Modeling Solute Transport in Volcanic Ash Soils with Cation Exchange and Anion Retardation

Groundwater under agricultural lands is often contaminated by nitrate. In southern Japan, aquifers are covered by volcanic ash soils that can leach nitrate to the groundwater. In this study, column experiments using two volcanic ash soils (Kuroboku and Akahoya) were carried out. A mixed solution of KNO₃ and K₂SO₄ was used in the leaching experiments. Based on the experiments, a reactive transport model was developed using the Constrained Interpolation Profile method for ion transport and used to calculate chemical equilibrium for the cation exchange reactions. Anion adsorption was modeled by retardation in the numerical model. The developed simulation model results were compared to results obtained by the reactive transport model PHAST. The developed model was shown to quite well reproduce general characteristics of the experimental results. Also, the developed model results agreed well with results from PHAST. Slight discrepancy between observed and calculated breakthrough curves was probably caused by ignoring the kinetic reaction in the model calculations.     

Evaluation of Numerical Modeling Methods for the Management of Produced Water Discharges in the Coastal Region with a Canadian Case Study

This study aims at evaluating two numerical methods for 3D simulation of marine pollutant dispersion problems: the random walk particle tracking (RWPT) method and an explicit second-order finite difference method (FDM) for assessing produced water discharges from offshore oil platform. Test cases in a steady flow field were used to evaluate the efficiency and accuracy of simulating pollutant concentration profiles obtained using both the FDM and RWPT method in comparison with an analytical solution. Additionally, a field study was conducted to simulate the lead concentration distribution of produced water discharged from an oil platform off Canada’s east coast, based on the Princeton Ocean Model modeling the ocean flow in the study area with field verifications. Results indicate that, with proper configuration of grid resolution and particle resolution, both FDM and RWPT method can provide accurate results with reasonable computational costs for complex field cases. Particularly, the satisfactory 3D simulations of marine pollutant dispersion in the far field by both FDM and RWPT numerical methods enable effective assessment and management of offshore waste discharges.     

Development of a Model for Simulation of Solute Transport in a Stream–Aquifer System

A model for simulation of solute transport in a dynamic stream–aquifer system is developed by integrating four existing sub-models. Interface packages are created to link the sub-models. The developed model is successfully used to simulate chloride transport in the stream–aquifer system of the Arkansas River and the Equus Beds Aquifer in Kansas and demonstrates that chloride concentration in the aquifer decreases in the vicinity of the simulated channel over time.     

PLS and PCR Methods in the Assessment of Coastal Water Quality

Partial least squares regression analysis (PLS) and principal component regression analysis (PCR) were examined asmethodological procedures for assessing the quality of coastalwaters in a tourist area. Four variables related to the trophicstate of waters, namely nitrate, nitrite, ammonia and phosphate were analyzed. The models resulting from PLS and PCR were verysimilar. Both defined three groups of water masses characterizedby different nutrient loadings. These groups were in accordancewith those obtained by numerical classification. The PLS methodwas selected as the optimal model, on the basis of its lowerprediction errors (lower Press and Rmsd values). For managementpurposes, this statistical model allows mesotrophic conditions,reflecting some nutrient enrichment over background conditions,to be characterized and the successful diagnosis of additionalsamples within this context.     

Comparison and Verification of Bacterial Water Quality Indicator Measurement Methods Using Ambient Coastal Water Samples

During the summers of 2002 and 2004, in-stream integrated flow and concentration measurements for the total dissolved solids in the Cheyenne River, South Dakota, USA was conducted in order to compare the obtained actual field measurements with the predictions values made by the Bureau of Reclamation in the Environmental Impact Statement. In comparison to the actual field measurements conducted in this study, The Bureau of Reclamation extension of a small database used in the analysis for the impact of operations at the Angostura Unit over the past 50 years and into the future to predict the annual total dissolved solid loadings doesn't represent the actual loading values and various conditions in the study area. Additional integrated flow and concentration sampling is required to characterize the impact of the current Angostura Dam operations and Angostura Irrigation District return flows on the Cheyenne River in different seasons of the year.     

