being in the excavating business for several years I can tell you getting the right amout of the right type of clay with the correct type of moisture is a very hard thing to do. I have worked on a couple of different race tracks in years past and one thing we did was to put a certain amout of a bio-degradable substance in the water to hold the dust down. Not sure what they use today if anything at all but the stuff we used was legal in California so it should be epa legal everywhere.