EVALUATION OF SURFACE AND GROUNDWATER HYDROLOGY IN THE BLACK RIVER AND NORTH BRANCH VALLEYS, WEATHERSFIELD, VERMONT

Bordering the Connecticut River, the town of Weathersfield is located in southeastern Vermont. Our work focused in the Black River valley on the west side of town. Medium to high grade metamorphic rocks occur west of the valley whereas an igneous stock is found on the eastern side of the valley. The surficial geology and hydrology of this area was mapped during the summer of 2016 while working as interns for the Vermont Geological Survey. Interpretations involving the surface and groundwater hydrology of the area are presented here using our understanding of glacial landforms and materials, satellite imagery, topographic maps, and water-well logs.

Geologic mapping of surficial materials, landforms, bedrock outcrops, and hydrologic features was performed using the smartphone GPS application Fulcrum. Glacial till and exposed bedrock comprise the upland elevations above 660 feet. The surficial geology of the Black River valley includes glacial landforms such as eskers and kettle bogs and relatively rare pockets of glaciolacustrine sediments. Esker sediments are partially covered by deltaic sediments reworked during the Holocene by modern alluvial processes.

 Some water-well locations were gathered during summer field work whereas most other wells were located using the Vermont Agency of Natural Resources’ "Natural Resources Atlas." An isopach map of surficial materials was drawn using both field observations and well logs. Lastly, a water table contour map was created using the known surface hydrology, field observations, and well logs. Using the groundwater contour map, groundwater divides were established and flow lines drawn. Most drilled wells tap into the secondary porosity of metamorphic bedrock at varying depths. Groundwater recharge in upland areas most commonly occurs through thin till and fractures in bedrock. Discharge of upland groundwater occurs through a network of small streams draining to the lowlands and ultimately the North Branch of the Black River. The sand/gravel deposits from both eskers, glacial outwash, and glacial deltas provide the most abundant source of groundwater in the area. Hurricane Irene was also taken into account when observing the most recent major changes to alluvial fans, channels, and large-scale movement of alluvium in the valley.