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Sustainable Groundwater Management Act 2019 Basin Prioritization Process and Results State of California California Natural Resources Agency Department of Water Resources Sustainable Groundwater Management Program APRIL 2019
Contents i Table of Contents I. Purpose of Report ___ 1
II. Introduction ___ 1
III. Background ___ 1
IV. SGMA 2019 Basin Prioritization ___ 3
V. Process ___ 4
Component 1: The population overlying the basin or subbasin ___ 4
Component 2: The rate of current and projected growth of the population overlying the basin or subbasin ___ 5
Component 3: The number of public supply wells that draw from the basin or subbasin ___ 8
Component 4: The total number of wells that draw from the basin or subbasin ___ 9
Component 5: The irrigated acreage overlying the basin or subbasin ___ 12
Component 6: The degree to which persons overlying the basin or subbasin rely on groundwater as their primary source of water ___ 13
Component 7: Any documented impacts on the groundwater within the basin or subbasin, including overdraft, subsidence, saline intrusion, and other water quality degradation ___ 17
Component 8: Any other information determined to be relevant by the department, including adverse impacts on local habitat and local streamflows ___ 22
Basin Priority ___ 30
VII.References ___ 31
Appendix 1 – Summary of SGMA 2019 Basin Prioritization Results . A-1 Appendix 2 – DWR standard land use legend (adapted for remote sensing crop mapping) (component 6.a . A-19 Appendix 3 – List of chemicals used in the evaluation of documented water quality degradation (component 7.d . A-20 Appendix 4 – Computed groundwater volume for non-adjudicated portion(s) of basins with adjudicated area used during evaluation (component 8.c.3 . A-22 Appendix 5 – Breakdown of area in basins with adjudications used during evaluation (component 8.c.3 . A-23 Appendix 6 – Groundwater Basins Identified with Groundwater-Related Transfers (component 8.d.2 .
Contents ii Figures Figure A-1 Statewide Map of SGMA 2019 Basin Prioritization Results, Phase 1 Final . A-2 Figure A-2 Statewide Map of SGMA 2019 Basin Prioritization Results, Phase 2 Draft . A-16 Tables Table 1 Component 1: Priority Points and Ranges for Population Density ___ 5
Table 2 Component 2: Priority Points and Ranges for Population Growth ___ 7
Table 3 Component 3: Priority Points and Ranges for Public Supply Well Density ___ 9
Table 4 Component 4: Priority Points and Ranges for Total Production Well Density ___ 11
Table 5 Component 5: Priority Points and Ranges for Density of Irrigated Acres ___ 12
Table 6 Component 6.a: Points and Ranges for Groundwater Use per Acre ___ 16
Table 7 Component 6.b: Points and Ranges for Percent of Total Water Supply Met by Groundwater ___ 17
Table 8 Sub-component 7.d.1: Points and Ranges for Documented Impacts – Water Quality Degradation – Average Relative MCL Exceedance ___ 21
Table 9 Sub-component 7.d.2: Points and Ranges for Documented Impacts – Water Quality Degradation – Prevalence of Groundwater Contamination ___ 21
Table 10 Sub-component 7.d: Points and Ranges for Documented Impacts – Water Quality Degradation ___ 22
Table 11 Component 7: Priority Points and Ranges for Documented Impacts – Cumulative Total ___ 22
Table 12 Sub-components 8.c and 8.d: Additional Conditions Analyzed Prior to Priority Determination ___ 25
Table 13 SGMA 2019 Basin Prioritization Priority Based on Total Priority Points ___ 30
Table A-1 Statewide SGMA 2019 Basin Prioritization Results, Phase 1 Final .
A-3 Table A-2 Statewide SGMA 2019 Basin Prioritization Results, Phase 2 Draft . A-17
Contents iii Acronyms and Abbreviations Cal-SIMETAW California Simulation of Evapotranspiration of Applied Water CASGEM California Statewide Groundwater Elevation Monitoring DOF California Department of Finance DWR California Department of Water Resources GAMA Groundwater Ambient Monitoring and Assessment GSA Groundwater Sustainability Agency GSP Groundwater Sustainability Plan MCL Maximum Contaminant Level NHD National Hydrography Dataset OSWCR Online System for Well Completion Reports PLSS Public Land Survey System PWSS Public Water System Statistics SGMA Sustainable Groundwater Management Act SWRCB State Water Resources Control Board USGS United States Geological Survey WCR Well Completion Report (DWR Form 188)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 1 I. Purpose of Report This report describes the background, process, and results of the Sustainable Groundwater Management Act (SGMA) 2019 Basin Prioritization. The California Department of Water Resources (DWR) is required to update California’s groundwater basin prioritization in accordance with the requirements of SGMA and related laws.1 II. Introduction Bulletin 118 – Interim Update 2016 (California Department of Water Resources 2016a) defined 517 groundwater basins and subbasins in California. DWR is required to prioritize these 517 groundwater basins and subbasins as either high, medium, low, or very low.
