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610-964-1477
Serving Montgomery, Chester, Delaware,
Phila. &
Lower Bucks Co's. in Southeastern PA.
Households not served by public sewers usually depend on a septic system to dispose of wastewater. There are many different types of septic systems designed to fit a wide range of soil and site conditions. These include mound systems, sand filter systems and pressure distribution systems. This MontGuide should help you understand the operation and maintenance of a conventional gravity-flow septic system.
A conventional septic system consists of two main parts: the septic tank and the soil drain field (also referred to as a leach field, absorption bed or absorption field). At the head of the drain field a distribution box or a manifold distributes wastewater to several absorption trenches. Some locations require that newly installed drain fields include a designated replacement area should the existing septic system need an addition, repair or replacement, the replacement area can then be used.
Courtesy National Small Flows Clearinghouse
The septic tank. A septic tank is a large, underground, watertight container, typically about 9 feet long, 4-5 feet wide and 5 feet tall that is connected to the home's sewer line. While typically designed with a 1,000-gallon liquid capacity, the size of the tank is legally determined by the number of bedrooms in the home. (Septic tanks come under the legal supervision of counties in Montana.) Septic tanks may be rectangular or cylindrical and may be made of concrete, fiberglass or polyethylene.
Raw waste water from the bathroom, kitchen and laundry room flows into the tank where the solids separate from the liquid. Light solids, such as soap suds and fat, float to the top and form a scum layer. This layer remains on top and gradually thickens until you have the tank cleaned. The liquid waste goes into the drain field, while the heavier solids settle to the bottom of the tank where they are gradually decomposed by bacteria. But some non-decomposed solids remain, forming a sludge layer that eventually must be pumped out.
Septic tanks may have one or two compartments. Two-compartment tanks do a better job of settling solids and are required in some areas for new installations. Tees or baffles at the tank's inlet pipe slow the incoming wastes and reduce disturbance of the settled sludge. A tee or baffle at the outlet keeps the solids or scum in the tank. All tanks should have accessible covers for checking the condition of the baffles and for pumping both compartments.
Figure 2: A Two-Compartment Septic Tank
Courtesy National Small Flows Clearinghouse
The Drain field. Further treatment of wastewater occurs in the soil beneath the drain field. The drain field consists of long underground perforated pipes or tiles connected to the septic tank. The network of pipes is laid in gravel-filled trenches (2-3 feet wide), or beds (over 3 feet wide) in the soil. Liquid waste or effluent flows out of the tank and is evenly distributed into the soil through the piping system. The soil below the drain-field provides the final treatment and disposal of the septic tank effluent. After the effluent has passed into the soil, most of it percolates downward and outward, eventually entering the groundwater. A small percentage is taken up by plants through their roots, or evaporates from the soil.
The soil filters the effluent as it passes through the pore spaces. Chemical and biological processes treat the effluent before it reaches groundwater, or a restrictive layer, such as hardpan, bedrock, or clay soils. These processes work best where the soil is somewhat dry and permeable, and contains plenty of oxygen for several feet below the drain field. The size and type of drain field depends on the estimated daily wastewater flow and soil conditions.
Even a properly designed and installed septic system cannot treat wastewater if the tank is not used and maintained properly. Here are a few tips for installing and using your septic system:
 | For future maintenance and to avoid deep root planting and other damaging activities in the drain field area, make an accurate diagram showing the location of your tank, drain field and replacement area. |
| Keep a record of pumping, inspection, and other maintenance. Include name, address and phone numbers for installers and pumpers. |
| To simplify tank access for inspection and maintenance, install a watertight concrete riser over the septic tank. |
| The area over the drain field should be left undisturbed, with only a mowed grass cover. Roots from nearby trees or shrubs may clog and damage your drain lines. |
| Keep automobiles and heavy equipment off the drain field. |
| Do not plan any building additions, pools, driveways, or other construction work near the septic tank, drain field or the replacement drain field area. |
| Do not put too much water into the septic system. |
Water overload occurs when the drain field is flooded with more water than it can effectively absorb, reducing the ability of the system to drain wastes and filter sewage before it reaches groundwater. It also increases the risk that effluent will pool on the ground surface and run off into surface water or down nearby water well casings. Typical indoor water use is about 50 gallons per day for each person in the family. Water-saving devices such as low-flow shower heads, faucet aerators, toilet dams or low-flow toilets can greatly reduce water flow into the system. Strategies such as taking short showers, spreading out laundry loads over the week and never allowing rain water from downspouts to enter the septic system will also help.
