Vertical Hydraulic Conductivity Research Articles

Numerical investigation of coupled density-driven flow and hydrochemical processes in coastal aquifers influenced by storm surges

Storm surges can result in significant damage to coastal aquifers. Studies have investigated groundwater salinization caused by storm surge inundation. However, the phenomenon of evaporation-driven mineral precipitation in saltwater lakes has not received much attention in the literature. To address this gap, this study simulated the impact of saltwater lakes formed after a storm surge on coastal aquifers by coupling the PHREEQC and SEAWAT models. Six scenarios were considered, with varying lake depth, area, evaporation rate and vertical hydraulic conductivity of lakebed. The results indicate that the total dissolved solids (TDS) and water level of saltwater lake are subject to constant changes due to evaporation. Scenario 2, with the smallest lake area exhibited the least susceptibility to evaporation, with a maximum TDS concentration in the lake of ∼86 g/L, and only dolomite and calcite reached saturation. However, infiltration of saline water into the aquifer was higher than for the other scenarios. A comparing of scenarios with different vertical hydraulic conductivities of lakebed (scenarios 5 and 6 have conductivities that are 0.1 × and 0.01 × that of scenario 1, respectively) shows that a smaller vertical hydraulic conductivity leads to less saline infiltration into the aquifer, but a greater amount of salt precipitates (precipitation ratios of 1.03%, 1.92%, and 5.73% for scenario 1, 5 and 6, respectively). The results of scenario 4, which has double the evaporation rate of the other scenarios, indicate that evaporation leads to significantly greater salt precipitation and a corresponding decrease in the amount of salt that enters the aquifer. The results of secondary salinization indicate that salt precipitated on the surface may infiltrate the aquifer through rainfall dissolution, causing groundwater to become saline again. These findings emphasize the importance of accounting for the impact of evaporation on saltwater lake dynamics and coastal groundwater salinization in future studies.

Improvement of in situ hydraulic conductivity tests for riverbeds under the influence of infiltration intake: A case study of the Oława River, SW Poland

The vertical hydraulic conductivity (KV) of riverbeds plays a pivotal role in controlling water exchanges between the surface water and groundwater. The recent papers have focused on the spatial and temporal variability of KV (K measured in the “z” direction), while point measurement schemes seem to require more attention. The most popular measurement technique is the falling head method, in which a PVC pipe is placed in the riverbed. The most commonly used formulas to determine hydraulic conductivity are those based on the Darcy's law and its modifications. This article presents how the falling head method should be carried out and what errors need to be considered in conditions of the riverbank intake. The simultaneous measurements and analyses of the falling head vs. the riverbed head can produce satisfying outcomes and reduce errors. A full utility MS Excel spreadsheet based on an automated formula with a solver was developed.

Parameter identification and range restriction through sensitivity analysis for a high-temperature heat injection test

In order to compensate for the variable mismatch between heat demand and heat production from renewable sources or waste heat, high-temperature aquifer thermal energy storage (HT-ATES) is a promising option. A reliable prediction of the energetic performance as well as thermal and hydraulic impacts of a HT-ATES requires a suitable model parameterization regarding the subsurface properties. In order to identify the subsurface parameters on which investigation efforts should be focused, we carried out an extensive sensitivity analysis of the thermal and hydraulic parameters for a high-temperature heat injection test (HIT) using numerical modeling of the governing coupled thermo-hydraulic processes. The heat injection test was carried out in a quaternary shallow aquifer using injection temperatures of about 75 °C over 5 days, accompanied by an extensive temperature monitoring. The sensitivity analysis is conducted for parameter ranges based on literature values, based on site investigation at the HIT site and based on a model calibrated to the measured temperature distribution following the heat injection. Comparing the parameter ranges thus obtained in this three-step approach allows to identify those parameters, for which model prediction uncertainty decreased most, which are also the parameters, that strongly affect the thermal behavior. The highest sensitivity is found for vertical and horizontal hydraulic conductivity as well as for groundwater flow velocity, indicating that investigation efforts for HT-ATES projects should focus on these parameters. Heat capacity and thermal conductivity have a smaller impact on the temperature distribution. Our work thus yields a consistent approach to identifying the parameters which can be best restricted by field investigations and subsequent model calibration. Focusing on these during field investigations thus enable improved model predictions of both HT-ATES operation and induced impacts.

