Sanitation

How a Wastewater Treatment Plant Cleans Water
Treatment Plants
Airport-Larkfield-Wikiup Sanitation Zone
Geyserville Sanitation Zone
Occidental County Sanitation District
Penngrove Sanitation Zone
Russian River County Sanitation District
Sea Ranch Sanitation Zones
Sonoma Valley County Sanitation District
South Park County Sanitation District
Discharge Permits
Recycled Water

ChlorineContact During a restructuring of the county government in 1995, the Agency assumed responsibility for managing the county sanitation zones and districts, which provide wastewater treatment, reclamation, and disposal for approximately 22,000 residences and businesses. Since some of the wastewater treatment plants have not been significantly improved in over 20 years, capital projects are needed to ensure compliance with state and federal treatment and discharge requirements. Each sanitation district and zone operates under unique, individual permits from the California State Regional Water Quality Control Board (San Francisco and North Coast regions) that sets the requirements for operation.

For sanitation billing inquiries, please call 707-547-1950.

HOW A WASTEWATER TREATMENT PLANT CLEANS WATER Back To Top

Wastewater treatment plants are all different, but this general description outlines how treatment plants work.

As wastewater enters a wastewater treatment plant, large and heavy solids are removed by bar screens and grit chambers. Bar screens remove very large solids like rags, cans and tree roots which find their way into the sewer. Grit chambers remove heavy solids like gravel and seeds that settle rapidly. After passing through the bar screens and grit chambers, the wastewater undergoes the first treatment step called primary treatment. Primary sedimentation tanks are tanks that slow down the water to allow heavy solids to settle to the bottom and light solids like Styrofoam to float to the top. After primary treatment, the partially treated sewage is called primary effluent.

Secondary treatment follows primary treatment. During secondary treatment the primary effluent is mixed with microorganisms (tiny animals and bacteria) and oxygen. The oxygen is used by the microorganisms to grow and multiply. As they grow, they eat solids and chemicals in the primary effluent. After secondary treatment is complete, the secondary effluent flows into tanks called clarifiers where any remaining solids and microorganisms settle to the bottom. Some treatment plants also have additional sand and gravel that filter the secondary effluent after the clarifiers. When this is done it is called tertiary treated water.

After primary and secondary (and some places tertiary) treatment, the effluent undergoes a process called disinfection. During disinfection, chlorine is used to kill disease-causing organisms like some types of bacteria. Chlorine can also kill fish and other aquatic organisms in the receiving waters, so after disinfection the chlorine is neutralized to protect aquatic organisms by a process called dechlorination. After dechlorination, the treated wastewater is called final effluent and is discharged into receiving water or used as reclaimed water. Reclaimed (recycled) water is valuable and used to water agricultural crops and golf courses.

TREATMENT PLANTS Back To Top

The County Sanitation Districts and Zones include wastewater facilities that collect and treat wastewater to secondary and tertiary standards. A wastewater treatment plant is a facility with a series of tanks, screens, filters, and other processes used to clean wastewater before it is returned to the environment. The average dry-weather flow for these treatment facilities range from 2,000 (Sea Ranch Central) to 3,000,000 (Sonoma Valley) gallons per day. Two of the systems operated by the Agency are collection systems only, and do not include treatment plants.

Airport-Larkfield-Wikiup Sanitation Zone Back To Top

Began Operation:1983
Service area: 2,100 acres
Service recipients: 3,464 Equivalent Single-Family Dwelling
Treatment level: Tertiary
Design capacity: 900,000 gallons per day (average daily dry weather flow)
Discharge: All of the recycled water is used for irrigation.

Geyserville Sanitation Zone Back To Top

Began Operation: 1978
Service area: 177 acres
Service recipients: 337 Equivalent Single-Family Dwelling
Treatment level: Secondary
Design capacity: 92,000 gallons per day (average daily dry weather flow)
Discharge: Recycled water from this plant is disposed through percolation and evaporation.

Occidental County Sanitation District Back To Top

Began Operation: 1950
Service area: 55 acres
Service recipients: 264 Equivalent Single-Family Dwelling
Treatment level: Secondary
Design capacity: 50,000 gallons per day (average daily dry weather flow)
Discharge: Between May 15 and September 30 the recycled water is irrigated on private property. Between October 1 and May 14 recycled water is discharged into Dutch Bill Creek.

