Selecting a Wellhead Protection Area Delineation Method

Site-specific delineation efforts are required for each public water supply well, wellfield or spring (WAC 246-290-130). Due to resource and information constraints, the initial minimum delineation method requirements are relatively unsophisticated (for most systems, the calculated fixed radius method).

Analytical methods can provide more reliable predictions of groundwater flow than a calculated fixed radius method because they incorporate a greater number of site-specific parameters.

When translating analytical predictions to boundaries on the ground, it is important to determine whether the results correspond well with the local hydrogeologic setting. Integrating a hydrogeologic mapping component (e.g. knowledge of hydrogeologic boundaries) into a model reduces the possibility of making improper assumptions about the groundwater system. Incorporating knowledge of groundwater flow, divides and aquifer boundaries into the groundwater model allows for more accurate understanding of groundwater flow patterns.

Sophisticated analytical methods, hydrogeologic mapping, and numerical groundwater flow models allow a very site-specific approach to boundary area simulation, but require large amounts of site-specific data and technical expertise to run and interpret the model results. As a result, these types of applications are generally considerably more expensive than many of the simpler models.

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