SUCCESSFUL IMPLEMENTATION OF AQUIFER STORAGE AND RECOVERY (ASR) IN A COLUMBIA RIVER BASALT GROUP (CRBG)-HOSTED AQUIFERS IN THE PACIFIC NORTHWEST

Despite the Pacific Northwest’s reputation for being “wet,” many cities find it increasingly difficult to meet peak water supply demand during the dry summer months. Aquifers in eastern OR and WA are the primary water sources for a vast agriculture industry and have experienced significant declines prompting regulatory restrictions. For these reasons, municipalities in OR and WA, as well as agricultural interests have opted to implement ASR projects as a unique water management technique to help meet peak summer water demands.

Unique to the Pacific Northwest are the Miocene-age continental flood-basalt flows of the CRBG which consists of a thick, areally extensive series of extraordinarily huge lava flows. The CRBG plays host to an extensive regional aquifer system in eastern WA, eastern OR, and western OR. The City of Beaverton’s ASR project uses CRBG aquifers to host its ASR project.

Since 1999, the City of Beaverton (City), OR (pop. 85,500) has installed 3 ASR wells in the CRBG aquifer. Currently, the City stores approximately 1,703,000 cubic meters (450 million gallons) of treated drinking water annually with its ASR wells. The 3 wells can provide up to about 22,700 cubic meters per day (6 million gallons per day) of peaking capacity, which is equivalent to 35 percent of the City’s summer peak day demand. Daily peak demands can also exceed the City’s source water pipeline capacity, allowing ASR to bridge the gap. Favorable hydrogeologic response and significant economic savings have made the City’s ASR system immensely successful.

Key lessons learned at the City’s ASR project includes: storage in CRBG aquifers is highly successful; understanding well and aquifer hydraulics in CRBG aquifers, however, is challenging because of their unique geologic characteristics (e.g., tabular interflows and compartmentalization); aquifer clogging by air entrainment is a concern, but can be managed with the installation of a downhole control valve; recharge well design is important; radon dissolves quickly into stored water; surface water and CRBG native groundwater have proven to be geochemically compatible in the Beaverton area; continuous monitoring of recharge linked to a downhole control valve has proven to be successful; and ASR has proven to be a cost-effective peak water management technique.