculated. However, some of the input parameters are
highly generalized (such as recharge) and others (such as the soil moisture retention exponent
b) are drawn from estimates rather than measured values. It is not clear in which direction
this uncertainty would affect the resu/i§,
August 1995 6-90
-------
6.0 FATE AND TRANSPORT MODELING
Food Chain Pathways
6.6 FOOD CHAIN PATHWAYS
Food chain pathways are divided into three groups: plant pathways, animal (beef and
milk) pathways, and fish pathways. These are covered in the following sections.
6.6.1 Plant Pathways
Figure 6-6 provides an overview of the fate and transport for plant pathways.
6.6.1.1 Scenarios
6.6.1.1.1 Human
Human exposure scenarios for plant pathways include ingestion of contaminated
aboveground fruits and vegetables and ingestion of contaminated root vegetables.
Aboveground fruits and vegetables are considered separately from root vegetables because
they may be contaminated by different pathways. Root vegetables are considered to be
"protected" because the edible portion is below ground and therefore protected from
contaminants in the air. Aboveground fruits and vegetables are considered "protected" if the
edible portion is enclosed in an outer covering that protects it from contaminants in the air,
aboveground fruits and vegetables not protected are considered to be "exposed" because the
edible portion is exposed directly to contaminants in the air. Only exposed aboveground
fruits and vegetables were included in the analysis.
Soa&Mton]
1
Partcutato
Efnfestont
+
tta /Vw^M%to
•tbvt 1
Figure 6-6. Fate and transport for plant pathways.
August 199S
6-91
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
Two receptors are considered for all plant pathways. The first is a home gardener
living at the fenceline (for active sites) or on site (for closed sites) who grows produce for
home consumption in a garden. The second is a subsistence farmer at the fenceline (for
active sites) or on site (for closed sites) who also grows produce for home consumption. The
difference between the home gardener and the subsistence farmer is that the subsistence
farmer is assumed to grow a greater fraction of all fruits and vegetables consumed than the
home gardener, thus consuming more contaminated produce. Fruits and vegetables bought
from a store to supplement home-grown fruits and vegetables are assumed to be uncontam-
inated. Table 6-7 summarizes the receptors modeled for the plant pathways.
6.6.1.1J Ecological
Ecological exposure scenarios for plant pathways include the ingestion of contaminated
forage grasses or aboveground leafy portions of plants. Abpveground vegetation was
considered separately from root portions of plants because different pathways apply to above-
and belowground plants. As stated above, root portions (i.e., vegetables) were not considered
in air deposition pathways. However, for ecological receptors, aboveground vegetation was
not considered "protected"; it was assumed that all exterior portions of forage (also fruits and
vegetables and seeds) could be consumed. The receptors for terrestrial plant pathways
included the following species of mammals and birds considered to be strict herbivores:
• Whitetail deer • Bobwhite quail
• Eastern cottontail
• Meadow vole
Table 6-7. Summary of Receptors for Plant Pathways
' Receptor
Adult Child Subsistence Hone Subsistence Fish
Pathway resident resident fanner gardener fisher consumer Worker
8: Air deposition- / /
veg/root
ingestion ^ :
8a; Direct atr-veg/m* / /
ingestion
9: Direct soil-veg/root /• /•
ingestion (on site)
9: Overiand-veg/toot S /"
ingestion (off site) . __
* Ckxed liad application unit only.
August 1995 6-92
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
For the ingestion of contaminated vegetation, receptors were assumed to feed at the
fenceline for active sites or on the contaminated site for closed sites. These herbivores may
ingest contaminated plants during sensitive stages or the contaminated area may be an
important food source over the course of their life cycle. It was implicitly assumed that the
contaminated areas could support sufficient vegetation to sustain at least one reproducing pair
from the population. However, it is unlikely that the size of the contaminated plot would be
adequate to sustain an entire reproducing population of animals. Animals that consume plants
as a part of their diet Gess than 50 percent) are discussed in Section 6.3.1.2 on soil pathways.
6.6.1.2 Pathway Algorithms
Plants can accumulate contaminants through several mechanisms. These include direct
uptake of vapor-phase contaminants by air-to-plant transfer, direct deposition of particulate-
phase contaminants on exposed plant surfaces, and root uptake from soil. In addition, soil
may become contaminated via deposition from air or soil erosion and runoff. Combinations
of these mechanisms make up the plant pathways.
The following sections describe the plant pathways and present the fate and transport
equations for them. These pathways are:
• Pathway 8: ingestion —» plant —> soil -» deposition —> air —> WMU
(Section 6.6.1.2.1)
• Pathway 8a: ingestion -» plant -» air -» WMU (Section 6.6.1.2.2)
• Pathway 9 (on site): ingestion -» plant -> WMU (soil) (Section 6.6.1.2.3)
• Pathway 9 (off site): ingestion -> plant -> soil -> overland -> WMU
(Section 6.6.1.2.4)
• Pathway Terr IV: ingestion'-» plant -» air -» WMU (Section 6.6.1.2.2)
• Pathway Terr V: ingestion -> plant -* soil -> deposition -» air -* WMU
(Section 6.6.1.2.1).
August 1995 6-93
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
6.6.1.2.1 Pathway 8 and Terr V: Ingestion -» Plant -» Soil -» Deposition -> Air
WMU
•Jt-w
^m: ——
Constituents sorbed to particles in the surface soil or waste matrix may be entrained
into the air from waste management units. Airborne participates may deposit on surface soils
and plants via deposition mechanisms (e.g., settling, dry deposition). Constituents may
deposit directly on exposed plant surfaces or on soils and be translocated from the soil into
edible plant tissues. Residents with home gardens and subsistence farmers located near a
WMU may be exposed to contaminated fruits and vegetables, particularly if the produce is
not sufficiently washed and/or cooked. Animals that feed on contaminated vegetation may
also be exposed.
This pathway is calculated slightly differently for aboveground fruits and vegetables and
root vegetables. For both aboveground fruits and vegetables and root vegetables, this
pathway includes air dispersion from the WMU to the plant location. Air dispersion
modeling is covered in Section 7.
Aboveground Fruits and Vegetables and Vegetation. For aboveground fruits and
vegetables, this pathway includes two concurrent mechanisms of plant uptake: deposition
directly to the plant, and deposition to soil followed by root uptake by the plant Three fate
and transport components are needed: root uptake from soil, deposition to soil, and
deposition to plant Each of these is discussed in the following paragraphs.
Root Uptake. The concentration of pollutant in plant tissue of aboveground vegetables
due to root uptake is determined from the soil concentration and the plant-soil bioconcentra-
tion factor for a plant group. This approach is based on plant-soil bioconcentration factors
from Travis and Arms (1988), as presented in the Indirect Exposure Methodology. The
Travis and Arms plant-soil bioconcentration factor, Br, was used for all constituents. In
addition to the benefit of its being generalizable based on Kow for organics, values for Br
have also been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
Deposition to Soil. The cumulative soil concentration of a pollutant as a result of
deposition is derived from the dry deposition rate over the time period of deposition and the
contaminant loss rate from the soil. The cumulative soil concentration represents the
concentration increment due to accumulation of contaminant deposited onto soil from one of
the WMUs. The cumulative soil concentration does not take into account background
concentrations of the contaminant that may already be present, whether natural or from other
August 1995 6-94
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
pollution sources. The algorithms for deposition to soil are from the Indirect Exposure
Methodology.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, k,, is the sum of the loss rates for each of these processes.
Losses due to degradation (ksg) are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k,,, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants, rather than vapor-phase contaminants). If such
redeposition occurred, the soil concentration would be higher than if such redeposition did not
occur. As a result, the algorithm as used (without redeposition) may underestimate soil
concentrations for compounds that would volatilize then dissolve in rainwater and be
redeposited; however, the revolatilization of semivolatile organic contaminants such as dioxin
that have been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by an equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a small area, such as a
garden; therefore, the soil loss constant used does not include a surface runoff loss constant or
a soil erosion loss constant The USLE is used to estimate unit erosion loss.
Deposition to Plant. Pollutants may be deposited on exposed plant surfaces by
deposition. Questions exist as to whether pollutants accumulated by direct deposition to plant
surfaces remain on the plant surface or are internalized by plants. In addition, the degree to
which pollutants are transported between plant organs through the vascular system is
uncertain. Thus, uptake via direct deposition was calculated for aboveground fruits and
vegetables but not root vegetables (which are protected) since the edible portions of the latter
are not in direct contact with the air. The algorithms for deposition to plant are from the
Indirect Exposure Methodology.
August 1995 6-95
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
The two plant uptake mechanisms (deposition to plant and deposition to soil followed
by root uptake) must be combined so that the deposition rate for soil is the same as the
deposition rate to plants. Equation 6-48 shows the backcalculation for deposition rate from
aboveground fruit and vegetable concentration. This first term in the denominator of this
equation accounts for deposition to soil followed by root uptake; the second term in the
denominator accounts for deposition to the plant Equations 6-49 through 6-56 present the
equations for calculating the soil loss constant, kg, which is used in Equation 6-48.
Root Vegetables. For root vegetables, this pathway includes only one mechanism of
plant uptake: deposition to soil followed by root uptake by the plant Uptake via direct
deposition to the plant is not considered, since the edible (root) portion is protected from
contact with contaminants in air, and it is unclear whether contaminants deposited on plant
surfaces are internalized by plants. Two fate and transport components are needed: root
uptake from soil and deposition to soil. Each of these is discussed in the following
paragraphs.
Root Uptake. The approach used in the Dioxin document (U.S. EPA, 1994a), which
was developed by Briggs (1982), was used in place of the Travis and Arms algorithm for
soil-to-belowground transfers to root vegetables. The Briggs approach uses a Root
Concentration Factor (RCF) to estimate plant concentrations instead of a plant-soil biotransfer
factor.
The Travis and Arms approach used for aboveground vegetables is an empirically
developed approach based on soil-to-aboveground plant transfers (e.g., translocation into
shoots), not soil-to-belowground transfers (e.g., translocation into roots and tubers), and may
therefore not be appropriate for belowground vegetables, such as root vegetables. A better
approach to vegetables for which roots are the edible portions, is to separate "aboveground"
and "belowground" vegetation, and state that belowground vegetation includes edible roots
such as carrots, potatoes, and radishes. This is the approach taken in the Dioxin document
(U.S. EPA, 1994a). It should be noted that concentrations of dioxin in carrots and potatoes
are among the highest found in vegetables/fruits.
The Briggs Root Concentration Factor is generalizable based on Kow for organics and
was used for all organic constituents. However, RCFs have not been compiled for metals.
Therefore, the Travis and Arms plant-soil bioconcentration factor, Br, was used for metals
(see discussion above for aboveground vegetables).
The Dioxin document uses an empirical correction factor, VG^, to reflect the fact that
the barley roots of Briggs' experiments are different than bulky belowground vegetables such
as potatoes or onions. Dioxin-like compounds will sorb to outer portions of belowground
vegetation, but inner translocation is negligible. Therefore, the concentrations in the barley
roots, for the lipophilic compounds used by Briggs in his experiments, would be higher on a
whole plant basis than concentrations that would result from soil-to-root transfers for bulkier
vegetation, due to the greater surface area to weight ratio of the barley roots compared to
bulkier vegetation. In other words, the whole barley root concentrations would be similar to
August 1995 6-96
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
concentrations near the skin of a potato, but not a whole potato. The Dioxin document uses
an empirical reduction factor of 0.01, which was estimated using a surface area volume to
whole plant volume ratio for a carrot A similar fix would not be appropriate for an RCF
developed for soluble compounds, which would have transpiration stream translocation and
more uniform vegetative concentrations.
Deposition to Soil. The cumulative soil concentration of a pollutant as a result of
deposition is derived from the dry deposition rate over the time period of deposition and the
contaminant loss rate from the soil. The cumulative soil concentration represents the
concentration increment due to accumulation of contaminant deposited onto soil from one of
the WMUs. The cumulative soil concentration does not take into account background
concentrations of the contaminant that may already be present, whether natural or from other
pollution sources. The algorithms for deposition to soil are from the Indirect Exposure
Methodology.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, k,, is the sum of the loss rates for each of these processes.
Losses due to degradation (k,g) are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k,.,, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
.Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants, rather than vapor-phase contaminants). If such
redeposition occurred, the soil concentration would be higher than if such redeposition did not
occur. As a result, the algorithm as used (without redeposition) may underestimate soil
concentrations for compounds that would volatilize then dissolve in rainwater and be
redepositcd; however, the revolatilization of semivolatile organic contaminants such as dioxiri
that have been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by an equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a garden, a small area
August 1995 6-97
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
within a watershed; therefore, the soil loss constant used does not include a surface runoff
loss constant or a soil erosion loss constant The USLE is used to estimate unit erosion loss.
Equation 6-57 shows the backcalculation for soil concentration from root vegetable
concentration. Equation 6-58 shows the backcalculation for deposition rate from soil
concentration. Equations 6-59 to 6-66 present the equations for the soil loss constant, ks,
which is used in Equation 6-58.
August 1995 6-98
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Crop Uptake from Deposition: Combined Deposition Rate—Aboveground
Vegetables
A,=T
y
Parameter
r
^plant
Br.(\ -e -*•'•). \
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Soil Loss Constant
*,«*,/
(6-49)
Parameter Definition
k, Soil loss constant (yr'1)
k,j Soil loss constant due to leaching (yr'1)
Central
tendency High-end
value value
Calculated
See Equation 6-50
Refer to
Soil loss constant due to degradation (yr"1)
6.7.6.1
Soil loss constant due to volatilization (yr'1)
See Equation 6-52
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-100
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Soil Loss Constant Due to Leaching
e»z»
i*
BD-Kd\
e
(6-50)
Parameter
Definitioo
Central
tendency
value
High-end
value
Refer to
Soil loss constant due to leaching (yr"1)
Calculated
Average annual recharge (cm/yr)
WMU-specific
6
Z
BD
*d
Soil volumetric water content (mL/cm3)
Soil depth from which leaching occurs (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
See Equation 6-51
20 (tilled) 10 (tilled)
1.5 1.2
Chemical-specific
6.7-3.3
6.7.3.1
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-101
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Soil Volumetric Water
r t '
8,8, JLP^
W
Parameter Definition
6 Soil volumetric water content (mL/cm3)
9, Soil saturated volumetric water content
(mL/cm3)
q Average annual recharge rate (cm/yr)
K, Saturated hydraulic conductivity (cm/yr)
b Soil-specific exponent representing water
retention (unitless)
Content
) (6-51)
Central
tendency High-end
value value Refer to
Calculated
0.43 0,55 6.7.3.1
WMU-specific
3,600 20,000 6.7.3.1
5.4 3.0 6.7.3.1
Source: SEAM (U.S. EPA. 1988a).
August 1995
6-102
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Soil Loss Constant Due to Volatilization
(6-52)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Soil loss constant due to volatilization (yr"1)
Calculated
Equilibrium coefficient (s/cm-yr)
Gas-phase mass transfer coefficient (cm/s)
See Equation 6-53
See Equation 6-54
Source: EM (U.S. EPA, 199Qe; 1993a).
August 1995
6-103
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
• '
Volatilization Equilibrium Coefficient
Parameter
Ke
H
Z
*d
R
T
BD
y = 3.1536»107j/>r
Definition
Equilibrium coefficient (s/cm-yr)
Henry's law constant (atm-m3/mol)
Soil depth from which volatilization occurs
(cm)
Soil water partition coefficient (mL/g)
Ideal gas constant (atm-L/mol-K)
Temperature (K)
Soil bulk density (g/cm3)
•103t/m3'//
T»BD
Central
tendency High-end
value value
Calculated
Chemical-specific
20 (tilled) 10 (tilled)
Chemical-specific
8.21 x 10'5
298
1.5 1.2
(6-53)
Refer to
6.7.6.1
6.7.3.3
6.7.6.1
. 6.7.7
6.7.2.2
6.7.3.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-104
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
Gas-Phase Mass Transfer Coefficient
-0.67 ,-0.11
(6-54)
Parameter
K,
u
Sc0
dc
Definition
Gas-phase mass transfer .coefficient (cm/s)
Windspeed (m/s)
Schmidt number on gas side (unitless)
Effective diameter of contaminated area (m)
Central
tendency High-end
value value Refer to
Calculated
WMU-specific
See Equation 6-55
See Equation 6-56
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-105
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Parameter
ScG
M,
P.
D.
Schmidt Number on
*C.J^_
Pa'D«
Definition
Schmidt number on gas side (unitless)
Viscosity of air (g/cm-s)
Density of air (g/cm3)
Diffusivity in air (cnr/s)
Gas Side
Central
tendency High-end
value value
Calculated
1.81e-4
1.2e-3
Chemical-specific
(6-55)
Refer to
6.7.7
6.7.7
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-106
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Effective Diameter
4M
(6-56)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Effective diameter, of
contaminated area (m)
Calculated
Area of contaminated area
(m2)
5.100 (garden) 2,024 (garden) 6.7.3.3
Source: EEM (U.S. EPA, 1990e; 1993a).
August 1995
6-107
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Crop Uptake from Soil: Soil Concentration—Belowground Vegetables
RCF'VG.
(6-57)
Parameter
C»ii
cw
*d
RCF
VG0«
Definition
Concentration in soil (mg/kg or ug/g)
Concentration in plant (mg/kg DW or ug/g
DW)
Soil- water partition coefficient (L/kg)
Root concentration factor - ratio of
contaminant concentration in roots to
concentration in soil water
(mg/kg plant/mg/kg soil water)
Empirical correction factor for lipophilic
contaminants (unitless)
Central
tendency value High-end
value
Calculated
From Equations 5-56 and 5-59
• Chemical-specific
Chemical-specific
0.01 (lipophilics)
1 (solubles)
Refer to
. 6.7.6.1
6.7.6.2
6.7.4.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-108
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Deposition to Soil: Combined Deposition Rate
i -V
1 -e '
(6-58)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Average annual combined deposition rate
(g/m2/yr)
Calculated
Concentration in soil at deposition location
(mg/g)
From Equation 6-57
z
BD
k,
t
Mixing depth (cm)
Soil bulk density (g/cm3)
Soil loss constant (yr'1)
Time period of deposition (yr)
20 (tilled) 10 (tilled)
1.5 1.2
See Equation 6-59
9 30
6.7.3.3
6.7.3.1
6.7.3.3 .
Source: ffiM (U.S. EPA, 1990e; 1993a).
August 1995
6-109
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
Soil Loss Constant
(6-59)
Parameter
k.
k-
Definition
Soil loss constant (yr*1)
Soil loss constant due to leaching (yr'1)
Central
tendency High-end
value value
Calculated
See Equation 6-60
Refer to
k,g Soil loss constant due to degradation (yr'1) 0 6.7.6.1
k^y Soil loss constant due to volatilization (yr'1) See Equation 6-62
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 . 6-110
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (SJerr V)
Soil Loss Constant Due to Leaching
e«z<
e
(6-60)
Parameter
Definitioo
Central
tendency High-end
value value
Refer to
Soil loss constant due to leaching (yr'1)
Calculated
Average annual recharge (cm/yr)
Soil volumetric water content (mL/cm3)
WMU-specific
See Equation 6-61
z
BD
Kd
Soil depth from which leaching occurs (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
20 (tilled) 10 (tilled)
1.5 1.2
Chemical-specific
6.7.3.3
6.7.3.1
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-111
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
- - Soil Volumetric Water Content
Parameter Definition
iU)
.K*\
Central
tendency High-end
value value
(6-61)
Refer to
0 Soil volumetric water content (mL/cm3) . Calculated
0, Soil saturated volumetric water content 0.43 0.55
(mlVcm3)
6.7.3.1
q Average annual recharge rate (cm/yr) WMU-specific
K, Saturated hydraulic conductivity (cm/yr) 3,600 20,000
b Soil-specific exponent representing water 5.4 3.0
retention (unitless)
6.7.3.1
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995
6-112
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
Soil Loss Constant Due to Volatilization
(6'62)
Central
tendency High-end
Parameter Definition value value < Refer to
k^ Soil loss constant due to volatilization (yr'1) Calculated
Ke Equilibrium coefficient (s/cm-yr) See Equation 6-63
K, Gas-phase mass transfer coefficient (cm/s) See Equation 6-64
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-113
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Volatilization Equilibrium Coefficient
Parameter
Ke
H
Z
Kd
R
T
BD
Source: IBM
,..3.1536.10^.1
/
Definition
Equilibrium coefficient (s/cm-yr)
Henry's law constant (atm-m3/mol)
Soil depth from which volatilization occurs
(cm)
Soil water partition coefficient (mL/g)
Ideal gas constant (atm-LAnol-K)
Temperature (K)
Soil bulk density (g/cm3)
(U.S. EPA, 1990e; 1993a).
tfUm>.H
•' D r^
p ^j
Central
tendency High-end
value value
Calculated
Chemical-specific
20 (tilled) 10 (tilled)
Chemical-specific
8.21 x 10'5
298
1.5 1.2
(6-63)
Refer to
6.7.6.1
6.7.3.3
6.7.6.1
6.7.7
6.7.2.2
6.7.3.1
August 1995
6-114
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Gas-Phase Mass Transfer Coefficient
f, =0.482 .u0'7
,-0.11
(6-64)
Parameter
K,
u
Sc0
de
Definition
Gas-phase mass transfer coefficient (cm/s)
Windspeed (m/s)
Schmidt number on gas side (unidess)
Effective diameter of contaminated area (m)
Central
tendency High-end
value value Refer to
Calculated
WMU-specific
See Equation 6-65
See Equation 6-66
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-115
-------
6.Q FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8,Terr V)
Schmidt Number on Gas Side
(6-65)
Central
tendency High-end
Parameter . Definition value value Refer to
ScG Schmidt number on gas side (unitless) Calculated
u. Viscosity of air (g/cm-s) 1.81e-4 6.7.7
p. Density of air (g/cm3) 1.2e-3 6.7.7
Dt Diffusivity in air (cm2/s) Chemical-specific 6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-116
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8,Terr V)
Effective Diameter
4M
(6-66)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Effective diameter of
contaminated area (m)
Calculated
Area of contaminated area
(m2)
5.100 (garden) 2,024 (garden) 6.7.3.3
Source: IEM (U.S. EPA, 1990e; 1993a).
August 1995
6-117
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8a,Terr IV)
6.6.1.2.2 Pathway 8a and Terr IV: Digestion -» Plant -> Air -> WMU
JL
Constituents may volatilize from land application units, wastepiles, surface
impoundments, or tanks. Constituents in the vapor phase can be translocated into plant tissue
during normal plant respiration. Residents with home gardens and subsistence farmers
located near a WMU may be exposed to contaminated fruits and vegetables, particularly if the
produce is not sufficiently cooked. Animals that feed on contaminated vegetation may also
be exposed.
This pathway .applies only to aboveground fruits and vegetables and vegetation. Air-to-
plant transfer does not apply to root vegetables, because the edible portion is protected from
direct exposure and it is not clear that contaminants are distributed throughout the plant. The
fate and transport components of this pathway are air dispersion from the WMU to the plant
location (which is covered in Section 7) and direct uptake of contaminant from air by plants.
Two parameters are necessary to estimate air-to-plant transfer: the air-to-plant
biotransfer factor and the atmospheric concentration of pollutant at ground level. The latter
includes only concentration of pollutant in the vapor-phase due to emissions from WMUs.
Consideration of concentration due to volatilization of pollutant deposited on the soil would
appear to be double-counting; therefore, it was not included. This concentration is likely to
be negligible in any case. The algorithms for air-to-plant uptake are from the Indirect
Exposure Methodology.
The air-to-plant biotransfer factor is based on work by Bacci et al. (1990, 1992). Bacci
conducted laboratory experiments on the air-to-leaf transfer of vapors of 14 organics using
azalea leaves and developed an empirical equation for a volumetric air-to-leaf biotransfer
factor. Bacci et al. (1990) also developed a conversion equation to convert the volumetric
transfer factor to a mass-based transfer factor; it is this mass-based transfer factor that is used
to determine plant uptake from an air concentration. Simonich and Hites (1994) have also
done experimental work to determine air-to-plant transfer factors for PAHs. These values
were used for PAHs instead of Bacci's correlation equation.
Bacci's work did not account for photodegradation of the chemicals from the leaf.
Experimental results presented by Macrady and Maggard (1993) suggest that the Bacci
algorithm may overpredict the air-to-plant biotransfer factor by a factor of 40 for dioxin-like .
August 1995 6-118
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (8a,Terr IV)
compounds. The Dioxin document (U.S. EPA, 1994a) recommmends reducing the air-to-
plant biotransfer factor calculated by the Bacci algorithm by a factor of 40 for dioxin-like
compounds.
See Section 6.7.6.2.3 for a detailed discussion of how air-to-plant transfer factors were
calculated.
The Dioxin document also uses an empirical correction factor, VG to reflect the fact
that the azalea leaves of Bacci's experiments are different than bulky aboveground fruits and
vegetables. This correction factor is based on the assumption that there is negligible
translocation of lipophilic contaminants to inner parts of bulkier vegetation so that the
concentration in the outer portion of the bulkier fruits and vegetables would be similar to that
predicted for azalea leaves, while the overall concentration would be lower. The value of
0.01 was estimated in the Dioxin document. This correction was applied for lipophilic
compounds (those with a log Kow > 4). For soluble compounds (log K^ < 4), this correction
factor was set to 1.
Equation 6-67 presents the equation for backcalculating air concentration from plant
concentration for aboveground fruits and vegetables.
August 1995 6-119
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (8a,Terr IV)
Crop Uptake from Air: Air Concentration
_ plant ra
(6-67)
Parameter
Definition
Central
tendency value High-end
value
Refer to
Concentration in air (ug/m3)
Calculated
Concentration in plant (ug/g DW)
Density of air (g/m3)
From Equations 5-56 and 5-59
UOO
P.
6.7.7
Bv
VG.
Air-to-plant biotransfer factor
(fog/g DWy[ug/g])
Chemical-specific
Empirical correction factor (unitless)
0.01 (lipophilics)
1 (solubles)
6.7.6.2
6.7.4.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-120
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (9)
6.6.1.23 Pathway 9 (On Site): Ingestion -> Plant -> WMU (Soil)
Constituents sorbed to particles in the surface soil matrix of closed sites may be
translocated from the soil into edible plant tissues. Residents with home gardens and
subsistence farmers located on the closed site may be exposed to contaminated fruits and
vegetables, particularly if the produce is not sufficiently cooked.
The fate and transport component for this pathway is root uptake from soil. This fate
and transport process is calculated slightly differently for aboveground fruits and vegetables
and root vegetables.
Aboveground Fruits and Vegetables. The concentration of pollutant in plant tissue of
aboveground vegetables due to root uptake is determined from the soil concentration and the
plant-soil bioconcentration factor for a plant group. This approach is based on plant-soil
bioconcentration factors from Travis and Arms (1988) as presented in the Indirect Exposure
Methodology. The Travis and Arms plant-soil bioconcentration factor, Br, was used for all
constituents. In addition to the benefit of its being generalizable based on Kow for organics,
values for Br have also been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
Equation 6-68 presents the equation for backcalculating soil concentration from plant
concentration for aboveground fruits and vegetables.
Root Vegetables. The approach used in the Dioxin document (U.S. EPA, 1994a),
which was developed by Briggs (1982), was used in place of the Travis and Arms algorithm
for soil-to-belowground transfers to root vegetables. The Briggs approach uses a Root
Concentration Factor (RCF) to estimate plant concentrations instead of a plant-soil biotransfer
factor.
The Travis and Arms approach used for aboveground vegetables is an empirically
developed approach based on soil-to-aboveground plant transfers (e.g., translocation into
shoots), not soil-to-belowground transfers (e.g., translocation into roots and tubers), and may
therefore not be appropriate for belowground vegetables, such as root vegetables. A better
approach to vegetables for which roots are the edible portions, is to separate "aboveground"
and "belowground". vegetation, and state that belowground vegetation includes edible roots
such as carrots, potatoes, and radishes. This is the approach taken in the Dioxin document
(U.S. EPA, 1994a). It should be noted that concentrations of dioxin in carrots and potatoes
are among the highest found in vegetables/fruits.
August 1995 6-121
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (9)
The Briggs Root Concentration Factor is generalizable based on Kow for organics and
was used for all twganic constituents. However, RCFs have not been compiled for metals.
Therefore, the Travis and Arms plant-soil bioconcentration factor, Br, was used for metals
(see discussion above for aboveground vegetables).
The Dioxin document uses an empirical correction factor, VG^, to reflect the fact that
the barley roots of Briggs' experiments are different than bulky belowground vegetables such
as potatoes or onions.. Dioxin-like compounds will sorb to outer portions of belowground
vegetation, but inner translocation is negligible. Therefore, the concentrations in the barley
roots, for the lipophilic compounds used by Briggs in his experiments, would be higher on a
whole plant basis than concentrations that would result from soil-to-root transfers for bulkier
vegetation, due to the greater surface area to weight ratio of the barley roots compared to
bulkier vegetation. In other words, the whole barley root concentrations would be similar to
concentrations near the skin of a potato, but not a whole potato. The Dioxin document uses
an empirical reduction factor of 0.01, which was estimated using a surface area volume to
whole plant volume ratio for a carrot. A similar fix would not be appropriate for an RCF
developed for soluble compounds, which would have transpiration stream translocation and
more uniform vegetative concentrations.
Equation 6-69 shows the backcalculation for soil concentration from root Vegetable
concentration.
August 1995 6-122
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (9)
Crop Uptake from Soil; Soil Concentration— Aboveground Vegetables
(6-68)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Concentration in soil (mg/kg or ug/g)
Concentration in plant (pg/g DW)
Calculated
From Equations 5-56 and 5-59
Br
Plant-soil bioconcentration factor
(frig/g
Chemical-specific
6.7.6.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-123
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (9)
Crop Uptake from Soil: Soil Concentration—Belowground Vegetables
RCF'VGi
(6-69)
Parameter
Cioil
Cpiait
Kd
RCF
VG*
Definition
Concentration in soil (mg/kg or ug/g)
Concentration in plant (mg/kg DW or ug/g
DW)
Soil-water partition coefficient (L/kg)
Root concentration factor - ratio of
contaminant concentration in roots to
concentration in soil water
(mg/kg plant/mg/kg soil water)
Empirical correction factor for lipophilic
contaminants (unitless)
Central
tendency value High-end
value
Calculated
From Equations 5-56 and 5-59
Chemical-specific
Chemical-specific
0.01 (lipophilics)
1 (solubles)
Refer to
6.7.6.1
6.7.6.2
6.7.4.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-124
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (9)
6.6.1.2.4 Pathway 9 (Off Site): Digestion -» Plant -* Soil -> Overland -> WMU
Constituents sorted to particles in the surface soil or waste matrix may be transported
over the ground to other locations via soil erosion. Constituents may then be translocated
from the soil into edible plant tissues. Residents with home gardens and subsistence farmers
located near a WMU may be exposed to contaminated fruits and vegetables, particularly if the
produce is not sufficiently cooked.
The fate and transport components for this pathway are root uptake from soil and soil
erosion from the WMU to the off-site field where plants are located. The soil erosion
component is discussed here, but the equations for it are presented in Section 7, because the
calculations are WMU-specific.
Root Uptake. Root uptake is calculated slightly differently for aboveground fruits and
vegetables and root vegetables.
Aboveground Fruits and Vegetables. The concentration of pollutant in plant tissue of
aboveground vegetables due to root uptake is determined from the soil concentration and the
plant-soil bioconcentration factor for a plant group. This approach is based on plant-soil
bioconcentration factors from Travis and Arms (1988), as presented in the Indirect Exposure
Methodology. The Travis and Arms plant-soil bioconcentration factor, Br, was used for all
constituents. In addition to the benefit of its being generalizable based on Kow for organics,
values for Br have also been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
Root Vegetables. The approach used in the Dioxin document (U.S. EPA, 1994a),
which was developed by Briggs (1982), was used in place of the Travis and Arms algorithm
for soil-to-belowground transfers to root vegetables. The Briggs approach uses a Root
Concentration Factor (RCF) to estimate plant concentrations instead of a plant-soil biotransfer
factor.
The Travis and Arms approach used for aboveground vegetables is an empirically
developed approach based on soil-to-aboveground plant transfers (e.g., translocation into
shoots), not soil-to-belowground transfers (e.g., translocation into roots and tubers), and may
therefore not be appropriate for belowground vegetables, such as root vegetables. A better
approach to vegetables for which roots are the edible portions is to separate "aboveground"
and "belowground" vegetation and state that telowground vegetation includes edible roots
such as carrots, potatoes, and radishes. This is the approach taken in the Dioxin document
August 1995 .6-125
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (9)
(U.S. EPAi 1994a). It should be noted that concentrations of dioxin in carrots and potatoes
are among the highest found in vegetables/fruits.
The Briggs Root Concentration Factor is generalizable based on Kow for organics arid
was used for all organic constituents. However, RCFs have not been compiled for metals.
Therefore, the Travis and Arms plant-soil bioconcentration factor, Br, was used for metals
(see discussion above for aboveground vegetables).
The Dioxin document uses an empirical correction factor, VGbg, to reflect the fact that
the barley roots of Briggs' experiments are different than bulky belowground vegetables such
as potatoes or onions. Dioxin-like compounds will sorb to outer portions of belowground
vegetation, but inner translocation is negligible. Therefore, the concentrations in the barley
roots, for the lipophilic compounds used by Briggs in his experiments, would be higher on a
whole plant basis than concentrations that would result from soil-to-root transfers for bulkier
vegetation, due to the greater surface area to weight ratio of the barley roots compared to
bulkier vegetation. In other words, the whole barley root concentrations would be similar to
concentrations near the skin of a potato, but not a whole potato. The Dioxin document uses
an empirical reduction factor of 0.01, which was estimated using a surface area volume to
whole plant volume ratio for a carrot. A similar fix would not be appropriate for an RCF
developed for soluble compounds, which would have transpiration stream translocation and
more uniform vegetative concentrations.
Soil Erosion. Contaminants sorbed to surface soil particles may be transported off site
through the process of soil erosion. The amount of contaminant transported to an off-site
field depends on the amount of soil loss from the site (a function of area and unit soil loss),
which quantifies the amount of soil eroded from the site; the sediment delivery ratio, which
accounts for soil that is redeposited before reaching the off-site field; and an enrichment ratio,
which refers to the fact that erosion favors the lighter soil particles, which have higher surface
area to volume ratios and are higher in organic matter content. Therefore, concentrations of
organic contaminants, which are a function of organic carbon content of sorbing media, would
be expected to be higher in eroded soil as compared to in situ soil.
Soil erosion from a WMU to an off-site field is not covered in the Indirect Exposure
Methodology, because the IEM was developed for combustors. However, the process is
essentially similar to deposition from air, except that contaminants plus soil are deposited by
soil erosion. The amount of soil eroded is negligible compared to the mass of soil already in
the field. The deposition rate from soil erosion may be backcalculated in the same manner as
deposition from air, and the concentration at the WMU may then be backcalculated from the
deposition rate of pollutant and the amount of soil eroded. These two steps were combined
into a single equation.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
August 1995 6-126
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (9)
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived 4rem data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
•
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
Equations 6-70 and 6-71 present the equations for backcalculating soil concentration
from plant concentration for aboveground fruits and vegetables and root vegetables,
respectively. The equations for backcalculating WMU concentration from soil concentration
due to erosion are covered in Section 7 since they are WMU-specific!
August 1995 6-127
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (9)
Crop Uptake from Soil: Soil Concentration—Aboveground Vegetables
'soil'
c
_ *~plant
Br
(6-70)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
c*,
Concentration in soil (rag/kg or ug/g)
Calculated
Concentration in plant (ug/g DW)
1 From Equations 5-56 and 5-59
Br
Plant-soil bioconcentration factor
([ug/g DW]/[ug/g])
Chemical-specific
6.7.62
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (9)
Crop Uptake from Soil: Soil Concentration—Belowground Vegetables
csoir
RCF'VG,,
(6-71)
Parameter
C.OU
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
6.6.1.3 Uncertainty
6.6.1.3.1 Biotransfer Factors
The correctness of the biotransfer factors for plant uptake are highly uncertain. The
factors are based on empirical relationships with Kow defined by studies on a relatively few
chemicals. Further, it is not clear to what extent study conditions mimic actual field condi-
tions. Using a regression equation on Kow is almost certainly an oversimplification that may
result in overestimate of a chemical's tendency to bioaccumulate.
