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B. Operating Onsite Disposal Systems Management

  1. Establish and implement policies and systems to ensure that existing OSDS are operated and maintained to prevent the discharge of pollutants to the surface of the ground and to the extent practicable reduce the discharge of pollutants into ground waters that are closely hydrologically connected to surface waters. Where necessary to meet these objectives, encourage the reduced use of garbage disposals, encourage the use of low-volume plumbing fixtures, and reduce total phosphorus loadings to the OSDS by 15 percent (if the use of low-level phosphate detergents has not been required or widely adopted by OSDS users). Establish and implement policies that require an OSDS to be repaired, replaced, or modified where the OSDS fails, or threatens or impairs surface waters;

  2. Inspect OSDS at a frequency adequate to ascertain whether OSDS are failing;

  3. Consider replacing or upgrading OSDS to treat influent so that total nitrogen loadings in the effluent are reduced by 50 percent. This provision applies only:

    • where conditions indicate that nitrogen-limited surface waters may be adversely affected by significant ground water nitrogen loadings from OSDS, and

    • where nitrogen loadings from OSDS are delivered to ground water that is closely hydrologically connected to surface water.

1. Applicability

This management measure is intended to be applied by States to all operating OSDS. Under the Coastal Zone Act Reauthorization Amendments of 1990, States are subject to a number of requirements as they develop coastal NPS programs in conformity with this management measure and will have flexibility in doing so. The application of management measures by States is described more fully in Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance, published jointly by the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce. This management measure does not apply to existing conventional OSDS that meet all of the following criteria: (1) treat wastewater from a single family home; (2) are sited where OSDS density is less than or equal to one OSDS per 20 acres; and (3) the OSDS is sited at least 1,250 feet away from surface waters.

2. Description

The purpose of this management measure is to minimize pollutant loadings from operating OSDS. This management measure requires that OSDS be modified, operated, repaired, and maintained to reduce nutrient and pathogen loadings in order to protect and enhance surface waters. In the past, it has been a common practice to site conventional OSDS in coastal areas that have inadequate separation distances to ground water, fractured bedrock, sandy soils, or other conditions that prevent or do not allow adequate treatment of OSDS-generated pollutants. Eutrophication in surface waters has also been attributed to the low nitrogen reductions provided by conventional OSDS designs.

Poorly designed or operating systems can cause ponding of partially treated sewage on the ground that can reach surface waters through runoff. In addition to oxygen-demanding organics and nutrients, these surface sources contain bacteria and viruses that present problems to human health. Viral organisms can persist in temperatures as low as -20 F, suggesting that they may survive over winter in contaminated ice, later becoming available to ground water in the form of snowmelt (Hurst et al., undated). Although ground-water contamination from toxic substances is more often life-threatening, the majority of ground-water-related health complaints are associated with pathogens from septic tank systems (Yates, 1985).

Where development utilizing OSDS has already occurred, States and local governments have a limited capability to reduce OSDS pollutant loadings. One way to reduce the possibility of failed systems is to required scheduled pumpouts and regular maintenance of OSDS. Frequent inspections and proper operation and maintenance are the keys to achieving the most cost-effective OSDS pollutant reductions. Inspections upon resale or change of ownership of properties are also a cost-effective solution to ensure that OSDS are operating properly and meet current standards necessary to protect surface waters from OSDS-generated pollutants. Where phosphorus is a problem, phosphate bans can reduce phosphorus loadings by 14 to 17 percent (USEPA, 1992). Garbage disposal restrictions and low-volume plumbing fixtures can help ensure that conventional systems continue to operate properly. Low-volume plumbing fixtures have been shown to reduce hydraulic loadings to OSDS by 25 percent.

An option for managing and maintaining OSDS is through wastewater management utilities or districts. From a regulatory standpoint, a wastewater management program can reduce water quality degradation and save the time and money a local government or homeowner may spend maintaining and repairing systems. A variety of agencies are taking on the responsibilities of managing OSDS. Water utilities are the leading decentralized wastewater management agency (Dix, 1992). The following case studies illustrate successful wastewater management programs used where there are OSDS.


The Georgetown Divide Public Utility District in California manages water reservoirs, two water treatment plants, an irrigation canal system, and two hydroelectric plants. Approximately 10 percent of the agency's resources are allocated to managing onsite systems in a large subdivision. The utility provides a comprehensive site evaluation program, designs the onsite system for each lot, lays out the system for the contractor, and makes numerous inspections during construction. There is also continued communication between the homeowners and the utility after construction, including scheduled inspections. For the service homeowners pay $12.50 per month for management of single-family systems. Owners of undeveloped lots pay $6.25 per month (Dix, 1992).


In addition to monitoring the operation of septic tank systems, the Stinson Beach County Water District in California monitors ground water, streams, and sensitive aquatic systems that surround the coastal community to detect contamination from OSDS. Routine monitoring has identified people who use straight pipes and failures due to residents using overloaded systems. Homeowners pay a monthly fee of $12.90, in addition to the cost of construction or repair.