A Numerical Model for the Transport of Chromium and Fine Sediments

A mathematical model which represents the transport processes of heavy metals and fine sediments in a fluvial stream was developed. The model consists of a three-equation system: the first one for total chromium concentration in the water column, C _Tw, the second one for total suspended sediment concentration, S _w, and the third one for chromium concentration in bed sediments, r. The third equation represents the chromium exchange between the water column and bed sediments by two processes: diffusion of soluble chromium and erosion/deposition of chromium sorbed to sediments. The basic assumption of the model is the instantaneous equilibrium. The main parameters are the partition coefficients in the water column and bed sediments, the depth of the active bed sediment layer, and the mass transfer coefficient between the water column and sediment pore water. The numerical model approximates the equations of advection–dispersion for chromium in water and suspended sediments by using a Eulerian third-order scheme. Numerical vs. analytical solutions were considered satisfactory for different initial, boundary, and sedimentological conditions. In order to estimate the impact of a chromium side discharge, the model was implemented for the Salado River in a reach of 65.6-km long (Santa Fe, Argentina). The results showed the effect of chromium discharge on almost the whole reach, then the vulnerability of the water quality in the Salado River when the flow was low was evidenced. When comparing the computed and measured results, the former showed a reasonable representation of the presence of chromium in water and bed sediments.     

Selection and Calibration of Numerical Modeling in Flow and Water Quality

Numerical modeling is frequently used in coastal engineering research and application. One possible issue associated with using this method however, is that initial outcomes might differ from expectation. Modeling manipulation addresses this issue by changing the initial parameters which in turn affects the final output results.The advancement of modeling techniques in recent years has seen a gradual but steady accruement of knowledge regarding the relationship between input parameters and possible outputs, which has resulted in improved accuracy and efficiency methods. The advancements within this field have predominantly occurred on an individual basis and as such lack standardisation. An expert numerical modeler may use this knowledge subconsciously, yet may not know how to convey it to the model users. This paper has been written to introduce a systematic intelligent coding schema designed to organise current coastal engineering modeling manipulation knowledge into a standardised format. This system is relevant to the development of appropriate strategies for improved accuracy and efficiency as well as model modification to simulate specific real phenomena in prototype application cases.     

Performance Evaluation of Multiple Groundwater Flow and Nitrate Mass Transport Numerical Models

Environmental Modeling & Assessment - Benchmarking of different numerical models simulating groundwater flow and contaminant mass transport is the aim of the present study, in order to...     

Numerical Analyses of Soft Bottom Macroinvertebrates to Diagnose the Pollution in Tropical Coastal Waters

Soft bottom benthic organisms especially polychaetes are known to adapt as r or k selected strategies to different gradients of pollution. This will result in changes of benthic community structure from that of normal structure. There are a number of techniques to assess the impact of pollution on benthic community structure. Hence, to test this hypotheses some of the univariate and multivariate techniques were applied to soft bottom macro-invertebrates data of coastal waters of Mangalore, central west coast of India, a hot-spot area. Univariate techniques such as Pearson Rosenberg Model (PRM), abundance biomass comparison curve (ABC), geometrical class distribution, dominance-diversity curve, benthic community structure indices and multivariate techniques such as cluster classification, multidimensional scaling (MDS) and principal component analysis (PCA) were used to discriminate and diagnose the disturbance among the sites. Effectiveness and applicability of some of the above techniques are highlighted and discussed with the present set of data for environmental impact assessment studies.     

Colloid-Associated Groundwater Contaminant Transport in Homogeneous Saturated Porous Media: Mathematical and Numerical Modeling

During the past two decades, significant efforts have been made to study contaminant transport in the presence of colloids. Several researchers reported that colloidal particles could enhance the migration of contaminants in groundwater by reducing retardation factor. When the colloidal particles are present in the aquifer, the subsurface system can be considered as a three-phase system with two solid phases and an aqueous phase. The interaction between contaminants, colloids, and solid matrix should be considered in assessing the fate and transport of the contaminant in the groundwater flow system. In this study, a one-dimensional numerical model is developed by employing a fully implicit finite difference method. This model is based on mass balance equations and mass partition mechanisms between the carriers and solid matrix, as well as between the carriers and contaminants in a saturated homogeneous porous medium. This phenomenon is presented by two approaches: equilibrium approach and fully kinetic first-order approach. The formulation of the model can be simplified by employing equilibrium partitioning of particles. However, contaminant transport can be predicted more accurately in realistic situations by kinetic modeling. To test the sensitivity of the model, the effect of the various chemical and physical coefficients on the migration of contaminant was investigated. The results of numerical modeling matched favorably with experimental data reported in the literature.     