6.6.1.32 Washing/Cooking of Vegetables
It is assumed that fruits and vegetables are not thoroughly washed or cooked. Failure
to wash vegetables would result in exposure to contaminants adhering to the surface that
might be washed off if the vegetable were washed. However, contaminant deposited on fruits
and vegetables may be taken up into the fruit or vegetable, so that washing would have little
beneficial effect. Cooking might cause transformations of contaminants into either more or
less toxic forms.
6.6.1.3J Universal Soil Loss Equation
Uncertainty arises out of the use of the Universal Soil Loss Equation. This is an
empirical, though widely used, model. It was intended for use in site-specific situations,
where highly specific input data can be used, and for relatively small fields. How well it
predicts soil erosion in a generic application, as here, and for fairly large sources of eroded
soil, is uncertain. It is most likely that it overestimates quantity of soil eroded.
6.6.1.3.4 Surface Water Modeling Framework
The surface water modeling framework presented in the Addendum (U.S. EPA, 1993a)
and used here is a new model that has not been peer-reviewed. Therefore, there is uncer-
tainty as to how well it represents actual surface water fate and transport processes. Most of
the existing peer-reviewed surface water models in use at EPA, such as WASP and EXAMS,
are so highly site-specific that they could not be feasibly adapted to a generic analysis such as
this. It is uncertain whether use of this model would overestimate or underestimate risk.
While the surface water model framework is designed to accomodate chemical trans-
formations within the water body, these were omitted from the analysis. These processes are
highly chemical- and site-specific. Assessing the potential for transformation of all 200
chemicals considered would be an extensive research project. However, chemicals were
screened to eliminate chemicals that hydrolyze completely in water, forming other com-
pounds. The effect of omitting such transformations could be either an overestimate or
August 1995 6-130
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
underestimate of the risk, depending on whether a chemical transforms into a more or less
toxic or mobile form.
6.6.1.3.5 Soil Loss Constant Term
The overall soil loss constant term, ks, is uncertain in several ways. This term is the
sum of loss rates for leaching, degradation, and volatilization. One uncertainty arises from
the assumption that all of these loss terms are first order and can therefore be added together.
This is a common assumption, but some of the processes may, in fact, be zero order. A first
order loss process may be characterized by a half-life, the time it takes half of the remaining
contaminant to be lost Therefore, the mass lost per unit of time varies with the
concentration. A zero order loss process is characterized by a constant mass loss per unit of
time. Neither of these processes can be said to be more conservative than the other, because
the first order rate depends on the starting concentration and the zero order rate does not, at
any given time, which one results in a higher concentration will depend on the starting
concentration. Therefore, it cannot be said whether incorrectly assuming that loss constant
that is actually zero order is first order will overestimate or underestimate soil concentration!
Another source of uncertainty regarding the soil loss constant is that the various loss
processes are calculated independently when, in fact, they occur simultaneously. As a result,
losses could be overpredicted because the amount of contaminant available to each process is
overestimated by not accounting for the other loss processes. This would result in an
underestimate of soil concentration.
Finally, degradation losses were set to zero. Degradation rates are highly dependent on
site-specific factors that cannot be accounted for in a generic analysis of this nature and may
be zero. To the extent that constituents do degrade into constituents of less concern, the
omission of degradation from the soil loss constant will underestimate losses and therefore
overestimate soil concentration.
The overall effect of all of the above uncertainties on the soil loss constant is not clear.
One of the factors would tend to underestimate soil concentration, one would tend to over-
estimate soil concentration, and the effect of one could be either an over- or underestimate of
soil concentration.
6.6.1.3.6 Soil Water Content Equation
The equation from the Superfund Exposure Assessment Manual (U.S. EPA, 1988a) used
to calculate soil water content based on recharge (the net effect of precipitation, irrigation,
evaoration, and runoff) and soil properties was developed for site-specific application. Its
application in a generic analysis raises uncertainty as to how well it predicts soil water
content A distribution of this value would have been preferred; however, it was not available
and so had to be calculated. However, some of the input parameters are highly generalized
(such as recharge) and others (such as the soil moisture retention exponent b) are drawn from
August 1995 6-131
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
estimates rather than measured values. It is not clear in which direction this uncertainty
would affect the results.
6.6.1.3.7 Translocation of Contaminants within Plants
The plant uptake models do not account for translocation of contaminants from one part
of a plant to another. In particular, deposition and direct uptake from air are not considered
for root vegetables, because it is not known if contaminants would translocate from the
aboveground portions of the plant (where deposition and direct uptake from air would occur)
to the edible, belowground portions of the plant To the extent that such translocation does
occur, the framework used will underestimate concentrations in root vegetables. However,
use of the same approach as for aboveground fruits and vegetables (including deposition and
direct uptake from air) would probably severely overestimate the concentration in the root
portion of the plant The possible underestimate was considered a smaller uncertainty than
such an overestimate.
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6.6 Food Chain Pathways
6.6.2 Animal Pathways
Figures 6-7 and 6-8 provide an overview of the fate and transport for animal pathways.
Figure 6-7 shows animal pathways involving air and soil transport mechanisms. Figure 6-8
shows animal pathways involving water fate and transport mechanisms.
6.6J.I Scenarios
6.6.2.1.1 Human
Human exposure scenarios for animal products include ingestion of beef and milk.
Other animal products such as poultry, eggs, and pork were not included. Contaminants that
bioaccumulate in the food chain tend to be lipophilic and accumulate in fat in the animal.
Beef and milk are higher in lipid content than poultry or eggs, so that relatively more
contaminant willl bioaccumulate in beef and milk than in poultry or eggs. Pork is high in
lipid content, but pigs do not graze, and thus do not ingest contaminated soil while grazing.
Therefore, pigs would tend to be exposed to less contaminant than cattle, which do graze.
Concentration in Animal Tissue
Air Concentration
of Volatiles
Figure 6-7. Fate and transport for beef and milk pathways
involving air and soil.
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6.6 Food Chain Pathways
Concentration in Animal Tissue
Bioconcentration
Water Concentration
Surface Water
Concentration
Volatile
Emissions
Overland Flow/
Soil Erosion
Deposition to
Watershed
Waste Concentration
Figure 6-8. Fate and transport for beef and milk pathways involving water.
Beef and dairy cattle are exposed to contaminants'through forage grown at the fenceline
(for active units) or on site (for closed units), through soil ingested while grazing, and through
contaminated surface water used as a cattle water source. Beef and dairy cattle may also
consume grain or silage or other feed materials in addition to forage. However, forage
typically makes up 65 to 75 percent of beef and dairy cattle diet, making it the largest
potential source of exposure. In addition, grain and silage (often com or grain) are protected
from airborne contaminants and would only be contaminated through soil transport
mechanisms. Therefore, grain and silage arc not considered. Exposure to cattle via
inhalation of contaminated air was also not considered; no data on bio transfer from air to
animal tissue are currently available.
Table 6-8 summarizes the receptors modeled for the animal pathways. The receptor
selected for the animal product pathways is a subsistence farmer who raises both beef and
dairy cattle, and consumes beef and milk from them. The general population does not
typically raise cattle for beef and milk; therefore, no general population receptor is considered
for these pathways.
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Table 6-8. Summary of Receptors for Animal Pathways
Receptor
Adult Child Subsistence Home Subsistence Fish
Pathway resident resident farmer gardener fisher consumer Worker
10: Air deposition- /
beef/milk ingestion
lOa; Direct air- /
beef/milk
ingestion
11: Direct soil-
beef/milk
ingestion (on site)
11: Overland-beef/milk
ingestion (off site)
33: Air diffusion (SW>
beef/milk ingestion
35: Overland (SW>
beef/milk ingestion
'
S
s
36: Air deposition
(OF/SW)-beef/milk
ingestion
Closed land application unit only.
6.6.2.1.2 Ecological Receptors
The food chain exposure scenarios for ecological receptors in the generic terrestrial
ecosystem are described in Section 6:3.1.2.
6.6.2.2 Pathway Algorithms
The calculations for beef and milk differ only in the value of the biotransfer factor used
to estimate beef or milk concentration from plant or soil concentration.
The following sections describe the animal pathways and present the fate and transport
equations for them. These pathways are:
• Pathway 10: ingestion —» animal —» plant —» soil —> deposition —> air —> WMU
(Section 6.6.2.2.1)
• Pathway lOa: ingestion —» animal —» plant —> plant —> air —» WMU
(Section 6.6.2.2.2)
• Pathway 11 (on site): ingestion —» animal —» plant -» WMU (soil)
(Section 6.6.2.2.3)
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
• Pathway 11 (off site): ingestion —> animal -» plant —> soil —> overland -> WMU
(Section-6.6.2.2.4)
• Pathway 33: ingestion —» animal —> surface water -» air —> WMU
(Section 6.6.2.2.5)
• Pathway 35: ingestion -» animal -> surface water -> overland -> WMU
(Section 6.6.2.2.6)
• Pathway 36: ingestion -» animal -> surface water -> overland -> deposition -> air
-> WMU (Section 6.6.2.2.7).
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
6.6 J.2.1 Pathway 10: Ingestion -* Animal -> Plant -> Soil -» Deposition -» Air
WMU- -
Constituents sorted to particles in the surface soil or waste matrix may be entrained
into the air from contaminated surface soils. Airborne particulates may deposit on surface
soils and plants via deposition mechanisms (e.g., settling, dry deposition). Constituents
deposited on soils may then be translocated from the soil into edible plant tissues. Livestock
that graze on contaminated pastures may be exposed to constituents that have been
translocated into plant tissue or deposited/adhered to the exterior plant tissue and to
constituents in soil. Subsistence farmers in the proximity of a WMU may be exposed through
the ingestion of contaminated beef or milk.
This pathway includes two concurrent mechanisms of plant uptake: deposition directly
to the plant, and deposition to soil, followed by root uptake by the plant Four fate and
transport components are needed: cattle ingestion of forage and soil, root uptake from soil,
deposition to soil, and deposition to plant. Each of these is discussed in the following
paragraphs.
Cattle Ingestion of Forage and Soil. The food chain model calculates the
concentration of pollutant in animal tissues by considering the concentration of pollutant in
plants and soil, the quantity of plants and soil that animals consume, and the biotransfer factor
for each type of animal tissue. A somewhat different model is used for dioxin-like
compounds, which tend to bioaccumulate in lipid material (i.e., fat). The general model is
from the Indirect Exposure Methodology; the dioxin-like compound model is from the Dioxin
document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow. The Dioxin document (U.S. EPA, 1994a) uses a bioconcentration factor,
which takes the ratio of the concentration of contaminant in cattle dry matter intake (mg/kg)
and translates it to a concentration in cattle body and milk fat (mg/kg lipid based
concentration). It is interesting to note that the dioxin document approach (developed by
Fries and Paustenbach) estimates similar 2,3,7,8-TCDD whole milk and whole beef
concentrations as those estimated using the Travis and Arms approach.
August 1995 6-137
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
The Travis and Arms biotransfer factor, Ba, was used for all constituents except dioxin-
like compounds._ In addition to the benefit of its being generalizable based on K^ for
organics, values for Ba have also been compiled for metals in U.S. EPA (1992e) and Baes et
al. (1984). For dioxin-like compounds, a bioconcentration factor from the Dioxin document
(U.S. EPA, 1994a) was used instead.
Some plants ingested by animals may not be contaminated. This calls for an additional
adjustment factor, F, which is defined as the fraction of the plant group eaten by the animal
which is grown on contaminated soil. The implicit assumption without this factor is that this
value is 1. A value less than 1 might be called for if cattle feed were purchased by the
farmer from a local distributor who gets it from a distant location. This factor is included in
the algorithms. •*
Root Uptake. The concentration of pollutant in plant tissue of aboveground vegetables
due to root uptake is determined from the soil concentration and the plant-soil bioconcentra-
tion factor for a plant group. This approach is based on plant-soil bioconcentration factors
from Travis and Arms (1988), as presented in the Indirect Exposure Methodology. The
Travis and Arms plant-soil bioconcentration factor, Br, was used for all constituents. In
addition to the benefit of its being generalizable based on Kow for organics, values for Br
have also been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
Deposition to Soil. The cumulative soil concentration of a pollutant as a result of
deposition is derived from the dry. deposition rate-over the time period of deposition and the
contaminant loss rate from the soil. The cumulative soil concentration represents the
concentration increment due to accumulation of contaminant deposited onto soil from one of
the WMUs. The cumulative soil concentration does not take into account background
concentrations of the contaminant that may already be present, whether natural or from other
pollution sources. The algorithms for deposition to soil are from the Indirect Exposure
Methodology.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, kj, is the sum of the loss rates for each of these processes.
Losses due to degradation (k3 ) are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k^, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
August 1995 6-138
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
affects particle-phase contaminants, rather than vapor-phase contaminants). If such
redeposition occurred, the soil concentration would be higher than if such redeposition did not
occur. As a result, the algorithm as used (without redeposition) may underestimate soil
concentrations for compounds that would volatilize then dissolve in rainwater and be
redeposited; however, the revolatilization of semivolatile organic contaminants such as dioxin
that have been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by ah equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a field, a small area within a
watershed; therefore, the soil loss constant used does not include a surface runoff loss
constant or a soil erosion loss constant The USLE is used to estimate unit erosion loss.
Deposition to Plant. Pollutants are deposited on exposed plant surfaces and soil by
deposition. Questions exist as to whether pollutants accumulated by direct deposition to plant
surfaces remain on the plant surface or are internalized by plants. In addition, the degree to
which pollutants are transported between plant organs through the vascular system is
uncertain. Thus, uptake via direct deposition was calculated for aboveground fruits and
vegetables but not root vegetables (which are protected) since the edible portion of the latter
are not in direct contact with the air. The algorithms for deposition to plant are from the
Indirect Exposure Methodology.
The cattle ingestion mechanisms (ingestion of forage and ingestion of soil) and the two
plant uptake mechanisms (deposition to plant and deposition to soil followed by root uptake)
must be combined so that the deposition rate for soil is the same as the deposition rate to
plants. Equation 6-72 shows the backcalculation for deposition rate from animal product
concentration. The first term in the denominator of this equation accounts for deposition to
soil followed by root uptake and ingestion of forage; the second term in the denominator
accounts for deposition to and ingestion of forage, and the third term in the denominator
accounts for deposition to and ingestion of the soil.- Equation 6-73 presents the modified
equation for dioxin-like compounds. Equations 6-74 through 6-81 present the equations for
calculating the soil loss constant, k^, which is used in Equations 6-72 and 6-73.
August 1995 6-139
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (10)
Deposition Rate (Crop Uptake from Deposition—Animal Ingestion)
g'g
Z'BD'k
»<•*,
Z'BD'k
(6-72)
The above equation was modified slightly for dioxins and PCBs, which tend to
bioaccumulate in lipid material (i.e., fat). (Dioxin document, U.S. EPA, 1992c)
F'DF,'
— Pn fl "V
Z'BD'k.
F'DF,'Bt'[l-t
Z'BD'k -
(6-73)
Parameter
°y
C«unaJ
Ba
B>i
k,
t
Z
BD
*»
kp
Yft
Definition
Average annual combined deposition rate
(g/m2/yr)
Concentration in animal product (ug/g)
Biotransfer factor for animal product (d/kg)
Soil-plant bioconcentration factor for
forage/hay ([ug/g DW]/[ug/g soil])
Soil loss constant (yr'1)
Time period of deposition (yr)
Soil mixing depth (cm)
Soil bulk density (g/cm3)
Plant interception fraction for forage/hay
(unitless)
Plant weathering loss coefficient (yr'1)
Crop yield for forage/hay (kg DW/m2)
Central
tendency High-end
value value
Calculated
From Equation
5-62
Chemical-specific
Chemical-specific
Refer to
6.7.6.2
6.7.6.2
See Equation 6-74
20
2.5 (untilled) 1
1.5
0.5
18
0.24
40
(untilled)
1.2
6.7.3.3
6.7.3.3
6.7.3.1
6.7.4.1
6.7.4.1
6.7.4.1
(continued)
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (10)
Parameter
QPi
F;
Qs
Cf«
F
DF;
B,
DF,
Definition
Quantity of forage eaten by animal (kg
DW/d)
Fraction of forage grown in contaminated
area (unitless)
Quantity of soil eaten by animal (kg/d)
Concentration in animal fat (ug/g)
Plant-animal biocohcentration factor
determined from cattle vegetative intake
(unitless)
Diet fraction that is forage (unitless)
Bioavailability of contaminant in soil vs.
vegetation (unitless)
Diet fraction that is soil (unitless)
Central
tendency High-end
value value Refer to
8.8 (beef) 6.7.4.2
13.2 (milk)
1 6.7.4.2
0.5 (beef) 6.7.4.2
0.4 (milk)
From Equation 5-63
Chemical-specific 6.7.6.2
0.75 (beef) • 6.7.4.2
0.65 (milk)
0.65 6.7.4J2
0.04 (beef) 6.7.4.2
0.02 (milk)
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
Soil Loss Constant
Parameter Definition
k, Soil loss constant (yr'1)
— If . + k +k
r **/ *jg *jv
Central
tendency High-end
value value
Calculated
(6-74)
Refer to
k,, Soil loss constant due to leaching (yr'1) See Equation 6-75
k, Soil loss constant due to degradation (yr'1) 0 6.7.6.1
kp, Soil loss constant due to volatilization (yr'1) See Equation 6-77
Source: EM (U.S. EPA, 1990e; 1993a).
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (10)
Soil Loss Constant Due to Leaching
e.z.
i*
flD.fl
e
(6-75)
Parameter
k^
Definition
Soil loss constant due to leaching (yr*1)
Central
tendency
value
High-end
value Refer to
Calculated
Average annual recharge (cm/yr)
WMU-specific
e
z
BD
*d
Soil volumetric water content (mL/cm3)
Soil depth from which leaching occurs (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
See Equation 6-76
2.5 (untilled) 1 (untilled)
1.5 12
Chemical-specific
6.7.3.3
6.7.3.1
6.7.6.1
Source: EEM (U.S. EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
Soil Volumetric Water Content
(6-76)
Parameter
e
Definition
Soil Volumetric water content (mL/cm3)
Central ,
tendency High-end
value value Refer to
Calculated
6, Soil saturated volumetric water content 0.43 ' 0.55 6.7.3.1
(mL/cm3)
q Average annual recharge rate (cm/yr) WMU-specific
K, Saturated hydraulic conductivity (cm/yr) 3,600 20,000 6.7.3.1
b Soil-specific exponent representing water 5.4 3.0 6.7.3.1
retention (unitless)
Source: SEAM (U.S. EPA, 1988a).
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6.6 Food Chain Pathways (10)
Soil Loss Constant Due to Volatilization
(6-77)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Soil loss constant due to volatilization (yr*1)
Calculated
Equilibrium coefficient (s/cm-yr)
.Gas-phase mass transfer coefficient (cm/s)
See Equation 6-78
See Equation 6-79
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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6.6 Food Chain Pathways (10)
Volatilization Equilibrium Coefficient
K =3.1536»107ly/y
Z;Kd*R
Parameter Definition
Ke Equilibrium coefficient (s/cm-yr)
H Henry's law constant (atm-m3/mol)
Z Soil depth from which volatilization occurs
(cm)
Kd Soil water partition coefficient (mL/g)
R Ideal gas constant (atm-L/mol-K)
T Temperature (K)
BD Soil bulk density (g/cm3)
r.l03I/m3»//
•T»BD
Central
tendency High-end
value value
Calculated
Chemical-specific
2.5 (unfilled) 1 (unfilled)
Chemical-specific
8.21 x 10'5
298
1.5 1.2
(6-78)
Refer to
6.7.6.1
6.7.3.3
6.7.6.1
6.7.7
6.7.2.2
6.7.3.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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Gas-Phase Mass Transfer Coefficient
(6-79)
Parameter
*t
u
Sc0
de
Definition
Gas-phase mass transfer coefficient (cm/s)
Windspeed (m/s)
Schmidt number on gas side (unitless)
Effective diameter of contaminated area (m)
Central
tendency High-end
value value Refer to
Calculated
WMU-specific
See Equation 6-80
See Equation 6-81
Source: EM (U.S. EPA, 1990e; 1993a).
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (10)
Schmidt Number on Gas Side
(6-80)
Central
tendency High-end
Parameter Definition value value Refer to
ScG Schmidt number on gas side (unitless) Calculated
u. Viscosity of air (g/cm-s) 1.81e-4 6.7.7
pt Density of air (g/cm3) 1.2e-3 6.7.7
Dt Diffusivity in air (cm2/s) Chemical-specific 6.7.6.1
Source: EEM (U.S. EPA, 1990e; 1993a).
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6.6 Food Chain Pathways (10)
Effective Diameter
—.
71
(6-81)
Parameter
Definition
Central
tendency
value
High-end
value '
Refer to
Effective diameter of
contaminated area (m)
Calculated
Area of contaminated area
(m2)
2,000.000 (field) 300,000 (field) 6,7.3.3
Source: EM (U.S. EPA, 1990e; 1993a).
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (lOa)
6.62.22 Pathway lOa: Ingestion -» Animal -» Plant -» Air -» WMU
JL
Constituents may volatilize from contaminated soils or wastes in land application units,
wastepiles, surface impoundments, or tanks. Constituents in the vapor phase can be
translocated into plant tissue during normal plant respiration. Livestock that graze on
contaminated pastures may be exposed to constituents that have been translocated into plant
tissue. Subsistence farmers in the proximity of a WMU may be exposed through the
ingestion of contaminated beef or milk.
The fate and transport components of this pathway are cattle ingestion of forage, direct
uptake of contaminant from air by plants, and air dispersion from the WMU to the plant
location (which is covered in Section 7).
Cattle Ingestion of Forage. The food chain model calculates the concentration of
pollutant in animal tissues by considering the concentration of pollutant in plants, the quantity
of plants that animals consume, and the biotransfer factor for each type of animal tissue. A
somewhat different model is used for dioxin-like compounds, which tend to bioaccumulate in
lipid material (i.e., fat). The general model is from the Indirect Exposure Methodology; the
dioxin-like compound model is from the Dioxin document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow. The Dioxin document (U.S. EPA, 1994a) uses a bioconcentration factor,
which takes the ratio of the concentration of contaminant in cattle dry matter intake (mg/kg)
and translates it to a concentration in cattle body and milk fat (mg/kg lipid based concentra-
tion). It is interesting to note that the dioxin document approach (developed by Fries and
Paustenbach) estimates similar 2,3,7,8-TCDD whole milk and whole beef concentrations as
those estimated using the Travis and Arms approach.
The Travis and Arms biotransfer factor, Ba, was used for all constituents except dioxin-
like compounds. In addition to the benefit of its being generalizable based on K,,w for
organics, values for Ba have also been compiled for metals in U.S. EPA (1992e) and Baes et
al. (1984). For dioxin-like compounds, a bioconcentration factor from the Dioxin document
(U.S. EPA, 1994a) was used instead.
August 1995 . , 6-150
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (lOa)
Some plants ingested by animals may not be contaminated. This calls for an additional
adjustment factor; F, which is defined as the fraction of the plant group eaten by the animal
which is grown on contaminated soil. The implicit assumption without this factor is that this
value is 1. A value less than 1 might be called for if cattle feed were purchased by the
fanner from a local distributor who gets it from a distant location. This factor is included in
the algorithms.
Plant Uptake from Air. Two parameters are necessary to estimate air-to-plant
transfer: the air-to-plant biotransfer factor and the atmospheric concentration of pollutant at
ground level. The latter includes only concentration of pollutant in the vapor-phase due to
emissions from contaminant sources. Consideration of concentration due to volatilization of
pollutant deposited on the soil would appear to be double-counting; therefore, it was not
included. This concentration is likely to be negligible in any case. The algorithms for air-to-
plant uptake are from the Indirect Exposure Methodology.
The air-to-plant biotransfer factor is based on work by Bacci et al. (1990, 1992). Bacci
conducted laboratory experiments on the air-to-leaf transfer of vapors of 14 organics, using
azalea leaves and developed an empirical equation for a volumetric air-to-leaf biotransfer
factor. Bacci et al. (1990) also developed a conversion equation to convert the volumetric
transfer factor to a mass-based transfer factor, it is this mass-based transfer factor that is used
to determine plant uptake from an air concentration. Simonich and Hites (1994) have also
done experimental work to determine air-to-plant transfer factors for PAHs. These values
were used for PAHs instead of Bacci's correlation equation.
Bacci's work did not account for photodegradation of the chemicals from the leaf.
Experimental results presented by Macrady and Maggard (1993) suggest that the Bacci
algorithm may overpredict the air-to-plant biotransfer factor by a factor of forty for dioxin-
like compounds. The Dioxin document (U.S. EPA, 1994a) recommmends reducing the air-to-
plant biotransfer factor calculated by the Bacci algorithm by a factor of forty for dioxin-like
compounds. See Section 6.7.6.2.3 for a detailed discussion of how air-to-plant transfer factors
were calculated.
Equation 6-82 presents the equation for backcalculating air concentration from animal
concentration. Equation 6-83 presents the modified equation for dioxin-like compounds.
August 1995 6-151
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (lOa)
Animal Ingestion, Crop Uptake from Air: Air Concentration
c*-
animal Pa
(6-82)
The above equation was modified slightly for dioxins and PCBs, which tend to
bioaccumulate in lipid material (i.e., fat). (Dioxin document, U.S. EPA, 1992c)
r
(6-83)
Parameter
c*
C«iin
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
6.6.2.2 J Pathway 11 (On Site): Ingest ion -> AnimaJ -> Plant -» WMU (Soil)
Constituents sorbed to particles in the surface soil matrix of closed sites may be
translocated from the soil into edible plant tissues. Livestock that graze on contaminated
pastures may be exposed to constituents that have been translocated into plant tissue.
Subsistence farmers in the proximity of a WMU may be exposed through the ingestion of
contaminated beef or milk.
The fate and transport components for this pathway are cattle ingestion of forage and
soil and root uptake from soil.
Cattle Ingestion of Forage and Soil. The food chain model calculates the
concentration of pollutant in animal tissues by considering the concentration of pollutant in
plants and soil, the quantity of plants and soil that animals consume, and the biotransfer factor
for each type of animal tissue. A somewhat different model is used for dioxin-like
compounds, which tend to bioaccumulate in lipid material (i.e., fat). The general model is
from the Indirect Exposure Methodology; the dioxin-like compound model is from the Dioxin
document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow. The Dioxin document (U.S. EPA, 1994a) uses a bioconcentration factor,
which takes the ratio of the concentration of contaminant in cattle dry matter intake (mg/kg)
and translates it to a concentration in cattle body and milk fat (mg/kg lipid based
concentration). It is interesting to note that the dioxin document approach (developed by
Fries and Paustenbach) estimates similar 2,3,7,8-TCDD whole milk and whole beef
concentrations as those estimated using the Travis and Arms approach.
The Travis and Arms biotransfer factor, Ba; was used for all constituents except dioxin-
like compounds. In addition to the benefit of its being gencralizable based on Kow for
organics, values for Ba have also been compiled for metals in U.S. EPA (1992e) and Baes et
August 1995 6-153
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
al. (1984). For dioxin-like compounds, a bioconcentration factor from the Dioxin document
(U.S. EPA, 1994a)-was used instead.
Some plants ingested by animals may not be contaminated. This calls for an additional
adjustment factor, F, which is defined as the fraction of the plant group eaten by the animal
which is grown on contaminated soil. The implicit assumption without this factor is that this
value is 1. A value less than 1 might be called for if cattle feed were purchased by the
farmer from a local distributor who gets it from a distant location. This factor is included in
the algorithms.
Root Uptake. The concentration of pollutant in plant tissue of aboveground vegetables
due to root uptake is determined from the soil concentration and the plant-soil bioconcentra-
tion factor for a plant group. This approach is based on plant-soil bioconcentration factors
from Travis and Arms (1988) as presented in the Indirect Exposure Methodology. The Travis
and Arms plant-soil bioconcentration factor, Br, was used for all constituents. In addition to
the benefit of its being generalizable based on Kow for organics, values for Br have also been
compiled for metals in U.S. EPA (1992e) and Baes et al (1984).
Equation 6-84 presents the equation for backcalculating soil concentration from animal
product concentration. Equation 6-85 presents the modified equation for dioxin-like
compounds.
August 1995 6-154
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (11)
Soil Concentration (Crop Uptake from Soil—Animal Ingest ion)
animal
(6-84)
The above equation was modified slightly for dioxins and PCBs, which tend to
bioaccumulate in lipid material (i.e., fat). (Dioxin document, U.S. EPA, 1992c)
(6-85)
Parameter
CfOd
CWMB*!
Ba
Br(
QPi
F<
Qs
Q.,
Definition
Concentration in soil (ug/g)
Concentration in animal product (ug/g)
Biotransfer factor for animal product (d/kg)
Soil-plant bioconcentration factor for forage
i ([ug/g DW]/[ug/g soil])
Quantity of forage eaten by animal (kg
DW/d)
Fraction of forage grown in contaminated
area (unitless)
Quantity of soil eaten by animal (kg/d)
Concentration in animal fat (ug/g)
Central
tendency High-end
value value . Refer to
Calculated
From Equation 5-76
Chemical-specific 6.7.6.2
Chemical-specific 6.7.6.2
8.8 (beef) 6.7.4.2
13.2 (milk)
1 6.7.42
0.5 (beef) ' 6.7.42
0.4 (milk)
From Equation 5-63
Plant-animal bioconcentration factor
determined from cattle vegetative intake
(unitless)
Chemical-specific
6.7.6.2
Diet fraction that is forage (unitless)
0.75 (beef)
0.65 (milk)
6.7.42
6.7.4.2
B,
Bioa variability of contaminant in soil vs.
vegetation (unitless)
0.65
DF
Diet fraction that is soil (unitless)
0.04 (beef)
0.02 (milk)
6.7.4.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-155
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
6.6J.2.4 Pathway 11 (Off Site): Ingestion -» Animal -» Plant -> Soil -» Overland
WMU- -
Constituents sofbed to particles in the surface soil or waste matrix may be transported
over the ground to other locations via soil erosion. Constituents may then be translocated
from the soil into edible plant tissues. Livestock that graze on contaminated pastures may be
exposed to constituents that have been translocated into plant tissue. Subsistence farmers in
the proximity of a WMU may be exposed through the ingestion of contaminated beef or milk.
The fate and transport components for this pathway are cattle ingestion of forage and
soil, root uptake from soil, and soil erosion from the WMU to the off-site field where plants
are located. The soil erosion component is discussed here, but the equations for it are
presented in Section 7, because the calculations are WMU-specific.
Cattle Ingestion of Forage and Soil. The food chain model calculates the
concentration of pollutant in animal tissues by considering the concentration of pollutant in
plants and soil, the quantity of plants and soil that animals consume, and the biotransfer factor
for each type of animal tissue. A somewhat different model is used for dioxin-like
compounds, which tend to bioaccumulate in lipid material (i.e., fat). The general model is
from the Indirect Exposure Methodology; the dioxin-like compound model is from the Dioxin
document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow. The Dioxin document (U.S. EPA, 1994a) uses a bioconcentration factor,
which takes the ratio of the concentration of contaminant in cattle dry matter intake (mg/kg)
and translates it to a concentration in cattle body and milk fat (mg/kg lipid based
concentration). It is interesting to note that the dioxin document approach (developed by
Fries and Paustenbach) estimates similar 2,3,7,8-TCDD whole milk and whole beef concentra-
tions as those estimated using the Travis and Arms approach.
The Travis and Arms biotransfer factor, Ba, was used for all constituents except dioxin-
like compounds. In addition to the benefit of its being generalizable based on Kow for
organics, values for Ba have also been compiled for metals in U.S. EPA (1992e) and Baes et
August 1995 6-156
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
al. (1984). For dioxin-like compounds, a bioconcentration factor from the Dioxin document
(U.S. EPA, 1994a)-was used instead.
Some plants ingested by animals may not be contaminated. This calls for an additional
adjustment factor, F, which is defined as the fraction of the plant group eaten by the animal
which is grown on contaminated soil. The implicit assumption without this factor is that this
value is 1. A value less than 1 might be called for if cattle feed were purchased by the
farmer from,a local distributor who gets it from a distant location. This factor is included in
the algorithms.
Root Uptake. The concentration of pollutant in plant tissue of aboveground vegetables
due to root uptake is determined from the soil concentration and the plant-soil
bioconcentration factor for a plant group. This approach is based on plant-soil
bioconcentration factors from Travis and Arms (1988), as presented in the Indirect Exposure
Methodology.
Soil Erosion. Contaminants sorbed to surface soil particles may be transported off-site
through the process of soil erosion. The amount of contaminant transported to an off-site
field depends on the amount of soil loss from the site (a function of area and unit soil loss),
which quantifies the amount of soil eroded from the site; the sediment delivery ratio, which
accounts for soil that is redeposited before reaching the off-site field; and an enrichment ratio,
which refers to the fact that erosion favors the lighter soil particles, which have higher surface
area to volume ratios and are higher in organic matter content Therefore, concentrations of
organic contaminants, which are a function of organic carbon content of sorbing media, would
be expected to be higher in eroded soil as compared to in situ soil.
Soil erosion from a WMU to an off-site field is not covered in the Indirect Exposure
Methodology because the IEM was developed for combustors. However, the process is
essentially similar to deposition from air, except that contaminants plus soil are deposited by
soil erosion. The amount of soil eroded is negligible compared to the mass of soil already in
the field. The deposition rate from soil erosion may be backcalculated in the same manner as
deposition from air, and the concentration at the WMU may then be backcalculated from the
deposition rate of pollutant and the amount of soil eroded. These two steps were combined
into a single equation.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
August 1995 6-157
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the-direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
Equation 6-86 presents the equations for backcalculating soil concentration from animal
product concentration. Equation 6-87 presents the modified equation for dioxin-like
compounds. The equations for backcalculating waste concentration from soil concentration
due to erosion are covered in Section 7, since they are WMU-specific.
August 1995 6-158
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (11)
Soil Concentration (Crop Uptake from Soil—AnimaJ Ingestion)
_ ^animal
'soir — ; ; 7 (6-86)
'i'QPi'Fi
The above equation was modified slightly for dioxins and PCBs, which tend to
bioaccumuiate in lipid material (i.e., fat). (Dioxin document, U.S. EPA, 1992c)
Parameter
C«»i
C«m«l
Ba
Br,
QPi
F>
Qs
cr*
F
DFi
B,
DF,
Source: EM
Definitioa
Concentration in soil (ug/g)
Concentration in animal product (ug/g)
Biotransfer factor for animal product (d/kg)
Soil-plant bioconcentration factor for forage
i ([ug/g DW]/[ug/g soil])
Quantity of forage eaten by animal (kg
DW/d)
Fraction of forage grown in contaminated
area (unitless)
Quantity of soil eaten by animal (kg/d)
Concentration in animal fat (ug/g)
Plant-animal bioconcentration factor
determined from cattle vegetative intake
(unitless)
Diet fraction that is forage (unitless)
Bioavailability of contaminant in soil vs.
vegetation (unitless)
Diet fraction that is soil (unitless)
(U.S. EPA. 1990e; 1993a).
>,-,)]
Central
tendency High-end
value value
Calculated
From Equation 5-62
Chemical-specific
Chemical-specific
8.8 (beef)
132 (milk)
1 ,
0.5 (beef)
0.4 (milk)
From Equation 5-63
Chemical-specific
0.75 (beef)
0.65 (milk)
0.65
0.04 (beef)
0.02 (milk)
i.o-3/;
Refer to
6.7.6.2 •
6.7.6.2
6.7.4.2
6.7.42
6.7.42
6.7.6.2
6.7.42
6.7.4.2
6.7.4.2
August 1995 6-159
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (33)
6.6.2.2.5 Pathway 33: Ingestion -> Animal -> Surface Water -> Air -» WMU
Constituents may volatilize to the air from many of the WMUs. These vapor-phase
constituents may diffuse into surface water from air. Livestock that are given the
contaminated surface water may ingest constituents dissolved in the surface water.
Subsistence farmers in the proximity of a WMU may be exposed through the ingestion of
contaminated beef or milk.
The fate and transport components of this pathway are cattle ingestion of water and
diffusion from air to surface water. See Section 6.5.2 for an overview of the surface water
model used. Surface water used for watering cattle is assumed to be unflltered; therefore,
total water concentration (including contaminant both dissolved and sorbed to suspended
solids) is used.
Cattle Ingestion of Water. Animal ingestion of water was calculated separately, but is
based on the same model as cattle ingestion of forage and soil.
