An onsite system at the Oakland Wood Rest Area on westbound Interstate 90 in Albert Lea, Minnesota, presented problems for the state Department of Transportation. Installed in soils left over from constructing the expressway, it never functioned as designed.

“Poor soil created a lot of challenges,” says designer Tom Wirtzfeld, owner of Advanced Septic Solutions in Northfield, Minnesota. In 2011, his company upgraded the existing system to handle 3,100 gpd. Major components were:

•   Existing 2,500-gallon dual-compartment septic tank

•   3,000-gallon single-compartment concrete tank (precast tanks from Wieser Concrete)

•   AdvanTex AX100 treatment pod (Orenco Systems)

•   7,500-gallon single-compartment concrete recirculation tank

•   1,500-gallon concrete dose tank with dual alternating 3/4 hp Orenco pumps

•   2,520 feet of 2-inch pressurized PVC pipe with 5/32-inch orifices on 36-inch centers

Wirtzfeld’s seven-member crew abandoned the old drainfield and built one with 20-chambered (Infiltrator Water Technologies) trenches 84 feet long in 10 zones. “We plumbed the tanks with 4-inch Schedule 40 PVC pipes, then pumped effluent 670 feet to the drainfield through two 3-inch pipes to two automatic distribution valves in deep heat risers,” says Wirtzfeld. “With the frost line at 3 feet or deeper, we had to insulate all the tanks and piping.”

Wirtzfeld invented the deep heat riser to protect the valves from freezing without using electric heat tape. For this job, he used 7-foot-high, 30-inch Ultra-Rib risers (Orenco Systems) with dose lines entering from the bottom. The pipes were insulated, then the risers filled with 5 or more inches of 1.5-inch rock for heat transfer and to bed the valve feeding the 2-inch dose lines to the chambers.

“We sprayed 2 inches of foam insulation around the outside of the risers from the lid to a depth of 4 feet, then built up a 4-inch-thick foam layer inside the lid,” says Wirtzfeld. “Foam is much faster to apply than sheet insulation, it seals better and seamlessly, and it has a higher R value for depth. It also provides more friction, especially for AX100 pods to help prevent flotation.”

The team completed the install in three weeks. Although the job was 70 miles from home, it proved to be a worthwhile project. Two years later, Wirtzfeld was hired to upgrade the Newmarket Rest Area on the Interstate 35 southbound lane. It had two AdvanTex AX100 pods and the system was almost twice as large as the Oakland Wood project.

Read more about Advanced Septic Solutions in a full profile.