It's been a few years since I have built any septic systems but I would like to comment on this
thread.
The new laws might say something about the leach field only being 18 inches deep, but I have built them up to three feet deep with no problems.
The anaerobic bacteria do their work in the septic tank, not the leach field. It goes without saying that some would ride the effluent out into the leach field, but they would not last long as they
feed mostly on the solid matter, and need an oxygen free environment in order to live.
Most tanks have two chambers or vaults, the first one catches all the material from the source, there is a pipe connecting the two chambers. The solids settle down into the lower levels of the first chamber, the liquids spill into the second chamber. the outlet pipe is slightly lower than the inflow pipe, this and the inflow pipe have tees on them with a short piece of pipe which extend down into the chamber for a short distance. This keeps anything floating from entering the leach field.
The depth of the leach field is really not that important as it is merely a drain. It carries the black water sans solids out into the leach field area where it is absorbed into the ground.
I am sure there is much new info being passed around about all the evils of nitrogen and how they are doing so much damage, but in my opinion I doubt there is that much leaving the area of the leach field. I have no data that supports that, just my own understanding of how these things work, what I have seen and knowledge from having worked on them.
In my opinion, the high nitrate levels that are of current concern are caused by the constant application of nitrates in the form of chemical fertilizers, and not from septic systems. It goes without saying that nitrate migration occurs from areas where large animal populations are present, such as modern feed lots, but that is something else entirely.
In my opinion, it is the synthetic nitrates that are causing such problems, not drain fields, they just are included in the witch hunt. One study I recently looked at cited Whatcom, Yakima, and Franklin counties here in Washington State, all areas with lots of farming, and virtually all of them using synthetic nitrates, for years and years, and years.
Not sniping at you here Sue, just commenting on what I perceive. The knowledge revolving around this sort of thing is subject to political and personal viewpoints (the kind of viewpoints such as "Ewwww, that stuff is draining into my drinking water!", and "Hey, we can create new laws over this subject!" and really
should be addressed to problems other than drain fields. IF it were draining directly into a water source then yes, there is a valid concern. However, from what I was taught way back when I first had a septic installers license, the water is virtually clean with the exception of any chemical agents present within 100 feet of the leach field. This view may have changed by now, although I don't know why the science regarding that from 25 years ago would have changed that much. I think there is a difference between chemically synthesized nitrates and naturally occurring nitrates, and how they move in the ground.
A properly operating septic system never needs to be pumped out.
I recently read about a "new" discovery where if you set up this "new" kind of system that agitated the effluent in the first chamber of the septic tank (the one where the material first drops into and where the anaerobic bacteria are present) to break up the scum then the tank would never have to be pumped. The point given was that it helps keep the bacteria active, which it would, but which happens anyway in a properly maintained system. In my
experience, if you do not ever flush anything into the septic tank that kills the bacteria, such as most chemical agents, then you don't even need this. It is true that scum forming on top of the effluent inhibits the bacteria, but not really that bad, unless it is accelerated by chemical agents.
I had a bootleg septic system on a piece of property we owned years ago. It was only a five hundred gallon single chamber tank with only 40 feet of single line drain field, it had 6 people on it for about 6 years and I checked it regularly up until we moved and it never built up any scum. Most tanks have to be pumped out in three to five years, this one never even got close.
I think we are constantly fed a bill of goods by the powers that be that we have to change this, do that, rebuild everything or we will all die sort of nonsense. I think it has more to do with money than with a real need.