The food chain model calculates the concentration of pollutant in animal tissues by
considering the concentration of pollutant in plants and soil, the quantity of plants and soil
that animals consume, and the biotransfer factor for each type of animal tissue. A somewhat
different model is used for dioxin-like compounds, which tend to bioaccumulate in lipid
material (i.e., fat). The general model is from the Indirect Exposure Methodology; the dioxin-
like compound model is from the Dioxin document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow.
The Travis and Arms biotransfer factor, Ba, was used for all constituents. In addition
to the benefit of its being generalizable based on Kow for organicsT values for Ba have also
been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
August 1995 6-160
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6,0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (33)
Diffusion from Air to Surface Water. The dissolved concentration in the waterbody
was assumed to reach equilibrium with a vapor phase concentration above the waterbody. At
equilibrium, gaseous diffusion into the waterbody is matched by volatilization out of the
waterbody. Gaseous diffusion is estimated with a transfer rate and a vapor phase air
concentration. The algorithms for air diffusion are from the Indirect Exposure Methodology.
Equation 6-88 presents the equation for backcalculating total water concentration from
animal product concentration. Equations 6-89 through 6-97 present the equations for
backcalculating air concentration over the waterbody from total surface water concentration.
August 1995 6-161
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Total Water Column Concentration (Animal Ingestion of Water)
'wt
, animal
Ba*Qw
(6-88)
Parameter
Definition
Central
tendency High-end
value value
Source: EM (U.S. EPA, 1990e; 1993a).
Refer to
c,*
C«MB«I
Ba
Qw
Total water column concentration (mg/L)
Concentration in animal tissue (mg/kg or
ug/g)
Biotransfer factor for animal tissue group
(d/kg)
Quantity of water ingested by animal (L/d)
Calculated
From Equation 5-62
Chemical-specific
50
6.7.6.2
• . 6.7.4.2
August 1995
6-162
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Air Concentration: from Total Water Column Concentration
(6-89)
Parameter
C
•If
C*.
H
vf.
.t~.
Definition
Concentration in air (ug/m3)
Total water column concentration (mg/L)
Henry's law constant (atm-m3/mol)
Waterbody flow volume (L/yr)
Fraction of total waterbody
contamination in water column (unitless)
..o-W/« ',
Central
tendency High-end
value value
Calculated
From Equation 6-88
Chemical-specific
3e+U 1.3e+10 .
See Equation 6-97
Refer to
6.7.6.1
6.7.5.1
Overall total water concentration
dissipation rate (yf1)
See Equation 6-90
V
KV
R
T
WAW
d.
"•
Flow-independent mixing volume (L)
Overall transfer rate (m/yr)
Universal gas constant (atm-m3/mol-K)
Waterbody temperature (K)
Waterbody surface area (m2)
Depth of water column (m)
Total depth of waterbody (water column
and sediment) (m)
6.7e+8
See Equation
821e-5
298
le+6
0.64
0.67
8.3e46
6-94
4.6e>4
0.15
0.18
6.7.5.1
6.7.7
6.7.5.2
6.7.5.1
6.7.5.1
6.7.5.1
Source: DEM (U.S. EPA, 1990e; 1993a).
August 1995
6-163
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Parameter
*,.
^
k.
-------
6.0 FATE AND TRANSPORT MODEUNG
6.6 Food Chain Pathways (33)
Rate of Burial
Xe • WAL • SZ>« 103 g/kg - VFX • TSS • 1(T3 s/m$ • 103L/ro3
Parameter
X
xe
WA,.
SD
vf,
TSS
WA.
BS
Pefinitkm
Rate of burial (m/yr)
Unit soil loss (kg/m2/yr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Total suspended solids (mg/L)
Waterbody surface area (m2)
Bed sediment concentration (kg sediment/L)
Central
tendency High<«nd
value value
Calculated
See Equation 6-92
lJe+9 6e+7
See Equation 6-93
3e+8 1.3e+7
10 80
le+6 4.6e-f4
1
Refer to
6.7.5.1
6.7.5.1
6.7.5.2
6.7.5.1
6.7.5.2
Source: JEM (U.S. EPA, 1990e; 1993a).
August 1995
6-165
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Universal Soil Loss Equation
Xe =/? •K«LS»C»/>«907.18 kg/ton • 245.7 acre/km • 10"6 km 2/m
2 "6 2 2
(6-92)
Parameter
Definition
Source: EM (U.S. EPA, 1990e; 1993a).
Central
tendency High-end
value value
Refer to
xe
R
K
LS
C
P
Unit soil toss (kg/hi2/yr)
USLE rainfall factor (yr'1)
USLE credibility factor (ton/acre)
USLE. length-slope factor (unitless)
USLE cover factor (unitless)
USLE erosion control practice factor
(unitless)
Calculated
WMU-specific
0.25
1 3
0.1 0.5
1
6.7.3.2
6.7.3.2
6.7.3.2
6.7.3.2
August 1995
6-166
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Watershed: Sediment Delivery Ratio
(WAL)
-0.125
(6-93)
Parameter
Definition
Central
tendency High-end
value value
Refer to
SD
sediment delivery ratio (unitless)
Calculated
empirical intercept coefficient (unitless)
area of watershed (m2)
0.6
1.3e+9
12
6e+7.
6.7.3.2
6.7.5.1
Source: EM (U.S. EPA. 1990e; 1993a).
August 1995
6-167
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Diffusion Transfer Rate
1 - 1 l
Parameter
KV
KL
KG
H'
Kv KL h
Definition
Overall transfer rale (m/yr)
Liquid phase transfer coefficient (m/yr)
Gas phase transfer coefficient (m/yr)
. Unitless Henry's law constant
:c./r.
Central
tendency High-end
value value Refer to
Calculated
See Equation 6-95
36,500 6.7.5.2
Chemical-specific 6.7.6.1
Source: EM (U.S. EPA, 1990e: 1993a).
August 1995
6-168
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Liquid Phase Transfer Coefficient
•3.15»1075/>T
(6-95)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Liquid phase transfer coefficient (tn/yr)
Diffusivity in water (cmz/s)
Current velocity (m/s)
Chemical-specific
0.7 0.5
6.7.6.1
6.7.5.1
Waterbody depth (m)
0.67
0.18
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-169
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6.0 FATE AND TRANSPORT MODEUNG
6.6 Food Chain Pathways (33)
Dissolved Fraction
(6-96)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Dissolved fraction (unitless)
Suspended sediment/surface water
partition coefficient (L/kg)
Chemical-specific
6.7.6.1
TSS
Total suspended solids (mg/L)
10
80
6.7.5.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-170
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (33)
Fraction of Contaminant in Water Column
/,
water
(6-97)
Parameter
f._
"~
TSS
d,
d,
«b.
K^
BS
\
Deflnitioa
Fraction of total wateitody contaminantion
in water column (unitless)
Suspended sediment/surface water partition
coefficient (LAg)
Total suspended solids (mg/L)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Bed sediment porosity (unitless)
Bed sediment/sediment pore water partition
coefficient (LAg)
Bed sediment concentration (sediment/L)
Depth of bed sediments (m)
Central
tendency
value
CalcuL
High-cad
value
ated
. Chemical-specific
10
0.64
0.67
0.6
80
0.15
0.18
Chemical-specific
1
0.03
Refer to
6.7.6.1
6.7.5.2
6.7.5.1
6.7.5.1
6.7.5.2
6.7.6.1
6.7.52
6,7.5.1
Source: IBM.
August 1995
6-171
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (35)
6.6.2.2.6 Pathway 35: Ingestion -» Animal -> Surface Water -> Overland -> WMU
Constituents sorbed to particles in the surface soil or waste matrix may be transported
over the ground to surface water via soil erosion and runoff. Contaminants in surface
impoundments may spill to nearby surface waters. Livestock that are given the contaminated
surface water may ingest constituents dissolved in the surface water or sorbed to suspended
solids in the surface water. Subsistence farmers in the proximity of a WMU may be exposed
through the ingestion of contaminated beef or milk.
The fate and transport components of this pathway are cattle ingestion of water and
overland transport (soil erosion and runoff) to surface water. See Section 6.5.2 for an
overview of the surface water model used. Surface water used for irrigation is assumed to be
unfiltered; therefore, total water concentration (including contaminant both dissolved and
sorbed to suspended solids) is used.
Cattle Ingestion of Water. Animal ingestion of water was calculated separately, but is
based on the same model as cattle ingestion of forage and soil.
The food chain model calculates the concentration of pollutant in animal tissues by
considering the concentration of pollutant in plants and soil, the quantity of plants and soil
that animals consume, and the biotransfcr factor for each type of animal tissue. A somewhat
different model is used for dioxin-like compounds, which tend to bioaccumulate in lipid
material (i.e., fat). The general model is from the Indirect Exposure Methodology; the dioxin-
like compound model is from the Dioxin document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available K,,w.
The Travis and Arms biotransfer factor, Ba, was used for all constituents. In addition
to the benefit of its being generalizable based on Kow for organics, values for Ba have also
been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984).
August 1995 6-172
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (35)
Soil Erosion and Runoff. Contaminant dissolved in annual surface runoff was
estimated as a function of the contaminant dissolved in soil water and annual water runoff.
For soil erosion, a sorbed concentration of contaminant in soil, together with an annual soil
erosion estimate, a sediment delivery ratio, and an enrichment ratio, were used to describe the
delivery of contaminant to the waterbody via soil erosion.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and.cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
A sediment delivery ratio serves to reduce the total potential amount of soil erosion
(i.e., the total potential equals a unit erosion rate as in kg/m2 times a watershed area, in m2)
reaching the waterbody recognizing that most of the erosion from a watershed during a year
deposits prior to reaching the waterbody. The enrichment ratio recognizes the fact that soils
which erode tend to be lighter in texture, more abundant in surface area, and have higher
organic carbon. All these characteristics lead to concentrations in eroded soils which tend to
be higher in concentration as compared to in situ soils for many constituents.
Equation 6-98 presents the equation for backcalculating total water concentration from
animal product concentration. Equations 6-99 through 6-106 present the backcalculaoons for
backcalculating soil concentration from total surface water concentration for overland
transport
August 1995 6-173
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Total Water Column Concentration (Animal Ingestion of Water)
r
^animal
(6-98)
Parameter
Definition
Central
tendency High-end
value value
Source: EM (U.S. EPA. 1990e; 1993a).
Refer to
C*,
C«i**i
Ba
Qw
Total water column concentration (mg/L)
Concentration in animal tissue (mg/kg or
ug/g)
Biotransfer factor for animal tissue group
(d/kg)
Quantity of water ingested by animal (L/d)
Calcufoted
From Equation 5-62
Chemical-specific
50
6.7.62
6.7.4.2
August 1995
6-174
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Soil Concentration: from Total Water Column Concentration
r •=
J w<
Parameter
C,«i
c.,
vf.
^wt \vJx9Jwater+Kwt'yr
A Rn /y ?r> FP K/i irr
*,
Defuiition
Concentration in soil (mg/kg)
* * • / . H- (fi.QQ)
•V/L+fy-lO^ro/c/n) di
Central
tendency High-cod
value value Refer to
Calculated
. Total water column concentration (mg/L) From Equation 6-98
Waterbody flow volume (L/yr)
3e-(-ll 1.3e+10 6.7.5.1
fwMcr Fraction of total waterbody contamination in See Equation 6-106
water column (unitless)
k^, Overall total water concentration dissipation See Equation 6-100
rate(yr-')
V
8.
Kd,
BD
A
*e
SD
ER
Rf
d.
Flow-independent mixing volume (L)
6.7e+8 8.3e4$ 6.7.5.1
Soil volumetric water content (unitless) See Equation 6-104
Soil-water partition coefficient (cmVg) Chemical-specific 6.7.6.1
Soil bulk density (g/cm3)
WMU area (m2)
Unit soil loss (kg/m2/yr)
Site sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yr)
Depth of water column (m)
1.5 1^ 6.7.3.1
WMU-specific
See Equation 6-102
See Equation 6-105
3 organics 6.7.3.2
1 metals
25 (Portland) 22 (Atlanta) 6.7.2.2
0.64 0.15 6.7.5.1
dz Total depth of waterbody (water column and 0.67 0.18 6.7.5.1
sediment) (m)
Source: EM (U.S. EPA, 199Cfe; 1993a).
August 1995
6-175
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Water Concentration
/
Ir =1-.= *bs+BS'Kdb.
1 +K/i • 7"^'
V
Parameter Definition
k^ Overall total water concentration dissipatio
rate (yr'1)
kfc Burial rate (yfl)
9^ Bed sediment porosity (unitless)
BS Bed sediment concentration (mg
sediment/L)
Kdj,, Bed sediment/sediment pore water partition
coefficient (LAg)
Kd,w Suspended sediment/surface water partition
coefficient (L/kg)
TSS Total suspended solids (mg/L)
Wb Rate of burial (m/yr)
Dm Waterbody depth (m)
Dissipation Rate
\
s'W-*kg/mg tWb (6.1(X))
'•IQ^kg/mg Dm
)
Central
tendency High-end
value value Refer to
n Calculated
Calculated
0.6 . 6.7.52
106 6.7.5.2
Chemical-specific 6.7.6.1
Chemical-specific 6.7.6.1
10 80 6.7.5J2
See Equation 6-101
0.67 0.18 6.7.5.1
Source: EEM (U.S. EPA, 1990e; 1993a).
August 1995
6-176
-------
6.0 TATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Rate of Burial
b
Xe • WAL • SD« 103 g/kg - VFX • TSS • 10'3 £/ro£ •
\
103ZVm3
\ ' /
Parameter Definition
Wb
xe
WAt.
SD
vf,
TSS
WA,
BS
Rate of burial (m/yr)
Unit soil toss (kg/m2/yr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Total suspended solids (mg/L)
Waterbody surface area (m2)
Bed sediment concentration (kg sediment/L)
Central
tendency
value
TSS + (6101)
BS
Highrend
value Refer to
Calculated
See Equation 6-102
1.3e+9
6e+7 6.7.5.1
See Equation 6-103
3e+8
10
le+6
1
1.3e+7 6.7.5.1
80 6.7^5.2
4.6e+4 6.7.5.1
•6.7.5.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-177
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Universal Soil Loss Equation
Parameter
x<
R
K
LS
C
P
Xe =/? *K»LS»C'P • 907.18 kg/ton «245
Definition
Unit soil toss (kg/m2/yr)
USLE rainfall factor (yfl)
USLE erodibdity factor (ton/acre)
USLE length-slope factor (unitless)
USLE cover factor (unittess)
USLE erosion control practice factor
(unitless)
.7 acre/km2*
Central
tendency
value
lO"6*/*2/™2
High-cnd
value
(6-102)
Refer to
Calculated
110 (Portland)
025
1
0.1
1
300 (Atlanta)
3
0.5
6.7.2.2
6.7.3.2
6.7.3.2
6.7.3.2
6.7.3.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-178
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Watershed: Sediment Delivery Ratio
SD=a • (WAL)
-0.125
(6-103)
Parameter
Definition
Central
tendency High-end
value value
Refer to
SD
sediment delivery ratio (unitless)
Calculated
empirical intercept coefficient (unitless)
area of watershed (m2)
0.6
1.3e+9
1.2
6e+7
6.7.3.2
6.7.5.1
WA,.
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-179
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (35)
Soil Volumetric Water Content
e=e
(6-104)
Parameter
8
8.
q
K.
b
Definition
Soil volumetric water content (mL/cm3)
Soil saturated volumetric water content
(ml/cm3)
Average annual recharge rate (cm/yr)
Saturated hydraulic conductivity (cm/yr)
Soil-specific exponent representing water
retention (unitless)
Central
tendency
value
High-end
value
Refer to
Calcinated
0.43
28
3,600
5.4
0.55
15
20,000
3.0
6.7.3.1
6.7.2 2
6.7.3.1
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995 6-180
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Site Sediment Delivery Ratio
SD = a • (As
°-125
(6-105)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
SD
Sediment delivery ratio (unitless)
Calculated '
Empirical intercept coefficient (unitless)
Area of WMU (m2)
WMU-specific
WMU-specific
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-181
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (35)
Fraction of Contaminant in Water Column
/,
water
(l +Kdsw*TSS» IQ^kg/mg) • Jl
\
(6-106)
Parameter
f~
Definition
Fraction of total waterbody contaminantion
in water column. (unitkss)
Central
tendency
value
High-end
value
Refer to
Calculated
Suspended sediment/surface water partition
coefficient (L/kg)
Chemical-specific
6.7.6.1
TSS
Total suspended solids (mg/L)
10
80
6.7.5.2
Depth of water column (m)
0.64
0.15
6.7.5.1
Total depth of waterbody (water column and
sediment) (m)
0.67
0.18
Source: EEM.
6.7.5.1
«b.
Kd*
BS
d.
Bed sediment porosity (unitless)
Bed sediment/sediment pore water partition
coefficient (Ukg)
Bed sediment concentration (sediment/L)
Depm of bed sediments (m)
0.6
Chemical-specific
1
0.03
6.7.5.2
6.7.6.1
6.7.5.2
6.7.5.1
August 199S
6-182
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (36)
6.6J.2.7 Pathway 36: Ingestion -* Animal -». Surface Water -» Overland
Deposition -» Air -» WMU
Constituents sorbed to particles in the surface soil or waste matrix may be entrained
into the air from many of the WMUs. Airborne particulates may deposit on surface soils via
deposition mechanisms (e.g., settling, dry deposition). Constituents deposited on soils may
then be transported over the ground to surface water via soil erosion and runoff. Livestock
that are given the contaminated surface water may ingest constituents dissolved in the surface
water or sorbed to suspended solids in the surface water. Subsistence farmers in the
proximity of a WMU may be exposed through the ingestion of contaminated beef or milk.
The fate and transport components of this pathway are cattle ingestion of water,
overland transport (soil erosion and runoff) to surface water, and deposition of contaminant
onto the watershed. See Section 6.5.2 for an overview of the surface water model used.
Surface water used for irrigation is assumed to be unfiltered; therefore, total water
concentration (including contaminant both dissolved and sorbed to suspended solids) is used.
Cattle Ingestion of Water. Animal ingestion of water was calculated separately, but is
based on the same model as cattle ingestion of forage and soil.
The food chain model calculates the concentration of pollutant in animal tissues by
considering the concentration of pollutant in plants and soil, the quantity of plants and soil
that animals consume, and the biotransfer factor for each type of animal tissue. A somewhat
different model is used for dioxin-like compounds, which tend to bioaccumulate in lipid
material (i.e., fat). The general model is from the Indirect Exposure Methodology; the dioxin-
like compound model is from the Dioxih document (U.S. EPA, 1994a).
The Travis and Arms biotransfer factor (Ba) is the only transfer factor in this analysis
that uses mass ingestion of contaminants (mg/d) by animals and translates them to a tissue
concentration (mg/kg whole concentration). Other approaches depend on a concentration in
media to concentration in tissue bioconcentration/biotransfer factor. The Travis and Arms
approach does have the advantage that the transfer factors are based on the commonly
available Kow.
The Travis and Arms biotransfer factor, Ba, was used for all constituents. In addition
to the benefit of its being generalizable based on Kow for organics, values for Ba have also
been compiled for metals in U.S. EPA (1992e) and Baes et al. (1984)..
August 1995 . 6-183
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Erosion and Runoff. Contaminant dissolved in annual surface runoff was
estimated as a function of the contaminant dissolved in soil water and annual water runoff.
For soil erosion, a sorbed concentration of contaminant in soil, together with an annual soil
erosion estimate, a sediment delivery ratio, and an enrichment ratio, were used to describe the
delivery of contaminant to the waterbody via soil erosion.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation. The USLE
uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
A sediment delivery ratio serves to reduce the total potential amount of soil erosion
(i.e., the total potential equals a unit erosion rate as in kg/m2 times a watershed area, in m2)
reaching the waterbody recognizing that most of the erosion from a watershed during a year
deposits prior to reaching the waterbody. The enrichment ratio recognizes the fact that soils
which erode tend to be lighter in texture, more abundant in surface area, and have higher
organic carbon. All these characteristics lead to concentrations in eroded soils which tend to
be higher in concentration as compared to in situ soils for many constituents.
Deposition to Soil. The cumulative soil concentration of a pollutant as a result of
deposition is derived from the dry deposition rate over the time period of deposition and the
contaminant loss rate from the soil. The cumulative soil concentration represents the
concentration increment due to accumulation of contaminant deposited onto soil from one of
the WMUs. The cumulative soil concentration does not take into account background
concentrations of the contaminant that may already be present, whether natural or from other
pollution sources.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, k^ is the sum of the loss rates for each of these processes.
August 1995
6-184
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (36)
Losses due to degradation (ksg) are empirically determined from field studies.
Degradation rates, vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
The equation for the loss constant due to leaching, k,,, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants, rather than vapor-phase contaminants). If such
redeposition occurred, the soil concentration would be higher than if such redeposition did not
occur. As a result, the algorithm as used (without redeposition) may underestimate soil
concentrations for compounds that would volatilize then dissolve in rainwater and be
redeposited; however, the revolatilization of semivolatile organic contaminants such as dioxin
that have been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by an equal amount that erodes or runs onto it from upgradient areas. On
the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a watershed; therefore, the
soil loss constant used includes both a surface runoff loss constant and a soil erosion loss
constant. The LISLE is used to estimate unit erosion loss.
Equation 6-107 presents the equation for backcalculating total water concentration from
animal product concentration. Equations 6-108 through 6-113 present the backcalculations for
backcalculating soil concentration from total surface water concentration for overland
transport Equation 6-114 shows the backcalculation for deposition rate from soil
concentration. Equations 6-115 to 6-124 present the equations for the soil loss constant, ks,
which is used in Equation 6-114.
August 1995 6-185
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Total Water Column Concentration (Animal Digestion of Water)
C_ animal
„,» —-
'wt
Ba*Qw
(6-107)
Parameter
Definition
Central
tendency High-end
value value
Source: EM (U.S. EPA, 1990c; 1993a).
Refer to
Cw,
c^
Ba
Qw
Total water column concentration (mg/L)
Concentration in animal tissue (mg/kg or
Mg/g)
Biotransfer factor for animal tissue group
(d/kg)
Quantity of water ingested by animal (L/d)
Calculated
From Equation 5-62
Chemical-specific
50
6.7.6.2
6.7.4.2
August 1995
6-186
-------
6.0 FATE AND, TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Concentration: from Total Water Column Concentration
'-
Parameter
W4 RD /Y ?n FJ? *v in~3
u, L P. . ,
Definition
1 3/L +fly • l
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Water Concentration Dissipation Rate
k =*,.
* *"
D
m
(6-109)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Overall total water concentration dissipation
rate (yr-1)
Calculated
Burial rate (yr~ ')
Calculated
Bed sediment porosity (unitless)
0.6
6.7.5.2
BS
Bed sediment concentration (mg
sediment/L)
106
6.7.5.2
Bed sediment/sediment pore water partition
coefficient (L/kg)
Chemical-specific
6.7.6.1
Suspended sediment/surface water partition
coefficient (L/kg)
Chemical-specific
Source: IBM (U.S. EPA, 1990e; 1993a).
6.7.6.1
TSS
wb
Dm
Total suspended solids (mg/L)
Rate of burial (m/yr)
Waterbody depth (m)
10 80
See Equation 6-110
0.67 0.18
6.7.5.2
6.7.5.1
August 1995
6-188
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Rate of Burial
Xe* WAL*SD* itfg/kg -VF^TSS* I0~3g/mg • itfi/m 3
WA
BS
ParameU
Wb
xe
WA,
SD
Vfx
TSS
WA,
BS
$
•r Definition
Rate of burial (m/yr)
Unit soil loss (kg/m2/vr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Total suspended solids (mg/L)
Waterbody surface area (m2)
Bed sediment concentration (kg sediment/L)
Central
tendency High-end
value value
CafrulafH
See Equation 6-111
1.3e+9 6e-«-7
See Equation 6-112
3e+8 1JW7
10 80
le+6 4.6c+4
1
Refer to
6.7.5.1
6.7.5.1
6.7.52
6.7.5.1
6.7.5.2
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-189
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Universal Soil Loss Equation
.1 acre/km1 *\V*km2lml (6-111)
Central
tendency High-end
Parameter
xe
R
K
LS
C
P
Definition
Unit soil loss (kg/m2/yr)
USLE rainfall factor (yr'1)
USLE erodibility factor (ton/acre)
USLE length-slope factor (unitless)
USLE cover factor (unitless)
USLE erosion control practice factor
(unitless)
value value
Calculated
WMU-specific
025
1 3
0.1 0.5
1
Refer to
6.7.3.2
6.7.3.2
6.7.3.2
6.7.3.2
Source: EM (U.S. EPA, 1990e: 1993a).
August 1995
6-190
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Watershed: Sediment Delivery Ratio
(w,)-°-125
(6-112)
Parameter
Definition
Central
tendency High-end
value value
Refer to
SD
Sediment delivery ratio (unitless)
Calculated
Empirical intercept coefficient (unitless)
Area of watershed (m2)
0.6
13e+9
12
6e+7
6.7.3.2
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-191
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Fraction of Contaminant in
(l+Kd^'TSS'W6
f = ,
( " gmg Tz
Parameter Definition
fw*cr Fraction of total waterbody contamination
in water column (unitless)
Kd^ Suspended sediment/surface water partition
coefficient (L/kg)
TSS Total suspended solids (mg/L)
dw Depth of water column (m)
dz Total depth of waterbody (water column and
sediment) (m)
6^ Bed sediment porosity (unitless)
Kdfc, Bed sediment/sediment pore water partition
coefficient (L/kg)
BS Bed sediment concentration (sediment/L)
dfc Depth of bed sediments (m)
Water Column
kg/mg) •-£.
'} * ^Kd»'BS) -T.
Central
tendency High-end
value value
Calculated
Chemical-specific
10 80
0.64 0.15
0.67 0.18
0.6
Chemical-specific
1
0.03
(6-113)
V" * *•>)
Refer to
6.7.6.1
6.7.52
6.7.5.1
' 6.7.5.1
6.7.52
6.7.6.1
6.7.5.2
6.7.5.1
Source: EM.
August 1995
6-192
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Deposition to Soil: Combined Deposition Rate
(6-114)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Average annual combined deposition rate
(g/m2/yr)
Calculated
-Mil
Concentration in soil at deposition location
(mg/g)
From Equation 6-106
z
BD
k.
t
Mixing depth (cm)
Soil bulk density (g/cm3)
Soil loss constant (yr"1)
Time period of deposition (yr)
2.5 (unfilled) . 1 (unfilled)
1.5 . 1.2
See Equation 6-115
20 (farmer) 40 (farmer)
6.7.3.3
6.7.3.1
6.7.3.3
Source: EM (U.S: EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Loss Constant
V " sg n
Parameter Definitioo
It, Soil loss constant (yr'1)
k,, Soil loss constant due to leaching (yr'1)
k^ Soil loss constant due to degradation (yr'1)
k^ Soil loss constant due to volatilization (yr*1)
•*,,+*« -.o-nj;
Central
tendency High-end
value value Refer to
Calculated
See Equation 6-116
0 6.7.6.1
See Equation 6-118
Soil loss constant due to surface runoff
(yr*1) .
See Equation 6-122
Soil loss constant due to soil erosion (yr'1)
See Equation 6-124
Source: IEM (U.S. EPA. 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Loss Constant Due to Leaching
e-z
i*
(6-116)
Parameter
k-
Dermitibo
Soil loss constant due to leaching (yr~l)
Central
tendency High-end
value value Refer to
Calculated
Average annual recharge (cm/yr)
WMU-specific
e
z
BD
*d
Soil volumetric water content (rnL/cm3)
Soil depth from whkh leaching occurs (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
See Equation 6-117
2J5 (untilled) 1 (uncilled)
1.5 \2
Chemical-specific
6.7.3.3
6.7.3.1
6.7.6.1
Source: EM (U.S. EPA, 1990e;.1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Volumetric Water Content
0=6
71
(6-117)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Soil volumetric water content (mL/cm3)
Calculated
e.
Soil saturated volumetric water content
(mL/cm3)
0.43
0.55
6.7.3.1
Average annual recharge rate (cm/yr)
WMU-specific
3,600 20,000
Saturated hydraulic conductivity (cm/yr)
6.7.3.1
Soil-specific exponent representing water
retention (unitless)
5.4
3.0
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (36)
Soil Loss Constant Due to Volatilization
(6-118)
Central
tendency High-end
Parameter Definition value value Refer to
1^ ' Soil loss constant due to volatilization (yr"') Calculated
K, Equilibrium coefficient (s/cm-yr) See Equation 6-119
K, Gas phase mass transfer coefficient (cm/s) - See Equation 6^120
Source: EM (U.S. EPA. 1990e: 1993a).
August 1995 6-197
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (361
Volatilization Equilibrium Coefficient
3.1536
Urn
Parameter
Ke
H
Z
Kd
R
T
BD
Definition
Equilibrium coefficient (s/cm • yr)
Henry's law constant (atm • m3/mol)
Soil depth from which volatilization occurs
(cm)
Soil water partition coefficient (mL/g)
Ideal gas constant (atm • L/mol • K)
Temperature (K)
Soil bulk density (g/cm3)
Central
tendency
value
High-end
value
Refer to
Calculated
Chemical-specific
2.5 (unfilled)
1 (unfilled)
Chemical-specific
8.21 x HT3
298
1,5
1.2
6.7.6.1
6.7.3.3
6.7.6.1
6.7.7
6.7.2.2
6.7.3.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (36)
Gas-Phase Mass Transfer Coefficient
, 0-78. c,-°-67.w -Mi (6-120)
Parameter Definition
K, Gas phase mass transfer coefficient (cm/s)
u Windspeed (m/s)
ScG Schmidt number on gas side (unitless)
de Effective diameter of contaminated area (m)
Central
tendency High-end
value value Refer to
Calculated
WMU-specific
See Equation 6-121
See Equation 6-123
Source: EM (U.S. EPA. 1990e; 1993a).
August 1995 6-199
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Schmidt Number on Gas Side
(6-121)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
SCr
Schmidt number on gas side (unitless)
Calculated
A.
p.
Viscosity of air (g/cm '• s)
Density of air (g/cm3)
1.81e-4
1.2e-3
6.7.7
6.7.7
Diffusivity in air (cm2/s)
Chemical-specific
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Loss Constant Due to Runoff
(e -z)
/ \
1
(6-122)
Paraneter
DcfloitkNi
Central
tendency
value
High-end
value
Refer to
Soil loss constant due to surface runoff
(yr'1)
Average annual runoff (cm/yr)
WMU-specific
Soil .volumetric water content (mL/cm3)
See Equation 6-117
BD
Soil mixing depth (cm)
Soil bulk density (g/cm3)
2.5 (untilkd)
1.3
1 (untilled)
12
6.7.3 J
6.7.3.1
Kd,
Soil-water partition coefficient (mL/g)
Chemical-specific
6.7.6.1
Source: IBM (U.S. EPA. 1990c; 1993a).
August 1995
6-201
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (36)
Effective Diameter
4M (6-123)
Central
tendency High-end
Parameter Definition value value Refer to
d,. Effective diameter of Calculated
contaminated area (m)
A Area of contaminated area 1.34e+9 (watershed) 6eV7 (watershed) 6.7.5.1
(m2) • • __
Source: IBM (U.S. EPA, 1990e; 1993a). .
August 1995 6-202
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (36)
Soil Loss Constant Due to Erosion
Parameter
k.
x«
e
z
BD
Kd.
(O.I'X
k -
* BD*2
\
t
Definition
Soil loss constant due to soil erosion
Unit soil loss (kgAn2/yr)
Of Kd^BD
'. 8 +Kd»BD
J\ J
Central
tendency
value
(yr~') Calculatt
See Equation
Soil volumetric water content (ml/cm3) See Equation
Soil mixing depth (on)
Soil bulk density (g/cm3)
2J (unfilled)
'I'J
High-end
value
*d
6-111
6-117
1 (unfilled)
12
Soil-water partition coefficient (mL/g) Chemical-specific
(6-124)
Refer to
6.7.3J
6.7.3.1
6.7.6.1
Source: EM (U.S. EPA, 1990c; 1993a).
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
6.6J.3 Uncertainty
6.6J.3.1 Biotransfer Factors
The correctness of the biotransfer factors for beef and milk that are the core of the
animal pathways are highly uncertain. The factors are based on empirical relationships with
KgW defined by studies on a relatively few chemicals. Further, it is not clear to what extent
study conditions mimic actual field conditions. Using a regression equation on Kow is almost
certainly an oversimplification that may result in overestimate of a chemical's tendency to
bioaccumulate. Similarly, the transfer factors for plant uptake are also uncertain for the same
reasons.
6.6JJJ Universal Soil Loss Equation
Uncertainty arises out of the use of the Universal Soil Loss Equation. This is an
empirical, though widely used, model. It was intended for use in site-specific situations,
where highly specific input data can be used, and for relatively small fields. How well it
predicts soil erosion in a generic application, as here, and for fairly large sources of eroded
soil, is uncertain. It is most likely that it overestimates quantity of soil eroded
6.6.2 JJ Surface Water Modeling Framework
The surface water modeling framework presented in the Addendum (U.S. EPA, 1993a)
and used here is a new model that has not been peer-reviewed. Therefore, there is
uncertainty as to how well it represents actual surface water fate and transport processes.
Most of the existing peer-reviewed surface water models in use at EPA, such as WASP and
EXAMS, are so highly site-specific that they could not be feasibly adapted to a generic
analysis such as this. It is uncertain whether use of this model would overestimate or
underestimate risk.
While the surface water model framework is designed to accomodate chemical
transformations within the waterbody, these were omitted from this analysis. These processes
are highly chemical- and site-specific. Assessing the potential for transformation of all 200
chemicals considered would be an extensive research project. The effect of omitting such
transformations could be either an overestimate or underestimate of the risk, depending on
whether a chemical transforms into a more or less toxic or mobile form.
6.6JJ.4 Soil Loss Constant Term
The overall soil loss constant term, ks, is uncertain in several ways. This term is the
sum of loss rates for leaching, erosion, runoff, degration, and volatilization. One uncertainty
arises from the assumption that all of these loss terms are first order and can therefore be
added together. This is a common assumption, but some of the processes may in fact be zero
order. A first order loss process may be characterized by a half-life, the time it takes half of
the remaining contaminant to be lost Therefore, the mass lost per unit of time varies with
August 1995 6-204
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
the concentration. A zero order loss process is characterized by a constant mass loss per unit
of time. Neither of these processes can be said to be more conservative than the other,
because the first order rate depends on the starting concentration and the zero order rate does
not, at any given time, which one results ina higher concentration will depend on the starting
concentration. Therefore, it cannot be said whether incorrectly assuming that loss constant
that is actually zero order is first order will overestimate or underestimate soil concentration.
Another source of uncertainty regarding the soil loss constant is that the various loss
processes are calculated independently, when in fact, they occur simultaneously. As a result,
losses could be overpredicted because the amount of contaminant available to each process is
overestimated by not accounting for the other loss processes. This would result in an
underestimate of soil concentration.
The inclusion of losses due to soil erosion and runoff in the soil loss rate may also
overstate the net loss of contaminant from soil, thus underestimating soil concentration. For
small areas, such as the home garden or yard used in soil ingestion and dermal soil pathways,
it could be argued that soil loss due to these mechanisms is offset by erosion and runon onto
the garden or yard. However, for large areas, such as the watersheds used in the surface
water pathways, such offsetting runon and soil erosion is less likely to occur, since any soil
erosion or runon will occur from within the watershed. It is the Addendum's current
recommendation to include these losses.
Finally, degradation losses were set to zero. Degradation rates are highly dependent on
site-specific factors that cannot be accounted for in a generic analysis of this nature and may
be zero. To the extent that constituents do degrade into constituents of less concern, the
omission of degradation from the soil loss constant will underestimate losses and therefore
overestimate soil concentration.
The overall effect of all of the above uncertainties on the soil loss constant is not clear.
Two of the factors would tend to underestimate soil concentration, one woul tend to
overestimate soil concentration, and the effect of one could be either an over- or under-
estimate of soil concentration.
6.6JJ.5 SoU Water Content Equation
The equation from the Superfund Exposure Assessment Manual (U.S. EPA, 1988a) used
to calculate soil water content based on recharge (the net effect of precipitation, irrigation,
evaoration, and runoff) and soil properties was developed for site-specific application. Its
application in a generic analysis raises uncertainty as to how well it predicts soil water
content A distribution of this value would have been prefered; however, it was not available
and so had to be calculated. However, some of the input parameters are highly generalized
(such as recharge) and others (such as the soil moisture retention exponent b) are drawn from
estimates rather than measured values. It is not clear in which direction this uncertainty
would affect the results.
