To Örebro University

Oil production (1942-1966) and uranium extraction (1953-1961) from the Alum Shale Formation in Kvarntorp, Sweden has had a great environmental impact on the area. Other industrial activities have also contributed to pollution. This study combines archive research with monitoring data and new sampling in order to assess the extent of the impact. During the production period, process water containing oil, phenols, sulfur compounds and high concentrations of iron reached the stream resulting in low water quality downstream. Also the landscape was reshaped, resulting in water filled pit lakes and a 100-meter-high shale waste deposit. Today, past alum shale activities still have an impact on the environment. Sulfate concentrations in the pit lakes are significantly higher than background values and downstream water also shows higher concentrations of elements such as nickel and uranium. The waste deposit still has a hot interior and an important question is the cooling rate and possible future leaching scenarios. Remaining hydrocarbons show today only a local impact while trace elements are transported downstream and affect a larger area.

Worldwide, black shales and shale waste are known to be a potential source of metals to the environment. This project demonstrates ongoing weathering and evaluates leaching processes at a 100-m-high shale waste deposit closed in the 1960s. Some deep parts of the deposit are still burning with temperatures exceeding 500 °C. To demonstrate ongoing weathering and leaching, analyses of groundwater and solid samples of shale and shale waste have been undertaken. Largest impact on groundwater quality was observed downstream the deposit, where elevated temperatures also indicate a direct impact from the burning waste deposit. Groundwater quality is largely controlled by pH and redox conditions (e.g., for arsenic, nickel, molybdenum, uranium and vanadium), and the mixture of different waste materials, including pyrite (acidic leachates) and carbonates (neutralizing and buffering pH). Analyses of shale waste from the deposit confirm the expected pyrite weathering with high concentrations of iron, nickel and uranium in the leachates. No general time trends could be distinguished for the groundwater quality from the monitoring in 2004-2019. This study has shown that black shale waste deposits can have a complex long-term impact on the surrounding environment.

Several large pits were left after alum shale was mined from 1942 to 1966 in the Kvarntorp area of Sweden. Of these, the pit lakes Polen and Norrtorpssjon are the focus of this study. They have elevated levels of Na, K, Mg, Ca, Al, Mn, Fe, and sulphate, as well as trace elements, from weathering of the exposed shale. Both lakes had a stable pH below 4 until 1996 when the pH in Norrtorpssjon started to increase, exceeding 8 in 2010, due to inflow of leachates from alkaline waste dumped in an adjacent waste deposit, similar to a large scale anoxic limestone drain (ALD). Iron and Al concentrations decreased as the pH increased, indicating formation of particulate species which accumulate as sediments. The Co, Ni, and Zn concentrations also decreased, probably due to association with the solid phases, while Cu was less affected by the increase in pH, possibly due to formation of complexes with dissolved organic matter. Vanadium concentrations show limited solubility, while Mo concentrations increased at higher pH. Uranium concentrations decreased from above 80 mu g/L to below 10 mu g/L before rising to 30-35 mu g/L due to the formation of soluble carbonate complexes at higher pH levels. The elevated levels of Li, Sr, and U indicate that weathering has continued despite the pH change. Both pit lakes are stratified, but no seasonal overturn has been observed. Long-term behaviour of this large-scale ALD and its implications are also discussed.

Due to scarcity of imported liquid fuel during World War II, alum shale was mined for oil production in the Kvarntorp area 1942-1966. The shale contains both organic matter (kerogen) and elevated concentrations of trace elements such as molybdenum, nickel, uranium and vanadium. Today there are several pit lakes in the area and a 100-meter-high waste deposit, Kvarntorpshögen, consisting mostly of crushed and burned shale but also some unburned crushed shale and lime waste.

The aim of this study was to get a better understanding of the environmental impact of alum shale mining with focus on trace metal release. During the production era, the surroundings were highly affected by both sulphur rich flue gas emissions and bad water quality in downstream waters. The former mining activities show impact also today, with higher concentrations in downstream water than upstream the area. Analyses and leaching tests of solid samples have shown pyrite weathering in shale and unburned shale waste with release of for example nickel and uranium.

