A Field Example of Bacteriophage as Tracers of Fracture Flow

Two bacteriophages, MS-2 and PRD-1, were added to water to an initial concentration of 10⁵−10⁶ pfu mL⁻¹ in a trench-to-trench lateral groundwater flow and tracer migration experiment in the upper 5.5 m of a weathered and fractured clay-rich till. Phage were detected in water from seepage collectors set in the wall of a downgradient (gradient = 0.24) trench, located 4 m from the source trench, between 1 and 2 days after the start of the injection. Peak phage concentrations in the collectors were typically 10²−10⁴ pfu mL⁻¹, and detectable phage (>0.1 pfu mL⁻¹) persisted for up to 5 days. In contrast, the travel time for bromide in the same trenches was several months. The colloidal phage are believed to have moved mainly through fractures with little diffusion into pores of the clay matrix. Phage attenuation was due to inactivation and either attachment to the fracture walls or diffusion into the larger pores. At the temperature of the current experiment (10–12 °C), phage inactivation rates were sufficiently low to permit their use as groundwater tracers over periods of several days.