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• piping connecting the building to the treatment tank
• a septic or treatment tank which retains solid waste
• piping connecting and conducting clarified effluent from the treatment tank to a distribution box
• a distribution box connecting the effluent line from the tank to the absorption system or "drain field"
• an absorption system which permits effluent to drain to soils below
• a bio-mat or bio-mass of pathogen-digesting bacteria which forms in soil below the absorption system.

Many variations on this general scheme are used, depending on local climate, soil conditions, available space, economy, and available materials. Special equipment and systems may be designed for problem or difficult sites such as rocky or wet ground, permafrost, or wet tropical marshlands.

More Reading:
Buyers' Guide: Home Buyer's Detailed Guide to Septic Systems - Buying a Home With a Septic Tank
Cesspools if you don't know what they are.
Components of a Septic System- the Basic Parts of a Conventional Septic Tank and Leachfield, a chapter in the Home Buyers Guide to Septic Systems
Drywells if you don't know what they are.
Don't Flush these things into a septic system
Safety Septic System, Septic Tank, & Cesspool Safety Warnings for Septic Inspectors, Septic Pumpers, and Homeowners.
Sketches of the Septic System Components Private Sewage Disposal Systems - Septic Drawing Library
What is a Septic System An Engineer's View - Types of treatment tanks, adsorption systems, pumps, and other special equipment are discussed in some further detail in this text

Septic Systems Online Book

SAFETY WARNINGS - Septic Tank Safety Warnings for Septic Inspectors, Septic Pumpers, and Homeowners

This chapter is maintained at Septic System, Septic Tank, & Cesspool Safety Warnings for Septic Inspectors, Septic Pumpers, and Homeowners but text is repeated here for readers who scroll down rather than linking to the separate chapter.

Providing inspection and diagnosis of on-site waste disposal systems is an extremely valuable public service which helps protect people from expensive unanticipated septic system repair costs and helps protect public health by assuring sanitary disposal of sewage and gray water waste from buildings. More importantly though, such inspections may detect and warn about serious safety hazards at some properties. The strong warnings issued below intend to reduce septic system safety hazards for inspectors and property owners/occupants, but it is not the author's intention to dissuade inspectors from providing this valuable service. But danger lurks at cesspools, open covers, tanks or tank covers in poor condition, and from high levels of methane gas. These risk collapse, falling, asphyxiation, and other potentially fatal hazards as well as risks of unsanitary conditions.

• Don't work alone: Falling into a septic tank or even leaning over a septic tank can be fatal. Do not work on or at septic tanks alone - workers can become suddenly overcome by methane gas.
• Do not ever go into a septic tank unless you are specially trained and are wearing the special equipment and gear for that purpose, including self-contained breathing apparatus.
• Don't enter the septic tank: Never go into a septic tank to retrieve someone who has fallen in and was overcome by toxic gases without a self-contained breathing apparatus (SCBA). if a SCBA is not available, call for emergency services and put a fan at the top of the tank to blow in fresh air.
• Don't lean over the septic tank openings Do not lean over or stick your head into the septic tank to examine its interior - you could fall in to the tank or become overcome by gases and fall into the tank, an event which is likely to be fatal.
• Don't ignite flames Do not light a flame at or near the tank - methane gas is explosive. At one tank pumpout my client described the explosion and burns received by the pumping contractor when he stood by the tank and lit a cigarette.
• Site must be ventilated: Decomposing wastes in the septic tank produce toxic gases (such as methane) which can kill a human in a matter of minutes. When working on a tank be sure the area is well ventilated.
• Rope off & Mark Dangerous Sites: If your inspection discover that there are dangerous conditions, such as an unsafe tank cover, tank collapse, or a home-made septic tank or cesspool (which are at increased risk of sudden collapse) such areas should be roped off and clearly marked as dangerous to prevent access until proper evaluation and repairs can be made.
• Safe covers: be sure that the tank and its access ports have sound and secure covers that do not risk collapse and which cannot be removed by children.
• Septic & Cesspool Collapse Hazards: Old steel tanks, thin, rusting steel or rotting home-made wood tank covers, site-built tanks and cesspools, and recently-pumped cesspools are at particular risk of collapse. Falling into a septic tank or cesspool is likely to lead to rapid asphyxiation from methane and in cases of collapse, there is risk of becoming buried. The author has consulted in cases involving such fatalities (homeowner fell into a site-built cesspool), and at one site inspection, walking near an overgrown area the author himself stepped through a rusting steel septic tank top, surviving only by throwing himself into a nearby clump of brambles! Beware of
  • flimsy, rusted, old-steel, home-made, or missing septic tank/drywell/cesspool covers
  • abandoned systems which may not have been filled-in
  • collapsed, or collapsing septic tanks or cesspools
  • possible presence of multiple components at a property, abandoned or in-use
• Unsanitary conditions: Be alert for unsanitary conditions such as surface effluent or sewage backups into buildings, events which risk serious viral and bacterial hazards and which indoors, may require professional cleaning. Be alert for personal sanitation hazards when working around septic systems, such as open cuts or failure to wash properly after working on systems.
• Damage to Septic Components: Avoid damaging septic system components or the building: Improper septic testing procedures, such as flooding a dosing-system, can damage the system. Also, remember to check for leaks into or under the building being tested when running water into the building fixtures and drains. Don't leave water running unattended - at risk of flooding the building.

