Hydraulic Conductivity Values Research Articles

THE ACCEPTABLE COMPACTION ZONE CRITERIA BASED ON HYDRAULIC CONDUCTIVITY FOR A COMPACTED MIXTURE OF RESIDUAL SOIL WITH BENTONITE AS A SOIL LINER

The significant criteria for compacted clay liner in landfill construction are the compaction characteristics and hydraulic conductivity value. The primary parameter for designing an efficient soil liner is ensuring a hydraulic conductivity value below 1x10-9 m/s to prevent contaminated seepage into the aquifer. Therefore, the compaction criteria are crucial in controlling the construction of hydraulic barriers for liners. In this study, laboratory testing such as permeability tests at varying compaction energies, were carried out on a blend of residual soil and bentonite. The aim was to establish an acceptable compaction zone based on the allowable hydraulic conductivity value and to outline suitable design considerations for compacted residual soil mixed with bentonite as a soil liner. The design parameters investigated included hydraulic conductivity at different compaction efforts. A comparison was made between traditional, common, and modern approaches to ensure construction quality assurance for compacted soil liners mixed with bentonite. The results indicated that all methods, traditional, common, and modern, successfully met the design objectives for hydraulic conductivity, creating acceptable compaction zones on the compaction plane curve. These acceptable zones for the mixture of residual soil with bentonite align with the lower bound limit of the compaction optimum line, with the shapes of the shaded zones influenced by the soil's moisture content and compaction characteristics.

Mineralogy and geochemistry of sands from Playa las Golondrinas, Puerto Rico: an approach to establishing a geogenic background

Sands from the dune, berm, and shore environments at Playa las Golondrinas (18° 30′ 51″ N, 67° 3′ 26″) were investigated to explore how beach sands could be applied as a potential environmental (geogenic) background for the local region. Grain size is dominantly unimodal classifying as fine to medium sand. Hydraulic conductivity values range from 1.07 cm/s (berm) to 1.49 cm/s (shoreface). Sample mineralogy as constrained by X-ray diffraction (XRD) reveals a dominance of quartz and feldspar with minor Mg-calcite, pyroxene, and olivine. Light microscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM–EDS) support XRD data and indicate the presence of oxide-bearing lithic fragments in addition to biologic materials (e.g., corals. forams). Reflective spectra are consistent with XRD and microscopy. Bulk element concentrations determined using inductively coupled plasma—mass spectrometry (ICP-MS) are consistent with derivation from the arc-related rocks of Puerto Rico’s interior exhibiting LILE enrichment, Pb-enrichment, and associated Nb–Ta depletion. The majority of the bulk elemental concentrations are below those of average upper continental crust (UCC) values and element co-variation trends (e.g., wt. % Fe2O3 vs. As) are interpreted as geogenic in origin. Berm sands are enriched in Fe, Mn, Ni, Cr, V, and As compared to dune and shore samples and this signature is interpreted as being from a wind-driven winnowing effect. The exact form of As (As3+ or As5+) remains unconstrained and thus it is unknown if As is mobile in this environment. Reflective spectra, supported by grain size, mineralogy, and bulk chemistry, enables future remote sensing investigations by providing detailed constraints on sand in environmentally sensitive areas. This study therefore provides local context for metal pollution studies across the region.

Integrated Simulation of Groundwater Flow and Nitrate Transport in an Alluvial Aquifer Using MODFLOW and MT3D: Insights into Pollution Dynamics and Management Strategies

