The GWMA includes the combined areas of Adams, FranklinGrant and Lincoln Counties in eastern Washington.  The GWMA boundaries incorporate 8,160 square miles or 5,222,210 acres.  The area includes all or portions of Water Resource Inventory Areas (WRIAs) numbered 33, 34, 36, 41, 42, and 43 falling within the geographical boundaries of these three counties. 

Within this area a majority of the population obtain potable water from both shallow and deep aquifers.  


The Columbia Basin Ground Water Management Area shares four recognizably distinct hydrogeological zones or aquifers.  The shallower zone consists of the overburden aquifer system reaching varying depths from the surface, but generally extending no more than 50 to 100 feet below land surface.  The next aquifer zones in depth vary in their relationship between the Saddle Mountain Aquifer system and the Wanapum Aquifer System.  The deepest zone underlying this area is the Grande Rhonde Aquifer System.  The three shallower zones provide approximately 85% of the water pumped to the surface in this area for domestic and irrigated uses.  The protection of these resources is of vital ecological and economic importance to the region. Adams, Franklin, and Grant Counties share over 95% of the current Columbia Basin Irrigation Project and surrounding deep well irrigated activities in this area.  The remaining areas of Adams, Franklin, and Grant counties are used largely as rangeland and for dryland farming.  Most of the area is considered an arid climate, receiving between 5 and 15 inches of precipitation per year.  A large portion of the area receives less than 10 inches of rainfall per year.  Local aquifer recharge historically resulted from outside the area.  With the advent of intensive irrigation in the past 40 plus years significant changes to the local aquifer recharge profiles have occurred.  Widespread irrigation activities, including delivery and recapture, result in significant recharge to the overburden aquifer system. 

While the Columbia Basin GWMA extends only to the political boundaries of Adams, Franklin, Grant, and Lincoln Counties, it is recognized that the hydrogeologic boundaries likely are significantly greater. 


Last Updated ( Tuesday, 29 May 2012 )