. 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 www.sonomacountywater.org
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
Groundwater Surface Water Connection Groundwater Affects Stream Flow Gaining Stream Gaining Stream High Groundwater Levels Groundwater Maintains Stream Flow Courtesy The Nature Conservancy
Groundwater Surface Water Connection Groundwater Affects Stream Flow Losing Stream Losing Stream Pumping Lowers Groundwater Levels Stream Loses Flow Flow to to Groundwater Courtesy The Nature Conservancy
USGS Santa Rosa Plain Groundwater Study 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 planning
Santa Rosa Plain Water Supply Water supply in the Santa Rosa plain comes from three primary sources: 1. Groundwater (>50%) 2. Russian River (~35%) 3. Recycled Water (>10%)
Water Wells in the Santa Rosa Plain Watershed Santa Rosa Plain Watershed Estimated Groundwater Demands by Use Type: Average for 1976-2010 (USGS, 2014) 18% 50% 32% Agriculture Rural Domestic Municipal Supply Santa Rosa Plain Groundwater Basin
Local Supplies Groundwater Production Santa Rosa Plain Watershed 60,000 Wet Years Estimated Pumpage in Acre-Feet Per Year 50,000 40,000 30,000 20,000 10,000 Agricultural Rural Domestic Public Supply Total End of current SRPHM simulation period (2010) 0 1975 1980 1985 1990 1995 2000 2005 2010 2015 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 Alluvium/Glen Ellen Petaluma Wilson Grove Sonoma Volcanics Santa Rosa Plain Groundwater Subbasin
Conceptual Model Groundwater 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 Bulletin 118 Basin Boundary
Changing Groundwater Flow Patterns 1951 Less groundwater pumping Groundwater flowing mainly east to west and discharging to Laguna de Santa Rosa 1990 Increases in groundwater pumping through 1980s and 1990s Pumping depressions developed in southern and western areas 2007 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
Santa Rosa Plain Groundwater Subbasin 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
USGS Santa Rosa Plain Groundwater Study GSFLOW Surface Water-Groundwater Model EXAMPLE MODEL INPUTS Precipitation Temperature Stream segments & conductivity 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 Groundwater Budget 1976-2010 Inflows = 80,600 Surface Percolation 41,000 Streambed Percolation 32,400 Outflows = 83,900 Well Pumping 35,600 Streambed Discharge 25,800 Groundwater Evapotranspiration 8,500 Springs and Seeps 6,100 Subsurface Aquifer Inflows 7,200 Subsurface Aquifer Outflows 7,900 Values in Acre Feet Per Year
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) Key USGS Findings Imbalance in the amount of inflows and outflows to the basin - could be exacerbated by future climate change Potential for lowering of groundwater levels, reduction of streamflows and affect on ecosystems Local Response Proactively and voluntarily develop non-regulatory Groundwater Management Plan Collaborative Stakeholder-driven Process
SRP Basin Advisory Panel Voluntary Management Components Stakeholder Involvement Integrated Planning Groundwater Protection Monitoring and Modeling Conservation and Efficiency Water Reuse Groundwater Recharge
Monitoring Network Groundwater Monitoring Wells Orange - <200 feet deep Green 200-500 feet deep Blue - >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 Santa Rosa Plain Groundwater Subbasin Santa Rosa Plain Groundwater Subbasin Shallow Zone Deeper Zones
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 Plain
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. Sustainability Progress Monitoring Program 4. Proposed Project and Management Actions 5. GSP Implementation Costs, Detailed Schedule, and Reporting 6. Compile Complete GSP and Prepare for Adoption All phases will be developed through iterative process with input from Advisory Committee, GSA Board and community members
New Requirements vs Existing Information: Plan Area and Basin Setting Example Groundwater Conditions Example of Required GSP Component* Information available from existing GMP or studies Additional GSP Requirements Groundwater Conditions Description of groundwater elevation trends over time, groundwater elevation hydrographs and contour maps, groundwater quality data. Annual and cumulative change in groundwater storage based on groundwater-level changes, description and map of known groundwater contamination sites and plumes, rates and map of land subsidence (as applicable) identification of interconnected surface waters and groundwater dependent ecosystems and estimates on timing and quantity of stream depletions. *Represents one of many required GSP components
Key Data Needs and Challenges Improved water use estimates for rural groundwater users (rural domestic and agriculture), which comprise an estimated 80% of the total groundwater use. Depth-dependent water level and water quality data to improve understanding of the hydrogeology and better define relationships between the shallow and deeper aquifer systems. Improved information is needed about well location, lithology and construction to better understand Basin hydrogeology and improve the groundwater model. Additional modeling of future projected conditions that simulate the impacts of climate change, land use changes, hydrology, and changes in demands.
Key Data Needs and Challenges More information to address potential depletion of interconnected surface water from groundwater pumping unique challenge for Santa Rosa Plain due to strong interconnection between surface water and groundwater and the many related policies, regulatory programs and diverse interests. Identifying undesirable results as defined in SGMA and establishing quantifiable thresholds. Transitioning from a voluntary groundwater management plan to a new plan with regulatory authority will require extensive public outreach and community engagement.
Next Steps 1. Share information and coordinate with newly formed Advisory Committee 2. Complete Work Plan for GSP Development for Prop 1 Grant Application Submittal by November 13, 2017 3. Assess and Scope Near-term monitoring and data needs 4. Coordinate with USGS in update of computer model 5. Develop Community Engagement Plan 6. Prepare and File Initial Notice of GSP Preparation 7. Initiate Development of GSP must be filed with DWR by January 2022
Questions and Discussion http://www.sonomacountygroundwater.org