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A mound system is a rock bed elevated on a mound of sand. The mound must be carefully constructed to provide adequate sewage treatment. Mound systems everage $10,000 each, considered one of the more expensive septic systems.
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A trench system is the most common type of septic system. It's a drain field or a trench, constructed by digging an 18- to 36-inch wide trench in the ground. The bottom of the trench must be level, as must the top of the rock in the trench.
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With a peat filter system, wastewater flows from the home into a septic tank where large solids settle out and the liquid flows into a pump tank. An effluent screen or filter is often installed to restrict smaller solids and grease from flowing out of the septic tank. The liquid effluent is then pumped to where it is filtered through two or more feet of peat.
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A sand filter uses sand rather than peat as a filter. The sand is in a container that filters the wastewater from the septic tank, where solids have been deposited. Sand filters can use a single-pass method, where wastewater goes through the system only once, or a recirculating method that passes the water through the filter as many as 10 times before it's released into the soil.
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The textile filter is a newer form of on-site sewage treatment. Textile filters consist of a box filled with random sized and shaped chunks of plastic or fibrous material. The "chunks" allow space for treating heavy flow of wastewater and little "homes" for bacteria and particles to be deposited as the water passes through. They generally do not require much space with some as small as 10 square feet and can handle large amounts of wastewater each day.
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Constructed (or engineered) wetlands wastewater treatment is becoming a popular option for home and cabin owners in the basin. Wetlands offer an excellent method of cleansing wastewater through natural processes and can provide a natural landscaping element. The wetlands receive wastewater after solids have been settled out in a septic tank. Additional filtration occurs through the gravel and roots of aquatic plants placed in the wetland bed.
By Jason Rice
They’re not exactly the stuff of polite dinner conversation, but septic systems are a prime topic for Lake Superior region homeowners.
Septics, or on-site wastewater treatment, are common lakewide, especially in rural areas, which means that homeowners and home buyers must tend to their wastewater rather than tapping a municipal sewer system. Rural areas around the lake average from 50 percent to almost 100 percent use of septic systems as is the case in Douglas County, Wisconsin. Some shore areas in Minnesota are at 80 percent and growing, reports the Natural Resources Research Institute at the University of Minnesota-Duluth. The NRRI has worked with system innovations.
A study by the Western Lake Superior Sanitary District (WLSSD) estimates that more than 50 percent of the district’s septic systems are failing.
That’s a lot of people with a mess in their back yards, made more alarming if those yards include shoreline. Indeed, so many septic systems were failing along a stretch of Minnesota’s Highway 61, which follows Lake Superior from Duluth to Two Harbors, that the whole area is being converted to city sewer, obligating homeowners to foot the huge cost.
Jeff Crosby, a sanitarian with the St. Louis County Department of Environmental Health, advises not to be panicked by system “failure” statistics if you own a home with a septic or are looking to buy one. It’s not as murky a situation as all that, says Crosby, who questions the word “failure” in those reports.
“Real septic failure that constitutes a public health issue is only about 3 percent,” he says.
Crosby says some functional, working septics have been labeled as “failing” because they do not comply with new codes, not because they constitute environmental or public health problems.
Septics that truly fail do so for a variety of reasons. Some are just old. Septics generally work for 20 to 50 years. Others are poorly maintained or shoddily installed. And lastly, our northern terrain can cause problems.
The prevalence of shallow bedrock, a shallow water table and high-clay soils all are familiar landscapes for Lake Superior’s northern and western shores and all spell trouble for traditional septic systems, says Rich Axler, a senior research associate with the NRRI.
You need soil and lots of it for traditional septic systems like trenches and mounds, and you’re in trouble if your property doesn’t have it.
Axler’s former NRRI colleague, Barbara McCarthy, now an expert on wastewater treatment for Minnesota Pollution Control Agency, notes the problem of seasonally saturated soil. “Septics need air. If they don’t have it, they don’t work properly.”
Not just northern shorelines are troublesome. In Wisconsin’s Douglas County, high-clay soils necessitate holding tanks. In Michigan, sandstone presents the same problem as northern rock – not enough soil, says Fred Benzie of the Marquette County Environmental Health Department. “The shoreline can be environmentally challenging for people who need to put in septic systems.”
Code-compliant septic systems concern homeowners and buyers. Minnesota’s St. Louis County now requires septic systems to be brought into compliance before they are sold.
What many of those homeowners don’t know is that alternatives exist to traditional trench and mound systems, ones that provide creative solutions to terrain problems.
Gene and Barb Curnow credit a new system with saving their lake. In the early 1990s, Curnows bought a cabin in Minnesota on Grand Lake – a slice of North Country heaven. They decided to turn the cabin into a home.
That’s when they discovered what other lake homeowners have learned: failing, aging septic systems were slowly tainting their lake.
“When you bought or remodeled a house out here, you were ‘grandfathered in,’ meaning, you just used what kind of septic was there,” Gene Curnow says. “But the septic systems were old and leaky and the wastewater wasn’t getting cleaned. It all ended up in the lake.”