For the purposes of groundwater basin prioritization, basins and subbasins are processed equally and are referred to as basins in this report. It is the policy of the State through SGMA that groundwater resources be managed sustainably for longterm reliability and multiple benefits for current and future beneficial uses. The State also recognizes that sustainable groundwater management is best achieved locally through the development, implementation, and updating of plans and programs based on the best available science. DWR plays a key role in providing the framework for sustainable groundwater management in accordance with the statutory requirements of SGMA and other provisions within the California Water Code (Water Code).
Other State agencies, including the State Water Resources Control Board (SWRCB) and California Department of Fish and Wildlife, play a role in SGMA implementation and are required to consider SGMA when adopting policies, regulations, or criteria, or when issuing orders or determinations, where pertinent.2 III. Background Groundwater basin prioritization was initially completed by DWR in response to legislation enacted in California's 2009 Comprehensive Water Package (California Department of Water Resources 2009), which established Part 2.11 of the Water Code requiring groundwater elevations be monitored seasonally in all groundwater basins identified in the Bulletin 118 - 2003 Update3 (California Department of Water Resources 2003a).
Part 2.11 added general provisions to the Water Code that required DWR to identify the extent of groundwater elevation monitoring undertaken within each basin and directed DWR to prioritize basins for that purpose. In response to the new requirements of Part 2.11, DWR established the California Statewide Groundwater Elevation Monitoring (CASGEM) Program. In June 2014, the CASGEM Program released its prioritization for the groundwater basins identified in Bulletin 118 - 2003 1 Water Code sections 10722.4 and 10933. 2 Water Code Section 10720.9. 3 Stats. 2009-2010, 7th Ex. Sess., c. 1 (S.B.6), § 1, eff.
California Department of Water Resources 2 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results Update. The CASGEM 2014 Basin Prioritization classified basins as high, medium, low, or very low based on the consideration of the eight components required in Water Code Section 10933(b). In September 2014, Governor Brown signed into law three bills that formed SGMA.4 SGMA required DWR to update basin priority for each groundwater basin no later than January 31, 2015, and reassess the prioritization anytime DWR updates Bulletin 118 basin boundaries.5 DWR applied the CASGEM 2014 Basin Prioritization as the initial SGMA 2015 Basin Prioritization under SGMA, resulting in the designation of 127 high and medium priority basins (California Department of Water Resources 2014a).
In the fall of 2016, DWR completed and released groundwater basin boundary modifications. Bulletin 118 – Interim Update 2016, which included the final boundary modifications, was published on December 22, 2016. As a result of these modifications, updated basin prioritizations were required for the 517 groundwater basins identified in Bulletin 118. In May of 2018, DWR released the draft basin prioritization results for the 517 basins and held a 94-day public comment period. Simultaneously, local agencies requested a subsequent round of basin boundary modifications. This required DWR to prioritize the basins in two phases (referred to as SGMA 2019 Basin Prioritization Phase 1 and 2).
The SGMA 2019 Basin Prioritization Phase 1 focused on the basins that used the Bulletin 118 – Interim Update 2016 basin boundary shapefile (California Department of Water Resources 2016b) and not affected by the 2018 basin boundary modifications. This phase allowed DWR to finalize in January 2019 the SGMA 2019 Basin Prioritization Phase 1 priorities that included 458 basins. SGMA 2019 Basin Prioritization Phase 2 covers the remaining 57 basins that include the 53 basins that were modified and approved, as well as two that were not approved by DWR as part of the 2018 basin boundary modifications, plus two basins whose boundary modifications were from Assembly Bill 1944.
All 57 basins of SGMA 2019 Basin Prioritization Phase 2 used the Bulletin 118 – Update 2019 basin boundary shapefile (California Department of Water Resources 2019).
SGMA applies to all California groundwater basins and requires that highand medium-priority groundwater basins form Groundwater Sustainability Agencies (GSAs) and be managed in accordance with locally-developed Groundwater Sustainability Plans (GSPs) or Alternatives to GSPs (Alternatives). Highand medium-priority basins that are identified in Bulletin 118 – Interim Update 2016 as a critically overdrafted basin are required to submit a GSP by January 31, 2020. The remaining highand mediumpriority basins identified in January 2015 are required to submit a GSP by January 31, 2022. Basins newly identified as highor medium-priority in the SGMA 2019 Basin Prioritization are required to form a GSA or submit an Alternative within two years from the date the basin’s priority is finalized and are required to submit a GSP five years from the same finalization date.
4 Stats.2014, c. 346 (S.B.1168), § 3, c. 347 (A.B.1739), § 18, c. 348 (S.B.1319), § 2, eff. Jan. 1, 2015. 5 Water Code sections 10722.4(b) and 10722.4(c)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 3 IV. SGMA 2019 Basin Prioritization The SGMA 2019 Basin Prioritization process was conducted to reassess the priority of the groundwater basins following the 2016 basin boundary modification, as required by the Water Code.6 For the SGMA 2019 Basin Prioritization, DWR followed the process and methodology developed for the CASGEM 2014 Basin Prioritization, adjusted as required by SGMA and related legislation.
