API PUBL 4643-1996

$30.55

Estimation of Infiltration and Recharge for Environmental Site Assessment

Published By	Publication Date	Number of Pages
API	1996	202

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Description

Chemicals released to the vadose zone may present an environmental risk if they leach into groundwater. The rates of chemical leaching and migration to groundwater are strongly controlled by the diffuse recharge that occurs over large areas of the landscape. This report reviews important processes pertaining to diffuse recharge and presents a review of current physical and chemical methods (applied to the vadose zone and groundwater) to quantify diffuse recharge. Readily available estimates of diffuse recharge are compiled and organized according to major watersheds throughout the country.

The recommended approach to quantify recharge depends upon site-specific conditions, project budget, time constraints, and the nature of the project. In some cases, sufficiently accurate estimates of recharge are available in the technical literature. In other cases, field measurements are required. The methods selected from among the many available physical and/or chemical techniques must be appropriate for the site conditions. Physical methods are based on hydraulic or geophysical data collected in the soil, groundwater, or streamflow. Chemical methods rely primarily on natural and anthropogenic tracers found in the soil or groundwater. Mathematical models of soil and groundwater flow are also valuable recharge quantification tools. For projects with limited budget and time available, recharge can be determined from methods that use a one-time sampling of data, such as collecting soil cores, analyzing chemical tracers, or obtaining existing water-level or streamflow records. Where site-specific recharge must be known accurately and time is no factor, large soil lysimeters are the best choice.

Regardless of the method to obtain recharge, there is an inherent uncertainty in the estimate or calculation. Unfortunately, the degree of uncertainty is difficult to predict a priori and depends in part on the method, conditions such as water content and site heterogeneity, as well as the skill of the analyst. When the results from two or more different recharge analyses reasonably agree, the recharge estimate can be applied with greater confidence.

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