Frequently Asked Questions (FAQs)
The purpose these FAQs are to provide stakeholders and the community with easy access to clear, concise answers to common questions and concerns regarding groundwater sustainability planning and sustainable groundwater management in the Napa Valley Subbasin. FAQs are compiled from questions received by GSA staff, the Groundwater Sustainability Plan Advisory Committee (GSPAC), as well as FAQs prepared by other GSAs in California. The GSA staff and the consultant team are using their resources, expertise and professional judgment to prepare and organize the FAQs.
The FAQs are dynamic. Questions may be combined, added and modified to create an approachable and informative knowledge base. Answers will be updated or improved upon over time as additional groundwater-related data are collected and as the Groundwater Sustainability Plan process progresses. Responses will refer, as appropriate, to published, authoritative sources and are meant to be well informed but should not be construed to be the unchanging, definitive answer to every single question.
- What is Sustainable Groundwater Management?
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The Sustainable Groundwater Management Act (SGMA) defines sustainable groundwater management as managing and using groundwater without causing undesirable results such as: chronic groundwater level declines, groundwater storage reductions, seawater intrusion, water quality degradation, land subsidence, and surface water depletions. SGMA requires that groundwater basins classified as either medium or high priority by the California Department of Water Resources achieve sustainable groundwater management within 20 years of adopting a Groundwater Sustainability Plan.
- What are undesirable results in the context of SGMA?
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SGMA defines undesirable results as “one or more of the following effects caused by groundwater conditions occurring throughout the basin:
- Chronic lowering of groundwater levels indicating a significant and unreasonable depletion of supply if continued over the planning and implementation horizon. Overdraft during a period of drought is not sufficient to establish a chronic lowering of groundwater levels if extractions and groundwater recharge are managed as necessary to ensure that reductions in groundwater levels or storage during a period of drought are offset by increases in groundwater levels or storage during other periods.
- Significant and unreasonable reduction of groundwater storage.
- Significant and unreasonable seawater intrusion.
- Significant and unreasonable degraded water quality, including the migration of contaminant plumes that impair water supplies.
- Significant and unreasonable land subsidence that substantially interferes with surface land uses.
- Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water.”
GSPs must address undesirable results and undertake management actions to ensure that they are avoided within 20 years of GSP adoption.
- What Groundwater Basins are located in Napa County?
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As part of SGMA, DWR recognizes 5 groundwater basins and subbasins in Napa County. Here is the list of the basins and subbasins, along with the priority that DWR gave to each basin:
- Napa-Sonoma Valley - Napa Valley Subbasin – high priority
- Napa-Sonoma Valley -Napa-Sonoma Lowlands Subbasin – very low priority
- Pope Valley Basin – very low priority
- Berryessa Valley Basin – very low priority
- Suisun-Fairfield Valley Basin – low priority
High and medium priority basins are subject to a variety of rules and regulations under SGMA. Low and very low priority basins are not required to take any action at this time. Learn more about requirements for each priority level here.
- Why is the Napa Valley Subbasin subject to Sustainable Groundwater Management Act?
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Napa Valley Subbasin is categorized by DWR as one of 46 high priority groundwater basins statewide. Medium and high priority basins are subject to the Sustainable Groundwater Management Act (SGMA) requirements. The Department of Water Resources (DWR) prioritized all basins in the state according to the following criteria:
- Population size
- Anticipated population growth rate
- Number of public supply wells
- Total number of wells
- Irrigated acreage
- The degree to which people rely on groundwater as their primary source of water.
- Any documented groundwater issues, such as overdraft, subsidence, saline intrusion, and other water quality degradation.
- Any other information determined to be relevant by DWR, including threats to local habitat and streamflows.
The Napa Valley Subbasin is categorized as high priority primarily due to the amount of irrigated lands, the density of wells, projected population growth, and the degree to which people rely on groundwater in the Subbasin.
DWR’s basin prioritization process is not a determination of whether groundwater basins are being managed sustainably. Rather, it is a way for DWR to determine the reliance on groundwater in individual basins across California and whether those basins should be subject to the requirements of SGMA.
- Why aren’t the hillsides included? Aren’t they important too?
