- July 18, 2020
- Posted by: pesenvironmental
PES designed and completed hydrologic and hydrogeologic studies to evaluate the effects of surface water-groundwater interaction due groundwater pumping from municipal water supply wells operated by the Russian River County Water District and Water Agency along the lower reach of the Russian River at Steelhead Beach Regional Park in Rio Dell, California. The municipal water supply wells pump groundwater from the alluvial aquifer adjacent to the river and downstream of the seasonal Warm Springs Dam. Results of the study also provided a basis for updating the water supply monitoring program to comply with the California Department of Health Services, Drinking Water Source Assessment and Protection (DWSAP) Program (i.e., now regulated under SWRCB, Division of Drinking Water [DDW]). Our services included:
- Preparing detailed scopes of work and technical specifications for contract preparation including the solicitation of competitive bids for subcontractor services;
- Planning, permitting, and scheduling of field activities with the SCWA and California Department of Fish and Game (i.e., CDFG now CDFW). The permitting performed exclusively by PES, included the successful petition to CDFG for waiver of Potential Streambed Alteration Notification related to work activities within the Russian River, including the installation of temporary mini-piezometers and related monitoring equipment;
- Completing a geophysical investigation 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 exploration soil borings to evaluate hydrogeologic properties of the alluvial aquifer system;
- Completion of 5 exploration borings including detailed lithologic logging and testing of soil samples for physical properties. Data collected from these borings served as the bases for design and construction of 5 groundwater monitoring wells. The groundwater monitoring wells were used to monitor groundwater levels and to conduct temperature profiling of the unconfined alluvial aquifer;
- Design and installation of staff gages and mini-piezometers (equipped with electronic pressure transducers and temperature probes) within the Russian River (under arrangements and permit waiver from CDFG to monitor river stage height, perform temperature profiling within the river and streambed, and quantitively measure streambed infiltration rates;
- Constructing groundwater monitoring wells to facilitate groundwater level monitoring and temperature profiling of the unconfined alluvial aquifer; and
- Preparing a technical report to summarize the details and results of the investigations.
The results of the hydrologic and hydrogeologic investigations were evaluated to assess variables related to streamflow depletion and suggested: (1) due to natural seasonal variations, the Russian River was a losing stream in the vicinity of Steelhead Beach during the Fall monitoring period; (2) the shallow alluvial aquifer is highly transmissive and the degree of connectivity between the river and alluvial aquifer is strongly influenced by groundwater pumping patterns at nearby water-supply wells; and (3) short-term increases in groundwater pumping patterns increased the area of riverbed where induced infiltration occurs and results in an overall increase to the volume of surface water inducement from the river to the aquifer. The results of the study also served a basis for updating the water supply monitoring program to comply with the DWSAP Program (i.e., groundwater under the direct influence of surface water [GUDI]).