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Groundwater in the Santa Rosa Plain
Marcus Trotta, PG, CHgPrincipal HydrogeologistSonoma County Water Agency
Santa Rosa PlainGroundwater Sustainability AgencyOctober 12, 2017
Presentation Overview
1. Background on Groundwater Science2. 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 Steps6. 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 LevelsGroundwater Maintains Stream Flow
Groundwater – Surface Water Connection
Pumping Lowers Groundwater LevelsStream Loses Flow to Groundwater
Groundwater Affects Stream Flow“Losing Stre“Losaimng ”Stream”
Pumping Lowers Groundwater LevelsStream Loses Flow to Groundwater Courtesy The Nature Conservancy
Santa Rosa Plain Groundwater StudyPart 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
USGS Santa Rosa Plain Groundwater Study
Santa Rosa Plain Water Supply
Water supply in the Santa Rosa plain comes from three primary sources:
1.
2.
3.
Groundwater (>50%)
Russian River (~35%)
Recycled Water (>10%)
Water Wells in the Santa Rosa Plain Watershed
Santa Rosa Plain Groundwater Basin
32%50%
18%
AgricultureRural DomesticMunicipal Supply
1976-2010 (US
Santa Rosa Plain Watershed Estimated Groundwater Demands by Use Type: Average for
GS, 2014)
Local Supplies – Groundwater ProductionSanta Rosa Plain Watershed
0
10,000
20,000
30,000
40,000
50,000
60,000
1975 1980 1985 1990 1995 2000 2005 2010 2015
Wet Years
Agricultural
RuralDomesticPublic Supply
Total
End of current SRPHMsimulation period (2010)
Est
imat
ed P
umpa
gein
Acr
e-Fe
et P
er Y
ear
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 PetalumaWilson Grove Sonoma Volcanics
Conceptual Model
Bulletin 118 Basin BoundaryGroundwater occurs
in all four primary formationsPrecipitation and streambed infiltration primary source of rechargePrimary discharge: Pumping ET Baseflow
Dominantly flows east to westStrong connectionbetween surface water and groundwater
Changing Groundwater Flow
Patterns
1951••
19•
•
20•
Less groundwater pumpingGroundwater flowing mainly east to west and discharging to Laguna de Santa Rosa
90Increases in groundwater pumping through 1980s and 1990sPumping depressions developed in southern and western areas
07 – 2015Reduction 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 StudyGroundwater 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 andorganic 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
•EXAMPLE MODEL INPUTS
PrecipitationTemperatureStream segments & conductImperviousnessSoil moistureGeologyHydraulic conductivityGroundwater wells
•••••••
ivity
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 StudyGSFLOW – Surface Water-Groundwater Model
USGS Santa Rosa Plain Groundwater StudyGroundwater Budget 1976-2010
Outflows = 83,900Well
Pumping35,600
StreambedDischarge25,800
GroundwaterEvapotranspiration
8,500
Springs and Seeps6,100
Values in Acre Feet Per Year
Inflows = 80,600Surface
Percolation41,000
Streambed Percolation
32,400
SubsurfaceAquiferInflows7,200
SubsurfaceAquifer Outflows
7,900
USGS Santa Rosa Plain Groundwater StudyPredictions 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
springsGroundwater 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 streamflowsand affect on ecosystems
Proactively and voluntarily develop
non-regulatory Groundwater
Management Plan
Collaborative Stakeholder-driven
Process
Local Response
Monitoring and Modeling
Stakeholder Involvement
Groundwater Protection
Water Reuse
Groundwater Recharge
Conservation and
Efficiency
Integrated Planning
SRP Basin Advisory Panel Voluntary Management Components
MonitoringNetwork
Groundwater Monitoring Wells
••••
Orange - <200 feet deepGreen 200-500 feet deepBlue - >500 feet deepYellow – 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 andSurface Water Resources
2. Careful Tracking and Management of Future Changes inStorage and Streamflow Depletion
3. Importance of Monitoring Programs and Data Collection4. Importance of Contributing Watershed Areas to Groundwater
Sustainability5. Close Coordination with Land-Use Planning6. Community Outreach will be Critical7. Support Pursuit of Strategies from the Original Plan8. 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 Setting2. Sustainable Management Criteria 3. Sustainability Progress Monitoring Program 4. Proposed Project and Management Actions5. GSP Implementation Costs, Detailed Schedule, and Reporting6. 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 Information available from Additional GSP RequirementsRequired GSP existing GMP or studiesComponent*
Description of Annual and cumulative change in groundwater storage based groundwater elevation on groundwater-level changes, description and map of known trends over time, groundwater contamination sites and plumes, rates and map Groundwater groundwater elevation of land subsidence (as applicable) identification of Conditions hydrographs and interconnected surface waters and groundwater dependent contour maps, ecosystems and estimates on timing and quantity of stream groundwater quality depletions. data.
*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 formedAdvisory Committee
2. Complete Work Plan for GSP Development for Prop 1 GrantApplication Submittal by November 13, 2017
3. Assess and Scope Near-term monitoring and data needs4. Coordinate with USGS in update of computer model5. Develop Community Engagement Plan6. Prepare and File Initial Notice of GSP Preparation7. Initiate Development of GSP – must be filed with DWR by
January 2022
Questions and Discussion
http://www.sonomacountygroundwater.org
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