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Frequently
Asked Questions
What is an Underground Injection Well (UIC)?
What is an Underground Injection Control (UIC) well?
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:
- Class 1: receives industrial, commercial, or municipal waste
fluids injected beneath the lowermost formation containing an underground
source of drinking water (USDW) within 1/4 mile of where the well was dug.
Class 1 wells are prohibited in Washington State.
- Class 2: receives fluids that are brought to the surface as part
of oil or natural gas exploration, recovery or production.
- Class 3: used for mineral extraction. 2 basic types: solution
mining and in-situ leaching for minerals. Class 3 wells are prohibited in
Washington State.
- Class 4: receives radioactive or hazardous waste injected into or
above underground sources of drinking water. Class 4 wells are banned nation
wide.
- Class 5: all other injection practices not included in the other
classes. Class 5 injection wells, the most common injection well in our
state, are generally shallow wells used to discharge fluids into or above an
underground source of drinking water. In many cases, these aquifers are
shallow, unconfined or surficial. Large on-site septic systems, serving 20
people or more per day or having a capacity of 14,500 gallons per day, are
considered Class 5 wells.
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?
- A gas station with a service floor drain that leads to a septic system.
(prohibited in WA State)
- An apartment building with a septic system for sanitary waste disposal.
- A municipality that uses a UIC well to recharge an aquifer and use it at
a future time.
- A strip mall, with small businesses such as a photo processor and a dry
cleaner, that discharge sanitary wastes mixed with process water into a
septic system. (prohibited in WA State)
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Last updated March 2005
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