Arup today announced the release of a new study and interactive map for the County of Sonoma, highlighting opportunities and challenges relating to wastewater treatment in vast areas of the county that are not currently served by a sewer system.
The study, presented on October 8 to the Sonoma County Board of Supervisors, examined the locations of septic systems and identified areas where existing or future wastewater management entities could serve rural property owners. It explored the feasibility of forming new wastewater districts or modifying the boundaries of existing districts to serve communities where septic systems are highly concentrated.
Onsite wastewater treatment systems (OWTS), also called septic systems, are useful and necessary for residents at locations that are removed from centralized wastewater treatment systems. When properly sited, designed, operated, and maintained, septic systems treat domestic wastewater to reduce its polluting impact on the environment and protect public health. However, if poorly maintained or improperly sited, septic systems can impact the environment and surrounding communities.
Working together with the County, Arup developed an interactive geospatial tool to help identify locations of septic systems across the county to inform decisions about wastewater infrastructure and about how wastewater may be managed and governed. Well managed and effective wastewater treatment benefits both the environment and communities. As the sole consultant on the project, Arup’s team of geospatial analysts and water engineers provided technical advice, incorporating local community and stakeholder feedback.
To conduct the study, Arup’s geospatial experts mapped the location and relative density of septic systems across the county, identifying over 36,000 known and suspected septic systems. The analyses showed significant concentrations in larger rural communities, and these higher-density parcels were collected into community clusters with similar existing or potential governance structures and similar technical conditions, such as slopes, soil types, and proximity to water bodies. The mapping work forms the basis for identifying and analyzing these clusters and suggests potential alternative wastewater infrastructure and management solutions to positively impact the community and the environment.
“The state is tightening requirements for septic systems to ensure the water in our rivers, creeks, lakes and underground aquifers is clean and safe,” Supervisor David Rabbitt, chair of the Board of Supervisors, said in a press release issued by the County of Sonoma. “This study, and its accompanying web hub, provides government and property owners with the data we need to find solutions that work for everyone.”
“Septic systems form an essential part of the wastewater infrastructure of Sonoma County, and this work helps communities use them most effectively,” said Roland Martin, Associate and Project Manager, Arup. “Our research provides information and suggestions that — when applied — will help create a healthier environment and community.”
An interactive map displaying the location of local septic systems and other data is available at gis-owts.sonomacounty.ca.gov. The site includes resources for property owners who rely upon septic systems. The Arup-led mapping study will help advance several efforts by the County and its partners to manage wastewater and increase climate resilience in their water systems.
