Tracer Tests Research Articles

Regional Analysis of Tracer Tests in the Karstic Basin of the Gacka River (Croatian Dinaric Karst)

Tracer testing is the only method in karst hydrogeology that can definitively determine whether a particular site belongs to a watershed of a particular karst spring. Therefore, it is an essential technique for delineating groundwater basins in karst areas. The availability of tracer test results is often limited due to the complicated and relatively expensive application of this approach, especially for large regional watersheds. The Croatian part of the Dinaric karst region extends for several hundred kilometers along the Adriatic coast and consists almost entirely of highly karstified carbonate rocks. The groundwater basins in these areas almost never match the surface morphology of the terrain. In practice, all available results of previous surveys are often used to define watersheds, regardless of the methodology and age of their implementation. This is also true for the earlier delineations of the Gacka River watershed, a regional karst basin in the Croatian Dinaric karst. However, tracer testing methods, especially the accuracy of tracer determination and monitoring, have improved significantly during this time. In order to assess the reliability of past tracing results in this significant karst basin, we reviewed reports of previous tracer tests. More recent tests, in particular the most recent multitracer injection test with continuous tracer detection on the major springs, produced high-quality data that allowed us to assess the reliability of the findings from prior research. A number of large karst springs with partially overlapping subcatchments feed the Gacka River. After discarding unreliable tracing data, we reevaluated the subcatchments of the main springs as well as the characteristics of the regional groundwater flow patterns throughout the basin, which is particularly important for water quality protection measures of the springs. The Gacka River basin is used as a case study to emphasize the importance of thoroughly assessing the reliability of previous tracing data before using them in regional analyses.

Effect of Rock Film Mulching on Preferential Flow at Rock–Soil Interfaces in Rocky Karst Areas

Preferential flow is the most common form of water loss occurring at the interface between rock and soil (hereinafter referred to as “rock–soil interface”) in karst areas, and it is also one of the important factors causing soil water leakage into the underground. Therefore, it is of great significance to cut off the pathway of soil water loss through control of preferential flow. In this experiment, rock film mulching (RFM) was used to control the preferential flow at the rock–soil interface, and its influence on the soil water infiltration pattern and soil water content was analyzed by simulating rainfall, dye tracer tests, and digging soil profiles. The results show that: (1) the RFM can significantly control the soil water loss at the rock–soil interface, (2) so that the water intercepted by the above-ground rocks changed from longitudinal infiltration to transverse diffusion, more water moved into the surrounding soil patches, and (3) the soil water content was significantly increased. These results indicate that the RFM has an important blocking effect on preferential flow at the rock–soil interface, which has important guiding significance for reducing soil water erosion in karst areas.

Channel Network Modeling of Flow and Transport in Fractured Rock at the Äspö HRL: Data‐Worth Analysis for Model Development, Calibration and Prediction

AbstractPerformance assessment of nuclear waste disposal in deep crystalline bedrock demands a thorough understanding of the related flow and transport processes. Uncertainties may arise both from the selection of the conceptual model as well as the estimation of the related model parameters. Discrete fracture network (DFN) models are widely used for such modeling while channel network models (CNM) provide an alternative representation, the latter focusing on the fact that flow and transport in deep fractured media often are dominated by a small number of long preferential flow paths. This study applies the principle of channel networks, implemented in the Pychan3d simulator, to analyze the hydraulic and tracer transport behavior in a 450‐m‐deep fractured granite system at the Äspö Hard Rock Laboratory in Sweden, where extensive site characterization data, including hydraulic and tracer test data are available. Semi‐automated calibration of channel conductances to field characterization data (flow rates, drawdowns, and tracer recoveries) is performed using PEST algorithm. It was observed that an optimal CNM connectivity map for channel conductance calibration can only be developed by jointly fitting flow rates, drawdowns and tracer mass recovery values. Results from data‐calibrated CNM when compared to a corresponding calibrated DFN model shows that the CNM calibrates and adapts better than a DFN model with uniform fracture surfaces. This comparative study shows the differences and uncertainties between two models as well as examines the implications of using them for long term model predictions.

