Modeling oil fate and subsurface exposure concentrations from the deepwater horizon oil spill

In support of the Deepwater Horizon (DWH) Oil Spill Natural Resource Damage Assessment (NRDA), oil fate modeling of the DWH discharge was performed to estimate oil droplet and dissolved hydrocarbon concentrations in the water column between the release location and the surface layer (i.e., to 20 m below the surface). Pipe-discharge, blowout and droplet size models were used to develop mass and droplet size distributions used as input to the far-field oil fate model. The concentrations of soluble and semi-soluble hydrocarbon components predicted by the simulation of the actual event were validated by comparisons with chemistry data from the NRDA program. Due to the differences between the modeled and actual field conditions and the patchiness of observed chemistry, there is the potential for displacement between modeled and observed concentrations in both space and time. Therefore, a direct overlay of the detectable chemistry measurements on the model would be insufficient for evaluating if the concentrations predicted by the model were realistic. To account for likely displacement, results are plotted as probability distributions within a spatial and time window containing a population of chemistry samples. The chemistry samples and modeled results were ordered by concentration so that the distributions could be compared. In general, the modeled concentrations of the various components were of the same order of magnitude as the measured concentrations