COMPARISON OF DRILLING AND MINING AS METHODS FOR OBTAINING MICROBIOLOGICAL SAMPLES FROM THE DEEP SUBSURFACE

Ashfall tuff samples for microbiological analysis were obtained by min ing and drilling within a 400 m deep tunnel system at Rainier Mesa, Ne vada Test Site. Comparison of microbiota revealed that bacteria recove red from the core samples were similar to those recovered from the min ed samples in abundance, diversity, evenness of distribution, and the numbers of distinct colony types. Cluster analyses based on the charac terization of one of each distinct bacterial type from cored and mined samples indicated morphological and physiological similarities betwee n some of the microbiota that were recovered. Drilling fluid microbiot a were more abundant, and were distinct from those recovered from core d or mined samples. Storage of both the mined and cored samples for 1 week at 4 degrees C led to the recovery of increased numbers of cultur able cells, but with decreased diversity. The presence of bromide trac er indicated penetration of drilling fluids into the cored rock sample s, a problem not encountered with mining. However, abundance and diver sity values, and isolate characterization indicate that valuable infor mation can be obtained from cored rock samples.