# Presentation: 424689

## Mine Waste and Modeling 

- David G. Jewett, Ph.D.
- USEPA/ORD/NRMRL Subsurface Protection and Remediation Division, Ada, OK
- Co-Director, Center for Subsurface        Modeling Support (CSMoS)

- ORD Mine Waste Scientist to Scientist Meeting15 June 2000, Las Vegas, NV

## Presentation Outline

- Modeling Basics
- Definition
- General Approach
- Types of Models
- Source
- Flow
- Reactive Transport
- Other
- Modeling Resources

## Definition

- Mathematical model:   simulates ground-water flow and/or solute fate and transport indirectly by means of a set of governing equations thought to represent the physical processes that occur in the system (Anderson and Woessner, 1992).

## Modeling Approach

- Establish purpose
- Develop conceptual model
- Select appropriate mathematical model
- Model design (iterative process)
- Calibration (including sensitivity analysis)
- Verification
- Prediction (including uncertainty analysis)

## Types of Models

- Source models
- Unsaturated and saturated flow models
- Reactive transport models
- Other models

## Source Models

- Estimate mass flux from a source area
- Characterize source areas in terms of source mineralogy and subsurface hydrogeological and geochemical conditions
- Describe loading as steady-state or as a function of time

## Source Code Example

- PYROX
- Univ. of Waterloo (Wunderly & Blowes, 1996)
- 1-D finite element code
- Sulfide mineral oxidation model
- Based on conceptualization and mathematical derivation of Davis and Ritchie
- Oxygen diffusion is rate-limiting factor
- Simulates release of Fe, SO**4****2-**, and H**+**

## Source Code Example

- MINTEQA2
- NERL-ERD (Allison et al., 1991)
- Versatile equilibrium solution chemistry code
- Calculates equilibrium mass distribution of dissolved and adsorped species and multiple solid phases
- Extensive thermodynamic database

## Flow Models

- Define water movement and variability of soil water tension or hydraulic head across domain of interest
- Unsaturated versus saturated flow
- Steady-state versus transient simulations

## Unsaturated Flow Code Example

- SOILCOVER
- Univ. of Saskatchewan (Wilson, 1994)
- 1-D finite element code
- Simulates water flux at atmosphere-soil interface and water movement in the near surface unsaturated zone
- Designed for developing soil covers for mine tailings and acid generating waste rock

## Unsaturated Flow Code Example

- HELP
- USACE for USEPA (Schroeder et al., 1991)
- Quasi-2-D layered water budget model
- Rapid estimation of surface runoff, subsurface drainage, and leachate production
- Extensive climate and soil characteristic databases

## Unsaturated Flow Code Example

- VS2DT
- USGS (Healy, 1996)
- 1-D or 2-D finite difference code
- Simulates water and solute movement in variably saturated porous media
- Distributed in VS2DI package as of 2/2000 (combined with VS2DH)

## Saturated Flow Code Example

- MODFLOW
- USGS (McDonald and Harbaugh, 1988; Harbaugh and McDonald,1996)
- 3-D finite difference ground-water flow code
- Modular structure for easy adaptation
- Ground-water flow model work horse
- Widely used and extensively tested
- GMS, Groundwater Vistas, Visual Modflow

## Saturated Flow Code Example

- FEMWATER
- ORNL (Yeh and Ward, 1979) and Penn State (Yeh, 1990)
- 3-D finite element ground-water flow code
- Saturated and unsaturated flow
- GMS

## Reactive Transport Models

- Define temporal and spatial distribution of dissolved contaminant mass in the model domain
- Incorporate the physical, chemical, and biological processes controlling solute fate and transport (sorption, abiotic transformations, biologically mediated transformations)

## Reactive Transport Code Example

- MINTRAN
- Univ. of Waterloo (Walter et al., 1994)
- Couples PLUME2D (2-D finite element solute transport code; Frind et al., 1990) and MINTEQA2
- Simulates multicomponent reactive transport in spatially discrete ground-water systems
- MINTOX = MINTRAN + PYROX

## Reactive Transport Code Example

- PHREEQC
- USGS (Parkhurst and Appelo, 1999)
- Low-temp aqueous geochemical model
- Calculations performed:
- Speciation and S.I. calculations
- Batch reaction and 1-D transport calculations
- Inverse modeling
- PHREEQCI

## Reactive Transport Code Example

- MT3D
- USEPA, 3-D solute transport (Zheng, 1990)
- MOC, MMOC, HMOC
- Runs with MODFLOW, or similar, flow output
- MT3D**96**, MT3D**99** (proprietary)
- RT3D
- PNNL, multi-species transport (Clement, 1997)
- Based on MT3D; includes 8 rxn modules

## Other Models

- Surface Water Models
- OTIS (USGS, 1998) simulates 1-D fate and transport of water-borne solutes in streams and rivers
- EFDC (Hamerick, 1999) simulates 3-D flow, transport, and biogeochemical processes in surface water systems

## Other Models (continued)

- Watershed Models
- BASINS (USEPA, 1998) multipurpose environmental analysis system for performing watershed- and water-quality-based studies
- Dynamic System Models
- STELLA (HPS, 1994) universal simulation tool to build understanding of dynamic systems and interrelationships

## USEPA Modeling Resources

- Center for Subsurface Modeling Support (CSMoS)
- NRMRL/SPRD – Ada, OK
- www.epa.gov/ada/csmos.html
- On-Line Model Database: www.epa.gov/ada/mdb_form.html

## USEPA Modeling Resources

- Center for Exposure Assessment Modeling (CEAM)
- NERL/ERD – Athens, GA
- www.epa.gov/ceampubl/ceamhome.htm
- EPA Scientific Model Database:
- 	athord1.ath.epa.gov:9876/Models.nsf

## Other Modeling Resources

- USGS Water Resources Software Page
- water.usgs.gov/software
- Richard B. Winston’s Home Page
- www.mindspring.com/~rbwinston/rbwinsto.htm
- Geotech & Geoenviron Software Directory
- www.ggsd.com
- Int’l Ground Water Modeling Center
- www.mines.edu/igwmc

## “The fascinating impressiveness of rigorous mathematical analysis, with its atmosphere of precision and elegance, should not blind us to the defects of the premises that condition the whole process.”
					- T.C. Chamberlin

“Everything should be made as simple as possible, but not simpler.” 
					- Albert Einstein

- 					- T.C. Chamberlin
- “*Everything should be made as simple as possible, but not simpler.”*
- 					- Albert Einstein