ALTERNATIVE SEPTIC SYSTEMS

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Mound Systems
Other Alternative Systems            View all SEPTIC SYSTEM articles

If the lot does not pass the perc test, some municipalities may allow you to build an alternative engineered system. Where the problem is soil that is too dense (or in some cases, too permeable), too shallow (over bedrock or hardpan), or the water table is too high, a “mound” system is often the first choice as it is works much the same as a standard system, only with the leach field raised above the natural grade. Alternative systems may also be required in waterfront properties to help protect water sources.

Alternative systems cost more because they have more moving parts and electrical components (pumps, monitors, alarms) and greater complexity. They require greater monitoring and maintenance to prevent problems. They also require expert design and installation. If either the designer or the installer is unfamiliar with the technology being used, it may not perform as intended. There is no one-size-fits-all solution. Design of a system is specific to the soil type, site conditions, and usage levels. Make sure your designer and installer both have proven track records with the specific system you are using.

Some states and municipalities only accept system types certified in their jurisdiction and may require that the owner maintain a maintenance contract with an approved vendor. Proper maintenance is critical for success with alternative systems.

MOUND SYSTEMS

Alternative septic system

Mound systems typically cost two to three times as much as a conventional septic systems, and require extra monitoring and maintenance. Click to enlarge. Source: Ohio State University Extension

The mound uses a series of small distribution pipes set in a layer of gravel on top of layer of sand, typically one to two feet deep. The tops and sides are covered with topsoil (see illustration). A mound system has one extra component, a dosing chamber (also called a pump chamber), which collects wastewater coming out of the septic tank. Using a pump and a float system, the dosing chamber pumps effluent at a controlled rate for uniform distribution into the leach field. Most have an alarm system that alerts the owner, or maintenance company, if the pump fails or the water raises too high in the tank. Observation tubes are also recommended which allow easy inspection of the tank without digging up the access port. Also monitoring wells are often installed to monitor the conditions in and around the leach field.

Alternative septic mound system used for failed perc test

The telltale shape of a mound system is a familiar sight in areas with heavy clay soil.

The biggest costs are the additional equipment as well as the earthwork and extra materials needed to build the mound. Depending on the system design and the local cost of sand and gravel, a mound system can add $10,000 or more to the price of a conventional system – often costing over $20,000 in some areas. Also, they require more frequent pumping and more monitoring and maintenance because of the added complexity. Annual maintenance costs can be as high as $500.

 

OTHER ALTERNATIVE SEPTIC SYSTEMS

Alternative septic sytstem. Aerobic treatment systems are used on waterfront and environmentally sensitive sites.

Aerobic treatment systems are common on waterfront sites and other environmentally sensitive areas.

There are a wide range of alternative septic systems on the market and new ones arriving all the time. Some are geared more to community systems serving several homes and are usually monitored professionally by a service company. However, some are well suited to individual homes, although the cost, complexity, and maintenance of these systems need to be carefully considered. Most use electric pumps or siphons as well as filters, all of which need more monitoring and maintenance than a traditional system.

Some larger community systems use pretreatment of the effluent before it reaches the leach field, a mini version of a sewage-treatment plan. But most single-home systems rely on bringing in natural or manufactured materials that require less surface area for leaching than the poorly draining native soils would require. There are many variations and combinations of systems and components used including:

  • Pressurized dosing: This uses a holding tank and pump to force the effluent though the distribution piping more evenly and in controlled doses, improving the performance of the leach field. It can be used to rehabilitate a leach field or in combination with other systems such as a mound system, sand filter, plastic leach fields,  or drip irrigation.
  • Sand filter: This is a large sand-filled box, 2-4 ft. deep, with a watertight liner of concrete or PVC. The sand is used to pre-treat effluent before disposal to the leach field. The boxes are usually partially or fully in the ground, but can also be above-grade when required. In the most common configuration,  effluent is dosed onto the top of the filter and collected at the bottom where it is pumped to the drain field. Some sand filters recirculate the effluent back to the tank several times before distributing it to the drain field. While most systems include a pump and controls, gravity distribution is possible in some cases.
  • Plastic chamber leach field: This is a standard septic system with an alternative leach field, which may be downsized in some jurisdictions, making it well suited to small building sites. The half-pipe plastic chambers create the void for effluent flow, so no gravel is needed. One example, the Infiltrator System, has been in use for over 20 years, and according to the company can support traffic loads with only 12 inches of compacted cover. The additional cost of the plastic components is partly offset by the savings on gravel and smaller size of the drain field.
  • Aerobic treatment system: Instead of a leach field, these systems use an aerobic process to treat the effluent in a large sand and gravel filter bed. Pumps circulate the effluent through perforated pipes in the filter bed, while blowers run constantly to inject air into the treatment tank. Aerobic systems can produce higher quality wastewater than a traditional system and may include a disinfectant component before the purified wastewater is discharged. These systems are often housed above grade in box built from pressure-treated timbers and are a growing choice for waterfront property and other environmentally sensitive areas. Technically these are not septic systems, but mini sewage-treatment plants.
  •  Drip distribution/irrigation: This uses a pump to distribute effluent through a filtering device to an array of drip tubes over a large area. The water  may used to water a lawn or non-edible plants, which remove the nitrogen from the wastewater. This type of system can be used with shallow soils, clays, and on steep slopes. Because the tubes are near the surface, freezing can be a problem in cold climates.
  •  Constructed wetlands. For the ecologically minded who want to play an active role in recycling their wastewater, these can work in almost any type of soil. The system uses a man-made shallow pond, which is lined and filled with rock, tire chippings, or other media. The media provides a habitat for special plants that treat wastewater and provide a pleasant environment. Wastewater from the septic tank is distributed by a perforated pipe across the media bed, where plant roots, bacteria, and other microorganisms break down the pollutants. A second pipe at the back of the wetland collects the treated water. The homeowners must plan to spent time planting, trimming, and weeding the wetlands area.

