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Public Hearing to consider Use Permit Application No. U-23-03 of Westervelt Ecological Services to develop the Cache Slough Mitigation Bank, a private commercial mitigation bank on approximately 330-acres. The project is located within unincorporated Solano County immediately northeast of the city limits of Rio Vista, at the southernmost reach of the Yolo Bypass at the confluence of Cache Slough, Sacramento River, and Steamboat Slough. The Planning Commission will also consider adoption of a Mitigated Negative Declaration prepared pursuant to the California Environmental Quality Act (CEQA). APNs: 177-110-260 and 177-150-010.
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Published Notice Required? Yes __X__ No _ _
Public Hearing Required? Yes __X__ No _ _
DEPARTMENTAL RECOMMENDATION:
The Department of Resource Management recommends the Planning Commission:
1. Conduct a noticed public hearing; and
2. Adopt a resolution (Attachment A) adopting the Mitigated Negative Declaration and approving Use Permit U-23-03 to develop the Cache Slough Mitigation Bank, a private commercial mitigation bank on approximately 330-acres pursuant to the mandatory findings and subject to the conditions of approval.
EXECUTIVE SUMMARY:
The Planning Commission is being asked to consider a Use Permit application to allow the operation of a commercial mitigation bank. Improvements will be made to the site to re-establish approximately 300 acres of tidal freshwater wetland and floodplain associated vegetation communities.
DISCUSSION:
Setting
The project site encompasses approximately 330 acres at the southernmost reach of the Yolo Bypass, immediately northeast of the city of Rio Vista (see Attachment B, Location Map). The project site is bounded on the north and northeast by Watson Hollow Slough, on the west by the Mellin Levee Extension, on the southwest by the Mellin Levee (a State Plan of Flood Control levee), and on the southeast by Solano County Levee 28, a restricted-height levee along Cache Slough and the Sacramento River. State Route (SR) 84 is situated on the top of the restricted-height levee and connects the city of Rio Vista to the Ryer Island Ferry.
Prior to the Flood Control Act of 1917 and construction of the Sacramento River Flood Control Project, the project site was inundated regularly as part of a larger tidal marsh complex associated with the Yolo Basin. Construction of the restricted-height levee along the west side of Cache Slough and along the Sacramento River separated the southern portion of the Yolo Basin from direct tidal influence and allowed for agricultural production.
The project site is used primarily for cattle grazing and for waterfowl habitat and hunting. It is divided into four former agricultural fields.
Project Description
Westervelt Ecological Services is developing the Cache Slough Mitigation Bank to restore approximately 300 acres of tidal wetlands and to establish a private mitigation bank.
The following project components are intended to restore tidal freshwater marsh and floodplain riparian habitats:
• Excavate approximately 14,000 linear feet of tidal channels to support the flow and ebb of tides for full tidal excursions and exchange to provide habitat for fish, and transport nutrients to support the food web in the connected waterways.
• Re-contouring the interior Bank habitat to promote diverse habitat associated with tidal wetlands and floodplains.
• Design and construct a breach in the existing levee/SR 84 at the confluence of Cache Slough, Sacramento River, and Steamboat Slough to allow unobstructed tidal flow into the Bank’s interior.
• Promote habitat resiliency through management and maintenance activities.
• Limit trespass and other unauthorized uses of the project site.
Fill material generated from excavating channels would be used to create varying topography throughout the site, which would support zones of wetland, riparian, and upland communities based on elevation and expected ecological benefits to the site and surrounding area
As part of restored daily tidal exchange, water would flow through a series of tidal channels into tule marshes. At higher elevations in the landscape, the riparian vegetation would shift to woodland or grassland habitat with an overstory that may comprise sycamore (Platanus racemosa), white alder (Alnus rhombifolia), northern California walnut (Juglans hindsii), and cottonwood (Populus fremontii). While riparian areas would be situated above the daily tidal zone, these floodplain-associated habitats would engage with tidal waters during high-flow periods (i.e., spring and king tides) and storm events. These higher elevation habitats would accommodate future sea level rise by allowing transitions from floodplain to tidal marsh.
