Question:You mention using clean sand in a lot of your columns. What do you mean when you say “clean sand?” I thought sand was sand. And why is clean sand so important?Answer:Your question is timely, because a series of mound systems have been reported failing in our area recently. Mound systems have had an excellent performance record in my home state, Minnesota, as well as many other states. So it was unusual that a series of mounds should start failing. The interesting fact was all these failing mounds had been installed by the same contractor under a local grant program
