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Design and testing of a process-based groundwater vulnerability assessment (P-GWAVA) system for predicting concentrations of agrichemicals in groundwater across the United States

Scientific Investigations Report 2014-5189
Prepared in cooperation with National Water-Quality Assessment Program
By:  and 
https://doi.org/10.3133/sir20145189

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Abstract

Efforts to assess the likelihood of groundwater contamination from surface-derived compounds have spanned more than three decades. Relatively few of these assessments, however, have involved the use of process-based simulations of contaminant transport and fate in the subsurface, or compared the predictions from such models with measured data—especially over regional to national scales. To address this need, a process-based groundwater vulnerability assessment (P-GWAVA) system was constructed to use transport-and-fate simulations to predict the concentration of any surface-derived compound at a specified depth in the vadose zone anywhere in the conterminous United States. The system was then used to simulate the concentrations of selected agrichemicals in the vadose zone beneath agricultural areas in multiple locations across the conterminous United States. The simulated concentrations were compared with measured concentrations of the compounds detected in shallow groundwater (that is, groundwater drawn from within a depth of 6.3 ± 0.5 meters [mean ± 95 percent confidence interval] below the water table) in more than 1,400 locations across the United States. The results from these comparisons were used to select the simulation approaches that led to the closest agreement between the simulated and the measured concentrations.

The P-GWAVA system uses computer simulations that account for a broader range of the hydrologic, physical, biological and chemical phenomena known to control the transport and fate of solutes in the subsurface than has been accounted for by any other vulnerability assessment over regional to national scales. Such phenomena include preferential transport and the influences of temperature, soil properties, and depth on the partitioning, transport, and transformation of pesticides in the subsurface. Published methods and detailed soil property data are used to estimate a wide range of model input parameters for each site, including surface albedo, surface crust permeability, soil water content, Brooks-Corey parameters, saturated hydraulic conductivity, macroporosity and sizes of microbial populations, as well as solute partition coefficients, reaction rates, and meso-micropore diffusion rates. To ensure geographic consistency among the predictions, the only site-specific input data that are used are those that are available for all of the 48 conterminous states.

Suggested Citation

Barbash, J.E., and Voss, F.D., 2016, Design and testing of a process-based groundwater vulnerability assessment (P-GWAVA) system for predicting concentrations of agrichemicals in groundwater across the United States: U.S. Geological Survey Scientific Investigations Report 2014–5189, 210 p., http://dx.doi.org/10.3133/sir20145189.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Study Design
  • Methods
  • P-GWAVA Simulation and Groundwater Sampling Results
  • Suggestions for Future Work
  • Summary and Conclusions
  • Acknowledgments
  • References Cited
  • Glossary
  • Appendix A. Previous Assessments of Groundwater Vulnerability
  • Appendix B. Equations Used to Estimate Deethylatrazine Formation Percentage
  • Appendix C. Groundwater Sampling Networks Examined
Publication type Report
Publication Subtype USGS Numbered Series
Title Design and testing of a process-based groundwater vulnerability assessment (P-GWAVA) system for predicting concentrations of agrichemicals in groundwater across the United States
Series title Scientific Investigations Report
Series number 2014-5189
DOI 10.3133/sir20145189
Year Published 2016
Language English
Publisher U.S Geological Survey
Publisher location Reston, V.A
Contributing office(s) Washington Water Science Center
Description xvi, 210 p.
Country United States
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
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