An Idaho waterfront community preserves resources with a large soil-absorption system.
By Darin Burt
The Crossing at Willow Bay was designed with a single goal in mind: to provide a luxury waterfront community tailored to a limited number of residents—those who want to live life to the fullest on one of the West’s most spectacular expanses of water, sky, and land.
This waterside community near Sandpoint, ID, is a special place where forest, meadow, and water come together in unspoiled harmony. The private, luxury community provides waterfront access to Lake Pend Oreille, Idaho’s largest lake and a natural habitat for a variety of game fish, as well as the bald eagle, osprey, geese, duck, and heron.
When Chief Executive Officer Jerald Hansen and business partner Jim Sullivan acquired the property, which included 180 acres and some 2,000 feet of waterfront, one of their main objectives was to provide a diversity of site options for potential homeowners.
In theory, they could have had 25 five-acre tracks or a bunch of small lots. With the help of site planner Steve Calhoon of W&H Pacific, a land-planning and site-engineering consulting firm located in Bothell, WA, they took all of the larger lots that were 2-acre and 3-acre parcels and put them on the periphery.
“The majority of the site is flat,” Hansen says, “but, when you get down on the edge, there is a break in the topography where it’s not real steep, but it’s enough that, on the rim, it created 16 view lots of varying sizes.”
“We know that we had a lot of waterfront, and it’s very hard to come by. Our water resources are the main feature for people here, as well as people outside the area,” Hansen adds. “We wanted a waterfront community, even though we only had nine waterfront lots. What we did was start carving out about 900 feet of community waterfront where the owner’s beach club is located, as is the marina and a beautiful cedar cove with a centuries-old freshwater spring coming out of the ground.”
Recognizing that one aspect of having a viable project was a good water supply, the crew installed two community wells. With that, came the need to protect the valuable water source.
“The entire site, except for that which is in close proximity to the river, is composed of sand and gravels. The whole thing perks quite well, and we made a decision—based on engineering and experience—that anything over one acre in size would have its own drainfield. You can get away with that in a rural setting if you have a public water source and good soils.”
A challenge was soon faced when it became clear that some of the high-dollar sites, especially those in close proximity to the waterfront, did not have suitable soils for drainfield disposal. The view lots on the rim had sustainable soil for individual drainfields, but developers did not want to take a risk of potentially contaminating the lots below.
“We were concerned with the clays on the waterfront; the soils weren’t the best for perking, and we felt that they could be problematic. We also have a beach club where there will be activities, and we didn’t want any issues with the water quality there. The waterfront cabin lots were a quarter-acre in size, and there wasn’t enough space between the structure and the drainfield, so that was a given,” Hansen points out.
“We’re touting this as a waterfront community, and the water quality was hugely important to us. We felt that we need to ensure that we could continue to protect it. We always figured on the side of caution.”
The first option considered was installing individual offsite drainfields for each of the troublesome lots. That quickly became impractical, because of the distance (approximately a half mile) to where there was suitable soil.
“It became cost prohibitive to put multiple small-diameter lines in the trench. The longer the pipe with small diameter, you wind up with high head loss when you try to pump over a long distance. The waterfront lots were also at the low point of the project, which means that not only would we be pumping long distances, but also uphill,” notes Ray Kimball, vice president of project development with Inland Northwest Consultants, of Post Falls, ID. Kimball was the design engineer for water, sewer, and roads on The Crossings development.
Daily loading was based on 300 gallons per day per home, and 1,320 gallons per day for the marina facility. Total daily loading was 9,720 gallons per day with A-2B soil groups. This placed the system in the large soil absorption system (LSAS) category.
Cluster systems have proved to be an invaluable method to provide communities with high quality, cost-effective wastewater management, while protecting the character of the community. The constraint of the LSAS regulations require that two complete drainfields be constructed, each sized to be able to handle the total daily loading. In addition, area for a third drainfield must be kept in reserve.