August 1995 6-205
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways
6.6J Fish Pathways
Figure 6-9 provides an overview of the fate and transport for fish pathways.
6.6J.I Scenarios
6.63.1.1 Human
Human exposure scenarios for fish include consumption of contaminated freshwater
fish. Table 6-9 summarizes the receptors modeled for the fish pathways.
Two receptors were selected for fish ingestion pathways: a general population fish
consumer who catches contaminated fish and a subsistence fisher who catches all their fish
for consumption from a contaminated surface waterbody and consumes a large quantity of
fish relative to the general population. A child receptor was not included because there is no
evidence that children consume more fish than adults relative to their body weight
Therefore, adult scenarios should be protective of children.
| Fish Concentration at Receptor)
I
| Btoconcentration {
==
Surface Water
Concentration
Figure 6-9. Fate and transport for fish pathways.
August 1995
6-206
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
Table 6-9. Summary of Receptors for Fish Pathways
^ Receptor
Adult Child Subsistence Home Subsistence Ffch
Pathway resident resident fanner gardener fisher consumer Worker
21: Air diffusion-fish / /
ingestion
23: Overland-fish / ^
ingestion . .
24: Air deposition-fish
ingestion
6.6J.L2 Ecological
The food chain exposure scenarios for piscivorous fish, birds, and mammals in the
generic freshwater ecosystem are described in Section 6.5.1.2.
6.6JJ Pathway Algorithms
Once contaminants are transported to surface water bodies, they may be incorporated
into the aquatic food chain. See Section 6.5.2 for a discussion of the surface water model
used in this analysis.
The following sections describe the fish pathways and present the fate and transport
equations for them. These pathways are:
• Pathway 21: ingestion -» fish -> surface water -> air -> WMU (Section 6.6.3.2.1)
• Pathway 23: ingestion -> fish -* surface water -» overland -» WMU
(Section 6.6.3.2.2)
• Pathway 24: ingestion -»fish -» surface water -» overland -» deposition -> air -»
WMU (Section 6.6.3.2.3). -
August 1995 6-207
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
6.6J.2.1 Pathway 21: Digestion -» Fish -» Surface Water -* Air -> WMU
Constituents may volatilize from many of the WMUs. These vapor-phase constituents
may diffuse into surface water from air. Once in the surface water, fish may "ingest"
constituents dissolved in the water during normal respiration across the gills. In addition,
contaminants that concentrate in the sediments may be introduced into fish through the food
chain, beginning with benthic organisms (i.e., bottom dwellers). Contaminants can
accumulate in fish from either or both of these exposure vehicles (i.e., water, food chain),
depending on the potential for bioconcentration of each constituent Fish consumers and
subsistence fishers using contaminated surface waters may be exposed through the ingestion
of contaminated fish.
The fate and transport components of this pathway are fish bioconcentration and
diffusion of vapor-phase contaminant into surface water.
Fish Uptake and Concentration. The concentration of contaminants in fish tissue may
be related to the water concentration using either a bioconcentration factor (BCF) or a
bioaccumulation factor (BAP). Bioconcentration is defined as the net uptake of a chemical
from an organism's surrounding medium through direct contact (e.g., uptake by a fish through
the gills and epithelial tissue) but excluding ingestion of a chemical in food (McVey, 1994).
Bioaccumulation is defined as the net uptake of a chemical from the environment from all
pathways (including direct contact and ingestion of contaminated food items). It is important
to recognize that the distinction between BCF and BAF has both practical and technical
implications. The route of exposure assumed for BCFs is direct contact and laboratory-
derived BCF values are typically generated from studies in which aquatic organisms are
exposed to the chemical only through the water (i.e., no contaminated food). For organic
chemicals with log Kow values below ~ 4.0, the BCF is a reasonable estimate of the
concentration potential of the chemical under field conditions. However, for more
hydrophobic organic chemicals Gog Kow » 4.0), uptake via the food chain will be an
increasingly important source of exposure and using the BCF value will tend to underestimate
the actual concentration of chemicals in fish tissue. Therefore, for hydrophobic organic
chemicals and other chemicals shown to bioaccumulate (e.g., mercury), a bioaccumulation
factor is the appropriate measure of the concentration potential in fish. Field studies on the
concentration potential of a chemical, regardless of the chemical, are typically viewed as
bioaccumulation studies since exposure may occur through direct contact as well as through
the food chain. Nevertheless, the primary route of exposure of hydrophilic (or weakly
August 1995 6-208
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
hydrophobic chemicals) is through direct contact and the concentration gradients required for
bioaccumulation to occur are unlikely (Gobas, 1993a).
In addition to the distinction between BCF and BAF, it is important to recognize the
difference between: (1) dissolved water concentrations vs. total water concentrations and (2)
lipid-based concentrations vs. whole-body concentrations. For organic chemicals with log
Kow below 4.0, chemical concentrations in water are typically regarded as freely dissolved,
although some small fraction is undoubtedly sorbed to suspended particles. In contrast, for
metals and hydrophobic organic chemicals having low solubility, water concentrations are
generally regarded as total water concentrations (Le., freely dissolved and particle-bound).
Because the freely dissolved fraction is considered to be the bioayailable fraction,* it is
crucial to distinguish between freely dissolved and total water concentrations when estimating
BCFs and BAFs as well as in conducting fate and transport modeling. Moreover, the Final
Chronic Values for fish and aquatic organisms reflect total water concentrations and, as a
result, estimation of protective exposure concentrations for piscivorous fish required BCFs for
total water concentrations. Using an FCV with a BCF for dissolved water concentration (i.e.,
BCF*1) would result in a higher acceptable tissue concentration in fish (TC) and, therefore, an
underprotective surface water concentration for fish and aquatic invertebrates. This
calculation is described fully in Section 5.3.2.1.2. BCF and BAF values for both freely
dissolved and total water concentrations were used in this analysis and were designated as "d"
(freely dissolved) or "t" (total) as appropriate. For organic chemicals, predicted BAFs from
the Thomann models (1989, 1992) and predicted BCFs from the Thomann model (1989) or
regression equations represent dissolved water concentrations. Measured BCFs for organic
chemicals with log Kow values below 4.0 were also considered dissolved. Measured BCFs for
metals and measured BAFs for hydrophobic organic chemicals (and mercury) were considered
to represent total water concentrations with the exception of DDT, which was based on the
freely dissolved fraction. Predicted, lipid-based BAFs were used for chemicals with log Kow
values between 4.0 and 6.5 unless: (1) the log KpW of the chemical was above 6.5, (2) the
chemical has been shown to be metabolizable in fish (e.g., PAHs), or (3) measured values
were significantly different than predicted values, i.e., greater than or less than the predicted
value by a factor of 4. The cutoff for measured versus predicted was based on a paper by
Randall et aL (1991), which suggested that the choice of extraction solvents and analytical
methods caused BAF estimates to vary between a factor of 2 to 4. Table 6-10 presents the
chemicals for which measured BAF values were used to estimate food chain exposures to
humans and ecological receptors. It should be noted that the selection process for appropriate
bioaccumulation and bioconcentration factors considered measured values presented by
Stephan (1993), the Great Lakes Initiative (1995a), and values identified in the open literature
as well as predicted BAFs and BCFs generated by models and regression equations,
respectively. However, given the variability in test methods and species uptake as well as the
general lack of data on many constituents of concern (e.g., most constituents had fewer than
"Particle-bound chemicals may also be ingested by fish and aquatic organisms. However, the contribution to
the overall exposure is generally considered to be small in comparison with direct contact with the freely
dissolved fraction and ingestion of contaminated prey.
August 1995 6-209
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
Table 6-10. Chemicals with Measured BAFs
CAS Number
56-55-3
218-01-9
72-55-9
50-29-3
206-44-0
86-73-7
87-68-3
319-84-6
319-85-7
58-89-9
7439-97-6
129-00-0
8001-35-2
Constituent
Benz(a)anthracene
Chrysene
DOE
DDT
Fluoranthene
Fluorene
Hexachloro- 1 ,3 -butadiene
a-Hexachlorocyclohexane
P-Hexachlorocyclohexane
Lindane
Mercury
Pyrene
Toxaphene
two measured BCF values), measured values were not preferred simply because they were
measured. Given the current state-of-the-science, predictive models may provide a more
defensible basis for estimating concentration potential. The uncertainty in using a single
measured BCF value may be considerably greater than using a predicted BCF based on the
empirical relationship between chemical properties and partitioning to fish lipids.
The distinction between lipid-based and whole-body fish concentrations is also critical
to the exposure calculations. Lipid-based BAFs and BCFs for organic chemicals are cal-
culated for the lipid portion of the fish. Because most of an organic chemical is assumed to
partition to lipids, all of the chemical is sequestered in fat compartment of the fish. Conse-
quently, lipid-based BAFs and BCFs (BAF/s and BCF/s) are numerically higher than whole-
body BAFs and BCFs since the chemical is "diluted" in a smaller volume. The bioaccumula-
tion models used in this analysis were constructed to estimate lipid-based BAF/s and BCF/s
that reflect dissolved water concentrations. In contrast, whole-body BAFs and BCFs are
numerically smaller than the lipid-based counterparts because they are based on the entire fish
and, therefore, a greater "dilution" volume. For organic chemicals, whole-body BAFs and
BCFs may be converted to lipid-based by dividing by the lipid fraction. For example, if a
whole-body BCF of 100 was measured for chemical X in a species of fish with 10 percent
lipids, the lipid-based BCF/ would be 100 -r 0.1 or 1,000. For metals, whole-body BCFs are
the appropriate measure for ecological receptors, and BCFs for muscle are the appropriate
measure for humans. For human exposures, lipid-normalized BCFs and BAFs were
August 1995 6-210
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
calculated to reflect the amount of lipid actually ingested by humans assumed to eat fish
fillets. Because humans are assumed not to eat the entire fish, it would be inappropriate to
calculate exposures to organic chemicals using BAFs and BCFs that are lipid-based or whole-
body. Using the lipid-based BAF/s and BCF/s would result in overprotective estimates of
acceptable surface water concentrations and using whole-body BAFs and BCFs would result
in inconsistent estimates of acceptable surface water concentrations. Since various species of
fish have different lipid fractions (ranging from approximately 3 to 25 percent), whole-body
BAFs and BCFs are considered inappropriate to use in exposure calculations. Therefore,
lipid-normalized BAFs and BCFs were calculated for large fish in trophic level 4 for humans.
The lipid-normalized values were calculated assuming that the portion of the fish eaten by
humans contains 5 percent lipid For example, to calculate the lipid-normalized value for a
chemical with a lipid-based BAF/ of 1,000, the BAF/ was multiplied by the lipid fraction or
1,000 x 0.05 or 50. The BAF of 50 is the bioaccumulation factor for humans eating fillets
from trophic level 4 fish assumed to contain 5 percent lipids. For measured BAFs and BCFs,
lipid-normalized values were calculated assuming that the fish contain 7.9 percent lipids.
For extremely hydrophobic constituents, the Agency has stated that reliable
measurements of ambient water concentrations (especially dissolved concentrations) are not
available and that accumulation of these constituents in fish or other aquatic organisms cannot
be referenced to a water concentration as required for a BCF or BAF (U.S. EPA, 1993i).
Fortunately, extremely hydrophobic constituents can be measured in sediments and aquatic
life and, because these chemicals tend to partition to lipids and organic carbon, a biological
uptake factor that reflects the relationship between sediment concentrations and organism
concentrations may be more appropropriate. Consequently, the biota-sediment accumulation
factor (BSAF) is the preferred metric for accumulation in the littoral aquatic ecosystem for
extremely hydrophobic chemicals (e.g., chemicals with :> log K,,w of - 6.5). For 2,3,7,8-
TCDD and PCBs, the BSAF in [mg/kg LP]/[mg/kg sediment OC] for trophic level 4 fish was
supplied by the U.S. EPA ORD Exposure Assessment Group in a memorandum to Addressees
by Matthew Lorber (September 1994). This memorandum updates the Addendum to the
Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor
Emissions (U.S. EPA, 1993a) and other EPA documents involving risk assessment of 2,3,7,8-
TCDD. This recommendation represents the current state-of-the-science at the Agency.*
Air DifAiaon to Surface Water. The dissolved concentration in the waterbody was
assumed to reach equilibrium with a vapor phase concentration above the waterbody. At
equilibrium, gaseous diffusion into the waterbody is matched by volatilization out of the
*It should be noted that of PCB exposures to ecological receptors, the BAFls generated for the Great Lakes
Water Quality Initiative (U.S. EPA, 1995a) were used for ecological receptors. Because humans are assumed to
eat only trophic level 4 fish, the BSAF was considered appropriate to use in the human exposure calculations.
However, accumulation factors for PCBs were required for trophic levels 2-4 and, lacking BSAFs for trophic
levels 2 and 3, it was determined that the BAFls were appropriate for ecological receptors. The use of BAFls
vs. the BSAF for trophic level 4 resulted in an insignificant change in the protective exposure concentrations for
receptors at the top of the food chain (e.g., eagle, heron).
August 1995 6-211
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6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
waterbody. Gaseous diffusion is estimated with a transfer rate and a vapor phase air
concentration.
Equations 6-125 tnrouth 6-127 present the equations for backcalculating dissolved water
concentration, total water concentration, or bottom sediment concentration, respectively, from
fish concentration. Equations 6-128 through 6-130 present the equations for backcalculating
air concentration over the waterbody from dissolved water concentration, total water
concentration, or bottom sediment concentration, respectively. Equations 6-131 through 6-138
calculate various inputs to the air diffusion equations.
August 1995 6-212
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(.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
Fish Bioconcentration: Dissolved Water Concentration
or- (6-125)
BCF BAF
Central
tendency High-«nd
Parameter Definition value value Refer to
Cj, Dissolved water concentration (mg/L) Calculated
Concentration in fish (mg/kg) From Equations 5-66 and 5-69
BCF Bioconcentration factor (LAcg) Chemical-specific 6.7.62
BAFC rairiiiaiad bioaccumulation factor (LAg) Chemical-specific 6.7.62
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-213
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6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Fish Bioconcentration: Total Water Column Concentration
C =
""
'wt
BAF
(6-126)
Parameter
Defiaitioa
Central
tendeocy
value
High-cod
value
Refer to
Total water column concentration (mg/L)
Concentration in fish (mg/kg)
From Equations S-66 and 5-69
BAF.
Measured bknccumulatkm factor (L/kg)
Chsmicai-specific
6.7.62
Source: IBM (US. EPA. 1990e; 1993a).
August 1995
6-214
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Fish Bioconcentration: Bottom Sediment Concentration
'bs
BW'flipU
(6-127)
Parameter
Defloitioa
Central
tendency High-cad
value value
Refer to
Concentration in bottom sediment (mg/kg)
BSAF
Mipid
Concentration in whole fish (mg/kg)
Biota to sediment accumulation factor
(unitless)
Correction factor to estimate whole fish
concentration (unitless)
From Equations 5-66 and 5-69
Chemical-specific 6.7.62
0.05 6.7.4.3
Fraction organic carbon in bottom sediment
(unitless)
0.024
0.008
6.7.52
Source: Dioxin document
August 1995
6-215
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Air Concentration: from Total Water Column Concentration
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Air Concentration: from Dissolved Water Concentration
Parameter
c*
cdw
H
vf,
f~
*»
V
TSS
Kv
R
T
WA,
x
"•
Definition
. Concentration in air (jig/m3)
Dissolved water concentration (mg/L)
Henry's law constant (atm-m3/mol)
Waterbody flow volume (L/yr)
Fraction of total wateitody
contamination in water column (unitless)
Overall total water concentration
dissipation rate (yf ')
Flow-independent mixing volume (L)
Suspended sediment/surface water
partition coefficient (L/kg)
Total suspended solids (mg/L)
Overall transfer rate (m/yr)
Universal gas constant (atm-m3Anol-K)
Waterbody temperature (K)
Waterbody surface area (m2)
Depth of water column (m)
Total depth of waterbody (water column
and sediment) (m)
\
Central
tendency
value
Calculate
dl
High-end
valne
.4
Refer to
From Equation 6-125
Chemical-specific
36411
See Equation
See Equation
6.7C48
1.3e4lO
6-138
6-131
83646
Chemical-specific
10
See Equation
821e-5
298
1646
0.64
0.67
80
6-135
4.6644
0.15
0.18
6.7.6.1
6.7.5.1
6.7.5.1
6.7.6.1
6.7.52
6.7.7
6.7.52
6.7.5.1
6.7.5:i
6.7.5.1
Source: IBM (US. EPA, 1990e; 1993a).
August 1995
6-217
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Air Concentration: from Bottom Sediment Concentration
This algorithm was used for dioxins and PCBs.
d
Refer to
From Equation 6-127
Chemical-specific
3e+ll
See Equation
See Equation
6.7e+8
IJe+IO
6-138
6-131
8Je4«
Chemical-specific
10
80
Chemical-specific
i
See Equation
821e-5
298
. le^
0.64
0.67
6-135
4.6e+4
0.15
0.18
6.7.6.1
6.7.5.1
6.7.5.1
6.7.6.1
6.7.52
6.7.6.1
6.7.7
6.7.52
6.7.5.1
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-218
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Water Concentration Dissipation Rate with Volatilization
f \
k ,-ki.+k =
l+Kd^'TSS'lO^kg/mg
\ >
b
m'wb + Kv'fd (6-131)
D D
Central
tendency High-end
Parameter Definition value value Refer to
k^ Overall total water concentration
dissipation rate (yr"1)
kfc Burial rate (yr'1)
ky Volatilization rale (yr'1)
9^ Bed sediment porosity (unitless) 0.6
BS Bed sediment concentration (mg 106
sediment/L)
Calculated
Calculated
Calculated
6.7.52
6.7.52
Kdfc. Bed sediment/sediment pore water Chemical-specific 6.7.6.1
partition coefficient (LAg)
Kdw Suspended sediment/surface water Chemical-specific 6.7.6.1
partition coefficient (LAg)
TSS Total suspended solids (mg/L) 10
80 6.7.52
Wb Rate of burial (m/yr) See Equation 6-132
D Waterbody depth (m) 0.67
0.18 6.7.5.1
1C, Overall transfer rate (m/yr) See Equation 6-135
fd . Dissolved fraction (unitless) See Equation 6-137
Source: IBM (US. EPA, 1990e; 1993a).
August 1995
6-219
-------
.6.0 FATE AND TRANSPORT MODELING
Food Chain Pathways (21)
Rate of Burial
Xe»WAL»SD* itfg/kg -VFX*TSS* lO^g/mg* l&L/m
BS
Parameter
Definition
Central
tendency High-end
value value
Source: IBM (U.S. EPA, 1990e; 1993a).
Refer to
w
b
xe
WA^
SD
vf, '
TSS
WAW
BS
Rate of burial (nVyr)
Unit soil loss (kg/m2/yr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Total suspended solids (mg/L)
Waterbody surface area (m2)
Bed sediment concentration (kg sediment/L)
Calculated
See Equation 6-133
1 .jC^if OCr /
See Equation 6-134
3e+8 lJe+7
10 80
le*> 4.6e+4
1
6.7.5.1
6.7.5.1
6.7.52
6.7.5.1
6.7.52
August 1995
6-220
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Universal Soil I
Xe*R*K*LS»C'P «907.18 kg/ton
Parameter Defioitioa
Xe Unit soil loss (kg/hi2/yr)
R USLE rainfall factor (yr'1)
K USLE credibility factor (ton/acre)
LS - USLE length-slope factor (unitless)
C USLE cover factor (unitless)
P USLE erosion control practice factor
(unitless)
-oss Equation .
•245.7 acre/km 2 • 10"6 km 2/m 2 (6-133)
Central
tendency High-end
value value Refer to
Calculated
WMU-specific
025 6.7.32
1 3 6.7.32
0.1 0.5 6.7.32
.1 6.7.32
Source: DEM (US. EPA, 1990e: 1993a).
August 1995
6-221
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
Watershed; Sediment Delivery Ratio
Central
tendency High-cod
Parameter Definition value value Refer to
SD Sediment delivery ratio (unitless) Calculated
a Empirical intercept coefficient (Unitless) 0.6 12 6.7.32
Area of watershed (m2) 1.3e+9 6e+7 6.7.5.1
Source: IBM (U.S. EPA. 1990e; 1993a).
August 1995 6-222
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Diffusion Transfer Rate
Kv KL
(6-135)
Parameter
Definition
Central
tendency
value
High-end
value
Refer to
Overall transfer rate (m/yr)
Liquid phase transfer coefficient (nVyr)
See Equation 6-136
Gas phase transfer coefficient (m/yr)
Unitless Henry's law constant
36,500
Chemical-specific
6.7.5.2
6.7.6.1
Source: IBM (U.S. EPA, 1990e; 1993a).
August 1995
6-223
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
Liquid Phase Transfer Coefficient
LL
AT,= -I _1_ 0.15.1075/>r (6'136)
Central
tendency High-end
Parameter Defiaitioa value value Refer to
KL Liquid phase transfer coefficient (m/yr) Calculated
Dw Diffusivity in water (cm2/s) Chemical-specific 6.7.6.1
u Current velocity (m/s) 0.7 OJ 6.7.5.1
J> Waterbody depth (m) 0.67 0.18 6.7:5.1
Source: IBM (US. EPA, 1990e; 1993a).
August 1995 6-224
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (21)
Dissolved Fraction
(6-137)
Parameter
Definition
Central '
tendency High-end
value value Refer to
Dissolved fraction (unitless)
Palrnlat^H
Suspended sediment/surface water
partition coefficient (L/kg)
Chemical-specific
1 6.7.6.1
TSS
Total suspended solids (mg/L)
10
80
6.7.52
Source: IBM (U.S. EPA, 1990e; 1993a).
August 1995
6-225
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (21)
Fraction of Contaminant in Water Column
L
water
Parameter
f_
*-
TSS
dw
d,
«*
^
BS
4k
Deflaitioa
Fraction of total waterbody contaminantion
in water column (unitless)
Suspended sediment/surface water partition
coefficient (Lfltg)
Total suspended solids (mg/L)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Bed sediment porosity (unitless)
Bed sediment/sediment pore water partition
coefficient (LAg)
Bed sediment concentration (sediment/L)
Depth of bed sediments (m)
Central
tendency
value
Calci
High-end
value
ilatrd
Chemical-specific
10
0.64
0.67
0.6
80
0.15
0.18
Chemical-specific
1
0.03
Refer to
6.7.6.1
6.7.52
6.7.5.1
6.7.5.1
6.7.52
6.7.6.1
6.7,52
6.7.5.1
Source: IBM.
August 1995 6-226
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
6.63.22 Pathway 23: Ingestion -* Fish -» Surface Water -» Overland -> WMU
Constituents sorbed to particles in the surface soil or waste matrix may be transported
over the ground to surface water via soil erosion and runoff. Contaminants in surface
impoundments may spill to nearby surface waters. Once in the surface water, fish may
"ingest" constituents dissolved in the water or sorbed to suspended solids in the water column
during normal respiration across the gills. In addition, contaminants that concentrate in the
sediments may be introduced into fish through the food chain, beginning with benthic
organisms (i.e., bottom dwellers). Contaminants can accumulate in fish from either or both of
these exposure vehicles (i.e., water, food chain), depending on the potential for bioconcen-
tration of each constituent Fish consumers and subsistence fishers using contaminated
surface waters may be exposed through the ingestion of contaminated fish.
The fate and transport components of this pathway are bioconcentration in fish and
overland transport by soil erosion and runoff from the WMU to surface water. Fish
bioconcentration is discussed in detail in Section 6.6.3.2.1.
Soil Erosion and Runoff. Contaminant dissolved in annual surface runoff was
estimated as a function of the contaminant dissolved in soil water and annual water runoff.
For soil erosion, a sorbed concentration of contaminant in soil, together with an annual soil
erosion estimate, a sediment delivery ratio, and an enrichment ratio, were used to describe the
delivery of contaminant to the waterbody via soil erosion.
Unit soil erosion loss is estimated with the Universal Soil Loss Equation, or USLE.
The USLE uses five terms:
• Rainfall factor, R—Represents the influence of precipitation on erosion and is
derived from data on the frequency and intensity of storms on a location-specific
basis.
• Erodibility factor, K—Reflects the influence of soil properties on erosion.
• Length-slope factor, LS—Reflects the influence of slope steepness and length of the
field in the direction of the erosion.
• Erosion control practice factor, P—Reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion.
August .1995 6-227
-------
6.0 FATE AND TRANSPORT MODELING 64 Food Chain Pathways (23)
• Cover factor, C—Primarily reflects how vegetative cover and cropping practices,
such as planting across slope rather than up and down slope, influence erosion.
A sediment delivery ratio serves to reduce the total potential amount of soil erosion
(i.e., the total potential equals a unit erosion rate as in kg/m2 times a watershed area, in m2)
reaching the waterbody recognizing that most of the erosion from a watershed during a year
deposits prior to reaching the waterbody. The enrichment ratio recognizes the fact that soils
which erode tend to be lighter in texture, more abundant in surface area, and have higher
organic carbon. All these characteristics lead to concentrations in eroded soils, which tend to
be higher in concentration as compared to in situ soils for many constituents.
Equations 6-139 through 6-141 present the equations for backcalculating dissolved
water concentration, total water concentration, or bottom sediment concentration, respectively,
from fish. Equations 6-142 through 6-145 present the equations for backcalculating soil
concentration from dissolved water concentration, total water concentration, or bottom
sediment concentration, respectively, for overland transport Equations 6-145 through 6-151
calculate various inputs to the overland equations.
August 1995 6-228
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
Fish Bioconcentration: Dissolved Water Concentration
or (6-139)
BCF BAF
Central
tendency High-end
Parameter Definition value value Refer to
€4, Dissolved water concentration (mg/L) Calculaied
Cf-1 Concentration in fish (mg/kg) From Equations 5-66 and 5-69
BCF Bioconcentration factor (Ukg) Chemical-specific 6.7.6.2
BAFC Cakulated bioapcumulation factor (L/kg) Chemical-specific 6.7.62
Source: IBM (U.S. EPA, 1990e: 1993a).
August 1995 6-229
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Fish Bioconcentration: Total Water Column Concentration
C
c
m
(6-140)
Parameter
DeflnitiM
.Central
tendency High-end
value value
Refer to
Total water column concentration (mg/L)
Palriilati»H
Concentration in fish (mg/kg)
BAF.
Measured bioaccumulation factor (L/kg)
From Equations 5-^6 and 5-69
Chemical-specific
6.7.62
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-230
-------
(.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Fish Bioconcentration: Bottom Sediment Concentration
(6-141)
Parameter
Definitioa
Central
tendency High-end
value value
Refer to
Concentration in bottom sediment (mg/kg)
BSAF
Concentration in whole fish (mg/kg)
Biota to sediment accumulation factor
(unitless)
From Equations 5-66 and 5-69
Chemical-specific
Correction factor to estimate whole fish
concentration (unitless)
0.05
6.7.62
6.7.4.3
OC.
Fraction organic carbon in bottom sediment
(unitless)
0.024
0.008
6.7.5J2
Source: Dioxin document
August 1995
6-231
-------
6.0 FATE AND TRANSPORT MODELING
6.6" Food Chain Pathways (23)
Soil Concentration: from Dissolved Water Concentration
'soil'
l
-------
6.0 FATE AND TRANSPORT MODELING
6,6 Food Chain Pathways (23)
Soil Concentration: from Total Water Column Concentration
C*M/'
•,+«,•*/>)
._?L (6-143)
Panuneter
Definition
Central
tendency High-end
value value
Refer to
Concentration in soil (trig/kg)
Total water oohmn concentration (mg/L)
vf,
Waterbody flow volume (L/yr)
From Equation 6-140
3e+ll
6.7:5.1
Fraction of total waterbody contamination in
water column (unitless)
See Equation 6-151
"-
V
e.
Kd,
BD
A
xe
SD
ER
Rf
d.
«•
Overall total water concentration dissipation
rate (yr'1)
Flow-independent mixing volume (L)
Soil volumetric water content (unitless)
Soil-water partition coefficient (cmVg)
Soil bulk density (g/cm3)
WMU area (m2)
Unit soil loss (kg/m2/yr)
Site sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yr)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
See Equation 6-145
6.7e+8 8Je+6
See Equation 6-150
Chemical-specific
U 12
WMU-speciftc
See Equation 6-147
See Equation 6-148
3 organics
1 metals
25 (Portland) 22 (Atlanta)
0.64 0.15
0.67 0.18
6.7.5.1
6.7.6.1
6.7.3.1
6.7.32
6.7.22
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990s; 1993a).
August 1995
6-233
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Soil Concentration: from Bottom Sediment Concentration
This algorithm was used for dioxins and PCBs.
10'3 m
I<
2/n/cm)
(6-144)
Parameter
C
•ou
^ .
Vfx
f—
*•*
V
9.
Kd,
BD
Kd"
TSS
*""•
A
X«
SO
ER
Kf
dw
•V
DeflaJtioa
Concentration in soil (mg/kg)
Contaminant concentration in bottom
sediment (mg/kg)
Waterbody flow volume (L/yr)
Fraction of total waterbody contamination in
water column (uriittess)
Overall total water concentration dissipation
rate^-1)
Flow-independent mixing volume (L)
Soil volumetric water content (unitless)
Soil-water partition coefficient (cm3/g)
Soil bulk density (g/cm*)
Suspended sediment/surface water partition
coefficient (Ukg)
Total suspended solids (mg/L)
Bed sedimentfsedijnent pore water partition
coefficient (LAg)
WMUareadn2)
Unit soil loss (kg/m2/yr)
Site sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yr)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
Central
tendeacy High-end
value value
Calculated
From Equation 6-141
3e+l! 13e+10
See Equation 6-151
See Equation 6-145
6.7e+8 ' 8 Je+6
See Equation 6-150
Chemical-specific
1.5 12
Chemical-specific
10 80
Chemical-specific
WMU-specific
See Equation 6-147
See Equation 6-148
3 organics
1 metals
25 (Portland) 22 (Atlanta)
0.64 0.15
0.67 0.18
Refer to
6.7.5.1
6.7.5.1
6.7.6.1
6.7.3.1
6.7.6.1
6.7.52
6.7.6.1
6.7.3J
6.7.22
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-234
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Water Concentration
*_,=*•»= *** * *
"* \+VA .TC<
l+Ka^'TSS
\
Parameter Definitioo
k^ Overall total water concentration dissipatia
rate (yr-1)
It* Burial rate (yf1)
9^ Bed sediment porosity (unitless)
BS Bed sediment concentration (mg
sediment/L)
Kd^, Bed sediment/sediment pore water partition
coefficient (L/kg)
Kd^ Suspended sediment/surface water partition
coefficient (LAg)
TSS Total suspended solids (mg/L)
Wb Rate of burial (m/yr)
D. Waterbody depth (m)
•
Dissipation Rate
N
r»10 kg/mg ^ Wb (6-145)
•.10-I^J 0.
Central
tendency High-cod
value value Refer to
n Cakulated '
Calculated
0.6 6.7.52
106 6.7.52
Chemical-specific 6.7.6.1
Chemical-specific 6.7.6.1
10 80 6.7.52
See Equation 6-146
0.67 0.18 6.7.5.1
Source: IBM (U.S. EPA, 1990e; 1993a).
August 1995
6-235
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Rate of Burial
-VFx»TSS* I0~3g/mg* l&L/m 3
WA
W
l&Um
.
DO
Parameter
W
o
xe
WA,..
SD
vf,
DefinitioB
Rate of burial (m/yr)
Unit soil loss (kg/m2/yr)
Watershed area (m2)
Watershed sediment delivery ratio (unitless)
Waterbody flow volume (m3/yr)
Central
tendency
value
Calculate
See Equation
lJe+9
See Equation
3e*8
High-ead
value
id
6-147
6e+7
6-149
lJe*7
Refer to
6.7.5.1
6.7.5.1
6.7.52
TSS
Total suspended solids (mg/L)
10
80
6.7.5.1
Waterbody surface area (m2)
1646
4.6e+4
6.7.52
BS
Bed sediment concentration (kg sediment/L)
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-236
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (23)
Parameter
X
^e
R
K
LS
C
P
'
Universal Soil I
Xe=R*K*LS*C*P '901.1* kg/ton
Definition
Unit soil loss (kgAn2/yr)
USLE rainfall factor (yf1)
USLE erodibiliry factor (ton/acre)
USLE length-slope factor (unitless)
USLE cover factor (unitless)
USLE erosion control practice factor
(unitkss)
XKS Equation
•245.7 acre/km 2 • 10"6 km 2/m 2
Central
tendency High-end
value value
Calculated
1 10 (Portland) 300 (Atlanta)
025
1 3
0.1 0.5
1
(6-147)
Refer to
6.7.22
6.7.32
6.7.32
6.7.32
6.7.32
Source: EM .(U.S. EPA, 1990e; 1993a).
August 1995
6-237
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
Site; Sediment Delivery Ratio
Central
tendency High-cad
Parameter Definition value value Refer to
SD Sediment delivery ratio (unitless) Calculated
a Empirical intercept coefficient (unitless) WMU-specific
\ Area of WMU (m2) WMU-specific
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995 6-238
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
Watershed: Sediment Delivery Ratio
(6-149)
Central
tendency High-end
Parameter Definition value value . Refer to
SD Sediment delivery ratio (unidess) Calculated
a Empirical intercept coefficient (unitless) • 0.6 12 6.1.32
Watershed area (m2) 13e+9 6e+7 6.7.5.1
Source: BEM (US. EPA. 1990s; 1993a).
August 1995 6-239
-------
6.9 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
Soil Volumetric Water Content
6=6,
Parameter Definition
9 Soil volumetric water content (mL/cn
J_|-BTT) (6-iso)
.**J
Central
tendency High-end
value value Refer to
n3) Calculated
9, Soil saturated volumetric water content 0.43 0.53 6.7.3.1
(mL/cm3)
q Average annual recharge rate (cm/yr)
28 (Portland) 15 (Atlanta) 6.1.22
K, Saturated hydraulk conductivity (cm/yr) 3,600 20,000 6.7.3.1
b Soil-specific exponent representing water 5.4 3.0 , 6.7.3.1
retention (unitless)
Source: SEAM (U.S. EPA, 1988a).
August 1995 6-240
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (23)
Fraction of Contaminant in Water Column
, d»
'T
f :
J water
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
6.6J.2J Pathway 24: Ingestion -» Fish -» Surface Water -> Overland -V Deposition
->Air-»WMU
•»: •.*•
-* . • •
Constituents sorbed to particles in the surface soil or waste matrix may be entrained
into the air. Airborne particulates may deposit on surface soils via deposition mechanisms
(e.g., settling, dry deposition). Constituents deposited on soils may then be transported over
the ground to surface water via soil erosion and runoff. Once in the surface water, fish may
"ingest" constituents dissolved in the water or sorbed to suspended solids in the water column
during normal respiration across the gills. In addition, contaminants that concentrate in the
sediments may be introduced into fish through the food chain, beginning with benthic
organisms (i.e., bottom dwellers). Contaminants can accumulate in fish from either or both of
these exposure vehicles (i.e., water, food chain), depending on the potential for bioconcen-
tration of each constituent Fish consumers and subsistence fishers using contaminated
surface waters may be exposed through the ingestion of contaminated fish.
The fate and transport components of this pathway are bioconcentration in fish, soil
erosion and runoff into the surface waterbody, and deposition of contaminant onto the
watershed. Fish bioconcentration is discussed in detail in Section 6.6.3.2.1, and soil erosion
and runoff are discussed in Section 6.6.3.2.2.
Deposition to Soil. The cumulative soil concentration of a pollutant as a result of
deposition is derived from the dry deposition rate over the time period of deposition and the
contaminant loss rate from the soil The cumulative soil concentration represents the
concentration increment due to accumulation of contaminant deposited onto soil from one of
the WMUs. The cumulative soil concentration does not take into account background
concentrations of the contaminant that may already be present, whether natural or from other
pollution sources.
Contaminants may be lost from soils as a result of numerous factors, including
leaching, abiotic and biotic degradation, volatilization, runoff, and soil erosion. The overall
soil loss rate, k,, is the sum of the loss rates for each of these processes.
Losses due to degradation GO are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
August 1995 • 6-242
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
The equation for the loss constant due to leaching, k,,, includes water balance terms to
account for precipitation, evapotranspiration, and surface runoff.
