INTEGRATING SURFACE AND BOREHOLE GEOPHYSICS WITH PUMPING TESTS TO INVESTIGATE THE HYDROSTRATIGRAPHY OF THE MARITIMES CARBONIFEROUS BASIN: CASE STUDY FROM SACKVILLE, NEW BRUNSWICK

The fractured sedimentary rocks of the Maritimes Carboniferous Basin are highly stratified and lenticular in nature, consisting of gradational sequences of mudstones, siltstones, sandstones, and conglomerates that appear in varying proportions. As part of the multidisciplinary Maritimes Groundwater Initiative, a site 3 km northwest of the municipality of Sackville, New Brunswick, was chosen to conduct a variety of complementary field measurements to characterize the local hydrogeologic system. Standard and specialty geophysical logs were obtained in two wells, pole-dipole electrical resistivity imaging was performed along three transects, and a pump test was conducted with hydraulic responses recorded in six nearby observation wells. Geophysical logs delineate lithologic boundaries, locate distinct fractures and determine their orientations, and distinguish the permeable fractures from the general population. Resistivity logs are used to calibrate the two-dimensional inversion of the electrical resistivity images that yield model cross-sections to a depth of about 75 m. Finally, the pump test quantifies the hydraulic properties of the aquifer, with transmissivity values averaging roughly 6x10-3 m2/s; responses from the monitoring wells identify areal zones of hydraulic communication among the six wells. Interpreted results derived from integrating all field measurements indicate a marked absence of high-angle fractures and a correspondingly low vertical transmissivity. General geologic structure is gently dipping, coincident with fracture strike, and aligned with a direction of significant preferential flow along the northeast-southwest. These hydrostratigraphic characteristics are consistent with more regional results determined across a large portion of the basin and, consequently, this site appears to serve as a useful microcosm for general basin hydrogeology within the shallow subsurface.