An intrinsic vulnerability approach to assess an overburden alluvial aquifer exposure to sinkhole-prone area; results from a Central Iran case study

DRASTIC is a model used to reliably assess the pollution potential of aquifers at global location. Despite various criticisms of this model or its optimization, sometimes the territorial or geological conditions still must rely on this model approach based on its simplicity. The existence of sinkholes in the alluvial aquifer with an underlying karst aquifer is a clear example of the need to change or optimize the DRASTIC model to improve accuracy of prediction. In this study, the DRASTIC model was changed by adding two factors, the distance to a sinkhole and the sinkhole catchment factors. The modified DRASTIC model was then used to evaluate the pollution potential of Abarkouh aquifer in Yazd province, Central Iran. The intrinsic vulnerability index of Abarkouh aquifer was calculated by the weighted sum method in GIS. The resulting numerical values ranged between 62 and 176 for full study area. Without adding the two layers related to Sin-DRASTIC, the generic DRASTIC Index map showed summed values ranging between 54 and 130. The final Sin-DRASTIC map was divided it into 4 orders very low (<106; 722 km2, 78%), low (107-133; 186 km2, 20%), low to moderate (133-160; 15.3 km2, 1.7%), and moderate vulnerability (161-176; 1.7 km2, 0.3%) vulnerability. Both of the created maps showed high Area Under the Curve values at 76% and 78% for the generic DRASTIC and Sin-DRASTIC respectively. However, the area of the aquifer containing the sinkholes showed low and very low zones of contamination vulnerability on the generic DRASTIC map. The sensitivity analysis showed that the aquifer vulnerability to pollution is mainly controlled by the vadose zone impacts and the sinkhole catchment factor. Therefore, it is concluded that for geologic settings containing sinkholes that are open or contain higher vertical hydraulic conductivity sediment compared to the general matrix of the unconfined aquifer, the Sin-DRASTIC model method yields a superior prediction.

Improved Darcian streambed measurements to quantify flux and mass discharge of volatile organic compounds from a contaminated aquifer to an urban stream

Quantifying VOC transport from contaminated groundwater to streams is challenging and important for understanding off-site migration of VOCs, cross-media contamination (groundwater to surface water and eventually air), and potential impacts on downstream ecosystems and human populations. A streambed point sampling approach was used to quantify fluxes of water and 14 VOCs from groundwater to an urban stream in North Carolina, USA, during summer (June 2015) and winter (January 2016). The approach is unique in coupling measurements of vertical hydraulic conductivity, vertical hydraulic head gradient, and groundwater VOC concentration at each individual sampling point, reducing or eliminating some potential concerns with other Darcian methods for quantifying VOC inputs to streams.Most results were consistent with discharge of two main VOC plumes on opposite sides of the stream. Plume 1 from the west side was dominated by cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) at mean concentrations of 19 and 11 μg L−1, respectively. Plume 2 from the east side was dominated by benzene (mean concentration 56 μg L−1). Plume 2 was not previously known, and the improved sampling approach allowed VOC discharge from both plumes to be quantified simultaneously.For 13 of the 14 detected VOCs, the mean VOC flux from groundwater to the stream (fVOC) was higher in January 2016 than in June 2015, mainly because groundwater flux was higher in January. The only exception was cDCE, the most abundant VOC in Plume 1, which had mean fVOC values of 9.8 and 9.5 mg m−2 d−1 in June 2015 and January 2016, respectively. Benzene was the most abundant VOC in Plume 2 and had mean fVOC values of 11 and 37 mg m−2 d−1 in June 2015 and January 2016, respectively. High groundwater flux drove almost all the occurrences of high VOC flux. For a given VOC, the flow-weighted mean concentration (with each VOC concentration weighted by the upward groundwater flux at the VOC sampling point) was generally larger than the unweighted mean concentration. Thus, flow-weighting of concentrations gave a more accurate indication of the average VOC concentration in net groundwater discharge to the stream.An estimate of total VOC mass discharge from groundwater to the study reach of the stream, 3.6 kg of VOC per year, was based on the fVOC results and streambed area in the reach. The bulk of this discharge was due to benzene, cDCE, and VC, with individual mass discharges of 2.1, 0.83, and 0.40 kg yr−1, respectively. Estimates of maximum potential VOC degradation in the streambed suggest that the 3.6 kg yr−1 estimate of mass discharge was not sensitive to potential degradation of VOCs in the streambed sediments above the groundwater sampling depth.

