3.2C – Construction Practices – Onsite Wastewater Treatment Systems (OWTS)

Management Measure

New Onsite Wastewater Treatment Systems (OWTS)

  1. Ensure that new OWTS are located, designed, installed, operated, inspected, and maintained to prevent the discharge of pollutants to the ground surface, surface waters, and to groundwater:
    • discourage the installation of garbage disposals to reduce hydraulic and nutrient loadings;
    • install low-volume plumbing fixtures in new developments or redevelopments as required by State law;
    • encourage installation of low-volume plumbing fixtures in existing developments; and
    • implement OWTS inspection schedules for pre-construction, construction, post-construction.
  2. Direct placement of OWTS away from unsuitable areas, which include areas:
    • with poorly or excessively drained soils;
    • with shallow water tables or high seasonal water tables;
    • within floodplains; or
    • where nutrient and/or pathogen concentrations in the effluent cannot be sufficiently treated or reduced before the effluent reaches sensitive water bodies.
  3. Establish protective setbacks from surface waters, wetlands, and floodplains for conventional as well as alternative OWTS. The lateral setbacks should be based on soil type, slope, hydrologic factors, and type of OWTS.
  4. Establish protective separation distances between OWTS system components and ground water. The separation distances should be based on soil type, distance to ground water, hydrologic factors, and type of OWTS.
  5. Where conditions indicate that nitrogen-limited surface waters may be adversely affected by excess nitrogen loadings from ground water, prohibit the installation of OWTS or require the installation of OWTS that reduce total nitrogen loadings.

Operation of Onsite Disposal Systems

  1. Reduce total phosphorus loadings to the OWTS by 15 percent (if the use of low-level phosphate detergents has not been required or widely adopted by OWTS users).
  2. Inspect OWTS at a frequency adequate to ascertain whether the OWTS are failing.
  3. Establish and implement policies that require an OWTS to be repaired, replaced, or modified when the OWTS fails or threatens or impairs surface waters.
  4. Consider replacing or upgrading OWTS to treat influent so that total nitrogen loadings in the effluent are reduced to meet water quality objectives. This provision applies only where (a) conditions indicate that nitrogen-limited surface waters may be adversely affected by significant ground water nitrogen loadings from an OWTS, and (b) nitrogen loadings from OWTS are delivered to ground water.

In many cases, when new areas are being developed in rural or urban fringe settings, treatment of sewage is performed onsite at the point of origin (home or business). This type of sewage treatment is particularly needed in areas where development density is low, causing sewerage projects to be prohibitively expensive compared with the number of customers served. Systems for storing and treating small residential and commercial waste streams are called Onsite Disposal Systems, or OWTS. OWTS typically consist of a septic tank for storage and a subsurface soil absorption field (USEPA, 2005).

Buried in the ground, septic tanks are essentially watertight, single- or multiple-chamber sedimentation and anaerobic digestion tanks that treat wastewater flowing through them. They are designed to receive and pretreat domestic wastewater, mediate peak flows, and keep settleable solids, oils, scum, and other floatable material out of the soil absorption field. Wastewater effluent is discharged from the tank and to a series of underground perforated pipes or perforated pipe wrapped in synthetic material. From there, the partially treated effluent flows onto and through the soil. Treatment occurs in the septic tank and within the biomat that forms at the soil infiltrative surface. The treated effluent also receives some treatment as it moves through the underlying soil profiles. Treated effluent that is not drawn into plant roots, incorporated into microbial biomass, or evaporated ultimately reaches ground water and/or surface waters.

Supplemental treatment systems (also known as alternative or innovative systems) such as mound systems, fixed-film contact units, wetlands, aerobic treatment units, and low-pressure drip applications, are used in areas where conventional soil-based systems cannot provide adequate treatment of wastewater effluent due to site constraints (USEPA, 2005). Areas that might not be suitable for conventional systems are those with nearby nutrient-sensitive waters, high densities of existing conventional systems, highly permeable or shallow soils, shallow water tables, large rocks or confining layers, and poorly drained soils. Supplemental systems feature components and processes designed to promote degradation and/or treatment of wastes through biological processes, oxidation/reduction reactions, filtration, evapotranspiration, and other processes. Cluster systems are also used to collect and treat wastewater from multiple facilities. In these systems, wastewater is collected from several locations and passed through a treatment unit (septic tank, lagoon, wetland or other supplemental treatment system) and is released to subsurface soils at a common site. Cluster systems often require individual septic tanks for each facility or home served to provide primary treatment and minimize fat, oil, grease, and solids loading to cluster system treatment unit. (Note: Cluster systems that serve 20 or more people may be regulated by a federal, State, and/or local Underground Injection Control Program for Class V facilities. Get more information.

