ISL stands for Isolated Sludge Landfill, the west section of the post-industrial waste landfill complex on Zielona street, commonly referred to by residents of Bydgoszcz as the “Zielona” waste landfill complex. 4.8 hectares in area, the ISL was developed in 1991 with intent to receive sludge from all installations operated as part of the “ZACHEM” S.A. Chemical Plant. Originally, the ISL received sludge from the Central Waste Equalisation Tank only; in later years, once the successive Plant installation had been launched, it was also fed from the Central Wastewater Neutralisation Station.

Owing to its trademark footbridge, the ISL became a symbol for the “Zielona” waste landfill complex. Nonetheless, this does not mean that it constitutes the most hazardous section of the Plant.

The history of waste depositing and landfill use on the former “ZACHEM” S.A. Chemical Plant site can be traced back to the 1940s, originally tying in with manufacturing operations of the DAG Fabrik Bromberg. Post-World War II manufacturing and resultant waste depositing resumed in 1948.

The current zone of the “Zielona” waste landfill complex was originally an area of extracting a fluvioglacial natural resource, in all probability sand. A landfill gradually developed in the excavation pit.

The developed industrial waste landfill the ISL is currently part of is located in the south-eastern section of the “ZACHEM” S.A. Chemical Plant in Bydgoszcz on Zielona street, on land parcels numbered 9/107, 9/105, 9/103 in geodesic area No. 137. Due to its location on Zielona street, the entire landfill is customarily referred to as the “Zielona” landfill complex. The landfill proper occupies an approximate total area of 11 hectares, with a complex of three smaller separate sites: the reclaimed general waste landfill to the east, the (centrally located) reclaimed former incineration yard, and the Isolated Sludge Landfill western section.

 

Location sketch for the Isolated Sludge Landfill against the “Zielona” waste landfill complex backdrop (to a drawing by Pietrucin, 2015)

Developed between 1987 and 1991, the Isolated Sludge Landfill (ISL) was located on what is the “Zielona” industrial waste landfill today, west of the incineration yard, and partly on the former excavation pit site (for a detailed description, see Point of Interest No. 3 of the Educational Virtual Tour). 4.8 hectares in area, the ISL was designed to accommodate 188,000 m³ of waste. The Isolated Sludge Landfill site bottom was insulated with two layers of PVC film and fitted with a drainage system, an observation (monitoring) network designed and constructed for the facility as well. The network comprised 11 piezometers – small-size diameter test holes; 168 mm in diameter each, they are still in use today to monitor the water table and collect water samples for quality testing. The piezometer grid designed to monitor the hydrogeochemical condition of Quaternary groundwater currently (2023) consists of piezometers marked “P” (P17, P18, P19, P20 and P21) or “Pz” (Pz1, Pz2, Pz3, Pz4, Pz5, Pz6, Pz7, Pz9, Pz12 and Pz13). All are located along the “Zielona” complex perimeter.

From the day construction works on the Isolated Sludge Landfill (ISL) had ended, the site began receiving sludge from the Central Waste Equalisation Tank (CWET).

Seven hectares in area, the Central Waste Equalisation Tank (CWET) was built in 1977. The Tank was used to deposit – or, in all actuality, equalise – all sludge generated in the process of mixing waste originating from the entire Chemical Plant area. The CWE Tank was duly encircled with a drainage system. While mostly filled with sludge in its regular condition, the Tank was unfit to receive any sludge over the years 1986-1987 because of a major malfunction. Consequently, all industrial wastewater was fed into an open ditch, the point of direct discharge into the River Vistula the next stop. In all probability, that major glitch had ended up highlighting the need to construct an auxiliary post-industrial sludge waste landfill the aforesaid ISL ultimately became.

Once the Bydgoszcz Chemical Plant had opened its Central Wastewater Neutralisation Station (CWNS), sludge was pumped directly to the ISL; once the sludge dewatering centrifuge was in place, the Plant began transporting sludge by road, the pumping process abandoned altogether.

While there is no detailed data available to describe the operating period of the wastewater pre-treatment plant, i.e. the Central Waste Equalisation Tank (CWET), Environmental Protection Department staff of the “ZACHEM” S.A. Chemical Plant did mention the “no longer existing (…) Central Waste Equalisation Tank (CWET)” at the 2005 Contemporary Hydrogeological Issues scientific conference, and specifically in the guidebook for the “Hydrogeology of the Kujawy and Lower Powiśle Region” field session.