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Model Report


Last Revision Date: 08/31/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Model Overview/Abstract:
Chemicals that readily vaporize at relatively low temperatures can migrate from contaminated soils into the atmosphere via a process called volatilization. Volatilization represents a potentially significant exposure pathway because humans can come in contact with volatilized compounds through inhalation. The EMSOFT manual describes a computer screening model that may be used 1) to determine concentrations of contaminants remaining in the soil over a given time (when the initial soil concentration is known); 2) to quantify the mass flux (rate of transfer) of contaminants into the atmosphere over time; and 3) to subsequently calculate contaminant air concentrations by inputting mass flux values into atmospheric dispersion models. Ingestion of contaminated soil and dermal contact are also potential exposure pathways requiring knowledge of the contaminant soil concentration to estimate potential risks. EMSOFT can also be used by risk assessors and exposure modelers to calculate average chemical concentrations at a given depth over time. This model, based on the theory and studies of Jury et al. (1983, 1990), addresses situations in which contaminated soils are located at the surface and buried beneath a clean soil cover. Through a series of menus the user is prompted for several input choices to select a calculation method, chemical data, soil properties, and layer properties. The various calculation methods include Time-Averaged Flux, Flux vs. Time, Time- and Depth-Averaged Soil Concentration, Depth-Averaged Soil Concentration vs. Time and Soil Concentration vs. Depth. The user also has the option to determine cover layer thickness; the number of contaminant layers and their corresponding thickness; and the time period for averaging flux and soil concentration.

Model Technical Contact Information:
Agency Contact
Amina Wilkins

Developer Contact
Environmental Quality Management
RTP, North Carolina

Model Homepage: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=2862
Plans for further model development: A Windows version is available for public release but has not been downloaded to the web.

User Information Back to Top
Technical Requirements
Computer Hardware
Compatible Operating Systems
Download Information
This model is available for download at: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=2862
Using the Model
Basic Model Inputs
Dept of cover, soil thickness, initial soil concentration, fraction organic carbon, soil water content, soil bulk density, soil porosity, temperature, evaporation rate, effective wind speed; Organic carbon partition coefficient, Henry’s law constant, air diffusion coefficient, water diffusion coefficient, half life, boundary layer thickness
Basic Model Outputs
Emission flux mg/cm2/day
User Support
User's Guide Available?
The User's Guide is available at: http://www.epa.gov/ncea/pdfs/emsoft.pdf

Availability of User Support
The program is not being supported and does not handle customer service requests and no further updates are being considered by NCEA at this time. Should significant interest be expressed, NCEA management might reconsider updating the software if it becomes necessary.
User Qualifications
No special training is needed to operate the model; however, an awareness of basic chemical and soil parameters would assist with inputting data and understanding the results. Much of this information is presented in the User’s Guide.

Model Science Back to Top
Problem Identification
EMSOFT is a screening model that may be used to assess the potential for such exposure to occur and quantify the mass flux of contaminants to the atmosphere over time. Mass fluxes can then be input to an atmospheric dispersion model to calculate exposure concentrations. Ingestion of contaminated soil and dermal contact are also potentially important exposure pathways. This model can also be used to calculate chemical concentrations in surficial soil layers over time for assessment of these exposures. The model addresses situations in which contaminated soils are located at the surface and buried beneath a clean soil cover.
Summary of Model Structure and Methods
Based on the algorithms of William Jury.
Model Evaluation
The EMSOFT model was used with the data sets presented in Section 5.3 for the model validation. Then, for some data sets, the model's sensitivity to parameter variability was tested by remodeling a data set with one input, such as the Henry's law constant, set equal to a new value. This was necessary because in searching for data for this modeling exercise, different values for some "constants" were cited. Also, if an uncertainty existed in an input value selected, such as the surface boundary layer, an alternative value was tested.

Key Limitations of Model Scope
Important limitations include:

  1. The duration of experiments simulated ranged from 7 to 36 days. Model performance for longer durations could not be validated.
  2. The influence of porewater flux (evaporation and leaching) was not examined. This parameter is difficult to specify accurately and varies over time. Jury et al. (1983) showed that emissions of some compounds are sensitive to changes in evaporation rate.
  3. Only "no cover" scenarios were simulated in this validation. Measurement studies of "clean cover" scenarios (contaminated soil covered by a layer of clean soil) were not found. As demonstrated in some of the simulations, it is important to carefully specify the input parameters, especially those which the model may be most sensitive to, such as Koc, foc, and KH. Parameter sensitivity of the model is chemical- and setting-specific, and may be difficult to forecast. Therefore, performance of sensitivity analysis for parameters with uncertain values is highly recommended.

Case Studies
Included in the User's Guide

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