3. Management Measure Selection

This management measure was selected to control OSDS-related pollutant loadings to surface waters. Numerous States have implemented inspection requirements at title transfer, low-volume plumbing fixture regulations, garbage disposal prohibitions, and other requirements. Conventional systems are designed to operate over a specified period of time. At the end of the expected life span, replacement is generally necessary. Because failures of conventional systems may occur if systems are not properly designed and maintained, it is essential that programs are established to inspect and correct failing systems and to reduce pollutant loadings, public health problems, and inconveniences. Low-flow plumbing fixture installations and garbage disposal restrictions should be encouraged because as many as 75 percent of all system failures can be attributed to hydraulic overloading (Jarrett et al., 1985). Failure occurs when a system does not provide the level of treatment that is expected from the specific OSDS design.

National and local studies have indicated that conventional OSDS experience a significant rate of failure. Failure rates typically range between 1 and 5 percent per year (De Walle, 1981). In the State of Washington, high failure rates were observed in coastal regions (failure rates in 1971: King County - 6.1 percent; Gray's Harbor - 3.3 percent; and Skasit County - 2.6 percent). It has also been estimated in various soils of Connecticut that 4 percent of conventional OSDS fail per year. The failure rate in coastal areas may be greater because many systems (such as those in North Carolina) are approved for unsuitable soil conditions (Duda and Cromartie, 1982). Jarrett and others (1985) presented suggestions from several researchers describing the possible causes of high OSDS failure rates. These suggestions include:

  • Smearing of trench bottoms during construction;
  • Inadequate absorption areas;
  • Improperly performed percolation tests;
  • Inadequate design;
  • Flooding and high water tables;
  • Improper construction and installation;
  • Inadequate soil permeability; and
  • Use of cleaners and additives.
As stated previously, conventional OSDS do not remove nitrogen effectively and OSDS nitrogen loadings have been linked to degraded surface waters and ground water (Chesapeake Bay Program, 1990).

States should consider replacement with denitrifying OSDS in areas with nitrogen-limited waters. While all OSDS should be inspected periodically (at a recommended interval of once every 3 years) and corrected if failing, requiring that denitrifying systems be installed in all cases where existing systems fail to adequately treat nitrogen was deemed unduly burdensome and impractical.

Refer to the selection statement in the New OSDS Management Measure for additional rationale for selections relating to denitrification, garbage disposals, and low-flow plumbing fixtures.

Phosphorus reductions have been implemented in a number of States (see Table 4-23). Significant reductions in phosphorus loadings (14 to 17 percent) have resulted from such phosphate reductions, with nominal increases in costs for phosphate-free detergents.

4. Practices

As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure described above.

  • a. Perform regular inspections of OSDS.

    As previously stated, the high degree of failure of OSDS necessitates that systems be inspected regularly. This can be accomplished in several ways. Homeowners can serve as monitors if they are educated on how to inspect their own systems. Brochures can be made available to instruct individuals on how to inspect their systems and the steps they need to take if they determine that their OSDS is not functioning properly. Trained inspectors, such as those in Maine, also can aid in identifying failing systems.

    State or local officials should also develop a program for regular inspection. By using utilities and wastewater management programs or agencies, the costs can be kept minimal. At a minimum, systems should be inspected when the ownership of a property is changed. If, prior to the transfer of ownership, the system is found to be deficient, corrective action should be taken. States and localities can also indirectly assess whether OSDS are failing through surface water and ground-water monitoring. If indicator pollutants (e.g., pathogens) are found during the course of monitoring, nearby OSDS should be inspected to determine whether they are the primary source of the indicators. USEPA (1991) has presented a method for tracing effluent from failing septic systems. This method could be followed as part of an indirect inspection program to locate failing systems.

  • b. Perform regular maintenance of OSDS.

    OSDS are not maintenance-free systems. Huang (1983) stated that half of OSDS failures are due to poor operation and maintenance. Most septic tanks are designed so that wastewater is held for 24 hours to allow removal of solids, greases, and fats. Up to 50 percent of the solids retained in the tank decompose naturally by bacterial and chemical action (Mancl and Magette, 1991). However, during normal use, sludge accumulates on the bottom of the tank, leaving less time for the solids in the influent to settle. When little or no settling occurs, the solids move directly to the soil absorption system and may clog (Mancl and Magette, 1991). Consequently, periodic removal of the solids from the tank is necessary to protect the soil absorption system.

    Management options for OSDS maintenance include (NSFCH, 1989):

    • Maintenance via contract;
    • Operating permits;
    • Private management systems; and
    • Local ordinances/utility management.
    Most tanks need to be pumped out every 3 to 5 years; however, several factors need to be considered when determining the frequency of pumping required. These factors include (Mancl and Magette, 1991):

    • Capacity of the tank;
    • Flow of wastewater (based on family size); and
    • Volume of solids in the wastewater (more solids are produced if a garbage disposal is used).
    Failure will not occur immediately if a septic system is not pumped regularly; however, continued neglect will cause the system to fail because the soil absorption system is no longer protected from solids and may need to be replaced (at considerable expense).

