Guidance for Project Activities Involved with Delineation of Wellhead-Protection Areas and Aquifer Vulnerability


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 

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 

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.