This study employs an integrated numerical modeling approach using MODFLOW and MT3D to simulate groundwater flow and nitrate transport in the alluvial aquifer of Hennaya plain. The groundwater flow model was calibrated and validated against observed hydraulic heads, showing excellent agreement in both steady-state and transient conditions, with a correlation coefficients (R2) of 0.99 and 0.987, respectively. Meticulous calibration yielded adjusted hydraulic conductivity values between 10−1 and 10−11 m/s, with effective porosity ranging from 0.03 to 0.34 and total porosity values varying from 0.29 to 0.38 across the aquifer. Water budget analysis revealed that the aquifer’s primary recharge occurs from the southern side. Nitrate transport modeling indicated that advection is the dominant process, with contaminants migration predominantly occurring from south to north, following the groundwater flow direction. Pollution levels were found to decrease gradually with distance from sources, confirming agricultural activities and sewage disposal as primary contributors to nitrate contamination. Predictive scenarios over a 40-year period explored various management strategies, which suggest that maintaining current nitrogen input rates will lead to continued increases in nitrate pollution, while a 50% reduction in agricultural inputs could significantly improve groundwater quality. However, even with substantial reductions, nitrate concentrations are not expected to reach levels safe for drinking within the simulation timeframe. This study underscores the need for immediate and sustained action to address nitrate pollution in the Hennaya Plain aquifer, emphasizing the importance of stringent nitrogen management practices, particularly in the agricultural sector.

Fracturing above longwall panels and the associated changes in hydraulic conductivity

Information from conditions observed when mining overlying seams have been combined with interpretations of surface subsidence surveys and physical models to develop a fracture model for subsidence above longwall panels. This model proposes zones of high hydraulic conductivity around the sides of collapsed goaf as an alternative to the existing layer models. In the absence of a thick spanning unit, fracturing can extend upwards from the longwall extraction to a height equal to twice the width of each longwall panel. An indication of whether fracturing has extended to the surface is if the relative deflection across the extraction exceeds about 0.4-0.6m. A simple method is proposed to estimate hydraulic conductivity values from measured vertical subsidence and the spacing of joints opened by the subsidence. The method produces hydraulic conductivity values that are consistent with reports of mine water inflows and impacts on shallow aquifers.

Simulation of Complex Groundwater Flow Processes in Low‐Fidelity Radial Flow Model Using a Mathematical Representation of the Variation of Vertical Hydraulic Conductivity With Depth

ABSTRACTNumerical groundwater models are key tools to calculate the deployable output from pumped boreholes. Their calibration requires undertaking multiple runs to optimise the parameter values. To maintain computational efficiency, the hydrogeological complexity of fractured and weathered aquifers is often represented in numerical models using a simplified approach consisting of a mathematical equation that describes the vertical variation of horizontal hydraulic conductivity () value with depth. In this article, we present the inclusion of the variation of the vertical hydraulic conductivity () with depth to a radial flow model. We derive the mathematical equation controlling the flow vertically between the numerical nodes. We show that the inclusion of variation with depth have a limited impact on the shape of the time drawdown curve at the early times of a pumping test but its significance is higher at later times. This also has a measurable impact on the water level inside the pumped borehole especially when the variations of both and are accounted for. We use a simple linear variation of with depth but the method is also applicable to complex profile of aquifer heterogeneity if this complexity can be represented using polynomial approximation. This illustrates the applicability of the proposed method to a wide range of weathered aquifer settings.

Groundwater dynamics simulation in Hodna (Algeria): aquifer modeling approach

Groundwater modeling using MODFLOW and GIS tools is crucial for understanding the complexities of groundwater dynamics in Algeria's semi-arid and arid climates. This study focuses on the quantitative assessment of the phreatic aquifer within the Hodna aquifer system over the period of 1973-2005. The study employs MODFLOW and GIS tools to model groundwater flow. Calibration and validation processes, using a trial and error technique, refine the models to understand water table behaviors and drawdown within the Hodna basin. Calibration efforts yield insights into groundwater dynamics, particularly significant drawdowns observed in cities like M’sila and Boussaada. Parameters such as hydraulic heads, piezometric levels, drainage, and hydraulic conductivity values are extracted from MODFLOW simulations. Analysis reveals a decline in groundwater volume and consistent drops in borehole water levels over the past 32 years, highlighting the challenges of comprehending recharge resources and the impact of groundwater depletion in the region. The study underscores the importance of calibrated groundwater models in managing and mitigating groundwater depletion in Algeria's Hodna basin. It elucidates predominant groundwater flow patterns towards Chott and emphasizes the need for comprehensive understanding and management strategies to sustainably manage groundwater resources in semi-arid and arid regions.

