Aquifer Layer Research Articles

Determination of Aquifer Hydraulic Characteristics from Surface Electrical and Borehole Measurements in Ozoro, Nigeria

Surface electrical and borehole measurements were undertaken in order to establish the hydraulic characteristics of alluvial aquifer in Ozoro, Delta State. Ten vertical electrical sounding data were acquired using Schlumberger Configuration. Borehole measurements which included pumping test, well logging and the distribution of grain size analysis were also carried out. The results of the electrical sounding indicate that the aquiferous layer is located between the fourth and fifth layers with resistivity ranged from 53.5 Ωm - 1279 Ωm. The aquifer thickness ranged from 7.67 m - 49.4 m and transmissivity values ranged from 41.4 - 330.5 𝑚2/day. The average hydraulic conductivity (k) value obtained is 6.2 m/day. The borehole lithology, resistivity and spontaneous potential log indicate the subsurface lithology to consists of top soil (brownish), clayey sand, clay, fine sand and gravelly sand. The Cooper Jacob solution was used in the analysis of the borehole pumping experiment and the obtained hydraulic conductivity, transmissivity, storativity and specific capacity are 6.8 m/day, 0.067 m2/min (96.48 𝑚2/day), 25.47 and 0.364 m2/min (524.6 m2/day) respectively. Also, the grain size distribution analysis using the Hazen approximation gave hydraulic conductivity as 11.55 m/day. The results showed that all three methods are applicable for determining aquifer hydraulic parameters.

Pemodelan 3 Dimensi Volume Rembesan Polutan Sampah untuk Penentuan Lapisan Akuifer

Research has been carried out with the title 3-dimensional modeling of the volume of waste pollutant seepage to create an aquifer layer at the Mancani Landfill, Palopo City. This study aims to determine the volume of waste pollutant seepage in the Mancani TPA Palopo City by knowing the depth of the air based on its resistivity value. Measurements were made with 5 tracks along the 200 meters using the Schlumberger configuration. The data is carried out using IP2Win Software to obtain resistivity values and depth and Voxler Software to obtain 3 Dimensional modeling, data interpretation based on resistivity tables. The results obtained are that the leachate at the Mancani landfill in Palopo City is at a depth of 1 - 4.5 meters with a resistivity value ranging from 11.00-23.39 Ωm and a seepage volume of 29,929 m3

Statistical analyses of hydrochemistry in multi-aquifers of the Pansan coalmine, Huainan coalfield, China: implications for water-rock interaction and hydraulic connection

Understanding the groundwater hydrogeochemical processes and aquifer hydraulic connections are essential for effective prevention of water inrush in concealed coal mines. In this study, 40 groundwater samples were collected from the loose layer aquifer (LA), coal measure aquifer (CA), and limestone aquifer (LA) in the Pansan coal mine, Huanan coalfield, China, and the major ion concentrations were analyzed by bivariate diagrams (Na+ + K+ - Cl− versus Ca2+ + Mg2+ - SO42− - HCO3− and CAI-I versus CAI-II), multivariate statistical methods, and receptor model in order to identify the water-rock interactions and aquifer hydraulic connections. Piper diagram showed that groundwater in LA and TA was dominated by the Na–Cl type, while groundwater in CA was mainly of the Na–HCO3 type. Based on the results of bivariate diagrams and PCA/FA, weathering of silicate minerals and cation exchange (source 1), sulfate dissolution (source 2) and chloride dissolution (source 3) were the main processes controlling the groundwater chemistry. Unmix model revealed that the mean contribution of source 1 to CA samples was 74%, while LA and TA samples have higher contributions from evaporite dissolution (source 2 and source 3) relative to CA samples. Moreover, both clustering analysis methods (Q-type hierarchical and K-means cluster) confirmed the existence of a hydraulic connection between LA and TA in the northeastern part of the study area. It is concluded that the application of multivariate statistical analysis to interpret groundwater chemistry can provide useful guidance to prevent water inrush in coal mines.

