Soils are classified into four main hydrologic soil groups (HSGs) A, B, C, and D. HSGs rate the amount of permeability throughout the entire soil profile and consider the depth to a restrictive layer (material that stops or slows downward water movement i.e. bedrock), high water table, and differences in clay content. All of these things can affect how fast water can move through the soil, which is referred to as the rate of infiltration. Group A soils have a high infiltration rate. These soils are, generally very sandy and allow water to pass through with very little natural filtration. Conversely, group D soils have a very low infiltration rate. Group D soils are generally very dense with high amounts of clay or have a very shallow water table preventing infiltration. This causes water to move very slowly through group D soils often resulting in standing water on flat surfaces and flowing water over sloped surfaces. HSG is a calculated value based on a set of soil properties in the National Engineering Handbook

There are also three sub groups (A/D, B/D, and C/D) these indicated the infiltration rate of the soils with respect to the water table. If the water table is high and blocking infiltration, these soils are considered to have a low infiltration rate and placed into group D, but when the water table is lower, these soils are similar to the first grouping (A, B, or C). Generally, these subgroups are used to represent a drained vs undrained soil.  If a soil is mapped as B/D which is fairly common in this part of the state, the soil will be identified as B if in a drained crop field vs a D in an undrained crop field or wetland area.

The soils within Dunn County range from very sandy group A soils in the southeast to less coarse group B and C soils in the west. Nearly 70% of the soils within Dunn County fall into either group A or B. This means that if there is nothing on the land to remove potential groundwater contaminants, the majority of the soils will provide little protection.

A county-wide map of hydrologic soil classifications can be viewed here. Additional site-specific soil information, an interactive mapping application, and use instructions can be found at: