The acute toxicity of bitumen-influenced groundwaters from the oil sands region to aquatic organisms.

The extraction of surface mined bitumen from oil sands deposits in northern Alberta, Canada produces large quantities of liquid tailings waste, termed oil sands process-affected water (OSPW), which are stored in large tailings ponds. OSPW-derived chemicals from several tailings ponds migrating past containment structures and through groundwater systems pose a concern for surface water contamination. The present study investigated the toxicity of groundwater from near-field sites adjacent to a tailings pond with OPSW influence and far-field sites with only natural oil sands bitumen influence. The acute toxicity of unfractionated groundwater and isolated organic fractions was assessed using a suite of aquatic organisms (Pimephales promelas, Oryzias latipes, Daphnia magna, Hyalella azteca, Lampsilis spp., Ceriodaphnia dubia, Hexagenia spp., and Vibrio fischeri). Assessment of unfractionated groundwater demonstrated toxicity towards all invertebrates in at least one far-field sample, with both near-field and far-field samples with bitumen influence toxic towards P. promelas, while no toxicity was observed for O. latipes. When assessing the unfractionated groundwater and isolated organic fractions from near-field and far-field groundwater sites, P. promelas and H. azteca were the most sensitive to organic components, while D. magna and L. cardium were most sensitive to the inorganic components. Groundwater containing appreciable amounts of dissolved organics exhibited similar toxicities to sensitive species regardless of an OSPW or natural bitumen source. The lack of a clear distinction in relative acute toxicities between near-field and far-field samples indicates that the water-soluble chemicals associated with bitumen are acutely toxic to several aquatic organisms. This result, combined with the similarities in chemical profiles between bitumen-influenced groundwater originating from OSPW and/or natural sources, suggests that the industrial bitumen extraction processes corresponding to the tailings pond in this study are not contributing unique toxic substances to groundwater, relative to natural bitumen compounds present in groundwater flow systems.

Non-target profiling of bitumen-influenced waters for the identification of tracers unique to oil sands processed-affected water (OSPW) in the Athabasca watershed of Alberta, Canada.

RATIONALE: The objective of this study was to identify unique chemical tracers of oil sands process-affected water (OSPW) to enable definitive discrimination of tailings pond seepage from natural bitumen-influenced waters from the Canadian Alberta McMurray formation. METHODS: The approach involved comparing unknowns from an unprecedented sample set of OSPW (n = 4) and OSPW-affected groundwaters (n = 15) with natural bitumen-influenced groundwaters (n = 20), using high-performance liquid chromatography/electrospray ionisation high-resolution mass spectrometry (HPLC/ESI-HRMS) operated in both polarities. RESULTS: Four unknown chemical entities were identified as potential tracers of OSPW seepage and subsequently subjected to structural elucidation. One potential tracer, tentatively identified as a thiophene-containing carboxylic acid [C15 H23 O3 S]- , was only detected in OSPW and OSPW-affected samples, thereby showing the greatest diagnostic potential. The remaining three unknowns, postulated to be two thiochroman isomers [C17 H25 O3 S]+ and an ethyl-naphthalene isomer [C16 H21 ]+ , were detected in one and two background groundwaters, respectively. CONCLUSIONS: We advanced the state of knowledge for tracers of tailings seepage beyond heteroatomic classes, to identifying diagnostic substances, with structures postulated. Synthesis of the four proposed structures is recommended to enable structural confirmations. This research will guide and inform the Oil Sands Monitoring Program in its efforts to assess potential influences of oil sands development on the Athabasca River watershed.

Use of mature willows (Salix nigra) for hydraulic control of landfill-impacted groundwater in a temperate climate.

Phreatophytic trees such as willows and poplars have a large capacity for extracting shallow groundwater, as evidenced by diurnal water table fluctuations corresponding to intensified transpiration during the day. As a result, they have been employed for phytoremediation of shallow contaminated groundwater. In this study, the water extraction (i.e. pumping) capacity of mature willows (Salix nigra) to capture shallow polluted groundwater in Belle Park, the site of a former landfill in Kingston, Ontario (Canada), was assessed using continuous field measurements of sap flow and water table levels associated with a single willow tree, combined with a transient numerical model (FEFLOW). On an annual basis, the sapflow averaged 2.3 m3d-1, with 70% of the cumulative sap flow occurring during the active growing season (May to September). The calibration showed a good fit (0.91 < R2<0.97) between measured groundwater levels from three shallow wells installed near the willow and the calculated water table level fluctuations, thus confirming that the water extraction rate based on sap flow data for the willow was appropriate. At stand level, additional modelling suggests that 3.4-4.7 ha of mature willows (i.e. between 7.8% and 10.6% of the Park area), could compensate for the current water volumes extracted by the municipality using a conventional pump and treat system. The results of this study indicate that willows can play a significant role in capturing contaminated groundwater underlying Belle Park, and potentially at other sites where removal of contaminants from shallow aquifers is desired.

Advances in Distinguishing Groundwater Influenced by Oil Sands Process-Affected Water (OSPW) from Natural Bitumen-Influenced Groundwaters.

The objective of this study was to advance analytical methods for detecting oil sands process-affected water (OSPW) seepage from mining containments and discriminating any such seepage from the natural bitumen background in groundwaters influenced by the Alberta McMurray formation. Improved sampling methods and quantitative analyses of two groups of monoaromatic acids were employed to analyze OSPW and bitumen-affected natural background groundwaters for source discrimination. Both groups of monoaromatic acids showed significant enrichment in OSPW, while ratios of O2/O4 containing heteroatomic ion classes of acid extractable organics (AEOs) did not exhibit diagnostic differences. Evaluating the monoaromatic acids to track a known plume of OSPW-affected groundwater confirmed their diagnostic abilities. A secondary objective was to assess anthropogenically derived artificial sweeteners and per- and polyfluoroalkyl substances (PFAS) as potential tracers for OSPW. Despite the discovery of acesulfame and PFAS in most OSPW samples, trace levels in groundwaters influenced by general anthropogenic activities preclude them as individual robust tracers. However, their inclusion with the other metrics employed in this study served to augment the tiered, weight of evidence methodology developed. This methodology was then used to confirm earlier findings of OSPW migrations into groundwater reaching the Athabasca River system adjacent to the reclaimed pond at Tar Island Dyke.

Assessing potential toxicity of chloride-affected groundwater discharging to an urban stream using juvenile freshwater mussels (Lampsilis siliquoidea).

Groundwater contaminants, such as chloride from road salt, pose a threat to aquatic ecosystems when and where they discharge to surface waters. Here we study the application of a laboratory toxicity bioassay to field-collected samples from contaminated groundwater discharging to an urban stream. The objectives were to assess the potential toxicity of the discharging groundwater, while also exploring the suitability of such standard tests to site groundwater. Juvenile freshwater mussels were chosen as a groundwater-appropriate (endobenthic) test organism. Groundwater was sampled from 6 sites at approximate depths of 0, 10, and 50 cm below the sediment. Concentrations of chloride and several metals were above aquatic life guidelines in some samples. Exposure (96-h) to site groundwater resulted in survival of 90-100% and 80-100% for the 0-cm and deeper samples, respectively, indicating that groundwater may pose a toxicological threat to freshwater mussels. Several samples with high chloride had a survival rate of 80%, but generally there was poor correlation between survival and individual contaminants. Parallel juvenile mussel exposures using reconstituted water and NaCl predicted survival in the natural groundwater below 50% based on chloride concentrations. This indicates some protective ability of groundwater, possibly associated with water hardness. Finally, some technical issues with performing bioassays with groundwater were noted. First, aeration of previously anoxic groundwater samples caused marked changes in water quality (especially metal concentrations). Second, calcite crystals formed on the mussel shells in samples with elevated chloride and water hardness, though with no apparent negative effects.

Elevated dissolved phosphorus in riparian groundwater along gaining urban streams.

