Septic systems, also known as onsite/decentralized wastewater treatment systems and subsurface sewage treatment systems (SSTS), treat sewage from homes and businesses that are not connected to a centralized wastewater treatment plant. Septic systems can vary in size and the number of dwellings served and include individual and cluster SSTS. Septic systems can be of conventional design (heavily relying on the soil for treatment along with dispersal) or use pre-soil treatment technologies like constructed wetlands, media filters, or aerobic treatment tanks followed by dispersal (with limited final treatment) in the soil. Soil treatment and dispersal options include in-ground trenches or beds or above ground at-grade or mound systems. The type of soil dispersal system is chosen based on the treatment abilities of the native soil in combination with the effectiveness of any pre-soil treatment that may be employed. SSTS can be protective of public health and water quality if properly planned, sited, designed, constructed, installed, operated, and maintained.
This fact sheet summarizes a step-by-step approach to developing a community management program for SSTS. It also provides an overview of the five management models outlined in EPA’s Voluntary National Guidelines for Management of Onsite and Clustered (Decentralized) Wastewater Treatment Systems. While this factsheet, based on EPA guidance, provides direction to MS4’s, Minnesota Statutes 115.55 and 115.56, which regulate SSTS, must also be consulted in the development of a comprehensive management program.
Although some management programs are effective, many existing rules that regulate septic systems are not adequate to ensure proper operation and maintenance. Failure of septic systems is a term subject to much debate. Based on local units of government estimates, approximately 10 percent of all systems back up into homes or have wastewater emerging on the ground surface, and approximately 25% of the systems in Minnesota fail to protect groundwater.
Systems may not receive proper maintenance because owners are either unaware of the need for maintenance, or believe it to be unnecessary or too costly. Improper operation and maintenance will result in premature clogging of the soil’s infiltrative surface which may result in system back-up or seepage on the ground surface. Generally improper maintenance does not result in groundwater contamination; improper operation of SSTS (such as the discharge of hazardous waste or other non-treatable wastes into the system) will result in groundwater contamination. The MPCA’s Detailed Assessment of Phosphorus Sources to Minnesota Watersheds has identified a method to quantify the phosphorus discharging from nonconforming or failing septic systems (MPCA, 2004) and could be used by an MS4 to estimate the phosphorus loads coming from local systems.
The study states that throughout Minnesota, failing septic systems have relatively direct connections to surface waters resulting in the increased potential that phosphorus from the systems will contribute to water quality problems and create an imminent threat to public health and safety and the environment. Ultimately, it is the absence of a fully implemented, comprehensive management program addressing each of these issues that limits the reliability and effectiveness of such systems. The potential for health and water quality problems from poorly managed systems is increased.