Groundwater System Source Water Protection Areas
Source Water Protection areas for public water supply systems using groundwater have been identified and delineated by methods that vary depending on system type. Groundwater Protection Areas exist for all public wells (Community and Non-Community) and represent the DNR's determination of the best available estimate of the “5-year groundwater time-of-travel zone” for the areas contributing recharge to public wells. This determination is based on the best available calculation method, ranging from simplified calculated fixed radius delineations to more advanced groundwater model-based delineations. Source Water Protection Areas may overlap when several public wells are located in close proximity. The following are baseline delineation methods used for the different types of groundwater public water supplies.
- Municipal wells:
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Approved wellhead protection plan recharge area delineations or other advanced delineations are used if available. For systems without advanced delineations we have performed calculated fixed radius (CFR) delineations for vulnerability assessments. These CFR delineations are based on a 5-year time period, open interval length, aquifer material porosities weighted by percent length of open interval and annual pumping history. Annual pumping history is used to determine the critical pumping rate variable used in the CFR delineations of municipal wells. As a safety factor, a 1,200-foot radius is used for all wells with a CFR of less than 1,200 feet because 1,200 feet is the maximum separation distance to any potential contaminant source found in the public water supply code (NR 811 Wis.Adm. Code).
- Other-than-municipal community wells and non-transient non-community wells:
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CFRs were evaluated for these types of wells, but it was determined that low pumping rates would result in all systems having less than 1,200-foot radius delineations. Therefore, the DNR uses a 1,200-foot fixed radius for these systems.
- Transient non-community wells:
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There are over 10,000 such wells in the state. DNR uses a 200-foot fixed radius delineation for all of these wells based on the impracticality of developing more intensive delineations for these systems. A Minnesota study suggests that a 200-foot radius area is an adequate source water area for those systems in homogeneous, unconfined aquifers.
Please note: in the Surface Water Data Viewer overlapping source water protection area boundaries have been merged for simplicity.
Contact information
- Amy Ihlenfeldt - information about the source water protection data layer.
- Brian Austin - information about the source water protection program.