Analyses of groundwater in eleven wells around the deposit show ongoing leaching of both shale waste generating a circumneutral leachate and unprocessed shale leading to acidic leachates.

All pit lakes in contact with alum shale waste or the shale horizon show elevated sulphate concentrations indicating pyrite weathering, although only one is still acidic today. Also Norrtorpssjön was acidic until a pH rise due to adjacent dumping of alkaline waste. The pH increase was followed by a decrease in aluminium, cobalt, magnesium and nickel.

Surface water analysis show that the waste deposit is estimated to contribute with less than a fifth of the mass transport whereas the western pit lakes contribute with the largest part.

Alum shale was mined for oil and uranium production in Kvarntorp, Sweden, 1942-1966. Remnants such as pit lakes, exposed shale and a 100-meter-high waste deposit with a hot interior affect the surrounding environment, with elevated concentrations of, e.g., Mo, Ni and U in the recipient. Today most pit lakes are circumneutral while one of the lakes is still acidic. All pit lakes show signs of sulfide weathering with elevated sulfate concentrations. Mass transport calculations show that for elements such as uranium and molybdenum the western lake system (lake Soderhavet in particular) contributes the largest part. For sulfate, the two western lakes contribute with a quarter each, the eastern lake Norrtorpssjon about a third and a serpentine pond system receiving water from the waste deposit contributes around 17%. Except for a few elements (e.g., nickel 35%), the Serpentine system (including the waste deposit area) is not a very pronounced point source for metal release compared to the pit lakes. Estimates about future water runoff when the deposit has cooled down suggest only a slight increase in downstream water flow. There could possibly be first flush effects when previous hot areas have been reached by water.

Alum shale residues in the form of nes and ash were leached at di erent pH and redox conditions. Total concentrations and mineral analysis indicate loss of some elements in burned shale, and redistribution of others. Uranium and nickel were shown to be more leachable from nes than from ashes. Decreased pH favoured leaching of Ni, U and V, whereas increased pH resulted in increased leaching of molybdenum. Redox conditions a ected leaching of Mo and V, but not U and Ni. us the method can be used as an estimate for leaching at di erent redox and pH conditions.

Due to oil production from alum shale, the Kvarntorp area is heavily polluted. A waste deposit consisting mostly of shale ash and fines is of important concern. Groundwater shows that parameters such as pH, U, V, Ni and Mo are different at different localities around the deposit. Leaching tests indicate that burned and unburned shale residues leave different signatures on leachates. Principal component analysis of groundwater and leaching tests suggest that ground-water is affected by the waste deposit and that it is more influenced by shale ash than by fines.

Due to oil production from alum shale, the Kvarntorp area is heavily polluted. A waste deposit consisting mostly of shale ash and fines is of important concern. Groundwater shows that parameters such as pH, U, V, Ni and Mo are different at different localities around the deposit. Leaching tests indicate that burned and unburned shale residues leave different signatures on leachates. Principal component analysis of groundwater and leaching tests suggest that ground-water is affected by the waste deposit and that it is more influenced by shale ash than by fines.

Scarcity of imported fuel led to oil production from alum shale in the Kvarntorp area, 200 km west of Stockholm, during 1941-1966. Remains from this are a 100 meter high waste deposit, Kvarntorpshogen, consisting mostly of shale ash and water filled open pits. As this shale is rich in sulphur and trace metals such as U, Ni and Mo, leaching from the waste deposit is feared. To elucidate the important question whether Kvarntorpshgen is the most important concern, or to what extent other sources might contribute with contamination, water sampling was extended to contain more localities than the ordinary control program. A new approach was the sulphur isotope analysis. The results point towards an area too complex for using sulphur isotopes for mixing calculations. Isotope fractionation during oil production is shown by the delta(34) difference between shale and shale ash. Current isotope fractionation indicates sulphate reduction. Some localities indicate pyrite weathering and others rather show buffer capacities due to the presence of lime. Sr concentrations also suggest weathering. It is indicated that Kvarntorpshgen has an impact on the surroundings, but also that the water filled open pits as well as an industrial area affect the water quality. It is concluded that Kvarntorpshgen is one of the most important contributors of metal dispersion, but other point sources cannot be discarded as environmental risks.