The use of the term "septic-system malfunction rate," or sometimes "failure rate," has been inconsistent in the industry and has caused confusion. The following discussion proposes definitions for the terms "septic-system malfunction rate" and "percentage of septic systems in malfunctioning status."
Two definitions are proposed:
* Annual malfunction rate is the number of new malfunctioning septic systems divided by the total number of septic systems in the study area during a 12-month period.
* The percentage of septic systems in malfunctioning status is the number of septic systems that are in malfunction condition at any time divided by the number of systems in the study area.
Onsite systems are susceptible to malfunctions of two main types-functional malfunctions and performance-related malfunctions. A functional malfunction prevents the onsite system from operating as planned or designed; the term covers malfunctions that impair the proper functioning of the system. Symptoms that might indicate such malfunctions include
* excessive septage pumping;
* surface breakout;
* plumbing backup--possibly due to plumbing problems, but sometimes to the onsite-system drainfield system; and
* direct discharge.
Functional malfunctions have public health implications. The first three symptoms generally occur when the drainfield has insufficient capacity to treat and transmit wastewater, usually as a result of biomat issues.
Performance malfunctions exist when the septic system inadequately treats wastewater as compared to performance standards. These malfunctions have implications for water quality and possibly public health. Symptoms of such malfunctions include
* excessive nutrient (nitrogen and phosphorous) release to groundwater and surface waters; and
* inadequate bacterial treatment, which may result in bacterial degradation of surface-water and groundwater quality.
There is a significant difference between annual malfunction rate and the percentage of septic systems in malfunction status. Annual malfunction rate, again, is the number of newly failing systems in a 12-month period divided by the total number of systems in the study area. The percentage of systems in malfunction status includes failed systems that have not been repaired as well as newly malfunctioning systems. Systems in malfunction status may not have been repaired for a number of reasons: No onsite solution may be possible (i.e., waiting for an offsite sewer solution), economic...