Update%20on%20USGS%20Santa%20Rosa%20Plain%20Cooperative%20Groundwater%20Study

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Update on USGS Santa Rosa Plain Cooperative
Groundwater Study
State of Laguna Conference and Science
Symposium October 14, 2009 Marcus Trotta, PG,
CHg Sonoma County Water Agency
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Alexander Valley Study Area Completed 2006
Santa Rosa Plain Study Area Initiated 2005
Sonoma Valley Study Area Completed 2006
Petaluma Valley Study Area
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Overview of Study and Cooperating Agencies

• Santa Rosa Plain Basin Study 5 Yr Study Began
  December 2005
• Complete in December 2010
• 2.2 Million (1.5 M local/0.7 M USGS)
• Cooperating and Funding Agencies
• Sonoma County Water Agency
• Cities of Santa Rosa, Rohnert Park, Cotati,
  Sebastopol, Town of Windsor
• County of Sonoma
• Cal American Water Co.

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Study Objectives

• Develop an updated assessment of the hydrogeology
  geochemistry of the Santa Rosa Plain (SRP).
• Develop a fully-coupled surface water/groundwater
  flow model for SRP.
• Evaluate the hydrologic impacts of alternative
  ground-water management strategies on the basin.
• What are efficient strategies for
  surface-water/ground-water management that will
  assure the long-term viability of water supply in
  the SRP?

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Santa Rosa Plain Groundwater Study Tasks

• Data Collection, Compilation Data Management
  (GIS)
• Water Level Quality, Geologic, Geophysical,
  Land Use
• Estimate Groundwater Demand Over Time
• Data Interpretation and Hydrogeologic
  Characterization
• Geologic Framework Model
• Conceptual Model
• Water Balance
• Fully Coupled Surface Water/Groundwater Flow Model

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Land Use Maps Water Use Estimates - Santa Rosa
Plain

• Historical Land Use
• 1959, 1974,1979, 1986, 1999
• Water Use Estimates
• Water use records - Urban
• Per capita Domestic Non-Urban
• Crop Use Factors - Agriculture

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Wilson Grove Formation
Gravelly unit south of Sebastopol
Upper sand unit west of Sebastopol

• West of Sebastopol, lower very fine-grained sand
• North of Sebastopol, massive fine-grained sand
• Southeast of Sebastopol, gravelly, grades into
  Petaluma Formation

Fine-grained unit Whitaker Bluff
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3D framework built withwell data
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3D Hydrogeologic Framework and Hydraulic
Properties Compilation
Defining heterogeneity in the hydrogeologic units
Construction of 3D hydrogeologic framework model
and determination of aquifer thickness

• Well lithology at 5-m increments
• Horizontal extrapolation away from each drill
  hole
• Highly dependent of density of well data

3D framework
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Oblique View of Depth to Basement Surface from
Geophysics

• Nearly 2,000 new gravity measurements in the
  northern San Francisco Bay area obtained to
  delineate to estimate the thickness of the
  valley-fill and volcanic aquifers.
• Santa Rosa Plain is underlain by two sedimentary
  basins (the Windsor and Cotati Basins) about 1 to
  2 km deep separated by the Trenton Ridge, a
  shallow west-northwest-striking bedrock ridge
  west of Santa Rosa.

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SRP Groundwater Quality Sampling Sites

• Water quality database 5,000 records
• Inorganic, trace element, nutrient, misc.
  parameters
• 411 wells
• 6 surface-water sites
• Database updated with Dept. Public Health data
• Database incorporates recent GAMA sampling program

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Development of GSFLOWFlow Model

• Coupled surface water (PRMS)-groundwater flow
  (MODFLOW) model
• Capable of simulating land surface processes
  (runoff, evapotranspiration, infiltration)
  coupled to groundwater flow
• Provides spatially distributed climate, land
  surface processes (overland flow, retention
  storage, etc)
• Upon completion, USGS will run several scenarios
  to assess potential future conditions (e.g.,
  climate change) alternative water management
  strategies (e.g., groundwater banking)

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Watershed Model

• Physical characteristics of watersheds
• topography
• hydrography
• vegetation
• soils
• geology
• land use
• streamflow gaging records
• meteorological data

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Ground-Water Flow Model

• Inputs include boundary conditions, aquifer
  properties, streams and lakes, flow barriers, and
  pumpage
• Parameter estimation

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Stakeholder Assessment Santa Rosa Plain
Groundwater Study

• In progress Conducted by Center for
  Collaborative Policy, California State
  University, Sacramento.
• Impartial assessments of issues and concerns
  related to groundwater management in the Santa
  Rosa Plain and to learn if and how stakeholders
  might want to address these issues.
• Conducted confidential interviews with nearly 50
  individuals representing over 30 organizations.
• Preliminary findings indicate differing
  interpretations on the value and potential of
  groundwater management planning as well as a lack
  of technical understanding of both surface and
  groundwater resources within the SRP.
• Completed assessment expected in late 2009

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Acknowledgements/Questions?
USGS Personnel

• Database/GIS
• Kathryn Koczot
• Andy Morita
• Donna Knifong
• Data Collection/Interpretation
• Loren Metzger
• Chris Farrar
• Geologic Modeling
• Victoria Langenheim
• Robert McLaughlin
• Robert Jachens

• Lithologic Modeling
• Don Sweetkind
• Emily Taylor
• Modeling
• Joe Hevesi
• Linda Woolfenden
• Diane Rewis
• Tracy Nishikawa
• Eric Reichard

http//ca.water.usgs.gov/user_projects/sonoma/sant
arosaplain.html