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Chloride Mass Balance in Streams to Estimate Recharge


GWRP supports applied research into the use of chloride mass to estimate groundwater recharge.

Purpose & Scope

Population growth in certain regions has raised concerns about the allocation of surface-water flow and the increased demands for groundwater resources. To address these concerns, there is a need for improved methods for accurately assessing regional groundwater resources. The objectives of this study are to develop hydrologic budgets for the watersheds and counties of central and western Virginia at both the watershed and county scale using chloride mass balance to estimate groundwater recharge. The study began in 2005 and is scheduled to be completed in late 2009.

Methods & Activities

Due to the chemically conservative behavior of chloride, an accounting of its mass has been used in different environments to estimate groundwater recharge. Most applications of this approach have been in environments where surface runoff can be neglected. However, a full accounting for chloride including the runoff component can be developed for a watershed. In this study, the hydrologic budget components to be considered include rainfall, total evapotranspiration, riparian evapotranspiration, infiltration, recharge, runoff, and baseflow. The watershed-scale hydrologic budget component values will be obtained using the chloride-mass balance method. These watershed-scale values will then be converted to a county-level scale.

In locations where chloride data are lacking, specific conductance data collected at stream-gaging sites will be used as a proxy. Use of stream-water specific conductance as a proxy for chloride concentration is possible because most stream-water chemistry shows a linear relation between chloride concentrations and specific conductance values. The use of specific conductance probes at real-time stream-gaging sites allows the collection of more data points over time in a manner that is more cost- and staff-efficient than manual water sampling for chloride concentrations at these locations.


Sanford, Ward E.; Nelms, David L.; Pope, Jason P.; Selnick, David L., 2012, Quantifying components of the hydrologic cycle in Virginia using chemical hydrograph separation and multiple regression analysis: U.S. Geological SurveyScientific Investigations Report: 2011-5198. Available online at

For more information:

For more information about this project, contact:
Ward Sanford, Research Hydrologist
(703) 648-5882

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