Management Practices

New OWTS Planning Process

  1. Develop a comprehensive plan that establishes and implements OWTS water quality planning processes, and coordinates with the overall land use planning process with that water quality planning process. Comprehensive planning by the regulatory authority includes measures to protect sensitive areas, such as nutrient-limited waters and shellfish harvest areas. Measures might include prohibitions, setbacks, or requirements for the use of innovative treatment systems to effect greater treatment of sewage. By coordinating water quality planning with land use planning, responsible agencies can more easily address the protection of sensitive areas. Also, responsible agencies can establish basic guidelines on issues regarding where conventional or alternative systems will be allowed, maximum OWTS densities, and consideration of alternative solutions such as the extension of sewer lines for developing areas (USEPA, 2005, 2002).
  2. Performance-based requirements for the sitting, design, and installation of OWTS involves four (A-D) components (USEPA, 2005):
    • A. Develop performance-based programs with specific goals and criteria that address public health and water quality;
    • B. Model system performance to determine the long-term impacts of OWTS on water resources;
    • C. Develop criteria for sitting OWTS, such as setback guidelines and official maps showing areas where conditions are suitable for installation, including the following:
      • Wastewater characterization and expected effluent volumes;
      • Site conditions (e.g., soils, geology, ground water, surface waters, topography, structures, property lines);
      • System capacity, based on estimated peak and average daily flows;
      • Location of tanks and appurtenances;
      • Tank dimensions and construction materials;
      • Supplemental treatment units and configuration;
      • Required absorption field dimensions and materials;
      • Requirements for alternative soil absorption field areas,
      • Sizing and other acceptable features of system piping;
      • Separation distances from other site features;
      • Operation and maintenance requirements (access risers, safety considerations, inspection points); and
      • Monitoring requirements (USEPA, 2002)
    • D. Develop site evaluation procedures to assess site suitability. Evaluation techniques are based on soils, hydrogeology, or multiple factors, such as soils, climate, ground water, OWTS densities, and distance to water resources. The following are procedures for site evaluation (USEPA, 2005; ASTM, 1995; ASTM, 1996):
      • Preliminary documentation (site survey maps, soil surveys, aerial photos, regulations and setbacks, loading rates)
      • Identification of unsuitable areas (water supply separation distances, buffer zones and setbacks, limiting physiographic features)
      • Subsurface investigations (depth to ground water, soil profiles, percolation tests)
      • Identification of recommended OWTS site (data integration, selection of preferred areas, gravity-based flow assessment, final selection).
  3. Inspection of newly installed systems, the OWTS should be inspected at various stages during and after installation. A post-construction inspection program should ensure that systems were installed properly, design specifications were followed, and soil absorption field areas were not compacted during construction. Inspections can be conducted by management personnel or trained/certified inspectors (USEPA, 2005, 1993). If necessary, repairs, replacements, or upgrades should be made to septic systems to meet performance requirements.

    Develop training and certification programs. This practice addresses the need for qualified professional personnel to oversee OWTS design, construction, maintenance, and monitoring. This can be performed through education, training, licensing and/or certifications for site evaluators, installers, designers, and inspectors. Certification and licensing of service providers can help ensure program effectiveness and compliance and reduce administrative burdens. Professional programs are typically the mechanism for certification, and include required coursework or training; an assessment of knowledge, skills, and professional judgment; past experience; and demonstrated competency. Most licensing programs also require attendance at continuing education workshops (USEPA, 2002).

    Inspection and maintenance programs for existing OWTS are useful to help catch systems that are performing poorly. They can be administered through a training program for homeowners, contracts with certified operators, or the management entity itself. System performance can be determined by visual, bacteriological, physical, chemical, and remote monitoring assessment techniques. An effective inspection, monitoring, operation, and maintenance program includes the following (USEPA, 2002):
    • Specified intervals for required inspections (e.g., every 3 months, every 2 years, or at the time of property transfer or change of use)
    • Legal authority to access system components for inspections, monitoring, and maintenance
    • Monitoring of overall operation and performance, including remote sensing and failure reporting for highly mechanical and complex systems
    • Monitoring of receiving environments at compliance boundaries to meet performance requirements
    • Review of system use or flow records, (e.g., water meter readings)
    • Required type and frequency of maintenance for each technology
    • Identification, location, and analysis of system failures
    • Correction schedules for failed systems through retrofits or upgrades
    • Record keeping on systems inspected, results, and recommendations
    In addition to ensuring the proper functioning of the system components, the effectiveness of the system as a whole can be improved through water conservation and pollutant reduction practices. This can be achieved through regulations or public education programs that discourage or prohibit the use of garbage disposals and the disposal of phosphate-containing detergents and household cleaners. Typical public outreach and education programs address the benefits of the onsite management program, water conservation, and household and commercial/industrial hazardous waste discharge prevention; see Management Measure 3.3 for information on education and outreach.

