SURVIVAL AND TRANSPORT OF SELECTED BACTERIAL PATHOGENS AND INDICATOR VIRUSES UNDER SANDY AQUIFER CONDITIONS

Microbial contamination of groundwater is a serious threat to public h ealth along the US-Mexico border. The survival and transport of two pa thogenic bacteria (Salmonella typhimurium and Klebsiella sp.) and two indicator viruses (bacteriophages PRD-1 and MS-2), were studied using microcosms to determine the behavior of pathogenic microorganisms in t he Rio Grande alluvium, which underlies the border between the United States and Mexico. Culturable populations of Salmonella typhimurium de clined rapidly ( > 5 log units) to below detection limits within 12 da ys, while as much as 10(3) CFU/mL of Klebsiella sp. was viable even af ter 30 days. Less than 1% of the surviving Salmonella sp. population w as viable based on microscopic viability assays. The population of bot h MS-2 and PRD-1 also declined rapidly (> 6 log units) to below detect ion limits within 10 days. Salmonella sp. exhibited a relatively great er ''straining'' or adsorbtion than the Klebsiella sp. under saturated conditions in a 0.2 m column. Even after flushing with 6 pore volumes , as much a 10(3) CFU/mL of both bacterial genera were obtainable from the columns. Both MS-2 and PRD-1 exhibited little straining or adsorp tion within the 0.2 m columns.