| Do not flush non-biodegradable materials such as plastics, disposable diapers, sanitary napkins and applicators they rapidly fill up the tank and will clog the system. |
| Restrict the use of your kitchen garbage disposal, it increases the amount of solids in the tank, making them slower to decompose. |
| Do not pour grease or cooking oils down the sink drain because they solidify and clog the soil absorption field. |
| Don't allow paints, motor oil, pesticides, fertilizers or disinfectants to get into your septic system. They can pass directly through the septic system and contaminate groundwater. These chemicals can also kill the microorganisms which decompose wastes and can damage the soil in the drain field. |
| Do not use caustic drain openers for a clogged drain. Instead use boiling water or a drain snake to free up clogs. Clean your toilet, sinks, shower and tubs with a mild detergent or baking soda rather than the stronger and potentially system-damaging commercial bathroom cleansers. |
| If a water softener is used in the home, the salt
recharge solution should not be allowed to enter the system if the predominant
soils in the drain field are very fine textured and drainage is very slow. In
these situations, sodium in the softener recharge solution may damage soil
structure in the drain field and plug the system. If you have a water softener,
the size of the absorption field must be increased to accommodate the
additional flow.  |
The frequency with which you will need to pump depends on three variables: the size of your tank, the number of people in the household contributing to the volume of your wastewater, and the volume of solids in your wastewater. If you are unsure about when to have the tank pumped, observe the yearly rate of solids accumulation in the septic tank. (See the MontGuide MT 9403 "Septic Tank Inspection and Trouble-Shooting.") The solids should be pumped out of the septic tank by a licensed septic contractor. Most county health departments recommend that the accumulated solids in the bottom of the septic tank be pumped out every three to five years although if the tank is large and the household is small a tank can function longer without requiring pumping (see Table 1).
|
Tank size* |
Household Size (number of people) |
|||||
|
(Gals) |
1 |
2 |
3 |
4 |
5 |
6 |
|
500 |
5.8 |
2.6 |
1.3 |
1.0 |
0.7 |
0.4 |
|
750 |
9.1 |
4.2 |
2.6 |
1.8 |
1.3 |
1.0 |
|
900 |
11.0 |
5.2 |
3.3 |
2.3 |
1.7 |
1.3 |
|
1000 |
12.4 |
5.9 |
3.7 |
2.6 |
2.0 |
1.3 |
|
1250 |
15.6 |
7.5 |
4.8 |
3.4 |
2.6 |
2.0 |
|
1500 |
18.9 |
9.1 |
5.9 |
4.2 |
3.3 |
2.6 |
|
1750 |
22.1 |
10.7 |
6.9 |
5.0 |
3.9 |
3.1 |
|
2000 |
25.4 |
12.4 |
8.0 |
5.9 |
4.5 |
3.7 |
|
2250 |
28.6 |
14.0 |
9.1 |
6.7 |
5.2 |
4.2 |
|
2500 |
31.9 |
15.6 |
10.2 |
7.5 |
5.9 |
4.8 |
* Your local health department may be able to tell you the size of your
tank.
What is septic system failure?
A septic system should effectively accept liquid wastes from your house and prevent biological and nutrient contaminants from getting into your well or nearby lakes and streams. Anytime these things do not happen, the system is failing.
For example, when waste backs up in your backyard, the system has obviously failed. If significant amounts of biological or nutrient contaminants reach your well or surface waters, the system is also failing, even though it may appear to be working just fine.
Most septic systems are designed to have a lifetime of 20 to 30 years, under the best conditions. However, many septic systems will fail before this time. Eventually, the soil around the absorption field becomes clogged with organic material, making the system unusable.
Many other factors can cause the system to fail well before the end of its "design" lifetime. Pipes blocked by roots, soils saturated by storm water, crushed tile, improper location, poor original design or poor installation can all lead to major problems.
But by far the most common reason for early failure is improper maintenance by homeowners. When a system is poorly maintained and not pumped out on a regular basis, sludge (solid material) builds up inside the septic tank, then flows into the absorption field, clogging it beyond repair.
