Table 9.

Reduction times for fecal bacteria in surface waters^a.

Bacterial group	Time for 50% reduction in concentration (days)
Total coliforms	0.9
E. coli	1.5–3
Enterococci	0.9–4
Clostridium perfringens	60 – > 300
Salmonella	0.1–0.67
Shigella	1

^aAdapted from Medema et al. [131].