Related links:  National Small Flows Clearinghouse     Inspectapedia.com

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Comments

  1. Donna Zullinger says:

    Buying House After Failed Perc Test

    I was looking at a house for sale. It was built in 1994 but it says land doesn’t perc. Didn’t it perc before they built it? Now what can be done? Thanks

    • buildingadvisor says:

      There are many possible explanations for how a house got built on land that does not perc under current regulations. However, this is a very big red flag.

      Unless there is a municipal sewage system to tie into, you might need to construct an expensive alternative system if it’s allowed, or the house may be legally uninhabitable. Since there is already a house on the site, the municipal government might work with you to help find a solution, but there are no guarantees.

      If you wish to pursue this further, contact the local (city/town/county) department of health or building inspection to find out what options might exist for this property. If the perc test results are on file, you can get the name of the firm that conducted the tests and contact them as well. They may be able to suggest alternative sites on the land to test or other strategies to pursue. Each town and state has different regulations and practices, so you need to pursue this at the local level.

      If an alternative system is allowed by the local government, you can contact a couple of septic system designers in your area to get a better sense of the options and costs. Alternative systems have much higher initial costs and maintenance costs, so don’t jump into this without doing the necessary research.

  2. gayle taylor says:

    Alternative Septic System for Clay Soil

    About 50 yrs. ago I purchased 7.5 acres of land..now I want to put a house on it, but the land has clay soil and will not perc. Can you suggest a septic system that will possibly be used on this land? If possible I would like to get an estimate of what it would cost. I realize that it has to be approved by the state or the county, i think. Any help i can get will be appreciated. Thank you very much.

    • buildingadvisor says:

      We live in an area (northern Vermont) with a lot of clay soils. The most common, and least expensive, alternative system in our area is the “mound system” — essentially a raised leach field that creates an elongated mound in the yard alongside the home. The cost of a mound system varies with the size of the system (how many bedrooms), soil conditions, type of pump and controls, local costs of sand and gravel, and regional construction costs. In this part of the country, mound systems often cost $20,000 or more. Annual maintenance can be $300 to $500, including more frequent pumping.

      There are a wide range of alternative systems, but you need to find one that is acceptable to local authorities. Also, you should choose a system with a strong track record in your area and an experienced installer. I would steer clear of innovative systems that haven’t yet proven themselves in the field in your area. A failed system can be a costly and unpleasant mess.

      Local septic system designers and installers can be a good source of information about what has been used successfully in your area. Also schedule a meeting with your local department of health (or building inspection), which oversees septic permitting in most areas.

      Best of luck in finding a cost-effective solution!

  3. Aerobic Treatment System for Waterfront Site?

    I am looking at purchasing a waterfront lot in the Chesapeake Bay watershed. I am in the feasibility study period. It is mostly considered wetlands, but the Army Corps of Engineers has deemed an area as dryland suitable for construction. The land has perced for alternative septic systems. Because of the wetland resource protection area setbacks, I am further limited for space for a drainage field. As an order of magnitude ballpark estimate, how much area is needed for a 3 bed/2 bath septic field? What system would require the least amount of space?
    Secondly, I really like the idea of the aerobic treatment system if it fits. I recognize there is more cost here and yearly costs for upkeep. But please explain what happens to the effluent in these cases. I have seen online what look to be prepackaged systems that seem to show the effluent getting sprayed, I assume as irrigation. They, however, recommend not doing this near pets or vegetable gardens. This idea seems like a non-starter. The image on this website shows an above ground gravel bed in a pressure treated wooden box. Is this for effluent disposal? Is the effluent supposed to evaporate? Please explain further.

