The Management of a Municipal Well Field Using a Calibrated Physically Based Flow and Contaminant Transport Model

The Reich Farm site is considered to be a possible source of contaminants to the aquifer that serves a major well field for Toms River, New Jersey. The contaminant plume is intercepted by 3 of the wells, treated and discharged to the surface. A physically based transient groundwater flow and transport model was developed to establish the historical relationship between the Reich Farm site and the municipal well field and to assist in the management and protection of the aquifer and well field. The model is used to establish pumping rates for the wells with the constraint being the protection of the currently non-contaminated wells. Groundwater flow was modeled for a thirty-year time period using FRAC3DVS. In the model, spatially and temporally varying recharge was incorporated to account for water level fluctuations in observation wells. The transient flow model was calibrated with the aid of approximately 9 years of data from continuous well records as well as data collected over the entire period of the study using sampling at irregular periods. The contaminant transport and source parameters were estimated and compared using optimization with a multi-start PEST algorithm and two heuristic search algorithms with these being a dynamically dimensioned search (DDS) and a parallelized micro genetic algorithm.

The contaminant transport model calibration results indicate that overall, multi-start PEST performs best in terms of the final best objective function values with equal number of function evaluations. Multi-start PEST was employed to identify contaminant transport and source parameters under different averaging schemes of the spatially and temporally varying recharge. The estimated transverse dispersivity coefficients are important in the prediction of the migration of the contaminant plume to the well field. The magnitude of the values was demonstrated to be heavily affected by averaging of the recharge.