Septic Systems Online Book

Septic System Safety Warnings for Home Owners and Home Buyers

Septic system concerns for a building owner start with safety. Here are some red flags:

• Signs of collapse-possible fatal hazards: include depressions or "soil subsidence" anywhere on or around the property. Any suspect area should be roped-off and absolutely no one should walk over or even close to such a spot until it has been investigated by a professional.
• Old or abandoned systems: such as site-built cesspools or drywells were often made with a thin steel or wood cover which with age can collapse. If the history of the site or visual observation suggests that there are or were old systems at the property, professional investigation is warranted. Improper "abandonment" (failing to fill-in a pit) can lead to sudden collapses. Signs that there may be old systems at a property might come from anecdotal evidence (ask a neighbor, ask the local septic installing or service companies), or visual evidence such as seeing abandoned waste pipes at basement or crawl space walls or floors. Don't assume that an old house which is now connected to the public sewer didn't previously have an on-site waste disposal system.
• Septic service by untrained workers: such as aerating, agitating, or pumping out an old site-built cesspool, can lead to sudden system collapse. Prevent access over or near any such systems.
• Unsanitary conditions such as discharge of sewage effluent to the yard surface, to a nearby well or stream, or previous septic backups into a building deserve professional attention. Indoors special cleaning may be needed to remove bacteria or other pathogens.
• Septic testing by inexpert "inspectors" who may not follow an adequate procedure increases the risk of a costly surprise.
• Uninformed homeowners may not notice a danger or malfunction .Homeowners should review the safety warnings listed above. The information here is general in nature. Since conditions and requirements vary widely at individual sites, the you should obtain qualified expert advice pertaining to the specific system about which you have questions, and should not rely on this general text for costly diagnostic/repair/replacement decisions. In other words, I'll try to give you some helpful information. In exchange, don't expect me to pay for your new septic system.

Septic Systems Online Book

Septic Inspector Qualifications/Licensing

If you perform septic inspections you are obligated to do so with proper information, training, procedures, and in some communities a license is required. Some states (e.g. CA, CT, NJ, MA) have specific certification requirements for inspectors of septic systems, as well as specific regulations regarding the performance of the inspection itself. Be sure to obtain information pertinent to your own state, usually from the state health department or state department of environmental protection. For example, Massachusetts septic inspectors will want to look at the links and the Title 5 regulations at our page on the Massachusetts Septic Testing Law. Other links to septic system installation and inspection regulatory agencies are at our "Local, State, U.S. Federal Government, & International Agencies & Resources for Septic Systems Wastewater Treatment" page.