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The Sustainable Groundwater Management Act (SGMA) requires that Groundwater Sustainability Plans (GSPs) or Alternatives to a GSP be developed for medium and high priority groundwater basins as delineated and ranked by the State Department of Water Resources (DWR). The hillsides do not fall within the Napa Valley Subbasin that the Basin Analysis Report addresses. Because the hillsides do not act as a basin, but instead as thousands of discrete subareas based on local geography, it is not scientifically or economically practical to “study the hillsides”. However, the hillsides are included in the Napa Valley Subbasin water budget by incorporating uplands runoff and subsurface inflow.
- What about the MST and Carneros, why aren’t they included? How will we know what’s going on in those areas/subbasins that are already having problems?
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The Sustainable Groundwater Management Act requires that Groundwater Sustainability Plans (GSPs) or Alternatives to a GSP be developed for medium and high priority groundwater basins as delineated and ranked by the State Department of Water Resources (DWR). The MST and Carneros Subareas are not state-defined basins, but they are subareas that Napa County has established based on watershed boundaries and the County’s environmental resource planning areas for the purposes of local planning, understanding, and studies. With regards to the MST, it is one of the most monitored areas of the county, with data dating back many decades. There are significant land use controls in place in the area (the county has not approved a discretionary project in the MST that couldn’t meet the “no net increase” standard since 2004), and significant effort has gone into constructing a recycled water pipeline to the area, that became operational in 2016. The Carneros Subarea partly overlaps with the Napa Sonoma Lowlands Subbasin which is a DWR-designated very low priority Subbasin for which a GSP or Alternative is not required. Updates on groundwater conditions in the MST and Carneros Subareas have been and will continue to be included in the County’s Annual Groundwater Monitoring Reports.
- Why did the County form the GSA?
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The preparation of a Groundwater Sustainability Plan (GSP) is required under the 2014 Sustainable Groundwater Management Act (SGMA). SGMA is comprised from a three-bill legislative package, including AB 1739 (Dickinson), SB 1168 (Pavley), and SB 1319 (Pavley), and subsequent statewide regulations issued by the Department of Water Resources (DWR).
GSPs must be prepared for all State-designated medium and high priority groundwater basins and subbasins. The Napa Valley Subbasin was designated as a medium priority by DWR in 2014. In 2019, the Napa Valley was re-designated as a high priority groundwater subbasin. The change in priority designation for the Napa Valley was not due to groundwater conditions. The high priority designation was based on changes in estimates for the Napa Valley regarding future population, the total number of wells, and water quality. On February 6, 2020, the Napa County GSA submitted notification to the Department of Water Resources of their intent to prepare a Groundwater Sustainability Plan for the Napa Valley Subbasin.
If the County did not form a GSA, then groundwater management would have been directly administered by the State Water Board. The GSA was formed to ensure that Napa Valley’s natural resources would remain under local control for the benefit of our residents and other beneficial users.
- What authority does a GSA have?
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SGMA gives GSAs numerous new tools and authorities to manage the groundwater and implement the objectives of the GSP. These include the authority to conduct investigations, determine the sustainable yield of a groundwater basin, measure and limit extraction, impose fees for groundwater management, and enforce the terms of a GSP. These authorities can be implemented by one or multiple GSAs. Chapter 5 of SGMA describes the powers and authorities in greater detail.
- What does a GSA do?
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The primary purpose of a GSA under SGMA is to develop and implement a Groundwater Sustainability Plan (GSP) to achieve long-term groundwater sustainability. GSAs are empowered to utilize a number of new management tools to achieve the sustainability goal, such as: register and meter groundwater wells, mandate annual extraction and water level reports from individual wells, impose limits on extractions, mitigate against overdraft, implement rules and regulations, and assess fees to support creation and implementation of a GSP.
- What is the legislative timeline for SGMA Implementation?
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In medium and high priority basins, including the Napa Valley Subbasin, GSAs were required to develop and adopt a Groundwater Sustainability Plan (GSP) with coordination agreements, or other agreements, as needed, for sustainable management of the basin by January 31, 2022. GSAs in critically overdrafted basins were required to complete their GSPs by January 31, 2020. The GSAs have 20 years following the relevant deadline for GSP adoption to achieve the sustainability goal for their basin, including avoidance of undesirable results.
