COMMITTEE AGENDA MEMORANDUM
Water Supply and Demand Management Committee
Government Code § 84308 Applies: Yes ☐ No ☒
(If “YES” Complete Attachment A - Gov. Code § 84308)
SUBJECT: title
Receive an Update on Valley Water’s South County Managed Aquifer Recharge Activities Including the Optimization Study for the San Pedro Ponds Groundwater Recharge Facility.
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RECOMMENDATION: Recommendation
Receive an Update on Valley Water’s South County Managed Aquifer Recharge Activities Including the Optimization Study for the San Pedro Ponds Groundwater Recharge Facility.
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SUMMARY:
Managed aquifer recharge continues to be essential for groundwater sustainability throughout Santa Clara County, but particularly in South County where local communities depend almost entirely on groundwater. Valley Water’s managed recharge using local and imported surface water helps balance groundwater pumping, and long-term planning helps ensure continued reliability far into the future. This memorandum goes over Valley Water’s South County recharge program, describes the four recharge projects that are being evaluated as part of the Water Supply Master Plan 2050, and elaborates on the pre-planning study that was conducted at one of these four sites-the San Pedro Ponds in Morgan Hill.
Background
For many decades, the amount of groundwater pumped in Santa Clara County has exceeded what is replenished naturally by rainfall or other sources. To ensure local groundwater supplies are sustainable, Valley Water augments natural groundwater recharge through the managed recharge of local and imported surface water. Water conservation and recycling programs as well as treated water deliveries (North County only) also protect groundwater supplies by reducing the need for groundwater pumping.
Each year, Valley Water determines optimal water supply operations, including managed recharge, based on available water supplies, projections of groundwater pumping locally, and maintenance schedule of conveyance and recharge facilities. Long-term water reliability is evaluated through Valley Water’s Water Supply Master Plan and Urban Water Management Plan, which assess projected future supplies and demands and are updated every five years. Investments and projects to meet projected future shortfalls and ensure continued reliability are identified in the Water Supply Master Plan 2050.
Current South County Recharge Facilities
South County overlies all or part of both primary groundwater basins in the county. This includes the Coyote Valley portion of the Santa Clara Subbasin (which extends north from the Cochrane Road area in northern Morgan Hill to the Coyote Narrows near Metcalf Road in San José) and the entire Llagas Subbasin (which extends south from Cochrane Road to the Pájaro River that forms part of the political boundary with San Benito County). Based on 2016 to 2025 data, average South County annual pumping is 54,800 acre-feet per year (AFY), while natural recharge is estimated at 26,100 AFY. To address the imbalance between the outflow (pumping) from the two subbasins and the natural inflow (recharge), Valley Water conducts an extensive, managed recharge program in South County and recharges, on average, 37,800 AFY of local and imported surface water.
Using established local surface water rights at Uvas, Chesbro, Coyote, and Anderson reservoirs, Valley Water captures and stores large volumes of upper watershed stormwater runoff for delivery to groundwater recharge facilities in South County. Valley Water also has contracts with both the State Water Project and Central Valley Project to receive imported water via San Luis Reservoir and the federal San Felipe Division system and uses it for managed recharge in South County. In-stream and off-stream recharge facilities are located in areas with permeable soils that are connected to deep drinking water aquifers.
Valley Water operates three groundwater recharge systems in South County as shown in Attachment 1. Releases into Coyote Creek replenish groundwater in the Coyote Valley and extend into North County. The Upper and Lower Llagas recharge systems replenish the Llagas Subbasin, which support communities in the cities of Morgan Hill and Gilroy as well as unincorporated areas including San Martín. In addition to municipal wells, thousands of privately owned domestic, agricultural, and industrial wells depend on local groundwater. As summarized in Table 1, the annual recharge capacity of the South County’s managed recharge facilities is over 54,000 AFY, with most capacity in creeks (73%) as compared to off-stream ponds (27%). Attachment 2 provides more detailed information on the recharge capacity of individual facilities within the South County recharge systems.
Table 1 - South County Managed Recharge Facility Capacity Summary
|
Groundwater Management Area |
In-Stream Recharge (AFY) |
Off-Stream Recharge (AFY) |
Total Recharge (AFY) |
|
Coyote Valley (Santa Clara Subbasin) |
14,600 |
0 |
14,600 |
|
Llagas Subbasin |
25,000 |
14,700 |
39,700 |
|
Total |
39,600 |
14,700 |
54,300 |
Note: The annual recharge capacity shown assumes water is available all year long and that ponds are in normal operational condition.
Potential South County Recharge Projects
Valley Water’s investments in local dams’ seismic retrofit projects, reservoir operations, imported water purchase and conveyance, and managed recharge facilities operations and maintenance have ensured reliable South County groundwater conditions for many decades. Valley Water closely monitors groundwater levels and prioritizes recharge to groundwater-dependent communities like South County, particularly during droughts. Groundwater recharge is essential for long-term reliability and has played a critical role in quick drought recovery. With "weather whiplash" (frequent shifts between extremely wet and dry years) becoming more common and given the region’s high reliance on local groundwater, there is a need for one or more additional recharge facilities in South County or expanding existing facilities’ recharge capacity.