Determination of the Hydraulic Conductivity Behavior of Seaweed Added Zeolite-Bentonite Mixtures in the Presence of Temperature with Empirical Relationships

The temperature factor is of great importance in areas that directly affect the environment and engineering parameters of liners, such as solid waste storage areas. It is known that the temperature value increases as a result of the degradation of waste in these areas, and temperature changes affect the engineering properties of the soils. Properties vary depending on the soil type, and additives that can be used to improve the engineering properties of soils come to the fore. One of the most important criteria is that the additive to be used is sustainable and environmentally friendly. Zostera marina, with its terminological name, or dried seaweed an aquatic plant and is a sustainable, low-cost material used in thermal insulation. In this study, dried seaweed additive was added to zeolite-bentonite mixtures and compression parameters were determined under room temperature and 40°C. Hydraulic conductivity values of seaweed-added mixtures were determined with the help of volumetric compression coefficient (mv) and consolidation coefficient (cv) parameters and empirical relationships obtained as a result of consolidation tests. Its potential to be used as a buffer material in the presence of temperature in solid waste storage areas evaluated. The tests results showed that the seaweed additive decreased the hydraulic conductivity values of zeolite-bentonite mixtures at room temperature and under 40°C.

Contaminant mass discharge estimation of a sulfonamide plume by use of hydraulic profiling tool (HPT) and fluorescence techniques

The contaminant mass discharge is a relevant metric to evaluate the risk that a groundwater plume poses to water resources. However, this assessment is often vitiated by a high uncertainty inherent to the assessment method and often limited number of measurement points to carry out the assessment. Direct-Push techniques in combination with profiling tools and dedicated sampling can be an interesting alternative to increase the measurement point density and hence reduce the mass discharge uncertainty. The main objective of our study was to assess if DP logging and sampling could be employed to get a reasonable estimate of contaminant mass discharge in a large sulfonamide contaminant plume (> 1500 m wide), compared to a more traditional approach based on monitoring wells. To do so, an Hydraulic Profiling Tool (HPT) logging with a dedicated site calibration was used to estimate the hydraulic conductivity field. The sulfonamide concentrations were inferred from the compound fluorescence properties measured by laboratory spectrofluorometry (λEx / λEm = 255/340 nm) and a dedicated log-log linear regression model. Our results show that HPT-derived hydraulic conductivity values are in good agreement with the monitoring well results, and within the order of magnitude reported in similar studies or indirect geophysical techniques. Fluorescence appears as a powerful proxy for the sulfonamide concentration levels. Ultimately, the contaminant mass discharge estimate from HPT and fluorescence techniques lies within a factor 2 from the estimate by monitoring wells, with 549 [274–668] and 776 [695–879] kg/yr respectively. Overall, this study highlights that DP logging tools combined with indirect methods (correlation with fluorescence) could provide a relevant contaminant mass discharge estimate for some optically active substances, given that a proper calibration phase is carried out.

Application of surface geophysical investigations and pumping test data analysis for better characterization of aquifer hydraulic parameters, Upper Awash Sub-Basin, Central Ethiopia

Study regionUpper Awash River Sub-basin in central Ethiopia Study focusThe research aimed to estimate aquifer parameters and conduct resistivity modeling in the study area. Data were collected from 890 Schlumberger Vertical Electrical Soundings (VES) points strategically distributed across six selected zones. The VES data were analyzed using computer modeling and curve-matching techniques to interpret the resistivity responses of the geological formations. This analysis provided insights into the subsurface characteristics and identified potential aquifer zones. New insights for the regionThe interpreted curves from the VES data and Root Mean Square (RMS%) values ranging from 0.36 % to 1.67 %, indicating a good fit between observed and modeled data. Resistivity modeling and geoelectrical sections were produced along specific lines, visualizing subsurface structures and confirming the resistivity responses of the geological formations. To determine aquifer parameters, the Dar-Zarrouk parameters were calculated from the interpreted curves, yielding crucial information about hydraulic properties such as hydraulic conductivity (K) and transmissivity (T). Hydraulic conductivity values ranged from 1.1 m/day to 21.7 m/day, while transmissivity values ranged from 144.3 m²/day to 2763.3 m²/day. Validation against borehole pumping test data showed strong correlations: R² = 0.9873 for transmissivity and transverse resistance, and R² = 0.9352 for hydraulic conductivity and resistivity. These findings enhance the understanding of the complex volcanic aquifer characteristics in the Upper Awash River Sub-basin, aiding sustainable groundwater management and development in the area.

