Table 3: Selected resources for evaluating environmental fate and transport.

Resource and accessPurpose and scopeCumulative risk remarks

(3.1) ChemBioFinder Database (private, linked via EPA at: http://www.epa.gov/oppt/sf/tools/measured.htm);
http://chemfinder.cambridgesoft.com/
An online, EPA-linked search engine that provides access to information on the chemical, physical, and biological properties of a large number of chemicals. Developed by CambridgeSoft, this tool can search per the chemical’s common name, brand name, Chemical Abstract Service (CAS) number, chemical formula, or other designations, including chemical structure. Can also be useful to indicate common characteristics to support chemical grouping (e.g., by soil-water partition coefficient ( ) for exposure analyses, or considering biological properties to support toxicity screening).

(3.2) Soil Screening Guidance (EPA), and Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites (EPA); http://www.epa.gov/superfund/health/
conmedia/soil/introtbd.htm;  
http://www.epa.gov/superfund/health
/conmedia/soil/index.htm
This guidance was published in 1996, with updates continuing through the 2002 supplement; it includes an extensive set of environmental and physical constants and parameters that can be used to model the fate and transport of chemicals in soil and to develop risk-based soil screening levels (SSLs) to protect human health. Tables of chemical-specific constants include organic carbon partition coefficient ( ), soil-water partition coefficient ( ), and water and air diffusivity constants ( and , resp.), as well as default values for such parameters as fraction of organic carbon in soil ( ), dry soil bulk density ( ), and water-filled soil porosity ( ), to support the evaluation of fate and transport. The primary goal is to provide simple screening information and a method for developing site-specific levels considering soil and groundwater; although presented in this section, it is also considered relevant to Table 4 for exposure-based screening. Developed for use at contaminated sites on the National Priorities List, the concepts can be extended to other sites and situations. It presents both detailed models and generic SSLs that can be used to quickly (and conservatively) assess what areas or pathways might warrant more detailed analyses. The guidance includes tables of chemical-specific constants such as the , , , and , as well as default values for parameters like , , and , to support analyses of fate and transport that can guide fate-based exposure groupings for CRAs.

(3.3) Guidance for Comparing Background and Chemical Concentrations in Soil for CERCLA Sites (EPA); http://www.epa.gov/oswer/riskassessment/
pdf/background.pdf
Published in 2002, this guidance outlines statistical methods for characterizing background concentrations of chemicals at contaminated sites. Developed for both human and ecological risk assessors as well as decision makers.This guidance explicitly acknowledges the important role of background concentrations in communicating cumulative risks associated with contaminated sites and indicates that cumulative risk considers all exposure pathways and the chemicals associated with them.

(3.4) SBAT, Soil BioAccessibiity Tool (EPA);
http://www.epa.gov/superfund//programs/
aml/tech/news/sbat.htm
Tool for estimating bioaccessibility of arsenic and chromium from soil on abandoned mine lands and implications for bioavailability (following ingestion). Results indicate that iron and manganese oxides can oxidize arsenic (III to V), and that organic matter and ferrous minerals reduce chromium (from VI to III), possibly reducing toxicities from oral exposure. Sequestration is enhanced by contact time (indicating less accessibility of metals from aged soils). Provides context for fate of these combined metals in soil, highlighting specific factors to be measured or otherwise evaluated to produce a more realistic and practical site-specific assessment; these include predicted bioavailability following intake (notably specific physical and chemical properties of the soil).

(3.5) SESOIL, SEasonal SOIL compartment model (in the public domain although updated versions are available from RockWare, Inc.);
http://www.rockware.com/;  
http://www.epa.gov/opptintr/exposure/pubs/gems.htm
SESOIL is a one-dimensional (1-D) vertical transport screening-level model for the unsaturated (vadose) zone that can be used to simulate the fate of contaminants in soil to support site-specific cleanup objectives. Simulates natural attenuation based on diffusion, adsorption, volatilization, biodegradation, cation exchange, and hydrolysis. The model can evaluate one chemical at a time; it does not predict interactions in environmental media.Results can indicate how far a contaminant plume could migrate; predicted concentrations can be compared to media-specific standards and can be used to estimate single-chemical risks based on standard default exposure parameters, locations, and times. The location- and time-specific predictions for single chemicals can be overlain to support grouping decisions for a cumulative assessment.

(3.6) Summers model (as for (3.5));
http://www.seview.com/
Screening-level leachate code that estimates groundwater concentrations based on mixing. Simulates dilution of soil in groundwater. The model can evaluate one chemical at a time; it does not predict interactions in environmental media.Same as (3.5) for SESOIL (and (3.7) for AT123D).

