Date of Award

2005

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Andrew Reeve

Second Committee Member

Frederick L. Paillet

Third Committee Member

Willem F. Brutsaert

Abstract

Characterization of groundwater flow in a fractured crystalline bedrock aquifer is dominated by the transmissivity of individual fractures and the interconnectivity of those fractures. The study of a fractured bedrock aquifer is influenced by the scale of the observations and that of the model used to explain those observations. Five clusters of observation wells, six bedrock boreholes and five overburden wells, were installed at the University of Maine in the spring of 2003. These wells were installed to give a field facility at the University of Maine for exploring the hydraulics and geochemistry of ground-water flow. The characterization of the fractured bedrock aquifer is an important step to understanding the hydrogeology at this facility and will provide a baseline for future work. The fractured bedrock aquifer at the University of Maine has been modeled on three scales: the borehole scale (>5 m), the cross-hole scale (~22m), and at the regional scale (1,500-2,000m). The modeling of each successively larger scale depends on an understanding of the smaller scales. For the borehole scale, it is important to identify fracture locations and condition of the borehole. Although fracture aperture at the borehole wall did not correlate to fracture transmissivity, this measurement is an important step to help understand anomalously low flow within the borehole. Modeled transmissivity, based on flow logs under ambient and stressed conditions, of the total borehole was within two orders of magnitude to the calculated slug test transmissivity, further validating the borehole flow model. Limitations to the applicability for borehole flow logging were encountered at the Stillwater River borehole. The transmissivity of a single fracture in this borehole was much larger than that of the additional fractures, dominating the system and preventing the characterization of these smaller fractures. A pair of boreholes on the southeastern edge of the study demonstrated a reproducible erratic flow decrease with depth. The cause of this erratic flow decrease has not been established. The cross-hole test provided data on the interconnectivity of fractures. It proved that the interconnectivity of the fractures in the recharge zone is orders of magnitude lower than the transmissivity of the individual fractures. The regional flow models were constructed to approximate the flow characteristics found in the boreholes at the discharge and recharge zones. Groundwater flow simulations demonstrate that a thin zone of high permeability fractures can dominate a flow network. Additional flow characteristics encountered are explained by the regional flow modeling.

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share