MPeat2D – a fully coupled mechanical–ecohydrological model of peatland development in two dimensions

Abstract. Higher-dimensional models of peatland development are required to analyse the influence of spatial heterogeneity and complex feedback mechanisms on peatland behaviour. However, the current models exclude the mechanical process that leads to uncertainties in simulating the spatial variability in the water table position, vegetation composition, and peat physical properties. Here, we propose MPeat2D, a peatland development model in two dimensions, which considers mechanical, ecological, and hydrological processes together with the essential feedback from spatial interactions. MPeat2D employs poroelasticity theory that couples fluid flow and solid deformation to model the influence of peat volume changes on peatland ecology and hydrology. To validate the poroelasticity formulation, the comparisons between numerical and analytical solutions of Mandel's problems for two-dimensional test cases are conducted. The application of MPeat2D is illustrated by simulating peatland growth over 5000 years above a flat and impermeable substrate with free-draining boundaries at the edges, using constant and variable climate. In both climatic scenarios, MPeat2D produces lateral variability in the water table depth, which results in the variation in the vegetation composition. Furthermore, the drop in the water table at the margin increases the compaction effect, leading to a higher value of bulk density and a lower value of active porosity and hydraulic conductivity. These spatial variations obtained from MPeat2D are consistent with the field observations, suggesting plausible outputs from the proposed model. By comparing the results of MPeat2D to a one-dimensional model and a two-dimensional model without the mechanical process, we argue that mechanical–ecohydrological feedbacks are important for analysing spatial heterogeneity, shape, carbon accumulation, and resilience of peatlands.

Geotechnical performance of black cotton clay in the presence of lead and cadmium solutions for geoenvironmental application

ABSTRACT The usage of bentonites and sand–bentonite mixtures as liners has become prevalent due to their low permeability. However, these materials are scarce and prohibitively expensive in India. Black cotton clay (BCC) was chosen as an alternative clay liner for this research due to its abundance in India and its mineralogical composition. Since heavy metals accumulation in municipal landfills is a rising issue with devastating effects on the ecosystem and human health, in this investigation, two heavy metals (lead and cadmium) were intended as permeants at three different concentrations (100, 500, and 1000 ppm) to imitate the impact of heavy metal leachate on BCC. The essential index and engineering properties of BCC were evaluated and compared under these two permeants from the liner perspective. Experimental results revealed that the free swell index, Atterberg limits, swelling and swelling pressures were reduced for a rise in concentration irrespective of metal type. However, this reduction was more with cadmium permeants compared to lead. The measured swelling data was compared with predicted swelling data using a rectangular hyperbola model, and a good correlation was achieved. The hydraulic conductivity (k) and unconfined compressive strength (UCS) values were increased for a rise in concentration with both metal permeants. At 1000 ppm concentration, the k values were raised to 3.5 and 6.7 times, and UCS values were enhanced by 8.3 and 5.5% for lead and cadmium permeants, respectively. At high concentrations, field emission scanning electron microscopy (FESEM) results showed the formation of huge voids and aggregation.

Assessment of Soil Structural Quality Under Area Closure and Open Grazing Land in Hidabu Abote District, North Shewa Zone, Oromia Regional State, Ethiopia