Fish populated the waters, but the septic situation still endangered the water quality of Grand Lake.
Many area homes were experiencing true septic failure, a serious environmental and public health threat that needed fixing – fast.
The problem was the terrain. The native soils are saturated with water much of the year … a recipe for disaster for septic systems. One family’s brand new mound system literally sank into soggy ground.
“Today we probably wouldn’t allow a development on land like that,” says Barb McCarthy, who worked on the solution for this area. “The houses and cabins on the Triple Lakes Road (where the Curnows live) is really a wetland. Basically, a swamp. It’s very difficult to build on and it’s hard to put utilities and roads in. In today’s land use practices we wouldn’t see this as a buildable place.”
Yet families already had homes and property on that “unbuildable” place. They needed a creative alternative to their septic problem.
The NRRI found it in the form of a “constructed wetland” system.
Constructed wetlands are marshy areas that receive the effluent (wastewater with solids removed) from septic systems and cleanse much of the water’s impurities through natural filtering by aquatic plants and a rocky gravel bottom. Cattails and bulrushes, common to our area, are two of the green players in the process.
The wetland ponds in this system look like any other swampy area, and on a large scale these engineered swamps can handle the wastewater of a whole cluster of homes.
Barb McCarthy was a wastewater researcher with NRRI when Grand Lake became her first experience in planning a constructed wetland.
“After meeting with the Grand Lake residents, it became a good option, maybe the only option for some of them,” says McCarthy.
Public health was the push for the Grand Lake system; NRRI tracked the wetlands system’s performance. Researchers liked what they saw, says McCarthy. “What we found was that the wastewater that once was leaching out into the lake and polluting it was now getting scrubbed quite clean before it would reach the lake again.”
Today 10 homes are connected to the system, which still operates nearly a decade after construction.
“At first, there were just a few homeowners enthusiastic about this idea,” Gene Curnow says, “but now pretty much everyone supports it. In the long-run, it has probably saved our lake. If things stayed the way they were, kids couldn’t go swimming out here and it just wouldn’t have been usable. Why live on a lake if you can’t use the lake?”
Exploring the Alternatives
Mound Systems
- A mound system is a rock bed elevated on a mound of clean sand. The mound must be carefully constructed to provide adequate sewage treatment. Mound systems average $10,000 each, considered one of the more expensive septic systems. A mound system should be considered if you have soils with a hardpan layer that restricts downward movement of water or have bedrock, both of which present problems for adequate treatment or dispersal of septic tank effluent.
Trench Systems
- The most common type of septic system is a drain field or a trench, constructed by digging an 18- to 36-inch-wide trench in the ground. The bottom of the trench must be level, as must the top of the rock in the trench. A vertical inspection pipe must be installed in each drain field rock layer of every trench to check for “ponding” – a pooling of water that signifies possible problems. Before this system can be used, the peak water table must be determined to know how deep to dig the trench, or whether a different system is necessary. This system requires soil that allows good drainage, but that doesn’t drain too quickly or too slowly. This system usually costs less than a mound system.
Peat Filter
- With a peat filter system, wastewater flows from the home into a septic tank where the large solids settle out and the liquid flows into a pump tank. An effluent screen or filter is often installed to restrict smaller solids and grease from flowing out of the septic tank. The liquid effluent is then pumped to where it is filtered through two or more feet of peat. After this filter, the water is delivered to the soil for final treatment. Peat filter systems are becoming more common in the Lake Superior region. They generally cost less than a mound system, but more than a simple trench system.
Sand Filter
- This system uses sand rather than peat as a filter. The sand is in a container that filters the wastewater from the septic tank, where solids have been deposited. Sand filters can use a single-pass method, where wastewater goes through the system only once, or a recirculating method that passes the water through the filter as many as 10 times before it’s released into the soil. The right type of sand may not be readily available in some locations.
Textile filter
- A newer form of on-site sewage treatment is the textile filter to treat the wastewater after solids have been removed. Textile filters consist of a box filled with random sized and shaped chunks of plastic or fibrous material. The “chunks” allow space for treating heavy flow of wastewater and little “homes” for bacteria and particles to be deposited as the water passes through. They generally do not require much space with some as small as 10 square feet and can handle large amounts of wastewater each day. Many times they are recirculating with the effluent passing through the filter several times before going into the soil for the final treatment phase. This system requires that the textile material occasionally be removed and replaced. Over time the material may fill with solids, grease and oil. Proper maintenance of the septic tank will facilitate longer life for the filter material.
Constructed Wetlands
- Constructed (or engineered) wetlands wastewater treatment is becoming a popular option for home and cabin owners in the basin. Wetlands offer an excellent method of cleansing wastewater through natural processes and can provide a natural landscaping element. The wetlands receive wastewater after solids have been settled out in a septic tank. Additional filtration occurs through the gravel and roots of aquatic plants placed in the wetland bed. The cleaning process is helped by air at the surface of the wetlands and by “leaking” of oxygen from the roots of cattails, bulrushes, reeds and other aquatic plants. Constructed wetlands require a significant amount of space, so many yards would not support such a system.