Refugio Lake Restoration Project

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Upcoming community meetings
Date	Time	Location
January 8, 2026	6:00 p.m.	City Hall Council Chambers, 111 Civic Drive, Hercules
February 7, 2026	11:00 a.m.	Intersection of Sanderling Drive and Willet Street, Hercules

Project No.

63079

Location

Refugio Valley Park

About the Project

The project will remove the majority of accumulated sediment from the lake at Refugio Valley Park while preserving emergent wetland vegetation along the periphery. Sediment removal will restore lake depths closer to their original elevations, which will reduce algae formation conditions. Invasive pampass grass, ivy and Himalayan blackberry vegetation surrounding the lake and creek will also be removed as part of this project and replaced with native vegetation as required mitigation by the Regional Water Quality Control Board.

Historical Background

Refugio Lake was last dredged in 2005. Over the past 20 years, sediment has been carried into the lake by Refugio Creek during large storms, causing the lake to become shallow. These shallow areas are unattractive and contribute to algae blooms during the warmer and more stagnant summer months. The City has countered algae blooms with aerator fountains and chemical treatments, but their effectiveness becomes more limited as the lake depths decrease.

In 2018, the City engaged LSA, an environmental consulting firm, to initiate the permitting process and develop preliminary dredging plans. The City paused the project however, due to the high estimated cost of disposal of the approximately 6,300 cubic yards of dredged material resulting from the project.

The City has since evaluated and confirmed the viability of a lower-cost option for spreading the dredged material on City-owned land. Due to the need for the project and the availability of one-time General Fund and Capital Reserves monies, the project is now able to resume. LSA is securing the necessary permits and a design consultant is being procured.

Project Details

The dredging project will involve the following key steps:

Preparation: Staging areas for heavy equipment will be set up in developed or landscaped areas near the pond, such as paved or turf upland areas. The periphery of the lake and the creek will be cleared of invasive vegetation. Portions of the trail around the pond will be closed to the public for the duration of the work.
Water Management: Before dredging, water will be diverted and the pond dewatered. This process is expected to take about three weeks. To protect aquatic life, all pump intake hoses will have screens. Temporary gravel bag cofferdams will be installed to isolate the dredging area and protect emergent seasonal wetlands and vegetation.
Dredging: Approximately 6,300 cubic yards of sediment will be removed from the pond. This will be done using an excavator.
Sediment Disposal: The removed sediment will be hauled to an approved off-site location designated by the City.

Site Restoration: After dredging, the work area will be cleaned up, and all equipment will be removed. Disturbed upland soils will be reseeded and replanted with native vegetation and returned to a pre-project condition.

Public Works Contact

Glenn Dombeck
Public Work Director/City Engineer
gdombeck@herculesca.gov
(510) 799-8241

Contractor

TBD

Project Updates

Click to view: Refugio Lake Restoration Meeting 1/8/26

November 2025 - 65% Design pending. Two community meetings scheduled – one at 6 pm on 1/8/26 at City Hall Council Chambers at 111 Civic Drive in Hercules and one at 11 am on 2/7/26 at the intersection of Sanderling Dr and Willet St in Hercules.

June 2025 - Ecological risk evaluation of proposed sediment reuse underway to guide dispersal of dredged material at City-owned open space properties. Construction work is anticipated to occur in late summer/early fall 2026, ahead of wet weather, which will minimize the duration the newly dredged lake will remain empty.

July 2025 - Ecological risk evaluation of proposed sediment reuse complete. Use of Refugio Lake dredged sediments as fill material in an upland area is not expected to result in adverse effects to wildlife. The potential for ecological risk can be further reduced by adding a layer of clean cover over the fill to depths of at least 12 inches, blending the dredged sediments with clean soils, and/or tilling the sediments into underlying soils.

Will there be a Community Meeting for the project?

Why is the dredging project necessary?

How long will the project take?

Will the park be open during the project?

What will happen to the fish and other wildlife in the lake?

How is the City protecting the environment and wildlife during this process?

The City of Hercules is committed to protecting the environment and wildlife during this project. The following measures will be implemented:

Water Quality: An Erosion and Sediment Control Plan will be developed and implemented to prevent sediment from entering Refugio Creek or being tracked on City streets.
Wildlife Protection: While no adverse effects on wildlife are anticipated, several precautions will be taken to protect special-status species like the California red-legged frog and the western pond turtle, should they be present. These measures include:
- Pre-construction surveys for these species will be conducted by a qualified biologist within 48 hours of the start of dredging.
- If work occurs during the nesting bird season (February 1 - August 31), nesting bird and raptor surveys will be conducted. If nests are found, buffer zones will be established.
- All project personnel will receive environmental awareness training.
- A biological monitor will be on-site during all work activities that could potentially impact sensitive species.

Work Hours: To minimize disturbance to wildlife and residents, work will be limited to daylight hours only.

Where will the City deposit any dredged sediment removed from the Lake?

Approximately 6,300 cubic yards of sediment is anticipated to be dredged from the Lake. The accumulated sediment comes from the upstream drainage area of Refugio Creek, which includes a mix of residential and open space properties. Following the project’s approval in 2019, costs to dispose of the dredged material in a landfill increased significantly. The City is thus currently evaluating an alternative reuse option to spread the material on City-owned open space property.

As part of this evaluation, the City’s consultant team is preparing an Ecological Risk Evaluation of Proposed Sediment Reuse to confirm that the deposit of the dredged materials will not have any impacts to the environment and to ensure that the approximately 2-acre portion of the City’s 11.2 acre Corporation Yard property located near the corner of Sycamore Avenue and Willet Street is an appropriate reuse site. Given that there are no wetland or flood plain areas present on the proposed reuse site, the City anticipates that the consultant team will confirm that the site is appropriate.