A CASE-STUDY SIMULATION OF DBCP GROUNDWATER CONTAMINATION IN FRESNO COUNTY, CALIFORNIA - 1 - LEACHING THROUGH THE UNSATURATED SUBSURFACE

This paper is the first installment of a multi-paper series concerned with simulating the potential vulnerability of groundwater in Fresno C ounty (California) to contamination resulting from long-term, agricult ure related, applications of the nematocide DBCP. In this paper our fo cus is on the surface and the unsaturated subsurface. Using PRZM-2, we quantitatively estimate, for a 35 year period, the potential fate and transport of DBCP between the surface and the water table for multipl e non-point source applications, related to different and changing lan d-use, between 1960 and 1977. Our transport simulations include consid eration for advection, decay, sorption, and volatilization. The result s presented here indicate tremendous spatial and temporal variability in DBCP loading at the water table at the regional scale. Our simulati ons also suggest that the DBCP loading to the water table, resulting f rom the legacy of the chemical's use, is currently well below the dete ctable limit. The characterization of spatially variable DBCP loadings to the saturated subsurface through time, which are presented in this paper, is used as input for the 3-D groundwater models of DBCP fate a nd transport in Fresno County between 1960 and 1994 that are reported in the companion paper (League et al., 1997). ''Data, Data, Data! He c ried impatiently. I can't make bricks without clay.'' Sherlock Holmes (C) 1998 Elsevier Science B.V.