3D surface–subsurface modeling of a bromide tracer test in a macroporous tile‐drained field: Improvements and limitations

AbstractThe assessment and forecasting of nutrient loss by tile drains in agricultural areas often rely on physically based models that have adequate representations of macropores and tile drains. Macroporosity has been adequately represented in hydrological models using a dual continuum approach. However, its implementation in hydrological and solute transport models is limited to plot‐scale or to one‐ and two‐dimensional models due to the large number of parameters that are rarely available and the long computational times. The purpose of this study is to simulate a tracer test using a 3D coupled surface–subsurface model to improve the representation of the tracer concentration at the drainage discharge. A three‐dimensional HydroGeoSphere model was developed and calibrated to simulate tile drainage discharge, Br mass discharge, and hydraulic heads from a Br tracer test in a densely tile‐drained field. The conductivity of the drain was one of the most important parameters for drain discharge and solute transport simulations. The model accurately simulated drainage discharge and Br transport to tile drains. However, most of the Br peaks and the late‐time Br mass in the drain outflow were underestimated. Our simulation results indicate that explicitly representing tile drains with seepage nodes allows for a physically based, yet computationally efficient representation of Br transport behavior surrounding tile drains at field scale. However, we cannot confirm that the single‐porosity model with immobile zone is suitable for simulating the Br peaks at the drain outlet and the late‐time Br mass. Improvements to the model include the implementation of heterogeneous soil layers and the inclusion of more measured data to reduce uncertainty during calibration.

Assessment of urban landslide groundwater characteristics and origin using artificial tracers, hydro-chemical and stable isotope approaches

In the framework of landslides, the hydrogeological features play an essential role in slope stability, governing water movement and thus resulting in modification of the effective stress in the soil. In this framework, the hydrogeological conceptualization of landslide areas and the identification of groundwater origin are key points to developing risk mitigation measures. In fact, groundwater recharge cannot always be attributed to local precipitation alone. Mixing processes between water derived from local infiltration and deep water upflow along tectonic lineaments or anthropogenic water can affect the groundwater balance on a local scale. This study aims to define the potential groundwater origin of one of the highest risk urban landslides in central Italy and to define a hydrogeological conceptual model by exploiting its existing drainage system network. This research is based on a multiple-techniques approach based on hydrological water balance, artificial tracer tests during recharge period, seasonal monitoring of the water stable-isotope content, hydro-chemical survey during low-flow periods, and analysis of the piezometric level fluctuation. All these analyses are coupled with a detailed reconstruction of the geology of the area depicted from boreholes and drill holes. Two groundwater bodies have been evidenced from the study. The shallower one is located in the landslide unstable zone and is hydraulically connected to a deeper groundwater body hosted in the underlying bedrock. Results highlighted that the local rainfall regime could not fully explain the hydro-chemical facies. Local water contributions to the landslide area coming from leakage of the urban sewerage system have been evidenced, excluding deep groundwater upflow from the fault system.

Evaluation and improvement of residence time distribution analysis methods

Although residence time distributions (RTDs) are frequently used in wetland studies, there is no consensus about the analysis method. Generally, two types of methods can be used to analyze RTD data: the method of moments and the RTD modeling method. RTD curves are obtained by tracer tests. The real RTD curves are usually imperfect due to the presence of random measurement errors, the unreasonable sampling intervals, and the premature termination of the tracer test. This study aims to find a better RTD analysis method providing robust results under these unfavorable factors, which includes: (i) evaluating the existing RTD analysis methods; (ii) improving the existing RTD analysis method using the Rational model. The influence of measurement error, sampling interval, and ending time in tracer tests on RTD analysis methods was first simulated. The results showed that effective volume ratio was a preferable indicator compared with the variance of RTD. The stability of the moment method decreased with the increase of the measurement error and sampling interval, and the accuracy of the moment method decreased with the decrease of the test time. Although the RTD modeling method showed better stability and accuracy, the implicit premise is that the RTD model adequately describes the observed data. Further, 36 observed RTD data sets were used to test the Tanks in Series (TIS) model and the empirical Rational model. The results showed that the widely used TIS model was only effective in partial cases, while the newly proposed Rational model showed broader applicability. Both the moment method and the TIS modeling method were proven to be inadequate. Finally, the moment method was improved by using Rational models to pre-process RTD data. Although the improved method is still affected by random measurement errors, it can significantly increase the accuracy of the moment method when sampling points are small or the test ends prematurely.