(3.7) AT123D, Analytical Transient 1-, 2- and 3-Dimensional Simulation of Waste Transport in the Aquifer System (EPA and private);
http://www.scisoftware.com/;  
http://www.epa.gov/opptintr/exposure/
pubs/gems.htm
Generalized three-dimensional (3-D) groundwater transport and fate model; processes simulated include advection, dispersion, adsorption, and biodegradation as a first-order decay process. Transport can be simulated over 10,000 years. When linked with SESOIL, the model can simulate up to 1,000 years of contaminant migration. It can evaluate one chemical at a time (including radionuclides), and it can also evaluate heat (as a physical stressor); it does not predict interactions in environmental media.Same as (3.5) and (3.6). This model can evaluate single chemicals, including radionuclides, and it can also evaluate heat (a physical stressor).

(3.8) MODFLOW, with many iterations/updates (USGS)
http://water.usgs.gov/nrp/gwsoftware/modflow.html
(Note Visual MODFLOW is available for a fee from the developer)
This widely used model numerically solves the 3-D groundwater flow equation for a porous medium by using a finite-difference method. Visual MODFLOW output is graphic, including 2-D and 3-D maps. Designed to model flow, it can evaluate one chemical at a time (information is input by the user); it does not predict interactions in environmental media.Results can indicate how far a contaminant plume could migrate; predicted concentrations can be compared to media-specific standards and can be used to estimate single-chemical risks based on standard default exposure parameters, locations, and times. Location- and time-specific predictions for single chemicals can be overlain to support grouping decisions for a cumulative assessment.

(3.9) MULKOM codes, including TMVOC (and predecessor T2VOC)
(Lawrence Berkeley Laboratory, DOE);
http://www-esd.lbl.gov/TOUGH2
Three-dimensional, three-phase flow of water, air, and volatile organic compounds (VOCs) in saturated and unsaturated (vadose) zones to support remediation evaluations such as for soil vapor extraction. TMVOC can address more than one volatile organic (e.g., to model a spill of fuel hydrocarbons or solvents).Similar to MODFLOW (see (3.8)), but it can address a mixture of VOCs. Like the other models, this set depends heavily on extensive site setting characterization for results to be meaningful; it can be difficult to get the data needed for all parameters.

(3.10) MT3D (links to MODFLOW);
http://www.ess.co.at/ECOSIM/MANUAL/mt3d.html
Three-dimensional transport model for simulating advection, dispersion, and chemical reactions in groundwater systems; it assumes first-order decay and addresses one chemical at a time.Chemical reactions can be addressed with a loss term (chemical data must be input by the user), but the degradation product is not tracked. Depends heavily on extensive site characterization; it can be difficult to get the data needed for all parameters.

(3.11) Guidance for Evaluating Vapor Intrusion into Buildings (EPA);
http://www.epa.gov/oswer/vaporintrusion; state example:  http://www.envirogroup.com/links.php; application:  http://www.deq.louisiana.gov/portal/
Portals/0/RemediationServices/RPform_5340.pdf
Provides a model to estimate convective and diffusive transport of chemical vapors to indoor air. Could offer insights for situations where indoor air exposures are a concern. More than half the states also provide simplified equations for screening chemicals via the vapor intrusion pathway. For an indication of states, see the second web link. Example application context is provided from the Louisiana Department of Environmental Quality (LDEQ) via the third web link. Model output can be used to support CRAs, as concentrations of multiple chemicals can be evaluated simultaneously.

(3.12) Risk Assessment Protocols for Hazardous Waste Combustion Facilities (EPA);
http://www.epa.gov/osw/hazard/
tsd/td/combust/risk.htm;  
http://www.epa.gov/osw/hazard/
tsd/td/combust/ecorisk.htm
In 1998, EPA Region 6 identified a need for guidance that consolidated information from earlier EPA documents and state environmental agency reports, to provide an integrated set of procedures for conducting site-specific combustion risk assessments addressing multiple sources and exposure scenarios. Two documents were prepared, the 1999 Screening Level Ecological Risk Assessment Protocol for Hazardous Waste Combustion Facilities (SLERAP) and the 2005 Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities (HHRAP). The objectives were to (1) apply the best available methods for evaluating risks to human health and the environment from operations of hazardous waste combustion units and (2) develop repeatable and documented methods for consistency and equity in permitting decisions. In addition to methods for evaluating multimedia, multipathway risks, the second document contains information on chemical, physical, and environmental properties of many chemicals, for use in modeling environmental fate and transport and exposure.Provides methods for evaluating multimedia, multipathway risks. Volume II contains information and data on the physicochemical and environmental properties of many chemicals, which can be used to model environmental fate and transport and exposure. This information could be used to predict which chemicals are likely to share a similar fate in the environment, to support exposure groupings for CRAs.

Information on the following models is available via compilations on EPA websites (including http://www.epa.gov/ada/csmos/ and http://www.epa.gov/esd/databases/datahome.htm); therefore, individual links are not provided in this section of the table.

