Once upon a time, Hooper, Utah, was a small, unremarkable rural community near Great Salt Lake. It looked much like any western settlement: friendly neighbors, plenty of space—and limited infrastructure.
In the 1990s Hooper began growing, and what was once a loose collection of houses separated by acres of farmland became a small town. Between 1990 and 2000 Hooper's population grew by 17%, to more than 4000, and it incorporated in 2000. Today, more than 5500 people call Hooper home, and the city continues to expand.
Although typical in many ways, Hooper is unique in geography and geology. Located in Weber County, it sits on essentially a peninsula in the Great Salt Lake, surrounded on three sides by wetlands. The terrain is extremely flat and the water table high.
When it incorporated, Hooper became the largest unsewered city in Utah; almost all residents relied on septic tanks and drain fields for sewage treatment. A 2001 study conducted by the Weber-Morgan Counties Board of Health raised significant concerns about the amount of sewage and gray water entering the groundwater supply.
“The Board of Health study led to further investigation of the situation by Hooper's public works officials, and what they found was troubling,” says Tracy Allen, PE, of Orem, Utah-based J-U-B Engineers Inc. Dozens of documented cases showed raw sewage or gray water entering the local waterways either directly or as a result of a septic tank overflow. This put Hooper at the top of the state's funding priority list.
The city formed a citizen's advisory committee in 2002 that authorized a sewer feasibility study. Conclusion: installing gravity sewers would be too expensive, both monetarily and aesthetically.
In cost projections for a gravity sewer, estimators had to allow for dewatering and installing foundation materials for the collection lines. Trenches about 20 to 25 feet deep would be needed in many locations to establish gravity flow, destroying several roads and existing utilities.
Designing a new sewer system was further complicated by the fact that some of the local real estate developers had created their own small sewer collection systems—all gravity, with small pumping stations—within city limits. Connecting the patchwork of sewers and integrating them into a master plan would add more costs.
Hooper's rapidly growing population and the need to eliminate sewage contamination of the groundwater added to the urgency. Also, the EPA's Phase II stormwater management program required towns like Hooper to reduce pollutants entering the stormwater outfall and, ultimately, the Great Salt Lake.
Gravity vs. Vacuum
Hooper decided to explore other options.
“The more we studied it, the more we realized that we could save a tremendous amount of money by installing vacuum sewers,” says Allen.
Vacuum sewers are relatively easy to install, and because the collection mains do not require a continual down-grade slope, they can be buried in shallower trenches, from 4 to 6 feet deep. Vacuum collection mains are also smaller in diameter. This means faster installation, less heavy equipment, and no dewatering or trench boxes.