Is it good for ground level water to go into septic tank?

not really as septic tanks are designed to separate solids and liquids. they are then connected by a pipe to a leech field which deals with the liquids.... so if ground water runs in, it could saturate the leech field such that it QUITS leeching-and now you have stinky mess rolling out the top of the septic tank. Even a running toilet is a big concern for the same reason.