A CASE-STUDY SIMULATION OF DBCP GROUNDWATER CONTAMINATION IN FRESNO COUNTY, CALIFORNIA - 2 - TRANSPORT IN THE SATURATED SUBSURFACE

This paper is the second installment of a multipaper series concerned with simulating regional-scale groundwater contamination in Fresno Cou nty, CA as the result of long-term nonpoint source applications of 1,2 -dibromo-3-chloropropane (DBCP). In the first part of this study [Leag ue, K., Lloyd, D., Nguyen, A., Davis, S.N,, Abrams, R.H., 1997. A case study simulation of DBCP groundwater contamination in Fresno County, California: 1. Leaching through the unsaturated subsurface. J. Contami n. Hydrol. (this issue)], our focus was on the unsaturated zone and DB CP leaching to the water table. Our focus in this paper is the assessm ent of DBCP transport in the saturated subsurface. Here, the groundwat er flow code MODFLOW is coupled to the solute transport code MT3D to s imulate the potential fate and transport of DBCP below the water table in the Fresno County study area for a 35-yr period. The results prese nted here illustrate the long-term regional-scale evolution of the DBC P plume in the study area. The simulated DBCP concentrations are limit ed to the relatively shallow younger sediments and are generally well below the maximum contaminant level set for the chemical. The simulati ons presented here suggest that nonpoint source applications of DBCP a re not responsible for the observed hot spots in the study area, At th e end of this paper we discuss the implications and extensions of the Fresno case study which has been reported here and in the companion pa per mentioned above (Loague et al., 1997). ''Eliminate the impossible. Whatever remains, however improbable, must be the truth.'' -Sherlock Holmes (C) 1998 Elsevier Science B.V.