Wastewater and Sanitary Sewers


Wastewater treatment and disposal are essential for all new developments. In most urban areas, a system of sanitary sewers conveys wastewater to a “downstream” treatment facility. After treatment, the effluent is either recycled as biosolids (where permitted) or is discharged into surface water or a permeable recharge area for an underground aquifer. Less developed areas use on-site septic systems or package treatment plants. Generally, Americans generate 80–100 gallons of sewage per capita per day (United States Geological Survey).

When analyzing impacts to wastewater treatment/disposal facilities, consider two factors: proximity of the service to the site and capacity of the service to accommodate the project.

Important Considerations

Sewer Systems

  1. What kind of wastewater/sewer system will provide satisfactory service to the proposal?
  2. Does the existing or proposed sewer system have the capacity to adequately service the proposed development?
  3. Will climate change–induced floods increase the risk of combined sewage overflow events? What populations are most exposed to pollution associated with these events?

On-Site Septic Systems

  1. If the sanitary sewers and wastewater disposal systems are non-municipal, have the appropriate authorities and agencies approved or permitted an acceptable system?
  2. Has a report of the soil conditions suitable for on-site septic systems been submitted? Does the report consider the likely impacts of climate change on soil conditions (e.g., increased temperature, increased saturation from heavier precipitation, etc.) that will affect soil treatment efficacy?
  3. Are soil conditions suitable for on-site septic systems? Is there a large variance in the water table elevation? (A high seasonal water table can prevent proper functioning of septic tank drain fields). Is the water table likely to rise significantly due to sea level rise in coastal areas?
  4. Does the septic disposal systems’ design, installation, and maintenance properly prevent effluent from contaminating soil or groundwater, including sole-source aquifers?
  5. How will climate change affect these suitability factors in the foreseeable future? As a rule of thumb, the useful life of the project may be used to set a minimum time horizon for such future considerations.

Analysis Techniques

First, compare the location of the site to municipal services and infrastructure, including the location and design of wastewater and effluent treatment facilities, if any. If the plan involves on-site disposal, determine the potential for groundwater or surface water contamination and identify septic tank feasibility. Estimate the likely water use and the likely volume of waste by looking at the type and density of the development.

Adverse effects are likely if:

  • The estimated sewage generation will exceed the capacity of sewers or treatment facilities
  • The project has an on-site waste disposal system in an area not suited for its use
  • Wastewater could potentially enter environmentally sensitive areas or water resources (e.g., groundwater, surface water)
  • Odors are likely, as they could negatively affect the quality of life of residents and present environmental justice concerns

Positive effects are likely if:

  • The estimated sewage generation is within the existing capacity of the sewers and treatment facilities
  • Stormwater is separated from the sewerage collection system

Additional Considerations

Clean Water Act, as amended (33 U.S.C. 1251 et seq.)

The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. Under the CWA, EPA has implemented pollution control programs such as setting wastewater standards for the industry. EPA has also developed national water quality criteria recommendations for pollutants in surface waters.

The Water Quality Standards Regulation (40 CFR 131)

The Water Quality Standards Regulation (40 CFR 131) establishes requirements for states and tribes to review, revise, and adopt water quality standards pursuant to section 303(c) of the Clean Water Act.

The EPA maintains a clearinghouse of state-specific water quality standards that they have approved. They may also include additional provisions outside the scope of the Clean Water Act. To find additional city water quality standards, it is important to contact the jurisdiction.

Mitigation Measures

The following measures can help mitigate potential problems:

  • Expanding the capacity of sewer lines and treatment facilities
  • Incorporating landscaping elements such as settling ponds or floodable infrastructure into planning
  • Using non-toxic wastewater from standard sinks in toilets or for landscaping purposes (known as grey water) to save water
  • Regionalizing wastewater treatment facilities (especially in small rural communities that may not independently have the financial or infrastructural capacity to have independent treatment systems, but collectively can install the required facilities)
  • Further processing highly treated sewage as biosolids (especially in agricultural areas, where permitted)
  • Using future, rather than historic, high water table projections to select septic system location and/or using a generous vertical distance between leachfield and groundwater table to provide an extra margin of error for potential future conditions

Resources to Reference/Experts to Contact

  • For areas requiring septic systems: the United States Department of Agriculture (USDA) Soil Survey available at the County/Parish USDA Service Center, or online, can help identify areas that are likely to be unsuited for septic systems
  • Engineers at local Sanitary District/Agency, City or County Engineering Department, or 208 Planning Agency
  • Engineers or Planners at local Planning Departments
  • Soils Scientist at U.S. Natural Resources Conservation Service (NRCS)
  • Engineers at State Health or Environmental Quality Agencies
  • Local 208 (Wastewater) Agency
  • Sole Source Aquifers