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WATER RESOURCES RESEARCH, VOL. 43, W06418, doi:10.1029/2006WR004865, 2007

Potential effects of regional pumpage on groundwater age distribution

Brendan A. Zinn

U.S. Geological Survey National Center, Reston, Virginia, USA


Leonard F. Konikow

U.S. Geological Survey National Center, Reston, Virginia, USA


Abstract

Groundwater ages estimated from environmental tracers can help calibrate groundwater flow models. Groundwater age represents a mixture of traveltimes, with the distribution of ages determined by the detailed structure of the flow field, which can be prone to significant transient variability. Effects of pumping on age distribution were assessed using direct age simulation in a hypothetical layered aquifer system. A steady state predevelopment age distribution was computed first. A well field was then introduced, and pumpage caused leakage into the confined aquifer of older water from an overlying confining unit. Large changes in simulated groundwater ages occurred in both the aquifer and the confining unit at high pumping rates, and the effects propagated a substantial distance downgradient from the wells. The range and variance of ages contributing to the well increased substantially during pumping. The results suggest that the groundwater age distribution in developed aquifers may be affected by transient leakage from low-permeability material, such as confining units, under certain hydrogeologic conditions.

Received 5 January 2006; accepted 13 March 2007; published 21 June 2007.

Keywords: Groundwater; age; transient.

Index Terms: 1829 Hydrology: Groundwater hydrology; 1832 Hydrology: Groundwater transport; 1846 Hydrology: Model calibration (3333).


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Citation: Zinn, B. A., and L. F. Konikow (2007), Potential effects of regional pumpage on groundwater age distribution, Water Resour. Res., 43, W06418, doi:10.1029/2006WR004865.