CHRONIC EXPOSURE MODULE

EXPOSURE CONTROLS TAB

The exposure controls tab allows the user to define the timing of exposure calculations, select exposure pathways to be included, and to select the method (and provide parameter values) for evaluation of the leaching rate constant for surface soils.

EC-TEXPOS
Units: yr
Range: 0.0

This is the time between the start of the analysis (e.g. definition of source term quantities and beginning of transport) and the time exposure begins.

EC-MAXTIM
Units: yr
Range: EC-TEXPOS - 5,000,000.0

This is the maximum time to consider in the exposure analysis. It is used to determine the length of each time increment in the exposure analysis [= (MAXTIM - TEXPOS) / NTIMES].

EC-NTIMES
Units: none
Range: > 0

This parameter allows the user to define the number of time increments used in the exposure analysis. If the value entered is zero, then time increments will be set to 1 year.

EC-KEXPTH--Exposure Pathways

This screen allows the user to select exposure pathways to be included in the current analysis. A pathway is selected for inclusion in the analysis by clicking on the box in front of the pathway name. Boxes with an "X" indicate the pathways to be included. Pathways are de-selected by clicking on the "X" again.

LEACH RATES

The leach rate tab allows the user to define the method for definition of surface soil leach rate constants, and to enter leach rates or related parameter values. The leach rate constant (1/yr) is used like a decay rate constant. A small value means there is little leaching and the material stays around for a long time. Enter a small value (e.g., 1.0E-06) to cause leaching to be ignored.

EC-LEACHOPTION--Leach rate selection option

The pull-down menu box has two options: "User provided leach rate constants" and "User provides soil and K_d parameters".

EC-SOILLR--Parent and progeny surface soil leach rate constant
Units: 1/yr
Range: 0 to 100.0

Leach rate constants are entered when "User provided leach rate constants" leach option is selected. A leach rate constant should be entered for each parent and progeny in the inventory list. The pull-down menu box is used to select the pollutant for data entry. If the pollutant has progeny to consider, then an entry set will appear (to the right of the parent set) allowing entry of leach rate constants for all progeny.
User supplied parameters for calculation of the leach rate constant are as follows. Numerical values and correct units must be entered for each parameter when the rate constant calculation option is selected.

EC-SOILKD--Parent and progeny surface soil adsorption coefficient
Units: mL/g
Range: greater than or equal to 0.0

EC-SOILKD represents the equilibrium (partition or distribution) coefficient K_d of constituent between top soil and moisture. Use laboratory or field-derived distribution coefficient (K_d) values if they are available from site documents or reports of studies using similar soil and constituent characteristics. Typical K_d values reported in peer review literature will be provided by the user interface if site-specific K_ds are not available. Several additional data are required for the user interface to compute a K_d value for each layer (see Section TOP SOIL PARAMETERS):
For inorganic chemicals:

- Soil pH (if unknown, assume neutral conditions)
- Weight percent clay and iron and aluminum oxyhydroxides

For organic chemicals:

- Percent sand, silt, and clay and organic matter

Theoretically, K_d is defined as:
K_d = C_p/C_d
where C_p is the particulate concentration (i.e., weight or activity of adsorbed constituent per weight of solid) and C_d is the dissolved concentration or activity (see Section WS-UNITS). Although the K_d value of a constituent of concern can be determined in the laboratory or obtained from published literature, such values can vary considerably depending upon the experimental or environmental conditions (e.g., characteristics of soil and water) and technique used. When choosing between K_d values, use the value which will provide the conservative results (e.g., highest risk). For example, a receptor that is living on or near the waste site and ingesting contaminated soil would have high risk with the large K_d value because the constituent would not be readily washed off by rain and retained in soils for an extended period of time. On the other hand, low K_d value would pose high risk to the offsite receptor that ingests water because the constituent is readily dissolved into water and is mobilized. Note that because of the uncertainty associated with K_d, it is preferably used as a calibration parameter to adjust the constituent velocity.

Selecting Adsorption Coefficient - The aquifer module can provide estimates of K_d for all constituents. For inorganic constituents, typical K_d values reported in the peer reviewed literature are provided by the user interface, via a lookup table, based on the soil water pH (KD-PH), percent clay (KD-CLAY) and percent iron and aluminum (KD-IRON). For organic constituents, the percent sand (KD-SAND), percent silt (KD-SILT), percent clay (KD-CLAY), and percent organic matter (KD-OMC) are used in an empirical equation to provide a K_d estimate. The soil characteristics values are enter through a form brought up by pressing the Soil-EC-Class button
The dropdown box gives the user the choice to select a K_d from

Database Value - provided by the connected chemical database module
Table Lookup Value - provided by the "KD_DATA.CSV" file. Primarily contains metals and radionuclides

K_d = lookup(casid,col_index) where column index is calculated by
sum = KD-OMC + KD-CLAY + KD-IRON
If PH >= 9.0 Then
. If sum >= 30.0 Then col_Index = 3
. else If sum >= 10.0 Then col_Index = 2
. else col_Index = 1
else If PH >= 5.0 Then
. If sum >= 30.0 Then col_Index = 6
. else If sum >= 10.0 Then col_Index = 5
. else col_Index = 4
else
. If sum >= 30.0 Then col_Index = 9
. else If sum >= 10.0 Then col_Index= 8
. else col_Index = 7

Estimated Value - calculated by the equation

K_d = 0.0001 * k_oc * (57.735 * KD-OMC + 2.0 * KD-CLAY + 0.4 * KD-SILT + 0.005 * KD-SAND)

EC-THICK--Surface soil thickness
Units: cm
Range: 0 to 1000

The thickness of the surface soil layer is the depth in which the contamination is mixed, representing an effective thickness for loss by leaching. For agricultural soils, the value is typically set to 15 cm representing the depth of the plow layer. For undisturbed soils a smaller value may be appropriate. If initial contamination of soil is represented, then the value should be based on information about the initial contamination depth.