The methods for evaluating the efficiency of EOR by SWCTT & PITT tracer tests

Background: In Russia, as well as in the whole world, the number of oil fields that at the last stage of development and characterized by a high water cut of the production is growing. In order to extend the period of their cost-effective operation, a transition from classical waterflooding to the use of chemical methods to enhanced oil recovery (hereinafter - EOR) is required, which implies a preliminary assessment of their potential effectiveness.
 Aim: To select and evaluate chemical compositions, test on core materials with subsequent recommendation of effective compositions.
 Materials and methods: This paper reviews a description of the SWCTT and PITT and evaluation is made of the place of these technologies in the chain of implementation of EOR from laboratory experiments to commercial implementation. The SWCTT method was developed in the 1970s to measure residual oil saturation in the near-wellbore zone after the application of oil enhancement methods. This method is based on the use of partitioning oil-soluble tracer, which forms a secondary non-separable water-soluble traces in the near-wellbore zone due to the hydrolysis process. Evaluation of residual oil saturation is carried out by the time delay in the arrival of the oil and water partitioning tracers.
 Results: As a result of the pilot project, experience was gained in implementing SWCTT technology to evaluate the effectiveness of surfactant flooding at a producing oil well in one of the fields of the Khanty-Mansiysk Autonomous Region.
 Conclusion: The evaluation and effectiveness of the technology with the selected formulations using simulation and the use of alternative SWCTT/PITT tracer methods has been proven by field tests.

A modified and rapid method for the single-well push-pull (SWPP) test using SF6, Kr, and uranine tracers

In the present study, a single-well push-pull (SWPP) test was conducted with multi-component tracers, including inert gas (SF6 and Kr) and uranine (conservative), to understand the volatile/semi-volatile component transport characteristics in the groundwater system. In an SWPP test, it is essential to obtain an initial breakthrough curve (BTC) of the inert gas concentration at the beginning of the pulling stage to analyze the hydraulic properties of the groundwater system. As a result of the SWPP test using a proposed method in this study, physicochemical parameters of the groundwater and BTC of gas tracers and uranine were acquired simultaneously and successfully. In addition, on-site measurements of uranine, pCO2, and water quality data, such as electrical conductivity (EC), temperature, pH, and dissolved oxygen, were undertaken. Modification of an existing pCO2 measuring system allowed the gas samples to be collected, transported, and analyzed for inert gas components within a few hours. As a result, reliable and interpretable data with a recovery ratio of 26%, 85%, and 95% for SF6, Kr, and uranine, respectively, were obtained. The differences in the recovery ratio were utilized to identify the environmental system, whether it contains gas inside the isolated system (closed) or not (open), and to understand plume behavior characteristics in the experimental zone. By applying a two-dimensional advection-dispersion model to the acquired tracer test data and comparing the observed and computed tracer concentrations, helpful information was obtained on the hydraulic and transport characteristics of the targeted zone. This method can be extended to the design of dissolved CO2 transport monitoring of an aquifer above a CCS site.

