In areas without municipal sewage systems, each home must treat its sewage on its own land using an “on-site sewage disposal system,” more commonly called a septic system. A typical system consists of a waste pipe from the house, a large concrete, fiberglass, or plastic septic tank, and a leach field.
The most common type of leach field consists of a series of perforated distribution pipes, each set in a gravel-filled absorption trench. Sometimes a small group of homes share a larger community septic system that performs much the same way as a single-house system.
After passing from the house, the wastewater collects in the septic tank. Septic tanks typically range from 1,000 to 2,000 gallons and are made of concrete, heavy plastic, or metal. High-quality concrete tanks are the most durable and, if not damaged, should last 40 years or more. Many modern tanks have two chambers to increase the efficiency.
Tanks are sized large enough to hold new wastewater for at least a day, giving it time for the solids to separate out and settle. In the tank, oil and grease float to the top of the tank as scum and solid waste sinks to the bottom as sludge. The partially treated wastewater, or effluent, is mostly clear (see illustration).
The solids at the bottom are subject to a host of bacteria and other microorganisms that begin breaking down the materials in an anaerobic (without oxygen) process. Over time, the sludge at the bottom and scum at the top build up thick layers. To keep the system working properly, the solids and grease must be pumped out during regular maintenance of the system.
As new wastewater enters the tank from the house, the partially treated water, or effluent, flows from the tank into the leach field, where most of the sewage treatment takes place. Each new gallon into the tank sends one gallon out to the leach field, leach pit, or similar treatment area. Too much water delivered too quickly to the tank will send untreated effluent, along with grease and solids, into the leach field, potentially clogging the field.
The leach field (also called a “drain field”) consists of rows of perforated pipes typically buried in gravel trenches 18 to 36 inches below grade — deep enough to avoid freezing, but close enough to the surface to allow air to reach the bacteria that further purify the effluent (see illustration below). Depending on soil type and local codes the distance to the surface may be as little as 6 inches.
The perforated pipes are covered with about two inches of gravel and a layer of topsoil, typically 18 to 24 inches deep. A sheet of geotextile (or hay in the old days) keeps the topsoil from clogging the gravel below. Grass is usually planted above. The grass helps remove excess moisture from the soil without sending down deep roots which can block the piping.
The effluent passes from the perforated pipes into the surrounding gravel and on to the native soil. Where the gravel meets the soil, a bacteria-rich slime mat grows and does the heavy lifting of water purification.
All elements carrying liquid must be buried deep enough to prevent freezing, as this will stop the bacterial action that the system depends on. Wastewater freezes at a much lower temperature than does pure water but freezing is still a concern in cold climates.
The remaining liquid, carrying small suspended solids, percolates though the native soil, where it receives its final treatment by bacteria and other tiny critters in the soil. These convert the remaining pathogens into important plant nutrients, while sand, gravel, and soil filter our any remaining solids.
Some of the liquid evaporates into the air, and some is absorbed by plant roots. At this point, if the system is working properly, the filtered wastewater returns to the aquifer as naturally pristine water, fit for human consumption. It’s a pretty neat trick that takes perfect advantage of nature’s highly effective process for recycling organic waste.
Where a conventional leach field will not work due to poor soil conditions or a high water table, an alternative system may be allowed. These often cost two or more times the price of a conventional system and require greater maintenance. Special systems may also be required near flood plains, bodies of water, or other environmentally sensitive areas.
For the system to work well, the leach field must be properly sized for the soil type and volume of wastewater, typically based on the number of bedrooms.
The soil, as measured by a perc test, must be porous enough to absorb the liquid, so the denser the soil, the larger the leach field required. For a three-bedroom house with normal soils, the total leach field area may vary from about 500 to 1,500 square feet.
It’s better to have excess capacity in your system than to cut it too close. Your family may grow or you may get an exceptionally wet spring with saturated soils and a higher-than-normal water table. If the ground cannot absorb the liquid, then sewage can back up into your home, pool on the surface, or pollute nearby groundwater.
