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Ground-water contribution to the vulnerability to contamination of public surface-water supplies in North Carolina
Conference Proceedings
By Jody L. Eimers, Elizabeth Morey, Silvia E. Terziotti, and J. Curtis Weaver
Abstract
The U.S. Geological Survey and North Carolina Public Water Supply Section developed methods to assess ground-water contribution to the vulnerability to contamination of approximately 250 public surface-water supplies in North Carolina. Ground-water contribution is calculated for a 1,000-foot buffer around surface-water bodies, and is intended to represent local flow, the part of the ground-water system having the most interaction with surface water.
The importance of ground-water in the possible contamination of surface-water supplies is assessed by using a rating composed of factors, including vertical series hydraulic conductance, land-surface slope, land cover, and land use. Depending on depth to water, locations in the Blue Ridge and Piedmont Provinces may incorporate estimates of vertical conductance for layers of soil, saprolite, and(or) fractured rock. For locations in the Coastal Plain Province, estimates of vertical conductance for layers of soil and(or) sedimentary formations may be required. Land-surface slope influences the amount of infiltration; other factors being equal, the greatest infiltration occurs in areas characterized by low slope. Land cover also slope influences the amount of infiltration; other factors being equal, the greatest infiltration occurs where land cover is pervious. Vegetation is another feature of land cover that influences infiltration. Finally, land use is included as a measure of the potential for generating nonpoint-source contamination at land surface.
The selection of factors, assignment of weighted values, and development of ratings were based on literature review and consultations with experts in hydrology, geology, forestry, agriculture, and water management. This method presumes that other groups of experts would come up with similar, but not necessarily the same weights and ratings. The weakness of this rating method is that consensus among experts does not imply veracity. A statistical investigation of the relations between contributing factors and particular water contaminants in North Carolina would, by quantifying these methods, contribute to public water-supply protection efforts in North Carolina.
Citation:
Eimers, J.L., Morey, Elizabeth, Terziotti, S.E., and Weaver, J.C., 2000, Ground-water contribution to the vulnerability to contamination of public surface-water supplies in North Carolina, in Proceedings of the 2000 Ground Water protection Council Annual Forum, Ft. Walton Beach, Fla., Sept. 24-27, 2000: Ground Water Protection Council and U.S. Environmental Protection Agency, p. 113-125.
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North Carolina Water Science Center
U.S. Geological Survey
3916 Sunset Ridge Road
Raleigh, North Carolina 27607
(919) 571-4000
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The proceedings are available from the Ground Water Protection Council. A copy of the paper can be obtained from the author(s). Eimers, Terziotti, and Weaver are with the U.S. Geological Survey, 3916 Sunset Ridge Road, Raleigh, NC 27607-6416, (919) 571-4000; Morey is with the N.C. Department of Environment and Natural Resources, Public Water Supply Section, 1634 Mail Service Center, Raleigh, NC 27699-1634 (919) 733-2321. |
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