凝聚法处理水中腐植质的初步研究

通过凝聚试验确定ＡＩ盐，Ｆｅ盐处理腐植持的最佳ｐＨ值，最佳投加量，并从机理入手探讨产生影响的原因，为改进对策提供理论依据。     

Quality of Shallow Groundwater and Drainage Water in Irrigated Agricultural Lands in A Mediterranean Coastal Region of Turkey

Spatial and seasonal differences in water quality of drainage water and unconfined shallow groundwater were related to irrigation in Samandağ, a Mediterranean coastal region. Eighteen wells, seven drainage points and Orontes River were monitored bimonthly for one year for analyses of electrical conductivity (EC), total dissolved solids (TDS), sodium adsorption ratio (SAR), cations (Na, K, Ca + Mg) and anions (CO₃, HCO₃, Cl and SO₄). Agricultural irrigation using saline groundwater decreased water quality of Orontes River during the irrigation season (May to September) more than during the non-irrigation season (October to April). Seasonal fluctuations in water quality of shallow groundwater were greater during the irrigation season than the non-irrigation season in the study area. Excessive use of groundwater resulted in a decline in the water table levels in the irrigation season. Water table level rose up to the soil surface in areas where there was a lack of drainage or poor drainage, due to the impact of precipitation in the winter. SAR and pH values of drainage water increased in the irrigation season, while the other properties of drainage water decreased. Irrigation water quality of Orontes River was classified as C₃S₁ in both seasons. Irrigation water quality of shallow groundwater and drainage water varied from C₂S₁ to C₄S₂ in one year. Drainage and well waters were found to be different on yearly basis in terms of Na, SAR (p<0.01) and Ca + Mg concentrations (p<0.001). Ca + Mg concentrations for both sources were different for all sampling dates (p<0.001).     

Numerical Modeling on the Effect of Dissolved Oxygen on Nitrogen Transformation and Transport in Unsaturated Porous System

Nitrogen pollution in groundwater resulting from wastewater application to land is a common problem, and it causes a major threat to groundwater-based drinking water supplies. In this study, a numerical model is developed to study the nitrogen species transport and transformation in unsaturated porous media. Further, a new mass transfer module for dissolved oxygen (DO) is incorporated in the one-dimensional numerical model for nitrogen species transport to describe the fate and transport of nitrogen species, dissolved oxygen, dissolved organic carbon (DOC), and biomass. The spatial and temporal variation of dissolved oxygen is incorporated in the model through the mass transfer from gaseous phase to water phase in an unsaturated porous system. The numerical results of the water flow model and single species and multispecies transport model in an unsaturated zone developed for this purpose have been validated with the available analytical/numerical solution. The developed model is applied in clay loam, silt, and sand soils to analyze the transport behavior of nitrogen species under unsaturated condition. The numerical results suggest that the high rate of oxygen mass transfer from the air phase to the water phase positively increases the dissolved oxygen in the applied wastewater and enhances the nitrification process. Because of this high oxygen mass transfer, the nitrate nitrogen concentration significantly increases in the unsaturated zone and the same is transported to a larger depth at higher simulation period. On the other hand, the low rate of oxygen mass transfer implicitly enhances the denitrification process and finally reduces the nitrate nitrogen concentration in the unsaturated zone. The numerical results also show that the nitrate nitrogen transport is rapid in sandy soil when compared with clay loam and silty soils under high oxygen mass transfer rate. In essence, the high oxygen mass transfer rate significantly increases the nitrate nitrogen in the unsaturated zone, especially at a greater depth at larger time levels and eventually affects the groundwater quality.     