Septic System Inspection Authorities

INSPECTION AUTHORITY: some municipalities and states (EG. Pennsylvania) provide septic inspection and testing certification. However a generalist inspector such as an ASHI professional, in the course of a home inspection, is permitted to observe and report visual evidence of defects, probable, or possible defects, just as any contractor might observe and report when coming to a property for any reason.

The next chapters discuss ways in which septic system components fail, and with the inspection of the individual septic system components.

Septic Systems Online Book

FAILURE CAUSES - Septic Failure Causes: How Does Each Septic System Component Fail? - What to Look For During a Septic Inspection

This chapter is maintained at Septic Failure Causes: How Does Each Septic System Component Fail? - What to Look For During a Septic Inspection, but text is repeated here for readers who scroll down rather than linking to the separate chapter.

This chapter discusses detailed "how to" steps instructing the investigator in how to inspect specific septic components for signs of failure. The following section will discuss types and causes of septic failure and will provide criteria that define "failure."

Before digging up your septic tank or calling a septic pumper, if you think the septic system is failed because of drain blockage or drains backing up into the building, you should to see "Diagnosing Clogged Drains: Is it a blocked drain or the septic system? - A First Step for Homeowners". If you link to that text, please return here using your browser's "BACK" button.

Onsite Waste Disposal System Failure Criteria

Massachusetts Title 5 lists specific failure criteria and serves as a good model for septic inspections anywhere.

• Backup anywhere in the system
• Discharge of effluent to the surface, stream, etc. regardless of whether or not septic dye is observed
• Static effluent level or floating scum over the top of the baffles in the septic tank [added by DF]
• Static effluent level above outlet in the D-box
• System has to be pumped more than 4x/year
• Metal septic tanks (municipality dependent; note that in special site conditions small metal tanks may be the "only" solution and may be approved by local officials. An owner/buyer must be informed of the implications of such installations.)
• Soil Absorption System (or cesspool, etc) is at a depth exposing it to the maximum groundwater level

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Inspecting Outside Waste Piping

Outside waste piping conducts sewage (black water and gray water) from the building to the treatment tank or "septic tank," and from the treatment tank to the distribution box. These lines should be of solid, non-perforated material and need to be protected from mechanical damage (such as by vehicles). Piping extending from the distribution box into drain fields is normally perforated, though solid lines might be used if effluent is being processed by more specialized devices such as seepage pits, galleys, or a sand-bed system.

House to tank

This line may become blocked by waste, damaged by collapse of a section, or invaded by roots. Detection of these conditions is fairly easy by routing a snake or power snake from the building drain to the septic tank. An experienced power snake operator can often tell by "feel" that a drain line is collapsed, partially collapsed, or invaded by roots. While you may make a temporary "repair" of such a condition by drain-cleaning, if the line is broken or root-invaded, you should expect to have to excavate and replace it soon.

Tank to Distribution Box

The same failures can occur on this line as from house to tank. Opening the D-box can also show whether or not effluent is being directed uniformly into each of the leach lines. A tipped D-box can overload one line and cause early failure of the absorption system. If this is happening, flow adjustment end-caps (eccentric holes) can be installed in the distribution box on the inlet end of each of the drain lines, permitting adjustment of effluent delivery into each line, perhaps relieving the problem line and redistributing effluent into the others.

Drain field piping

In a conventional "drain field" of perforated pipes buried in gravel-filled trenches, a drain line may be invaded by tree roots. This is why experts advise keeping tree and shrub plantings away from drain fields. Vehicle traffic can also collapse this or any outdoor waste piping, which is why experts advise against ever driving over a drainfield or over any other septic system components.

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INSPECTING TANKS - Inspecting Septic Tank Condition

This chapter is maintained at Septic Tank Condition - How to Inspect Septic Tanks but text is repeated here for readers who scroll down rather than linking to the separate chapter.

