34 Environmental Geoscience (Posters)

Monday, 21 March 2011
8:00 AM - 12:00 PM
Grand Ballroom/Urban Room

EVALUATION OF GROUNDWATER RESOURCES IN THE TOWN OF CRAFTSBURY, NORTHEASTERN VERMONT USING BEDROCK, SURFICIAL, AND TOPOGRAPHIC MAPS

Paper number: 34-19
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The Town of Craftsbury straddles the Richardson Memorial Contact (RMC)- a regional lithotectonic boundary that separates metamorphic rocks of the Green Mountain Belt (GMB) to the west from those of the Connecticut Valley Belt (CVB) to the east. The RMC is a Silurian unconformity that is locally coincident with a Devonian fault(s). The GMB is composed of pre-Silurian phyllites and phyllitic quartzites of the Moretown and Cram Hill fms. whereas Silurian-Devonian siliceous marbles, phyllites and isolated granites comprise the CVB.

The marble-rich lithologies directly to the east of the RMC have been eroded to form a broad depression in which the Black River and a number of elongate N-S lakes are found. Uplands composed of pre-Silurian and Silurian-Devonian metamorphic rocks are located to the west and east, respectively, of the Black River Valley lowlands.

Uplands are primarily underlain by dense silt- and fine-sand-matrix glacial till. Till is thin (<20’) on hilltops and bedrock outcrops are abundant. Striations and grooves indicate ice motion of ~170-195°. Scattered ice-contact sand and gravel deposits overlie till in places. Glaciolacustrine deposits are common below ~1120’. Probable delta deposits are found at ~1120’.

There are 328 accurately located groundwater wells in Craftsbury and 96% (n=315) were completed in bedrock. Wells in Silurian-Devonian bedrock have slightly higher average yields and total depths (13 gpm; 267’) than those in pre-Silurian bedrock (10 gpm; 259’). Surficial wells (n=13) have average yields of 40 gpm. Preliminary analysis suggests that the elevated yields of some bedrock wells may be related to the presence of thick, saturated, and porous surficial deposits that overlie the bedrock.

Further analysis seeks to correlate well yields with other factors such as fracture domains, topographic slope, proximity to water bodies or lineaments, and drainage area(s).