Also, if there is not enough depth of good soil before reaching rock, impervious hardpan, or the water table, then the system will not work correctly. Dense clay soils will not absorb the liquid fast enough, causing backups.
But the soil can also be too porous. If the soil consists mostly of course sand and gravel, it can drain so fast that untreated sewage can pollute the aquifer or nearby bodies of water are polluted. System designers need to take all these variables into account.
Where a conventional leach field will not work due to poor soil conditions or a high water table, an alternative system may be allowed. These often cost two or more times the price of a conventional system and require greater maintenance. Special systems may also be required near flood plains, bodies of water, or other environmentally sensitive areas.
Treat your system well and you will be rewarded with years of trouble-free service. Periodic pumping of the septic tank is essential to remove the solids (sludge) and grease layer (scum) from the tank. Otherwise, solids will eventually overflow the tank and flow into the leach field, reducing its effectiveness and shortening its life. It is difficult or impossible to rehabilitate a clogged leach field, so regular pumping is critical! Forgetting to pump out the tank is the leading cause of premature failure of septic systems.
Cooking fats, grease, and solids can also wash into the leach field if the tank is too small for usage levels or is overloaded periodically. Fats, petroleum products, and solids that reach the leach field can clog the biological mat where the leach trenches meet the soil and interfere with its job of purifying the effluent.
Excessive water from heavy household usage or yard drainage can overload the system, carrying grease and solids into the leach field. To avoid problems, direct yard drainage away from the leach field. And don’t do a week’s worth of laundry for a family of five in one day. This will help keep the load manageable and prolong the life of your system. To avoid overloading the system:
Also avoid putting solids, harsh chemicals, and just about anything else down the sink or toilet other than biological wastes and white toilet paper. Avoid the use of kitchen disposals. If you must have one, use it only for minor non-meat scraps. Avoid dumping chemicals or paints down the drain as many chemicals can kill friendly bacteria or lead to water pollution nearby. Avoid putting these down the drain:
It’s best to plant grass over the leach field and not to drive or park in this area. Placing heavy loads above the leach field can compact the soil reducing the effectiveness of the drain field. Also trees and plants with invasive roots can clog drain lines. To avoid damage to the leach field:
Even with gentle use and regular maintenance, however, leach fields will not last forever. The soil will eventually become clogged from dissolved materials in the wastewater, and the soil will be unable to absorb the incoming water. An odorous wet area over the leach field, or plumbing backups in the house, are often the first signs that things are amiss.
Many areas require septic system designs to include a second “reserve drain field” under the assumption that the first field will eventually fail. A properly designed and maintained system should serve for 20 to 30 years or more. After a few tears, the first field will naturally recover and can be used again when needed.
Most septic system problems are a result of poor initial design, misuse, or physical damage, such as driving heavy vehicles over the leach field. Common conditions that can cause a septic system to perform poorly include:
• House plumbing. clogged or inadequate plumbing vents, blockage between the house and septic tank, or inadequate pitch in sewer pipe from house
• Septic tank to leach field. Blockage between the septic tank and leach field caused by a plugged or broken tank outlet, or a plugged line to the leach field cause by tree roots, or by solids that overflowed from the tank
• Leach field piping. Driving or parking heavy vehicles over the leach field can break the perforated leach pipe, especially if it is not uniformly supported by the gravel bed. Usually tree roots do not penetrate through the gravel bed into the perforated piping.
• Leach field sizing: Drain field may be too small for current flow levels out of the home. Reducing flows though use of flow restricters, and low-flow faucets and fixtures might help.
• High water table. A seasonal high water table can saturate the soil around the trenches impairing the soil’s ability to absorb wastewater. This is sometimes an issue on relatively flat building sites with poor surface drainage. This can often be fixed by installing subsurface drains or curtain drains to intercept the water flow toward the leach field area and to lower the water table locally.
I’m trying to find what the code says about reusing the existing septic tank. It’s 48.3 from and encased well. The engineer wants a new tank. The tank didn’t fail; only leach field because it was a seepage pit. I’m selling so I’d rather not put more money into it than I need to. It’s NJ. I called the health dept., but it seems they are in bed with the engineer, who also brought an excavator to deliver the plans. Seems unethical to me. I already paid $5k so I can’t do another.