Penngrove Sanitation Zone (Collection System) Back To Top

Began Operation: not available
Service area: 475 acres
Service recipients: 501 Equivalent Single-Family Dwelling
Treatment level: None (see Discharge below)
Design capacity: Not applicable (collection system only)
Discharge: The collected sewage from the Penngrove Sanitation Zone is routed through the Penngrove Sanitation Zone's lift station to the City of Petaluma's system for treatment.

Russian River County Sanitation District (View brochure) Back To Top

Began Operation: 1983
Service area: 2,700 acres
Service recipients: 3,161 Equivalent Single-Family Dwelling
Treatment level: Tertiary
Design capacity: 710,000 gallons per day (average daily dry weather flow)
Discharge: Between October 1 and May 14 recycled water is discharged into the Russian River. Between May 15 and September 30 the recycled water is used for irrigation on forested land adjacent to the treatment plant and on the Northwood Golf Course.

Sea Ranch North (N) and Central (C) Sanitation Zones Back To Top

Began Operation: 1971 (C), 1972 (N)
Service area: 4,600 acres
Service recipients: 544 Equivalent Single-Family Dwelling
Treatment level: Secondary
Design capacity: 27,000 (C) & 160,000 (N) gallons per day (average daily dry weather flow)
Discharge: Treated wastewater from Sea Ranch North Sanitation Zone is treated to tertiary standards at the Gualala Community Services District Treatment Plant and used to irrigate the Sea Ranch Golf Links. Treated wastewater form the Sea Ranch Central Sanitation Zone Treatment Plant is used for irrigation.

Sonoma Valley County Sanitation District Back To Top

Began Operation: 1977
Service area: 4,500 acres
Service recipients: 17,027 Equivalent Single-Family Dwelling
Treatment level: Tertiary
Design capacity: 3,000,000 gallons per day (average daily dry weather flow)
Discharge: Between May 1 and October 30 the recycled water is used for irrigation. Between November 1 and April 30 recycled water is discharged into Schell Slough or Hudeman Slough.
Click here to take a virtual tour of the Sonoma Valley treatment plant
View time lapse video of the new tertiary treatment plant being built

South Park County Sanitation District (Collection System) Back To Top

Began Operation: Not available
Service area: 1,460 acres
Service recipients: 3,894 Equivalent Single-Family Dwelling
Treatment level: none (see Discharge below)
Design capacity: not applicable (collection system only)
Discharge: Collected influent is routed through the Todd Road Lift Station, located at Todd Road and Moorland Avenue, to the Laguna Subregional system for treatment.

DISCHARGE PERMITS Back To Top

The respective Regional Water Quality Control Boards (RWQCB) issues discharge permits for these facilities. The Sonoma Valley CSD and Sears Point Sanitation Zone treatment facilities are located within the jurisdiction of the San Francisco Bay Region of the RWQCB. The remaining facilities are located in the North Coast RWQCB jurisdiction area.

RECYCLED WATER Back To Top

In 1996, the Agency began to evaluate the potential for using recycled water in irrigation. The Agency has worked closely with agricultural and environmental groups, cities, towns, and districts to evaluate the potential for a recycled water distribution system that would link the reclamation systems operated by four municipalities and two sanitation districts. These facilities currently produce between 30,000 and 40,000 acre-feet of recycled water per year, a significant source for agricultural and municipal use. Of this, approximately 15,000 acre-feet are reused for urban and agricultural irrigation, with the remainder discharged during the winter into the Petaluma River, San Pablo Bay, or the Russian River and its tributaries. With the proposed construction of additional reservoirs, recycled water could instead be stored and used for agricultural and municipal irrigation, thereby reducing demand on the overall water supply system, enhancing the quality of surface waters, and contributing to the recovery of threatened fish and wildlife.

The Agency is currently studying water reuse systems that could be constructed in its service area to irrigate large landscaped areas with recycled water. Such water reuse systems have been already studied by the Agency's water contractors for their individual service areas. The Agency's study will consist of (1) reviewing existing water reuse studies prepare by the water contractors, (2) identifying water reuse sites in areas where no previous water reuse studies have been performed, (3) estimating the reduction in peak water demands that are possible through water reuse, and (4) assessing construction costs associated with potential water reuse systems.

Learn more about recycled water