Characterizing the Quality of Effluent and Other Contributory Sources During Peak Wet Weather Events

A quantitative microbial risk assessment of wastewater treatment plant blending: case study in San Francisco Bay

“…Weak stratification is conservative because the plume is more likely to surface during these conditions. Comparison of the initial dilution results calculated by each model indicated that they were similar 6 and the dates selected for running the RMA bay model coincide with the conservative assumptions to provide exposure input for the QMRA.…”

“…Table 1 contains a summary of the measured parameters as well as the analytical method and associated sample volume and applicable minimum detection limit. 6 Table 2 contains a summary of the pathogen monitoring results for Giardia spp., Cryptosporidium spp., and adenovirus at a number of plant locations (influent, and primary, secondary effluent and final (disinfected) effluents), and limited data at the outfall. Pathogen data collected in the receiving waters are limited, therefore effluent concentration data were used as input to characterize exposure as part of the receiving water modeling.…”

“…Pathogen concentrations were modeled using an existing San Francisco Bay water quality model (Bay model) developed and maintained by Resource Management Associates (RMA). 6 Input into the water quality model included flow and microbial pathogen concentration field sampling data to characterize treatment plant effluent under blending and non-blending conditions. The model was used to produce a 15 minute interval time-series of concentrations at each of the four exposure sites for a 35 day period from December 1, 2005 to January 5, 2006, when there was most available measured pathogen concentration data.…”

“…To help ensure that decisions regarding wastewater infrastructure improvements to properly manage peak wet weather wastewater flows are optimized based on quantifiable water quality and public health benefits a Water Environment Research Foundation (WERF) funded study was conducted by the East Bay Municipal Utility District (EBMUD) for the collection of additional data on peak wet weather events in San Francisco. 6,7 The WERF investigation evaluated the impacts of blending practices at a municipal wastewater treatment plant on effluent and receiving water quality, and estimated public health risks associated with recreation in surface waters receiving blended flows. Field samples were collected at the EBMUD municipal wastewater treatment plant for inplant processes and receiving waters during wet weather blending and non-blending events.…”

“…As described below, because we found evidence of elevated Giardia and adenovirus concentrations between blending and non-blending periods, the focus of our analysis was on the incremental risk associated with increased concentrations of these pathogens during wet season exposure. Data on the other microbial pathogens and indicators are contained in the final WERF 6 report.…”