THE WEBER RIVER BASIN AQUIFER STORAGE AND RECOVERY PILOT PROJECT - GEOLOGIC SETTING AND IMPLEMENTATION

The Weber River Basin Aquifer Storage and Recovery pilot project is a three-year, multi-agency effort to evaluate the feasibility of artificial recharge by surface-water spreading in the Weber Delta area, northern Utah. Declining water levels, drought, increasing water use, and the likelihood of success based on previous experiments drove the project.

The project area is 2 miles west of Weber Canyon, where the Weber River flows through the Wasatch Range. Sand and gravel deposits of the Weber Delta, formed where the Weber River entered Pleistocene Lake Bonneville, make up the principal Delta aquifer, which is 50-300 feet thick, and thins westward away from Weber Canyon; its top is close to the land surface near the mountain front and dips gently west. Recharge is mainly by infiltration from the Weber River and underflow from Wasatch Range bedrock. Ground-water levels declined 30-80 feet during the past 50 years due to withdrawal by wells, which increased from 6,000 acre-ft/yr in the 1950s to 44,000 acre-ft/yr in the 2000s.

The infiltration site includes 4 infiltration basins totaling 3.7 acres. A new observation well, constructed to monitor water-level changes and ground-water chemistry, encountered a 2-foot-thick clayey silt layer at 116 feet.

During spring 2004, 800 acre-feet of water was diverted from the Weber River and infiltrated into the Delta aquifer. The observation-well water level rose only one foot. The infiltrated water spread over, and percolated downward through, about 16 acres on the fine-grained layer. TDS in Weber River water decreased during peak flow, then returned to normal values. TDS in all measured water wells remained constant. During spring 2005, 450 acre-feet of water was diverted and infiltrated. Seepage into an adjacent gravel pit forced early termination of the experiment. Due to a wet winter and spring, infiltration from the Weber River was greater than in 2004; the water level in the observation well rose 9 feet.

Future viability of artificial recharge at this site is uncertain due to continuity of the fine-grained layer between the infiltration site and the adjacent gravel quarry. Possible solutions include lease of the quarry, slower infiltration, or conversion to injection wells screened below the confining layer. Previous successful experiments were conducted closer to the mountain front, where fine-grained layers are absent.