Stormwater infiltration testing is required for projects that require stormwater management. In most cases, the infiltration rate computed by these tests are fine, but in some cases, testing doesn’t work due to limiting zones. A limiting zone is defined as the upper limit of any zone or soil layer that is expected to limit the soil’s ability to treat the wastewater. More or less, it means that water cannot infiltrate the ground in this area. Some forms of limiting zones are high water tables, shallow bedrock, and redoximorphic features in soils. High water table and shallow bedrock are pretty much straightforward. You dig down and hit solid rock, there’s your limiting zone. You dig down and the hole begins to fill up with water, there’s your limiting zone.

But what are redoximorphic features? These features can form when the soil is saturated to the point that most all pores are filled with water and there is an absence of oxygen, or when changes to the chemical processes in the soil occur. When the hole is dug for the test, an examination of the soil is necessary to determine if these features occur. A way to determine this is if the soil has a reddish color to it. This shows that the section of soils has a potential to contain groundwater at certain times of the year.

If these features are encountered during the time of testing, a new location must be chosen, or the infiltration system bottom must be set at a minimum of two feet above the limiting zone.  Contact D.L. Howell & Associates, Inc. for all your infiltration testing needs.