DUDEK - Constructing a Gravity Sewer Interceptor

Infrastructure Development

Constructing a Gravity Sewer Interceptor through Protected Land
When growth in Chula Vista, California produced the need for an additional sewer line, the city worried that its 9,000 acre preserve - and long-term conservation plans – were about to be spoiled. Traditional pipelines and their access roads intruding into preserves can impact sensitive habitats, while pumping sewage around the area was less efficient and more prone to spills.

The alternative? A new breed of sewer.

“The most significant environmental issue when a sewer is in a preserve area is that you need to have an access road and manholes to get to blocked lines,” said Joe Monaco, Dudek’s senior environmental project manager. “The roads facilitate human access into a preserve and have the potential to create impacts such as increased noise, dust, pollution and unauthorized activities.”

Collaborating Towards a Solution
To come up with an acceptable solution, hundreds of meetings between the city, environmental groups, and Dudek ensued. After much deliberation, the team finally found its answer: a dual-pipe sewer line.

The system works like this: If a blockage occurs in one pipe, the sewage is automatically diverted over a Weir wall into a second pipe running parallel to it. A sensor detects when the sewage level has risen higher than normal and sends the information to the city’s SCADA system. The dual-pipe system covers one mile of line that runs through the preserve – the other 13 miles are traditional single pipe sewers - and a flow splitter or flow joiner structure connects the dual pipe to the single pipe on either end.

“This doesn’t solve the original blockage problem - you still have to get out there and clean the sewer,” said Dale Gruel, Dudek’s principal engineer for the project. “The concept is you don’t have an immediate need to send equipment out. If, for example, a blockage occurs in the middle of the bird breeding season, you now have the opportunity to wait until that critical period of time is over to do the repairs, when the least environmental disruption occurs.”

Plans also permitted construction only within a narrow, 20-foot-wide corridor to reduce impacts to sensitive habitats and species from construction. Engineers buried manholes to prevent vandalism, and workers reintroduced native species to the land following completion of the sewer construction.

Beyond a Simple Pipeline
The project went far beyond federal, state, and local permits and regulations.

“Mostly sewers are a pipe underneath the street,” said Gruel. “And you have to deal with traffic control and upset neighbors, but that’s all. This went way beyond that.”

“A lot was riding on the completion of this project,” said Kirk Ammerman, senior civil engineer for Chula Vista. “It would’ve had a huge impact on development if it hadn’t been completed on time.”

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