Reducing capture zone uncertainty with a systematic sensitivity analysis

Area of Science:

• Environmental Science
• Hydrogeology
• Water Resource Management

Background:

• Wellhead protection areas (WHPAs) are crucial for safeguarding community wells from surface contamination.
• Traditional methods for delineating capture zones often rely on simplified models or arbitrary zones, especially in data-scarce regions.
• Accurate capture zone delineation is essential for effective WHPA planning.

Purpose of the Study:

• To introduce a numerical modeling approach for defining wellhead protection areas (WHPAs).
• To investigate the impact of recharge to hydraulic conductivity ratios (R/K) on capture zone size and shape.
• To provide a more robust method for capture zone delineation in areas with limited hydrogeological data.

Main Methods:

• Calibration of a numerical groundwater flow model to regional topography.
• Application of a matrix of plausible recharge to hydraulic conductivity (R/K) ratios.
• Development of a composite capture zone encompassing multiple model simulations.

Main Results:

• The numerical approach yields multiple plausible capture zones rather than a single uncertain one.
• The composite capture zone provides a more conservative and protective boundary for WHPAs.
• The method demonstrated effectiveness in delineating capture zones within alluvial aquifers.

Conclusions:

• Numerical modeling offers advantages over analytical or arbitrary methods for capture zone delineation.
• A composite capture zone approach enhances the reliability of wellhead protection area definitions.
• This systematic method improves groundwater resource protection for community wells, particularly in alluvial settings.