As required by the US Environmental Protection Agency and the Federal Safe Drinking Water Act, a susceptibility analysis is conducted to determine the susceptibility of a public water supply system to each of the potential contaminant sources identified in the source water assessment area. Under the Source Water Assessment and Protection program, susceptibility is defined as the potential for a public water supply system to draw water contaminated at concentrations that would pose concern in the well or surface-water intake.
Relative to each public water supply system, each potential contaminant source is assigned a score based on several risk factors. The risk factors are categorized as "intrinsic" and "induced." Intrinsic risk factors are risk factors that exist by virtue of the hydrogeologic and physical setting of the water supply such as depth to the water table. Induced risk factors are risk factors that exist due to human activities at the various potential contaminant sites, such as volume of a potential contaminant stored at a facility.
A regulated facility that is in compliance with local, State and Federal environmental regulations is less likely to cause pollution than an unregulated facility, due to regulatory controls. Therefore, South Dakota’s susceptibility analysis includes a provision for a regulatory compliance credit (Scompliance) that would be applied where appropriate. The potential contaminant source score (SPCS), which represents the susceptibility of the public water supply system to an individual potential contaminant source, is obtained by combining the intrinsic (Sintrinsic) and induced (Sinduced) risk scores using the root-mean-square equation in combination with the compliance credit. The possible scores, and therefore potential risks, under this system are divided into high, moderate and low ranges.