Findings of low concentrations of dissolved phosphorus in groundwater in large surveys [e.g., United States Geological Survey's National Water-Quality Assessment (NAWQA) Program ( Dubrovsky, N. M.; et al. The Quality of Our Nation's Water: Nutrients in the Nation's Streams and Groundwater, 1992-2004 . U.S. Geological Survey Circular 1350; USGS : Reston, VA , 2010 . ); >5000 wells] support the common perception that groundwater is generally of little importance for transporting phosphorus. Here, we address whether this applies to urban riparian settings, where discharging groundwater may potentially contribute to urban stream syndrome and downstream eutrophication problems. This survey study includes 665 samples of groundwater collected along gaining stream reaches at six urban sites. Considering the combined sample set, 27% had soluble reactive phosphorus (SRP) concentrations >0.1 mg L(-1), which is more than double that determined in the NAWQA Program (12%), while for individual sites the range was 12-52%, excluding one site with consistently low SRP (0%). None of the sites showed significant correlation between SRP and the artificial sweetener acesulfame, a promising wastewater indicator, including two with known wastewater contamination (but the lowest SRP). Rather, high SRP concentrations were associated with geochemically reducing conditions. This could mean that natural aquifer or stream sediment materials were a primary contributor of the elevated SRP observed in this study.

Profiling oil sands mixtures from industrial developments and natural groundwaters for source identification.

The objective of this study was to identify chemical components that could distinguish chemical mixtures in oil sands process-affected water (OSPW) that had potentially migrated to groundwater in the oil sands development area of northern Alberta, Canada. In the first part of the study, OSPW samples from two different tailings ponds and a broad range of natural groundwater samples were assessed with historically employed techniques as Level-1 analyses, including geochemistry, total concentrations of naphthenic acids (NAs) and synchronous fluorescence spectroscopy (SFS). While these analyses did not allow for reliable source differentiation, they did identify samples containing significant concentrations of oil sands acid-extractable organics (AEOs). In applying Level-2 profiling analyses using electrospray ionization high resolution mass spectrometry (ESI-HRMS) and comprehensive multidimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF/MS) to samples containing appreciable AEO concentrations, differentiation of natural from OSPW sources was apparent through measurements of O2:O4 ion class ratios (ESI-HRMS) and diagnostic ions for two families of suspected monoaromatic acids (GC × GC-TOF/MS). The resemblance between the AEO profiles from OSPW and from 6 groundwater samples adjacent to two tailings ponds implies a common source, supporting the use of these complimentary analyses for source identification. These samples included two of upward flowing groundwater collected <1 m beneath the Athabasca River, suggesting OSPW-affected groundwater is reaching the river system.

Natural attenuation of perchlorate in denitrified groundwater.

Monitoring of a well-defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO4⁻) under denitrifying conditions in the field. The septic system site at Long Point contains ClO4⁻ from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO3⁻ -N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35 m from the tile bed. The ClO4⁻ natural attenuation occurs at the site only when NO3⁻ -N concentrations are <0.3 mg/L, after which ClO4⁻ concentrations decline abruptly from 187 ± 202 to 11 ± 15 ng/L. A similar pattern between NO3⁻ -N and ClO4⁻ was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO4⁻ may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO4⁻ contaminated groundwater.

Artificial sweeteners as potential tracers of municipal landfill leachate.

Artificial sweeteners are gaining acceptance as tracers of human wastewater in the environment. The 3 artificial sweeteners analyzed in this study were detected in leachate or leachate-impacted groundwater at levels comparable to those of untreated wastewater at 14 of 15 municipal landfill sites tested, including several closed for >50 years. Saccharin was the dominant sweetener in old (pre-1990) landfills, while newer landfills were dominated by saccharin and acesulfame (introduced 2 decades ago; dominant in wastewater). Cyclamate was also detected, but less frequently. A case study at one site illustrates the use of artificial sweeteners to identify a landfill-impacted groundwater plume discharging to a stream. The study results suggest that artificial sweeteners can be useful tracers for current and legacy landfill contamination, with relative abundances of the sweeteners potentially providing diagnostic ability to distinguish different landfills or landfill cells, including crude age-dating, and to distinguish landfill and wastewater sources.

Toxic groundwater contaminants: an overlooked contributor to urban stream syndrome?