Restoration would expand available juvenile rearing habitat and increase food web support for the following fish species:
• California Central Valley steelhead (Oncorhynchus mykiss)
• Sacramento River winter-run Chinook salmon (Oncorhynchus tshawytscha)
• Central Valley spring-run Chinook salmon (Oncorhynchus tshawytscha)
• North American green sturgeon (Acipenser medirostris)
• Delta smelt (adult and juvenile) (Hypomesmus transpacificus)
• Longfin smelt (adult and juvenile) (Spirinchus thaleichthys)
Restoration of tidal freshwater wetlands also would restore and protect suitable habitat for giant garter snake (Thamnophis gigas).
Access
Access to the project site for construction activities will be from State Route (SR) 84 within and directly abutting the project site (see Attachment B, Location Map). All construction staging areas would be contained within the project site and will be shown on the final grading plans. Staging areas that are not within the restoration footprint would be maintained as designated maintenance pads as part of the project.
To restore tidal connection to the project site, the project proposes installing a new low water crossing structure (i.e., free span bridge) under SR 84 between Post Mile (PM) 2.1 and PM 2.2 to connect the restoration site to Cache Slough/Sacramento River and provide fish access to the restored habitat (see Attachment G, Slough Crossing Structure). The new water crossing structure would consist of a 61-foot-long, 40-foot-wide, and 2.5-foot-thick precast prestressed concrete slab bridge, a 5” thick poured-in-place concrete deck (finish surface), bridge abutments each supported by 13 cast-in-steel shell (CISS) cast in shell piles, and barriers/wing walls to be poured-in-place. The bridge abutment will be protected by 1/4-ton rock from erosive forces caused by the ebb and flow of tidal activity passing underneath the structure. The water crossing structure will conform to Caltrans and County standards.
The roadway portion would include two 12-foot travel lanes with 8-foot shoulders on both sides that transition to 12-foot travel lanes on both sides of the bridge with shoulders varying between 1 and 8 feet. The water crossing structure would maintain a similar elevation to the existing roadway with a rise of less than 12 inches. The roadway in both directions would be aligned to conform to the new bridge approaches. Guardrails will be constructed at bridge railings per Caltrans standards.
The abutments for the water crossing structure would be constructed outside the top of bank of Cache Slough/Sacramento River and the limits of the ordinary high-water mark (OHWM). The structure would be a free-span, open bottom, and with no support piers. The water crossing structure design was informed by the results of geotechnical investigations and is consistent with Caltrans standards. Construction for the water crossing structure will require installation of sheet piles on the waterside to prevent water intrusion into the work area.
Concurrent with the water crossing structure construction, a subtidal channel will be constructed to create a tidal connection by removing the existing SR 84 pavement and embankment fill. The subtidal channel will be constructed at a constant elevation to ensure consistent water flows between the project site and the river. The subtidal channel will be lined with appropriately sized rock to prevent erosion and scour at the bridge abutments and maintain a stable channel.
The tidal opening was designed to ensure that tidal flows leaving the Bank would not be too rapid or turbulent to prevent access by fish, particularly juvenile salmon. Based on hydraulic modeling, the tidal opening was designed to achieve full tidal exchange and provide daily (non-storm) flows that are generally less than 2 feet per second (fps) with the occasional maximum of 7 feet per second to provide flushing flows to reduce non-native aquatic floating vegetation. Target fish species, including juveniles, would have access to the bank site during much of the daily tidal flows since they would ride the incoming (flood) tide through the opening and could swim against the outgoing (ebb) tides that would generally not exceed 2 feet per second.
During construction, a portion of the embankment would be left intact to prevent intrusion of water into the work zone. Upon completion of the water crossing structure construction, the remaining embankment fill would be removed to allow tidal waters to engage with the project site.
Staged Construction on State Route 84
In response to concerns from Caltrans regarding potential traffic during construction, two potential construction sequencing scenarios are summarized below with further detail provided in the alternative descriptions.
The first would maintain one lane of traffic on the existing State Route (SR) 84 pavement while the construction occurs on the other side. Traffic will alternate flowing in each direction on the remaining open lane.
The second alternative construction sequence scenario would be to construct a temporary road for two-way traffic to detour onto during the construction of the bridge. After the bridge construction is complete, traffic would be shifted back to the existing road and the pavement work could be completed by closing one lane during work hours so that traffic through the work zone would be restricted to one-way with controlled on both sides of the construction area.
For both alternatives, flaggers are anticipated during construction activity. For the first alternative temporary signals will control traffic during non-construction hours. Final construction sequencing will be as proposed by the contractor and approved by the project Engineer.