    • buildingadvisor says:

      This is a complex topic with a lot of options. Each system has to be engineered to work with local conditions and local regulations. There are a lot of companies selling manufactured components and packaged systems. But separating the hype from proven real-world performance is tricky. Also regulators are reluctant to approve new systems without an established track record in their area.

      I would only trust a licensed designer, preferably an engineer, with a lot of experience with the specific type of system you are considering. In essence, you a building a mini sewage-treatment plant which needs a lot more monitoring and maintenance than a conventional passive system.

      On the plus side, the effluent is a lot cleaner than from a conventional system and can be discharged near open water or, in some case, sprayed above ground for irrigation, as you mentioned. Direct discharge often requires disinfectant to be added before the effluent is discharged.

      The aerobic system pictured on this page (see photo) was installed recently on a waterfront home. The raised gravel bed functions as the leach field – roughly half the size of a conventional field. For a three-bedroom system (designed for up to six occupants) that would be about 200-300 sq. ft. The one pictured is about 10 ft. x 20 ft. FYI, the pressure-treated timber box in this system was not properly built and started to come apart at the corners, so reinforcement and cross pieces were added later as reinforcement. I learned this from a friend who lives next door. The neighbor has also noticed some mild odors at times, something to consider with any above-ground system.

      With any active system like this, you have pumps, blowers, valves, electrical connections, and alarms to maintain – and possibly chemicals to add. Most owners, or HOAs for a community system, contract with a company to maintain the system. One reason that municipalities shy away from this type of system is that they fail rapidly when not properly maintained. You can read a good article on the topic at this link.

  4. Alternative System Denied Approval

    I recently purchased a five-acre parcel knowing that it failed a perc test and had a high water table. I was told I could appeal, so I searched for options to overcome the obstacles, and the one I ended up proposing (based on feedback from a variety of local excavators) was to simply bring in a lot of fill dirt and sand in order to keep the drainfield 6-8 feet above the original grade (which is mainly clay). We felt confident in this proposal because it was the same process used on the neighboring property.

    We didn’t find out until the hearing, however, that the other parcel had more sand in the soil, and our county prefers/requires a certain type of soil, even if that soil is partially removed and then covered up with 6-8 feet of approved sand. I doubt I can change the minds of the county, but it is frustrating because all of the excavators I talked to said this method provides a perfectly safe drainfield, even if the soil far below is clay.

    Can you comment on this and/or direct me to resources the confirm our proposal? If we can find enough evidence that enough fill sand over clay soil offers an acceptable environment for a safe septic system, we can potentially change their mind. The next option otherwise would be an advanced system. Any recommendations on inexpensive options that would reduce/eliminate the need for a drainfield?

    • buildingadvisor says:

      Sounds like you are dealing with two issues – poorly draining clay soil and a high water table.

      We have a lot of clay soil in our area and the most common solution, and least expensive, is a mound system. Because you are raising the level of the leach field with substitute soils, this helps with both the soil problems and the water table. In most cases these systems have an additional dosing chamber and pump to control the flow of effluent to the drain field. In theory, this provides better control and treatment of the effluent. With the added fill, extra tank, pump and alarm system, these are not cheap systems, but usually cheaper than other approaches. Also, they are a proven solution where the variables and performance is well understood.

      Another option to consider is an aerobic treatment system, commonly used near surface water because of the high quality of the effluent. Like a mound, this is an above-grade system, usually housed in a bed of sand and gravel enclosed by heavy landscape timbers. The downside is even more moving parts (pumps and blowers) to keep it operating. You can read about this and other alternative systems here.

      In my experience, most towns will not go for the solution you describe whether or not it will work. If the native soils do not drain well or you have a high water table, then they want an engineered solution such as a mound system.

      As a practical matter, it seems to me that the best strategy is to bring a plan designed and stamped by a licensed septic system designer or sanitary engineer who does a lot of business in the town or county where you are building. They will know what will fly in your area and what type of evidence will persuade the local officials. These folks work together on a regular basis, know each other, and know the ropes. There are so many options and without this type of guidance you are shooting in the dark.

      Municipal governments don’t like to take risks on building plans – septic, structural, or whatever – that are outside their normal standards and comfort zone. In that case, they want a suitable professional to take responsibility (and potential liability) for the nonstandard construction.

