Integrated Solid Phase, Aqueous Phase and Numerical Investigation of PlumeGeochemistry at an Oil Sand Mining Facility

Earth Sciences;Geochemistry;Hydrogeology;Oil Sand;Naphthenic Acid

Oiffer, Alexander

University of Waterloo

关键词: Earth Sciences;    Geochemistry;    Hydrogeology;    Oil Sand;    Naphthenic Acid;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/1210/1/aaloiffe2006.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

A plume of process-affected groundwater was identified in a shallow sand aquiferadjacent to a tailings impoundment at Syncrude Canada Ltd. Quantitative and qualitativeNaphthenic Acid (NA) analyses were performed on groundwater samples to investigateNA fate and transport properties in the subsurface. Analysis of dissolved organic andinorganic components was undertaken to identify, quantify and assess the mobility ofother dissolved components of environmental significance. NAs at concentrations up to87 mg/L were found to represent the major contributor to aquatic toxicity. Attenuationof NAs by biodegradation is not observed based on screening techniques developed todate. Retardation of NAs observed at the field scale, is consistent with weak sorptionobserved in the laboratory by other authors. Concentrations of ammonium approached 4 mg/L in the plume, however mobility is limited by cation exchange. Aromatics and trace metals are present in low quantities (i.e. <10 µg/L) and are only detected in groundwater immediately adjacent to the toe of the tailings impoundment. Cl and Na are found at concentrations of up 282 and 579 mg/L respectively. Dissolved oxygen is typically < 1 mg/L within the plume, while redox indicators Mn(II), Fe(II) and methane are detected between <0.1 - 2.6, 0.2 - 3.5 and <0.1 - 2.1 mg/L respectively within the plume. Solidphase geochemistry, determined through solid phase extractions, was coupled with aqueous geochemistry and reactive transport modeling to identify the dominant geochemical processes occurring within the plume. Based on scenarios evaluated using reactive transport modeling, the most likely origin for the presently observed, weakly reducing conditions in the plume appears to be the presence of a small amount of disssolved, degradable organic carbon. The dominant terminal electron acceptors appearto be Fe(III) and Mn(III/IV) in the plume core and dissolved oxygen at the plume fringe. Dissolved Fe and Mn are observed to enter the domain at the upgradient boundary at maximalconcentrations of 4.2 and 0.7 mg/L respectively. Trace metal geochemistry of the aquifer material was also assessed using solid phase extractions. The potential for trace metal release via reductive dissolution of the native geologic material is considered minimal in this case, based on the weakly reducing nature of the plume and a lack of excessive trace metal content in the aquifer material.