BACTERIAL TRANSPORT IN VOLCANIC TUFF CORES UNDER SATURATED FLOW CONDITIONS

An antibiotic-resistant bacterium was rested for transport through vol canic tuff and sandstone cores. Tuff Scores were representative of the geology of Rainier Mesa located on the Nevada Test Sire (NTS). Rapid bacterial transport occurred in some of the tuff cores and all sandsto ne cores under the hydraulic heads used (5-500 cm). Hydraulic conducti vity of the tuff cores ranged widely, 9.6 x 10(-5) to 1.2 x 10(-3) cm h(-1). A much narrower range was observed for sandstone cores, 1.6 x 1 0(-2) to 5.9 x 10(-2) cm h(-1), which served as experimental controls. The percentage of the initial bacterial inoculum recovered within 3 p ore volumes from tuff and sandstone cores ranged from 9.4 to 54.7% and 0.20 to 2.9%, respectively. Bacterial recovery appeared to be control led by the structure of the flow paths in rock cores and not by overal l hydraulic conductivity. Saturated clay-infiltrated and unfractured z eolitized tuff cores were impermeable to wave flow, and therefore bact erial transport was not detected. Three routes of bacterial transport were discerned in permeable rock cores by comparison of the breakthrou gh patterns of bacteria and tracer solution (chloride ions) in cores o f differing lithologies. In sandstone cores, where water flowed evenly through the matrix, bacteria were transported in a dispersed manner t hroughout the sandstone, whereas bacteria were transported primarily a long preferred flow paths (fractures or macropores) in permeable tuff cores.