I don’t know why the town is requiring that you put in a new septic tank. You need to contact the local health dept. and ask. Every state, city, and town in the US has its own septic system regulations Like all laws, they are often subject to interpretation, so it might be a judgment call that you need a new tank, and there may be some flexibility on that issue. I’m assuming the engineer did a full inspection of the existing system. If it was he that decided a new tank was needed, then the town would be unlikely to overrule his professional judgement. An engineer’s stamp on a plan relieves the town of liability if there are problems down the line. In that case, ask the engineer why a new tank is needed at this point and whether you can re-use the existing one. It may be that it is so old that it is past its normal service life, or it may have some damage.
The tank passed inspection, but the engineer is requiring noted that the tank is 48.3 ft away from the well and needs to be 50 ft. under the current law. This tank was replaced about 15 years ago. The health dept. said they would allow the tank to be reused, but they want to go by the engineer’s plans. Or for me to get another engineer. I paid the sum of 5k already and can’t afford to do more.
Engineers tend to be conservative in their recommendations. For example, they use large “safety factors” in structural work. Since they cannot confirm the exact condition and lifespan of the septic tank, it’s safer for them to simply specify a new one. I would go back to the engineer and tell him that the health department is OK with the existing septic tank. If he is not comfortable with approving the existing tank, tell him you will sign a waiver releasing him from any liability related to the septic system. This is called a “hold harmless” or “indemnification” clause with language such as this: “[your name] shall defend, indemnify and hold [the engineer] harmless from any and all claims, injuries, damages, losses or suits including attorney fees, arising out of or in connection with the performance of this Agreement.” If the engineer will still not cooperate, you can try to negotiate with the town. No one wants the liability if the system fails prematurely. A properly built and installed concrete tank that is pumped regularly will typically last 40 years or longer, but a defective tank (low quality concrete), highly acidic soil, or infrequent pumping can shorten its life.
I’ve seen designs where the leach field has a vent and some that don’t. When should you install one? Thanks,
Neal
Leach fields need ventilation to prevent the buildup of noxious gases. Some of these combine with water to form corrosive acids that can damage septic system components and lead to early failure of the system. Excessive corrosion may be visible during inspection of system components such as the D-box, septic tank, and lift station (in pumped systems). On smaller, conventional residential systems, adequate ventilation is provided by your home’s rooftop plumbing vents. Return air from outdoors enters through the soil above the drain field. For larger systems, deeply buried drain fields, deep leach pits, many alternative systems, or other systems with poor ventilation, you will see one or more white PVC “candy canes” vents sticking out of the ground. The septic system designer will specify one or more surface vents as part of the site plan, if required.
Is there a maximum range a septic/drain field/etc can be from the house? I have a large piece of land next to a river. Our “first homesite” is level, and the perc test came out just fine. The riverview, however, is just so so. At our 2nd site, with a spectacular riverview, the perc tests haven’t worked out too well. The site’s high up on some bluffs, overlooking the river. It’s a lot of rock, mostly.
My question is, the 1st site is 200-300 feet or so from the 2nd site. If it conceivable that the sewage could get pumped, or some such, away was the site with failed perc tests to the site with a qualified perc test? tia
In general there is no code limit on the length of drain lines to your septic tank or drain field. As long as you follow the rules for setbacks and clearances, you can place the drainfield anywhere on your site. As a practical matter, however, you can only go so far before the drain line gets too deep for the tank or drain field trenches. Septic system drainage lines are typically sloped at ¼ in. per ft. (or 1/8 in. in some jurisdictions). For the distance you want you will probably need a pump. With a pump, the drain lines can be any length as long as you install cleanouts every 75 feet. The cleanouts allow you to access the line for servicing if needed. There are different ways to add a pump, but the easiest is to use a packaged sewage pump station which installs after the septic tank. Many pre-packaged systems include the recommended alarm to notify you if the pump fails. Also needed is a check valve is to prevent backflow and a pre-filter to prevent solids from clogging or damaging the pump. It’s best to get a professional septic system designer to specify the equipment and to plan on regular maintenance including cleaning the filter. With regular maintenance, these systems can be very reliable, but it is more work than a conventional gravity system.