Site planner Steve Calhoon, of W&H Pacific, was very creative with his layout, and, fortunately, there were several large tracts of open space approximately three-quarters of a mile away, with excellent soils and mild slopes, where an LSAS could be safely constructed.
Although there was room available, the desire to maintain the open space in a natural state, as well as economic concerns, drove the design towards a gravelless chamber system. Infiltrator Quick4 chambers were the immediate choice.
State regulations allow for a 40% reduction in drainfield size with chamber systems. This reduced the drainfield size to 2.3 acres, which could be accommodated in an existing meadow. Not only did this shorten necessary trench lengths, but no outside rock was needed to fill in the trenches.
Even in frigid weather, construction progressed quickly with a single three-man crew installing between 400 and 500 feet of drainfield per day. “With the dome chambered system, all we essentially had to do was dig a 3-foot deep flat bottom trench, place the dome chambers inside, attach the poly with holes drilled in it to the inside of the chamber, run it down the shallow trench, and then backfill over the top of them,” Kimball says. “The dome chambers are completely covered, and, not only that, but they are strong enough that you can actually drive a tracked vehicle over the top of them with only about a foot of cover.”
The Infiltrator Chamber System is a direct replacement for old-fashioned stone and pipe leach fields installed in a 3-foot wide trench. Infiltrator chambers, instead, represent open bottom pipe with a louvered sidewall that allows effluent to pass laterally into the soil. The angled louvers prevent backfill intrusion into the chamber while one-quarter-inch slots allow lateral leaching.
Being completely open, the chamber bottom promotes effluent infiltration into the soil with 100% efficiency. The open-bottom area, in combination with the Micro-Leaching sidewall, provides maximum infiltrative capacity—basically it’s a contained environment where effluent can come into contact with the ground so that the soil can affect the treatment.
“If you compare it to sanitary sewers, it’s a much more economically feasible and sustainable model than the old big pipe and wastewater treatment plant,” says Dennis F. Hallahan, technical director with Infiltrator Systems Inc. “Twenty years ago, there was basically only one product that you could use in a leach field, and that was a crushed stone trench or bed. The benefit of the chamber system is that it saves time, costs, and space.”
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Photo: Infiltrator Systems, Inc |
| A John Deere backhoe excavates a trench. |
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Photo: Infiltrator Systems, Inc |
| Visual markers provide reference points. |
For example, cluster systems allow lots to be positioned for optimal market value, and not just based on where the good soils are. Cluster systems can be designed to preserve open space. Due to the open space and smaller lot sizes, cluster system developments can have a reduced amount of roadway construction, thereby resulting in lower construction costs; this cost savings is not reflected in the cost comparisons. Finally, cluster systems are much more practical to operate from a management, operation, and maintenance standpoint.
In all, 1,700 Quick4 Standard chambers were installed for The Crossings system. The system covers more than 3.5 acres, including setbacks to accommodate the soil conditions, and the requirement for area for three drain fields.
The system was designed so that each home would pump from an individual septic tank to a common force main, which led to the LSAS site. That force main discharges to a 1,000-gallon holding/dosing tank equipped with a float-activated duplex pump system. The pump system alternates between each drainfield, dosing approximately 200 gallons per cycle to 3,600 liner feet of trench. Lateral spacing is at nine feet center-to-center. Each drainfield consists of six modules, with each module comprised of six laterals. An Orenco Systems distributing valve circulates the dosing through each module to maintain even distribution throughout the system.
“A decentralized onsite wastewater system is very sustainable in the sense that you will pull water out of the ground, use it, and then replace it in the ground. You are sustaining the watershed, water table, and the whole environment around it,” Hallahan says. “Conversely, as soon as you put in a deep sewer with pump stations, you’re going to drain the groundwater, and you’re also taking the water out and putting it into a river somewhere else.”
“The one negative with decentralized is that it is land-intensive for the drainfield, but with all these new developments you must have open space anyway,” he adds. “You can be very creative with the layout of the system; it can go practically anywhere underground, even in a road right of way if you’re trying to have a beautiful entry statement to a subdivision.”
