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made in connection with RCRA standards. Accordingly, EPA has determined that the best <br />course is to defer the "technical standards for Class IV wells which inject above USDWs until <br />fall 1980. <br />Finally, Class V wells include all wells not covered by the preceding categories, and those <br />wells for which EPA currently lacks comprehensive information. With the exception of wells <br />injecting radioactive waste, which are covered under Class IV and V, the Agency has reason to <br />believe that Class V wells pose a significantly lesser environmental danger than do other <br />categories of wells. Some Class V wells can cause risks to public health, of course, but many of <br />them can be actually beneficial to groundwater. Due to incomplete data, EPA has classified <br />these remaining wells together and is proposing no immediate performance criteria for them at <br />this time. Instead, these wells are to be assessed and, based on that assessment, EPA will <br />formulate a regulatory program suitable.for them at a later time. In the meantime, if remedial <br />action appears necessary, an individual permit maybe required (§ 122.37) or the Director may <br />require remedial action or closure by order (§ 122.37(c)). <br />PERFORMANCE CRITERIA <br />The regulations propose the use of a variety of measures to assure that injection wells will <br />not jeopardize underground sources of drinking water. This section addresses, the major <br />technical requirements by discussing each in conjunction with the particular problem it is <br />designed to prevent or remedy. The "problems" are basically six in number, and are described <br />here as "pathways of <br />contamination" - ways in which fluids can escape the well or injection horizon and enter <br />underground sources of drinking water. These "pathways" are the following: <br />1. movement of fluids through a faulty injection well casing; <br />2. movement of fluids through the annulus located between the casing and <br />well bore; <br />3. movement of fluids from'an injection zone through the confining strata; <br />4. vertical movement of fluids through improperly abandoned and improperly <br />completed wells; <br />lateral movement of fluids from within an injection zone into a protected <br />portion of that stratum; and <br />6. direct injection of fluids into or above an underground source of drinking <br />water. <br />Page 7 of 20