Program of the Month
An international team of scientists use a drilling rig (above) to drill deep into the impact crater on the Eastern Shore of Virginia. An update to a ground water flow model used by DEQ's Ground Water Withdrawal Management Program will include results from an investigation of the impact crater.
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Ground water withdrawal permits
Managing ground water withdrawals
About 35 million years ago a comet or meteorite plowed into the seafloor off the coast of what is now Virginia. The impact blew sediment, rock and water into the air, creating a 56-mile-wide crater and altering the availability of ground water supplies for present-day residents in Virginia’s coastal areas.
Layers of sand, clay and other sediments that lie beneath the communities of Tidewater Virginia and the Eastern Shore have buried the crater. Today the Department of Environmental Quality’s Office of Ground Water Withdrawal Management issues permits for significant water withdraws in these areas and studies the relationship between the region’s geology and ground water flow.
The goal of the program is “to protect existing ground water users now and in the future so that ground water can be a reliable source for water supply,” said Terry Wagner, DEQ’s water resources division director.
For decades DEQ and its predecessor agencies have been studying the structure of the layers of sediment containing water (called aquifers) within Virginia’s Coastal Plain, generally the area east of Interstate 95. Researchers have long known that the flow of ground water in the Coastal Plain did not follow an expected pattern and that salt water was found inland. In the 1990s, scientists determined that the buried crater controls the Coastal Plain’s altered ground water flow and results in pockets of salt water.
Since 2000 DEQ, the U.S. Geological Survey, and the Hampton Roads and Eastern Shore planning district commissions have been cooperating in a project to update and improve models that simulate ground water flow in Virginia’s coastal areas. DEQ uses the models to determine the effects of all withdrawals throughout coastal areas and the potential effects of a significant individual withdrawal.
While the existing ground water flow model accounts for the altered ground water flow caused by the impact, this update (available in 2006) will be the first to include conclusions from an investigation of the impact crater conducted by the USGS, DEQ, and international, federal and state partners.
“A model is a way to manage information within a conceptual framework that describes a natural system, and we are changing how we manage the data as well as our understanding of the system,” Wagner said.
The model is just one tool DEQ uses when deciding if a withdrawal is appropriate.
Permits are issued by DEQ’s Tidewater and Piedmont regional offices, and the agency’s central office in Richmond conducts the technical evaluation of permits. Agency staff members consider a number of factors when issuing a permit, including the extent to which the withdrawal will lower the ground water level in the surrounding area and affect nearby withdrawals.
Applicants must include plans to prevent unintended effects from the withdrawal and must show “that they are using the smallest amount and lowest quality water to meet their needs,” Wagner said.
DEQ issues permits for water withdrawals of 300,000 gallons per month or more in two ground water management areas – parts of Tidewater Virginia and the Eastern Shore. The agency has about 209 active permits with some withdrawing millions of gallons per day. The permit holders are typically industries, businesses and municipalities. The ground water is usually used in industrial processes or as a supply of drinking water.
As for the future of the program, Wagner says that DEQ will begin studying the Middle Peninsula and Northern Neck areas to see if they qualify as ground water management areas. This work will in part be supported by the addition of six proposed staff positions.
Although the proposed staff will provide additional support and allow the program to expand, the challenges will remain. As the requests for additional ground water withdrawal increases, the need to accurately assess the availability of ground water will become increasingly important to ensure that it will remain a reliable natural resource.