I wasn't going to write about this 14 percent thing because I didn't really think it needed explanation to begin with. But, there it is, still out there. Like a thing that exists, because it came out of the mouth of County Commissioner Gary Edwards:
The main thing we need to get to the bottom of is what science brought this about because it has been alleged that 14 percent of septic systems failing each year — that is pure malarkey. That means at the end of a seven-year period we would have had 98 percent of septic system fail, that is pure ludicrous.Basically, there's a fairly good estimate out there that somewhere around 14 percent of septics system are polluting into streams and bays each year. This data, in the case of Thurston County came from an on-site study of septic systems around Henderson Inlet in the late 90s.
What county staff did was put a dye into the septic systems around Henderson Inlet and 14 percent of the tested systems leaked that dye into places where they shouldn't be leaking anything because septic systems shouldn't be polluting. But they did.
What that particular study didn't say is that 14 percent fail each year. Obviously, if you go around and test septic systems at one point in time and finding a failure rate, what you're doing is finding how many septics would be failing at any given point.
Commission Edwards apparently picked up his bad math from Glen Morgan's blog.
What is a little more interesting is that the 1999 study took a look at two places, Henderson Inlet and the Thurston County stretch of the Nisqually reach. The Nisqually reach septics had an even worse failure rate, in the neighborhood of 20 percent.
Morgan took a shot at the 14 percent number by pointing out that repair permits issued by the county indicate that less that one percent of the septics in the Deschutes watershed had failed. That assumes a one to one ratio of permits for repair and actually polluting septics.
But, it would seem that a failing to the point of needing obvious repair and a polluting septic are not the same thing:
Sometimes a (septic) failure is obvious, other times it’s not so obvious and not an easy thing to confirm. When a failure is not obvious but water quality data or other information seems to implicate a system as a problem system, additional measures must be taken.
Dye testing is an effective way to verify a failure, but must be done correctly based on established procedures. Little is more definitive than seeing bright green dye flowing in a backyard or in surface water after passing through a property’s plumbing.Waiting for a homeowner to ask for a permit to repair their septic system is a very low bar to estimate failing septic systems. And, not all backed up or broken septics are polluting. And, certainly, there are septic systems that would work from the point of view of the homeowner but would leach pollutants.
Dye testing, the type of study that the 14 percent number came from, is much more accurate to asses the one thing that we're talking about here, whether a septic system is polluting.