Preventing Excess Stormwater in Sanitary Sewers

Stormwater entering the sanitary sewer system can cause sanitary sewer overflows (SSOs) during wet weather events. While Hillsborough is working with other jurisdictions and regulators to expand treatment capacity, town officials have identified capacity problems in the sanitary sewer collection system such as insufficient flow capacity in the Crystal Springs / El Cerrito Sewer Trunk. This has caused SSOs on the 700 block of El Cerrito every winter. In the past 12 years, more than $19 million has been spent to repair and upgrade sewer mains and trunk lines. As a result of a Cease and Desist Order (R2-2009-0020) the town has been ordered to complete more than $13 million in capital improvements over the next 5 years.

As part of the Cease and Desist Order, the town is currently in the process of video inspecting every public sewer main and studying the hydraulic model of the system to determine the areas with the worst storm water issues. Unfortunately, the video inspections are revealing numerous defects within the 100 miles of sewer mains; some require immediate repair, while others can be addressed through capital improvement projects over the next 10 years. By November 2011, the town will submit a 5 and 10 year capital improvement plan to the Regional Water Quality Control Board. This will be subsequent to the town's first comprehensive evaluation to the entire system.


It should be noted there were no above ground signs this public main was damaged. The longitudinal crack suggests further failure of the main will occur in the future. This video was made during dry weather. During wet weather, it is highly likely ground water infiltration is occurring from this crack. There are no roots in this main because it was treated with an herbicide and cleaned prior to video inspection.

As with the other video, no above ground indication that the sewer main was obstructed was known in advance of video inspection. The root masses in this main cause some surcharging within the main. Wherever roots are found in a public main or private lateral, in wet weather inflow of storm waters will also be found. The amount of gravel in this main suggests that an upstream section of the pipe is broken, and allowing dirt / rocks to enter the main.