Effects of Electroosmosis on Soil Temperature and Hydraulic Head. I: Field Observations

A field test to quantify the changes in soil temperature and the hydraulic head during electroosmosis was conducted. The anode (3.1?m×3.4?m) was created by laying pieces of titanium mesh coated with mixed metal oxides on top of a 3 cm thick sand layer to a depth of 0.4 m. The cathode (2.5 m in radius) was a hydraulic fracture filled with granular graphite to a depth of 2.2 m. A constant voltage of 47 V was applied for 4 weeks, resulting a nearly constant current of 42 A between the electrodes. The electrical potentials and soil temperatures were monitored at 7.5 cm depth intervals at distances 0.6, 1.2, 2.1, and 3.0 m from the cathode well. Arrays of piezometers were installed at various depths and at radial distances from the cathode well to monitor the hydraulic head distribution. The initial soil temperature decreased by 2–3°C/m of depth with a minor radial gradient. After the power was turned on, the temperature of soil in the vicinity of the graphite increased significantly. The increased temperature propagated outward as a contour in the radial direction of the graphite well causing the vertical temperature gradient to disappear. The propagating speed of the temperature contours decreased with the energy input. In addition, the temperature contours close to the edges of both the mesh and the graphite electrodes increased and propagated outward vertically. In the regions where these three propagating fronts met, the soil temperature profiles were distorted and formed “S” shaped contours. The hydraulic head close to the anode decreased between 0 and 10 cm, whereas it increased between 2 and 6 cm close to the cathode. The results show that electroosmosis caused a hydraulic gradient that was opposite to the electroosmotic flow.     

Effects of Electroosmosis on Soil Temperature and Hydraulic Head. II: Numerical Simulation

A numerical model to simulate the distributions of the voltage, soil temperature, and hydraulic head during a field test of electroosmosis was developed. The two-dimensional governing equations for the distributions of the voltage, soil temperature, and hydraulic head within a cylindrical domain are derived based on the principles of charge, energy, and mass conservations, Darcy’s law, Ohm’s law, and Fourier’s law of heat conduction. We assumed that the voltage distribution was at steady state, whereas the soil temperature and hydraulic head were at transient states during the test. The simulated domain was segmented with a block-centered finite-difference scheme and the resulting equations were solved numerically with the successive overrelaxation method. The parameters (such as electrical, thermal, hydraulic, and electroosmotic properties of the soil, graphite, and sand) that were required by the model were measured either using core samples or slug tests. The model is able to predict the pattern as well as the magnitude of the voltage profiles observed. The simulated temperatures are similar in pattern and are within 3°C of the values observed in the four casings during 4 weeks of electroosmosis. The changes in the rates of temperature with an increase in energy input predicted by the model are in agreement with the observed changes. The output from the hydraulic head simulations showed that the model could predict patterns of hydraulic head changes in the vicinity of mesh and graphite electrodes. The model, however, underestimated the magnitude of the changes close to the anode. The simulated electroosmotic flow rate of 0.9 L/h is also consistent with the observation of 0.6–0.8 L/h.     

Effect of Soil Type on Electrokinetic Removal of Phenanthrene Using Surfactants and Cosolvents

Numerous sites have been contaminated with polycyclic aromatic hydrocarbons (PAHs), and these sites pose a significant risk to public health and the environment because PAHs are often toxic, mutagenic, and/or carcinogenic. Furthermore, these sites are often difficult or costly to remediate because PAHs are hydrophobic and highly resistant to degradation. The in situ flushing process using surfactants and/or cosolvents has shown great promise for sites possessing uniform and high-permeability soils, but it is generally ineffective for sites containing heterogeneous and/or low-permeability soils. Thus, for difficult soil conditions, electrokinetics can be integrated with the in situ flushing process to improve soil-solution-contaminant interaction. This investigation was conducted to evaluate the effects of two different low-permeability soils, kaolin and glacial till, on electrokinetically enhanced flushing. Each soil type was used in three bench-scale electrokinetic experiments, where each test employed a different flushing solution, deionized water, a surfactant, or a cosolvent. The results indicated that the contaminant was more strongly bound to the glacial till than the kaolin, and this was attributed to its higher-organic content. The glacial till also generated a greater electrical current and electro-osmotic flow, and this was probably a result of its higher-carbonate content and more diverse mineralogy. Based on the contaminant mass remaining in the soil, it was apparent that the surfactant or cosolvent solution caused contaminant desorption, solubilization, and/or migration in both soils, but additional research is required to improve PAH removal efficiency.     

