Sewer Authority Mid-Coastside
SAM provides wastewater treatment services to its member agencies.
The SAM Wastewater Treatment Plant is located in Half Moon Bay. The service area is approximately 30,000 people and includes the City of Half Moon Bay, El Granada, Montara, Moss Beach, and Princeton areas.
SAM’s service area is along the Pacific coast, 30 miles south of San Francisco.
The Sewer Authority Mid-Coastside (SAM) is a California joint powers authority (JPA). SAM provides wastewater conveyance and treatment services to its three member agencies:
Montara Water and Sanitary District (MWSD), Granada Community Services District (GCSD) and the City of Half Moon Bay.
The Intertie Pipeline System (IPS) is the backbone of SAM’s wastewater conveyance system. It is comprised of a series of force mains, pump stations, junction structures, and interceptors that convey the majority of wastewater to SAM’s treatment plant.
The Granada Force Main is the last pressurized segment on the IPS and is critical to transporting wastewater from the communities of Montara, Moss Beach, Princeton-by-the-sea, El Granada, and Miramar to the plant in Half Moon Bay.
Interactive Map
Preliminary Treatment
Influent Flow Meter: Measures and tracks flow rate trends to ensure greatest efficiency and service.
Bar Screens: Trash and solid debris is captured and removed by an automatic rake mechanism.
Influent Pump Station: All the wastewater that flows into the plant is pumped 20 vertical feet by eight solids-handling centrifugal pumps.
Primary Treatment
Grit Chambers: Allows grit particles (e.g. sand and coffee grounds) unable to be removed by bar screens to settle to the bottom of two aerated tanks where they can be easily removed.
Primary Clarifier: Heavy sediments that are too fine for previous steps (a.k.a "sludge") settle to the bottom of the two long rectangular tanks and are mechanically removed by scrappers. Lighter solids, such as fats, oils, and grease, rise to the top where they are skimmed off and discarded to the landfill.
Secondary Treatment
Secondary Treatment at Aeration Basin 3: Over a thousand fine bubble diffusers on the floor of the basins release a massive volume of dissolved oxygen into the wastewater stream. Microorganisms consume the oxygen-rich air for respiration as they feed on the nutrient-rich wastewater and naturally break down organic wastes into carbon dioxide.
Secondary Clarifiers: The clarifiers are circular structures, 85 feet in diameter and 14 feet deep and have a large surface area that allows the flow to slow down so that settling can occur naturally. Sludge sinks to the bottom of the clarifiers and lighter particles float to the top where they are removed by mechanical scrapers.
Disinfection and Discharge
Chemical Storage Facility: Stores two chemicals used to treat wastewater: sodium hypochlorite and sodium bisulfite.
Chlorine Contact Tanks: Sodium hypochlorite, is added to the wastewater to disinfect germs, bacteria, and viruses, as it flows through the tanks. The wastewater is dechlorinated with sodium bisulfite before being discharged into the marine environment.
Effluent Pump Station and W3 Pumps: Three vertical turbine pumps ensure the treated flow leaves the plant and travels safely to the outfall pipeline for discharge into the Pacific Ocean. Some of the treated wastewater is recycled back into the plant and used in a variety of the treatment processes to reduce the use of potable water. This non-potable water is referred to as No. 3 Water.
Ocean Outfall: Treated wastewater is discharged through the Ocean Outfall, a 20-inch diameter pipe, 50 feet underwater, and 3,000 feet away from land.
Solids Treatment
Rotary Drum Thickener: Slowly rotates sludge while liquid drains out. This process thickens the sludge to prepare it for the next stage of processing in the Anaerobic Digesters.
Anaerobic Digesters: Sludge and scum is pumped to the Anaerobic Digesters to feed anaerobic microorganisms in an oxygen-free environment in the heated Digester tanks. This process kills harmful pathogens and reduces the volume of organic solids. A byproduct of this process is methane, also called biogas. Biogas can be used to generate electricity for use at the wastewater treatment plant and beyond. It can also generate heat to keep the digesters warm to promote the biological process.
Belt Filter Press: Fully-processed sludge from the Anaerobic Digesters is now squeezed between perforated conveyor belts and large rollers to remove excess water. The product is a dried “cake” of biosolids that can easily be disposed of at the landfill or reused at certain compost facilities.
Supporting Systems
Electrical Room: Houses the treatment plant’s motor control centers, also known as MCCs. Controls all of the treatment plant equipment such as pumps, motors, lights, and critical control systems.
Emergency Generator: In the event of a power failure, the generator will turn on and produce enough electricity to power all of the essential treatment processes.
Turbo Blowers: Four 125-horsepower Turbo Blowers provide aeration to the Secondary Treatment of wastewater. The blowers must run constantly to ensure that the microorganisms in the Aeration Basins remain alive and healthy.
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