Welcome to the Ground Water Interference Website

The Source Permitting process for Public Water Sources requires measuring and evaluating whether pumping a proposed drinking water source will withdraw enough water to reduce water levels in the surrounding area. When the pumping well takes water away from other drinking water sources (wells or springs), this is called “interference”. This interference can be tiny – less than a tenth of a foot to completely drying up the other water source. Adverse or unacceptable interference is required to be mitigated before a Source Permit can be issued.

The majority of PCWS sources in Vermont are wells completed in fractured crystalline bedrock aquifers, with fewer completed in sand and gravel aquifers present in some valley locations. Due to the non-homogenous, anisotropic nature of these aquifers, the impact of water withdrawal on nearby private and public wells and springs is difficult to predict unless measured in the field. By monitoring water levels in nearby water supply wells and springs during a constant discharge test (pumping test) the observed or estimated impact can be predicted. These calculations are required as part of a Source Evaluation Report.

Source evaluation reports prepared between 1980 and 2008 by the environmental consulting community were reviewed to develop a geodatabase that includes key information about the production (pumped) well and observation wells and springs monitored during these tests. This information includes specific pumping test information, derived values such as aquifer transmissivity and storativity, the degree of interference noted at observation locations, and a determination of acceptable versus unacceptable interference. The geodatabase was developed in conjunction with Stone Environmental, Inc. of Montpelier, Vermont and presented in the Vermont Rural Water Association Report 2009.

This database is dynamic and will be populated by the most current information available as part of the ongoing DEC Source Permitting process. Public water system source testing information has been added for evaluations completed from 2008 to present. These data may include other water systems where interference analyses were done such as Non-Transient Non-Community and Transient Non-Community wells.

The compilation of this considerable amount of data into an easy to use Database and GIS format marks the first time that this information has been assimilated and organized into a single geodatabase that can be used to provide information about PCWS sources and observation well responses around the state.

The Vermont Rural Water Association (VRWA) completed an assessment of groundwater interference caused by the pumping of Public Community Water Supply (PCWS) sources throughout Vermont. This study was completed in June 2009 under a contract with the Vermont Department of Environmental Conservation Drinking Water and Groundwater Protection Division (DWGPD).

The VRWA final report was limited to currently active or permitted drilled PCWS sources. This represents 203 PCWS sources and 1,082 observation points evaluated across the state up to 2008. The results of the study indicate that, overall, groundwater interference is not a chronic problem in Vermont. However, unacceptable interference – where a specific observation well source could no longer meet its design demand – was noted in several instances in areas of higher concentrations of PCWS sources.