Survival and transport of selected bacterial pathogens and indicator viruses under sandy aquifer conditions

Microbial contamination of groundwater is a serious threat to public health along the US-Mexico border. The survival and transport of two pathogenic 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 the Rio Grande alluvium, which underlies the border between the United States and Mexico. Culturable populations of Salmonella typhimurium declined rapidly ( > 5 log units) to below detection limits within 12 days, while as much as 10(3) CFU/mL of Klebsiella sp. was viable even after 30 days. Less than 1% of the surviving Salmonella sp. population was viable based on microscopic viability assays. The population of both MS-2 and PRD-1 also declined rapidly (> 6 log units) to below detection limits within 10 days. Salmonella sp. exhibited a relatively greater ''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 adsorption within the 0.2 m columns.