Optical Properties of Water for Prediction of Wastewater Contamination, Human-Associated Bacteria, and Fecal Indicator Bacteria in Surface Water at Three Watershed Scales

Relations between
spectral absorbance and fluorescence properties
of water and human-associated and fecal indicator bacteria were developed
for facilitating field sensor applications to estimate wastewater
contamination in waterways. Leaking wastewater conveyance infrastructure
commonly contaminates receiving waters. Methods to quantify such contamination
can be time consuming, expensive, and often nonspecific. Human-associated
bacteria are wastewater specific but require discrete sampling and
laboratory analyses, introducing latency. Human sewage has fluorescence
and absorbance properties different than those of natural waters.
To assist real-time field sensor development, this study investigated
optical properties for use as surrogates for human-associated bacteria
to
estimate wastewater prevalence in environmental waters. Three spatial
scales were studied: Eight watershed-scale sites, five subwatershed-scale
sites, and 213 storm sewers and open channels within three small watersheds
(small-scale sites) were sampled (996 total samples) for optical properties,
human-associated bacteria, fecal indicator bacteria, and, for selected
samples, human viruses. Regression analysis indicated that bacteria
concentrations could be estimated by optical properties used in existing
field sensors for watershed and subwatershed scales. Human virus occurrence
increased with modeled human-associated bacteria concentration, providing
confidence in these regressions as surrogates for wastewater contamination.
Adequate regressions were not found for small-scale sites to reliably
estimate bacteria concentrations likely due to inconsistent local
sanitary sewer inputs.