- Does the GSA regulate surface water?
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The regulation of surface water diversion and use is solely the authority of the California State Water Board. The county has no regulatory ability to affect this issue.
- What is a GSP?
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A Groundwater Sustainability Plan (GSP) is the state-mandated plan to sustainably manage groundwater. Each GSP will contain an assessment of each basin, measurable objectives that are specific, and quantifiable goals for the maintenance or improvement of specified groundwater conditions that lead to achieving the sustainability goal for the basin. A GSP must also include any necessary monitoring, management, enforcement, and other requirements to achieve and maintain sustainability.
- What is the goal of the GSP?
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The goal of SGMA is to ensure that local or regional agencies have the necessary support and authority to properly manage groundwater resources through the use of information and evaluations to protect communities, farms, and the environment against prolonged dry periods and climate change, and to preserve water supplies for existing and potential beneficial uses. The goal is eliminating all undesirable results within 20 years of GSP approval and continue to sustainably manage the subbasin over the next 50 years and beyond.
- What are required elements of a GSP?
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Required elements of a GSP are:
A description of the physical setting and characteristics of the aquifer system underlying the basin, including:
- Historical data
- Groundwater levels, groundwater quality, subsidence, and groundwater-surface water interaction
- Historical and projected water demands and supplies
- A map of the basin area and the boundaries of the groundwater sustainability agencies that overlie the basin
- A map identifying existing and potential recharge areas for the basin
Measurable objectives to achieve the sustainability goal in the basin within 20 years of the implementation of the plan, including interim milestones.
- How the plan helps meet each objective
- How each objective is intended to achieve the sustainability goal
A planning and implementation horizon
Information about the following, as applicable:
- The monitoring and management of groundwater levels within the basin.
- The monitoring and management of groundwater quality, groundwater quality degradation, inelastic land surface subsidence, and changes in surface flow and surface water quality that directly affect groundwater levels or quality or are caused by groundwater extraction in the basin.
- Mitigation of overdraft.
- How recharge areas identified in the plan substantially contribute to the replenishment of the basin.
- A description of surface water supply used or available for use for groundwater recharge or in-lieu use.
- A summary of existing monitoring efforts, including site types, measured data, and monitoring frequency. These include all locations monitoring groundwater levels, groundwater quality, subsidence, streamflow, precipitation, evaporation, and/or tidal influence.
- Monitoring protocols for detecting changes in groundwater levels, groundwater quality, and flow and quality of surface water that are linked to groundwater levels, quality, or extraction.
- An assessment of how the GSP may affect applicable county and city general plans, as well as the various adopted water resources-related plans and programs within the basin.
More detailed requirements are identified in Section 10727 of the California Water Code.
- How do the GSP and the Napa Valley Integrated Hydrologic Model account for future development?
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Section 8 of the GSP addresses future development and population change in the context of the water budget analysis, using best-available data. Projections of future development in the Subbasin are incorporated to provide consistency with local land use agency assumptions and projections. Projected water budget results were made available in Summer 2021. For more information, see Section 8 of the GSP.
- Does the water budget account for extractors of groundwater and surface water outside of the Subbasin?
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SGMA and DWR GSP Regulations require that GSPs include a water budget that quantifies inflows to, outflows from, and changes in storage for the relevant groundwater basin or subbasin. For this reason, the water budget presented in the GSP will address the Napa Valley Subbasin. However, the County and technical team recognize the potential for land uses adjacent to the Subbasin to affect the Subbasin water budget and have expanded the Napa Valley Integrated Hydrologic Model (MODFLOW-OWHM) domain to include areas adjacent to the Napa Valley Subbasin including the Milliken-Sarco-Tulucay and Carneros Subareas as well as other areas of developed land use that are contiguous with the Subbasin. These additional areas include areas served by the City of Napa potable water system west of the Subbasin, the Yountville Veterans Home, and agricultural lands contiguous with the Subbasin boundary.
- What is the timeline for GSP submittal?
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The implementation process of the GSP is continuous and will be ongoing over at least the next 50 years. The GSA adopted the Groundwater Sustainability Plan on January 11, 2022 and submitted the GSP to DWR on January 31, 2022. DWR has 20 days to complete their initial review prior to making the GSP public on their SGMA portal. DWR will then offer a 75-day public comment period. DWR has two years to determine whether the GSP meets the requirements of SGMA.