These symptoms tell you that you have a serious problem:
| Sewage backup in your drains or toilets. This is often a black liquid with a disagreeable odor. |
| Slow flushing of your toilets. Many of the drains in your house will drain much slower than usual, despite the use of plungers or drain cleaning products. |
| Surface flow of wastewater. Sometimes you will notice liquid seeping along the surface of the ground near your septic system. It may or may not have much of an odor associated with it. |
| Lush green grass over the absorption field, even during dry weather. Often, this indicates that an excessive amount of liquid from your system is moving up through the soil, instead of downward, as it should. While some upward movement of liquid from the absorption field is good, too much could indicate major problems. |
| The presence of nitrates or bacteria in your drinking water well. This indicates that liquid from the system may be flowing into the well through the ground or over the surface. Water tests available from your local health department will indicate if you have this problem. |
| Buildup of aquatic weeds or algae in lakes or ponds adjacent to your home. This may indicate that nutrient-rich septic system waste is leaching into the surface water. This may lead to both inconvenience and possible health problems. |
| Unpleasant odors around your house. Often, an improperly vented plumbing system or a failing septic system causes a buildup of disagreeable odors around the house. |
A number of products are marketed with the pledge that they can keep septic systems operating smoothly, correct system upsets, or do away with the need to pump the tank periodically. Chemical additives are strong acids or alkalis, or organic solvents. Biological additives are cultures of harmless bacteria, plus waste-digesting enzymes. These sometimes contain yeast cultures.
Although some manufacturers of additives have test data showing how their products perform, there has been almost no independent testing of these products in full-sized septic systems. The information that exists does not show improved long-term performance in systems where additives have been used. If a system is not being misused by the homeowner, these products are unlikely to pose a benefit. The amount of material added with each dose of product is very small compared to the biological material already present and working in the tank.
Occasionally a system suffers an upset, when the septic tank bacteria are harmed or destroyed. This can happen if the home is vacant for a long period and the tank receives no fresh wastewater, or if strong cleaning agents are flushed down the drain. After a few days of normal use, the biological system in the tank will re-establish itself. In this situation the biological additives may help speed the recovery of the septic tank.
Every septic tank needs to be pumped periodically, because all wastewater contains inert matter that cannot be degraded in the tank. No additive can do away with this need.
The biological additives are unlikely to be harmful. The chemical additives could definitely harm your system. These products have the potential to sterilize your system temporarily. The resulting passage of raw sewage into the drain field will hasten its failure. The acid and alkali products can corrode the plumbing and the tank. The organic solvents pass through the system unchanged. They can then infiltrate into the groundwater, creating a chemical plume that endangers nearby wells.
For information on evaluating a septic system when selling or purchasing property, inspecting solids levels in a septic tank and septic system trouble-shooting, see MontGuide 9403," Septic Tanks: Inspecting and Trouble-Shooting." Required design features are set forth in circular WQB-6, "Standards for Individual Sewage Systems," published by the Water Quality Division, Montana Department of Environmental Quality.
by Michael P. Vogel, Ed.D.*, MSU Extension Service Housing Specialist
*The sections on trouble-shooting are adapted from a publication by James C. Converse, Agricultural Engineering Department, University of Wisconsin, 1977.
How to evaluate septic systems when selling or purchasing property, why septic systems fail, how to know when to pump a septic tank and troubleshooting for other problems.
Households not served by public sewers usually depend on a septic system to dispose of wastewater. Proper maintenance of the system is as important as proper installation (see MontGuide MT 9401 "Septic Tank and Drain field Operation and Maintenance.") This MontGuide goes into greater detail on evaluating a septic system when selling or purchasing property, inspecting solids levels in a septic tank and troubleshooting problems in a septic system.
Evaluating a septic system when selling or purchasing property
Conducting a septic system evaluation prior to sale or purchase of property protects both the buyer and the seller. Most importantly, an evaluation helps to protect the value of the buyer's investment by ensuring that the system is functioning properly and will continue to do so. It also protects the buyer from potentially tremendous costs of system repair or replacement soon after the sale.
For a seller (and realtor, too), a septic system evaluation will minimize the possibility of unknowingly selling a house with a defective or failing system, and could help avoid possible lawsuits that might arise as a result. A properly functioning system can also be a good selling point and enhance the value of the house.
A septic system evaluation should be conducted as soon as the property is placed on the market so that necessary repairs can be made to the system. The evaluation should definitely be done before the sale is completed.
At a minimum, an evaluation should examine these things:
· The location, age, size and original design of the septic system.
· The soil conditions, drainage, seasonal water table and flooding possibilities on the site where the septic system is located.
· The history of the system if records are available.
· The condition of the plumbing fixtures and their layout to determine whether structural changes have been made to the plumbing that would increase flow to the septic system above capacity. System components that could affect the system for example, water softeners draining to the septic tank or the presence of footing drains should also be inspected. Slow-flushing toilets and slow drains may indicate a failing system.