Soil concentration depletion due to volatilization is modeled to obtain a better
prediction of soil concentration. However, this mass flux never experiences rainout or
washout and subsequent redeposition (this should not be confused with wet deposition, which
affects particle-phase contaminants, rather than vapor-phase contaminants). If such
redeposition occurred, the soil concentration would be higher than if such redeposition did not
occur. As a result, the algorithm as used (without redeposition) may underestimate soil
concentrations for compounds that would volatilize then dissolve in rainwater and be
redeposited; however, the revolatilization of semivolatile organic contaminants such as dioxin
that have been deposited on soils is very small and can generally be ignored.
The overall soil loss constant may be calculated either with or without pollutant losses
from surface runoff and soil erosion. For a small land area within a watershed, it could be
argued that the soil loss constant does not need to consider such losses if whatever erodes or
runs off in the downgradient direction from a site of concern (i.e., a farm where exposures
occur) is matched by an equal amount which erodes or runs onto it from upgradient areas.
On the other hand, for entire watersheds, losses due to soil erosion and surface runoff are
important and need to be accounted for. This pathway considers a watershed; therefore, the
soil loss constant used includes both a surface runoff loss constant and a soil erosion loss
constant The USLE is used to estimate unit erosion loss.
Equations 6-152, 6-153, and 6-154 present the equations for backcalculating dissolved
water concentration, total water concentration, or bottom sediment concentration, respectively,
from fish. Equations 6-155, 6-156, and 6-157 present the equations for backcalculating soil
concentration from dissolved water concentration, total water concentration, or bottom
sediment concentration, respectively, for overland transport Equations 6-158 through 6-162
calculate various inputs to the overland equations. Equation 6-163 shows the backcalculation
for deposition rate from soil concentration. Equations 6-164 through 6-173 present the
equations for calculating the soil loss constant, k,, which is used in Equation 6-163.
August 1995
6-243
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Fish Bioconcentration: Dissolved Water Concentration
BCF BAFC
(6-152)
Central
tendency High-end
Parameter Definition value value Refer to
Cj, Dissolved water concentration (mg/L) Calculated
Concentration in fish (mg/kg) From Equations 5-66 and 5-69
BCF Bioconcentration factor (L/kg) Chemical-specific 6.7.62
BAFC rqiriii^tBH btoaccumulation factor (L/kg) Chemical-specific 6.7.62
Source: IBM (US. EPA. 1990e; 1993a).
August 1995 6-244
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Fish Biocoocentration: Total Water Column Concentration
'wt
JAF
(6-153)
Parameter
Definite*
Central
tendency
value
High-end
value
Refer to
Total water column concentration (mg/L)
BAF_
Concentration in fish (mg/kg)
Measured bioaccumulation factor (L/kg)
From Equations 5-66 and 5-69
Chemical-specific
6.7.62
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-245
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Fish Bioconcentration: Bottom Sediment Concentration
'*»•
BSAF •/,.-.
(6-154)
Parameter
DefUtfcM
Central
tendency High-«Bd
value value
Refer to
Concentration in bottom sediment (mg/kg)
BSAF
Concentration in whole fish (mg/kg)
From Equations 5-66 and 5-69
Biota to sediment accumulation factor
(unitless)
Chemical-specific
Correction factor to estimate whole fish
concentration (unitless)
0.05
6.7.62
6.7.4.3
OC
Fraction organic carbon in bottom sediment
(unitless)
0.024
0.008
6.7.52
Source: Dioxin document
August 1995
6-246
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Concentration: from Total Water Column Concentration
Csotr-
• JI (6-155)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Concentration in soil (mg/kg)
Total water column concentration (mg/L)
From Equation 6-153
Waterbody flow, volume (L/yr)
3e+ll
13e+10
6.7.5.1
Fraction of total waterbody contamination in
water column (unidess)
See Equation 6-162
Overall total water concentration dissipation
rate (yr'1)
See Equation 6-158
V
«,
Kd,
BD
WA,.
xe
SD
ER
Rf
d.
*
Flow-independent mixing volume (L)
Soil volumetric water content (unitless)
Soil-water partition coefficient (cm3/g)
Soil bulk density (g/cm3)
Watershed area (m2)
Unit soil loss (kg/m2/yr)
Watershed sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yr)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
6.7e+8 8.3*46
See Equation 6-166
Chemical-specific
1J 12
Ue+9 6e+7
See Equation 6-160
See Equation 6-161
3 organics
1 metals
WMU-specifk
0.64 0.15
0.67 0.18
6.7.5.1
6.7.6.1
6.7.3.1
6.7.5.1
6.7.3.2
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA. 1990e; 1993a).
August 1995
6-247
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Concentration: from Dissolved Water Concentration
>Kdlw»TSS*10~*kg/mg)
>m*/L
(6-156)
Central
tendency High-end
Parameter
C«!
Caw
Vf,
f—
W.
V
e.
Kd.
BD
Kd~
TSS
V/AL
*e
SD
ER
Rf
dw
di
Definition
Concentration in soil (mg/kg)
Dissolved water concentration (mg/L)
Waterbody flow volume (L/yr)
Fraction of total waterbody contaminantion
in water column (unitless)
Overall total water concentration dissipation
rate (yr'1)
Flow-independent mixing volume (L)
Soil volumetric water content (unitless)
Soil-water partition coefficient (cm3/g)
Soil bulk density (g/cm3)
Suspended sediment/surface water partition
coefficient (L/kg)
Total suspended solids (mg/L)
Watershed area (m2)
Unit soil loss (kgAn2/yr)
Watershed sediment delivery ratio (unitless)
Soil enrichment ratio (unitless)
Average annual runoff (cm/yr)
Depth of water column (m)
Total depth of waterbody (water column and
sediment) (m)
value value
Palriilateri
From Equation 6-150
3e+ll 13e+10
See Equation 6-162
See Equation 6-158
6.7e+8 8Je46
See Equation 6-166
Chemical-specific
1.5 12
Chemical-specific
10 80
1.3e+9 6e+7
See Equation 6-160
See Equation 6-161
3 organics
1 metals
WMU-specific
0.64 0.15
0.67 0.18
Refer to
6.7.5.1
6.7.5.1
6.7.6.1
6.7.3.1
6.7.6.1
6.7.5J2
6.7.5.1
6.7.3.2
6.7.5.1
6.7.5.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-248
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Concentration; from Bottom Sediment Concentration
This algorithm was used for dioxins and PCBs.
^^^ .
J
water
•££> •* • SD • ER • to/ • 10
(6-157)
x Parameter Definition
C^ Concentration in soil (mg/kg)
Cfc, Contaminant concentration in bottom
sediment (mg/kg)
Vfx Waterbody flow volume (L/yr)
fw-tf Fraction of total waterbody contaminantion
in water column (unitkss)
k^ Overall total water concentration dissipation
rate (yr'1)
VPlrfett/*nvinMw4f>nt mi vino vnliimlp (\ \
6, Soil volumetric water content (unitkss)
Kd, Soil-water partition coefficient (cm3/g)
BD Soil bulk density (g/cm3)
Kd fc Suspended sediment/surface water partition
coefficient (Meg)
TSS Total suspended solids (mg/L)
IT'L DM! tjui ii ILM tl Ajuli ii LMJ! rwp water nsirtiti/vi
coefficient (L/kg)
WAL Watershed area (in2}
Xc Unit soil loss (kg/nvVyr)
SD Watershed sediment delivery ratio (unitkss)
Rf Average annual runoff (cm/yr)
d. Depth of water column (m)
dx Total depth of waterbody (water column and
sediment) (m)
Central
tendency High-end
value value
OUculated
From Equation 6-152
3e+ll 1.3e+10
See Equation 6-162
See Equation 6-158
ft 7f*& ft 1**L/\
See Equation 6-166
Chemical-specific
L5 12
. Chemical-specific
10 80
1 ^ ^ * ^ ft^t i ^
l^JVT^ \JCr f
See Equation 6-160
See Equation 6-161
.
j or games
1 metals
WMU-specific
0.64 0.15
0.67 0.18
Refer to
6.7.5.1
67 S I
6.7.6.1
6.7.3.1
6.7.6.1
6.7.52
6761
.6.7.5.1
f. 7 a 7
6.7.5.1
6.7.5.1
Source: IBM (U.S. EPA. 1990e; 1993a).
August 1995
6-249
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Water Concentration Dissipation Rate
W,.
m
(6-158)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Overall total wafer concentration dissipation
rate (yr'1)
Calculated
Burial rate (yf1)
Bed sediment porosity (unitless)
0.6
6.7.5.2
BS
Bed sediment concentration (mg
sediment/L)
106
6.7.52
Bed sediment/sediment pore water partition
coefficient (LJkg)
Chemical-specific
6.7.6.1
Suspended ffft*ncnt/8urfarf water partition
coefficient (LAg)
Chemical-specifk
Source: IBM (VS. EPA. 1990e; 1993a).
6.7.6.1
TSS
Wb
D.
Total suspended solids (mg/L)
Rate of burial (m/yr)
Waterbody depth (m)
10 80
See Equation 6-159
0.67 0.18
6.7.52
6.7.5.1
August 1995
6-250
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Rate of Burial
Xe • WAL • S0» 103 g/kg - VFX* TSS • 1(T3 £/rog • 103I/m 3
WA'TSS' 10? Urn 3 • lQ~3g/mg
5S
Parameter
Wb
D«naitioo
Rale of burial (m/yr)
Central
tendency
value
Cateii
High-end
value
dated
Refer to
Unit soil toss (kg/m2/yr)
See Equation 6-160
SD
Watershed area (m2)
6e-»-7
6.7.5.1
Watershed sediment delivery ratio (uniUess)
See Equation 6-161
Waterbody flow volume (m3/yr)
3e+8
lJe+7
6.7.5.1
TSS
Total suspended solids (mg/L)
10
80
6.7.52
WA.
Waterbody surface area (m2)
1646
4.6e+4
6.7.5.1
BS
Bed sediment i
miration (kg sedimeni/L)
6.7.52
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-251
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Universal Soil
Loss Equation
Xe */? »AT *LS •€ 'P «907. 18 kg/ton • 245.7 acre/km 2 • 10"* km 2/m 2
Parameter
V
R
K
LS
C
P
Definition
Unit soil loss (kg/m2/yr)
USLE rainfall factor (yr'1)
USLE erodibUity factor (ton/acre)
USLE length-slope factor (unidess)
USLE cover factor (unitless)
USLE erosion control practice factor
(unitless)
Central
tendency High-end
value value
Calculated
WMU-specific
0.25
1 3
0.1 ' OJ
1
(6-160)
Refer to
6.7.32
6.7.32
6.7.32
6.7.32
Source: EM (US. EPA, 1990e; 1993a).
August 1995
6-252
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Watershed; Sediment Delivery Ratio
(6-161)
Central
tendency High-end
Parameter Definition value value Refer to
SD Sediment delivery ratio (unitless) Calculated
a Empirical intercept coefficient (unitless) 0.6 1.2 6.7.3.2
Area of watershed (m2) lJe+9 6e+7 6.7.5.1
Source: IBM (U.S. EPA, 1990e; 1993a).
Aiifiiat 1995 6-253
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Fraction of Contaminant in Water Column
/.
(l
(6-162)
Parameter Definition
f^e. Fraction of total waterbody contaminantion
in water column (unitless)
Kd^ Suspended sediment/surface water partition
coefficient (IJkg)
TSS Total suspended sotius (mg/L)
dy Depth of water column (m)
d, Total depth of waterbody (water column and
sediment) (m)
8^ Bed sediment porosity (unitless)
Kdfc, Bed sediment/pediment pore water partition
coefficient (Meg)
BS Bed sediment concentration (sediment/L)
d^ Depth of bed sedunents (m)
Central
tendency
value
High-end
value
Refer to
Cafrulatfd
Chemical-specific
10
0.64
0.67
0.6
80
0.15
0.18
Chemical-specific
1
0.03
6.7.6.1
6.7.52
6.7.5.1
6.7.5.1
6.7.52
6.7.6.1
6.7.52
6.7.5.1
Source: IBM.
August 1995
6-254
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Deposition to Soil: Combined Deposition Rate
*ks • 10* cm 2/m 2
(6-163)
Parameter
Definition
Central
tendency High-end
value value
Refer to
Average annual combined deposition rate
(g/m2/yr)
Calculated
Concentration in soil at deposition location
(mg/g)
Source: EM (U.S. EPA. 1990e; 1993a).
From Equations 6-155. 6-156.
6-157
z
' BD
k,
t
Mixing depth (cm)
Soil bulk density (g/cm3)
Soil loss constant (yr'1)
Time period of deposition (yr)
2.5 (unnlled)
1.5
See Equation
9
1 (untilled)
12
6-164
30
6.7.3.3
6.7.3.1
6.7.3J
August 1995
6-255
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Loss Constant
*,•*,* +**
Parameter
DefloinoB
Central
tendency High-cod
value value
Refer to
Soil loss constant (yr1)
Soil loss constant due to leaching (yr*1)
See Equation 6-165
Soil loss constant due to degradation (yT1)
6.7.6.1
Soil loss constant due to volatilization (yr'1)
See Equation 6-167
Soil loss constant due to surface runoff
(yr1)
See Equation 6-169
Soil loss constant due to soil erosion (yr'1)
See Equation 6-171
Source: EM (ILS. EPA, 1990e; 1993a).
August 1995
6-256
-------
(.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Loss Constant Due to Leaching
e»z<
e
(6-165)
Parameter
k,, Soil lo
Definition
ss constant due to leaching (yf1)
Central
tendency High-end
value value Refer to
Calculated
Average annual recharge (cm/yr)
WMU-specific
e
z
BD
K-
Soil volumetric water content (mL/cm3)
Soil depdi from which leaching occurs (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
See Equation 6-166
2J (untUkd) 1 (untilled)
1.5 12
Chemical-specific
6.7.3J
6.7.3.1
6.7.6.1
Source: IBM (U.S. EPA. 1990e; 1993a).
August 1995
6-257
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Soil Volumetric Water Content
(6-166)
Parameter
e
e.
q
K,
b
Definition
Soil volumetric water content (mL/cm3)
Soil saturated volumetric water content
(mL/cm3)
Average annual recharge rate (cm/yr)
.Saturated hydraulic conductivity (cm/yr)
Soil-specific exponent representing water
retention (unities)
Central
tendency
value
High-end
value
Refer to
falrifl^fr*}
0.43
0.55
6.7.3.1
WMU-specific
3.600
5.4
20,000
3.0
6.7.3.1
6.7.3.1
Source: SEAM (U.S. EPA, 1988a).
August 1995 6-258
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Soil Loss Constant Due to Volatilization
(6-167)
Central
tendency High-end
Parameter Definition value value Refer to
k^ Soil loss constant due to volatilization (yr'1) raifi)iat»d
K. Equilibrium coefficient (s/cm-yr) See Equation 6-168
Gas phase mass transfer coefficient (cm/s) See Equation 6-169
Source: EM (US. EPA. 1990e; 1993a).
Aufust 1995 6-259
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Volatilization Equilibrium Coefficient
Parameter
^
H
Z
K-
R
T
BD
Source: IBM
K = 3.1536»107j/y
Definition
Equilibrium coefficient (s/cm • yr)
Henry's law constant (aim • mVmol)
Soil depth from which volatilization occurs
(cm)
Soil water partition coefficient (mL/g)
Ideal gas constant (atm • LAnol • K)
Temperature (K)
Soil bulk density (g/cm3)
(U.S. EPA, 1990e; 1993a).
i /\3 / /••• 3 ^ //
r * \\J Ljlfl *lT
•r»s£>
Central
tendeacy High-end
value value
Calculated
Chemical-specific
2.5 (unfilled) 1 (untilled)
Chemical-specific
821 x HT3
298
1.5 12
(6-168)
Refer to
6.7.6.1
6.7.3.3
6.7.6.1
6.7.7
6.7.22
6.7.3.1
August 1995 6-260
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Gas-Phase Mass Transfer Coefficient
ParaBeter
K,
DefUtiM
Gas phase mass transfer coefficient (cm/s)
Central
tendency
value
Calcu
High-end
value
dated
Refer to
Windspeed (m/s) WMU-specifk
Schmidt number on gas side (unitless) See Equation 6-170
Effective diameter of contaminated area (m) See Equation 6-172
Source: IBM (US. EPA, 1990e; 1993a).
August 1995 6-261
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Schmidt Number on Gas Side
(6-170)
Parameter
Definition
Central
tendency
value
High-cod
value
Refer to
Schmidt number on gas side (unities)
Calculated
p.
Pi
Viscosity of air (g/cm • s)
Density of air (g/cm3)
1.81c-4
1.2e-3
6.7.7
6.7.7
Diffusivity in air (cm2/s)
Chemical-specific
6.7.6.1
Source: IBM (U.S. EPA, 1990e; 1993a).
August 1995
6-262
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Loss Constant Due to Runoff
(6-171)
Parameter
Definition
Central
tendeacy
value
High-end
value
Refer to
Soil loss constant due to surface runoff
(yr'1) '
Average annual runoff (cm/yr)
WMU-specifk
e
z
BD
Kd,
Soil volumetric water content (mL/cm3)
Soil mixing depth (cm)
Soil bulk density (g/cm3)
Soil-water partition coefficient (mL/g)
See Equation 6-164
2.5 (unfilled) 1 (unfilled)
U 12
Chemical-specific
6.7.3J
6.7.3.1
6.7.6.1
Source: IBM (US. EPA, 1990c; 1993a).
August 1995
6-263
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways (24)
Effective Diameter
4M (6-172)
Central
tendency High-end
Parameter Definition value value Refer to
de Effective diameter of Calculated
contaminated area (m)
Area of contaminated area 1.34e+9 (watershed) 6e+7 (watershed) 6.7.5.1
Source: EM (U.S. EPA. 1990e; 1993a).
August 1995 6-264
-------
6.0 FATE AND TRANSPORT MODELING
6.6 Food Chain Pathways (24)
Soil Loss Constant Due to Erosion
ParuKtcr
k.
x.
e
z
BD
Kd.
, , >'*.)
• * \BD'Z
v '
DeffaftiM
Kdt*BD
6 +KdsBD
< J
Central
tendency High-end
value value
(6-173)
Refer to
Soil loss constant due to soil erosion (yr'1) Calculated
Unit soil Ion (kg/hi2/yr)
Soil volumetric water content (mL/cm3)
Soil mixing depth (cm)
Soil bulk density (g/cm3)
Soil-waier partition coefficient (mL/g)
See Equation 6-160
See Equation 6-166
2 J (unfilled) 1 (unfilled)
1.5 1.2 .
Chemical-spec ifk
6.7.3J
6.7.3.1
6.7.6.1
Source: EM (U.S. EPA, 1990e; 1993a).
August 1995
6-265
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
\ . <*
6.6J.3 Uncertainty
6.6J.3.1 Surface Water Modeling Framework
The surface water modeling framework presented in the Addendum (U.S. EPA, 1993a)
and used here is a new model that has not been peer-reviewed. Therefore, there is
uncertainty as to how well it represents actual surface water fate and transport processes.
Most of the existing peer-reviewed surface water models in use at EPA, such as WASP and
EXAMS, are so highly site-specific that they could not be feasibly adapted to a generic
analysis such as this. It is uncertain whether use of this model would overestimate or
underestimate risk.
While the surface water model framework is designed to accomodate chemical
transformations within the waterbody, these were omitted from this analysis. These processes
are highly chemical- and site-specific. Assessing the potential for transformation of all 200
chemicals considered would be an extensive research project However, chemicals were
screened to eliminate chemicals that hydrolyze completely in water, forming other
compounds. Also, several classes of chemicals (benzo(a)pyrene and chlorophenols) were
omitted from fish pathways due to evidence that thes chemicals transform to innocous forms
in fish. The effect of omitting such transformations could be either an overestimate or
underestiamte of the risk, depending on whether a chemical transforms into a more or less
toxic or mobile form.
6.6332 Universal Soil Loss Equation
Uncertainty arises out of the use of the Universal Soil Loss Equation. This is an
empirical, though widely used, model. It was intended for use in site-specific situations,
where highly specific input data can be used, and for relatively small fields. How well it
predicts soil erosion in a generic application, as here, and for fairly large sources of eroded
soil, is uncertain. It is most likely that it overestimates quantity of soil eroded.
6.6333 SoU Loss Constant Term
The overall soil loss constant term, k,, is uncertain in several ways.. This term is the
sum of loss rates for leaching, erosion, runoff, degradation, and volatilization. One uncer-
tainty arises from the assumption that all of these loss terms are first order and can therefore
be added together. This is a common assumption, but some of the processes may in fact be
zero order. A first-order loss process may be characterized by a half-life, the time it takes
half of the remaining contaminant to be lost Therefore, the mass lost per unit of time varies
with the concentration. A zero-order loss process is characterized by a constant mass loss per
unit of time. Neither of these processes can be said to be more conservative than the other,
because the first-order rate depends on the starting concentration and the zero-order rate does
not, at any given time, which one results in a higher concentration will depend on the starting
August 1995 6-266
-------
6.0 FATE AND TRANSPORT MODELING 6.6 Food Chain Pathways
concentration. Therefore, it cannot be said whether incorrectly assuming that loss constant
that is actually zero order is first order will overestimate or underestimate soil concentration.
Another source of uncertainty regarding the soil loss constant is that the various loss
processes are calculated independently when, in fact, they occur simultaneously. As a result,
losses could be overpredicted because the amount of contaminant available to each process is
overestimated by not accounting for the other loss processes. This would result in an
underestimate of soil concentration.
The inclusion of losses due to soil erosion and runoff in the soil loss rate may also
overstate the net loss of contaminant from soil, thus underestimating soil concentration. For
small areas, such as the home garden or yard used in soil ingestion and dermal soil pathways,
it could be argued that soil loss due to these mechanisms is offset by erosion and run-on onto
the garden or yard. However, for large areas, such as the watersheds used in the surface
water pathways, such offsetting run-on and soil erosion is less likely to occur, since any soil
erosion or run-on will occur from within the watershed. It is the Addendum's current
recommendation to include these losses.
Finally, degradation losses were set to zero. Degradation rates are highly dependent on
site-specific factors that cannot be accounted for in a generic analysis of this nature and may
be zero. To the extent that constituents do degrade into constituents of less concern, the
omission of degradation from the soil loss constant will underestimate losses and therefore
overestimate soil concentration.
The overall effect of all of the above uncertainties on the soil loss constant is not clear.
Two of the factors would tend to underestimate soil concentration, one would tend to over-
estimate soil concentration, and the effect of one could be either an over- or underestimate of
soil concentration.
6.6JJ.4 Soil Water Content Equation
: The equation from the Superfund Exposure Assessment Manual (U.S. EPA, 1988a) used
to calculate soil water content based on recharge (the net effect of precipitation, irrigation,
evaporation, and runoff) and soil properties was developed for site-specific application. Its
application in a generic analysis raises uncertainty as to how well it predicts soil water
content A distiibution of this value would have been preferred; however, it was not available
and so had to be calculated. However, some of the input parameters are highly generalized
(such as recharge) and others (such as the soil moisture retention exponent, b) are drawn from
estimates rather than measured values. It is not clear in which direction this uncertainty
would affect the results.
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
6.7 FATE AND TRANSPORT INPUTS
This section is organized into seven sections covering approach to selecting values,
meteorological data, soil data, foodchain parameters, surface water parameters, chemical-
specific data, and basic constants.
6.7.1 Approach to Selecting Values
6.7.1.1 Central Tendency vs. High End
To support the establishment of human health-based exit criteria, concentrations
protective of the high end risk posed by all potential exposure pathways and routes were
desired by the Agency. The high-end risk distribution is, conceptually, above the 90th
percentile of the actual (either measured or estimated) distribution. This concept is discussed
in more detail in Section 1. As described there, this analysis uses an approach to estimating
high-end risk recommended in the Guidance for Risk Assessment (U.S. EPA, 1991e) in which
the most sensitive parameters are identified, and then maximum or near maximum values
used for one or a few of these variables, leaving others at their mean values. The WMUs,
fate and transport pathways, constituent-specific parameters, and reasonable exposure
scenarios were identified and characterized using a combination of typical and high-end
values for all input parameters.
For this analysis, two WMU, fate, and transport parameters were set to high-end values,
while all other WMU, fate, and transport parameters were set to central tendency or typical
values. Due to the range between central tendency values and high-end values for many of
the source, fate, and transport parameters, these parameters tended to overshadow exposure
parameters. Therefore, to account for high-end exposure scenarios, two exposure parameters
were also set to high-end values, while all other exposure parameters were set to central
tendency or standard default values. In summary, a total of four parameters were set to high-
end values: two source, fate, and transport parameters and two exposure parameters. Expo-
sure parameters are discussed in Section 5. WMU parameters are discussed in Section 7.
This section describes the fate and transport parameters.
In this report, "typical" or "central tendency" refers to central tendency or midpoint
values such as the median or mean of a distribution of values. The Guidance for Risk
Assessment notes that the arithmetic mean is not necessarily a good indicator of the midpoint
of a skewed distribution and that a median or geometric mean is preferable. Due to the
skewness of the distributions of many of the parameters used in this analysis, the median (or
50th percentile) was preferred to the mean as the typical or central tendency value of a
distribution. Given the often limited nature of the available data and the interdependence of
certain parameters, it was not always possible to obtain and/or use the mean or median value.
In such cases, a best estimate was made of a central or typical value.
Before high-end values were selected, the algorithms were analyzed, and, where
necessary due to the complexity of algorithms, sensitivity analyses were conducted to
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
determine the effect of every input parameter individually on the contaminant concentration in
the environmental media of interest and its ultimate effect on the resultant human health risk.
The results of these analyses were u^ed to determine the magnitude of the high-end parameter
relative to central tendency for each parameter. For instance, larger values from a range of
values may yield more conservative results for some parameters, whereas smaller values from
a range of values may yield more conservative results for other types of parameters.
Therefore, the high-end parameter is not always equivalent to the large value from a given
range of parameter values but is a value that will give more conservative results. In the
context of setting parameter values, "high end" refers in this report to approximately the 90th
percentile or maximum (or 10th percentile or minimum) of a distribution of values.
Percentile values were preferred to maximum or minimum values when they were available,
so as to eliminate the use of outliers as a high-end value whenever possible. If percentile or
maximum/minimum data were not available, a best estimate was made from the available
data.
Central tendency and high-end values were collected for as many of the parameters as
possible. Some parameters were determined to be interdependent, such as watershed area and
waterbody flow. In order to prevent unrealistic combinations (say of a very large watershed
and a very small stream) interdependent parameters were varied together and treated as a
single parameter. For a few parameters, only central tendency values were used. This
occurred when (1) only one (usually typical) data value could be located, or (2) sensitivity
analysis showed that the results "were insensitive to a parameter over a wide range of potential
values.
The two most sensitive WMU, fate, and transport parameters varied by WMU, pathway,
and constituent In order to identify the most important WMU, fate, and transport parameters
consistently, the calculations were run for all possible combinations of two high-end WMU,
fate, and transport parameters for which both a central tendency and high-end value were
available. The lowest (most stringent) result was used as the exit criteria.
6.7.1.2 Level of Review
An extensive selection of potential references was reviewed for use in setting typical
and high-end values for the parameters for this analysis. Many references were eliminated
after an initial review determined that they did not contain relevant information on the
specific parameter values sought
When multiple references contained relevant data on specific parameters, these were
ranked according to their technical credibility and according to the level of detail on data
distribution (e.g., the availability of percentile dati versus mean, maximum, or minimum
data). References conventionally used by the Agency (e.g., the Exposure Factors Handbook)
were given the highest preference. References that are not conventionally accepted sources
were selected on the basis of peer judgments of their technical credibility. References with
greater detail on the distribution of data values were also given higher preference. Some
references provide data in the form of values used in example calculations. These were
August 1995 6-269
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
avoided whenever possible, although references cited for such values were examined if they
were available.
Because the methodology used for this analysis was designed to be a^ consistent as
possible with the Combustor Indirect Exposure methodology, recommendations for parameter
values provided in the Addendum to the Combustor Indirect Exposure (U.S. EPA, 1993a)
were given special consideration. The work group that generated the Addendum performed
extensive review of the recommended values in the original Combustor Indirect Exposure
document; therefore, these were considered to be highly credible values. In some parts of the
Combustor Indirect Exposure methodology, especially in the surface water impacts frame-
work, many parameters were not commonly used parameters with readily available values but
were highly specific to the Addendum methodology, making the accompanying
recommendations the only reliable data source for those parameters.
Extensive references were not available for some parameters. When only a single
reference could be located, it was used unless its technical credibility was deemed
unacceptably low. If no acceptable references could be located for a parameter, a best
estimate of the typical or high-end value was made. In making these estimates, limitations on
the range of values possible were considered (e.g., a fraction must by definition lie between 0
and 1), as well as similarities to other parameters.
6.7J Meteorological Data
6.7.2.1 Selection of Locations for Meteorological Data
The approach to setting central tendency and high-end meteorological conditions for
this analysis was to evaluate sets of meteorological data from a variety of locations, and
select locations that reflected central tendency or high-end conditions. This was dictated by
the air dispersion models, which require hourly meteorological data for a specific location.
A set of 29 meteorological stations identified in Environmental Quality Management
and E.H. Pechan and Associates, Inc. (1993) as representative of the United States was
selected as the set of locations from which locations would be selected for this analysis.
Section 7.1.5.4 provides a more detailed discussion of how these locations were selected.
Pairs of central tendency and high-end locations were then selected from these 29 locations
for air pathways and overland transport pathways.
For air pathways, the selection was WMU-specific and based on extensive sensitivity
analysis. Only the effect of meteorological data on emissions and dispersion was considered
in selecting locations for air pathways; however, for consistency, once a pair of locations was
selected for a pathway, any meteorological data used in that pathway were selected to cor-
respond to the locations chosen, even in any overland transport component of the pathway.
The sensitivity analyses used to select locations for air pathways are described in more detail
in Section 7.1.5.4. The specific locations selected for each WMU are identified in Sections
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
7.2.4 (ash monofill), 7.3.3 (land application unit), 7.4.3 (wastepile), 7.53 (surface
impoundment) and 7.6.3 (aerated tank).
Ovcriand pathways are driven by soil erosion, for which the critical meteorological
input is the Universal Soil Loss Equation (USLE) rainfall factor (R). Therefore, to select
central tendency and high-end locations for overland pathways, the 29 locations were ranked
on rainfall factor, and the 50th and 90th percenti'.e locations chosen for all overland pathways.
These locations were Portland, Maine (central tendency) and Atlanta, Georgia (high end).
The rainfall factor is discussed in more detail below in Section 6.7.2.2. Table 6-11 shows the
29 locations ranked by rainfall factor.
Only meteorological data for the overland pathways are presented in the equation tables
in Sections 6.2 through 6.6; meteorological data for air pathways are listed as WMU-specific.
Therefore, only meteorological data for the two overland locations (Portland and Atlanta) are
provided in the following section. Meteorological data for all locations are provided in
Section 7.7.1.
6.7.2.2 Annual Average Meteorological Data for Overland Pathways
Annual average meteorological data needed for the overland transport modeling
included recharge and runoff. Table 6-12 shows values for these parameters for Portland and
Atlanta.
Recharge values were based on averages of recharge rates presented in the following
sources: Aller et al. (1988), Heath (1984), and USGS (1984).
Runoff was based on isopleths of annual average surface-water runoff from the Water
Atlas of the United States (Gcraghty et al., 1973) (plate 21). The Water Atlas defines surface-
water runoff as all flow contributions to surface waterbodies, including direct runoff, shallow
interflow, and groundwater recharge. The Addendum (U.S. EPA, 1993a) recommends
reducing this value by 50 percent to estimate surface runoff; this was done.
An additional parameter typically associated with meteorological data and used in the
fate and transport modeling is temperature. However, temperature is used here to
dimensionalize Henry's law constant (Le., convert it to a unitkss value). In this application,
the temperature needed is the temperature to which the dimensional Henry's law constant was
adjusted, rather than the average ambient air temperature. Since Henry's law constant values
were always adjusted to 25 °C, the temperature is set to 25 °C accordingly.
6.73 SoU Data
6.7J.I SoU Properties
A variety of soil parameters were required for the modeling. These parameters are
interdependent and depend on the type of soil (e.g., loam, clay). However, values for these
August 1995 6-271
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-11. USLE
Location
Miami. FL
Houston, TX
Charleston. SC
Atlanta, GA
Little Rock, AK
Raleigh-Durham. NC
Philadelphia, PA
Chicago, tt.
Hartford, CT
Huhtington, WV
Lincoln. NE
Cleveland, OH
Minneapolis, MN
Hanisburg. PA
Portland. ME
_ Phoenix, AZ
Bismarck. ND
Fresno. CA
Los Angeles, CA
Salem, OR
San Francisco. CA
Albuquerque. NM
Denver. CO
Boise, ED
Salt Lake City, UT
Seattle, WA
Casper, WY
Las Vegas, NV
Winnentuca, NV
•
Rainfall Factor Values for Meteorological
Rainfall Factor (jr1)
450
440
400
300
275
250
185
Iff
150
150
150
125
125
115
110
75
65
50
50
50
50
4j
45
35
35
35
20
20
10
Locations Used
Percentile
. 100
96
92
89
85
82
78
64
64
64
64
57
57
53
50
46
42
28
28
28
28
21
21
10
10
10
3
3
0
August 1995 6-272
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-12. Meteorological Data for Overland Pathways
Recharge Runoff Windspeed
Location (cm/yr) (cm/yr) (m/s)
Portland 28 25 4.6
Atlanta 15 22 4.6
parameters may also vary within a soil type. Because these parameters are interdependent,
they are varied as a set, with one set for central tendency properties and one set for high-end
properties.
.. • ' \
A loam soil was chosen to characterize both the on-site and off-site soils simulated in
this modeling effort All soils are composed of varying percentages of sand, silt, and clay.
Loam, by definition, is composed of fairly equal proportions of sand, silt, and clay; therefore,
its physical properties represent a fairly typical soil type as it represents a combination of
each of the individual soil textures. Loam type soils are also fairly prevalent in the United
States. Central tendency and high-end values were selected from the range of values for loam
soil so that each individual soil parameter required by the model is consistent with a loam
soil
Table 6-13 summarizes the soil properties data evaluated and used. Because many of
the parameters are interdependent, they are set to central or high-end values as a set: they are
either all central or all high end.
Many of the soil properties are based on bulk density. Bulk densities for loam were
taken from Carsel et aL (1988). This paper presented mean, median, 25th percentile, 75th
percentile, and standard deviation by hydrologic soil class and depth. Data for hydrologic
class A were considered to best correspond with loam, and data for surface soils (depth 0-30
cm) were selected. The median value was selected as a central tendency value. A low value
was desired for the high-end bulk density, as lower bulk density results in higher soil
concentrations. Since 10th percentile data were not provided, a high-end value had to be
estimated. For normally distributed data, the 10th percentile may be estimated by subtracting
1.282 times the standard deviation from the mean. Based oh the similarity of mean and
median values, the data distribution was assumed to be approximately normal, and a high-end
value was estimated in this way. As a check, this value was compared to the provided 25th
percentile and was lower, as would be expected.
Porosity (n), also sometimes called saturated water content (9^), is calculated from
bulk density (BD) and particle density (p,) as follows:
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6.0 FATE AND TRANSPORT MODELING
6.7 Fate and Transport Inputs
Table 6-13. Summary of Soil Data for Loam
Parameter Mean
Bulk density (g/cm3) 1.45
Total porosity (cm3/cm3)
Saturated water content
(cm3/cm3)
Partkle density (g/cm3)
Saturated hydraulk
conductivity (cm/yr)
Sand content (%) 40
Clay content (%) 19.7
SUt content (%)
Soil moisture retention 5J9
index (unities*)
Percent organk matter 0.86
Fraction oceanic carbon
Standard 25th 75th
Median deviation percentile pcrcentile
1.53 024 1.4 1.6
Cakulated
No distribution available
CakuUled
NA 6.5 NA NA
NA f.2 NA NA
Cakulated
NA 1.87 NA NA
0.62 0.79 NA NA
Cakulated
Central High
tendency end
1.5 12
0.43 OJ5
2.65
3.600 20.000
40
19.7
40.3
5.4 3.0
1 . OJ
0.006 0.002
(unitless)
(6-174)
NA = Not applicable.
«»e =i-££
** Ps '
Bulk density was set as described above. The value used for particle density, pr is a
standard value for mineral material.
