The area of review for each injection well or each field, project or area of the State shall be determined according to either paragraph (a) or (b) of this section. The Director may solicit input from the owners or operators of injection wells within the State as to which method is most appropriate for each geographic area or field.
where:
r = Radius of endangering influence from injection well (length)
k = Hydraulic conductivity of the injection zone (length/time)
H = Thickness of the injection zone (length)
t = Time of injection (time)
S = Storage coefficient (dimensionless)
Q = Injection rate (volume/time)
hbo = Observed original hydrostatic head of injection zone (length) measured from the base of the lowermost underground source of drinking water
hw = Hydrostatic head of underground source of drinking water (length) measured from the base of the lowest underground source of drinking water
Sp Gb = Specific gravity of fluid in the injection zone (dimensionless)
[PI] = 3.142 (dimensionless)
The above equation is based on the following assumptions:
In determining the fixed radius, the following factors shall be taken into consideration: Chemistry of injected and formation fluids; hydrogeology; population and ground-water use and dependence; and historical practices in the area.
40 C.F.R. §146.6