DIVERSITY - A NEW METHOD FOR EVALUATING SENSITIVITY OF GROUNDWATER TOCONTAMINATION

This study outlines an improved method, DIVERSITY, for delineating and rating groundwater sensitivity. It is an acronym for Dlspersion/VEloc ity-Rated SensitivITY, which is based on an assessment of three aquife r characteristics: recharge potential, flow velocity, and flow directi ons. The primary objective of this method is to produce sensitivity ma ps at the county or state scale that illustrate intrinsic potential fo r contamination of the uppermost aquifer. Such maps can be used for re cognition of aquifer sensitivity and for protection of groundwater qua lity. We suggest that overriding factors that strongly affect one or m ore of the three basic aquifer characteristics may systematically elev ate or lower the sensitivity rating. The basic method employs a three- step procedure: (1) Hydrogeologic settings are delineated on the basis of geology and groundwater recharge/discharge position within a terra ne. (2) A sensitivity envelope or model for each setting is outlined o n a three-component rating graph. (3) Sensitivity ratings derived from the envelope are extrapolated to hydrogeologic setting polygons utili zing overriding and key factors, when appropriate. The three-component sensitivity rating graph employs two logarithmic scales and a relativ e area scale on which measured and estimated values may be plotted. Th e flow velocity scale ranging from 0.01 to more than 10,000 m/d is the keystone of the rating graph. Whenever possible, actual time-of-trave l values are plotted on the velocity scale to bracket the position of a sensitivity envelope. The DIVERSITY method was developed and tested for statewide use in Kentucky, but we believe it is also practical and applicable for use in almost any other area.