The purpose of the treatment tank or "septic tank" is to contain solid waste and to permit the beginning of bacterial action to process sewage into a combination of clarified effluent, settled sludge, or floating scum in the tank. An intact, un-damaged septic tank is normally always filled with these materials. However the inspector performing a "visual" check of the septic system needs to be alert for some important findings:

• Subsidence at the tank location - may risk dangerous, potentially fatal collapse
• Evidence of recent work
• Evidence of backup or effluent breakout at the surface in the tank area

Only by pumping and visual inspection can actual tank capacity and condition be completely determined. Probing in the area of a tank, without excavation, is not recommended as the probe may damage a steel or fiberglass tank. When a tank is uncovered for pumping additional critical details may be observed before the pumping operation

• Condition and safety of the tank and access covers
• Liquid and waste level in the tank - evidence of waste passing over the baffles - a flooded system, an indicator of system failure
• damage to the tank baffles

When the tank is opened and to be cleaned or pumped out additional information is available:

• Thickness of scum and sludge levels: Septic tank maximum scum and sludge buildup prior to pump out, and instructions for measuring the floating scum layer thickness and settled sludge layer thickness in a septic tank are available in a separate chapter at Septic Tank Pumping Guide
• Back-flow of effluent into the tank during pumpdown - an indicator of flooded leach fields
• Additional evidence of damage to the tank baffles
• Evidence of damage to the tank itself - cracks, leaks

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Steel septic tanks

Steel tanks typically last 20-25 years, then rust, and collapse. Before this time steel baffles may rust off (damaging the drain field with sludge) or the tank top may become rusty and unsafe. Since steel tank tops can be replaced while leaving the old tank in place, the condition of the top itself is not a reliable indicator of tank condition.

Rusting steel tank covers can cause death! Rusted covers can collapse. I have reports of children and adults who have died from this hazard, as recently as December 1997. In 2000 I consulted in a fatality involving an adult falling into a cesspool. At a building inspection I myself stepped through a hidden, rusted-through steel septic tank cover. Falling into a septic tank, drywell, or cesspool is quickly fatal, either from being buried by falling soils and debris, or by asphyxiation. Septic gases are highly toxic and can kill in just minutes of exposure. Even leaning over an empty (just pumped) tank has led to collapse and fatality of a septic pumper.

Steel tank baffles: rust out and fall off, permitting solids to enter the soil absorption system

Steel tank bottoms rust out permitting effluent to leak into soils around the tank, possibly giving a large void in tank at time of testing, thus subverting a loading or dye test.

Concrete septic tanks

Concrete tanks at an existing septic installation are usually viable, but might have damaged baffles or cracks that permit seepage of groundwater in or septic effluent out around the tank. Occasionally we've seen tanks made of poor-quality concrete (insufficient portland cement) which eroded badly. If the tank outlet or absorption system have been blocked, examination of the tank interior may show that effluent is or has been above the top of the baffles (see "baffles" below) thus indicating a system failure discussed next.

Concrete tanks can crack or sections may separate causing leaks with the result of not only improper disposal of effluent (wrong location) but also subverting an attempt at a septic loading and dye test since when the system is un-used the tank liquid levels drop abnormally. The inspector may detect this condition only if there is a tank inspection port which is readily and safely accessible for before, during, and after inspection when running a loading and dye test.

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Home made or "site built tanks- [TBD]

Site built systems, in my experience, are often under-sized and worse, dangerous. There is a serious risk of collapse of old rotting wood covers, collapsing concrete block dry-laid tank or "cesspool" walls, etc. Other types of tanks and home-made onsite systems are described below at Septic Tank Type, Capacity, Material Details

Baffles: Inspecting the Condition of Septic Tank Baffles

Baffles in a septic tank are provided to keep solids and floating scum and grease inside the tank. Baffles are provided at both the inlet to the tank (from the building) and the outlet from the tank (to the absorption system).

