AWWA WQTC60720

Under southern and eastern Australian conditions, concentrations and loads of watershed pathogens were evaluated in six systems that spanned a wide range of conditions consisting of fully-protected, open grazing country to semi-rural, intensive (dairy), to on-site septic-impacted. Compared to baseflow pathogen concentrations, historically small rainfall run-off events (1 per mo to 1 in 4 y) increased the concentration of microbial parameters up to four orders of magnitude (i.e. by a factor of 10,000), and the load flux (units of contaminant.sec^-1.unit^-1 area of watershed) by up to seven orders of magnitude. Maximum observed concentrations of contaminants from the most impacted watersheds were ca 1000 Cryptosporidium oocysts.10 L^-1; >100 mpn.100 mL^-1, Campylobacter spp.; 50,000 mpn.100 mL^-1, E. coli/enterococci; and 5000 ng.L^-1, total â-stanols. In contrast, from two fully-protected watersheds almost no pathogens were detected even during event conditions and only E. coli/enterococci increased in some of the major tributaries (unrelated to pathogen occurrence), highlighting the value of watershed protection. Fecal sterol/stanol biomarkers provided evidence of sewage impact during event hydrographs in otherwise herbivore-dominated fecal contamination, which was not evident from the above mentioned microorganism assays, and suggested periods of potential human virus impact. The biomarkers enabled estimates of the equivalent wastewater released from septic tanks to urban streams (ca 500,000 L per day-event). An overall risk assessment matrix was produced that linked watershed development, off-take location and level of run-off event impact. The need to assess watershed pathogen impacts during run-off events can not be overstated, yet few report the hydrological state when sampling for microbiology, and indeed, typically select against such periods to sample. Includes 16 references, tables, figures.