Investigation and Design Assistance
Flue Gas Desulfurization Ponds State of Wyoming

Situation

Several holding ponds, including a 40-acre flue gas desulfurization (FGD) pond, had leaked into aquifers underlying a coal-fired power plant. The only groundwater data available had been collected after pond leakage had affected area water levels. Hydro Geo Chem was retained to define the impacts of FGD pond leakage and to determine operational and remedial alternatives.

Hydro Geo Chem's Approach

We established the extent of FGD and other pond leakage by reconstructing the aquifers' historical flow fields by means of a 3-dimensional transient inverse model, by installing wells and conducting aquifer and tracer tests to determine aquifer parameters, by employing stable isotopes to identify the contributions from the various pond sources, by a spontaneous potential and seep-meter leakage survey of the FGD pond, and by modeling the fate and transport of salts from the ponds. We then used these models to predict the FGD pond lifetime and to assist in the design of a 300-acre replacement FGD pond.

Results

We found that the aquifer areas affected by the FGD saline plume had stabilized and would disappear after plant operations had ceased. We concluded that no remediation was necessary. These conclusions were presented to and accepted by the Wyoming Department of Environmental Quality (DEQ). We also determined that the new pond would not significantly increase the aquifer area affected by seepage, and that the clay liner originally part of the pond design provided no additional protection. Our recommendations were incorporated into the new pond design, which was accepted by the Wyoming DEQ. A savings of $15 million was realized by not installing this liner.

Figure: Self-Potential (SP) Survey of FGD Pond Bottom