Journal of contaminant hydrology最新文献

The dissolution of polycyclic aromatic hydrocarbons (PAHs) from coal tar at former manufactured gas plant (FMGP) sites is a long-term threat to groundwater quality. The dissolution rate is often limited by an increase in the viscosity of the non-aqueous phase liquid (NAPL) as the lower molecular weight compounds are depleted over time, and this slow mass transfer prevents the effective application of remediation technologies that rely on NAPL-to-water mass transfer to remove or degrade mass. Increasing subsurface temperatures has the potential to increase mass transfer at FMGP sites by increasing PAH solubility and reducing NAPL viscosity. This study investigated the mass transfer of PAH compounds from a synthetic NAPL mixture and FMGP residual at 25, 50 and 80 °C using well-mixed batch experiments. Effective solubilities increased by up to an order of magnitude and mass transfer rate coefficients increased by up to a factor of 45. Enhancements were greater for higher molecular weight compounds, and for the more complex FMGP NAPL compared to the synthetic mixture due to a more substantial decrease in NAPL viscosity. Simulations using a screening-level model demonstrated the potential for sub-boiling temperature to increase NAPL mass removal at FMGP sites, with increases in concentration up to a factor of seven, and 6 to 87 % of mass remaining after heating to 80 °C for 120 days compared to 25 °C.

Polymer material (PM) is a novel vertical barrier material, demonstrated to be effective in impeding pollutants. However, the associated transport research is limited. This study aims to develop an analytical solution for two-dimensional transport of organic contaminant in the PM-enhanced composite cutoff wall (CCW) system, where the variable substitution and Fourier transform methods are used. This analytical solution, available in various simplifications, is effectively validated via several comparisons. Following this, the analyses show that an increase in the non-uniformity of pollution source concentration distribution shortens the PM-enhanced CCW's breakthrough time (t_b), while exhibits a marginal effect on the total flux at its exit. The increment of aquifer horizontal thickness prolongs the t_b to some extent, whereas an increase in its hydraulic conductivity slightly reduces the t_b. Additionally, the PM layer location is found to have a little effect on the PM-enhanced CCW's barrier performance. Furthermore, the equivalent performance assessment reveals that the improvement gained from increasing the PM layer thickness far surpasses that from increasing the single-layered cutoff wall thickness, and this difference may exceed 10. For a PM layer with low hydraulic conductivity, it is more suitable for engineering scenarios with the higher hydraulic head difference. Totally, the proposed analytical solution offers a valuable tool for designing the PM-enhanced CCW.

Sandstone-hosted uranium is mined in the Sahel regions of Niger. The Teloua aquifer is located beneath the ore-processing facilities of one such former mine, COMINAK. The pores of the sandstone bedrock are partially filled by tosudite, a clay with sorption capacities. The local groundwater presents a strong oxidizing signature and very low water recharge. This study aims to determine the geochemical baseline of anthropogenic activity for uranium under such extreme conditions. The major and trace elements of both the contaminated and the pristine local groundwaters were sampled and analyzed to develop geochemical and reactive transport models. Kd distribution coefficients were calculated a posteriori from the mechanistic simulations. The entire water chemistry, with large variations in calcium, carbonate and sulfate concentrations, had to be taken into account to properly simulate the speciation and migration of U(VI) in the aquifer locally affected by the mining activities. U(VI) sorption significantly decreases during the propagation of the contaminant plume, due to the formation of Ca_nUO₂(CO₃)₃^(4-2n)- complexes that were clearly demonstrated by TRLFS acquisition. The sorption of UO₂(CO₃)_n^(2-2n) can play a key role in the immobilization of U(VI). The mitigating factors for U(VI) are sorption on clay and the dispersion/dilution of the contaminated source terms within the groundwater, in which the strong ternary complexes are less important. There should be an efficient immobilization of fixed anthropic uranium by natural attenuation once the contaminant source terms have become depleted.

Soil samples collected from an aqueous film-forming foam (AFFF)-impacted sandy soil formation at two depth intervals above the water table were used in bench-scale column experiments to evaluate the release of poly- and perfluoroalkyl substances (PFASs) under different degrees of water saturation. Artificial rainwater was applied to the soils under constant and variably saturated conditions. Results from constant saturation experiments suggest that retention of PFAS mass at air-water interfaces was evident in the deep soil (f_oc < 0.00068 g/g), particularly for longer chain and zwitterionic compounds, while PFAS mass release from the shallow soil (f_oc = 0.0034 g/g) was consistent with kinetically controlled desorption from the soil. The release profiles for the perfluoroalkyl sulfonamides (FASAs) differed from other PFASs examined, with more FASAs generally being eluted under fully saturated conditions from both the shallow and deep soils. Importantly, variably saturated conditions resulted in more PFAS eluting from the soils: the average release rate of PFHxS from both soils was 10-fold higher under variably saturated conditions than under constant conditions. Both soils retained significant fractions of the total PFAS mass even after extensive flushing (51-83.8 % for PFOS). These results suggest that PFAS transport in vadose zone soils is influenced by air-water interfaces, but solid-phase desorption also plays a role. Overall, these results are consistent with observations in the field and serve to confirm key mechanisms that control PFAS leaching.