EC-MOIST--Surface soil moisture content
Units: fraction
Range: 0. to 1.0

The surface soil moisture content should be set representative of the surface soil layer at the exposure location.

EC-BULKD--Surface soil bulk density
Units: g/cm³
Range: 0.5 to 3.0

The bulk density is the density of surface soil at the exposure location.

EC-LEACV--Total infiltration
Units: cm/yr
Range: 0 to 500

The total infiltration rate may be evaluated as the total annual precipitation + irrigation rate - evapotranspiration rate.

CONSTITUENT PROPERTIES TAB

FS-CNAME--Name of constituent(s) for current transport scenario

This field shows the constituents that are selected for the scenario. Use the arrow buttons to scroll through the list of constituents and enter an adsorption coefficient and water solubility for each one, and a degradation/decay half-life for non-radionuclides. If a constituent has decay products, they will be shown on the bottom part of this screen.

EC-GHALF--Physical loss half-time in ground water
EC-WHALF--Physical loss half-time in surface water
EC-SHALF--Physical loss half-time in soil
EC-THALF--Physical loss half-time in air
Units: yr
Range: greater than 0.0

This parameter is the half-life of the constituent in the respective media. For radionuclide and non-radionuclide constituents, this value defaults to the data in the constituent database, but the value can be changed to a site-specific value. This parameter can be used to implement other degradation rates (e.g., biodegradation, photo degradation, etc...) when they are converted to equivalent half-lives.

Chemical/Radionuclide Air, Soil, and Water Half-Life/Half-Time Requirements in the Human Exposure Module When Linked to the Atmospheric, Source-Term, Groundwater, and Surface Water Transport Modules (see footnote)
Transport Modules Providing Boundary-Condition Input to the Human Exposure Module (e.g. Atmospheric = air module boundary condition to the exposure module)	Half-Life/Half-Time Values Needed by the Human Exposure Module
	Air Half-Life/Half-Time needed in Human Exposure Component?	Soil Half-Life/Half-Time needed in Human Exposure Component?	GW Half-Life/Half-Time needed in Human Exposure Component?	SW Half-Life/Half-Time needed in Human Exposure Component?
Atmospheric	YES (for plant retention from deposition prior to harvest)	YES (for deposition to soil for crops, animal products, and resuspension; in addition to leaching losses)	YES (for food holdup, after harvesting before consumption but in a closed system)	NO
Soil (initial concentration)	NO	YES (for soil loss)	YES (for food holdup, after harvesting before consumption but in a closed system)	NO
Soil (known concentrations)	NO	NO	YES (for food holdup, after harvesting before consumption but in a closed system)	NO
Groundwater	YES (for irrigated plant retention prior to harvest)	YES (for irrigation to soil for crops and animal products; in addition to leaching losses)	YES (for drinking water holdup and food holdup, after harvesting before consumption but in a closed system)	NO
Surface Water	YES (for irrigated plant retention prior to harvest)	YES (for irrigation to soil for crops and animal products; in addition to leaching losses)	YES (for drinking water holdup, fish holdup, and food holdup, after harvesting before consumption but in a closed system)	YES (for sediments pathways, near or on shore)
Footnote: For example, the GW half-life/half-time is used by the Human Exposure module to represent decay or loss from closed aqueous systems, such as drinking water contained within the pipes of the water distribution system, or foods (crops, animal products, or fish) where the material is contained (packaged) and is not subject to volatilization losses; therefore, when the Human Exposure module is linked to, say, the Surface Water module, the GW half-life/half-time is used by the Human Exposure module to evaluate drinking water holdup, fish holdup, and food holdup. Holdup is the delay between harvest and consumption for food products. For drinking water, it is the delay time between entering the domestic water supply system and delivery to the house where the water is consumed. For home wells, the delay time would be small.

GROUND WATER TAB

The information described below must be provided for each ground water receptor location identified for the facility. Each ground water receptor location involves water usage that results in one or more of the following exposure routes: ingestion of drinking water from a contaminated well, ingestion and inhalation while showering, and ingestion of crops and animal products produced with contaminated well water. Irrigation with contaminated water is the primary route of exposure for crops and animal products, although animal products may also become contaminated when animals drink contaminated water or ingest soil contaminated by water. Ground water transport that results in surface water contamination and exposure is considered in the surface water exposure section (see Section SURFACE WATER TAB).