DWR is required to prioritize basins for the purposes of SGMA,7 which was enacted, among other things, to provide for the sustainable management of groundwater basins. This entailed a reassessment of factors that had been utilized in the CASGEM program to prioritize basins based on groundwater elevation monitoring. SGMA also required DWR to continue to prioritize basins based on a consideration of the components specified in Water Code Section 10933(b), but the list of components had been amended to include the italicized language: 1. The population overlying the basin or subbasin. 2. The rate of current and projected growth of the population overlying the basin or subbasin.
3. The number of public supply wells that draw from the basin or subbasin. 4. The total number of wells that draw from the basin or subbasin. 5. The irrigated acreage overlying the basin or subbasin. 6. The degree to which persons overlying the basin or subbasin rely on groundwater as their primary source of water.
7. Any documented impacts on the groundwater within the basin or subbasin, including overdraft, subsidence, saline intrusion, and other water quality degradation. 8. Any other information determined to be relevant by the department, including adverse impacts on local habitat and local streamflows [emphasis added]. DWR incorporated new data, to the extent data are available 8 , and the amended language of Water Code Section 10933(b)(8) (component 8) to include an analysis of adverse impacts on local habitat and local streamflows as part of the SGMA 2019 Basin Prioritization. Evaluation of groundwater basins at a statewide scale does not necessarily capture the local importance of groundwater resources within the smaller-size or lower‐use groundwater basins.
For many of California’s low‐use basins, groundwater provides close to 100 percent of the local beneficial uses. Thus, when reviewing the SGMA 2019 Basin Prioritization results, it is important to recognize the findings are not intended to characterize groundwater management practices or diminish the local importance of the smaller-size or lower‐use groundwater basins; rather, the results are presented as a statewide assessment of the overall importance of groundwater resources in meeting beneficial uses.
6 Water Code Section 10722.4(c) 7 Water Code Section 10722.4(a) 8 Water Code Section 10933(b)
California Department of Water Resources 4 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results The following information was deemed relevant and considered as part of component 8 for the SGMA 2019 Basin Prioritization based on SGMA:
Adverse impacts on local habitat and local streamflows.
Adjudicated areas.
Critically overdrafted basins.
Groundwater-related transfers. Additional information about how each of these components were analyzed can be found in the process section of this document.
V. Process The CASGEM 2014 and SGMA 2019 basin prioritization used the basin’s total priority points assigned to each of the eight components to determine the priority. Based on the total accumulated priority points, the basin was assigned a very low, low, medium, or high priority. Both prioritization processes included additional evaluations of the basins that could alter the points assigned and thus the priority. The data sources, processes, and steps used to evaluate each of the eight components of Water Code Section 10933(b) for the SGMA 2019 Basin Prioritization are described below. Supplemental data submitted during the May 2018 Draft Basin Prioritization comment period was also considered before finalization.
Component 1: The population overlying the basin or subbasin9 Data Source
2010 United States Census population block data (California) Process Population density was analyzed for the SGMA 2019 Basin Prioritization using the same methods and data relative to the CASGEM 2014 Basin Prioritization. The 2010 United States Census population block data (United States Census Bureau 2010a and 2010b) was used to calculate the population overlying each groundwater basin using the following methods:
For population blocks contained wholly within a basin boundary, all population in the block was included in the basin population total.
For population blocks located partially within the basin, the proportion of the population included was equal to the proportion of the area of the block contained within the basin and was applied to the basin population total. For example, if 60% of the population block was within basin boundaries, then 60% of the reporting block total population was attributed to the total population of the basin. 9 Water Code Section 10933(b)(1)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 5 Step 1 – Calculate Basin’s Total Population: The basin’s total population was calculated by summing all the included population blocks per the two methods described above.
Step 2 – Calculate the Population Density: The basin’s 2010 population density was calculated by dividing the basin’s total population (Step 1) by the basin’s area (square miles – Appendix 1). Table 1 lists the priority points and associated ranges of population density.
Table 1 Component 1: Priority Points and Ranges for Population Density Priority Points Population Density (people/square mile) ‘x’ = population density 250 2 250 ≤ x < 1,000 3 1,000 ≤ x < 2,500 4 2,500 ≤ x < 4,000 5 x ≥ 4,000 Component 2: The rate of current and projected growth of the population overlying the basin or subbasin10 Data Source
2000 and 2010 United States Census population block data (California)
California Department of Finance (DOF) current trend 2030 county population projections
2000 and 2010 county population estimates developed for the California Water Plan Update 2018 (California Department of Water Resources 2018a) Process Population growth was analyzed for the SGMA 2019 Basin Prioritization using the same methods and data relative to the CASGEM 2014 Basin Prioritization.
