Groundwater in the Santa Rosa Plain Santa Rosa Plain Groundwater - - PowerPoint PPT Presentation

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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

“Los

a

im ng ” 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 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%

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

10,000 20,000 30,000 40,000 50,000 60,000 1975 1980 1985 1990 1995 2000 2005 2010 2015 Wet Years Agricultural Rural Domestic Public Supply Total

End of current SRPHM simulation period (2010)

Estimated Pumpage in Acre-Feet Per Year

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 Boundary

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

Changing Groundwater Flow Patterns

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

• rganic 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

Precipitation Temperature Stream segments & conduct Imperviousness Soil moisture Geology Hydraulic conductivity Groundwater 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 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 8,500 Springs and Seeps 6,100

Values in Acre Feet Per Year

Inflows = 80,600

Surface Percolation 41,000 Streambed Percolation 32,400 Subsurface

Aquifer Inflows 7,200

Subsurface

Aquifer Outflows 7,900

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

• f 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 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

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

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

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

• f 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 Information available from Additional GSP Requirements Required GSP existing GMP or studies Component*

Description of Annual and cumulative change in groundwater storage based groundwater elevation

• n groundwater-level changes, description and map of known

trends over time, groundwater contamination sites and plumes, rates and map Groundwater groundwater elevation

• f 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

• utreach 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

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