GEOSTATISTICAL ANALYSIS OF REGIONAL HYDRAULIC CONDUCTIVITY VARIATIONSIN THE SNAKE RIVER PLAIN AQUIFER, EASTERN IDAHO

The regional spatial correlation structure of bulk horizontal hydrauli c conductivity (K-b) estimated from published transmissivity data from 79 open boreholes in the fractured basalt aquifer of the eastern Snak e River Plain was analysed with geostatistical methods. The two-dimens ional spatial correlation structure of ln K-b shows a pronounced 4:1 r ange anisotropy, with a maximum correlation range in the north-northwe st-south-southeast direction of about 6 km. The maximum variogram rang e of In K-b is similar to the mean length of flow groups exposed at th e surface, The In K-b range anisotropy is similar to the mean width/le ngth ratio of late Quaternary and Holocene basalt lava flows and the o rientations of the major volcanic structural features on the eastern S nake River Plain, The similarity between in K-b correlation scales and basalt flow dimensions and between basalt flow orientations and corre lation range anisotropy suggests that the spatial distribution of zone s of high hydraulic conductivity may be controlled by the lateral dime nsions, spatial distribution, and interconnection between highly perme able zones which are known to occur between lava flows within flow gro ups. If hydraulic conductivity and lithology are eventually shown to b e cross correlative in this geologic setting, it may be possible to st ochastically simulate hydraulic conductivity distributions, which are conditional on a knowledge of volcanic stratigraphy.