MICROBIAL PATHOGEN AND SURROGATE IDENTIFICATION IN SHALLOW GROUNDWATER AND SPRING COLLECTION SYSTEMS IN YELLOWSTONE NATIONAL PARK FOR IMPROVED GWUDI CLASSIFICATIONS

The US Environmental Protection Agency (EPA) and Yellowstone National Park (YNP) collaborated on a 5-month sampling campaign in 2021. The goal of the effort was to characterize the microbial quality in shallow well and spring water collection systems used to supply drinking water for the park. For the EPA, the study results contributed to an ongoing program to (1) characterize associations between waterborne pathogens and potential microbial surrogate indicators across watersheds with varying degrees of human impaction, and (2) gain additional insight into the quality of a water source serving 39 surrounding communities with populations below 500 in the state of Wyoming. For YNP, the study results provided insight into the quality of source water supplying potable water to more than 180,000 visitor person-days annually. Samples were analyzed for Cryptosporidium, Giardia, E.coli, enterococci, MS2 coliphage, somatic coliphage, total aerobic spores, total coliforms, turbidity, and 2H/1H and 18O/16O stable isotope ratios. Where possible, the study also utilized spring box water levels, temperature, dissolved oxygen, and precipitation data.

The stable isotope readings corresponded with the global and local meteoric water lines, confirming that the sampled groundwaters were derived from geologically recent local precipitation. Highly variable depths in spring boxes correlate with precipitation and water levels in hydraulically linked surface waters. Consistent with the relatively unimpacted nature of the watersheds, all samples tested negative for Cryptosporidium, Giardia, E. coli, enterococci, MS2 coliphage, and somatic coliphage. However, the aerobic spore and total coliform results indicated differences in water quality between shallow wells, spring collectors, and surface waters that are hydraulically linked to the spring collectors. For example, the percentages of samples testing positive for aerobic spores in wells, springs, and associated surface waters were 63%, 96%, and 100%, respectively. Maximum spore counts in those sources were 35, 850, and 2300 SFU/100 mL in wells, springs, and surface waters, respectively. For total coliforms, the percentages of samples testing positive in wells and springs were 20% and 57%, respectively.