What can I place above a leach field? I am currently developing a pickleball facility and I was wondering if the leach field could serve for social areas and such as picnic tables and a place where people can set chairs and watch a game.
The general recommendation from septic system designers is to plant grass over the leach field and use it as a lawn. Lightweight, non-permanent accessories such as chairs, picnic tables and lawn ornaments are OK. Heavy-weight, permanent structures such as decks and gazebos are not recommended. In general, you do not want to use the land in a way that would damage underground components or compress the soil as this could prevent oxygen from reaching the leach pits. You also don’t want to raise the level of the soil for the same reason. Standard recommendations for the drain field area are: • Do not drive on the drain field, or use heavy equipment.
• Do not add soil, mulch, or other ground coverings, or change the grade.
• Do not direct gutters, sump pumps, culverts, or other surface drainage onto the drain field.
• Don’t plant trees, large scrubs, or anything with deep roots on or near the drain field. So I wouldn’t locate a sports court on the drain field, but you could place a few picnic tables there for occasional use. However, having crowds regularly tromping around on the drain field, compressing the soil, is probably not a good idea. All this assumes that the drain field is functioning properly. If the septic system is failing, or overloaded, the drain field area may become soggy and emit a septic odor, in which case no one will want to use the area for anything
I just had a new drain field installed several months ago. My problem is the system is on a hill where a lot of rain runoff flows. I didn’t have much of a choice as I live on a lake. The system is not very deep in the ground on one end. Water will come out of the ground near the low points or stay saturated. Is there anything I can do short of redoing the system.?
My first guess – and it is only an educated guess – is that surface water from rain runoff, and possibly subsurface water as well, is flooding your system resulting in the surfacing of wastewater at the low end of the drain field. Surfacing of wastewater in a drain field is clearly a sign that the system is not working properly and poses a potential health risk to you and to the lake. If the water smells only mildly of septic odors, that would suggest that the water coming to the surface is heavily diluted by the runoff. That’s better than straight raw sewage, but still requires attention. Assuming that the drain field was designed by an engineer or other professional, I would suggest asking them to visit the site to analyze the problem and recommend solutions. If you can confirm that the system was designed properly in terms of slope, depth, size, and other design parameter, and does not have a blockage or other mechanical flaw, then the designer will most likely look for ways to direct the runoff away from the drain field area. This is typically done using some combination of swales, ditches, and curtain drains to direct the runoff coming from you house and the hillside away from the drain filed. If needed culverts and underground piping may also be used to move the water to a safe drainage area. Unless your situation is extreme, then redirecting runoff is usually not very difficult or expensive to do – certainly less costly than building a new drain field.
Am I allowed to do any grading over the septic system drain field site? There are leaves, brush, and a few trees over the drainage field location?
You should never drive vehicles or operate heavy equipment such as a skid steer or Bobcat over the drain field. The weight can compress the soil or damage the pipe, connections, or distribution box. You also don’t want to add a significant amount of soil or change the grade as the distance from the drainage trenches to the surface is part of the septic system plan. The distance from the top of the drain pipes to the surface typically ranges from 18 to 36 inches, but may be as little as 6 in. depending on soil type and local codes. Adding more soil than the system is designed for could reduce evaporation and impair the system’s performance. In some cases, it may be OK to add a few inches or more of top soil, but I would check first with the system designer or the town’s health department, which may have a copy of the system plan on file. It’s certainly OK to add soil where you have removed a tree or other plant. System designers recommend planting grass only over the drain field, although decorative plants and small shrubs with shallow root systems are usually not a problem. Large shrubs with woody roots and most trees can clog the drain lines. Especially bad are willows, poplars, and other water-hungry species, which should be placed a safe distance from the field.
Thanks, Steve, for the reply. I should have been more clear. I haven’t put the system in yet. I am wondering if I take out some trees and then grade away the top foot to flatten area so it is clean flat and I’m back to undisturbed soil, will the county tell me I can no longer put a system in that location. I’m on a high spot so drainage or high water table is not an issue.
