APPENDIX 3A – WELL INVENTORY OF SUPPLY WELLS IN THE BUTTE
SUBBASIN
INTRODUCTION
A supply well inventory was conducted as part of the Butte Periodic Evaluation to compile well construction records for analysis and mapping within the Butte Subbasin and for evaluating potential impacts to beneficial users of groundwater. The inventory began with the full California Department of Water Resources (DWR) Online Well Completion Report (OWSCR) database, which contains all statewide well records. Additional data sources used in the well inventory included the California Statewide Parcels Public feature service (CA Public Parcels) for parcel matching and geocoding of well locations; the dataset is a standardized statewide parcel layer compiled from county assessor data and published by CAL FIRE.
METHODS
Wells were extracted from the statewide OWSCR dataset to include only those within the Butte Subbasin boundary. This reduced the dataset to 3,213 wells, forming the starting point for the inventory (Figure 1). The inventory was checked to verify there were no duplicate records, ensuring each well record is unique and no wells are double counted. Wells classified as “Other” under the Bulletin 118 Well Use column were also removed, and included cathodic protection, dewatering, injection, monitoring, sparging, test, and vapor extraction wells. These well types are not used for groundwater supply. Wells that were flagged as destroyed by their record type were also removed.
Figure 1. Butte Subbasin and Initial Well Inventory
The assessor's parcel numbers (APNs) and addresses in the inventory were standardized, and wells were matched to the CA Public Parcels feature service using the standardized APNs. In the source data, well locations were generally assigned to the center of their Township, Range, and Section (TRS) based on the Public Land Survey System (PLSS) grid, rather than precise parcel coordinates. For wells successfully matched to parcels, coordinates were updated to parcel centroids. For wells where APNs were unavailable for matching, PLSS section centroids were retained.
Once well locations were refined, parcels containing more than one domestic well were reviewed to remove wells from the inventory that were likely replaced. If duplicate records were identified, the newest well on a domestic parcel was retained, and older wells were removed only if constructed before 2010. All other wells were kept, including non-domestic and domestic wells from 2010 or after.
Refined coordinates also revealed that some wells originally mapped to PLSS section centers fell within the Subbasin boundary, but their actual locations were outside the Subbasin. These wells were removed to maintain geographic accuracy. Wells lacking essential construction details, such as completed depth or screen depths were also removed. After all processing steps, the final inventory contains 2,625 wells categorized by type, Domestic, Irrigation, Industrial, Public Supply, and Unknown (Table 1). Coordinate sources for mapping include the newly derived parcel centroids, and the original PLSS section centroids (Figure 2).
Table 1. Well Installations by Decade and Type
Decade Domestic Industrial Irrigation Public Supply Unknown 1910 1 0 1 0 2
1920 0 0 2 0 2
1930 3 0 5 1 5
1940 34 1 57 0 74
1950 121 7 121 3 34
1960 351 11 79 3 17
1970 325 5 295 3 11
1980 157 5 111 2 63
1990 148 4 177 6 13
2000 102 5 66 3 17
2010 24 2 80 0 3
2020 9 0 23 0 0
Note: 31 wells in final inventory are missing completion date; table shows count for 2594 of 2625 wells
Figure 2. Butte Subbasin and Final Well Inventory
RESULTS
Analysis of the refined well inventory shows clear long-term shifts in well installation patterns within the Subbasin. Drilling activity peaked during the 1960s and 1970s, including a pronounced surge in the 1976–1977 drought period, when more wells were constructed than in any other two-year span. Since 1980, installation rates have declined steadily, with only 32 new wells recorded to date in the 2020s (Figure 3).
Figure 3. Yearly Supply Well Installations and Cumulative Count since 1950 Over the same period, well construction has shifted toward deeper completions, average installation depths increased from roughly 150 feet in the 1950s to more than 300 feet in the 2010s and 2020s, and wells deeper than 300 feet now constitute nearly half of all new installations, compared to less than 10 percent prior to 1970. Depth trends vary by use type, with domestic wells remaining predominantly shallow (generally less than 200 feet), while irrigation wells are typically much deeper, most often completed between 301 and more than 500 feet (Table 2, Figure 4).
Table 2. Well Count by Depth and Type
Well Depths Domestic Industrial Irrigation Public
Supply Unknown
0-100 ft 881 14 134 2 176
101-200 ft 363 18 302 5 46
201-300 ft 28 5 220 8 14
301-400 ft 5 1 146 6 6
401-500 ft 3 2 90 0 8
501+ ft 2 1 131 0 8
Figure 4. Supply Well Installations and Well Type by Decade
REFERENCES
California Department of Water Resources (DWR). 2025. Online Well Completion Report (OWSCR) Dataset: Statewide Well Completion Records. California Department of Water Resources.
CAL FIRE, Fire and Resource Assessment Program (FRAP). 2025. California Statewide Parcels – Public Dataset. CAL FIRE FRAP.
Appendix 4A
Representative Monitoring Sites
Groundwater Level Hydrographs
Primary Aquifer Groundwater Level
Representative Monitoring Site Hydrographs
Table 1. Spring and Fall Groundwater Elevation Measurements for Butte Subbasin Primary Aquifer RMS Network (2021-2025) State Well Number MO MT
WY 2021 WY 2022 WY 2023 WY 2024 WY 2025
Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall 17N01E06D001M 59 28 --- --- 59.84 --- 63.07 47.67 62.13 56.97 61.53 58.42 17N01E10A001M 58 31 58.54 47.84 57.64 --- 60.24 56.74 60.14 51.24 59.44 58.34 17N01E17F001M 52 25 55.27 40.12 54.82 43.5 56.76 48.69 56.49 48.82 56.31 50.8 17N01E24A006M 67 44 67.8 66.65 67.52 59.45 68.7 67.09 68.85 67.3 69.12 67.1 17N01W10A004M 60 34 59.68 52 59.49 48.95 62.25 60.26 61.35 60.12 61.205 60.49 17N01W27A003M 54 27 54.42 46.77 53.61 43.43 57.1 54.35 56.3 --- 56.017 54.49 17N02E14A001M 78 50 75.89 --- 76.89 72.99 82.79 77.69 82.19 75.89 82.09 76.69 17N02E14H001M 75 42 74.59 71.99 75.59 71.79 81.89 75.09 80.99 --- --- 73.84 17N03E08K002M 83 58 81.57 79.17 81.97 80.37 85.67 81.57 86.27 82.77 82.67 82.27 18N01E13A002M 75 39 75.44 66.04 74.34 71.14 76.44 74.74 76.64 75.44 76.34 74.74 18N01E15D002M 69 41 70.8 --- 70.2 --- 71.25 68.6 71.3 68.7 71.35 67.09 18N01W02E003M 60 19 --- 49 56.02 51.32 75.17 57.67 74.02 57.48 75.969 57.33 18N01W14B001M 58 19 60.28 45.28 55.68 --- 69.28 54.28 68.48 53.98 69.28 --- 18N01W17G001M 61 30 --- 55.19 --- --- --- --- --- --- 68.89 --- 18N01W22L001M 62 33 61.4 53.2 58.1 53.3 66.4 --- 67.29 --- --- --- 18N02E16F001M 77 53 76.52 74.82 76.02 75.12 78.12 76.12 78.22 75.82 77.82 76.32 18N02E25M001M 81 51 81 77 80 79.1 84.8 80 84 80 83.7 80 18N03E08B003M 93 60 91.2 87.6 88.2 87.3 96.8 86.6 98.1 97.1 105.8 86.5 18N03E18F001M 89 67 91.5 84 90.1 84.8 94.4 88.9 95 89 --- --- 18N03E21G001M 84 70 82.78 80.48 84.28 81.68 87.58 --- --- --- 90.38 85.68 19N01E09Q001M 87 58 88.16 85.56 87.46 85.26 --- --- --- --- 88.86 87.56 19N01E27Q001M 82 33 83.45 77.43 82.05 79.15 84.05 82.45 85 --- --- 82.97 19N01E35B001M 82 52 82.6 79.58 81.76 80.11 83.1 81.68 83.33 81.5 83.005 81.91 19N01W15D002M 72 40 75.8 63.7 74.2 69.2 82.7 72.1 84 --- 82 --- 19N01W22D007M 68 33 64.57 61.33 69.53 60.68 80.63 65.03 80.53 65.78 79.78 67.09 19N01W27R001M 62 22 65.18 48.88 59.78 49.98 75.78 57.88 75.78 58.08 77.38 56.98 19N02E07K004M 99 68 99.66 89.54 98.18 96.76 100.77 97.48 100.11 98.14 100.06 98.51 19N02E13Q001M 114 88 116.22 114.93 116.04 --- 117.36 115.93 117.49 116.13 117.28 115.81 19N03E05N002M 114 65 115.81 111.31 115.01 110.31 114.71 113.61 115.61 113.31 117.41 112.01 20N01E18L003M 102 79 103.26 99.03 102.45 98.84 104.45 99.87 104.55 100.26 103.432 99.47 20N01E35C001M 99 75 99.35 97.95 98.25 97.55 100.35 97.85 100.45 99.65 99.65 98.15 20N01W11N002M 93 70 90.47 --- 93.67 88.07 100.47 91.67 100.37 91.32 99.87 91.47 20N02E15H001M 100 41 --- 91.91 108.32 97.9 109.91 98.7 112.89 99.06 116.05 101.03 20N02E16P001M 107 16 --- --- 113.03 106.03 115.43 --- 118.13 110.13 120.53 111.73 20N02E28N001M 117 93 118.83 116.63 117.63 116.13 119.13 117.33 118.93 117.19 119.18 117.62 21N01E08K002M 104 50 108.64 --- 102.04 94.94 107.24 103.74 114.34 103.74 117.44 102.84 21N01W11A002M 114 92 114.86 113.59 113.35 111.39 118.26 113.88 121.21 113.91 118.06 114.66 21N01W13J003M 103 57 107.4 95.91 104.19 96.46 110.06 103.52 113.66 103.35 115.76 106.17 21N01W23J001M 106 80 105.36 100.96 105.36 100.66 115.66 103.56 114.76 103.26 114.56 104.46 21N01W35K002M 98 74 97.61 93.96 97.64 93.5 106.81 96.25 106.36 95.83 --- 96.51 22N01E32E004M 113 78 117.23 --- 112.72 103.64 117.57 110.14 123.79 --- 125.44 115.54 All values are in feet above mean sea level
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
63.4 59
28 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 110-500 ft bgs
Ground Surface Elevation: 63.4 ft bgs
Aquifer Screened: Primary
17N01E06D001M: 393619N1219101W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
65.3 58
31 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 66-110 ft bgs
Ground Surface Elevation: 65.3 ft bgs
Aquifer Screened: Primary
17N01E10A001M: 393457N1218375W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
59 52
25 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-90
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 130-150 ft bgs
Ground Surface Elevation: 59 ft bgs
Aquifer Screened: Primary
17N01E17F001M: 393257N1218830W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.8 67
44 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 45-55 ft bgs
Ground Surface Elevation: 72.8 ft bgs
Aquifer Screened: Primary
17N01E24A006M: 393169N1218004W005
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
64.3 60
34 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 88-98 ft bgs
Ground Surface Elevation: 64.3 ft bgs
Aquifer Screened: Primary
17N01W10A004M: 393437N1219519W004
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
66.6 54
27 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 160-170 ft bgs
Ground Surface Elevation: 66.6 ft bgs
Aquifer Screened: Primary
17N01W27A003M: 393010N1219528W003
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
84.8 78
50 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 70-102 ft bgs
Ground Surface Elevation: 84.8 ft bgs
Aquifer Screened: Primary
17N02E14A001M: 393337N1217097W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
86.3 75
42 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 60-102 ft bgs
Ground Surface Elevation: 86.3 ft bgs
Aquifer Screened: Primary
17N02E14H001M: 393269N1217096W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
91.3 83
58 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 91.3 ft bgs
Aquifer Screened: Primary
17N03E08K002M: 393383N1216575W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
79.3 75
39 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 80-317 ft bgs
Ground Surface Elevation: 79.3 ft bgs
Aquifer Screened: Primary
18N01E13A002M: 394204N1218040W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.4 69
41 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 56-112 ft bgs
Ground Surface Elevation: 72.4 ft bgs
Aquifer Screened: Primary
18N01E15D002M: 394202N1218537W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
78.5 60
19 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 110-120 ft bgs
Ground Surface Elevation: 78.5 ft bgs
Aquifer Screened: Primary
18N01W02E003M: 394419N1219433W003
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.4 58
19 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 59-173 ft bgs
Ground Surface Elevation: 72.4 ft bgs
Aquifer Screened: Primary
18N01W14B001M: 394199N1219385W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
81.4 61
30 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 48-108 ft bgs
Ground Surface Elevation: 81.4 ft bgs
Aquifer Screened: Primary
18N01W17G001M: 394130N1219913W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.4 62
33 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 76-124 ft bgs
Ground Surface Elevation: 72.4 ft bgs
Aquifer Screened: Primary
18N01W22L001M: 393976N1219617W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
82.3 77
53 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 20-60 ft bgs
Ground Surface Elevation: 82.3 ft bgs
Aquifer Screened: Primary
18N02E16F001M: 394141N1217561W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
89.3 81
51 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 61-220 ft bgs
Ground Surface Elevation: 89.3 ft bgs
Aquifer Screened: Primary
18N02E25M001M: 393816N1217040W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
112.3
93 60
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 156-463 ft bgs
Ground Surface Elevation: 112.3 ft bgs
Aquifer Screened: Primary
18N03E08B003M: 394355N1216575W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
99.8 89
67 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 99.8 ft bgs
Aquifer Screened: Primary
18N03E18F001M: 394164N1216790W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
106.3
84 70
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 106.3 ft bgs
Aquifer Screened: Primary
18N03E21G001M: 394023N1216391W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
92.4 87
58 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 140-200 ft bgs
Ground Surface Elevation: 92.4 ft bgs
Aquifer Screened: Primary
19N01E09Q001M: 395095N1218644W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
87.4 82
33 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 260-280 ft bgs
Ground Surface Elevation: 87.4 ft bgs
Aquifer Screened: Primary
19N01E27Q001M: 394642N1218445W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
86.5 82
52 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 85-135 ft bgs
Ground Surface Elevation: 86.5 ft bgs
Aquifer Screened: Primary
19N01E35B001M: 394635N1218276W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
91 72
40 Manual Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 250-295 ft bgs
Ground Surface Elevation: 91 ft bgs
Aquifer Screened: Primary
19N01W15D002M: 395074N1219670W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
87.4 68
33 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 80-90 ft bgs
Ground Surface Elevation: 87.4 ft bgs
Aquifer Screened: Primary
19N01W22D007M: 394927N1219648W004
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
83.4 62
22 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 68-108 ft bgs
Ground Surface Elevation: 83.4 ft bgs
Aquifer Screened: Primary
19N01W27R001M: 394644N1219514W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
102.7
99 68
Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 140-150 ft bgs
Ground Surface Elevation: 102.7 ft bgs
Aquifer Screened: Primary
19N02E07K004M: 395118N1217880W003
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
119.9
114
88 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 130-210 ft bgs
Ground Surface Elevation: 119.9 ft bgs
Aquifer Screened: Primary
19N02E13Q001M: 394944N1216931W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
142.3
114
65 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
0 10
20 30
40 50
60 70
80 90
100
110
120
130
140
150
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 24-48 ft bgs
Ground Surface Elevation: 142.3 ft bgs
Aquifer Screened: Primary
19N03E05N002M: 395240N1216653W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
107.3
102
79 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 100-110 ft bgs
Ground Surface Elevation: 107.3 ft bgs
Aquifer Screened: Primary
20N01E18L003M: 395771N1219083W002
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
102.4
99 75
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 50-92 ft bgs
Ground Surface Elevation: 102.4 ft bgs
Aquifer Screened: Primary
20N01E35C001M: 395511N1218295W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
107.4
93 70
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 84-170 ft bgs
Ground Surface Elevation: 107.4 ft bgs
Aquifer Screened: Primary
20N01W11N002M: 395982N1219515W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
144
100
41 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
0 10
20 30
40 50
60 70
80 90
100
110
120
130
140
150
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 170-180 ft bgs
Ground Surface Elevation: 144 ft bgs
Aquifer Screened: Primary
20N02E15H001M: 395891N1217303W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
131.8
107
16 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
140
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 131.8 ft bgs
Aquifer Screened: Primary
20N02E16P001M: 395826N1217545W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
123.4
117
93 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 160-277 ft bgs
Ground Surface Elevation: 123.4 ft bgs
Aquifer Screened: Primary
20N02E28N001M: 395539N1217622W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
146
104
50 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
0 10
20 30
40 50
60 70
80 90
100
110
120
130
140
150
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 19-181 ft bgs
Ground Surface Elevation: 146 ft bgs
Aquifer Screened: Primary
21N01E08K002M: 396891N1218854W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
129.3
114
92 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 125-185 ft bgs
Ground Surface Elevation: 129.3 ft bgs
Aquifer Screened: Primary
21N01W11A002M: 396943N1219410W002
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
127.7
103
57 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 355-385 ft bgs
Ground Surface Elevation: 127.7 ft bgs
Aquifer Screened: Primary
21N01W13J003M: 396730N1219206W003
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
121.4
106
80 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 121.4 ft bgs
Aquifer Screened: Primary
21N01W23J001M: 396583N1219394W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
114.4
98 74
Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 75-135 ft bgs
Ground Surface Elevation: 114.4 ft bgs
Aquifer Screened: Primary
21N01W35K002M: 396301N1219407W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
150.9
113
78 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
160
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 85-160 ft bgs
Ground Surface Elevation: 150.9 ft bgs
Aquifer Screened: Primary
22N01E32E004M: 397190N1218983W001
Very Deep Aquifer Groundwater Level
Representative Monitoring Site Hydrographs
Table 1. Spring and Fall Groundwater Elevation Measurements for Butte Subbasin Very Deep Aquifer RMS Network (2021-2025) State Well Number MO MT
