某市岩溶地下水六价铬污染及控制因素分析

Study On Sexavalent Chrome Comtamination And Controlling Factors of Karst Groundwa ter of A City

某市市区东郊为工业和生活聚集区,20世纪80年代前,因区内某液压件厂电镀车间废水下渗,造成土壤和地下水体Cr6+污染。据初期监测,污染中心区土壤中的Cr6+含量高达2044.46mg/kg,高出其它地区几十倍。同时岩溶地下水也受到污染,Cr6+污染区呈以半径为0.5km的圆形分布,污染中心为液压件厂井,井水中Cr6+浓度最高达63.2mg/L(2007年1月)。监测资料表明污染区年内Cr6+浓度变化受降雨量的控制,表现出丰水期高、枯水期低的趋势,且浓度的升高相对于降雨有一定的滞后性,这主要是由于蓄积在土壤中的高浓度Cr6+受降雨淋溶所致。人工水动力场对Cr6+的空间分布起控制作用:Cr6+污染范围与漏斗中心区形态基本吻合;随着污染中心区域水源井开采量的减少及北部水源井停采的影响,污染中心液压件厂井水中Cr6+浓度迅速上升,污染羽逐渐向东部扩展,且浓度下降速度趋缓。

The concentration area with industry and living was located in the east suburbs of a City. Due to the leakage of wastewater from a machinery works where its chromium-plating workshop uses chromic acid,the soil and groundwater in this area have been seriously polluted by hexavalent chrome before 1980s. According to the results of initial monitoring,the hexavalent chrome in soil reached 2044.46mg/kg in the centre of polluted area,which is dozens of times higher than that in ambient areas. The karst groundwater was also polluted by s hexavalent chrome. The contaminated area,whose center is Yeyajianchang Well with the highest concentration of 63.2mg/L(January,2007) ,is distributed as a circle with the radius of 0.5km. Monitoring data indicated that the variation of hexavalent chrome concentration inside a year is controlled by rainfall:the concentration in high flow period is higher than that in drought period,and the concentration rise lags behind the rainfall. The main cause is that absorbed hexavalent chrome is leached into groundwater by storm. The spatial distribution of hexavalent chrome is controlled by artificial hydrodynamic filed of groundwater. The scope of hexavalent chrome pollution is similar with the cone of depression. The plume is expanded towards south and the decline of hexavalent chrome concentration in the plume is slower because of the reduction of water exploitation in the center of the polluted areas and the halt of northern water supply wells.