A GIS-BASED APPROACH TO CHARACTERIZING VERMONT’S GROUNDWATER RESOURCES

The Vermont Geological Survey (VGS) is developing a framework for characterization of groundwater resources (GWR) by integrating bedrock and surficial maps with existing water well data. In 2008, the VGS began assessing GWR using: 1) the Centennial Geologic Map of Vermont (1:250000 scale), 2) digital compilation of 1:62500 scale surficial maps, 3) water well database, and 4) available data such as DEM, soils, and potential pollution sources. Completed maps based on these data include: Thickness of Overburden in Vermont (Springston et al, 2012), Statewide Analyses of Bedrock Water Well Data (Gale et al, 2009) and 11 county maps. Other data include a groundwater use study (Medalie and Horn, 2010) and a well interference study (VT Rural Water, 2009).

The Dept. of Environmental Conservation water well database contains >100,000 records with 76 fields such as use codes, reported yield and depth, date completed, well type, location, and the type and thickness of materials. We developed protocols for improved well locations by linking well records to E911 addresses. A hydrogeological classification code was developed based on porosity and thickness of surficial materials and assigned to each well. The resulting maps 1) provide favorability assessments for surficial aquifers, 2) allow for spatial analyses within a geographic information system (GIS), and 3) facilitate integration of geochemical and structural data with geologic materials, water quality data and water use data to produce maps which focus our efforts for more detailed projects. GWR maps also show areas of thin overburden where bedrock wells are needed, areas of thick overburden and favorable materials for higher yield surficial wells, generalized areas of lower yield, relationships to designated town growth areas, and areas of thick impermeable overburden which impede recharge and may promote surface run-off. Although detailed geologic studies are preferred for site work, GIS analyses allow the VGS to generate statewide and county scale maps within a reasonable time frame that can be used to understand and address GWR identification and protection.