(This will only be of interest to people installing or repairing septic systems.)
I retired from publishing info on onsite wastewater disposal with a recent article in Mother Earth News, but I’m still interested in the state of the art. Today I talked to Simon Cartwright, who works for Orenco (at an adjacent booth), the country’s foremost manufacturer of septic tank pumps, tanks, and related hardware. He says that typically, in 80% of cases, the soil takes care of pathogens and nitrates, meaning that a conventional gravity-powered tank and leachfield will suffice. But for the other 20%, a more advanced system is necessary. Most commonly in recent years, this has consisted of the “mound system,” an expensive and ecologically disruptive method of treatment. Simon adds that with respect to the 80/20 ratio, soil differs from one county to another and you need to check with local officials.
Orenco has come up with the Advantex system, which replaces the the mound with a treatment box with a footprint smaller than a 4 x 8 sheet of plywood. From the box (adjacent to the tank), Orenco prefers that the treated effluent flow into a shallow gravel-less leachfield. Simon: “10-12″ of soil is where all the action happens.” You dig a 10-12″ ditch with a shovel, lay a piece of pressure pipe (with 1/8″ holes drilled every 2 feet) on the ground. You cover the pressure pipe with a 6″ chamber of half-pipe (created by band-sawing a 12″ piece of plastic pipe in half); this provides an air chamber above the pressure pipe. Then you backfill with soil. You can check out details on Orenco’s website https://www.orenco.com/
The Advantex system has by now been approved in many parts of the country, but for some strange reason, health officials in certain areas have OK’d dispersal via drip systems (great as long as they don’t eventually clog), but not dispersal in shallow gravel-less leachfields. Doesn’t make sense to me, since the nitrates and pathogens of the effluent have already been treated to a very high level.