During construction, the project would comply with Caltrans guidelines consistent with the California Manual on Uniform Traffic Control Devices (2014).
Construction
Construction activities would be conducted using heavy equipment, which may include excavators, scrapers, bulldozers, skip loaders, compactors, front end loaders, belly-dump trucks, and water trucks. Construction would take place between the hours of 7:00 a.m. and 7:00 p.m., Monday through Saturday. Sundays may be used for equipment cleaning and maintenance.
Construction equipment, staging, and employee parking will be restricted to designated staging areas contained within the project site. All onsite contractors would be properly trained and certified for construction activities and best management practices (BMPs) inspection prior to construction. BMPs will include soil conservation, water conservation, spill containment, waste containment, and avoidance and minimization of potential impacts on sensitive environments or species.
Water used for dust control would come from nuisance water encountered and captured during excavations as well as from the adjacent Watson Hollow Slough using riparian water rights tied to the site.
Approximately 250,000 cubic yards of material is planned to be excavated from the project site and would be balanced onsite (no offsite haul or disposal is required). Excavated soils would be distributed across the project site to create varying topography and placed within a habitat berm along the southwest, west, north, and northeast boundaries of the project site to act as a hydraulic buffer from adjacent facilities. The project would achieve balanced cut and fill.
Williamson Act Contract
A portion of the project site is enrolled in a Williamson Act contract as an Agricultural Preserve, which allows for open space uses, including marsh preservation. Continuation of the Williamson Act contract would continue and is consistent with the goals of the project.
Utilities
Two existing 21 kilovolt (kV) electrical distribution lines traverse the project. Restoration of tidal wetlands on the project site would result in greater inundation frequency for the existing utility poles, which would conflict with routine pole maintenance activities. WES is coordinating with Pacific Gas and Electric Company (PG&E) to remove and relocate one or both of the electrical distribution lines, consisting of up to 30 poles. Most of the utility relocation work would occur on the project site within the existing restoration footprint and along the SR 84 disturbed road shoulder but outside the existing Caltrans easement. However, some pole replacement and reconductor activities would be performed offsite on adjacent WES-owned property along exiting utility lines. Access routes were sited along existing graveled and dirt farm roads and the proposed staging area is on a previously disturbed site that is routinely used for staging farm equipment.
GENERAL PLAN and ZONING CONSISTENCY:
Solano County General Plan Consistency
Surrounding General Plan, Zoning and Land Uses
Property General Plan Zoning Land Use
North Agricultural A-80 Agricultural
South Agricultural and A-80 Agricultural
Southwest Urban Industrial - City of Rio Vista C-3-I Industrial/grazing
East Agricultural A-80 Agricultural
West Agriculture A-20 Sand Mining
The project site is designated as Agricultural with a Resource Conservation Overlay (RCO) in the General Plan.
According to the General Plan the purpose of the RCO identifies and protects areas of the county with special resource management needs. This designation recognizes the presence of certain important natural resources in the county while maintaining the validity of underlying land use designations. The overlay protects resources by (1) requiring study of potential effects if development is proposed in these locations, and (2) providing mitigation to support urban development in cities. Resources to be protected through this overlay are those identified through technical studies as the highest priority areas within the habitat conservation planning process.
Establishment of a mitigation bank is consistent with the agriculture land use and RCO overlay and will preserve and enhance the resources within this area.
In addition, a small portion (approximately 6.4 acres) of the project site ownership also lies within the Rio Vista city limits and is identified in the General Plan as Commercial (C-3-1) (see Attachment D, Zoning Map). This portion of the site will remain in agriculture as part of the project and would not be improved as part of the project. The County does not have permit approval authority over this parcel and, as such, is not part of the project application being considered by the Planning Commission.
Zoning
The portion of the project site located within the Solano County planning area is zoned as Exclusive Agriculture Minimum 80 acres (A-80) pursuant to Section 28.21.020 of the Solano County Code (zoning regulations), which permits conservation and mitigation banking as an allowable use with a use permit (Section 28.79.A) (Attachment D, Zoning Map).
The 6.4-acre portion of the project site that is within the city limits of the City of Rio Vista is zoned general and service commercial and/or industrial. No habitat restoration activities will occur within the boundaries of the city of Rio Vista and existing land uses within this area will not change as a result of the project.