The GSP must be updated every five years. Annual reporting is required to demonstrate implementation actions and progress towards either achieving or maintaining groundwater sustainability. SGMA Annual Reports are due to DWR every April 1; the next Annual Report is due April 1, 2022. The next GSP update will be due in 2027.
- How is the GSP related to the Napa Valley Drought Contingency Plan?
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Both planning efforts will propose projects and management actions to achieve their respective goals. While the two efforts are on slightly different timelines, there is opportunity for collaborating on potential joint projects that address both groundwater and drought resiliency. The Draft Napa Valley DCP is expected to be available in Spring 2022 while the adopted GSP is currently available.
- What is the study of Hennessey and Milliken watersheds and how does it relate to the GSP?
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In 2017, the City and County of Napa entered into an agreement to study surface water quality within the municipal watersheds of the reservoirs that provide the City with the majority of its drinking water. The Study provides detailed and comprehensive data that can be used by both the City and the County to improve reservoir and land use management to better protect the public’s water supply.
The Study calls for collecting water quality samples from 20 locations along streams that flow into Milliken and Hennessey reservoirs. Samples are collected during storm events throughout the winter months and analyzed for nearly 30 different constituents. The voluntary 2017 agreement commits both the City and County to each spend up to $200,000 annually over three years to conduct this Study, for a total cost of $1.2 million.
Samples were collected over three years, although the last two years were very dry and there were not many storms where measurements could be collected, so data was limited. However, no significant contamination has been detected to date.
The study does not directly relate to the GSP, as it analyzes water quality in the upper watersheds, outside of the Napa Valley Subbasin. But it does complement the GSP, as it provides valuable information on the water quality of surface flows in the tributaries that flow into the subbasin.
- What role does the State Water Project (SWP) play in the GSP?
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The Napa County Flood Control and Water Conservation District (District) entered into a Water Supply Contract (Contract) with DWR on December 19, 1963. This contract provided the District with water supplies from the SWP. Subsequently, the District entered into sub-contracts with the cities of Napa, American Canyon and Calistoga. These agencies are referred to as "Member Units."
The District may request up to 29,025 acre-feet of water annually from the SWP, for use by the three cities. For 2021, the approved allocation was 5% or 1,451 acre-feet. There is a prior year carryover of 4,853 acre-feet.
The SWP applies to the sustainability of ongoing municipal water service deliveries. Surface water resources are accounted for in the water budget for the subbasin in the GSP.
- What did the Local Agency Formation Commission (LAFCO) recommend in their Municipal Service Review (MSR) and how does that affect the GSA?
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On October 5, 2020, the LAFCO adopted the Napa Countywide Water and Wastewater Municipal Service Review (MSR). LAFCO is required to prepare a Countywide Water MSR by the Cortese-Knox-Hertzberg Local Government Reorganization Act of 2000 (Government Code §56000, et seq.), which took effect on January 1, 2001. The water and wastewater service review examines services provided by public agencies whose boundaries and governance are subject to LAFCO.
The MSR reviewed the water service adequacy for each of the 14 agency providers, including distribution system integrity as defined by breaks and leaks and system water loss, and drinking water quality. Based on these indicators, it was found that all agencies in Napa provide at least minimally adequate water service.
The MSR identified various challenges to water service providers in Napa County, including:
- Lack of a regional outlook for water resources,
- A need for cohesive and comprehensive policies affecting both growth and water supply (i.e., trucked water policies),
- Lack of a single entity accounting for water supply and demand throughout the County to better leverage available resources,
- Collaboration on a case-by-case scenario,
- Some County water resources not being used to the fullest extent possible,
- A need for greater oversight of all jurisdictions providing water services in the County,
- A need for support buying on the spot market,
- Certain redundancies with several smaller systems around the County, which could be eliminated,
- A need for support of mutual water companies and small non-public water systems,
- A need for supplemental technical expertise and support, and
- A lack of economies of scale in the smaller water and wastewater systems.
