Joe,
Yeah, that sounds like a lot. Also keep in mind the additional 30% could vary depending on the size of pond and mainly the amount and slope of the shoreline. Larger ponds and lakes may only see an additional 5-15% increase over the water's surface area.
The NRCS used to recommend 1 to 2 lbs per square foot, but in marginal soils, it didn't perform well. The better your soils, the less you have to use. Believe it or not, 6-8 lbs per square foot is just less than 1" thickness.
Then again, shop around and find some land with some good clay topsoil. Even if it's just 3-5 feet of clay on the top, you can stockpile it and come back and line the pond with the good clay without having to use bentonite.
Trent