Comprehensive Water Inrush Risk Assessment Method for Coal Seam Roof

In order to prevent coal mine water inrush accidents, it is necessary to appropriately assess the water abundance of coal mines based on drilling and geophysical data. This paper studied a comprehensive risk assessment method of water inrush. First, a water inrush risk index was proposed based on the analytic hierarchy process-entropy method (AHP-EM) and the water-rich structure index was proposed based on the geological data coupled calculation, then weighted two indices above which established the comprehensive water inrush risk assessment method. Secondly, eight factors were chosen as risk control factors of water inrush: core recovery, aquifer thickness, distance from the indirect aquifer to the coal seam, aquiclude thickness, height of water-conducting fracture zone, sand-mud ratio, total layers of aquifer and aquiclude, and the equivalent thickness of sandstone. Finally, the No. 2 coal seam of Dahaize coal mine was taken as the research object, the factors were calculated, and a comprehensive water inrush assessment model was constructed. With site investigation and observation, the water inrush risk assessment model of the No.2 coal seam roof is consistent with the actual mining situation, which verifies the validity of the model. In addition, this method was used to evaluate the water-richness of the weathered bedrock fractured aquifer in the Zhangjiamao coal mine. The practical application of the two mines has verified the generality of the approach. The research could provide scientific assistance for mine water hazard mitigation and mining safety.

Water Quality Assessment Bias Associated with Long-Screened Wells Screened across Aquifers with High Nitrate and Arsenic Concentrations.

Semi-arid regions with little surface water commonly experience rapid water table decline rates. To hedge against the falling water table, production wells in central Mexico are commonly installed to depths of several hundred meters below the present water table and constructed as open boreholes or perforated casings across their entire length. Such wells represent highly conductive pathways leading to non-negligible flow across chemically distinct layers of an aquifer—a phenomenon known as ambient flow. The objectives of this study were to estimate the rate of ambient flow in seven production wells utilizing an end-member mixing model that is constrained by the observed transient chemical composition of produced water. The end-member chemical composition of the upper and lower layers of an urban aquifer that overlies geothermal heat is estimated to anticipate the future quality of this sole source of water for a rapidly growing urban area. The comprehensive water chemistry produced by seven continuously perforated municipal production wells, spanning three geologically unique zones across the city of San Miguel de Allende in Guanajuato State, was monitored during one day of pumping. The concentration of conservative constituents gradually converged on steady-state values. The model indicates that, relative to the lower aquifer, the upper aquifer generally has higher specific conductance (SC), chloride (Cl), nitrate (NO3), calcium (Ca), barium (Ba) and magnesium (Mg). The lower aquifer generally has a higher temperature, sodium (Na), boron (B), arsenic (As) and radon (Rn). Ambient flow ranged from 33.1 L/min to 225.7 L/min across the seven wells, but this rate for a given well varied depending on which tracer was used. This new 3D understanding of the chemical stratification of the aquifer suggests that as water tables continue to fall, concentrations of geothermally associated contaminants of concern will increase in the near future, potentially jeopardizing the safety of municipal drinking water.

Pemodelan Sistem Dinamik Eco-Drainage di Wilayah Tanah Basah (Studi Kasus Kawasan Kelapa Gading DKI Jakarta)

An Ecological drainage becomes an application in this development project in the Kelapa Gading area. The drainage concept that is applied is a drainage system in which rainwater that falls on road surface runoff will flow directly into the water infiltration system and directly fill the ground surface water. G eologically, it can be seen that North Jakarta is an area with a fairly high ground water level (MAT), and has an average MAT elevation of 2 - 2.5 m. This study intends to determine the ability of this ecodrainage to reduce runoff/floods that often occur in areas with a fairly high MAL. What direct benefits can be felt in the use of ecodrainage in these flood-prone areas, thus making the basic reason for applying this ecodrainage. This study uses a dynamic systems approach. In the preparation of the dynamic system model, Powersim Studio Version 10 software will be assisted. The simulation results show that an increase in rainfall every year will provide an increasing flood potential. By using eco-drainage, it is felt that it is not optimal enough to reduce runoff in areas that have high MAT levels. However, this ecodrainage still provides broad sustainability benefits. The quantity of groundwater will slowly be filled up to the aquier layer through this ecodrainage. This step is considered to be able to help prevent the aquifer layer from being exposed and have an impact on the rate of land subsidence so that the potential for flooding will decrease.

