Evaluation of saline tracer performance during electrical conductivity groundwater monitoring

Predicting leachate impact on groundwater using electrical conductivity and oxidation-reduction potential measurements: An empirical and theoretical approach

This study developed innovative predictive models of groundwater pollution using in situ electrical conductivity (EC) and oxidation-reduction potential (ORP) measurements at livestock carcass burial sites. Combined electrode analysis (EC and ORP) and machine learning techniques efficiently and accurately distinguished between leachate and background groundwater. Two models-empirical and theoretical-were constructed based on a supervised classification framework. The empirical model constructs a classifier with high accuracy, sensitivity, and specificity, utilizing the comprehensive in situ EC and ORP measurements. The theoretical model with only two end members achieves comparable performance by simulating the leachate-groundwater interactions using a geochemical mixing model. Besides enhancing the early detection capabilities, our approach considerably reduces the reliance on extensive hydrochemical analyses, thus streamlining the monitoring process. Moreover, the use of field parameters was found to proactively identify potential pollution incidents, enhancing the efficiency of groundwater monitoring strategies. Our approach is applicable to various waste disposal sites, indicating its extensive potential for environmental monitoring and management.

Experimental approach and analysis of the effectiveness of a tubular helical flow flocculator for water supply in developing communities

The main objective of this study was to evaluate the impact of the length and retention time of a tubular helical flow flocculator (THFF) on the elimination of turbidity and color from raw water, to obtain quality treated water for consumption in areas rural. For this, a large-scale field experimental system was used, the THFF was built with 4-inch diameter polyethylene hose and coupled to a sedimentation and filtration process. For the different experimental tests, aluminum sulfate was chosen as the coagulant. To find the optimal dose of coagulant, jar tests were previously carried out. For the tests the length of the THFF was varied (50 m and 75 m), flow rates of 0.25, 0.5, 0.75, 1 and 2 L/s and turbidity ranges of <10, 10-20, 21-50, 51-100 and > 100 NTU of raw water were tested. An evaluation of the hydraulic behavior of the THFF was carried out through an analysis of the temporal distribution curve of the concentration of a tracer, applying the Wolf-Resnick model. The average results revealed a haze and color removal efficiency of 98.07 % and 98.50 %, respectively. The residence time and velocity gradient exhibited variations in a range of 2.25-35.0 min and 3.64 to 56.94 s-1, respectively. It was evident that the operation and effectiveness of THFF are directly influenced by the turbidity of the raw water, the residence time and the velocity gradient. These findings indicate that THFF could play a valuable role as a flocculation unit in a purification system, mainly the existence of a plug-type flow was observed. The findings indicate that THFF, complemented by settling and filtration processes, could be a valuable tool for implementation in rural areas.

A comprehensive dataset for the evaluation of a horizontal tubular flocculator implemented for drinking water treatment

This article presents a set of data obtained during the evaluation of a horizontal flow tubular flocculator for the provision of drinking water in developing communities. The HFTF is presented as an alternative technology to replace conventional flocculators, allowing high efficiency in the subsequent sedimentation and filtration processes. For obtaining the data, experimental tests were carried out using lengths of 68.4 m and 97.6 m for the HFTF, these lengths were combined with flow rates of 0.25, 0.5, 0.75, 1.0 and 2.0 L/s, as well as raw water turbidities of 10, 20, 50, 100 and 200 NTU. The data set generated from measurements and observations made during experimental field tests is detailed. The resulting data set covers the main parameters that determine the quality of drinking water, such as turbidity and colour, as well as flocculation efficiency data. The data from the experimental system were compared with a conventional treatment plant that has a baffle flocculator. Likewise, data on the retention time and velocity gradient are presented that allowed the hydraulic characteristics of the HFTF are evaluated. This data set has significant potential for reuse in future research and development related to water treatment technologies in developing community settings. Detailed data has been collected on various operating conditions of the HFTF, such as different lengths, water flow rates and turbidity levels, as well as measurements of key parameters such as turbidity, colour, flocculation efficiency, retention time and velocity gradient, these Data could be used in future research and development related to water treatment technologies. Furthermore, a comparison of data from the experimental system with a conventional treatment plant provides useful insight into the relative performance of different water treatment technologies, which could be of interest to researchers, system designers and public policymakers in the field of drinking water supply in developing communities.

