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Let's agree on definitions!

* Onsite systems are susceptible to malfunctions of two main types:

1. functional malfunctions and

2. performance malfunctions.

* A functional malfunction prevents the onsite system from operating as planned or designed.

* Symptoms that might indicate such malfunctions include

-- excessive septage pumping,

-- surface breakout,

-- plumbing backup, and

-- direct discharge.

* Functional malfunctions have implications for public health.

* Performance malfunctions cause the septic system to inadequately treat wastewater.

* 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.

* Performance malfunctions have implications for water quality and possibly for public health.

* The use of the term "septic-system malfunction rate," or sometimes "failure rate," has been inconsistent in the industry and has caused confusion.

* The article proposes the following definitions:

-- Annual malfunction rate is the number of annual 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 one time divided by the number of systems in the study area.

* The annual malfunction rate is a critical component in cost-effectiveness analysis.

* It is a way of stating economic useful life.

* In sewerage systems, treatment plants generally have an economic life of 20 years and sewers of 60 years.

* Sewers can represent 60 percent of the cost of the sewerage system.

* So a weighted average for the useful economic life of sewerage systems is approximately 44 years.

* When the capital cost for onsite systems is similar to that of sewers, the onsite systems need to have an economic life of at least 40 years to be cost-effective.

* When onsite systems are less expensive than sewers, they can have an economic life of less than 40 years and be cost-effective.

* Thus, communities with annual failure rates in the range of 1 to 3 percent per year have economically attractive and sustainable wastewater management systems.

* The percentage of septic systems in malfunction status is an indication of how severe the onsite wastewater situation is in a community.

* If this value exceeds approximately 15 to 20 percent, the community is likely at serious risk from the standpoints of public health, water quality, and economics.

* The authors suggest that in general, the percentage of septic systems in malfunction status should not exceed approximately 5 to 10 percent.
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Title Annotation:Practical Stuff!
Publication:Journal of Environmental Health
Geographic Code:1USA
Date:Nov 1, 2006
Words:406
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