The following steps are provided: 1) obtain information on domestic water usage from municipal water supply departments or from published municipal water reports; 2) record the sources of all information, including information obtained by telephone, in a reference or footnote. This reference should state who was contacted (with phone number), their position (and company), and the nature of the information obtained.

EG-KGDR--Domestic Usage

This pull-down menu box allows selection of the domestic uses of ground water: "no domestic water usage", "shower use only" or "shower and drinking water". Select the desired option by clicking on the line describing the option. Domestic water use may include exposure pathways of drinking water ingestion, shower water ingestion, shower water dermal contact, and inhalation of volatile compounds during shower (or indoor inhalation).

EG-KGIR--Type of irrigation use at current usage location

This pull-down menu box allows selection of uses for irrigation water in production of crops and animal products. The options to select from include:

No farm production
Animal drinking only (no irrigation water use)
Crops and animals (feed and water)
Crops and animals (feed only, no animal drinking water)

Animal ingestion of soil is included when animal feed ingestion is included. To inhibit animal soil ingestion, set the animal soil intake parameter to zero, for meat animals or milk (EC-USMLT) animals (EC-USMLK).

DURATIONS

The durations tab under the ground water tab allow for input of exposure duration to domestic water pathways and the holdup time for water transport from the water intake plant to the point of consumption.

EG-DGWED--Exposure duration
Units: yr
Range: 1.0 to 100

The exposure duration is the number of years that individuals are exposed do domestic water use pathways. (Note: while it is possible to enter different exposure durations for each media/transport types, the same exposure durations should be used for all pathways if the MEPAS Human Health Impact Module is to be used. In that module, a single exposure duration is used for all media/transport types.)

EG-TWTR--The average distribution time for the water supply system for the current usage location
Units: day
Range: 0.0 to 100.0
Default Value: 1.0

This parameter represents the average distribution time, in days, for the water supply system. The distribution time is the interval between the time the water is pumped from the ground and when it is consumed or used by the public. Use a typical value of 1.0 days if no value is given (NRC 1977).

DOMESTIC USAGE
Ground water Drinking Water Usage

Only usage locations involving potentially contaminated ground water need to be included. Required information about the ground water drinking water pathway includes the number of people served by the supply system, whether or not water is treated, and the water distribution time.

EG-LTRTL--Indicates whether or not the domestic water supply for the current receptor location is treated

Click on the box if the drinking water is treated ("x" in box). If the water is not treated, the box should be blank. If no treatment information is available, assume no water treatment. If water concentrations are based on measurements of finished drinking water (i.e., tap water), then no water treatment should be indicated.

IRRIGATION USAGE
Ground water Irrigation Usage

Use of contaminated water for crop irrigation may result in human exposure through the ingestion of contaminated agricultural products. Input required on this screen is the fraction of a year that irrigation occurs, and the irrigation rate.

EG-FIRR--Fraction of the year that ground water is used for irrigation
Units: none
Range: 0.0 to 1.0
Default Value: 1.0

Irrigation of crops generally does not occur throughout the entire year. This parameter allows the user to define the fraction of the year that irrigation water is applied. Use of this parameter should be coordinated with the irrigation rate. If the irrigation occurs only 6 months of the year the fraction would be set to 0.5 and the irrigation application rate (during the 6 months) would be divided by 0.5 (to give the annual average rate). Use for surface water and ground water is the same. The default is set for irrigation during the entire year.

EG-CIRR--The irrigation rate for the current water usage location
Units: L/m²/mon
Range: 0.0 to 999.9

This parameter represents the irrigation rate over the irrigation period for the current water usage location. Obtain the average irrigation rate from county extension agents or local irrigation districts.

SURFACE WATER TAB

The information described in this section must be provided for each receptor location identified for the facility. The following activities are possible exposure routes resulting from usage of contaminated surface water: drinking water, bathing, eating fish caught in the water, irrigating farm products, and using waters for recreation. Data requirements for each of these pathways are described below.

Information on domestic water usage can be obtained by calling municipal water supply departments or from published water supply reports. Recreational activities (and fish production) for local waters may be obtained from parks and recreation departments. Record the sources of all information, including information obtained by telephone, in a reference or footnote. This reference should state who was contacted (with phone number), their position (and company), and the nature of the information obtained.

EW-KSDR--Domestic usage

This pull-down menu box allows selection of the domestic uses of surface water: "no domestic water usage", "shower use only" or "shower and drinking water". Select the desired option by clicking on the line describing the option. Domestic water use may include exposure pathways of drinking water ingestion, shower water ingestion, shower water dermal contact, and inhalation of volatile compounds during shower (or indoor inhalation).

EW-KSIR--Type of irrigation use at current water usage location

This pull-down menu box allows selection of uses for irrigation water in production of crops and animal products. The options to select from include:

No farm production
Animal drinking only (no irrigation water use)
Crops and animals (feed and water)
Crops and animals (feed only, no animal drinking water)

Animal ingestion of soil is included when animal feed ingested is included.