A three-dimensional full-scale model for predicting the performance of deep-buried ground heat exchanger considering groundwater flow

It is critical to precisely determine the performance of deep-buried ground heat exchangers involving different geological layers in engineering projects of the geothermal energy utilization. Compared to the existing approaches solving only conduction between the ground heat exchanger and the surrounding ground based on the two-dimensional model, this paper established a three-dimensional full-scale coaxial ground heat exchanger model containing both aquifer and aquifuge layers involving groundwater effect. The convective heat transfer in pipes was calculated using the empirical correlation of Nusselt number to improve the computation efficiency. The groundwater velocity in the energy governing equation was assumed to be constant and along with the horizontal direction to further simplify the computation. The developed method was applied to a 2800 m and 2600 m depth ground heat exchangers with different geological conditions, and was validated by the field test and published data. The relative errors are less than 6.9%. The thermal influence ranges of the aquifer layer and the aquifuge layer close to aquifer are asymmetric about the circumferential direction. The results demonstrated that the three-dimensional full-scale model is necessary for accurately evaluating the performance of ground heat exchangers when there is groundwater migration.

Identification of Seismic Response to Aquifer System with A Synthetic Modelling Approach

The microseismic method is relatively new in groundwater exploration, especially in Indonesia. This study will examine the response of microseismic to groundwater aquifer systems. This study aims to analyze the response of seismic waves and to interpret the seismic wave response characteristics to the aquifer system model. The modeling of the aquifer system was carried out using seismic stratigraphy data. This data was used as input data to model the exposed HVSR curve using the Microtrem program in MATLAB. The study of physical parameters and supporting parameters of the aquifer layer and the air contained in it was carried out to support this modeling. The aquifer system modeling was carried out with various parameters, including saturation, porosity, and thickness of the aquifer layer. Furthermore, an analysis of the model is carried out to determine the response characteristics of the aquifer system to microseismic waves. The results show that the frequency range as a marker of the presence of the aquifer ranges from 2-4 Hz, which is determined by parameters within a specific value.

Application of Seismic Reflection Survey for Aquifer Layers Characterization at the Felda Lepar Utara Area, Pahang, Malaysia

Precise determination of subsurface structure is crucial in hydrogeological studies to correctly determine the potential of groundwater resources, and the sustainability of those resources. This study used the seismic reflection method to characterize the aquifer layer in Ladang Lepar Utara 8 (Line 1) and Ladang Sungai Rengai (Line 2) in the Felda Lepar Utara area, Pahang, Malaysia, due to its high accuracy, high-resolution and deeper penetration. The field data acquisition survey involved roll-along techniques with shot spacing of 5m along the line using 24-channels ABEM terraloc Mark-6 and CMP (common mid-point) profiling techniques. Seismic interpretation of reflection data and tubewell information from nearby borehole data indicates that the area consists of a single type of rock known as phyllitic meta-sedimentary rocks of the Sri Jaya beds that have been deformed by intense faulting and fracturing (from about 30 to 750 m depth in Line 1 and about 75 m to 500m depth in Line 2). This formation is overlain by recent alluvium that ranges in thickness from 30 to 75 m and is underlain by Lepar Granodiorite. The alluvium is a shallow aquifer system that can be classified as an unconfined aquifer, whereas the phyllitic meta-sedimentary rock of the Srijaya Beds is a deep aquifer system that can be classified as a confined aquifer with an alluvium layer (up to 75 m thick) on top as a confining bed. The occurrence of intense faulting and fracturing increases the porosity and permeability of the rock formation and hence increases its potential as a groundwater prospective/promising zone.

