Hydrogeologic and Groundwater Resource Evaluations, Healdsburg, California

PES was awarded contracts (1998 to 2004) to perform hydrogeologic evaluations at six properties along the middle reach of the Russian River. The shallow alluvial deposits which underlie the Russian River range in thickness from 25 to more than 100 feet. The primary source of groundwater recharge to the alluvial aquifer is through infiltration of surface water from the Russian River, ponds operated by SCWA, and precipitation. SCWA operates six radial collector wells and seven conventional wells adjacent to the Russian River. The series of studies performed by PES were designed to characterize the site-specific hydrogeologic conditions associated with the shallow alluvial aquifer, further advance the understanding of surface water-groundwater interaction at these properties, and provide data to enhance SCWA’s MODFLOW groundwater flow model further developed by PES to simulate groundwater flow conditions and groundwater production scenarios along the middle reach of the Russian River. Findings and recommendations from these studies were incorporated into the Environmental Impact Report prepared for the Water Supply and Transmission System Project and continue to represent the basis for potential future alternatives of development for RBF and groundwater resources to meet projected future water-supply demands of Sonoma and Marin Counties. Highlights of these projects, which demonstrate PES’ technical capabilities included:

  • Preparing detailed scopes of work and technical specifications for contract preparation including the solicitation of competitive bids for subcontractor services;
  • Planning and scheduling of field activities with private property owners and the Water Agency;
  • Design and analysis of surface geophysical surveys (using seismic refraction techniques) to assess the thickness and distribution of alluvial deposits; depth to bedrock; presence of previously unidentified faults; and occurrence and potential waterbearing characteristics of deeper water-bearing formations;
  • Completion of more than 36 exploration borings including detailed lithologic logging and testing of soil samples for physical properties;
  • Design and construction of 60 groundwater monitoring wells, test wells and mini-piezometers;
  • Monitoring of groundwater levels and collection of groundwater samples for chemical analysis;
  • Siting, design, and providing construction oversight services for high capacity test wells at three properties with groundwater production capacities ranging from approximately 1,100 to 2,500 gallons per minute;
  • Design, performance, and analysis of complex aquifer testing programs, which involved the design and installation of a comprehensive network of approximately 30 observation wells, and 20 riverbed mini-piezometers, to characterize hydrogeologic properties and surface water-groundwater interactions at each property;
  • Evaluation and assessment of surface water recharge characteristics to the shallow alluvial aquifer using heat tracing techniques;
  • Revising and calibrating an existing MODFLOW groundwater flow model for a 7milelong segment of the shallow aquifer system along the Russian River. The objectives of the modeling activities were to assess steady-state and transient surface water-groundwater interactions and estimate the steady-state groundwater production rate for Wohler Collector Well 6 with both a conventional and enhanced horizontal lateral system; and
  • Performing “Water Quality Profile Studies” to further understand natural filtration processes (riverbank filtration) and mitigate potential risks from surface water contaminants (coliform bacteria, Giardia and Cryptosporidium, chemicals of emerging concern [CECs] including pharmaceuticals and personal care products [PPCPs], and organic chemicals) at six radial collector well locations adjacent to the Russian River.

During performance of these programs, PES developed and maintained an excellent relationship with numerous landowners, including premium vineyard associations, the County of Sonoma Regional Parks Department, California Department of Fish and Game, private residents, and representatives of local Sand and Gravel Quarry operations.