Broken baffles or high sludge levels can cause solids to flow out of the tank and into the absorption system. The result is reduced absorption into surrounding soil and eventual failure of the system. Floating scum thickness and settled solids thickness can be measured through access ports into the tank or cesspool. Finding solids at or covering the outlets or damaged baffles should result in report of a very questionable adsorption system and possible major repair cost.

Concrete tank baffles: may erode from chemicals, detergents, poor concrete mix, water flowing over top of baffles, or may be broken by improper pumping procedures

If baffles are lost or damaged (rusted off on a steel tank or broken off on a concrete tank), they can be repaired or replaced. For example at a steel tank the contractor may simply insert a plastic piping "Tee" into the tank inlet or outlet to create a new baffle system.

However, depending on how long the tank was used without good baffles, the volume of solids and grease that moved from the tank to the absorption system will have begun clogging soils there and will have reduced the future life expectancy of the absorption system.

Baffle damage and repair, or even a complete tank replacement when the absorption system has been left alone always lead the author to warn the building owner that the future life of the absorption system may be in doubt and that additional expense will be involved.

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Solids: Inspecting the Level of Accumulated Solids, Sludge and Floating Scum in Treatment Tanks

Solids entering a septic tank are intended to remain there until pumped out during tank service. A large portion of solids settle to the bottom of the tank as sludge. Grease and floating scum remain at the top of the sewage in the tank. Baffles (discussed above) help keep solids, scum, and grease in the tank. Bacterial action in the tank make a modest reduction in the solids volume and begin the processing of sewage pathogens, a step later completed by soil bacteria in the absorption fields.

Net free area: If the sludge level becomes too high or the floating scum layer too thick, in addition to risking passage of solids out of the tank (damaging the absorption system), the remaining "net free area" of liquid in the tank is reduced. When the net free area becomes too small, there is insufficient time for waste entering the tank to settle out as bottom sludge or top floating scum. That is, for an in-use septic tank with a small net free area, the frequent entry of solid and liquid waste will keep the tank debris agitated, thus forcing floating debris into the absorption system where the life of that component will be reduced (due to soil clogging).

The importance of keeping an adequate net free area in a septic tank is the reason that tanks need to be pumped at regular intervals. Building owners who never pump a tank until it is clogged have already damaged the absorption system.

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Measuring septic tank sludge thickness & scum layer

Septic tank maximum scum and sludge buildup prior to pump out, and instructions for measuring the floating scum layer thickness and settled sludge layer thickness in a septic tank are available in a separate chapter at Septic Tank Pumping Guide: When, Why, How to Pump A Septic Tank

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TANK TIPS - Septic Tank Types, Capacity, Material Details

Septic Tank Types: concrete and steel septic tanks and warnings are discussed above at Inspecting Septic Tank Condition.

Septic Tank Size Requirements and How to Calculate the Size and Volume of a Septic Tank are discussed in a separate chapter, " Table of Required Septic Tank Sizes: Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow & How to Calculate the Size (in gallons) of a Septic Tank"

Other septic tank types: might include site-built cesspool using concrete blocks or rubble, steel drums, or other. Beware of very limited capacity, failure to comply with local codes, etc. Steel tanks are at high risk of rust and collapse, and higher risk of loss of baffles; frequently tank cover is damaged by excavation for pumping if no cleanout opening is provided.

Limited Capacity of site-built equipment: Homemade systems are very likely to be in violation of local plumbing codes and standards; significant costs to cure may be involved. Tanks smaller than 900 gallons are below minimum size in some jurisdictions. Areas of wet soils, or very small yards should suggest that there may not be room for a conventional absorption system.

Extra costs will be involved in repairing or extending such installations. Sand-bed filtration systems may have to be replaced with other more costly systems when their operation fails or a use permit expires. Systems that dump into local waterways may require periodic inspection and re-certification by state departments of environmental conservation, or may be outlawed. Use of "drywells" to separate graywater from sewage may be clues of limited system capacity. Graywater may not be discharged to the surface nor to storm sewers.

