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HomeMy WebLinkAbout6/16/2026 Item 7b, Scott and Boerman - Staff Agenda CorrespondenceCity of San Luis Obispo, Council Memorandum City of San Luis Obispo Council Agenda Correspondence DATE: June 15, 2026 TO: Mayor and Council FROM: Shawna Scott, Assistant Director of Utilities Prepared By: Mychal Boerman, Deputy Director, Water VIA: Whitney McDonald, City Manager SUBJECT: ITEM #7b – ADOPTION OF THE 2025 URBAN WATER MANAGEMENT PLAN, 2025 WATER SHORTAGE CONTINGENCY PLAN, AND RECEIPT AND FILING OF THE 2026 WATER SUPPLY AND DEMAND ASSESSMENT Staff received questions regarding the planned addition of groundwater to the City’s water supply portfolio. A summary of the approved groundwater project is provided below, followed by questions received (in bold) and staff’s responses (in italics). Background The City is implementing the Groundwater Clean -up Project, which includes the drilling of two production wells, construction of a granulated activated carbon (GAC) system to treat tetrachloroethylene (PCE) contamination within the aquifer, and installation of monitoring wells and well meters to monitor the progress of the clean -up project and ensure compliance with the Sustainable Groundwater Management Act (SGMA) and San Luis Obispo’s Groundwater Sustainability Plan (GSP), including safe yield extractions, protection of flow within San Luis Obispo Creek, and prevention of adverse effects such as subsidence. Extracted and treated groundwater will be added to the City’s drinking water system and will provide a supplemental source of potable water for our community. The work is being funded by a $7.8 million grant from the California State Water Resources Control Board. The first two phases of the project are near completion, including the drilling of a new well and installation of the monitoring wells. The third phase of the project will include equipping the two wells for groundwater pumping and construction of the treatment and distribution system, to be completed in 2027. 1) Groundwater pumping during the 1987 –1993 drought created subsidence near Los Osos Valley Road and resulted in a multimillion -dollar settlement with impacted businesses. Why is this danger not dealt with or mentioned in the Urban Water Management Plan? The Urban Water Management Plan (UWMP) supports the City’s long-term resource planning to ensure that adequate water supplies are available to meet existing and future water needs. The Draft UWMP does not describe previously experienced subsidence in detail because the San Luis Obispo Valley Groundwater Sustainability Plan (GSP) is the principal technical and regulatory framework for managing groundwater levels, storage, water quality, and interconnected surface water, and avoiding undesirable effects such as subsidence. ITEM #7b – UWMP, WSCP, and Water Supply and Demand Assessment Page 2 The GSP documents that increased pumping by the City and private groundwater users during the 1987–1991 drought caused the Basin’s most severe recorded subsidence along the Los Osos Valley Road corridor, damaging homes and businesses. It also states that the City discontinued significant pumping in that area and that subsidence has not been observed since. For context, it is important to note that 1) during the worst two years of the drought the City was pumping approximately 2,000 acre-feet of groundwater per year and other predominantly agricultural groundwater users were also pumping uncharacteristically high volumes of water, and 2) many of these agricultural areas have since been redeveloped and no longer utilize groundwater, reducing overall groundwate r use in the basin when compared with 1987-1991 pumping volumes. The GSP establishes groundwater-level and land-surface monitoring requirements and thresholds intended to prevent a recurrence of subsidence. Those include monitoring through satellite-based data collection/analysis and a groundwater - level monitoring. The UWMP’s 700-acre-foot annual groundwater value is not an unconditional commitment to pump that amount regardless of basin conditions . The UWMP states that future production will be coordinated with GSP implementation and will consider groundwater levels, water quality, monitoring results, basin-management criteria, regulatory requirements, surface -water conditions, creek flow conditions, and dry-year limitations. As noted above, the City’s Groundwater Clean-up Project includes the use of monitoring wells within the aquifer, which will provide data informing pumping schedules and amounts to ensure compliance with the GSP. 2) How would pumping out 700 acre-feet a year impact subsidence? The City will manage and adjust operation of the groundwater extraction wells to avoid “undesirable” effects such as subsidence. Groundwater extraction and operation of the wells will occur in compliance with State Division of Drinking Water regulations, SGMA, and the GSP. The GSP identifies sustainability indicators (which are used to define undesirable results), including but not limited to: chronic lowering of groundwater levels, reduction of groundwater storage, land subsidence, and depletion of interconnected surface water. The GSP includes minimum thresholds for each