Part A: Estimating Basin and Non-Basin Population within each County Step 1 – Calculate the 2000 and 2010 Basin Population: The 2000 (United States Census Bureau 2000a and 2000b) and 2010 population were estimated for all basins and portions of basins within each county using the methods described for component 1. Step 2 – Calculate the 2000 and 2010 Non-Basin Area Population by County: For each county, the 2000 United States Census population block data (United States Census Bureau 2000a and b) and 2010 10 Water Code Section 10933(b)(2)
California Department of Water Resources 6 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results United States Census population block data were used to calculate the population overlying the non-basin area in each county:
For population blocks contained wholly outside of a basin boundary and within the county, all population in the block was included in the non-basin population total for the county.
For population blocks located partially outside of a basin boundary and within the county, the proportion of the population block contained outside of a basin was applied to the non-basin population total for the county. For example, if 40 percent of the reporting block total population was located outside of a basin boundary, 40 percent of the population was attributed to the total population of the non-basin area.
For population blocks located outside of a basin boundary and partially outside of the county, the proportion of the population block contained within the county was applied to the non-basin population total. For example, if 60 percent of the population block was within county boundaries, then 60 percent of the reporting block total population was attributed to the total population of the non-basin area. Step 3 – Calculate the Difference Between the 2000 and 2010 Population: The difference between the 2000 and 2010 population estimates for each of the basins, portions of basins, and non-basin areas was calculated within each county.
Step 4 – Calculate the Share of the Basin’s Population Growth: The total population difference for the county was determined by summing the values from Step 3. The share (percentage) of the basin’s population growth over the 2000 to 2010 decade was calculated by dividing the total basin population difference by the total county population difference. Step 5 – Calculate the Projected Population Change from 2010 to 2030: The DOF current trend 2030 population projection for the county was used to determine the total change in county population between 2010 estimates and 2030 population projections.
Step 6 – Calculate the 2030 Population Projection: Each basin and non-basin share percentage (Step 4) was multiplied by the total 2030 projected change (Step 5) to produce a 2030 population projection for each basin and non-basin area within the 58 counties. For most basins located within a single county, the 2030 population projection was considered complete. Some low-population basins required minor adjustments when the projected population resulted in a negative value. In these situations, the population was adjusted to zero and the initial basin’s results were redistributed to the other basin and non-basin areas in the county.
For basins located in more than one county, the 2030 population projections for each portion of a basin that crossed a county boundary were summed to produce a 2030 population projection for the entire basin.
Estimates of population growth obtained using the methods described above were evaluated and adjusted, as necessary, to conform with DOF current trend 2030 county projections per California Government Code Section 13073(c). Part B: Determining the 2030 Population Growth (Percentage)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 7 The projected percent growth within each basin was determined by subtracting the 2010 population estimate (component 1) from the 2030 population projection (Step 6 of Part A) and dividing the result by the 2010 populations estimate: Percent Growth = ((Projected 2030 Basin Population – 2010 Basin Population) / 2010 Basin Population) * 100 Part C: Determining the Priority Points for Population Growth Using the percent growth calculated in Step 4 of Part A, the basin was assigned the preliminary priority points identified in Table 2. Before determining the priority points, additional analysis was completed to determine if the basin met the minimum requirements for population growth as defined in the CASGEM 2014 Basin Prioritization process (California Department of Water Resources 2014b):
Does the basin have zero 2010 population?
Does the basin have less than or equal to zero percent growth?
Is the basin’s 2010 population (component 1) less than 1,000 people and does the basin have growth greater than zero?
Is the basin’s 2010 basin population less than or equal to 25,000 and is the basin's 2010 population density less than 50 people per square mile? If the answer was ‘yes’ to any of the four questions above, the priority points for component 2 were recorded as zero. If the answer was ‘no’ to all four questions above, the priority points were applied to each basin based on the percentage of population growth. Table 2 lists the priority points and associated ranges of population growth percentage.
Table 2 Component 2: Priority Points and Ranges for Population Growth Priority Points Population Growth (percent) ‘x’ = Population growth percentage 15 3 15 ≤ x < 25 4 25 ≤ x < 40 5 x ≥ 40
California Department of Water Resources 8 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results Component 3: The number of public supply wells that draw from the basin or subbasin11 Data Source
SWRCB, Division of Drinking Water - Public Supply Database, March 2016
Verified local public supply well location and use information received through public comment process Process Public supply wells were analyzed for the SGMA 2019 Basin Prioritization using the same methods and updated data relative to the CASGEM 2014 Basin Prioritization.
The SWRCB public supply well database (State Water Resources Control Board 2016) was used to calculate the number of public supply wells that draw from the basin, as it is the only statewide dataset that includes records associated with supply water for the public. The SWRCB public supply well database was accessed during March 2016 for the SGMA 2019 Basin Prioritization process. Each record in the database contains fields for active and inactive systems, water source (groundwater or surface water), and testing location. Different records for the same public supply system can exist due to separate testing locations for water quality.
