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Rating unsaturated zone and watershed characteristics of public water supplies in North Carolina
Conference Proceedings
By Jody L. Eimers, Eliabeth Morey, Silvia Terziotti, and J. Curtis Weaver
Abstract
Overlay and index methods were developed by the U.S. Geological Survey and North Carolina Public Water Supply Section to rate the unsaturated zone and watershed characteristics for use in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes statewide for vulnerability to contamination. Factors selected for rating the vulnerability of the unsaturated zone to surface contamination were vertical series hydraulic conductance, land-surface slope, land cover, and land use. Factors selected for rating vulnerability of watersheds to surface contamination were average annual precipitation, land-surface slope, land cover, land use, and ground-water contribution. Selection of factors, development of ratings, and assignment of weights were based on literature and consultations with experts in hydrology, geology, forestry, agriculture, and water management.
Rating factors were assigned values from 1 to 10, covering the possible range of values of a given factor in North Carolina. Factors were weighted 1, 2, or 3 to reflect their relative influence on the vulnerability of the water supply. Factor values were put into geographic information system layers, which were grids having 30-meter by 30-meter cells.
The weakness of these rating methods is that consensus among experts does not imply veracity. An investigation of the statistical relations between contributing factors and particular water contaminants in North Carolina would, by confirming these methods, contribute to public water-supply protection efforts in North Carolina. Efforts to increase the accuracy of source water assessment area delineations for public water-supply wells also would contribute to public water-supply protection efforts in North Carolina.
Citation:
Eimers, J.L., Morey, Elizabeth, Terziotti, Silvia, and Weaver, J.C., 2000, Rating unsaturated zone and watershed characteristics of public water supplies in North Carolina, in Conference Proceedings of the NWQMC National Monitoring Conference 2000, Monitoring for the Millennium, April 25-27, 2000, Austin, Tex.: National Water Quality Monitoring Council, p. 447-461.
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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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Available from the National Water Quality Monitoring Council, Conference
Proceedings, April 25-27, 2000, Austin, Tex. 15 p. 2 figs.
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