A comparison of uncertainty analysis methods for the modeling of land disposal of petroleum exploration and production waste

Three uncertainty analysis methods, namely : (1) Monte Carlo (MC) simulation, (2) First-Order Second Moment (FOSM) method, and (3) Modified Point Estimate (MPE) method, were compared in terms of computational efficiency and accuracy for evaluation of contaminant concentration at a down-gradient receptor.

Benzene and chloride, two contaminants most commonly found in petroleum exploration and production waste, were analyzed for two waste disposal scenarios, i.e. (1) closed waste pit, and (2) landspreading.

Using MC method as the basis for comparison, results of the analysis suggested the use of FOSM method as the most attractive alternative to the more tedious MC method. Based on 2000 MC simulations for analysis, the FOSM method required 1.053% of the computational effort required for the MC analysis. Considering a regulatory guideline of 85% probability level of exceedance, results of the analysis indicated that the MPE method consistently underestimated the benzene concentration and overestimated the chloride concentration at a receptor, whereas the FOSM analyses indicate good agreement with MC method. However, in the event where a more precise and complete analysis is mandatory, the MC method remains the most appropriate methodology available.