Part One, of a two-volume set, this report gives groundwater managers a thorough understanding of aquitards. Utilizing both provides technical guidance for evaluating aquitard integrity and predicting chemical and microbial transport to underlying aquifers. Aquitards, with their low permeability, help protect underlying aquifers and water wells from contamination. The degree of protection provided by an aquitard, or aquitard integrity, depends on types of contaminants, hydrogeology, flow dynamics, and local effects of groundwater pumping. (Part Two ISBN: 1583214992)