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Preventing Septic System Failure

Minimum Measure: Illicit Discharge Detection and Elimination

Subcategory: Decentralized Wastewater

Photo Description: Failing septic systems can cause significant water quality problems.
Failing septic systems can cause significant water quality problems. (Source: King County, Washington)


Septic systems treat household wastes in areas without access to public sewers or where a sewer system is not feasible. For example, in a decade more than 80 percent of the land developed in Maryland had been outside the sewer and water "envelope" (MOP, 1991). An estimated 25 percent of the U.S. population rely on onsite wastewater systems to treat and dispose of their household waste. Of that number, about 95 percent of the disposal systems are septic tank systems. The goal of this fact sheet is to prevent new septic systems from failing and to detect and correct existing systems that have been failing.

A failing septic system discharges effluent with pollutant concentrations exceeding established water quality standards. Failure rates for septic systems typically range between 1 and 5 percent each year (De Walle, 1981) but can be much higher in some regions (Schueler, 1999).

A number of factors can cause on-site disposal systems to fail, including unsuitable soil conditions, improper design and installation, and inadequate maintenance practices. Failing septic systems discharge more than one trillion gallons of waste each year to subsurface and surface waters (NSFC, 1995). Such systems contribute significant amounts of pollutants, especially nitrogen and microbiological pathogens. Identifying and eliminating failing septic systems help control untreated wastewater discharges that contaminate ground and surface water supplies.


Conventional septic systems are used throughout the United States. They are the wastewater treatment method most commonly selected for areas without public sewer systems and treatment plants. In areas without sewer systems, a number of factors should be examined to determine if conventional septic systems are the right treatment choice. The first is the size of the lot where the system is installed. Conventional septic systems have a relatively large lot-size requirement to allow for uniform effluent distribution across the drainfield. A second factor is the region's soil type. Soil type influences the ability of the soil to purify effluent and to allow the effluent to percolate. Other conditions that can affect septic system applicability include separation distance from the water table and bedrock, topography, flooding frequency, density of development, and distance to streams or shorelines.

Siting and Design Considerations

To prevent septic system failure, ensure that new systems are properly sited and sized, and employing appropriate treatment technology. Septic systems should be located to ensure an adequate horizontal distance from surface waters and vertical separation from ground water. States or regions determine the vertical and horizontal setback requirements for soil absorption fields located near building foundations, property boundaries, water supply wells, and other surface waters. Distances between septic system components and man-made or natural water supplies will vary according to local site factors, such as soil percolation rate, grain size, and depth to water table. Individual site assessment conducted prior to installation is the best way to determine siting distances needed for efficient on-site wastewater disposal.

To avoid hydraulic overloading, it's necessary to properly size a system. Overloading can cause system back ups or force waste through the septic tank before it receives adequate treatment (Perkins, 1989). Overloading can create anaerobic conditions in the drainfield, and it might not give solids time to settle out before being pushed through the system.

In some cases, it may be necessary to modify a septic system to ensure proper treatment of wastewater discharges. Septic drainfields must be enlarged where soil permeability is low, steep slopes are present, or where increases in daily sewage flow are expected. Limiting factors such as inadequate lot size, limited separation distances, and the presence of problem pollutants like nitrogen may require alternative on-site disposal systems, such as mound or re-circulating sand filters. Selecting the right system to handle site-specific problems will decrease the likelihood of septic failure. Systems can be designed to control pollutants like nitrogen and phosphorus (de-nitrification systems or aquaculture systems) or as retrofits for conventional systems inadequately sited or sized (alternating bed system, mound system, pressure distribution (low-pressure pipe) system, sand filter system, or constructed wetlands).

Proper siting and postconstruction inspection will help prevent new systems from failing, but planning for existing systems is also needed. A septic system management program of scheduled pumpouts and regular maintenance is the best way to reduce the possibility of failure for currently operating systems. A number of agencies have taken on the responsibility for managing septic systems. Table 1 provides some examples of programs and how they seek to control system failures.

