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This article in JEQ

  1. Vol. 28 No. 2, p. 429-446
    Received: Nov 18, 1997

    * Corresponding author(s): keith@pangea.stanford.edu
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DBCP Contaminated Groundwater: Hot Spots and Nonpoint Sources

  1. Keith Loague * and
  2. Robert H. Abrams
  1. Dep. of Geological and Environmental Sciences, Stanford Univ., Stanford, CA 94305.



The regional-scale nonpoint source (NPS) solute transport simulations reported by Loague et al. (1998a,b), for DBCP (1,2-dibromo-3-chloropropane) for east-central Fresno County (California), are the foundation of the work reported in this paper. This effort is divided into two phases. In the first phase we revisit our coupled 3-D deterministic-conceptual simulations of groundwater vulnerability for the Fresno study area (Loague et al., 1998a,b) and quantitatively evaluate the model performance by rigorously comparing the simulated DBCP concentrations, in both space and time, with field observations. The regional-scale simulation results presented here indicate tremendous spatial and temporal variability in the estimates of DBCP loading at the water table based on NPS applications and illustrate a potential long-term evolution scenario for the DBCP plume in the study area. The simulations presented here suggest that NPS applications of DBCP may not be totally responsible for all the observed hot spots in the Fresno County study area. Reverse flow path and forward solute transport simulations, with MODPATH and MT3D, respectively, were used in the second phase of this effort to determine if the isolated, high DBCP concentrations were likely to be the result of NPS applications. Unreasonably high simulated application rates were needed to generate a targeted observed DBCP hot spot if the sole source of the high concentrations was due to NPS agricultural applications. Potential sources for the DBCP contaminated groundwater, other than NPS label-recommended application rates, are discussed.

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