Saturated hydraulic conductivity was calculated from a regression equation presented in
Carsel and Parrish (1988), relating saturated hydraulic conductivity to porosity, sand content,
and clay content Sand and clay content were taken from Carsel and Parrish (1988), which
presents means and standard deviations for these values for various soil types. Mean values
for loam were used. Silt content is calculated from sand and clay content so that the three
values sum to 100 percent Central tendency and high-end porosity values calculated as
described above were used; central tendency saturated hydraulic conductivity is based on the
central tendency porosity, and high-end saturated hydraulic conductivity on the high-end
porosity.
The soil moisture retention index is a measure of the ability of a soil to retain water.
Mean and standard deviations for this parameter for loam soil are presented in Clapp and
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Hornberger (1978). A low value was desired for the high-end soil moisture retention index as
lower values result in higher soil concentrations. Since 10th percentile data were not
provided, a high-end value had to be estimated. For normally distributed data, the 10th
percentile may be estimated by subtracting 1.282 tunes the standard deviation from the mean.
The data distribution was assumed to be approximately normal, and a high-end value was
estimated in this way.
Percent organic matter is based on data from Carsel et al. (1988), which presents mean,
median, and standard deviation by hydrologic soil class and depth. Data for hydrologic class
A were considered to best correspond with loam, and data for surface soils (depth 0 to 30 cm)
were selected. A value of 1 percent was selected as a central tendency value. A low value
was desired for the high-end percent organic matter, as lower organic matter results in higher
soil concentrations. Since 10th percentile data were not provided, and the data did not appear
to be normally distributed, a high-end value had to je estimated A value of 0.3 percent was
used, based on best professional judgment Percent organic matter was then converted to
fraction organic carbon, as follows: ,
f - %OM (6-175)
* 1.724.100
6.7J.2 Soil Erosion Parameters
Soil erosion parameters include the USLE input parameters, enrichment ratio, and the
empirical sediment delivery ratio intercept, a. These are described in the following sections.
6.7J.2.1 USLE Factors
The USLE rainfall/erosivity factor, R indicates the intensity and erosion potential of
local/regional rainfall. This factor is derived from data on the frequency and intensity of
storms. This value is typically derived on a storm-by-storm basis, but it has been compiled
regionally for the development of average annual values. Given that this parameter is a
function of the meteorological conditions in an area, the rainfall/erosivity factor corresponding
to the locations selected for meteorological data was used. Values for the USLE rainfall
factor were based on an isopleth map from Wischmeier and Smith (1978). For the United
States, values range from <20 to 550 yr*1. Values for Portland and Atlanta are 110 yr'1 and
300 yr*1, resepctively. Table 6-10 in section 6.7.2.1 shows the values used for all 29
meteorological locations considered (see Section 7.1.5.4 for a discussion of how these
locations were selected).
The USLE credibility factor, K, reflects how easily a particular soil will erode, based
on the soil's physical properties, independent of rainfall, slope, or other factors. The
credibility factor can range from <0.1 to 0.7 tons/acre. Wischmeier and Smith (1978) present
a nomograph from which the USLE credibility factor may be estimated using percent silt,
percent sand, and percent organic matter for the soil. This gives a first approximation of K
that Wischmeier and Smith suggest is applicable to most agricultural soils. Further
August 1995 6-275
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
refinements to K may be made based on soil structure and permeability for other types of
soils; however, this was not done because the soils considered are agricultural soils. The
percent silt, percent sand, and percent organic matter for loam presented in Table 6-13 were
used to estimate a USLE credibility factor of 0.25. The difference in organic matter for the
central tcncdoncy and high-end soil characterizations is not sufficient to make any difference
to the credibility factor thus estimated. Therefore, the credibility factor was not varied.
The USLE length-slope factor, LS, reflects the influence of slope steepness and length
of the field in the direction of the erosion. Steeper slopes and longer lengths lead to higher
length-slope factors. Therefore, the two key considerations for its assignment are the size of
the field for which erosion estimates are being made and the slope of that field. The length
slope factor can range from <0.1 to 20. The values selected, 1 for central tendency and 3 for
high end, are applicable to a variety of slope lengths (mostly in excess of 100 m) and
steepnesses ranging from gentle to moderate slopes. Very large slopes were not considered
due to the fairly long lengths being considered.
The USLE cover and management practice factor, C, primarily reflects how vegetative
cover and cropping practices, such as planting across slope rather than up and down slope,
influences erosion. This factor ranges from 0 to 1. A value of 1 represents bare soils;
however, if even the slightest amount of vegetation is present, C typically does not exceed
0.5. C varies with type and extent of vegetative canopy and type and extent of ground cover.
For this assessment, no appreciable canopy was assumed to exist The central tendency and
high-end values selected for C, 0.5 and 0.1 were selected to correspond to vegetative cover
values of 0 and 50 percent, respectively, based on a table in Wischmeier and Smith (1987).
The value used for 50 percent was interpolated from values for 40 and 60 percent vegetative
cover for weeds and grasses.
The USLE supporting practice factor, P, reflects the use of surface conditioning, dikes,
or other methods to control runoff/erosion. This i actor can be no greater than 1. Howeve:,
values less than 1 should only be assigned when specific practices are employed which are
designed to reduce erosion. A supporting practice factor of 1 was used in this assessment,
reflecting the implementation of no erosion control practices.
6.73^2 Enrichment Ratio
Enrichment refers to the fact that erosion favors lighter soil particles, which have higher
surface area to volume ratios and are higher in organic matter content Therefore,
concentrations of organic contaminants, which are a function of organic carbcr. content of
sorbing media, would be expected to be higher in eroded soil as compared to in situ soil. As
stated in the Addendum (U.S. EPA, 1993a), while enrichment is best ascertained with
sampling or site-specific expertise, generally it has been assigned values in the range of 1
to 5. The enrichment ratio would be expected to be higher in sandy soils as compared to
silty or loamy soils because the finer silt particles that erode from a soil generally
characterized as sandy are more a deviation from the norm compared to silt particles which
erode from a soil generally characterized as silty or loamy. A value of three for organic
August 1995 6-276
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
contaminants would be a reasonable estimate for loamy or silty soils. The value is set to 1
for metals, reflecting that absorbdon of metals to soil particles is not correlated to organic
matter content
6.7J.2J Empirical Intercept Coefficient, a
This coefficient is used to calculate sediment delivery ratio for erosion on a large area.
Its value depends on the area of the watershed or field under consideration. The Addendum
(U.S. EPA, 1993a) presents Agency interim recommendations for values of a based on area;
these are shown in Table 6-14.
6.7JJ Other Soil-Related Parameters
Other soil related parameters include area of garden or agricultural field, mixing depth,
and time period of deposition or irrigation.
6.7J.3.1 Area of Garden and Agricultural Field
No data were available on the size of home gardens, gardens on subsistence farms, or
yards of residential lots (for soil ingestion). Therefore, a single set of central tendency and
high-end values was estimated for these, based on best professional judgment; this set is
refered to as garden area, even though it might also apply to a yard Because a larger area
leads to greater dilution of deposited or eroded contaminant, a high-end garden would be one
that was relatively small The selected values, 5,100 m2 and 2,024 m2, correspond to 1.25
acres and 0.5 acres, respectively.
Areas for agricultural fields were estimated from data in the 7992 Census of Agriculture
(U.S. Department of Commerce, 1992). The Census gives average farm acreage by State for
48 States (the data are not yet complete for the two missing States). No percentile data were
available. The State averages r».-ge from 76 to 5,173 acres (308,000 to 21,000,000 m2). The
average of the Statt averages (with some outliers from the high end of the distribution
Table 6-14. Values for Empirical Intercept Coefficient a
/
Area (mi2) •
stn 2.1
1 L9
10 M
100 12
1.000 0.6
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
omitted) was 462 acres, or 1,872,000 m2. This was rounded to one significant figure
(2,000,000 m2 or 500 acres) and used as the central tendency value. Because a larger area
leads to greater dilution of deposited or eroded contaminant, a high-end field would be one
that was relatively small. Therefore, an acreage from the low end of the range was desired
for the high-end value. Since averaging by State eliminates the extremes, the minimum State
average value was selected as the high-end value; smaller values would clearly exist if the
unaggregated data were available. The minimum Scate average was 76 acres (308,000 m2),
which was rounded to one significant figure (300,000 m2 or 75 acres). These data do not
distinguish between commercial and subsistence farms.
6.7 J.3.2 Mixing Depth
Mixing depth reflects the depth of soil into which deposited or eroded contaminant is
mixed. It is important to distinguish between soil that is tilled for agricultural purposes and
soil that is unfilled in determining appropriate mixing depth values. A lower mixing depth
results in less dilution of contaminant, and therefore higher soil concentrations; therefore, a
high-end mixing depth would be smaller than a central tendency mixing depth.
For tilled soils, the Indirect Exposure Document (U.S. EPA, 1990e) suggests a range of
10 to 20 cm for tilled mixing depth. The Addendum (U.S. EPA, 1993a) recommends that 20
cm is a value "commonly used for tilled agricultural fields and home gardens." Based on
these sources, a mixing depth of 20 cm was selected as central tendency and a mixing depth
of 10 cm was selected as high end.
For untilled soils, mixing depth would be expected to be considerably smaller than for
tilled soils. The Addendum (U.S. EPA, 1993a) recommends that 1 cm is a value "commonly
used for non-tilled situations such as undeveloped land, pasture land, or residential
properties." U.S. EPA (1990b) provided a second value, 2.5 cm. These were the only values
located for untilled mixing depth. Therefore, 2.5 cm was used as the central tendency value
and 1 cm as the high-end vak_.
6.7.3.3.3 Time Period of Deposition or Irrigation
Time period of deposition or irrigation was set equal to die exposure duration. Central
tendency and high-end values for exposure duration are 9 and 30 years for most receptors; for
fanners, they are 20 and 40 years. See Section 5 for a discussion of exposure inputs.
6.7.4 Foodchain Data
6.7.4.1 Plant Parameters
i
The parameters contained in this section were used to calculate the contaminant
concentration in the various types of vegetation consumed by either humans or livestock.
Data ranges were not available for most of these parameters; therefore, best estimates were
used.
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
6.7.4.1.1 Crop Yield .
a"
Values for crop yield are rarely available. However, crop yield may be estimated from
dry harvest yield and area harvested as follows (Shor et al., 1982):
v Yh
Yp"-k <6-176'
where
Yp = Crop yield (kg DW/m2)
Yh = Dry harvest yield (kg DW)
Ah = Area harvested (m2).
Crop yield is needed for fruits and aboveground vegetables and forage. It is not needed for
root vegetables.
Fruits and Aboveground Vegetables. Crop yield for fruits and aboveground
vegetables was estimated as a consumption weighted average of values for fruits, fruiting
vegetables, legumes, and leafy vegetables. Table 6-15 lists the specific fruits and vegetables
included in each of the four groups.
Table 6-16 summarizes the calculations. U.S. average harvest yield and area harvested
values for 1993 for the fruits and vegetables listed in Table 6-15 were used (USDA, 19945;
1994c). Average harvest yield values were converted to dry weight using average conversion
factors for fruits, fruiting vegetables, legumes, and leafy vegetables (Baes et al., 1984). Crop
yields were then calculated for fruits, fruiting vegetables, legumes, and leafy vegetables using
the equation above. The crop yields were then weighted by relative consumption of each
group to determine the weighted average crop yieli of 1.7 kg DW/m2.
The consumption rate for fruits was based on a whole weight intake of 88 g/day from
the Dioxin document (U.S. EPA, 1994a) and an average whole-weight to dry-weight
conversion factor for fruits (excluding plums/prunes, which had an extreme value) of 0.15
from Baes et al (1984). The rest of the consumption rates are from Technical Support
Document for Land Application of Sewage Sludge (U.S. EPA, 1992e); these were presented as
dry weight in the source document The consumption rates used for weighting the three
vegetable categories do not correspond exactly to the consumption rate for aboveground
vegetable used to calculate exposure. The consumption rates used to calculate exposure were
considered to be the best currently available; however, they were not broken down into
categories of vegetables as was needed here.
Forage. Crop yield for forage was estimated as a weighted average of crop yields for
pasture grass and hay. A crop yield value for pasture grass of 0.15 kg DW/m2 was used
(Dioxin document, U.S. EPA, 1994a); this was a direct estimate, as estimates of harvest yield
and acres harvested are not available for pasture grass.
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6.0 FATE AND TRANSPORT MODELING
6.7 Fate and Transport Inputs
Table 6-15. Fruits and Vegetables Included in Crop Yield Calculations
Fruits
Apple
Apricot
Berry
Chary
Cranberry
Grape
Peach
Pear
Plum/prune
Strawberry
Fruiting vegetables Legumes
Asparagus Snapbeans
Cucumber
Eggplant
Sweet pepper
Tomato
Leafy vegetables
Broccoli
Brussels sprout
Cabbage
Cauliflower
Celery
Lettuce
Spinach
Table 6-16. Calculation of Crop Yield for Fruits and Aboveground Vegetables
•
Fruit
Leafy
vegetables
Fruiting
vegetables
Legumes
Area
harvested
(-')
8.10E+09
237+09
2.64E+C9
1.15E+09
Harvest
yield
(kgDW)
2.05E+09
5.82E408
2.78E+10
8.59E+07
Unweighted
crop yield
(kg DW/m2)
0.25
0.24 .
10.5
0.075
Intake
(g DW/d)
13.4
2S>
42
8.8
Weight
0.47
0.07
0.15
031
Weighted
crop yield
(kg DW/m2)
0.12
0.017
1.6
0.023
1.7
For hay, a dry harvest yield of 1.22e+ll kg DW was estimated from the U.S. average
harvest yield for hay for 1993 of 1.35e+ll kg (USDA, 1994a) using a dry weight conversion
factor of 0.9 (Fries, 1994). U.S. average area harvested for hay for 1993 was 2.45e+ll m2
(USDA, 1994a). From these, a crop yield of 0.5 for hay was estimated using the above
equation.
These crop yields were weighted based on the fraction of a year cattle could be
pastured; the weights used were 0.75 for pasture grass and 0.25 for hay, based on 9 months
per year in pasture and 3 months per year not in pasture (and fed hay). This resulted in a
weighted crop yield for forage of 0.24 kg DW/
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
6.7.4.1J Interception Fraction
The interception fraction for the various vegetation of interest". . . accounts for the fact
that not all of the airborne material depositing within a unit area will initially deposit on
edible vegetation surfaces." (Indirect Exposure Document, U.S. EPA, 1990e). Interception
fraction is calculated from crop yield. '
Fruits and Aboveground Vegetables. The interception fraction for fruits and above-
ground vegetables was estimated as a consumption weighted average of values for fruits,
fruiting vegetables, legumes, and leafy vegetables. Table 6-15 lists the specific fruits and
vegetables included in each of the four groups.
Baes et al. (1984) gives the following general equation for calculating interception
fraction: ,
Rp'.l-e^f (6-177)
where
Y = Empirical constant
Yp = Crop yield (kg DW/m2).
Table 6-17 summarizes the calculations for interception fraction. Unweighted crop
yields (see previous section) were used with values for the empirical constant suggested by
Baes et aL (1984) for each type of fruit or vegetable. The interception fractions for fruits,
fruiting vegetables, leafy vegetables, and legumes were then weighted by relative consumption
of each group to determine the weighted average interception fraction of 0.05.
The consumption rate for fruits was based on a whole weight intake of 88 g/day from
the Dioxin document (U.S. EPA, 1994a) and an average whole-weight to dry-weight
conversion factor for fruits (excluding plums/prunes, which had an extreme value, of 0.15
from Baes et aL (1984). The rest of the consumption rates are from Technical Support
Document for Land Application of Sewage Sludge (U.S. EPA, 1992e); these were presented as
dry weight in the source document The consumption rates used for weighting the three
vegetable categories do not correspond exactly to the consumption rate for aboveground
vegetable used to calculate exposure. The consumption rates used to calculate exposure were
considered to be the best currently available; however, they were not broken down into
categories of vegetables as was needed here.
Forage. The interception fraction for forage was estimated from the weighted average
crop yield for pasture grass and hay (see previous section) as follows (Chamberlain, 1970):
--W <6'178)
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-17. Calculation of Interception Fraction for
Fruits uid Aboveground Vegetables
Fruit
Leafy
vegetables
Fruiting
vegetables
Legumes
Unweighted
crop yield
(kg DW/ma)
025
024
10.5
0.075
Y
0.0324
0.0846
0.0324
0.0324
Unweighted
interception
fraction
(unities)
8.14e-3
0.021
029
0.0024
Intake
(g DW/d)
13.4
2.0
42
8.8
Weight
0.47
0.07
0.15
0.31
Weighted
interception
fraction
(uniUess)
0.0038
0.0014
0.042
0.00075
045
where
Y = Empirical constant
Yp = Crop yield (kg DW/m2).
Chamberlain (1970) gives a range for the empirical constant of 2.3 to 3.33. The midpoint of
the range, 2.88, is used, as suggested by Baes et al. (1984). The resulting interception
fraction is 0.5.
6.7.4.1 J Plant Surface Loss/Weathering Coefficient
The value for the plant surface loss coefficient parameter corresponds to physical
processes that remove particles from the plant surface. As cited in the Addendum (U.S. EPA,
1993a), the value used of 18 yr*1 (which corresponds to a half-life of 14 days) is recommend-
ed for pollutants that do not degrade or degrade very slowly, such that the loss coefficient is
based on physical processes removing particles from plants. A plant surface loss coefficient
that incorporated both physical and chemical degradation processes was also presented for a
single chemical in this reference. However, the chemical-specific data needed to include
chemical degradation processes in this parameter were not available. Therefore, the afore-
mentioned recommended value was used as the central tendency value and was not varied.
6.7.4.1.4 Length of Exposure to Deposition Before Harvest
Information pertaining to the length of plant's exposure to deposition per harvest is
limited and is highly site specific as it depends on the length of the local growing season.
The value of 0.16 yr (60 days) used for the aboveground fruits and vegetables was cited in
August 1995 6-282
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
the Combustor Indirect Exposure document (U.S. EPA, 1990e). This value reflects the time
period between successive hay harvests from Belcher and Travis (1989). However, due to the
limited availability of this va_uc in the literature, it was necessary for the aforementioned
reference to extrapolate this value to the foods consumed by humans. The limited availability
of appropriate data resulted in using this value as a central tendency value which was not
varied
/
The length of exposure to deposition value for forage was also obtained from the
Combustor Indirect Exposure document However, this value (0.12 yr or 45 days) represents
the average of the period between successive hay harvests (60 days) and the period between
successive cattl* grazing in any one field (30 days) from Belcher and Travis (1989). Here
again, the limited availability of appropriate data resulted in using this value as a central
tendency value which was not varied.
6.7.4.1.5 Correction Factors for Plant Uptake (VG^ and VG^)
Fruits and Aboveground Vegetables. VGM is a correction factor for air-to-leaf
transfer of contaminants recommended by the Dioxin document (U.S. EPA, 1994a). The air-
to-plant transfer factor used to estimate plant concentration due to uptake of vapor-phase
contaminants was based on data from experiments with azalea leaves. This correction factor
is based on the assumption that there is negligible translocation of lipophilic contaminants to
inner parts of bulkier vegetation so that the concentration in the outer portion of the bulkier
fruits and vegetables would be similar to that predicted for azalea leaves, while the overall
concentration would be lower. The value of 0.01 was estimated in the Dioxin document
This correction was applied for lipophilic compounds (those with a log K^ > 4). For soluble
compounds Gog Kow < 4), this correction factor was set to 1.
Root Vegetable? This is a correction factor for root uptake of contaminants for root
vegetables for lipophilic compounds recomn (ended by the Dioxin document (U.S. EPA,
1994a). The root concentration factor used to estimate root uptake for root vegetables was
based on data from experiments with barley roots. This correction factor is based on the
assumption that there is negligible translocation of lipophilic contaminants to inner parts of
bulky vegetation, so that the concentration in the outer portion of the root vegetable would be
similar to that predicted for barley roots, while the overall concentration would be lower. The
value of 0.01 was estimated in die Dioxin document and was used for lipophilic compounds
Gog K^,, > 4). For soluble compounds (log Kow < 4), it was set to 1.
6.7.4 .2 Animal (Terrestrial) Parameters
The parameters in this section are used io calculate contaminant concentration in animal
tissue. Data ranges were not available for many of these parameters; therefore, best estimates
were used.
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6.7 Fate and Transport Inputs
6.7.4.2.1 Consumption Rate of Forage/Diet Fraction that is Forage
Consumption rates of forage for beef and dairy cattle are based on data on average dry
matter intake from NAS (1987) and percent of diet that is forage from Boone et al. (1981).
These values are somewhat different for beef and dairy cattle. For beef cattle, the data reflect
unsupplemented beef cattle. For dairy cattle, the data reflect dairy cattle on subsistence
farms. Table 6-18 summarizes the data used to j-et a forage consumption of 8.8 kg DW/d for
beef cattle and 13.2 kg DW/d for dairy cattle. These reflect 75 and 65 percent of the cattle
diet for beef and dairy cattle, respectively.
6.7.4.2.2 Fraction of Forage Contaminated
This value is assumed to be 1 for forage because all forage would be grown on the
farm and would therefore potentially be contaminated.
6.7.4.2 J Consumption Rate of Soil/Diet Fraction that is Soil
Consumption rates of soil for beef and dairy cattle are based on data on average dry
matter intake from NAS (1987) and soil consumption as a percent of dry matter intake from
Fries (1994). These values are somewhat different for beef and dairy cattle. For beef cattle,
the data reflect unsupplemented beef cattle. For dairy cattle, the data reflect dairy cattle on
subsistence farms. Table 6-18 summarizes the data used to set a soil consumption of 0.5 kg/d
for beef cattle and 0.4 kg/d for dairy cattle. These reflect 4 and 2 percent of the cattle dry
matter intake for beef and dairy cattle, respectively.
6.7.4J.4 SoU Bioavailability
The bioconcentration factor used to estimate concentration of dioxin-like compou ids in
animal tissues is based on uptake from cattle feed. The soil bioavailability factor accounts for
Table 6-18. Summary of Cattle Diet Data
Tjpeof
cattle
Beef
Dairy
Average
body weight
(BW)
(kg)
590
630
Dry natter intake
(DMI)
%of
BW
2%
32%
kg
DW/d
11 A
20J
Forage
consunptMM
%of
DMI
75%
65%
kg
DW/d
8.8
132
Soilcoofl
%of
DMI
4%
2%
imptk»
kg/d
0.5
0.4
August 1995
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
soil being a less efficient vehicle of transfer compared to cattle feed Hence, the soil bio-
availability factor is used to reduce the bioconcentration ratio of contaminant as determined
from cattle vegetative intake such that the bioconcentradon ratio of contaminant reflects that
for catde soil intake. A reasonable value for 2,3,7,8-TCDDioxin of 0.65, as presented in the
Dioxin document, was used as a central tendency value and not varied for this modeling
effort
6.7.4.2.5 Consumption Rate of Water
The Combustor Indirect Exposure document and the Addendum did not present a range
of water consumption rate values for cattle. Rather, the values presented in these references
represent average consumption rates. No other data on cattle consumption of water were
found; therefore, the average water consumption rate of 50 L/d was used as the central
tendency value and was not varied.
6.7.4.3 Fish Parameters
6.7.4J.1 Fraction Lipid
For dioxin-like compounds, the Biota Sediment Accumulation Factor relates concentra-
tion in sediment to concentration in fish lipid. However, receptors consume fish muscle and
lipid This is a correction term used for dioxin-like compounds to estimate whole fish
concentration from fish lipid concentration. The term is the fraction of whole fish that is
lipid, and its use distributes the contaminant in the fish lipid over the entire body of the fish.
A value of 0.05 was used for this term, as recommended in the Proposed Water Quality
Guidance for the Great Lakes System (58 FR 20802, April 16, 1993). This value reflects the
lipid content of the body of the fish and excludes the head, which has a higher lipid content
but is not typically eaten.
6.7.5 Surface Water Data
6.75.1 Waterbody/Watershed Characterization
The parameters contained in this section characterize the surface waterbody (a river)
simulated by the model The waterbody characterization parameters are another example of a
set of parameters that are interdependent; therefore, they were set and varied as a group.
Van der Leeden et al. (1990) ranked over 2 million streams located throughout the
United States according to their stream order. A first-order stream has no tributary channels;
a second-order stream forms when two first-order streams converge, and so on through stream
order 10. Each successive stream order is characterized by a larger flow volume. For each
stream order, van der Leeden presented typical values for flow, waterbody area, watershed
area, depth, and various other parameters. The central tendency and high-end waterbody were
characterized by selecting a central tendency and high-end stream order and using van der
Leeden's typical values for the chosen stream order. A stream smaller than the central
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6.0 FATE AND TRANSPORT MODELING
6.7 Fate and Transport Inputs
tendency stream was desired for high end, since a smaller stream will dilute contaminants
discharged into it less than a larger stream. Van der Leeden's data are reproduced in Table
6-19.
Stream orders 1 and 2 are typically too small to sustain an appreciable amount of
aquatic life for fishing and were therefore eliminated from consideration. Of the stream
orders sufficiently large to support aquatic life for fishing (stream orders 3 through 10),
stream order 5 was selected as representative of central tendency stream characteristics, based
on the number of streams in the United States that have streams of each stream order. There
was a significant drop in die number of streams between stream orders 5 and 6. It appeared
that the number of streams in the United States that could be classified as stream order 6 or
above was too low to use any of those stream orders to represent a national average or central
tendency. However, a significant number of streams fell into stream order classification 5.
Because a smaller stream was needed for high enc, stream order 3, the smallest that would
support significant aquatic life was selected to characterize a high-end stream.
Table 6-20 summarizes the stream data used to characterize the central tendency and
high-end waterbodies. These values have been converted to metric units, as needed by the
model. Watershed area (called drainage area by van der Leeden), flow, depth, and velocity
were taken directly from van der Leeden. Waterbody area was calculated from average
length and width. Flow independent mixing volume was calculated from average length,
width, and depth, as suggested in the Addendum.
Table 6-19. Summary of U.S. Stream Data
Strean
order
1
2
3
4
5
6
7
8
9
10
Nwber
of
1.370,000
350,000
80400
18400
4,200
950
200
41
8
1
Total
lOftfe
(•0
1,570,000
810,000
420.000
220,000
116.000
61.000
30£00
14,000
6,200
1,800
Average
kngtfe
(«0
1.0
2.1
53
12
28
64
147
338
777
1,800
DraJMfe
area
(ml2)
1.0
4.7'
23
109
518
2JOO
1ZOOO
56.000
260,000
1.250,000
Surface
area
(•ft
1200
1,500
1.400
1,500
1.600
1.800
1.800
1.700
1300
1.000
Meu
now
(eft)
0.65
3.1
15
71
340
1.600
7,600
36.000
171.000
810.000
Men
wtdtfc
(ft)
4
10
18
37
75
160
320
650
1300
2,800
Meu
deplk
(ft)
0:15
029
OJ8
1.1
23.
4.1
8D
15
29
55
Meaa
velocity
<«/•)
1.0
1J
1.5
\A
23
2.7
33
3.9
5.6
5.9
Source Van der Leeden (1990).
August 1995
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6.0 FATE AND TRANSPORT MODELING
6.7 Fate and Transport Inputs
Table 6-20. Characterization of Central Tendency and High-End Waterbodies
Parameter
Stream order
Watershed area
Flow
Velocity
Depth (wateibody)
Width
Length
Waterbody area
(length x width)
Flow independent mixing volume
(length x width x depth)
Depth (bed sediment)
Depth (water column)
Central tendency
5
1.3e+9 m2
3e+8 mVyr
(3e+llL/yr)
0.7mA
0.67 m
23m
45,000m
1646 m2
6.7e+5 m3
(6.7e+8L)
0.03 m
0.64m
High end
3
6e+7m2
1.3e+7 m3/yr
(1.3e+10 Uyr)
0.5 m/s
0.18m
5.5m
8.500m
4.6e-Ht m2
8 Je+3 m3
(8J**L)
0.03 m
0.15 m
The surface water model requires three different depth measurements as inputs: depth
of the water column, depth of bed sediment, and total waterbody depth (which is the sum of
the water column and sediment depths). The depths from van der Leeden were total water-
body depth. The Addendum suggests a typical bed sediment depth of 0.03 m; this was used,
and the water column depth calculated as the difference between the total waterbody depth
from van der Leeden and the bed sediment depth of 0.03 m.
6.7.5.2 Other Surface Water Parameters
6.7.5.2.1 Total Suspended Solids
The Addendum suggests that total suspended solids (TSS) can range from 1 to 100
mg/L and suggests a typical value of 10 mg/L for streams and rivers. This value is used as
the central tendency value. A higher value was needed for high end No data on frequency
of values in actual streams was available to estimate a 90th percentile value. The Addendum
suggests that 80 mg/L is a cutoff value for protection of aquatic life; this is also toward the
high end of the range suggested Therefore, 80 mg/L is used as a high-end value.
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
6.7.5.2.2 Bed Sediment Concentration
The bed sediment concentration term is analogous to the bulk density for soil in that it
describes the concentration of solids in terms of a mass per unit volume. The Addendum ,
notes that bed sediment concentration should range from 0.5 to 1.5 kg/L and that a reasonable
value for most applications is 1 kg/L. The range suggested was sufficiently narrow, thus, no
advantage would be gained by setting a high-end value for this parameter, therefore value
suggested of 1 kg/L (le+6 mg/L) is used.
\
6.7.5JJ Bed Sediment Porosity
The bed sediment porosity describes the volume of water per volume of bcnthic space.
Bed sediment porosity is calculated from bed sediment concentration and sediment density as
follows (Addendum, U.S. EPA, 1993c):
, (6-179)
P,
where
6te = Bed sediment porosity (L/L)
BS = Bed sediment concentration = 1 kg/L = 1,000,000 mg/L (see Section
6.7.5.2.2) . '
pg = Sediment density = 2.65 kg/L (a standard value for mineral materials).
This results in a value of 0.6.
6.7.5.2.4 Gas-Phase Transfer Coefficient
The gas-phase transfer .oefftcent is used to estimate volatile losses from the waterbody.
Volatile losses are calculated using a two-layer resistance model that incorporates a gas-phase
transfer coefficent and a liquid-phase transfer cocfficcnt Both transfer coefficients are
controlled by flow induced turbulence in flowing systems. The liquid-phase transfer
coefficient is calculated based on chemical-specific properties as specified in the Addendum;
this calculation is included in the model equations set out in Sections 6.5 through 6.6. The
Addendum gives a single value for the gas-phase transfer coefficient for flowing systems of
36,500 rh/yr. This value is used and is not varied.
There :s some uncertainty around setting this parameter to a single value that is not
chemical specific. It is reasonable to assume that chemical properties affecting volatility
would have some effect on this value, although it is not known how large such an effect
would be. The Addendum does give an equation (using chemical-specific properties) for
calculating this parameter for stagnant systems, such as lakes or ponds. However, the transfer
coefficients for stagnant systems are dominated by wind-induced turbulence rather than flow-
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
induced turbulence; therefore, this equation is not applicable to flowing systems such as are
modeled here and is not used.
6.7.5.2.5 Fraction Organic Carbon in Bottom Sediment
The fraction organic carbon in bottom sediment is derived from the fraction organic
carbon in watershed soils. The Addendum suggests that for a fraction organic carbon of
about 0.01 in the watershed, the fraction organic carbon for bottom sediments will typically
be 0.03 to 0.05. The midpoint of this range, 0.04, was divided by the stated fraction organic
carbon of the watershed (0.01) to derive a multiplier of 4 for calculating fraction organic
carbon in bottom sediments from fraction organic carbon in watershed soils. The values used
of 0.024 and 0.008 correspond to the central tendency and high-end values for soil fraction
organic carbon of 0.006 and 0.002, respectively. See Section 6.7.3.1 for a discussion of the
derivation of fraction organic carbon in soil. The fraction organic carbon in the bottom
sediments is varied with the fraction organic carbon in soil.
6.7.5.2.6 Waterbody Temperature
An average surface waterbody temperature of 298 K (25 °Q was considered a
"common assumption for water temperature" in the Addendum to the Combustor Indirect
Exposure Document (U.S. EPA, 1993a). While this value is somewhat high, the results are
insensitive to this parameter, and reasonable lower values should have no effect on the
results; therefore, this parameter is not varied. This temperature value was used to estimate
gaseous diffusion loads into the surface waterbody.
6.7.6 Chemical-Specific Data
The chemical specific data are presented in Appendix A. This section describes how
values were obtained for each parameter. Section 6.7.6.1 describes the physical-chemical
properties of the chemicals; Section 6.7.6.2 describes the various biotransfer factors.
6.7.6.1 Physical-Chemical Properties
Physical-chemical properties were not varied. Best estimates of the values were set for
some properties, while some properties were calculated from one or more of the other
properties. The following values were set to best estimates:
• Diffusivity in air and water
• Vapor pressure
• Solubility
• Molecular weight
• Octanol-water partition coefficient (Kg,,).
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FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
The following properties were calculated from one or more of the other properties:
• Henry's law constant
• Soil-water partition coefficients
• Organic carbon partitioning coefficient
• All transfer factors.
Further details on the calculation of these properties are provided later in this section under
each property (except for the organic carbon partitioning coefficient, which is discussed in the
soil-water partition coefficient section.
The approaches to determining a best estimate for those properties that were not
calculated varied somewhat depending on the variability of the property and the availability of
data. These approaches included use of default values, use of recommended values from
several comprehensive sources, and use of geometric mean of all plausible values located in
the literature. The choice of approach depended on the variability of the property, both
between chemicals and between different values for the same chemical; for example, a default
value approach was considered appropriate only for properties of little variability between
chemicals, while a geometric mean approach was considered more appropriate for properties
with considerable variance between values for a specific chemical.
Among the literature reviewed, the two best sources for chemical properties were The
Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic
Chemicals (Mackay et aL, 1992, 1993) and Handbook of Fate and Exposure Data (Howard et
al, 1990-1993); these are referred to throughout this section as Mackay et al. and Howard,
respectively.
Mackay et aL conducted a thorough review of available environmental handbooks,
chemical reference books, and original literature papers in compiling chemical properties for
the handbooks. Mackay et aL evaluated the compiled data and selected a "best" or
representative value for each property. When selecting a representative value, Mackay et al.
considered age of the data, method of data determination, the research objective, and the
reported values for structurally similar compounds. Similarly, Howard et aL conducted a
literature review, evaluated the resultant data, and selected a "best" value. When a chemical
was listed in either Mackay et aL or Howard et al., the selected values in those references
were used. Mackay et aL was preferred over Howard et al. because it is more recent and it
reviewed data from Howard et aL
Many HWIR chemicals were not in Mackay or Howard, but properties of these
chemicals were available from a variety of other references. Where multiple literature values
were available, a geometric mean of the literature values was used. The types of literature
reviewed included original experiments, handbooks, and EPA reports and databases.
Some references were used only on a limited basis. The U.S. EPA ASTER (1992-
1993) database and the Superfund Public Health Evaluation Manual (U.S. EPA, 1986d) were
August 1995 6-290
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
two such references. ASTER was considered a poor source of information because much of
the data itf ASTER was not referenced. Furthermore, the values in ASTER often differed
greatly from values in other, well-respected references. U.S. EPA (1986d) was considered a
poor reference because much of the data in the report was compiled from unreliable sources.
Two chemicals presented a special case in terms of data sources. These were mercury
and 2,3,7,8-tetrachlorodibenzo(p)dioxin (2,3,7,8-TCDD) Toxicity Equilavents (TEQs). Data
for divalent mercury (mercuric chloride) were taken from the Mercury Study Report to
Congress (U.S. EPA, 1994b). Data for dioxin TEQs were based on weighted values for all
congeners with nonzero toxicity equivalence factors (TEFs) developed by ORD.
For each property that was not calculated, the approach used is identified below; for
more details on a specific property, see the property-specific sections that follow.
Diffusivity in air and water tend not to vary much even among chemicals. A single,
fairly comprehensive source for these values was available, the CHEMDAT7 database, and
this was used. If data for a specific chemical were not available, default values were used.
Vapor pressure values presented in the literature for a specific chemical can vary
considerably. If a recommended value was available in either Mackay et al. or Howard et al.,
that was used. Otherwise a geometric mean of literature values was used. If no value could
be found, the chemical was eliminated from the analysis.