WY 2021 WY 2022 WY 2023 WY 2024 WY 2025
Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall 17N01E24A003M 70 39 71 59.9 67.97 55.8 70.11 68.95 73.1 69.05 73.55 69.39 17N01W10A001M 55 4 58.54 --- 55.26 37.32 57.91 52.93 62.1 52.86 62.655 54.16 18N01E35L001M 69 34 71.78 58.87 68.85 56.99 71.36 69.35 73.51 67.3 73.528 68.58 18N01W02E001M 68 20 --- 56.84 69 56.39 74.69 68.69 76.64 68.74 77.469 69.02 19N01E35B002M 87 54 89.36 82.2 86.21 79.38 87.81 86.89 90 87.53 90.615 87.96 19N01W22D004M 76 40 78.58 69.06 74.88 65.98 78.88 74.48 81.38 75.54 82.28 75.7 19N02E13Q003M 114 86 116.28 113.98 115.63 --- 116.96 115.38 117.23 115.43 117.2 115.18 20N01E18L001M 96 45 99.78 89.6 94.72 87.24 97.8 94.59 101.22 95.68 102.97 96.74 21N01W11A001M 107 75 112.6 100.52 108.2 100.97 114.22 107.41 117.79 106.67 119.76 110.12 21N01W13J001M 102 66 107.15 98.14 102.42 93.81 108.16 102.04 113.04 101.28 114.48 104.79 All values in feet above mean sea level
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.8 70
39 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 770-790 ft bgs
Ground Surface Elevation: 72.8 ft bgs
Aquifer Screened: Very Deep
17N01E24A003M: 393169N1218004W002
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
64.3 55
4 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 770-800 ft bgs
Ground Surface Elevation: 64.3 ft bgs
Aquifer Screened: Very Deep
17N01W10A001M: 393437N1219519W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
70 69
34 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-80
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 816-836 ft bgs
Ground Surface Elevation: 70 ft bgs
Aquifer Screened: Very Deep
18N01E35L001M: 393678N1218288W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
78.5 68
20 Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 719-729 ft bgs
Ground Surface Elevation: 78.5 ft bgs
Aquifer Screened: Very Deep
18N01W02E001M: 394419N1219433W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
86.5 87
54 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 930-950 ft bgs
Ground Surface Elevation: 86.5 ft bgs
Aquifer Screened: Very Deep
19N01E35B002M: 394634N1218278W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
87.4 76
40 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 780-790 ft bgs
Ground Surface Elevation: 87.4 ft bgs
Aquifer Screened: Very Deep
19N01W22D004M: 394927N1219648W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
119.9
114
86 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 670-680 ft bgs
Ground Surface Elevation: 119.9 ft bgs
Aquifer Screened: Very Deep
19N02E13Q003M: 394944N1216932W002
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
107.3
96 45
Manual Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 767-894 ft bgs
Ground Surface Elevation: 107.3 ft bgs
Aquifer Screened: Very Deep
20N01E18L001M: 395771N1219082W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
129.3
107
75 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 810-1,280 ft bgs
Ground Surface Elevation: 129.3 ft bgs
Aquifer Screened: Very Deep
21N01W11A001M: 396943N1219410W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
127.7
102
66 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
120
130
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 780-820 ft bgs
Ground Surface Elevation: 127.7 ft bgs
Aquifer Screened: Very Deep
21N01W13J001M: 396730N1219206W001
Interconnected Surface Water
Representative Monitoring Site Hydrographs
Table 1. Spring and Fall Groundwater Elevation Measurements for Butte Subbasin Interconnected Surface Water RMS Network (2021-2025) State Well Number MO MT
WY 2021 WY 2022 WY 2023 WY 2024 WY 2025
Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall 17N03E05C003M 80 47 82.28 81.68 69.98 81.78 92.38 85.48 91.78 83.68 92.18 86.18 17N03E16N001M 71 42 76.77 65.37 69.57 --- 69.27 --- --- 77.07 78.27 77.67 18N01E05D002M 71 53 --- --- --- --- --- 74.1 --- --- --- --- 18N01W14B001M 58 28 60.28 45.28 55.68 69.28 54.28 68.48 53.98 69.28 --- 18N01W17G001M 61 44 --- 55.19 --- --- --- --- --- --- 68.89 --- 18N02E16F001M 77 63 76.52 74.82 76.02 75.12 78.12 76.12 78.22 75.82 77.82 76.32 18N03E21G001M 84 68 82.78 80.48 84.28 81.68 87.58 --- --- --- 90.38 85.68 19N01E35B001M 82 62 82.6 79.58 81.76 80.11 83.1 81.68 83.33 81.5 83.005 81.91 19N01W22D007M 68 47 64.57 61.33 69.53 60.68 80.63 65.03 80.53 65.78 79.78 67.09 19N01W27R001M 62 34 65.18 48.88 59.78 49.98 75.78 57.88 75.78 58.08 77.38 56.98 20N01E35C001M 99 85 99.35 97.95 98.25 97.55 100.35 97.85 100.45 99.65 99.65 98.15 20N02E15H002M 121 105 --- --- --- --- 116.92 113.42 120.3 114.37 122.66 116.18 All values are in feet above mean sea level
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
97.3 80
47 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 97.3 ft bgs
Aquifer Screened: Primary
17N03E05C003M: 393600N1216628W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
87.3 71
42 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 87.3 ft bgs
Aquifer Screened: Primary
17N03E16N001M: 393222N1216472W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
79 71
53 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 79 ft bgs
Aquifer Screened: Primary
18N01E05D002M: 394493N1218914W002
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
72.4 58
28 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-70
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 59-173 ft bgs
Ground Surface Elevation: 72.4 ft bgs
Aquifer Screened: Primary
18N01W14B001M: 394199N1219385W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
81.4 61
44 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 48-108 ft bgs
Ground Surface Elevation: 81.4 ft bgs
Aquifer Screened: Primary
18N01W17G001M: 394130N1219913W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
82.3 77
63 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 20-60 ft bgs
Ground Surface Elevation: 82.3 ft bgs
Aquifer Screened: Primary
18N02E16F001M: 394141N1217561W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
106.3
84 68
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: Unknown
Ground Surface Elevation: 106.3 ft bgs
Aquifer Screened: Primary
18N03E21G001M: 394023N1216391W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
86.5 82
62 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 85-135 ft bgs
Ground Surface Elevation: 86.5 ft bgs
Aquifer Screened: Primary
19N01E35B001M: 394635N1218276W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
87.4 68
47 Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 80-90 ft bgs
Ground Surface Elevation: 87.4 ft bgs
Aquifer Screened: Primary
19N01W22D007M: 394927N1219648W004
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
83.4 62
34 Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-60
-50
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 68-108 ft bgs
Ground Surface Elevation: 83.4 ft bgs
Aquifer Screened: Primary
19N01W27R001M: 394644N1219514W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
102.4
99 85
Manual Measurement
Questionable Hand
Measurement
Ground Surface Elevation
Measurable Objective
Minimum Threshold
-40
-30
-20
-10 0
10 20
30 40
50 60
70 80
90 100
110
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 50-92 ft bgs
Ground Surface Elevation: 102.4 ft bgs
Aquifer Screened: Primary
20N01E35C001M: 395511N1218295W001
1970
197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018202020222024
WATER YEAR
-100
10 20
30 40
50 60
70 80
90 100
110
120
130
140
150
GROUNDWATER ELEVATION IN FEET ABOVE MEAN SEA LEVEL
144.1
121
105
Manual Measurement
Questionable Hand
Measurement
Transducer
Ground Surface Elevation
Measurable Objective
Minimum Threshold
0 10
20 30
40 50
60 70
80 90
100
110
120
130
140
150
DEPTH TO WATER IN FEET BELOW GROUND SURFACE
Wet
Above Normal
Below Normal
Dry
Critical
Climate Classification
Screen Interval: 55-65 ft bgs
Ground Surface Elevation: 144.1 ft bgs
Aquifer Screened: Primary
20N02E15H002M: 395892N1217304W001
Appendix 4B
MT/MO Revision Technical Memorandum
Summary of Potential MO/MT Adjustments 1 05/10/2023 (11/05/2024)
TECHNICAL MEMORANDUM (TM)
To: Butte Subbasin GSA Managers
From: Davids Engineering, Inc.
Date: 05/10/2023
Updated: 11/05/2024
Subject: Summary of Need for Measurable Objective (MO) and Minimum Threshold (MT) Adjustments in the Butte Subbasin and Potential MO/MT Adjustments Note: As described below, the adjustments to Measurable Objectives (MOs) and Minimum Thresholds (MTs) in the Butte Subbasin (Subbasin) are not due to changes to the methodology (or underlying objectives) used to calculate MOs/MTs, as described in the Groundwater Sustainability Plan (GSP).
The MOs/MTs have been recalculated based on the best available information at the time of the 2022 Annual Report, which differs from the information (groundwater level data) used to calculate the original MOs/MTs shown in the GSP. This TM was updated in Fall 20241 .
1 Summary of Changes to Measurable Objectives (MOs)
During development of the 2022 Annual Report on GSP implementation and Subbasin conditions, it was observed that actual historical groundwater elevations at some of the Representative Monitoring Site (RMS) locations did not align with the Measurable Objective (MO), as outlined and identified in the GSP.
In most cases, the MO was notably lower than historical groundwater levels. MO values in the GSP were calculated as “the average of the most recent five years of elevations available at each well. The MO is not a running average and will not be changed over time in response to additional monitoring results.” (see Appendix 4.A of the Butte Subbasin GSP). At the time, the “last five years” generally corresponded to 2012‐2017 (Table 2). It should also be noted that Interim Milestones (IMs) for the Butte Subbasin are set equal to the MOs.
Davids Engineering (DE) investigated these differences in an effort to better understand the original cause of the misalignment of MOs with historical groundwater levels; the investigation included review of GSP materials, review of available data at RMS well locations, and coordination with the subconsultant (Woodard & Curran, W&C) that helped prepare Sustainable Management Criteria (SMC) and MOs for the Butte Subbasin GSP. The cause of the issue was unable to be isolated to a single source, but it was determined that it was influenced by both use of incorrect data when calculating the original MOs (e.g., use of modeled values rather the actual observed values) and additional data and corrections to existing data (e.g., adjustments to the elevations for the ground surface, reference point, or 1 The following updates to this TM were completed in Fall 2024: Corrections were made to the MO and MT values reported from the GSP (after differences were noted between values in GSP and those reported here for GSP at some RMS), text was added clarifying that Interim Milestones (IMs) are equal to MOs for the Butte Subbasin, and the same recalculation of MOs and MTs for Groundwater Level RMS (previously completed and documented in Sections 1 through 3) was completed for the MOs and MTs for Interconnected Surface Water RMS (not previously completed or documented, now included as Section 4).
Summary of Potential MO/MT Adjustments 2 05/10/2023 (11/05/2024) groundwater level observations) being uploaded by the California Department of Water Resources (DWR) for these well locations in the time since GSP development.
DE recalculated the MOs at each of the RMS sites (41 in the Primary Aquifer, 10 in the Very Deep Aquifer) based on available data from DWR2 at the time of 2022 Annual Report development and the original 5‐year period used to calculate MOs for the GSP. Most data from the DWR dataset are measurements taken manually four times per year reflecting spring, summer, and fall groundwater elevations. However, the dataset also includes measurements recorded more frequently (e.g., monthly, weekly, or daily) for some wells during some periods of time. This dataset also includes daily measurements from DWR's automated monitoring network of groundwater sites when available (e.g., not all monitoring wells have a data logger). Table 1 includes a summary of changes to the MOs based on this recalculation. The majority of the wells show either no change or increases in MOs (i.e., a higher elevation relative to mean sea level, a shallower depth‐to‐water from the ground surface) from this recalculation; the average change in the Primary Aquifer is an increase of four feet. Table 2 summarizes the changes for RMS wells individually and includes the State Well Number (SWN), the 5‐year period over which the average groundwater elevation is calculated (based on last available measurement at the time of MO calculation for inclusion in the GSP), aquifer, MO as shown in the GSP, recalculated MO, and the difference between the two. In total, the MOs for 33 of 41 RMS wells (80%) in the Primary Aquifer changed and four of 10 Very Deep RMS wells (40%) changed.
Three examples of changes to individual MOs, including hydrographs displaying groundwater elevations, are presented to illustrate results at individual RMS wells. Figure 1 depicts the hydrograph for SWN 17N03E08K002M used to develop the MO for the GSP, the hydrograph available from DWR at the time of the 2022 Annual Report, and the MOs from the GSP, and from the recent recalculation. It shows an increase in elevation of five feet from 78 to 83 feet above mean sea level in the recalculation of the MO.
Figure 2 depicts the hydrographs and MOs for SWN 20N01E35C001M and shows an increase in elevation of two feet from 97 to 99 feet above mean sea level in the recalculation of the MO. Figure 3 depicts the hydrographs and MOs for SWN 21N01E08K002M and shows an increase in elevation of six feet from 98 to 104 feet above mean sea level in the recalculation of the MO. For all three of these hydrographs, the most recently available groundwater elevations (Fall 2022) lie below the recalculated MO, but above the MO calculated as part of the GSP. This is influenced by recent drought and, assuming drought does not persist, recovery of groundwater levels to a level above the recalculated MO would be expected.
Table 1. Summary of Measurable Objective (MO) adjustments by aquifer depicting the total RMS wells, RMS wells with a change to MO based on groundwater elevations available at the time of 2022 Annual Report development, and the average, minimum, and maximum changes to MOs. Positive change numbers represent higher elevations relative to mean sea level, or shallower depths to water from the ground surface, and vice versa.
Aquifer
Total
RMS
Wells
RMS Wells
with MO
Change
Average
Change
(ft)
Minimum
Change
(ft)
Maximum
Change
(ft)
Primary 41 34 5 ‐1 12
Very Deep 10 1 0 0 1
2 Periodic groundwater level measurements are available at: https://data.cnra.ca.gov/dataset/periodic‐ groundwater‐level‐measurements. Data were downloaded on February 17, 2023.
Summary of Potential MO/MT Adjustments 3 05/10/2023 (11/05/2024) Table 2. Summary of MO adjustments for each of the 51 RMS wells that depicts State Well Number (SWN), Principal Aquifer the well is located in, 5‐Year Period for Measurable Objective (MO) Calculations, the MO calculated for the GSP (GSP MO), the recalculated MO for the 2022 Annual Report (Recalculated MO) expressed in feet above mean sea level, and the difference between the two MOs.
SWN Principal
Aquifer
Initial
Date of 5‐
Year
Period
Final
Date of 5‐
Year
Period
GSP
MO (ft
amsl)
Recalculated
MO (ft amsl)
MO
Difference
(ft)
17N01E06D001M Primary 8/2/12 8/2/17 57 59 2
17N01E10A001M Primary 3/13/12 3/13/17 48 58 10
17N01E17F001M Primary 8/2/12 8/2/17 52 52 0
17N01E24A006M Primary 8/2/12 8/2/17 67 67 0
17N01W10A004M Primary 8/2/12 8/2/17 59 60 1
17N01W27A003M Primary 8/2/12 8/2/17 53 54 1
17N02E14A001M Primary 8/2/12 8/2/17 70 78 8
17N02E14H001M Primary 7/3/12 7/3/17 63 75 12
17N03E08K002M Primary 8/3/12 8/3/17 78 83 5
18N01E13A002M Primary 8/3/12 8/3/17 67 75 8
18N01E15D002M Primary 8/3/12 8/3/17 65 69 4
18N01W02E003M Primary 7/31/12 7/31/17 60 60 0
18N01W14B001M Primary 3/14/12 3/14/17 46 58 12
18N01W17G001M Primary 3/14/12 3/14/17 60 61 1
18N01W22L001M Primary 7/31/12 7/31/17 55 62 7
18N02E16F001M Primary 8/3/12 8/3/17 69 77 8
18N02E25M001M Primary 8/2/12 8/2/17 71 81 10
18N03E08B003M Primary 8/3/12 8/3/17 83 93 10
18N03E18F001M Primary 8/3/12 8/3/17 86 89 3
18N03E21G001M Primary 8/3/12 8/3/17 75 84 7
19N01E09Q001M Primary 8/3/12 8/3/17 81 87 6
19N01E27Q001M Primary 8/3/12 8/3/17 78 82 4
19N01E35B001M Primary 8/3/12 8/3/17 83 82 1
19N01W15D002M Primary 6/26/12 6/27/17 66 72 6
19N01W22D007M Primary 7/31/12 7/31/17 67 68 ‐1
19N01W27R001M Primary 7/31/12 7/31/17 50 62 12
19N02E07K004M Primary 8/3/12 8/3/17 98 99 1
19N02E13Q001M Primary 8/4/12 8/4/17 115 114 ‐1
19N03E05N002M Primary 8/4/12 8/4/17 105 114 9
20N01E18L003M Primary 8/2/12 8/2/17 102 102 0
20N01E35C001M Primary 4/13/10 4/13/15 96 99 3
20N01W11N002M Primary 8/3/12 8/3/17 85 93 8
20N02E15H001M Primary 8/4/12 8/4/17 100 100 0
20N02E16P001M Primary 8/4/12 8/4/17 102 107 5
Summary of Potential MO/MT Adjustments 4 05/10/2023 (11/05/2024) SWN Principal
Aquifer
Initial
Date of 5‐
Year
Period
Final
Date of 5‐
Year
Period
GSP
MO (ft
amsl)
Recalculated
MO (ft amsl)
MO
Difference
(ft)
20N02E28N001M Primary 8/3/12 8/3/17 111 117 6
21N01E08K002M Primary 7/31/12 7/31/17 97 104 7
21N01W11A002M Primary 7/31/12 7/31/17 114 114 0
21N01W13J003M Primary 7/31/12 7/31/17 103 103 0
21N01W23J001M Primary 7/31/12 7/31/17 98 106 8
21N01W35K002M Primary 8/4/12 8/4/17 96 98 2
22N01E32E004M Primary 7/31/12 7/31/17 112 113 1
17N01E24A003M Very Deep 6/30/12 6/27/17 70 70 0
17N01W10A001M Very Deep 7/3/12 6/27/17 54 55 1
18N01E35L001M Very Deep 7/5/12 6/27/17 69 69 0
18N01W02E001M Very Deep 7/4/12 6/27/17 68 68 0
19N01E35B002M Very Deep 7/6/12 6/27/17 87 87 0
19N01W22D004M Very Deep 7/1/12 6/27/17 76 76 0
19N02E13Q003M Very Deep 6/29/12 6/27/17 114 114 0
20N01E18L001M Very Deep 6/27/12 6/27/17 96 96 0
21N01W11A001M Very Deep 7/2/12 6/27/17 107 107 0
21N01W13J001M Very Deep 7/8/12 6/27/17 102 102 0
2 Summary of Changes to Minimum Thresholds (MTs)
Based on the observed differences between MOs calculated as part of the GSP and actual historical groundwater elevations at RMS locations available at the time of 2022 Annual Report (as described above), it was determined that Minimum Thresholds (MTs) would also need to be recalculated, since the methodology used to calculate MTs is also dependent on historical groundwater elevations. As described in the GSP, MT values were calculated “based on the shallowest3 of the following criteria:
1. Shallowest 7th percentile of domestic well depths to protect at least 93% of the domestic wells in DWR’s well completion database, and
2. 100% of historical range or 20 feet4
, whichever is greater, to protect conjunctive use of
groundwater.
