Research on the Method for Reasonably Determining the Target Value of Soil Heavy Metal Anomaly Remediation: A Case Study of a Chemical Factory Decommissioning Site in Zhejiang Province

The soil arsenic detected at a decommissioned chemical plant site in Zhejiang Province is significantly high than the screening value of 20 mg·kg^-1. However, the correlation with potential anthropogenic arsenic contamination from historical industrial activities is low, whereas the correlation with local soil arsenic anomalies, attributed to the high natural geological background, is higher. It is necessary to systematically determine the restoration target value after the geological and geochemical background survey. Based on the regional geological background features, this study conducted background investigations and sampling, and identified that hydrothermal activity as the predominant factor for soil arsenic anomalies in the region. Statistical methods were employed to determine the upper limit of the 95% confidence interval (mean ±3 standard deviations) at 83.63 mg·kg^-1, representing the background value after outlier removal. Analysis and verification indicate that using this statistical background value as a remediation target is reasonable and feasible, and can potentially reduce the volume of soil requiring remediation by up to 65 000 m³ compared to conventional methods. The proposed method for background investigation and value determination is applicable to soil investigation and treatment in areas with high natural background anomalies, effectively avoiding over-investigation and over-remediation.