to Andrew Cronell: I had the exact same problem with part of my basement. What I did was dug a trench around the walls of the basement about 12 inches deep and 12 inches wide. Lined it with a filter fabric, put roughly 3 inches of 1 inch gravel in the bottom of the trench, placed a four inch corrigated drain tile along the entire length of the trench and filled it the rest of the way with the gravel. I ran the drain tile into a sump pit that I placed in a corner. Installed a pump and ran a pvc discharge line outside the wooden frame of a basement window. I have not had a drop of water come through the floor since I installed this drain line. As far as cost, Cheap, if you do it yourself. I did mine for about $150. The drain tile comes in 10' lengths and I think I paid about 3or4 bucks a lenght. The sump pit liner was $12. 11/2 tons of 1 inch gravel was $40 delivered. sump pump and hardware ran about $80. However this was very labor intense for me, working in by spare time it took me about 2 months. I worked during the winter months. I was affraid that if I did this during the summer months and it rained, I could run into a real mess if these trenches started filling with water before I had the gravel and drain tiles in place. I can't say this is the best solution to your problem because I am sure every house is different. Before I did this I consulted a contractor and was told that this would work for my situation. As far as how thick is the concrete. I do not know, I have a similar question out there. P.S. A good home Improvement book might give you some ideas. Good luck.