Temporary clogging effects induced by a sustainable anti-icing hydrogel on the hydraulic conductivity and inertia coefficient of open-graded asphalt pavements

Open-graded asphalt pavements require special winter maintenance procedures to ensure the effectiveness of anti-icing and deicing measures. A recently developed solution for this type of pavement is represented by an environmental friendly thickened bio-based salt hydrogel, which consists of a thermo-sensitive sodium chloride (NaCl) brine admixed with a gellant agent (seaweed fibers) having the ability to form a gel-like structure when hot-sprayed on a cold surface. This thin salt layer results in a long-lasting residual efficacy of the winter maintenance product and in a reduction of salt consumption, but affects the drainage capacity of the pavement. These transient clogging effects were evaluated on laboratory-made specimens through the measurement of their vertical hydraulic conductivity variations before and after the hydrogel application, using a 1-D air permeameter and a constant head water permeameter. The analyses, based on Darcy–Forchheimer model and Darcy model for lower Reynold numbers, revealed a significant short-term reduction of the hydraulic conductivity, that, anyway, tends to be almost totally restored once the critical weather event is over (after about 6 h).

Spatial variability of the vertical saturated hydraulic conductivity of sediments around typical thermokarst lakes

The formation and development of thermokarst lakes is a key factor causing permafrost degradation, in which the vertical hydraulic conductivity (Kv) of lakebed sediments plays an important role as it affects the water and heat transfer between thermokarst lakes and permafrost. However, the spatial variability of Kv of lakebed sediments in the Qinghai–Tibet Plateau (QTP) remains unclear. Hence, in this study, the Kv values of sediments in two thermokarst lakebeds were measured in situ using the standpipe method, and the grain size of the sediments was analyzed. The statistical results showed that BLH-A and B (lakes A and B in Beiluhe) had moderate and strong spatial variabilities, respectively. Lilliefors test results showed a log-normal distribution of the Kv measurements of the sediment samples. From the results of the geostatistical method, it was concluded that the Gaussian model best fitted the variograms of the Kv values. The d50 (grain size for which 50 % of grains are finer) had the strongest correlation with Kv, and the relationship between Kv and the grain size of d50 was a quadratic function. The estimated Kv value (0.03 m/d) was close to the measurements (0.005–0.58 m/d), and the specific discharge of BLH-B ranged from − 0.0038 to 0.00056 m/d. BLH-A and BLH-B would gradually expand under the influence of future climate due to the special geology (low Kv). This basic research on thermokarst lake regions can help understand the properties of thermokarst lakebed sediments and provide parameters for the numerical simulations of the hydrological cycle in thermokarst lake regions.

Groundwater flow numerical model to evaluate the water mass balance and flow patterns in Groundwater Circulation Wells (GCW) with varying aquifer parameters

Groundwater Circulation Wells (GCW) can be an effective in-situ remediation option allowing high mass recovery of contaminants in cases where contamination hotspots are located in saturated soil having low hydraulic conductivity. Traditional treatment options such as Pump&amp;Treat, Air Sparging (AS)/Soil Vapor Extraction (SVE) and Multi Phase Extraction (MPE) typically require long operation times and significant costs for long-term plume management. GCWs induce meaningful changes in the groundwater flow introducing vertical flows both downward and upward, generating a “circulation cell”, which facilitates contaminant desorption from the soil. This study aims to understand the effects of a GCW on an aquifer in terms of both groundwater flow directions and water balance. A groundwater numerical model was built using MODFLOW-2005 to simulate the effect of the hydraulic parameters of the aquifer on the hydraulic circulation pattern of the GCW. The use of particle tracking simulated by MODPATH 7 showed the circulation cells and the impact on groundwater directions induced by different configurations of hydraulic parameters. The water flowing into the cell comes from both the injection well and the surrounding aquifer and the model shows how the hydraulic parameters of the aquifer, in particular the horizontal and vertical hydraulic conductivity, have a paramount influence in determining the shape and dimension of the circulation cell. A water mass balance analysis was carried out. It allowed to predict the groundwater flows exchanges between the GCW system and the surrounding aquifer, and to verify the sensitivity of the water budget to specific aquifer parameters. The results of this study are useful for further understanding the hydraulics of a GCW remediation system in order to support the design and to predict its performance.