More Reading:
Septic Tank Pumping Guide which gives the tank pumping schedule as a function of tank size and wastewater usage (or occupants).
Septic System Additives & Chemicals and advice about using them to "help" or "inoculate" or "fix" your septic system.

Septic Systems Online Book

INSPECTING THE D-BOX - Inspecting the Septic System Distribution Box

The distribution box (more than one may be in use) connects a single effluent line from the septic tank to a network of absorption system components such as drainfield leach lines or to a network of seepage pits or galleys. The photo above shows the adjustable weir outlets that permit balancing flow among drainfield lines. (Source EPA who used photo from Ayres Associates.) More sketches of D-box layouts and configurations are shown in this EPA drawing.

Regulating effluent distribution: In good system design the outlet openings from the distribution box to each drainfield line can be adjusted to regulate the flow among the various absorption lines. Elegantly simple, a plug with an eccentric hole is inserted into the end of each leach line fed from the D-box. By turning the plug in the end of the leach line pipe one can place the eccentric hole higher or lower with respect to the bottom of the distribution box, thus compensating for a slightly tipped box, differences in leach line length, or differences in leach line condition.

Uneven effluent distribution: If a distribution box becomes tipped (or clogged) effluent may be routed to only a portion of the absorption system, thus overloading it and leading to a "breakout" of effluent at the surface or to clogging and system backup. An examination of the box interior may show flood lines in the box if the drain field has been clogged or saturated in the past even if at the time of inspection the box is not flooded.

If the fields have been flooded you should be pessimistic about the remaining life of the absorption system. If the box is tipped and/or effluent has not been uniformly distributed among the drainfield lines (assuming they are of equal length and in equally good soils), only a simple adjustment of the outflow may be needed. Round plugs with eccentric openings may be present or can be inserted in the D-box outlet openings to regulate flow among the individual absorption lines. (C)Trap Daniel Friedman Copyright Protected text.

Tipped or flooded distribution boxes, resulting in uneven loading of soil absorption system lines. This condition can flood one or two lines leading to early field failure.

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INSPECTING FIELDS - Inspecting the Absorption System or Drainfield

This chapter is maintained at SEPTIC FIELD INSPECTION - Septic Failure Causes: How Does Each Septic System Component Fail? - What to Look For During a Septic Inspection. Text is repeated here for readers who scroll down rather than linking to the separate chapter.

This chapter discusses types of septic system failure in the drain field, leach field, seepage bed, or similar component. We list the causes of each type of septic component failure, and list the septic component failure criteria or in other words what conditions are defined as "failure"?. The detailed "how to" steps instructing how to inspect specific septic components for signs of failure are discussed in the text above.

Absorption Field Failure Causes of drainfields and leaching beds

• Soil clogging at the biomat layer which forms below and around the drainfield trenches (or other absorption systems). The biomat is a bacteria layer which forms in soil below and around drainfield trenches where septic effluent or wastewater is discharged. This layer is critical in the processing of fine biological solids and pathogens which are in the effluent, and without it the septic system would not be adequately treating the effluent. Inadequately-treated effluent released into the ground risks contamination of nearby ponds, wells, streams, etc.
• Driving over the absorption system, leach field, drainfield
• Paving over the absorption system
• Flooding the absorption system with surface or roof runoff, or rocky, poorly-drained or under-sized sites may simply lack capacity
• Use of septic tank or drain field additives which claim to extend system life can generate so much activity in the tank that solids are held in suspension and forced into the soil absorption system! Do not add any treatments, chemicals, yeast, or other treats to a septic system. In general these treatments don't work, may ruin the system, and are illegal in many localities. There is no magic bullet to repair a bad SAS.
• Improper original construction , especially on rocky, poorly-drained sites (pipes settle, for example)
• Houses clustered around a lake: often will have a marginal system as properties were crowded together, built as part-time summer-camps, were built without code supervision, and often were built using amateur, marginal home-made systems.
• Age: eventually even a well-maintained SAS will clog and have to be replaced.