Table 1: Examples of septic system management programs (Sources: CWP, 1995; USEPA, 1993)

Georgetown Divide Public Utilities (CA)

  • Approximately 10% of agency's resources are allocated to septic system management
  • Provides comprehensive site evaluation and septic system design, and makes inspections during construction
  • Conducts scheduled post-construction inspections
  • Homeowners pay $12.50 per month for services

Stinson Beach County Water District (CA)

  • Monitors septic system operation to identify failures
  • Detects contamination of ground water, streams, and sensitive aquatic systems from septic systems
  • Homeowners pay $12.90 per month, plus cost of construction or repair

Puget Sound Water Quality Authority (WA)

  • Member jurisdictions have established revolving loan funds to provide low-interest loans for repair of failing septic systems

Chesterfield County (VA)

  • Private pumpers submit form to county, and county maintains database of tracking pumpout
  • Every 5 years county sends residents notification for pumpout requirement
  • County contracts to have pumpout performed if owner does not comply and can fine or back-charge to owner.

Programs addressing failing septic systems should consider field screening to pinpoint areas warrenting more detailed on-site inspection surveys. There are many references available that discuss field screening techniques for identifying sources of contamination (Lalor and Pitt, 1999; Center for Watershed Protection, 1999).

Odors, surface pooling, and isolated patches of green grass sprouting out of season are common indicators of a failing septic system. Simple field tests can help locate illicit discharges. For example, excess ammonia indicates anaerobic conditions. Fecal coliform and laundry detergent chemicals indicate an inadequate or failing system (Cox, personal communication, 2000).

Two field screening techniques capable of identifying the locations of failing septic systems are the brightener test and color infrared (CIR) aerial photography. The first uses specific phosphorus-based elements found in many laundry products. Often called brighteners, they indicate the presence of failing on-site wastewater systems. The second technique uses color infrared (CIR) aerial photography to characterize septic system performance. This method quickly and cost-effectively assesses the potential effects of failing systems. It uses variations in vegetative growth or stress patterns over septic system field lines to identify potentially malfunctioning systems. A detailed on-site visual and physical inspection will confirm if the system has failed and determine the extent of the repairs needed. County health departments or other authorized personnel may carry out such inspections.

The EPA has created a website that describes steps that can be taken after a system has failed [].


Septic systems can affect ground and surface water quality in several ways. Failing systems or systems improperly located can discharge inadequately treated sewage. Sewage can run off into surface waters. Sewage can contaminate water supply wells if vertical distances from ground water are insufficient. Wastewater and sewage discharged from failing on-site systems contain bacteria and viruses that can endanger human health and harm aquatic organisms. Additionally, excess nitrogen and phosphorus can cause oxygen-reducing algal blooms that prevent sunlight from reaching submerged aquatic vegetation.

Failing or overtaxed systems also create economic effects. Beach and shellfish bed closures affect tourism and the vitality of local businesses that rely on fishing and seafood. Additionally, economics also affect the repair of failing systems. Septic owners may not have adequate funding to install new systems.

Reliance on individual on-site inspections to detect failed systems is another major limitation. Individual on-site inspections are labor-intensive and require access to private property to pinpoint the location of failing systems. Property owners might be reluctant to provide this access, and an ordinance mandating inspection authority may be required. A number of communities have dealt with access issues by using an ordinance requiring inspection at time of property transfer to pinpoint systems requiring repairs. An example of this type of ordinance is available at the Center for Watershed Protection Exit EPA Site website in the illicit discharge category.

Perhaps the biggest limitation to correcting failing septic systems is the lack of techniques for detecting individual failed systems. While visual inspections and dye testing can locate a malfunctioning system, they require access to private property and demand staff time. Dealing with failing septic systems requires a stronger emphasis on developing screening techniques that local governments can use to detect and correct improperly operating systems.

In many urbanized areas, replacing septic systems is impossible due to site limitations. Municipalities should consider eliminating septic system discharges to MS4 sanitary sewers.

Maintenance Considerations

Periodic maintenance of on-site systems ensures their proper functioning. Since many homeowners do not employ routine maintenance practices, it may be necessary for agencies to establish programs to track pumpout and maintenance requirements. The programs in Table 1 include maintenance tracking as part of their plans.


