The site that I am planning to start my garden, is just down hill from our septic system. We have had loads of rain this season and we have a verry wet line of soil that does not seam to be drying like the rest of the soil. It runs right through my garden. I am concerned that it could be coming from the septic system. Does anyone know how I can check this out myself?

Depending on what kind of septic system you have, it might not be a problem. If you have an aeration unit, consider it extra moisture for the garden and don't worry about it. If you have a regular septic system and it is leaking, it is usually state law that you have to get it fixed. But all septic systems have effluvia that must emerge, usually in liquid form. I would recommend that you plant a row of comfrey between the leakage (if it is just normal septic effluvia) and the garden. If the area is a leach area, then don't put any veggies that are root crops over it unless you have about a three foot raised bed over it, and you should be fine. Be a great place for planting fruit trees if it is the leach area.

I'd agree with brennewoman that it might not be a problem at all. Effluent is meant to flow out of a septic system and if you've had lots of rain your ground is having trouble absorbing the rainwater and the effluent. The question though is if you can detect any unpleasant odor from this wet line of soil. If not I'd say you're fine. If you're planning to start your garden does that mean you're new to this property? If that's so it might take some time to know what your septic system can and cannot handle. Depending on a system's age or whether it's a good design some can't handle a lot of rain plus loads of laundry, many showers, etc.

If you really need peace of mind a dye test can be performed by a septic testing company but if I were you I wouldn't worry about it unless there's unpleaseant smells and I'd also wait some more until it really dries out and see what happens.

The only way to tell for sure is to dig down and look.

The house I recently sold had a similar problem.
We had an engineer come and do the dye test.
Turned out all the wet and water was from surface stream run-off, not our leachfield. But you should get someone to check it out.
What I ended up planting there were red twig dogwoods, ferns, hemlocks and in spring had oodles of daffodils(somehow the bulbs did OK in that area)

If you want to replace your leach lines sooner than expected and loss the trees, that is what will happen if you plant trees over a leach bed. Average lifetime of leach lines is 20 years(this depends on frequency of use, volume, and surrounding soil conditions). Remember, a leach field is made to percolate, and tree roots will infiltrate very easily. You will know when your lines back up into the house or when toilets flush slow. This means that tree roots have entered the leach lines and are preventing the effluent from flowing out of the line into the field. When the flow is slowed, waste water will stand in the sewage line and build up will continue until a blockage occurs. Then the next flush will end up exiting at the lowest point with least resistance. If you have a basement or down stairs toilet, that is where it will exit. There are some trees that will intrude faster than others, such as Willows and River Birches.

Chiming in on the septic issue here, since the first 2 years that we were in our house we had nothing BUT problems whith our septic tank (had to depend on the landlord to fix, and he did a pretty half-a$$ed job). When was the last time your septic tank was pumped out? Turned out that was the majority of our problem...we have a 2-tank system (a 1,000 gallon tank which feeds into a 500 gallon "dry well" that then feeds into the leach field), but NOBODY knew about the "main tank". As soon as we bought the house, we had the septic repair guy start digging until they found out what the problem was. You guessed it, they found the main tank, and it was packed FULL of over 35 years worth of %^^%--they were surprised that it hadn't backed up into the house! Also, when the previous owner put in the sand bed, he never hooked the feeder pipe into the dry well--DUH! Got the main tank pumped, the feeder line hooked up, and haven't had ANY more problems since (and it's been 4 years now). On the septic guy's recommendation, we now get the tank pumped every 2 years for a family of 3. For a larger family, once every 12-18 months should keep things in working order.

Something I forgot to add. Septic tanks are usaully sized by the number of bedrooms a house has. That is with new construction now. Can't speak for older methods and homes, it probably varies from state to state anyway. Around here the recommendation is every 5 years regardless of how many occupants there are. Another reason for failure I forgot to mention earlier was driving heavy loads over the leach field. This will compact the field and even constrict the drain lines.

Let me just chime in here. I bought a new house on two acres two years ago. Last summer, I had that wet spot below the septic tank. I didn't even know what a septic tank looked like or did! Before I knew it, I had the county breathing down my neck and demanding that I put in a new septic tank, so tread very carefully. (I went there for the records on the septic field.) If you go on line, you can look up septic tanks and they tell you all about them. The line to my house was completely jammed and besides, had no drop to speak of....it is a wonder that anything worked. I cleaned out my tank & distribution box, installed a new line from the house to the septic tank with adequate drop or fall and checked out the drain (leach) field...which had never seen the first drop of water. It cost me $1500.
This should have been simple, but after 2 months of haggling with the County Inspectors,I had to get a variance, because the County wanted me to install a new system but nothing perked anywhere but up hill through my NEW hand-dug fish pond and herb garden and would have required a PUMP. This is a septic system which costs $7500 with the electrical work involved as opposed to the $3500 a normal system costs. I got the variance because they'd approved the existing septic system less than one year before! Anyway, as my brother said: "You fool, never call the County unless you have to!"

You are absolutely CORRECT! Always seek your advice elsewhere first before going to the county health dept. Alot of times you might solve the problem for hundreds or thousands less. Once they are involved, they will make an inspection. If it fails they will condemn it and force you by law to make repairs. Then you will have to pay for something, or take a loan you cannot afford.