Monitoring spore washoff during a biological contamination incident response using automated stormwater samplers and sensors to predict contamination movement.

This study examined the washoff of Bacillus globigii (Bg) spores from concrete, asphalt, and grass surfaces by stormwater. Bg is a nonpathogenic surrogate for Bacillus anthracis, which is a biological select agent. Areas (2.74 m × 7.62 m) of concrete, grass, and asphalt were inoculated twice at the field site during the study. Spore concentrations were measured in runoff water after seven rainfall events (1.2-65.4 mm) and complimentary watershed data were collected for soil moisture, depth of water in collection troughs, and rainfall using custom-built telemetry units. An average surface loading of 10 Bg spores/m resulted in peak spore concentrations in runoff water of 102, 260, and 4.1 CFU/mL from asphalt, concrete, and grass surfaces, respectively. Spore concentrations in the stormwater runoff were greatly reduced by the third rain event after both inoculations, but still detectable in some samples. When initial rainfall events occurred longer after the initial inoculation, the spore concentrations (both peak and average) in the runoff were diminished. The study also compared rainfall data from 4 tipping bucket rain gauges and a laser disdrometer and found they performed similarly for values of total rainfall accumulation while the laser disdrometer provided additional information (total storm kinetic energy) useful in comparing the seven different rain events. The soil moisture probes are recommended for assistance in predicting when to sample sites with intermittent runoff. Sampling trough level readings were critical to understanding the dilution factor of the storm event and the age of the sample collected. Collectively the spore and watershed data are useful for emergency responders faced with remediation decisions after a biological agent incident as the results provide insight into what equipment to deploy and that spores may persist in runoff water at quantifiable levels for months. The spore measurements are also a novel dataset for stormwater model parameterization for biological contamination of urban watersheds.