Airport Land Use Commission (ALUC)
The project is within the boundary of the Rio Vista Airport Influence area. The Rio Vista Municipal Airport at Baumann Field is located along the north side of Baumann Road in the northern portion of Rio Vista.
The City of Rio Vista operates a municipal airport which has a helipad and two runways, one 4,200 feet and the other 2,200 feet which serves corporate and business users. The proposed project would not impact the airport, and recommended mitigation measures have been incorporated into the project to reduce potential impacts particularly with wildlife/bird strike hazards. Westervelt provided outreach to the airport to discuss the project and mitigation measures at the Rio Vista Airport Advisory Committee meeting on May 12, 2025.
Development Review Committee
The Project was referred to the Development Review Committee (DRC) for Solano County. Comments were received from the Environmental Health, Public Works, and Building and Safety Divisions. Their requirements have been incorporated as conditions of approval in the attached resolution.
AGENCY REVIEW:
As part of the Department of Resource Management development review process, the application materials have been reviewed by various County Departments/Divisions, as well as Local and Regional Agencies. The following entities may have jurisdiction over the project:
Regional and State Agencies
Central Valley Regional Water Quality Control Board
Central Valley Flood Protection Board
California State Lands Commission
Delta Stewardship Council
California Department of Transportation (Caltrans)
California Fish and Wildlife Department
As part of the project, a detailed Consistency Findings analysis will be formally submitted to the Delta Stewardship Council outlining how the project is consistent with the Delta Plan. The project initiated informal consultation with the Delta Stewardship Council Staff on May 14, 2025, to discuss the draft submittal documents. If the Project is approved by the County, the Consistency Findings document will be posted to the Delta Stewardship Council’s website for a 30-day public review.
ENVIRONMENTAL ANALYSIS:
The Department of Resource Management prepared an Initial Study and Mitigated Negative Declaration (IS/MND) which circulated for a 30-day public review from January 29, 2025, to February 27, 2025 (Attachment I). Responses to comments received during the public comment period are included as Attachment J.
The MND identified certain potential impacts with proposed measures or mitigation to reduce the impacts to a less than significant level.
Comments were received from the following individuals, agencies and interest groups:
1. Delta Stewardship Council
2. Central Valley Regional Water Quality Control Board
3. Solano County Airport Land Use Commission’s Wildlife Hazards Subcommittee
4. California Department of Transportation
5. Solano County Water Agency
6. Delta Protection Commission
7. California Department of Fish and Wildlife
Generally, the comments raised included:
a) Impacts to State Highway 84 during construction
b) Vegetation and Wildlife
c) Wildlife hazards particularly to Rio Vista airport
d) Potential flooding and cumulative impacts
A response to each comment is found in Attachment J. As documented in the MND, there are no significant impacts that would result from the project after implementation of the identified mitigation. None of the comments resulted in a need to recirculate the MND. All impacts can be mitigated to a less than significant level.
Public Outreach
The applicant has provided outreach to surrounding properties and adjacent jurisdictions consistent with the County’s Good Neighbor policies. Attachment K provides additional detail relating to outreach efforts.
PUBLIC HEARING NOTICE:
In compliance with §28.04 of the Solano County Code, a public hearing notice was published in the Daily Republic and the Rio Vista Beacon with a scheduled hearing date June 5, 2025.
RECOMMENDATION:
Based on the discussion above, staff recommends that the Planning Commission ADOPT a resolution adopting the Mitigated Negative Declaration and APPROVE Use Permit Application U-23-03 to establish and operate the Cache Slough Mitigation Bank.
ALTERNATIVES:
The Planning Commission could also choose to:
1. Continue this item to another hearing date for further consideration. This is at the Planning Commission’s discretion and may be necessary if additional specific information is required that cannot be obtained during this public hearing; or
2. Deny the request. This action is not recommended because the General Plan land use, and size of the project are consistent with agriculture and resource preservation and Zoning Ordinance.
ATTACHMENTS:
A. Planning Commission Resolution
B. Project Location Map
C. Aerial Photograph of Site
D. Zoning Map
E. Existing Site Elevations
F. Proposed Site Elevations
G. Cache Slough Water Crossing Structure
H. Project Site Photographs
I. Mitigated Negative Declaration and Mitigation Monitoring Report
J. Response to comments on the Mitigated Negative Declaration
K. Public Outreach