The effects of carbon dioxide leakage on fractures, and water quality of potable aquifers during geological sequestration of CO2

Since industrial revolution, the ＂greenhouse effect＂ is one of the most important global environmental issues. Of all the greenhouse gases, CO2 is responsible for about 64% of the enhanced ＂greenhouse effect＂, making it the target for mitigation, so reducing anthropogenic discharge of carbon dioxide attracts more and more attention. Geological sequestration of CO2 in deep saline aquifers is one of the most promising options. But because unknown fractures and faults may exist in the caprock layers which can prevent the leakage of CO2, CO2 will leak upward into upper potable aquifers, and lead to adverse impacts on the shallow potable aquifers. In order to assess the potential effect of CO2 leakage from underground storage reservoirs on fractures and water quality of potable aquifers, this study used the non-isothermal reactive geochemical transport code TOUGHREACT developed by Xu et al to establish a simplified 2-D model of CO2 underground sequestration system, which includes deep saline aquifers, caprock layers, and shallow potable aquifers, and study and analyze the changes of mineral and aqueous components. The simulation results indicated that the minerals of deep saline aquifers and fractures should be mainly composed of aluminosilicate and silicate minerals, which not only enhance the mass of CO2 sequestrated by mineral trapping, but also decrease the porosity and permeability of caprock layers and fractures to prevent and reduce CO2 leakage. The results from deep saline aquifers showed that the mass of carbon dioxide trapped by minerals and solution phases is limited, the rest remained as a supercritical phase, and so once the caprock aquifers have some unknown fractures, the free carbon dioxide phase may leak from CO2 geologic sequestration reservoirs by buoyancy.     

Geochemistry of soils derived from black shale, central Hunan, China

The black shale formed under anoxic conditions usually contains high concentrations of many metals. Weathering of such black shale might cause the emission of many metals. Moreover, soils derived from black shale （SBS） are believed to be affected by black shale weathering. In recent years, many studies such as Lee et al. （2002）, Woo et al. （2002）, Fang et al. （2002）, Pasava et al. （2003）, and Peng et al. （2004） have approached the heavy metal contaminations of SBS, but systematical geochemical study is rare. Presently, the SBS and its corresponding black shales （CBS） were both sampled from central Hunan （China）, and analyzed for a large number of elements, using an Elan6000 ICP-MS/AES machine at Guangzhou Institute of Geochemistry, CAS. In this paper, some preliminary results are reported. The analytical results show that the SBS in central Hunan contains very high concentrations of heavy metals such as Co, Cu, Hg, Mo, Pb, Zn, U, Th, Sb, T1, Cd, Cr, Sc, V, Sn, As, Se, and Ni.     

Heavy metal contamination in the sediment of the Second Songhua River

The Second Songhua River was subjected to a large amount of untreated effluent from petrochemical industries in Jilin City in the 1960s to the 1970s. The objectives of this study were to investigate the mercury and other heavy metal contamination in the sediment of the river. The river bottom sediment was sampled from the river segment between Jilin City to Haerbin City in 2005. Total concentrations of Hg, Cd, Cu, Cr, Pb, Zn, Ni, As, Sc, and major cations （A1, Fe, Mg, Ca, K, Na） in the sediment were measured by atomic fluorescence spectrometer, ICP-MS, and ICP-OES, respectively, following digestion with various acids. We found the concentrations of most elements in the uncontaminated sediment were significantly correlated to those of Sc.     

Influence of humic acid on bioavailability of heavy metals in sediments

The mimetic ocean environment and chemical method were used to research the bioavailability effect of humic acid on five heavy metals in sediment, including Cd, Cu, Zn, Pb and Ni. The sediment was separated into four containers with artificial seawater, and each of them had different concentrations of humic acid. The values of concentrations covered the whole range found in natural sediment （0.1%-10%）. According to the 48 hours LC50 of clam and distribution coefficient, metals were added in artificial seawater, and their speciation was determined at first and then after two days＇ incubation. It was found the bioavailability of heavy metals was reduced in the presence of humic acid. The obvious negative effect on Zn was observed, but the influence on Cd was not remarkable. In addition, the contents of Pb and Ni increased obviously in organic phase, and they are correlative with the concentrations of humic acid.     

山丘平原过渡区土壤重金属污染特征及评价——以四川省五通桥区为例

采集和分析了五通桥区不同功能区和乡镇73个土壤样品，以了解山丘平原过渡区土壤重金属的含量和污染特征。结果表明，重金属的平均含量为Pb32．18mg／kg、Cd0．82mg／kg、Cu28．61mg／kg、Zn108．08mg／kg、Ni32．66mg／kg、Cr72．44mg／kg；与四川土壤背景值相比，Cu、Ni、Cr的含量与之持平，Pb增加了0．11倍，Zn增加了0．32倍，Cd的积累较为严重，比背景值增加了10倍。污染评价结果显示该过渡区存在一定程度的重金属污染问题，不同功能区的污染程度排序为工业区〉生活区〉农业区。Cd在六种元素的土壤污染分担率中占55．46％，是最主要的污染元素；土壤Cd含量与Pb和Zn存在较高的相关性（相关系数为0．525和0．500），表明存在Pb—Cd和Zn—Cd的复合污染。     

自适应网格技术在MM5中的应用研究

结合一次暴雨过程，将自适应网格技术应用于中尺度模式MM5中进行数值试验，同时对比自适应网格方案和固定网格方案的优劣，对模拟结果作了诊断分析。结果表明：对于此次降水过程，自适应网格模拟的效果取决于一些参数的选择。     

2002年7月沈阳一次降水过程的催化数值模拟研究

应用三维对流云模式和探空资料，对沈阳地区2002年7月12日发生的一次东北冷涡降水过程进行了数值模拟研究。结果表明，这次降水主要是由积层混合云引起的，其中冰相过程占主导地位，霰的融化是最主要的雨生成项。催化模拟试验表明，当云体处于成熟稳定的积层混合云阶段，在0℃层高度以上播撒AgI能起到显著的增雨效果。积层混合云具有巨大的人工增雨潜力。     

长江下游一次大暴雨的中尺度模拟分析

运用中尺度数值模式（MM5V3.6）对2004年6月25日长江下游地区一次大暴雨天气过程进行了数值模拟,结合天气形势和卫星云图对此次过程进行了分析.结果表明：在东北冷涡和西太平洋副热带高压两大天气尺度系统的作用下,西南低空急流的再次加强和中低层切变线共同作用是此次大暴雨过程的主要原因.螺旋度分析表明,在不均匀的强上升气流的作用下,涡旋的水平分量向垂直分量转化是此次强降水的可能机制之一.