Modelling of chemical migration under the overlapping impact of multiple and diverse pollution sources in the area of the “Zachem” Chemical Plant (Bydgoszcz, northern Poland)

Abstract

Modeling studies of chemical migration in the area of the “Zachem” Chemical Plant in Bydgoszcz started from the analyses of the production profile. Those studies were conducted to investigate the potential contaminants. Organic compounds still represent a substantial concentration in soil and water environment, including total organic carbon (TOC) reaching values above 1600 mg/L, aniline, nitrobenzene and phenol (up to 500-800 mg/L), organochloride and organometallic compounds, as well as hydrocarbons, such as benzene, toluene and PAHs. Groundwater contains most of the major ions (chlorides, sulphates and bicarbonates, sodium and calcium) and trace elements (Al, Co, Cr and Ni).

A reliable conceptual model of the geological structure was constructed for 3 continuous layers with variable bottom morphology. This model represents the complex structure containing permeable and impermeable Quaternary and Neogene deposits. A hydrogeological numerical model was created for the area of the “Zachem” Chemical Plant using the Visual MODFLOW program. Low values of two key statistical measures confirm a good model fitness to the measured conditions: root mean square (RMS) amounts to only about 1.5 m and normalized RMS reaches only about 4.4%. The differences between measured and calculated values are normally distributed. A Modpath module was used to analyze the potential extent of contaminant plume. Accurate hydrogeological 3D sampling was conducted using a “low flow” technique.

The results of full and reliable modeling of the chemical migration under the overlapping impact of multiple and diverse pollution sources in the area of the “Zachem” Chemical Plant are essential for further planning of remedial strategies.