The experiment was conducted at Sire Morise kebele, Hidabu Abote district, to assess soil structural quality of different land management system (area closure and open grazing land). In this study, area closure land management practice was compared with open grazing land management practice in similar slope positions for soil structural quality build up. Soil samples were collected from both land management system at three slope position with three times replication. Totally 36 undisturbed soil blocks were collected from both land management system at 10 and 20 cm sampling depths. The finding of the study showed that the average value of volumetric moisture content and saturated hydraulic conductivity of soil were greater at area closure than open grazing land management system and also higher at bottom slope position than middle and upper slope position. The mean value of air-filled porosity and bulk density were lower at both area closure management practices and bottom slope position. Bulk density, volumetric soil moisture content and saturated hydraulic conductivity at 20 cm sampling depth were shows significantly different with respect to management practices. According to visual assessment in the field, soil physical quality was unfavourable in open grazing land management system and upper part of landscape position soils and the visual assessment scores showed that the soils under area closure had a good soil structural quality. There were strong relations among the three visual field assessment methods and also between visual assessment methods and laboratory determined soil properties of both land management system. In general, the result of the study showed that physical and structural quality of soil in area closure was improved due to good land management system. Based on the result of study it can be conclude that area closure improves soil physical and soil structural qualities and from the technical point of view, open grazing lands in hilly area should be changed to area closure before soil properties and soil nutrient contents are exhausted more.

A Statistical Approach for the Assessment of Saturated Hydraulic Conductivity Values of Unsaturated Urban Soils Obtained by Field Infiltration Tests

An evaluation and interpretation of the obtained results focusing the hydraulic conductivity of anthropogenic saturated soil, k, has been performed on an urban area vadose zone. Four methods have been used to quantify the hydraulic conductivity: the tube infiltrometer (TI), the double ring infiltrometer (DRI), the minidisk infiltrometer (MDI) and the inversed auger (IA). This study comprises (a) a comparative analysis of the results obtained by each method between several trials performed at the same location and at distinct locations within the plot, (b) a comparative analysis of the results of all methods, and (c) a statistical analysis regarding the correlation between k as a dependent variable and the infiltration area A as the main independent variable. To select the k values close or corresponding to the saturation state for TI and IA methods, a domain of validity was defined. A new parameter, k* = k/A, was introduced which represents the hydraulic conductivity corresponding to an infiltration surface unit (1 cm2). An increase in this ratio with the increase in the infiltration area, within the same method or between different methods, indicates the heterogeneity of the terrain but especially the fact that the infiltration area no longer represents the main independent variable on which the hydraulic conductivity depends for the saturated state.

Optimal landfill site selection through the application of GIS analysis & geotechnical investigation

ABSTRACT Disposal of municipal solid waste is a significant environmental issue that has detrimental effects on both the environment and human life. The selection of landfill sites is critical and essential to implementing a comprehensive waste management strategy. This study optimizes the selection of landfill sites in Kuwait through the use of overlay analysis and Geographic Information System in conjunction with multi-criteria decision analysis. The study analysis takes into account human, physical economical, environmental, and governmental factors. Seven optimal locations are depicted on the resulting suitability map, each occupying 10 square kilometres or more and have the capacity to handle solid waste for at least one decade per site, considering the current reported waste generation rate. Furthermore, results of a preliminary geotechnical investigation encompassing field and laboratory tests conducted on soil samples collected at one of the proposed sites are presented. The characterization of the retrieved samples included major geotechnical parameters that are of concern in landfill design and siting studies. The results indicate that the soil at the proposed site exhibited low values of hydraulic conductivity, ranging between 3.50 X 10−07 and 8.96 X 10−08 cm/sec, confirming its suitability for siting landfills. There is an urgent need to develop and implement an integrated waste management system in Kuwait. By leveraging the findings of this study, policymakers and governmental authorities can optimize their decision-making procedures to ensure more effective site selection. This approach will significantly reduce contamination risks and enhance sustainability, leading to a more environmentally responsible waste management system in the country.

Geoelectric Investigation for Groundwater in Imo State University Campus and Environs using Direct Current Electrical Resistivity Method

