9 Failing Septic Systems

The previous sections have outlined the relatively high degree of treatment that properly functioning septic system can provide for many wastewater constituents. Nonetheless, studies have documented impacts on surface water courses at sites where septic systems are in use (Iverson et al., 2018; Withers et al. 2011; Arnscheidt et al., 2007). In most cases, data suggested that the stream impacts were the result of seepage of untreated wastewater from ‘failing’ septic systems. Septic system failure is the term used when wastewater discharged to a drainfield does not percolate into the subsurface, but rather, breaks out onto the surface and drains into a nearby surface water course. This can result from inadequate permeability of the drainfield sediments, from high water table conditions, or from mechanical failures that allow direct hydraulic connection to surface drainage ditches or drain pipes. For example, Withers and others (2011) documented soluble N and P concentrations that were 3 to 12 times higher in a headwater stream in the United Kingdom, at a location immediately downstream from a village where septic systems were in use. The site was on clay rich soils where high water table conditions were present and elevated nutrient values were observed in drainage ditches and pipes that serviced the village. Furthermore, dissolved N occurred primarily as NH₄⁺, rather than as NO₃^–, as would be the case for untreated wastewater leaking from a failing septic system.