Thanks,
Most septic system codes require that the septic tank and drain field go on “original, undisturbed” soil unless there is some sort of approved, engineered plan that calls for modifications to the soil. In general, septic regulations also require the drain field to follow the original slope and contour of the land. So you risk running into permitting problems if you regrade or modify the soil in the area of the proposed septic system. Best to check with your septic system designer, if you have one, or your local building inspector or health department before monkeying around with the soil in the area of proposed septic system.
We are looking at some land that was already perk-tested and has an engineered septic permit in place. Does the engineered septic have to be set in a certain place or can we place it wherever we would like on the land?
In general, the drain field on a conventional or engineered septic system needs to go in the same location where the soil and perc testing were done. That’s because the soil, water table, and drainage characteristics may vary from one part of the site to another. The system is only approved for the area where the soil and groundwater level were tested. Most septic plans I’ve seen have included a site plan with a specific location for the drain field and other system components. Because of setback restrictions to property lines, wells, water lines, structures, etc. there is often little flexibility in where the septic system (and the house) can be located. In some cases, you can change the location of the septic tank or pumping station, but not the drain field or main treatment unit in an engineered system. On larger sites, you often have greater flexibility for locating the house and septic system, but will need to check with the engineer about what flexibility, if any, you have in locating the system. You should be able to put your hands on the septic permit from the health department, DEQ, or whoever issued the permit, which is a matter of public record. It may indicate any limitations on placement of the system. Also check to see if a septic system design has been drawn up and where it shows the location on the site. For further clarification, check with the health department or the engineering firm.
The ground continues to settle around the engineered system installed October 2017. Seven loads of topsoil were used but it continues to settle. Is this a normal occurrence? Should the contractor have used more initially? They have not been the easiest to work with so I’m trying to do some homework on this.
Not sure exactly what type of “engineered” system you have, but a well-designed system should not have excessive settlement. Some degree of settlement is normal in the topsoil layer. However, excessive settlement might indicate an inadequate barrier between the soil and aggregate below. In any system that uses aggregate (gravel or crushed stone) for dispersal of the effluent, the topsoil should be separated from the aggregateby a geotextile which stops the soil above from migrating into the stone, but allows air and moisture to pass through freely. Some older systems used building paper or a few inches of straw as the barrier material, but these are not widely used today. The topsoil layer is typically 18-24 inches deep, but can be a little more or less, depending on the specific design. If the barrier is inadequate, the topsoil can infiltrate the aggregate layer and reduce its effectiveness. The soil place on top should be free of vegetation, rubble, or other foreign materials that can also lead to excessive settlement. It’s best if the soil over the drain field is slightly raised above the surrounding area so heavy rainfall does not collect in the area and saturate the system. Excessive settlement could create a dip where water tends to pond. I would contact the designer of the system to find out what he has specified, and ask for a schematic of the system. Then ask the contractor whether he has followed these specifications. If you do not get satisfactory answers, then you may want to have the designer do an “as-built” inspection of the system, which is required in some jurisdictions. If the contractor did not follow the plan, then he will have to do the remedial work necessary to get the job done right. Read more about Alternative Septic Systems
In general, a leach field can be constructed on a wooded site that has been cleared, but it would have to be completely cleared and stumps removed over and around the drain field. When clearing the land, however, you don’t want the excavator to disturb or compress the soil any more than necessary to get the job done. ALso, do not regrade in the area of the drain field. Codes generally require that the leach lines be constructed over undisturbed, native soil. You will also need to clear the area around the leach field so that trees and large shrubs are a safe distance from the drain pipes. Not surprisingly, tree roots are attracted to the nutrient-rich water in the perforated drain pipes and can invade and block the pipes, causing the system to fail. The minimum recommended distance from the drain pipes to trees and large shrubs is 20 to 50 ft., with a greater distance to larger trees or tree species with aggressive root systems. Problem trees include maples (except Japanese), birch, beech, willow, ash, aspen, and poplar. Our sister site, Inspectapedia, recommends that trees are no closer to the leach field than the height of the mature tree. In some cases, you may be able to shrink the size of the leach field by using engineered gravel-less leach lines or other alternative systems. Drip irrigation can also be designed to work on heavily wooded sites. Which alternative systems are allowed in your area varies with local codes. Be aware that most alternative systems have higher initial costs and higher maintenance costs. Best of luck with your land purchase and new home!
