Guidance for Project Activities Involved with Delineation of Wellhead-Protection Areas and Aquifer Vulnerability OFFICE OF GROUND WATER TECHNICAL MEMORANDUM NO. 00.01 Subject: Guidance for Project Activities Involved with Delineation of Wellhead-Protection Areas and Aquifer Vulnerability The purpose of this memorandum is to review appropriate limits of participation by the U.S. Geological Survey (USGS) in projects that support source-water assessments, which include delineation of protection zones around public-supply wells and delineation of aquifer vulnerability. This memorandum updates guidance provided in Water Resources Division Memorandum 89.26, which initially established guidance for these types of projects. On occasion, agencies with regulatory responsibilities request USGS assistance in the determination of wellhead-protection areas, determination of recharge areas, estimation of areas vulnerable to ground-water contamination, and other similar studies. The work and products from these studies may be controversial. They have the potential for being perceived as regulatory and may be viewed as being in competition with the private sector. The intent of this memorandum is to clarify the appropriate role of the USGS in undertaking these types of studies, emphasizing the importance of scientific standards and use of documented methodologies. This memorandum, however, should not be construed as any sort of discouragement of USGS involvement in providing the scientific information needed for ground-water protection programs. Statutes such as the Safe Drinking Water Act highlight the Nation's intention to protect the quality of ground-water resources. As the Nation's principal earth-science agency, it is imperative that the USGS provides the scientific information needed for such protection programs as personnel and resources allow. The mission of the USGS is to provide geologic, biologic, topographic, and hydrologic information that contributes to the wise management of the Nation's natural resources and that promotes the safety and well-being of the public. Thus, providing hydrologic information, including the results of analytical and numerical modeling applications, to regulatory agencies charged with responsibilities for wellhead and ground-water protection is a proper function of USGS. There is a clear distinction, however, between studies to determine sources of water to wells and aquifers and studies to determine wellhead protection or source-water protection areas. Determination of sources of water to wells, the delineation of the associated areas contributing recharge to wells, or the delineation of recharge areas for an aquifer are based on scientific hydrologic analysis, while delineation of wellhead and source-water protection areas are legal/regulatory functions that reflect political and sociological considerations. USGS studies must, therefore, emphasize the scientific analyses and leave the responsibility for designation of an area for wellhead or source-water protection with the appropriate regulatory agency. The scope of USGS studies should include only objective scientifically based hydrologic and geochemical analyses. Studies on the source of water to wells and aquifers should include the best possible analysis of the flow system and provide technical information, such as aquifer properties, gradients, flow rates, delineations of recharge and contributing areas, and calculations relative to characteristics of the flow system. Studies on the occurrence of contaminants or the potential for contaminants to occur in an aquifer (ground-water vulnerability studies) should also be supported by field data, such as concentrations of constituents or age dates based on environmental tracers in addition to information on the flow system. Indexes of ground-water vulnerability based solely on the combination of arbitrarily weighted physical attributes (such as, geology, soils, depth to water) should be avoided because the method is subjective and virtually unverifiable. Reports describing the results of these studies should include: (1) a clearly defined description of the objectives of the report; (2) a justification of the hydrologic techniques that were applied; (3) assumptions inherent in the techniques; (4) a detailed assessment of the methodology used in the hydrologic analysis; and (5) a complete and frank discussion of the limitations and uncertainty of the methods, data, and results. Similar guidelines have long been in effect for USGS reports containing aquifer-test analyses and the application of numerical modeling techniques. By following these guidelines, personnel working on wellhead protection and similar-type studies will focus on the hydrologic analyses, and will provide the appropriate level of documentation required for Director's approval of their reports. In summary, there is a role for USGS in studies involving wellhead protection, ground-water vulnerability, and identification of aquifer recharge areas. Care must be taken to ensure that our work includes only the objective scientific analysis and does not include subjective results based on regulatory considerations. Reports describing the results of wellhead protection and similar-type studies should include a justification of the technique and a discussion of the assumptions, methodology, and limitations of the analyses. William M. Alley Chief, Office of Ground Water Distribution: A, B, S, FO, PO Regional Ground-Water Specialists, NR, SR, CR, WR This memorandum supersedes Water Resources Division Memorandum No. 89.26.