sustainability indicator, including an identified groundwater level elevation (96 feet) at a monitoring well located proximate to San Luis Creek. In addition to the monitoring well identif ied in the GSP, the monitoring wells proposed as part of the Groundwater Clean -up Project will provide groundwater level data, will be equipped with telemetry to monitoring pumping, and allow for adjustments in pumping rates. In addition to the monitoring wells, the City will ensure compliance by installing well meters and implementing an Operations and Maintenance Plan, which includes groundwater level and pumping monitoring at the extraction wells. ITEM #7b – UWMP, WSCP, and Water Supply and Demand Assessment Page 3 The City has the ability to reduce or suspend pumping at one or both of the wells to ensure GSP compliance and avoidance of subsidence. The UWMP simulates a significant reduction in groundwater pumping during dry-year events, with periods of extended drought reducing groundwater pumping to as low as 50 acre -feet per year. 3) Would pumping out 700-acre feet a year deplete the aquifer? How much water does the aquifer contain and at what rate does it recharge? How much water would be left in the aquifer after pumping out 700-acre feet? Based on the GSP’s long-term average water budget, up to 700 acre-feet per year of groundwater pumping (extraction) in the San Luis Valley subarea would not be expected to cause persistent long-term depletion. As noted above, actual annual groundwater extraction from the two wells will depend on data collected from the extraction and monitoring wells. The GSP (Table 6-14) estimates approximately 34,940 acre-feet of groundwater in storage in the San Luis Valley subarea under Spring 2019 conditions. That number is not the same as the amount that can safely or sustainably be pumped. The GSP expressly cautions that a total-storage estimate does not establish sustainable yield or annual rechar ge and is primarily used to evaluate changes in storage over time. The GSP estimates: • Long-term average groundwater recharge of approximately 3,700 acre-feet per year. • Approximately 1,200 acre-feet per year of groundwater use by wetlands. • A sustainable yield of approximately 2,500 acre-feet per year. • An estimated pumping volume of approximately 1,800 acre-feet per year (includes estimated City groundwater pumping and private wells). • An estimated difference (surplus) between available supply and expected demand of approximately 700 acre-feet per year, which is the amount the UWMP identifies as a supplemental source of water. Based on the dynamic nature of an aquifer, identifying how much water would remain after 700 acre-feet per year of groundwater pumping is not a safe or reliable way to quantify or manage an available water supply. The GSP’s identification of safe yield, estimated surplus, and monitoring of other sustainability criteria are appropriate means for complying with SGMA and ensuring sustainable use of groundwater. ITEM #7b – UWMP, WSCP, and Water Supply and Demand Assessment Page 4 4) Why not create an injection well field to store surplus wastewater? This strategy was part of an approved plan earlier. The concept of indirect potable reuse through groundwater recharge by injection is identified in the City’s 2022 Potable Water Reuse Implementation Plan. This concept is not included as a quantified UWMP supply because no project has been selected, permitted, funded, or designed. As described in the Potable Reuse Implementation Plan, advanced treated water from the Water Resource Recovery Facility (WRRF) could be injected either inside or outside City limits, using either a non-reverse osmosis (RO) treatment approach that would require alternative DDW approval or an RO-based approach, which would require brine disposal. The concept has not been abandoned, but substantial analysis and funding is necessary for design, evaluation, and implementation. The Potable Reuse Implementation Plan identifies significant additional work that would be needed, including the construction of advanced treatment facilities, conveyance pipelines, pump stations, injection and extraction locations, regulatory approval, monitoring, and public outreach. The Plan also notes that if water were injected outside City limits, a return pipeline would be needed, and if RO treatment were used, a pipeline to an ocean outfall would likely be required for brine disposal. In addition, before advancing an injection project, the City also needs more operational information about how the San Luis Valley subarea responds to groundwater pumping. Monitored and controlled groundwater production will help the City understand groundwater-level response and recovery, water quality, storage availability, and management of pumping and recharge to avoid undesirable results such as subsidence. The next steps would include inclusion of the project in the City’s Capital Improvement Program and Financial Plan, and additional feasibility work, informed by monitored groundwater operations, regulatory and stakeholder outreach and coordination, public engagement, and Council direction. It is important to clarify that the City would not simply be storing “surplus wastewater” if this concept is