Sewer Collection System

The City of Rohnert Park's sewer system has two primary functions which are to first collect the City's wastewater and then to transport it the Subregional Water Reclamation System of Santa Rosa for treatment.

The City's sanitary sewer system facilities include 100 miles of gravity sewers, 7.5 miles of force mains, 16 inverted siphons, and three pump stations. From the pump stations the wastewater directed to the Santa Rosa Subregional treatment facility on Llano road.

During a 24-hour period the amount of wastewater entering the system fluctuates from 1 to 7 million gallons per day. The average dry weather wastewater flows are 3.5 MGD (million gallons per day), and up to 15 MGD during winter months.

To view the City's updated Sewer System Management Plan adopted by the City Council on September 3, 2019 click here.


City of Rohnert Park Wastewater System
Annual Performance Report 2022
(January 2022 – December 2022)

 

  1. General Information

    Facility/System Name: City of Rohnert Park
    Wastewater Collection System

    Responsible Entity: Vanessa Garrett, PE, MPA, 
    Director of Public Works

    Persons in Charge: Mark Hendersen, 
    Utilities Operations Manager
    Warren Naumann, 
    Collection System Supervisor

    Applicable Permits: State Water Resources Control Board 
    Order No. 2006-0003-DWQ 
    Statewide General WDR for Wastewater Collection Agencies

    Description of Collection System:

    Rohnert Park's sewer system serves two primary purposes. The first purposes to safely collect the City's wastewater. The second purpose is to transport it to the regional treatment plant in Santa Rosa, where it can be treated and recycled water produced. The City's sanitary sewer system facilities include 100 miles of sewers that function primarily on gravity, 7.5 miles of pressurized sewer, 16 siphons (pipes that cross underneath things like creeks), and 3 pump stations that assist in getting sewage to the treatment plant. The majority of facilities were installed between 1956 and 1980. The collection system's underground network of pipes range in size from 6 to 42 inches in diameter.

     

     II. Performance Summary for the Period of January 2022 – December 2022

The City of Rohnert Park collected a total of 1.058 billion gallons of wastewater in 2022. The wastewater was collected and pumped to the Santa Rosa Subregional Wastewater plant for treatment, which is located approximately 7 miles west of the city. Once treated, the majority of the wastewater returns as recycled water through a separate dedicated network of pipes throughout the City. The recycled wastewater is primarily used for irrigation purposes at facilities such as Foxtail Golf Course, Sonoma State University, the City’s Community Center, and numerous parks throughout the City.

 

Sanitary Sewer Overflows

The Department of Public Works – Sewer Division strives for goal of zero (0) sanitary sewer overflows (SSOs) from the collection system. An SSO is when sewage reaches the surface of a road or other property due to a blockage or capacity issue. Some of the primary causes of SSOs include inflow and infiltration due to high water levels during storm events, obstructions caused from rags, roots, and grease accumulations. To help reduce the potential for SSOs the staff compiled a Sewer System Master Plan that identifies areas with high levels of inflow and infiltration and capacity deficiencies. Staff works on these projects and our operations team clean sewer lines year-around to keep our system flowing properly. The City also maintains backup generators at our pump stations so we can keep sewer flowing during a power outages. Customers, both residential and commercial, can help prevent SSOs by properly disposing of waste products such as grease/oils, food scraps, and sanitary wipes into solid waste containers, instead of down the drain.

We are pleased to announce the City had only (1) incident of sanitary sewer overflows within the public wastewater water system this reporting period. The state average, for comparison, is between three (3) and four (4) per year. The incident occurred on Commerce Blvd/Hinebaugh Creek. The City’s sewer line that crosses under Hinebaugh Creek (siphon) became obstructed due to excessive grease. City staff cleared the blockage. Several food preparation facilities in the area were issued notice of violations for failure to maintain their grease interceptors properly.

Table 1 below compares the sewer spill rates of three different areas per 100 miles of sewer line per year:

• The City of Rohnert Park
• The state-wide municipal average
• The regional municipal average

For comparison, the City has had an average of 0.84 spills per 100 miles of sewer line this past year, compared to a state-wide average of 3.64 and a regional average of 4.62.

 

Calendar Year

Historical Data

Below is the city’s historical overflow data for the last 5 years (2017-2022):

SSOs from City facilities

# SSOs per 100 miles of sewers (gravity and force mains)

Collection System Improvements

The City utilizes a Supervisory Control and Data Acquisition (SCADA) and alarm systems to remotely monitor all pump stations. Sewer collections staff follow sewer line cleaning schedules that have been identified in the City’s Sewer System Management Plan adopted by City Council September 3, 2019 Resolution NO. 2019-099. The following repairs and improvements were made in the collection system during 2021:

• Repaired Manholes: 17
• Abandoned old sewer intertie with Cotati for roundabout project
• Installed new digester station #3
• Sewer Lines Cleaned: 17.0 Miles
• Replaced wet well ventilation station #2
• Completed Sewer System Management Plan audit
• Implemented mobile maintenance platform – Mobile MMS
• Upsizing 940 linear feet of sanitary sewer main from 18” to 30”
• Diverting 500 linear feet of sewer away from homes and through       public right of way to decrease risk to the public

 

     III. Notification

This report is available in PDF here and also can be requested by contacting staff at (707) 588-3300.