(a) The area of review for an injection well or project will be a fixed radius of one-forth of a mile from the well, field or project.

(b) The zone of endangering influence is the lateral area around the injection well or project in which the injection zone pressures may cause movement of fluid into an underground source of drinking water (USDW) if there are improperly sealed, completed or abandoned wells present. A zone of endangering influence may be determined by EPA through the use of an appropriate formula that addresses the relevant geologic, hydrologic, engineering and operational features of the well, field, or project.