Groundwater - Vulnerable Resource—groundwaterquality

Until the mid-twentieth century, people believed that soil provided a barrier or protective filter that neutralized the downward migration of contaminants from the land FIGURE 4.8
Sources of groundwater contamination
SOURCE: "Figure 6-2. Sources of Ground Water Contamination," in 2000 National Water Quality Inventory, U.S. Environmental Protection Agency, August 2002 surface and prevented water resources from becoming contaminated. The discovery of pesticides and contaminants in groundwater, however, demonstrated that human activities do influence groundwater quality.

The potential for a contaminant to affect groundwater quality is dependent upon its ability to migrate through the overlying soils to the groundwater resource. Figure 4.8 shows the different mechanisms that can lead to groundwater contamination. Contamination can occur as a relatively well-defined localized plume coming from a specific source. It also can occur as a generalized deterioration over a large area because of diffuse nonpoint sources such as fertilizer and pesticide application.

Once it became apparent that groundwater was being contaminated, the questions of which waters were polluted, the severity of contamination, and what should be done about it had to be addressed. Many government and private organizations are working to find the answers, but it is not an easy task. As with other types of pollution control, problems include lack of accurate data, inadequate reporting and measurement techniques, the difficulty of setting acceptable standards, illegal dumping, designation of cleanup responsibilities, and funding.

The quality of most available groundwater in the United States is believed to be good according to the EPA's Safe Drinking Water Act, Section 1429 Groundwater Report to Congress (October 1999) and its 2000 National Water Quality Inventory. The worst groundwater contamination is generally in the areas where use is heaviest—towns and cities, industrial complexes, and agricultural regions such as California's Central Valley.

Although positive strides were made in assessing water quality in 2000, groundwater data collection is still too immature to provide a good national assessment. Accurate and representative assessment of groundwater quality requires a well-planned and well-implemented monitoring plan. The states are working to develop and execute these plans as manpower and monetary resources allow. At this time because the aquifer monitoring data reported by states represent different sources and differing monitoring purposes, care must be exercised in drawing conclusions.

Recognizing the need to protect valuable and vulnerable groundwater sources, the states have begun to implement comprehensive groundwater protection programs. These programs are being integrated with surface water protection programs in recognition of the fact that base-flow in the nation's surface waters is dependent on groundwater.