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A secondary treatment unit with recirculating and dosing compartments enables a contractor to remediate a failed sand filter in southwest Oregon

Homeowners in Roseburg, Ore., wanted to stop the smelly water from ponding in their back yard. Two contractors advised the couple to poke holes in the liner of their sand filter. Instead, they sought a third opinion.

When Chris Semrau of North Bank Excavation in Roseburg arrived, he found the 18- by 20-foot sand filter in failure. The small fenced-in yard also held a swimming pool, dog kennel, equipment shed, detached garage/office, and four mature oaks. With no room to replace the sand filter, remediation was the only solution.

Semrau knew that Orenco Systems Inc. in Sutherlin, Ore., was looking for a site to demonstrate its AdvanTex AX20RT three-in-one treatment, recirculating, and dosing tank. Semrau called sales director Darren Simmie, and they teamed up to repair the onsite system. The unit’s design enabled them to keep the existing septic tank and drainfield, while its compact shape expedited installation and minimized disruption.

Site conditions

The 0.68-acre subdivision lot has 36 to 48 inches of loam over clay with some river rock. Because the repair used existing components, soils and test pits were unnecessary.

System components

Semrau designed the system to handle 500 gpd. Its major components are:

• Existing 1,000-gallon, single-compartment concrete septic tank made by Willamette Graystone, Roseburg, Ore.

• 4-inch effluent filter, model FTS0444-36 (Orenco Systems Inc.).

• 800-gallon AX20RT secondary treatment system with recirculation and dosing compartments (Orenco Systems Inc.).

• Biotube pump vault with 4-inch turbine 1/2-hp effluent pump (Orenco Systems Inc.).

• Universal flow inducer pump system with 4-inch turbine 1/2-hp demand-dose discharge pump.

• VeriComm telemetry monitoring system and control panel (Orenco Systems Inc.).

System operation

Wastewater gravity flows into the septic tank, then through a 4-inch ABS pipe to the 600-gallon recirculation compartment of the AX20RT, which uses packed bed filter technology. Every 20 minutes, the pump sends 8.5 gallons in 15 seconds to the top of the synthetic media. As the liquid trickles through hanging textile curtains, microorganisms remove impurities.

A recirculation splitter baffle at the bottom of the media sends 80 percent of the treated water back to the recirculation compartment and 20 percent to the 200-gallon dosing compartment. When the house is empty during the day, a low-level equalization check valve in the baffle directs all the treated water to the recirculation compartment. If the effluent pump receives no flow for 24 hours, the dosing cycle increases to 40 minutes. After 48 hours with no flow, the dosing cycle increases to 60 minutes.

“One benefit of packed bed filter technology is that you don’t need a colony of established microbes to achieve treatment,” says Simmie. “Just pushing the effluent through the media produces an immediate reduction in TSS and BOD.” Sampling results show BOD at 6.4 mg/l and TSS at 5.9 mg/l. The on-demand 10-gpm discharge pump in the dosing compartment sends 40 gallons four times per day to the drainfield — two rock-and-pipe gravity trenches each 64 feet long on 10-foot centers.

Installation

Semrau and partner Scott Hammerschmidt removed the pump vault in the septic tank, then installed an effluent filter and a gravity outlet tee that plumbed to the recirculation compartment.

The only available place for Semrau’s 15,000-pound KX160 Kubota excavator was on top of the sand filter. As he dug the 78-inch-deep hole for the 102- by 62- by 72-inch-tall RT (recirculating tank) unit, he had to avoid undermining the concrete floor in the dog kennel and hitting the overhanging gutters. “I had a 2-foot soil buffer between the RT and sand filter, and from the inlet of the RT to the eaves,” he says. “A detached garage/office was to the south. It was like working in a shoe box.”

To everyone’s surprise, the excavator bucket dug up the original 1-inch PVC Schedule 40 plumbing from the 450-gallon concrete dosing tank. “It ran backward out of the tank toward the house, made two tight 90-degree turns, then went out to the drainfield,” says Semrau. “The silver lining was now we knew where it was and could tie in the RT’s discharge line.” Semrau excavated the supply line enough to verify that the bucket hadn’t cracked or split it.

The excavator’s 10-foot reach enabled Semrau to park back from the edge of the sand filter. “My biggest concern was having the sand collapse and dump the machine in the pit,” he says. “That’s where the RT’s shallow bury really helped. I removed two-thirds as much material when compared to a standard installation. That’s a 33 percent reduction in spoil and digging time.” The septic tank and RT were side by side and 50 feet from the drainfield.

After he dug the pit, the edge of the sand filter began sloughing, allowing the bellied-out liner to hang into the excavation. The men quickly installed the 900-pound fiberglass unit on 6 inches of compacted pea gravel, then backfilled to the mid-seam to support the liner.

The following morning, Semrau and Hammerschmidt found 8 inches of effluent in the excavation and the sand filter sloughing even more. Using a liquid transfer pump, Semrau pumped the effluent into the dosing tank, then programmed the control panel to pump down the tank. Most of the effluent drained from the sand filter and stopped trickling into the excavation.

When Semrau tried pulling back some of the sloughed sand filter, the excavator bucket grabbed the electrical conduit for the old control panel and yanked out the wires. Deciding it was time to decommission the dosing tank, the men filled it with sand, cut off the riser below grade, and backfilled.

Normally, the RT is installed 2 inches above grade. However, to maintain the correct elevation with the septic tank, Semrau installed the tank almost at grade. As a precaution against water possibly ponding, he laid perforated pipe and some drain rock around the lid, then ran the line to a drainpipe in the yard.

The control panel needed a phone line, but the junction box was on the opposite side of the home. “The electrician couldn’t drill through the foundation because a stem wall anchored each new addition to the ground,” says Semrau. “We had no idea what we were going to do until one of the men discovered a phone jack and power panel in the garage/office. They were perfect.”­ During the installation, two neighbors approached Semrau about their problem sand filters. The systems, all at the end of their useful lives, are prime candidates for remediation.

Maintenance

Orenco holds the two-year service contract and will continue collecting field data.

Twice a year, a technician takes effluent field samples to confirm performance, checks the effluent filters, cleans the laterals in the RT, checks the liquid levels, runs the pumps, and looks for signs of owner abuse.



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