If the shallowest value from the two criteria above is shallower than the deepest observed groundwater level, the MT is set 10 feet deeper than the deepest observed groundwater level.” (see Appendix 4.A of the Butte Subbasin GSP).
3 Shallowest is expressed in reference to the ground surface (i.e., the shallowest depth is the one closest to the ground surface). 4 Although not explicitly stated in the GSP text, the “100% of historical range or 20 feet, whichever is greater” is calculated as the distance below the minimum observed water level at each well.
Summary of Potential MO/MT Adjustments 5 05/10/2023 (11/05/2024) Davids Engineering (DE) recalculated MTs using historical groundwater elevations at RMS locations based on the dataset described above for the MO calculations5 and the shallowest 7th percentile of domestic well depths as determined during GSP preparation. Table 3 includes a summary of changes to the MTs based on this recalculation. The criteria used to calculate the MTs changed for 15 of the 51 total RMS wells (27%). The MTs themselves changed for 28 of 51 RMS wells (55%). The average change in the Primary Aquifer was an increase in groundwater elevations (i.e., higher elevations relative to mean sea level, shallower depth‐to‐water from the ground surface) of nine feet, and the average change in the Very Deep Aquifer was a decrease in groundwater elevations of one foot. The MT elevation changes in the Primary and Very Deep Aquifers ranged from zero to 47 feet and from one to negative seven feet, respectively.
Table 3. Summary of Minimum Threshold (MT) adjustments by aquifer depicting the total RMS wells, RMS wells with a change in MT criteria, RMS wells with change to the MT based on groundwater elevations available at the time of 2022 Annual Report development, and the average, minimum, and maximum changes to MTs. Positive change numbers represent higher elevations relative to mean sea level, or shallower depths to water from the ground surface, and vice versa.
Aquifer
Total
RMS
Wells
RMS Wells
with MT
Criteria Change
RMS Wells
with MT
Change
Average
Change
(ft)
Minimum
Change
(ft)
Maximum
Change
(ft)
Primary 41 11 30 3 ‐36 27
Very Deep 10 3 4 ‐1 ‐7 1
Table 4 summarizes the changes for RMS wells individually and includes the SWN, principal aquifer, the MT calculation criteria/methodology and MT elevation from the GSP, the recalculated MT calculation criteria/methodology, and recalculated MT elevation (based on groundwater elevations available at the time of 2022 Annual Report development), and the difference between the two MT elevations.
To evaluate potential impacts on sustainability under the GSP due to changes to MTs, Table 5 includes the SWN, principal aquifer, date of the most recently available groundwater measurement (typically Fall 2022 or Winter 2023), the measurement itself, and the distance to the MT. Importantly, although MT elevations on average have increased due to the recalculation, based on the most recent measurement (disregarding questionable measurements), the groundwater levels at all RMS sites were still above the MT elevations. On average across all RMS wells, groundwater elevations in Table 5 were 30 feet higher than the MT elevations.
The three example hydrographs in Figures 1 through 3 (for SWNs 17N03E08K002M, 20N01E35C001M, and 21N01E08K002M) also depict the MTs from the GSP and the recalculated MTs. The recalculated MT shows an increase in groundwater elevation in each of the three instances, ranging from four to 13 feet. 5 The period of record utilized for the recalculation of MTs at each RMS well was the earliest available measurement through the latest date used for the 5‐year period in calculation of MOs (i.e., 08/04/2017).
Summary of Potential MO/MT Adjustments 6 05/10/2023 (11/05/2024) 3 Conclusions and Recommendations
The recalculated MOs were included in the 2022 Annual Report for the Butte Subbasin, along with the following note: “MOs have been recalculated based on DWR data retrieved from the California Natural Resource Agency Open Data Portal in February 2023. More information on this change, subject to revision, will be documented in a forthcoming technical memo.” This technical memo documents adjustments to MOs and MTs based on the best available information at the time of the 2022 Annual Report (which, as described above, differs from the information used to calculate MOs and MTs for the GSP). As noted initially, these adjustments are not due to changes to the methodology (or underlying policy objectives) used to calculated MOs/MTs, but due to differing historical groundwater elevation data available now, as compared to the dataset used at the time of GSP preparation.
The adjustments to MOs were calculated in February 2023, documented in March 2023, and included in the 2022 Annual Report, which was due by April 1, 2023. The adjustments to MTs were calculated in April 2023, following 2022 Annual Report submittal, and were not included in the 2022 Annual Report.
The decision for how to proceed with addressing adjustments to MOs/MTs in the GSP will need to be decided by the Butte Subbasin GSAs. Potential options include:
1. Coordinate with DWR immediately to determine requirements and procedures for updating MOs and MTs in the GSP, Annual Reports, and SGMA Data Portal
2. Do not address until DWR’s GSP determination is released (expected before or by 1/31/2024):
a. If GSP is approved with recommended corrective actions, address the adjustments to MOs and MTs along with other recommended corrective actions during the 5‐Year Update.
b. If GSP is incomplete with required corrective actions, address the adjustments to MOs and MTs along with required corrective actions within 180 days of determination.
Additionally, the GSA Managers will need to consider how to address potential adjustments to MOs and MTs in future Annual Reports (only adjusted MOs were prepared in time for the 2022 Annual Report).
Future efforts could also consider whether only manual measurements or a combination of data collected manually and via data loggers are included in the dataset to calculate MOs and MTs.
Summary of Potential MO/MT Adjustments 7 05/10/2023 (11/05/2024) Table 4. Summary of MT adjustments for each of the 51 RMS wells summarizing GSP and recalculated MT results.
SWN Principal Aquifer GSP MT Methodology (GSP) GSP MT (ft amsl) Recalculated MT Methodology (GSP) Recalculated MT (ft amsl) MT Difference (ft) 17N01E06D001M Primary 20 feet below Historical Low 28 20 feet below Historical Low 28 017N01E10A001M Primary 20 feet below Historical Low 24 20 feet below Historical Low 31 717N01E17F001M Primary 20 feet below Historical Low 25 20 feet below Historical Low 25 017N01E24A006M Primary 20 feet below Historical Low 44 20 feet below Historical Low 44 017N01W10A004M Primary 20 feet below Historical Low 26 20 feet below Historical Low 34 817N01W27A003M Primary 20 feet below Historical Low 23 20 feet below Historical Low 27 417N02E14A001M Primary Shallowest 7th Percentile of Domestic Well Depths 29 20 feet below Historical Low 50 2117N02E14H001M Primary 10 feet below Historical Low 33 Shallowest 7th Percentile of Domestic Well Depths 42 917N03E08K002M Primary 20 feet below Historical Low 54 20 feet below Historical Low 58 418N01E13A002M Primary 100% Historical Range 26 20 feet below Historical Low 39 1318N01E15D002M Primary 100% Historical Range 14 20 feet below Historical Low 41 2718N01W02E003M Primary 100% Historical Range 28 100% Historical Range 19 ‐918N01W14B001M Primary 100% Historical Range 15 100% Historical Range 19 418N01W17G001M Primary 100% Historical Range 34 100% Historical Range 30 ‐418N01W22L001M Primary 100% Historical Range 23 20 feet below Historical Low 33 1018N02E16F001M Primary 10 feet below Historical Low 43 10 feet below Historical Low 53 1018N02E25M001M Primary 100% Historical Range 32 20 feet below Historical Low 51 1918N03E08B003M Primary 10 feet below Historical Low 54 10 feet below Historical Low 60 618N03E18F001M Primary 100% Historical Range 56 20 feet below Historical Low 67 1118N03E21G001M Primary 10 feet below Historical Low 57 Shallowest 7th Percentile of Domestic Well Depths 70 1319N01E09Q001M Primary 100% Historical Range 50 20 feet below Historical Low 58 819N01E27Q001M Primary 100% Historical Range 40 100% Historical Range 33 ‐719N01E35B001M Primary 20 feet below Historical Low 52 20 feet below Historical Low 52 019N01W15D002M Primary 20 feet below Historical Low 38 100% Historical Range 40 2 Summary of Potential MO/MT Adjustments 8 05/10/2023 (11/05/2024) SWN Principal Aquifer GSP MT Methodology (GSP) GSP MT (ft amsl) Recalculated MT Methodology (GSP) Recalculated MT (ft amsl) MT Difference (ft) 19N01W22D007M Primary 100% Historical Range 38 100% Historical Range 33 ‐519N01W27R001M Primary 100% Historical Range 19 100% Historical Range 22 319N02E07K004M Primary 20 feet below Historical Low 68 20 feet below Historical Low 68 019N02E13Q001M Primary 20 feet below Historical Low 88 20 feet below Historical Low 88 019N03E05N002M Primary 100% Historical Range 65 100% Historical Range 65 020N01E18L003M Primary 20 feet below Historical Low 79 20 feet below Historical Low 79 020N01E35C001M Primary 20 feet below Historical Low 69 20 feet below Historical Low 75 620N01W11N002M Primary 100% Historical Range 57 20 feet below Historical Low 70 1320N02E15H001M Primary 100% Historical Range 66 100% Historical Range 41 ‐2520N02E16P001M Primary 100% Historical Range 52 100% Historical Range 16 ‐3620N02E28N001M Primary 100% Historical Range 75 20 feet below Historical Low 93 1821N01E08K002M Primary 100% Historical Range 67 100% Historical Range 50 ‐1721N01W11A002M Primary 20 feet below Historical Low 92 20 feet below Historical Low 92 021N01W13J003M Primary 100% Historical Range 68 100% Historical Range 57 ‐1121N01W23J001M Primary 100% Historical Range 68 100% Historical Range 80 1221N01W35K002M Primary 20 feet below Historical Low 74 20 feet below Historical Low 74 022N01E32E004M Primary Shallowest 7th Percentile of Domestic Well Depths 78 Shallowest 7th Percentile of Domestic Well Depths 78 017N01E24A003M Very Deep 100% Historical Range 43 20 feet below Historical Low 39 ‐417N01W10A001M Very Deep 100% Historical Range 4 100% Historical Range 4 018N01E35L001M Very Deep 100% Historical Range 34 100% Historical Range 34 018N01W02E001M Very Deep 100% Historical Range 20 100% Historical Range 20 019N01E35B002M Very Deep 100% Historical Range 56 20 feet below Historical Low 54 ‐219N01W22D004M Very Deep 100% Historical Range 40 100% Historical Range 40 019N02E13Q003M Very Deep 100% Historical Range 93 20 feet below Historical Low 86 ‐720N01E18L001M Very Deep 100% Historical Range 45 100% Historical Range 45 021N01W11A001M Very Deep 100% Historical Range 74 100% Historical Range 75 1 Summary of Potential MO/MT Adjustments 9 05/10/2023 (11/05/2024) SWN Principal Aquifer GSP MT Methodology (GSP) GSP MT (ft amsl) Recalculated MT Methodology (GSP) Recalculated MT (ft amsl) MT Difference (ft) 21N01W13J001M Very Deep 100% Historical Range 66 100% Historical Range 66 0 Table 5. Summary of most recent groundwater elevation measurement and vertical distance to the recalculated MT for each of the 51 RMS wells summarizing GSP and recalculated MT results. All recent measurements have been above recalculated MT elevations.
SWN Principal Aquifer Date of Most Recent Measurement Groundwater Elevation (ft amsl) Distance to Recalculated MT (ft) 17N01E06D001M Primary 1/24/2023 62 3417N01E10A001M Primary 3/7/2022 58 2717N01E17F001M Primary 10/12/2022 44 1917N01E24A006M Primary 10/12/2022 59 1517N01W10A004M Primary 1/24/2023 63 2917N01W27A003M Primary 1/24/2023 56 2917N02E14A001M Primary 1/19/2023 81 3117N02E14H001M Primary 1/19/2023 78 3617N03E08K002M Primary 10/18/2022 80 2218N01E13A002M Primary 10/12/2022 71 3218N01E15D002M Primary 8/1/2022 61 2018N01W02E003M Primary 10/17/2022 51 3218N01W14B001M Primary 3/11/2022 56 3718N01W17G001M Primary 10/14/2021 55 2518N01W22L001M Primary 3/9/2020 63 3018N02E16F001M Primary 10/12/2022 75 2218N02E25M001M Primary 10/12/2022 79 2818N03E08B003M Primary 10/18/2022 87 2718N03E18F001M Primary 7/7/2021 83 1618N03E21G001M Primary 10/18/2022 82 1219N01E09Q001M Primary 10/13/2022 85 2719N01E27Q001M Primary 10/12/2022 79 4619N01E35B001M Primary 10/13/2022 80 2819N01W15D002M Primary 10/17/2022 69 29 Summary of Potential MO/MT Adjustments 10 05/10/2023 (11/05/2024) SWN Principal Aquifer Date of Most Recent Measurement Groundwater Elevation (ft amsl) Distance to Recalculated MT (ft) 19N01W22D007M Primary 10/17/2022 61 2819N01W27R001M Primary 10/17/2022 50 2819N02E07K004M Primary 10/13/2022 97 2919N02E13Q001M Primary 8/3/2022 111 2319N03E05N002M Primary 10/17/2022 110 4520N01E18L003M Primary 10/12/2022 99 2020N01E35C001M Primary 10/13/2022 98 2320N01W11N002M Primary 10/14/2022 88 1820N02E15H001M Primary 10/13/2022 98 5720N02E16P001M Primary 10/13/2022 106 9020N02E28N001M Primary 10/13/2022 116 2321N01E08K002M Primary 1/20/2023 101 5121N01W11A002M Primary 10/14/2022 111 1921N01W13J003M Primary 1/20/2023 105 4821N01W23J001M Primary 10/13/2022 101 2121N01W35K002M Primary 10/13/2022 94 2022N01E32E004M Primary 1/20/2023 111 3317N01E24A003M Very Deep 10/12/2022 56 1717N01W10A001M Very Deep 1/24/2023 50 4618N01E35L001M Very Deep 10/12/2022 57 2318N01W02E001M Very Deep 10/17/2022 56 3619N01E35B002M Very Deep 10/13/2022 79 2519N01W22D004M Very Deep 10/17/2022 66 2619N02E13Q003M Very Deep 8/3/2022 107 2120N01E18L001M Very Deep 10/12/2022 87 4221N01W11A001M Very Deep 10/14/2022 101 2621N01W13J001M Very Deep 1/20/2023 102 36 Summary of Potential MO/MT Adjustments 11 05/10/2023 (11/05/2024) Figure 1. Hydrograph for SWN 17N03E08K002M depicting the record of groundwater elevations used to calculate the Measurable Objective (MO) and Minimum Threshold (MT) for the Butte Subbasin GSP (GSP 2021) and the groundwater elevations obtained in February 2023 (DWR 2023) for use in the 2022 Annual Report that were used to recalculate the MO and MT (2022 Annual Report). The MO/MT from the Butte Subbasin GSP and the recalculated MO/MT are also depicted.
