Study On Shallow Groundwater Contaminated By Organic Chemicals In The Suburb Of A City

In the last few years, with the development of the industry and agriculture, the groundwater contamination is gradually serious. In regard to the category and scope of contamination and its harm to human health, organic chemicals in groundwater are the first one. Because they can cause cancer, abnormality and mutation, many organic chemicals have been regarded by the public in the world. By the restriction of the technique and expenses of analysis, the systemic research on organic chemicals in groundwater still has not been reported in China. Based on "key item of the national land resources "and" research of national key foundation 973 project", this paper sets a precedent for the systemic research on groundwater contaminated by organic chemicals in China.The results indicate that the 25 organic compositions occur in all 40 ones in groundwater, which are aromatic hydrocarbons, halogenated hydrocarbons and polycyclic aromatic hydrocarbons. Chlorinated aliphatic hydrocarbons(CAHs) which contain trichloromethane(TCM), phenixin(CT), trichloroethylene(TCE) and tetrachloroethylene(PCE) are common in groundwater in the studied area, the frequency of occurrence is 60. 27%, 29. 45%, 30. 82% and 32.19% respectively. The concentration of CAHs ranges between 0. 09 n g/ L and 71. 89 u g/ L. The distribution of chloroaliphatic hydrocarbons (CAHs) in groundwater is of point characteristic, whose heavy contaminated points mainly concentrate at west suburb of the studied area, have already become a heavy local contaminated section, piecemeal distribution in other place. The scope of heavy contaminated section is about 5 km'', whose main contaminants are TCE and PCE above 10 u g/ L. The frequency and concentration of occurrence in phretic aquifer is higher than in confined aquifer and their transition zone. High concentration points mainly concentrate on pretic aquifer.The evaluation from the single factor contamination index method and the synthetic contamination index method indicate that TCE and PCE are the major organic contaminants in the groundwater in the studied area. The points of heavy contamination (IV) which contain at least one-organic composition in the groundwater whose concentration is 10 times more than background concentration, and the points of serious contamination (V) which contain at least one organic composition in the groundwater is 50 times more than background value. These two kinds of points primarily distribute in the south western phretic aquifer and the central part of the transition zone and the confined aquifer is not contaminated. In summary, contamination in the western region is heavier than that in the eastern region. Similarly, contamination in southern region is heavier than that in the northern region.The evaluation of groundwater quality demonstrates that the groundwater qualityin the studied area is good on the whole, but individual composition has already exceeded to the standard of drinking water quality. The organic chemicals that threaten the groundwater quality is primarily TCE and PCE which exceed 14. 38 times and 9. 128 times respectively more than the drinking water standard.Organic solvent extensively used in the factory is a major source of CAHs in groundwater in comparison with landfill leachate and contaminated rivers. 83.3% Wells of heavy contamination(FV) and serious contamination(V) in the studied area are located in the industrial estate. Wells contaminated by TCE and PCE in the industrial estate which exceed drinking water standard are 80 and 87. 5 percent of the total wells which exceed the drinking water standard.Groundwater contaminated by CAHs is relevant to the physical property of CAHs, the construction of vadose zone, the hydraulic condition etc. Due to factor R of CAHs is very small, they very easily move in the underground environment. For this reason, the frequency of occurrence of CAHs in groundwater has been high, which have already become local heavy contaminative section. Wells contaminated by CAHs is located in phretic aquifer and the t...