Seasonal change of groundwater response to Earth tides

• Tidal response of groundwater may change from being confined-like to unconfined-like. • The tidal change may be attributed to seasonal vertical conductivity changes in aquitard. • Saturation changes in fractures could result in the vertical conductivity changes. Groundwater is an important natural resource and its security depends largely on the confinement of the aquifer. Here we use ten-years of continuous groundwater data from a well in Southwest China to show that seasonal precipitation may change the aquifer's response to Earth tides from being confined-like during dry seasons to being unconfined-like during rainy seasons. Comparing the response of water level in this well with the theoretical prediction from a leaky aquifer model, we show that the observed changes of aquifer confinement reflect a seasonal increase of the vertical hydraulic conductivity from being low in the dry season when the water level is low to being high in the rainy season when the water level is high. Such seasonal change of aquifer confinement has not been reported before and may impact our understanding on the subsurface transport, the security of groundwater resources, and the safety of toxic waste repositories.

Influence of inter-aquifer leakage on well-injection capacity: Theory and aquifer-scale mapping for artificial recharge

Aquifer storage and recovery (ASR) is an important water resources management technique that involves the injection of a large volume of water underground. For the successful implementation of an ASR project, a target aquifer should have a sufficient injection capacity, which is the maximum volume of water that can be safely injected. In nature, no aquitard is perfectly impermeable, and inter-aquifer leakage may have a major impact on injection capacity. Despite the importance of determining the injection capacity for ASR planning, there is no quantitative methodology that estimates the injection capacity of leaky aquifers. In this study, we first develop a solution for injection capacity with inter-aquifer leakage based on the Hantush - Jacob solution, and conduct a comprehensive sensitivity analysis to elucidate the influence of inter-aquifer leakage on injection capacity. From the sensitivity analysis, we show that inter-aquifer leakage can impact injection capacity by more than one order of magnitude, depending on the hydrogeological and operational parameters. We then develop a practical mapping methodology that estimates the injection capacity of leaky aquifers. We demonstrate the proposed methodology by applying it to a potential ASR site in Minnesota, USA, where ASR is considered as a solution to alleviate groundwater contamination by PFAS chemicals. The case study results reveal significant spatial variability in injection capacity over the study area and show an average increase in the injection capacity of about 26% compared to that in the nonleaky scenario. We also analyze the uncertainty in the estimated injection capacity due to the variability of aquitard properties and show that the variability of aquitard vertical hydraulic conductivity leads to a larger uncertainty in the estimated injection capacity than does the variability of aquitard thickness. This study elucidates the effects of inter-aquifer leakage on injection capacity and provides a practical methodology for injection capacity mapping.

Parametric study of fluidization conditions of bed sediments in the hyporheic zone

AbstractThe phenomenon of fluidization of the bed sediment of the hyporheic zone involves the production of dynamic suspension of solid particles in a stream of water flowing in the direction opposite to gravity. Fluidization may be permanent; then, it becomes a spring or a headwater zone, where groundwater discharge rate is almost unchanged within an entire hydrological year. But it can also occur periodically, depending on the changing hydrodynamic conditions. In such cases, the fluidization of the bed sediment of the hyporheic zone may disturb its functioning by changing the conditions of surface water and groundwater exchange. The disturbances affect hydrodynamic and hydrochemical processes connected with water exchange, but first of all, the living conditions of hyporheic zone flora and fauna. Therefore, the phenomenon of fluidization is significant for broadly understood ecology of the hyporheic zone. The paper presents the analysis of conditions of fluidization occurrence depending on the main hydrodynamic parameters that may affect this process. The authors analysed the influence of the difference in water level between the drained aquifer and the river, the hydraulic conductivity and anisotropy of the aquifer, the vertical hydraulic conductivity in the hyporheic zone, thickness of the hyporheic zone, and the width of the river on the possibility of fluidization of the bed sediment of the hyporheic zone. The range of variability of particular parameters corresponds to the actual variability of those parameters in natural conditions. It was proved that the fluidization of the bed sediment of the hyporheic zone mostly depends on: water level difference, hydraulic conductivity of the aquifer, and value of vertical hydraulic conductivity in the hyporheic zone. The other parameters have little influence on this process.