The Study of Porous TH Model of CO2-EGS in ChingHsui, ILan Assessment

本研究之目的為探討以超臨界二氧化碳（supercritical CO2）為取熱流體之二氧化碳增強型地熱系統（CO2-EGS）開發之可行性並預估其取熱產能以活化暫停開發之地熱井。為此，本研究以紅柴林2號井（HCL-2）與結元井（JY-1）為基礎，使用有限元素分析法建立了結合裂隙網路（fracture network）、孔隙熱傳與達西流（Darcy’s law）的孔隙-熱-水模型（porous-thermal-hydraulic model），並探討了儲集層於不同注入條件下的溫度變化趨勢及CO2-EGS之總產能。<br>由本研究可知當注入質量流率愈大，注入井底溫度變化大，生產井產出溫度愈高，使得EGS總產能愈高；大的注入質量流率可有效降低工作流體沿生產井流出時的溫降；然注入流體溫度對儲集層溫度分布幾乎沒有影響，生產井溫度對之亦較不敏感。在本研究中，CO2-EGS在注入質量流率為4 ton/hr與0.0005 ton/hr之條件比較發現，生產井口溫度增加約21.5%；溫降降低約16.96%，僅為約0.04%；總產能由23.6 kW增加到219 MW。而流量為4 ton/hr之比產能為571.4 kJ/kg，相較0.0005 ton/hr之比產能增加約11.8%。<br>未來本研究可結合更進一步之現地示蹤劑試驗數據做產能預估，評估以此二井為基礎建立CO2-EGS之產能與效益，可為活化已暫停開發之地熱井做出貢獻。The re-utilization and activation of the abandon geothermal well was an economic concept for increasing the geothermal potential. The purpose of this study was to evaluate the feasibility of CO2 enhanced geothermal systems (CO2-EGS) based on the geothermal well HCL-2 and JY-1 and to estimate their capacity. A porous-fracture thermal-hydraulic model combined the fracture network, porous heat transfer model and Darcy's Law was established by finite element analysis. The temperature variation of the reservoir under different injected conditions and the total geothermal capacity of CO2-EGS are discussed. <br>The results show that the higher the mass flow rate of injection, the higher the outer temperature of the production well, the higher the total EGS capacity. The temperature difference of the production well decreased as the injected mass flow rate increased. The reservoir temperature distribution could be affected by the injected fluid temperature slightly. In this study, the temperature of the production wellhead of CO2-EGS increased about 21.5% when the injected mass flow rate was from 0.0005 ton/hr to 4 ton/hr. The specific capacity increased about 11.8%. <br>In future, this study can be combined with further in-situ tracer test data to estimate the capacity realistically, which can contribute to the activation of the abandon geothermal wells.

Effects of spectral variability due to sediment and bottom characteristics on remote sensing for suspended sediment in shallow rivers

Advances in remote sensing techniques for water environments have led to acquisition of abundant data on suspended sediment concentration (SSC). However, confounding factors, such as particle sizes, mineral properties, and bottom materials, have not been fully studied, despite their substantial interference with the detection of intrinsic signals of suspended sediments. Therefore, we investigated the spectral variability arising from the sediment and bottom using laboratory and field-scale experiments. In the laboratory experiment, we focused on measuring spectral characteristics of suspended sediment according to particle size and sediment type. The laboratory experiment was conducted under conditions of completely mixed sediment and non-bottom reflectance using a specially designed rotating horizontal cylinder. To investigate the effects of different channel bottoms under sediment-laden flow conditions, we performed sediment tracer tests in field-scale channels comprising sand and vegetated bottoms. Based on experimental datasets, we performed spectral analysis and multiple endmember spectral mixture analysis (MESMA) to quantify the effect of spectral variability of sediment and bottom on the relationship between hyperspectral data and SSC. The results showed that optimal spectral bands were precisely estimated under non-bottom reflectance conditions, and the effective wavelengths depended on the sediment type. The fine sediments had a higher backscattering intensity compared to the coarse sediments, and the reflectance difference according to the particle size difference increased as the SSC increased. However, in the field-scale experiment, the bottom reflectance substantially decreased the R2 in the relationship between the hyperspectral data and SSC. Nevertheless, MESMA can quantify the contribution of suspended sediment and bottom signals as fractional images. Moreover, the suspended sediment fraction had a clear exponential relationship with SSC in all cases. We conclude that MESMA-driven sediment fractions could be an important alternative for estimating SSC in shallow rivers, as it quantifies the contributions of each factor and then minimizes the bottom effect.

Influence of Paulownia fortunei (Seem.) Hemsl. roots on preferential flow in the red soil hilly region