Denitrification has been identified as a significant nitrate attenuation process in groundwater systems. Hence, accurate quantification of denitrification rates is consequently important for the better understanding and assessment of nitrate contamination of groundwater systems. There are, however, few studies that have investigated quantification of shallow groundwater denitrification rates using different analytical approaches or assuming different kinetic reaction models. In this study, we assessed different analytical approaches (reactant versus product) and kinetic reaction (zero-order and first-order) models analysing observations from a single-well, push-pull tests to quantify denitrification rates in shallow groundwater at two sites in the Manawatū River catchment, Lower North Island of New Zealand. Shallow groundwater denitrification rates analysed using the measurements of denitrification reactant (nitrate reduction) and zero-order kinetic models were quantified at 0.42-1.07 mg N L^-1 h^-1 and 0.05-0.12 mg N L^-1 h^-1 at the Palmerston North (PNR) and Woodville (WDV) sites, respectively. However, using first-order kinetic models, the denitrification rates were quantified at 0.03-0.09 h^-1 and 0.002-0.012 h^-1 at the PNR and WDV sites, respectively. These denitrification rates based on the measurements of denitrification reactant (nitrate reduction) were quantified significantly higher (6 to 60 times) than the rates estimated using the measurements of denitrification product (nitrous oxide production). However, the denitrification rate quantified based on the nitrate reduction may provide representative value of denitrification characteristics of shallow groundwater systems. This is more so when lacking practical methods to quantify all nitrogen species (i.e., total N, organic N, nitrite, nitrate, ammoniacal N, nitrous oxide, nitric oxide, and nitrogen gas) in a push-pull test. While estimates of denitrification rates also differed depending on the kinetic model used, both a zero-order and a first-order model appear to be valid to analyse and estimate denitrification rate from push-pull tests. However, a discrepancy in estimates of denitrification rates using either reactant or product and using zero- or first-order kinetics models may have implications in assessment of nitrate transport and transformation in groundwater systems. This necessitates further research and analysis for appropriate measurements and representation of spatial and temporal variability in denitrification characteristics of the shallow groundwater system.

Controlled laboratory experiments were carried out using the hanging column method. Prior to the experiments, three uniform silica sands, which were originally water-wet, were aged in contact with crude oil until they were moderately oil-wet. Five fractionally wet sands were obtained by mixing the water-wet sands with oil-wet sands containing 25, 50 and 75 vol% oil-wet sands. A total of 11 tests formed the basis for the present study. The measured water retention curves showed that the capillary pressure heads were greatly reduced in sands that were oil-wet or fractionally wet. Changes in the wettability of the sands also affected their irreducible water saturation: The higher the proportion of oil-wet sand in the sand mixtures, the lower the irreducible water saturation. To quantify the characteristics of the measured water retention curves, the Van Genuchten model was used. The two optimized parameters seem to indicate a general trend: The higher the volume fraction of oil-wet sand, the higher is α and the lower is n. For the three unaged sands and the aged medium-sized sand, it was found that each of the two branches of the measured retention curves can be suitably scaled to a unique curve if, in addition to the petrophysical parameters (intrinsic permeability, porosity, surface tension, gas-water contact angle), the irreducible residual water saturation and the residual air saturation are taken into account. To quantify the observed deviations of the other two aged sands from the unified Leverett J-function, a theoretical fit function was used to match the experimental data of the three unaged sands. The experimental data sets for P2040ag and P100ag were found to be overestimated overall by the fit function. However, when the petrophysical parameters of the unaged sands were used instead of the actual measured parameters, the individual experimental Leverett J-functions came closer to the uniform J-curve. Based on this, it could be concluded that the apparent differences in pore structure between aged and unaged sands in addition to wettability, expressed by the cosine of the contact angle, may have contributed to a further reduction in the capillary pressure plateaus of the aged sands, which was particularly visible and significant in the P2040 and P100 sand. Using the measured static contact angles for two-phase gas-oil and oil-water systems and the measured interfacial tensions when the porous medium is either water-wet or moderately oil-wet, it was shown that the Bartell-Osterhof equation overestimates the measured gas-water contact angles. Reasonable agreement was achieved when a calibrated roughness factor of the solid surface was considered in the Young's contact angle.