(3.13) 2DFATMIC and 3DFATMIC Simulates the subsurface flow, transport, and fate of contaminants that are undergoing chemical and/or biological transformations. Applicable to transient conditions in both saturated and unsaturated zones. Results can indicate how far a plume may migrate. Predicted concentrations can be compared to media-specific standards to assess single-chemical risks using exposure parameters, locations, and times. The model can evaluate one chemical at a time; it does not predict interactions in environmental media. Location- and time-specific predictions for single chemicals can be overlain to support grouping decisions for a cumulative assessment.

(3.14) BIOCHLOR Screening model that simulates remediation by natural attenuation of dissolved solvents at sites with chlorinated solvents. Can be used to simulate solute transport without decay and solute transport with biodegradation modeled as a sequential first-order process within one or two different reaction zones. Same as (3.13) and (3.15).

(3.15) BIOPLUME II and BIOPLUME III Model 2-D contaminant transport under the influence of oxygen-limited biodegradation (BIOPLUME II) and under the influence of oxygen, nitrate, iron, sulfate, and methanogenic biodegradation (BIOPLUME III). Model advection, dispersion, sorption, biodegradation (aerobic and anaerobic), and reaeration (BIOPLUME II) through instantaneous, first order, zero order, or Monod kinetics (BIOPLUME III). BIOPLUME III was developed primarily for modeling the natural attenuation of organic contaminants in groundwater; it is particularly useful at petroleum-contaminated sites. Same as (3.13) and (3.15).

(3.16) BIOSCREENScreening-level groundwater transport model that simulates the natural attenuation of dissolved-phase hydrocarbons. It is based on the Domenico analytical contaminant transport model and can simulate natural attenuation based on advection, dispersion, adsorption, and biological decay. It estimates plume migration to evaluate risk at specific locations and times. (Selected model comparisons indicated that concentrations may be underestimated compared with AT123D and MODFLOW/MT3D.)Predicted concentrations can be compared to media-specific standards and can be used to estimate single-chemical risks based on standard default exposure parameters, locations, and times. The model can evaluate one chemical at a time; it does not predict interactions in environmental media. Location- and time-specific predictions for single chemicals can be overlain to support grouping decisions for a cumulative assessment.

(3.17) CHEMFLO Simulates 1-D water and chemical movement in the vadose zone. Models advection, dispersion, first-order decay, and linear sorption. Results can indicate how far a plume will migrate. Same as (3.16).

(3.18) GEOEAS, Geostatistical Environmental Assessment Software Enables geostatistical analysis of spatially correlated data. Can perform basic statistics and scatter plots/linear and nonlinear estimation (kriging). Same as (3.16).

(3.19) GEOPACK Comprehensive package for geostatistical analyses of spatially correlated data. Can perform basic statistics, variography, and linear and nonlinear estimation (kriging). Same as (3.16).

(3.20) HSSM, Hydrocarbon Spill Screening Model Can simulate light nonaqueous phase liquid (LNAPL) flow and transport from the ground surface to the water table; radial spreading of the LNAPL phase at the water table; dissolution and aquifer transport of the chemical. It is 1-D in the vadose zone, radial in the capillary fringe, and provides a 2-D vertically averaged analytical solution of the advection-dispersion equation in the saturated zone. (It is available in Spanish.) Predicted concentrations can be compared to media-specific standards and used to estimate single-chemical risks based on exposure parameters, locations, and times. The model can evaluate one chemical at a time; it does not predict interactions in environmental media. Location- and time-specific predictions for single chemicals can be overlain for CRA groupings.

(3.21) PESTAN, Pesticide Analytical ModelVadose zone modeling of the transport of organic pesticides. Models advection, dispersion, first-order decay, and linear sorption. Results can indicate how far a contaminant plume will migrate. Same as (3.20).

(3.22) STF, Soil Transport and Fate Database Provides data on the behavior of organic and a few inorganic chemicals in soil. (EPA review was designed to verify data accuracy; the information is believed to be accurate, but EPA does not make any claim regarding data accuracy and is not responsible for its use.) This general-use tool can be used to evaluate the physicochemical properties of environmental contaminants for CRAs. The focus is one chemical at a time; interactions are not addressed.

(3.23) UTCHEM Three-dimensional model that simulates aqueous phase and nonaqueous phase liquid (NAPL) movement in the subsurface. It can address multiple phases, dissolution, and/or mobilization by nondilute remedial fluids, chemical and microbiological transformations (including temperature dependence of geochemical reactions), and changes in fluid properties as a site is remediated. This general-use tool can be applied to evaluate environmental contaminants for CRAs. It can be interesting when used to assess cumulative risk because NAPL is commonly a complex mixture itself and can be present in multiple phases, which are assessed by the model.