Mighty Tight Squeeze

Peat fiber biofilters provide a treatment solution for a tiny lakeside lot in New York state where an old septic system had failed.

Sewage backing up in a three-bedroom home on Lake Carmel in Carmel, N.Y., had created a hazardous mold condition under a bathroom floor.

The homeowners summoned Pat Tyndall of Tyndall Septic Systems Inc. in Brewster, N.Y. He pumped the concrete block septic tank and put the people in touch with Chris Dellaripa, project coordinator for the Putnam County Septic Repair Program.

Dellaripa immediately stopped the homeowners from using the bathrooms. Because the home was within a 500-foot radius of Lake Carmel’s high-water mark, the onsite system qualified for free replacement under the county program.

“This was one of the most challenging jobs I’ve done in awhile,” says John Kalin, P.E., of Design Concepts Engineering in Pawling, N.Y. “The only place for the secondary treatment system was a 9- by 24- foot area at the back of the house. It was like working in a planter box.”

Tyndall won the bid. He faced a 2:1 grade change from the road to the bottom of the 60- by 90-foot lot, and had no clear access. At the heart of the system are three peat fiber biofilter systems.

Site conditions

Soils are well-drained brown sandy loam with no groundwater, mottling or rocks. A failing dry well next to the house was within 25 feet of the lot’s potable well, and within 65 feet of potable wells to the east and west. Half the septic tank extended into the neighbor’s backyard, where the system’s clay tile drainfield was ponding.

System components

Kalin designed the system to handle 450 gpd. Its major components are:

• 1,000-gallon Fralo Plastech dual-compartment septic tank from Roth Global Plastics.

• A300 effluent filter, Zabel Environmental, a division of Polylok

• 1,000-gallon single-compartment pump tank

• 1/3-hp low-head PE31M Hydromatic pump

• Three 150-gallon pre-engineered Puraflo peat fiber biofilters, Bord na Mona Corp.

• Installer Friendly Series single- phase timed dose/alarm panel, SJE-Rhombus.

System operation

Wastewater gravity flows through a 4-inch PVC Schedule SDR-35 lateral to the septic tank, then into the pump tank. The pump runs 75 seconds every two hours, sending 30 gallons of effluent through a 2-inch PVC line tied to the biofilters.

A spray manifold in each module evenly doses the peat. Purification occurs as the liquid percolates through the media over 36 to 48 hours. The peat also suppresses odors.

Weep holes topped with clean stone on either side of the modules disperse effluent to the ground through 7- by 24-foot by 6-inch deep beds of washed gravel.

The units produce effluent averaging less than 10 mg/l TSS and BOD, and a 99 percent reduction in fecal coliforms with no pathogens.


The front of the house faces a road. A flight of 20 steps leads down to a patio, from which an identical stairway goes to the backyard. To get the Komatsu PC35 zero-tail-swing compact excavator to the foot of the property, Tyndall and his two men cut a road. They used the smaller machine to build a platform halfway down the hill, then parked the bigger Volvo EC55B Pro compact excavator on the platform.

The crew first abandoned the 20-foot-deep hand-dug well and original septic tank. “I ordered 8 cubic yards of concrete, and when the mixer arrived, the driver dumped it into the excavator bucket a load at a time,” says Tyndall.

The Volvo excavator transferred the concrete to the Komatsu waiting below. Then that operator took it down the hill to the well. Most materials were handled this way. The men removed a chain-link fence along the east property line, then filled the septic tank with concrete.

A foundation drain pipe protruded from the walk-out basement, and 3 feet of soil was pushed against the wall. The crew removed the pipe and soil, using the latter to backfill the well and septic tank.

It took two days to excavate the three 24- by 7- by 4-foot-deep holes for the biofilters, which fit next to the basement and paralleled the east property line. “We’d extract and move a bucket of soil to a position the Volvo could reach,” says Tyndall. “That driver piled it on the road. When the hole was dug, the Komatsu went up the hill to load the soil into our dump container.”

Workers shoveled gravel into wheelbarrows from a pile midway down the hill, then transported it to the holes. Moving and setting the 1,800-pound biofilters taxed the smaller excavator to its limit. After installing and plumbing a module, the men erected a 4-foot-high retention wall along the property line behind it.

“We couldn’t set all three biofilters at once because we had an area only 2 feet wide in which to install the 2-inch inflow and outflow pipes,” says Tyndall. The Volvo lowered five pallets of Unilock blocks, and the men carried each 50-pound block down the stairs or moved them in wheelbarrows.

After covering the basement wall and retention wall behind the first biofilter with rubber membrane, they repeated the process for the second and third modules. The liner prevents water from leaching horizontally.

“We laid plywood sheets on top of the biofilters, then ran over them with the wheelbarrows and dumped gravel into the holes,” says Tyndall. “We also used the wheelbarrows to backfill with spoil.”

Excavating the two 9- by 5- by 4-foot-deep holes for the fiberglass tanks along the side of the house was easier, as there was more room for the machine to maneuver. The pump tank sat 15 feet from the first biofilter. The tanks, installed one at a time and side-by-side on a 6-inch-deep gravel bed, were backfilled with more spoil, only this time using the Komatsu excavator.

Because the biofilters were so close together, the pump could dose them in 40 seconds, but the manufacturer recommends running it for at least a minute. Tyndall installed a valve and throttled back the pump to 75 seconds. A weep hole drains effluent into the pump tank, preventing the liquid from freezing in the line. “A normal installation of these components takes three days,” says Tyndall. “This one took two weeks.”


Under the Septic Repair Program, the system’s installer is responsible for maintaining it for the first two years. Twice per year, Tyndall observes the float, pump and lids. He checks the sludge level in the septic tank and cleans the effluent filter. At the end of two years, he draws an effluent sample and sends it to a lab for analysis. The system is operating as designed.


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