EW-KSAQ--Aquatic food usage

There are two possible food categories in the aquatic-food ingestion pathway: finfish (e.g., trout, catfish) and shellfish (e.g., clams, mussels, crab). A usage location for aquatic food production may be a river, stream, reservoir, lake, or bay. The usage may be either commercial harvesting or sport fishing.
This pull-down menu box allows selection of aquatic food types harvested from the surface water exposure location. Available options include:

None
Finfish
Shellfish
Both finfish and shellfish

EW-KSR--This parameter indicates the type of recreational surface water usage

This pull-down menu box allows selection of aquatic recreational activities for the surface water exposure location. Available options include:

None
Swimming only
Boating only (applies only to radionuclides)
Shoreline activities only
All, swimming, boating, and shoreline activities (default value if radionuclides are included in the constituent list).

DURATION

This tab allows input of surface water exposure duration, transit time from release, and water distribution time.

EW-DSWED--Exposure duration
Units: yr
Range: 1.0 to 100

This parameter is the duration of exposure to surface water pathways. (Note: while it is possible to enter different exposure durations for each media/transport types, the same exposure durations should be used for all pathways if the MEPAS Human Health Impact Module is to be used. In that module, a single exposure duration is used for all media/transport types.)

EW-TWTR--The average distribution time for the water supply system
Units: day
Range: 1.0 to 100
Default Value: 1.0

This parameter represents the average distribution time, in days, for the water supply system. The distribution time is the interval between the time the water is pumped from the surface water body and when it is consumed or used by the public. Use a typical value of 1.0 days if no value is given (NRC 1977).

DOMESTIC

This screen allow definition water treatment prior to domestic water use.

EW-LTRTL--Parameter indicates whether or not water is treated

Click on the box if the drinking water is treated ("x" in box). If the water is not treated, the box should be blank. If no treatment information is available, assume no water treatment. If water concentrations are based on measurements of finished drinking water (i.e., tap water), then no water treatment should be indicated.

IRRIGATION USAGE
Surface Water Irrigation Usage

The same type of data is required for this pathway as was described for the irrigation section of the ground water pathway. Use of contaminated surface water for irrigation may result in human exposure through ingestion of contaminated crops and animal products. Input required on this screen is the fraction of a year that irrigation occurs, and the irrigation rate.

EW-FIRR--Fraction of the year that surface water is used for irrigation
Units: none
Range: 0.0 to 1.0
Default Value: 1.0

Irrigation of crops generally does not occur throughout the entire year. This parameter allows the user to define the fraction of the year that irrigation water is applied. Use of this parameter should be coordinated with the irrigation rate. If the irrigation occurs only 6 months of the year the fraction would be set to 0.5 and the irrigation application rate (during the 6 months) would be divided by 0.5 (to give the annual average rate). Use for surface water and ground water is the same. The default is set for irrigation during the entire year.

EW-CIRR--The irrigation rate for the current water usage location
Units: L/m²/mon
Range: 0.0 to 999.9

Provide the average irrigation rate over the irrigation period.

AQUATIC FOOD

There are two possible food categories in the aquatic-food ingestion pathway: finfish (e.g., trout, catfish) and shellfish (e.g., clams, mussels, crab). A usage location for aquatic food production may be a river, stream, reservoir, lake, or bay. The usage may be either commercial harvesting or sport fishing.

EW-TFSH--This parameter represents the time between harvest and consumption of finfish for the current surface water usage location
Units: day
Range: 0.0 to 999.9
Default Value: 10.0

This parameter represents the time between harvest and consumption of finfish for the current surface water usage location. A typical value for the time delay between harvest and consumption is 10 day (NRC 1977). An example is presented in Section EW-TINV.

EW-TINV--This parameter represents the time between harvest and consumption of shellfish for the current surface water usage location
Units: day
Range: 0.0 to 999.9
Default Value: 10.0

This parameter represents the time between harvest and consumption of shellfish for the current surface water usage location. The typical value for the time delay between harvest and consumption is 10 day (NRC 1977).

EW-TISSUE--This parameter is a correction factor to be applied to finfish bioaccumulation factors to represent concentration in edible fish as opposed to whole fish.
Units: none
Range: 0.0001 to 9999.9

This parameter modifies the bioaccumulation factors read from the database or estimated by MEPAS using correlation relationships. It should only be applied (i.e., changed from a value of 1.0) if the data values for BAF are based on whole fish measurements and not edible fish tissue (e.g. muscle). When a value is given for an analysis, it is applied to all constituents included in the analysis.

RECREATIONAL

Recreational activities in surface waters may result in exposure to chemicals through swimming (inadvertent ingestion, dermal contact), shoreline (inadvertent ingestion and dermal contact with sediment), and exposure to radionuclides through swimming, boating, and shoreline activities. When radionuclides are not present in the source term, only swimming- and shoreline-related data need to be identified. The parameters described below must be defined for each surface-water usage location.

EW-TSS--Thickness of shoreline sediments
Units: m
Range: 0.0001 to 5.0

Material deposited from surface water onto shoreline sediments is assumed to be mixed in a layer of sediments. The thickness of this layer is represented by this parameter. The value is used to estimate the sediment concentration for the dermal exposure and sediment ingestion exposure pathways.

EW-RHOSS--Density of shoreline sediments
Units: g/cm3
Range: 1.0 to 4.0

The density of shoreline sediments is used to estimate the constituent concentration in sediments.