    Guidelines for the disposal of residuals are necessary to ensure proper handling and disposal of sludge (septage) removed from septic tanks. Septage is usually managed via land application, treatment at a wastewater treatment plant, or treatment at a special septage treatment plant. State and local septage management programs that incorporate land application or burial of septage must comply with Title 40 of the U.S. Code of Federal Regulations (CFR), Parts 503 and 257. USEPA has published specific guidance on these topics in the Process Design Manual: Land Application of Sewage Sludge and Domestic Septage.


County health departments generally regulate OWTS, but Regional Boards also have the authority to regulate them. Note that OWTS are prohibited in some areas, such as where receiving waters are nutrient or pathogen sensitive, where there is a high density of existing OWTS, or where geologic conditions prevent adequate treatment of sewage. Check with your county government to determine what types of systems are allowed in your area.

  • California Onsite Wastewater Association (COWA) is an association of industry professional that work in the OWTS field.
  • Marin County Septic Systems Program evaluates and permits onsite sewage systems, as well as gray water systems and septage haulers. The program’s Website contains procedures for conducting performance inspections, fee schedules, background information on septic systems, links to articles with maintenance information for homeowners, and relevant regulations.
  • Stinson Beach County Water District’s Onsite Wastewater Management Program, established in 1978, manages the permitting and inspection of Onsite Disposal Systems and conducts water quality monitoring. The County Water District is responsible for the introduction of special treatment systems designed specifically to address problems with water tables and poor percolation rates.
  • USEPA, Septic Onsite Systems, has developed several documents outlining its mission, priorities and regulatory authorities as well as guidance and technical information to help communities establish comprehensive septic (onsite) management programs.

Information Resources

Homeowner Education

  • Stinson Beach County Water District, Onsite Wastewater Management Program, Homeowner’s Guide this manual provides information for homeowners on septic system function and maintenance, signs of failure, and basic dos and don’ts.
  • Stormwater Manager’s Resource Center, Septic System Controls describes ways to develop a comprehensive management program to reduce pollution from septic systems using public outreach and education, regulatory techniques, and maintenance programs.
  • USEPA, Education and Outreach materials contains a number of activities and tools available below to help raise public awareness and engage interested or affected individuals in the proper management of septic (onsite) wastewater systems.

System Siting and Design

  • San Diego County, Land Use Program Guidelines provides a number of guidance documents pertaining to the sitting, design, and maintenance of OWTS as regulated in San Diego.
  • USEPA, 2002. Onsite Wastewater Treatment and Disposal Systems (OWTS) this design manual provides up-to-date information on OWTS: sitting, design, installation, maintenance, and replacement. It reflects significant advances that the expert community has identified to help OWTSs become more cost-effective and environmentally protective, particularly in small suburban and rural areas.
  • USEPA, Environmental Technology Verification, Water Quality Protection Center has verified technologies in a range of categories, including decentralized wastewater treatment, watershed protection, urban infrastructure rehabilitation, mercury amalgam separation, and on-site residential nutrient reduction.
  • Watersheds: Water, Soil and Hydro-Environmental Decision Support System, Septic Systems describes management practices for OWTS, including alternative treatment technologies such as denitrification systems and regulatory practices such as restrictions on garbage disposals and chemical additives.

Training and Certification Programs

System Inspection, Operation, and Maintenance

Septage/Residual Disposal


American Society for Testing and Materials (ASTM). 1995. Standard Practice for Surface Site Characterization for On-Site Septic Systems. Practice D5879-95e1. American Society for Testing and Materials, Conshohocken, PA.

American Society for Testing and Materials (ASTM). 1996. Standard Practice for Subsurface Site Characterization of Test Pits for On-Site Septic Systems. Practice D5921-96e1. American Society for Testing and Materials, Conshohocken, PA.

USEPA. 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. EPA 840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

USEPA. 2002. Onsite Disposal Systems Manual. EPA/625/R-00/008. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

USEPA. 2005. National Management Measures to Control Nonpoint Source Pollution from Urban Areas. EPA 841-B-05-004. U.S. Environmental Protection Agency, Washington, DC.

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