1. Approaches and Considerations for Assessing Groundwater-Surface Water Interaction in Sonoma County
Stream Depletion Through SGMA Lens Workshop
Groundwater Resources Association of California
August 29, 2017, Sacramento, California
Marcus Trotta, PG, CHg, Principal Hydrogeologist
Sonoma County Water Agency

2. Overview of Presentation
Background on Sonoma County Water Agency
Focused Studies at Riverbank Filtration Facility/Russian River Alluvial Aquifer
Basin-wide Assessment Approaches
Considerations for SGMA Implementation

3. Sonoma County Water Agency
Wholesale Water Supply
Flood Control
Sanitation
Energy Production
Cooperative groundwater study programs with USGS
Pre-SGMA: Lead Agency for two Voluntary Groundwater Management Programs
Part of and providing Technical Services to three GSAs

4. Riverbank Filtration System
Russian River
Riverbank Filtration System
One of the largest riverbank filtration systems in the world
Treatment accomplished via natural filtration.
Production Capacity of up to 92 million gallons per day
Overview of Water Agency Riverbank Filtration System
Six radial collector wells at the Wohler and Mirabel production facilities adjacent to the Russian River. Each collector well consists of a 13 to 18 foot diameter concrete caisson extending approximately 60 to 110 feet into the alluvial aquifer.
Russian River Well Field consisting of seven vertical wells located in the Mirabel area. These wells are currently not operated as primary production facilities, but are maintained for standby production and may be used as primary production facilities as needed.
Inflatable dam on the Russian River near Mirabel that allows for operation of five infiltration ponds at Mirabel that increase the area of infiltration along the Russian River.
The pumping capacity of the six radial collector wells is estimated to be approximately 92 mgd; however, significant variations to this estimated capacity can occur due to seasonal variations in river flows, operation of infiltration ponds, and sedimentation patterns along the riverbed.
6 Radial Collector Wells
5 Infiltration Ponds
Inflatable Dam

5. Russian River Facilities: Focused Surface Water-Groundwater Assessment Techniques and Methods
Temperature as a tracer
Seepage meters
Riverbed sediment sampling program
Geophysical Methods to Evaluate SW-GW Interactions
Electrical Resistivity
Spontaneous Potential
Water-Level measurements & vertical gradient analysis
Surface water and groundwater quality studies

8. Method: Temperature Profiling
20cm
50cm
80cm
Riverbed
June (Near Thalweg)
June (Edge of Channel)
Diurnal signals extend beneath riverbed – losing conditions
Differences in spatial propagation of diurnal signal reflect highly localized variations in streambed morphology
Decrease in depth of diurnal temperature signal between June and September – increase in riverbed clogging
Stand alone data loggers logging every 10 min, Lack of diurnal variations at depth indicate lower permeability zone, Short/long residence times
September (Edge of Channel)

9. Methods: Seepage Meters and Cryocoring
Seepage meter: steel 55-gal drum, hose connection (~2m), and bag shelter
Seepage
Cryocoring: Retains structure, pore fluids & microbial ecology
Single point measurement of vertical flux (downward or upward)
Biomass

10. Method: Electrical Resistivity
Resistivity along A-A’
(red indicates dryer regions)
Apparent resistivity increases captures spatial and seasonal temporal changes (May through November)
Unsaturated zone development ~4 to 6 feet below riverbed, with exception of area beneath thalweg
Describe may is background and that inversions were constrained by using YSI field conductivity probe and water depths. and july is after deposition, Piezometer installation during Sept campaign confirmed unsaturated zone at 1.5m depth

11. Sonoma County Medium Priority Basins
3/17/2015
Became law in 2015
Affects Medium & high priority DWR Bulletin 118 basins: Sonoma & Petaluma Valleys, Santa Rosa Plain

12. Basin-wide Surface Water-Groundwater Assessment Techniques and Methods
Seepage runs (synoptic streamflow measurements)
Paired streamflow gauge/groundwater monitoring wells
Regional Numeric Groundwater Flow Models
GSFLOW: Santa Rosa Plain
MODFLOW-OHM: Petaluma Valley and Sonoma Valley

13. Sonoma Valley: Seepage Runs
Discharge Segments (Groundwater flows into Stream)
Most of Sonoma Creek
Most of Calabazas
Lower reaches of Fryer and Nathanson
Recharge Segments (Stream recharges Groundwater)
Sonoma Creek near Kenwood
Carriger
Upper reaches of Fryer and Nathanson
Portion of Felder Creek
May 2010
Paired Gauge Location

14. Paired Stream/Groundwater Monitoring Location

15. Simulated Change in Streamflow With and Without Groundwater Pumping (USGS, 2014)
Average 8% change in total simulated streamflow (35 year simulation)
USGS currently updating model and developing stream capture maps (USGS project with SWRCB )

16. Unique Features/Challenges
Limited long-term streamgage records
Geologic Complexities
Majority of groundwater pumping not measured/reported
Habitat and ESA Considerations with SW-GW Interactions
Biological Opinion issued by NMFS
SWRCB Emergency Drought Regulations - Priority Russian River Tributary Watersheds
California Water Action Plan Priority Streams - Mark West Creek

17. Considerations for SGMA
Spatial and temporal scales for assessing streamflow depletion as an undesirable result
Start with broader-scale assessments
Finer-scale assessments/monitoring as needed
Consider addressing spatial scale through Management Areas?
Consideration of other regulatory programs and standards
Surface water rights and surface water diversions
Instream flow requirements
Basin Plans
Others?