I wonder what the material is? I am taking the use of concrete mixers as an indication that they encased the chemical in concrete indicating it must be hazardous. What is strange is that they would bury it in Sunni territory?
I think because they trust the Sunnis more than the Shia not to tell the UN inspectors about it. The material must be a weapon grade Chemical material or else they will not do all this to bury and hide it.
From my understanding the Sunnis were Saddam's puppets. They made up most of his Republican Guard and were well subsidized. This is one of the reasons that the bloody insurgency in mostly made up of Sunnis. They had to give up a very cushy life under Saddam.