ABSTRACT: Evaluating Hydrologic Parameters with Geophysical Techniques to Aid in the Design and Siting of Aquifer Pump Tests
BLACK, WILLIAM E., and KENNETH G. BLOM, NORCAL Geophysical Consultants, Inc., Petaluma, CA
The siting and design of groundwater collection systems along the Russian River in Sonoma County, California, require knowledge of the local hydrologic conditions. Of particular interest is the thickness and continuity of permeable materials and the influence of adjacent groundwater collection systems. A well-designed and strategically
located aquifer pump test program allows effective assessment of these parameters. To this end, a geophysical investigation determined the lithology, thickness, and lateral extent of the river deposits forming the local aquifer. An additional objective was to map the direction of groundwater movement and possible preferred groundwater paths.
The geophysical investigation consisted of seismic refraction, electrical resistivity, and self-potential surveys. These surveys were done over a 5-ac parcel adjacent to the Russian River and near high-volume groundwater collection systems. The findings of these surveys provided information on the thickness of river deposits overlying moderately to slightly weathered bedrock, the locations of areas with the greatest thickness of coarse-grained materials, and the location of zones where groundwater seepage exhibits the most fluctuation as a result of nearby pumping.