More Reading:
The formation, clogging, and measures to protect and extend the life of the biomat is discussed at Septic System Absorption System Biomat Formation as a subchapter of this text.

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DISPOSAL vs TREATMENT - Effluent Disposal and Drain Clogging Failures

In simplest terms, there are two visible septic effluent or onsite wastewater disposal failures:

• Toilets or other fixtures back up into the house - but first see "Diagnosing Clogged Drains then return here using your browser's "BACK" button.
• Effluent or sewage appears at the surface of the yard, or the neighbor's yard!

Septic odors may also indicate a system failure or an imminent failure. But such odors may also be produced by defects in the plumbing vent system or other site conditions. Beware, sewer gas contains methane and is explosive if it reaches a dangerous concentration inside a building.

Typical causes range from things that are easy and cheap to repair, to a need for complete system replacement:

• Clogged pipes
• Broken pipes
• Damaged tank
• Tipped distribution box
• Clogged/broken soil absorption piping
• Clogged absorption soils (grease & solids)
• Saturated soil absorption area

However there can also be treatment failures. Effluent may not back up or appear on the surface, but if insufficiently treated effluent reaches a private well or any stream or waterway, the environment is being contaminated -- an unacceptable condition. Historically many people have just worried about disposal. As the quality of drinking water deteriorates in many areas and as population grows in many previously thinly-populated areas, proper treatment has become the real concern for everyone's health.

For example, if there is not sufficient soil between the bottom of the soil absorption system trenches and the local groundwater, the local environment is being contaminated.

FIELD FAILURE CRITERIA - Soil Absorption System Failures: (leach fields, drain fields, seepage pits)

Drainfield life: What destroys or shortens the life of the absorption system?

It's easy to ruin or shorten the life of a drainfield/leaching bed:

• install a drainfield in wet weather (which compacts the soil)
• drive over the drainfield or build a parking lot over it (compacts soil, breaks pipes)
• plant trees on the septic absorption field (roots enter pipes)
• put a swimming pool in the middle of a drainfield - yes I've seen people do this!
• forget to pump out the septic tank regularly (solids/grease are discharged into the fields, clogging the soil)
• direct roof runoff or surface runoff across the drainfield or into the septic tank (flooding the system)
• install the drainfield in an area of high seasonal water tables (flooding the system)
• use the septic system to dispose of illegal oils, chemicals, fats, greases - one system in New York near the Taconic State Parkway was connected to house in which was operated an illegal drug manufacturing operation. So much contaminant was flushed down house drains that the workers contaminated their own well and poisoned themselves
• discharge excessive salts or other chemicals which destroy the The formation, clogging, and measures to protect and extend the life of the biomat is discussed at biomat in the drainfield

Soil Absorption System Failure Criteria

• Breakout of effluent observed (& I consider odors as well)
• BOH evaluation in MA if within 100 ft of surface water supply
• within Zone 1 of a public well
• within 50ft of a private well
• between 50ft and 100ft of a private well if well fails bacteria test.

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The Drainfield: Leaching Bed Soil Condition & Liquid level

The absorption system or "drain field" has two jobs. First, it disposes of liquid effluent by permitting it to seep into the soil below. Second, a "bio-mat" of bacteria which forms in the soil below the drainage field processes pathogens in the septic effluent to make the effluent sufficiently sanitary as to avoid contaminating nearby ground water.

This distinction between successful "disposal" and successful "treatment" is important to avoid groundwater contamination but has not been addressed by regulation in every municipality. Municipalities which require a minimum distance between the bottom of the drain field trenches (or equivalent component) and the top of the seasonal high ground water table have recognized the importance of a working bio-mat and the need to provide adequate dry soil for it to function.

Even in a well-designed drainage field, eventually the soil surrounding the drainfield device (perforated pipe in gravel trench or other seepage system) becomes clogged with grease and debris. Examining an excavated cross-section of a failed drainfield will often display a black or gray band of sludge and grease of about 1" thickness at the inside perimeter of the gravel trench. When this layer of soil becomes sufficiently clogged the passage of effluent into the soil below is slowed and eventually blocked, leading to the need for replacement. Keeping a tank pumped so as to reduce the passage of debris and grease into a drain field will extend its life.

