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

Ashfall tuff samples for microbiological analysis were obtained by mining and drilling within a 400 m deep tunnel system at Rainier Mesa, Nevada Test Site. Comparison of microbiota revealed that bacteria recovered from the core samples were similar to those recovered from the mined samples in abundance, diversity, evenness of distribution, and the numbers of distinct colony types. Cluster analyses based on the characterization of one of each distinct bacterial type from cored and mined samples indicated morphological and physiological similarities between some of the microbiota that were recovered. Drilling fluid microbiota were more abundant, and were distinct from those recovered from cored 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 culturable cells, but with decreased diversity. The presence of bromide tracer indicated penetration of drilling fluids into the cored rock samples, a problem not encountered with mining. However, abundance and diversity values, and isolate characterization indicate that valuable information can be obtained from cored rock samples.