Private Well Owners: Important Information, please read below. Residents on Public Water Supply: This information does not apply to you.

Arsenic & Uranium MassGIS Mapping Tool

Introduction: This well locator tool is designed to allow the user to select a well location from a street map or satellite image view to obtain the percent probability that water from a bedrock well at that location may exceed the public drinking water standard for arsenic or uranium. All percent probability ranges presented are from the USGS Scientific Investigations Report 2011-5013. The information provided by this tool only applies to bedrock aquifers. If your well is located in a sand aquifer, or sand-and-gravel aquifer, this information does not apply. Most private drinking water wells installed in the Plymouth-Carver Aquifer and on Cape Cod, Martha's Vineyard, and Nantucket are completed in sand or sand and gravel deposits rather than bedrock. Therefore, this tool does not apply to those areas.

Uses Outside the Study Area: This well locator tool may also be used for private wells in bedrock-aquifer areas in Massachusetts that are located outside of the study area to determine if you are in an area that is mapped as granite or pegmatite. Although no statistical estimates are provided for these locations, in general, bedrock wells completed in granites or pegmatites are known to have an increased probability of water quality that does not meet the public drinking water standard for uranium and other radiological contaminants such as radium and radon. Please note that there may be other types of bedrock or other areas in Massachusetts both within and outside of the study area that have arsenic and uranium concentrations in well water that are above the public drinking water standards.

Uncertainties in the Probability Estimates: This tool is provided for informational purposes only. There are uncertainties associated with the probability results that are provided. A probability estimate is only as accurate as the bedrock geologic mapping that is available and the amount and accuracy of water quality analytical data that is available. The user of this application should be aware that the probability estimates provided may be inaccurate if the bedrock map shows the wrong type of bedrock at the location that you have selected. Buffers of 1,000 feet were applied to the geologic units of higher arsenic and uranium probabilities in an effort to conservatively adjust geologic contacts for mapping uncertainties. However, this buffering still does not guarantee that a well at a given location may not actually be located in a geologic unit that has a greater or lower probability of exceeding a drinking water standard.

Likelihood of Radon & Radium Exceedances: If you are located in an area that has an increased probability of not meeting the drinking water standard for uranium, there is generally also an increased probability of not meeting the drinking water standards for radium and radon. However, probability estimates for exceeding the radium and radon standards were not determined by the USGS investigation.