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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
October 27, 2016SGMA GSA Eligible Meeting Series #4 3
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 4
Butte County Regional Setting
October 27, 2016SGMA GSA Eligible Meeting Series #4 5
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 6
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)
October 27, 2016SGMA GSA Eligible Meeting Series #4 7
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 8
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?
October 27, 2016SGMA GSA Eligible Meeting Series #4 9
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 10
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)
October 27, 2016SGMA GSA Eligible Meeting Series #4 11
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?
October 27, 2016SGMA GSA Eligible Meeting Series #4 12
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 13
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)
Questionable Measurement
Ground Surface
Sustainability Indicator #1Chronic Lowering of Groundwater LevelsWest Butte Subbasin
October 27, 2016SGMA GSA Eligible Meeting Series #4 14
0
1
2
3
4
5
6
7
8
9
1999 2004 2009 2015De
pth
to G
roun
dwat
er (f
eet)
20N01E18L003M (4)
Ground Surface
Sustainability Indicator #1Chronic Lowering of Groundwater LevelsWest Butte Subbasin
October 27, 2016SGMA GSA Eligible Meeting Series #4 15
0
10
20
30
40
50
60
70
80
1999 2004 2009 2015De
pth
to G
roun
dwat
er (f
eet)
20N02E24C001M (3)
Ground Surface
Sustainability Indicator #1Chronic Lowering of Groundwater LevelsEast Butte Subbasin
October 27, 2016SGMA GSA Eligible Meeting Series #4 16
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)
Questionable Measurement
Ground Surface
Sustainability Indicator #1Chronic Lowering of Groundwater LevelsEast Butte Subbasin
October 27, 2016SGMA GSA Eligible Meeting Series #4 17
0
10
20
30
40
50
60
1999 2004 2009 2015De
pth
to G
roun
dwat
er (f
eet)
17N04E09N002M (6)
Questionable Measurement
Ground Surface
Sustainability Indicator #1Chronic Lowering of Groundwater LevelsNorth Yuba Subbasin
October 27, 2016SGMA GSA Eligible Meeting Series #4 18
October 27, 2016SGMA GSA Eligible Meeting Series #4 19
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)
October 27, 2016SGMA GSA Eligible Meeting Series #4 20
October 27, 2016SGMA GSA Eligible Meeting Series #4 21
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 22
-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
October 27, 2016SGMA GSA Eligible Meeting Series #4 23
-60
-50
-40
-30
-20
-10
0
10
20
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
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 24
-80
-60
-40
-20
0
20
40
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
Subbasin Storage in Butte County = 1.4 MAF
Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion East Butte Subbasin in Butte County
October 27, 2016SGMA GSA Eligible Meeting Series #4 25
-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
)
Spring Change in Storage from Prior Year Cumulative Change in Storage
Subbasin Storage in Butte County = 2.5 MAF
Sustainability Indicator #2: Reduction of Groundwater Storage 2009 through 2016Portion of North Yuba Subbasin in Butte County
October 27, 2016SGMA GSA Eligible Meeting Series #4 26
-20
-15
-10
-5
0
5
10
15
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
Subbasin Storage in Butte County = 0.3 MAF
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 27
Sustainability Indicator #2:Reduction of Groundwater Storage
Sustainability Indicator #3:Seawater Intrusion
• Physically impossible; therefore, exempt
October 27, 2016SGMA GSA Eligible Meeting Series #4 28
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 29
Sustainability Indicator #4:Degraded Water Quality
• 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
October 27, 2016SGMA GSA Eligible Meeting Series #4 30
• 14 water quality monitoring wells in the County’s monitoring program
• Annual surveys 2002 through 2016
October 27, 2016SGMA GSA Eligible Meeting Series #4 31
Sustainability Indicator #4:Degraded Water Quality
2016 Sampling Results Summary Relative to US EPA Secondary Standards
October 27, 2016SGMA GSA Eligible Meeting Series #4 32
