A GIS raster technique to optimise contaminated soil removal

A geographic information system (GIS) raster technique has been developed a nd used interactively with remediation designers to evaluate the optimum ex tent of excavating soil contaminated by chlorinated solvents. The technique and the results of its application are presented. The site was a former ch emical storage plant for acids and solvents. Two distinct solvent plumes we re detected within the ground using a photo-ionisation detector. The solven ts were found to be dissolved in the groundwater and migrating in the gener al direction of groundwater flow. A remediation strategy was proposed invol ving the localised excavation of contamination 'hot spots' followed by the implementation of a groundwater remediation system. A number of excavation options were discussed and the GIS raster technique was developed to evalua te these options in terms of contaminant removed and excavation cost. The plumes were initially mapped using a triangular irregular network (TIN) . These TIN models were rasterised to produce a regular grid of rectangular cells, each cell having a value relating to the concentration of contamina nt at that spatial point. The proposed excavation zones were then overlaid on to the raster models as masks. The relationship between the value of con taminant concentration of cells within the mask (or excavation zone) and th e total value of contaminant concentration of cells within the solvent plum e was used to determine the efficiency of the excavation. The excavation options were compared taking into account the percentage of the contaminant plume removed, the excavation area (soil volumes) and relat ed costs. Once the GIS raster technique had been developed, it proved very quick to rerun the analysis for the other excavation zones. The optimum exc avation zone, based upon cost and contaminant recovery, was found for the s ite. The technique helped by targeting the worst area of contamination and provided the client with a cost-benefit analysis of the different remediati on options. (C) 2001 Elsevier Science B.V. All rights reserved.