Technical Abstract: Aims: Evaluate the survival of Campylobacter jejuni relative to that of Escherichia coli in groundwater microcosms with variations in nutrient composition. Methods and Results: Studies were conducted in groundwaters and de-ionized water incubated for 400 days at 4 ºC. Samples were taken for culturable and total cell counts, nutrient and molecular analysis. Die-off in groundwater microcosms was between 2.5 and 13 times faster for C. jejuni than for E. coli. Survival of C. jejuni was greatest when DOC (4 mg/L) was high, while E. coli survival was greatest when total dissolved nitrogen (12.0 mg/L) was high. The transition of C. jejuni to the coccoid stage was independent of culturability and was associated with the nutrient composition of the microcosm. Conclusion: Differences in the response of E. coli and C. jejuni to variability in the chemical composition of groundwater sources brings into question the adequacy of using E. coli as an indicator of C. jejuni. Significance and Impact of the Study: Data from these studies will aid in evaluation of the utility of E. coli as an indicator of C. jejuni. This study also provided new information about the effect of nutrient composition on C. jejuni viability and morphological transitions.