We propose that the Town of Cary acquire an Air-Spade and train a crew to operate it.
The video explains well the mechanics of Air-spade operation. I think the This Old House guys were not focused on anything more than the main problem caused by volcano mulching.
Volcano mulching causes a variety of ills in trees. Of major concern is when the moisture in the mulch causes the tree bark to rot, which allows the inner layer of the tree [the cambium, its circulatory system] to become exposed and infected. A volcano mulched tree will never reach its potential. If it were to die (say) overnight, or within a few weeks or months, the problem would be apparent. But trees have a strong will to live, and can subsist under horrible conditions for long periods. When a concerned citizen consults the landscaper who piled the mulch on the tree and asks the cause of its desiccation and failure to flourish, he/she will be told (a) it was that drought last summer, or (b) it's being attacked by an invasive pest from Madagascar, or (c) it was the hard freeze two years go, or (d) [the best I've heard!], it needs fertilizer so we'll put some on and add more mulch.
The process of volcano mulching is a major problem, not just locally but also nationally and internationally. There are tens of thousands of trees in Cary that are volcano mulched, hundreds of thousands in Wake County, and millions in the state of North Carolina. We bemoan the fact that children today are three times more likely to get asthma and other bronchial diseases as were the children of 30 years ago, yet we do nothing about it. Although we know that polluted air makes us much more likely to suffer from heart disease and hypertension, we believe that "other people" will get those diseases and not us.
Cary's rapidly increasing population adds about six or seven cars a day, every single day, to Cary's roads. We chop down about 450 acres of trees every year for construction, and volcano mulch what we plant back. Let us bring our reason to bear on the point. We need our air cleaned. Nurturing trees is the way to do it. All reputable scientists agree. There is no magic bullet.