A low-cost model for slug tests in a confined aquifer with skin-zone effect

While the effect of small-scale skin has been extensively investigated, numerical models incorporating the effect require expensive computational cost due to fine spatial discretization of the skin and have not been widely available. This study develops a new model for slug tests at a partially-penetrating well in a two-zone confined aquifer of skin and formation zones. A new basic formulation defines transient flow in the skin with an additional skin factor reflecting the skin storage effect. The formulation assumes horizontal flow in the skin with excluding the vertical skin hydraulic conductivity. The analytical solution and finite element solution of the model are developed. The analytical expression relating the skin factor to the skin specific storage is derived. Results suggest the formulation is a useful alternative to conventional flow equation for the skin in achieving coarse spatial discretization and low computational cost. The present solution agrees well with the field head data obtained from Butler (2019). To conclude, this study presents theoretical advance and efficient simulation in modeling of well hydraulics.

Quantifying the Impact of Lagged Hydrological Responses on the Effectiveness of Groundwater Conservation

AbstractMany irrigated agricultural areas seek to prolong the lifetime of their groundwater resources by reducing pumping. However, it is unclear how lagged responses, such as reduced groundwater recharge caused by more efficient irrigation, may impact the long‐term effectiveness of conservation initiatives. Here, we use a variably saturated, simplified surrogate groundwater model to: (a) analyze aquifer responses to pumping reductions, (b) quantify time lags between reductions and groundwater level responses, and (c) identify the physical controls on lagged responses. We explore a range of plausible model parameters for an area of the High Plains aquifer (USA) where stakeholder‐driven conservation has slowed groundwater depletion. We identify two types of lagged responses that reduce the long‐term effectiveness of groundwater conservation, recharge‐dominated and lateral‐flow‐dominated, with vertical hydraulic conductivity (KZ) the major controlling variable. When high KZ allows percolation to reach the aquifer, more efficient irrigation reduces groundwater recharge. By contrast, when low KZ impedes vertical flow, short term changes in recharge are negligible, but pumping reductions alter the lateral flow between the groundwater conservation area and the surrounding regions (lateral‐flow‐dominated response). For the modeled area, we found that a pumping reduction of 30% resulted in median usable lifetime extensions of 20 or 25 years, depending on the dominant lagged response mechanism (recharge‐ vs. lateral‐flow‐dominated). These estimates are far shorter than estimates that do not account for lagged responses. Results indicate that conservation‐based pumping reductions can extend aquifer lifetimes, but lagged responses can create a sizable difference between the initially perceived and actual long‐term effectiveness.

Numerical Investigation of Hydraulic Conductivity Variation on Highway Slopes Made of Expansive Yazoo Clay

Expansive soils cover more than 25% of the total area of the United States and are subjected to shrink-swell behavior with moisture variation. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of the expansive soil is subjected to change because of the development of shrinkage cracks which affect the vertical hydraulic conductivity, whereas the horizontal hydraulic conductivity remains negligibly constant. This affects the percolation behavior of the subgrade soil and, in turn, reduces the soil strength, as one of the major factors of slope failure. However, no study has been done on the change in the hydraulic properties of expansive soil with time and its effect on highway slopes. The current study intends to investigate the hydraulic conductivity and matric suction variation at different wet-dry cycles on highway slopes. An instantaneous profile method to investigate the changes in hydraulic conductivity during 1N to 5N wet-dry cycles was utilized. The finite element method in Plaxis was conducted to evaluate the effect of different frequencies and duration of rainfall on water intrusion, and the corresponding change in the matric suction of the highway slope. The selected rainfall pattern is evaluated at different intensities and durations of rainfall based on 100-years return periods. The flow analysis showed that the suction dropped at the highway slope with the presence of rainfall.

