Case Study: Church Cuts Stormwater Costs by Third With Subsurface System

• By Gina Carolan
• Sep 14, 2011

For more than 30 years, Acton Faith Bible Church has served the spiritual needs of residents in Acton, Calif., a small community in the rugged Sierra Pelona Mountains. To accommodate the growing congregation, the church began building a new facility in 2006. The place of worship has been developed in four phases on a 10-acre property on Soledad Canyon Road. The finished facility will feature seven buildings, including the sanctuary, pastor’s residence and school, and about 200 parking spaces and landscaped areas.

The church’s building committee invited the engineers at Carlton Pacific Inc. to provide a hydrology study, grading plan, site plan revisions and street improvement design for the project. The engineers also had to design a new stormwater system for the developing site, located about 300 feet from the Santa Clara River. Before the development, the surface drainage was a sheet flow to Soledad Canyon Road. The Acton Faith Bible Church location is regulated by the Los Angeles County Department of Public Works, which mandates that stormwater discharge from a development be kept to pre-development levels.

To address the requirement, the engineers had to create a detention system that would reduce peak discharge rates and then release runoff slowly into the swale that had handled stormwater off the site previously. However, it was not necessary to detain and meter off the delta in runoff volume from the site because of the church’s proximity to the Santa Clara River.

The engineers initially designed an open detention basin at the front of the site. The property had little space for a stormwater solution, and to build a detention basin on the low side against the property line and have a fill slope for a parking lot required a retaining wall at the toe of the slope. Construction of the basin and retaining wall was estimated at $318,000, according to Ray Hensley with Stormwater Central Inc., the project contractor who also served on the church’s building committee.

“The site did not have adequate space for a detention basin,” Hensley said. “Some people in the community were also concerned about the visual impact of the retaining wall along Soledad Canyon Road, a scenic route."

Considering possible alternatives to the detention pond, Hensley, a 15-year stormwater industry veteran, recommended CULTEC’s underground stormwater chambers. Subsurface chamber systems can be used in almost any type of stormwater situation and can serve as subsurface retention or detention systems and as replacements for ponds, concrete structures or pipe and stone installations. One of the system’s main benefits is that it leaves space for additional buildings, parking and landscaping.

Specific to the Acton Faith Bible Church site, the system is designed to detain stormwater from the parking lot located above it and other impervious surfaces. The chambers will also infiltrate runoff, reducing the post-development volume. This Best Management Practice resulted in the post-redevelopment discharge rate of 7.5 cubic feet per second (cfs), even less than the pre-development discharge rate of 12.7 cfs.

The use of CULTEC’s underground system eliminated the need for the retaining wall. Additionally, the contractor and other members of the church donated their time, manpower and some equipment, bringing the final cost of the stormwater management solution down to about $106,000.

“CULTEC’s system enabled the church to utilize the space that would have otherwise been taken up by an open detention basin,” confirmed Blaine Carlton, engineer with Carlton Pacific. “The basin would have also required an expensive retaining wall and yearly maintenance.”

Designed to handle a 25-year storm, the system has a storage capacity of 25,027 cubic feet. It features 258 Recharger^® V8 chambers, the largest chamber from the company’s nine sizes. The engineers were able to use this model because the ground water was more than 30 feet deep. Each V8 unit is 32 inches high and 60 inches wide, with a bare chamber capacity of 8.68 cubic feet per linear foot. Generally, engineers and contractors benefit from selecting the tallest chamber possible as using the largest unit typically results in the lowest cost per cubic foot. Additionally, the heavy-duty construction of the V8 model makes it especially well-suited for high-traffic applications.

At Acton Faith Bible Church, stormwater enters the underground system through four catch basins on both sides of the system via 12-inch inlets. Catchments installed on the inlets collect debris, oil and sediment to prevent them from entering the detention system.

The runoff then enters an internal manifold system that conveys it throughout the bed of stormwater chambers. A conventional manifold consists of a pipe and fitting configuration; however, the Recharger V8 has an internal manifold feature unique to CULTEC chambers. Two side portals located on each chamber allow manifolding to take place at any point within the system, eliminating the need to build external manifolds, thereby condensing the system by decreasing the required footprint.

From the underground system, stormwater is directed into the swale and public right-of-way via a 10-inch pipe. Ultimately, runoff is discharged into the Santa Clara River.

Within 10 days, Hensley and other members of the church had installed the CULTEC system themselves for the first time with the help of a CULTEC representative. The process began with excavating two beds, laying CULTEC’s non-woven polypropylene filter fabric along the sides and bottoms of each bed and then adding crushed stone. After the chambers were arranged in the beds, backfilled with stone and covered with a layer of filter fabric, the site was prepared for asphalt. The filter fabric encapsulated all the stone to ensure protection from soil intrusion.

“The stormwater system’s cost-saving was a very important aspect for our small church,” Hensley said. “The best part was that we were able to install the system ourselves with the guidance of CULTEC”