Just joined the board and am going to start with a big post.
Purchased a house about a year ago. Originally build back in the 40s (at least), and rebuilt due to fire in 89'. Basement is buried about 6' deep in front. Yard in back is at ground level and slopes away...about 5-8 feet 100 feet away from back door. Front yard is the problem. The frond yard is only about 25 feet to the street. The yard slopes up about 2 feet to the street. There is a drainage ditch next to the street about 2 feet deep that drains okay, but may have some standing water in it after a heavy rain. On the other side of the street there is a deep ditch that has water in it much of the time because its over a foot deeper than the train tube. The neighbors yard on the other side of the street slopes up about 20 feet over about 75 feet. My yard drains well, but probably because it soaks in and then drains towards the house. No noticeable water flowing on the surface towards the house. After a heavy rain and/or long continuous rain the entire front of the basements gets water in. It comes in from the junction of the wall (block) and the floor. I know the water is not coming up from underneath because I installed a sump pump last year and it rarely runs and the pit drains very well. Water is building up in the wall because last year after some good rains I drilled a hole in the block about 6 inches up the wall and water poured out like a hose! The soil in the yard is composed of about 6 inches of top soil and the rest underneath is all red clay.
So, I know that the best fix would be to dig out around the house (not fond of any of the plants so I won't be heartbroken by their loss), waterproof the wall, back fill and install a french drain. After all of the above my question is...how deep do I install the drain? Does it need to be all the way down at the base of the wall or only a foot or two deep? If the water is soaking into the ground through the top soil, flowing along the clay level to the house and then flowing down the wall and/or seeping into the block then I can see a foot or two into the clay will divert the water from getting to the wall. My concern is that it may soak into the clay and moving to the house (if this is actually possible). The first situation makes sense but I would like some advice.