In many cases, the application of in situ technologies evolved as a necessity from a cost perspective. However, the basic understanding of the mechanisms and theory behind these technologies was treated as a "black box." Although we have seen some tremendous successes in the application of remediation technologies over the past several years, we have also seen many cases in which a technology has been incorrectly or inappropriately applied. In most cases, this misapplication has been the result of a poor understanding of the basic concepts and mechanisms behind the technologies. Without proper understanding, the potential for misapplication of technologies remains a serious economic and technical threat.