Preferential water flow in soil significantly affects runoff, water infiltration, storage, groundwater environment, and soil stability. Plant roots positively affect preferential flow development. This study explored the relationship between the root system of <i>Paulownia fortunei</i> (Seem.) Hemsl. and preferential flow using dyeing tracer test and image analysis techniques. A typical red soil hilly region on the outskirts of Guilin City (Guangxi, China) was selected as the study area. A Bright Blue solution was used to visualize the pathways followed by the infiltrated water in simulated rainfall experiments, and Image Analyzer of Plants was used to analyze the root length, surface area, and volume. The results revealed significant differences in the root surface area density of coarse roots (RSAD-CR) and length index of preferential flow (LI) among soil profiles at various distances from the tree trunk. The root volume density of coarse (RVD-CR) and total roots (RVD-TR), the root length density of coarse roots (RLD-CR), and RSAD-CR were significantly correlated with the characteristics of dyeing morphology. Conversely, the root length density and root surface area density of fine (RLD-FR and RSAD-FR, respectively) and total roots (RLD-TR and RSAD-TR, respectively), and the root volume density of fine roots (RVD-FR) were not significantly correlated with the characteristic parameters of dyeing morphology. The root systems of <i>P. fortunei</i> were critical for enhancing soil water infiltration and developing preferential flow in red soil hilly regions. Coarse roots had a greater impact on the development of preferential flow than fine roots, and root volume had a greater influence on preferential flow development than root length and root surface area. This study contributes to a better understanding of the hydrological cycle at the plant-soil interface in red soil hilly regions.

Mise à la masse, essais de traçage et détection de cavités pour l’analyse de la distribution et la structure des conduits karstiques parcourus par des rivières souterraines : une étude de cas des conduits de Dafengdong dans la province de Guizhou, Chine

Mise à la masse, essais de traçage et détection de cavités pour l’analyse de la distribution et la structure des conduits karstiques parcourus par des rivières souterraines : une étude de cas des conduits de Dafengdong dans la province de Guizhou, Chine

Water mixing in rectangular storage tanks: small-scale versus field tests

ABSTRACT Mixing and renewal processes are crucial for maintaining adequate drinking water quality in storage tanks. This paper studies the influence of baffle structures and of fill-and-draw cycles on water mixing and renewal in rectangular cross-section tanks through laboratory tracer tests carried out in two small-scale tanks (with and without baffles) and compares with results from a full-scale test. This study shows that the use of baffles inhibits water mixing and keeps older water pockets in small recirculation zones, though baffles allow faster water renewal than in open tanks for lower flow rates. High water volume variation in fill-and-draw cycles (between 50% to 80%) promotes water renewal, independently of the tank configuration (i.e. cross-section and the existence of baffles). Despite the existing baffle structure in the full-scale rectangular tank with 20% water volume variation, the high flow rates allowed a rapid renewal of the stored water.

A Method for Calibrating the Transient Storage Model from the Early and Late-Time Behavior of Breakthrough Curves

Solute transport in rivers is controlled by mixing processes that occur over a wide spectrum of spatial and temporal scales. Deviations from the classic advection–dispersion model observed in tracer test studies are known to be generated by the temporary trapping of solutes in storage zones where velocities and mixing rates are relatively small. In this work, the relation between the early and late-time behavior of solute breakthrough curves (BTCs) and the key parameters of the Transient Storage Model (TSM) is analyzed using non-asymptotic approximations of the model equations. Two main slopes are identified corresponding to the rising and decreasing limbs of the BTCs which are linked by specific relationships to transport and storage parameters. The validity of the proposed approximations is demonstrated with both synthetic and experimental data. Consistent with the TSM assumptions, the range of validity of the proposed approximations represents the limit of separability between surface dispersion and transient storage and can be expressed as a function of a nondimensional parameter. The results of this work can help environmental scientists identify solute transport and transient storage parameters and support the design of enhanced field tracer experiments.

Influence of vegetation maintenance on flow and mixing: case study comparing fully cut with high-coverage conditions

Abstract. In temperate climates, agricultural ditches are generally bounded by seasonal vegetation, which affects the hydrodynamics and mixing processes within the channel and acts as a buffer strip to reduce a load of pollutants coming from the surrounding cultivated fields. However, even if the control of such vegetation represents a key strategy to support sediment and nutrient management, the studies that investigated the effect of different vegetation maintenance scenarios or vegetation coverage on the flow and mixing dynamics at the reach scale are very limited. To overcome these limitations and provide additional insights into the involved processes, tracer tests were conducted in an agricultural ditch roughly 500 m long close to Warsaw in Poland, focusing on two different vegetation scenarios: highly vegetated and fully cut. Under the highly vegetated scenario, sub-reaches differing in surficial vegetation coverage are analysed separately to better understand the influence of the vegetation conditions on the flow and mixing parameters. Special attention has been paid to the longitudinal dispersion coefficient in complex natural conditions and its dependency on vegetation coverage (V). The vegetation maintenance decreased the travel and residence times of the solute by 3–5 times, moderately increasing the peak concentrations. We found that the dispersion coefficient decreased approximately linearly with the increase of vegetation coverage at V&gt;68 %. Further research is needed at lower vegetation coverage values and different spatial plant distributions. The obtained longitudinal dispersion coefficient values complement dispersion value datasets previously published in the literature, which are barely available for small natural streams. The new process understanding supports the design of future investigations with more environmentally sound vegetation maintenance scenarios.

