The California Water Boards' Annual Performance Report - Fiscal Year 2010-11

MEASUREMENTS  - Data last updated on: 

WHAT THE MEASURE IS SHOWING

The data is showing that the number of sanitary sewer overflows (SSO) events are still concentrated in Regions 2 and 5, between the two regions they account for 40% of the total size of collection systems with 78% of the total number of sewage spills. These two regions also have some of the larger collection systems in the State. The average spill volume though varies significantly around the State with Region 9 accounting for the largest average spill amount (50,439 gallons per spill). Region 7 recorded the lowest number of reported spill events.

WHY THIS MEASURE IS IMPORTANT

SSOs often contain high levels of suspended solids, pathogenic organisms, toxic pollutants, nutrients, oil, and grease. Typical consequences of SSOs include the closure of beaches and other recreational areas, inundated properties, and polluted rivers and streams. This measure tracks the reporting required by the Statewide Sanitary Sewer Order and will help to determine if the sewer system management plans (SSMP), also required by the order, are contributing to a reduction in the number of SSO events.

TECHNICAL CONSIDERATIONS

• Data source: CIWQS. Period July 1, 2010 to June 30, 2011. Extracted on August 9, 2011.
• Unit of Measure: Average Number of Spills per 100 miles: Measures the number of sewer overflows per 100 miles of sewer lines. Average Volume of Spills per 100 miles: Measures the volume in gallons of sewer overflows per 100 miles of sewer lines.
• Data Definitions: Sanitary Sewer: A pipe or conduit (sewer) intended to carry wastewater or water-borne wastes from homes, businesses, and industries to the POTW. Sanitary Sewer Overflows (SSO): Untreated or partially treated sewage overflows from a sanitary sewer collection system.
• References: Information on the Sanitary Sewer Overflow Reduction Program
  The Sanitary Sewer Overflows Incident Map
  The Interactive SSO Report

GLOSSARY

Sanitary Sewer Overflow

A sanitary sewer overflow (SSO) is any overflow, spill, release, discharge or diversion of untreated or partially treated wastewater from a sanitary sewer system. SSOs do not include overflows from blockages or other problems within a privately owned lateral.

Sanitary Sewer Overflow Reduction Program

In May, 2006, the State Water Board adopted a Statewide Sanitary Sewer Order ( ORDER NO. 2006-0003-DWQ ) to address the issue of SSOs in a consistent and uniform manner statewide. Through the order, California became the first state in the nation to implement a program focused on the regulation of sanitary sewer systems. Sanitary sewer system agencies covered under the order, referred to as Enrollees, are required to report all SSOs for which their agency has responsibility into the State Water Board's SSO database. Enrollees are also able to report sewage discharges from privately owned laterals or collection systems, for which the Enrollee has knowledge of the event but is not responsible, on a voluntary basis.

( Page last updated:  9/23/11 )