By offering greater infiltrative capacity per linear foot, Infiltrator Chamber Systems can require as little as half the space as conventional systems, depending on state and local regulations. The patented interlocks add strength, and latch the chambers together quickly, end to end, so installation takes less than half the time of a laborious stone and pipe job. Another plus is that the polypropylene material of the chamber system is not as susceptible to failure as a common pipe in the drainrock and dirt.
“You have a large void in the soil where you have good surface area for bacteria to grow and multiply, and eat up all the ‘bad nasties,’ and properly work as a wastewater treatment system,” Kimball says. “You don’t have to worry about the void getting filled in with silt, and fines migrating in because of surface water infiltration. You end up with something that, is not only easy to install and maintain, but, has a lesser rate of failure.”
Structural tests show that Quick4 Standard Chambers will withstand 16,000 pounds per axle with only 12 inches of cover, and the chambers now articulate 10% right or left at each joint, allowing septic systems to be constructed on sloped leach field sites, and avoid obstructions without additional parts or accessories.
Hallahan adds that, while the plastic will last beyond our lifetime, the system is no different than your car or your roof, in that you need to maintain it in order to realize its maximum design life (10–20 years for a single-family home is common). He further states that the only real maintenance involved is to pump the individual septic tanks every few years when the capacity of the solids starts eating into the volume of the tanks by more than one-third.
According to Kimball, one of the biggest challenges, when it comes to design of an LSAS, is the requisite Nutrient Pathogen (N-P) Study. An approved N-P evaluation must demonstrate that the proposed onsite wastewater treatment system will not degrade groundwater or surface water quality beyond existing “background levels” (i.e., the development cannot cause concentrations of nutrients or pathogens in groundwater or surface water that exceed those concentrations that exist at the site prior to the development). As a practical application of this policy, the DEQ usually considers the fate of nitrate discharged to the subsurface.
“The study is fairly lengthy and convoluted. It’s not at all something to be taken lightly,” Kimball states. “As soon as the drainfield is in, and there is waste water being injected into the ground, there could be very serious implications if there is a negative effect on the groundwater source on a well downstream or in the area.”
According to Hansen, when Bonner County approved the development, officials said it was the best-planned community they’d approved to date. Construction of the drainfield was completed in December 2006, in a little over three weeks. As part of ongoing system operation and maintenance, a visual and audible alarm was installed onsite and at the caretaker’s residence.
“The county recognizes the benefits of a controlled environment,” Hansen says. “We have private roads, water, and sewer. All of these add up to make a unique project in the fact that we’re about 15 to 20 minutes out of Sandpoint, and usually communities that can provide these types of systems and amenities are 400- to 500-unit lots.”
According to Kimball’s records, cost for the project was of about half that of a conventional pipe system. Additional long-term savings include decreased maintenance costs. With a conventional pipe system, should an individual drain field fail, that property owner would have been solely responsible for fixing it.
“In this case, there are multiple homes using one system, and the costs of any maintenance are shared by a number of homeowners and spread out over time,” Kimball points out. “Our experience has been that, when you spread out that kind of cost over multiple users, you typically end up with better maintenance of the system.”
When it comes to a choice between an LSAS system versus common drain fields, Kimball will spec out a dome chamber system every time. “It’s cheaper, easier to install and takes up less room,” he says. “It’s a good solution to a common problem.”
For Hansen and the residents of The Crossing at Willow Bay it’s what they didn’t build that makes the development special.
“It’s always been my philosophy that if you find a beautiful setting, you leave it intact, maintain its integrity, and understand how it works,” he says. “You don’t want to cut down all the trees, fight with people, have lawsuits, and take something beautiful that should be the cornerstone of the project, and erode it in the process. We created a high quality project that is also very responsible, and the sewer system is a major component of that.”
Darin Burt is based in the Pacific Northwest.
OW - March/April 2008 |
