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 BasicsDefinitionGeneral Approach

Types of ModelsSourceFlowReactive TransportOther

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

1. Establish purpose

2. Develop conceptual model

3. Select appropriate mathematical model

4. Model design (iterative process)

5. Calibration (including sensitivity analysis)

6. Verification

7. 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

PYROXUniv. 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, SO42-, and H+

Source Code Example

MINTEQA2NERL-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

SOILCOVERUniv. of Saskatchewan (Wilson, 1994)1-D finite element codeSimulates water flux at atmosphere-soil interface and water movement in the near surface unsaturated zoneDesigned for developing soil covers for mine tailings and acid generating waste rock

Unsaturated Flow Code Example

HELPUSACE for USEPA (Schroeder et al., 1991)Quasi-2-D layered water budget modelRapid estimation of surface runoff, subsurface drainage, and leachate productionExtensive climate and soil characteristic databases

Unsaturated Flow Code Example

VS2DTUSGS (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

MODFLOWUSGS (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

FEMWATERORNL (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

MINTRANUniv. 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

PHREEQCUSGS (Parkhurst and Appelo, 1999)

Low-temp aqueous geochemical model

Calculations performed:Speciation and S.I. calculationsBatch reaction and 1-D transport calculations Inverse modeling

PHREEQCI

Reactive Transport Code Example

MT3DUSEPA, 3-D solute transport (Zheng, 1990)

MOC, MMOC, HMOC

Runs with MODFLOW, or similar, flow output

MT3D96, MT3D99 (proprietary)

RT3DPNNL, multi-species transport (Clement, 1997)

Based on MT3D; includes 8 rxn modules

Other Models

Surface Water ModelsOTIS (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 ModelsBASINS (USEPA, 1998) multipurpose environmental analysis system for performing watershed- and water-quality-based studies

Dynamic System ModelsSTELLA (HPS, 1994) universal simulation tool to build understanding of dynamic systems and interrelationships

USEPA Modeling ResourcesCenter 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 Pagewater.usgs.gov/software

Richard B. Winston’s Home Pagewww.mindspring.com/~rbwinston/rbwinsto.htm

Geotech & Geoenviron Software Directorywww.ggsd.com

Int’l Ground Water Modeling Centerwww.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