Reducing Capture Zone Uncertainty with a Systematic Sensitivity Analysis
Article first published online: 2 APR 2008
© 2008 The Author(s) Journal compilation © 2008 National Ground Water Association
Volume 46, Issue 4, pages 570–578, July–August 2008
How to Cite
Esling, S. P., Keller, J. E. and Miller, K. J. (2008), Reducing Capture Zone Uncertainty with a Systematic Sensitivity Analysis. Ground Water, 46: 570–578. doi: 10.1111/j.1745-6584.2008.00438.x
- Issue published online: 4 JUL 2008
- Article first published online: 2 APR 2008
- Received May 2007, accepted January 2008.
The U.S. Environmental Protection Agency has established several methods to delineate wellhead protection areas (WHPAs) around community wells in order to protect them from surface contamination sources. Delineating a WHPA often requires defining the capture zone for a well. Generally, analytical models or arbitrary setback zones have been used to define the capture zone in areas where little is known about the distribution of hydraulic head, hydraulic conductivity, or recharge. Numerical modeling, however, even in areas of sparse data, offers distinct advantages over the more simplified analytical models or arbitrary setback zones. The systematic approach discussed here calibrates a numerical flow model to regional topography and then applies a matrix of plausible recharge to hydraulic conductivity ratios (R/K) to investigate the impact on the size and shape of the capture zone. This approach does not attempt to determine the uncertainty of the model but instead yields several possible capture zones, the composite of which is likely to contain the actual capture zone. A WHPA based on this composite capture zone will protect ground water resources better than one based on any individual capture zone. An application of the method to three communities illustrates development of the R/K matrix and demonstrates that the method is particularly well suited for determining capture zones in alluvial aquifers.