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PATHWAY 1 - MIGRATION OF FLUIDS THROUGH A FAULTY INJECTION <br />WELL CASING <br />The casing of a well can serve a variety of purposes. It supports the well bore to prevent <br />collapse of the hole and consequent loss of the well, serves as the conductor of injected fluids <br />from the land surface to the intended injection zone, and supports other components of the well. <br />If a well casing is defective, injected fluids may leak through it. Such migration can contaminate <br />an underground source of drinking water.10 <br />To prevent migration of fluids in this manner, the promulgated regulations require that <br />wells in Class I use casing sufficient to prevent the movement of fluids into any underground <br />source of drinking water. Casing requirements for Class II and III wells are different and are <br />discussed in more detail below." The impact of this standard should vary on a well-by-well <br />basis. In some instances, injection wells would only need a minimal surface casing to prevent <br />migration of fluids into underground sources of drinking water. In other cases, multiple strings <br />of casing might be necessary. EPA is proposing this flexible, goal-related standard, rather than a <br />fixed requirement, in order to allow State Directors the discretion to vary the requirement, as <br />appropriate, in each instance. Allowing this discretion should lessen the cost of the requirement <br />while still accomplishing its preventive objective." <br />The regulations also require wells to comply with certain operational requirements which <br />can serve to minimize migration of fluids through casing. Foremost among these are the <br />requirements to demonstrate mechanical integrity. 13 A mechanical integrity test is used to verify, <br />as its name indicates, the "integrity" of a well, i.e., whether there is an absence of significant <br />leaks.14 <br />The determination of what constitutes a significant leak is left to the Director. This <br />acknowledges the site-specific nature of the question and allows a case-by-case review of <br />important local phenomena that must be considered in establishing-"significance". The <br />regulations require operators of all new Class I-III wells (wells coming into operation after an <br />to Report to Congress, Section XI, XIII; An Introduction to the Technology o <br />Subsurface Wastewater Injection U.S. Environmental Protection Agency (December, 1977), <br />Chapter 7 ("Subsurface Wastewater Injection"). <br />11 § 146.12(b). For a full discussion of the requirements for Class II, and III wells, see pages <br />11-12 below. <br />" Subsurface Wastewater Injection, Chapter 7. <br />13 § 146.08. <br />" See generally, Mechanical Integrity Testing of Injection Wells, Geraghty and Miller, <br />Inc., April 30, 1980. <br />Page 8 of 20