colusa county groundwater assessment...• damage to foundations, roads, bridges, other...

Butte County Reconnaissance-Level Groundwater Sustainability Risk

Assessment

SGMA GSA Eligible Meeting Series #4

Davids Engineering, Inc.October 27, 2016

Approach• Governance is all about decision making

• If important decisions will be made, then governance is important; otherwise, not so much

• What are the key decisions embedded in preparing a Groundwater Sustainability Plan (or Plans)?

• “Key decisions” are ones that could affect the availability and/or the cost of groundwater to overlying landowners

• Be thinking about: “How should GSA’s be formed to make these key decisions (and many others) appropriately?”

October 27, 2016SGMA GSA Eligible Meeting Series #4 2

Outline• Butte County Setting• Key Decisions Embedded in GSP Development• Sustainability Assessment by Groundwater

Sustainability Indicator• Look into the Crystal Ball

• Questions & Answers, Discussion


Notes and Ground Rules

• Publicly available data sources used primarily

• Judgment necessarily involved; feel free to disagree, draw your own conclusions

• Acknowledge uncertainty in numbers • Covering a wide technical range • Burning questions okay; please hold

comments and discussion for later


Butte County Regional Setting


County

Subbasin Area (acres)

VinaWest Butte East Butte

North Yuba

Butte 85,893 93,732 211,351 47,212

Colusa - 42,942 33 -

Glenn 765 44,174 14 -

Sutter - 629 53,498 319

Tehama 37,921 - - -

Yuba - - 416 55,621

Total 124,579 181,477 265,312 103,152

438,188 Acres in Butte County Overlying Alluvial Basins Subject to SGMA


Butte County Regional Setting:Groundwater Elevation Change 2008 to 2016

Data Source: DWR Groundwater Information Center. Water level measurements are from wells in the unconfined to uppermost semi-confined aquifers. (Generally corresponding to wells depths between 100 and 450 feet.)

Butte County Land Use 2011(Source: DWR)


105 101 106 101

85 89 94 97

30 29 20 18

15 16 14 20

0

50

100

150

200

250

1995-1999 2000-2004 2005-2009 2010-2014

Acre

s (Th

ousa

nds)

Rice Orchards Other Cropland Idle Cropland

Butte County Water Source 2011(Source: DWR


Key Decisions Embedded in GSP Development

• Setting criteria for how the basin will be sustainably managed

• Defining “Undesirable Results”: do they exist now; will they potentially occur in the future?

• Establishing “Minimum Thresholds” and “Measureable Objectives” for each Sustainability Indicator

• Deciding how sustainability will be achieved • What Management Actions and Projects may be

required? • Where?• Cost and who pays?


SGMA Sustainability Indicators1) Chronic Lowering of Groundwater Levels

2) Reduction of Groundwater Storage

3) Seawater Intrusion

4) Degraded Water Quality

5) Land Subsidence

6) Depletions of Interconnected Surface Water


Undesirable Results• GSPs may, but are not required to, address

undesirable results that occurred before, and have not been corrected by, January 1, 2015 (per authorizing legislation; not expressed in GSP regs)

• An agency that is able to demonstrate that undesirable results…are not present and are not likely to occur…shall not be required to establish criteria (in the GSP) (§354.26)


Sustainability Indicator #1Chronic Lowering of Groundwater Levels

• Minimum Threshold: “…the groundwater elevation indicating a depletion of supply at a given location that may lead to undesirable results.”§ 354.28 (c) (1)

• Potential Undesirable Results:• Well stranding• Increased well construction costs• Increased groundwater pumping costs• Induced water quality degradation• Inelastic land subsidence• Streamflow depletion• Impacts to Groundwater Dependent Ecosystems• Others?


Sustainability Indicator #1Chronic Lowering of Groundwater LevelsVina Subbasin

0

10

20

30

40

50

60

1956 1962 1967 1973 1978 1984 1989 1995 2000 2005 2011 2016De

pth

to G

roun

dwat

er (f

eet)

23N01W36P001M (1)

Questionable Measurement

Ground Surface


0

10

20

30

40

50

60

70

1943 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 2009 2015

Dept

h to

Gro

undw

ater

(fee

t)21N01E27D001 (2)


Ground Surface

Sustainability Indicator #1Chronic Lowering of Groundwater LevelsWest Butte Subbasin


0

1

2

3

4

5

6

7

8

9

1999 2004 2009 2015De

pth

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roun

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eet)

20N01E18L003M (4)

Ground Surface

Sustainability Indicator #1Chronic Lowering of Groundwater LevelsWest Butte Subbasin


0

10

20

30

40

50

60

70

80

1999 2004 2009 2015De

pth

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roun

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eet)

20N02E24C001M (3)

Ground Surface

Sustainability Indicator #1Chronic Lowering of Groundwater LevelsEast Butte Subbasin


0123456789

10

1943 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 2009 2015

Dept

h to

Gro

undw

ater

(fee

t)18N02E16F001 (5)


Ground Surface

Sustainability Indicator #1Chronic Lowering of Groundwater LevelsEast Butte Subbasin


0

10

20

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60

1999 2004 2009 2015De

pth

to G

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17N04E09N002M (6)


Ground Surface

Sustainability Indicator #1Chronic Lowering of Groundwater LevelsNorth Yuba Subbasin



Crystal Ball:• Will definitely need to be addressed in GSP• Minimum Thresholds, Measureable Objectives

and Interim Milestones will need to be established in the GSP

• At what elevations do results become undesirable?