Eighteen, vertical electrical soundings (VES), were carried out in Imo State University and Environs to delineate the potential site for groundwater. Data were acquired using ABEM SAS 300 resistivity meter. Schlumberger array and maximum electrode spread of 700m were adopted. Data were interpreted with IP2WIN software. Contour maps were done using Sulfer 20 software. Geoelectric cross-sections constructed along three profile lines delineated subsurface stratification. Sediments consist of sequence of sandstone/gravel, silty sand/sand and clay with geology representing the Benin Formation. Groundwater was delineated within the zone interpreted to be sand with quartz making up more than 95% of all grains. Resistivity of aquifer varies across study area and ranges from 159Ωm, observed around Library and Information Department (VES 11) to 100000Ωm recorded at IMSU Plaza (VES 10). Depth to water table also varied across study area with higher values of 150m and 130m observed at College of Health Science (VES 3) and Behind Old ETF (VES 4). A relatively shallow aquifer is delineated behind Senate Building and Okwu-Uratta with water table at depths of 23.5m and 26.5m. The transmissivity values are moderately high except at some locations. The variation in longitudinal conductance and transverse resistance values show that part of the study area such as Aso Rock, Female Hostel, Law Faculty and IMSU Plaza are underlain by relatively resistive (low longitudinal conductance) aquifer material. Distribution of hydraulic conductivity and electrical conductivity values indicates that in some of the VES points, the values are fairly constant. This could be seen as areas with similar geologic settings and water quality. Storativity of study area ranges from 0.00003 at VES 1 and 12 to 0.00028 at VES 4. Study area shows a good prospect for groundwater development, except at Library and Information Department, where the zone delineated is an aquitard.

Hydrogeochemical Investigation and Estimation of Aquifer Properties at Dhaka University Campus

The University of Dhaka has its own water supply system and entirely relies on groundwater. Ten groundwater samples were collected from 10 production wells of 120-320 m depth across the University campus from upper and lower Dupi Tila aquifers. The pH values revealed that water is mildly acidic to neutral and electrical conductivity (EC) values ranging from 325 to 654 μS/cm, indicating fresh groundwater. The total hardness (TH) of the samples ranges from 76-203 mg/L, suggesting moderately hard to very hard water. Of the ten groundwater samples, nine are of Ca-Mg-HCO3 type, whereas one shows Ca-Na-HCO3 type of groundwater. The saturation indices show that the groundwater samples are near-saturated for calcite, dolomite, gypsum, siderite, and rhodochrosite, indicating the low potential for dissolution-precipitation of these mineral. Notably, the results of WQI indicate that all the wells are safe for drinking. As of July 2023, the groundwater level was 72 m below ground level with a declination rate of 2.8 m/year. The estimated hydraulic conductivity values of 20 to 90 m/day and transmissivity values of 637 to 2740 m²/day suggest better permeability and water transmission potential within the lower aquifer. These results provide essential information for the university authority to implement appropriate strategies for efficient groundwater management. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 12(2), 2023, P 55-67

Porosity and hydraulic conductivity of gap graded natural sand considering shape parameters

Gap graded natural sand is widely used in hydraulic structures, foundation treatment and recharge well fillers, and it’s also common in geological structures such as landslide deposits. In order to study the influence of grain shape on its pore and permeability characteristics, river sand in Yichang (YS), standard sand in Henan (HS) and standard smooth glass beads (BZ) are selected as test materials, and the grain shape parameters of three materials are analyzed on multiple scales. Then tests on porosity and hydraulic conductivity of gap graded natural sand were conducted. On this basis, a numerical model considering grain size distribution, coarse grain content and grain shape was established. The results showed that the average values of the shape parameters increased or decreased with the increase of grain size, and the coefficients of variation for the parameters were between 0.026 and 0.208. The shape parameters showed a negative skewness distribution, but the absolute value of the skewness coefficient was small (0.254–0.616). Grain size distribution and grain shape are the main factors controlling the porosity and hydraulic conductivity of gap graded natural sand. The minimum values of porosity and hydraulic conductivity appear at about 70 % and 30 % of large grains, respectively. The closer the grains are to the sphere, the closer the material is stacked, and the smaller the porosity value is. The grain size ratio has a significant effect on the minimum porosity of the mixture and the minimum porosity increases with the increase of the grain size ratio. The porosity of gap graded natural sand obtained by numerical method is accurate, and the error is within 10 %. The hydraulic conductivity is obtained by deriving fluid grid information and the results show that the simulated value of hydraulic conductivity is highly matched with the experimental value, and the error range is roughly between 10 % and 30 %.