Using Automated Seepage Meters to Quantify the Spatial Variability and Net Flux of Groundwater to a Stream

AbstractWe utilized 251 measurements from a recently developed automated seepage meter (ASM) in streambeds in the Nebraska Sand Hills, USA to investigate the small‐scale spatial variability of groundwater seepage flux (q) and the ability of the ASM to estimate mean q at larger scales. Small‐scale spatial variability of q was analyzed in five dense arrays, each covering an area of 13.5–28.0 m2 (169 total point measurements). Streambed vertical hydraulic conductivity (K) was also measured. Results provided: (a) high‐resolution contour plots of q and K, (b) anisotropic semi‐variograms demonstrating greater correlation scales of q and K along the stream length than across the stream width, and (c) the number of rows of points (perpendicular to streamflow) needed to represent the groundwater flux of areas up to 28.0 m2. The findings suggest that representative streambed measurements are best conducted perpendicular to streamflow to accommodate larger seepage flux heterogeneity in this direction and minimize sampling redundancy. To investigate the ASM's ability to produce accurate mean q at larger scales, seepage meters were deployed in four stream reaches (170–890 m), arranged in three to six transects (three to eight points each) per reach across the channel. In each reach, the mean seepage flux from ASMs was compared to the seepage flux from bromide tracer dilution. Agreement between the two methods indicates the viability of a modest number of seepage meter measurements to determine the overall groundwater flux to the stream and can guide sampling for solutes and environmental tracers.

Theory of transient confined-unconfined flow in a confined aquifer considering delayed responses of water table

A semi-analytical solution is developed for drawdown of transient confined-unconfined flow towards a fully penetrating well in a confined aquifer. The proposed solution considers the aquifer anisotropy and the drainage from the unsaturated zone above the water table in the transient unconfined region. Based on the work by Moench (1995), the parameter of γ related to vertical hydraulic conductivity, aquifer thickness, specific yield and a delayed coefficient is introduced to investigate the delayed responses of flow behaviours, i.e., drawdown and development of the transient unconfined region. The results indicate that the flow behaviours simulations by the proposed solution are identical to that by Visual-MODFLOW Flex and finite difference method. The drawdown delayed responses occur in the early and intermediate segments, and disappear at the late segment during the transient confined-unconfined conversion. The increasing of the vertical hydraulic conductivity and the delayed coefficient can decrease the drawdown and limit the development of transient unconfined region, thus, and postpone the time of transient confined-unconfined conversion in a radial distance. The release of water by gravity storage nearby the piezometer surface is quick, resulting in an obvious log–log S-shaped drawdown-time curve. As buried depth increases, the effect of artesian storage is more pronounced. This paper provides much-needed insights of drawdown delayed response during the confined-unconfined conversion.

Revealing vertical aquifer heterogeneity and hydraulic anisotropy by pumping partially penetrating wells

The stratification of sedimentary aquifers introduces spatial variability in hydraulic conductivity, primarily between individual horizontal layers. On larger scales, the vertical heterogeneity enhances hydraulic anisotropy, with the horizontal conductivity typically exceeding the vertical one. In this study, the hydraulic anisotropy of a stratified aquifer is estimated from data of hydraulic tests in which water is sequentially extracted from well sections screened at different depths, and the hydraulic response is measured at various multilevel observation wells. The applicability of the method is demonstrated by field tests in a fluvial gravel aquifer in the Upper Rhine Valley, Germany. A homogeneous anisotropic model, and models with three and five anisotropic layers, are fitted to the measured drawdowns in the steady-shape regime, in which differences in hydraulic head between observation locations do not change over time even though the head values themselves change. The position of the five horizontal layers is based on the lithology of the drilling profile at the pumping-well location. The three-layer model is achieved by merging insensitive or similar layers with sensitive layers. The fits result in estimates of the radial and vertical hydraulic conductivities for all layers of the respective models, which are upscaled to effective parameters over the entire depth in the case of the multilayer models. The homogeneous model shows significantly higher errors than those of the heterogeneous models. The heterogeneous locally anisotropic models not only reveal vertical variability of hydraulic conductivity, but also lead to a three-times larger anisotropy ratio upon upscaling.

Experimental study on anisotropy of hydraulic conductivity for municipal solid waste.