Vertical tubular flocculator: Alternative technology for the improvement of drinking water treatment processes in rural areas

The guarantee of access to safe drinking water for rural communities is a great challenge due to the increase in contamination and deterioration of water sources. Rural areas face technological, financial, and operational limitations, having poor water quality, generally. The purpose of this study was to evaluate the efficiency of a vertical tubular flocculator (VTF) to be used as part of the purification process in rural areas where small flows are used. An experimental treatment system (ETS) implemented in the field was used. The VTF was implemented using PVC pipes and fittings. Tests were carried out with the same raw water used from a conventional treatment plant with aluminum sulfate as a coagulant. The optimal coagulant dose applied in the ETS was determined by the jar test. In the VTF, the length, turbidity, and flow of the raw water were varied. The hydraulic behaviour of the VTF was evaluated with the analysis of the time distribution curve of concentration of a tracer applying the Wolf-Resnick model. A low residence time VTF was obtained, representing a new efficient flocculation model for the reduction of turbidity and colour. The results showed that the turbidity of the raw water, the residence time, and the degree of agitation are important parameters in the operation and efficiency of a VTF. There was a predominance of plug flow in the reactor. The obtained results were compared with the efficiency of a conventional water treatment plant used in the study site. The results obtained indicated that this ETS that integrates a VTF with settling and filtration can be a useful tool for rural areas. It was recommended to replicate this study with wastewater, other dimensions of the VTF, to establish a specific methodology for the design of the VTF, to evaluate the dosage with dose bombs for improving the results of VTF, and to elaborate a hydraulic model for VTF.

Flow path monitoring by discontinuous time-lapse ERT: An application to survey relationships between secondary effluent infiltration and roots distribution

The infiltration of secondary treated effluent (STE) into the soil downstream of wastewater treatment plants is becoming increasingly common in a climate change context. In STE infiltration, STE is discharged onto the soil over a large surface allowing for a gradual infiltration of the water. This paper investigates a novel time-lapse electrical resistivity tomography strategy to evaluate the impact of STE infiltration on the water pathways of two planted loamy-soil trenches located in a Fluvisol region in southwestern France. The system has been monitored for 3 years using discontinuous monitoring of electrical resistivity tomography during four saline tracer tests. Results show that: 1) the new methodology has successfully highlighted the evolution of water pathways in the soil over time; 2) such evolution is in agreement with reeds root distribution in the trenches which seems to be affected by water quality i.e. sludge losses and TSS, for this study case. Indeed, for the infiltration trench receiving STE with lower pollution levels (2.2 mg TSS. L^-1, 26 mg COD. L^-1), the infiltration capacity is maintained over the years (4-6 mm h^-1) and reed roots developed deeper in the soil. A sludge deposit present at the bottom of the second infiltration trench receiving higher pollution levels (7.2 mg TSS. L^-1, 45 mg COD. L^-1, plus episodic sludge release) could lead roots to develop close to the surface affecting the infiltration capacity which did not evolve over time. This work highlights the importance of long-term flow pathway monitoring in understanding the hydraulic behavior of infiltration surfaces submitted to STE.

Measurement of contaminant adsorption on soils using cycling modified column tests

An innovative cycled column test with supporting batch equilibrium and kinetic analysis for adsorption or desorption were developed for evaluation of adsorption behavior of soils. Non-equilibrium adsorption was observed in the cycled column tests as the traditional testing methods. The isotherm of local equilibrium of the soil was conducted based on the testing results within a relatively short duration with simple analysis. The concentration curves of influent and effluent of the cycled column tests were simulated by dual-porosity (DP) model with a modified inlet boundary. Based on the modeling results, the isotherm of local equilibrium is close to that of the mobile phase adsorption capacity, whereas the immobile phase of the soil is nearly inactive in the retardation of the contaminants. The testing results from cycled column tests are hardly interfered by desorption or the sorption rate according to the modeling for corresponding scenarios. The cycled column test can be used as an alternative or supplementary method to the traditional column test for the determination of local equilibrium isotherm, with advantages of shorter testing duration and easier data analysis.

