Arsenic and Chloride Fate and Transport Modeling for Water Supply Permitting, Dayton, Ohio (with AMEC, Inc.)

The City of Dayton, Division of Water Supply, underwent expansion from a two-well to a four-well operation for one of its well fields on the north side of the city along the Great Miami River. Within a half mile distance of the well field occur two closed landfills. Both landfills are managed and monitored; however, their presence is considered a potential threat to water quality by the Ohio EPA through the capture of arsenic by the increased well field production. As part of conditional approval to the well field expansion, Ohio EPA required fate and transport modeling to evaluate this issue. AMEC, Inc., a groundwater consultant to the City of Dayton, subcontracted Terran to prepare, calibrate and simulate a groundwater computer fate and transport model. MODFLOW was used to simulate the groundwater flow regime and MT3D was used to simulate fate and transport of arsenic and chloride.

Foot print of Landfills

Chloride foot print of subject landfills establish initial concentration for calibration and simulation purposes.

Model capture zones

Model results for four-well operation indicate well capture zones and arsenic lateral extent for 50-year simulation time step.

The MODFLOW model was calibrated to 17-years of ground water data collected from both consultant and City monitoring. The fate & transport model was constructed with initial arsenic and chloride concentrations from the early 1990s when their concentrations were highest. Curve matching of model concentrations to lab results was conducted for calibration purposes.

The calibrated model was used to evaluate contaminant capture for the well field at increasing production upwards of 50 years. Model results indicated no landfill arsenic or chloride leachate capture is expected for the well field under the most conservative scenarios simulated for the two new wells.

Engineering and Environmental consulting firms, Terran is a small business enterprise that can assist you with ground water modeling and related services. Please contact us at (937) 320-3601 to discuss your project requirements.

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