COMPUTED SOURCE TERM RELEASE MODULE

OPTIONS

1) Surface water media type is a holding pond or water filled ditch that is contaminated.
2) Soil/Vadose type is contaminated surface and/or subsurface soil.
3) Aquifer media type is a contaminated saturated zone.

1) Turn off pathway turns off the leaching loss route for the scenario and it is not included in the mass balance and partitioning calculations
2) Known infiltration rate requires the user to input the infiltration rate(s) for the waste zone but the constituent mass flux(es) are computed by the model based on site characterization data, constituent inventory/concentration, and physical properties.
3) Known constituent flux requires the user to input the infiltration rate(s) for the waste zone and the constituent mass flux(es)
4) Compute pathway requires the model to compute the infiltration rate and constituent mass flux(es) for the waste zone based on the regions local climatology data (see Section AC-LCDREF), site characterization data, constituent inventory/concentration, and physical properties.

1) Turn off pathway turns off the overland runoff loss route for the scenario and it is not included in the mass balance and partitioning calculations.
2) Known water erosion rate requires the user to input the water erosion rate(s) for the waste zone but the constituent mass flux(es) are computed by the model based on site characterization data, constituent inventory/concentration, and physical properties.
3) Known constituent flux requires the user to input the water erosion rate(s) for the waste zone and the constituent mass flux(es).
4) Compute pathway requires the model to compute the water erosion rate for the waste zone based on the regions local climatology data (see Section AC-LCDREF), site characterization data, constituent inventory/concentration, and physical properties.

1) Turn off pathway turns off the wind suspension loss route for the scenario and it is not included in the mass balance and partitioning calculations.
2) Known wind erosion rate requires the user to input the wind erosion rate(s) for the waste zone but the constituent mass flux(es) are computed by the model based on site characterization data, constituent inventory/concentration, and physical properties.
3) Known constituent flux requires the user to input the wind erosion rate(s) for the waste zone and the constituent mass flux(es).
4) Compute pathway requires the model to compute the wind erosion rate for the waste zone based on the regions local climatology data (see Section AC-LCDREF), site characterization data, constituent inventory/concentration, and physical properties.

1) Turn off pathway turns off the volatilization loss route for the scenario and it is not included in the mass balance and partitioning calculations.
2) Known constituent flux requires the user to input the constituent mass flux(es) based on volatilization for the waste zone.
3) Compute pathway requires the model to compute the constituent mass flux(es) for the waste zone based on site characterization data, constituent inventory/concentration, and physical properties.

1) Turn off pathway turns off the external source/sink loss route for the scenario and it is not included in the mass balance and partitioning calculations.
2) Known constituent flux requires the user to input the constituent mass flux(es) for the external sources and sinks loss route.

WASTE ZONE

OVERLAND

1) Storm Type I. Maritime climate associated with southern and central California ( Figure 2.14).
2) Storm Type II. Associated with a) the eastern portions of California (i.e., east of the Sierra Nevada); b) all of Idaho, Montana, Nevada, Utah, Wyoming, Arizona, and New Mexico; and c) the remaining portions of the United States not covered by Storm Types I and IA (see Figure 2.14).
3) Storm Type IA. Associated with coastal areas of northern California, Oregon, and Washington, and the western slopes of the Sierra Nevada mountains (see Figure 2.14).

PARTICLE SUSPENSION

1) 0% <= x <= 1%
2) 1% < x <= 10%
3) 10% < x <= 100%

1) None
2) Dirt
3) Paved
4) Both

High ADT roads: Normal conditions = 0.1 g/m^2; Worst-case conditions = 0.5 g/m^2
Low ADT roads: Normal conditions = 0.4 g/m^2; Worst-case conditions = 3 g/m^2

Dust emissions from unpaved roads have been found to vary directly with the fraction of silt (particles smaller than 75 micrometers [µm] in diameter) in the road surface materials.1 The silt fraction is determined by measuring the proportion of loose dry surface dust that passes a 200-mesh screen, using the ASTM-C-136 method. A summary of this method is contained in Appendix C of AP-42. Table 13.2.2-1 contained in EPA AP-42,Section 13.2.2 Unpaved Roads, Rev. 9/98 (Internet URL http://www.epa.gov/ttn/chief/ap42/ch13/final/c13s02-2.pdf) summarizes measured silt values for industrial and public unpaved roads. It should be noted that the ranges of silt content vary over two orders of magnitude. Therefore, the use of data from this table can potentially introduce considerable error. Use of this data is strongly discouraged when it is feasible to obtain locally gathered data.

Because the silt content of a rural dirt road will vary with geographic location, it should be measured for use in projecting emissions. As a conservative approximation, the silt content of the parent soil in the area can be used. Tests, however, show that road silt content is normally lower than in the surrounding parent soil, because the fines are continually removed by the vehicle traffic, leaving a higher percentage of coarse particles.

HYDROLOGY

1. Antecedent moisture condition (AMC). Determine the AMC as I, II, or III from Figure 2.13. AMC I, II, and III refer to watershed soils under dry, normal, and wet moisture conditions, respectively. If the site borders two AMC classifications, use the higher index number (e.g., III rather than to II).

2. Hydrologic soil type (textural classification)/name. Determine the hydrologic soil textural classification for the site as described in WTCLASS .

3. Classification of hydrologic soil group. The classification of hydrologic soil group (A, B, C, or D) can be determined directly from SCS (1972), or from the SCS Technical Release 55, Urban Hydrology for Small Watersheds (SCS 1986).

Group A soils have high infiltration rates and low runoff potential, even when thoroughly wetted and consist chiefly of deep, well-drained to excessively drained sands or gravels. These soils have a high rate of water transmission (i.e., percolation).

Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately well-drained to well-drained soils, with moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission.

Group C soils have slow infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water or soils with moderately fine to fine texture. These soils have a slow rate of water transmission.

Group D soils have very slow infiltration rates and high runoff potential when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanently high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission.

4. Soil and condition. Determine the soil and site condition in Table 2.2 that is the most appropriate description for your site. Most waste sites tend to be bare soil. The surrounding uncontaminated area is likely to be vegetated.

5. SCS runoff curve number for antecedent moisture condition II. Determine the SCS runoff curve number for AMC II from Table 2.2 , as follows. For the appropriate soil and site condition (found in step 4 above), and the appropriate hydrologic soil group (A, B, C, or D from step 3 above), determine the corresponding runoff curve number. This curve number is for antecedent moisture condition II. If your AMC is I or III, adjust the curve number as described in step 6.

If an overland segment is composed of several hydrologic soil groups, then determine the runoff curve number for each soil group. Determine a composite runoff curve number for the overland segment by weighing the individual runoff curve numbers by the percentage of the total area that soil group occupies.

6. Adjusted SCS runoff curve number. If the AMC for your site is not II, then the runoff curve number needs to be adjusted. Use Table 2.3 to adjust the curve number to antecedent moisture conditions I or III.

MONTHLY CLIMATOLOGY

Kd's

1. Database Value - provided by the connected chemical database module
2. 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 = WZ-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 Then 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

3. Estimated Value - calculated by the equation

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

CONSTITUENT PROPERTIES

KNOWN MEDIA RELEASES

KNOWN CONSTITUENT FLUX

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

- Percent sand, silt, and clay and organic matter

(H₁-H₂)/d = hydraulic gradient, defined as the difference in head or hydraulic potential at two points in the aquifer, divided by the distance (d) between the two points. This can be obtained from water table or potentiometric surface maps or from well logs.