Groundwater flow modeling of an abandoned mine lands site scheduled for reclamation Robert C. Waddle, CGDA and Department of Geological Sciences, Indiana University Greg A. Olyphant, CGDA and Department of Geological Sciences, Indiana University A tool to evaluate probable outcomes of reclamation design

Minnehaha abandoned mine lands site Potentially unstable levee and the contribution of AMD Scheduled for reclamation by the IDNR- DOR seep

What should reclamation accomplish? Current goals of IDNR-DOR Want to re-direct AMD away from seep for on-site treatment Want to re-direct AMD away from seep for on-site treatment Want to lower the water table (levee stability) Want to lower the water table (levee stability) Do both while minimizing volume of sediment disturbance

Why use a groundwater flow model for AML reclamation? Cost effective way to preview hydrologic outcomes under different reclamation scenarios

Modeling Approach Fully 3-dimensional, transient model, incorporates effects of local topography Treats the groundwater system as a whole (specifically the unsaturated-saturated zone as a continuum) Any configuration of boundary conditions

Theory: Darcy’s Law and Mass Balance Freeze (1971) K = hydraulic conductivity ψ = pressure head, where h = ψ + z C = specific moisture capacityρ and ε are the density and compressibility of water θ = volumetric moisture contentη and β are the porosity and compressibility of the porous media Unsaturated Hydraulic Parameters van Genuchten (1980) van Genuchten characteristic equation parameters: K 0  n θ s θ r and m=1-1/n L assumed to be ½ specific moisture capacity effective saturation hydraulic conductivity

Solution Method Implicit finite-difference approximation Block-centered nodal grids with variable size Surface boundary condition driven by time-dependent meteorological data Freeze (1971)

142.3 m m m m lower boundary (clay) upper boundary (ground surface) ∆x = ∆y = 5.0m ∆z = 1.0m, 0.5m Total grid cells = 2,408,000

Monitoring wells, sediment types, and boundary conditions

Calibration Procedure Initial K 0 estimates obtained from slug and pumping test data and van Genuchten parameters from literature Started with most sensitive parameter (K 0 ) then proceed with other parameters Vary hydraulic parameter values until minimum RMSE (simulated and observed water levels) for a period of 50 days Weather driven transient simulations

Calibration Results Model Parameters K 0 (cm/s)α (cm -1 )nθsθs θrθr RMSE (m) 1.0E Model Parameters K 0 (cm/s)α (cm -1 )nθsθs θrθr RMSE (m) 5.0E Model Parameters K 0 (cm/s)α (cm -1 )nθsθs θrθr RMSE (m) 5.0E

Resolved flow at water table: current

Proposed Valley Network Main segment follows existing ditch Three additional branches extending toward levee Graded at 1:500 down to Mud Creek elevation (NW) 35,000 cubic meters sediment excavation

Resolved flow at water table: valley network

Difference in pre and post reclamation water tables Fine-grained refuse average water table pre: m post: m

Conclusion Study shows that an appropriate GW model can predict the probable outcomes of reclamation experiments In this case, it appears that a simple construction implementation could accomplish the goals of reclamation as specified by the IDNR-DOR Currently exploring additional applications of this model to the hydrology of reclamation sites.

Acknowledgements Dr. Sally LetsingerJohn T. Haddan Funding for this project was provided through a contract with the Indiana Department of Natural Resources – Division of Reclamation. The contributions of Dr. Sally Letsinger (GIS analysis), John T. Haddan (field work) Center for Geospatial Data Analysis, Indiana Geological Survey are especially appreciated. QUESTIONS?

Blackfoot

Example Models MODFLOW (USGS): 2D (quasi-3D), heterogeneous, saturated, numerical GFLOW: 2D, homogeneous, saturated, analytical element model Freeze (1971): fully 3D, heterogeneous, sat/unsat, numerical

References Freeze, R. A Three-dimensional, transient, saturated-unsaturated flow in a groundwater basin. Water Resources Research 7(2), van Genuchten, M. T A closed-form equation for predicting the hydraulic properties of unsaturated soils. Soil Science Society of American Journal 44, Schaap, M.G., J.L. Feike, and M.T. van Genuchten Estimation of the soil hydraulic properties. In: Looney, B.B., Falta, R.W. (Eds.), Vadose Zone: Science and Technology Solutions, vol. 1. Battelle Press, Columbus, OH, pp

Equations

More Equations

K = cm/s n = 3.18 α = cm -1 θ s = θ r = TailingsGobSoil "clayey" Theta_s (poros) Theta_r alpha n K05.00E E E-05

Resolved flow at water table: valley network