基于级别特征值的岩溶含水层水质模糊综合评价修正

An improved fuzzy comprehensive evaluation of water quality in karst aquifer based on level characteristic values

为改进传统水质模糊综合评价中存在评价指标不能全面反映水质状况、评价结果不清晰,评价等级区分度不明显等缺陷,文章以位于六枝特区威宁-郎岱褶皱群的第一层岩溶含水层水质为例,根据岩溶区水质评价特点和研究区含水层超标因子特征,建立涵盖物理、化学和微生物等因子的评价指标体系,利用级别特征值对传统模糊综合评价结果进行了适当修正,并与综合污染指数法、传统模糊评价综合法的评价精度进行定量化比较。研究结果表明:六枝特区的研究区探采点水质综合评价等级都达到Ⅲ类生活饮用水卫生标准,但仍有71%的探采点存在氨氮(NH_4^+)、氟化物(F^-)、高锰酸盐指数(COD_(Mn))、溶解性总固体(TDS)和大肠杆菌等指标超标,且超标因子浓度呈点状扩散分布于三叠系中下统地层;另外,传统模糊综合评价中有57.1%的水质达到Ⅰ类标准,与多个探采点存在因子超标的情况不符,而通过级别特征值修正的模糊综合评价结果中分别有57.1%和28.6%的探采点水质为Ⅱ类或Ⅲ类标准,与着重突出最大超标因子权重的综合指数法类别标准差低0.011。因此,基于级别特征值的模糊综合评价能有效的反映水质整体水平,探采点水样超标因子浓度和同类水质的区分度,评价结果合理、可信。

The aim of this study is to improve traditional fuzzy logic approach to water quality evaluation, due to some drawbacks such as unrepresentative evaluation indexes for water pollution assessment, indeterminate evaluation results and obscure grade boundaries for fuzzy evaluation. The first layer of karst groundwater in Liuzhi special district Weining--Langdai folding area was selected as the modelling object. Based on the karst water quality analysis, factors for the fuzzy logic process were selected from those analysed constituents which were in excess of relevant wa- ter quality regulations, from which establishing the evaluation index system which includes physical, chemical, and microbiological factors, and modifying the method of traditional fuzzy comprehensive evaluation. Consequently, results of the new model were assessed and compared with those from the methods of both comprehensive pollution index and traditional fuzzy comprehensive evaluation. Results of the fuzzy comprehensive evaluation show that water quality reaches class 111 in light of national drinking water standard in Liuzhi special district. However, there are still 71% sampling points where the concentrations of ammonia nitrogen （NH＋ ）, fluoride （F-）, permanganate index （CODMn） and total dissolved solids （TDS） exceed the water class; and these points mostly occur in the strata of the middle and the late Triassic. On the other hand, the groundwater of 57.1 % sampling points falls in class I, resulted from previous method of fuzzy comprehensive evaluation, which is not in accord with the reality. In addition, through the fuzzy comprehensive evaluation calibrated with level characteristic values, the water quality of 57.1% and 28.6% points fall within class Ⅱ and class Ⅲ, respectively, of which the standard deviation is 0. 011 lower than that from the comprehensive index method which stresses much on weight factor for the element with highest concentration. Therefore, current method for comprehensive evaluation of karst water quality can effectively reflect over- all water quality level, water chemical anomalies and quantitative quality classification. It is trusted that the evaluation results are reliable.