ATMOSPHERIC TAB

The release of constituents to the atmosphere may result in widespread exposures by inhalation of airborne material or by ingestion of farm products contaminated by deposition on soil or plants. A typical release might involve the emission of volatile compounds (vaporization) or wind suspension of particulate material.

Atmospheric releases are may result in widespread exposures to individuals in the region and via contamination of agricultural products.

EA-KAIN--Regional exposure

Regional exposure pathways include air inhalation, external exposure to contaminated air, external exposure to deposited contamination, ingestion of contaminated soil, and dermal contact with contaminated soil. The pull-down menu box allows selection of these regional pathways or skipping of regional pathways.

EA-KAAG--Agricultural exposure

Agricultural exposures occur when airborne contamination is deposited onto plants or cropland soil and subsequently contaminates food crops or animal products. If any agricultural exposure pathways are to be included in the analysis, then the agricultural option should be selected from this pull-down menu.

EA-ATED--Exposure duration
Units: yr
Range: 1.0 to 100

This parameter is the exposure duration for atmospheric pathways. (Note: while it is possible to enter different exposure durations for each media/transport types, the same exposure durations should be used for all pathways if the MEPAS Human Health Impact Module is to be used. In that module, a single exposure duration is used for all media/transport types.)

EA-TAS--Thickness of soil receiving deposition
Units: m
Range: 0.0001 to 5.0

Material deposited from air onto soil is assumed to be mixed in a layer of soil. The thickness of this layer is represented by this parameter.

EA-RHOAS--Density of soil receiving deposition
Units: g/cm3
Range: 1.0 to 4.0

The density of surface soils is used to estimate the constituent concentration in soil.

KNOWN SOIL CONTAMINATION TAB

SOIL CONCENTRATION MODEL SELECTION

Two methods for defining the time variation in soil concentration are available. "Use time varying soil concentrations from the SCF" and "Use initial soil concentration from the SCF to compute time varying soil concentrations.". These methods are selected by the soil model parameter, SOILMOD, defined as follows.

EM-SOILMOD--Soil Model Selection Flag
Units: none
Range: True or False

All soil concentration data is supplied via the soil concentration file (extension SCF). When the time variation of soil concentration is to be defined by the user (and supplied via the SCF file), then the soil concentration usage option "Use time varying soil concentrations from the SCF" is selected (the flag is set to False) and all data provided in that file is read and used. In this case, no features of the MEPAS soil concentration model are used in the analysis.

When the MEPAS soil model is to be used, the soil concentration usage option "Use initial soil concentration from the SCF to compute time varying soil concentrations" is selected (SOILMOD = True). The first soil concentration data point is read from the SCF file and used as the initial soil concentration. Variation in soil concentration with time is evaluated using the MEPAS soil model that includes leaching, volatilization loss, and radioactive decay.

When soil concentration values are available, the MEPAS exposure module can be used to evaluate exposure from soil ingestion, soil external exposure, soil dermal contact, and inhalation of suspended material. The parameter needed for this analysis is the exposure duration to contaminated soil.

EM-SMED--Soil exposure duration
Units: yr
Range: 1.0 to 100

This parameter is the exposure duration for exposure to measured soil concentrations. (Note: while it is possible to enter different exposure durations for each media/transport types, the same exposure durations should be used for all pathways if the MEPAS Human Health Impact Module is to be used. In that module, a single exposure duration is used for all media/transport types.)

EXPOSURE MODULE CUSTOMIZATION PARAMETERS

The following parameter values are available for modification by the user to provide customized analyses.

SOIL AND CROP TAB

EC-DEN--Agricultural areal soil density
Units: kg/m²
Range: 1.0 to 2000
Default Value: 240

The agricultural areal soil density is the mass of soil in the active layer (15 cm plow zone) per unit area of land. The default value is based on a soil thickness of 15 cm and a soil density of 1.6 g/cm3 (NRC 1977). The areal soil density is calculated from the thickness and density as follows.

Areal density (kg/m2) = 10 x Thickness (cm) x Density (g/cm3)
EC-RET--Agricultural plant retention fraction of deposited activity
Units: fraction
Range: 0.0 to 1.0
Default Value: 0.25

Deposition of constituents to plants by air or irrigation water deposition results in only part of the material being retained on the plant surfaces. The retention fraction indicates the fraction of the deposition that is retained on the plants. The default value of 0.25 is for irrigation deposition and is used also for airborne deposition (NRC 1977). The value supplied is used for all deposition calculations performed within a run. If different values are desired for irrigation and airborne deposition, then it is necessary to perform two analyses, one for irrigation and one for airborne deposition, with appropriate values set for each analysis.

EC-YLDLEAF--Yield of leafy vegetable crops
Units: kg/m²
Range: 0.01 to 20.0
Default Value: 2.0

The yield of a crop represents the mass of edible food produced in one crop growing season per unit area of soil (NRC 1977).

EC-YLDVEG--Yield of other vegetable crops
Units: kg/m²
Range: 0.01 to 20.0
Default Value: 2.0

The yield of a crop represents the mass of edible food produced in one crop growing season per unit area of soil (NRC 1977).

