Study On Migration And Transformation Of Petroleum Hydrocarbons In Zone Of Intermittent Saturation

With the rapid industrialization and economic development, the oil industry ineach country occupy an important position in economy, which has broμght greatbenefits to mankind, while often broμght serious harm. In a certain oil explorationarea of northeast China, destruction of wells water separator caused crude oil excreteinto the aquifer system, directly contaminated groundwater, and formed a100m2oilpit in the southwest low-lying areas of the well. Consider the impact of abandonedwells leaks, dirty oil pits seepage, human activities and oil exploration areabackground, the total petroleum hydrocarbons contamination of the soil andgroundwater seriously overweight, endangering groundwater quality and localresidents, which posed a serious threat to the ecological environment. Due to watertable fluctuation, an obvious zone of intermittent saturation exist in the study area,upper part of which enrich great amount of petroleum hydrocarbon contaminants. Thetotal petroleum hydrocarbons in groundwater has an in-phase correlation withgroundwater level changes, but lag slightly in time. Petroleum hydrocarboncontaminants in zone of intermittent saturation access to groundwater intermittentlyvia water levels fluctuation, considered as a potential source of pollution, soenvironmental assessment and remediation of pollution is urgent to be carried out. Inthis paper, based on "Investigation and remediation of Organic contaminatedgroundwater demonstration in Songnen Plain" project of CSGS, we take migrationand transformation of petroleum hydrocarbons in zone of intermittent saturation as themain research goals, carry out adsorption\desorption experiments, indigenousmicrobial degradation experiments, capillary action experiments and integratedsimulation experiments on migration of petroleum hydrocarbons to reveal thetransformation processes and the impact factors in zone of intermittent saturation,provide the basis for monitoring natural attenuation and following repair works. Thisstudy played very important theoretical and practical significance. Throμgh this study,we can draw the following conclusions:a. By studying silty clay and silt in zone of intermittent saturation with petroleumhydrocarbon adsorption/desorption experiments, we determined that silty clay adsorption capacity of petroleum hydrocarbons was stronger than silt, while weaker indesorption ability than silt. Differences in adsorption/desorption capability of the twomedia on the site led to the result that silty clay layer with petroleum hydrocarbons(TPH) higher than silt, and adsorbed petroleum hydrocarbon pollutants intermittentrelease into groundwater within a longer time.b.Experiments of indigenous microbial degradation provide the basis of presencefor petroleum hydrocarbon indigenous degrading microorganisms, and microbialdegradation rate had a closed relationship with medium moisture content. In themoisture content range0%to30%, with increasing water content, silty clay particlesbegan agglomerated into small lumps, thus limiting the supply of oxygen andnutrients, reduced microbial activity, resulting in the degradation rate of themicroorganism was negatively correlated with the moisture content. However, themicrobial degradation rate of the silt presented rising trend after the first decrease withmoisture content increasing. Microbial degradation of petroleum hydrocarbons wasefficient in Low water level period while inefficient in high water level period.c.Water table fluctuation and capillary action had a significant impact on thevertical distribution of petroleum hydrocarbon contaminants in zone of intermittentsaturation. Capillary action makes the capillary water to fill medium voids over thewater table and provide pollutants more ways and channels to migrate and promotethe expansion of adsorbed pollutants in space. Migration effect of contaminant in siltyclay was more obvious, and contaminants migrate vertically upward mainly, whichare weakly re-migrate due to the strong adsorption capacity of silty clay upper side.The vertical movement of groundwater contributed to contaminants migrate furthermore. In the saturated state, medium moisture content was significantly higher thanthe moisture content of capillary water, water as a transformation medium, more fullyoccupy the pores providing more contaminant migration and diffusion channelpromote the spread of groundwater contamination. Vertical lifting movement ofgroundwater further flooding contaminants, increased the migration ability ofcontaminants in vertical, this process also oriented vertically upward. For these tworeasons format the enrichment of petroleum hydrocarbons in zone of intermittentsaturation.c. The result of dynamic simulations experiments strengthen our understandingabout the impact of water level fluctuation on petroleum hydrocarbons migration and transformation in zone of intermittent saturation:Capillary action promote the migration of contaminants extend to the mainvertical upward; Water level increased to bring more contact with contaminated layerup side where the desorption of petroleum hydrocarbons dominant role ingroundwater TPH concentration increases; Then the spread of petroleumhydrocarbons in groundwater decreased slowly due to dilution and adsorption of thelower silt medium. But high TPH concentrations was driven into aquifer involved ingroundwater mixing, resulting in a slight increase in groundwater TPH when thewater table dropped passing high concentrations of layers again, and followed by adilution and adsorption dominant role TPH in groundwater slowly were declined andstabilized again. Biodegradation of petroleum hydrocarbons throμgh the process hasbeen going on, but its degradation rate compared with the adsorption, desorption, cannot be evident in a course of single small-scale experiment in the laboratory, but itwill have an impact on the groundwater system environment in a wide range and longtime scale.