Frack Sand

Looking for any input from people currently hauling or marketing frack sand, either from MN/WI or some of the newer mines in TX. Is it directly contracted from the supplier by the end user? Who brokers the shipping? Are there many companies other than suppliers or end users that put on physical positions? Are larger companies i.e. Halliburton the typical end user or are there smaller players at work? Any idea if the lower quality southern product will be competitve with higher quality northern silica? How much is transported via hopper/pneumatic vs. rail?