I am sorry I really don't know. A friend had connections and supplied the concrete and labour. I never thought to ask him because I was so busy with the construction of the tank and all my other activities at the time. I can not find that info for the 50k+ either. The walls are 1 foot thick on both tanks. Since I built the 15k in an existing basement (Which has 2 walk outs) I only went 6 inches thick on the floor beacuse the existing floor was also 6 inches thick. The small tank has a lot of glass. There are 75 feet of glass sides on the small tank. Approx 320 square feet of 3/4" glass. The glass in the big tank is 1" thick. NO PROBLEMS YET!!!! The big tank starts its 12th year in 2006 and the small tank its 10th year.