Central Marin Sanitation Agency

Aerial view of CMSA looking east.

Plant view at Dusk

View of plant  at dusk looking west

Kids Playing in Classroom

A juggler helps kids learn about water conservation during a school presentation

As a regional agency dedicated to the health of our community and the environment, our expert staff focuses on providing high quality wastewater-related services for the residents and businesses of central Marin County.

CMSA operates the largest wastewater treatment facility in Marin County. We treat and dispose of the wastewater and biosolids collected from households and businesses in central Marin County. Approximately 6 billion gallons of wastewater are treated and released as clean effluent into San Francisco Bay each year, and we consistently meet and exceed all Federal and State regulatory requirements.


Our History

In October 1979, four of the local agencies that provided wastewater services in central Marin county entered into a Joint Powers Agreement (JPA):

  • San Rafael Sanitation District
  • Ross Valley Sanitary District
  • Sanitary District No. 2 of Marin County
  • The City of Larkspur

This agreement created a separate governmental entity, the Central Marin Sanitation Agency (CMSA), to oversee the construction and operation of a regional wastewater treatment facility. CMSA became operational in January 1985. The City of Larkspur withdrew from the JPA in January, 2020.


We Are Both Regulated and Regulators

CMSA has a National Pollutant Discharge Elimination System (NPDES) permit issued by the San Francisco Regional Water Quality Control Board which details the Agency's wastewater treatment and reporting requirements.

We, in turn, regulate the commercial, industrial and institutional discharges into the sewage collection system of our member districts.


Biosolids Reuse, Educational Programs, Environmental Services 

Wastewater treatment is only part of what we do...

Each year about 6,500 tons of biosolids are beneficially reused as alternate daily cover at the Redwood Landfill, and as land-applied fertilizer for feed crops for livestock.

We also have a comprehensive pollution prevention program, lead an award-winning county-wide water/wastewater public education program, and provide various environmental services to local agencies.





  • High level of regulatory compliance
  • Awards received for facilities, programs and individuals 
  • Effective source control and educational programs
  • Clearly presented, award-winning and transparent financial documents
  • Talented and highly-skilled professionals recognized for workgroup and individual achievements
  • Consistently provide safe working conditions for staff and outside contractors