EC-YLDMEAT--Yield of meat animal feed
Units: kg/m²
Range: 0.01 to 20.0
Default Value: 0.7

The yield of a crop represents the mass of edible food produced in one crop growing season per unit area of soil (NRC 1977).

EC-YLDMILK--Yield of milk animal feed
Units: kg/m²)
Range: 0.01 to 20.0
Default Value: 0.7

The yield of a crop represents the mass of edible food produced in one crop growing season per unit area of soil (NRC 1977).

ANIMAL INTAKE RATES TAB

EC-UMT--Meat animal intake rate of feed
Units: kg/day
Range: 0.0 to 200.0
Default Value: 68.0

The intake rate of animal feed is the total daily ingestion rate (wet weight) by the animal of feed (contaminated and uncontaminated). The default values are taken from Strenge, Peloquin, and Whelan (1986). Note: if this parameter is changed, it may be necessary to also modify the meat animal intake rate of soil as the two parameters are related. See parameter EC-USLMK below.

EC-UMK--Milk animal intake rate of feed
Units: kg/day
Range: 0.0 to 200.0
Default Value: 55.0

The intake rate of animal feed is the total daily ingestion rate (wet weight) by the animal of feed (contaminated and uncontaminated). The default values are taken from Strenge, Peloquin, and Whelan (1986). Note: if this parameter is changed, it may be necessary to also modify the milk animal intake rate of soil as the two parameters are related. See parameter EC-USLMT below.

EC-WMT--Meat animal intake rate of water
Units: L/day
Range: 0.0 to 300.0
Default Value: 60.0

The intake rate of animal water is the total daily ingestion rate by the animal of water. The default values are taken from Strenge, Peloquin, and Whelan (1986).

EC-WMK--Milk animal intake rate of water
Units: L/day
Range: 0.0 to 300.0
Default Value: 50.0

The intake rate of animal water is the total daily ingestion rate by the animal of water. The default values are taken from Strenge, Peloquin, and Whelan (1986).

EC-USLMT--Meat animal intake rate of soil
Units: kg/day
Range: 0.0 to 20.0
Default Value: 0.8

Animals grazing or in feed lots will consume soil while browsing. The soil intake rate is defined to represent uptake of contaminated soil by animals resulting in contaminated animal products. The default soil intake rate is a nominal value representing approximately 4% of the meat and milk animal dry feed intake (Thorne 1984). The value is based on the default intake rates of meat animal feed, converted to a dry-weight basis assuming the feed plants are 75% water.

EC-USLMK--Milk animal intake rate of soil
Units: kg/day
Range: 0.0 to 20.0
Default Value: 0.7

Animals grazing or in feed lots will consume soil while browsing. The soil intake rate is defined to represent uptake of contaminated soil by animals resulting in contaminated animal products. The default soil intake rate is a nominal value representing approximately 4% of the meat and milk animal dry feed intake (Thorne 1984). The value is based on the default intake rates of milk animal feed, converted to a dry-weight basis assuming the feed plants are 75% water.

TRANSLOCATION FACTORS TAB

EC-TRNLEAF--Translocation factor to edible parts of leafy vegetables
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

The translocation factor is the fraction of material deposited onto plant surfaces (by air or water deposition) that is retained by the plant in edible parts of the plant. The default values are from Napier et al. (1988).

EC-TRNVEG--Translocation factor to edible parts of other vegetables
Units: fraction
Range: 0.0 to 1.0
Default Value: 0.1

The translocation factor is the fraction of material deposited onto plant surfaces (by air or water deposition) that is retained by the plant in edible parts of the plant. The default values are from Napier et al. (1988).

EC-TRNMT--Translocation factor to edible parts of meat animal feed
Units: fraction
Range: 0.0 to 1.0
Default Value: 0.1

The translocation factor is the fraction of material deposited onto plant surfaces (by air or water deposition) that is retained by the plant in edible parts of the plant. For animal products the translocation factor is applied in estimation of the concentration in the plant used for animal feed. The default values are from Napier et al. (1988).

EC-TRNMK--Translocation factor to edible parts of milk animal feed
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

The translocation factor is the fraction of material deposited onto plant surfaces (by air or water deposition) that is retained by the plant in edible parts of the plant. For animal products the translocation factor is applied in estimation of the concentration in the plant used for animal feed. The default values are from Napier et al. (1988).

FEED AND WATER CONTAMINATION TAB

EC-FFCMT--Fraction of meat animal's feed that is contaminated
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

Beef animals fed contaminated feed may not get all of their intake from contaminated sources. The feed contamination fraction allow the user to represent the situation where part of the animal feed is uncontaminated. The default values represent all animal intake coming from contaminated sources.

EC-FFCMK--Fraction of milk animal's feed that is contaminated
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

Milk animals fed contaminated feed may not get all of their intake from contaminated sources. The feed contamination fraction allow the user to represent the situation where part of the animal feed is uncontaminated. The default values represent all animal intake coming from contaminated sources.

EC-FWCMT--Fraction of meat animal's water that is contaminated
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

Beef animals fed contaminated water may not get all of their intake from contaminated sources. The water contamination fraction allow the user to represent the situation where part of the animal water is uncontaminated. The default values represent all animal intake coming from contaminated sources.

