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    Groundwater in the Santa Rosa Plain

    Marcus Trotta, PG, CHg Principal Hydrogeologist Sonoma County Water Agency

    Santa Rosa Plain Groundwater Sustainability Agency October 12, 2017

  • Presentation Overview

    1. Background on Groundwater Science 2. Santa Rosa Plain Groundwater Studies 3. Voluntary Groundwater Management Planning

    • Basin Advisory Panel Insights and Recommendations 4. Groundwater Sustainability Plan Requirements

    and Data Needs 5. Next Steps 6. Questions & Discussion

  • Hydrologic Cycle

    US Geological Survey Circular 1139

  • Courtesy The Nature Conservancy

    “Gaining Stream”

    Groundwater – Surface Water Connection

    Groundwater Affects Stream Flow “Gaining Stream”

    High Groundwater Levels Groundwater Maintains Stream Flow

  • Groundwater – Surface Water Connection

    Pumping Lowers Groundwater Levels Stream Loses Flow to Groundwater

    Groundwater Affects Stream Flow “Losing Stre“Losaimng ”Stream”

    Pumping Lowers Groundwater Levels Stream Loses Flow to Groundwater Courtesy The Nature Conservancy

  • Santa Rosa Plain Groundwater Study Part 1 - Completed July 2013 • Hydrology, Hydrogeology and

    Groundwater Quality

    Part 2 - Completed April 2014 • Fully Coupled Surface Water-

    Groundwater Model • Evaluate Potential Future

    Conditions and Alternative Water Management Strategies

    Serves as scientific foundation for management


    USGS Santa Rosa Plain Groundwater Study

  • Santa Rosa Plain Water Supply

    Water supply in the Santa Rosa plain comes from three primary sources:




    Groundwater (>50%)

    Russian River (~35%)

    Recycled Water (>10%)

  • Water Wells in the Santa Rosa Plain Watershed

    Santa Rosa Plain Groundwater Basin



    Agriculture Rural Domestic Municipal Supply

    1976-2010 (US

    Santa Rosa Plain Watershed Estimated Groundwater Demands by Use Type: Average for

    GS, 2014)

  • Local Supplies – Groundwater Production Santa Rosa Plain Watershed








    1975 1980 1985 1990 1995 2000 2005 2010 2015

    Wet Years


    Rural Domestic Public Supply


    End of current SRPHM simulation period (2010)

    E st

    im at

    ed P

    um pa

    ge in

    A cr

    e- Fe

    et P

    er Y

    ea r

    Note: Estimated pumpage for rural domestic and agricultural uses based on 1976 – 2010 simulations from calibrated Santa Rosa Plain Hydrologic Model (USGS, 2014)

  • Santa Rosa Plain Geology and Primary Hydrogeologic Units

    Santa Rosa Plain Groundwater Subbasin

     Alluvium/Glen Ellen  Petaluma Wilson Grove  Sonoma Volcanics

  • Conceptual Model

    Bulletin 118 Basin BoundaryGroundwater occurs in all four primary formations Precipitation and streambed infiltration primary source of recharge Primary discharge:  Pumping  ET  Baseflow

    Dominantly flows east to west Strong connection between surface water and groundwater

  • Changing Groundwater Flow


    1951 • •

    19 •

    20 •

    Less groundwater pumping Groundwater flowing mainly east to west and discharging to Laguna de Santa Rosa

    90 Increases in groundwater pumping through 1980s and 1990s Pumping depressions developed in southern and western areas

    07 – 2015 Reduction in groundwater pumping within southern area due to increased Russian River water use, conservation and recycled water use

    • Southern area pumping depression has predominantly recovered

  • USGS Santa Rosa Plain Groundwater Study Groundwater Quality Sampling

    Over 160 Wells Sampled

    • •

    Many wells in the Santa Rosa Plain produce high quality water

    Large variability: some areas of naturally occurring iron, manganese, arsenic

    Localized impacts of nitrates and organic contaminants

    Higher salinity water with depth

    Some secondary water quality parameters, including chloride and mineral content increasing in southern Santa Rosa Plain

