In the mid 70' s, someone noticed that the ratio of two indicator bacteria in fecal wastes - fecal coliforms (FC) and fecal streptococci (FS) - was characteristic of particular animal wastes. In human wastes, the fecal coliform/fecal streptococci ratio (FC/FS ratio) was greater than 4. In domesticated animals, like cattle, the ratio was between 0.1 and 4.0. In wild animals, the ratio was less than 0.1. Since that time, many attempts have been made to use the ratio to determine the source of fecal bacteria in contaminated ground water.
Coyne, Mark S. and Howell, J. M., "The Fecal Coliform/Fecal Streptococci Ratio (FC/FS) And Water Quality in the Bluegrass Region of Kentucky" (1994). Soil Science News and Views. 34.