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Nutrient Offset Program
What is the Laguna de Santa Rosa?The Laguna de Santa Rosa is an ecologically sensitive freshwater wetlands complex, home to a number of rare and endangered plant and animal species. It’s a mix of diverse habitats, including multiple creeks that feed into marshy ponds and pools, forested areas and other lake-like features. The 22-mile-long waterway starts in Cotati, surrounds the west side of Santa Rosa and empties into the Russian River.
Why is the Laguna important?During heavy rains, the Laguna serves as an extensive floodplain, storing large volumes of storm water and ultimately delivering water and nutrients to thousands of acres of farmland. Because the Laguna naturally filters many sediments and pollutants, it’s often called the Russian River’s “kidney.”
How has the Laguna been impacted over time?Over the past few centuries as the Santa Rosa plain was settled, the Laguna’s historic wetlands were drained and filled, converted to farmland and its streams reshaped to reduce flooding around growing urban areas. These actions decreased the natural function of the Laguna and trapped nutrients, like nitrogen and phosphorus, in sediment deposits, negatively impacting its water quality. These conditions have allowed Ludwigia, an invasive plant, to flourish and form dense masses of weeds that crowd out native species and further degrade water quality. The ecological condition of the Laguna is now formally declared as “impaired” under the Clean Water Act with specific concerns about the levels of sediment, nutrients, temperature, mercury and dissolved oxygen in its waters.
How is Santa Rosa helping to restore and protect the Laguna de Santa Rosa watershed?
The City of Santa Rosa is playing an important role in protecting and restoring the Laguna. Santa Rosa operates the Regional Water Reuse System which serves 230,000 people and recycles billions of gallons of treated wastewater from homes and businesses each year.
Nearly 100% of this high-quality recycled water is beneficially reused for urban and agricultural irrigation, as well as sent to Calpine, via the Geysers Pipeline, to produce clean energy. This reuse process allows more water to naturally remain in rivers, lakes, and streams, thus preserving sensitive habitat for fish, plants, and wildlife. However, during wet years with above average rainfall, recycled water discharges into the Laguna are carefully managed through a process that meets stringent water quality regulations.
To reduce potential impacts of necessary recycled water discharges into the Laguna, Santa Rosa filters and cleans wastewater entering the Regional Water Reuse Plant through a sophisticated treatment process that significantly reduces nitrogen and phosphorus levels. Santa Rosa carefully manages recycled water storage volumes to minimize controlled discharges into the Laguna and maximize reuse during the dry season.
During a public hearing on August 20, 2020, the Regional Water Board adopted Resolutions No. R1-2020-0012 incorporating the Water Quality Trading Framework for the Laguna de Santa Rosa Watershed (WQTF) into the wastewater NPDES permit for the City of Santa Rosa. The approved Framework replaced the existing Santa Rosa Nutrient Offset Program and is available to both the City of Santa Rosa and the Town of Windsor as an approved method for complying with “no net loading” effluent limitations for total phosphorus in each of their NPDES permits.
The Water Quality Trading Program enables Santa Rosa to further remove sources of nitrogen and phosphorus from the Laguna and comply with its regulatory requirements. Through the use of best management practices and restoration actions, the program allows Santa Rosa to generate nutrient credits that “offset” any nutrient that might be released into the Laguna and its tributaries by the Regional Water Reuse system.
Santa Rosa’s approach to maintaining permit compliance and improving water quality is an innovative way to protect and restore the Laguna. The Water Quality Trading Program provides long-term ecological value to the region and may offer the most effective and beneficial way to use ratepayer funds to comply with regulations and put the Laguna back on a healthy path.