Removal of Hexachlorobenzene and Phenanthrene from Clayey Soil by Surfactant- and Ultrasound-Assisted Electrokinetics

Removal of nonpolar contaminants such as most organic compounds are transported primarily by electroosmosis in electrokinetic remediation, thus the process is effective only if the contaminants are soluble in pore fluid. Hydrophobic organic compounds such as hexachlorobenzene (HCB) and phenanthrene (PHE) can adsorb strongly to clayey soil. Therefore, in this study, enhancements were done by adding 2-hydroxylpropyl-β-cyclodextrin surfactant and ultrasonication comparably to assist the electrokinetic treatment in improving the mobility of these hydrophobic compounds. The results show that HCB and PHE were mobilized and removed in both cases. But HCB is more difficult to remove than PHE, because of its highly stable nature and low water-solubility property. Ultrasound-assisted test performed better PHE reduction than surfactant-assisted test, because ultrasound can degrade the contaminant through oxidation by free radicals.     

Energy Equation for Volatile Liquid Transport in Porous Media

Two energy balance equations widely used to describe simultaneous transfer of heat and mass in porous media are inconsistent with control volume energy conservation. Potential energy, enthalpy, and internal energy terms are involved in the discrepancies. Energy within a volume is properly counted as the sum of internal, potential, and kinetic energy. However, one equation uses enthalpy where internal energy should have been used. In the other, potential energy and shifts in internal energy associated with heat of wetting are not included. Energy conservation for a control volume dictates summing convective fluxes of internal, potential, and kinetic energy at the control volume surface along with conducted heat and work crossing the boundary. The pressure–volume (pv) work at the volume surface may be combined with internal energy convection so that flow of enthalpy is used in the flux term. Examples of energy change versus work input in adiabatic processes illustrate the error introduced when enthalpy rather than internal energy is used to compute control volume energy content. For porous media flows kinetic energy can be dropped. A consistent equation based on the control volume approach is presented. It includes effects due to internal energy, potential energy, heat of wetting, conducted heat, non-pv work, enthalpy, and mass flow. Substantial temperature changes due to heat of wetting have been found experimentally in a separate work. A comparison is needed of the experiments and a numerical simulation based on the new equation.     

Tied-Back Excavations in Alluvial Soil of Taipei

In this paper we present monitored results of three tied-back excavations carried out in the alluvial soil of Taipei. All three cases involved large excavations and were supported by a diaphragm wall and multilevel tieback anchors. Based on the anchor loads measured during excavation, the apparent lateral pressure diagrams are calculated following Terzaghi and Peck’s method. It is found that the apparent lateral pressures increase approximately linearly with the depth. As the excavation reaches its final depth, the apparent lateral pressure diagrams tend to converge for the cases studied here. The measured lateral pressure diagrams for these tied-back excavations are close to the summation diagrams of groundwater pressure and lateral pressure calculated from the method of Terzaghi and Peck in 1967 or Tschebotarioff in 1973 for sandy soil but with a minor difference. The dominant sandy soil layer and groundwater pressure played a major role in determining the anchor load diagrams. The measured lateral wall movement for these tied-back excavations is found to be similar to that of cross-lot braced excavations in alluvial soil of Taipei both in magnitude and in profile.     

