Delineation
The delineation of Wellhead Protection Areas (WHPAs) is an important means for directly safeguarding the public water supply. As defined in the 1986 Safe Drinking Water Act Amendments, a WHPA is “the surface and subsurface area surrounding a water well or well-field, supplying a public water system, through which contaminants are reasonably likely to move toward and reach such water well or well-field.” An initial delineation of one-quarter mile around each SAWS public supply well was completed for the Wellhead Protection Program. However, due to the complex geologic structure of the Edward Aquifer, the large distance between the recharge zone and SAWS public supply wells, a more scientifically based methodology of delineation is required.
A good aquifer model is necessary to properly design and plan an aquifer protection program that recognizes the extent of the aquifer and its overlying and upgradient region. SAWS staff has been trained on software programs that will enable the development of a model that can be used to better delineate the Source Water Protection areas. Utilizing this model in conjunction with those used by other agencies, such as the U.S.G.S. and the Texas Water Development Board (TWDB), will allow a better understanding of the impact of potential contaminants within the contributing area. Conditions of both surface and groundwater flow patterns must be factored into the delineation of aquifer contributing areas. The goal is to develop a model that will provide a more accurate definition of SAWS WHPAs.