EC-FWCMK--Fraction of milk animal's water that is contaminated
Units: fraction
Range: 0.0 to 1.0
Default Value: 1.0

Milk animals fed contaminated water may not get all of their intake from contaminated sources. The water contamination fraction allow the user to represent the situation where part of the animal water is uncontaminated. The default values represent all animal intake coming from contaminated sources.

HARVEST DELAY TIMES TAB

EC-TCRPLEAF--Leafy vegetable crop ingestion harvest delay time
Units: day
Range: 0.0 to 365.0
Default Value: 1.0 days

The holdup time for farm products is the time between harvesting of the food product and consumption by individuals in the general population. During this period, the concentration in the food product may change because of radioactive decay or volatile losses from the food. The default value is taken from NRC 1977.

EC-TCRPVEG--Other vegetable crop ingestion harvest delay time
Units: day
Range: 0.0 to 365.0
Default Value: 60.0 days

The holdup time for farm products is the time between harvesting of the food product and consumption by individuals in the general population. During this period, the concentration in the food product may change because of radioactive decay or volatile losses from the food. The default value is taken from NRC 1977.

EC-TCRPMT--Meat product ingestion harvest delay time
Units: day
Range: 0.0 to 365.0
Default Value: 20.0

The holdup time for farm products is the time between harvesting of the food product and consumption by individuals in the general population. During this period, the concentration in the food product may change because of radioactive decay or volatile losses from the food. The default value is taken from NRC 1977.

EC-TCRPMK--Milk product ingestion harvest delay time
Units: day
Range: 0.0 to 365.0
Default Value: 4.0

The holdup time for farm products is the time between harvesting of the food product and consumption by individuals in the general population. During this period, the concentration in the food product may change because of radioactive decay or volatile losses from the food. The default value is taken from NRC 1977.

GROWING PERIODS TAB

GROUND WATER

EG-TGRWLEAF--Leafy vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EG-TGRWVEG--Other vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EG-TGRWMT--Meat animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

EG-TGRWMK--Milk animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

SURFACE WATER

EW-TGRWLEAF--Leafy vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EW-TGRWVEG--Other vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EW-TGRWMT--Meat animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

EW-TGRWMK--Milk animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

ATMOSPHERIC

EA-TGRWLEAF--Leafy vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EA-TGRWVEG--Other vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EA-TGRWMT--Meat animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

EA-TGRWMK--Milk animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

MEASURED SOIL

EM-TGRWLEAF--Leafy vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EM-TGRWVEG--Other vegetable growing period
Units: day
Range: 10.0 to 365.0
Default Value: 60.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The default value is taken from NRC 1977.

EM-TGRWMT--Meat animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

EM-TGRWMK--Milk animal feed growing period
Units: day
Range: 10.0 to 365.0
Default Value: 30.0

The growing period for each crop represent the length of time necessary to grow and harvest one crop. For example, if two crops can be harvested (successive growing periods) during a 6 month period, the growing period for one crop is 3 months and the crop growing period to use here is 90 days. The growing period for animals represent the nominal time to grow one feed crop (hay for meat animals, and fresh forage for milk animals). The default value is taken from NRC 1977.

RESUSPENSION TAB

EC-CML--Airborne particulate mass loading factor
Units: kg/m³
Range: 0.0 to 1E-4
Default Value: 1.00E-08

The airborne particulate mass loading factor is used to estimate the air concentration above contaminated soil for the measured soil analysis. The mass loading factor defines the mass of soil that is suspended in the air above the contaminated soil. This defines the concentration of constituents in air for the inhalation pathway. The default value (1.E-8 kg/m³) represents a nominal air particulate concentration of 10 micrograms/m³. This is based on recommendations of Anspaugh et al. (1975) to be used for predictive purposes.

EC-RESFAC--Atmospheric resuspension factor
Units: m^-1
Range: 0.0 to 2E-4
Default Value: 1.00E-07

Material deposited onto surface soil is subject to resuspension resulting in inhalation exposure of individuals. The resuspension factor relates the soil concentration to the air concentration above the contaminated soil.

INDOOR AIR TAB

EC-ANDFC--Andelman inhalation factor for volatile chemicals
Units: L/m³
Range: 0.0 to 20.0
Default Value: 0.5

The Andelman indoor air inhalation factor gives the ratio between average indoor air concentration and the concentration in the domestic supply water. Default values is from Andelman (1990).

EC-ANDFR--Andelman inhalation factor for Radon-222
Units: L/m³
Range: 0.0 to 20.0
Default Value: 0.1

The Andelman indoor air inhalation factor gives the ratio between average indoor air concentration and the concentration in the domestic supply water. Default values is from Andelman (1990).

EC-ANDFO--Andelman inhalation factor for other pollutants
Units: L/m³
Range: 0.0 to 20.0
Default Value: 0.0

The Andelman indoor air inhalation factor gives the ratio between average indoor air concentration and the concentration in the domestic supply water. The default value of zero represents no volatilization.

WS-UNITS--Index of concentration units
Units: none

WS-UNITS identifies the waste-site concentration units associated with the measured environmental constituent levels in the section on initial constituent concentration.

