3 The New Bedrock Geologic Map of Vermont: New Answers, New Problems, and New Uses of Bedrock Geologic Data

Sunday, 14 March 2010
7:50 AM - 12:05 PM
Liberty A

VERMONT APPLIED PROJECTS AS A GUIDE FOR USE OF THE NEW STATE BEDROCK MAP

Paper number: 3-3
Program: Symposia Sessions
Time: 11:45 AM – 12:05 PM

Authors

Abstract

Geologic map data created in tandem with the development of the new cooperative 1:100,000 scale Bedrock Geologic Map of Vermont (VT) are fundamental in case studies of groundwater, natural hazards, and energy issues. The 1961 state bedrock map by Doll is now the 1:250,000 scale base for comparison of 137 rock types and 92,315 water wells for gallons per minute (gpm), depth, and specific capacity gpm/ft. A 2002 statewide compilation indicates the presence of elevated naturally occurring radioactivity relative to surrounding areas while highlighting the Clarendon Springs Fm (CSF). A highway rockfall study uses structural data to address risks to the traveling public. In NW VT, from a developing cross section for the new state bedrock map, the depth and thickness of thrust repeated shales with natural gas potential is interpreted. Enhanced and critical analyses will follow with the new map and digital data. Low yield inverse distance weighted analysis will be a guide for aquifer study at larger scales. A well interference analysis will first be integrated with new data in Dover VT. Siting considerations for enhanced geothermal power facilities will reference the new cross sections and the VT power transmission network.

Application of 1:24,000 scale data used in the new compilation include studies of groundwater quantity and quality and landslide potential. The structure and composition of upper plate phyllites and schists and lower plate carbonates of the Hinesburg Thrust is crucial for understanding potential well yields and radionuclide occurrences. In Woodstock, VT, wells drilled in bedrock may provide exceptionally low yields where schist layers are vertical, compared to flatter alternating sandy marble and schist. In the Colchester Quad, all wells with elevated radioactivity were in the CSF leading to a ‘Zones of Concern’ map for town residents. Mapping and geophysics in the Montpelier area identified potential sources of radionuclides in the Waits River Formation. In East Montpelier, VT, a study integrating bedrock mapping, structural analysis, monitoring well data and geophysics addresses the occurrence of elevated nitrates in domestic water wells next to a large farm. In Smugglers Notch, a rockfall hazards study indicates most blocks detaching from the cliffs are delimited by three principal sets of joints.