HYDROGEOLOGIC INVESTIGATION OF SURFACE WATER BIAS TO A SIGNIFICANT ZONE OF SATURATION

A lined sediment pond was excavated into a significant zone of saturation (SZS) at a sanitary landfill in Ohio. National Pollution Discharge Elimination System (NPDES) samples of the pond's surface water show a higher historical concentration of sodium and chloride than historical ground water from the SZS. It was suspected that pond infiltration into the SZS resulted in increased sodium and chloride concentrations in the SZS ground water at a down-gradient SZS monitoring well. This triggered regulatory actions caused by the “statistically significant” increase of sodium and chloride in the well.

Hydraulic connection between the sediment pond and the SZS was demonstrated by: measuring the water levels in both the affected monitoring well and the pond over time, comparing water levels in SZS wells and the pond, identifying and documenting the presence of muskrat burrows that provided a conduit through the pond's recompacted clay liner, and evaluating chemical concentrations in both ground and surface water over time.

Lowering the pond water elevation below the potentiometric level of the SZS reversed the flow of water from the pond to the SZS. Unbiased samples of SZS ground water were then obtained that prove that the pond was the source of sodium and chloride and that a release from the landfill had not occurred.