Decentralized Wastewater Treatment Systems

Soil-based septic systems serve between 20-25% of the households in the United States (U.S. Census Bureau, 2007; USEPA, 2008), and about 1.5 million homes in New York (Geisinger and Chartier, 2005). Assuming each house to have 3 bedrooms with a design capacity of 120 gallons per bedroom per day, roughly 540 million gallons of wastewater is treated per day throughout New York through decentralized treatment systems. However, in its report to the U.S. Congress, the United States Environmental Protection Agency (USEPA) stated that onsite septic systems constitute the third most common source of groundwater contamination and that these systems fail due to inappropriate siting, poor design, or inadequate maintenance (USEPA, 1996). The discharge of partially treated sewage from malfunctioning onsite systems was identified by USEPA as a contributor to excess nutrients in ponds, lakes and coastal estuaries; contamination of drinking water and groundwater sources, and a cause of several viral and bacterial illnesses through consumption of drinking water contaminated by failing septic systems (USEPA, 1996a, 2000b). In its follow-up report to the Congress, USEPA stated that “adequately managed decentralized wastewater systems are a cost-effective and long-term option for meeting public health and water quality goals, particularly in less densely populated areas” (USEPA, 1997). Some communities in New York, such as those around Keuka Lake (Herring, 1996), Au Sable Forks (Geisinger, 2005) and others (Allee et al., 2001) have been successfully utilizing onsite systems for wastewater management.

Are they appropriate?

The current paradigm of wastewater treatment is that of being a septic skeptic. Decentralized systems long have been considered to be a temporary solution until centralized collection and treatment infrastructure gets installed. This thought-process may have persisted due to seemingly favorable features offered by centralized systems such as reliability, modern technology, ease of monitoring and regulation, and a better quality product. This paradigm worked because federal and state governments provided funding to small communities that wanted to build small-scale centralized collection and treatment systems. With the reduction in federal and state support, much of the financial burden of supporting centralized infrastructure is falling on small communities. Advances in onsite treatment technologies allow decentralized systems to be built and maintained to protect public health and water quality at costs lower than centralized systems. A lot of the cost savings in decentralized systems come from the elimination of collection systems (pipes that carry wastewater, pumping stations, etc.). In a centralized treatment system, sewage collection costs roughly 60-70 percent of the total system cost. Decentralized systems come in various sizes and forms, and can be adapted for local conditions and community requirements. Depending on the housing density, onsite systems (leach fields, mounds, sand filters, etc.) or cluster systems (septic tank effluent gravity (STEG), septic tank effluent pump (STEP), etc.) may be appropriate. The diagram below shows the appropriateness of decentralized systems based on housing density.

Septic systems failure

Septic systems are not perfect. Like any biological/mechanical system, regular maintenance is required to achieve good performance. USEPA estimates from the 1990s on failure rates across the country vary from less than 5% (Arizona, California, Florida, Maryland, New Hampshire, New York) to 50% or higher (Minnesota, Missouri, West Virginia). More recent data on failure rates show 18% in Delaware (EFC, 2008), 20-24% in Pennsylvania (Day et al., 2008) and 30% of systems in Ohio (ODH, 2008) fail. A study in Erie County, NY estimated the failure rate to be 27% (Irvine et al., 2006). It is to be noted that the definition of failure rate varies across states and many states lack resources to accurately measure failure rates. Several of these numbers are estimates based on secondary information such as repair permits or scaled-up based on localized surveys conducted by county health departments. Septic systems fail due to one or a combination of the following reasons: improper siting in soils with restrictive conditions, under-design, age, and failure to remove excess sludge. Proper siting and design, and periodic removal of sludge can significantly enhance the performance of the septic systems and prolong its operational life. Proper siting of septic systems can offer other economic benefits such an improvement in the value of your property (Vedachalam et al., 2013), reduced health costs and increased tourism and recreation in the region. Regulatory changes at the level of local governments can ensure mandatory creation of responsible management entities (RMEs) that are tasked with regular maintenance and upkeep of these systems. RMEs collect periodic user fees (similar to utility fees paid for wastewater treatment in urban areas) and are, in turn, legally and financially responsible for protecting public health and the environment. For more on RMEs, see English and Yeager (2002). If designed and maintained well, decentralized systems can be a “green” alternative to the traditional sewer network. They keep the water in the same watershed, recharge groundwater, and cost less.

Where to get more specific information?

Cornell Cooperative Extension has extensive reading materials on designing, maintaining, and trouble-shooting septic systems, which can be found here. If you are in New York, you can also talk to someone at your local County Extension Office. See the list of Extension offices here. During Winter 2013, Cornell University, in partnership with local lake associations conducted 4 workshops on septic systems in Otsego and Chautauqua counties. View more information and resources provided during the workshops.

References and additional readings

  • English, C.D., and Yeager, T.E. 2002. Responsible management entities as a methods to ensure decentralized wastewater system viability. Small Flows Quarterly, 3(2):25-35 [pdf].
  • Geisinger, D., and Chartier, G. 2005. Managed onsite/decentralized wastewater systems as long-term solutions. Clearwaters, Fall:6-11 [pdf].
  • Vedachalam, S., Hitzhusen, F.J., and Mancl, K.M. 2013. Economic analysis of poorly sited septic systems: A hedonic pricing approach. Journal of Environmental Planning and Management, 56(3):329-344 [pdf].