When the Driveway is the Only Place to Put a Drainfield

Greeted with a postage stamp-size lot and a 4,000-square foot lake home, Washington state onsite professionals dig in to find a winning solution

When the Driveway is the Only Place to Put a Drainfield

 Landscaping shown at top covers the treatment tanks and camouflages the panels and blower housing for the BioMicrobics MBR. The fence at right marks the border of the yard next to the street. (Photos courtesy of A-Advanced Septic)

Originally built in 1977, the house on Lake Tapps, 36 miles south of Seattle, had started as a small dwelling that previous owners expanded to about 4,000 square feet. 

“You’re talking about a million-dollar house on the lake, and they had not given a lot of thought to the septic system,” says Keith Pelzel of Westside Septic Design, who created a solution to a new owner’s problem. The problem was effluent surfacing from a failing onsite system installed without a permit by someone working for the previous owner. 

Aside from a relatively small lot, Pelzel confronted two added challenges: a steep slope dropping about 30 feet to the lakeshore and not suitable for a drainfield, and a house, garage and driveway that took up most of the remaining space.

Pelzel used a BioMicrobics BioBarrier membrane bioreactor combined with Infiltrator chambers. He also designed an unusual solution for the drainfield. It didn’t meet state code, but after three to four months of meetings, the project received a variance.

System flow

Wastewater flows out of the house through a 4-inch Schedule 40 pipe. Technicians from A-Advanced Septic decommissioned the old pump tank and repurposed the old septic tank into a pump tank. Both are located at the top of the slope.

The old septic tank was waterproofed, and technicians added a Hydromatic SP 40 pump. From this pump tank, water moves on demand through 79 feet of 1 1/2-inch Schedule 40 pipe to the back of the lot and into a two-compartment 1,500-gallon concrete tank from Northwest Cascade. 

The first compartment is 500 gallons and settles solids. A BioMicrobics SaniTEE SNT 416 filter separates the compartments. In the second compartment is the BioMicrobics MBR. The MBR sends water to a 1,500-gallon pump tank, also from Northwest Cascade. Another Hydromatic SP40 pushes water through 9 feet of 1 1/4-inch Schedule 40 pipe to the drainfield. A manifold distributes effluent into 270 feet of 1 1/4-inch Schedule 40 pipe divided into 12 laterals and with 3/16-inch holes drilled on 3-foot centers on each lateral. Laterals are covered by Infiltrator H20 (traffic-rated) stormwater chambers. 

A BioMicrobics panel runs the MBR, and a SJE Rhombus IFS panel handles the drainfield. Dosing for the drainfield is set at six times per day at 60 gallons per dose. 

Risers and lids were UltraRib (Orenco Systems).

The one piece of heavy equipment that A-Advanced Septic used to put the system in was a Kubota 40 Series mini-excavator. 

Faux rocks in the landscaping conceal the tank lids. The artificial rocks are still heavy and hard to move, and it makes maintenance more difficult, but the owner was willing to pay the extra cost for service, says Andrew Gunia, who owns A-Advanced Septic.

Drainfield option

In such a tight space, the only place for the drainfield was under the driveway for the two-car garage. 

“In Washington state you’re not allowed to put drainfields under driving,” Pelzel says. “But I did not have anywhere else to go, and none of the neighbors had any room. I would have loved for him to have gotten an easement. We tried that.”

“So you either take a million-dollar house and say it’s unlivable, or you come up with a plan that the Health Department will sign off on,” he says.

On top of the drainfield Pelzel specified a new slab with lengths of No. 5 rebar spaced 2 feet apart. 

“I didn’t want the driveway to sink and crush any of the laterals,” he says. “You’re basically building a bridge over the top of the drainfield even though the driveway is sitting on dirt.” 

The old system was bootlegged in without a permit and by someone who may or may not have known what they were doing, Pelzel says. “I’m going to guess they didn’t know what they were doing because of the material that came out of it — corrugated ABS pipe, which is not permitted in Washington state for drainfields.” 

Staged construction

Installation of the system itself posed its own challenges. The waterline to the house had to be sleeved because it came within 10 feet of the onsite system components. 

Construction had to be carefully staged, he says, because the lot was so tight that technicians had nowhere to pile dirt. Work on each stage was coordinated with Pelzel and county inspectors so they could see each part of the system before it was covered, Gunia says.

The owner and his family never had to vacate the home, he says. They agreed to minimize their use of water during the four days of construction, and for that time the old septic tank became a holding tank. 

Another wrinkle emerged after the system was in. The owner is Asian and his family cooks traditional Asian food. He bought vinegar by the case, Gunia says. In addition, the owner used the same cleaning service for his house that he did for his business, and that company used the same commercial-strength chemicals for the house. 

All of this combined to create a caustic effluent that damaged microbes and in the MBR, causing issues, Gunia says. Education solved the problem, he says. Excess vinegar now goes into a bottle and into the trash, instead of down the drain, and the owner hired a different cleaning company. Since then, the system has functioned normally and needed only standard maintenance.

People problem

The other quirk of the project involved the bootleg system. As the project became more complicated, such as reworking the driveway to accommodate the drainfield, costs increased. What started as a $65,000 project was looking like a $95,000 project as it went on, Gunia says. (Final cost was just over $100,000.) That was a lot for the owner to swallow and Gunia, as a disinterested person, volunteered to call the previous owner and see whether he could work out some payment toward the new system.

Gunia says he started the conversation by telling the previous owner that he had apparently been misled by people in the industry. But, Gunia added, the bootleg repair showed that the previous owner knew there was a problem, and a neighbor confirmed the bootleg system was installed just before the sale.

“I said, ‘Look, I’ve been here before as a professional witness, and I can tell you how this plays out,’” Gunia says. Everyone hires lawyers, the case goes to arbitration, and the arbitrator works to have everyone meet in the middle. The best outcome, Gunia told the previous owner, is that he would pay half the cost of the new system plus $30,000 or $40,000 in fees for his attorney. Worst case, Gunia told him, is that he would be ordered to pay the full cost of the new system, plus the new owner’s attorney fees, plus his own attorney fees.

“I said, ‘So why don’t we cut to the chase, leave the attorneys out of it, and you agree to pay for half now,’” Gunia says. “The next day he calls back, and he says, ‘You know, I think we’ll take you up on that opportunity.’” 


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