API 4643 : 1996

EXECUTIVE SUMMARY
1 INTRODUCTION
2 RECHARGE CONCEPTS AND TERMINOLOGY
       SUMMARY OF SOIL PHYSICS PRINCIPLES
          Water Content
          Hydraulic Head and Pressure Head
          Soil-Water Retention Curve
          Hydraulic Conductivity
          Infiltration, Redistribution and Recharge
    CONTAMINANT TRANSPORT
    DIFFUSE RECHARGE CONCEPTS
3 METHODS TO QUANTIFY DIFFUSE NATURAL RECHARGE
       PHYSICAL METHODS FOR DETERMINING DIFFUSE RECHARGE
          Soil-Water Balance
          Soil-Water Storage
          Lysimeter Measurements
          Darcy Flux Method
          Plane of Zero Flux Method
          Soil Temperature Methods
          Electromagnetic Methods
          Groundwater Basin Outflow Method
          Water-Level Fluctuations
          Stream Gauging
   CHEMICAL METHODS FOR DETERMINING DIFFUSE RECHARGE
          Chemical Methods in the Vadose Zone
          Chemical Tracers in Aquifers
   MATHEMATICAL MODELS FOR ESTIMATING RECHARGE
          Soil-Water Balance
          Stream Gauging
          Darcy Flux and Plane of Zero Flux Methods
          Soil-Water and Groundwater Models
          Lysimetry
          Other Physical Techniques
          Chemical Methods
          Aquifer Hydrochemistry
5 CONSIDERATIONS AND RECOMMENDATIONS FOR SELECTING
    RECHARGE ESTIMATION TECHNIQUES
       CONSIDERATIONS
       RECOMMENDATIONS
          Estimation Methods for Humid Climates
          Estimation Methods for Arid Climates
6 FUTURE RESEARCH
REFERENCES
GLOSSARY
Appendix A
ESTIMATE OF DIFFUSE ANNUAL RECHARGE

A Risk-Based Corrective Action analysis of a site suspected of chemical contamination requires site-specific knowledge of the rate water infiltrates through the soil to the water table. A comprehensive discussion of the current physical/chemical methods and mathematical models available to quantify those rates along with suggestions for selecting an appropriate technique, depending on site conditions, are provided.