speaking from experience
We went through the same thing last year. We did not have the option of going with some of the experimental systems that are currently on the market, as our health department wouldn't approve such systems. We ended up going with a typical mound system which did minimize the space we needed to tear up.
Our lot was actually on a north facing slope. What the engineers did is build the mound into the slope, in an area that was nothing but dying sumac. You wouldn't even know there is a septic system where ours is right now. The septic field is surrounded by woods, and for our size house it was a 60x40 foot area. The mound system is very environmentally friendly. You usually have two tanks and a filter between them, so that what goes to the septic field is more filtered than with a typical system. The mound includes a lot of gravel and sand on top of the regular soil, and all of that filters a great deal out before any water from the septic reaches the existing soil. We were told that you could actually plant small trees on the mound (i.e. we had several people tell us that we could have trees the size of the small sumacs we lost on the mound). We did not risk that, as the expense of replacing the system doesn't seem worth the risk. We ended up planting the mound with native grasses, partridge pea, and native wildflowers.
The first summer was rough because the work didn't finish until July. It was very difficult to get things to grow that first year. This year the whole mound is completely overgrown with purple coneflower, bee balm, partridge pea, cosmos, wild bergamot, black-eyed susans, and much more that I'm sure I'm forgetting. We have deer that sleep there every night, tons of rabbits, and a wide variety of birds that take advantage of all the seeds (including tons of hummingbirds. So I guess my point is that you can make the best of it. We love the space and we feel it's as beneficial now for wildlife as it was before we had to have the work done. Also, because the mound was put back in the woods a way (a pump moves the water from the tanks to the mound), we are one of the only houses in our area that can actually have big trees around the house. Almost everyone else has to have a huge expanse of grass in their front or backyard for a septic field. Additionally, everyone's septic field in our neighborhood has faild and they just don't care. People think a nasty septic smell all summer is just normal! We have lots of clay, and many places where there just isn't much soil, and traditional septic systems just don't work, let alone ones that are 40 years old.
Anyway, we've been very happy with our system. Our contractor was terrible, but they only charged $7000. Believe me, we paid a lot more for that low price though. Our contractor constantly put off doing the work, with every excuse under the sun. They tore up a lot of the yard, getting to where they had to do the work, and never fulfilled half the promises they made (reseeding the mound, reseeding the yard, taking three days to do the job, etc), and we had to constantly bring in the county health department to keep them from cutting corners. As an example, they didn't want to put in a drainage pipe at the bottom of our mound, which is required in our state. They tried to skip installing the filter, which was in our quote, and only did so after I caught that it wasn't installed. We really had to watch them every step of the way. In hindsight, I probably would have paid several thousand more to get a better contractor, but from what I've heard, there are a lot of bad ones, and paying more doesn't guarantee you are going to get any better work.
Oh, and one more note, we do have trees right up to the border of our mound. They had to tear up a slightly bigger area than the mound, so they could work around it. We planted all that area last year. We have white pines, pin oak, swamp white oak, and bald cypress all fairly close to the mound. There is actually only one large main pipe in our septic field, and that pipe is wrapped in fabric so roots can't easil clog the system. That whole setup is laid in gravel and sand, so even with trees nearby, there's less chance of problems than with a typical system.
I have before and after pictures if you are interested, and I'd be happy to answer any other questions you have. It was a real nightmare having the work done, and seeing how much was torn up, but after a year, we really feel like we made the right decision and have a system that will work well for as long as we have the house. My advice though is that whatever you do, ask a ton of questions, work very closely with your health department, make sure you get everything in writing, and make sure you are there to supervise!
