> 1 - e -5Kc In this equation, Ef is the treatment works effluent BOD5. d) K2 = stream reaeration constant; units = 1/day; this constant describes the rate at which atmospheric oxygen diffuses into the water of a flowing stream. Its value depends upon the hydraulic and geometric properties of the stream in question. Many investigators have developed equations to predict K2. The equation given below has been shown to yield results which best fit the field observations of many researchers over a wide variety of stream types: K2 = (110.5H = 0.5832V2)

>
H2
In this equation, "H" is average depth of flow in feet, "V" is
stream average velocity in feet per second, and "S" is the
dimensionless parameter, stream slope, ft./ft. Velocity and
average depth of flow may not be estimated but must be field
measured at the 7-day 10-year low flow stream condition or
computed from field measurements of stream geometry (cross
sections and slopes using ordinary principles of open-channel
hydraulics). Significant changes in stream geometry will change
average velocity and average depth of flow. K2 must be computed
for each stream segment as defined in Appendix C.
e) e = the Naperian logarithm base, dimensionless; e = 2.71828...
f) t = time; units = days.
g) Kn = nitrogenous decay constant; units = 1/day; this constant
describes the rate at which nitrogenous BOD is utilized in a
stream. Its value may be determined experimentally for a specific
effluent and a specific stream. Previous experimental work has
established a range of typical values for Kn of 0.25 to 0.37 per
day with an average of 0.29 per day. It should be noted that the
higher values of Kn yield generally more conservative results when
applied to the Streeter-Phelps Equation.
h) Lan = ultimate nitrogenous demand; units = mg/l; this term may be
calculated, once the initial ammonia nitrogen concentration is
established, by use of the following formula:
Lan = 4.57 (Amm-N concentration in mg/l).
i) tO = nitrogenous lag time; units = days; when a waste contains
both carbonaceous and nitrogenous oxygen demand, there is usually
a time lag before the onset of nitrogenous oxygen demand. The
time lag may typically vary from 0-10 days with its actual value
dependent upon the complex chemical characteristics of the waste
as well as various stream characteristics. The value of tO may be
experimentally determined where effluent or stream field
measurements are practicable. In the case of well nitrified
effluents, the value of t0 may generally be considered to be less
than 1 day. Note that for t less than t0 the nitrogenous term,