Numerical Simulation of Gas Injection in Vertical Water Saturated Porous Media

We present numerical simulations of drainage induced by air injection in a vertical water-saturated Hele-Shaw cell filled with glass microbeads. We use the macroscale Subsurface Transport Over Multiple Phases (STOMP) simulator developed by the Pacific Northwest National Laboratory’s Hydrology Group. To trigger fingering, we use random permeability fields consistent to capillary entry pressure fields. We compare the numerical results to our own experimental results shown in a previous study. We analyze the effects of the microheterogeneity degree as well as the macroscopic parameters on the gas saturation results. The main objective of the work is to investigate how microscopic effects could be accounted for by macroscopic variables during drainage.     

Quantification of Water, Salt and Nutrient Exchange Processes at the Mouth of A mediterranean Coastal Lagoon

Vassova lagoon is a typical Mediterranean (small, shallow, micro-tidal, well-mixed) coastal lagoon, receiving limited seasonal freshwater inflows from direct precipitation and underground seepage. An intensive study was carried out in order to quantify the mechanisms responsible for the intra-tidal and residual transport of water, salt, nutrients and chlorophyll at the mouth of this lagoon and to assess the lagoon's flushing behavior. Results indicated that although the system is micro-tidal, tidal effects appeared to be the dominant factor for the longitudinal distribution of physical and chemical parameters, while the associated residual flow is also important and serves as a baseline measure of overall circulation. However, analysis of the net longitudinal currents and fluxes of water, salt and nutrients revealed the importance of non-tidal effects (wind effect and precipitation incidents) in the mean tidal transport. It is shown that the Eulerian residual currents transported water and its properties inwards under southern winds, while a seaward transport was induced during precipitation incidents and northern winds. The Stokes drift effect was found an order of magnitude lower than the Eulerian current, directed towards the lagoon, proving the partially-progressive nature of the tide. Nutrients and chlorophyll-α loads are exported from the lagoon to the open sea during the ebb phase of the autumn and winter tidal cycles, associated with the inflow of nutrient-rich freshwater, seeped through the surrounding drainage canal. The reverse transport occurs in spring and early summer, when nutrients enter the lagoon during the flood tidal phase, from the nutrient-rich upper layer of the stratified adjacent sea. Application of a tidal prism model shows that Vassova lagoon has a mean flushing time of 7.5 days, ranging between 4 to 18 days, affected inversely by the tidal oscillation.     

Impact Modeling of Sewage Discharge From Georgetown of Penang, Malaysia on Coastal Water Quality

Currently about 200,000 persons of the Penang Georgetown population is served by a sewerage system which conveys the raw sewage to an open channel flume in Jelutong for discharge into the Western Channel. This has resulted in the degradation of coastal water quality in the affected areas. Therefore, there exists an urgent need to look for other alternatives for sewage treatment and disposal. This paper presents the results of computer simulations on the impacts of sewage discharge on Penang coastal waters under two treatment and disposal options. The preferred option is a conventional activated sludge treatment system capable of treating the sewage to secondary level with a submerged outfall to the Western Channel for the disposal of the treated effluent. The results of computer simulations show that the quality of coastal waters, other than in the immediate vicinity of the discharge point, would be able to achieve the Malaysian proposed criterion for recreational waters up to year 2020.     

Atrazine Transport Within a Coastal Zone in Southeastern Puerto Rico: a Sensitivity Analysis of an Agricultural Field Model and Riparian Zone Management Model

Agrichemical runoff from farmland may adversely impact coastal water quality. Two models, the Agricultural Policy/Environmental eXtender (APEX) and the Riparian Ecosystem Management Model (REMM), were used to evaluate the movement of the herbicide atrazine to the Jobos Bay National Estuarine Research Reserve from adjacent fields. The reserve is located on Puerto Rico’s southeast coast. Edge-of-field atrazine outputs simulated with the APEX were routed through a grass-forest buffer using the REMM. Atrazine DT₅₀ (half-life) values measured in both field and buffer soils indicated that accelerated degradation conditions had developed in the field soil due to repeated atrazine application. APEX simulations examined both the measured field and buffer soil atrazine DT₅₀ and the model’s default value. The use of the measured field soil atrazine degradation rate in the APEX resulted in 33 % lower atrazine transport from the field. REMM simulations indicated that the buffer system had the potential to reduce dissolved atrazine transport in surface runoff by 77 % during non-tropical storm events by increasing infiltration, slowing transport, and increasing time for pesticide degradation. During a large runoff event due to a tropical storm that occurred close to the time of an atrazine application, the REMM simulated only a 37 % reduction in atrazine transport. The results indicate that large storm events soon after herbicide application likely dominate herbicide transport to coastal waters in the region. These results agree with water quality measurements in the reserve. This study demonstrated the sensitivity of these models to variations in DT₅₀ values in evaluating atrazine fate and transport in the region and emphasizes that the use of measured DT₅₀ values can improve model accuracy.     