MEPAS Exposure Model Internal Default Values

Parameter	Description	Value	Range	Units	Reference
RWPF	Default water purification factor	1		none	no removal
DFLAM	Default decay rate constant	1.00E-08		1/day	Small value
none	Default maximum half life	3.70E+09		>day	Large value
CNST	Henry's law conversion factor: 1 / (RT) = 1 / (8.2E-5 * 310)	3.93E+01	fixed value	g-mole per (m^³ atm)	Based on 310 degrees Kelvin for shower water
ALPL	Plant weathering rate constant	0.049511	fixed value (based on 14 day half time)	1/day	NRC 1997

MEPAS Exposure Model Undocumented Equations

Deposition Velocity for Organic Chemicals
If the input value for the deposition velocity (RVDP) is zero and the constituent is an organic chemical as determined by a positive value provided for the octanol-water partition coefficient (RKOW), then the deposition velocity will be estimated by the following method.

       Vd = (0.436681)(1.1E-7)(0.9 + 0.1 * Kow) / [HLC*1000 + 4.8E5 (0.9 + 0.1 * Kow)]

Where
      Vd = deposition velocity for transfer of constituent from air to plants (m/sec)
      HLC = Henry�s Law Constant for the constituent (atm m³/g-mole)
      Kow = octanol-water partition coefficient (dimensionless)
      0.9 = fraction of plant that is water
      0.1 = fraction of plant that is organic mater
      0.436681 = empirical constant
      1.1E-7 = empirical constant
      4.8E5 = empirical constant
      1000 = empirical constant.

A correction factor is calculated as:
      CF = 1 / (Vd * 1000)^1/4

If CF is greater than 1, then the deposition velocity is multiplied by CF.
      Vd = CF * Vd (from above equation)

Food Pathway Transfer Factors
Estimation methods are used to fill in for missing (zero) values for food pathway transfer factors for organic chemicals. If a positive value is provided for the octanol-water partition coefficient, then an estimate for the missing food transfer factor will be generated. The correlations used are as follows.

Finfish
The transfer from water to finfish is estimated using the correlation of Bintein, DeVillers, and Carcher (1993) as follows:
      Log10 (BFF) = 0.910 Log10 (Kow) + 1.975 Log10 (6.8E-7Kow + 1) + 0.786
   Where
      BFF = water-to-finfish bioaccumulation factor (L water / kg finfish)
      Kow = octanol-water partition coefficient (dimensionless)

Shell Fish
The transfer from water to shell fish meat is estimated using the correlation from Southworth (1978) as follows:
      Log₁₀ (BFI) = 0.819 * Log₁₀(CKOW) - 1.146
   Where
      BFI = water-to-shell fish bioaccumulation factor (L water / kg shell fish)
      Kow = octanol-water partition coefficient (dimensionless)

Meat (beef)
The feed-to-meat transfer factor is estimated using the correlation from Travis and Arms (1988) as follows:
      Log₁₀ (BMT) = -7.60 + Log₁₀(Kow)
   Where
      BMT = feed-to-meat transfer factor (mg/kg meat per mg/day intake by animal)
      Kow = octanol-water partition coefficient (dimensionless)

Milk (cow)
The feed-to-milk transfer factor is estimated using the correlation from Travis and Arms (1988) as follows:
      Log₁₀ (BMK) = -8.10 + Log₁₀(Kow)
   Where
      BMK = feed-to-milk transfer factor (mg/L milk per mg/day intake by�animal)
      Kow = octanol-water partition coefficient (dimensionless)

Plants
The soil-to-plant uptake factor is estimated using a correlation from Travis and Arms (1988) as follows:
      Log₁₀(BVF) = 0.986 - 0.578 * Log₁₀(Kow)
   Where
      BVF = soil-to-plant uptake factor (kg dry soil / kg wet plant)
      Kow = octanol-water partition coefficient (dimensionless)

The correlation has been modified to provide the soil-to-plant uptake factor on a wet-weigh of plant basis.

References

Andelman, J. B. 1990. Total Exposure to Volatile Organic Chemicals in Potable Water. N. M. Ram, R. F. Christman, K. G. Cantor (eds.). Lewis Publishers, Boca Raton, Florida.

Anspaugh, L.R., J.H. Shinn, P.L. Phelps, N.C. Kennedy, 1975. "Resuspension and Redistribution of Plutonium in Soils.". Health Physics. 29:571-582.

Napier, B.A., R.A. Peloquin, D.L. Strenge, and J.V. Ramsdell. GENII - The Hanford Environmental Radiation Dosimetry Software System. December 1988. PNL-6584, Vol. 1. Pacific Northwest Laboratory, Richland, Washington.

NRC. 1977. Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR Part 50, Appendix I. Regulatory Guide 1.109, Rev. 1, US Nuclear Regulatory Commission, Washington, D.C.

Strenge, D.L., R. A. Peloquin, G. Whelan. 1986. ALDTAP II - Technical Reference and User Guide. U. S. Nuclear Regulatory Commission. NUREG/CR-4013. Washington, D.C.

Thorne, M.C. 1984. ECOS: Values of Parameters to be Used for Domestic Animals. ANS Report No. 372, Associated Nuclear Services, Epsom, Surrey, England, U.K.