In most cases, the only distinction is in the location name. The public supply data was processed by taking the following steps: Step 1 – Query the Public Supply Well Database for Active Wells: The individual public supply wells that draw from each basin were determined by querying the public supply well database for entries classified as ‘active,’ and ‘groundwater,’ and that contained the word ‘well’ in the location name. Only wells active as of the time the data was extracted (March 2016) were included in this analysis. The number of individual public supply wells determined in this manner is not intended to establish an absolute value for any given basin, but to provide a relative measure of such wells between basins.
Step 2 – Perform Quality Control of Public Supply Well Coordinates: Each record from Step 1 was reviewed to identify incomplete or blank coordinates. Incomplete coordinates did not include enough decimal places in the coordinates to reliably map. They were corrected, when possible, using available attributes provided with public supply data. Records with blank coordinates were also corrected, when possible, using available attributes provided with public supply data. Wells with corrected coordinates were identified as modified with a “DWR” tag.
Step 3 – Compare Coordinates to County Codes: Public supply well locations were compared to the two-digit County Code included in the Public Water System Identification Number. If the well location did not fall within the proper county and location information was not readily available in the public supply well attributes, the public supply well was not included in the dataset. 11 Water Code Section 10933(b)(3)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 9 Step 4 – Sum of Wells in Basin: Using Geographic Information System (GIS) software, the number of wells in each basin were counted based on the reconciled information from Steps 2 and 3.
Step 5 – Calculate the Public Supply Well Density: To calculate the public supply well density, the number of public supply wells (Step 4) was divided by the basin area (square miles). Priority points were applied to each basin based on the calculated public supply well density. Table 3 lists the priority points and associated ranges of public supply well density.
Table 3 Component 3: Priority Points and Ranges for Public Supply Well Density Priority Points Public Supply Well Density (x = wells per square mile) 0.1 2 0.1 ≤ x < 0.25 3 0.25 ≤ x < 0.5 4 0.5 ≤ x < 1.0 5 x ≥ 1.0 Component 4: The total number of wells that draw from the basin or subbasin12 Data Source
Online System for Well Completion Reports (OSWCR) (California Department of Water Resources 2017)
Verified local well location and use information received through public comment process Process Production wells were analyzed for the SGMA 2019 Basin Prioritization using updated methods and data relative to the CASGEM 2014 Basin Prioritization. Updated methods included defining production wells and improving the well location process. Both updated methods are further described below. DWR’s new OSWCR database, which was not available at the time of the CASGEM 2014 Basin Prioritization, was used for the SGMA 2019 Basin Prioritization. The OSWCR database is a statewide dataset of well completion reports (WCRs). Each WCR contains useful information including well type, location, construction details, time of drilling, well performance, and aquifer characteristics. 12 Water Code Section 10933(b)(4)
California Department of Water Resources 10 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results Part A – Identifying Production Wells The OSWCR database was used to identify production wells whose well use type within the WCR is listed as agriculture, domestic, irrigation, municipal, commercial, stock, industrial, or other extraction. If the well use type was not provided on the WCR, the following information, if present, was evaluated to determine if the WCR would be used for component 4.
Many WCRs with an ‘unknown’ well type provide information about the well casing size and total depth.
Criteria for separating production from non-production wells based on well casing size and total depth was established by reviewing domestic and water quality monitoring WCRs. It was determined that screening for a well casing greater than or equal to 4 inches and a total depth greater than or equal to 22 feet to identify production wells would provide the best balance between the urban and rural well characteristics. If the criteria of a well casing greater than or equal to 4 inches and a total depth greater than or equal to 22 feet were met, the WCR was considered to represent a production well.
In some cases, the WCR only provided information on either well casing diameter or well depth information. For WCRs that only provided well casing size, the casing had to be greater than or equal to 4 inches to be considered a production well. For WCRs that only provided well depth, the well depth had to be greater than or equal to 22 feet to be considered a production well. Part B – Determining the Location of Production Wells to the Highest Resolution Well locations were determined using information included on the WCRs. For WCRs that included latitude and longitude, the coordinates were used to determine well locations.
The spatial resolution in these cases was assumed to be absolute.
For WCRs that provided a spatial reference location based on Public Land Survey System (PLSS) data, a centroid location was assigned. The spatial reference location for a well gives a general well location within a known area rather than the actual well location. The process for assigning a well location to a spatial reference location based on information provided in the WCRs is discussed below:
WCRs with township-range-section, baseline meridian, and county information: For WCRs that included township-range-section, baseline meridian, and county information, a section centroid was used as the well location. If the given section was split by a county line, a county-section was created for each portion of the section, and WCRs that identified the county and PLSS location were assigned to that county-section. WCRs were assigned coordinates representing their respective county-section centroid. The spatial resolution in these cases was less than or equal to one square mile.
