Characterization of Non-point Source Vadose Zone Pesticide Leaching at the Regional Scale Using a Transfer Function ApproachEPA Grant Number: U915138
Title: Characterization of Non-point Source Vadose Zone Pesticide Leaching at the Regional Scale Using a Transfer Function Approach
Investigators: Stewart, Iris T.
Institution: Stanford University
EPA Project Officer: Lee, Sonja
Project Period: December 1, 1997 through December 1, 2001
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1997) RFA Text | Recipients Lists
Research Category: Fellowship - Geology , Academic Fellowships , Ecological Indicators/Assessment/Restoration
The objective of this research is to develop a comprehensive and versatile protocol for the assessment of regional-scale, non-point source groundwater contamination from agricultural chemicals, using a linear systems (transfer function [TF]) approach.
Transfer function (TF) models are so-called "black box" models that relate a given input (i.e., a pesticide application) to an output (i.e., a solute concentration distribution within a soil profile) through an impulse response function. Central to my work is the new concept of what I termed "type" transfer functions (TTFs), designed to give a representative response of solute concentrations in space and time for predefined ranges of conditions relevant to the transport processes that are important at the regional scale. TTFs are a new contribution in that they allow the upscaling of TFs from the laboratory or plot scale to the regional scale.
My approach is developed and tested in three phases:. Phase I focused on initial TTF concept development. A steady-state TTF model was based on three typing factors, and developed from a regional-scale simulated data set of pesticide leaching for east-central Fresno County (see Loague, et al., 1998). Results from the Phase I component of my work showed that the TTF model was capable of predicting contaminant concentrations within the same order of magnitude as the process-based model PRZM-2 (Stewart, et al., 1999). In Phase II, the TTF model is extended to be generally applicable for pesticide leaching assessments. TTFs are developed for all 12 soil textural classes with the aid of synthetic data sets generated with three-dimensional process-based stochastic simulations of fluid flow and solute transport. A variety of climatic conditions, irrigation schedules, pesticides, and application histories will be considered. The TTF model formulation is expanded to explicitly consideraccount for decay and sorption, and it is capable of making predictions outside the calibrated depth range. The result of this effort will be an indexed set of TTFs that can be applied to give a prediction of pesticide concentrations at a depth of interest for any agricultural region for which information on soil texture, pesticide application, and irrigation inputs are available. In Phase III, the TTF approach will be used to make the first quantitative regional-scale groundwater vulnerability assessment for the San Joaquin Valley, CA.