Identification of Seawater Intrusion Using Geoelectrical Method with Wenner-Schulumberger Configuration: A Case Study in Southern Tolonuo Island, North Halmahera Regency, Indonesia

Research on seawater intrusion has been carried out on the southern Tolonuo island, Tobelo sub-district, North Halmahera Regency, Indonesia using the Wenner-Schlumberger configuration resistivity geoelectric method supported by the Naniura NRD 300 HF tool, this study aims to determine the distribution pattern of seawater intrusion and to determine the resistivity value of each subsurface rock layer in the study area. The measurement results are processed using the RES2DINV software to obtain a 2-D pseudo resistivity section that describes the distribution value of the layer that the soil surface is shown in color images. The measurement results on line 1 show that there is seawater intrusion with a resistivity value range of 0.338 m - 2.44 m which is at 4 – 20 meters with a certain pattern, line 2 also has sea water intrusion at a depth of 5 m – 20 m with a resistivity value of 1.31 Ωm – 6.50 Ωm. On line 3, it is clear that there is a good correlation between the intersection of line 1 and line 2, where there is a low resistivity contrast on the line 1 with a stretch of 35 m – 50 m at a depth of 10 m – 20 m and the line 2 with a span of 80 m - 100 m at a depth of 10 m - 20 m. The distribution pattern of seawater intrusion from the south to the north of Tolonou Village with a wide range of up to 200 meters from residential areas from the shoreline. The research area has layers of clay rock with a resistivity value between 30 – 80 Ωm, and breccia rocks around it with a resistivity value of 100 – 200 Ωm. On the other hand, between clay and breccia there is impermeable rock which is thought to be conglomerate rock with a resistivity value of 200-500 Ωm, besides that in the study area there is also a layer suspected to be a groundwater aquifer layer with a resistivity value (ρ) 10 m.

Hydromechanical characterization of tide-induced head fluctuations in coastal aquifers: The role of delayed yield and minor permeable layers

Tidal analysis is an aquifer scale testing that is a low-cost alternative to pumping tests for evaluating aquifer hydraulic parameters without groundwater extraction. Many analytical solutions may be used to assess aquifer head fluctuations in response to tidal fluctuations. Nonetheless, they are rarely used in practice. Aside from that, most analytical solutions are based on a conceptual model that typically consists of an unconfined aquifer and a confined aquifer separated by an aquitard, where hydraulic head fluctuations in the unconfined aquifer part are commonly neglected. Additionally, the frequent confined aquifer short response time to sea-level fluctuations cannot rely on hydraulic connection of the confined aquifer to the sea through the aquitard. As a consequence, when analytical solutions are applied to real-world cases, the hydraulic diffusivity is overestimated. In this study, we investigate through different numerical simulations the fluctuations of the phreatic surface by considering the delayed yield. Numerical results demonstrate that the mechanical effect generated by the load over the sea bottom exerted by sea-level fluctuations is a key factor when determining aquifer parameters. We further show that in multilayer systems, head fluctuations in various aquifer layers can cause interferences and, consequently, increased attenuation of the tidal signal, resulting in an overestimation of the inferred hydraulic diffusivity. Our results provide guidance on how to properly reproduce tidal responses in coastal aquifers.

Hydrogeophysical Investigation of Aquifer Layers in Nkporo, Ohafia Local Government Area

Drilling a borehole in Nkporo area of Ohafia in Abia state without proper investigation may lead to wasting resources if water bearing formation is not achieved. This is because borehole drilling is very expensive. It is therefore necessary to carry out proper hydro-geophysical investigation in order to identify a good aquifer before borehole drilling. Electrical resistivity method has been chosen for the investigation of the water bearing formation. The use of Schlumberger array (Vertical Electrical Sounding (VES)) method of electrical resistivity was chosen based on the geology of the study area. This method was chosen because not only will it delineate the layers of the near surface aquifer but will also determine the thickness and depth to the aquifer. Five (5) vertical electrical soundings data were obtained from five (5) locations in the community using the Schlumberger array method. The investigations reveal that the area is mostly underlain shale. The formations are poor in aquifer materials. Borehole therefore, in the area should be drilled deep to depths ranging between 700 – 900m into sandstone as revealed in VES 3 and VES 4.

