South Dakota’s Wellhead Protection Program served as the basis for assessing the ground water supplied public drinking water systems in the state. A combination of wellhead protection delineation methods were used to define source water assessment areas depending on the type of public water supply system. As DENR continues to do source water assessments for new or modified public water supply systems (PWSS), the delineation methods below will continue to be used.
Community public water supply systems serve a permanent population and include municipalities, rural water systems, mobile home courts, and housing developments. Non-transient non-community (NTNC) public water supply systems are nonresidential water systems that serve the same population for at least six months per year and include factories and schools. Approximately 85% of South Dakota’s population are served by community and NTNC systems. Therefore, a comprehensive effort using available hydrogeologic information is applied to these systems. However, the amount and quality of information available will dictate the delineation method used. The delineation method for these systems will include one or a combination of hydrogeologic mapping, analytical methods, or a calculated fixed radius method.
Hydrogeologic mapping methods define source water assessment areas by identifying aquifer boundaries and other areas possibly contributing water to the public water supply well. Analytical mapping methods define source water assessment areas by solving mathematical ground water flow equations to delineate the area of contribution to a pumping well. A calculated fixed radius is a circle drawn around a well, the size of which is calculated using aquifer, well, and pumping rate information.
Transient, non-community public water supply systems serve a transient or nonresidential population and include campgrounds, rest stops, and resorts. South Dakota uses a calculated fixed radius delineation method to assess these systems. A more advanced delineation method is not necessary for these systems because the water is not used consistently by individuals on a daily basis.
A consecutive public water supply system is a water system served by another public water system. For example, a municipal public water supply system that maintains its own well for emergency or back-up purposes, may be served by a regional rural water system. If a public water supply system uses back up wells for drinking water purposes, DENR delineates a two-year time-of travel using the calculated fixed radius method. Because of the limited use of these wells, South Dakota does not believe these systems warrant the same assessment effort as active systems.
Public water supply systems located in non-sensitive hydrogeologic settings require less stringent protective measures from potential pollution sources due to the confined nature of the aquifer which makes it less likely that contaminants will reach the ground water. Therefore, South Dakota l delineates a 500-foot arbitrary fixed radius around the wellhead for these systems.