This is the most expensive problem to correct. Look for septic effluent seepage to ground surface in area of equipment or downhill from such equipment. Look for (illegal) drain field line extensions to nearby streams, storm drains, or adjoining properties where the temptation to "fix" a failing system by sending the effluent to an improper destination overwhelmed a previous owner or repair company. In some areas inspectors use septic loading and dye test. Seepage may be due to overloaded tank, failed absorption system, or blocked/broken piping (may be less costly).

An excavator or septic contractor will often explore one or more drain lines (or similar components) by excavating a portion of it to look for evidence of flooding or soil clogging. We've used a simple probe at the end and along a leach bed to check for flooding of that component. (Be careful not to break or collapse old piping.)

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PERC TESTS - Septic Soil Percolation Requirements and Soil Depth Requirements for Septic Absorption Systems / Septic System Drainfields

This chapter is maintained at Soil Percolation Requirements and Soil Depth Requirements for Septic Absorption Systems / Septic System Drainfields but text is repeated here for readers who scroll down rather than linking to the separate chapter.

Perc Tests: What is a septic system soil percolation test?

In specifying the size and type of absorption field (leach field, seepage pits, galleys, other) a septic engineer or health department official will require that a soil percolation test or "perc" test be performed. You may hear it described as a "deep hole test." The first time I participated in this procedure I found myself smiling with surprise at how low-tech the procedure actually was (in New York State.) After identifying the most-likely location on the lot for placement of a septic drainfield, the excavator used a backhoe to dig a rough hole about 5 ft. deep. Happily no groundwater immediately filled in the hole (which would have been bad news).

Perhaps this is why builders try to have this test done in July which is the period of most-dry weather and lowest groundwater table levels. After digging this rough hole, the septic engineer poured a 5-gallon (joint compound) bucket of water into the hole. In some cases a few buckets might be dumped therein.

After that sophisticated move, the observers simply watched the rate at which the water disappeared. a one-inch drop in water level in this hole in three minutes was considered very good. If the water was found still in the hole at no drop in level the next morning, this was considered seriously bad and probably requiring some soil exchange or other special design measures.

What are the soil perc standards> and other soil requirements for septic systems?

I like the Massachusetts Title 5 Septic Inspection criteria for defining a (at least possibly) functional drainfield, as the text explains the role of the biomass below the absorption bed, sets soil depth requirements, and recognizes the importance of keeping the bottom of the working biomass area in well drained soil sufficiently above the seasonal high water table.

Here is an example of soil requirements for a functional drainfield. This version is particularly clearly written and is for residents of Ohio but the principles apply anywhere. "In Ohio, soil absorption systems can be used in areas where the percolation rate of the soil is between 3 and 60 minutes per inch (soil permeability between 1 and 20 inches per hour).

At least 4 feet of suitable soil is required under the soil absorption system to provide adequate treatment of the septic tank effluent. To accommodate the construction of the system and provide adequate soil cover to grade, a minimum of 5 1/2 to 6 1/2 feet of suitable soil is needed above the limiting layer.

A limiting layer may be bedrock, an impervious soil layer (hardpan, fragipan) or a seasonally high water table (gray soil or mottles). The soil absorption system must be at least 8 feet from any drain line on the lot, 50 feet from a water supply, and 10 feet from the property line, right-of-ways and the house. Septic systems cannot be placed on the flood plain and are limited to areas with less than a 15 percent slope." http://ohioline.osu.edu/aex-fact/0743.html Ohio State University Fact Sheet "Septic Tank - Soil Absorption Systems"

Our separate article by Lockwood includes a description of the calculations to answer the question: How Big Should the Leach Field Be? and includes a practical example using sample calculations and a table of soil percolation rate vs. field size

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