The 1000' sensitive area setbacks are intended to identify those areas where there are higher risks of contamination by spills or other releases, simply due to their proximity to the water body. The sensitive area setbacks are identified as a minimum of 1000' from centerline of the intake stream and all perennial tributaries within the delineated drinking water watershed. The distance of 1000 was based on EPA national guidance for the distance to conduct the potential contamination source inventories adjacent to streams. The slope for a map unit is a weighted average of the average slope. The K-factor used is a weighted average of only the value for the surface layer of the map unit.
Alluvial deposits are typically very high permeability soils.
Class D soils, which are defined as soils with very slow infiltration rates were mapped as sensitive areas within the boundaries of the drinking water protection area. Map units are assigned to hydrologic groups based on their majority component. A Class D soil is typified as clayey, has a high water table, or an impervious layer occurs at a shallow depth. Soils with these characteristics would have the potential for rapid runoff and subsequent transport of sediments and possible contaminants to the surface water body supplying the public water system. There may be other natural characteristics within a watershed that can be mapped as sensitive.