Mainly designed to capture Quaternary contaminated groundwater migrating from the “Zielona” waste landfill complex towards the neighbourhoods of Łęgnowo-Wieś and Plątnowo, the barrier intake was developed in the years 1991-1992 as a system of three wells: A₁, B and C. The pumping system was intended to halt any contaminated water along the railway line connecting Bydgoszcz to Toruń. Regrettably, the well system would be shut down annually from December until March to prevent surface infrastructure from freezing during the winter months; even when operational, downtimes on the intake were frequent, especially during Plant malfunctions or power supply interruptions. It turned out soon that operating the intake barrier over the intended period of April until November was not feasible anyway because of acidic wastewater in the Central Waste Equalisation Tank. Acidic wastewater would be mixed with polluted groundwater from the barrier intake. Humongous volumes of poisonous hydrogen sulphide (H₂S) were generated as a result.

The “Zielona” waste landfill complex remains the main source of pollution causing environmental degradation in the Łęgnowo-Wieś area. The pattern of organic and inorganic contaminant migration across groundwaters is directly related to the local geological structure. 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 glacial till- and loam-containing formation ceiling found at greater depths. The water table is unrestricted, flow directions determined by local uplifts and poorly permeable layer inserts in the substrate glacial till ceiling. In general, water tends to flow north-east and east, in the general direction of the Vistula riverbed. The surface aquifer of the “Zielona” waste landfill complex area is approximately several to over ten metres thick, the permeability coefficient for saturation zone sands reaching 4.0×10^-5÷1.69×10^-4 m/s.

Components distorting the natural groundwater flow direction in the landfill area included an anti-filtration screen, drainage system included, and the no longer operational intake barrier located along the pollutant plume spill, i.e. north-east of the landfill.

Designed to capture contaminated groundwater flowing east and north-east of the “Zielona” waste landfill complex, the barrier intake was developed in the years 1991-1992. Formally speaking, the intake formed part of service resources for the Area d900 cooling water intake of the “ZACHEM” S.A. Chemical Plant in Bydgoszcz. It was located at an approximate distance of 800-1,000 m east of the Chemical Plant boundary perimeter, near the Plątnowska street / Bydgoszcz-Toruń connection railway tracks intersection.

The intake comprised three wells (A, B, C) 19.0 to 23.5 m deep, and monitoring boreholes BP1, BP2 i BP3. A barrier intake service depth of 85 m³/h was approved for a (groundwater table) depression depth of 4.0 m. The water permit specified respective capacities of 30 m³/h and 700 m³/d. Well A capacity having sharply declined after 1996, the well was duly decommissioned, substitute monitoring borehole A₁ drilled in 1997.

Despite considerable groundwater pollution and actual threat to residents of the area located along the groundwater outflow from the “Zielona” waste landfill complex towards the River Vistula, the intake was only operational from April 1^st until November 15^th. Records also show intake shutdowns chiefly caused by power outages or – less frequently – equipment malfunction.

The table below shows technical parameters for individual barrier intake wells and piezometers:

TECHNICAL PARAMETERS FOR BARRIER INTAKE WELLS, 2005

Parameter / Borehole	Barrier intake wells			Monitoring piezometers
	A1	B	C	BP1	BP2	BP3
Depth [m]	20.5	19.0	23.5	26.0	26.0	25.5
Aquifer thickness [m]	15.0	13.5	16.0	22.0	>22.5	17.5
Filter	Mesh 11¾”	PVC Pressag 280 mm	PVC Pressag 280 mm	PVC Pressag 165 mm	PVC Pressag 165 mm	PVC Pressag 165 mm
Filter length [m]	5.0	3.0	6.0	4.0	4.0	4.0
Maximum capacity [m3/h]	28.4	15.0	40.0	-	-	-
Depression [m]	3.4	3.5	4.0	-	-	-
Filtration coefficient [m/s]	2.03×10-4	1.97×10-4	3.25×10-4	-	-	-

Groundwater pumped from the barrier intake was fed into the Plant’s sewage grid, then to the Central Waste Equalisation Tank (CWET). Shortly after barrier intake commissioning, in 1992, it turned out that continuous intake operation over the intended period of April until November was not feasible. The discharge of highly contaminated acidic water into the sewage grid gave rise to hydrogen sulphide presence, and humongous related air emissions. The process was particularly intense in sewage collectors and cascades, and the no longer existing Central Wastewater Neutralisation Station, the concentration rate sum for hydrogen sulphide and sulphides (H₂S + S^2-) reaching 30 to 40 mg/L.

Issues with safe water discharge from the intake caused extremely irregular barrier intake use over the years 1992-1994 (essential conditions for operating the intake included a neutral or alkaline wastewater pH value at the barrier intake-to-sewage grid water discharge location). The contemporaneous 24-hour intake operational time ranged from over ten minutes to over ten hours, average hourly capacity (1992-1994) reaching 15.4 m³/h, 13.7 m³/h and 30.5 m³/h for wells A, B and C, respectively. Approximately 117,500 m³ of polluted water was pumped from the intake over the period. Intending to avoid hydrogen sulphide emission issues, the Research & Development Department of the “Organika – Zachem” Chemical Plant designed a technology of treating barrier intake water, involving the oxidation of sulphides (S^2-) into sulphates (SO₄^2-) with the use of sodium hypochlorite and a Rang-19 catalyst.

 

HYDROTECHNICAL INFRASTRUCTURE LOCATION SCHEMA FOR THE “ZIELONA” WASTE LANDFILL COMPLEX (to Pietrucin, 2015)