Contaminated Groundwater Flow Control Across an Inverted Groundwater Divide With Three Groundwater Control Systems

Abstract

The potential impacts from legacy, unlined landfills to surrounding hydrological systems are substantial challenges in the management of waste and water quality. Because these landfills do not have passive controls (i.e. liners), groundwater controls (pumping wells, trenches, etc.) can be necessary to minimize impacts. However, the function and interaction of multiple groundwater control devices in combination with complicated hydrogeologic settings are poorly characterized.Most research on groundwater control device interactions relies on simulation experiments and either measures the effectiveness of a system using a limited set of groundwater control devices or focuses on a single aquifer. This thesis examines three groundwater control devices (a slurry wall, a pumping trench, and a pumping well) installed near an active legacy landfill to evaluate changes in the flow of contaminated groundwater off site. This system of control devices was evaluated using monthly water quality data from a spring where changes in water quality were observed prior to installation of the groundwater control system. The water geochemical results indicate that the contaminated groundwater flows primarily through the fractured rock in the ridge (contrary to expectations), and therefore the collection trench is more effective in contaminant flux reductions.The groundwater pumping well, designed to capture contaminated groundwater flow through the coal seams and sandstone, is less effective, likely due to limited transport through the coal aquifers.Although the groundwater control system reduces the amount of contaminated groundwater flow off site, these controls must operate until the landfill is closed and a permanent control (i.e. installation of a clay cap which will reduce infiltration and should result in reduced groundwater elevations) can be installed which may take decades. The results provide fundamental information Landfills with no liner system cause water to pool and the water levels in the landfill can impact groundwater quality, recharge area, geomorphic changes, and storage of an aquifer. The primary effect of water pooling in landfills is on flow direction and groundwater levels. For example, changes in groundwater flow direction were observed following the construction of Lake Diefenbaker on the Saskatchewan River (Schmid, 2003). Prior to construction of the dam, groundwater flow direction was toward the river valley in a generally flat topography. After the reservoir was filled, the flow direction reversed and generally flowed away from the river valley 2 up to 5 kilometers upstream of the dam. Additionally, the water levels in the dam caused groundwater levels in the bedrock aquifer through both increased infiltration and the rise in hydraulic base level (Wildi, 2010). In general, this rise in groundwater levels causes the changes in groundwater flow direction. Increased water elevations in the groundwater aquifer were observed in the Riverhurst section of the Lake Diefenbaker dam. When water levels in the lake ...