WCRs with incorrect or without baseline meridian: For WCRs that either did not provide a baseline meridian or provided an incorrect baseline meridian, the county location information was relied upon to locate the well to a county-section and assign a respective centroid. The spatial resolution in these cases was less than or equal to one square mile.
WCRs with incorrect or without county: For WCRs that either did not provide a county or provided an incorrect county, the township-range-section and baseline meridian information was relied on to locate the well to a section and assign a respective centroid. The spatial
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 11 resolution in these cases was less than or equal to one square mile.
WCRs without township-range-section, baseline meridian, and county information: All WCRs that did not provide township-range-section, baseline meridian, and county information were discarded from the analysis. Part C – Estimating Number of Production Wells within a Basin The total number of production wells in a basin was estimated by considering all the wells actually and potentially located in the basin. Wells assigned a centroid location were proportionally counted because the exact location of the wells was unknown. The process for proportionally counting wells is described below: Step 1 – Map Wells using GIS Software: All wells with coordinates (absolute or section centroid coordinates) were mapped using Geographic Information System (GIS) software. Step 2 – Sum Wells Wholly in Basin: Based on results from Step 1, if a well’s absolute location or entire section’s area associated with the centroid was wholly within a basin boundary, it was counted as one well.
Step 3 – Sum Wells Partially in Basin: Based on results from Step 1, if a section’s area associated with the centroid was only partially located in a basin, all the wells within the section were proportionally counted based on the proportion of the spatial reference area located in the basin. For example, if only 50 percent of a section’s spatial reference area was located in a basin, then all the wells in the section’s spatial reference area were given a weighted value of 0.50 for that basin.
Step 4 – Calculate Total Number of Production Wells: The total number of production wells (Steps 2 and 3) in each basin was summed and then rounded down to the nearest whole number.
Part D – Determining the Basin Production Well Density Once production well totals were calculated for each basin (Part C), the production well density was calculated by dividing the basin’s total number of production wells by the basin’s area (square mile). Table 4 lists the priority points and associated ranges of production well density. Table 4 Component 4: Priority Points and Ranges for Total Production Well Density Priority Points Production Well Density (x = production wells per square mile) 10 4 10 ≤ x < 20 5 x ≥ 20
California Department of Water Resources 12 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results Component 5: The irrigated acreage overlying the basin or subbasin13 Data Source
Statewide Crop Mapping 2014 (California Department of Water Resources 2014c)
Verified local land use information received through public comment process Process The consideration of irrigated acreage as a component of the SGMA 2019 Basin Prioritization used the same methods with updated data relative to the CASGEM 2014 Basin Prioritization. The CASGEM 2014 Basin Prioritization used DWR Land Use mapping data to determine irrigated acres. However, the land use data represented multiple years of survey efforts throughout the State. For the SGMA 2019 Basin Prioritization, the Statewide Crop Mapping 2014 dataset was used to provide statewide coverage for a single year. The Statewide Crop Mapping 2014 dataset is a statewide, comprehensive field-level assessment of summer-season agriculture, managed wetlands, and urban boundaries for the 2014 year. For the purposes of basin prioritization, all agriculture identified in the Statewide Crop Mapping 2014 dataset was identified as irrigated unless an agricultural field had been previously identified by DWR as dry-farmed. Only irrigated acreage inside the basin boundaries was included in the calculation and analysis. This was accomplished by overlying the spatial crop mapping data on groundwater basin boundaries to determine total agricultural field acreage overlying the basin. The basin’s irrigated acreage density was calculated by dividing the basin’s total irrigated acreage by the basin’s area (square mile).
Table 5 lists the priority points and associated ranges of density of irrigated acres. Table 5 Component 5: Priority Points and Ranges for Density of Irrigated Acres Priority Points Density of Irrigated Acres (x = acres of irrigation per square mile) 25 2 25 ≤ x < 100 3 100 ≤ x < 200 4 200 ≤ x < 350 5 x ≥ 350 13 Water Code Section 10933(b)(5)
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 13 Component 6: The degree to which persons overlying the basin or subbasin rely on groundwater as their primary source of water14 The groundwater reliance component in basin prioritization is comprised of two elements: total estimated groundwater use in the basin, referred to as Groundwater Use (sub-component 6.a), and the overall percent groundwater represents of the estimated total water use in the basin, referred to as Groundwater Reliance (sub-component 6.b).
Sub-component 6.a: Evaluating Volume of Groundwater Use The consideration of groundwater use as a sub-component of the SGMA 2019 Basin Prioritization groundwater reliance component used updated methods and data relative to the CASGEM 2014 Basin Prioritization. The CASGEM 2014 Basin Prioritization used the DWR Agricultural model. For the SGMA 2019 Basin Prioritization, agricultural groundwater use was calculated by incorporating the crop types and total acreage from component 5 (above) into the California Simulation of Evapotranspiration of Applied Water (Cal-SIMETAW) v3.2 model (Morteza et al.
