IMPROVING THE LOCATION ACCURACY OF VERMONT’S PRIVATE WATER WELL SYSTEMS: LEVERAGING DIGITAL WELL RECORDS, PARCEL DATA AND PROPERTY INFORMATION IN GIS

Previous work by the USGS suggests that private drinking water supplies (i.e., groundwater wells) serve approximately 40% of Vermont’s population, compared with about 14% of the national population. At the county level, Vermont’s private water systems range from 19% of the population served in Chittenden County to 66% in Orange County. Prior to commencement of a Water Use and Data Research (WUDR) Grant awarded to Vermont by the USGS in 2017, Vermont’s accurately located digital well record percentage was 21%. Utilizing digital well records, property tax data and digital parcel records with ArcPy, the python data analysis library ‘pandas’ and ArcGIS Pro geographic information system (GIS), Vermont’s private well database of approximately 120,000 records is, to date, 42% accurately located by GPS location or Enhanced 911 (E911) address.

The need for accurately located private well geodata, for both geologic and water quality investigations, is paramount. Subsurface mapping of geologic deposits conducted by the Vermont Geological Survey (VGS) utilize attributes such as well depth, lithology, overburden thickness and static water level coded in mandatory well competition report forms to create isopach, bedrock surface and potentiometric surface maps to evaluate the fate and transport of chemical contaminants in groundwater.

Since 2005, Vermont’s well completion database necessitates well drillers to list borehole GPS coordinates, but prior to that requirement, many wells in the data set were not accurately geolocated or the accuracy is unknown. Recent standardization of Vermont’s digital parcel and ‘grand list’ property tax information allows the VGS to link these disparate datasets via pieces of well and property owner names, unique parcel account numbers and parts of addresses with the digital well spatial database. A supervised workflow using code developed for ArcGIS Pro allows a user to link a digital well record with the appropriate land parcel via matching historical property tax owner information. When compared with more expensive and time-consuming field derived data such as visiting a Town Clerk’s office or physical mapping, the ArcPy tool has a 94% successful location rate. Current limitations of this tool include legacy data entry errors and manual supervision of the workflow.