· The date the septic tank was last pumped.
· The sludge level in the septic tank if it has not been recently pumped.
· The condition of the absorption field. Look for evidence of liquid waste reaching the soil surface, draining toward nearby lakes and streams, or clogging the soil and gravel beneath the field. (This usually requires digging up a small portion of the field.). Look for evidence that heavy equipment has been on the drain field, causing compaction and possible damage.
Figure 1: A Two-Compartment Septic Tank Courtesy National Small Flows Clearinghouse
What is septic system failure?
A septic system should effectively accept liquid wastes from your house and prevent biological and nutrient contaminants from getting into your well or nearby lakes and streams. Anytime these things do not happen, the system is failing.
Why septic systems fail
By far the most common reason for early failure is improper maintenance by homeowners. When a system is poorly maintained and not pumped out on a regular basis, sludge (solid material) builds up inside the septic tank, then flows into the absorption field, clogging it beyond repair.
How will I know when to pump the tank?
The frequency with which you will need to pump depends primarily on these variables: 1) the size of your tank, 2) the number of people in the household contributing to the volume of your wastewater, 3) the volume of solids in your wastewater and 4) use of a garbage disposal. If you are unsure about when to have the tank pumped, observe the yearly rate of solids accumulation.
The primary maintenance point in a septic system is the septic tank. Inspection is accomplished by measuring the scum depth and sludge depth in the tank once a year. The tank should be pumped if the sludge layer has built up to within 18 inches of the tank outlet or if the scum layer thickens to within 3 inches of the bottom of the outlet baffle or sanitary tee. Follow these steps and Figure 2 for measuring scum and sludge depth.
Measuring scum depth
1. Attach a 6 inch square board to the bottom of a stick about 6 feet long.
2. At the outlet end of your tank, extend the stick through the scum layer to find the bottom of the baffle or effluent pipe.
3. Mark your stick to indicate that point.
4. Raise the stick unit you "feel" or see the bottom of the scum layer.
5. Mark your stick again to indicate that point.
6. If the two pencil marks are 3 inches apart or less, or if the scum surface is within 1 inch of the top of the outlet baffle, the tank requires cleaning.
Measuring sludge depth
1. Wrap 3 feet of white rag or toweling around a long stick.
2. Place the stick into the sludge, behind the outlet baffle if possible.
3. Hold the stick there for several minutes.
4. Remove the stick noting the sludge line.
5. If the sludge line is within 12 inches of the outlet baffle, or within 18 inches of the outlet fitting, the tank requires cleaning.
While the above inspection steps can determine necessary pumping frequency most
accurately, this task is unpleasant. Therefore the best solution is to have the
tank pumped by a certified contractor on a routine basis. If the septic system
is not used very often (as in an infrequently used vacation home with a
correctly sized tank), it will probably not need to be pumped as frequently.
Table 1 lists how often you need to pump out your tank on average, given the
size of the tank and the number of persons living in the household. These
figures were calculated assuming there was no garbage disposal unit hooked up to
the system. The use of a kitchen garbage disposal will increase the amount of
solids in the holding tank by as much as 50 percent.
Troubleshooting septic system problems
Following are suggestions for troubleshooting and correcting septic system problems when they arise. This guide outlines:
1. The two most common symptoms of system malfunction,
2. The potential causes of each and how to check them out, and
3. Suggested solutions to the problems once identified. To facilitate troubleshooting, you should have a map of your system, showing location of the absorption field and tank clean-outs. This simplifies repair and prevents the lawn from being torn up needlessly.
Symptom A: House drains don't work or sewage backs up into basement
First, the trouble must be pinpointed. Measure the liquid level in the septic tank. If it's normal (i.e., a foot or so below the top of the tank), go to Cause A.1 or A.2; if above normal, go to Cause A.3.
Cause A.1. A blockage between house and septic tank. The blockage may be in the house sewer, or the scum layer could be plugging the inlet pipe at the tank. If scum is the problem, the tank should be pumped. Have the inlet baffle checked at that time. If functioning properly, it should keep floating scum away from the tank inlet.
A house sewer blockage can be removed with a sewer routing tool from the clean-out at the house end of the line. Sewer cleaning is usually a job for a professional. If root penetration is the reason for the blockage, pipe joints should be resealed after routing to make them watertight.
If the blockage recurs in a new system, the problem may be improper sewer line slope and the only lasting solution is to relay the line, using the correct slope. If the blockage recurs in a previously trouble-free system, the most likely cause is a broken sewer pipe section, which must be located and replaced.
