California Water Boards' Annual Performance Report - Fiscal Year 2017-18
PLAN AND ASSESS: SEWAGE SPILLS
SANITARY SEWER OVERFLOWS (Collection Systems)
SIZE OF SEWER SYSTEMS SEWAGE SPILLS
Approximately 39 percent of the collection systems regulated under the SSO program reported one or more sewage spill during FY 2017-18.
| KEY STATISTICS FOR FY 2017-18 | |
| Number of SSO Events: | 2,920 |
| Volume of Sewage Spills (gallons): | 8,465,520 |
MEASUREMENTS - Data last updated on: 08-30-2018 (4:15 pm)
| Region | Miles of Gravity Sewer |
Miles of Pressure Sewer |
Total Size of Collection System (Miles) |
Facilities With 1 or More Sewage Spill | Number of SSO Events | Volume of SSOs | Average SSOs per 100 miles | Average Volume of Spills per 100 miles | SSO Events per Facility with Spills |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1,964 | 70 | 2,034 | 29 | 66 | 258,514 | 3.24 | 12,710 | 2.28 |
| 2 | 15,696 | 137 | 15,833 | 98 | 832 | 982,384 | 5.25 | 6,205 | 8.49 |
| 3 | 4,196 | 105 | 4,301 | 45 | 129 | 3,808,801 | 3.00 | 88,556 | 2.87 |
| 4 | 20,705 | 143 | 20,848 | 60 | 297 | 611,585 | 1.42 | 2,934 | 4.95 |
| 5 | 21,828 | 401 | 22,229 | 112 | 1,273 | 1,524,038 | 5.73 | 6,856 | 11.37 |
| 6 | 3,856 | 71 | 3,927 | 12 | 59 | 272,095 | 1.50 | 6,929 | 4.92 |
| 7 | 2,885 | 32 | 2,917 | 9 | 18 | 11,728 | 0.62 | 402 | 2.00 |
| 8 | 14,828 | 94 | 14,922 | 39 | 105 | 308,903 | 0.70 | 2,070 | 2.69 |
| 9 | 10,519 | 66 | 10,585 | 30 | 141 | 687,472 | 1.33 | 6,495 | 4.70 |
| TOTAL | 96,477 | 1,119 | 97,596 | 434 | 2,920 | 8,465,520 | 2.99 | 8,674 | 6.73 |
WHAT THE MEASURE IS SHOWING
The data show that in Fiscal Year (FY) 2017-18 sanitary sewer overflows (SSO) events were concentrated in the San Francisco Bay (Region 2) and Central Valley (Region 5) regions. The two regions have some of the largest collection systems in the State; combined the two regions account for almost 40 percent of the State's total size (in miles) of collection systems. These two regions account for 30% of the total volume of sewage spills in 2017-18, while the Central Coast Region (Region 3) accounted for 45% of the total volume. The number of spills and the average spill volume varied significantly throughout the State; Region 3 reported the largest average spill volume (with 88,556 gallons spilled per 100 miles), while the Colorado River Basin Region (Region 7) reported an average spill volume of 402 gallons spilled per 100 miles.
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, 2017 to June 30, 2018 .
- 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.
