DTD is currently (May 2011) engaged in a directional sampling project to characterize soil at a Superfund site in eastern Washington state. One interesting development in the project has taken advantage of the extreme flexibility of directional drilling to back up and change the path of a bore during advancement.
When unexpected material was encountered in one of the bores at the site, the DTD team backed up several rods and redirected the bore to lower elevations. In fact, they did it twice! This resulted in the unique opportunity to sample at the same X-Y location, with a vertical separation of about 10 feet between samples (see profile, and click to enlarge). This ability of HDD equipment to navigate, steer, back up, and redirect, provides engineers and scientists with the ability to obtain samples in bore configurations not available through vertical methods.