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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