TRACKING AQUIFER RECHARGE THROUGH PERTURBATIONS IN THE AMBIENT SEISMIC FIELD ALONG A MOUNTAIN-FRONT INTERFACE IN THE COLUMBIA RIVER BASALT PROVINCE

The heterogeneity and anisotropy of a fractured rock and interbedded sediment aquifer, such as those in the Columbia River Basalt Province, present challenges to water resource managers for determining the sustainable use of an aquifer. The ability to discriminate and quantify seasonal patterns of aquifer recharge is critical for water resource management. Prior work in the study area determined a snowmelt driven recharge to the aquifer system along a mountain-front interface, which is composed of a thick sedimentary sequence outside the extent of the basalt flows. A linear temporary network of 11 seismic stations, utilizing Raspberry Shake 1D’s, was deployed across the likely recharge zone to measure changes in the ambient seismic field. The seismic monitoring was paired with continuous water-level monitoring by a transducer in a control well located near the center of the seismic station network. The differences in velocity of seismic perturbations were correlated between each seismic station and the transducer’s water level to produce a record of the water level across the seismic station network. Available geologic information was used to determine hydraulic conductivity, saturated thickness and hydraulic gradient for each seismic station area. Using water level and hydraulic properties of each seismic station area, the recharge volume moving across the seismic station network was determined for monthly, seasonal and annual periods.