AH, HA You assume the operation is legit!! A call to the county health dept can verify this. When I started work at the Health Dept there were a couple pumpers causing serious problems with their dumping. This situation became a health priority and ended with one individual serving a jail term and the other going out of business. Unless you have knowledge otherwise - do not assume the operation is legit. The local health dept should have knowledge of this operation. And yes, in more urban areas it is normal that the "load" be taken to the local sewage treatment facility for processing.
Part of living in the county is and will always be - unusual sewage disposal practices - not previously experienced by urban folks - - large operations raising animals, be it horses, cows, pigs etc and even sewage disposal facilities. All of these practices are legislated to the rural areas by our elected officials because urban folks don't really appreciate the activities.

That is what everyone says......Where should it go? The waste has been tested for pathogens and is likely less harmless than the air you normally breathe. If they are already spreading it, they have waded through mountains of regulations, miles of red tape, and the easiest way to get way from it is to move.
I have a large Hog Farm near me. The world needs food and I would rather catch a faint whiff for 24 hrs once a year than to have neighbors for the other 364 days.
Around here the local septic tank pumpers take the load to be processed at a large waste water treatment plant. It is illegal to "dispose" of it any other way. They are audited and need to show where it came from and where it went.
While I was Director of EH(16 years) in Anchorage we had many pumpers because the majority of the population lived beyond public sewer and our ground conditions were not that favorable for on-site disposal. However, into every life a little sun must shine and in this case its a humorous story - at least it was for us in the health field. One of the large communication companies in Anchorage put their communication sub-stations in below ground "bunkers". And you know whats coming - the above ground entrance looked EXACTLY like a sewer manhole. The cost to the pumping company(beyond their insurance coverage) to affect repairs to that facility put them out of business. Can you imagine the first worker who opened the lid to that communication bunker after 1500 gal of raw sewage had been dumped. I had heard that the pumper exited the scene prior to the communication company arrival but they were to identify the guilty party thru some means. Needless to say, the entrances to below ground communication facilities were immediately & plainly identified.
I have a large Hog Farm near me. The world needs food and I would rather catch a faint whiff for 24 hrs once a year than to have neighbors for the other 364 days.
Jinman,
Domestic residential sewage is difficult to pin down. Normally solids will be only 0.1 to 0.75%(less than one percent) by volume. This is one of the reasons it is costly to treat - so much liquid to solid and once the liquid & solid are mixed the mixture must all receive treatment.
That's Human Bio-Solids ... and I'm almost too close for comfort.
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It's people. Soylent Green is made out of people. They're making our food out of people. Next thing they'll be breeding us like cattle for food. You've gotta tell them. You've gotta tell them!