Modelling of Predicted Environmental Concentration of Copper Contaminated Leachate in Sandy Soils using HYDRUS-2D

Modelling the predicted environmental concentration (PEC) of heavy metals in soils is of a paramount importance for several reasons. On the one hand, these inorganic pollutants can pose a significant health risk to living organisms, as they are toxic and poisonous at low concentrations. Moreover, they can be presented in the soil for a long period of time, taken up by plants, thus entering the food chain. On the other hand, properly parameterised and validated models can provide a good basis for environmental risk assessment resulting in the development of more efficient remediation strategies. Nowadays, hydrodynamic models are able to simulate the interactions of different pollutants, soil and water, and the transport of solutes. In addition, these models can take into account the physical and hydraulic properties of the soil layers, the amount and distribution of precipitation, and the physical and chemical properties of the pollutants, which can be used to predict the environmental concentration of heavy metals in the soils with a greater accuracy.

A 2D model was built in HYDRUS software for the long-term prediction of the environmental concentration of copper based on the data of the previously surveyed soil profiles (loamy sand) in the city of Debrecen, Hungary. The database of the Hungarian Meteorological Service was used to retrieve daily precipitation data for the period 2012-2020 (approx. 3000 days). After setting up the boundary conditions of the 10×20 m domain, observation nodes were assigned to different depths: 0 m (soil surface), 0.5 m, 1 m, 1.5 m, 2 m, 2.5 m, 3 m, 5 m, 10 m and 20 m. Firstly, the model was used to investigate the mobility of copper in sandy soils, considering the application of a theoretical copper contaminated leachate with the concentration of 1 mgL^-1 on the soil surface. The soil adsorption coefficient was set to 4×10^-7 m³g^-1, while the diffusion coefficient in water was 6.33×10^-5 m²day^-1. The specific quantity of the leachate applied on the soil surface was chosen to be 100 Lm^-2. Then, three different scenarios were made: 1) single contamination (once, on the first day), 2) regular contamination (once a month for a year), 3) continuous contamination (every day for a month).

The model results showed that the concentration of copper exceeded the contamination threshold (200 μgL^-1) at depths between 0-1.5 m during the first 50 days of the studied period in case of the single contamination. In deeper layers, the predicted environmental concentration of the copper was below the contamination threshold. In case of the regular copper contamination scenario, it was observed that almost a year is needed to decrease the contamination level below the threshold at the depths between 0-1.5 m. Deeper soil layers experienced the copper contamination with a substantial delay. The continuous copper contamination scenario resulted in a peak concentration of the copper with 1mgL^-1 at the depths between 0-5 m within a month.

The research presented in the article was carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF-2.3.1-21-2022-00008 project.