Also, to understand the interrelationship between the test results and the fundamental clay behavior on a microscopic scale, a knowledge of chemistry, physicochemistry, and biology is needed. This working knowledge of chemistry is essential to the actual understanding of a given test result, which quantitatively measures the effect of a particular pore fluid on a specified clay or a clay property. An understanding of this process is essential to the engineering utilization of naturally occurring materials for the containment of hazardous and toxic wastes. Without this knowledge of clay behavior in response to hazardous wastes, any engineering systems design, such as remedial action programs, can have no sound basis on which to project the long-term behavior of that system.