• Projects and Management Actions may need to be identified in GSP if levels continue to decline

Sustainability Indicator #1Chronic Lowering of Groundwater Levels

Sustainability Indicator #2:Reduction of Groundwater Storage

• Minimum Threshold: “…a total volume of groundwater that can be withdrawn from the basin without causing conditions that may lead to undesirable results.” § 354.28 (c) (2)

• Potential Undesirable Results:• Reduced water supply reliability (reduced drought

reserves)



Sustainability Indicator #2:Reduction of Groundwater StorageSubbasin Storage Capacities (DWR Bulletin 118)

SubbasinTotal Area

(acres)

Area within Butte

County(acres)

Percentage Acres within

Butte County

Total Subbasin

Storage, MAF(Bulletin 118)

Subbasin Storage in Butte Co,

MAF

Vina 124,579 85,893 69% 1.5 1.0

West Butte 181,478 93,732 52% 2.8 1.4

East Butte 265,313 211,351 80% 3.1 2.5

North Yuba 103,152 47,212 46% 0.6 0.3

Total 674,522 438,188 65% 8.0 5.2

Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portions of Vina, West Butte, East Butte and North Yuba Subbasins in Butte County Combined


-250

-200

-150

-100

-50

0

50

100

2009 2010 2011 2012 2013 2014 2015 2016

Chan

ge in

Sto

rage

(taf

)

Spring Change in Storage from Prior Year Cumulative Change in Storage

Total Combined Groundwater Storage = 5.2 MAF

Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion of Vina Subbasin in Butte County


-60

-50

-40

-30

-20

-10

0

10

20

2009 2010 2011 2012 2013 2014 2015 2016

Chan

ge in

Sto

rage

(taf

)


Subbasin Storage in Butte County = 1.0 MAF

Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion of West Butte Subbasin in Butte County


-80

-60

-40

-20

0

20

40

2009 2010 2011 2012 2013 2014 2015 2016

Chan

ge in

Sto

rage

(taf

)



Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion East Butte Subbasin in Butte County


-70

-60

-50

-40

-30

-20

-10

0

10

20

30

2009 2010 2011 2012 2013 2014 2015 2016

Chan

ge in

Sto

rage

(taf

)



Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion of North Yuba Subbasin in Butte County


-20

-15

-10

-5

0

5

10

15

2009 2010 2011 2012 2013 2014 2015 2016

Chan

ge in

Sto

rage

(taf

)



Crystal Ball:• Recent reductions in groundwater storage (during

the past 8 years) are modest relative to the total volume of groundwater in storage (~3% to 4%)

• Other sustainability indicators will pose sustainability challenges or subbasin operational limits before reduction of groundwater storage

• May be able to treat summarily in GSP


Sustainability Indicator #2:Reduction of Groundwater Storage

Sustainability Indicator #3:Seawater Intrusion

• Physically impossible; therefore, exempt


Sustainability Indicator #4:Degraded Water Quality

• Minimum Threshold: “…degradation of water quality…that may lead to undesirable results.”§ 354.28 (c) (4)

• Potential Undesirable Results:• Unsuitable quality for beneficial uses

• Agriculture• Drinking water• Stock water• Environmental uses

• Reduced crop yields• Increased water treatment costs• Inability to comply with regulatory standards

• Drinking water regulations• Basin Water Quality Control Plan



• Butte County Groundwater Quality Monitoring Trend Program

• Per County Code (Chapter 33A):• Monitoring of temperature, pH, and salinity (electrical

conductivity, EC) at least annually

• Ambient monitoring of groundwater quality trends, with particular emphasis on saline intrusion from underlying aquifers (below approx. 1,500 to 3,000 feet below ground surface)

• Does not address monitoring of contaminant plumes


• 14 water quality monitoring wells in the County’s monitoring program

• Annual surveys 2002 through 2016



2016 Sampling Results Summary Relative to US EPA Secondary Standards


Parameter

Secondary Standard or

Water Quality Threshold

Range of 2016

ValuesNotes Regarding

2016 Results

pH 6.5 to 8.5 7.0 – 7.8Within range of secondary water

quality thresholds

Electrical Conductivity

(EC)

< 900 µS/cm(drinking

water)

< 700 µS/cm(ag water)

159-581

Within range of secondary water

quality thresholds

Conclusions from 2016 Annual Report (Interdepartmental memorandum)

