Groundwater Interference

"This is a searchable database representing over 40 years of hydrogeologic information based on yield testing required for new and existing public water supply sources in Vermont. The VRWA final report (the basis for the development of SQL database) 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.
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 will be added soon 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.
Since late 1980, protocols for the testing of new PCWS groundwater sources (e.g., drilled bedrock wells, drilled gravel wells), have existed in Vermont. These protocols were initially developed by the VDOH, which at that time was the regulatory body for new PCWS sources in Vermont. Since the transfer of PCWS regulatory authority to the WSD in 1991, requirements associated with the testing and permitting of new PCWS sources has been codified in the Environmental Protection Rules, Chapter 21: The Water Supply Rule.  
One aspect of the Source Permitting process is measuring and evaluating whether pumping a proposed PCWS will withdraw enough water to reduce water levels in the surrounding area. 
The majority of PCWS sources in Vermont are wells completed in fractured crystalline bedrock aquifers, with a more limited number 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.  The impact to existing drinking water supplies is called Interference and can range from non-existent to adverse � where there isn�t enough water to meet the demands of the current use. Adverse or unacceptable interference is required to be mitigated before a Source Permit can be issued.
Existing 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 pumped wells 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 database currently contains data from 1980-2008. Data from tests conducted from 2009 to the present will be entered over the next several months."

Tags: appmapsandmapping, deptdec, divdwgwp, isothemewater, nodevtanr, subthemehydro, vt-anr-open-data
Organization: Vermont Center for Geographic Information