A hydrogeological and hydrogeochemical study of the evolution of ground water in a fractured granite, Holyrood Newfoundland

• Main Author: Sargent, Nicolas J.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1994
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/6761/; https://research.library.mun.ca/6761/1/NicolasJSargent.pdf; https://research.library.mun.ca/6761/3/NicolasJSargent.pdf

An extensive set of hydrogeological and geochemical data has been collected from a 150 m deep borehole in the near coastal discharge area of the Holyrood Granite, Newfoundland. Because of the selected location of the borehole, over the underlying saltwater wedge, it was possible to intersect flow paths that are believed to have extended considerably deeper within the aquifer than the depth of the borehole. -- The physical data indicate that the geometric average of the hydraulic conductivity over the length of the borehole is approximately 4 x 10⁻⁹ m/s and that the open fractures, controlling most of the flow in the aquifer are approximately vertical and parallel to the coast. Fractures of this nature have been postulated by others to have resulted from isostatic post glacial rebound. The hydraulic conductivity (measured at approximately 2 m intervals along the entire length of the borehole) shows a decrease of approximately three orders of magnitude with depth. Based on the hydraulic conductivity measurements made in the study borehole, known hydraulic gradients and probable flow-path length, it is believed that water samples collected may have had residence times of the order of 1000 a. -- Inspection of aqueous chemical data reveals that some parameters have a strong correlation with depth while other analytes have a strong inverse correlation with hydraulic conductivity. In general the water quality reflects the effect of low-temperature weathering of an alumino-silicate rich granite. However, the water samples collected were all relatively rich in chloride. Though there is no direct evidence of the source or sources of chloride in the study area, evidence from other granitic terrains indicate that the likely sources of chloride in the groundwater are from the rock mass (possibly from fluid inclusions) and from seawater. -- Study and analysis of fracture plane mineralogy using X-ray diffraction (XRD) and scanning electron microscopy (SEM) has provided evidence for a suite of minerals which may control the ...