    Santa Rosa Plain Groundwater Subbasin


    Precipitation Temperature Stream segments & conduct Imperviousness Soil moisture Geology Hydraulic conductivity Groundwater wells

    • • • • • • •


    EXAMPLE MODEL USES •Estimate hydrologic budget •Identify recharge areas •Evaluate water-resource management strategies •Evaluate climate-change impacts •Evaluate effects of changes in land-use

    USGS Santa Rosa Plain Groundwater Study GSFLOW – Surface Water-Groundwater Model

  • USGS Santa Rosa Plain Groundwater Study Groundwater Budget 1976-2010

    Outflows = 83,900 Well

    Pumping 35,600

    Streambed Discharge 25,800

    Groundwater Evapotranspiration


    Springs and Seeps 6,100

    Values in Acre Feet Per Year

    Inflows = 80,600 Surface

    Percolation 41,000

    Streambed Percolation


    Subsurface Aquifer Inflows 7,200

    Subsurface Aquifer Outflows


  • USGS Santa Rosa Plain Groundwater Study Predictions of Climate Change Scenarios

    • Simulated increases in groundwater pumping due to higher temperatures and drier soils

    Overall lowering of groundwater levels•

    • Reduced – Groundwater flows to streams (baseflow), wetlands and

    springs Groundwater evapotranspiration (potential loss of riparian habitat)

  • Voluntary Groundwater Management Planning (2012 – 2017)

    Imbalance in the amount of inflows and outflows to

    the basin - could be exacerbated by future

    climate change

    Key USGS Findings

    Potential for lowering of groundwater levels,

    reduction of streamflows and affect on ecosystems

    Proactively and voluntarily develop

    non-regulatory Groundwater

    Management Plan

    Collaborative Stakeholder-driven


    Local Response

  • Monitoring and Modeling

    Stakeholder Involvement

    Groundwater Protection

    Water Reuse

    Groundwater Recharge

    Conservation and


    Integrated Planning

    SRP Basin Advisory Panel Voluntary Management Components

  • Monitoring Network

    Groundwater Monitoring Wells

    • • • •

    Orange - 500 feet deep Yellow – depth unknown

    • Need to increase monitoring program to comply with SGMA

    Santa Rosa Plain Groundwater Subbasin

  • Five-Year Trends in Groundwater Levels

    Shallow Zone

    Santa Rosa Plain Groundwater Subbasin

    Deeper Zones

    Santa Rosa Plain Groundwater Subbasin

  • SRP BAP Insights and Recommendations

    1. Encourage Conjunctive Management of Groundwater and Surface Water Resources

    2. Careful Tracking and Management of Future Changes in Storage and Streamflow Depletion

    3. Importance of Monitoring Programs and Data Collection 4. Importance of Contributing Watershed Areas to Groundwater

    Sustainability 5. Close Coordination with Land-Use Planning 6. Community Outreach will be Critical 7. Support Pursuit of Strategies from the Original Plan 8. Represent Multiple and Diverse Interests in the Santa Rosa


  • Groundwater Sustainability Plan Requirements  DWR developed requirements and regulations - 2016  Require significant level of technical work  Avoid “significant and unreasonable” undesirable results for

    the following sustainability indicators:  Chronic lowering of groundwater levels  Reduction of groundwater storage  Seawater intrusion  Degraded water quality  Land subsidence  Depletions of interconnected surface water that have adverse

    impacts on beneficial uses of the surface water  Require setting of measureable thresholds and objectives

    for each sustainability indicator  Identify projects and actions needed to achieve sustainability

  • Draft GSP Work Plan Objectives

    • Meet SGMA requirements - establish criteria and management actions to achieve and maintain sustainable groundwater.

    • Build on strong technical foundation established through previous technical studies and voluntary groundwater management activities.

    • Provide opportunity for significant public and community engagement and integrate the perspectives and address the needs of the many diverse users and uses of groundwater resources within the basin.

    • Leverage local resources through continued regional coordination and information sharing.

  • Phased Approach to GSP Development

    Six General Phases following DWR’s GSP Regulations

    1. Plan Area and Basin Setting 2. Sustainable Management Criteria 3. Sus