Karst thermal reservoir tracer test and seepage characteristics analysis in Niutuozhen geothermal field in Xiong’an New Area

The carbonate rock karst thermal reservoir in the Niutuozhen geothermal field is a high-quality geothermal resource with significant development potential. However, due to the strong heterogeneity of karst thermal reservoirs, the connectivity between recharge and production wells is hard to determine, which seriously restricts the sustainable development of the Niutuozhen geothermal field. Therefore, this study revealed the hydraulic connection between the recharge and production well through the tracer test, quantitatively characterized the seepage characteristics of the reservoir combined with the numerical simulation, and proposed the deployment of the recharge well. The results show that the total recovery rate of the tracer is 0.42%, indicating that there are a small number of communication channels with a good hydraulic connection between the recharge and production well in the experimental area, and the recharge will not cause thermal breakthrough within a short time period. The velocity of recharge water can reach 359 m/d at the fastest, and the directions of dominant channels are concentrated in the NW, N, and E directions centered on the recharge well, this is consistent with the characteristics of regional fractures, recharge wells should be avoided to deployed in those directions. The results provide effective information for the prediction of the thermal breakthrough time and the accurate establishment of the thermal reservoir model in the Niutuozhen geothermal field, also provide a scientific basis for the sustainable utilization of the carbonate karst thermal reservoir geothermal resources.

Investigation of replacing tracer flooding analysis by capacitance resistance model to estimate interwell connectivity

Interwell connectivity is an essential parameter for managing waterflooding operations in a field. Analysis of the tracer injection operation is a well-known approach to studying injected fluids distribution in a reservoir and toward producer wells. Developed in the early 2000s, Сapacitance-Resistance Model (CRM) is an analytical approach for waterflooding modeling and optimization. Production/injection data are used as input to model the mass balance and estimate parameters such as the interwell connectivity. In this work, we investigated the accuracy of applying the Capacitance-Resistance Model to mimic a tracer test. Such an approach helps assess the connection between the wells and decide on further field development steps cheaper and quicker. Connectivity values estimated by tracer tests and CRM were analyzed and compared for synthetic and real fields. CRM was capable of modeling waterflooding and estimating production in both fields with acceptable accuracy. Parameters such as well spacing and fluid loss during the injection were considered to improve the accuracy of the CRM approach to calculate the interwell connectivity between injector/producer pairs. Our study showed that CRM could serve as a tool for a quick approximate estimation of interwell connectivity under certain assumptions and is recommended as a replacement for tracer flooding analysis, where the tracer test is not possible or is expensive.

3D Discrete Fracture Network Modelling from UAV Imagery Coupled with Tracer Tests to Assess Fracture Conductivity in an Unstable Rock Slope: Implications for Rockfall Phenomena