50556065707580859095
1/2000 9/2002 6/2005 3/2008 12/2010 9/2013 6/2016 3/2019 11/2021 Groundwater Elevation (ft amsl)
Date
SWN: 17N03E08K002M
Groundwater Elevations (DWR 2023) Groundwater Elevations (GSP 2021)Measurable Objective (2022 Annual Report) Measurable Objective (GSP 2021)Minimum Threshold (2022 Annual Report) Minimum Threshold (GSP 2021) Summary of Potential MO/MT Adjustments 12 05/10/2023 (11/05/2024) Figure 2. Hydrograph for SWN 20N01E35C001M depicting the record of groundwater elevations used to calculate the MO and MT for the Butte Subbasin GSP (GSP 2021) and the groundwater elevations obtained in February 2023 (DWR 2023) for use in the 2022 Annual Report that were used to recalculate the MO and MT (2022 Annual Report). The MO/MT from the Butte Subbasin GSP and the recalculated MO/MT are also depicted. 65707580859095
100105
1/1947 9/1960 5/1974 1/1988 10/2001 6/2015
Groundwater Elevation (ft amsl)
Date
SWN: 20N01E35C001M
Groundwater Elevations (DWR 2023) Groundwater Elevations (GSP 2021)Measurable Objective (2022 Annual Report) Measurable Objective (GSP 2021)Minimum Threshold (2022 Annual Report) Minimum Threshold (GSP 2021) Summary of Potential MO/MT Adjustments 13 05/10/2023 (11/05/2024) Figure 3. Hydrograph for SWN 21N01E08K002M depicting the record of groundwater elevations used to calculate the MO and MT for the Butte Subbasin GSP (GSP 2021) and the groundwater elevations obtained in February 2023 (DWR 2023) for use in the 2022 Annual Report that were used to recalculate the MO and MT (2022 Annual Report). The MO/MT from the Butte Subbasin GSP and the recalculated MO/MT are also depicted. 35455565758595
105115125135
1/2000 9/2002 6/2005 3/2008 12/2010 9/2013 6/2016 3/2019 11/2021 Groundwater Elevation (ft amsl)
Date
SWN: 21N01E08K002M
Groundwater Elevations (DWR 2023) Groundwater Elevations (GSP 2021)Measurable Objective (2022 Annual Report) Measurable Objective (GSP 2021)Minimum Threshold (2022 Annual Report) Minimum Threshold (GSP 2021) Summary of Potential MO/MT Adjustments 14 05/10/2023 (11/05/2024) 4 Summary of Changes to Measurable Objectives (MOs) and Minimum Thresholds (MTs) for Interconnected Surface Water Monitoring Wells In addition to the recalculation of the MOs and MTs for the groundwater level RMS wells completed in 2023 and described previously in Sections 1 to 3, DE has also recalculated the MOs and MTs of the twelve interconnected surface water (ISW) RMS wells based on data available from DWR. The recalculation of MOs and MTs for ISW RMS wells was completed in Fall 2024. The methodology for calculating MOs is the same for ISW and groundwater level RMS wells: the average groundwater elevation for the most recent 5‐year period data were available (typically 2012 to 2017 based on when methodology was finalized). Also, the IMs are set equal to the MOs. The methodology for calculating the MT for the ISW wells is to be 10 feet below the historical low for each well. These methodologies are described in the Butte Subbasin GSP in Section 4.6.3.
The original MO and MT from the GSP are shown below in Table 6, along with recalculated values based on data available from DWR, and a calculation of the difference between the two. Figure 4 shows a hydrograph for SWN 18N01W14B001M along with the well's original MO and MT from the GSP, recalculated MO and MT, and MT as a groundwater level RMS well6 (which uses different criteria and methodology to calculate the MT).
Table 6. Summary of MO and MT elevations for the 12 ISW RMS wells as shown in the GSP and as recalculated based on data from DWR, and a comparison of the two elevations.
SWN GSP MO
(ft amsl)
GSP MT
(ft amsl)
Recalculated
MO (ft amsl)
Recalculated
MT (ft amsl)
MO
Difference
(ft amsl)
MT
Difference
(ft amsl)
17N03E05C003M 69 38 80 47 11 9
17N03E16N001M 65 38 71 42 6 4
18N01E05D002M 71 53 71 53 0 0
18N01W14B001M 46 25 58 28 12 3
18N01W17G001M 60 44 61 44 1 0
18N02E16F001M 69 43 77 63 8 20
18N03E21G001M 75 57 84 68 9 11
19N01E35B001M 83 62 82 62 ‐1 0
19N01W22D007M 67 48 68 47 1 ‐1
19N01W27R001M 50 29 62 34 12 5
20N01E35C001M 96 79 99 85 3 6
20N02E15H002M 121 100 121 105 0 5
With one exception (different RMS wells for MO and MT), the recalculation of MOs and MTs results in the same or higher groundwater elevations. It is recommended that the same process for managing adjustments to MOs/MTs for the groundwater level RMS wells be applied for the ISW RMS wells. 6 Eight of the twelve ISW RMS wells are also in the groundwater level RMS well network; SWN 18N01W14B001M is one of these eight.
Summary of Potential MO/MT Adjustments 15 05/10/2023 (11/05/2024) Figure 4. Hydrograph for SWN 18N01W14B001M depicting the record of groundwater elevations obtained in February 2023 (DWR 2023) that were used to recalculate the MO and MT. The MO/MT from the Butte Subbasin GSP (GSP 2021) and the recalculated MO/MT (Recalculated) are both depicted, along with the recalculated MT for groundwater levels (GWL Recalculated). This well is in both the GWL and ISW RMS networks. The recalculated MT for the GWL RMS is shown to illustrate the difference between the different MT criteria and resulting elevations for different Sustainability Indicators. 15202530354045505560657075
1/2000 9/2002 6/2005 3/2008 12/2010 9/2013 6/2016 3/2019 11/2021 Groundwater Elevation (ft amsl)
Date
SWN: 18N01W14B001M
Groundwater Elevations (DWR 2023) Measureable Objective (Recalculated) Measurable Objective (GSP 2021)Minimum Threshold (Recalculated) Minimum Threshold (GSP 2021) Minimum Threshold (GWL Recalculated) Appendix 4C
2025 Groundwater Quality Trend Monitoring Program
Results
Water and Resource Conservation Kamela Loeser, Director 308 Nelson Avenue T: 530.552.3595
Oroville, California 95965 F: 530.538.3807
buttecounty.net/waterresourceconservation
[email protected]
TECHNICAL MEMORANDUM
2025 Groundwater Quality Trend Monitoring Program Results Prepared by: Kelly Peterson, Water Resources Scientist, Department of Water and Resource Conservation Background and Purpose
The Butte County Department of Water and Resource Conservation (WRC) continued its groundwater quality trend monitoring within the County in August of 2025to provide information on groundwater quality conditions for salinity, measured as specific conductivity (SC). Conductivity is a basic groundwater quality characteristic to evaluate a subbasin for evidence of saline intrusion: as conductivity increases, salinity increases. Conductivity measures the ability of water to pass an electrical current, such as those from dissolved ions i.e. salts and other inorganic chemicals. Overtime with regular measurements, comparisons to baseline conditions can show trends in changing conditions.
Originally required by Chapter 33A, the Basin Management Objective Program, ran by the County has been monitoring wells for evidence of saline intrusion since 2001. In 2014, SGMA required Groundwater Sustainability Agencies (GSAs) to develop and submit Groundwater Sustainability Plans (GSPs) to the California Department of Water Resources (DWR) by 2022. The Butte, Vina and Wyandotte Creek Subbasin GSPs include a conductivity monitoring plan to avoid groundwater quality degradation (Davids, 2021; Geosyntec Consultants, Inc., 2021a; Geosyntec Consultants, Inc., 2021b). With the onset of SGMA, Chapter 33A was sunset in 2019, however the Department continues to conduct the Groundwater Quality Trend Monitoring Program to support the GSAs with their monitoring needs and to fulfill the program’s original objectives of:
Establishing a baseline of information to reveal trends over time of Butte County groundwater quality.
Measurements taken serve as initial indicators of changes in water quality that may warrant further investigation or testing.
2 Ensuring that groundwater resources are well managed by documenting the quality of local groundwater.
Availability and distribution of this information will be a useful educational tool.
The purpose of this memo is to summarize the groundwater quality conditions for salinity, measured as specific conductance in the Butte, Vina and Wyandotte Creek Subbasins during the fourth year (2025) of groundwater quality monitoring related to their respective Groundwater Sustainability Plans (GSPs) per the Sustainable Groundwater Management Act (SGMA) of 2014.
The network of wells changed significantly in 2022 as a result of the GSPs. The redefined network targeted inclusion of deep wells (where available) within each subbasin to track the migration of connate water upwelling from deep portions of the aquifer.
Conductivity is affected by temperature and increases as water temperatures increase. The terms “specific” and “electrical” conductivity are often used interchangeably in the literature to report the same measurement, however; specific conductivity refers to conductivity measured with a temperature compensation factor and standardized to 25°C. Electrical conductivity (EC) however, generally refers to measurements that are not standardized to a specific temperature, unless specified. The equipment that has been used to measure groundwater conductivity measurements by the WRC since 2022 reports values as SC.
Salinity is the only water quality constituent for which sustainable management criteria (SMC) goals were set in all three subbasins and is measured in the field as SC. Each subbasin specifically defines how conductivity measurements are reported as related to the SMC in each respective GSP. In the Vina, and Wyandotte Creek Subbasins, specific conductivity is identified for the SMC, while in the Butte Subbasin GSP electrical conductivity is identified for the SMC. For the Butte Subbasin, these measurements can therefore be reported as EC @ 25°C for comparison to their SMC.
Methodology
Conductivity measurements are taken at each monitoring well once per year. The wells are typically measured within the month of August during the peak of the irrigation season.
In 2021, the Department purchased a Solinst 107 temperature, level and conductivity (TLC) meter which includes a probe that measures SC in microsiemens (µs) / centimeter (cm), as well as temperature and water level (similar to an electric sounder) on a 1,000-foot-long laser-marked flat tape with markings every 1/100th ft. This meter has been used since 2022 to conduct conductivity monitoring at various depths within the monitoring wells. The Solinst SC meter is only lowered in wells without pumping equipment i.e. observation wells, in order to avoid potential damage to the equipment through entanglement in the wiring or pumps. 3 At the beginning of each monitoring day the meter was calibrated with known standard solutions according to the manufacturer’s specifications. At each site, the probe is lowered to the water surface and a depth to water measurement is recorded. It is then lowered to the midpoint of each screened interval(s) within the well to record the conductivity of the water entering the well from that portion of the aquifer. In prior reports (2022 and 2023), conductivity measurements from each screened interval were depicted in the graphs. Since 2024, the average of the conductivity measurements collected at the midpoint of every screened interval within each well is displayed in the graphs, unless there are variances in where measurements were recorded.
For example, if one of the measurements was not taken within a screened interval due to limits of the equipment (i.e the length of the tape the SC probe is attached to was too short to reach a screened interval) the data taken outside of the screened interval was not included in reported average and is noted as such in the graphs. If not all measurements were able to be taken within the screened intervals for other reasons such as obstructions within the well preventing the equipment from reaching the screened depths, the measurements were deemed as questionable measurements and depicted as such in the graphs.
For most of the remaining wells in the monitoring network with pumps, the Solinst probe was used in the field to measure a water sample collected from a spigot or sprinkler after the well was purged of standing water by pumping it for at least 20 minutes. One exception, well 19N01W28A001M located in the Glenn County portion of the Butte Subbasin was measured with a Hach Sension 156 meter by Glenn County staff after being purged; however it was only pumped for 10 minutes before the sample was collected to measure.
Some water quality monitoring sites do have intermittent conductivity data collected by other entities, however most sites do not. Data in the graphs referred to as “Other Data” or “Historic SC” reflects any other SC data located for the well and is sourced from a variety of entities including DWR’s 2020 Northern Sacramento Valley Groundwater Quality Assessment (DWR, 2020), data retrieved from DWR’s Water Data Library (WDL) website (DWR, 2025) and data provided by DWR’s Northern Region Office Water Quality Section where available. Methodologies of how these measurements were collected vary; however in cases where data included both field and lab conductance values on the same date, the average of the two is reported; most variance of the two values is minimal (under 50 µs/cm) with only one well reporting a variance of about 225 µs/cm.
Monitoring Network
The GSPs define the groundwater quality monitoring Representative Monitoring Site (RMS) well networks to include wells distributed spatially throughout the Subbasins, focusing on the inclusion of wells screened deep enough to capture changes in conductivity in the deeper portions of the aquifer, where any changes in conductivity would be expected to be detected first. There are however a few shallower wells within the network, due to a lack of deeper wells available. Modifications to the networks have been made including the removal and addition of wells for various reasons as described in more detail below and in Table 1.
In 2025, the overall revised monitoring network in the Vina Subbasin included seven RMS wells as identified in the GSP. One RMS well, 28J005 was removed from the network in 2024 due to an obstruction preventing 4 the equipment from reaching the mid-point of the screening interval to measure conductivity. Based on field observations, and a video logging survey conducted by DWR in 2025, well 28J005, drilled in 1955, has filled in with sediment approximately 600 feet above the first screened interval.
In 2025, the overall revised monitoring network in the Butte Subbasin included seven RMS wells as identified in the GSP and one additional new well added to the network in 2024. One deep multicompletion well, 20N01E18L001M, an extensometer site used to monitor potential inelastic subsidence was removed from the network in 2024 due to obstructions from the extensometer elements preventing the equipment from reaching the mid-point of the deepest screening interval to measure conductivity. This obstruction was confirmed from a video logging survey conducted by DWR in 2023. Another multi-completion well at the same location, 20N01E18L002M measuring the intermediate zones of the aquifer, was added to the network in 2024 and measured without issue; however in 2025, this well had sediment preventing the equipment from reaching the deepest screened interval in the well. The sediment obstruction was confirmed from a video logging survey conducted by DWR in 2025.
In 2025, the overall revised monitoring network in Wyandotte Creek Subbasin included two RMS wells as identified in the GSP; 18N04E08M001M and 18N04E19D001-3M. As depicted in Table 1. four RMS wells identified in the GSP were removed from the monitoring network for the following reasons:
• Two RMS wells were removed from the network per the request of the landowners, 28L001M in 2022 and 16Q001M in 2023.
• RMS well 13B002M was removed from the monitoring network in 2022 due to an inoperable pump. • Well CWS-02 was removed from the monitoring network in 2023 due to water quality issues at the well which have persisted.
Well 06E002M was added to the network in 2022. This well was historically measured for groundwater quality as part of the Butte County Basin Management Objective (BMO) program. One more additional well, 09N002M was added into the monitoring network in 2023.
A map of each subbasin and the revised network of 2025 groundwater quality sites is shown in Figure 1.
As part of their GSP Periodic Evaluations (due in January 2027), the GSAs will continue to consider modifications to the groundwater quality RMS network.
The monitoring network details including well type, monitoring equipment, total well depth, depth of the screened zones(s) in each well and notes are provided in Table 1. The portion of the state well number in bold indicates the RMS well identification numbers for each well, where applicable. 5 Most wells in the network are located with Butte County with the exception of two wells; 17N01W10A001M located in Colusa County and 19N01W28A001M located in Glenn County. The RMS wells within the Butte Subbasin are predominantly multi-completion wells (multiple wells at a single location screened at different depths below the ground surface) with the exception of 18N01E35L001M, a single observation well and 19N01W28A001M, a shallow irrigation well. One RMS well in the Butte Subbasin 19N01E35B002M is also an extensometer site which continuously monitors for potential inelastic land subsidence. The RMS wells within the Vina Subbasin are all multi-completion wells sampling from the deepest completion at each location. In the Wyandotte Creek subbasin, there are a variety of well use types in the monitoring network including irrigation, municipal and observation wells.
Sustainable Management Criteria
In these three subbasins, the groundwater quality SMC are established to address degraded groundwater quality caused by groundwater pumping where the potential exists for movement of underlying brackish water from greater depths, upward into the freshwater aquifer where groundwater pumping for beneficial uses occurs. One objective of the groundwater quality monitoring program is to measure conductivity levels in the RMS wells and compare those to the Measurable Objectives (MO) and Minimum Thresholds (MT) set for each RMS well as identified in the GSPs, as a way to gauge whether undesirable results are occurring in the subbasin. In each subbasin’s GSP, MTs were established to be protective of water uses and users. When considering MTs, it is important to note that in the case of groundwater levels, exceedance of a MT is caused by groundwater levels dropping below the threshold. However, for groundwater quality, exceedance of a MT is counterintuitively caused by measuring levels higher than the threshold. The MT for groundwater quality is a highest allowable value, rather than lowest.
As shown in Table 2., in the Bute Subbasin the MO for each RMS well for salinity is set at 700 μs/cm for agricultural use, consistent with the historic Butte County BMO program. The MTs at the RMS wells are set as either the higher of 900 μs/cm or the measured historical high, whichever was greater in the Butte Subbasin.
This MT was set based on best available data, the 19-year dataset of the Butte County BMO program, and maximum contamination levels established by the State. The occurrence of an Undesirable Result occurs in the Butte Subbasin if 25% of RMS wells exceed their MTs for 24 consecutive months.
As shown in Table 2., in the Vina and Wyandotte Creek Subbasins, the MOs for salinity are set at 900 μs/cm and the MTs are 1,600 μs/cm, which is the upper limit of the Secondary Maximum Contaminant Level (SMCL) based on State Secondary Drinking Water Standards. Secondary Drinking Water Standards are set on the basis of aesthetic concerns, values exceeding this number are typically unacceptable for drinking water.
The occurrence of an Undesirable Result occurs in the Vina and Wyandotte Creek Subbasins when two RMS wells within each Subbasin exceeds their MTs for two consecutive non-dry years. 6 Table 1. 2025 Groundwater Quality Trend Monitoring Network Information Subbasin State Well Number RMS
well? Well Type Monitoring Equipment
Total Well
Depth (feet)
Depth of
Screened
Zone(s) (feet)
Notes
17N01E24A003M Yes Observation Solinst 107 833 770 - 790 17N01W10A001M Yes Observation Solinst 107 820 770 – 780, 790-800
18N01E35L001M* Yes Observation Solinst 107 899 816 – 836 19N01E35B002M* Yes Observation Solinst 107 980 930 – 950 19N01W28A001M Yes Irrigation Hach Sension156 140 120 – 140 19N02E13Q003M Yes Observation Solinst 107 690 670 – 680 20N01E18L001M Yes Observation Solinst 107 1,000 767 – 810, 873–894
Removed from the network due
to obstruction.