2013). The Cal-SIMETAW model was used for the SGMA 2019 Basin Prioritization to be consistent with the California Water Plan Update 2018. The model results were represented by evapotranspiration of applied water for each crop in the basin, representing total water demand not met by precipitation in Water Year 2014. The updated process for this sub-component also included the use of Water Year 2014 (October 1, 2013 to September 30, 2014) data for both agricultural applied water and urban water used. Water Year 2014 was used because the Statewide Crop Mapping 2014 dataset was the best statewide land use information available at the time of analysis.
The 2014 land use information also serves as a bench mark of water use prior to the enactment of SGMA.
The updated process for calculating urban groundwater use (Part B, below) included the use of local agency data provided in the SWRCB Public Water System Statistics (PWSS) database (California Department of Water Resources 2014d) and water purveyor boundaries. Part A: Estimating Agricultural Groundwater Use Data Source
California Simulation of Evapotranspiration of Applied Water v3.2
Irrigated Acres (component 5)
Water balance data developed to support the California Water Plan
Verified local agricultural information received through public comment process Process Agricultural groundwater use was estimated using the most recent Statewide Crop Mapping 2014 survey for land use acreages and the Cal-SIMETAW model, which incorporates local soil information, growth 14 Water Code Section 10933(b)(6)
California Department of Water Resources 14 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results dates, crop coefficients, and evapotranspiration data from the Spatial California Irrigation Management Information System for water use demand estimates. Estimates were calculated using the following steps: Step 1 – Determine Total Acres of Each Major Crop: The DWR Statewide Crop Mapping 2014 acreage data were overlaid on groundwater basin boundaries to determine the total acres of each DWRdefined major crop class (see Appendix 2) within the groundwater basins.
Step 2 – Determine Applied Water per Acre per Major Crop: The Cal-SIMETAW model was used to determine the volume of applied water for the DWR-defined major crop classes within the groundwater basins. Applied water per single acre of each DWR-defined major crop class was then estimated within each basin.
Step 3 – Calculate Total Applied Water for Each Crop: The estimates of applied water per single acre for each major crop class (Step 2) were multiplied by the total acres of DWR-defined major crop classes (Step 1) to estimate the total applied water for each crop class. The total applied water for each crop class was added to determine the total applied water for agriculture in the basin. The total applied water for each crop represents the combination of surface water and groundwater. Step 4 – Calculate Total Groundwater Use: The total groundwater use (acre-feet) for the basin was estimated by multiplying the total applied water (Step 3) by the groundwater percentage of total applied water provided in the California Water Plan Update 2018.
Part B: Estimating Urban Groundwater Use Data Source
Public Water System Statistics (PWSS) database (California Department of Water Resources 2014d)
Water purveyor boundaries (multiple sources)
United States Department of Agriculture (USDA) National Agricultural Statistics Service CropScape and Cropland data layers (Urban portion) 2014
Land Use surveys (Urban portion) (2000 through 2014)
Groundwater Basin population data (2014)
Verified local urban water use information received through public comment process Process Urban groundwater use was estimated within each groundwater basin using the data sources listed above. The data sources were processed using the following methods: Step 1 - Determine Groundwater Basin Population: Actual census population block data and DOF population estimates are only available for years ending in a zero. DWR required 2014 population data to process the urban groundwater volumes. DWR accessed a third-party demographics software (Nielsen Claritas 2014) that estimated the population based on groundwater basin boundaries to determine the 2014 population.
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 15 Step 2 - Refine Water Purveyor Service Area: Service area boundaries were compiled using multiple sources including a DWR database, direct inquiries, and information included in Urban Water Management Plans. The service area boundaries were then refined based on the urban land use data (U.S. Department of Agriculture 2014; California Department of Water Resources 2000 through 2014) and overlaid on groundwater basin boundaries. The basin fraction value of the boundary that overlies each basin was used in subsequent steps.
Step 3 – Determine Population Served Within Groundwater Basin: Urban water purveyors’ PWSS water use and population served data (California Department of Water Resources 2014d) were linked to their respective service area boundaries as refined in Step 2. The basin fraction value (Step 2) of the water purveyor boundary was applied to the total population served to determine the population served within the basin. Step 4 - Determine Self-Supplied Population: The self-supplied population was determined by calculating the difference between population served in the basin (Step 3) and the basin population (Step 1).
Step 5 – Determine Water Purveyor Per-Capita Water Use: The water purveyors’ PWSS water use and population served data were used to develop their respective per-capita water use. Step 6 – Determine Groundwater Basin Per-Capita Water Use: The water purveyors that were identified as having all or part of their service area within a basin were used in this calculation. Each water purveyors’ per-capita water use was averaged together using their respective population served and basin fraction value (Step 2).
Step 7 – Calculate Population-Based Water Use: Groundwater basin per-capita estimates (Step 6) were multiplied by the corresponding groundwater basin 2014 population (Step 1) to produce an estimated population-based urban water use.
