a surprise under the concrete

We are remodleing a basement bathroom that some previous owner installed. Breaking out the concrete patch in order to move pipes. This is about 3 feet below grade, and 10 feet in from the closest outside wall. The first surprise is that the soil is damp. Not wet, but damp. I kind of expected it to be very dry. the second surprise is tree roots! The closest tree is about 20 feet away, but its roots are here. So I am alarmed but I am unsure about what. Should it be damp there? Should I be looking for a leak? It just smells of earth. If there is a leak, I assume that fixing it will cause the tree to lose interest. If no leak, is there anything I can do short of cutting down the tree? If the pipes are not leaking, I guess I would be in the wrong forum

The company has a reason to be called Roto-Rooter. If you have a leak, the tree roots will find it and will fill the pipe with fine little roots that will plug the pipe. I cleaned out a drain pipe (not sewer) that had 6 ft of matted fine roots filling 2/3 of a 4-inch pipe.

You could have dampness under the floor without a leak. It can seep in from the edge of the foundation, or can percolate up from groundwater. That is why there is often a vapor barrier under the concrete.

You might deal with future growth of existing roots by trenching outside your foundation. Dig down below the footing level, and cut off any roots that are going under the foundation. AFTER you cut them off, you could apply a very strong dose of Round-Up and/or 2-4-D to the fine root system under your floor to try to kill anything that is already there. If you put some down the drain it might kill any roots that are already in your pipe. I'm not sure the Round-Up or 2-4-D will work but I believe in the Shock and Awe principle of attack.

Round-Up and 2-4-D will not do any good. Each of these must be absorbed through the leaves and neither sterilize the soil. You can use Round-Up to kill unwanted plants and plant into that soil a few days later. You can spray Round-Up on tree trunks and not injure the tree. 2-4-D is a broadleaf plant killer, that's the basic chemical used in the Weed-Be-Gone and Weed and Feed. There may be some product that will do what you are after, but it isn't either of these.

roots

I have had innumerable toilets plugged with roots that are growing under the concrete slab and then up through the gap between the toilet pipe and the concrete floor, and finally through the wax ring and down into the toilet pipe. In some cases the toilet is 25 feet from the exterior wall but the roots still knew where to find water.

wow. this is not a problem I ever though of dealing with. Sounds like the best I can do is try to trench on that side of the house, and cross my fingers! I agree about the weed killers, they are systemic. HJ, at least if they are coming up the toilet, they are not cracking the slab--I was worried about that. Thanks for the input.