One recommendation to address various challenges to water service provisions identified in the MSR is to promote regionalization of planning and solidarity of organization for water resources. Governance options include a single agency to conduct water supply management on a regional or countywide level, such as a county water agency and/or an agency to provide management and operational support to the smaller utility systems that could benefit from the consolidation of certain services (i.e., lab testing) or from fully transitioning to operations by a regional agency, such as a county water district. A county water agency, county water district, or joint powers authority would provide a means to improve efficiency of water supply management in the County, as well as continued and enhanced resource sharing.
- Would a single county-wide water agency solve the drought?
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The MSR identified several challenges to forming a countywide water agency or district, including:
- Achieving agency consensus on forming a single governance
- Maintaining local control over water service
- Agency representation within a countywide provider
- Revenue generation
- Changes to existing water rates, and
- Redefining existing agency roles.
It should also be noted that there are multiple agencies (Federal, State, and local) involved in regulating and supplying water. The LAFCO study identified 14 cities, town, and districts that provide water service. There are also over 150 community water systems, and transient and non-transient non-community water systems. This is in addition to the thousands of individual domestic and agricultural wells. These water systems and wells are not inter-connected into an integrated water supply system of pipes and canals; there is no ability to move water from where it is plentiful to where it is needed without trucking. The level of complexity and effort required to develop a plan for countywide water distribution would take many years to complete (assuming that all parties were agreeable and no outside parties litigated) and would not provide any immediate solutions for the current emergency.
- What steps is City of Napa taking to limit the sale of trucked water to residents in the unincorporated area?
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In 2017, the City allowed 11.6 million gallons of trucked water for non-construction related uses, equivalent to 3,612 truckloads or 35.47 acre-feet. City staff estimated at that time that approximately 50% of all non-construction trucked water was for residential use.
As part of a proposal to expand water restrictions, the City of Napa is considering the following additional requirements:
- Prohibit all trucked water usage except for residential indoor domestic use;
- Limit indoor residential use to 6,000 gallons per property per month (approximately 0.15 acre-feet per year);
- Limit water for construction use to those parcels served by City water;
- Require all water haulers to sign an agreement with the City;
- Require all water haulers to be State licensed/certified potable haulers;
- Limit water haulers to 80% of the amount of water they hauled last year; and
Terminate all temporary hydrant meters beginning August 1 – contracts will be required to re-establish temporary hydrant meters after August 1.
- How is the GSP related to the Napa Valley Drought Contingency Plan?
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Both planning efforts will propose projects and management actions to achieve their respective goals. While the two efforts are on slightly different timelines, there is opportunity for collaborating on potential joint projects that address both groundwater and drought resiliency. The Draft Napa Valley DCP is expected to be available in Spring 2022 while the adopted GSP is currently available.
- What is the Annual Groundwater Report and what are its most recent findings?
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Napa County has been monitoring groundwater conditions since the 1960s, when it collaborated with the U.S. Geological Survey on a study of groundwater resources in Napa Valley. Since 2009, the County has implemented additional programs to implement the General Plan and better understand, assess, and maintain groundwater sustainability. To further General Plan implementation, the County appointed a Groundwater Resources Advisory Committee (GRAC) in 2011. One of the Committee’s products was the 2013 Napa County Groundwater Monitoring Plan (GMP), to document and enhance the groundwater monitoring efforts that had previously been conducted under the County’s Comprehensive Groundwater Monitoring Program. The GMP recommended annual reports on groundwater conditions and modifications to the countywide groundwater monitoring program as needed. The first report was issued in 2015, analyzing 2014 water year data.
For the 2020 water year report (published in 5/2021), groundwater monitoring was conducted at 107 wells across Napa County that are representative of various geologic and geographic conditions. These included 60 wells within the Subbasin, as well as 47 wells located in other areas of the County. The cost for preparing the report this year was $42,000.
In the spring of 2020, groundwater depths in the alluvial aquifer of the Napa Valley Subbasin ranged from 7 feet to approximately 50 feet below the surface. Groundwater level trends in the alluvial aquifer system of the Napa Valley Subbasin are stable in most wells with long-term groundwater level records. Changes in groundwater levels from one year to the next generally reflect the amount of rainfall received.