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 33
Sustainability Indicator #4:Degraded Water Quality
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 34
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
October 27, 2016SGMA GSA Eligible Meeting Series #4 35
October 27, 2016SGMA GSA Eligible Meeting Series #4 36
Source: Land Subsidence from Groundwater Use in California, Luhdorff & Scalmanini Consulting Engineers
Sustainability Indicator #5:Land Subsidence
October 27, 2016SGMA GSA Eligible Meeting Series #4 37
Sustainability Indicator #5:Land Subsidence
October 27, 2016SGMA GSA Eligible Meeting Series #4 38
Sustainability Indicator #5:Land Subsidence
Three Extensometer Wells in Butte County, None
Indicating Subsidence
Extensometer Wells in Adjoining
Counties Indicating Subsidence
Sustainability Indicator #5:Land 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
October 27, 2016SGMA GSA Eligible Meeting Series #4 39
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)
October 27, 2016SGMA GSA Eligible Meeting Series #4 40
Sustainability Indicator #6Depletions of Interconnected Surface Water
• 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
October 27, 2016SGMA GSA Eligible Meeting Series #4 41
• 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
Sustainability Indicator #6Depletions of Interconnected Surface Water
October 27, 2016SGMA GSA Eligible Meeting Series #4 43
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
-250
0
250
500
750
1,000
1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s
Aver
age
Annu
al A
ccre
tions
(TAF
)
Decade
Sustainability Indicator #6Depletions of Interconnected Surface Water
Sustainability Indicator #6Depletions of Interconnected Surface Water
Existing Monitoring Wells near Streams of Potential Significance in or Bordering Butte County:• Feather River• Sacramento River• Big Chico Creek• Butte Creek• Others?
October 27, 2016SGMA GSA Eligible Meeting Series #4 44
0
5
10
15
20
25
30
35
40
1943 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 2009 2015
Dept
h to
Gro
undw
ater
(fee
t)17N03E03D001M (7)
Questionable Measurement
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Feather River
October 27, 2016SGMA GSA Eligible Meeting Series #4 45
0
5
10
15
20
25
30
35
1967 1972 1977 1983 1988 1994 1999 2005 2010 2016De
pth
to G
roun
dwat
er (f
eet)
23N02W25C001M (8)
Questionable Measurement
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Sacramento River
October 27, 2016SGMA GSA Eligible Meeting Series #4 46
0
5
10
15
20
25
2008 2008 2009 2010 2011 2012 2013 2014 2015 2016De
pth
to G
roun
dwat
er (f
eet)
20N01W04J001M (10)
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Sacramento River
October 27, 2016SGMA GSA Eligible Meeting Series #4 47
0
10
20
30
40
50
60
70
1958 1963 1968 1973 1978 1984 1989 1994 1999 2004 2010 2015De
pth
to G
roun
dwat
er (f
eet)
22N01E28J003M (12)
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Big Chico Creek
October 27, 2016SGMA GSA Eligible Meeting Series #4 48
0
5
10
15
20
25
30
35
40
45
50
1992 1997 2002 2007 2012De
pth
to G
roun
dwat
er (f
eet)
22N01E32E004M (14)
Questionable Measurement
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Big Chico Creek
October 27, 2016SGMA GSA Eligible Meeting Series #4 49
0
10
20
30
40
50
60
70
80
90
100
1995 2000 2005 2010 2015
Dept
h to
Gro
undw
ater
(fee
t)21N02E20P001M (15)
Questionable Measurement
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Butte Creek
October 27, 2016SGMA GSA Eligible Meeting Series #4 50
0
5
10
15
20
25
30
35
40
45
50
1947 1952 1957 1962 1967 1973 1978 1983 1988 1993 1999 2004 2009 2014
Dept
h to
Gro
undw
ater
(fee
t)20N02E06Q001M (17)
Questionable Measurement
Ground Surface
Sustainability Indicator #6Depletions of Interconnected Surface Water: Butte Creek
October 27, 2016SGMA GSA Eligible Meeting Series #4 51
Sustainability Indicator #6Depletions of Interconnected Surface Water
October 27, 2016SGMA GSA Eligible Meeting Series #4 52
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)
October 27, 2016SGMA GSA Eligible Meeting Series #4 53
How should governance be structured to make key decisions appropriately?
October 27, 2016SGMA GSA Eligible Meeting Series #4 54
? ?
? ??
Discussion
October 27, 2016SGMA GSA Eligible Meeting Series #4 55