Dixon’s Wastewater Treatment Facility Earns Envision Silver Award from Institute for Sustainable Infrastructure

Dixon’s Wastewater Treatment Facility in California is the recent recipient of the Institute for Sustainable Infrastructure (ISI) Envision Silver award. The Envision sustainable infrastructure rating system verifies the sustainability of infrastructure projects across the full range of environmental, social, and economic impacts.

The City of Dixon’s Wastewater Treatment Facility Improvements project is the culmination of years of collaboration between the city, Stantec Consulting, state of California environmental regulators, and the public. Improvements to the facility address a range of community needs, goals, and issues such as upgrading the aging wastewater treatment facility without an undue burden on ratepayers, meeting increased capacity demands, and addressing salinity limits placed on the facility by the state.

“The completion of Dixon’s Wastewater Treatment Project signifies the accomplishment of a significant milestone, decades in the making, in which so many folks played pivotal roles,” said Joe Leach, PE, city engineer/public works director. “With the support of key Stantec personnel, the leadership of past and current City Councils and the construction partner, C. Overaa Construction, the city is pleased that we have a facility that is in compliance with regulations and provides a safe environment in which staff is able to operate a state-of-the-art facility that will provide sustainable capacity for the foreseeable future.”

“This award recognizes the efforts of dozens of engineers, scientists, and project specialists of the Stantec design team, as well as the city, state, and regional stakeholders, to work collaboratively to apply proven, cost effective, technology in a new way to address the long-term problem of salinization of the soils and groundwater in agricultural regions such as Dixon,” said Joe DiGiorgio, PE, Stantec’s project/construction manager. “I am proud to have been involved for more than 20 years working from the bottom up on this project. To see it through to the ribbon cutting has been an honor. I was pleased to learn that the framework for success that was started so long ago meshed well with the Envision verification process.”

Leach said it’s important that smaller public entities receive recognition for their efforts to design and build sustainable projects. “Often, smaller jurisdictions don’t receive credit for the creative ways they deliver projects for the benefit of the community and the environment. While it’s an honor to receive such a prestigious national award, the dedicated staff of the city works collaboratively with our design and construction partners each and every day. This project, due to its financing constraints, required innovative design, construction and regulatory collaboration that transitioned naturally to an Envision application,” said Leach.

The Envision sustainable infrastructure rating system is a collaboration between ISI and the Zofnass Program for Sustainable Infrastructure at the Harvard University Graduate School of Design and holistically rates the sustainability of infrastructure projects. The Envision system measures sustainability in five categories: Quality of Life, Leadership, Natural World, Resource Allocation, and Climate and Risk. These key areas contribute to the positive social, economic, and environmental impacts on a community.

Some of the sustainable accomplishments of the Dixon Wastewater Treatment Facility Improvements project include:

Leadership: The city demonstrated leadership and a strong commitment to stakeholders by establishing a Wastewater Citizens Advisory Committee in 2007. The committee’s mandate was to determine viable options to address state-imposed sodium and chloride effluent limits while upgrading aging components of the existing facility that were unsafe and costly to maintain at or above their rated capacity. Options were put forward by the committee and evaluated by the City Council. Once the successful option to upgrade the aging facility was selected, a robust public outreach program was initiated to inform and educate the public on the project plans, including incentives to remove salt-discharging water softeners, the benefits of the selected treatment technology, and any rate implications. This outreach program helped address concerns and ultimately led to public and state regulatory approval of the facility improvements project.

In addition to engaging stakeholders throughout the process, the project team incorporated full life-cycle thinking to extend the project’s useful life. The oxidation ditch design with the activated sludge process technology was chosen. The decision was due to factors bearing on long-term performance and resilience of the project, including the ability to adapt to future permit requirements, cost-effectiveness, changes in capacity demand, ease of retrofitting and repair, and the ability to accommodate new features, such as solar power and the use of recycled water at the plant or in the community. Robust nitrogen removal was included in the process because it saves energy and costs long term, and proactively addresses groundwater nitrate contamination, which has been identified as the largest long-term threat to groundwater drinking quality in agriculturally dominated areas worldwide, including the Central Valley of California.

Resource Allocation: Dixon’s Wastewater Treatment Facility implements a cost-effective and energy-efficient method to minimize salinity impacts to groundwater. The facility’s large 130-acre treatment ponds were replaced with an oxidation ditch design that has a significantly smaller exposed surface area, which reduces evaporative water losses by 100-fold. The retained water serves to keep the dissolved wastewater salts diluted, which reduces the effluent salinity. By solving the salinity issues through evaporation reduction and the activated sludge process, the wastewater treatment facility avoided more conventional salt removal treatment methods, such as reverse osmosis or electrodialysis reversal that are costly, consume significant amounts of energy, and produce a hazardous brine waste that is costly to manage in inland locations.

Climate and Risk: The project team conducted a comprehensive assessment of vulnerabilities that could create long-term costs and risks for the Dixon Wastewater Treatment Facility and the community it serves. Four specific risks to the project were identified by the project team and mitigated by the design, including potential seismic activity such as liquefaction and ground shaking; flooding and extreme rainfall events; long-term drought conditions and related water-supply shortages; as well as changing economic conditions. Ultimately the project was designed to be resilient and adaptive to these potential changes in the operating environment over the course of its 50-to-100-year design life.

“ISI is pleased to present the Dixon Wastewater Treatment Facility Improvements project with the Envision Silver award for sustainable infrastructure,” said ISI President and CEO John Stanton. “This project helps to address the salinity issues affecting groundwater resources in the area, and it is a clear example of infrastructure responding directly to community needs, goals, and concerns, making it a sustainable and resilient infrastructure project. Residents, businesses and industries in the City of Dixon will benefit from the improved wastewater treatment capacity for decades to come.”

The award, including a commemorative plaque, will be presented to the City of Dixon by the Stantec design team at a City Council meeting on July 11, 2017.

To learn more about the City of Dixon Wastewater Treatment Facility Improvements project, please visit www.dixonwwtf.org