implemented in the future. Available WRRF flows must be evaluated in light of recycled-water demands, required discharge to San Luis Obispo Creek, seasonal flow variations, treatment requirements, and future changes to wastewater-flow volumes. For these reasons, injection wells remain a potential future strategy, but the UWMP appropriately treats potable reuse as a future opportunity rather than a committed supply source. ITEM #7b – UWMP, WSCP, and Water Supply and Demand Assessment Page 5 5) Why not bring recycled water to the northern part of the City and Cal Poly? The City has previously evaluated this option. The City had numerous meetings with University staff to determine whether the use of City -provided recycled water was a feasible option to help Cal Poly meet its long -term water supply needs. Ultimately, Cal Poly elected to construct their own Water Reclamation Facility and produce their own recycled water for campus agricultural and landscape irrigation. The existing recycled-water distribution system identified in the 2017 Recycled Water Plan primarily serves the southern portions of the City, where it is closest to the WRRF and where significant new development has been constructed with recycled-water infrastructure. The UWMP does not preclude expansion to northern San Luis Obispo. Subject to Council’s direction, an amendment to the Recycled Water Plan to include a northern extension could be reevaluated using current construction costs, an analysis of potential users, updated recycled -water availability, and an extensive analysis of the retur n on the capital investment. It is important to note that the City’s recycled water distribution system, pump station, and tank, were not designed to deliver water to the northern side of the City. An expansion beyond the current recycled water use area would require reconstruction of these facilities alongside installation of a significant volume of new recycled water pipeline. Associated design and construction costs would be significant (exceeding $20 million), in addition to operational and maintenance costs. 6) What effect would Cal Poly's creation of its own WRF have on the City's future planning projections for recycled water production? Operation of Cal Poly’s WRF will result in a reduction of the volume of wastewater that flows into the City’s WRRF, which will then later increase in conjunction with Campus build-out. The temporary reduction has been accounted for in future projections, and the City and Cal Poly continue to collaborate and work in partnership to identify and evaluate the changes in flow over time. The UWMP currently identifies that the largest restriction to recycled water system expansion and an increase in recycled water use is related to the City’s existing recycled water storage tanks and pump station, not volumes of available wastewater flowing into the WRRF. 7) At what stage in the Water Shortage Contingency Plan (WSCP) would water for nonfunctional turf be prohibited? The WSCP does not establish a separate automatic shortage stage and response action solely applicable to irrigation of nonfunctional turf. Under the Draft WSCP, the following stages and associated actions impact all turf irrigation: • At the Extreme Stage, when less than three years of supply remain, the City may implement additional restrictions on turf and spray irrigation. ITEM #7b – UWMP, WSCP, and Water Supply and Demand Assessment Page 6 • At the Critical Stage, when less than 2.5 years of supply remain, irrigation would no longer be permitted except for approved exemptions. Separate from the WSCP, California Water Code Section 10608.14 and City Municipal Code Section 13.07.070 prohibit the use of potable water for nonfunctional turf according to a statutory schedule that applies regardless of whether the City has declared a water shortage. 8) Why not research the feasibility of potable reuse during the next five years? In order to further examine potable reuse, one important next step is to restore and carefully monitor City groundwater production. The City has already completed a planning-level potable reuse evaluation, including groundwater recharge by injection and surface-water augmentation of Whale Rock Reservoir. However, the feasibility of indirect potable reuse through groundwater recharge depends on understanding how the groundwater basin responds to actual pumping under current conditions. Controlled groundwater pumping will help the City evaluate groundwater -level response, recovery rates, water quality, interaction with nearby wells and surface water, and whether pumping can occur while remaining protective of GSP criteria, including subsidence protections. That information would directly inform future analysis of injection locations, extraction locations, groundwater travel time, storage capacity, and operational limits for a potential groundwater -recharge project. For that reason, potable reuse is not yet a committed UWMP supply. The next phase, following data gathering during actual groundwater pumping periods, would include additional feasibility analysis, regulatory coordination, public outreach, funding, and Council direction before potable reuse could be included in the City’s quantified supply portfolio.