In order to protect a water supply, it is critical to determine the land area contributing water to the well within which potential sources of contamination can be identified and managed. This zone, called a wellhead protection area, can be generally described as the surface and subsurface area through which water and contaminants move toward a well. The process of establishing a wellhead protection area is called wellhead protection area delineation.
In developing wellhead protection programs, most States have already determined which approaches are to be used for delineating wellhead protection areas in the State. Communities in these States, therefore, will generally need only contact their State agency for appropriate approach.
In defining appropriate delineation approaches, States generally have considered cost, ease of application, suitability to the State's hydrogeological settings, the State's institutional capability to implement the approach, ease of field verification, acceptability to the public, and capability to stand legal challenge in addition to considering the threats from direct introduction of contaminants, microbial contaminants, and chemical contaminants.
Delineation is based on three components: criteria, criteria thresholds, and methods. Criteria and criteria thresholds form the basis for the delineation while the methods are the means by which the criteria and criteria thresholds are applied in developing on-the-ground or on-the-map wellhead protection area boundaries.
For instance, a wellhead protection area
might be delineated using a distance criterion, with a 1
mile criterion threshold and an arbitrary fixed radius
method. This wellhead protection area would consist of a
circle surrounding a well with a radius of 1 mile.
Another example would be the use of the time of travel
criterion with a 10 year criterion threshold and the
analytical techniques method to delineate the wellhead
protection area. This wellhead protection area would
consist of an irregularly shaped area with the boundary
representing a 10 year time of travel. Not all methods
are accepted in all States, so it is necessary to contact
the State agency for guidance on acceptable delineation
approaches.
Once the wellhead protection area has been identified, its boundaries can be drawn on a city, county or other appropriate map. Mapping the wellhead protection area, as well as the potential sources of contamination, can serve as a useful educational tool for citizens and businesses as well as assisting in emergency situations.
Continue to 3-Contaminant Source Identification