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MODULE-2 Wellhead Protection Areas
Wellhead Protection Area Delineation Methods
Calculated Fixed Radius
The Calculated Fixed Radius method draws a circular protection area for a specified time of travel threshold. This method often provides a good estimate for time of travel zones. A simple volumetric flow equation can be used to calculate the radius. Data required are 1) well pumping rate, 2) porosity of aquifer and 3) open or screened interval of well. If a site-specific estimate of aquifer porosity is lacking, a generalized value of 0.22 may be substituted. If the actual screened interval is unknown, or if the well is constructed with an open interval at its base, a value of 10 feet should be used.
This delineation method is easy to apply and relatively inexpensive; it requires a minimum level of technical expertise. Because of its simplicity, it can be used as a delineation method for moderate and small systems. It should be used by many systems as a first cut method for identifying immediate threats to the water quality. The calculated fixed radius method is part of the basic Washington state susceptibility assessment. A major drawback of this model is that rarely does groundwater behave as simply as this model predicts. Susceptibility Assessment forms are available for calculated fixed radius solutions for selected well settings.