      Since you probably don’t want to pay for a full plan at this point, ask the system designer for a feasibility study that you can take to the local dept. of health or whoever regulates on-site sewage in your area.

      A professional might also provide you with a greater level of comfort that the system will work as planned. An underperforming or failed septic system is not a pretty sight and can be very costly to make right.

      Best of luck with your local health department, who can also be a good resource for telling you what types of systems they might approve. In general, I’ve found town officials to be pretty helpful about regulatory issues if you approach them respectfully, explain what you are trying to do, and ask for their advice. They usually appreciate being consulted ahead of time.

  5. Tom McConaghie says:

    Site Perced Before, Failed Now

    About 40 years ago I bought a lot in a trailer park called Sea Village located in Brunswick County, NC with the plan of retiring there. At the time, the property perced, however; now that I’m retired, it has since failed 2 perc tests. It’s a sandy soil with a high water content. Can you recommend a system or steer me in the right direction that will satisfy the perc requirements?

    • buildingadvisor says:

      Sorry to hear about your situation. A failed perc test is never good news.

      In general, sandy soils drain well unless it is very fine sand. In fact, some course sand soils perc so fast that the effluent can pollute the aquifer if the system is not properly designed. However, if the soil on your site is saturated due to a high water table, then it will fail no matter what the soil type. Perhaps development in the surrounding area over the years has changed the drainage characteristics of your building site, making it wetter.

      There are a variety of alternative systems that may work on your site. The most common alternative is the mound system, which can be used on sites with high water tables. Check with your local health department to find out what types of alternative systems are allowed in your area. Then you would need to consult with a sanitary engineer or soil scientist to find out what options would work for your site. In some cases, you may be able to tie into a municipal or community system.

      Alternative septic systems are more expensive than conventional systems and generally have higher maintenance costs as well. Most have pumps and an alarm that sounds if the pump fails. Some of the more innovative systems have not been around long enough to have established engineering standards and a track record, so towns may be reluctant to approve them. Before making a choice, make sure you understand the costs and risks involved in an alternative system as a failed system is unpleasant to live with and a potential health hazard.

      I hope you are able to find a workable solution for your site. If you are unable to build, or it is too expensive, it may be possible to sell the lot to a neighbor who wants the land as a buffer or to enlarge their yard area. Best of luck!

      Our sister site, Inspectapedia.com has has a lot of good information on alternative septic systems.

  6. Constructed Wetlands in Cold Climate?

    Aloha,

    My wife and I currently live in Honolulu, but we are planning to buy some property in the San Bernardino Mountains (California) and build a house there. We’ve been told that the property we have our eye on has had percolation problems, but there hasn’t been a perc test in 15 years.

    If it is impossible to create a working septic system, we simply can’t buy the property and build. However, if there’s a way to build an alternative system even if the perc tests aren’t good, then we’d definitely want to buy this. (The land is flat, and the houses in the neighborhood all apparently have working septic systems.)

    Any help or advice you can provide would be helpful. I’m really interested in the idea of a constructed wetlands, but I don’t know if that would work in a place where it gets cold enough to snow several months of the year (it’s Southern California, but it’s at 6000 feet).

    Mahalo!

    • buildingadvisor says:

      Your options for an alternative septic system are determined by both technical and regulatory issues. Each local building jurisdiction (town, city, or county, and some states) has its own rules about what types of alterntive systems are allowed and under what conditions.

      Your first step should be to contact the department of health or sanitation where the lot is located to find out what is allowed on this site and under what conditions.

      If it sounds at all promising, you’ll need have a new perc test conducted as the results are typically valid for only 1-3 years. If the site has failed in the past, chances are it will fail again, but you may find a portion of the site with better soil conditions. It’s best to make any offer to purchase the land contingent on a successful perc test.

      If the site does not meet the requirements of a conventional system, the most common alternative is a “mound” system, where suitable soils are brought in and placed on top of existing soils creating a mound. These usually require a pump and monitoring/alarm system and can be double the cost of a conventional system. A big factor in the cost is the price of sand and granular fill (crushed stone or gravel) in your area.

      There are a variety of other options, including manufactured leach fields, drip irrigation, and constructed wetlands. I only have experience with mound systems, which are very common where I live as we have a lot of dense, clay soils in my area with very poor drainage.

      I know of a couple of constructed wetlands in rural areas with less restrictive building codes. These require a fairly large area and can be designed for either surface flow or subsurface flow. Surface systems have more issues with odors and may have performance problems with freezing temperatures. These systems are uncommon and must be built and maintained correctly to function properly. So finding a designer with many successful systems under his belt is essential unless you want to be a guinea pig for an experimental system.

      Read more at this link.

      Best of luck with your building plans!

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