A mathematical model that can be used for optimal design and operation of land treatment systems for petroleum hydrocarbon containing wastes is described. The model is composed of system simulator and optimization submodels. Selected model applications are presented demonstrating its applicability and utility, which include determination of the optimal design and operation conditions for land treatment of petroleum hydrocarbon containing wastes under various site and soil environmental conditions and practical waste disposal scenarios. Simulation runs involve demonstrating the performance of a land treatment system for oily wastes at sites with loam, clay and sand soil, representing a wide spectrum of hydrologic regimes. Benzene is selected as the index compound because it is a high priority pollutant for most water quality concern. Biodegradation is responsible for ~ 90% of total mass fluxes in loam and clay soils and 60% for sand soil. For multiple waste loadings, attenuation characteristics of the soil media is observed especially at shallow depths.