Although there is a limited number of surface water PWSS in the state, approximately 27% of South Dakotans receive their water exclusively from surface water systems. Therefore, a significant portion of the population is dependent on surface water as a source of drinking water. The delineation method for surface water systems includes the entire watershed area upstream of the public water supply intake up to the tribal or state border. The delineated assessment areas extends 10 river miles upstream from the surface water intake. Additionally, a one-half mile wide contributing zone extending laterally beyond any upstream alluvial aquifer is also delineated to provide for an adequate evaluation of potential contaminant sources to a particular surface water supply. This delineated area is considered "Zone A". A detailed potential contaminant source inventory is conducted in this delineated zone. The "Zone B" assessment area will include a 25-mile radius from the PWSS intake, within the delineated watershed. The remaining delineated watershed is considered "Zone C". A less detailed inventory is conducted in "Zone B" and "Zone C".
This generalized assessment method for surface water systems provide for the protection and benefit of surface water supplies by delineating the area contributing water to the system and identifying sources of potential contaminants that may impact the water system through overland flow, or contribute through base flow of adjacent aquifers. Depending on the location of the surface water intake, such as on a river or a lake, the generalized surface water assessment approach will vary.