I am looking to buy a piece of property and the county soil maps show that the parcel has both high shrink-swell soils and low shrink-swell soils. When trying to find the right place for building, how do I take into account these soil results as far as the type of septic system I will need? Thanks.
High shrink-swell soils have a high clay content, which means the soil will not absorb water well, making it unsuitable for a conventional septic system. Because of the slow absorption of water, soils with high clay content are likely to fail the perc test. This type of soil is often referred to as “expansive clay,” which is bad for any type of building. Unless the foundation is engineered for expansive clay soil, you can end up with extensive foundation damage over time. The “low shrink-swell” soils are certainly a better bet for building, but no guarantee that the site will perc. It could still have high clay content or other problems such a high water table or impermeable soil too close to the surface. That’s why every site needs a perc test to determine whether it is suitable for a septic system and to properly size the leach field. County maps are a good place to start, but the information is rarely accurate enough to site your house and septic system. You really need to visit the site and examine the soils.
My land passed the perc test. I will put in a 1000 gallon septic tank. There will be two people living in the house. How much lateral line will I need?
The size of the leach field and linear feet of trenches, depend on the number of bedrooms (not the number of people), tank size, soil characteristics, and local regulations. Better draining soils require less area. Also modern houses with low-flow fixtures have lower daily flow rates than older houses, so the leach field may be smaller. Septic system designers calculate the required length of the trenches from the total daily flow, the absorption rate of the soil, and the width of each absorption trench. Maximum trench length, distance between trenches, and added “reserve” space are also determined by local code. Codes typically limit trench length to about 60 feet. Total drainfield size for a typical 3 -bedroom system may range from a 4,500 sq. ft. for good soil to twice that size for poor draining soil. For a more technical explanation of leachfield sizing, please refer to our sister site Inspectapedia at this link.
My mother owns about ten acres of rural land in PA. She is subdividing the land and selling me three acres. Our surveyor says that the law for subdivided properties is that in order to build on the land, my mother’s septic system must be evaluated and brought up to current codes. Her septic would be about 300 yards from my septic. Why is this an issue?
The short answer is that local governments (town, city, county, state) can require septic system inspections whenever they want to, in accordance with local laws. Each jurisdiction makes its own rules and these vary a great deal from place to place. Where inspections are mandatory, they are typically required when you build, remodel, subdivide, or do other work that requires a permit – that is, when the local government has the leverage to force you to perform an inspection and upgrade the system to current code, if required. Inspections and upgrades may also be required before transferring title to a new owner. In some cases, the inspection requires partial excavation to inspect the leach field or septic tank. The cost of an inspection can range from $200-$600 or more depending on the requirements. If repair or replacement of the septic system is required, the cost can be anywhere from a few thousand dollars to $10,000 or much more if an alternative septic system is required. This can come as a big shock to homeowners planning to remodel or sell their home. It may seem unfair that you are required to inspect a septic system when you are not changing the rated use of that system, such as adding a bedroom, but this is becoming more common as local governments get more aggressive about protecting groundwater. You can contact your local health department or building department for further information about why an inspection is required, who can perform it, and what are the consequences of a failed inspection. A conventional leach field that was well-designed and maintained should last 25 to 30 years, or longer if usage was light. Best of luck with your septic inspection and planned subdivision!
In general, any residential dwelling unit or commercial building with a kitchen and/or bathroom would require a septic system. You would not need an on-site sewage system for an uninhabited storage building without running water.
If you have utility sinks or other water uses in a commercial building, but no bathroom, you might be able to get by with some type of wastewater holding tank that would need periodic pumping. The type of system will depend on the type of wastewater being disposed. Since these regulations vary from town to town and state to state, you need to check in with your local health or building department to find out what rules would apply to your intended uses.
