Soil sampling at Dåva DAC
On October 1, 2024, soil from an old landfill at Dåva DAC, where the sulfidic soils had been deposited partly under stabilised sulfide soils, sewage sludge, peat and lime, was sampled. pH was measured directly in the field at different locations and various depths and at the laboratory at Novia, the pH/redox potential was measured, the sulfide content was quantified using sulfur speciation, and DNA was extracted from the soil samples for microbial analyses. The rest of the samples were frozen for later analyses.
The results will be compared with corresponding samples from the more recently constructed Dåva Norra landfill and from the mesocosm experiment.
The screw and core sampling were done by LejonGEO AB.
Fig.1. Soil sampling at Dåva DAC.
Fig. 2. Screw sampling showing the different layers of the landfill.
Final sampling of field boxes
On September 3-4, 2024, we completed the STASIS field box experiment that was started in 2020 (preliminary results from the project can be found here on pages 28-30).
The first day we did the last round of sampling drainage water from the boxes. We measured pH, conductivity and ORP, and took samples for acidity, metals and anions and ferrous iron from the drainage water. At the Novia UAS laboratory we later analysed ferrous iron by spectrophotometry, anions with ion chromotagraphy, and acidity by titration.
The second day we measured pH at various depths and then took several soil samples from all the boxes. At the laboratory we measured the pH/redox potential, prepared the soil samples for microbial analyses and quantified the sulfide content using sulfur speciation. The rest of the samples were frozen for later analyses.
Fig.1. Measuring pH of the soil in the field experiment boxes.
Presentation at ECSMGE24 conference
Alaleh Ziagharib participated in the ECSMGE24 (XVIII European Conference on Soil Mechanics and Geotechnical Engineering) conference organised August 26-30, 2024, in Lisbon, Portugal, where she presented her paper titled "Validation of a Sulfide Soil Landfill Numerical Model."
Her research, based on data collected from the Dåva DAC landfill sensor installation, aims to improve the understanding of sulfide soil landfilling practices. The study focuses on enhancing landfill efficiency and preventing potential acidification, which poses environmental hazards.
Ziagharib’s work contributes to advancing landfill management practices, promoting a more sustainable and environmentally friendly approach to dealing with sulfide-rich soils.
Fig.1. Alaleh Ziagharib giving a presentation at the ECSMGE24 conference.
Fig.2. Installation of the sensors at Dåva DAC.
Meetings in Umeå
On June 17-18, 2024, the project members met for two nice days in Umeå, Sweden. On Monday we held the second steering group meeting and followed up with a project meeting to discuss upcoming tasks and look over preliminary results. On Tuesday we headed for the site of Dåva deponi och avfallscenter i Umeå AB for a sampling trip. We took samples of a sulfidic soil that had been excavated from a bridge construction project in 2020 and deposited at Dåva.
Fig.1. Steering group meeting with the project members
Fig.2. Preparing to sample sulfidic soil from Dåva DAC.
Mesocosm sampling
On May 21, 2024, the first water samples were taken from the mesocosm field experiment installed at the Risöfladan field in Vasa, Finland. It was a warm and sunny day, perfect for working outdoors.
We collected samples for acidity, metals and anions, ferrous iron and total organic carbon (TOC) by pumping groundwater from each of the 15 mesocosm tubes. This was done by inserting a flexible tube down to 110 cm depth and pumping up water using a peristaltic pump.
At the Novia UAS laboratory we later analysed ferrous iron by spectrophotometry, anions with ion chromatography, acidity by titration and TOC with nondispersive infrared spectroscopy.
Fig.1. Sampling groundwater from the Mesocosm tubes. Outdoor laboratory set up by the road for easy sampling.
Fig.2. Pumping water from a Mesocosm tube with a peristaltic pump.
Fig.3. Titrating acidity at the Novia UAS laboratory.
Sampling of field boxes
On May 7, 2024, water samples from a field box experiment that was started in the previous STASIS project were collected.
The field boxes contain dredged hypersulfidic sediments that have been mixed or layered with agricultural lime, ultrafine-grained lime and peat. The boxes were placed outside in the autumn of 2020 and have since been exposed to repeated freeze and thaw cycles. Preliminary results from drainage water sampled from the boxes show that if hypersulfidic dredge materials are left untreated they turn sulfuric and result in leaching of acidity and metals. However, if the sediments are mixed with lime, the pH is stabilised and only minor leaching of metals takes place. The preliminary results from the STASIS project can be found here (pages 28-30).
At the field site we measured pH, conductivity and ORP, and took samples for acidity, metals and anions and ferrous iron from the drainage water from the boxes. At the Novia UAS laboratory we analysed ferrous iron by spectrophotometry, anions with ion chromotagraphy, and acidity by titration.
Fig.1. Field boxes containing hypersulfidic dredge materials from the STASIS project.
Fig.2. Field box drainage water measurements of pH, conductivity and ORP.
Fig.3. Filtering samples for ferrous iron.
Mesocosm experiment started
The mesocosm field experiment started on October 4, 2023 at the Risöfladan field in Vaasa, Finland.
Installation of the mesocosm pipes was done using an excavator pushing 15 two-meter-long tubes down into the soil. After installation, the tubes were filled with some topsoil up to ground level.
Two m deep groundwater pipes and 60 cm and 110 cm treatment pipes were installed inside the mesocosm tubes.
Treatment was done by pumping water and suspensions with different amendments in the 60 cm deep treatment pipes. For the reference tubes 10 litres of tap water was used. The different amendments used were 300 g of C2 CaCO³ (Nordkalk, particle size <2.5 µm) suspended in 10 litres of tap water, 300 g of C2 CaCO³ suspended in 10 litres of filtered peat leachate, 300 g of CaSO₄·2H₂O (≥98.0%, Thermo Scientific) suspended in 10 litres of tap water and 300 g of CaSO₄ suspended in 10 litres of filtered peat leachate. All treatments were done in triplicate.
As the initial plan of using peat particles proved troublesome for pumping, a filtered peat leachate was produced. Kekkilä natural peat (50 L) was bought, and 5 kg peat was suspended in 50 liters of tap water in three 80 L containers. After mixing, the peat suspension was allowed to stand for 13 days before it was filtered through 0.5, 0.25 and a 0.125 mm sieves to get a leachate containing some peat particles. TOC analysis of the peat leachate showed that it contained 105 mg TOC/l.
After the treatments were done, the tubes were filled with water to cover the topsoil and then capped.
Using the excavator, a 2 m deep hole was dug near the mesocosm tubes. Samples for sulfur speciation, IR and DNA was taken from soil depths of 180, 135, 100 and 60 cm. For selected depths samples were taken from both the inner core and macropore surfaces.
The experiment will continue for 6 years and and water samples will be taken periodically from the groundwater pipes. The first five tubes will be excavated after two years and the following five two years after that, leaving the last five tubes in the ground until the end of the experiment. As the tubes are excavated the soil column will be sampled for geochemical and microbiological analyses.
Fig.1. Excavator pushing mesocosm tubes into the soil
Fig.2. Pumping suspension into the treatment pipes