The stability of a rock slope is strongly influenced by the pattern of groundwater flow through the fracture system, which may lead to an increase in the water pressure in partly open joints and the consequent decrease in the rock wall strength. The comprehension of the fracture pattern is a challenging but vital aspect in engineering geology since the fractures’ spatial distribution, connectivity, and aperture guide both the water movement and flow quantity within the rock volume. In the literature, the most accepted methods to hydraulically characterise fractured rocks in situ are the single borehole packer test, the high-resolution flow meters for fractures, and the artificial tracer tests performed in boreholes. However, due to the high cost a borehole requires and the general absence of wells along coastal cliffs, these methods may not be appropriate in rockfall-prone areas. In this study, an unsaturated rocky cliff, strongly affected by rockfalls, was investigated by combining kinematic analysis, Discrete Fracture Network (DFN) modelling, and artificial tracer tests. The DFN model and potential rock block failure mechanisms were derived from high-resolution 3D virtual outcrop models via the Structure from Motion (SfM) photogrammetry technique. An artificial tracer was injected using a double ring infiltrometer atop the recharge zone of the slope to determine the infiltration rate and validate the DFN results. The DFN and tracer test methods are frequently used at different spatial scales and for different disciplines. However, the integration of digital photogrammetry, DFN, and tracer tests may represent a new step in rockfall and landslide studies. This approach made possible the identification of groundwater flow patterns within the fracture system and revealed about a 10-day tracer transit time from the injection area and the monitored slope, with similar conductivity values gathered from both the DFN and tracer test. Planar and wedge failures with volumes ranging from 0.1 and 1 m3 are the most probable failure mechanisms in the areas. The results were consistent with the delay between the intense rainfall and the slope failures previously documented in the study area and with their mechanisms.

Experimental Evaluation of Tubular Flocculator Implemented in the Field for Drinking Water Supply: Application in the Developing World

The purpose of this study was to evaluate the efficiency of a large-scale Horizontal Tubular Flocculator (HTF) as an easy-to-implement technology for potable water provision compared to the efficiency of a traditional baffle flocculator. The HTF was built with a 4-inch diameter PVC pipe and coupled to a sedimentation and filtration process. Experimental tests were performed using lengths of 68.4 m and 97.6 m for the HTF. These lengths were combined with raw water flow rates of 0.25, 0.5, 0.75, 1, and 2 L/s and five turbidity ranges &lt;10 NTU, 10–20 NTU, 21–50 NTU, 51–100 NTU, &gt;100 NTU, giving a total of 100 tests for one year. Jar tests were performed to determine the optimal dose of aluminum sulfate used as a coagulant. Hydraulic characteristics such as time of retention (TR) and velocity gradient (G) were evaluated; likewise, plug flow, dead volume, and short-circuit ratios were determined by tracer tests using the Wolf–Resnick model. The average results determined a removal of 98.8% of turbidity and 99.93% of color. The TR varied between 4.62 and 36.97 min and G varied between 6.15 and 109.62 s−1. The results showed that HTF can be useful as a flocculation unit in a purification system.

Hydrodynamic and hydrodispersive behavior of a highly karstified neoproterozoic hydrosystem indicated by tracer tests and modeling approach

Brazilian Neoproterozoic carbonate rocks, dating from about 740–590 million years ago, contain the oldest karst-structured terrains on Earth, resulting in groundwater flow pathways in highly heterogeneous and anisotropic conduit networks. Unlike Paleozoic and Mesozoic rocks, in Neoproterozoic karst systems, groundwater circulates and stores practically through dissolution features characterized as tertiary porosity, as the rock’s primary porosity is recrystallized, considered negligible. However, studies using hydrodispersive equilibrium and non-equilibrium models to estimate flow and transport parameters to base the hydrodynamic behavior of these areas are not common. This paper proposes this, by a set of techniques involving dye tracer tests and the analysis of breakthrough tracer curves (BTCs) in a highly karstified Neoproterozoic terrain. For this, three karst springsheds, in the east, west, and south areas of the São Miguel river watershed, in Alto São Francisco karst region, Brazil, were choose and studied with dye tracer tests using Rhodamine WT and Uranine during dry and wet seasons, associated with regional/local (hydro)geological-structural, geomorphological, and speleological data. The results identified spatial and seasonal variations of water flow and transport parameters, recharge and discharge zones, and water dynamic and speleogenetic evolutions. BTCs models showed the karst systems are very dynamic with seasonal variations, and heterogeneities (bypass, loops and stagnant zones) control the variation of flow and transport parameters. The hydrodispersive parameters (mean flow velocity, and longitudinal dispersion coefficient) and coefficients of non-equilibrium models (partition, β, and mass transfer, ω) show a direct dependence on hydrogeological and speleogenetic contexts. Furthermore, the comparison with other karst systems around the world showed that Neoproterozoic karst has a more stable hydrodynamic behavior under hydrological conditions.