Special Report: Is Sonoma Valley’s sanitation plant maxing out?

Down on Eighth Street East towards Hwy. 121 you’ll find the Sonoma Valley County Sanitation Plant, the place where sewage from as far north as the Developmental Center gets treated, cleaned and discharged into San Francisco Bay or purple-piped for use in vineyards. Combining holding ponds with treatment facilities, the plant has a capacity of 3-million gallons per day in the dry season. During the rainy season it often exceeds its treatment capacity, which is why holding ponds dot the property.

It’s not that more toilets are flushing when it rains, which increases the sewage flow up to 6-million or 7-million gallons per day; rather, the increased flow is due to aging pipes and a sewage collection system into which groundwater leaks and adds to the volume. It is for this reason that the district has been fined and is under a “cease and desist order” from the Regional Water Quality Control Board that requires the district to fix it’s leaky collection and transmission system by 2026.

Until repaired, the resulting high-flow periods will produce sewer system overflows of raw sewage up and out of manholes and into the streets and surface waters.

Recent communication with the Regional Water Quality Control Board revealed that the dry season daily average was below the 3-million per day capacity (MGD). A representative of the board also commented: “The flow during the dry weather months is less than the maximum allowed by the permit. Furthermore, the effluent results indicate that the plant is performing well. This indicates that the plant is not being overloaded and can handle additional flow without affecting the plant’s performance.”

The Board has accepted that raw sewage flows will continue during inclement weather, and are indeed acceptable until the collection system repairs are complete. The system was flagged in the past as #2 on the list of highest raw sewage overflows in the entire State of California. What is less clear is what new connections to the system from large projects (hotels, sub-divisions, etc.) will produce in terms of rainy season sewage overflows.

The Regional Board has referred to these increases as “marginal” as compared to the overall system volume at that time of year, but others in the community feel otherwise. Yet the Regional Board is the enforcement arm for the Clean Water Act, and any change in their decision seems unlikely at this time, despite public opinions otherwise.

The effect of new large projects

Meanwhile, new large projects are nearing completion or are in the planning stage. The new 60-unit Mid-Pen apartments are near completion, and two hotels are in the planning phase in the City of Sonoma, along with a high-density affordable housing project on Broadway. This raises an obvious question about how much more volume the sanitation plant can accommodate.

Figures indicate somewhere between 300,000 and 600,000 gallons per day additional capacity is available before reaching the plant’s 3-million gallon per day dry-season capacity. How many housing units or hotel rooms does this represent? At the current build-out plans in the Valley and Valley and the City of Sonoma, when will this maximum capacity be reached?

As there is no agreed-upon formula for how much water a hotel room, or new home or business, uses in a given period, those figures are impossible to predict.

Opponents of large projects argue that if capacity is limited, doesn’t it make sense to reserve it for housing instead of tourists? Hotel developers propose that hotel rooms will use less water and produce less sewage than housing, but hotel opponents find such statements hard to believe. They argue that between daily laundry service, spas, restaurants and swimming pools a hotel logically would use more water per-person per-day than a single dwelling with one or two people. Developers point to studies to justify their claims. Sorting it all out is the responsibility of the Planning Commission and specialists.

Private holding tanks for sewage

One hotel proposal concedes that the sewage flows are problematic, and proposes that sewage holding tanks be constructed as part of the hotel to regulate the timing of the discharge into the collection system. A review of the Regional Board conditions of operation, however, suggest that the District and the District alone must operate all elements associated with its sewage collection system, and if that is correct, a private operator is not allowed. Time will tell whether or not this is a deal-breaker. It does represent a first in proposing that a private property owner control the collection and discharge timing of large amounts of sewage into the public system.

One thing is clear: forecasting the point at which the Treatment Plant reaches capacity is not easy. The debate about housing vs. hotels intersects with the reality of the capacity of our existing infrastructure, setting aside the issue of raw sewage overflows that will continue for at least another half-a-decade until the system is repaired. Ultimately, the decision-makers in Sonoma County and the City of Sonoma need to put their heads together and work out their priorities or at some point in time such decision-making will be moot as the Treatment Plant reaches its design capacity.