Ill. Admin. Code tit. 35, pt. 378, subpt. C, app A
The first order die-off equation provides a method of estimating fecal coliform die-off in a receiving water as a function of time:
Definition and discussion of terms:
Nt is the predicted concentration of fecal coliform at travel time t downstream; units = #/100 ml.
Nu is the fecal coliform concentration upstream of the source being modeled; units = #/100 ml.
This term will often be negligible relative to the contribution of the source.
No is the fecal coliform concentration in the effluent of the source; units = #/100 ml.
d is the ratio of the receiving water discharge directly upstream of the source to the discharge of the source; no units.
k is the first order die-off rate constant; units = 1/hours. The value of
k can vary as a function of receiving water characteristics, including temperature, exposure to sunlight, and turbidity.
t is the travel time to the point of interest below the source; units = hours.
e = 2.718
Ill. Admin. Code tit. 35, pt. 378, subpt. C, app A