Publications—Scientific Investigation Report

Ground-Water Flow Model of the Boone Formation at the Tar Creek Superfund Site, Oklahoma and Kansas

By T.B. Reed and John B. Czarnecki

U.S. Geological Survey Scientific Investigations Report 2006-5097—ONLINE ONLY

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Abstract

Extensive mining activities conducted at the Tar Creek Superfund site, one of the largest Superfund sites in the United States, pose substantial health and safety risks. Mining activities removed a total of about 6,000,000 tons of lead and zinc by 1949. To evaluate the effect of this mining on the ground-water flow, a MODFLOW 2000 digital model has been developed to simulate ground-water flow in the carbonate formations of Mississippian age underlying the Tar Creek Superfund site. The model consists of three layers of variable thickness and a grid of 580 rows by 680 columns of cells 164 feet (50 meters) on a side. Model flux boundary conditions are specified for rivers and general head boundaries along the northern boundary of the Boone Formation. Selected cells in layer 1 are simulated as drain cells. Model calibration has been performed to minimize the difference between simulated and observed water levels in the Boone Formation. Hydraulic conductivity values specified during calibration range from 1.3 to 35 feet per day for the Boone Formation with the larger values occurring along the axis of the Miami Syncline where horizontal anisotropy is specified as 10 to 1. Hydraulic conductivity associated with the mine void is set at 50,000 feet per day and a specific yield of 1.0 is specified to represent that the mine void is filled completely with water. Residuals (the difference between measured and simulated ground-water altitudes) has a root-mean-squared value of 8.53 feet and an absolute mean value of 7.29 feet for 17 observed values of water levels in the Boone Formation.

The utility of the model for simulating and evaluating the possible consequences of remediation activities has been demonstrated. The model was used to simulate the emplacement of chat (mine waste consisting of fines and fragments of chert) back into the mine. Scenarios using 1,800,000 and 6,500,000 tons of chat were run. Hydraulic conductivity was reduced from 50,000 feet per day to 35 feet per day in the model cells corresponding to chat emplacement locations. A comparison of the simulated baseline conditions and conditions after simulated chat emplacement revealed little change in water levels, drainage and stream flux, and ground-water flow velocity.

Using the calibrated flow model, particle tracks were simulated using MODPATH to evaluate the simultaneous movement of particles with water in the vicinity of four potential sites at which various volumes of chat might be emplaced in the underground mine workings as part of potential remediation efforts at the site. Particle tracks were generated to follow the rate and direction of water movement for a simulated period of 100 years. In general, chat emplacement had minimal effect on the direction and rate of movement when compared to baseline (current) flow conditions. Water-level differences between baseline and chat-emplacement scenarios showed declines as much as 2 to 3 feet in areas immediately downgradient from the chat emplacement cells and little or no head change upgradient. Chat emplacements had minimal effect on changes in surfacewater flux with the largest simulated difference in one cell between baseline and chat emplacement scenarios being about 3.5 gallons per minute.


CONTENTS

Figures
  1. Map showing location of model area
  2. Map showing land-surface altitude in the model area
  3. Generalized geologic section showing relations of rock formations to water-filled mines
  4. Thickness of the Boone Formation
  5. Altitude of the bottom of the Boone Formation
  6. Water-level altitudes in Boone Formation in spring 2004
  7. Finite difference grid of active cells of the model showing river cells and general head boundary cells
  8. Selected zones used for uniform horizontal hydraulic conductivity with final calibration values
  9. Diagram showing volumetric budget components for the first stress period
  10. Map showing streams, constant head, and drain fluxes in the Boone Formation at the end of stress period 1
  11. Map showing simulated water-level altitudes in Boone Formation in layer 3 at the end of stress period 1
  12. Map showing water-level residuals for observation wells in the Boone Formation at the end of stress period 1
  13. Graph showing difference between measured and simulated water levels in the Boone Formation at the end of stress period 1
  14. Graphs showing sensitivity analysis for input model variables
  15. Location of chat emplacements for scenario 1
  16. Location of chat emplacements for scenario 2
  17. Water-level altitude differences between baseline and scenario 1
  18. Water-level altitude differences between baseline and scenario 2
  19. Difference between baseline and scenario 1 drain and stream fluxes
  20. Difference between baseline and scenario 2 drain and stream fluxes
  21. Graphs showing the distribution of simulated ground-water velocities in the mined zone for each scenario
  22. Diagrams showing flow paths for simulated particles for all scenarios

Tables

  1. Information pertaining to measured and simulated water levels at wells in the Boone Formations


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