Calibration of Electromagnetic Induction for Regional Assessment of Soil Water Salinity in an Irrigated Valley

Electromagnetic instruments are increasingly being used for in situ analysis and mapping of soil salinity in irrigated soils. This study develops calibration models for salinity assessment over regional scales on the order of tens of thousands of hectares. These models relate apparent soil electrical conductivity measured with the EM-38 electromagnetic induction meter (Geonics Ltd.) to traditional laboratory-measured saturated paste electrical conductivities (ECe). The study area is located in the Lower Arkansas River Valley, Colo. and is divided into two regions. At each of 414 randomly selected calibration sites, an EM-38 reading was taken and multiple soil samples were extracted for analysis. The sites chosen have soil ECe values ranging from 1?to?18?dS/m, gravimetric water contents (WC) from 0.02 to 0.4, and textures ranging from sands to clays. The best model for predicting soil ECe in both study regions is bivariate nonlinear and includes EM-38 vertical readings (EMV) and WC as covariates. Uncertainty in the calibration equations is addressed and tests are conducted at 48 independent sites. Results indicate that, while uncertainty is considerable in regional scale surveys, electromagnetic instruments can be calibrated for rapid reconnaissance of soil water salinity, providing reasonably accurate identification of salinization categories.     

Extreme-Value Climatology of Maximum Soil Freezing Depths in Contiguous United States

Extreme-value statistics for the maximum depth of soil freezing are developed based on a physical soil freezing model and a semiphysical soil water budgeting scheme. The model uses only daily air temperature, snow depth, and precipitation data. These data are available from a relatively dense network of observing stations, permitting the development of a national climatology of extreme soil freezing levels. A set of adjustment factors is also presented that allows conversion between the mapped base-soil freezing depths and those associated with other soil conditions. Surface cover characteristics of bare soil with and without ambient snow cover and turf are analyzed. The deepest soil freezing levels within the United States are found across the Dakotas, where persistent subfreezing winter temperatures, and relatively little soil moisture and snow cover combine to maximize soil freezing. Ample winter snow cover mitigates soil freezing extremes in the Great Lakes, northern New England, and western mountains. Soil freezing is unlikely south of northern Florida and the immediate Gulf Coast, along the California coast, and in southern Arizona.     

Wedge Failure Analysis of Soil Resistance on Laterally Loaded Piles in Clay

A fundamental study of pile-soil systems subjected to lateral loads in clay soil was conducted by using experimental tests and a lateral load-transfer approach. The emphasis was on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. A framework for determining the p-y curve on the basis of both theoretical analysis and experimental load test results is proposed. The proposed p-y method is shown to be capable of predicting the behavior of a large-diameter pile under lateral loading. The proposed p-y curves with an improved wedge model are more appropriate and realistic for representing a pile-soil interaction for laterally loaded piles in clay than the existing p-y method.     

Long-Term Dynamic Modeling Approach to Quantifying Attached Algal Growth and Associated Impacts on Dissolved Oxygen in the Lower Truckee River, Nevada

Nutrient loads enter the lower Truckee River of western Nevada, affecting the growth of attached algae (periphyton) which causes depressed nighttime dissolved oxygen (DO) levels. The lower Truckee River is home to the endangered cui-ui and threatened Lahontan cut-throat trout, with DO standards being established to in part protect these species. Hydrodynamics, nutrient concentrations, periphyton biomass, and DO data spanning August 2000–December 2001 were used to calibrate and verify a modified version of the Water Quality Analysis Simulation Program Version 5 (WASP5). Under typical loading conditions the periphyton community is nitrogen limited, however nitrogen loading from an upstream wastewater treatment facility increased greatly during the analysis period due to approved site construction activities (discharge permit excursion) causing the periphyton community to temporarily become phosphorus limited. The developed modeling approach, with limited calibration, was able to accurately track dynamic system responses. Removing the impact of the noted discharge permit excursion resulted in a minimum computed DO value of 4.13?mg/L, occurring at the downstream end of the modeling domain on August 8, 2001. Additionally removing the impact of all nutrient loads from area agriculture resulted in a predicted minimum DO value of 4.54?mg/L, while also shifting its location significantly upstream and its timing to April 26, 2001. Meeting all prescribed DO standards required establishing a minimum in-stream flow value of 1.81?m3/s (64.0?ft3/s) downstream of Derby Dam.     

