[Calculation of the Soil Risk Control Value through a Hydrus-1D Model for Groundwater Protection]

A combined Hydrus-1D and groundwater dilution model was employed to determine the risk control value and risk control volume of soil in correspondence of an electroplating workshop located in the Pearl River Delta. In particular, we considered the risk control value and risk control volume of soil in relation to characteristic chromium (Ⅵ) and nickel pollutants, which can affect the quality of groundwater. Based on the absorption of pollutants by the soil in the vadose zone, we obtained soil risk control values of 41.6 mg·kg^-1 and 619.1 mg·kg^-1 for chromium (Ⅵ) and nickel, respectively. These values were 10 and 45 times greater than those obtained from theoretical calculations (based on the soil/water partition equation combined with the groundwater dilution model), while the soil risk control volumes of chromium (Ⅵ) and nickel were 1804 m³ and 44590 m³, respectively. The soil risk control values calculated through the soil/water partition equation combined with the groundwater dilution model tend to be excessively conservative for the contaminated sites of the Pearl River Delta (characterized by a shallow buried depth of the underground water level and a close hydraulic connection); hence, it is necessary to carry out further hydrogeological surveys and fully consider the migration process of pollutants in the vadose zone. We conclude that the combined Hydrus-1D and groundwater dilution model for groundwater protection can be used to determine the soil risk control value, potentially saving the costs involved in later remediation and risk control.