Screening for common groundwater contaminants was performed along eight urban stream reaches (100s-1000s of m) at approximately 25-75 cm below the streambeds. Four sites had known or suspected chlorinated-solvent plumes; otherwise no groundwater contamination was known previously. At each site, between 5 and 22 contaminants were detected at levels above guideline concentrations for the preservation of aquatic life, while several others were detected at lower levels, but which may still indicate some risk. Contaminants of greatest concern include numerous metals (Cd, Zn, Al, Cu, Cr, U), arsenic, various organics (chlorinated and petroleum), nitrate and ammonium, and chloride (road salt likely), with multiple types occurring at each site and often at the same sampling location. Substantial portions of the stream reaches (from 40 to 88% of locations sampled) possessed one or more contaminants above guidelines. These findings suggest that this diffuse and variable-composition urban groundwater contamination is a toxicity concern for all sites and over a large portion of each study reach. Synergistic toxicity, both for similar and disparate compounds, may also be important. We conclude that groundwater contaminants should be considered a genuine risk to urban stream aquatic ecosystems, specifically benthic organisms, and may contribute to urban stream syndrome.

Proactive screening approach for detecting groundwater contaminants along urban streams at the reach-scale.

Here we outline and demonstrate a screening approach for the detection of groundwater contaminants along urban streams within unconsolidated beds. It involves the rapid acquisition of groundwater samples along urban stream reaches at a spacing of about 10 m and from depths of about 25-75 cm below the streambed, with analyses for a suite of potential contaminants. This screening approach may serve two functions: a) providing information for assessing and mitigating the toxicity and eutrophication risks to aquatic ecosystems posed by groundwater contaminants and b) detecting and identifying groundwater contamination in urban settings more rapidly and inexpensively compared to land-based well installations. The screening approach was tested at three urban streams, each affected by a known chlorinated-solvent plume. All three known groundwater plumes were detected and roughly delineated. Multiple, previously unknown, areas or types of groundwater contamination were also identified at each stream. The newly identified contaminants and plumes included petroleum hydrocarbons (BTEX, naphthalene, MTBE), 1,4-dioxane, nitrate and phosphate, road salt, and various metals (including arsenic, cadmium, chromium, copper, lead) at elevated concentrations compared to background values and relevant Canadian water quality guidelines. These findings suggest that this screening approach may be a useful tool for both ecologists performing ecological assessments and stream restorations and for hydrogeologists undertaking groundwater protection activities. Given the numerous contaminants detected, it may be appropriate to apply this technique proactively to better determine the pervasiveness of urban groundwater contaminants, especially along urban streams.

Measurements of groundwater velocity in discrete rock fractures.

Estimating groundwater velocity in fracture networks using a Darcy or cubic law calculation is complicated by the wide distribution of fracture aperture often found in these systems and by the difficulty in measuring hydraulic head in discrete fracture features. Although difficult to conduct in a fractured rock setting, the point dilution method can be utilized to collect direct measurements of groundwater velocity in individual fractures. To compare measured against calculated velocities, more than 100 point dilution experiments were conducted within a 35 x 35 m area of a single fracture and in discrete fracture features within a fracture network at a larger scale. The dilution experiments were conducted by isolating a fracture feature in a borehole, measuring the hydraulic aperture, and measuring the decay of an injected tracer due to the advective groundwater flux across the fracture. Groundwater velocity was estimated using the hydraulic aperture and the rate of decay of the injected tracer. Estimates of the local hydraulic gradient were calculated via the cubic law using the velocity estimate and the hydraulic aperture. The results of the tests conducted in the single fracture show variable (1 to 33 m/day) but on average higher velocities in comparison to that measured during a natural gradient tracer experiment conducted previously (in which the effects of matrix diffusion were accounted for) and to that which would be calculated using the cubic law. Based on these results, it was determined that the best estimate of the average groundwater velocity, at the scale of the measurement area used for the cubic law calculations, could only be obtained using the largest apertures in the aperture distribution. Variability of the velocity measurements was also observed over time. Increases in velocity were attributed to the effect of rainfall although concurrent increases in hydraulic gradient were not detected (likely within the tolerance of the measuring devices). The groundwater velocities measured in the fracture network varied over a wider range than at the scale of the single fracture (from 2 to 388 m/day). No correlation, however, was observed between the size of the fracture aperture and measured velocity.