Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

This indicator would describe changes in water levels in major regional aquifers by reporting the fraction of the total area of regional aquifers that declined, increased, or remained stable in comparison to a previous period, and would be reported every 5 years. An example of the kind of data that are available for some major aquifers, and which would be used to develop a national indicator, can be seen in a series of maps depicting changes in the High Plains aquifer, which underlies eight states in the central United States (see McGuire et al. 1999).

The Data Gap

This indicator would require significant data on water levels in major regional aquifers (see below). It would also require a scheme for classifying changes in aquifer level as “significant increase,” “significant decrease,” or “no significant change.” Changes in groundwater level have unique levels of significance in different aquifers; a change of a few feet in a shallow coastal aquifer may be quite important in terms of susceptibility to saltwater intrusion, while a change of 10 feet on a very large aquifer may not be as significant. Logically, the values for “stable” will be different in different aquifers (e.g., the High Plains case defined –5 feet to +5 feet as “no significant change”). Therefore, definitions of significant increase or decrease (and thus, no significant change) should be determined on an aquifer-by-aquifer basis. Water-level data are available for all or parts of every state, but these data cannot be aggregated to provide national coverage because of limited coverage of most aquifer systems and lack of electronic availability of much of the monitoring data. The High Plains aquifer is one of the few multistate aquifers with systematic and coordinated water-level monitoring. States or areas with good water-level-monitoring programs include parts of Florida, Long Island (NY), Pennsylvania, and Utah. To ensure national coverage, the following points must be addressed:

• Data must be collected from areas that represent the full range of topographic, hydrogeologic, climatic, and land use environments within the major aquifers.
• Data must be collected using standardized methods from monitoring wells or other wells not affected by local pumping. Procedures for well selection and data collection are available in Chapter 2 of the USGS’s 1980 National Handbook of Recommended Methods for Water-Data Acquisition.
• There must be agreement on timing of water-level measurements across the country so that the status of major aquifers in a region or in the entire country can be presented as a snapshot in time.
• Plans must be in place to ensure long-term viability of observation-well networks and data collection programs, including plans for a combination of data collection at long-term monitoring wells and periodic synoptic measurements.
• There must be agreement among the agencies or other sources of data on electronic data storage, access, and dissemination. The agencies that will be responsible for leadership in compiling and publishing the data must be identified.

References

McGuire, V.L., C.P. Stanton, and B.C. Fischer. 1999. Water level changes, 1980 to 1997, and saturated thickness, 1996–97, in the High Plains aquifer. U.S. Geological Survey Fact Sheet. FS-124-99. http://ne.water.usgs.gov/highplains/hp97_web_report/97fs.pdf.