Differences in the subsurface geology of the Napa Valley Subbasin are important to the interpretation of groundwater levels, particularly for wells constructed entirely or partially within the alluvium in Napa Valley. Wells located entirely within the alluvium have relatively shallow spring depths to groundwater. Wells built partially or entirely in geologic formations below the alluvium may experience different depths to groundwater. As a result, two wells located very near to each other may have very different depths to groundwater depending on how these wells are constructed and whether they are tapping into the alluvial aquifer or a deeper, confined aquifer.
- What is the recharge rate of the Napa Valley Sub-basin and what does that mean?
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Overall, the Napa Valley Subbasin remains full. The sustainable yield is estimated at between 17,000 and 20,000 acre-feet (AF) per year. (An acre-foot is equal to 325,851 gallons.) The stability of water levels over the past 10 years indicates that the amount of groundwater extraction has been balanced by the amount of groundwater recharge.
Over 100 wells are monitored at least twice a year to track groundwater conditions. Of these, 24 wells in the monitoring network were measured in the spring of 2020 to calculate the change in groundwater storage for the 2020 water year. Consistent with a Very Dry water year, the amount of groundwater in storage decreased in 2020 from 221,358 AF to 196,651 AF.
The volume of groundwater in storage in spring 2020 is below the average (209,407 AF) and median (210,929 AF) volumes calculated from 1988 to 2020. The amount of groundwater storage changes from year to year depending on how much rainfall was received the previous year. Rainfall during water year 2020 (12.19 inches) was the driest year recorded since 1977 (11.23ches). Since 1950, the median annual rainfall at the Napa State Hospital has been 22.84 inches. In 2020, rainfall at the State Hospital was 53% of the median.
Total water use from all sources (State Water Project, surface water, groundwater, and recycled water) within the Napa Valley Subbasin was estimated at 38,073 AF in 2020. Of the total water use, 17,933 AF (47%) came from groundwater pumping. The other 20,140 AF (53%) came from reservoirs, State Water Project, and recycled water.
About 71% of the groundwater used within the subbasin in 2020 was for agricultural irrigation (12,675 AF). Another 27% was used for unincorporated residential and business use (4,840 AF). The remaining 2% (418 AF) went to urban uses in the City of St. Helena.
The amount of water used by groundwater dependent ecosystems was estimated at 4,184 AF.
- What can I do to reduce water use?
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Please visit the County’s Water Conservation website for ways to reduce water use in your home and garden.
- Will Domestic wells be required to have meters?
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At this early stage of SGMA implementation, we don’t know what tools will be used locally to monitor and ensure sustainable groundwater management. SGMA provides an array of regulatory and non-regulatory tools – mostly optional – from which Groundwater Sustainability Agencies (GSAs) can choose to achieve and monitor groundwater sustainability. The Napa County GSA will need to collect sufficient data on groundwater conditions in order to demonstrate progress toward achieving the sustainability goal and measurable objectives, but this doesn’t necessarily mean that all wells must be metered. In fact, SGMA does not authorize GSAs to require metering of wells used to supply two acre-feet per year or less for domestic purposes. SGMA requires that public stakeholders be engaged in the development and implementation of the Groundwater Sustainability Plan, which will allow additional opportunity for interested stakeholders to provide input on this issue.
Much of the groundwater delivered by local agencies is already metered, and other data sources (such as land use data) provide solid information to estimate groundwater use.
- Do domestic well users have to comply with SGMA?
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Wells pumping less than 2 acre-feet per year (1,785 gallons per day) for domestic purposes are considered to be “de minimis” and could be exempt from most SGMA requirements. This includes exemption from metering, reporting requirements, and fees. Most private, non-agricultural wells will fall into this “de minimis” category.
- How will SGMA projects be evaluated for environmental impacts?
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SGMA explicitly exempts Groundwater Sustainability Plans from evaluation under the California Environmental Quality Act (CEQA). However, GSAs will need to evaluate and mitigate any environmental impacts from any projects or management actions that they determine are required for sustainable groundwater management.
- Is groundwater quality currently being monitored?
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Community water systems, such as those serving municipalities, are required by state law to monitor the quality of the water they supply to the public. Small water systems, such as schools, mobile home parks, and food facilities that use groundwater wells to supply their drinking water are also required by the state to monitor water quality. Other state programs require groundwater quality monitoring for locations near regulated facilities (an example of a type of regulated facility includes leaking underground fuel tanks). A statewide database through the State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Program (GAMA) integrates and displays groundwater quality information.
