Recharge Assessment of the Lower Tuscan Formation Butte and Tehama Counties, California

The Lower Tuscan Aquifer (LTA) is the primary aquifer of Butte and Tehama Counties in the Northern Sacramento Central Valley of California.  The Lower Tuscan Aquifer Project is funded by a Proposition 50 Grant awarded by the California Department of Water Resources (DWR) and managed by Butte County Department of Water and Resource Conservation (BCDWRC) to investigate natural recharge and flow characteristics of the LTA.  It is hypothesized that the streams flowing from the east out of the Sierra Nevada foothills recharge the aquifer where the Lower Tuscan Formation outcrops intersect them.  The Tuscan Formation is comprised of interbedded volcaniclastic derived debris flows, lahars, and fluvial reworked volcanic materials into moderately cemented conglomerates and sandstones.  These outcrops make up the butte and bluff topography observed along the foothills on the east side of the North Central Sacramento Valley.  Recharge of the LTA is being studied using several approaches, differential stream discharge monitoring, near stream temperature-flux monitoring, and dual ring soil infiltrometer testing.  Stream gauging has been implemented on 5 streams.  Each creek is instrumented with two stations, one up stream and one down stream with the entire reach occurring over outcrops of the LTA formational materials.  The streams are gauged using an Acoustic Doppler Current Profiler (ADCP) to attain high resolution discharge measurements.  In addition to stream gauging, a pilot test is being performed to assess if temperature-flux profiles are capable of observing stream aquifer interactions in this type of geologic material.  The dual ring infiltrometer testing is being conducted at 12 sites across the outcrops of the Lower Tuscan Formation at a variety of locations with differing mapped soil types.  The results of this study will improve the understanding of the aquifer based on direct observation of existing conditions to enhance protection and management of the resource.