THE STATE OF COLUMBIA RIVER BASALT GROUP AQUIFERS IN THE PACIFIC NORTHWEST: CAN THIS DUMPSTER FIRE BE EXTINGUISHED?

Groundwater levels are declining markedly in Columbia River Basalt Group (CRBG) aquifers throughout the Pacific Northwest. Declines exceed100 meters in some areas, and management strategies appear mostly ineffective. Research has shown the principle causes of the declines are overpumping from aquifers and depressurization of aquifers through intraborehole flow in commingling wells.

Reducing groundwater pumping is often legally and politically difficult, and socially and economically disruptive. Effectively managing well construction (to reduce commingling) requires a thorough understanding of the CRBG aquifer systems not yet developed in many areas. It also requires increased institutional fortitude and resources at the regulatory agencies charged with setting and enforcing well construction standards.

An approach to overcoming these obstacles has been developed by stakeholders in the Mosier Creek basin, a small watershed that is tributary to the Columbia River in North-Central Oregon. Groundwater levels in CRBG aquifers in the Mosier area have declined 44 meters during the past 45 years, and have continued to decline despite the Oregon Water Resources Commission’s closure of the three uppermost CRBG aquifers to additional irrigation and municipal water rights 30 years ago. The Mosier Watershed Council, Wasco County Soil and Water Conservation District, and Oregon Water Resources Department have been working together to address groundwater level declines by: 1, establishing Special Area Well Construction Standards to ensure new wells are constructed to prevent commingling, 2, providing incentives for owners to repair or abandon (i.e., seal) existing commingling wells, and 3, supporting exploratory drilling of “deep” wells that can be used to transfer some of the groundwater pumping stress out of the shallower declining aquifers. This approach was made possible by an understanding of the CRBG hydrology in the basin from groundwater research by private, state, and federal investigators. It also required cooperation and support of water users. Although promising, continued monitoring of groundwater levels and groundwater discharge to streams will be necessary to judge the effectiveness of these approaches.