- Is there a link between groundwater and surface water, and if so, how will it be managed?
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In general, there are linkages between surface water and groundwater. Understanding the spatial and temporal interconnection between surface water and groundwater is a requirement of the GSP and appropriate management actions have been included in the Plan.
- What is a water budget?
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A “water budget” is the accounting of the total groundwater and surface water entering and leaving a basin, including the changes in the amount of groundwater stored in the basin. Basic components of water budgets are:
- Precipitation (rain)
- Evapotranspiration (a combination of evaporation from the soil and transpiration by plants)
- Surface water flow (streams and lakes) infiltrating or leaving the groundwater basin
- Groundwater flow (aquifers) into and out of the groundwater basin
- Change in groundwater storage
- Groundwater pumping and consumed or exported from the basin.
- What is irrigation system efficiency and what factors affect the efficiency?
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Irrigation system efficiency is a ratio of the amount of irrigation water consumed by plants to the total amount of irrigation water supply. The irrigation efficiency depends on a variety of factors, including topography, soil characteristics, water conveyance system, crop type, and irrigation practices.
- What is the current status of the Napa River for impairment under the Clean Water Act?
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The Napa River is designated under the Clean Water Act as impaired by nutrients, pathogens, and sediment. As of October 2020, the State Water Resources Control Board and San Francisco Bay Regional Water Quality Control Board have approved delisting non-tidal areas of the Napa River for nutrient impairment.
- How is climate change taken into account in considering and planning for groundwater sustainability?
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The Groundwater Sustainability Plan Advisory Committee (GSPAC) received a presentation from Paul Wells of the Department of Water Resources (DWR) on November 12, 2020 regarding SGMA requirements for addressing the effects of climate change in GSPs. Technical staff working on the GSP have separately coordinated with Tyler Hatch (a DWR Supervising Engineer and groundwater modeler) and Paul Wells in developing the approach to incorporating climate change into the Napa Valley Integrated Hydrologic Model and GSP for the Napa Valley Subbasin.
Given uncertainty in future climate projections, climate change was evaluated using multiple future climate scenarios. The analysis relied on downscaled results from peer-reviewed global atmospheric circulation models to generate multiple sets of climactic (e.g. precipitation and potential evapotranspiration) and hydrologic (e.g. stream inflow) inputs for Napa Valley. The projections spanned a 50-year period, consistent with the requirements of the GSP Regulations. The future scenarios used in the model have been selected because they provide meaningful bounds on best-available climate projections for the North Bay. The future scenarios were chosen based on collaboration with the Pepperwood Preserve and U.S. Geological Survey as described in the presentation by Lisa Micheli at the November 12, 2020 GSPAC meeting.
The results of the climate change analysis are included as part of the projected water budget presented in section 8 of the GSP.
- How does the groundwater basin affect flows within the Napa River?
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Surface waters that support groundwater dependent ecosystems (GDEs) in the Subbasin include springs, wetlands, and surface water channels. These include springs in the vicinity of Calistoga and estuarine and riverine tidal channels in the southern portion of the Subbasin, extending to within the City of Napa.
The amount of water used by groundwater dependent ecosystems (flowing from the aquifer into the Napa River) is estimated at 4,184 acre-feet.
- If groundwater conditions are so good, why did my well go dry?
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Overall groundwater levels in the main Napa Valley Subbasin have been stable for decades. Groundwater conditions outside the Napa Valley Subbasin are more variable, such as in the Milliken-Sarco-Tulucay (MST) area. In addition to the effects of the recent drought, the productivity of an individual well can depend on a number of things including the depth and serviceable life of the well, local aquifer properties, and amount and rate of nearby pumping from surrounding wells. Report dry wells here.
- If depth to groundwater is so shallow, why do wells seem to be getting deeper to find water?
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Generally, groundwater levels across the Napa Valley Subbasin have been stable for decades. In limited areas, newer wells may be deeper to produce at dependable rates. This would include areas where seasonal variability is high, or the Northeastern Napa Subarea where water level declines in wells monitored by the County east of the Napa River were observed over approximately the decade prior to 2009, but have since stabilized.
