Frequently Asked Questions

What is an Underground Injection Well (UIC)?

A UIC well is a man-made hole in the ground that is used to put water and other fluids into the ground. In Washington, most of these wells are dug to dispose of waste water (example: septic drain field) and runoff or storm water (example: trench holding a pipe with holes in it, i.e., perforated pipe).

Examples of underground injection wells include drywells, drainfields, and infiltration trenches that contain perforated pipe. A fluid is any flowing matter, regardless of whether it is in a liquid, semisolid, sludge, or gaseous state.

The U. S. Environmental Protection Agency (EPA) groups injection wells into five classes, depending on the type of fluid to be disposed in them:

Is a stormwater pond or trench an UIC well?

A stormwater infiltration pond is not a UIC well as long as it is not deeper than it is wide at the land surface and or contain perforated pipe. An infiltration trench is not considered an UIC well if it does not contain perforated pipe or drain tile.

What are some other examples of UIC wells?

Frequently Asked Questions about Underground Injection Control Program
Frequently Asked Questions about Underground Injection Control (UIC) Program Rule Revision


For more information please contact:

Mary Shaleen-Hansen
Water Quality Program
WA Department of Ecology
P.O. Box 47600
Olympia, WA 98504-7600
Phone: 360.407.6143


Last updated March 2005