20N01E18L002M No Observation Solinst 107 581 510 – 530, 550-560
Added in 2024 to supplement
network
21N01W13J001M Yes Observation Solinst 107 830 780 – 820 20N02E24C003M Yes Observation Solinst 107 520 484 – 505 21N01E13L002M Yes Observation Solinst 107 771 735 - 760 21N02E18C001M Yes Observation Solinst 107 914 770 – 780, 830–840,
21N02E26E003M Yes Observation Solinst 107 660 610 – 620 22N01E28J005M Yes Observation Solinst 107 948 740 - 800 Removed from the network due to obstruction.
23N01W03H002M Yes Observation Solinst 107 553 510 – 540 23N01W28M002M Yes Observation Solinst 107 1,031
791–801,
881–891,
951–961,
1011–1021
23N01W31M001M Yes Observation Solinst 107 1,055 969–979, 1,020-1,030
17N03E13B002M Yes Irrigation Solinst 107 320 120 – 320 Removed from the network due to inoperable pump.
17N04E09N002M No Irrigation Solinst 107 325 100 – 112 Added in 2023 to supplement network
18N04E08M001M Yes Irrigation Solinst 107 ~350 168–204, 208 - 244
18N04E19D001M Yes Observation Solinst 107 744 700 – 720 18N04E19D002M 594 430–450,
550–570
18N04E19D003M 220 120 – 130,
18N04E28L001M Yes Irrigation Solinst 107 190 n/a Removed from the network due to landowner request.
19N03E16Q001M Yes Residential Solinst 107 120 100 – 120 Removed from the network due to landowner request.
19N04E06E002M No Municipal Solinst 107 196 110–130,
164–174
Added in 2022 to supplement
network
CWS-02 Yes Municipal Solinst 107 340 60 – 190, 300-
322
Removed from the network due
to water quality issues.
* Extensometer sites that measure inelastic land subsidence.
Vina
Wyandotte
Creek
Butte
7 8
Figure 1. Groundwater Quality Trend Monitoring well locations in the Vina, Butte and Wyandotte Creek Subbasins in 2025
Table 2. 2022 GSP Measurable Objectives, Minimum Thresholds for Conductivity [microsiemens (µs) / centimeter (cm)] and definition of Undesirable Results in each Subbasin Results
In 2025, the third non-dry water year type in a row, the majority of all wells monitored within each subbasin had groundwater quality conditions, measured as SC, that fell within the acceptable range of groundwater quality values set forth by the GSPs as summarized in Table 2. No major shifts occurred in the conductivity measurements in the sampled wells. Details of the monitoring results for each Subbasin are described below.
Butte Subbasin
In the Butte Subbasin the majority of RMS wells measured in 2025 had conductivity values that were lower than the MO of 700 μS/cm and therefore lower than each well’s MT. The MTs vary per well since they are based on historic data, if available. Figure 2. displays the overall results for the 2025 water quality wells within the Butte Subbasin. Graphs of historic data for individual wells for previous years can be found in Appendix A. Results from one RMS well, 17N01W10A001M, a deep multi-completion well located in Colusa County, has had conductivity measurements slightly higher than the MT in 2023, 2024 and again in 2025. Historic (DWR, 2020, DWR 2023a) and recent data for this well are shown in Figure 3. This well is near the Sutter Buttes mountain range in an area known for high concentrations of conductivity (Davids, 2021). Future plans of the GSAs may include the formation of the Sutter Buttes Water Quality Interbasin Working Group as described in more detail in section 6.1.2.2 of the Butte Subbasin GSP (Davids, 2021) to focus on collaborative discussions, consensus building and planning to address groundwater quality matters associated with the unique geology of the Sutter Buttes area.
Subbasin Measurable Objective Minimum Thresholds Undesirable Result Butte 700 μS/cm The greater of 900 μS/cm or
the measured historical high
25% of RMS wells exceed MTs for
24 consecutive months
Vina 900 μS/cm 1,600 μS/cm 2 RMS wells exceed their MT for two consecutive non-dry years
Wyandotte
Creek 900 μS/cm 1,600 μS/cm 2 RMS wells exceed their MT for two consecutive non-dry years 9 Figure 2. Groundwater quality monitoring results in the Butte Subbasin for the 2025 water year 10 Figure 3. Current and historic groundwater quality data for well 17N01W10A001M in the Butte Subbasin.
Vina Subbasin
In the Vina Subbasin all RMS wells measured in 2025 had conductivity values that were lower than the MO of 900 μS/cm and therefore lower than the MT of 1,600 μS/cm as shown in Figure 4. Two wells, 28M002M, and 31M001M the length of the tape the SC probe is attached to was too short to reach the last screened intervals of the wells. The graphs reflect an average of the SC measurements recorded at the other screened intervals.
Wyandotte Creek Subbasin
In the Wyandotte Creek Subbasin the majority of RMS wells measured in 2025 had conductivity values that were lower than the MO of 900 μS/cm and therefore lower than the MT of 1,600 μS/cm as shown in Figures
5. and 6.
11 * Indicates a measurement was not taken within a screened interval due to limits of the equipment. Data taken outside of the screened interval is not included in the average.
Figure 4. Groundwater quality monitoring results in the Vina Subbasin for the 2025 water year In the multi-completion well drilled in 2021 by DWR through the Technical Support Services program to measure three distinct zones of the aquifer in one location, there were two zones, intermediate (19D002M) and deep (19D001M), which exhibited high conductivity levels in 2025, exceeding the MT depicted in Figure
6. This multicompletion well was constructed after the GSA set the sustainable management criteria for water quality. Both zones of this well had high levels of conductivity, greater than the MT when initially developed, prior to the adoption of the GSP and again when the wells were re-tested months after their initial development. ss shown in Figure 6. as ‘Other Data’. Anecdotally, this general area of the subbasin is known to have geologic formations bearing groundwater with high concentrations of salinity and natural gas. Better characterization of naturally occurring salinity is needed to help improve appropriate monitoring and management of groundwater with respect to water quality in this Subbasin. The Butte County Technical Advisory Committee may consider making recommendations to the GSA regarding changes to the monitoring network of wells and collection of additional long-term data in the future. DWR has recently collected groundwater quality measurements at 19D002M (intermediate zone of the multicompletion well in the Wyandotte Creek Subbasin) as depicted in Figure 6. DWR has also indicated that there are plans to deploy continuous data loggers to record hourly conductivity data in the wells in the future which will highlight any changes during the peak irrigation season as compared to baseline conditions throughout the water year. 12 Figure 5. Groundwater quality monitoring results in the Wyandotte Creek Subbasin excluding 19D001-3M for the 2025 water year
13 Figure 6. Current and historic groundwater quality data for zones in RMS well 19D001-3M in the Wyandotte Creek Subbasin.
Discussion
Groundwater quality monitoring serves to establish baseline levels for salinity (via conductivity) throughout the Subbasins so that any future changes may be identified and further investigation and or additional monitoring can subsequently be developed. Table 3. below summarizes the status of monitoring results in relation to exceedances of MTs and whether or not Undesirable Results occurred based on the SMC established for each subbasin. While there was one RMS well in exceedance of a MT for conductivity within the Butte Subbasin over the past 24 months, this does not indicate the presence of Undesirable Results in the Subbasin for degraded water quality, as only one well exceeded the MT over 24 months, not two, as described in the GSP. Importantly, the observed conductivity in the well is in the range of previously observed historical levels and does not indicate a changed condition or upward trend. The WRC may consider adding another 14 well to the monitoring network given the obstructions observed in 20N01E18L001-2M over the past few years.
DWR has indicated there are plans to install continuous data loggers in all four multicompletion wells at the 17N01W10A001-4M well and to conduct monthly water quality monitoring at the shallow-intermediate Table 3. Conductivity monitoring results and the presence of Undesirable Results since 2022 in relation to each well’s Minimum Thresholds in the Butte, Vina and Wyandotte Creek Subbasins.
Subbasin State Well
Number
2022
Dry
Year
2023
NonDry
Year
2024
NonDry
Year
2025
NonDry
Year
Undesirable
Result
Identification
Indication of
Undesirable
Results?
Was measurement above the
Minimum Threshold?
Butte
17N01E24A003M No No No No
When 25%
of RMS
wells (2 of 8)
exceed their
MT for 24
consecutive
months
No
17N01W10A001M No Yes Yes Yes
18N01E35L001M No No QM No
19N01E35B002M No No No No
19N01W28A001M n/a No No No
19N02E13Q003M No No No No
20N01E18L001M Removed from the network in
2022
21N01W13J001M n/a No No No
Vina
20N02E24C003M No No QM No
When 2
RMS wells
exceed their
MT for two
consecutive
non-dry
years.
No
21N01E13L002M No No No No
21N02E18C001M No No No No
21N02E26E003M No No No No
22N01E28J005M Removed from the network in
2022
23N01W03H002M No No No No
23N01W28M002M No No No No
23N01W31M001M No No No No
Wyandotte
Creek
CWS-02 No Removed from the
network in 2022
17N03E13B002M Removed from the network in
2022
18N04E08M001M QM QM No No When 2 RMS
wells exceed
their MT for
two
consecutive
non-dry years.
No
18N04E19D001-3M QM QM QM Yes
18N04E28L001M Removed from the network in
2022
19N03E16Q001M No Removed from the
network in 2023
Note: The portion of the State Well number in bold is the RMS well identification number. QM indicates a questionable measurement and n/a indicates the well was not measured.
Multicompletion well 18N04E19D001-3M is reported as an average of all three zones 15 zoned portion of multicompletion well 17N01E24A004M. WRC may include any data available from this effort in future reports.
There were no RMS wells in exceedance of any MTs in the Vina Subbasin in 2025 and therefore no indication of Undesirable Results as defined in the GSP. The WRC may consider adding another well to the monitoring network given the obstructions observed in 28J005M over the past few years. DWR has indicated there are plans to conduct monthly water quality monitoring at the shallow-intermediate zoned portion of multicompletion well 28M004M. WRC will include any data available from this effort in future reports.
There were two zones within the multicompletion well 18N04E19D001-3M in the Wyandotte Creek Subbasin in exceedance of the MTs in 2025; however, this does not indicate the presence of Undesirable Results in the subbasin for degraded water quality, as only one well exceeded the Minimum Threshold for one year, not two, as described in the SMC. These completions monitor the deep and intermediate zones in this multi-completion well drilled in 2021 by DWR through their Technical Support Services program. When the well was first developed, the baseline conductivity was 3,910 µs/cm and 2,480 µs/cm respectively, roughly 1.5 and 2.5 times higher than the MT for these wells as shown in Figure 6. Approximately four months after initial development, DWR conducted additional water quality sampling after the well had time to settle. Results indicated a drop in conductivity to 903 µs/cm for 19D001M (deep zone) but an increase in 19D002M (intermediate zone) to 2,890 µs/cm. Baseline conditions at these wells are not well understood, but clearly exhibit naturally occurring high levels of conductivity. Revisiting the sustainable management criteria of this well seems appropriate. Additional characterization through additional data collection of naturally occurring salinity is needed to help improve appropriate monitoring and management of groundwater with respect to groundwater quality in this Subbasin. The WRC may consider adding other wells to the monitoring network given the low number of wells currently in the monitoring network. DWR has indicated there are plans to install continuous data loggers in all three multicompletion wells at the 19D001-3M well. WRC may include any data available from this effort in future reports.
Additional monitoring will continue to be conducted by DWR and other agencies to track constituents not managed under the current GSPs, or WRC’s Groundwater Quality Trend Monitoring Program, including a variety of minerals, metals, pesticides and herbicides. Data from ongoing monitoring by various state and federal agencies will be available to the GSAs to augment local datasets and their understanding of groundwater quality and can be found on the State Board’s Groundwater Ambient Monitoring and Assessment (GAMA) program at https://www.waterboards.ca.gov/gama.
The County will continue to work with the GSAs within the Butte, Vina and Wyandotte Creek Subbasins as available, to recommend modifications to the monitoring networks, to conduct monitoring to support data collection that compliments the GSAs SGMA requirements, and to ensure that conductivity data is shared with the GSAs.
16 References
California Department of Water Resources (DWR), Northern Regional Office. 2020. Northern Sacramento Valley Dedicated Monitoring Well Groundwater Quality Assessment Technical Information Record (TIR) NRO-2019-01. Red Bluff, CA
California Department of Water Resources (DWR). 2025. Available at:
https://wdl.water.ca.gov/waterdatalibrary/Map.aspx
Davids Engineering (Davids). 2021. Butte Subbasin Groundwater Sustainability Plan. Available at:
https://sgma.water.ca.gov/portal/gsp/preview/98
Geosyntec Consultants, Inc. 2021a. Vina Groundwater Sustainability Plan. Available at:
https://sgma.water.ca.gov/portal/gsp/preview/86.
Geosyntec Consultants, Inc. 2021b. Wyandotte Creek Groundwater Sustainability Plan. Available at:
https://sgma.water.ca.gov/portal/gsp/preview/99.
17 Appendix A
2025 Butte, Vina and Wyandotte Creek Subbasin
Groundwater Quality Monitoring Results
1 Appendix A. Historical and current conductivity data for individual wells in the Butte, Vina and Wyandotte Creek Subbasin’s 2025 water quality monitoring network.
Butte Subbasin
2 .
3 4
5 6
Vina Subbasin
7 8
9 10
Wyandotte Creek Subbasin
11 12
13 Appendix 6A
Hydrogeologic Conceptual Model Evaluation
Sub-Terra Heritage Resource Investigations
3153 Chico Ave., Chico, CA
www.sub-terraheritage.com
To: Evan Davis January 23, 2025
From: Todd Greene, Ph.D.
Principle Investigator
Email: [email protected]
Subject: Butte Subbasin Monitoring Wells
cc: Eddy Teasdale
Purpose
The purpose of this project was to provide a stratigraphic context for the screened intervals in the monitoring wells in the Butte groundwater Subbasin. The information can be used to help guide the location and screen intervals for future monitoring well sites.
Executive Summary
A total of 51 screened intervals are placed in a stratigraphic context within the Butte Subbasin; 33 wells are single completion wells (although 3 wells have no screen information) and 9 wells have multiple completions covering 18 screened intervals. As deliverables, we provide a spreadsheet and GIS shapefile with borehole information and interpreted stratigraphic interval of screens with corresponding depths.
Although the stratigraphic nomenclature developed of the Butte Subbasin Groundwater Sustainability Plan (GSP) is consistent throughout the Subbasin, we recognize that here are significant differences in stratigraphy. For this work, we interpret 2 main areas, northern and southern, that contain distinct stratigraphic intervals (Table 1). The main difference in these areas is that the northern area contains the Tuscan Formation, and the southern area contains the Laguna Formation as well as the Sutter Buttes Rampart (volcaniclastic debris derived from the Sutter Buttes volcanic complex). It is uncertain how the Tuscan and Laguna formations are laterally connected; however, the east side of basin appears to show a direct connection between the two formations in the form of coarse-grained deposits.
In the southern area of the Butte Subbasin, we utilize the nomenclature of Springhorn (2008). The stratigraphy can be divided into the following units (from oldest to youngest): pre-Laguna (pre-L), Laguna Fm. (L), and Quaternary (Q) formations. For the portion of the southern area that contains deposits of the Sutter Buttes Rampart, it is easiest to divide the stratigraphy in 3 intervals: pre-Rampart (pre-R), Rampart (R), and post-Rampart (post-R: includes L and Q).
In the northern area of the Subbasin, the stratigraphic nomenclature is similar to what was used in the Vina Subbasin. This framework includes the time-equivalent Tuscan and Tehama formations overlain by Quaternary formations. From oldest to youngest, we place the screened intervals within the following units: Lower Tuscan (LT), Upper Tuscan/Tehama 2 (UTT2), Upper Tuscan/Tehama 1 (UTT1), and Quaternary (Q). Although the western portion of the northern area contains all 4 stratigraphic intervals, the eastern area south of Chico combines Upper Tuscan 2 (UT2) and LT into a single unit (UT2/LT) as well as UTT1 and Q.
Table 1. Stratigraphic relationship between the southern and northern areas of the Butte Subbasin. Dashed line denotes uncertainty of how the formations connect laterally.
We also used over 640 additional boreholes and two vintages of Airborne Electromagnetic (AEM) data profiles from the Department of Water Resources (DWR) W07 region and the Stanford Groundwater Aquifer Project (GAP) pilot survey to guide interpretations. Most of the screened intervals cross stratigraphic boundaries leaving very few monitoring wells that target a single stratigraphic unit. This information can be used to guide wellbore construction for future monitoring wells.
Background
Luhdorff & Scalmanini Consulting Engineers, Inc. (LSCE), was contracted by Butte County to be responsible for the deliverables outlined in the Butte Subbasin Monitoring Well Characterization Task Order. LSCE then sub-contracted with Sub-Terra Heritage Resource Investigations and Geophysical Imaging Partners to provide stratigraphic context for the existing monitoring wells.
The Butte Subbasin lies in the eastern central portion of the Sacramento Groundwater Basin. The Subbasin is bounded in the south by the Sutter Subbasin, in the west by the Sacramento River and the Colusa Subbasin, in the north by the Corning and Vina Subbasins, and in the east by the Feather River and the Wyandotte Creek Subbasin (Butte Subbasin GSP, 2022).
