Environmental impact assessment on oil shale extraction in Central Jordan

This study focuses on the environmental impact assessment of trace elements concentrations in spent shale, which is the main residual besides gas and steam from the utilization of oil shale. The study area El-Lajjun covers 28 km2, located in the centre of Jordan approximately 110 km south of Amman. It belongs mainly to the Wadi Mujib catchment and is considered to be one of the most important catchments in Jordan. The Wadi El-Lajjun catchment area (370 km2) consists of two main aquifer systems: The intermediate aquifer (Amman Wadi As Sir Aquifer or B2/A7) and the deep sandstone aquifer (Kurnub/Ram Group Aquifer). The B2/A7 aquifer (Upper Cretaceous) is considered as the main source of fresh water in Jordan. El-Lajjun oil shale was deposited in a sedimentary basin and comprises massive beds of brown-black, kerogen-rich, bituminous chalky marl. The oil shale was deposited in shallow marine environment. It is by definition a sedimentary rock containing organic material in the rock matrix. The shale oil extraction is an industrial process to decompose oil shale and to convert the kerogen into shale oil by hydrogenation, pyrolysis or by a thermal dissolution. Several classifications of extraction technologies are known; the classification with respect to the location where the extraction takes place distinguishes between off-site, on-site, and in situ. The oil shale utilization may have serious repercussions on the surrounding environment if these issues are not investigated and evaluated carefully. Ten representative oil shale rock samples with a total weight about 20 kg were collected from different localities of oil shale exposures in the study area. A standardized laboratory Fischer Assay test was performed with the samples to determine oil shale characteristics and to obtain spent shale, which was used in this study for further investigations. Sequential extraction was used to evaluate the changes in the mobility and distribution of the trace elements: Ti, V Cr, Co, Zn, As Zr, Cd, Pb and U. Column leaching experiments were performed to simulate the leaching behavior of the above elements from oil shale and spent shale to evaluate the possible influence on the groundwater in the study area. The concentrations in the leachate were below the maximum contaminant levels of the Environmental Protection Agency (EPA) for drinking water and the Jordanian standards for drinking water. An immobilization method by using Kaolin was applied to reduce the mobilization and bioavailability of the trace elements fraction that are contained in the spent shale. Immobilization was evaluated as a function of liquid-solid ratio (solid-liquid partitioning) and as a function of pH. A comparison between the results obtained from column leaching experiments and the results that were obtained from immobilization for the oil shale and spent shale samples indicated that the immobilization reduced the mobility of the trace element except for Ti, V, and Cr. However, even the concentrations of these elements were lower than the maximum acceptable limits of the Jordanian Standard Specifications for waste water. The catchment of the study area (Wadi El-Lajjun catchment) is ungauged. Therefore, the soil conservation service (SCS) runoff curve number method was used for predicting direct runoff from rainfall. The results obtained showed that the infiltration of water is very small (approximately 0.6 cm/year) and rarely can´t reach the groundwater through the oil shale beds. Thus, a contamination of groundwater is unlikely under normal conditions. DRASTIC was used to assess groundwater vulnerability for the B2/A7 aquifer with respect to pollution by oil shale utilization. The aquifer vulnerability map shows that the area is divided into three zones: low (risk index 10-100; intermediate (risk index 101–140) and high groundwater vulnerability (risk index 141-200). The high risk areas are small and mainly located in the northeastern corner of the El-Lajjun graben, where the hydraulic conductivity is relatively high and rocks are highly fractured and faulted. The water table of the deep sandstone aquifer (Kurnub/Ram group) in the El-Lajjun area is relatively deep. At least two geological formations above the Kurnub aquifer are aquitards and protect the deep aquifer. However, the area is highly fractured and thus there is a certain possibility for contact with surface pollutants. Finally, further research with respect to trace elements including REE elements and isotopes in the intermediate and deep sandstone aquifers are highly recommended. Isotopic signatures will be very helpful to investigate to which extend hydraulic connections between the aquifers exist. Further and in particular mineralogical studies on the spent shale and the possibilities for industrial utilization are recommended because huge quantities of spent shale are expected. Because most oil shale extraction technologies especially the power generation require considerable amounts of water detailed studies on water supply for the oil shale treatment have to be performed