Apr 15, 2015

Lessons Learned

California school’s storm water redesign utilizes unique system that drains by gravity

In recent years, 70-year-old Acacia Middle School in Hemet, Calif., has seen a significant growth in its student population, and to provide students with a safe and comfortable learning environment, the facility chose to undergo extensive improvements to the west side of its campus. This included a new driveway and parking lot, classroom modernization and construction of a new gymnasium.

The Challenge

Engineers from Tory R. Walker Engineering Inc. of Vista, Calif., who specialize in hydrology and optimization, were tasked with redesigning the school’s storm water management system. The project was to be carried out in three separate phases.

Initially a drainage system was developed to hold most of the runoff in underground systems; however, it was determined that after a storm, some of the runoff might pump back onto the street. The engineers realized that the runoff would exceed its peak flow to the street if nothing was done, and they proposed using a system that would drain largely by gravity.

The site is very flat, and there is no onsite drainage system. The flat terrain would make it difficult for various areas to drain by gravity when the water is directed into an underground system because the site lacks an MS4 underground drainage pipe.

The Solution

A three-basin system was designed to drain as much water volume by gravity as possible; any water that cannot be drained by gravity is directed to a parking lot next to the street. The first two basins are hydraulically connected, and a third long basin was added in lieu of a drainage pipe for drainage considerations and to enhance infiltration. Using this type of system eliminated the need for a pumping system and any associated maintenance.

“The area just a bit further from the lowest elevation point in the school has enough topographic difference to drain by gravity, but the portion closest to the street does not,” said Luis A. Parra, Ph.D., P.E., CPSWQ, D.WRE, ToR, senior project manager at Tory R. Walker Engineering Inc. “In this case, we designed the system so it would drain by gravity up until a certain point, and from that point on, it would percolate into the soil.”

Given the requirements of the site, the team chose CULTEC’s Recharger V8HD, as it provides a large storage volume within the horizon between the groundwater and the cover requirement in a compact footprint. Each chamber measures 32 in. high and 60 in. wide and has a bare chamber capacity of 8.68 cu ft per linear ft.

A pretreatment system consisting of a vortex pre-filter was installed with the CULTEC chambers to allow for maintenance at a single access point. The filter extends the useful life of the underground system by trapping oils, large sediment particles and other debris before they can reach and contaminate the chamber system.

The Results

The use of gravity helps to get rid of runoff quickly after treatment, and only a small portion of water is required to infiltrate into the soil to drain. The hydraulic system meets the site’s requirements by maximizing the use of the limited space while providing the school with a significant cost savings.

The Recharger V8HD provided a storage volume of 58,383 cu ft. In addition, the V8HD model is able to withstand traffic loading with minimal cover—a major site requirement, since the chambers will largely be covered with parking areas. The chambers are divided into three separate beds, one of which is located beneath a grassy area dedicated to a playground; the other two are installed beneath parking lots.

“The new storm water system accommodates a large volume of runoff because we can get a lot of rainfall in this area,” said Mike Houghton, contractor with Genesis Construction, which installed the system. “CULTEC’s chambers provide the storage we need. Plus, they fit together and install very easily, and you can’t beat their integrity.”

Gina Carolan is COO and director of marketing at CULTEC Inc. USA. She can be reached at 203.775.4416 or [email protected].



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