Perfect Interception

Precast is the material of choice for grease interceptor, septic tanks and pump tank at outdoor wilderness camp.

By Bridget McCrea

It’s not often that children and families who live in the city get to experience the excitement of a rural, outdoor camping adventure. Thanks to the long-time director of Phoenix’s Parks and Recreation Department, they’re getting to do just that and more at Camp Colley.

This 3-year-old wilderness camp in northern Arizona fulfills a long-time dream of camp creator James Colley, who recently passed away: to give vulnerable youngsters a new, hopeful view of the world through outdoor adventure.

Located about 50 miles north of Payson, near the Blue Ridge Reservoir at an elevation of 6,700 feet, the camp provides structured, supervised recreational opportunities for children and families. The camp recently underwent expansion and now features a dining hall supported by several precast concrete wastewater collection structures that were manufactured and installed in fall 2005. When this second expansion phase is complete, there will be a bath house and cabins that can accommodate groups of up to 60 people.

Joan Gable, engineer with Phoenix-based Wass, Gerke and Associates specializing in wetlands treatment, says the first phase of the camp expansion included the design and construction of a dining hall (by Amon Builders of Payson, Ariz.), the drinking water system upgrade, and the wastewater treatment system that is comprised of several underground precast structures, as well as a treatment wetland feature. Gable says her firm has been involved with Phoenix’s wetlands research and design for several years, including a proposed 300-acre wetland facility in the city.

“The Parks and Recreation Department wanted to incorporate constructed wetlands into the on-site treatment system as an educational opportunity provided at Camp Colley,” Gable says. “We were brought in to design the on-site wastewater treatment system primarily to include the subsurface wetland as part of that opportunity.” The completed on-site wastewater treatment system is comprised of the grease interceptor, a septic tank, a sub-surface constructed treatment wetland, a dosing tank and drip irrigation field.

A typical subsurface treatment wetland is a constructed basin with a 2-foot depth of gravel media where the wastewater flows through the porous gravel matrix. Wetland plants, such as bulrush and cattail, are planted in the gravel matrix. The wastewater travels through the plant root zone and is treated by the microbial community living in that zone. The plants take up water and nutrients as well. The result is a highly treated wastewater discharging out to a drip irrigation field.

Wass, Gerke and Associates also designed the additional collection and treatment aspects of the system, for which it considered several materials and options before selecting precast concrete. Fiberglass was one option, Gable says, based on the issues surrounding the existing bedrock and excavating costs.

“Product and delivery costs (for delivering the product up into the mountains) were also issues,” Gable says, “which is why we steered away from fiberglass.” Gable says she found a better solution when the project’s excavator, Smith & Sons Excavating of Flagstaff, Ariz., pointed her in the direction of Prescott, Ariz.-based Yavapai Precast.

Gable spoke with the precast firm’s sales manager, Mark Boehle, and discovered that precast concrete would be ideal for the project. The firm designed a system that collected the treated water, which in turn dosed out into a drip irrigation field. A grease interceptor, situated before the septic tank, protects the other system components – precast septic tank, wetlands and drip field – from clogging.

For the Camp Colley project, the precaster manufactured and delivered a 1,700-gallon, two-compartment grease interceptor, 5,500-gallon and 2,500-gallon septic tanks, and a 2,500-gallon pump tank. All interconnected, the pieces serve as both the grease interceptor for the dining hall and the wastewater treatment system for the camp.

Working quickly
A winter season known for making an early appearance in Arizona’s higher elevations threatened contractors on the Camp Colley project. With ground-freezing temperatures in mind, the project’s owners fast-tracked a tight timeline for getting the underground work completed. “We specified it knowing that Yavapai Precast was close by, and that they could fabricate it, deliver it and have it put in place within five weeks,” Gable says.

Boehle says the tight schedule presented challenges for the precaster, but not enough to hold the project back in any way. Already in the throes of its busy season, the firm kicked into overdrive to help the city button up the project before winter hit.

The product design itself was straightforward and basic, Boehle says, who estimates that the city saved approximately 30 percent to 40 percent in manufacturing costs by using precast concrete over fiberglass. Lead times for the latter were much longer, he adds, making precast all the more attractive for the time-strapped project. “We were able to set everything up and have it done within five weeks,” Boehle says. “That was a very big consideration for the project’s owners.”

From the engineering perspective, Gable says her firm’s challenges included developing a system that could fit in a tight space. Setback constraints for the camp itself and the surrounding ephemeral washes gave the firm little wiggle room. “We were also piping in several different buildings, where previously just one septic line ran from a cabin to the system,” Gable says, who adds that Yavapai Precast also provided the required manhole. “It was great to be able to go through one vendor who not only made everything, but delivered it too.”

With the deliveries complete, Smith & Sons took over. Richard Smith, Smith & Sons president, says the company worked from mid-August to mid-September hammering out “extensive amounts of rock” to achieve the desired result.

Smith credits Yavapai Precast with manufacturing a quality system that was easy to install.

Dining out
Gable says precast not only saved money on the Camp Colley project, but also provided a sound foundation for the creation of the desired wetlands. The treatment wetlands are a natural system requiring minimal maintenance as long as the mechanical and hydraulic structures operate properly.

The precast tanks before and after the wetlands can provide the owners and caretakers reassurance that the treatment wetlands can perform optimally. With winter looming, she says the speed at which the grease interceptor and ancillary products were developed, manufactured and installed also went a long way toward creating a successful project. When the thaw comes to Camp Colley next spring, the wetland vegetation will be planted and given time to grow and stabilize in time for the camp summer season.

Once the Camp Colley caretaker is trained on the maintenance and usage of the grease interceptor, Gable says the system, which was meant to accommodate future camp growth, will be ready for use.

“It’s a very low-maintenance system that’s designed for commercial use,” Gable says. “As with any design, we wanted to make sure we were providing the camp with a safe, beneficial system as a way to ward off any future issues.”

Project: Camp Colley grease interceptor, septic tanks and pump tank for dining hall at outdoor w ilderness adventure camp
Owner: City of Phoenix
Engineers: Wass, Gerke & Associates, Phoenix
Contractor/Installer: Smith & Sons Excavating, Flagstaff, Ariz.
Precast Manufacturer: Yavapai Precast, Prescott, Ariz.