It depends is this inside or outside if your putting a tank in the ground then you need a company to do that if it's drain pipes flanges ect inside the home then a plumber can do that.
New installs are often done by excavator types...while routine care can be done plumber types
You need in NJ a license to design and install these systems. If your in Lakewood area and have a three bedroom, two and one half bath, expect to spend $80,000 for design, and install for your system. This is exactly why its very important that you pump every three years as suggested, and if your buying a home that it is pumped and checked with camera then load tested. Cost around $800 for this but look at the alternative if its not done correctly.
I know of no plumbers that do this work. There are several engineers however that does this type of work. If you need a few names, contact me via email or call me on number on profile page area.
Depends on your market....in the larger metro areas....septics are handled by specialists. Smaller markets, like where I grew up, plumbers do it all
Chezwhich - I don't trust inspectors that install/repair. Call Bob http://www.rkrutan.com/ He only does inspections - he does not repair or replace - therefore he is honest in his determination. I paid him $500 to inspect the system and then paid $30,000 for a brand new system installed by a very reputable company - the name escapes me at the moment but I can find it if you'd like me too. 4 bedroom 3 bath home. I hope this helps.
Did not know Rutan had a web site. I used him quite a bit when doing septic inspections. Good to know that he has one. I would recommend him highly.
He's a good guy. Let's invite him to HomeTalk.