In general, any residential dwelling unit or commercial building with a kitchen and/or bathroom would require a septic system. If you are using a lot for storage buildings only without any running water, then you shouldn’t need any sort of on-site sewage system. If you have utility sinks or other water uses in a commercial building, but no bathroom, you will probably need at a minimum some type of wastewater holding tank. The type of system will depend on the type of wastewater being disposed. Since these regulations vary from town to town and state to state, you need to check in with your local department of health or building department to find out what rules would apply to your intended uses.
I am looking at purchasing 5-10 acres with the hopes of placing a 3-bedroom home and possibly two or three “Tiny Homes” to use as rental units on the same property. I have seen several properties that perc in numerous places on the property. Does this mean that there could be more than one septic system and leach field if the different locations are far enough apart?
In general, the answer is yes, it’s possible to have multiple septic systems on one property, but it may be more economical to tie into one large system. At most, you would want two systems – one for the main house and one for the Tiny Houses. These issues are heavily regulated by the local health department, so you need to check with them to see what is allowable. The distance from one leach field to the another is generally not a concern. Of greater concern to regulators – and to you – is the distance from the leach field to a well, house foundation, potable water piping, and open water (lakes, ponds, streams). Also, you need to consider what is at the ground surface. In general, you don’t want trees near the piping or drain field or roads running over any of the components, unless they are specifically designed to handle traffic overhead. If the buildings are spread out, having more than one system may make sense. Typically, the distance from the house to the septic tank is in the range of 10 to 20 feet, but could go farther. The distance from the tank to the leach field can be much greater as the effluent at this point is clear liquid. If you cannot drain by gravity to the leach filed, a pump is needed which increases cost, complexity, and maintenance. Talk to your town or county health department about your ideas and see what options are acceptable in your jurisdiction. Best of luck with your project.
How do you know when a drain field is “used up”? We are looking at a home with a 26 year old drain field. It held a family of six for the first 10 years and then dwindled to the last two lovely owners who hold grand parties of 40-60 guest two to three times each year, the tank is pumped every five years presently. The home in in South Carolina and has two large creeks on one side of the home, a flood plain area, and an acre pond below the drain field and house. General information online says a field will last 15-30 years. How do you know when it is at the end? Is there a way to test and have a better understanding of the potential longevity of an old field?
The numbers I consistently hear from septic system designers and installers are 20 to 30 years for a properly designed and maintained drain field. A lightly used and well-maintained field can certainly last longer. The longevity depends heavily on the original design, usage level, and maintenance. Water-saving fixtures will help extend its life. Harsh chemicals, grease, animal fats, disposals, and solid materials disposed into a drain field can shorten its life. Assuming that the original design is adequate and usage moderate, the most important factor is regular pumping, which it sounds like the previous owners have done. A septic system contractor can tell you if you have a failed system, but I’m not aware of a test to determine how long a functioning system has left. The typical signs of a failed system are slow drainage or backups, and a soggy, smelly mess at the surface of the ground over the leach field. If you have slow drainage or backups, you will need to determine if these are caused by problems with the tank and other components or by a failed leach field. When they pump the system, the pumping contractor can usually identify problems. If necessary, a dye test can be used to confirm that the field has failed. Being surrounded by water and a flood plain could also be a concern. A water table that is too high can impair the drain field and also lead to contamination of the aquifer or pond. Modern codes call for the drain field to be a minimum distance above the seasonal high water table and may require a raised drain field (mound system) or other alternatives in that case. Pollution of the aquifer would show up as an elevated nitrate level in your well or pond, so you might consider a water test, which can usually be arranged through your town or county health department for a nominal fee. I recommend visiting our sister site, Inspectapedia.com, which has excellent information on SEPTIC SYSTEM TESTING and related topics. Dan Friedman, of Inspectapedia, recommends the following. • Find out what sort of tank is installed. Steel with rusted baffles is bad. Concrete in good condition with a safe cover is good. • Try asking the septic pumper if, the last time they pumped the tank, they saw trouble signs like backflow into the tank from the drain field or damaged baffles, or evidence of a damaged tank. Low sewage levels indicates tank leaks. Unless the pumpout was recent,however, they may be reluctant to provide information. • We don’t test the leach field biomat itself. But you could have a septic loading and dye test done. Read more at SEPTIC LOADING & DYE TEST. That can at least tell you if the system has already failed. You can also tell this from on-site inspection: look for odors, liquid “breakout” on the surface, or funny grass. Read more on Septic System Lifespan
I am in the early planning stages of construction in the Teton Valley of Idaho. I would like to do a geothermal loop and I am wondering if I could use the same trenches for the leach field. Since the GT lines are approximately 6-7 feet in the ground I could cover with a few feet of dirt and add the drain pipe, then cover the remaining 3-4 feet. Thoughts?