Agricultural phosphorus (P) losses may result from either recently applied fertilizers or from P accumulated in soil and sediment. While both P sources pose an environmental risk to freshwater systems, differentiating between sources is crucial for identifying and implementing management practices to decrease loss. In this study, laboratory rainfall simulations were completed on runoff boxes and undisturbed soil columns before and after fertilizer application. The oxygen-18 signature of phosphate (δ¹⁸O_PO4) in fertilizer, surface runoff, subsurface leachate, and soil were analyzed (n = 107 samples) to quantify new (recently applied) and old (soil) P losses in runoff and leachate. Results showed that dissolved reactive P (DRP) concentration in runoff and leachate substantially increased during the rainfall simulation immediately after fertilizer application, with runoff and leachate δ¹⁸O_PO4 similar to fertilizer δ¹⁸O_PO4 signatures. Greater than 90 % of the DRP load during this event could be attributed to direct loss of P from fertilizer using δ¹⁸O_PO4. Beyond the first rainfall event after fertilizer application, DRP concentration decreased and leachate δ¹⁸O_PO4 values differed from the fertilizer values. Interpretation of isotope results was challenging because both abiotic (isotope fractionation during transport) and biotic (P cycling) processes may have influenced δ¹⁸O_PO4 signatures during these subsequent events. While abiotic effects on δ¹⁸O_PO4 appear more probable given the experimental conditions in the current study (high soil test P concentration, short duration between rainfall simulations, and strong relationship between event water and δ¹⁸O_PO4 signature), tracing or separating P sources remains highly uncertain during these events post-fertilizer application. Findings highlight both potential opportunities and challenges of using δ¹⁸O_PO4 to trace sources of P through the landscape.

Plastics pollution has become a serious threat to the people and environment due to the mass production, unreasonable disposal and continuous pollution. Polyethylene (PE), one of the most utilized plastics all over the world, is considered as a highly recalcitrant environmental destruction problem on account of strong hydrophobicity and high molecular weight. Therefore, it is urgently necessary to seek economical and efficient treatment and disposal methods for PE. Considering microorganisms can use various carbon sources for anabolism, they are recognized to have great potential in the biodegradation of microplastics including PE. From this point of view, the present review concentrates on providing information regarding the current status of PE biodegradation microorganisms (bacteria and fungi), and the influencing factors such as PE characteristics, cellular surface hydrophobicity, physical treatments, chemicals addition, as well as environmental conditions for biodegradation are thoroughly discussed. Furthermore, the possible biodegradation mechanisms for PE involve the biofilm formation, biodeterioration, fragmentation, assimilation, and mineralization are elucidated in detail. Finally, the future research directions and application prospects of microbial degradation are prospected in this review. It is expected to provide reference and guidance for PE biodegradation and their potential applications in real contaminated sites.

As the COVID-19 pandemic began in 2020, plastic usage spiked, and microplastic (MP) generation has increased dramatically. It is documented that MP can transfer from the source to the ocean environment where they accumulate as the destination. Therefore, it is essential to understand their transferring pathways and effective environmental factors to determine the distribution of MPs in the marine environment. This article reviews the environmental factors that affect MP distribution in the oceans including abiotic such as ocean currents and wind direction, physical/chemical and biological reactions of MPs, natural sinking, particle size and settling velocity, and biotic including biofouling, and incorporation in fecal material. It was found that velocity and physical shearing are the most important parameters for MP accumulation in the deep ocean. Besides, this review proposes different research-based, national-level, and global-level strategies for the mitigation of MPs after the pandemic. Based on the findings, the level of MP pollution in the oceans is directly correlated to coastal areas with high populations, particularly in African and Asian countries. Future studies should focus on establishing predictive models based on the movement and distribution of MPs to mitigate the levels of pollution.

This study addresses the critical challenge of assessing the quality of groundwater and surface water, which are essential resources for various societal needs. The main contribution of this study is the application of machine learning models for evaluating water quality, using a national database from Mexico that includes groundwater, lotic (flowing), lentic (stagnant), and coastal water quality parameters. Notably, no comparable water quality classification system currently exists. Five advanced machine learning techniques were employed: extreme gradient boosting (XGB), support vector machines, K-nearest neighbors, decision trees, and multinomial logistic regression. The performance of the models was evaluated using the accuracy, precision, and F1 score metrics. The decision tree models emerged as the most effective across all water body types, closely followed by XGB. Therefore, the decision tree models were integrated into the AQuA-P software, which is currently the only software of its kind. It is recommended that these innovative water classification models be used through the AQuA-P software to facilitate informed decision-making in water quality management. This software provides a probability-based classification system that contributes to a deeper understanding of water quality dynamics. Lastly, an open-access repository containing all the datasets and Python notebooks used in our analysis is provided, allowing for easy adaptation and implementation of our methodology for other datasets worldwide.