Integrating hydraulic profiling tool pressure logs and hydraulic tomography for improved high-resolution characterization of subsurface heterogeneity

• HPT pressure logs ( P c ) can be rapidly collected in unconsolidated deposits. • P c data provide information on sharp and gradually-varying layer boundaries. • Integrating HPT-derived hydrostratigraphy and HT yields a K field with sharp boundaries. • HPT K estimates require additional evaluations for highly heterogeneous deposits. Hydraulic tomography (HT) has been developed as a robust technique in characterizing subsurface heterogeneity over the last two decades. Hydraulic conductivity ( K ) and specific storage ( S s ) estimated by geostatistically-based HT inversion approaches are typically smooth and lack geological features when observation data density is sparse. Although integrating geological information can be helpful in adding structural features into parameter fields, costly efforts are required to obtain borehole logging through conventional coring and sampling. Also, identification of geological features such as layer boundaries from sampled materials can be a subjective process. In this study, corrected pressure ( P c ) logs collected during hydraulic profiling tool (HPT) surveys are utilized to derive the local hydrostratigraphic layers of the glaciofluvial deposit at the North Campus Research Site (NCRS) in Waterloo, Ontario, Canada. Site-specific geological models representing aquifer and aquitard layers are developed and calibrated to drawdown data of multiple pumping tests. Results show that estimated K fields correctly reflect the variation features of permeameter-estimated K profiles, as well as the spatial distribution of high and low K sediments. The calibrated geological models performed better than the geostatistically-based inversion approach in predicting independent pumping tests used for model validation. Moreover, by including K estimates of geological models as prior means, the estimated K fields reveal both intra- and interlayer heterogeneity, and the performances of drawdown prediction are further improved for the geostatistical inversion approach. Overall, our study suggests that, integration of stratigraphic information derived from HPT P c logs is useful for HT to capture the sharp boundaries in K fields, especially when the pumping test data is sparse.

Identification of the Aquifer Layer using the Geoelectric Method in Teupin Batee Village, Aceh Besar

The need for clean water around the world is related to the increasing population, especially in Teupin Batee Village, Aceh Besar District. In addition to surface water, groundwater is one of the potentials that can be utilized by the community, particularly for household needs. The purpose of this study is to identify the aquifer layer using the geoelectric method. One of the geophysical methods that can be used to map groundwater potential is the geoelectrical method based on the resistivity value of subsurface rocks. This study uses the Wenner-Schlumberger array because it can map subsurface structures both vertically and horizontally. From the results of the study, it was found that there are four different layers in this research area including, the top soil layer, hard rock, tuffaceous sand and sand layer as aquifer layer. The top soil layer is mixed with tuff, sand and volcanic breccia to a depth of 8 m with a resistivity value of 5-25 ?m. The Hard rock layer is at a depth of 8 m – 30 m with a resistivity value of 45-220 ?m. The tuffaceous sand layer has a resistivity value ranging from 25-55 ?m. While the sand layer or aquifer is at a depth of 10 m – 60 m with a resistivity value of <10 ?m which is separated by a layer of tuffaceous sand between the two aquifer layers.

