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formulae are acceptable 38 <br />If a suitable formula indicates that no problem exists, injection could commence without <br />any obligation to repair faulty wells found within the area of review. If it did indicate a problem, <br />however, the well operator would be expected to correct it. Correcting the problem could mean <br />that the well operator would have to plug a faulty well at his/her expense. In other cases, the <br />operator might simply have to modify injection pressure to assure that the rise of fluids caused <br />would not cause fluids to enter an underground source of drinking water. <br />The use of a formula to determine the area of review may not always be feasible. In some <br />instances, necessary information may be lacking. Such formulae also do not have universal <br />applicability: Mathematical formulae, because they are based on ideal conditions (that aquifers <br />are homogeneous, isotropic, and infinite in extent, for example), may not always reflect actual <br />subsurface conditions. Moreover, they assume radial flow in all directions and, in some cases, <br />will not yield a finite distance measurement for well review purposes. <br />Because of these possibilities, the regulations offer a second method for determining the <br />area of review. Directors may use (in lieu of a case by case formula) a fixed radius of one- <br />quarter mile or greater. The Agency selected this minimum radius after consideration of current <br />state practices and after applying it to a randomly selected population of well fields representing <br />various geologic conditions. EPA had considered use of more extensive review requirements, <br />particularly the use of one-half mile radius for area of review computation, but decided-against <br />them because the less rigorous requirement is more cost-effective, and the one-fourth mile radius <br />proved satisfactory in actual applications" In many cases, use of a larger fixed radius would <br />result in duplicative review of the same wells. <br />Moreover, the quarter-mile radius is compatible with coverage practiced in most states. <br />Generally, states impose review requirements on we'll operators in a range of 1000 feet from the <br />injection site up to two miles. EPA's selection of the quarter-mile distance represents its <br />assessment of the effectiveness of these varying requirements in the state programs.ao <br />EPA has modified the area of review requirement for Class II wells 41 Unlike the <br />proposal for wells in Classes I and III, the regulations require that only new Class 11 wells <br />observe area of review requirements. Class H is characterized by large numbers of wells <br />clustered in oil fields. Because new injection wells are interspersed with existing Class II wells, <br />imposing the area of review requirements on new Class II wells should still result in discovery <br />38 § 146.06(a). <br />39 See generally Oil and Gas wells Chapter VIII. <br />90 Preliminary Evaluation of Well Injection Practices. <br />91 § 146.24(a),(2). <br />Page 15 of 20