Characterizing selenium leaching and transport from southern West Virginia valley

fill alternatives

Leslie Hopkinson1

Nathan DePriest1

John Quaranta1

Paul Ziemkiewicz2

WEST VIRGINIA UNIVERSITY Department of Civil and Environmental Engineering

1West Virginia University2West Virginia Water Research Institute

Can Se concentrations be reduced through physical means?

• Leaching of Se from blasted rock overburden used to construct valley fills

• Chemical treatment effective in removal of Se, but is a costly and continual problem

• Effectiveness of reducing Se loads through physical means (alternative surface construction techniques) is unknown

Geomorphic reclamation is expected to reduce contaminant loads

• Curvilinear slope surface design and reclaimed surface hydrology

• Increase runoff, reduce infiltration

• Minimize groundwater contact with contaminated internal fill materials

The State of Geomorphic Research in Central Appalachia

• Large scale conceptual designs have investigated geomorphic principles.

• Small scale designs have confirmed issues with respect to steep slopes and material volumes.

• Stability analyses have shown both issues and benefits of geomorphic reclamation.

• Benefits to geomorphic reclamation with respect to groundwater and contaminant transport are unknown.

Objective: Characterize leaching and transport of mobile Se for southern WV valley fill alternatives

1. Laboratory column leaching tests of mine overburden

2. Numerical groundwater modeling of reclamation alternatives

3. Calculation of desorbed Se loads based on laboratory leaching and numerical groundwater results

Study Site

Collected blasted rock overburden from two active surface mines

Mine A: Shale Mine B: Sandstone

Performed unsaturated column leaching tests on duplicate overburden samples

pH, conductivity, and TDS reached equilibrium by leached volume of 10.1 L

Selenium desorption was highest in first few infiltration events

Conceptual geomorphic design was generated as an alternative to an existing valley fill at Mine A

Undisturbed valley Conventional fill Geomorphic fill

Finite element groundwater modeling considered transient, variably-saturated flow

Unsaturated hydraulic property functions were developed with grain-size data and established estimation techniques

Boundary conditions considered reduced infiltration into the geomorphic fill

Conventional

Geomorphic

Fill infiltration (55% of precipitation)

Fill infiltration (55% of precipitation) Stream infiltration (≤55% of precipitation)

Review boundary

Review boundary

Establishing a stream on the geomorphic fill resulted in decreased infiltration and discharge

  Normalized percent change (%)

 Geomorphic

without stream Geomorphic with stream

Infiltration volume 0 -45

Discharge rate -19 -39

Discharge volume -17 -39

Degree of saturation 0.14 3.0

Geomorphic fill with reclaimed stream reached condition in which water was discharging at or higher than the rate it was infiltrating

Seepage particle tracking was combined with laboratory leaching data to calculate desorbed Se

Conventional

Geomorphic

Fill volume contacted by infiltrating water over time was calculated from transient groundwater flow paths

Laboratory Se leaching rates were applied to groundwater models during individual infiltration events

Increased groundwater residence time within each infiltration event was assumed to result in increased desorption

Geomorphic fill exhibited shorter groundwater residence time through larger fill volumes

Reduced infiltration and groundwater residence time resulted in reduced Se desorption for geomorphic fill

Conclusion: Se desorption was reduced through physical means by geomorphic reclamation

• Unsaturated leaching of Se was highest in initial infiltration events.

• Establishing a stream on the geomorphic fill surface reduced infiltration, discharge rate, and discharge volume.

• Reclaimed stream also allowed water to discharge at or faster than it infiltrated.

• Reduced infiltration and reduced groundwater residence time resulted in reduced Se desorption.

Ongoing and Future Work

• Three-dimensional groundwater modeling and Se desorption calculation to investigate entire curvilinear surface design

• Expanded testing of unsaturated soil property functions

• Long-term leaching of Se under variably saturated conditions

• Contaminant desorption modeling tool• Pilot construction project and monitoring

Questions?

The project described in this paper was supported by Grant/Cooperative Agreement Number G11AP20114 from the United States Geological Survey. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USGS.