| Contaminated soil formed by the diffusion of polluted liquid are harmful to the environment and human health directly or indirectly. The contaminated soil from Huainan landfill, Xixi wetland and Fuyang Zhongda project are the research object in this article. The distribution and migration characteristics are deduced by the site survey, concentration of different pollutants measured in soil.Chloride ions and total nitrogen in soil are used as tracer contaminants. With the comparison of measured data and the theoretical analysis results, the reasonable pollutant migration parameters are obtained to predicte the diffusive trend of pollutants in soil. The performance of vertical anti-seepage curtain blocking the diffusive of pollutants in soil are verified.(1) The method of drilling is used in landfill and industrial pollution aera for deep soils sampling.It should be attention to using garbage to keep slumping hole from collapse. Hollow core tube sampler is used to drill out long complete soil samples, which avoid soil samples are contaminated by pollutant. It is commonly for the sampling depth reaching impervious layer. It is difficult to drill the sediment sample in river than in land. In this paper, the sediment sampler is our research group's patent invention.which can drill deep sediment samples more than 2m long. Soil samples drilled by that method is very simple, and the sediment samples will not be influenced by polluted water.(2) The pollutants detected in this paper including heavy metals, organic matter, COD. ammonia nitrogen, total nitrogen, total phosphorus, chloride ion and trace-level organic compounds, etc.; With the total digested methode. the concentration of heave metal could evaluate the quality level.Gradually extraction and test of heavy metal in soil shows the various forms in soil.Use distillation titration ammonia nitrogen, total nitrogen content in different soil depth could evaluate eutrophication level.(3) Huainan landfill belongs to the concentrated pollution sources.In the bottom layer, the heavy metals in the depth range of 0-2m had high content levels..and it gradually decreased with depth and approaches the background value. Beneath the landfill soil the exchangeable heavy metals is less than 1% of the total content, and most of the heavy metals are mainly in residual form, manganese and orgnic bound state, which significantly limits the heavy metals migration in groundwater. The percentage of orgnic states of heavy metal in which leachate full contacted with the organic layer was higher than of the background values, but with the depth increase, a significant reduction in organic content and tends to the background.The distribution of organic matter content along depth are similar to it. which indicating that high soil organic matter content of various heavy metals have a strong adsorption capacity. From Accumulate Index, Enrichment Factor and Ecological Risk Index for different depths of soil heavy metal pollution evaluation.it is shown that Im depth of the landfill Cu, Pb, Cr are moderate polluted, and lm below the depth of landfill external field are non-polluting to moderate soil contamination.(4) There is near 10m head in the landfill and the chloride ion is choiced to predict the contaminants migration. The results shows that after 30 years the chloride can migrate underground 4m depth; about 5.5m depth afer 50 years, and it reached 6-7m in depth afer 100 years.In the horizontal direction, the migration of chloride ions to the downstream is approximately 50m distance after 100 years.The high head in landfill is the main factor of the migration and diffusion of pollutants in soil strata under the landfill.Through the numerical simulation results show that the the head decreased to 4m, the migration of contaminants are effected seriously.(5) The contents of heavy metals.TN,TP,OM in the sediments at different depths were tested to evaluate the heavy metals pollution degree, as well as to determine their distribution along depth in this wetland. The tests and evaluation results show that the sediments were moderately polluted within 0.6m below the river bed, and not polluted at the depth deeper than 0.6m with index evaluation methods. The amount of heavy metals are not exceeding II limit of National Soil Standard.The amount of N.P in the shallow sediments was found to be far more than that in pore water, which is in turn much more than that in the above water. So N and P in pore water of sediments could be released into the above water due to the concentration gradient.(6) The TN is used to simulate transport of pollutants in sediments, and the results show that the TN can infiltrate to lm depth in sediment after 15 years.1.5m depth after 30 years.2m depth afer 60 years and 2.5m depth after 120 years. The numerical simulation results also showed that the water qulity meet the national III standard afer a half years if just using th method of dredging sediment without implementation of the overlying water replacement.and the TN content reached 3.22mg/L, exceeding the amount of state V water quality standard afer 5 years. Therefore, sediment dredging, and the replacement of the overlying water is the key to solve water eutrophication. According to the simulation results, the top 0.6 m sediment should be dredged from an economy point of view. Sediment covering method has simple construction, low-cost advantages in controling contaminated sediment, but more conditions on the application requirements. (7) The region of Fuyang Zhongda project is a typical chemical industrial pollution sites. and the test results show that the main pollutant within the region are heavy metal and chemical organic pollutants. Along the depth direction, heavy metal Zn in 1.75-6.75m depth range concentration is higher, but there is no apparent rules. Most of the contaminant concentration in soil samples are over the A class of exhibition soil standards, but not more than class B standard. Organic pollutants are concentrated in 1.8-5.5 m depth. From plane look, regional 1 and regional 2 pollution is serious, especially Trimethyl Benzene in some regional are more than grade B standard nearly 50%, was the most serious regional organic pollution is the place, need to undertake focused and control of position.(8) Large projects on polluted soil Fuyang containment method used to control the numerical simulation results show that when the basement floor does not improve, if the spread of contaminant transport to the main halo in 70 years after the pollution inside will be shipped in the Wall moved 34cm, not yet reached the non-contaminated areas; if the walls above the water level in the long-term water level of one meter outside the wall, the wall 70 years after the levels of contaminants in non-contaminated areas is 25 mg/kg, more than the A level standard, you need to control the Head inside and outside walls to ensure good play impervious curtain blocking effect; If the floor to enhanced 2m, the pollutants still can not reach the basement floor in the service life of 72 years, which have good control effect, and this method can be used as the first choice for control this type polluted soil strata. |
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