[Application of tiered approach to assess the impact of backfilling remediated soil on groundwater].

The tiered approach for assessing the impact of backfilling treated contaminated soil on groundwater was presented in details with a case study. The soil was contaminated by 1,2-dicholorenthane and 9 other organic pollutants and had been remediated before backfilling to meet the pre-set remediation goals based on health risk assessment. The results from tiered I assessment indicate that the concentrations of 8 contaminants in the leachate of the backfilling soil layer would exceed the assessment standards probably leading to groundwater contamination. However, the results from tiered II assessment, in which the adsorption and retardation of vadose zone soil was taken into account and the concentrations of pollutants reaching the groundwater table were predicated, reveal that only the concentrations of 6 contaminants would exceed the assessment standards. Further, taking the dilution and mixing of the groundwater into consideration, tiered III assessment was adopted and the results reveal that only 4 contaminants were beyond the standards. Finally, tiered IV assessment, aiming at predicting the concentration at the target well downstream, was carried out by considering the retardation of contaminants in saturated layer, and the results indicate only 1 pollutant was above the assessment standard. Therefore, it can be seen that the predicted concentrations of the target pollutants at advanced assessment levels will be closer to those at the target drinking water well and the amount of contaminants whose initially-set remediation goals need to be modified will decrease correspondingly, indicating the reduction in pollution prevention cost, although more efforts should be made and more field data should be collected to implement the advance assessment level.