Protecting the bay, rain or shine

Rainfall refreshes our watersheds and replenishes our reservoirs. But winter storms also pose unique challenges to the robust wastewater treatment EBMUD provides to protect the health of San Francisco Bay. Fortunately, we’re at the ready, rain or shine.

When heavy rains saturate the ground, water infiltrates aging city sewers. The result is a surge of water that flows to EBMUD’s wastewater interceptors, the giant underground pipes along the East Bay shoreline that collect and channel sewage to our wastewater treatment plant where it is cleaned up before being released into the bay. During heavy storms, our infrastructure must handle inflows more than ten times that of an average dry day.

EBMUD boasts a remarkable record of public health and environmental protection since the wastewater treatment plant began operating 71 years ago. But our system has its limits. A single atmospheric river on December 31, 2022, brought the largest 24-hour rainfall total since records began in Oakland in 1894. Wastewater flows peaked at 655 million gallons a day and overwhelmed the capacity of segments of the interceptor system, leading to a release of untreated wastewater into the bay.

To better prepare for such wet weather surges and prevent future overflows, our wastewater treatment operators build upon their skills with monthly trainings. Weather forecasts, operational strategies and equipment are reviewed before each storm. Enhancements to level-monitoring stations, upgraded data communications and power supply reliability improvements also aid operations. EBMUD rehabilitated 4,740 feet of aging large-diameter interceptor pipe last year. We will tackle additional sections following risk-based assessments. We’re also evaluating ways to lower the levels of nitrogen, phosphorous and other nutrients discharged to the bay. A system tested last summer, for example, removed more than 20 percent of total inorganic nitrogen in treated wastewater.

Together, these continuous improvements strengthen our ability to meet regulatory requirements and protect the bay we love. Learn more at