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methods " In fact, based upon the type of well involved, it is possible that an alternative to <br />tubing and packer or fluid seal might actually provide a greater degree of protection 24 When <br />other effective methods are proposed, EPA.does not oppose their use. Prior to use, however, EPA <br />reserves the right of review and approval. <br />The final provision by which the regulations propose to eliminate contamination through <br />this first pathway is to require that Class I and Class III wells-which in ect corrosive fluids be <br />constructed of corrosion'-resistant materials. " This standard is intended to prolong the operating <br />life and continued viability of wells. <br />PATHWAY 2 - MIGRATION OF FLUIDS THROUGH THE ANNULUS LOCATED <br />BETWEEN THE CASING AND THE WELL BORE <br />A second way by which contaminants can reach underground sources of drinking water is <br />by migrating upward through the annulus located between the drilled hole and the casing. Under <br />usual injection conditions, injected fluids, upon leaving the well in the injection zone, enter a <br />stratum which to some degree resists the entry of the fluids. Resistance results from friction <br />created by extremely small openings in the materials which comprise the injection zone. <br />Because fluids tend to take the path of least resistance unless properly contained, they may travel <br />upward through this annulus. If sufficient injection pressure exists, the fluids could migrate into <br />an overlying source of drinking water. <br />The measures taken in the regulations to prevent contamination by this pathway are <br />parallel to those already mentioned concerning Pathway 1. In this case, well injectors must <br />demonstrate to the satisfaction of the Director that there is no significant fluid movement into <br />underground sources of drinking water through this annulus. Mechanical integrity tests can be <br />conducted to provide information on contamination by this route.26 As with Pathway 1, and for <br />the same reasons, mechanical integrity must be demonstrated at least every five years. <br />For Class I and III wells, the annulus between the hole and casing must also be filled with <br />cement adequate to prevent the flow of fluids into an overlying drinking water source. 27 <br />Depending upon the complexity of the well, this cementing can be accomplished in different <br />" §146.12(c)(1). <br />" Subsurface Wastewater Injection, Chapter 7; See also Cook, T.D. Underground Waste <br />Management and Environmental Implications. American Association of Petroleum Geologists <br />(Tulsa, Okla., 1972). <br />" § 146.12(c). <br />26 §146.08 <br />2' §§146.12(b); 146.32(a). <br />Page 11 of 20