Installer Uses Technology To Place A Septic System On A Small Waterfront Lot On The Puget Sound

Membrane bioreactor technology allows a nonconforming repair on a tiny waterfront lot in an environmentally sensitive area of Washington State.
Installer Uses Technology To Place A Septic System On A Small Waterfront Lot On The Puget Sound
Andrew Gunia directs Keith Pelzel as he lowers the 1,000-gallon Infiltrator Systems Inc. plastic septic tank. Tom Armijo helps guide it, while Jerry Arthur observes.

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Fecal coliform from a failed septic system on Purdy Spit, Wash., threatened a potable well and a commercial oyster farm a mile away in Puget Sound.

George Waun, environmental health specialist II at the Tacoma-Pierce County Health Department, knew no ordinary solution would meet code based on designs he had approved for neighboring systems. He worked with Andrew Gunia, owner of A Advanced Septic Services, a company in Puyallup, Wash.

Gunia had recently installed the first BioBarrier membrane bioreactor from Bio-Microbics in the state. “We were confident the technology would protect the sensitive waters,” he says. The unit is NSF/ANSI certified to Standard 40 Class 1, Standard 245 (nitrogen reduction) and Standard 350 Class R (water reuse).

Keith Pelzel, of Westside Septic Design in Tacoma, Wash., designed the nonconforming repair and helped install it. Despite requiring waivers, customized septic tanks and a barge to reach the site, Gunia’s crew completed the system in three days.

Site conditions

Soils are beach sand with a loading rate of 0.6 gpd per square foot and 20- to 24-inch high water table. The one-bedroom home on a 120- by 50-foot-wide lot is accessible from the beach only at low tide.

System components

Major components of the 240 gpd system are:

  • 1,000-gallon IM-1060 single-compartment plastic septic tank (tanks made by Infiltrator Systems)
  • 1,000-gallon, dual-compartment IM-1060 treatment tank with Sanitee-418 4-inch effluent filter and BioBarrier 0.5 membrane filter (Bio-Microbics)
  • 540-gallon IM dose tank with Hydromatic 4/10 hp pump and 3G ultraviolet disinfection chamber (Salcor Inc.)
  • 27 ARC36 LP 8-inch leaching chambers (Advanced Drainage Systems)
  • 135 feet of 1.25-inch Schedule 40 PVC laterals
  • Control panel (Bio-Microbics)

System operation

Wastewater drains through a 4-inch PVC Schedule 40 line to the septic tank, then to the settling zone of the treatment tank. Effluent passing through the angled slots in the effluent filter enters the bioreactor’s anoxic zone. The pump runs 30 minutes on, 30 minutes off to keep solids in suspension.

The flat-sheet membrane bioreactor module in the aerobic zone attaches to an aeration grid with a 10 to 40 cfm blower. The vigorous upward flow of air between the double membrane plates scours them and provides high surface treatment while acting as a physical barrier for most wastewater contaminants.

On demand, a 5 gpm discharge pump draws 20 gallons per dose through the membrane pores to the space between the plates, then pumps permeate through a 4-inch line to the disinfection unit inside the dose tank. Retention time in the treatment tank is 12 hours. The system requires no backwash.

An anti-siphon valve and check valve in the dose tank prevent backflow from the 2-inch Schedule 40 PVC supply line. Every two hours, the pump sends 20 gallons to a manifold that splits the flow to three 45-foot-long rows of low-pressure leaching chambers on 4.5-foot centers. The chambers have 1.25-inch laterals with 3/16-inch orifices drilled 3 feet apart, spraying up.


A bridge connects the spit to the mainland, but the only parking space at the site was a small public area on the opposite side of a busy highway. “Traffic rounds a curve at more than 50 mph,” says Gunia. “If we survived the crossing, a 3-foot-wide stairway dropped almost vertically for 35 feet to the back lawn. The house was 30 feet away on a terraced plateau.”

Unable to pump the original septic tank from the parking area, the operator drove the truck off the highway, parked it on a boat ramp 900 feet away, and dragged the hose across the beach and over the 10-foot-high seawall. Meanwhile, Gunia’s crew loaded the 10,000-pound Kubota KX121-3 Super Series compact excavator and other equipment on a steel barge rated for 30,000 pounds.