Solubility values presented in the literature for a specific chemical tend not to vary
greatly, although there are significant differences in solubility between chemicals. If a
recommended value was available in either Mackay et aL or Howard et aL, that was used.
Otherwise a geometric mean of literature values was used. If no value could be found, the
chemical was eliminated from the analysis.
Molecular weight valuer for a specific chemical do not vary. Therefore, once a value
was located in ai.y source, it was used.
K,,w values presented in the literature for a specific chemical can vary considerably.
Because many of the biotransfer factors are based on K^, this is a critical parameter.
Therefore, as many values as possible were located in the literature for K^, and a geometric
mean approach used.
6.7.6.1.1 Diffusivity in Air and Water
The dJfusivides in air and water were obtained directly from the CHEMDAT7
database. If constituents of interest were not found in this source, the standard default values
presented in this reference were assigned for these parameter values. These parameters do
not vary much, and the default values appear to be within the range of typical values. Values
for diffusivity in air range from about 0.01 to 0.1 cm2/s; the default value was 0.08 cir^/s.
August 1995 6-291
-------
FATE AND TRANSPORT MODELING - 6.7 Fate and Transport Inputs
Values for diffusivity in water range from about le-6 to le-5 cm2/s; the default value was 8e-
6 cm2/s.
6.7.6.1J Henry's Law Constant (H and H')
The Henry's law constant (H) is applicable only to organic compounds and can be
derived by a number of methods. It can be calculated from the theoretical equation defining
the constant, measured, or estimated from the chemical structure. Because Henry's law
constant can be difficult to measure accurately, values calculated from the theoretical equation
are preferred to measured values. Where possible, Henry's law constant was calculated using
the theoretical equation as presented in Lyman et al. (1990)
(6-180)
5
where
H = Henry's law constant (atm-m3/mol)
VP = Vapor pressure (atm)
MW = Molecular weight (g/mol)
S = Solubility (g/nr).
Vapor pressures and solubilities were taken from Mackay et al. (1992, 1993) or Howard
et al. (1990-1993) if possible. A literature search for vapor pressure and solubility values was
also conducted, and the geometric mean of values found in the literature was calculated and
used for chemicals not reported in Mackay et aL or Howard et al. Vapor pressures from the
EPA data base ASTER were used when no other data were available. Table 6-21 lists the
references from which vapor pressure values were taken. Solubilities from U.S. EPA (1985k)
were used when no other data were available; however, many of these values are calculated
from octanol-water partition coefficient (KgW). When the K^ upon which the solubility is
based may differ from the K^ selected for this analysis, the solubility values were not used.
For a few chemicals that are irascible with water, solubility data were not available.
Estimates of solubility for those chemicals were made using the Henry's law constant and
vapor pressure cited in Howard et aL (using the above equation solved for S). Table 6-22
lists the references from which solubility values were taken. Vapor pressure and solubility
were corrected to 25 °C before calculating Henry's law constant
Molecular weights are constant for a specific compound and should not vary.
Therefore, geometric means were not used for molecular weight — a single valrr from any
source was considered acceptable. Table 6-23 lists the references from which molecular
weight values were taken.
A literature search for Henry's law constant was also conducted; if one of the inputs
needed to calculate Henry's law constant was not available, the geometric mean of measured
values from the literature was used Table 6-24 lists the references used for Henry's law
constant
August 1995 6-292
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-21. References for Vapor Pressures
Aldrich Catalog. 1982-1983*. Aldrich Catalog Handbook. Aldrich Chemical Company, Inc.. Milwaukee, WI.
As cited in U.S. EPA. 1984. Data Acquisition for Environmental Transport and Fate Screening for
Compounds of Interest to the Office of Emergency and Remedial Response. EPA/60
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-21 (continued)
Great Lakes Chemical Corporation. As cited in U.S. EPA. 1976. Investigation of Selected Potential
Environmental Contaminarts: Haloalkyl Phosphates. EPA/560/2-76-007. U.S. Environmental Protection
Agency. Washington, DC.
Harden, J.M., and CE. Burklin. 1985. Characterization of Transfer. Storage, and Handling of Waste with High
Emissions Potential. Phase 1. Prepared for the U.S. Environmental Protection Agency, Thermal Destruction
Branch, Cincinnati, OR As cited in Smith, D.L., and TJC Pierson. 1986. Development and Validation of
Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S. Environmental Protection
Agency. Office of Solid Waste, Washington, DC.
Howard. PH. (ed.). 1993. Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Vol.
IV. Lewis Publishers, Incorporated, Boca Raton, PL.
Huston. R.F.. 1955. The Dow Chemical Co., Freeport, TX. Private communication. As cited in Dilling. W.L.
1977. Interphase transfer processes, n. Evaporation rates of chloromethanes, ethanes, ethylenes, prepares
and propylenes from dilute aqueous solutions: Comparisons with theoretical predictions. Environ. Sci.
Technol. 11:405-409.
IARC. 1978. Some N-Nitrbso Compounds IARC Monographs on the Evaluation of the Carcinogenic Risk of
Chemicals to Man. WHO, IARC, Vol. 17, Lyon, France.
loffe. LI., and E.S. Yamnolskaya. 1944. Zh. Prik. Khim. 17.527. As cited in Boublik. T., V. Fried, and E.
Hala. 1973. The Vapour Pressures of Pure Substances. Elsevier Scientific Publishing Company. New
York.
Jaber, RM., and E.C. Gunderson. 1983. Data acquisition for environmental transport and fate screening for
compounds of interest to the Office of Emergency and Remedial Response: Pan II. Vapor Pressure
Measurements. As cited in U.S. EPA. 1984. Data Acquisition for Environmental Transport and Fate
Screening for Compounds of Interest to the Office of Emergency and Remedial Response. EPA/600/6-84-011.
Office of Health and Environmental Assessment, Office of Research and Development, Washington, DC.
Jordan, TJL 1954. Vapor Pressure if Organic Compounds Interscience Publishers, Inc., New York. 266 pp
Kahttaum, G.W.A. 1894. Z. Phys. Chem. 13.14. As cited in Boublik. T.. V. Fried, and E. Hah. 1973. The
Vapour Pressures of Pure Substances. Elsevier Scientifk Publishing Company.
Klein, R.G. 1982. Calculations and measurements of the volatility of N-nitrosoamines and their aqueous
solutions. Toxfcotocr23:135-147. As cited in Montgomery. JJL, and L.M. Welkonx 1990. Groundwater
Chemicals Desk Reference, Vol. 1. Lewis Publishers, Chelsea. ML
Mackay. D., A. Bobra. D.W. Chan, et aL 1982. Vapor pressure correlations for low-volatility environmental
chemicals. Environ. Sci. Technol. 126:645-649. As cited in Montgomery. J.R. and LM. Wdkom. 1991.
Groundwater Chemicals Desk Reference, VoL 2. Lewis Publishers, Chelsea. ML :
(continued)
August 1995 6-294
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-21 (continued)
Macka>, D., and PJ. Leinonen. 1975. Rate of evaporation of low-solubility contaminants from water bodies to
atmosphere. Environ Sci Tech. 13(9): 1178-1180. As cited in Smith, D.L., and T.K. Pieraon. 1986.
Development and Validation of Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S.
Environmental Protection Agency. Office of Solid Waste. Washington, DC.
Mackay, D., W.Y. Shiu, and K.C. Ma. 1992a. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume f—Monoaromatic Hydrocarbons, Chlorobenienes, and
PCB's. Lewis Publishers, Boca Raton, FL.
Mackay, D., W.Y. Shiu, and K.C. Ma. 1992b. Illustrated Handbook of Physical-Chemical P> jperties and
Environmental Fate for Organic Chemicals: Volume It—Polynuclear Aromatic Hydrocarbons, Pofychlorinated
Dioans and Dibenzofurans. Lewis Publishers, Boca Raton. FL.
Mackay, D., W.Y. Shin, and ICC. Ma. 1993. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume III—Volatile Organic Chemicals. Lewis Publishers.
Boca Raton, FL.
Maksonov. Y.Y. 1968. Zh Fix. Khim. 42, 2921.
Marsden, C. and S. Mann (eds.). 1963. Solvents Guide. Cleaver-Hume Press Limited, London.
Martin. R, and CR. Worthing. 1977. Pesticide Manual, 5th ed. British Crop Protection Council,
Worcestershire, England.
Nathan, MJ. 1978. Choosing a process for chlorine removal. Chem. Eng. 85:93-100. As cited in
Montgomery, J.R, and L.M. WeJkom. 1991. Groundwater Chemicals Desk Reference, VoL 1 Lewis
Publishers, Chelsea. MI.
Nedy, W.B., and G.E. Blao. 1985. Environmental Exposure from Chemicals. Vol. 1. CRC Press. Inc., Boca
Raton, FL. pp. 30-31. As cited in U.S. EPA. 1987. Health and Environmental Effects Profile for
3J'-Dimethyibenzidine. EPA/600A-87/391. Office of H< alth and Environmental Assessment, Cincinnati,
OR
Nelson, OA., and R Wales. 1927. /. Am. Chem. Soc. 47. 867. As cited in Boublik, T.. V. Fried, and R Hala.
1973. The Vapour Pressures of Pure Substances. Elsevier Scientific Publishing Company.
Perry, RJL, and CJL Chillon. 1973a. Chemical Engineers Handbook, 5th ed. McGraw-Hffl Book Co., New
York. Tables 3-1. 3-8 and pp. 3-25. 3-49. As cited in Smith. D.L., and TJC. Pienon. 1986. Development
and Validation of Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S.
Environmental Protection Agency, Office of Solid Waste, Washington, DC.
RenCro, J.C. 1967. The Dow Chemical Co.. Fneport, TX, Private commuoicatioo. As cited Ji Difling. Wl..
1977. Interphase transfer processes. H. Evaporation ratis of chtoromethanes, ethanes, ethylenes, propanes
and propylenes from dilute aqueous solutions: Comparisons with theoretical predictions. Environ. Set.
Technol. 11:405-409.
(continued)
August 1995 6-295
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-21 (continued)
Riddick, J-A., W.B. Hunger, and TJC Sakano. 1986. Organic solvents: Physical properties and methods of
purification, 4th ed. John Wiley & Sons, New York. As cited in Howard. PJi. (ed). 1993. Handbook of
Environmental Fate and Exposure Data for Organic Chemicals. Vol. IV. Lewis Publishers, Incorporated,
Boca Raton, FL.
Sax, N.I., and RJ. Lewis. 1987. Hawley's Condensed Chemical Dictionary, llth ed. Van Noftrand ReinhoM
Co., New York.
Schmidt-Sleek. R, W. Haberland. A.W. Klein, and S. Caroii. 1982. Steps towards environmental hazard
int of now chemicals. Chemosphere 11(4):383-415.
Schwilte, F. 1988. Dense Chlorinated Solvents. Lewis Publishers, Inc.. Chelsea. MI. As cited in Montgomery.
J.H., and L.M. Welkom. 1990. Groundwater Chenicals Desk Reference, VoL 1. Lewis Pub^shers, Chelsea,
MI.
Smith, D.L., and TJC. Piersdn. 1986. Development and Validation of Henry's Law Constants for Appendix VIII
Constituents. Prepared for the U.S. Environmental Protection Agency, Office of Solid Waste, Washington,
DC.
Stull, D.R. 1947. Industrial and Engineering Chemistry. Vol.39. As cited in Weast, R.C. (ed.). 1985. CRC
Handbook of Chemiary and Physics. 66th ed. CRC Press, Inc., Cleveland, OR
Suntio, L.R., W.Y. Shiu. and D. Mackay. 1988b. Critical review of Henry's law constants for pesticides
Reviews of Environmental Contamination and Toxicology 103:1-61.
U.S. EPA (Environmental Protection Agency). 198 la. Treatability Manual. Vol. 1. EPA/600/2-82-00 la. Office
of Research Development. As cited in U.S. EPA. 1986. Superfund Public Health Evaluation Manual.
EPA/S40/1-86/060. U.S. Environmental Protection Agency. Office of Emergency and Remedial Response,
Office of Solid Waste and Emergency Response, Washington, DC. 175pp.
U.S. EPA (Environmental Protection Agency). 1992g. RREL Treatability Data Base. Version 4.0. Computer
Software. As cited in US EPA. 1992b. Handboor of RCRA Ground-Water Monitoring Constituents:
Chemical & Physical Properties. EPA/S3Q/R-92/022. Office of Solid Waste. Washington, DC.
U.S. EPA (Environmental Protection Agency). 1992c-1993. ASTER database.
Verschueren. K. 1977. Handbook of Environmental Data on Organic Chemicals, 1st ed. Van Noctrand
Renhoid Co, New York. As cited in US. EPA. 1985. Physical-Chemical Properties and Categorization of
RCXA Wastes According to Volatility. EPA/450/3-85AM7. U.S. Environmental Protection Agency,
Springfield, VA.
Verschueren. K. 1983. Handbook of Environmental Data on Organic Ctemtat/i, 2nd ed. VaBNostrand
RemhoU Co., New York.
(continued)
August 1995 6-2%
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-21 (continued)
Weast R.C. (ed). 1973. CRC Handbook of Chemistry and Physics, 54th ed CRC Press. Inc.. Cleveland, OH.
As cited in U.S. EPA.. 1981. Vapor Pressure Distribution of Selected Organic Chemicals.
EPA/600/2-81-021. Office of Research and Development, Cincimuti, OH.
Weast, R.C. (ed). 1980. CRC Handbook of Chemistry and Physics, 61st ed. CRC Press, Inc.. .Cleveland OR
As cited in Smith, DJ,., and T.K. Pit.son. 1986. Development and Validation of Henry's Law Constants for
Appendix VIII Constituents. Prepared for the U.S. Environmental Protection Agency. Office of Solid Waste;
Washington, DC.
Weast, R.C. (ed). 1983b. CRC Handbook of Chemistry and Physics, 64th ed CRC Press, Inc.. Cleveland OH.
As cited in U.S. EPA. 198S. Physical-Chemical Properties and Categorization ofRCRA Wastes According
to Volatility. EPA/450/3-85AW7. U.S. Environmental Protection Agency, Springfield VA.
Weast. R.C. (ed). 1985. CRC Handbook of Chemistry and Physics. 66th ed CRC Press. Inc.. Cleveland. OH.
Windholz, M (ed). 1976a. Merck Index, 9th ed Merck and Co.. Inc.. Rahway. NJ. As cited in [ARC. 1978.
m-Phenylenediamine. In: Some Aromatic Amines and Related Nitro Compounds. LARC Monographs on the
Evaluation of the Carcinogenic Risk of Chemicals to Man. WHO. IARC. VoL 16, Lyon, France.
pp. 111-124.
Windholz. M. (ed). 1976c. Merck Index, 9th ed Merck and Co.. Inc., Rahway. NJ. As cited in US. EPA.
1985. Physical-Chemical Properties and Categorization ofRCRA Wastes According to Volatility.
EPA/450/3-85AM7. ILS. Environmental Protection Agency. Springfield VA.
Yoshida, K., T. Shigeoka, and F. Yamauchi. 1983. Non-steady state equilibrium model for the preliminary
prediction of the fate of chemicals in the environment. Eco. Toxical. Environ. Safety 7:179-190.
August 1995 6-297
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-22. References for Solubilities
Andrew. LJ.. and R.M. Keefer. 1950. Cation complexes of compounds containing carbon-carton double bonds.
J. Am. Soc. 72(11):5034-5037. As cited in Montgomery, J.R, and L.M. WeBcom. 1991. Groiuidwater
Chemicals Desk Reference, Vol. 2. Lewis Publishers, Chelsea, MI.
Angelescu. 1925. Bull. Soc. Chim. Romania, 7:79. As cited in Seidell, A. 1941. Solubilities of Organic
Compounds: Vol. n, 3rd ed. Van Nostrand Company, Inc., New York.
Briggs, G.G. 1981. Theoretical and experimental relationships between soil adsorption, octanol-water partition
coefficients, water solubilities, bioconcentration factors and the parachor. /. Agriculture Food Chemistry
29(5): 1050-1059.
Budavari S.. MJ. O'Neil, A. Smith, et al. (eds.). 1989. The Merck Index: An Encyclopedia of Chemicals.
Drugs, and Biologicals, llth ed. Merck & Co., Inc., Rahway. NJ.
Chiou, C.T.. D.W. Schmediding. and M. Manes. 1982. Partitioning of organic compounds in octanol-water
systems. Environ. Sci. Techno!. 16:4-10.
Clayton, GJ>., and E. Florence (eds.). 1981. Patty's Industrial Hygiene and Toxicology, 3rd ed. John Wiley
and Sons, Inc. New York. As cited in Smith, D.L., and T.K. Pierson. 1986. Development and Validation of
Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S. Environmental Protection
Agency, Office of Solid Waste, Washington, DC.
DeBenedictis, A. 1979. Chkrocarbons—Hydrocarbon (allyl chloride). In: Kirk-Othmer Encyclopedia of
Chemical Technology, 3rd ed. Grayson, M., and D. Eckroth (eds.). John Wiley and Sons, Inc., New York.
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Desvergnes. 1925. Moniteur Scientifique 5(15):73-8, 149-58. As cited in Seidell A. 1941. Solubilities of
Organic Compounds: VoL n, 3rd ed. Van Nostrand Company, Inc., New York.
Desvergnes. 1926. Moniteur Sdentfflque 5<16):201. As cited in Seidell, A. 1941. Solubilities of Organic
Compounds: VoL U, 3rd ed. Van Nostrand Company, Inc., New York.
Dilling, Wi. 1977. Inlerphase transfer processes, n. Evaporation rates of chloromethanes. ethanes, ethylenes,
propanes and propyknes from dilute aqueous solutions: Comparisons with theoretical predictions. Environ.
Sci. Technol. 11:405-409.
Dow Chemical Compmy, Midland, MI. As died in Goring, C.AJ. 1962. Adv. Pest Control Res. 5:47-84.
Druckey, H., R. Preussmann, S. Ivankovic, and D. SchmahL 1967. Organotrope carcuwgene Wirkungen bei 65
venchiedenen N-Nitaxo-Verbindimgen an BD ratten. Z Krebsforsch. 69:103-201. As cited in IARC. 1978.
Some N-Nitroso Compounds IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to
Man. WHO, IARC VoL 17. Lyon, France.
Faucon. A. 1910. Ann. Chim. Phys. 8(19):70-152. As cited in Seidell, A. 1941. Solubilities of Organic
Compounds: VoL n, 3rd ed. Van Nostrand Company, Inc., New York.
(continued)
August 1995 6-298
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-22 (continued)
Felsot A., and P.A. Dahm. 1979. Sorption of organophosphorus and carbcmate insecticides by soil /. Agric.
Food Chem 27(3):557-563.
Gomez, A. 1971. Thesis. Leuven. As cited in Huyskens, P.. J. Mullens. A. Gomez, and J. Tack. 197S.
Solubility of alcohols, phenols, and anilines in water. Bull. Soc. Chim. Belg. 84:253-262.
Great Lakes Chemical Corporation. As cited in U.S. EPA. 1976. Investigation of Selected Potential
Environmental Contaminants: Haloalkyl Phosphates. EPA/560/2-76-007. U.S. Environmental Protection
Agency, Washington, DC.
Hine, J., and PX. Mookerfee. 1975. The intrinsic hydrophilic character of organic compounds. Correlations in
terms of structural contributions. J. Org. Chem. 40:292-298. As cited in U.S. EPA. 1984. Health and
Environmental Effects Profile for Ethylene Thtourea. EPA/600/X-84/131. Office of Health am4 Environmental
Assessment, Cincinnati, OR
Howard. AH. (ed.). 1993. Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Vol.
IV. Lewis Publishers, Incorporated, Boca Raton. FL.
Huyskens. P.. J. Mullens, A. Gomez and J. Tack. 1975. Solubility of alcohols, phenols, and anilines in water.
Bull. Soc. Chim. Belg. 84:253-262.
IARC. 1978. Some N-Nitroso Compounds IARC Monographs on the Evaluation of the Carcinogenic Risk of
Chemicals to Man. WHO, IARC. Vol. 17, Lyon, France.
Kamlet MJ., R.M. Doherty. M.H. Abraham, P.W. Carr. RJ. Doherty, and R.W. Taft 1987. Linear Solvadon
Energy Relationships. /. Phys. Chem. 91(7): 1966-2004.
Krijgsheld, K.R., and A. van der Gen. 1986. Assessment of impact of the emission of certain organchlorine
compounds on the aquatic environment, Chemosphere 15(7):861-880.
Link, WP. 1958. Solubilities >f Inorganic and Metal Organic Compounds. VoL 1 and 2. Van Nostrand
Company, Inc., New York. As cited in Smith, DJ-., and TJC Pierson. 1986. Development and Validation of
Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S. Environmental Protection
Agency, Office of Solid Waste, Washington. DC.
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McGraw-Hifl Book Co. New York. As cited in U.S. EPA. 1986. Health and Environmental Effects Profile
for Hexachlorophene. EPA/600/X-86V085. Office of Health and Environmenial Assessment, Cincinnati. OH.
Lyman, WJ.. WJ. ReehL and DJL Rosenblatt. 1982c. Handbook of Chemical Property Estimation Methods.
McGraw-Hill Book Co., New York. As cited in U.S. EPA. 1987. Health and Environmental Effects Profile
forJJ'-Dimethylbenadine. EPA/600/X-87/391. Office of Health and Environmental Assessment. Cincinnati,
OH.
(continued)
August 1995 6-299
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-22 (continued)
Mackay, D., W.Y. Shiu, and K.C. Ma. 1992a. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume f—Monoaromaa'c Hydrocarbons. Chlorobenzenes. and
PCB's. Lewis Publishers, Boca Raton, FL.
Mackay, D., W.Y. Shiu. and ICC Ma. 1992b. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume It—folynuclear Aromatic Hydrocarbons, Potychlorinated
Dioans and Dibemofurans. Lewis Publishers, Boca Raton, FL.
Mackay, D.. W.Y. Shiu. and K.C. Ma. 1993. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume III—Volatile Organic Chemicals. Lewis Publishers,
Boca Raton. FL.
Martin, R, and CR. Worthing. 1977. Pesticide Manual. 5th ed. British Crop Protection Council.
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compounds. /. Phys. Chem. 700(4): 1267-1275. As cited in Montgomery. J.R, and L.M. Welkom. 1991.
Groundwater Chemicals Desk Reference, VoL 2. Lewis Publishers. Chelsea, ML
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10(4): 1175-1199.
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Perry, RJl, and OH. Chiton. 1973b. Chemical Engineers Handbook, 5th ed. McGraw-Hill Book Co., New
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Profile for Nfl-Dipnenylamine. EPA/600/X-85/393. Office of Health and Environmental Assessment,
Cincinnati, OR .
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Pet. Geol. Bull. 60(2):213-244. As cited in Montgomery. JJi, and L.M. Welkom. 1991. Groundwater
Chemicals Desk Reference, VoL 2. Lewis Publishers, Chelsea, MI.
Riddkk, J.A., W.B. Banger, and TJC Sakana 1986. Organic solvents: Physical properties and methods of
purification, 4th ed. John Wiley ft Sons, New York.
Sanemasa, I., M. Araki, T. Deguchi. and R Nagai. 1982. Solubility measurements of benzene and the
alkylbenzenes in water making use of solute vapor. Bull. Chem. Soc. Jpn. 55(4): 1054-1062. As cited in
Montgomery, J.R, and L.M. Welkom. 1991. Groundwater Chemicals Desk Reference, VoL 2. Lewis
Publishers, Chelsea, MI.
(continued)
August 1995 6-300
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-22 (continued)
Sax. N.I., and RJ. Lewis, 1987. Hawley'i, Condensed Chemical Dictionary, llth ed. Van Nostrand Reinhold
Co.. New York. As cited in U.S. EPA. 1984. Data acquisition for environmental transport and fate
screening for compounds of interest to the Office of Emergency and Remedial Response. EPA/600/6-84-011.
Office of Health and Environmental Assessment, Office of Research and Development. Washington. DC.
Schmidt-Sleek, R. W. Haberland, A.W. Klein, and S. Caroii. 1982. Steps towards environmental hazard
assessment of new chemicals. Chemosphere 11(4):383-415.
Schottz. 1912. Arch. Pharm. 250:418. As cited in SeidelL A. 1941. Solubilities of Organic Compounds: Vol.
U, 3rd ed. Van Nostrand Company, Inc., New York.
Seidell, A. 1941. Solubilities of Organic Compounds: Vol. 0. 3rd ed. Van Nostrand Company, Inc., New
York.
Smith, D.L., and TJC. Pierson. 1986. Development and Validation of Henry's Law Constants for Appendix VIII
Constituents. Prepared for the U.S. Environmental Protection Agency, Office of Solid Waste, Washington,
DC.
Slockdate, M.. and M. Sdwyn. 1971. Eur. J. Biochem. 21:365. Chlorophenols. IK Kirk-Otluner
Encyclopedia of Chemical Technology, 3rd ed. Grayson, M.. and D. Eckroth (eds.). John Wiley and Sons,
Inc., New York. VoL 5, pp. 763-773.
Suntio, LA., W.Y. Shiu. and D. Mackay. 19885. Critical review of Henry's law constants for pesticides.
Reviews of Environmental Contamination and Toxicology 103:1-61.
Suntio, LA., W.Y. Shiu, and D. Mackay. 1988a. A review of the nature and properties of chemicals present in
pulp mill effluents. Chemosphere 17(7): 1249-1290.
Sutton, C, and LA. Calder. 1975. Solubility of alkylbenzenes in distilled water and seawater at 25 "C. /.'•
Chem. Eng. Data. 20(3):320-322. As cited in Montgomery. J.H., and L.M. Welkom. 1991. Groundwater
Chemicals Desk Reference, VoL 2. Lewis Publishers, Chelsea, ML
U.S. EPA (Environmental Protection Agency). 198Ib. Treatability Manual. Vol. I. EPA/600/2-8240ta.
Office of Research Development As cited in U.S. EPA. 1986. Superfund Public Health Evaluation Manual.
EPA/540/1-86/060. U.S. Environmental Protection Agency, Office of Emergency and Remedial Response.
Office of Solid Waste and Emergency Response, Washington, DC. 175 pp.
U.S. EPA (Environmental Protection Agency). 1985J. Physical-Chemical Properties and Categorisation of
RCRA Wastes According to Volatility. EPA/450/3-85/007. U.S. Environmental Protection Agency.
Springfield, VA.
U.S. EPA (Environmental Protection Agency). 1990c. Basics of Pump-and-Treat Ground-Water Remediation
Technology. EPA/500/8-90-003. Office of Research and Development. Ada. OK.
(continued)
August 1995 6-301
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-22 (continued)
U.S. EPA (Environmental Protection Agency). 1992g. RREL Treaiability Data Base. Versior 4.0. Computer
Software. As cited in U.S. EPA. 1992b. Handbook ofRCRA Ground-Water Monitoring Constituents:
Chemical & Physical Properties, EPA/530/R-92/D22. Office of Solid Waste. Washington. DC.
U.S. EPA (Environmental Protection Agency). 1992-1993a. HSDB database.
U.S. EPA (Environmental Protectior. Agency). 1992-1993b. ASTER database.
Verachueren, K. 1983. Handbook of Environmental Data on Organic Chemicals, 2nd ed Van Nostrand
ReinhoU Co.. New York.
Weast. R.C. (ed). 1983a. CRC Handbook of Chemistry and Physics, 63id ed. CRC Press, Inc., Cleveland,
OR As cited in Smith, J.L., and TJC. Pierson. 1986. development and Validation of Henry's Law
Constants for Appendix VIII Constituents. Prepared for the U.S. Environmental Protection Agency. Office of
Solid Waste, Washington, DC
Windholz, M. (ed). 1968. Merck Index, 1st ed Merck and Co., Inc., Rahway. NJ. As cited in Smith, Dl...
and TJC Pierson. 1986. Development and Validation of Henry's Law Constants for Appendix VIII
Constituents. Prepared for the U.S. Environmental Protection Agency, Office of Solid Waste, Washington,
DC.
Windholz, M. (ed). 1976b. Merck Index, 9th ed Merck and Co., Inc., Rahway, NJ. As cited in U.S. EPA.
1984. Health and Environmental Effects Profile for Ethylene Thiourea. EPA/600/X-84/131. Office of Heakh
and Environmental Assessment, Cincinnati, OH.
Windholz, M (ed). 1983, Merck Index, 10th ed Merck and Co., Inc., Rahway. NJ.
Zalai. 1910. Gyogyszeresa Ertestie Budapest 19:366. As cited in SeideU, A. 1941. Solubilities of Organic
Compound* VoL H. 3rd ed Van Nostrand Company, Inc.. New York.
August 1995 6-302
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6.0 FATE AND TRANSPORT MODELING 6.1 Fate and Transport Inputs
Table 6-23. References for Melting Points and Molecular Weights
Aldrich Catalog. 1992-1993. Aldrich Catalog Handbook. Aldrich Chemical Company, Inc.. Milwaukee, WL
Budavari S., MJ. O'Neil, A. Smith, et al. (eds.). 1989. The Merck Index: An Encyclopedia of Chemicals.
Drugs, and Biologicals, llth ed. Merck & Co., Inc., Rahway, NJ. As cited in U.S. EPA. 1992b. Handbook
ofRCRA Ground-Water Monitoring Constituents: Chemical & Physical Properties. EPA/530/R-92/022.
Office of Solid Waste, Washington, DC.
Dean, J.A. (ed.). 1979. Lange's Handbook of Chemistry, 12th ed. Lewis Publishing, Boca Raton, FL.
Grasselli, J.G. (ed.). 1973. CXC Atlas of Spectral Data and Physical Constants for Organic Compounds. CRC
Press, Cleveland, OH.
Howard, PJi. (ed.). 1993. Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Vol.
IV. Lewis Publishers, Incorporated, Boca Raton, FL.
IARC. 1974. 3 J'-Dimethoxybenzidine. In: Some Aromatic Amines and Related Nitro Compounds. IARC
Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man. WHO, IARC. VoL 4, Lyon.
France, pp. 41-47.
Mackay. D.. W.Y. Shiu. and K.C. Ma. 1993. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume HI—Volatile Organic Chemicals. Lewis Publishers,
Boca Raton, FL.
Schmidt-Bleek, F.. W. Haberland, A.W. Klein, and S. Caroli. 1982. Steps towards environmental hazard
ment of new chemicals. Chemospnere 11(4):383-415.
Stenger, V.A. 1978. Bromine compounds. In: Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed..
Vol. 4. Grayson, M.. and D. Eckroth (eds.). John Wiley and Sons, Inc., New York. pp. 252, 253. As cited
in U.S. EPA. 1987. Health and Environmental Effects Profile for Methylene Bromide. EPA/6(XVx-87/093.
Office of Health and Environmental Assessment
Suntio, LJt., W.Y. Shiu, and D. Mackay. 1988b. Critical review of Henry's law constants for pesticides.
Reviews of Environmental Contamination and Toxicology 103:1-61.
U.S. EPA (Environmental Protection Agency). 1976. Investigation of Selected Potential Environmental
Contaminants: HaloaUyi Phosphates. EPA/560/2-76-007. U.S. Environmental Protection Agency,
Washington, DC.
U.S. EPA (Environmental Protection Agency). 1984b. Health and Environmental Effects Profile for Toluidines.
1984. Office of Health and Environmental Assessment. EPA/600A-84/151. Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). 1992g. RREL TreatabiMty Data Base. Version 4.0. Computer
''Software. As eked in U.S. EPA. 1992b. Handbook ofRCRA Ground-Water Monitoring Constituents:
Chemical & Physical Properties. EPA/530/R-92/022. Office of Solid Waste, Washington. DC.
U.S. EPA (Environmental Protection Agency). 1992-1993c. IRIS database.
August 1995 6-303
-------
6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-23 (continued)
U.S. EPA (Environmental Protection Agency). 1992-19935. ASTER database.
Verschueren, K. 1983. Handbook of Environmental Data on Organic Chemicals. 2nd ed. Van Nostrand
Reinhold Co., New Yoric.
Weast, R.C. (ed). 1986. CRC Handbook of Chemistry and Physics. 67th ed. CRC Press, Inc., Cleveland, OH.
As cited in U.S. EPA. 1992b. Handbook of RCRA Ground-Water Monitoring Constituents: Chemical &.
Physical Properties. EPA/530/R-92/D22. Office of Solid Waste, Washington, DC,
Windholz, M (ed.). 1983. Merck Index, 10th ed. Merck and Co., Inc. Rahway. NJ.
Aufust 1995 6-304
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-24. References for Henry's Law Constants
Dilling, W.L. 1977. Interphase transfer processes. II. Evaporation rates of chloromethanes, ethanes, ethylenes.
profanes and propyienes from dilute aqueous solutions: Comparisons with theoretical predictions. Environ.
Sci. Techno!. 11:405^09.
Harden, J.M., and C.E. Burklin. 1985. Characterization of Tranter. Storage, and Handling of Waste with High
Emissions Potential, Phase 1. Prepared for the U.S. Environmental Protection Agency. Thermal Destruction
Branch, Cincinnati, OR As cited in Smith, DJL, and TJC. Pierson. 1986. Development and Validation of
Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S. Environmental Protection
Agency, Office of Solid Waste, Washington. DC.
Howard, P.H. (ed.) 1993. Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Vol.
IV. Lewis Publishers, Incorporated, Boca Raton, PL
Mackay. D. and PJ. Leinonen.' 1975. Rate of evaporation of low-solubility contaminant from water bodies to
atmosphere. Environ Sci Tech. 13(9):1178-118n As cited in Smith, DJL, and T.K. Pierson. 1986.
Development and Validation of Henry's Law Constants for Appendix VIII Constituents. Prepared for the U.S.
Environmental Protection Agency, Office of Solid Waste, Washington, DC.
Mackay, D., and W.Y. Shiu. 1981. Critical review of Henry's law constants for chemicals of environmental
interest /. Phys. Chen. Ref. Data 10(4): 1175-1199.
Mackay, D., W.Y. Shiu, and K.C. Ma, 1992a. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume t—Monoaromatic Hydrocarbons. Cnlorobenzenes. and
PCB's. Lewis Publishers, Boca Raton, PL.
Mackay. D., W.Y. Shiu, and K.C. Ma. 1992b. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume Il—Polynuclear Aromatic Hydrocarbons, Potychlorinated
Dioxinsand Dibenzofurans. Lewis Publishers, Boca Raton, FL.
Mackay. D., W.Y. Shiu, and K.C Ma, 1993. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume III—Volatile Organic Chemicals. Lewis Publishers,
Boca Raton, PL.
U.S. EPA (Environmental Protection Agency). 1981b. Treatability Manual. Vol. I. EPA/600/2-82-001a,
Office of Research Development As cited in Montgomery, JJL, and L.M. Weflmm. 1991. Groundwater
Chemicals Desk Reference. Vol. 2. Lewis Publishers, Chelsea, ML
US. EPA (Environmental Protection Agency). 1982. Aquatic Fate Process Data for Organic Priority
Pollutants. EPA/440/4-81-014. Washington, DC.
U.S. EPA (Environmental Protection Agency). 1992g. RREL Treatability Data Base. Version 4.0. Computer
Software. As cited in U.S. EPA. 1992b. Handbook ofRCRA Ground-Water Monitoring Constituents:
Chemical & Physical Properties. EPA/530/R-92j022. Office of Solid Waste, Washington, DC.
Yaws, C. RC. Yang, and X. Pan. 1991. Henry's law constants for 362 organic compounds in water.
Chemical Engineering 98dl):179-185.
August 1995 6-305
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6.0 FATE AND TRANSPORT MODELING 6.1 Fate and Transport Inputs
Some models require a dimensionless form of Henry's law constant, H', which is
calculated as follows:
H' = JL- (6-181)
where
H' = Dimensionless Henry's law constant (unitless)
H - Henry's law constant (atm-m3/mol)
R = Universal gas constant = 8.205e-5 atm-m3/mol-K
T = Temperature (K).
The temperature in the above equation should be the same as the temperature to which the
Henry's law constant (H) has been corrected; in this case, 25 °C.
6.7.6.1 J Soil-Water Partition Coefficient (K,,)
For organic compounds, past research has demonstrated that for hydrophobic organic
compounds, soil organic matter is the dominant sorbing component in soil. Therefore, the
soil-water partition coefficient, Kj, is calculated from the organic carbon partition coefficient
and the fraction of organic carbon in soil for the organic constituents, as follows (Addendum,
U.S. EPA, 1993a):
where
Kj = Sol1 water partition coefficient (mL/g)
K^ = Organic carbon partition coefficient (mL/g)
foe '= Fraction on^nic carbon in soil (unitless).
