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ATTACHMENT A:AREA OF REVIEW METHODS TABLE A-1 Measured Reservoir Properties 06/08/93 12/04/02 12/03/03 12/14/04 2/8/07 03/28/08 Selected Net Sand Thickness, ft 230 320 320 320 320 320 230 Reservoir Conductivity, 12,500 61,400 66,600 55,300 26,964 56,435 12,500 and-ft Permeability, and 54.4 192 208 173 84 176 54.4 Area of Review The AOR around one or more injection wells is the area of most detailed study related to the Underground Injection Control (UIC) permit(EPA,2002). The primary concern of the UIC program is the potential for injected fluid or poor quality native formation fluids to move from the injection interval due to inadequate confinement or the presence of natural or man- made conduits. Examples of natural conduits include transmissible faults or fractures that penetrate the confining zone. Man-made conduits at this depth are generally wells that may not be properly constructed and/or plugged to prevent movement of fluids from deeper zones to shallower zones. The area of review may be based on a fixed radius around the well,or it may be calculated based on site-specific data. There are three types of evaluations to determine an appropriate area of review: 1. Fixed Radius 2. Volumetric Calculations 3. Pressure Calculations These methods are considered and compared in the following sections. Fixed Radius The fixed radius method is mandated by the U.S. Environmental Protection Agency (EPA) based on experience in a variety of geologic settings. The method does not take into account any site-specific information,but provides a minimum distance to consider when conducting an AOR analysis. In California,EPA Region 9 requires a minimum 1/4-mile distance around the well to be evaluated. This minimum value is compared to calculated values below. Volumetric Calculations A volumetric assessment is a simple method for estimating the area of review (AOR) using site-specific information. This method calculates the area over which a given volume of injected fluid will spread, given total formation thickness and porosity. The methodology assumes that the injection fluid will fill an expanding cylinder moving away from the injection well. It assumes that formation thickness and porosity are uniform. This method A-2 SAC/371322/082550016(ATTACHMENT-A.DOC)