NapaSan Fosters a Culture of Stewardship, Excellence, and Sustainability 

Roni Gehlke, Clean Water Magazine editor , Resource Recovery

The Napa Sanitation District (NapaSan) credits its long-standing record of no permit violations to its unwavering commitment to excellence, sustainability, and efficient operations, supported by a top-notch maintenance program. While all of these efforts would make this agency a worthy winner of CWEA’s Medium Plant of the Year, NapaSan’s Operations SVC Director, Jim Keller, attributes a culture of stewardship across the organization as the real reason for the win.

“Each employee here at NapaSan strives to do their best to meet the expectations of the ratepayers and their coworkers,” he said. “The Board and staff work well together with a culture of holistic stewardship.”

Over the past two decades, the agency has built a Grade V water recycling facility, a top-notch biosolids land distribution program, and has begun building an innovative energy production program that, when complete, will power NapaSan’s treatment facility 100% green.

“NapaSan is dedicated to recovery and beneficial reuse. This can be seen in the recovery of energy from waste, the recycled water program, and our biosolids application program,” Keller said. “NapaSan applies ingenuity and takes strides as an environmental steward.”

Soscol Water Recycling Facility (SWRF)

NapaSan’s SWRF is classified as a Grade V secondary treatment facility, providing activated sludge and oxidation pond secondary treatment for domestic, commercial, and industrial wastewater from the City of Napa and adjacent unincorporated Napa County. The estimated service area is approximately 83,000 people. The District operates approximately 270 miles of gravity sewer main, with one mile of pressure sewer forcemains and four pumping stations covering a collection service area of approximately 21 square miles. Added to the SWRF the District owns and operates two recycled water distribution pumping stations and a forcemain system supplying 230 customers.

The treatment plant has a capacity of 15.4 mgd. It involves primary and secondary treatment using activated sludge and/or oxidation pond systems. Secondary effluent is followed by disinfection and then discharged to the Napa River during the wet season. Recycled water is produced by further treating the secondary effluent to tertiary (sand filter) standards, then disinfected and stored in covered reservoirs for distribution. About half of the secondary effluent is released into the Napa River, while the other half is treated to meet Title 22 specifications and used in local golf courses, vineyards, cemeteries, ball fields, and landscaping. Currently, all of NapaSan’s Title 22-compliant recycled water is fully allocated.

Biosolids program

NapaSan owns and operates three biosolids application sites, totaling approximately 830 acres, which are situated very close to the WWTF. The furthest site is within two miles of the facility, minimizing emissions associated with transport. The other two are located directly adjacent to the facility. All of the ranches are certified as Fish Friendly Farming and follow established farming plans associated with each site. The crops grown on these ranches are used to feed livestock.

Energy production

In 2016, the District implemented a battery storage project in partnership with Tesla and PG&E. The project was set to meet one of NapaSan’s strategic goals in sustainable energy and to demonstrate the benefits of Tesla’s battery storage systems for demand charge management at an industrial facility.

“The five Tesla batteries were able to capture and store 1MW/2MWh of electricity and helped reduce NapaSan’s electricity costs,” Keller said.

Telsa also helped pay for operations and maintenance for the project’s term. At the end of the five-year term, Telsa offered to donate the batteries to NapaSan. However, the District chose not to accept Telsa’s offer because it was already working on other energy-saving programs that did not require the batteries for another five years. Additionally, it was concerned about the potential high cost of disposing of the batteries.

In 2017, NapaSan continued its efforts to generate on-site electricity in order to control its electrical costs, hedge against future cost increases, and transition to cleaner energy sources. The District was granted permission to operate a 1-megawatt solar array, along with a battery, which continues to allow the ability to export power to PG&E’s electric grid. The solar grid allows the District to purchase solar-generated power far lower than the market rate.

Biogas into energy

“NapaSan is currently working on the construction of a Mainspring linear generator. The generator boasts high efficiency of up to 45% and very low emissions. It will operate in parallel with our cogeneration engine. We anticipate that the generator will be in operation by this summer,” Keller said.

To contribute to the anaerobic digester production, NapaSan also accepts anaerobically digestible materials from the community, such as winery waste, as well as fats, oils, and grease.

By combining the power generated from solar, cogeneration, and the linear generator, the District will meet 75% of the facility’s power needs. The remaining 25% of the power will be obtained from Marin Clean Energy’s Deep Green program, ensuring that all the power used by the treatment facility is 100% green.

Solar on ponds

NapaSan is considering a project that would involve leasing out the surface of the District’s oxidation ponds to a floating solar company. The solar company would install solar panels on the 50 acres of the pond surface. The goal is to connect to PG&E’s electric utility grid, providing a significant amount of green energy to grid users.

“In addition to the lease revenue used to fund the District’s low-income program, NapaSan recycled water users will see improved water quality as pond evaporation is reduced, subsequently reducing chloride concentration in the irrigation water. Additionally, shading of the pond will reduce algae growth and further reduce the treatment chemicals associated with clarification and filtration,” Keller said.

The Plant of the Year award was presented at the CWEA’s Annual Conference in early April. Keller stated that the NapaSan Board and staff are honored to receive the award in the medium category and are excited to highlight their successful agency.