If the groundwater basin did not have any organized water purveyors, DWR provided an estimated average per-capita use to be used in the calculation. Step 8a – Calculate Groundwater Use for Population Served by Water Purveyor: The urban water purveyors’ PWSS data also reports the source of water used in their systems. DWR used this information along with the basin fraction value (Step 2) to calculate the basin’s surface water and groundwater volume and the respective percent of total water supplied.
Step 8b – Calculate Groundwater Use for Self-Supplied Population: Self-supplied groundwater use was calculated by multiplying the per-capita value determined in Step 6 by the self-supplied population. DWR determined the source of supply for the self-supplied population to be groundwater in most cases. Step 9 – Estimate Additional Groundwater Use: Additional urban water uses (such as golf courses, parks, and self-supplied industrial) were calculated if data were available from local sources such as Urban Water Management Plans.
Step 10 – Calculate Total Urban Groundwater Use: The groundwater amounts calculated in Steps 8a, 8b, and 9 were combined to obtain the total urban groundwater use.
California Department of Water Resources 16 Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results Part C: Calculating Total Groundwater Use Total groundwater use was calculated by adding agricultural groundwater use (Part A, Step 4) and urban groundwater use (Part B, Step 10). Basin groundwater use per acre was calculated for each basin by dividing the total acre-feet of groundwater use by the basin area (acres). Table 6 lists the points and associated ranges of groundwater use per acre.
Table 6 Component 6.a: Points and Ranges for Groundwater Use per Acre Points Groundwater Use per Acre (x = acre-ft / acre) 0 x < 0.03 1 0.03 ≤ x < 0.1 2 0.1 ≤ x < 0.25 3 0.25 ≤ x < 0.5 4 0.5 ≤ x < 0.75 5 x ≥ 0.75 Sub-component 6.b: Evaluating Overall Supply Met by Groundwater Data Source
Sub-component 6.a Process The consideration of overall supply met by groundwater (percent) as a component of the SGMA 2019 Basin Prioritization used the same methods and updated data relative to the CASGEM 2014 Basin Prioritization.
After developing the total groundwater volume for the groundwater basin (see sub-component 6.a – Evaluation of Volume of Groundwater Use), the percentage of groundwater supply was derived as the ratio of total groundwater volume to total water use. Step 1 – Calculate Total Groundwater Use: Agricultural groundwater use was added to urban groundwater use to determine the total groundwater use for each basin (sub-component 6.a, Part C). Step 2 – Calculate Total Water Use: Agricultural applied water (surface water and groundwater) was added to urban total supply (surface water and groundwater) to determine total water used within each basin.
Step 3 – Calculate Percent of Total Water Supply Met by Groundwater: Total groundwater used (Step 1) was divided by total water used (Step 2) to calculate the groundwater portion of the total water supply. Table 7 lists the points and associated ranges of percent of total water supply met by groundwater.
Sustainable Groundwater Management Act 2019 Basin Prioritization | Process and Results 17 Table 7 Component 6.b: Points and Ranges for Percent of Total Water Supply Met by Groundwater Points Total Supply Met by Groundwater (x = Groundwater Percent) 20 2 20 ≤ x < 40 3 40 ≤ x < 60 4 60 ≤ x < 80 5 x ≥ 80 Calculating the Total Priority Points for Groundwater Reliance Priority Points for the degree to which persons overlying the basin rely on groundwater as their primary source of water was calculated by averaging the points for groundwater volume density (6.a) and percent of total water supply met by groundwater (6.b).
Average (6.a Points + 6.b Points) = Priority Points Component 7: Any documented impacts on the groundwater within the basin or subbasin, including overdraft, subsidence, saline intrusion, and other water quality degradation15 Documented impacts on groundwater were analyzed for the SGMA 2019 Basin Prioritization using updated data and methods relative to the CASGEM 2014 Basin Prioritization. The CASGEM 2014 Basin Prioritization treated all four of the sub-components (overdraft, subsidence, saline intrusion, and other water quality degradation) as a single impact and assigned up to five priority points to the basin based on the effect of the combined documented impacts.
The SGMA 2019 Basin Prioritization included separate evaluation of documented groundwater impacts for each of the four sub-components. Points were assigned based on the presence or absence of documented impacts for each sub-category, with the exception of water quality degradation for which points were assigned based on the magnitude and extent of the reported contaminant levels. The updated process is summarized below and described in detail in the following sections.
Each of the four sub-components of component 7 were assigned different maximum points based on the nature of the impact, and whether the impact was susceptible to avoidance or remediation through sustainable groundwater management practices, as follows:
Basins with declining groundwater levels were assigned 7.5 points.
Basins with current inelastic subsidence were assigned 10.0 points; basins with only historical inelastic subsidence were assigned 3.0 points.
Basins with saline intrusion were assigned 5.0 points.
Basins with water quality measurements that exceed maximum contaminant levels (MCLs) 15 Water Code Section 10933(b)(7)