Density Intrusion and Variation in Dissolved Oxygen Concentrations in a Bay with a Sill at Its Mouth

This paper describes the influence of water outside a bay on water quality within the bay for a typical enclosed bay with a sill at its mouth. The influence of water outside Ohfunato Bay, Japan was expressed in a one-dimensional vertical dissolved oxygen (DO) model as the rate of seawater exchange caused by tides and the density difference between water inside and outside the bay. A nonhydrostatic, three-dimensional model was used to confirm the occurrence of density intrusions. A one-dimensional vertical DO model was used to examine long-term changes in DO concentrations in the bottom layer of the bay. Results indicated that seawater exchange caused by density differences had a significant effect on the formation and disappearance of anoxic water in the bay’s bottom layer.     

Analysis of Laterally Loaded Piles in Soil with Stiffness Increasing with Depth

This article reports a variational solution and its spreadsheet calculation procedure for the analysis of laterally loaded piles in a soil with stiffness increasing with depth. The aim of the paper is to provide solutions that can be used simply with recourse only to spreadsheet calculation to solve the displacement and bending moment of laterally loaded piles, so that they can be easily applied in practice as an alternative approach to analyze the response of laterally loaded piles.     

Effect of Loading in Soil Slurry-Sequencing Batch Reactors on Biosurfactant Production and Foaming

A soil contaminated with diesel fuel (DF) was treated in 8-L soil slurry sequencing batch reactors with 10-day retention times and different volumetric loadings: 5, 10, and 50% of the reactor volume per cycle. Concentrations of DF, DF-degrading microorganisms, and biosurfactant were measured, with emulsification capacity (EC), foam thickness, and O2 uptake. Foaming coincided with nonzero values of EC, a measure of free (i.e., non-DF-bound) surfactants. Higher surfactant levels increased DF emulsification and foaming and reduced DF stripping. Concentrations of Candida tropicalis, Brevibacterium casei, Flavobacterium aquatile, Pseudomonas aeruginosa, and Pseudomonas fluorescens were determined. Biosurfactant production and DF degradation increased with increased loading. Biosurfactants exceeded the critical micelle concentration early in the cycle but were completely degraded by the cycle’s end. Orders-of-magnitude differences in effluent concentrations of individual species were observed. Culture-based counts of surfactant-producing species (C. tropicalis, P. aeruginosa, P. fluorescens) relative to total counts increased from 21 to 86% as loading increased from 5 to 50%.     

熔渣中氧传递机理的研究

介绍了熔渣中氧的扩散系数以及气-渣、气-渣-金及渣-金体系中氧的传递现象,分析了电子电导对熔渣中氧传递的影响,总结了熔渣中氧的传递机理,并认为改变电化学因素可以控制渣相中氧离子的迁移。     

Hydraulic Conductivity of Soil Sorptive Zones Created by In Situ Injection of a Cationic Surfactant

The sorptive capabilities of soils for organic contaminants can be greatly enhanced by treatment with cationic surfactants, and this has been suggested as a potential in situ approach for contaminant plume management. The hydraulic properties of soils modified by injection of hexadecyltrimethylammonium (HDTMA) were investigated using soil columns and a fixed-ring consolidometer. Oshtemo soil (87% sand, 10.5% clay, 2.5% silt) under two different effective stresses, was equilibrated with 1?mM NaCl and treated by recirculation of two different HDTMA soil concentrations, one above and one below the cation exchange capacity. No statistically significant changes in hydraulic conductivity occurred as a result of HDTMA treatment at any of the experimental conditions studied. These results suggest that sorptive zones created in situ with HDTMA may be hydraulically feasible.     

Depth-Integrated Estimation of Dissolved Oxygen in a Lake

The majority of variable estimation studies in water resources investigate the temporal variation of the variable. In this study, we examined the depth-dependent estimation of a lake’s dissolved oxygen (DO) using two artificial neural network (ANN) methods: (1) the radial basis functions (RBFs) and the feed forward back-propagation (FFBP), and (2) the multilinear regression (MLR). We tested two different input layer configurations. In the first case, we employed all other available lake parameters—total dissolved solids (TDS), pH, conductivity, lake depth, and lake temperature—to estimate DO. In the second case, we considered only depth and temperature to estimate DO. The performance evaluation criteria of these two cases were close. ANN estimation performances were noticeably superior to those of MLR, as reflected in the performance evaluation criteria and DO lake depth plots. We saw that the spatial variation of the lake’s DO can be captured by ANNs satisfactorily, even if available measurements are quite limited.     