According to the Butte Subbasin GSP, the main aquifer unit is in the Tuscan Formation with lesser contributions from the Laguna Fm., and Quaternary formations of the Riverbank, and Modesto formations. However, based on the AEM data and prior work of Springhorn (2008), we recognized 2 areas that contain distinct stratigraphy: southern and northern.
Methods
In addition to the WO7 DWR AEM profile data, this study also uses the results from the Stanford GAP pilot study conducted in the Corning, Colusa, and Vina Subbasins (https://mapwater.stanford.edu/) using data acquired in 2018. The GAP study calibrated AEM data to 152 existing resistivity logs to provide approximately 800 km of resistivity profiles (see Kang et al., 2021 for detailed methods). In addition, this study also utilizes point-count information from 4 wells in order to place well intervals into their appropriate stratigraphic formation based on sediment composition (e.g. Ingersoll et al., 2016; Greene and Hoover, 2014; Davis, 2023).
We used the software GeoScene3D (I-GIS) to place the monitoring wells, borehole data, geologic map, and AEM profile data, along with other geographic data in a software mapping platform. All well data are publicly available (except for 6 Cal Water Service wells in Chico) at the DWR website under Area WO7 (https://data.cnra.ca.gov/dataset/aem) and the DWR SGMA Data Portal (https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#currentconditions). Well data from the monitoring wells were also provided by LSCE. In addition, interpretations from the southern area relied on cross-sections in Springhorn (2008).
Results and Interpretations
The deliverables include a spreadsheet and shapefile that includes the following information for each screened interval:
1) Basic well data: Excel spreadsheet
2) Geologic unit with the corresponding screen interval in feet below ground surface (bgs) 3) Confidence: confidence on geologic units from high to low: 1, 2 4) Northern or Southern area
5) Isotopic interpretation from Grimm (2020)
6) Name of well containing detailed description from Springhorn (2008) 7) Model layer from Butte Basin Groundwater Model
The southern area of the Butte Subbasin has portions that are influenced by the Sutter Buttes Rampart (R). Therefore, inside the area that contains Rampart deposits, the stratigraphy is (from oldest to youngest): pre-Rampart (pre-R), Rampart (R), and post-Rampart (post-R). The pre-Rampart (also known as the Sutter formation of Springhorn, 2008) is equivalent to (from oldest to youngest): Ione Formation, Upper Princeton Valley fill, and the Mehrten Formation. The post-R contains the Laguna Formation and Quaternary formations of the Red Bluff Fm., Turlock Lake Fm., Riverbank Fm., and Modesto Fm.
The portions of the southern area that do not contain the Rampart are dominated by the Laguna Formation. Therefore, the stratigraphy in this area contains: pre-Laguna (pre-L), Laguna (L), and the Quaternary formations (Q) mentioned above.
The northern area of the Butte Subbasin is similar to the Vina Subbasin stratigraphy (from oldest to youngest): Lower Tuscan (LT), Upper Tuscan-Tehama 2 (UTT2), the Upper Tuscan-Tehama 1 (UTT1), and Quaternary formations (Q). It is important to realize the Tuscan and Tehama Formations interfinger within individual layers and in the upper portions it is often not possible to know which formation is being represented; therefore, those layers are called Upper Tuscan/Tehama (UTT1 and UTT2). However, the lower portion of the Tuscan Formation (Lower Tuscan: LT) is readily noticeable with no lower Tehama represented in the Subbasin. Additionally, the east side of the Butte Subbasin does not contain any Tehama deposits.
The boundary between the northern and southern areas is complex and poorly understood. In the east side of the Butte Subbasin, the Laguna Formation and the Lower Tuscan appear to a continuous coarsegrained unit based on the AEM response. However, this connection fades to the west both in AEM resistivity response as well as an apparent mismatch of depths. This is due to either western deepening (making AEM less reliable) or more fine-grained material on the west side leading to a lower resistivity response in the AEM data.
Limited isotopic data on for some of the monitoring wells are also complex. While some deep screens have “fossil” water as determined by (Grimm, 2021), other deep wells have a “mixed” signature between fossil water and “modern” water (e.g. 19N01E35B002M at 930’-950’ bgs and 21N01W11A001M at 810’-1280’ bgs). In addition, while some shallow screens indicate modern signatures, others contain mixed water (e.g. 21N01W11A002M at 125’-185’ bgs, 19N02E13Q001M at 130’-210’ bgs, and 19N01W22D007M at 80’-90’ bgs). These examples could be indicative of significant vertical movement of groundwater.
Conclusion/Recommendations
Based on 51 screened intervals from 33 single-completion wells and 9 multi-completion wells within the Butte Subbasin monitoring network, we place each screened interval into one or more the following stratigraphic intervals. In the southern portion of the Subbasin, from oldest to youngest, we include:
pre-Rampart or pre-Laguna (pre-R or pre-L), Laguna Formation (L), Rampart (R), and post-Rampart or Quaternary (post-R or Q). In the northern area of the Butte Subbasin, we recognize, from oldest to youngest: Lower Tuscan (LT), UTT2 (Upper Tuscan/Tehama 2), UTT1 (Upper Tuscan/Tehama 1), a combined UT2/LT in eastern portion of the northern area, and Quaternary (Q).
Most of the interpretations are based on incomplete descriptions of sediment by non-geologists from well completion reports. The interpretations from this report could be improved with additional drilling along with accurate descriptions made by geologists at the well-site. In addition, we highly recommend drill cuttings be made available to analyze the composition to better place the sediments in their respective formations based on criteria from Springhorn (2008), Ingersoll et al., (2016), Blair et al. (1991), and Greene and Hoover (2014).
References
Blair, T.C., Baker, F., and Turner, J., 1991, Cenozoic fluvial facies architecture and aquifer heterogeneity, Oroville, California, Superfund site and vicinity, in Tyler, N., and Miall, A.D., editors, Threedimensional facies architecture of terrigenous clastic sediments and its implications for hydrocarbon discovery and recovery: SEPM Concepts in Sedimentology and Paleontology, No. 3, p. 147-159.
Davis, E., 2023, A Petrographic Analysis and Analog Outcrop Investigation to Refine the Stratigraphy of the Tuscan Aquifer System, northern Sacramento Valley, California; [M.S. Thesis] California State University, Chico, 103 p.
Greene, T. J., & Hoover, K., 2014, Hydrostratigraphy and pump-test analysis of the lower Tuscan/Tehama Aquifer, Northern Sacramento Valley, CA. Center for Water and the Environment.
Grimm, N. F., 2020, Comparing Model-Computed Turnover Rates With Isotopic Ages For Sustainable Groundwater Management; [M.S. Thesis] California State University, East Bay, 134 p.
Ingersoll, R. V., Steinpress, M. G., & Spangler, D., 2016, Application of actualistic sand petrofacies in hydrogeology: An example from the northern Sacramento Valley, California, USA. GSA Bulletin, 128 (3–4), p. 661–668.
Kang, S., Knight, R., Greene, T., Buck, C., & Fogg, G., 2021, Exploring the model space of airborne electromagnetic data to delineate largescale structure and heterogeneity within an aquifer system.
Water Resources Research, 57, e2021WR029699. https://doi.org/10.1029/2021WR029699 Springhorn, S. T., 2008, Stratigraphic Analysis and Hydrogeologic Characterization of Cenozoic Strata in the Sacramento Valley near the Sutter Buttes; [M.S. Thesis] California State University, Sacramento, 246 p.
Attachments
Spreadsheet of well data from monitoring wells
GIS shapefile with well data from monitoring wells
Appendix 6B
GDE Health Evaluation Methodology
APPENDIX 6B - BUTTE SUBBASIN GROUNDWATER DEPENDENT
ECOSYSTEMS HEALTH ANALYSIS DATA SOURCES
The groundwater dependent ecosystem (GDE) health analysis conducted within the Butte Subbasin relied on a GDE dataset and remotely sensed Normalized Difference Vegetation Index (NDVI) data.
Mapped polygons identified as GDEs within the Butte Subbasin served as the spatial basis for the analysis. GDE polygons correspond to the “Likely a GDE” designations developed in the Butte GSP (Appendix Section 2E), which were derived from the Natural Communities Commonly Associated with Groundwater (NCCAG) database and refined by GSA Managers using local hydrologic information, vegetation indicators, and drought-year imagery to confirm areas most likely dependent on shallow groundwater.
As part of the GDE health analysis, polygons associated with permanently flooded or riverine environments were excluded from the vegetation health summaries. These areas are already identified within the GDE dataset using existing wetland classification attributes, including features such as riverine and seasonally or permanently flooded systems. This group includes the Sacramento River corridor, where vegetation patterns are strongly influenced by surface water, channel migration, seasonal inundation, and exposed sediment. In these dynamic settings, satellite-based vegetation indices tend to reflect hydrologic and geomorphic processes rather than vegetation condition or groundwater support. Excluding these areas allows the analysis to focus on vegetation dominated GDEs where NDVI provides a more consistent and comparable indicator of plant health.
The remaining GDE polygons were uploaded into the Google Earth Engine platform, which is used for processing large remote-sensing datasets. Annual vegetation indices were derived for each polygon using a combination of The Nature Conservancy (TNC) composite imagery, which was accessed by Google Earth Engine, and custom workflows adapted from TNC. NDVI was selected as the indicator of vegetation health because it is a widely used and reliable metric for assessing plant vigor in GDE, essentially measuring the greenness of vegetation, which is strongly correlated with plant health. For 2020 through 2025, annual NDVI values were pulled directly from the GDE Pulse composite image collection, as shown on the figures below. These annual results were compiled into a single dataset and supplemented with additional calculated fields, including the GDE health categories based on thresholds commonly used by TNC to provide a framework for understanding the general condition of vegetation of GDEs. The regional health maps that follow present GDE health categories for each analysis year from 2020 through 2025.
Butte Subbasin GDE Health Region Maps
Area 1
Big Chico Creek to Glenn County Regional GDE Health,
2020 to 2025
Area 2
Glenn to Colusa County Regional GDE Health,
2020 to 2025
Area 3
South of Glenn County Regional GDE Health,
2020 to 2025
Area 4
Feather River Corridor Regional GDE Health,
2020 to 2025
Appendix 6C
Water Use Analysis Methodology
1 of 6
TECHNICAL MEMORANDUM
To: Luhdorff and Scalmanini Consulting Engineers
From: Davids Engineering, Inc.
Date: March 3, 2025
Subject: Annual Report Water Use Analysis Methodology
1 Introduction
Pursuant to the Groundwater Sustainability Plan (GSP) regulations (23 CCR1 Section 356.2), the GSP Annual Report for the Butte Subbasin (Subbasin) includes quantification of water supplies and water uses in the reporting year, including groundwater extraction by water use sector2. Water supplies and water uses in the Subbasin have been quantified based on the best available data sources and information, either collected from measured records or estimated where necessary.
While some groundwater extraction in the Subbasin is measured, most groundwater extraction is unmeasured, including extraction from privately owned wells. For the Butte Subbasin Annual Report (Annual Report), the approach used to estimate unmeasured groundwater extraction for the agricultural water use sector is referred to as the Groundwater Extraction Estimates from Earth Observations (GEEEO) process. In this approach, a spatial water use analysis is computed on a monthly basis using current land use data, climate conditions (e.g., precipitation and evapotranspiration), crop water demands, and other local information, allowing for estimation of total water use and estimated groundwater extraction, after accounting for the use of other available water supplies.
This approach differs from the water budget methodology used in GSP development, where the Butte Basin Groundwater Model (BBGM) was used to generate historical, current, and projected water budgets for the Subbasin. The shift toward the GEEEO process is due to the time and cost constraints associated with updating the GSP groundwater model annually. Despite this change, key inputs and results from the GEEEO process have been compared with those of the GSP groundwater model to ensure consistency in the water use analyses.
This technical memorandum (TM) describes the methodology and data sources used in the GEEEO process. Results of the GEEEO process are documented in the Annual Report. 1 California Code of Regulations, Title 23, Division 2, Chapter 1.5, Subchapter 2. Groundwater Sustainability Plans. 2 Water use sectors are identified in the GSP Regulations as “categories of water demand based on the general land uses to which the water is applied, including urban, industrial, agricultural, managed wetlands, managed recharge, and native vegetation” (23 CCR Section 351(al)). 2 of 6
2 GEEEO Process and Computational Approach
2.1 Computational Approach
The GEEEO process utilizes available geospatial data and information to quantify water use, including groundwater extraction volumes, spatially across the Subbasin:
1. First, geospatial evapotranspiration (ET) information at a pixel-scale is used to quantify the total consumptive water use and total applied water requirements during a given time period in a given area of the Subbasin, and geospatial land use information is used to help identify where irrigation water may have been applied (i.e., whether the area in question features irrigated agricultural land, versus idled land or undeveloped vegetation).
2. After quantifying total applied water requirements, available surface water supply and groundwater extraction data is incorporated into the GEEEO process by distributing that water out to specific regions where that water is applied (e.g., irrigated lands in surface water supplier service areas).
3. The remaining groundwater extraction needed to meet applied water demands is then calculated based on the difference between total applied water requirements and available water supply information, with consideration for effective precipitation.
4. Finally, the pixel-scale results can then be aggregated to the desired spatial or temporal domains of interest.
The result is a spatially distributed water use analysis calculated with a finer spatial resolution than was possible in the GSP water budgets. The pixel-scale water budget results provide greater insight into where water use occurs in the Subbasin and are configurable to create water use summaries for any region of the Subbasin. Additional details about the GEEEO computational approach are provided in Attachment A, generally following the process described in Hessels et al. (2022).
2.2 Spatial Resolution
GEEEO quantifies water use and groundwater extraction volumes with pixel-scale resolution (30 meters (m) x 30 m), corresponding to the spatial resolution of satellite imagery used in developing many of the GEEEO inputs. For those inputs that are not available at the 30 m x 30 m resolution, available data and information is distributed as averages over the area where that information is applicable (e.g., districtreported surface water deliveries are distributed as an average acre-feet per acre (AF/ac) over irrigated lands in that district’s service area3
). Additional information about the spatial resolution of specific data sources is provided in Section 3.
The fine spatial resolution of the GEEEO inputs and computations allows for highly configurable GEEEO results summaries. For the Annual Report, results are summarized by subregions that are defined to roughly correspond with the boundaries of the water budget regions in the GSP groundwater model, with distinction between water districts, managed wetlands and refuge areas, and out-of-district lands. 3 Future refinements to the GEEEO process could potentially incorporate field-scale surface water delivery records to improve spatial detail of results rather than equally distributing surface water deliveries across the irrigated lands within the district’s service area.
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2.3 Period and Timestep
For each Annual Report, the GEEEO process operates from 2016 through the current reporting year4 on a monthly timestep, although only the results from the current reporting year are included in the Annual Report. The period and timestep are set according to data availability and reporting needs. However, the GEEEO process is configurable to operate on different timescales (e.g., daily or weekly). The start year is currently limited by the availability of geospatial ET information from OpenET, although further historical ET information is expected to be available in the near future. 3 Data Sources
The GEEEO process uses data sources and information that capture the unique, local conditions within the Subbasin to the extent available. Details about the data and information used in the GEEEO process are described below.
3.1 Evapotranspiration
ET, or consumptive water use, is the major driver of water use in the Subbasin, particularly agricultural use. In this context, consumptive water use is defined as “the part of water withdrawn that is evaporated, transpired, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment” (ASCE, 2016). Unlike surface runoff or infiltration of water into the groundwater system (through seepage, deep percolation, managed recharge, or other means), ET is water that cannot be recovered or directly reused in the Subbasin.
In the GEEEO process, ET is quantified from satellite-based remote sensing analyses available from OpenET. OpenET is a multi-agency web-based geospatial information system (GIS) utility that quantifies ET over time with a spatial resolution of 30 m x 30 m (approximately 0.22 acres). OpenET information is available in raster coverages of the Subbasin on both a daily and monthly timestep from 2016 through present.5 The GEEEO process utilizes monthly rasters of the ensemble ET from OpenET to calculate total water use for the Annual Report.
While OpenET is a new utility, the underlying methodologies to quantify ET apply a variety of wellestablished modeling approaches that are widely used in government and research applications. The OpenET modeling approaches are also similar to the approaches used to quantify ET in the GSP groundwater model. Additional information about the OpenET team, data sources, and methodologies are available at: https://openetdata.org/.
3.2 Land Use
Areas in each water use sector in the Subbasin were identified using the most recent and reliable spatial land use data in the region, including:
1. Local land use coverage for Water Year 2024 developed by Land IQ for Butte County and the surrounding area (Land IQ, 2025).
4 Annual Reports are required to be submitted by April 1 each year following the adoption of the GSP. The current reporting year for each Annual Report is the preceding water year (i.e., October 1 through September 30) 5 OpenET raster information is typically available within about one month after the period has ended. 4 of 6
2. Statewide crop mapping, available from the California Department of Water Resources (DWR) (DWR, 2024).
3. CropScape Cropland Data Layer coverage, available from the United States Department of Agriculture (USDA, 2024).
Land use data from these sources were compiled into 30 m x 30 m raster coverages of the Subbasin. To prepare the GEEEO process inputs, DWR data, which includes extensive ground-truthing review of results, is preferentially used to identify agricultural land (including irrigated and non-irrigated lands) and urban areas, and then USDA data is utilized to back-fill gaps of non-irrigated, idled, and nondeveloped land in the Subbasin. Local refinements are also applied, as needed, to account for local land use information.
