I don't know too much about septic, I'm a city dweller. But, from what you said, I wonder if the previous owner before you, just used it for a mountain home, like weekends and stuff and never even had a perk test done for the leech field. You might want to have one done.
Anyway, I found this looking around, thought it might be useful for you......
When you do not have city sewer you need a septic field. You generally do not install a septic field until your land has passed a perk test by the health department. Do not purchase the land on an old perk test unless you have a written statement from the health department in the county you're purchasing in, that the old perk test is valid. Many times the old perk test is out of date because of new laws and it is then invalid. At which point there would need to be a new perk test done. The normal cost on a perk test is about $150 for the county to do their part and an additional $300 or so to get a proper back hoe to the site for the test. On occasion, a hand auger is sufficient to properly analyze the soil types. Most perk tests are valid for a year only.
If the property cannot pass a perk test then your next option is to install an engineered field ( if the county allows it). The problem with an engineered field is the cost. If you do not need an engineered field the normal cost is between $3,000 to $4,000. A reasonable rule of thumb to add to this figure if you need to go to an engineered field is $1,000 for each extra foot you have to go down. To spend a total of $20,000 for an engineered field is somewhat common.
One problem you run across with a septic field is where to put it in relationship to the house location. Make sure your lot is going to be big enough to hold both the size of house you want to build and the septic field also. Just because a certain part of the lot perks does not mean all of the property perks. You have to have a spot perk where you want to put the septic field.