- Why are streams that used to flow in the summer now dry?
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Reaches of the Napa River have over many decades (since the 1930s) experienced low to no-flow conditions during the summer-to-fall period for a variety of reasons. Stream flow is very dependent on seasonal rainfall, small dams (both legal and illegal) that have been constructed to block stream flow, withdrawals of surface water (both legal and illegal) from the creeks, as well as reduced groundwater discharge into the stream channel. The duration of annual no flow days varies from year-to-year and increases during extended droughts as during recent years.
- Since surface water and groundwater are connected, isn’t groundwater pumping dewatering the Napa River and threatening our remaining native fish populations?
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The Basin Analysis Report finds that overall, groundwater levels in the Napa Valley Subbasin have been stable for decades, demonstrating that current groundwater pumping has not contributed to chronic depletions of groundwater storage and that pumping has likely been below the sustainable yield for the Subbasin. Surface water and groundwater are connected; therefore, seasonal and year to year variability in precipitation and other factors have affected both surface water and groundwater. Since at least the 1930s, periods of no flow days have been observed in the Napa River system, particularly during drier years. Based on the analyses of surface water and groundwater interconnections, including the relationship of this connection to seasonal and annual groundwater elevation fluctuations, the Basin Analysis Report uses 16 wells (and other data including stream gage data) in the Subbasin to monitor groundwater level impact on the Napa River. As long as the fall water levels in these 16 wells remains above the determined level, (the “minimum threshold”), the contribution of groundwater to flow in the Napa River is determined to be no less than has occurred historically in the fall. On average, it is preferable for fall water levels in these wells to approximate their individual measureable objective, which is a level higher than the minimum threshold.
- Are you doing anything about well problems in the county like the Petra Dr / Soda Canyon area?
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Water levels in northeastern Napa Subarea wells monitored by the County east of the Napa River have stabilized since 2009, though declines were observed over approximately the prior decade. The study, conducted between 2016 and 2017, included evaluation of the potential effects from pumping in the overall Study Area, potential mutual well interference in an area of interest near Petra Drive, and potential streamflow effects. As part of the Special Study, a transient numerical groundwater flow model was developed that incorporates the data collected for a base period of water years from 1988 to 2015 to analyze groundwater conditions in the Study Area and the area of interest near Petra Drive. At their meeting on October 24, 2017, the Board of Supervisors supported the findings and recommendations of the Special Study Report and directed staff to develop documentation (2018 Amendment) to formally establish the Northeast Napa Management Area covering approximately 1,960 acres within the 45,928- acre Napa Valley Subbasin. This 2018 Amendment provides additional detail about conditions in the Northeast Napa Management Area and establishes additional sustainable management criteria and management actions intended to support continued groundwater sustainability in the Napa Valley Subbasin as a whole. The 2018 Amendment designates seven representative monitoring sites as a subset of the monitoring sites in the Northeast Napa Management Area for the purpose of monitoring groundwater conditions that are representative of the management area, consistent with the GSP Regulations (Section 354.36). For SGMA purposes for the Napa Valley Subbasin, these seven sites are where sustainability indicators are monitored, and minimum thresholds and measurable objectives are defined. For more information, read the Northeast Napa Special Groundwater Study and Presentation.
- Why did the GSA use surveys about the Draft GSP Sections?
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Napa County Groundwater Sustainability Agency (GSA) staff used surveys as an important tool to gather ideas and feedback from Groundwater Sustainability Plan Advisory Committee (GSPAC) members and the public on key issues and draft sections of the Groundwater Sustainability Plan (GSP). The GSP development process was an iterative one, where groundwater sustainability issues and draft GSP sections were presented, discussed, and refined over time. Survey feedback helped the GSA build a stronger draft GSP that was presented for public comment in Fall 2021. In addition, the surveys were intended to gather broad input from GSPAC members and the public on issues to be addressed in the GSP and capture community interests and concerns about groundwater planning and sustainability. While each survey was focused on specific draft sections of the GSP, the surveys enabled respondents to share additional comments, interests, concerns, or questions regarding the GSP.
- What was done with the survey input?
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Survey results were compiled on a regular basis, presented at the GSPAC meetings, and posted online. GSP sections were revised to integrate survey feedback as appropriate.