It’s an Uphill Battle For a Connecticut Residential System

Intensive excavation, a Scavenger effluent pump and Eljen Corporation treatment modules help create a level playing field on a challenging home site
It’s an Uphill Battle For a Connecticut Residential System
Jovany Sandoval from Green Construction Management mixes mortar in front of the 4-inch pipe connecting the United Concrete Products Low-boy septic tank to the dose tank.

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Sewage percolating from saturated ground spelled trouble for the owners of a three-bedroom home in Newtown, Connecticut. The couple hired an engineer whose system design required removing the water and gas lines to install, and it didn’t meet setbacks. The local health department rejected the plan.

A friend of the couple recommended Mark Lancor, P.E., principal engineer at DYMAR in Southbury, Connecticut. Lancor took Mark Green, owner of Green Construction Management in Waterbury, Connecticut, with him to do soil tests. “The only area for a drainfield that met setback requirements was 92 feet up a 1:1 wooded hill behind the house,” says Green. “The Mantis leaching system from Eljen Corporation had enough size reduction to fit that space.” The product is approved only in Connecticut.

Two weeks of the three-week installation were devoted to site preparation, drainfield work and grading. Gravity was Green’s greatest challenge, and rain was his greatest fear.

Site conditions

Soils are loam with weathered rock at 33 inches and a percolation rate of 1 inch per 12 minutes. The hill on the half-acre lot rises from 27 to 45 degrees near the top.

System components

Lancor designed the system to handle 750 gpd. Major components are:

  • a 1,000-gallon dual-compartment Low-boy septic tank with Polylok Inc. / Zabel inlet baffle, effluent filter, risers and covers (tanks and distribution box from United Concrete Products)
  • a 1,000-gallon dose tank with 1/2 hp ABS EF05W Scavenger effluent pump (Sulzer Pumps Solutions Inc.)
  • 13 Mantis 536-8 treatment modules (Eljen Corporation)
  • a control panel and CS1200 tank alarm (CSI Controls)

System operation

A 4-inch PVC house lateral runs 32 feet to the septic tank, and then effluent flows 10 feet to the dose tank with an on-demand pump. It sends 26 gallons 92 feet through a 2-inch force main to the distribution box. The rise in elevation from the dose tank to the box is 20 feet.

The drainfield has a 45-foot in-line trench connected by a 22-degree 4-inch elbow to a 20-foot in-line trench. A 4-inch pipe in the distribution box connects to the factory-installed pipe near the top of the leaching modules. Holes in the pipe are at 5, 7, and 12 o’clock. Each 5-by-3-by-1.5-foot-high unit has eight vertical Bio-Matt filters (Eljen Corporation) separated by 3-inch-wide compartments (spacers) filled with ASTM C33 sand. Open air channels within the filters promote fixed aerobic bacterial growth on the geotextile fabric. Final polish occurs in the sand bed beneath the modules.


Green, his father Wayne, and laborer Jovany Sandoval built one temporary silt fence 3 feet in front of the asphalt driveway and another fence 77.5 feet up the hill from it. They spent two days cutting and clearing the hill, which involved half the backyard.

A swale on top of a 6-inch PVC perforated underdrain enclosed a 2,363-square-foot lawn in almost a complete semicircle. Because the septic code specified tight pipe for underdrains within 25 feet of septic tanks, Lancor cut off the top 8 feet of the arch and replaced it with a 45-foot straight run of SDR 35 solid pipe.

“We hand-dug to expose the existing drain, and then cut it at 27 feet from the septic tank,” says Green. “As we dug the new trench across the yard, our shovels hit ledge in two places, which surprised us.” Green mounted a jackhammer on his rubber-tracked Volvo EC35C mini-excavator and chipped out sufficient rock to complete the installation. The underdrain and swale were backfilled later with topsoil.

To stabilize his machine while preparing the drainfield, Green took fill up the hill and built a level shelf 15 feet downgrade from the trench area. He then used the platform to excavate the 4-foot-wide by 24- to 30-inch-deep trenches and scarify the receiving layer. Meanwhile, a truck from Independent Crushing arrived hourly to deliver 200 tons of septic gravel.

“We built solid timber cribbing over the curb, enabling drivers to back over it and come alongside the house,” says Green. “They had only 5 feet to dump and roll out before the raised body would take down a 14-foot-high power line. Its location prevented us from stockpiling more than one load at a time.”

Wayne Green supervised truck traffic, handled the tickets, and shot elevations. Sandoval, operating a rubber-tracked Volvo MCT125C skid-steer loader, shuttled gravel up the hill and along another shelf Mark Green had built close to the drainfield. “From there, I cast gravel into the trenches to make a 3-foot-deep bed,” he says. “Afterward, I rode the excavator up above the trenches to level and compact the stone.”

Prepping modules

As Independent Crushing delivered 50 tons of sand, Sandoval transferred it to Green, who placed and leveled 6 inches of it in the trenches. After carrying the 35-pound treatment modules to the drainfield, the crew removed the bottom cardboard supports before setting and connecting 10 units in one trench and three in the short trench.

Then, they removed the modules’ top cardboard supports and began the labor-intensive task of compacting multiple layers of sand in the spacers. “The quickest and easiest method is to pound away with two-by-fours,” says Green. “Simultaneously, we tramped down 6 inches of sand on either side of the modules. Everything settled overnight and had to be checked before we added the final inch of cover sand fabric the next morning.” Sand also extended 6 inches beyond the end of the first and last unit.

After backfilling the area with topsoil and grading it per the plan, Green and the homeowner didn’t like what they saw. The 45-degree slope near the top was too steep to walk up. The homeowner agreed with his plan to haul in more fill and grade the area to a gentler slope.

While Independent Crushing delivered 400 cubic yards of topsoil and Sandoval stockpiled it on the hill, Green excavated the 20-by-20-by-5-foot-deep hole for the tanks. At a depth of 2 feet, the bucket teeth hit solid ledge.

“No one knew it was there because we had no reason to dig test pits near the dry well,” says Green. After the first day of jackhammering, he changed the 5-foot 11-inch-high regular septic tank specified on the design to a 4-foot 6-inch-high low-boy tank. Another day of hammering removed a total of 3 feet of rock. By switching to the shallow tank, Green shortened the time spent hammering by a day and a half.

Finishing touches

Able to dig again, Green scooped out a bucketful of soil. Immediately, the hole filled with wastewater. Green dug a sump to contain it, but the soil was so saturated that a septic company had to pump the sump three times. Green bedded the excavation with 6 inches of gravel, and then a driver from United Concrete Products set the tanks.

The crew also severed the 4-inch cast-iron house lateral 2.25 feet from the basement wall and connected it with a stainless Fernco to a Schedule 40 pipe. Meanwhile, Jeff Carlascio, owner of Carlascio Electric, hooked up the pump tank as well as the control panel and alarm in the garage. “The property had a homemade cinder block septic tank encased in plywood,” says Green. “We abandoned it once the replacement system was functional.”

With mounds of topsoil in position, Green returned to filling in and grading. Working down 15 feet at a time from the top of the trenches, he built shelves and then blended the topsoil to create a 4:1 slope to the street. Randy Olmstead of All Green Hydroseed sprayed a custom mix of grass and wildflower hydroseeds over the disturbed area. “Until this point, one rainy day would have washed everything downhill,” says Green. The dry weather held.


The state department of public heath requires pumpouts every three to five years.


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