Mapping of aquifer hydraulic properties in Ogbeje and Umeghe in Abraka, Delta State Nigeria: insights from geophysical and hydrogeological methods

Vertical Electrical Sounding (VES), Pumping test, well logging and grain size analysis were conducted with the aim of studying the subsurface geophysical formation in order to determine aquifer characteristics such as hydraulic conductivity, transmissivity and other parameters for groundwater exploration purposes around Ogbeje and Umeghe, Abraka Delta State. Nine (9) VES stations were occupied and the results obtained from the computer iterations suggest 4 to 5 geoelectric layers. The aquiferous layers wwerefound at a depth ranging from 20.0 m – 38.3 m with resistivity ranging from 2200 ?m to 8500 ?m and thickness varying between 6.7 and 20.0 m. The VES study reveals the possibility of having a maximum drill depth the o water table of about 38 m. The results obtained from the pumping test and well logginwereas used to estimate the transmissivity value of T = 0.0722 m2/min, storativity S = 0.00063, specific capacity of the well = 0.39 m2/min and hydraulic conductivity, K= 8.5 m/day while the result from the grain size analysis gave hydraulic conductivity as Kmin= 12.96 m/d to Kmax = 26.96 m/d respectively. Thus, these results indicate that the aquifer is capable of proda ucing sufficient amount of water for both domestic and industrial purposes for the people in the area. 

Comparison of IDW and Kriging Interpolation Methods Using Geoelectric Data to Determine the Depth of the Aquifer in Semarang, Indonesia

Several areas in Semarang City have been unable to get a clean water supply through the Local Water Company (PDAM) channel. One of the solutions that can be done to overcome this problem is by utilizing groundwater, which can be obtained by building a deep well made to obtain rock layers that can accommodate and drain groundwater (aquifer layer). To find out the approximate depth of the aquifer layer, it is necessary to conduct a preliminary investigation before drilling. There are so many methods that can be done, and one of them is by using the geoelectric method. After using the geoelectric method, we can determine the distribution of the depth of the aquifer in Semarang City by using interpolation analysis. In this study, the IDW and Kriging interpolation methods were used. The two methods were then compared to show the difference in the distribution of aquifer depths in areas that lack clean water using the two interpolation methods above. Besides that, we are using RMSE and MAPE analysis to find the error rate of the two methods. The results obtained were the RMSE of the IDW and Kriging methods amounting to 5,829 and 5,433, and the MAPE results were 10.90% and 10.34%. Based on this, the Kriging method tends to have better results when interpolating using geoelectric data. With this research, it is hoped to provide knowledge to determine the most suitable interpolation method used in determining the depth of the aquifer and also can be used as an illustration of the depth of the aquifer in the area that lacked clean water in Semarang City, so that it can be used as a reference in estimating the design of deep good development more accurately.

Estimation of parameters of gas storage operation in inhomogeneous aquifers

The purpose of the article is development and testing of a mathematical model of gas storage in a layered aquifer with a low permeabilityinterlayer for a case of plane-parallel and axial-symmetric filtration. Methodology. One of the most common models of anisotropy of rocks is a model of a layered seam, which is explained by geological conditions of sedimentation, which lead to stratification of layers with different collecting properties. In the practice of underground gas storage, consideration of such a model is of particular importance.This is due to possible significant difference in advancing a boundary of gas-water contact through the interlayers with different filtration characteristics caused by changes in a position of a gas zone. A comprehensive approach is applied, which includes collection, systematization and analysis of actual data on filtration and physical and mechanical properties of host rocks that affect the formation of natural and technogenic deposits, as well as analytical and numerical methods for solving equations of gas-water contact in different conditions. Results. Gas-hydrodynamic model of underground gas storage in an inhomogeneous aquifer is justified for calculation of its cyclic operation in a three-layer seam considering cross-flows through a low permeability interlayer.The results can be used in evaluation calculations at a design stage of gas storage facilities in aquifers. Scientific novelty. A mathematical model of gas storage in a layered aquifer with a low permeability interlayerfor a case of plane-parallel and axial-symmetric filtration is developed and tested. A new method of linearization of a system of differential equations for determining pressures in a collectingseamis obtained in the article and it is a generalization of previously used methods, with an introduction of "boundary schemes". Practical significance. Calculation results indicate a significant influence of characteristics of a layered porous medium on the advance of gas-water contact along individual layers. The results can be used in the evaluation calculations at a design stage of gas storage facilities in aquifers.

