To ensure adjacent groundwater users are not impaired by a new use (in areas in Spokane County not served by public water), an ordinance was passed which, among other things, establishes setback requirements. A setback requirement establishes the distance that a well, that will be put into use for a building, must be from other nearby existing wells in use.
If a well is at a sufficient distance from another well it is reasonable to conclude that the new use will not impair an existing user. Spokane County evaluates the distance between a well associated with a proposed new use and existing uses in a 3-tier system:
1. General Setback - A well associated with a new use is 500 ft away from any existing wells in use.
2. Aquifer Dependent Setback – A well in a specific aquifer can be closer than 500 ft.
Sand and gravel aquifer – 100 ft
Clay and silt aquifer – 200 ft
Granitic bedrock aquifer – 200 ft
Basalt aquifer – 500 ft (same as general setback)
Sand and gravel aquifer – 150 ft
Clay and silt aquifer – 300 ft
Granitic bedrock aquifer – 300 ft
Basalt aquifer – 750 ft (same as general setback)
3. Site Specific Setback – A property owner can hire a licensed hydrogeologist or professional engineer to use site specific aquifer parameters (how thick the aquifer is, how fast the water moves, how it stores water, etc.) to determine a setback distance at which the new well will not induce greater than a 10 ft. drawdown on an adjacent well that is in use (see diagram below.)
It is highly recommended that you read the entire ordinance No. 17-0537 for a full understanding of all requirements. A complete description of the site-specific criteria can be found in the ordinance.