Cause A.2. A plugged house sewer vent. In some cases, a plugged sewer vent (or soil stack) can slow the rate at which sewer lines drain to the point that solids settle out. A plugged or incorrectly installed vent sometimes results in a sewer gas smell around house drains; but more typically, it will just cause a gurgling sound as air is pulled through the trap into the house sewer when drains are used.
Plugged-vent problems should not occur if the plumbing code was followed during construction. However, temporary blockage can occur in winter when undersized roof vent openings freeze shut. The soil stack should be 4 inches in diameter where it passes through the roof, and should either extend 6 inches above the roof or 2 feet higher than any point on the roof that is 10 feet away (as measured horizontally), whichever is greater. Needed vent corrections should be made by a qualified plumber.
Cause A.3. A blockage between septic tank and absorption field. If the liquid level in the septic tank is found to be above normal, either: (a) the tank outlet is plugged, (b) the line to the absorption field is obstructed, or (c) the absorption field is clogged. If the latter is the case, there will probably be evidence of seepage or general wetness in the absorption area.
a. Plugged tank outlet. In septic tanks which have been used for many years, the outlet baffle sometimes disintegrates or collapses. This allows scum and sludge solids to overflow and plug the outlet or the line to the absorption field. The cure is pumping the tank down, routing out the line and replacing the defective baffle.
b. Obstruction of tank-to-field line. Likely causes are solids overflowing the tank, tree roots getting into pipe joints or collapse of a pipe section. Again, the immediate remedy is pumping the tank and clearing the line, followed by repair of the leaky joint or broken section.
Sewer pipe can break if not uniformly supported on solid or gravel fill or if shallow line is driven over by heavy vehicles. Tree roots can get into sewer lines through leaky pipe joints. Pipe plugging should not be a problem in the trench area, since tree roots seldom penetrate very far into the gravel fill around the pipe.
c. Clogged absorption field. See discussion under Cause B.2 below.
Symptom B. Seepage or Swampy Conditions in Absorption Field Area
Cause B.1. Too small a filter field. Many older homes have septic systems that are inadequate to handle the large amounts of water used in modern living, especially in cases where the original home has been enlarged without expansion of the septic system. If this describes your situation, consult your county health personnel to see if the absorption field is properly sized for your home and soil conditions.
If found to be seriously undersized, the present field should be enlarged or a new one constructed. In fact, the best decision might be a completely new system, since the septic tank also is probably too small. Often the old field can be reused as an alternate absorption area after resting a year or two.
If capacity is inadequate but not severely so, one solution could be to install water conservation devices in the home. Low-flow toilets and shower heads, faucet aerators and other devices can cut water use significantly with very little change in life-style.
Cause B.2. Clogged soil absorption field. Soil absorption fields naturally clog over time, since effluent from the septic tank contains some suspended materials. Over a long period, development of a "clogging mat" reduces soil permeability to the point where tank effluent cannot be absorbed at the rate it is produced.
The best solution to a soil clogging problem is to rest the absorption field. This allows the organic matter to decompose, thus restoring the permeability of the soil around the trenches to near its natural state. Resting the area, however, requires that a second filter field be available to accept effluent for a year's time. Being able to switch from one absorption area to the other every year reduces soil clogging problems and significantly lengthens the life of the total system. Switching fields should be done during the summer when soil temperatures are high to obtain the best soil treatment of sewage. Alternating fields is especially effective in slowly permeable (high clay) soils.
Cause B.3. High water table in spring. Septic system operation can become sluggish and even fail in the spring, because a seasonal high water table may saturate the soil around the trenches. Home sites and absorption fields in flat areas having poor surface drainage are especially susceptible. If this describes your situation, about the only thing you can do is to use subsurface tile drainage to lower the water table. The drainage tile must discharge to a surface ditch or to a larger tile drainage system.
If your system is located on a sloping site, installation of drain tile up slope from the absorption field should be very effective in lowering the water table. Place the tile at least 25 feet away from the filter field and at least as deep as the bottom of the trench. Home water conservation devices and practices may also be needed to make it through wet spring times and prolonged rainfall periods.
Cause B.4. Solids carryover. The overflow of solids from a septic tank which has filled with sludge can seriously affect absorption field operation. The cure, of course, is periodic tank clean-out.
Cause B.5. Leaking faucets and toilets. The increased water load from leaky faucets and toilets can also affect absorption field operation. The cure is to keep plumbing fixtures in good repair.