Interesting idea and could save you some money, but I’m not sure it will fly. First off, I would make sure it passes muster with both the septic system designer/installer and geothermal contractor – as well as the local code officials, assuming you have building codes in your area. A couple of key issues occur to me: 1. The soil around the geothermal loop gets chilled all winter and could freeze in your area over the course of the winter (which is why most ground loops use antifreeze). Since freezing can be an issue with septic systems in cold climates, it’s possible that combining the two systems would increase the likelihood of septic system freeze-ups. 2. Leach fields are generally placed on well-drained, undisturbed soil. The percolation rate of the soil (along with the usage) determines the size of the leach field. If you are building your leach field on backfill, you will need to take that into account and use suitable fill. In general, geothermal systems like dense and moist soil, while septic systems like dry and granular soils, so finding a soils type that works for both could be tricky. Anyone else have experience with similar installations? You can read an interesting discussion on this topic at:
https://www.geoexchange.org/forum/threads/installing-a-horizontal-loop-under-a-septic-field.710/
A piece of land I am considering purchasing already has a septic system installed for a 3 bedroom 2 bath structure. Should I still request a soil test for a foundation be done and make the purchase contingent on that? I have been told that since a standard septic was allowed that the land should be suitable to build on as it is. If the owner refuses this, are they expensive to have done?
If you are in an area that requires perc testing and approved septic system designs, I would ask for certification that the town/county health department (or building department) has approved this system for a three-bedroom house. You can never assume that proper testing or design was done for the existing system. Also, you should ask for septic system maintenance records and have the system inspected during your “study period”. If the system has been poorly maintained or is near the end of its service life, then you could be in for an expensive upgrade in the near future. A perc test should not be necessary unless there are questions about the current system. As for soil testing or an engineering review of the site, this is usually not required unless you have reason to believe there are special problems such as buried toxic waste, filled land, organic soils such as peat, solid ledge (a problem if you want a basement), wetland areas where building is prohibited, or a site with extreme water problems. While these problems are relatively uncommon, they are certainly worth considering when evaluating a building lot. Almost all of these problems can be solved with money. Even building on regulated wetlands is sometimes allowed if you create replacement wetland areas. An inspection, typically by a civil or soils engineer, can help you identify and budget for these types of problems. If you have reason to suspect problems, or just want to sleep easier, by all means get an engineer to examine the soil and drainage conditions in the area where you intend to locate the house. Allow time in your study period to perform the necessary inspections. I can’t tell you what it will cost, but, around here, I’ve have engineers do limited inspections of structural plans or land issues for well under $1,000. Find a small engineering firm, describe what you need done, and get cost estimate before proceeding. The more you can narrow his scope, like inspecting for just for water issues, the less you will pay.
Nice article – helpful and clear. A common problem on older sites is that there is or was a septic tank or cesspool and drainfield but no one is quite sure where. It’s often possible to make an intelligent guess by examining the lay of the land, slopes, location of mature trees, etc. asking “where would an excavator have considered it possible to *put* a septic system tank and drainfield? I’d add a safety warning to beware of abanodoned or old, poor condition septic tanks, cesspools, and drywells; if a cover is unsafe or if someone falls into one of these it can be fatal very quickly.
