The better a soil "percs" (that is, percolates), the less distance needed to filter out the effluent from the septic. This means with better soil, there are two things that make life easier. First you have to buy and to install less pipe. Secondly, in cramped quarters, you have much more choice of where to put stuff. Poorly drained soil may require three times the pipe length that well-drained soil needs and take up three times the space underground. Towns with large amount of poorly-drained soils are understandably fussier on what they require than other Towns. Charleston, the "wettest" town in Montgomery County, for example, simply requires everyone to put in a mound system, effectively dispersing with the need for perc tests.
OK, what is a mound system? This is well-drained soil hauled in and placed in a mound near the septic tank. The leach field runs through it, usually a series of parallel pipes. These things are not huge. One I have in a house I own in the Town of Root is 2' high and probably 16x24'. Urban planners and engineers love them because they don't cause them any problems. I have exactly the opposite attitude. I dislike them. First, they can be unsightly (though, I admit, a inventive person can incorporate them into the landscaping and use them to advantage). Secondly, sometimes you cannot avoid having to pump the effluent from the pipes into the septic. "Pump" implies expense - and eventual repair. Conventional leach fields run by gravity which of course is free and rarely breaks down. Thirdly, mound systems can be expensive. Figure on $10000 to start with and $18000 if everything is wrong. I kind of figure that if you really and truly need a mound, then maybe you have selected the wrong site for your new home. You will be cursed with a lawn that is soggy and wet and a basement which is the same way. There are other reasons for wet basements, but a wet lawn has only one cause - a poor site. But mounds allow one to build in places that were previously considered unbuildable.
How does one do a perc test and isn't it expensive? It's ridiculously easy to do and need not cost a penny. Unfortunately many over-zealous Towns, especially those in over-populated and well-to-do areas, make it expensive by requiring that engineers do the work and that backhoes be brought in to do the digging. The engineers keep one from cheating, but if you are not a low-brow developer and are doing it for yourself, to cheat would only be to cheat yourself. Here's how they are done. You dig a hole that is 2' deep, fill it with water. Then you let the water drain out completely before you fill it again. This time, you measure how long it takes the water level in the hole to drop an inch. Simple. Hardly rocket science or computer engineering. Then you consult a chart, lining up the speed by which it drops with the number of bedrooms in the home and you have the amount of needed leach field. Not hard, and it works.
How about cost of a septic system? I have put in quite a few now, over the years. The first was in 1974 and cost me $1000. Things were easier then. I called a excavation contractor, and he did the rest. Bingo, 4 hours work, and he was done. The next was 20 years later. I was selling the first home that I had rehabbed for resale and had secured a buyer, Harvey. He was poking around after I left for the day. He called me up asking what was that big pipe over by the creek? Could it be the septic? What big pipe? I knew of none. So, I went back over and met him. Hidden in the weeds by the creek was a huge concrete pipe, 18" or so in diameter. It was dry inside and had a thin black streak on the bottom. I have no idea what this was but had this feeling that I wasn't going to like it when I learned. Harvey asked if he could dig in the lawn around it to learn more. Of course, I agreed. The next day, he struck pay dirt. What he discovered was the home's "septic". When I bought the place, I had asked the owner and also the neighbor about the septic. Both gave the same answer. They didn't really know anything about it, other than it always worked, but it wasn't much. It sure wasn't, Harvey discovered. What he found was a small wooden box, covered by rotting 2x4s. The big pipe fed any effluent that did not leach out the sides of this contraption. That pipe fed 15', directly into the creek. My God, people have known for centuries that this was a terrible idea. But there it was. While we were working there, we used the toilet and the water as needed and I could not figure out why that pipe was bone-dry with that much water going through the system. That wooden box worked better than I have ever believed it could. Hurriedly, for a closing was coming soon, I called a contractor. He did the perc test with me, the Code Enforcement Officer told us how many feet of leach field we needed, and $1000 and two days later, it was all done. This one perced far better than the first one I did (if it perced at all- I don't recall that contractor doing any such test).
I have done at least three more since. The most expensive was my own, where I live. That was $3500 and I think I was taken for more than it needed to be. The backhoe guy hauled in load after load of stone to backfill the holes into which the pipe went. I now think the soil he took out would have been well-drained enough to backfill with and that I didn't need no stinkin' stone. It is a little late for that attitude now. But after 10 years of use, we have not had the slightest problem with it. And grass does not even grow greener over it, indicating an excellent dispersal. Along the way, I learned a cheaper way to do septics. You hire the backhoe guy by the hour and buy the parts yourself. Tanks cost less than $400, delivered and set into place. The drain line and a few odds and ends will add another $3-400. That way the contractor cannot take a cut of the materials cost, nor does he have to pad his quote to account for potential lost time and delays.
Take pictures of the process and show in at least one of them the tank in place along with its relation to the home. Don't lose it. They will demonstrate that you put it in correctly. On one installation I did, the Code guy didn't show up to inspect it. We waited a few days, then took the picture, and filled it in - we'd waited long enough. When he eventually got around a week later, he was not too pleased to find it filled in, but I told him that an empty hole was a danger to the neighbor's children and that we also had a schedule to make and could only wait an extra day beyond when he had promised me he'd be back. The picture proved it was done right, so he didn't take it any further. He was fired 2 months later on trumped up charges about using Town stamps to mail personal letters. I never learned the real reason he lost his job. The picture serves another purpose - 10, 20, maybe 30 years later, that tank will have to be pumped. It always eventually happens (in areas where people are anal - and wealthy - they sometimes even require regular pumping, whether or not it is needed). Don't worry, if your tank needs pumping, you will know - everything starts working slowly and, a couple of days later, suddenly stops working at all. Unless there is a woods or a cornfield near, you'll get it done - quick. These things have a way of becoming priorities. But after that 10-30 years, you may not remember just where that tank was located, Or maybe a previous owner did the installation. Out comes the picture you saved and you save having to dig up the yard.
I cannot think of septic tanks without remembering a Garrison Keillor Lake Wobegon routine. It seems the Tom, the town handiman was called by his Aunt Agatha for a plumbing problem one Saturday. Couldn't it wait? His daughter was Homecoming Queen and Tom wanted to share in the festivities. As a matter of fact, his daughter was counting on him showing up for once, to celebrate the big event in her life and he had promised, promised, that he'd be there, no matter what happened. But no, Aunt Agatha insisted, it couldn't wait. So, he trucked out at daybreak only to discover her tank needed pumping. He hurried back home to get his backhoe, came back and dugs it out - only to discover that she never had a tank in the first place. Instead, someone had used a '37 Ford, which had by now rusted out and had collapsed. The hilarious thing here is, yes, we all know that someone, somewhere has tried that very stunt. So, this poor guy loaded it on his trailer to take it to the dump and return with a new tank, knowing all the while that the time before the Homecoming festivities begin is drawing nigh. Tom is in a rush now and, calculating how much time he had left, decided to take a short cut in town, only to find himself in a street blocked off by traffic with police frantically waving at him to back up. But you can't back up a trailer in a narrow street, not one lined with parked cars, especially when your vision is blocked by a rusted '37' Ford that is dripping shit off all sides. And what does he meet coming down the street from the other direction? You guessed it, his daughter in the Homecoming float, surrounded by her Court, every one of which instantly recognized him, his dirty clothes, his truck and filthy trailer with it's dripping load. It ended up predictably, with her totally mortified and a laughingstock as well, her worst fears exceeded. And the entire Homecoming Parade had to back up the street or pull over while he went sheepishly past. Only then could they continue the parade, now driving over a street now decorated with fully ripened human waste. A Homecoming to remember!