Ariz. Admin. Code § R18-9-B612 - Area of Review

A. The area of review for each injection well or each field, project or area of the State shall be determined according to 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.

B. Where the area of review is determined according to the zone of endangering influence:

1. The zone of endangering influence shall be:

a. In the case of application or applications for well permit or permits under R18-9-C616 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 USDW; or

b. In the case of an application for an area permit under R18-9-C624, the project 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 USDW.

2. Computation of the zone of endangering influence may be based upon the parameters listed in the following equation 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.

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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)

h_bo = Observed original hydrostatic head of injection zone (length) measured from the base of the lowermost USDW

h_w = Hydrostatic head of USDW (length) measured from the base of the lowest USDW

S_p G_b = Specific gravity of fluid in the injection zone (dimensionless)

[PI] = 3.142 (dimensionless)

The above equation is based on the following assumptions:

1. The injection zone is homogeneous and isotropic;

2. The injection zone has infinite area extent;

3. The injection well penetrates the entire thickness of the injection zone;

4. The well diameter is infinitesimal compared to "r" when injection time is longer than a few minutes; and

5. The emplacement of fluid into the injection zone creates instantaneous increase in pressure.

C. Where Fixed Radius is used, the following shall apply:

1. In the case of application of applications for well permit or permits under R18-9-C616 a fixed radius around the well of not less than one-quarter mile may be used.

2. In the case of an application for an area permit under R18-9-C624, a fixed radius width of not less than one-quarter mile for circumscribing area may be used.

3. 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.

D. If the area of review is determined by a mathematical model according to subsection (B) of this Section, the permissible radius is the result of such calculation even if it is less than one-fourth mile.

Notes

Ariz. Admin. Code § R18-9-B612

New Section made by final rulemaking at 28 A.A.R. 1903, effective 9/6/2022.