Tight Spot. Few Answers. Onsite Pros Save a Lakefront Homeowner.

A gravity-flow mound system using Eljen sand filter modules brings effective treatment in an almost-impossible system replacement design scenario

Tight Spot. Few Answers. Onsite Pros Save a Lakefront Homeowner.

Tom Collins of Collins Excavating Grading uses a Kobelco SK115 RDZ tracked excavator with tooth bucket to chisel plow a 22-by-58-foot area for the mound. (Photos by Josh Lacko)

Finding a 5-foot-diameter hole in his lakefront lot in Eagle River, Wisconsin, confirmed the location of the homeowner’s 1960s steel septic tank.

“The tank lid had collapsed, and the dry well was in groundwater and failing,” says Rick Neis, owner of Muskyland Plumbing in Eagle River. “My greatest challenge was finding a system that physically fit the site.”

The 50-foot-wide, two-bedroom home is centered on a 260-by-80-foot-wide parcel with a potable well. The neighbors on both sides also have potable wells, each with 50-foot setbacks.

The only advantage Neis had was topography. A 13 percent slope at the front of the house drops 8 feet to a plateau to the lake. The elevation of the replacement tank alongside the home was just enough for Neis to design a gravity-flow mound system with sand filter modules from Eljen.

State code, however, specified pressurized distribution for mounds, resulting in a 30 percent larger footprint. “It wouldn’t fit on the lot,” Neis says. “The homeowner had two choices: gravity flow or a holding tank with regular pumping.”

To expedite permitting of the design, Neis worked with Dale Schlieve, P.E., owner of C.E.C., an engineering firm in nearby Rhinelander. When the permit arrived, it was the third issued in the state for a gravity-flow mound.

Site conditions

Soils are loamy sand and sandy loam with an acceptance rate of 1.0 gpd per square foot. The seasonal high water table is 24 inches below grade.

System components

Neis and Schlieve designed the system to handle 300 gpd. Major components are:

  • IM-1,060-gallon single-compartment plastic septic tank (Infiltrator Water Technologies) and FT0822-14 effluent filter (Orenco Systems)
  • Model 3B Dynamic Fluid Manifold with riser and lid (SeptiSurge)
  • 10 B43 sand filter modules (Eljen)
  • Valve box (Orenco Systems)

System operation

All lines are 4-inch SDR 35 polyvinyl chloride pipe. Wastewater flows 6 feet through the house lateral to the septic tank, then 5 feet to the tub liner in the distribution box. Rising effluent in the liner trips a center float valve, rapidly releasing liquid through the single outlet to the supply line, and resetting the float seal to begin the next fill-purge cycle.

Each 4.95-gallon dose flows 15 feet to a 4-by-41-foot-long cell in the mound. Effluent drips through left and right aligned one-half-inch holes spaced every 12 inches in the 4-inch perforated pipe above the treatment modules. Each 48- by 36- by 7-inch-high unit has an interwoven plastic corrugated core and black geotextile fabric discharging to 12 inches of ASTM C-33 washed sand over native soil.

“Compared to conventional absorption systems, the media has approximately eight times more surface area per square foot,” Neis says.


While waiting for the state and Vilas County permits, Neis covered the hole in the backyard (faces road) with two-by-fours and plywood. “The system was limping along with minimum use,” he says.

Neis also hired Tom Collins, owner of Collins Excavating Grading. “Tom has the machines to work on these narrow, tight lake lots,” Neis says. The system was built out backward.

The weather forecast called for drizzle on the day of the install, but state code prohibited installing mounds in those conditions because chisel plowing may smear the native soil. Neis received permission from Vilas County Zoning & Planning to proceed provided he cover the drainfield area with a tarp overnight.

Working in the mid-August drizzle, Neis mowed the grass on the slope, then Collins used his Kobelco SK115 RDZ tracked excavator with tooth bucket to chisel plow a 22-by-58-foot area. Neis supervised all excavation work.

Meanwhile, Mike’s Septic Pumping pumped the septic tank and dry well. Muskyland Plumbing employees Pete Kaiser and Bob Balek extracted the collapsed tank and filled the hole. They laid plywood over an interlocking walkway from the road to that location, enabling Collins’ two dump trucks to back up and stockpile 60 cubic yards of sand.

“We were 5 miles from the gravel pit, which is rare,” Neis says. “Its proximity saved the homeowner a lot of money in hauling fees.”

Using a New Holland C185 tracked skid-steer, Collins transported 3 cubic yards of sand per load 40 feet to the mound site. Building the bed out from the slope, he established the 3-foot separation between the bottom of the system and the seasonal high water table and extended the sand 6 inches beyond the ends of the first and last modules.

Setting and plumbing the modules was straightforward. The valve box with 12-inch-diameter lid was installed in the middle of the 38-foot run. “There are no valves,” Neis says. “The box is an observation port for monitoring effluent and possible ponding.” Work began at 8 a.m., and the mound was inspected, covered, and seeded by 1 p.m.

The 20-foot-long supply line fell 1/4 inch per foot from the house to the mound. “Making it happen was like cutting diamonds,” Neis says. He shot repeated elevations using a LL100N Laser Level (Spectra Precision/Trimble), while Collins did the delicate groundwork.

Kaiser set and plumbed the distribution box at the top of the slope and installed the insulation panel in the riser before screwing on the lid.

“The unit saved the homeowner the expense of a dose tank, pump, and control panel for pressure dosing, and the maintenance and electricity associated with them,” Neis says.

Collins dug the hole for the 10.5- by 5- by 4.5-foot-high septic tank in the 15-foot-wide area between the house and property line. Workers again covered the path from the excavation to the road with plywood over the interlocking walkway. Dump truck drivers reversed over it to collect spoil from the 7-foot-deep hole, thereby saving as much of the manicured lawn as possible.

“We were in 0.7 gpd sandy soil and didn’t need gravel to bed the hole,” Neis says. “It was another welcome savings for the customer.”

The installation ended as it had begun, in drizzle with the crew leveling the topsoil before seeding and mulching it. They drove away at 4 p.m.


Vilas County requires septic tanks to be inspected every three years and pumped if one-third full of solids. SeptiSurge recommends an annual inspection of the distribution box and effluent filter. 


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