Waste Water Treatment Plant Air Quality Update

This article was originally published in October 2018. It was updated in December 2018.

The City of Mill Valley, Sewerage Agency of Southern Marin (SASM) Board and the staff of the Waste Water Treatment Plant located on Sycamore Avenue have received questions and heard concerns from parents of Middle School students regarding the air quality around the plant.

“The City of Mill Valley and SASM are good stewards of the environment and care deeply about healthy practices for the community and our staff,” said Board President Lew Kious. “The treatment plant staff work to insure compliance with the regulations which govern the operation of our facility.”

Air quality standards are established and enforced by the Bay Area Air Quality Management District (BAAQMD). BAAQMD inspectors have evaluated the air quality at the Waste Water Treatment Plant and the Mill Valley Middle School and taken measurements utilizing precisely calibrated instruments. Inspectors tested for the presence of hydrogen sulfide and additional potential volatile organic compounds.

BAAQMD inspectors verbally reported that their instruments primarily detected typical background air concentrations. The few substances they did detect were well below the normal threshold of OSHA-designated permissible exposures. They informed SASM staff that no compliance issues exist. SASM requested a written statement of their test results.  Recently the Laboratory Results and a report titled Interpretation of 10 17 2018 Sampling Results at SASM, were received by SASM.

Community members have raised specific concerns regarding hydrogen sulfide. The Waste Water Treatment Plant has a robust gas monitoring system, both stationary and mobile. Staff has, and will continue to check hydrogen sulfide levels at these monitors daily. Test results continue to indicate that the hydrogen sulfide levels at the plant are well below the OSHA permissible exposure limit, and outside the plant are negligible.

The SASM Board and staff are committed to protecting the health and safety of residents and the environment. We are aware that some of the operations at the plant produce an unpleasant odor. This is not new, nor is it exclusive to our treatment facility. The intensity of this odor varies seasonally and throughout the day depending on a number of weather and operational factors.

We have heard and noticed ourselves that odors have been more pronounced recently. We believe that this is a logistical issue associated with construction of a comprehensive $20 million renovation of the facility. The construction activities have interrupted some of the normal treatment processes and exposed certain operations that have historically been sealed—hence the increased odor noticed outside the plant. This is a short term challenge associated with the long term operational and odor management improvements expected as a result of the major renovation.

Treatment staff have instituted operational changes shifting some treatment activities to alternate hours to reduce overlap with Middle School activities. Staff is in regular communication with Mill Valley School District staff and Board regarding our treatment plant operations and construction activities. We have regularly followed-up with the school regarding community concerns providing information that they may share with school families.

Background and Additional Resources

The Waste Water Treatment Plant is undergoing a major improvement project to ensure reliable treatment of wastewater and continued compliance with regional, State and Federal regulations. As part of the planning for the project, SASM hired a consultant to study the emissions from the plant. The conclusions are summarized in an Odor Evaluation Report. The study found that the plant’s emissions are not negatively impacting public health, within the plant or at the nearby Middle School.

Based on this report, SASM’s design consultant, Carollo Engineers, designed a new odor scrubbing system to replace the approximately 40-year-old system. The SASM Board specifically prioritized this component to be included in the first phase of the improvement project to minimize odor impacts and address community concerns. This new system was initially projected to be activated by the Spring of 2019. Staff is working toward accelerating this schedule, and hope to start up the new system before February of 2019. A temporary scrubbing system is in place while the new scrubbing system is under construction.

City and plant officials will continue to work with school administrators and community members to communicate our plans and be available to answer questions on an ongoing basis.

Questions or comments may be directed to Mark Grushayev, Waste Water Treatment Manager at (415) 388-2402 or email