These land use data sources and applications were similar to those used in development of the GSP water budgets. Comparisons were made to evaluate the consistency of the datasets and with earlier land use analyses; good correspondence was found for the major land use classes found in the Subbasin.
DWR data is typically available in provisional form approximately two years after a given year has passed. USDA data is typically available for the prior year in early- to mid-February. When data for the current reporting year is not yet available, raster coverages of the Subbasin are generally assembled utilizing land use data from the most recent, hydrologically similar year (i.e., similar water supply conditions and similar cropping patterns, to the extent possible). Idling of annual and ponded crops in a given year may also be locally refined through comparison with USDA data for the current reporting year or through an analysis of vegetation coverage in the current reporting year. However, it is noted that land use data is only used in the GEEEO process to identify areas in each water use sector where water is applied. The total water use for lands in the agricultural and managed wetlands water use sectors are determined through an analysis of OpenET data, regardless of the precise land use classification.
3.3 Precipitation
Spatial precipitation estimates were extracted from the Parameter-elevation Regressions on Independent Slopes Model (PRISM), developed by the PRISM Climate Group at Oregon State University.
PRISM quantifies spatial precipitation estimates, among other climate parameters, based on available weather station data and modeled spatial relationships with topography and other factors influencing weather and climate.
PRISM data is available in raster coverages of the Subbasin on both a daily and monthly timestep, with a spatial resolution of 4 kilometer (km) x 4 km. The GEEEO process utilizes monthly rasters for the Annual Report analysis, and the precipitation results for each 4 km pixel are applied to each of the 30 m pixels within it (i.e., downscaled) for which ET and land use data are available. Additional information about the PRISM data and methodologies are available at: https://prism.oregonstate.edu. PRISM precipitation data is consistent with the historical precipitation inputs to the GSP groundwater model.
To calculate effective precipitation and, subsequently, evapotranspiration from precipitation (ETPR), PRISM precipitation data, estimated crop rooting depths, and soil property information are used as inputs. Estimated rooting depths are taken from the ranges listed in Appendix B of ASCE 70 (2016). For crops not listed in ASCE 70, rooting depths are based on the rooting depths of similar crops and professional judgement. Relevant soil properties include total soil depth, depth to restrictive layer, and 5 of 6
available water holding capacity. Estimated soil properties are aggregated from the USDA soil survey geographic database (SSURGO) (Soil Survey Staff, 2025). ETPR is computed using the input parameters (soil, precipitation, and rooting depth) and either the U.S. Bureau of Reclamation (USBR) method (Stamm, 1967) or the National Engineering Handbook Part 623 method (USDA, 1993), depending on local data availability, results, and conditions. For the USBR method, the effective precipitation bins have been modified from the original bins outlined in the USBR method documentation to match regional hydrology patterns..
3.4 Local Water Supply Data
As described in Section 2, available surface water supply and groundwater extraction data is incorporated into the GEEEO process to quantify the amount of known water supply available, prior to estimating the remaining groundwater extraction needed to meet demand. Where field-scale delivery measurements are available, the water supply volume delivered was distributed evenly across all irrigated areas of that field. Where field-scale delivery measurements are not available and only diversion volumes or aggregated delivery volumes for a larger area are available, water supply data is distributed evenly over the area where that water can be delivered for irrigation (e.g., average AF/ac over lands where that water is available for use).
Surface water supply and groundwater extraction data are collected from both publicly available and local sources. Information gathered may include, where applicable:
1. Water supply contract delivery records, from the United States Bureau of Reclamation (USBR), State Water Project (SWP), or other publicly available sources as applicable.
2. Water rights diversions records, from the State Water Resources Control Board (SWRCB) through the Electronic Water Rights Information Management System (eWRIMS).
3. Data requests to local water agencies and water users, requesting surface water diversions, surface water deliveries, surface water outflows, groundwater pumping records, or other available water use data. At the most detailed possible level, these include field-scale volumetric delivery measurements taken by Water or Irrigation District water operators, as required per the Water Conservation Act of 2009.
In cases where current surface water data is not available, general information on surface water inflows and outflows may be gathered from other local sources as available (e.g., Agricultural Water Management Plan water budgets). More information about surface water data sources is described in the Annual Report.
While groundwater extraction data is not available in many parts of the Subbasin, local data is requested each year so that new data can be incorporated into the GEEEO process as it becomes available. It is noted that while groundwater extraction for municipal water supply systems is generally reported for urban areas in the Annual Report based on SWRCB and locally provided data, groundwater extraction for municipal areas is not directly included in the GEEEO process due to underlying differences in how the majority of water is used in urban areas. This also applies to estimates of rural residential groundwater use (e.g., domestic water use pumped through private domestic wells) outside of urban areas. The data sources and approaches used to quantify municipal and rural residential groundwater extraction are described in the Annual Report.
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3.5 Other Agronomic Data
Other agronomic and climate-related data that is incorporated into the GEEEO process includes:
1. Representative consumptive use fractions for crops (i.e., fraction of total applied water that is consumed through ET). Values are based on typical irrigation methods and efficiencies for crops.
2. Conveyance system fractions for subregions (i.e., fraction of diverted water that is delivered, accounting for losses).
3. Reuse fractions for subregions (i.e., fraction of delivered water that is reused).
Information gathered from local sources is used where available, otherwise representative values for agronomic practices in the region are used.
4 References
American Society of Civil Engineers (ASCE). 2016. ASCE Manuals and Reports on Engineering Practice No. 70, Evaporation, Evapotranspiration, and Irrigation Water Requirements (Second Edition).
California Department of Water Resources (DWR). 2024. Provisional 2022 Statewide Crop Mapping GIS Data, Updated January 2024. Available at: https://data.cnra.ca.gov/dataset/statewide-crop-mapping.
Hessels, T., Davids J. C., and Bastiaanssen W. 2022. Scalable Water Balances from Earth Observations (SWEO): Results from 50 Years of Remote Sensing in Hydrology. Water International, 47(6), 866-886.
Land IQ. Land Use Coverage for Butte County and Surrounding Areas for the 2024 Water Year. Provided by Land IQ staff via email. February 2025.
Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Soil Survey Geographic (SSURGO) Database for California. Available online. Accessed January 15, 2025.
Stamm, G.G. (1967). Problems and Procedures in Determining Water Supply Requirements for Irrigation Proiects. In Irrigation of Agricultural Lands (eds R.M. Hagan, H.R. Haise and T.W. Edminster). https://doi.org/10.2134/agronmonogr11.c45
United States Department of Agriculture (USDA). 2024. CropScape – 2023 Cropland Data Layer, Released January 2024. Available at: https://nassgeodata.gmu.edu/CropScape/.
United States Department of Agriculture (USDA); National Agricultural Statistics Service (NASS). 2024. 2023 Nationwide Crop Mapping GIS Data, Released January 31, 2024. Available at:
https://croplandcros.scinet.usda.gov/.
United States Department of Agriculture (USDA). 1993. National Engineering Handbook (NEH). Chapter 2, part 623, Irrigation water requirements. Washington, D.C.: U.S. Dept. Of Agriculture, Soil Conservation Service.
A-1
Attachment A. GEEEO Computational Approach Details
Figures A-1 and A-2, below, present a schematic of the GEEEO computational approach as it has been developed and is being generally applied to support Annual Report Development.
A-2
Figure A-1. Inflows and Outflows to Each 30 m x 30 m Pixel in the GEEEO Process.
A-3
Figure A-2. Solution Steps for Calculating Applied Groundwater (AGW) in Each 30 m x 30 m Pixel in the GEEEO Process.
Appendix 7A
GSP Revised 2027 Broad and RMS Monitoring Networks
Table 7A-1. GSP Revised 2027 Broad and RMS Monitoring Networks State Well Number (SWN) Well Type
Aquifer Zone Repersented
(Primary <700feet,
Very Deep >700feet)
Well Depth
(feet)
Screened Interval Depths
(feet) Groundwater Substainability Agency (GSA) Representitive Monitoring Site (RMS)?
RMS Substainability
Indicator Monitored*
17N01E06D001M Irrigation Primary 500 110-140, 200-220, 240-260, 280-300, 440-500 Reclamation District No. 1004 GSA - Butte 1 Y GWL 17N01E10A001M Residential Primary 110 66-110 Biggs-West Gridley Water District GSA Y GWL 17N01E17F001M Observation Primary 160 130-150 County of Butte GSA - Butte 1 Y GWL 17N01E17F002M Observation Primary 326 312-323 County of Butte GSA - Butte 1 17N01E17F003M Observation Primary 556 505-535 County of Butte GSA - Butte 1 17N01E24A002M Observation Very Deep 1,131 1,063-1,083 County of Butte GSA - Butte 1 17N01E24A006M Observation Primary 75 45-55 County of Butte GSA - Butte 1 Y GWL 17N01E24A004M Observation Primary 480 371-381, 430-440 County of Butte GSA - Butte 1 17N01E24A005M Observation Primary 305 220-240 County of Butte GSA - Butte 1 17N01W10A004M Observation Primary 117 88-98 Reclamation District No. 1004 GSA - Butte 1 Y GWL 17N01W27A003M Observation Primary 203 160-170 Reclamation District No. 1004 GSA - Butte 1 Y GWL 17N01W10A002M Observation Primary 475 380-390, 415-425 Reclamation District No. 1004 GSA - Butte 1 17N01W10A003M Observation Primary 204 148-158 Reclamation District No. 1004 GSA - Butte 1 17N02E14A001M Irrigation Primary 102 70-102 Butte Water District GSA - Butte Y GWL 17N01W27A001M Observation Primary 581 430-440, 500-510 Reclamation District No. 1004 GSA - Butte 1 17N01W27A002M Observation Primary 285 260-270 Reclamation District No. 1004 GSA - Butte 1 17N02E14H001M Irrigation Primary 102 60-102 Butte Water District GSA - Butte Y GWL 17N03E08K002M Residential Primary 100 n/a Butte Water District GSA - Butte Y GWL 18N01E13A002M Irrigation Primary 317 80-317 Richvale Irrigation District GSA Y GWL 17N02E19J001M Irrigation Primary 365 130-148, 172-250, 250-365 Biggs-West Gridley Water District GSA 17N03E05C003M Irrigation Primary 120 n/a Butte Water District GSA - Butte Y ISW 18N01E15D002M Observation Primary 112 56-112 Richvale Irrigation District GSA Y GWL 17N03E16N001M Irrigation Primary 178 48-178 Butte Water District GSA - Butte Y ISW 18N01E01H001M Irrigation Primary 335 120-160, 220-260, 265-335 Richvale Irrigation District GSA 18N01E05D001M Irrigation Primary n/a n/a Western Canal Water District GSA 18N01E05D002M Irrigation Primary 240 120-240 Western Canal Water District GSA 18N01W02E003M Observation Primary 200 110-120 Reclamation District No. 2106 GSA Y GWL 18N01W14B001M Irrigation Primary 204 59-83, 145-173 Reclamation District No. 2106 GSA Y GWL, ISW 18N01E21L001M Irrigation n/a n/a n/a Richvale Irrigation District GSA 18N01W17G001M Irrigation Primary 108 48-108 Reclamation District No. 2106 GSA Y GWL, ISW 18N01W22L001M Irrigation Primary 124 76-92, 108-124 Reclamation District No. 2106 GSA Y GWL 18N01W02E002M Observation Primary 492 450-460 Reclamation District No. 2106 GSA 18N02E16F001M Irrigation Primary 80 20-60 Biggs-West Gridley Water District GSA Y GWL, ISW 18N02E25M001M Irrigation Primary 220 61-220 Butte Water District GSA - Butte Y GWL 18N03E08B003M Irrigation Primary 463 156-463 County of Butte GSA - Butte 1 Y GWL Table 7A-1. GSP Revised 2027 Broad and RMS Monitoring Networks State Well Number (SWN) Well Type
Aquifer Zone Repersented
(Primary <700feet,
Very Deep >700feet)
Well Depth
(feet)
Screened Interval Depths
(feet) Groundwater Substainability Agency (GSA) Representitive Monitoring Site (RMS)?
RMS Substainability
Indicator Monitored*
18N03E21G001M Irrigation Primary 125 n/a County of Butte GSA - Butte 1 Y GWL, ISW 19N01E09Q001M Irrigation Primary 200 140-200 Western Canal Water District GSA Y GWL 19N01E27Q001M Observation Primary 548 260-280 Richvale Irrigation District GSA Y GWL 18N02E32H001M Residential Primary 115 n/a Biggs-West Gridley Water District GSA 19N01E35B001M Observation Primary 156 85-95, 125-135 Richvale Irrigation District GSA Y GWL, ISW 18N03E18F001M Irrigation Primary 462 100-150, 190-220 Western Canal Water District GSA 19N01W15D002M Residential Primary 300 250-260, 275-295 Reclamation District No. 2106 GSA Y GWL 19N01W22D007M Observation Primary 120 80-90 Western Canal Water District GSA Y GWL, ISW 19N01W27R001M Irrigation Primary 465 68-108 Reclamation District No. 2106 GSA Y GWL, ISW 19N02E07K004M Observation Primary 192 140-150 Western Canal Water District GSA Y GWL 19N02E13Q001M Observation Primary 221 130-140, 200-210 Western Canal Water District GSA Y GWL 19N01E35B003M Observation Primary 523 490-510 Richvale Irrigation District GSA 19N03E05N002M Residential Primary 180 24-48 County of Butte GSA - Butte 1 Y GWL 20N01E18L003M Observation Primary 173 100-110 Western Canal Water District GSA Y GWL, GWS 19N01W22D005M Observation Primary 555 520-530 Western Canal Water District GSA 19N01W22D006M Observation Primary 380 340-350 Western Canal Water District GSA 20N01E35C001M Residential Primary 92 49.5-92 Western Canal Water District GSA Y GWL, ISW 20N01W11N002M Observation Primary 170 84-170 Reclamation District No. 2106 GSA Y GWL 19N01W28A001M Irrigation Primary 140 120-140 Glenn Groundwater Authority GSA Y GWQ 19N02E07K002M Observation Primary 600 560-570 Western Canal Water District GSA 19N02E07K003M Observation Primary 368 330-340 Western Canal Water District GSA 20N02E15H001M Observation Primary 180 170-180 Western Canal Water District GSA Y GWL 20N02E28N001M Other Primary 277 160-277 Western Canal Water District GSA Y GWL 19N02E13Q002M Observation Primary 495 460-470 Western Canal Water District GSA 21N01E08K002M Irrigation Primary 181 19-181 (open hole) County of Butte GSA - Butte 1 Y GWL 19N02E15N002M Irrigation n/a n/a n/a Richvale Irrigation District GSA 19N02E17A001M Residential Primary 150 n/a Richvale Irrigation District GSA 21N01W11A002M Observation Primary 200 120-135, 175-185 County of Butte GSA - Butte 1 Y GWL 20N01E13Q002M Irrigation n/a n/a n/a Western Canal Water District GSA 21N01W13J003M Observation Primary 400 355-385 County of Butte GSA - Butte 1 Y GWL, GWS 20N01E18L002M Observation Primary 583 510-530, 550-560 Western Canal Water District GSA Y GWQ 21N01W23J001M Irrigation Primary 54 n/a County of Butte GSA - Butte 1 Y GWL, GWS 21N01W35K002M Observation Primary 270 75-135 County of Butte GSA - Butte 1 Y GWL, GWS 20N01W04J001M Irrigation Primary 175 1.0-94 Reclamation District No. 2106 GSA 22N01E32E004M Residential Primary 160 85-160 County of Butte GSA - Butte 1 Y GWL 17N01E24A003M Observation Very Deep 833 770-790 County of Butte GSA - Butte 1 Y GWL, GWQ Table 7A-1. GSP Revised 2027 Broad and RMS Monitoring Networks State Well Number (SWN) Well Type
Aquifer Zone Repersented
(Primary <700feet,
Very Deep >700feet)
Well Depth
(feet)
Screened Interval Depths
(feet) Groundwater Substainability Agency (GSA) Representitive Monitoring Site (RMS)?
RMS Substainability
Indicator Monitored*
20N02E15H002M Observation Primary 75 55-65 Western Canal Water District GSA Y ISW 20N02E16P001M Irrigation Primary 466 n/a Western Canal Water District GSA 17N01W10A001M Observation Very Deep 828 770-780, 790-800 Reclamation District No. 1004 GSA - Butte 1 Y GWL, GWQ 18N01E35L001M Observation Very Deep 899 816-836 Biggs-West Gridley Water District GSA Y GWL, GWQ, LS 18N01W02E001M Observation Very Deep 739 719-729 Reclamation District No. 2106 GSA Y GWL 19N01E35B002M Observation Very Deep 980 930-950 Richvale Irrigation District GSA Y GWL, GWQ, LS 21N01W11A003M Observation Primary 104 30-50 County of Butte GSA - Butte 1 19N01W22D004M Observation Very Deep 820 780-790 Western Canal Water District GSA Y GWL 21N01W13J002M Observation Primary 610 570-590 County of Butte GSA - Butte 1 19N02E13Q003M Observation Very Deep 690 670-680 Western Canal Water District GSA Y GWL, GWQ 20N01E18L001M Observation Very Deep 940 767-810, 873-894 Western Canal Water District GSA Y GWL, LS 21N01W24B001M Irrigation Very Deep 1,018 800-820 County of Butte GSA - Butte 1 21N01W11A001M Observation Very Deep 1,311 810-820, 960-970, 1,050-1,060, 1,270 - 1,280 County of Butte GSA - Butte 1 Y GWL
21N01W13J001M Observation Very Deep 830 780-820 County of Butte GSA - Butte 1 Y GWL, GWQ 21N01W11A002M Observation Primary 160 85-160 County of Butte GSA - Butte 1 GWQ - Groundwater Quality
GWS - Groundwater Storage
LS - Land Subsidence
*GWL - Groundwater Level
ISW - Interconnected Surface Water
Note: Table prepared by Butte County Department of Water and Resource Conservation Appendix 8A
Second Amendment to Cooperation Agreement
Appendix 10A
Interbasin Coordination Factsheet
Antelope | Butte | Colusa | Corning | Los Molinos | Red Bluff | Vina Northern Sacramento Valley | Sustainable Groundwater Management Act Interbasin Coordination in the North Sacramento River Corridor Sustainable
Groundwater
Management
Act
The California Sustainable Groundwater Management Act (SGMA) requires that Groundwater Sustainability Agencies (GSAs) develop and implement Groundwater Sustainability Plans (GSPs) to manage groundwater resources and conditions in each of the State’s groundwater basins. One of the requirements for a GSP is that it does not adversely affect sustainable groundwater management in an adjoining groundwater basin or subbasin.
