CP-1994-05
Wellhead protection strategy for small aquifers: A study of Hawaii.
Lau, L. Stephen, Delwyn S. Oki, and John F. Mink.
Small aquifers, especially those of high permeability and with well-defined boundaries, lend themselves to alternative approaches to wellhead and groundwater protection. This type of aquifer is common in Hawaii, and many occur elsewhere. Development of a wellhead protection strategy for Hawaii is technically difficult because of the wide range of aquifer types and groundwater extraction units. Three protection approaches are currently being considered for Hawaii. The first approach involves the delineation of wellhead protection areas around individual extraction units. This is the approach originally envisioned by the U.S. Environmental Protection Agency in its guidelines for delineation of wellhead protection areas. We have identified appropriate delineation methods for the principal extraction units in Hawaii. The second approach involves delineation of aquifer protection areas, which are based on aquifer boundaries. The aquifer protection area approach is conceptually superior to the wellhead protection area approach by virtue of its comprehensiveness since the entire aquifer is protected, rather than just isolated areas surrounding the wellheads. The third is a time-phased approach that involves the initial delineation of wellhead protection areas followed by an aquifer protection area; that is, delineate wellhead protection areas during the early stage of groundwater exploitation, and then switch to an aquifer protection area at a later stage of exploitation near the sustainable yield of the aquifer. These approaches provide a choice, depending on the degree of protection desired and the extent of groundwater development in the aquifer.