Fate and Transport

1998-1999: Site-Scale Fate & Transport Modeling Eastern Pennsylvania
Dr. Hazlett modeled groundwater flow, the fate and transport of 1,2-DCE, benzene, naphthalene, toluene, and ethylbenzene in groundwater, and bioretardation effects for a client’s site located in Berks County, PA. The objective of the modeling was to provide the client with predictions of the plume location and concentration for the five contaminants with respect to a 30-year time frame and 1000 ft from the property boundary. Modeling was completed in two phases. In Phase One, a conceptual model was developed based on pump test interpretations and water levels collected by the previous consultants. A steady-state groundwater flow model was then constructed, calibrated, and verified by comparing to existing pumping test data. The model MODFLOW, a finite-difference model, was used for groundwater flow simulation. Finally, transient fate and transport models for the dissolved-phase constituents were developed using MT3D, a finite-difference fate and transport model. The results of the Phase One modeling indicated that two of the five site-constituents, 1,2-DCE and benzene, could potentially flow offsite within 30 years. The model predicted the arrival times and concentrations for impacts to 4 nearby wells and a stream.
	Figure 1. Map view of predicted 30-year, 1000 ft, 1,2-DCE plume with bioretardation. The plume is predicted to leave the site within 30 years, but is not predicted to impact nearby sensitive receptors.
		In Phase Two, the bioretardation of 1,2-DCE and benzene in groundwater were simulated. Bench-scale biotreatability test was performed to develop first -order decay constants for the two contaminants in groundwater. The results of the bioretardation modeling demonstrated a potentially significant decrease in the total distance of plume advection. The results of both phases of modeling were presented to the Pennsylvania Department of Environmental Protection to portray a convincing case for natural attenuation. The state and client eventually agreed to an enhanced natural attenuation remedial action.

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