Ensuring Regionally Sustainable Groundwater Management
In the Northern Sacramento Valley, our
groundwater subbasins are hydrologically
connected – water management decisions and
actions in one subbasin can affect neighboring
subbasins.
The Department of Water Resources (DWR) reviews
groundwater sustainability plans for:
Relevant interbasin coordination efforts
Alignment of thresholds and objectives
Potential impacts to or from adjacent
subbasins
Regional coordination also offers significant
opportunities for:
Joint learning and understanding
Protecting shared water resources
Reducing duplicative efforts
Collaborative problem-solving
Through coordinated efforts, we can achieve
long-term groundwater sustainability across
the region while maintaining local control.
Why Regional Coordination Matters
www.buttecounty.net/2221/North-Sacramento-River-Corridor-Inter-Ba Who is Involved?
Collaborative efforts have been ongoing since the early phases of SGMA when 11 subbasins in the Northern Sacramento Valley (Antelope, Bowman, Butte, Colusa, Corning, Los Molinos, Red Bluff, Sutter, Vina, Wyandotte Creek, and Yolo) created an Interbasin Coordination Report outlining a framework for sustained coordination during GSP implementation.
Seven of those subbasins make up the North Sacramento River Corridor (Antelope, Butte, Colusa, Corning, Los Molinos, Red Bluff, and Vina). The GSAs have delved into more focused conversations and analyses to outline a path forward for interbasin coordination across these seven subbasins.
June 2026
Subbasin
(with website links)
GSA(s)
Antelope Tehama County Flood Control and Water
Conservation District (FCWCD)
Butte
Biggs-West Gridley WD, Butte County, Butte WD, City
of Biggs, City of Gridley, Colusa Groundwater
Authority, Glenn County, RD 1004, RD 2106, Richvale
ID, Western Canal WD
Los Molinos Tehama County FCWCD
Red Bluff Tehama County FCWCD
Corning
(Corning | Tehama)
Corning Sub-basin GSA, Tehama County FCWCD
Colusa
(Glenn | Colusa)
Glenn Groundwater Authority; Colusa Groundwater
Authority
Vina
(Vina | RCRD)
Rock Creek Reclamation District, Vina GSA With all GSPs approved by the State, implementation is underway. Through funding from DWR’s SGM grant program, a technical analysis by Montgomery & Associates evaluated GSP contents across subbasins, identified boundary flow patterns, and analyzed differences in sustainability criteria between neighboring areas.
Building on this work, GSA representatives are now developing the NSRC IBC Framework Five-Year Implementation Update, which will guide regional coordination through the Periodic Evaluations due in 2027 and beyond. Key coordination priorities include understanding cross-boundary data gaps, regional modeling, interconnected surface water management, analyzing boundary flows, coordinating on state-required Recommended Corrective Actions, and exploring opportunities for joint projects.
The Interbasin Coordination Framework is based on a foundation of five “pillars” of collaboration – Information sharing ensures all subbasins stay informed about changing conditions and management approaches. Through joint analysis and evaluation, the GSAs developed a shared understanding of policies adopted across the region’s GSPs; this analysis is complete and informing individual Periodic Evaluations. Under coordination on mutually beneficial activities, GSAs are pursuing joint projects and funding opportunities, with Interconnected Surface Water (ISW) management emerging as the region’s current top coordination priority. Coordinated communication and outreach ensures consistent messaging to stakeholders and the public. Finally, an issue resolution process provides a pathway for addressing potential conflicts before they escalate.
Five Pillars of Coordination
Where We Are Now
What’s Coming Next
GSA representatives will continue
meeting through summer 2026 to
finalize the NSRC IBC Framework FiveYear Implementation Update.
In January 2026, the GSAs held a public webinar to
provide an overview of coordination activities and share progress on the Five Pillars. A public meeting is planned for June 2026 to present updates on the IBC effort and
the ISW Technical Work Plan, and to hear from the
community.
The implementation framework update guides
coordination over the next five years through 2032,
supporting each subbasin’s path to sustainability while maintaining local control.
Receive Updates - Sign up for your GSA’s interested
parties list.
Contact Your GSA - Talk to your GSA representative
Attend Meetings – Attend public meetings and GSA
Board meetings
How to Get Involved
5-Pillar Framework
for Regional
Coordination
June 2026
Appendix 10B
Interconnected Surface Water Factsheet
https://www.buttecounty.net/2221/North-Sacramento-River-Corridor-Inter-Ba
NORTH SACRAMENTO RIVER CORRIDOR INTERBASIN COORDINATION Antelope | Butte | Colusa | Corning | Los Molinos | Red Bluff | Vina Working Together on Interconnected Surface Waters
A State Requirement and a Regional Opportunity
California's Sustainable Groundwater Management Act
(SGMA) requires local agencies to understand how
groundwater pumping affects nearby rivers and streams
– a relationship known as Interconnected Surface Waters, or ISW. In its first review of local Groundwater
Sustainability Plans, the Department of Water Resources issued every subbasin in the North Sacramento River
Corridor a Recommended Corrective Action for ISW --
one of the six SGMA sustainability indicators each
subbasin must manage. Addressing this requirement is
essential for maintaining SGMA compliance and keeping
groundwater management under local control.
Why a Regional Approach?
In this valley, hydrological connectivity is the rule, not the exception. The Sacramento River runs through the
corridor and forms subbasin boundaries, while tributaries like Butte Creek cross multiple subbasins.
Groundwater and surface water interact throughout the region, and the effects of pumping on streamflow do not stop at subbasin lines. Understanding those effects (and demonstrating that management in one subbasin does not adversely affect neighboring subbasins, as SGMA requires), demands a regional approach.
Regional Tools for a Robust Understanding
A shared regional groundwater-surface water model is the most effective path forward, but getting there requires work. Existing local models have limitations for regional ISW analysis, and existing regional tools need refinement.
Targeted data collection is needed to fill gaps and build confidence in model results. If each subbasin pursued this independently, the cost would be higher and the methods would likely be incompatible – making cross-boundary
analysis harder, not easier. Coordinating with DWR reduces costs to individual subbasins and produces tools that are commonly accessible across the region.
June 2026
https://www.buttecounty.net/2221/North-Sacramento-River-Corridor-Inter-Ba Value in Working Together
Better information
A shared regional model gives each
subbasin more reliable, consistent
data for ISW evaluations, boundary
flow analyses, and cross-boundary
impact assessments.
Lower cost
Collaborative data collection and
modeling costs far less than seven
subbasins duplicating the same
work independently.
Local authority stays local
This joint effort does not take away
any GSA's local authority. It provides
shared information to inform each
GSA's decisions – every agency sets its
own sustainability criteria.
What Is Being Proposed?
The local water managers are exploring a joint technical work plan to collect data, refine regional models, and develop consistent information each agency can use to meet its staterequired obligations. The effort is built around three interrelated steps:
1) Regional Data Collection: Field teams would collect
measurements along the Sacramento River, Feather River, Butte Creek, and other shared streams to improve
understanding of how water moves between rivers and
underground aquifers across the region.
2) Refined Regional Modeling: Using that data, technical teams would work with DWR to improve an existing
regional model so they can better simulate how
groundwater pumping affects streamflow across subbasin
boundaries.
3) Local Policy Support: Drawing on the modeling results, a regional guidance document would provide each agency
with options and examples to define its own sustainability standards – while each agency retains full authority over its own decisions.
Where Things Stand
An ISW work plan describing these three steps in greater detail is in draft form and under review by local water managers. It has not been formally adopted, and funding has not yet been secured.
Getting Involved. Local GSA boards will decide whether to move forward with this approach. If they do, this work is expected to support each subbasin’s compliance obligations in 2027 and beyond. Your voice matters in that process.
This effort advances Pillar 3 of the Northern Sacramento Valley Interbasin Coordination Framework – Coordination on Mutually Beneficial Activities – the regional structure that guides collaboration among the seven NSRC subbasins since 2022. Visit the website to learn more.
Appendix 10C
Interbasin Coordination Framework 5-Year
Implementation Update
NORTH SACRAMENTO RIVER CORRIDOR I REGIONAL INTERBASIN COORDINATION DRAFT Interbasin Coordination Framework 5-Year Implementation Update 1 This 5-year update advances coordinated regional implementation of the Northern Sacramento Valley Interbasin Coordination Framework's Five Pillars through the Periodic Evaluation/Plan Amendment process and over the subsequent 5 years between 2026–2032. The update focuses on topics relating to regionallyscaled coordination among subbasins in the North Sacramento River Corridor, including Red Bluff (5-021.50), Antelope (5-021.54), Los Molinos (5-021.56), Corning (5-021.51), Vina (5-021.57), Colusa (5-021.52), and Butte (5-021.70), and identifies each GSA's commitments to implement the Framework over that period. Interbasin coordination on specific boundary topics is ongoing and will occur on a neighbor-to-neighbor basis.
Interbasin Coordination Five Pillars Scope of Activities Implementation Deliverables Pillar 1. Information-sharing
a. Inform each other on changing
conditions (i.e., surface water
cutbacks, land use changes, policy
changes that inform groundwater
management)
b. Share annual reports and interim
progress reports
c. Share data and technical
information and work towards
building shared data across and/or
along basin boundaries (e.g.,
monitoring data, water budgets,
modeling inputs and outputs, and
Groundwater Dependent
Ecosystems)
• Convene at least one regional meeting annually with GSA Coordination representatives (and more often, as warranted) • Ongoing informal outreach to neighbors
• Continue to use other existing collaborative venues to report out progress and coordinate, as needed (e.g., Northern
Sacramento Valley IRWM, NCWA Groundwater Task Force,
etc.)
Timeline
• Near-term (Periodic
Evaluation, January
2027)
• At least annually
through next Periodic
Evaluation term (2027-
2032)
Responsible Parties
• Consensus Building
Institute (CBI)
(facilitation through
2026)
• GSAs
Funding Source(s)
• Facilitation Support
Services (through 2026)
• In kind GSA
representative time
• Agendas and
associated materials
for formal meetings
posted to regional
interbasin
coordination
website
• 2025 GSP Annual
Reports:
5-021.57 Vina
5-02.70 Butte
5-021.50 Red Bluff
5-021.54 Antelope
5-021.56 Los
Molinos
5-021.51 Corning
5-021.52 Colusa
Pillar 2. Joint analysis & evaluation
a. Evaluate and compare contents of
GSPs with a focus on establishing
Inter-basin Coordination Analysis and Modeling Project Timeline • Completed in 2025
North Sacramento River
Corridor Results
• Webinar Recording
This project builds on work completed from 2020-2022 to develop the Northern Sacramento Valley Inter-Basin Coordination Report which established an Interbasin Coordination Framework for SGMA implementation. Additional background information on North Sacramento Valley regional interbasin coordination can be found at the following website: https://www.buttecounty.net/1234/Inter-Basin-Coordination Interbasin Coordination Framework 5-Year Implementation Update (Version: June 5, 2026) 2 Interbasin Coordination Five Pillars Scope of Activities Implementation Deliverables a common understanding of basin
conditions at boundaries
b. Identify significant differences,
uncertainties, and potential issues
of concern related to groundwater
interaction at the boundaries
c. Engage in analysis and evaluation
of SMCs between GSPs to assess
impacts and identify significant
differences and possible impacts
between subbasins that could
potentially lead to undesirable
results
• Evaluated and compared contents of GSPs in the North
Sacramento River region with a focus on establishing a
common understanding of basin conditions at boundaries. • Identified significant differences, uncertainties, and potential issues of concern related to groundwater interaction at the boundaries.
• Analyzed SMCs between GSPs to identify significant
differences and possible impacts between Subbasins that could potentially lead to undesirable results.
• Updated Butte Basin Groundwater Model and use the revised model to compute subbasin flows and stream-aquifer
interaction flows at subbasin boundaries.
Responsible Parties
• Butte County contracted
with Montgomery &
Associates, technical
consultant
Funding Source(s)
• DWR SGMA
Implementation Funding
(awarded to Vina and
Wyandotte Creek
Subbasins)
• Presentation Slides
• Technical Memo
Interbasin Flow
Evaluation with Regional
Model
• Webinar Recording
• Presentation Slides
• Technical Memo
Pillar 3. Coordination on mutually
beneficial activities
a.Communicate, coordinate, and
collaborate on mutually beneficial
activities, which could include
joint monitoring, joint reporting,
regional modeling, and other
efforts to address data gaps at
subbasin boundaries
b.Collectively pursue funding and
collaborate on mutually agreed
upon projects and management
actions that provide benefits
across boundaries
c. Leverage existing collaboratives
Priority Activity (2026-2032):
• Interconnected surface waters (ISW): develop and seek funding for a regional approach to interconnected surface waters that considers coordinated monitoring and modeling to consistently respond to Recommended Corrective Actions that each subbasin received. https://data.ca.gov/dataset/sgmadepletions-of-interconnected-surfacewater/resource/38c8ab75-f8b3-4c00-aabb-38db84cccc94 Areas of Interest for Ongoing Exploration:
• Boundary flow analysis and modeling: model-based boundary flow analysis to better understand, quantify, and predict how water flows across basin boundaries and if the actions of one subbasin are affecting flow in another. Preparing for the analysis will include a discussion of the use of existing models and the possible coordination on shared modeling tools, when possible.
• Monitoring: Discuss monitoring networks with a focus on shared boundaries, identification of data gaps in groundwater level, water quality, and subsidence data.
• Joint project implementation: Leverage resources and pursue funding opportunities to implement projects that could offer regional solutions, noting the potential to consider mutually beneficial projects, such as recharge, among others.
Timeline
• Document progress in
the 2027 Periodic
Evaluations (PE) related
to ISW
• Long-term (through the
next Periodic Evaluation
in 2032)
Responsible Parties
• Northern California
Water Association
(NCWA) contracting with
MBK Engineers,
technical consultant,
GSA consultants working
on PEs
• Coordination with the
Department of Water
Resources regarding
regional modeling tools
Funding Source(s)
• Northern California
Water Association
(NCWA)
• Northern Sacramento
Valley ISW Work Plan
Factsheet
• Additional work
products TBD overtime
within areas of
interest for ongoing
exploration
Interbasin Coordination Framework 5-Year Implementation Update (Version: June 5, 2026) 3 Interbasin Coordination Five Pillars Scope of Activities Implementation Deliverables • GSAs through technical
consultants (SGM
implementation
funding)
• Possible future grant
funding through
Proposition 4
Pillar 4. Coordinated communication
and outreach
a.Coordinate and collaborate on
regional-scale public engagement
and communication strategies
that promote awareness on
groundwater sustainability,
enhance public trust, and
maintain institutional knowledge
b.Maintain list of GSA/subbasin staff
contacts and websites
• Create a list of GSA/subbasin staff contacts and websites • Develop informational materials that could be distributed across the region within each of the subbasins’ using existing communication mechanisms and venues; update materials
periodically to reflect ongoing implementation activities. • Continue to utilize the regional interbasin coordination webpage hosted by Butte County to post information and work products related to regional interbasin coordination activities. • Utilize existing regional venues to coordinate communications and outreach, including: 1) NCWA Groundwater Task Force; 2) NSV IRWM, and others, as warranted.
• Periodically host public workshops coordinated through Pillar 1 GSA meetings.
Timeline
• Near Term (By 2027)
• Long-term (through the
next Periodic Evaluation
in 2032)
Responsible Parties
• CBI (through 2026)
• GSA representatives
Funding Source(s)
• Facilitation Support
Services (through 2026)
• In-kind website
administration (Butte
County)
• In-kind staff time and
venue use
• GSA Directory with
points of contacts
for each subbasin
• General Factsheet
• Public webinar
recording and slide
deck (January 28,
2026)
• Public webinar
materials for the
June 16, 2026 will
be added following
webinar.
Pillar 5. Issue-resolution process
a. Establish and follow an agreedupon process for identifying and resolving conflicts between GSAs
• GSAs confirmed the approach described in the Sacramento Valley Inter-Basin Coordination Report (See Appendix D on pages 37-38)
• GSAs will continue to implement this framework and can activate an issue resolution process on an as-needed basis. • GSAs will use consistent language in the subbasins respective Periodic Evaluations describing regional Interbasin
Coordination in the North Sacramento River Corridor.
Timeline
• Ongoing
Responsible Parties
• CBI (through 2026)
• GSA Coordination Group
meetings (see Pillar 1)
Funding Source(s)
• Facilitation Support
Services (through 2026)
• In-kind staff time
Appendix 11A
Adopted Resolution by the Butte Subbasin GSAs