Dissolved Oxygen Downstream of an Effluent Outfall in an Ice-Covered River: Natural and Artificial Aeration

In ice-covered rivers, dissolved oxygen (DO) might fall below critical levels for aquatic biota in the absence of surface aeration, combined with low winter flow conditions and reduced photosynthesis rates. Open-water zones, however, can be created downstream of a diffuser by warm effluent discharges, resulting in an increase in surface aeration. In this study, we modeled the behavior of the effluent plume and the resulting open-water lead development in the Athabasca River, Alberta, Canada downstream of a pulp mill diffuser. The DO was found to increase by 0.26?mg/L due to surface aeration of an open-water lead of 6.07?km. We also evaluated oxygen injection into the effluent pipeline to increase the DO in the river. At an injection rate of 3,500 and 5,000?lb/day of liquid oxygen, the DO was increased by 0.16 and 0.21?mg/L, which corresponded to an absorption efficiency of about 50%. The artificial aeration technique evaluated here appears to be an effective alternative to increase DO levels in ice-covered rivers. The results of this study are important in developing accurate DO models for ice-covered rivers and in evaluating oxygen injection systems.     

Development of Downdrag on Piles and Pile Groups in Consolidating Soil

Development of pile settlement (downdrag) of piles constructed in consolidating soil may lead to serious pile foundation design problems. The investigation of downdrag has attracted far less attention than the study of dragload over the years. In this paper, several series of two-dimensional axisymmetric and three-dimensional numerical parametric analyses were conducted to study the behavior of single piles and piles in 3×3 and 5×5 pile groups in consolidating soil. Both elastic no-slip and elasto-plastic slip at the pile–soil interface were considered. For a single pile, the downdrag computed from the no-slip elastic analysis and from the analytical elastic solution was about 8–14 times larger than that computed from the elasto-plastic slip analysis. The softer the consolidating clay, the greater the difference between the no-slip elastic and the elasto-plastic slip analyses. For the 5×5 pile group at 2.5 diameter spacing, the maximum downdrag of the center, inner, and corner piles was, respectively, 63, 68, and 79% of the maximum downdrag of the single pile. The reduction of downdrag inside the pile group is attributed to the shielding effects on the inner piles by the outer piles. The relative reduction in downdrag (Wr) in the 5×5 pile group increases with an increase in the relative bearing stiffness ratio (Eb/Ec), depending on the pile location in the group. Compared with the relative reduction in dragload (Pr), Wr at the corner pile is less affected by the group interaction for a given surcharge load. This suggests that the use of sacrificing piles outside the pile group will be more effective on Pr than on Wr. Based on the three cases studied, the larger the number of piles in a group, the greater the shielding effects on Wr. Relatively speaking, Wr is more sensitive to the total number of piles than to the pile spacing within a pile group.     

Eutrophication Model for the Patuxent Estuary: Advances in Predictive Capabilities

A robust eutrophication and sediment diagenesis model has been developed for the Patuxent Estuary to study the impact of different nutrient loadings on phytoplankton biomass and dissolved oxygen (DO) levels. The modeling approach was to begin with an existing water quality model (CE-QUAL-W2) for the Patuxent Estuary (hereafter referred to as the Estuary). First, formulations for the water column kinetics were completely replaced with routines based on the WASP/EUTRO5 water quality model. Then, a sediment diagenesis component was added to simulate the accumulation and mineralization of organic matter in the sediment, the generation of sediment oxygen demand, and the flux of phosphate and ammonia from the sediment. Loadings from the tributaries for nutrients and flow were based on a combination of watershed modeling and sampling by scientists at the Smithsonian Environmental Research Center. The new model was able to reproduce the ambient water quality data from 1997 to 1999 by adequately simulating the high concentrations of phytoplankton and low DO levels in the Estuary. The model was then used to evaluate the response to various hypothetical nutrient loading scenarios. Model results show that phytoplankton growth in the upper Estuary is much more sensitive to nutrient loading from tributaries than in the lower estuary. Further, model results indicate that DO concentrations in the lower Estuary are largely influenced by levels of nutrients and organic carbon at the mouth of the Estuary.