• Recent (15-year) history shows no significant changes in groundwater quality

• No major shifts in salinity (as indicated by EC) have been detected, and the basin appears to be free of saline intrusion



Crystal Ball:• Subject to ongoing monitoring, unlikely that water

quality degradation will pose sustainability challenges or subbasin operational limitations

• County’s existing water quality monitoring program a major asset that will support GSP development

• Contaminant plumes will need to be addressed separately


Sustainability Indicator #5:Land Subsidence

• Minimum Threshold: “…the rate and extent of subsidence that substantially interferes with land surface uses and may lead to undesirable results.” § 354.28 (c) (5)

• Potential Undesirable Results:• Permanent loss of aquifer storage capacity• Damage to foundations, roads, bridges, other

infrastructure• Change in surface topography that reduces

conveyance capacities of canals, natural channels, floodplains

• Other effects



Source: Land Subsidence from Groundwater Use in California, Luhdorff & Scalmanini Consulting Engineers




Three Extensometer Wells in Butte County, None

Indicating Subsidence

Extensometer Wells in Adjoining

Counties Indicating Subsidence


Crystal Ball:• No detectable land subsidence in the County yet

based on extensometer well data• May know more when new GPS survey results are

published in 2017

• Land subsidence will definitely need to be addressed in GSP, with emphasis on monitoring

• May be able to defer determination of Minimum Thresholds and Measureable Objectives until subsidence is detected


Sustainability Indicator #6Depletions of Interconnected Surface Water

• Minimum Threshold: “…the rate or volume of surface water depletions caused by groundwater use that has adverse impacts on beneficial uses of surface water and may lead to undesirable results.”

• Potential Undesirable Results:• Reduced water availability to legal users of surface

water• Reduced water availability to “Groundwater

Dependent Ecosystems” (GDE’s)



• Effects of pumping on both Groundwater Dependent Ecosystems (GDEs) and streamflow depletion may be potentially significant but data are lacking

• DWR developing analytic tools• C2VSim Model Update (“fine grid” model)• Best Management Practices (BMPs) for local agencies to

consider adopting for monitoring and analyzing effects of declining groundwater elevations

• The Nature Conservancy leading statewide effort to develop GDE guidelines for local agencies

• County staff collaborating with TNC


• Interaction depends on relative groundwater levels and properties of streambed and aquifer

• The uppermost groundwater sustains Groundwater Dependent Ecosystems, and river and stream flows

42

Source: The Nature Conservancy

October 27, 2016SGMA GSA Eligible Meeting Series #4



According to DWR’s existing C2VSim model,

Sacramento Valley streams have gone from net “gainers” to

net “losers” over recent decades.

953845 906

642

402

17282

-357 -358

-500

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750

1,000

1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s

Aver

age

Annu

al A

ccre

tions

(TAF

)

Decade



Existing Monitoring Wells near Streams of Potential Significance in or Bordering Butte County:• Feather River• Sacramento River• Big Chico Creek• Butte Creek• Others?


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1943 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 2009 2015

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(fee

t)17N03E03D001M (7)


Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Feather River


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1967 1972 1977 1983 1988 1994 1999 2005 2010 2016De

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23N02W25C001M (8)


Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Sacramento River


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2008 2008 2009 2010 2011 2012 2013 2014 2015 2016De

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20N01W04J001M (10)

Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Sacramento River


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1958 1963 1968 1973 1978 1984 1989 1994 1999 2004 2010 2015De

pth

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22N01E28J003M (12)

Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Big Chico Creek


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1992 1997 2002 2007 2012De

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22N01E32E004M (14)


Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Big Chico Creek


0

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1995 2000 2005 2010 2015

Dept

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(fee

t)21N02E20P001M (15)


Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Butte Creek


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1947 1952 1957 1962 1967 1973 1978 1983 1988 1993 1999 2004 2009 2014

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(fee

t)20N02E06Q001M (17)


Ground Surface

Sustainability Indicator #6Depletions of Interconnected Surface Water: Butte Creek




Crystal Ball:• Will definitely need to be addressed in GSP with

emphasis on monitoring to fill data gaps and analysis to characterize connections

• Biggest potential challenges (in Butte County) appear to be associated with streams, not Sacramento and Feather Rivers

• Highly uncertain whether streamflow depletion will or may pose operational limitations

• Effects of streamflow depletion are cumulative within the basin as a whole

Sustainability IndicatorsSummary Recon-Level “Risk Assessment”

• Categorically eliminate from consideration:• Seawater Intrusion (#3)

• Address but unlikely to pose operational constraints; focus on monitoring:

• Reduction of Groundwater Storage (#2)• Degraded Water Quality (#4)• Land Subsidence (#5)

• Potential to pose operational constraints and require Projects and/or Management Actions:

• Chronic Lowering of Groundwater Levels (#1)• Depletions of Interconnected Surface Water (#6)


How should governance be structured to make key decisions appropriately?


? ?

? ??

Discussion


colusa county groundwater assessment...• damage to foundations, roads, bridges, other...

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