Study On Pollution Mechanism Of Petroleum Contamination In Groundwater System Under A Refinery

With the rapid development of economic, our environment is facing great pressure. In addition to excessive exploitation of natural resources, various kinds of pollutants discharged from industrial production also create a series of environmental problems. Petroleum hydrocarbon contamination has become a main kind of pollution of the world because of the special physical and chemical properties of organic hydrocarbon material and the harm extent of it. In this paper, I take the area surrounding the refinery in the southwest of Jinan City as the research object, and study the pollution characteristics of petroleum hydrocarbon pollutants in the underground environment as well as the transport mechanism of it in the aquifer system.Most parts of the refinery area are covered with exposed limestone and thinner layer of Quaternary soil. It is Paleozoic Ordovician limestone and quaternary loose rocks aquifer in this area. And the main rock group is Ordovician limestone, which is karst developed and has water-rich conditions, aquifer stability and water permeability. The contaminants are carried into the aquifer mainly with the surface water passing through unsaturated zone. Therefore, the general pollution system of groundwater is composed of pollution sources, unsaturated zone and aquifer.The experiments designed to study the adsorption mechanism of petroleum hydrocarbon in the undisturbed soil show that, with the decreasing of pH values, the surface area of the solid particles of soil increase as a result of the reaction between calcium carbonate and hydrogen ion, thus adsorption capacity of the solid-phase increases. Ionic strength has a certain role in promoting the adsorption function, and the adsorption mode can be described as Henry-type adsorption isotherm. The experiments designed to study the desorption mechanism of petroleum hydrocarbon in the disturbed soil show that, the surface of solid particles has been changed as the increasing of pH, so that the amount of adsorption on solid-phase decreased.In the leaching experiments of undisturbed soil by sewage with petroleum hydrocarbon, we set two parallel soil columns with the same state of experiment conditions, but filling with different concentration of sewage into each column, one with 56.52mg/L and another 5.6mg/L. The leaching results show that the retention capacity of this study area for petroleum hydrocarbon is limited, and beyond a certain level, the petroleum hydrocarbon pollutants will enter the aquifer system and cause groundwater contamination. Differences in the concentration of leaching water have a certain influence on the retaining capacity of the soil. When the sewage concentration is low, the concentration of the water leaching out has no notable change. The experiments of disturbed soil leached by clean water show that the release of petroleum hydrocarbons from oil-contaminated soil material accounted for only 0.3%. While the leaching continues, the release amount is certainly increasing over time, but with a low rate. The vadose zone environment will be polluted in the long-term.As a conclusion of the soil column leaching experiments, sorption is one of the most important functions that controls the transportation of petroleum hydrocarbons in vadose zone. The model equation is impacted by convection less than diffusion. The model equation will fit better if wastewater containing high concentration of petroleum hydrocarbons. By comparing the error function ERROR, I find that the display difference scheme is able to better simulating one-dimensional advection-dispersion process.I choose a profile through the line from Jingjia Ditch to Lashan Mountain, and generalize it with two layers, the Quaternary clay layer and the ordovician limestone fracture. For the limestone fracture is stable and uniform, it can be generalized as a layer with homogeneous medium. In this situation, I use a two dimensional convection dispersion equation to simulate the migration of petroleum hydrocarbon with implicit difference method. All the matrix calculation is done within the software MATLAB, and the results show the relative error is less than 10%, which means the model is right for simulating the migration of petroleum hydrocarbon contaminants. The calculating results in the future 10 and 15 years show that the oil pollution condition in the aquifer system is getting worse, and the concentration is over 0.05mg/L in most parts, especially around Jingjia Ditch and Back Weihua.