The fM term is a soil-specific parameter. See Section 6.7.3.1 for a discussion of how
values were selected
An extensive literature search was conducted for K^ values; however, these values can
vary enormously for one chemical. The literature values obtained were not considered
sufficiently reliable and consistent for use in this analysis. Therefore, K^. is calculated from
octanol-water partition coefficent (K^) using two correlation equations. These correlation
equations are based on literature values of KQW and K^. for a variety of compounds for which
good data were available. The equation is from Di Tore et al. (1991):
+0.00028 . (6-183)
For 2,3,7,8-TCDDioxin, a weighted value reflecting all congeners with nonzero toxicity
equivaknce factors (TEFs) is used
August 1995 6-306
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
The search strategy for log K,,w values for HWIR constituents proceeded in several
phases. Initially, log Kow values were identified in summary texts on physicochemical
properties such as the Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals—Volumes l-lll (Mackay et al., 1992) and the
Handbook of Environmental Fate and Exposure Data for Organic Chemicals (Howard et al.,
1990-1993).
In subsequent phases of the analysis, additional compendia of log Kow values were
identified and evaluated, including the:
• Derivation of Proposed Human Health and Wildlife Bioaccumulation Factors for the
Great Lakes Initiative (Stephan, 1993)
• Aqueous Solubility and n-Octanol/Water f <
-------
6.0 FATE AND TRANSPORT MODELING „ 6.7 Fate and Transport Inputs
generally consistent with methods developed for the Great Lakes Water Quality Initiative
Technical Support Document (U.S. EPA, 1995a). The following criteria were used to
determine the log Kow value used throughout the analysis.
• Log Kow values were recorded for a variety of analytical techniques, including the
slow stir method, generator column, shake flask, and reverse phase high performance
liquid chromatography (RP-HPLC).
• Outliers were eliminated by inspection based on an evaluation of the study,
particularly with respect to the analytical method chosen for a chemical. For
example, the shake flask and RP-HPLC methods have been shown to be unreliable
for highly hydrophobic chemicals (~ log Kow > 6.0).
• For chemicals with log Kow values below S.O, the average of measured values was
typically recommended as the log K^ Usually, the average was taken for log Kow
values from all measurement methods, excluding those RP-HPLC values that
appeared to be outliers (i.e., average calculated for slow stir, generator column, and
shake flask). Newer measurement techniques such as counter-current
chromatography and centrifugal partition chromatography were included as
appropriate.
• For chemicals above log Kow of S.O, measured values from slow stir and generator
column studies were generally preferred to shake flask and RP-HPLC Slow stir
values took precedence over generator column values when the latter appeared
unreasonably low. However, values were not eliminated based strictly on the
analytical method; there are shake flask values for highly hydrophobic organic
chemicals that are valid (e.g., benzo(a)pyrene).
• Dr. Karickhoff calculated a log Kow value for each chemical using (1) the SPARC
model for estimating physicochemical properties from chemical structure and (2) the
Pomona College CLOGP program (current version).
• Dr. Karickhoff determined a recommended log Kow value for each chemical
Predicted values were only used where (1) measured values were not available or (2)
the measured values were considered to be unreliable. Often, the avenge of the
SPARC value and the CLOGP value was adopted as the recommended value.
However, in some cases either the SPARC or CLOGP value was recommended based
on Dr. Karickhoff s professional judgment as to the compatibility of th~. model with
the structure of a particular chemical.
Table 6-25 lists the references from which the log Kow values were taken. These
values and the rationale for recommended log Kow values are summarized in the Internal
Report on Summary of Measured, Calculated, and Recommended Log Kw Values (Karickhoff
and Long, 1995).
August 1995 6-308
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-25. References for Kow
Briggs, G.G. 1981. Theoretical and experimental relationships between soil adsorption, octanol-water partition
coefficients, water solubilities, bioconcentration factors and the parachor. J. Agriculture Food Chemistry
29(5): 1050-1059.
Chiou, C.T., D.W. Schmediding, and M. Mann. 1982b. Partitioning of organic compounds in octanoi-water
systems. Environ. Sci. Techno!. 16:4-10. As cited in Rogers, R.D.. and J.C. McFarlane. 1981. Sorption of
carbon tetrachloride, ethylene dibromide, and trichloroethylene in soil and clay. Environ. Monti. Assess.
1:155-162.
DeNeer, J.W., TJ- Sinnige, and W. Seinen. 1987. Quantitative structure-activity relations for the toxicity and
bioconcentratidn factor of nitrobenzene derivatives towards the guppy (Poecilia retifulata). Aquat. Toacol.
10:115-129.
Felsot A., and PA. Danm. 1979. Sorption of organophosptKTUs and carbamate insecticides by soil. /. Agric.
Food Chem. 27(3):557-563.
Galassi, S., M. Minagazzini, L. Vigano, D. Cesareo, and ML. Tosato. 1988. Approaches to modeling toxic
responses of aquatic organisms to aromatic hydrocarbons. Ecotoi. Environ. Safety 16(2): 158-169. As cited in
Montgomery. J.R, and L.M. Welkom. 1991. Croundwater Chemicals Desk Reference, VoL 2. Le<"is
Publishers, Chelsea, MI.
Hansch, C, and AJ. Leo. 1979. Substituent Constants for Correlation Analysis in Chemistry and Biology.
John Wiky and Sons, New York. pp. 171-321.
Hansch, C, and AJ. Leo. 1981. Medchem Project Issue. 19. Pomona College. Claremont CA. As cited in
U.S. EPA. 1984. Health and Environmental Effects Profile for Ethylene Thiourea. EPA/600/X-84/131.
Office of Health and Environmental Assessment, Cincinnati, OR
Hansch, C., and AJ. Leo. 1984. Medchem Project Issue. 2. Pomona College, Claremont CA. As cited in
U.S. EPA. 1986. Health jnd Environmental Effects Profile for Allyl Chloride. EPA/600/X-86/ i98. Office of
Health and Environmental Assessment, Cincinnati, OH.
Hansch, C, and AJ. L o. 1985*. Medchem Project Issue. 26. Pomona College, Claremont CA. As cited in
U.S. EPA. 1987 and 1992-1993. HSDB database.
Hansch. C.. and AJ. Leo. 1985b. Medchem Project Issue. 26. Pomona College, Claremont CA. As cited in
U.S. EPA. 1987. Health and Environmental Effects Profile for 3J'-Dimethylbenadine. EPA/600/X-87/391.
Office of Health and Environmental Assessment Cincinnati, OH.
Howard, PJi (ed.). 1993. Handbook of Environmental Fate and Exposure Data far Organic Chemicals. VoL
IV. Lewis Publishers, Incorporated, Boca Raton, FL.
Krijgsheld, ICR., and A. van der Gen. 1986. Assessment of impact of the emission of certain organchlorine
compounds on the aquatic environment Chemosphere 15(7):861-880.
(continued)
August 1995 6-309
-------
6.0 FATE AND TRANSPORT MODELING 6.1 Fate and Transport Inputs
Table 6-25 (continued)
Leo, A., C. Hansch, and D. EUrins. 1971a. Partition coefficients and their uses. Chem. Rev. 71:525-616. As
cited in Chiou. C.T.. D.W. Schmediding. and M. Manes. 1981 Partitioning of organic compounds in
octanol-water systems. Environ. Sci. Technol. 16:4-10.
Leo, A., C. Hansch, and D. Ellrins. 197 Ib. Partition coefficients and their uses. Chem. Rev. 71:525-616, As
cited in Montgomery, JJL. and L.M. v^elkom. 1991. Groundwater Chemicals Desk Reference, Vol. 2.
Lewis Publishers, Chelsea. ML
Lyman, WJ., WP. Reehl, and DJt Rosenblatt 1982a. Handbook of Chemical Property Estimation Methods.
McGraw-Hill Book Co., New York.
Mackay, D., W.Y. Shiu, and K.C. Ma. 1992a. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume f—Monoaromatic Hydrocarbons, Chlorobenzenes. and
PCB's. Lewis Publishers, Boca Raton, FL. .
Mackay. D., W.Y. Shiu, and K.C. Ma. 1992b. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume ll—folynuclear Aromatic Hydrocarbons, Pofychlorinated
Dioans and Dibenzofurans. Lewis Publishers, Boca Raton, FL.
Mackay, D., W.Y. Shiu, and K.C. Ma. 1993. Illustrated Handbook of Physical-Chemical Properties and
Environmental Fate for Organic Chemicals: Volume III—Volatile Organic Chemicals. Lewis Publishers.
Boca Raton, FL.
Montgomery, J.R. and L.M. Welkom. 1990. Groundwater Chemicals Desk Reference, VoL 1. Lewis
Publishers, Chelsea. MI.
\
Montgomery, J.R, and L.M. Welkom. 1991. Groundwater Chemicals Desk Reference. VoL 1 Lewis
Publishers, Chelsea. ML
QSAJL 1986. Developed by the U.S. Environmental Protection Agency. ERL-Duluth, Montana Stale University
Center for Data Systems and Analysis, and the Pomona College Medicinal Chemistry Project As cited in
Kollig, HJ>. 1993. Environmental Fate Constants for Organic Chemicals Under Consideration for EPA's
Hazardous Waste Identification Projects. Prepared for the U.S. Environmental Protection Ager. ;y. Office of
Research and Development
ScheUenberg, K.. C. Leuenberger. and RJ*. Schwarzenbach. 1984. Sorpoon of chlorinated phenols by natural
sediments and aquifer materials. Environ. Sd. Tech. 18:652-657.
Steinberg. SJML. JJ. PtgnateUo, Bi. Sawney. 1987. Persistence of 1,2-dibromoethane in soils: Entrapment in
intraparticle micropares. Environ. Sd. Technol. 21:1201-1208.
Suntio, LJt, W.Y. Shin, and D. Mackay. 1988a. A review of the nature and properties of chemicals present in
pulp mill effluents. Chemosphere 17(7): 1249-1290. :
Suntio, L.R., W.Y. Shiu. and D. Mackay. 1988b. Critical review of Henry's law constants for pesticides.
Reviews of Environmental Contamination and Toxicology 103:1-61.
(continued)
Aufust 1995 6-310
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-25 (continued)
U.S. EPA (Environmental Protection Agency). 1980. Sorption Properties of Sediments & Energy-Related
Pollutants. EPA/600/3-80-041.
U.S. EPA (Environmental Protection Agency). 1984a. Data Acquisition for Environmental Transport and Fate
Screening for Compounds of Interest ") the Office of Solid Waste. EPA/600/6-84-010. NTIS PB84-243906.
SRI International, Menlo Park, CA.
U.S. EPA (Environmental Protection Agency). 1986f. Graphical Exposure Modeling System (GEMS). Fate of
atmospheric pollutants (FAP) and Octanol Water Partition Coefficient (CLOGP) database, Washington, DC.
As cited in ATDSR. Draft Toxkological Profile for -1 J-Dichloropropene and trans-1-3-Dichloropcopene.
1991. Agency for Toxic SuNtances and Disease Registry. U.S. Public Health Services.
U.S. EPA (Environmental Protection Agency). 1986g. Suptrfund Public Health Evaluation Manual.
EPA/340/1-86/060. Office of Emergency and Remedial Response, Office.of Solid Waste and Emergency
Response, Washington, DC. 175pp.
U.S. EPA (Environmental Protection Agency). 1988m. OctanoUWater Partition Coefficients for Evaluation of
Hazardous Waste Land Disposal: Selected Chemicals. EPA/600/M-88/D10. U.S. Environmental Protection
Agency, Athens, GA. As tited in Kollig. HJ>. 1993. Environmental Fate Constants for Organic Chemicals
Under Consideration for EPA's Hazardous Waste Identification Projects. Prepared for the U.S.
Environmental Protection Agency. Office of Research and Development
U.S. EPA (Environmental Protection Agency). 198%. Computer Prediction of Chemical Reactivity: The
Ultimate SAR. EPA/600/M-89/D17. US. Environmental Protection Agency. Athens, GA. As cited in Koilig.
HJ*. 1993. Environmental Fate Constants for Organic Chemicals Under Consideration for EPA''s Hazardous
Waste Identification Projects. Prepared for the U.S. Environmental Protection Agency, Office of Research
and Development
U.S. EPA (Environmental Protection Agency). 1990a. Bioaccumulation of Selected Pollutants In Fish—A
Motional Study. EPA/S60/6-90AX)lb. Office of Water Regulations and Standard.
U.S. EPA (Environmental Protection Agency). 1990c. Bares of Pump-and-Treat Ground-Water Remediation
Technology. EPA/600/8-90-003. Office of Research and Development Ada. OK.
U.S. EPA (Environmental Protection Agency). 1991L Chemical Specffic Parameters for Toacity Characteristic
Contaminants. EPA/60(V3-91/004. U.S. Environmental Protection Agency, Athens GA. As cited in Kollig.
HP. 1993. Environmental Fate Constants for Organic Chemicals Under Consideration for EPA's Hazardous
Waste Identification Projects. Prepared for the U.S. Environmental Protection Agency. Office of Research
and Development
U.S. EPA (Environmental Protection Agency). 1992g. RREL Treatability Data Base. Version 4.0. Computer
Software. As cited in U.S. EPA. 1992b. Handbook ofRCRA Ground-Water Monitoring Constituents:
Chemical & Physical Properties. EPA/530/R-92/D22. Office of Solid Waste, Washington. DC.
(continued)
• • r
August 1995 . 6-311
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Table 6-25 (continued)
U.S. EPA (Environmental Protection Agency). 1992-1993b. ASTER database.
Venchueren, K. 1983. Handbook of Environmental Data on Organic Chemicals, 2nd ed. Van Nostrand
Reinhold Co., New York.
Ybshida. K.. T. Shigeoka. and F. Yamauchi. 1983. Non-steady state equilibrium model for the preliminary
prediction of the fate of chemicals in the environment. Eco. Torical. Environ, Safety 7:179-190.
August 1995 6-312
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
Unlike organic compounds, in which Kd is largely controlled by the soil organic carbon
content, Kj values for inorganics are significantly affected by a variety of soil conditions.
The more important of these c re pH, oxidation-reduction conditions, iron oxide content, soil
organic matter content, cation exchange capacity, and major ion chemistry. It is difficult to
derive generic Kj values for inorganics becarse of the numerous significant influencing
parameters. The K^ values for inorganic constituents were generated by EPA using an
equilibrium geochemical speciation model (MJNTEQA2).
6.7.6.1.4 Suspended Sediment-Water Partition Coefficient
For organic compounds, past research has demonstrated that for hydrophobic organic
compounds, organic matter is the dominant sorbing component in suspended sediments.
Therefore, the suspended sediment-water partition coefficient, Kd,w, is calculated from the
organic carbon partition coefficient (K^ and Jie fraction of organic carbon (1^,^ in
suspended sediments for the organic constituents, as follows (Addendum, U.S. EPA, 1993a):
Kd =K •/ (6-184)
nusw noc Joc,sw ^ '
where
= Suspended sediment-water partition coefficient (mL/g)
= Organic carbon partition coefficient (mL/g)
= Fraction organic carbon in suspended sediment
Derivation of K^ values is described above, under Kj. The f,^^ is derived from the
fraction organic carbon for soil The Addendum suggests that for a fraction organic carbon of
about 0.01 in the watershed, the fraction organic carbon for suspended sediments will
typically be O.OS to O.I. The midpoint of this range, 0.075, was divided by the stated fraction
organic carbon of 0.01 ro derive a multiplier of 7.5 for calculating fraction organic carbon in
suspended sediments from fraction organic crrbon in watershed soils. The f^.^ was then
varied with the f^ for soiL
Unlike organic compounds, in which K,, is largely controlled by the soil organic carbon
content, Kj values for inorganics are significantly affected by a variety of soil conditions.
The more important of these are pH, oxidation-reduction conditions, iron oxide content, soil
organic matter content, cation exchange capacity, and major ion chemistry. It is difficult to
derive generic Kj values for inorganics because of the numerous significant influencing
parameters. The Kj values for inorganic constituents were generated by EPA using an
equilibrium geochemical speciation model (MINTEQA2), and the same values were used for
soil, suspended solids, and bottom sediments.
6. 7. 6.1.5 Bottom Sediment-Water Partition Coefficient (Kd,J
For organic compounds, past research has demonstrated that for hydrophobic organic
compounds, organic matter is the dominant sorbing component in bottom sediments.
Therefore, the bottom sediment-water partition coefficient, Kd^, is calculated from the
August 1995 6-313
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
organic carbon partition coefficient (K^.) and the fraction of organic carbon (f^bJ in
suspended sediments for the organic constituents, as follows (Addendum, U.S. EPA, 1993a):
•*«•/<*.* . (6'185)
where
= Bottom sediment-water partition coefficient (mL/g)
= Organic carbon partition coefficient (mL/g)
- Fraction organic carbon in bottom sediment
Derivation of K^. values is described above, under Kj. The f^^ is derived from the
fraction organic carbon for soil. The Addendum suggests that for a fraction organic carbon of
about 0.01 in the watershed, the fraction organic carbon for bottom sediments will typically
be 0.03 to 0.05. The midpoint of this range, 0.04, was divided by the stated fraction organic
carbon of 0.01 to derive a multiplier of 4 for calculating fraction organic carbon in bottom
sediments from fraction organic carbon in watershed soils. The f^ ta was then varied with
the fL. for soil.
*oe
Unlike organic compounds, in which K,, is largely controlled by the soil organic carbon
content. Kg values for inorganics are significantly affected by a variety of soil conditions.
The more important of these are pH, oxidation-reduction conditions, iron oxide content, soil
organic matter content, cation exchange capacity, and major ion chemistry. It is difficult to
derive generic Kg values for inorganics because of the numerous significant influencing
parameters. The Kj values tor inorganic constituents were generated by EPA using an
equilibrium geochemical speciation model (MINTEQA2), and the same values were used for
soil, suspended solids, and bottom sediments.
6.7.6.1.6 Soil Loss Constant due to Degradation
Losses due to degradation (k,f) are empirically determined from field studies.
Degradation rates vary greatly, depending on site-specific conditions, and may be zero.
Because conditions that affect degradation cannot be predicted on a national basis, the
degradation rate was set to zero.
6.7^2 Bkrtransfer Factors
6.7.6.2.1 Plant-Soil Bioconcentration Factor
The plant-soil bioconcentration factor (Br) accounts for the contaminant uptake from
soil and the subsequent transport of contaminants to the aboveground plant parts. This
transport and uptake is a function of the water solubility, which is inversely proportional to
K^. This factor is defined as the pollutant concentration in the plant divided by the pollutant
concentration in the soil The following equation presented in the Combustor Indirect
Exposure Document (U.S. EPA, 1990e) was used to calculate this value for each of the
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
organic constituents. No literature search was made for measured values for organic
constituents.
log (Br)* 1.588 -0.578 log (K^) (6-186)
where
Br = Plant-soil bioconcentration factor ([mg/kg DW plant]/[mg/kg soil])
Kow = Octanol-water partition coefficient (IVkg).
Derivation of K,,w values is described above under the Soil-water partition coefficient (K^).
The Br factor for inorganic constituents was obtained from U.S. EPA (1992e).
Although Br values for inorganics are calculated differently from the organic Br values, they
both are a function of the pollutant's bioavailability in the soil. The data in this, reference
were presented in terms of a plant uptake response slope father than a bioconcentration factor.
These slopes were calculated from field data contained in various literature sources, such as
metal loading rates and soil metal concentrations. The slope units were given in terms of a
soil area whereas a soil mass was required. Therefore, the soil bulk density and mixing depth
conversion factors recommended in the Combustor Indirect Exposure Document were used to
derive bioconcentration factors with the proper units. Br values for metals not covered in the
above reference were taken from Baes et al. (1984).
Br was obtained only for aboveground fruits and vegetables. A different factor, the
root concentration factor, was used for root vegetables.
6.7.6.12 Root Concentration Factor
A root concentration factor (RCF) is a term ultimately used to calculate the below
ground transfer of a contaminant in soil to a root vegetable. As recommended in the
Addendum to the Combustor Indirect Exposure Document (U.S. EPA, 199 3 a), the following
approach was used to calculate the RCF:
-0.82) -0.771og(Hrflw)-lJ2 (6-187)
where
RCF » Root concentration factor ([mg/kg plamJ/[mg/L soil water])
K,,w » Octanol-water partition coefficient (L/kg).
Derivation of K,,w values is described above under the soil-water partition coefficient (Kj).
The RCF is a ratio of concentration in roots to the concentration in soil pore water.
The relationship between RCF and K^ was derived from experimental results based on
uptake of chemical by barley roots. No literature search was made for measured values of
RCF.
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
6.7.6.2 J Air-to-Plant Biotransfer Factor .
The air to plant biotrans«er factor is defined in the Combustor Indirect Exposure
Document (U.S. EPA-, 1990e) as the ratio of contaminant concentrations in aerial plant parts
to the concentration of pollutant in air. This chemical specific factor is calculated from
equations in Bacci et al. (1990, 1992) Bacci et al. (1990) gives the following equation for
calculating a volumetric air-to-plant biotransfer factor, Bvol:
log^-1. 065 logA^-logf-^Ll- 1.654 (6-188)
where
Bvol = Volumetric air-to-plant biotnusfer factor ([ug/L wet leaf]/[ug/L air])
Kow = Octanol water partition coefficient (unitiess)
H = Henry's law constant «,atm-m3/mol)
R •= Universal gas constant = 8.21e-5 atm-m3/mol-K
T = Temperature = 298.1 K (= 25 °Q.
The volumetric air-to-plant biotransfer factor, Bvol, may be converted to a mass-based
biotransfer factor as follows (Bacci et al., 1992):
0 '/water) '
where
(6-189)
Bv = Mass-based air-to-plant biotransfer factor ([ug/g DW plantj/[ug/g air])
B^i = Volumetric air-to-plant biotransfer factor ([pg/L wet IcafJ/lpg/L air])
p^ = Density of air = 1.19 g/L
Pterf = Density of leaf = 770 g/L (Macrady and Maggard, 1993)
fwaiv = Fraction of leaf that is water = 0.85 (Macrady and Maggard, 1993).
Experimental results presented by Macrady and Maggard (1993) suggest that the Bacci
algorithm may overpredict Bv by a factor of 40 for dioxin-like compounds. Experimental
work by Simonich and Kites (1994) on PAHs indicates that the overproduction may be even
greater (up to a factor of 100) for PAHs. These results suggest that the Bacci algorithm is
not a good predictor of Bv for highly lipophilic compounds. The Dioxin document (U.S.
EPA, 1994a) recommends reducing the Bv calculated by the Bacci algorithm by a factor of
40 for dioxin-like compounds, based on Macrady and Maggard' s results.
As a result of these findings, the following heirarchy was established for setting Bv for
highly lipophilic compounds: (1) literature or other Agency value or (2) Bacci Bv divided by
40.
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&0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
EPA has recently established interim values for chemical properties for dioxin toxicity
equivalents (TEQs) using a weighted average of dioxin and furan congeners with nonzero
toxicity equivalence factors (TEFs). These data include Bv, and that value was used for
dioxin.
The Bv for mercury was based on the value recommended for mercuric chloride in the
Mercury Study Report to Congress ( U.S. EPA, 1994b).
The experimental values of Simonich and Hites (1994) were used for the following
PAHs:
• Benzo(a)pyrene
• Benz(a)anthracene
• Chrysene
• Fluoranthene
• Indeno (cd-123) pyrene
• Pyrene.
The Bv calculated by the Bacci algorithm was reduced by a factor of 40 for the
following compounds:
• Benzo(6)fluoranthene
• Bis (2-ethylhexyl) phthalate
• Dibenz(a,A)anthracene
• Dimethylbenz(a)anthracene
• Di-n-octyl phthalate
• Hexachlorobenzene
• Methylcholanthrene
• PCBs
• Pentachlorophenol
• 2,3,4,6-Tetrachlorophenol.
For all other compounds, the unmodified Bv calculated by the Bacci algorithm was used.
As discussed in Belcher and Travis (1989), metals are assumed not to experience air to
leaf transfer. Therefore, a Bv value was not calculated for metals as they were not expected
to become airborne to any significant degree. Bv values were calculated only for above-
ground, exposed produce; root vegetables are assumed to be protected from air-to-plant
transfer.
6.7.6.2.4 Biotransfer Factor for Beef and Milk
The Combustor Indirect Exposure Document (U.S. EPA, 1990e) defines biotransfer
factors as the ratio of pollutant concentration in animal tissue to the daily intake of pollutant
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
by the animal. The beef biotransfer factor indicates the extent to which contaminants are
transported from an environmental media to beef. Similarly, the milk, biotransfer factor
indicates the extent to which contaminants are transported from an environmental media to
milk. The following equations were derived by Travis and Arms (1988):
.
oga-og-S.l
where
Babeef = Beef bioconcenfration factor ([mg/kg beef]/[mg/kg DW feed])
B^Wlk = Milk bioconcenlration factor ([mg/kg milk]/[mg/kg DW feed])
Kow = Octanol-water partition coefficient (L/kg).
Derivation of Kow values is described above under the soil-water partition coefficient (Kj).
Tliese equations were used to calculate the respective biotransfer factors for the organic
constituents of interest No literature search was made for measured values.
The biotransfer factors for all of the inorganic constituents, except cadmium, mercury,
selenium, and zinc, were obtained from Baes et al. (1984). The values for cadmium,
mercury, selenium, and zinc were derived from uptake slopes (or bioconcentration factors) in
Technical Support Document for Land Application of Sewage Sludge (U.S. EPA, 1992e) by
dividing by daily consumption rate (20 kg DW/d; used for consistency with original studies).
6.7.6^5 Beef and Milk Bioconcentration Factor for Dioun-like Compounds
The lipophilic nature of dioxin and PCB causes them to transfer directly to the lipid
within the beef and mill: as opposed to adsorbing to both beef muscle and beef fat, or in the
case of milk, milk and mi'k fat Therefore, ;ji alternative methodology was employed to
calculate the PCB and dioxin concentrations in beef and milk. This methodology was
developed under the following assumptions, "contaminants bioconcentrate equally in the fat
portions of beef and milk" and "... the fraction of ingested contaminant which is adsorbed
into the body depends on die vehicle of ingestion. . .", according to the Dioxin document
(U.S. EPA, 1992c). Therefore, the beef and milk biotransfer factors could no longer be used
given the assumptions of die new methodology. Subsequently, the following parameters were
generated for thi» particular methodology, "the bioconcentration ratio of contaminant as
determined from cattle vegetative intake" and "the bioavailability of contaminant on the soil
vehicle relative to the vegetative vehicle," as stated in the Dioxin Document These new
parameters replaced the beef and milk biotransfer factors.
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6.7.6.2.6 Fish Uptake and Concentration
The concentration of contaminants in fish tissue may be related to the water
concentration using either a bioconcentration factoi (BCF) or a bioaccumulation factor (BAF).
Bioconcentration is defined as the net uptake of a chemical from an organism's surrounding
medium through direct contact (e.g., uptake by a fish through the gills and epithelial tissue),
but excluding ingestion of a chemical in food (McVey, 1994). Bioaccumulation is defined as
the net uptake of a chemical from the environment from all pathways (including direct contact
and ingestion of contaminated food items). It is important to recognize that the distinction
between BCF and BAF has both practical and technical implications. The route of exposure
assumed for BCFs is direct, contact and laboratory-derived BCF values are typically generated
from studies in which aquatic organisms are exposed to the chemical only through the water
(i.e., no contaminated food). For organic chemicals with log K^ values below - 4.0, the
BCF is a reasonable estimate of the concentration potential of the chemical under field
conditions. However, for more hydrophobic organic chemicals (log KQW » 4.0), uptake via
the food chain will be an increasingly important source of exposure and using the BCF value
will tend to underestimate the actual concentration of chemicals in fish tissue. Therefore, for
hydrophobic organic chemicals and other chemicals shown to bioaccumulate (e.g., mercury), a
bioaccumulation factor is the appropriate measure of the concentration potential in fish. Field
studies on the concentration potential of a chemical, regardless of the chemical, are typically
viewed as bioaccumulation studies since exposure may occur through direct contact as well as
through the food chain. Nevertheless, the primary route of exposure of hydrophilic (or
weakly hydrophobic) chemicals is through direct contact and the concentration gradients
required for bioaccumulaticn to occur are unlikely (Gobas, 1993).
In addition to the distinction between BCF and BAF, it is important to recognize the
difference between (1) dissolved water concentrations vs. total water concentrations and (2)
lipid-based concentrations vs. whole-body concentrations. For organic chemicals with log
KOW below 4.0, chemical concentrations in water \n typically regarded as freely dissolved,
although some small fraction is undoubtedly sorbed to suspended particles. In contrast, for
metals and hydrophobic organic chemicals having low solubility, water concentrations are
generally regarded as total water concentrations (Le., freely dissolved and particle-bound).
Because the freely dissolved fraction is considered to be the bioavailable fraction,* it is
crucial to distinguish between freely dissolved and total water concentrations when estimating
BCFs and BAFs as well as in conducting fate and transport modeling. Moreover, the Final
Chronic Values for fish and aquatic organisms reflect total water concentrations and, as a
result, estimation of protective exposure concentrations for piscivorous fish required BCFs for
total water concentrations. Using an FCV with a BCF for dissolved water concentration (i.e.,
BCF4) would result in a higher acceptable tissue concentration (TC) in fish and, therefore, an
underprotective surface water concentration for fish and aquatic invertebrates. This
*Particie-boand chemicals may also be ingested by fish and aquatic organisms. However, die contribution to
the overall exposure is generally considered to be small in comparison with direct contact with the freely dissolved
fraction and ingestion of contaminated prey.
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calculation is described fully in Section 5.3.2.1.2. BCF and BAP values for both freely
dissolved and total water concentrations were used in this analysis and were designated as "d"
(freely dissolved) or V (total) as appropriate. For organic chemicals, predicted BAFs from
the Thomann models (1989, 1992) and predicted BCFs from the Thomann model (1989) or
regression equations represent dissolved water concentrations. Measured BCFs for organic
chemicals with log K^ values below 4.0 were also considered dissolved Measured BCFs for
metals and measured BAFs for hydrophobic organic chemicals (and mercury) were considered
to represent total water concentrations with the exception of DDT which was based on the
freely dissolved fraction. Predicted, lipid-based BAFs were used for chemicals with log Kow
values between 4.0 and 6.5 unless (1) the log Kow of the chemical was above 6.5, (2) the
chemical has been shown to be metabolizable in fish (e.g., PAHs), or (3) measured values
were significantly different than predicted values, i.e., greater than or less than the predicted
value by a factor of 4. The cutoff for measured versus predicted was based on a paper by
Randall et aL (1991) which suggested that the choice of extraction solvents and analytical
methods caused BAF estimates to vary between a factor of 2 to 4. Table 6-10 presents the
chemicals for which measured BAF values were used to estimate food chain exposures to
humans and ecological receptors. It should be noted that the selection process for appropriate
bioaccumulation and bioconcentration factors considered measured values presented by
Stephan (1993), the Great Lakes Initiative (1995a). and values identified in the open literature
as well as predicted BAFs and BCFs generated by models and regression equations,
respectively. However, given the variability in, test methods and species uptake as well as the
general lack of data on many constituents of concern (e.g., most constituents had fewer than 2
measured BCF values), measured values were not preferred simply because they were
measured. Given the current state of the science, predictive models may provide a more
defensible basis for estimating concentration potential. The uncertainty in using a single
measured BCF value may be considerably greater than using a predicted BCF based on the
empirical relationship between chemical properties and partitioning to fish lipids.
The distinction between lipia-based and whole-body fish concentrations is also critical
to the exposure calculations. Lipid-based BAFs and BCFs for organic chemicals are
calculated for the lipid portion of the fish. Because most of an organic chemical is assumed
to partition to lipids, all of the chemical is sequestered in fat compartment of the fish.
Consequently, lipid-based BAFs and BCFs (BAF/s and BCF/s) are numerically higher than
whole-body BAFs and BCFs since the chemical is "diluted" in a smaller volume. The
bioaccumulation models used in this analysis were constructed to estimate lipid-based BAF/s
and BCF/s that reflect dissolved water concentrations. In contrast, whole-body BAFs and
BCFs are numerically smaller than the lipid-based counterparts because they are based on the
entire fish and, therefore, a greater "dilution" volume. For organic chemicals, whole-body
BAFs and BCFs may be converted to lipid-based by dividing by die lipid fraction. For
example, if a whole-body BCF of 100 were measured for chemical X in a species of fish with
10 percent lipids, the lipid-based BCF/ would be 100 + 0.1 or 1,000. For metals, whole-body
BCFs are the appropriate measure for ecological receptors and BCFs for muscle are the
appropriate measure for humans. For human exposures, lipid-normalized BCFs and BAFs
were calculated to reflect the amount of lipid actually ingested by humans assumed to eat fish
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6.0 FATE AND TRANSPORT MODELING 6.7 Fate and Transport Inputs
fillets. Because humans are assumed not to eat the entire fish, it would be inappropriate to
calculate exposures to organic chemicals using BAFs and BCFs that are lipid-based or whole-
body. Using the lipid-based BAF/s and BCF/s would result in overprotective estimates of
acceptable surface water concentrations and using whole-body BAFs and BCFs would result
in inconsistent estimates of acceptable surface water concentrations. Since various species of
fish have different lipid fractions (ranging from approximately 3 to 25 percent), whole-body
BAFs and BCFs are considered inappropriate to use in exposure calculations. Therefore,
lipid-normalized BAFs and BCFs were calculated for large fish in trophic level 4 for humans.
The lipid-normalized values were calculated assuming that the portion of the fish eaten by
humans contains 5 percent lipid. For example, to calculate the lipid-normalized value for a
chemical with a lipid-based BAF1 of 1,000, the BAF/ was multiplied by the lipid fraction or,
1,000 x 0.05 or 50. The BAF of 50 is the bioaccumulation factor for humans eating fillets
from trophic level 4 fish assumed to contain 5 percent lipids. For measured BAFs and BCFs,
lipid-normalized values were calculated assuming that the fish contain 7.9 percent lipids.
For extremely hydrophobic constitu...^, the Agency has stated that reliable
measurements of ambient water concentrations (especially dissolved concentrations) are not
available and that accumulation of these constituents in fish or other aquatic organisms cannot
be referenced to a water concentration as required for a BCF or BAF (U.S. EPA, 1993i).
Fortunately, extremely hydrophobic constituents can be measured in sediments and aquatic
life and, because these chemicals tend to partition to lipids and organic carbon, a biological
uptake factor that reflects the relationship between sediment concentrations and organism
concentrations may be more appropropriate. Consequently, the biota-sediment accumulation
factor (BSAF) is the preferred metric for accumulation in the littoral aquatic ecosystem for
extremely hydrophobic chemicals (e.g., chemicals with > log K,,w of - 6.5). For 2,3,7,8-
TCDD and PCBs, the BSAF in [mg/kg LP]/[mg/kg sediment OC] for trophic level 4 fish was
supplied by the U.S. EPA ORD Exposure Assessment Group in a memorandum to Addressees
by Matthew Lorber (September 1994). This memorandum updates the Addendum to the
Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor
Emissions (U.S. EPA, 1993a) and other EPA documents involving risk assessment of 2,3,7,8-
TCDD. This recommendation represents the current state of the science at the Agency.*
*It should be noted that of PCB exposures to ecological receptors, the BAF/s generated for the Great Lakes
Water Quality Initiative Technical Support Document (U.S. EPA. 1995a) were used for ecological receptors.
Because humans are assumed to eat only trophic level 4 fish, the BSAF was considered appropriate to use in the
human exposure calculations. However, accumulation factors for PCBs were required for trophic levels 2 to 4
and, lacking BSAFs for trophic levels 2 and 3. it was determined that the BAF/s were appropriate for ecological
receptors. The use of BAF/s vs. the BSAF for trophic level 4 resulted in an insignificant change in the
protective exposure concentrations for receptors at the top of the food chain (e.g., eagle, heron).
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6.7.7 Basic Constants
The following basic constants were used:
• Universal Gas Constant, R = 8.21e-5 atm-L/mol-K
• Viscosity of air = 1.81e-4 g/cm-s
• Density of air = 1.2e-3 g/cm3.
These values were taken from the CRC Handbook (Weast, 1980) and reflect standard
conditions (temperature = 20 °C, pressure = 1 atm or 760 mm Hg).
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