Excessive Rain and Unseen Obstacles Create a Nightmare Project

A two-stage pretreatment leaching system provides effective treatment in a small footprint on a 2-1 slope for a Connecticut homeowner

Excessive Rain and Unseen Obstacles Create a Nightmare Project

Wiring the pump tank’s electrical connections.

Buying a four-bedroom home with a flooded basement heightened the risk factor for a house flipper in Southbury, Connecticut.

A management company hired to extract the standing water opened the septic clean-out and pumped in 26,000 gallons, destroying the 1,000 gpd system with stone-and-pipe drainfield. That day, the flipper sold the house, unaware of the mishap.

The flipper hired Mark Lancor, P.E., owner of DYMAR in Southbury, to design a replacement. Lancor hired Mark Green, owner of Green Construction Management in Waterbury, to dig the test holes and install the system before the home sale closing date.

“The house sits in a depression at the back of the lot, and everything drains down a 2-1 slope to it,” Green says. “I dug two 3-foot-deep pits 30 feet apart and on either side of a mature white oak on top of the hill, and a third near the road. It was mid-September and we were in a drought. The soils looked good.”

Like the topography, everything went downhill from there. Hidden obstructions required multiple revisions to the design incorporating a Mantis leaching system with low-pressure dosing. During the last week of October, two massive rainstorms saturated the county. “I was so frustrated,” Green says. “I was taking one step forward and sliding back two.”

Site conditions

Soils are loam and sandy loam with a percolation rate of 1 inch per 12 minutes. The 1.41-acre lot rises from 27 to 45 degrees where the hill meets the road.

System components

Lancor designed the system to handle 1,000 gpd. Major components are:

Existing 1,250-gallon dual-compartment concrete septic tank

1,000-gallon dose tank (United Concrete Products) with 1/2 hp EH522DS effluent pump from Barnes Pumps (Crane Pumps & Systems)

DB-6 concrete distribution box (United Concrete Products) with speed levelers (TUF-TITE)

17 Mantis 536-8 treatment modules (Eljen).

System operation

Wastewater flows through the house lateral to the septic tank, then to the dose tank. The on-demand pump cycle sends 173 gallons at 40 gpm 55 feet through the 1.5-inch PVC force main to the distribution box feeding a 4-foot-wide trench on either side. The 45-foot-long trench No. 1 has nine 60- by 36- by 18-inch-high treatment modules; the 40-foot-long trench No. 2 has eight units.

In the distribution box, 4-inch pipes connect to the factory-installed pipe near the top of the 15-gallon capacity modules. Holes in the pipe are at 5, 7, and 12 o’clock. Each unit has eight vertical Bio-Matt filters 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 used a rented 55 XA self-propelled lift (Haulotte North America) to cut down the oak and smaller trees in the drainfield area. While clearing the stumps, he hit ledge. “The oak had been growing right out of the middle of it,” Green says. “The rock was too dense for the jackhammer on my rubber-tracked Volvo MCT125C skid-steer loader to break.”

Lancor moved the drainfield’s location 5 feet to the east, but Green hit ledge while digging the test holes. “The Pomperaug District Department of Health and the homeowner were very understanding of our difficulties,” Green says. “The homeowner especially, since we cut down his trees when we didn’t have to, and it cost him $3,000.”

On the third try, Green and Lancor found suitable soils and no ledge, but town officials wanted further confirmation. Green returned and dug four more holes without hitting ledge. The closing date was eight days away.

The health department quickly approved the new design, and Green raced to scarify the drainfield area as H.L. Bennett Jr. Septic Systems pumped the septic tank and liquid draining back from the absorption bed. Green’s father, Wayne Green, directed the sand and fill trucks from Independent Crushing, handled the tickets, and shot elevations. “The site was too small for more than two people to work, so it was just Dad and I,” Green says.

Meanwhile, Lancor inspected and pressure-tested the septic tank. “The tank was sound, but the outlet had holes, the lid wasn’t sealed, and there were no risers,” he says. “Inflow had to be significant.”

Using the skid-steer, Green shuttled 200 tons of septic sand and 350 tons of clean fill to the site, then he dug the trenches with a Volvo EC35C rubber-tracked mini-excavator. Installing the treatment modules was straightforward but left a gully between trench No. 1 and the oak tree’s former location, both on the same elevation. Green filled the depression and graded the soil into the hill.

Trench No. 2 sloped toward the house. “I explained to the owner that nothing we built on a 27-degree angle would hold,” Green says. The owner gave permission to order more clean fill, and Green tapered it into the slope, achieving a 3-1 ratio.

When it rains, it pours

The following Tuesday, 4 to 6 inches of rain fell. “It settled the sand and nothing washed out, so we were good with that,” Green says. “When the property dried sufficiently to support the excavator, I dug the hole for the pump tank and a 50-foot-long trench to the house for the 1-inch Schedule 40 electrical conduit.” All structures were bedded on 6 inches of 3/4 inch crushed stone.

Per Lancor’s specifications and to prevent inflow, the tank arrived with 15 mils of Epoxy Waterproofer (Chargar) on the inside and 15 mils of 220AF Cold-Process Fibered Asphalt Roof Coating (Karnak) on the outside. Green hooked up the tank’s electrical connections and the inlet and outlet pipes before laying the conduit.

“The electrical inspector wanted to see the line, so we went home Friday night without backfilling the excavations,” Green says. “That made me nervous because another storm was in the forecast.”

Over the weekend, 6 inches of rain fell, flooding the excavations and submerging the front yard; however, the drainfield faired well. Green spent half a day dewatering the tank hole and trench using a 2-inch 1 hp Multiquip pump. “I was discharging to a swale with a slow percolation rate,” he says. “In addition, clear stormwater kept draining back from the old absorption bed.”

Meanwhile, Jeff Carlascio, owner of Carlascio Electric, arrived to hook up the alarm disconnect switch at the house and found the electrical box full. After purchasing a second panel, he spent half a day rewiring the boxes.

After the onsite and electrical inspections, Green installed a PL-122 Polylok effluent filter in the septic tank, then used concrete blocks and mortar to lay up square risers to grade. He topped them with cast iron manhole frames and lids.

Green ordered more fill and topsoil to landscape the front yard, but as soon as a truck left the driveway, the tires spun out on the remaining waterlogged grass. One tri-axle sank in the mud.

“The driver dumped his load where he was and called an empty truck to pull him out,” Green says. “I shuttled tons of material with the skid-steer. The extra work made us miss the closing date and stretched the actual installation to 10 days instead of three to four.”

Before the Greens departed, Randy Olmstead of All Green Hydroseed sprayed a custom grass seed mix over the topsoil to reduce erosion.


Green recommended the septic tank be pumped every two to three years. 


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.