Leaving the site of the former “ZACHEM” S.A. Chemical Plant by symbolically passing through one of the exit gates does not necessarily mean that the Plant’s impact on the land-and-aquatic environment also observes formal or ownership boundaries. The mere presence of surface fencing or gates is regrettably not tantamount to the obstruction to the flow of water, or any substance dissolved therein. Pollutants infiltrating the environment in the vicinity of the “Zielona” waste landfill are freely transported in the overall direction of Łęgnowo, Plątnowo and the River Vistula River – main drainage basin for the former “ZACHEM” S.A. Chemical Plant site. The geological structure and related hydrogeological conditions are key to determining the contaminated groundwater’s flow direction and migration.

The geological structure of the small-size area of the “Zielona” industrial waste landfill complex differs from the geological structure schema of the entire “ZACHEM” S.A. Chemical Plant: deep within the Plant’s bedrock lies a sand-and-gravel formation layer several metres thick, with a subsoil complex of glacial till and loamy sands. The glacial till / sandy loam / loamy sand layer with minuscule sand interbedding forms a geological complex, layer thickness ranging from over ten to several dozen metres. The ceiling of said layer in the immediate vicinity of the “Zielona” landfill complex reaches an elevation of 48.0÷55.1 m ASL, or 7.8÷14.7 m above landfill subsoil. Nonetheless, that self-same layer occasionally rises well-nigh to the surface. An analysis of the geological structure north-east of the “Zielona” landfill complex in the direction of the River Vistula proves that poorly permeable formations occur in the form of light-grey silts at a depth of 8.0÷18 m below ground level, the glacial till layer ebbing, as shown in the geological cross-section below.

A layer of fine and medium sands of fluvioglacial origin and sand-and-gravel deposits rests upon an unbroken, poorly permeable layer of glacial till, sandy loam and loamy sands, with minuscule sand interbedding (except areas of the layer reaching the surface). This layer is present on the surface, barring areas which had undergone heavy anthropogenic change – waste, industrial waste included, deposited directly on land surface. In the subsoil of the “Zielona” waste landfill complex, the ceiling of aforesaid sandy formations was identified at a depth of 5.5÷7 m below ground level. One would be hard-pressed to clearly delineate the local periphery between waste and primary Quaternary sediments, given the liquid waste deposits infiltrating deep into the landfill, and contaminants leached along with water permeating the dump.

ogical cross-section in the “Zielona” waste landfill complex area, including the primary range of the polluted groundwater plume (to a graph by Pietrucin, 2015, based on Narwojsz, 1989) 1 – sand, 2 – loam, 3 – silts and sludges, 4 – range of the polluted groundwater plume, 5 - piezometer

Waste found in the “Zielona” waste landfill complex is on average several dozen years old. Throughout the period, chiefly as a result of soil-infiltrating precipitation, the boundary between the true primary soil and actual waste deposits was blurred, all matter mixed. Geologically speaking, the youngest sediments have as a result been redefined to include anthropogenic deposits comprising waste layers of considerable vertical and horizontal variability, present across most of the surface of the “Zielona” landfill complex. Types of waste deposited at the complex are a direct derivative of the types of production engaged in during the different periods of Chemical Plant operation. Industrial production waste aside, identified matter included post-demolition construction debris and bricks, sandy and loamy interbedding, and concrete slabs delineating technological lanes across the landfill. The land is covered with a top layer of sand, securing, as it were, the “Zielona” landfill complex surface. The top layer further includes bulk and big-bag packaged waste.

The intricate geological structure of the “Zielona” waste landfill complex, tying in with manifold interbedding and inserts of formations with extreme filtration properties – permeable and poorly permeable alike – bears direct influence on hydrogeological conditions, specifically the below-surface groundwater flow, and its capacity for long-range transportation of chemical substance compounds polluting the environment.

In the “Zielona” waste landfill complex area, a Quaternary aquifer has been identified in fluvioglacial fine and medium sands and gravels. The permeable formation layer ties in with a lowering of the poorly permeable formation ceiling. The local water table is unrestricted, flow directions determined by the morphology of the substrate glacial till ceiling. In general, water tends to flow north-east. The aquifer of the “Zielona” waste landfill complex area is approximately several metres thick, the permeability coefficient for saturation zone sands reaching 4.0×10^-5÷1.69×10^-4 m/s.

A barrier intake and anti-filtration screen located north-east of the landfill were recognised as objects interfering with the natural groundwater flow direction in the “Zielona” waste landfill complex area in the 1990s. All that remains in 2023 includes an ineffective anti-filtration screen, and activities altering hydrodynamic conditions in the aquifer as a result of ongoing soil-and-aquatic environment remediation in the landfill’s impact zone.

 

S Location sketch for the watertight wall at the “Zielona” waste landfill complex (to a drawing by Pietrucin, 2015) (REPEAT THE FIGURE FROM POINT OF INTEREST 3)