Atherton Water Capture Facility Project

Atherton Water Capture Project Key Milestones

Project Frequently Asked Questions Sheet (PDF)

Time Line (PDF)

The Town has hired Tetra Tech Inc. to prepare preliminary engineering concept designs for a water capture facility in Holbrook-Palmer Park. The project would include a diversion structure to re-direct all dry-weather urban runoff and the first flush of wet-weather runoff from the Atherton Channel through a pre-treatment device to remove trash, debris, and sediment before conveying the water into a buried multi-chambered storage/infiltration facility with a targeted storage capacity of eight (8) to ten (10) acre-feet.

The need for a stormwater detention/storage facility was identified in in the Town-wide Drainage Study Update prepared in 2015 to reduce flooding associated with the Atherton Channel. Approximately 10 acre-feet of detention/storage capacity is needed to manage a 10-year storm event to minimize flooding associated with the existing Marsh Road box culvert. Additionally, the Town is required to comply with the Municipal Regional Permit (MRP) issued by the San Francisco Bay Regional Water Quality Control Board. The MRP requires all permittees to implement green infrastructure improvements to reduce the amount of mercury and polychlorinated biphenyl (PCB) in stormwater discharges to the San Francisco Bay. Caltrans has agreed to contribute an amount not to exceed $13,600,000 to the Town of Atherton to construct a water capture and treatment facility in the Town, to assist with their stormwater permit requirements.

The Town-wide Drainage Study Update identified three potential sites for The 2015 Town-wide Drainage Study Update looked at three possible sites to capture stormwater from the Atherton Channel: Las Lomitas Elementary School, Holbrook-Palmer Park, and the JL Dixon Stables. Because of the complexity of working with a privately owned site at some distance from the Channel, the Town chose not to relocate the project to the JL Dixon Stables. The Town first attempted to work with the Las Lomitas Elementary School District on a water capture project at the school. However, the Town was not able to come to an agreement with the School District. he Town moved the project downstream to Holbrook-Palmer Park - actually a better site because of a larger tributary area and more space available for construction of the project.

The engineering concept designs will evaluate the potential for a water capture facility located near the southwest corner of the Holbrook–Palmer Park in a lawn area beyond the existing baseball diamond. The exact location may change based on design needs and Park requirements. For example, the site may be moved closer to the Park entry if it meets the needs of engineering and design solutions. City Council will ultimately make the final location decision. The project would include a diversion structure to re-direct all dry-weather urban runoff and the first flush of wet-weather runoff from the Atherton Channel through a pre-treatment device to remove trash, debris, and sediment before conveying the water into a buried multi-chambered storage/infiltration facility with a targeted storage capacity of eight (8) to ten (10) acre-feet. Depending on the results of a geotechnical analysis, engineered dry well(s) on the bottom of the storage chamber or nearby are proposed to be constructed to facilitate infiltration.

A similar project funded by Caltrans is nearing completion at Bolivar Park in Lakewood California. The City Council, along with the Chair of the Park & Recreation Committee and Atherton Public Works Director visited the Bolivar Park facility on February 28.

Atherton Water Capture Project Meeting Notices

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