Combined effects of geological heterogeneity and discharge events on groundwater and surface water mixing

Stream water (SW) infiltration to the subsurface and subsequent mixing with groundwater (GW) is crucial for controlling water quality in river-corridors. Mixing of solutes from SW and GW triggers biogeochemical reactions, which can attenuate contaminant influx from upstream SW or from GW that eventually enters the river in downstream regions. It is known that geological heterogeneity affects SW-GW exchange fluxes (EF), however, the combined effects of both hydrological and geological aspects (e.g., sand fraction present in the aquifer material) on EF and on SW-GW mixing in strong contrasting bimodal aquifer units remain unclear. Here, we examined this gap by combining geostatistical realizations, fully-integrated numerical flow simulations, and a mixing-cell routine to assess the major controls on EF and to evaluate how mixing develops and is affected by stream discharge events with different magnitudes and durations. Results show that subsurface heterogeneity at the river-reach scale mainly affects EF magnitudes rather than EF patterns. Yet, both EF magnitudes and SW-GW mixing increased with the introduction of subsurface heterogeneity and with the increase of average hydraulic conductivity (K) values and sand fraction in the models. The simulations further indicated a larger potential for mixing under more frequent, short events regardless of the aquifer material, however, mixing values were generally higher for sandier and heterogeneous models. Lastly, for a high K contrast between subsurface units, these effects were more pronounced. This characterization is critical for river restoration strategies and for downstream management of dam-regulated rivers. Our study elucidates the interplay between hydrological and geological controls on the development of SW-GW mixing at intermediate scales and highlights the importance of considering aquifer characteristics in future studies.

Development of a multi-layer green-ampt infiltration based modeling framework for hydrologic process simulation and design of various low impact development measures for mitigating urban flooding

ABSTRACT Low Impact Development (LID) measures have proven to be effective in reducing the runoff volume and the peak of runoff at small spatial scales. Assessment of the hydrological impacts of LID measures at river basin scales is currently limited by the absence of adequate physically-based process models that can simulate LID processes at such scales. In this study, an attempt has been made to develop LID modules to simulate the water balance and hydrological processes based on the Multi-Layer Green-Ampt (MLGA) infiltration method, which is an advancement to the existing LID modeling techniques. The performance of the MLGA-based LID modules was benchmarked with the process-intensive numerical tool HYDRUS 1D for about 5000 soil samples across the soil textural classes. The results indicated that the MLGA-based model simulates the hydrological processes in close agreement with HYDRUS for soils with moderate-to-high hydraulic conductivity values, which are amenable for LID implementation.

Sand-bentonite backfill amended with composite polymer exposed to organic acid: Hydraulic performance and microstructural properties

Soil-bentonite (SB) backfills in vertical cutoff walls are used extensively to contain contaminated groundwater. Previous studies show that the hydraulic conductivity of backfill can exceed the typically recommended maximum value (k = 1 × 10−9 m/s) if exposed to groundwater impacted by organic acids commonly released from uncontrolled landfills and municipal solid waste dumps. Polymer amended backfills exhibit excellent chemical compatibility to metal-laden groundwater. However, few studies to date have explored the effect of organic acid contaminated groundwater on hydraulic performance of polymer amended backfills. This study presents an experimental investigation on the hydraulic performance and microstructural properties of a composite polymer amended backfill used to contain flow of acetic acid-laden groundwater. A series of laboratory experiments were performed to evaluate free-swell indices of the composite polymer amended bentonites, liquid limits of the composite polymer amended and unamended bentonites, and slump heights and hydraulic conductivity (k) values of the amended backfills to acetic acid solutions with varying concentrations. The results were compared with those of the unamended bentonites and unamended backfills reported in a previous study. The results showed that the free-swell index and liquid limit of the amended bentonites were higher than those of the unamended bentonites. Permeation with acetic acid solutions with concentrations ranging from 40 mmol/L to 320 mmol/L conducted on the amended backfill only resulted in an increase in k of less than a factor of about 10 related to that based on permeation with tap water (4.41 × 10−11 -1.68 × 10−10 m/s to acetic acid solution versus 1.65 × 10−11 m/s to tap water). Mechanisms contributing to enhanced chemical compatibility of amended backfill were ascertained based on scanning electron microscopy, mercury intrusion porosimetry, and zeta potential analyses.