We moved into a house that the landlord had given up on long time ago. we agreed to repair the house. Being?

inside city limits we assumed that it is city sewage. (bill charges us sewage) but there is a septic system outside on one side of the house and 3 round concrete "things" on the other side of the house. We checked an because we didn't know...the breaker has been turned off since we know of, December. But it could have been off for years. When we flipped the breaker the red light came on. the plumbing seems to be fine. drains well flushes well there is just a horrid sewage smell coming form the house. Now...while we were working in the yard and burning a trash pile, we pulled on the hose pipe to cool it down and busted the pipe. this made the area around the sewage system flood and there was a nasty black spot in the yard with what looked liked leaches crawling around in it. it has been a week now and it has dried up leaving a dead nasty looking ring around the area but we are still having the smells in the house and we are scared to flip back on the breaker because the red light comes on. what can we check before having to call in the"big guns" ??? please help