Hydrogeologic Evaluation of Surface Water-Groundwater Interaction, Hanson Aggregates and Town of Windsor Properties, Windsor, California

PES designed and performed a hydrogeologic investigation to characterize site-specific hydrogeologic conditions of the unconsolidated alluvial deposits and evaluate surface water groundwater interaction of the alluvial aquifer at the Hanson Aggregates and Town of Windsor properties located along the Russian River. Hanson Aggregates once operated in-stream and wet-pit aggregate mining operations along the Russian River, and most of the area has since been reclaimed as quarry ponds and riparian habitat. The Town of Windsor operates three municipal water supply wells and a small water treatment on the elevated alluvial terrace above the Hanson property. The objectives of this hydrogeologic investigation included:

  • Characterization of the geometry, lithologic characteristics, and hydraulic properties of the shallow alluvial aquifer;
  • Evaluating the presence and characteristics of deeper aquifers within the study area;
  • Assessment of hydraulic properties of the alluvial aquifer and surface water-groundwater interaction; and
  • Evaluating hydraulic responses of the shallow alluvial aquifer in relation to groundwater pumping from the Town of Windsor Municipal Supply Wells, rainfall events, and diurnal variations in surface water temperature.
  • The hydrogeologic program included: (1) Completing a geophysical investigation at each property to characterize the lithology, saturated thickness, and base of the unconsolidated alluvial deposits. Results from the geophysical survey assisted in the selection of locations for design of the monitoring program; (2) Installation of exploration borings; observation wells and nested, multi-depth observation wells; and mini-piezometers; and (3) Performing water level and temperature monitoring programs.

Significant findings from these evaluations indicated:

  • The shallow alluvial aquifer is highly permeable at the two properties and, in some areas, underlain by deeper water-bearing sedimentary deposits. The variation in sediments is likely due to the presence of the Wallace Creek Fault Zone which was identified based data from the borehole drilling and geophysical survey. The characteristics of the deeper sedimentary deposits may be conducive to alternative groundwater uses (e.g. conjunctive use of the shallow and deeper aquifer systems and/or aquifer storage and recovery within the deeper water bearing zones);
  • The shallow alluvial aquifer is a highly transmissive, unconfined aquifer, which is hydraulically connected to the Russian River. The analysis of the water-level data and pumping schedules associated with the Town of Windsor Municipal Supply Wells identified an average transmissivity for the alluvial aquifer of approximately 142,300 square feet per day and a hydraulic conductivity of approximately 2,450 feet per day; and
  • Water-level elevations and temperature profiles from the Fall monitoring program indicate the Russian River is a gaining stream near the reclaimed quarry ponds and losing stream near the Town of Windsor Municipal Supply Wells. Temperature profiles observed during the study indicate that the river and pond provide a significant source of thermal energy to groundwater.