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STATEMENT OF BASIS AND PURPOSE <br />INTRODUCTION <br />This document is intended to summarize the basis and purpose underlying the <br />underground injection control regulations promulgated in 40 CFR Part 146. It sets forth <br />generally the reasoning behind the Agency's regulatory choices and references data upon which <br />EPA relied. <br />This statement first discusses the categorization of wells. It then surveys the major <br />pathways which contaminants can take to enter underground sources of drinking water and the <br />requirements which these regulations impose to assure that movement of fluids resulting from <br />well injection does not contaminate underground sources of drinking water. Programmatic <br />requirements of Part 146, such as monitoring and reporting, are covered in the concluding <br />section. <br />In general, the requirements of the regulation differ from those of the initial proposal of <br />this regulation (41 FR 36730, August 31, 1976) and the reproposal of this regulation (44 FR <br />36730) in that they furnish a greater degree of flexibility to State Directors in regulating well <br />injection. EPA has modified its earlier proposal in this way as it became more fully aware of <br />various well injection practices, the characteristics of substrata into which fluids are injected, and <br />the range of methods by which well injection is accomplished. <br />CATEGORIZATION OF WELLS <br />The regulations separate wells into distinct categories. This categorization is necessary to <br />assure that wells with common design and operating techniques will be required to meet <br />appropriate performance criteria. <br />In categorizing wells, EPA first looked to available literature regarding the injection <br />practices. It considered information on existing and abandoned injection well practices, well <br />construction technology, and on the variety of fluids injected into wells. It discussed with <br />regulatory agency personnel from many States their experience with then-existing well injection <br />regulatory practices and reviewed existing regulations in a number of States! After such review <br />and discussions, it commissioned a reputable consulting organization to provide assessments and <br />a report on types of wells and their typical operation.z EPA then studied this information to <br />arrive at a consistent and comprehensive well classification scheme. As a result, EPA decided to <br />classify wells into the following five groups: <br />1 Interviews with State officials from Texas, Florida, Kansas, California and Michigan. <br />Preliminary Injection Well Practices, Geraghty and Miller, Inc., Tampa, Florida; 1977. <br />Page 2 of 20