Soil conditioners effects on hydraulic properties, leaching processes and denitrification on a silty-clay soil

Agricultural landscapes are often affected by groundwater quality issues due to fertilizers leaching. To address this worldwide problem several agricultural best practices have been proposed, like limiting the amount of fertilizers and increasing soil organic matter content. To evaluate if these practices may promote groundwater quality enhancement, vadose zone retention time and complex biogeochemical processes must be known in detail. In this study, sequential undisturbed column experiments were performed to determine the amount of nutrients and heavy metals leached after simulated stormwater events. The column was amended with urea then flushed for two pore volumes, then straw residuals were incorporated and flushed for two pore volumes and finally compost was incorporated and flushed for six pore volumes. Dissolved ions, major gasses and heavy metals were determined in leachate samples. Nitrate and nitrite were leached in the urea treatment producing the highest concentrations, followed by compost and straw residuals. The redox conditions were aerobic in all treatments and pH was circumneutral or slightly basic. Denitrification was low but increased with the addition of straw residuals and compost. Heavy metals were all at very low concentrations except for lead and cadmium, which slightly exceeded threshold limits (10 and 1 μg/L, respectively) in all the treatments. The compost treatment, after three pore volumes, was affected by clay swelling due to sodium dispersion, which in turn provoked a reduction of porosity and hydraulic conductivity.

Collected Rain Water as Cost-Efficient Source for Aquifer Tracer Testing

Locally collected precipitation water can be actively used as a groundwater tracer solution based on four inherent tracer signals: electrical conductivity, stable isotopic signatures of deuterium [δ² H], oxygen-18 [δ¹⁸ O], and heat, which all may strongly differ from the corresponding background values in the tested groundwater. In hydrogeological practice, a tracer test is one of the most important methods for determining subsurface connections or field parameters, such as porosity, dispersivity, diffusion coefficient, groundwater flow velocity, or flow direction. A common problem is the choice of tracer and the corresponding permission by the appropriate authorities. This problem intensifies where tracer tests are conducted in vulnerable conservation or water protection areas (e.g., around drinking water wells). The use of (if required treated) precipitation as an elemental groundwater tracer is a practical solution for this problem, as it does not introduce foreign matters into the aquifer system, which may contribute positively to the permission delivery. Before tracer application, the natural variations of the participating end members' tracer signals have to be evaluated locally. To obtain a sufficient volume of tracer solution, precipitation can be collected as rain using a detached, large-scale rain collector, which will be independent from possibly existing surfaces like roofs or drained areas. The collected precipitation is then stored prior to a tracer experiment.

How long do natural waters “remember” release incidents of Marcellus Shale waters: a first order approximation using reactive transport modeling

Natural gas production from the Marcellus Shale formation has significantly changed energy landscape in recent years. Accidental release, including spills, leakage, and seepage of the Marcellus Shale flow back and produced waters can impose risks on natural water resources. With many competing processes during the reactive transport of chemical species, it is not clear what processes are dominant and govern the impacts of accidental release of Marcellus Shale waters (MSW) into natural waters. Here we carry out numerical experiments to explore this largely unexploited aspect using cations from MSW as tracers with a focus on abiotic interactions between cations released from MSW and natural water systems. Reactive transport models were set up using characteristics of natural water systems (aquifers and rivers) in Bradford County, Pennsylvania. Results show that in clay-rich sandstone aquifers, ion exchange plays a key role in determining the maximum concentration and the time scale of released cations in receiving natural waters. In contrast, mineral dissolution and precipitation play a relatively minor role. The relative time scales of recovery τ_rr, a dimensionless number defined as the ratio of the time needed to return to background concentrations over the residence time of natural waters, vary between 5 and 10 for Na, Ca, and Mg, and between 10 and 20 for Sr and Ba. In rivers and sand and gravel aquifers with negligible clay, τ_rr values are close to 1 because cations are flushed out at approximately one residence time. These values can be used as first order estimates of time scales of released MSW in natural water systems. This work emphasizes the importance of clay content and suggests that it is more likely to detect contamination in clay-rich geological formations. This work highlights the use of reactive transport modeling in understanding natural attenuation, guiding monitoring, and predicting impacts of contamination for risk assessment.