The effectiveness of septic systems at removing pollutants from wastewater depends on the type of system used and the conditions at the site. Even a properly operating septic system can release more than 10 pounds of nitrogen per person per year to ground water (Matuszeski, 1997). Table 2 provides an overview of the average effectiveness of seven types of on-site systems at removing total suspended solids (TSS), biological oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), and pathogens. Table 2 shows that even properly operating conventional septic systems can have relatively low nutrient removal capability and can be a cause of eutrophication in lakes and coastal areas. Communities may elect to require new septic systems to use more advanced treatment technologies to address concerns regarding pollutant loads from improperly functioning systems.

Table 2. Average effectiveness of on-site disposal systems (total system reductions) (Source: USEPA, 1993)

Disposal practice

TSS (%)

BOD (%)

TN (%)

TP (%)

Pathogens (Logs)

Conventional System






Mound System






Anaerobic Upflow Filter






Intermittent Sand Filter






Recirculating Sand Filter






Water Separation System






Constructed Wetlands






Cost Considerations

Once a failing septic system has been identified, procedures must be in place to replace it. Replacing a septic system typically costs between $3,000 and $7,000 per unit (NSFC, 1999), but costs vary significantly depending on site conditions and geographic location. Various methods have been used to finance septic system replacement, including money from state revolving funds or from local utilities through user fees.

The costs associated with detecting and correcting septic system failures are subject to several factors, including availability of trained personnel, cost of materials, and the level of follow-up required to fix system problems. The Mason County, Washington, Department of Health Services has conducted on-site sewage inspections for a number of years and has found that dye tests, while reasonably affordable, were too costly to conduct on a regular basis. The estimated cost for each dye test survey conducted was $290 dollars, and the cost for each visual inspection was $95 (Glasoe and Tompkins, 1996). The causes of most system failure were found to be relatively easy and inexpensive to repair, and the cost to oversee the repairs was estimated to be $285.

The costs of various technologies available for on-site wastewater treatment vary widely. Table 3 provides both capital and maintenance costs for seven different on-site disposal systems. The installation cost for alternative systems may be higher due to variables such as requirements for additional system equipment and the cost of permit approval for the system. Differences in maintenance costs may be due to factors such as increased demand for replacement of treatment media and the lack of available personnel with training in maintenance of alternative systems.

Table 3. Cost of on-site disposal systems (Source: USEPA, 1993)

Disposal Practice

Capital Cost ($/House)

Maintenance ($/Year)

Conventional System



Mound System



Anaerobic Upflow Filter



Intermittent Sand Filter



Recirculating Sand Filter



Water Separation System



Constructed Wetlands




Center for Watershed Protection. 1999. Resources for Detecting Bacterial Sources. Watershed Protection Techniques 3(1).

De Walle, F.B. 1981. Failure Analysis of Large Septic Tank Systems. Journal of Environmental Engineering. American Society of Civil Engineers.

Glasoe, S. and M. Tompkins. 1996. Sanitary Surveys in Mason County. Puget Sound Water Quality Authority, Puget Sound Notes Number 39, June 1996.

Lalor, M. and R. Pitt. 1999. Use of Tracers to Identify Sources of Contamination in Dry Weather Flow. Watershed Protection Techniques 3(1), April, 1999.

Maryland Office of Planning. 1991. Maryland's Land: 1973-1990, A Changing Resource. Maryland Office of Planning, Baltimore, MD

National Small Flows Clearinghouse (NSFC). Summer 1995. Pipeline. Vol. 6, No. 3.

Perkins, Richard. 1989. Onsite Wastewater Disposal. Lewis Publishers, Inc., Chelsea, MI.

Sagona, Frank. 1986 Monitoring and Planning for Onsite Wastewater Disposal Along TVA Reservoirs. Lake and Reservoir Management: Volume II, 1986. North American Lake Management Society, Madison, WI.

Sagona, Frank. 1988. Color Infrared Aerial Surveys of Septic Systems in the Tennessee Valley Region. Tennessee Valley Authority, Water Quality Branch, Chattanooga, TN.

Texas Water Resource Institute. 1997. Brazos River Authority Uses "Bright" Idea to Search for Failing On-Site Wastewater Systems. Texas Water Resources Institute, Texas A&M University, College Station, TX.

USEPA. 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

USEPA. No date. Septic Systems. U.S. Environmental Protection Agency, Office of Wastewater Management. []. Accessed May 4, 2006.


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Last updated on May 24, 2006