Several South County managed recharge projects were evaluated through the Water Supply Master Plan 2050 that was adopted by the Board of Directors on November 12, 2025. The proposed recharge projects include:
A) Madrone Channel Expansion - to increase recharge capacity to the existing facility by adding one or two ponds at the downstream end of the channel on land owned by Valley Water;
B) Coyote Valley Recharge Pond - to construct a new off-stream recharge pond(s) near the Cross Valley Pipeline in the southern part of Coyote Valley to increase operational flexibility, reduce reliance on Coyote Creek flows, and help balance increased pumping in the Coyote Valley that extends from Anderson Dam in Morgan Hill to the Coyote Narrows at Metcalf Road in south San José;
C) Butterfield Channel Recharge - to connect the Butterfield Channel that is owned by the City of Morgan Hill to Valley Water’s raw water conveyance system so imported water can be recharged when the channel is not used for stormwater flows; and
D) San Pedro Ponds Improvement Project - to implement project(s) to enable the existing seven ponds to be operated at full capacity without interfering with septic systems on several adjacent residential properties in the unincorporated areas of Santa Clara County.
Not all four managed recharge projects are needed to ensure reliable groundwater supplies, and most of these projects are in the early conceptual phase. Staff will continue to evaluate which of the four managed recharge projects will best support water supply needs. Valley Water is currently working with a consultant on the pre-feasibility study for the Coyote Valley off-stream recharge pond.
Optimization Study for the San Pedro Ponds
Among the aforementioned four conceptual projects, more substantial evaluation was conducted for the San Pedro Ponds. Valley Water hired GEI Consultants in early 2022 for a desktop feasibility (or pre-planning) study to examine the issues that limit groundwater recharge at the San Pedro Ponds. The study looked at addressing the issue of high groundwater table impacting the septic systems at properties surrounding the San Pedro Ponds. GEI Consultants investigated the historical problem and proposed methods to address the issue, as shown in their November 2023 report titled Optimization Study for the San Pedro Ponds Groundwater Recharge Facility. This feasibility study identified eight alternatives that could fully or partially restore the 4,700-AFY operating capacity of the San Pedro Ponds.
GEI Consultants worked with Valley Water staff to score the eight alternatives shown in Table 2. The scoring criteria were as follows: Impact on septic systems; performance improvement; ease of implementation of solution; ease of operation; and cost. Each criterion had a weighting factor ranging from 2 to 5. The theoretical maximum possible score is 72 and the minimum is 18. The eight alternatives in Table 2 received scores ranging from 42.5 to 57.
Table 2 - Eight Alternatives to Fully or Partially Restore San Pedro Ponds’ Capacity
|
Alternative |
Description |
|
1. Low Pond Operation |
Operating the San Pedro Ponds with less than five (5) feet of standing water to lower groundwater levels at adjacent properties; requires modifications to conveyance between the individual ponds at the site. |
|
2. Extraction Wells |
Operating a line of extraction wells along the south and west boundaries of the site to lower groundwater levels at adjacent properties. |
|
3. Cut-off Wall |
Creating a horizontal flow barrier along the south and west boundaries of the site to block recharge water flowing offsite and lower groundwater levels at adjacent properties. |
|
4. Subdrain |
Creating a horizontal drain along the south and west boundaries of the site to increase vertical flow of recharge water and lower groundwater levels at adjacent properties. |
|
5. Passive Infiltration |
Creating vertical bore holes/conduits throughout the site to increase vertical flow of recharge water and lower groundwater levels at adjacent properties. |
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6. Alternative Wastewater Treatment Systems |
Replacing existing septic tank systems at each adjacent property affected by high groundwater levels with new, alternative wastewater treatment systems that can safely operate under high groundwater conditions. In the case that there are property owners who are unwilling to replace their septic system, Valley Water would need to work with the owners to purchase the properties, replace the septic systems, and put the properties back on the market for sale or devise other solutions to work with the owners to replace their septic systems. |
|
7. Sanitary Sewer Connection |
Connecting each adjacent property affected by high groundwater levels, located within the unincorporated areas of the County, to the City of Morgan Hill’s sanitary sewer system. |
|
8. Property Acquisition |
Valley Water would acquire all properties affected by high groundwater levels, including through use of eminent domain if there is no other means of purchasing a property. The properties would be converted to a use that does not require septic systems and eliminates restrictions on groundwater levels, such as open space. Valley Water would maintain the purchased properties. |
Alternative 6 received the highest score (57) and is considered the preferred alternative. Not far from the top-scoring alternative, the three other alternatives are:
• Alternative 1 (score 56): Even though this alternative has the second highest score, its disadvantage is that it partially restores the ponds’ recharge capacity.
• Alternative 7 (score 56): The only drawback of this alternative is the need to secure buy-in from the Local Agency Formation Commission of Santa Clara County (LAFCO) and City of Morgan Hill to connect each adjacent property affected by high groundwater levels to the City of Morgan Hill’s sanitary sewer system.
• Alternative 8 (score 54): Its con is that it could be expensive to purchase multiple properties, especially if they are turned into open space. One workaround could be to purchase the properties, replace the old septic systems with modern ones that are not impacted by high water table, then resell the properties. However, this would need to be further studied during the planning phase if this project is ever funded as a capital project.
ENVIRONMENTAL JUSTICE IMPACT:
There are no environmental justice impacts associated with this item.
ATTACHMENTS:
Attachment 1: South County Recharge Facility Map
Attachment 2: South County Recharge Facility Capacity
Attachment 3: San Pedro Groundwater Recharge Ponds Map
Attachment 4: PowerPoint
UNCLASSIFIED MANAGER:
Manager
Gregory Williams, 408-630-2867