1,2,4,5-苯四酚-四乙酸光度比浊法测定水样中钾含量的研究

研究了在聚乙烯醇介质中,钾离子与1,2,4,5－苯四酚－四乙酸形成稳定的胶体沉淀,钾含量在0－48mg/L内符合比耳定律,方法可用于水样中钾含量的测定,结果满意。     

A Comprehensive Numerical Model Simulating Gas,Heat, and Moisture Transport in Sanitary Landfills and Methane Oxidation in Final Covers

A model to simulate gas, heat, and moisture transport through a sanitary landfill has been developed. The model not only considers the different processes that go on in a landfill but also the oxidation of methane in the final cover. The model was calibrated using published results and field data from a pilot scale landfill in Calgary. The model captures the physics of the different processes quite well. Simulations from the model show that waste permeability had a significant impact on the temperature, pressure distribution, and flux from a landfill. The presence of the final and intermediate covers enhanced the gas storage capacity of the landfill. Biodegradation of the waste was enhanced as the final cover minimized the atmospheric influences. In addition, the composition of landfill gas emitted to the atmosphere was significantly different from the composition of gas generated in landfill due to the presence of covers as some of the methane is oxidized to carbon dioxide. There was no significant benefit of using a final cover of higher depth. The presence and number of intermediate covers had an impact on gas flux and temperature distribution within a landfill.     

Insecticide Contamination of Jamaican Environment. IV. Transport of the Residues Coffee Plantations in the Blue Mountains to Coastal Waters in Eastern Jamaica

A survey of 120 coffee farmers in the Portland watershed revealed that they lacked training in pesticide application, and had no concept of the transport of residues in the environment and their impact on non-target organisms.Residues of organochlorine (OC) and organophosphorous compounds (OP) were monitored monthly for over a year in plantation soil, and water, sediment and fauna of three rivers and coastal waters of Portland watershed by gas chromatography. OP residues were not detected in any sample while OC residues were below detection levels in Rio Grande. The mean concentration ± standard error of residues detected in water (g L^_1), sediment (ng g^_1) and fauna (ng g^_1 in wet weight) were: -endosulfan 2.7 ± 1.29, 3.8 ± 0.15 and 15.9 ± 1.61, respectively, in Spanish River, 1.56 ± 0.43, 24.3 ± 16.44 and 9.0 ± 1.86, respectively, in Swift River; 0.40 ± 0.02, 1.77 ± 0.68 ± 12.63, respectively, in sea coast; -endosulfan, 1.2 ± 0.48, 0 and 8.1 ± 1.99, respectively, in Spanish River, 1.9 ± 0.49, 0.75 ± 0.32 and 11. ± 4.32, respectively, in Swift River; 0, 5.1 ± 0.30 and 30.9 ± 15.96, respectively, in sea coast; endosulfan sulphate, 0.12 ± 0.12, 4.8 ± 1.62 and 10.0 ± 2.02, respectively, in Spanish River, 3.6 ± 0.95, 3.1 ± 0.56 and 7.9 ± 1.29, respectively, in Swift River and 0, 3.9 ± 2.17 and 24.0 ± 14.67, respectively, in sea coast.Dieldrin residues were detected only once in water (0.2 ± 0.03) and sediment (0.02 ± 0.003) of Spanish River, water (0.76 ± 0.09) of Swift River and sediment (0.1 ± 0.005) of sea coast; pp DDE was found twice in water (3.1 ± 1.53) and sediment (0.1 ± 0.007) of Swift River and water (0.8 ± 0.22) and sediment (6.14 ± 0.41) of sea coast. Arochlor was detected only twice (0.011 and 0.153) in water of Spanish River.