A Tight Fit Between Water and Woods

An onsite system using low-pressure dosing to sand filter modules saves an Upper Peninsula Michigan recreational vehicle campground

A Tight Fit Between Water and Woods

Using a Caterpillar 299C skid-steer and RL-H4C laser (Topcon Positioning Systems), workers from Primrose Acres build up the 12-inch-deep sand mound for the 58-by-36-foot-wide drainfield B. In the background is the 58-by-24-foot-wide drainfield A.

The owners of a RV campground in Ontonagon, Michigan, faced a complex situation when the onsite system serving the showers, restrooms and camper dump station failed.

Although the owners signed a pumping contract, the Ontonagon County Health Department wouldn’t accept it until they hired an engineer to design a replacement system and a contractor to install it.

The site was too small for a standard pressure distribution mound, so the engineer suggested various alternative technologies. All were beyond the owners’ financial situation. They wanted hard facts and figures, but contractors couldn’t provide them without the design. The Health Department had to submit the design to the Michigan Department of Environmental Quality, but the agency wouldn’t approve it unless it maximized the available space.

On a recommendation, the owners contacted John Kaat, proprietor of Primrose Acres in Bruce Crossing. Kaat and associate Chris Holmes, P.E., project manager for U.P. Engineers and Architects, designed a low-pressure distribution system using geotextile sand filter modules (Eljen).

The tricky bit was limited space for the L-shaped drainfield. The horizontal leg ended against the house’s deck, a U-shaped asphalt driveway enclosed two sides of the beds, and behind them was a 13-foot drop to the Union River.

Holmes wedged the fields into the space by eliminating 10 of the 50 campsites and receiving a 50-foot variance separation to the river’s flood plain. Primrose Acres finished the install in time for the 2019 summer season.

Site conditions

Soils are fine sandy loam to clay loam with a loading rate of 0.704 gpd per square foot and the limiting layer 10 inches below grade. The property, in the foothills of the Porcupine Mountains, is bordered by Lake Superior and the river.

System components

Holmes designed the system to handle 2,450 gpd. Major components are:

  • Existing 1,500-gallon septic tank at the campground
  • Tank No. 1: 1,650-gallon combination precast septic/pump tank (Concrete Products) with LT-1/8 high-capacity effluent filter (Lifetime Filters), PE31M 1/3 hp pump (pumps from Goulds Water Technology, a Xylem brand), and PS Patrol control panel (SJE Rhombus)
  • Tank No. 2: 1,650-gallon combination precast settling/pump tank (Concrete Products) with PL-525 effluent filter (Polylok), dual PE41M 4/10 hp pumps, and EZ Series duplex control panel (SJE Rhombus)
  • V6605A distribution valve (Orenco Systems)
  • 56 B43 GSF modules (Eljen) in drainfield A
  • 84 B43 modules in drainfield B

System operation

Effluent from the campground tank flows 322 feet through a 4-inch Schedule 40 PVC main paralleling the road to tank No. 2. Wastewater from the house flows 15 feet through a 4-inch lateral to tank No. 1. Its on-demand pump sends 140 gallons 198 feet through a 2-inch force main that tees to the campground main 4 feet behind the second tank.

Every 17.5 minutes, alternating pumps in the second tank send 140 gallons 82 feet to the distribution valve dosing five zones. Drainfield A has two zones of paired laterals and drainfield B has three zones of paired laterals, all on 6 foot centers. Both fields have 58-foot-long laterals totaling 3,480 square feet.

A 4-inch pipe tops each row of 48- by 36- by 7-inch-high modules. Sleeved inside these pipes are 1.50-inch distribution laterals with 3/16-inch orifices spaced 4 feet apart, four holes up and one down in sequence. Liquid discharges to 12 inches of washed sand over native soil.

Drainfield installation

Holmes and Sam Grulke, representing First Supply, an Eljen distributor, were concerned that the campground effluent would be too concentrated for the modules. Although the three-bedroom home and office had a functioning, grandfathered gravity system, they upgraded it, using the house effluent to dilute the campground effluent. The inflow from both would create sufficient turbulence to homogenize the liquids.

Kaat had his own concerns. “In this northwest region of the Upper Peninsula, snow melts in mid- to late-April and seasonal highway weight restrictions are sometimes in effect through May,” he says. “The campground opens the end of May, leaving the first two weeks in June as the only window for the install.”

When his crew arrived on May 31, the owners had cleared mature trees where needed for site work. “We had permission to begin the project before the permit arrived on June 6, so we scarified the soil and began building the 12-inch-deep raised sand beds,” Kaat says.

In 26 loads, 536 tons of 2NS sand were transported from a quarry 90 minutes away. The distance enabled the crew to spread the material as fast as the trucks arrived, using a Caterpillar 299C skid-steer and RL-H4C laser (Topcon Positioning Systems). They also laid 4-by-8-foot ground cover mats (AlturnaMATS by Checkers Industrial Safety Products) for stabilization and floatation of equipment and materials through wet areas and to prevent damage to the asphalt parking lot.

“It’s a beautiful facility with mature trees everywhere,” Kaat says. “We wanted it looking as pristine as possible when we left.”

The owners wanted an unobstructed sightline between the office and campground, but without the absorption area resembling a plateau. Kaat worked with Holmes and Grulke to contour the zones, blending them into the topography as it sloped 2 feet or more toward the river. “We stepped the whole bed: 6 inches between the two zones in drainfield A and 12 inches between the two fields,” Kaat says. Grulke also helped install the modules.

Tank installation

The biggest challenge to setting the tanks was backing the truck between the dense trees. “It was tight quarters even for the Volvo ECR145CL zero-tail-swing excavator,” Kaat says. “There was always the danger of dinging up the bark.”

Ron Cleary, owner of Peninsula Septic Cleaning, pumped the tanks. The new house tank occupied the same location as the original concrete block septic tank. “The joints had eroded, and the tank crumbled to pieces as we exposed it,” Kaat says.

Because tank No. 2 sat in a ravine, the seasonal water table was higher than the lid. To prevent the tank from flooding, the crew ran a drain tile discharging to the flood plain around the back of the excavation.

When digging the force main trench from the house to the second tank, the excavator operator followed the contour lines at the bottom of the hill, then went up the ravine as it rose 8 feet in elevation. Backfilling the EZset risers (Infiltrator Water Technologies) to grade required 3 feet of bank sand.

The supply line from the campground septic tank passed under the driveway to a distribution box dosing the saturated existing drainfield. To maintain gravity flow, the trench from the box to tank No. 2 fell 80.5 inches in elevation over 322 feet.

“We dug backward from the second tank and parallel to the drive,” Kaat says. “When we came alongside the old drainfield, effluent ran out. It made a bit of a mess, but drained nicely.”

Covering the drainfield modules, backfilling the tanks and grading required 278 cubic yards or 22 loads of clean bank sand from a pit 30 minutes away. Kaat brought in 266 cubic yards or 17 loads of screened topsoil from his quarry 45 minutes away. He used a John Deere four-wheel drive tractor loader and bale shredder for mulching the area after seeding on June 18.


Until the Health Department hires a maintenance contractor, Primrose Acres will sample effluent, check floats and ball valves, and flush the laterals annually. Pumping is on the same schedule.

In late summer, Kaat and Eljen representatives returned to check the system and found what appeared to be plastic scum on the effluent filters. “I’ve never seen it before, but it could be polymers,” Kaat says. “Recent studies suggest that the plastic molecules used for fillers in cheap soaps and body washes will clog the Bio-Matt fabric (Eljen). If confirmed, discharge of polymers will have an adverse effect on all contractors and their clients using sand filter module systems.” 


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