Todd Preston

Expertise:
Hydrogeology and contaminate transport within clay rich glacial tills of northeastern Montana

Research interests:
I am interested in how subsurface geology controls the rate of groundwater and the dispersion of associated contaminates in glacial environments


Thesis Title: Stratigraphic Controls on Brine Contamination in the Prairie Pothole Region of Montana

Thesis Abstract: The prairie pothole region of Montana contains thousands of wetlands which provide critical habitat for numerous migratory bird species. Co-produced waters from oil-field activities have introduced the potential for brine contamination to many of these wetlands. Quantifying this risk requires a better understanding of the subsurface geology and regional groundwater system.

The prairie pothole region is part of the Missouri Coteau, an elevated highland southwest of the Missouri escarpment overlain by Pleistocene glacial deposits, and is characterized by unintegrated drainage. Ongoing hydrological investigations of wetlands within Sheridan Country, initiated in 2008, will be used to determine the movement of groundwater within the region. Selected wetlands have had stilling well and piezometer well pairs installed, surveyed to a common datum, and equipped with capacitance rods to monitor water levels. Water-level measurements, recorded at thirty minute intervals, provide hydraulic gradients and groundwater flow directions. The hydraulic conductivities of sediments underlying and adjacent to these wetlands were determined from rising-head and falling-head single-well slug tests.

The near-surface stratigraphy is a complex, 3-D matrix of sediments from three depositional environments: fine grained lacustrine deposits, coarse grained fluvial outwash channels, and poorly sorted, vertically fractured till. The degree of fracturing and sediment heterogeneity largely controls local hydraulic conductivity values. Piezometer data from thirteen wetlands exhibited large variability in hydraulic conductivity, ranging from 6.98E-05 to 6.33E-01 ft/day, with a median of 1.03E-01 ft/day. The seasonal reversals in hydraulic gradient exhibited at several sites indicate that many of these wetlands fluctuate between sources of groundwater discharge and recharge.

Current Research Projects:
Brine Contamination to Prairie Potholes from Energy Development in the Williston Basin


Publications:
Petrographic Analysis of the Camp 26 Nunatak. 2003 Juneau Icefield Research Project open file report