“The only way we moved everything in one trip was by Infiltrator shipping the tanks as half shells,” says Gunia. Normally, supply houses assemble the 160-pound injection-molded halves to retain their waterproof warranty. Gunia’s supplier, H.D. Fowler, instructed workers on how to position the reinforced watertight mid-seam rubber gasket, then fasten the halves with plastic alignment dowels and locking seam clips.

When the low-riding barge reached shore, Ian Midgette guided Tom Armijo as he drove the excavator down wooden ramps and onto the beach. Armijo transported every component from the barge and lifted it over the seawall and into the front yard. Then he ran the excavator up the repositioned ramps and cleared the wall.

Removing the old tank

The homemade septic tank, located between the side of the house and neighbor’s wood panel fence, had a concrete floor and lid and cinder block walls. The 15-foot-wide work area gave Pelzel just enough room to smash the concrete with the excavator bucket and break the chunks into manageable pieces. Stockpiling them and the excavated sand required him to swing the bucket over the fence to reach the space behind him.

The size of the original tank almost matched the size of the new tank taking its place. As Pelzel excavated, 18 to 20 inches of groundwater poured in from the saturated hillside. Even four electric 1/3 hp sump pumps discharging to a soil test pit couldn’t keep up with the flow. “We recalled the vacuum truck to assist in lowering the water enough to install the tanks,” says Gunia. The truck ran for 10 hours over two days.

Meeting the 5-foot setbacks from the house and property line left 5 feet for the tanks. “Code specifies a 1,500-gallon septic tank, which was too wide,” says Gunia. “George allowed us to install a 1,000-gallon tank, which just fit.” They removed the baffle in the tank to allow more nutrients to reach the treatment tank.

With no room on either side to bring in components, Gunia asked permission to backfill as they set the tanks in series. Waun agreed, provided Pelzel was present throughout the installation. He was.

Gunia was concerned the high groundwater would blast the buoyant plastic tanks out of the ground if they didn’t anchor them, especially when pumping the septic tank. The crew strapped galvanized chain over the anchoring locations on the tanks, then laid excess chain in the bottom of the holes.

“We put stockpiled pieces of concrete along the base of the tanks, hauled in three pallets of Ready-Mix and poured 1,000 pounds of concrete on top of the rubble and chains,” says Gunia. The slabs were 2 feet deep.

Beginning treatment

Before setting the treatment tank, workers drilled holes for the piping and removed plastic shavings and anything that could damage the sensitive membranes. After setting the tank, they lowered the module and secured it with mounting brackets.

“At startup, I added 5 gallons of dewatered sludge to the anoxic zone, filled the tank with water and turned on the system,” says Gunia. “In 15 minutes, clear, odorless treated water came out.”

The length of the mandated 1,000-gallon dose tank would encroach into the drainfield, so Waun waived the capacity rule. “Although permeate from the bioreactor usually doesn’t require disinfection, having the UV chamber made everyone feel more comfortable about the nonconforming system,” says Gunia.

Armijo dug 12-inch-deep trenches as workers laid laterals and covered them with 8-inch-high chambers. “We balanced the site and didn’t have to haul off a single shovelful of spoil,” says Gunia. “It all became backfill.”


A Advanced Septic Services maintains the system. Quarterly visits include drawing permeate samples from after the bioreactor and disinfection chamber to analyze differences in BOD, TSS, FOG and fecal coliform. “Sampling was part of our agreement with Bio-Microbics,” says Gunia. “Once the state approves a technology, our county doesn’t require sampling.”

The control panel sends an alert when scaling reduces the membranes’ efficiency. “We won’t clean the module on site because it soaks in a citrus acid solution for some time,” says Gunia. “We’ll exchange it with an extra module. The critical factor is wet membranes are ruined if they dry out.”

More Information

Advanced Drainage Systems, Inc. - 800/821-6710 -

Bio-Microbics, Inc. - 800/753-3278 -

Infiltrator Systems, Inc. - 800/221-4436 -

Kubota Tractor Corporation - 310/370-3370 -

Pentair Water - Hydromatic - 888/416-9513 -

Salcor, Inc. - 760/731-0745


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