Anisotropy of hydraulic conductivity is an important parameter controlling fluid movement in municipal solid waste (MSW) landfills, while measurements of anisotropy are rare. In this study, a laboratory-scale enhanced reactor was built to create MSW samples with different degrees of degradation. Vertical and horizontal hydraulic conductivities of these samples were measured in a self-designed permeameter to study the effects of compression and degradation on anisotropy of MSW. CT scanning was performed to observe the internal pore-structure of MSW under compression. A prediction model of anisotropy under compression was established. It was found that as degradation time increased from 0month to 18months, the dry mass percent of 0D particles increased from 12.3% to 38.8%, while 2D particles content decreased from 78.7% to 47.2%. As vertical stress increased from 50kPa to 400kPa, dry unit weight (γd) increased from 3.26 kN/m3 to 5.51 kN/m3, anisotropy (A) increased from 1.26 to 5.17. It was because that the size and continuity of pores decreased and the angle of pore arrangement tended to be horizontal as the vertical stress increased. The relation between anisotropy and vertical stress could be well fitted with the prediction model. When degradation time increased from 0month to 18months, A decreased linearly from 5.02 to 2.75 due to the decreasing content of 2D particles. Anisotropy also decreased with the decreasing C/L. Compression has much greater influence on waste anisotropy than that of degradation. Anisotropy of MSW at different depths of landfills could be determined based on the trend lines in this study.

Vertical Leakage Occurred after an Earthquake: Suggestions for Utilizing the Mixed Flow Model

Abstract Permeability is an important parameter of shallow crust that affects underground water migration. It is important to calculate the permeability changes caused by earthquakes for underground engineering safety and pollutant dispersion. The response analysis of groundwater in wells, to Earth tides, has been widely used to calculate permeability. However, the calculation results and the judgment of leakage are controversial. In this study, the water level response of both the M2 and O1 tidal waves in the Zuojiazhuang well was analyzed. An optimization fitting, using the mixed flow model, was performed to calculate the hydraulic parameters of aquifers and aquitards. After the Wenchuan earthquake, the horizontal transmissivity of aquifers increased temporarily and then slowly recovered. However, after the Tohoku earthquake, the horizontal transmissivity increased permanently by one order of magnitude. The vertical hydraulic conductivity increased permanently by three orders of magnitude, meaning that vertical leakage occurred. As both the M2 and the O1 waves are used as constraints for the calculation with the mixed flow model, the results of this study are more precise than those of previous ones. This article also gives some suggestions for utilizing the mixed flow model.

Estimation of anisotropic hydraulic conductivity using geophysical data in a coastal aquifer of Karnataka, India

AbstractEstimation of hydraulic parameters is essential to understand the interaction between groundwater flow and seawater intrusion. Though several studies have addressed hydraulic parameter estimation, based on pumping tests as well as geophysical methods, not many studies have addressed the problem with clayey formations being present. In this study, a methodology is proposed to estimate anisotropic hydraulic conductivity and porosity values for the coastal aquifer with unconsolidated formations. For this purpose, the one‐dimensional resistivity of the aquifer and the groundwater conductivity data are used to estimate porosity at discrete points. The hydraulic conductivity values are estimated by its mutual dependence with porosity and petrophysical parameters. From these estimated values, the bilinear relationship between hydraulic conductivity and aquifer resistivity is established based on the clay content of the sampled formation. The methodology is applied on a coastal aquifer along with the coastal Karnataka, India, which has significant clayey formations embedded in unconsolidated rock. The estimation of hydraulic conductivity values from the established correlations has a correlation coefficient of 0.83 with pumping test data, indicating good reliability of the methodology. The established correlations also enable the estimation of horizontal hydraulic conductivity on two‐dimensional resistivity sections, which was not addressed by earlier studies. The inventive approach of using the established bilinear correlations at one‐dimensional to two‐dimensional resistivity sections is verified by the comparison method. The horizontal hydraulic conductivity agrees with previous findings from inverse modelling. Additionally, this study provides critical insights into the estimation of vertical hydraulic conductivity and an equation is formulated which relates vertical hydraulic conductivity with horizontal. Based on the approach presented, the anisotropic hydraulic conductivity of any type aquifer with embedded clayey formations can be estimated. The anisotropic hydraulic conductivity has the potential to be used as an important input to the groundwater models.