ESCI 455 - Physiography of the United States - Spring, 2006 - Coastal Plains

The groundwater resource of Long Island, NY - W. W. Locke

The coastal plain is one of the most intensely urbanized areas of the country, and that populace draws heavily on groundwater resources. Nowhere is this dependence clearer than on Long Island, NY. Urban growth has drawn down water tables, caused saltwater intrusion, and polluted surface waters. Responses to the problem include management of runoff to enhance recharge, but require understanding of the groundwater system.

Long Island has multiple aquifers (Fig. 1), including Holocene coastal sands, Pleistocene till and outwash, Quaternary sands and gravels, and Tertiary and Cretaceous gravel, interbedded with aquitards, SE-dipping and superimposed upon metamorphic basement rocks. These aquifers reflect the long-term geological evolution of the coastal plain, plus the local effects of glaciation (Fig. 2) and coastal sand transport.

Ongoing problems include saltwater intrusion into deep aquifers, pollution of shallow ones, and drawdown of all aquifers. The obvious response, even in an area of 20-25 inches annual recharge (U.S. National Atlas, 1970) is to increase infiltration, but should that involve only rainwater, or treated wastewater as well? No single answer is applicable in all settings, but several alternatives (from Foxworthy, 1978) will be discussed in class.

REFERENCES CITED

• Fuller, M.L., 1914: The geology of Long Island, New York. USGS Prof. Paper 82, 231 p.
• Foxworthy, B.L., 1978: Nassau County, Long Island, NY: Water problems in humid country. USGS Prof. Paper 950, 55-68.

Figure 1. Diagrammatic cross-section (after Fuller, 1914, and Foxworthy, 1978)

Figure 2. Glacial map of Long Island and vicinity (from Fuller, 1914)