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United States : Study Assesses Threats to Groundwater Availability and Sustainability in Northern Atlantic Coastal Plain.

Threats to groundwater availability and sustainability in the Northern Atlantic Coastal Plain are dependent to a large degree by the type of aquifers used for water supply, according to a new regional assessment by the U.S. Geological Survey.

The water challenges faced in the highly populated area, which ranges from Long Island, New York to North Carolina, vary greatly, as do the causes.

Block diagram showing the Northern Atlantic Coastal Plain aquifer system, which includes the areas east of the Fall Line.

Block diagram showing the Northern Atlantic Coastal Plain aquifer system, which includes the areas east of the Fall Line from Long Island to northern North Carolina. This multilayer system consists of confined aquifers and confining units capped by an unconfined, surficial aquifer. Groundwater flows predominantly from west to east from the Fall Line to the Atlantic Ocean, except where high-capacity pumping wells alter this regional flow pattern., USGS

Were looking at water situations in the north and south of the region that might be seen as two sides of the same coin, said John Masterson, a USGS hydrologist and lead author of this assessment. In the north, the greatest threat to sustainability is the ecological impacts that may result from overpumping, whereas in the south, depletion of the groundwater resource is the biggest sustainability concern.

In places like Long Island and New Jersey, in the northern part of the study area, groundwater depletion is not a serious concern. There, shallow aquifers used for drinking-water supply are well connected to the land surface and easily replenished by rainwater that seeps into the ground as aquifer recharge.

The tradeoff to pumping this water is that, although there appears to be plenty of it, removing any of it from the aquifer comes at the expense of the freshwater needed to keep streams flowing and to support the marine life that depend on fresh groundwater discharge to coastal estuaries, said Masterson. Pumping these wells for human use captures the groundwater that otherwise would have become streamflow or gone into the coastal waters. Reducing flows from aquifers to these surface waters, if great enough, can result in adverse ecological effects.

In the southern part of the study area, in places like Virginia and North Carolina, the situation is reversed. The aquifers used for drinking-water supply typically are deep and not well connected to land surface. Pumping in this area therefore does not have a large effect on surface waters; however, the restricted connections between the deep aquifer and surface waters can potentially lead to groundwater depletion. Although only 14 percent of the total pumping from all aquifers in the Northern Atlantic Coastal Plain occurs in Virginia and North Carolina, it accounts for almost half of the total groundwater depletion in the entire aquifer system.

In this area, most of the pumping occurs in the deep confined aquifers that are not well-connected to land surface and the water pumped from these wells isnt groundwater that otherwise would have discharged to streams or to coastal estuaries, said Masterson.

Masterson characterized this groundwater depletion as a real concern, saying it may lead to land subsidence, which is the gradual lowering of the land surface, and intensify the effects of local sea-level rise, particularly in the Lower Chesapeake Bay area in southern Virginia. An additional concern for this part of the aquifer system is that in coastal areas, groundwater depletion can result in the landward encroachment of salty groundwater, diminishing the quality of the drinking water in those areas.

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Publication:Mena Report
Geographic Code:1U5NC
Date:Sep 7, 2016
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