The evaluation of groundwater vulnerability to pesticides

The groundwater in china is showing signs of contamination from a wide variety of pesticides. Assessing the fate and behavior of the pesticide pollutants is a complex environmental problem due to heterogeneity of the subsurface system and the spread of pesticides over large areas in relatively low concentrations. Vulnerability evaluation is used in this case as a too] to determine areas where groundwater protection or monitoring are critical. One of the widely used groundwater vulnerability mapping methods is DRASTIC Index System. For some reasons, DRASTIC mole] is not match to the reality of China. Therefore, by studying, a method, Modified MDRASIC Index System (MDRASTIC), in the operation and comparison of different area in China on groundwater Vulnerability to pesticides was carried Out. In the MDRASTIC method, six indexes data are required, i.e., depth to groundwater, soil texture, topography (slope), lithology of the aquifer, use of land, and irrigation and rain. By introducing the two indexes, use of land and irrigation and rain, MDRASTIC become more suitable to the vulnerability evaluation of groundwater to pesticides. For each cell, the MDRASTIC rating for each input layer was multiplied by the pesticide MDRASTIC weight for that layer and summed to determine the MDRASTIC index. The weighting scheme (i.e., 3:3): 1: 1: 1: 1) were designed by conducting correlations between two data sets as follows: ( I) pesticide concentrations found in groundwater samples in the study area, and (2) six index values at the same location, respectively. Scheme represented the weights or Influence factors for six indexes, respectively. Depth to groundwater played the most important role and was assigned the highest weight. To test the relationship between those Vulnerability values and available data derived from actual observations. vulnerability values, produced according to the function (2.3.2), were compared to groundwater quality data of the study area. The comparisons were conducted by correlations between the following data sets: (I) concentrations of some pesticide found in groundwater samples in the study area, and (2) vulnerability scores of the place where the samples were selected. Repeating this process enough times, as a result, a most Suitable weights scheme (i.e., 3:2.5:1.5:1.5:1.0:0.5) was got. Finally, use geographic information system (GIS) technology to produce maps of the study area showing relative vulnerability of groundwater to pesticide pollution, and to develop a model for predicting the degrees of susceptibility of groundwater to contamination by pesticides. By this way, a satisfied weights scheme is conducted for the city of Jingzhona. The resulting pesticide MDRASTIC vulnerability map indicates that the hi hest potential sites 9 9 for contamination are in the west of the study area.