Evaluation of the Environmental Impacts of Water Disposal Associated With Crude Oil Production on El-Moghra Aquifer in Abu El-Gharadig Basin, South East Qattara Depression

/year. This is due to the limited water resources compared with the water demands. The physical and chemical properties of the groundwater differ from surface water related to the environment in which it occurs. Groundwater is affected by surface activities, rainwater, seepage, irrigation water and drainage water and other effluents. Shortage of water sources in Egypt bring out the issue of using non-conventional water resources.Industrial activities represent the most hazardous source of ground water pollution and disposal lagoons for water associated with crude oil production represent the main source of pollution to Moghra aquifer in the study area. The large quantities of water drained daily to the un-lined disposal lagoons, facilitate the salt water intrusion to the aquifer layer. There are three main water disposal lagoons in the study area, the surface area of the main lagoons ranges from 0.08 to 2.08 Km

Numerical Simulation of the Enrichment of Chemotactic Bacteria in Oil-Water Two-Phase Transfer Fields of Heterogeneous Porous Media

Oil pollution in soil-groundwater systems is difficult to remove, and a large amount of residual oil is trapped in the low permeable layer of the heterogeneous aquifer. Aromatic hydrocarbons in oil have high toxicity and low solubility in water, which are harmful to the ecological environment. Chemotactic degrading bacteria can perceive the concentration gradient of non-aqueous phase liquid (NAPL) pollutants in the groundwater environment, and enrich and proliferate around the pollutants, thus achieving a more efficient and thorough remediation effect. However, the existing theoretical models are relatively simple. The physical fields of oil–water two-phase flow and oil-phase solute convection and diffusion in water are not coupled, which further restricts the accuracy of studies on bacterial chemotaxis to NAPL. In this study, geometric models based on the actual microfluidic experimental study were constructed. Based on the phase field model, diffusion convection equation and chemotaxis velocity equation, the effects of heterogeneity of porous media, wall wettability and groundwater flow rate on the residual oil and the concentration distribution of chemotaxis bacteria were studied. Under all of the simulation conditions, the residual oil in the high permeable area was significantly lower than that in the low permeable area, and the wall hydrophilicity enhanced the water flooding effect. Chemotactic bacteria could react to the concentration gradient of pollutants dissolved into water in the oil phase, and enrich near the oil–water interface with high concentration of NAPL, and the density of chemotactic bacteria at the oil–water interface can be up to 1.8–2 times higher than that in the water phase at flow rates from 1.13 to 6.78 m/d.

A novel analytical model of solute transport in a layered aquifer system with mixing processes in the reservoirs.

Analytical models of solute transport have been widely used to aid the understanding of the physical and chemical processes undergone by substances introduced in a layered aquifer system. However, in previous studies, the advection component of transport was assumed to be one dimensional, while also ignoring the mixing processes that occur in the inlet and the outlet reservoirs. In this study, new sets of models describing those mixing processes are presented. Beyond that, these models were integrated into already existing models and the result is a novel analytical model of solute transport in aquifer-aquitard systems. The novel analytical solution was derived by the Laplace transform method and the finite-cosine Fourier transform method under the mobile-immobile (MIM) framework. The calculations take into account: the longitudinal and vertical dispersion, the molecular diffusion and the horizonal and vertical advection components of solute transport, as well as first-order chemical reaction, in both the aquifer and the aquitard. A finite-difference solution of the model is tested against experimental data in order to critique its reliability. Results indicate that the numerical and analytical solutions of the new model match well with experimental data. This new model outperforms the previous models in terms of interpreting experimental data. The mixing old and new water in the reservoirs during solute transport in aquifer-aquitard systems is important. Global sensitivity analysis demonstrates that the output concentration of solute in the aquifer-aquitard system is most sensitive to the volume of water in the inlet reservoir. The contribution of the molecular diffusion effect to the total mass flux of the tracer cross the aquifer-aquitard interface is much smaller than the contribution of the dispersive and advective effects.