Underground Injection Control (UIC)

Underground Injection Control (UIC) wells are structures put in place below ground that are used to discharge fluids into the subsurface.  There are six classes of UIC wells, “Class V” being the most common in Washington.  Some examples of Class V UIC wells are French drains, stormwater chambers, and drywells – you’ll see drywells in Asotin County more than any other Class V well!

Stormwater collected in drywells drains through perforations in the sidewall of the drywell itself and into surrounding soil.  Depending on the depth of the groundwater below the drywell, and the type of soil surrounding the drywell, the stormwater may drain, or infiltrate, into the aquifer.  Stormwater that collects contaminants and then enters a drywell could eventually end up in groundwater, and contamination of the groundwater could occur If the drywell is not properly constructed or maintained.

Discharge of stormwater from UIC wells is regulated by the Department of Ecology (Ecology) through the UIC Program.  There are two basic requirements:

• Owners must locate and register their UIC wells with Ecology unless the wells are located on tribal land (those wells must be registered with the EPA).
• Make sure that current and future underground sources of groundwater are not endangered by pollutants in stormwater discharge (non-endangerment standard).

Ecology requires registration of UIC wells, with the exemption of injection wells used to collect roof-runoff from a single-family home or duplex, or prevent a basement from flooding, and injection wells located on Tribal lands.  UIC wells constructed before February 3, 2006, are considered "existing", and those constructed on or after February 3, 2006, are considered "new".

For existing UIC well registration, Ecology needs information about the land use and activities around the well (which affect the quality of the discharge), the local geology, depth of the groundwater table in relation to the UIC well, whether the UIC well is located within a groundwater protection area, and pollutant loading classification for the areas from where stormwater runoff is originating.

Ecology requires registration of a new UIC well prior to its construction.  Most new UIC wells in Washington are rule-authorized, meaning they do not need a permit.  To be rule-authorized, an injection well must be registered, and water discharged from the well must meet the non-endangerment performance standard – that is, to prevent the contaminated stormwater into groundwater.

Asotin County Regional Stormwater is currently creating an inventory of all Program-owned new and existing UIC wells, and will begin to register the wells once the inventory process is complete. For more information about Ecology's UIC Program, click here!