[Code of Federal Regulations]
[Title 40, Volume 21]
[Revised as of July 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR146.6]

[Page 704-705]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 146_UNDERGROUND INJECTION CONTROL PROGRAM: CRITERIA AND STANDARDS
--Table of Contents
 
                      Subpart A_General Provisions
 
Sec. 146.6  Area of review.

    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.
    (a) Zone of endangering influence. (1) The zone of endangering 
influence shall be:
    (i) In the case of application(s) for well permit(s) under Sec. 
122.38 that area the radius of which is the lateral distance in which 
the pressures in the injection zone may cause the migration of the 
injection and/or formation fluid into an underground source of drinking 
water; or
    (ii) In the case of an application for an area permit under Sec. 
122.39, the proj ect area plus a circumscribing area the width of which 
is the lateral distance from the perimeter of the project area, in which 
the pressures in the injection zone may cause the migration of the 
injection and/or formation fluid into an underground source of drinking 
water.
    (2) Computation of the zone of endangering influence may be based 
upon the parameters listed below and should be calculated for an 
injection time period equal to the expected life of the injection well 
or pattern. The following modified Theis equation illustrates one form 
which the mathematical model may take.
[GRAPHIC] [TIFF OMITTED] TC15NO91.140


where:
[GRAPHIC] [TIFF OMITTED] TC15NO91.141

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:
    (i) The injection zone is homogenous and isotropic;
    (ii) The injection zone has infinite area extent;
    (iii) The injection well penetrates the entire thickness of the 
injection zone;
    (iv) The well diameter is infinitesimal compared to ``r'' when 
injection time is longer than a few minutes; and
    (v) The emplacement of fluid into the injection zone creates 
instantaneous increase in pressure.
    (b) Fixed radius. (1) In the case of application(s) for well 
permit(s) under Sec. 122.38 a fixed radius around the well of not less 
than one-fourth (\1/4\) mile may be used.
    (2) In the case of an application for an area permit under Sec. 
122.39 a fixed width of not less than one-fourth (\1/4\) mile for the 
circumscribing area may be used.

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

[[Page 705]]

dependence; and historical practices in the area.
    (c) If the area of review is determined by a mathematical model 
pursuant to paragraph (a) of this section, the permissible radius is the 
result of such calculation even if it is less than one-fourth (\1/4\) 
mile.

[45 FR 42500, June 24, 1980, as amended at 46 FR 43161, Aug. 27, 1981; 
47 FR 4999, Feb. 3, 1982]