Petroleum Coke Leachate And Its Potential Impacts On Groundwater

Two petroleum coke cells were constructed, then sampled over a period of three years (2008 – 2011). The study aimed to address concerns identified by Alberta Environment (AENV) in response to Suncor’s application to make coke stockpiles at the 86/17 Oil Sands Facility permanent. Cell 1 (flow-through cell) is 1 m deep and Cell 2 (accumulation cell) is 2 m deep. Design assumed overall water balance was positive, resulting in a net accumulation within the cells, and that analytes detected were related to loading from the coke rather than atmospheric deposition. Water was collected from each cell during 10 sampling events between 2008 and 2011. Coke leachate from each cell was collected and submitted for comprehensive chemical analysis and ecotoxicity testing. Chemical analysis included routine analysis, hydrocarbons, dissolved and total metals and trace elements, PAHs, naphthenic acids and phenols. Ecotoxicity testing included assessment of acute and chronic endpoints for aquatic invertebrates and fish. Chemistry data were compared to AENV and Canadian Council of Ministers of the Environment (CCME) guidelines for protection of freshwater aquatic life.

Several parameters exceeded guidelines on one or more samples: iron, fluoride, total ammonia as N, phenols, dissolved and total cadmium, copper, lead, manganese, molybdenum and zinc, total selenium and PAHs, with several exceeding guidelines throughout. In Cell 1, total vanadium increased. In Cell 2, dissolved sulphate increased. Decreases in bicarbonate, dissolved boron and dissolved strontium were observed. Acute toxicity to fathead minnows and chronic toxicity to Ceriodaphnia and fathead minnows was observed from several samples. Concentrations of substances released from the coke seemed dependent on water residence time rather than coke mass, suggesting release and adsorption may be influencing leachate composition. Several parameters consistently found in the leachate – dissolved and total metals and trace elements, cadmium, copper and lead – were also consistently reported in historical rainfall data collected from the site, suggesting they may not be related to coke leachate. Manganese, molybdenum and vanadium appear to be related to coke leachate. Concentrations of manganese and molybdenum in leachate did not differ substantially from groundwater data collected proximal to the coke storage area. Groundwater quality data are limited and interpretation is semi-quantitative at this time.