    Table 4-24 shows an estimate of how often a septic tank should be pumped based on tank and household size. The Arlington County, Virginia, Chesapeake Bay Preservation Ordinance requires that all septic tanks be pumped at least once every 5 years.

    Alternative OSDS may have maintenance requirements in addition to septic tank pumping. These maintenance requirements are discussed in the descriptions of the systems presented in Management Measure V.A.

  • c. Retrofit or upgrade improperly functioning systems.

    Improperly functioning systems are usually the result of failure of the soil absorption field. Several practices are available to retrofit these failing systems so that they operate properly. The most common reason for failure of the absorption field is hydraulic overload. Jarrett and others (1985) and other researchers have had good success in retrofitting failing systems by combining the construction of backup soil absorption fields with water conservation measures. A backup absorption system is constructed so that water can be diverted from the primary absorption system. The primary system is rested, and in many cases biological activity will unclog the system and aerobic conditions will be restored in the soil. Scheduling is then done to alternate the use of the primary and backup systems (e.g., use of each system 6 months of the year), so that systems in marginally permeable soils can continue to operate properly. Garbage disposals should be eliminated, and low-volume plumbing fixtures should be installed in cases where the absorption field has failed in order to reduce total pollutant and water loads to the field. (Refer to discussion in Management Measure V.A.)

    In some cases, either because of improper siting (e.g., inadequate separation distance, proximity to surface water, poor soil conditions, or lack of land available for a backup absorption system) or the inadequacy of conventional OSDS to remove pollutants of concern, the above retrofit practice may not be feasible. In these cases, alternative OSDS, constructed wetlands, filters, or holding tanks may be necessary to adequately protect surface waters or ground water. Descriptions of these systems and their respective effectiveness and cost are provided in Management Meausre V.A.

  • d. Use denitrification systems where conditions indicate that nitrogen-limited surface waters may be adversely impacted by excessive nitrogen loading.

    As stated previously, even properly functioning conventional OSDS are not effective at removing nitrogen. In areas where nitrogen is a problem pollutant, existing conventional systems should be retrofitted to denitrification OSDS to provide adequate nitrogen removal. Several systems such as sand filters and constructed wetlands have been shown to remove over 50 percent of the total nitrogen from septic tank effluent (see Table 4-21 (31k)). Descriptions of these types of systems and their effectiveness and cost are presented in Management Measure V.A.

  • e. Discourage the use of phosphate in detergents.

    Conventional OSDS are usually very effective at removing phosphorus. However, certain soil conditions, combined with close proximity to sensitive surface waters, can result in phosphorus pollution problems from OSDS. In such cases the use of detergents containing phosphates may need to be discouraged or banned. Low-phosphate detergents are commercially available from a variety of manufacturers with negligible increases in cost. Eliminating phosphates from detergent can reduce phosphorus loads to OSDS by 40 to 50 percent (USEPA, 1980).

  • f. Eliminate the use of garbage disposals.

    As presented in Table 4-22, eliminating the use of garbage disposals can significantly reduce the loading of suspended solids and BOD to OSDS. Total nitrogen and phosphorus loads may also be slightly reduced because of decreased loadings of vegetative matter and foodstuffs. Eliminating garbage disposals can also reduce the buildup of solids in the septic tank and reduce the frequency of pumping required. Reduction of the solids also provides added protection against clogging of the soil absorption system.

  • g. Discourage or ban the use of acid and organic chemical solvent septic system additives.

    Organic solvents used as septic system cleaners are frequently linked to pollution from septic systems. Many brands of septic system cleaning solvents are currently on the market. Makers of these solvents, which often contain halogenated and aromatic hydrocarbons, advertise that they reduce odors, clean, unclog, and generally enhance septic system operations. Manufacturers also advertise that cleaning solvents provide an alternative to periodic pumping of septage from septic tanks. However, there is little evidence indicating that these cleaners perform any of the advertised functions. In fact, their use may actually hinder effective septic system operation by destroying useful bacteria that aid in the degradation of waste, resulting in disrupted treatment activity and the discharge of contaminants.

    In addition, since the organic chemicals in the solvents are highly mobile in the soils and toxic (some are suspected carcinogens), they can easily contaminate ground water and surface waters and threaten public health. Research on the common septic system cleaner constituents (methylene chloride (MC) and 1,1,1-trichloroethane (TCA), which are listed on EPA's priority pollutant list and for which EPA's Office of Drinking Water has issued health advisories) has shown that application rates recommended by the manufacturer have resulted in high MC and moderate TCA discharges to ground water.

    This issue is discussed further in the pollution prevention section.

  • h. Promote proper operation and maintenance of OSDS through public education and outreach programs.

    This practice is discussed in the pollution prevention section (Section VI).

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