Kaolinite and Cd2+ Transport and Interaction in Sand Media: Batch and Column Experiments

Batch sorption and column transport experiments were used to investigate kaolinite colloids and Cd(II) ions (Cd2+) co-transport in water-saturated sand media. Batch sorption was used to evaluate Cd2+ sorption onto kaolinite clay as a function of the initial Cd2+ concentrations and solution ionic strengths as well as determining the equilibrium sorption isotherms. For very low ionic strength (~0 mM), the Langmuir isotherm was the more suitable isotherm for the experimental results while at higher ionic strength (> 0.45 mM) the Freundlich isotherm was the more suitable isotherm. The sorption parameters, KF, KL, n, and qm, were found to decrease with increasing ionic strength. For column transport experiments, Cd2+-bearing kaolinite colloids were found to be retained more in the column for an increase in the solution ionic strength. For example, the steady state breakthrough rate of Cd2+-bearing kaolinite colloids was 0.2 Ci/C0 for an ionic strength of 0.0 mM compared to about 0.05 Ci/C0 for ionic strengths of 0.45 and 0.9 mM. This increased Cd2+-bearing kaolinite colloid retention trend with increased solution ionic strength was likely due to the reduced zeta-potential and increased size of the colloid particles at higher ionic strengths. Consequently, the kaolinite-facilitated Cd2+ concentration decreased with increasing solution ionic strength. In summary, solution ionic strength had a strong effect on the transport behavior of kaolinite-facilitated Cd2+ and Cd2+-bearing kaolinite colloids through the sand column

Isotope Evidence of Rainfall and Groundwater for Tracing Recharge Areas in Kaeng Khoi District, Saraburi Province, Thailand

This study was conducted in the districts of Kaeng Khoi and Muang, located in the center of Saraburi province, Central Thailand. The purpose was to use a stable isotope technique to identify recharge areas where rainfall infiltrates. Analysis of stable isotopes in groundwater, surface water and rainwater were conducted in September 2014. Isotope compositions of groundwater were found to have δD values that ranged from -37.55‰ to -48.04‰ while δ18O values ranged from -5.30‰ to -7.34‰. The Local Meteoric Water Line (LMWL) in the study area was indistinguishable from the Bangkok Local Meteoric Water Line (BKK LMWL), and the stable isotope values of rainwater in area were more depleted than BKK LMWL. The isotope compositions of surface water revealed that the effect of evaporation could divide the groundwater into two groups, with the first group locally receiving rainfall and the second group interacting directly with surface water. Therefore, care must be taken to prevent groundwater contamination in the latter group due to polluted surface water caused by human activities

Groundwater Recharge Potential Using GIS around the Land Development Facilities of Chulalongkorn University at Kaeng Khoi District, Saraburi Province, Thailand

Kaeng Khoi District (Saraburi Province, Thailand) suffers from a surface water shortage due to increasing demand from domestic use and crop production, particularly in the drought season. Groundwater resources are an additional source of freshwater in this area, especially for agricultural purposes, but to be sustainable its usage should not exceed long-term groundwater recharge. Evaluation of the groundwater recharge potential is therefore essential to determine the sustain-able use level for groundwater resources. This study aimed to determine the groundwater recharge potential using the geographic information system (GIS) around the Land Development Facilities of Chulalongkorn University at Kaeng Khoi District, Thailand. The hydrologic and geologic features affecting groundwater recharge potential into the groundwater system are the lineaments, drainage density, lithology and land cover/land use. The weighting of these factors were derived from integration of the interrelationship of the major and minor effects of each contributing factor. Then GIS overlay was used to determine the influence of the hydrologic and geologic effects on total groundwater recharge potentiality, classified into five categories: very high, high, moderate, low and very low. The highest recharge potential zone was located in the downstream areas. The map generated revealed that about 50 % of the study area had a medium groundwater recharge potential, mainly located in the eastern upstream part and the central area

Spatial Evolution of Coastal Tourist City Using the Dyna-CLUE Model in Koh Chang of Thailand during 1990–2050

Spatial evolution can be traced by land-use change (LUC), which is a frontier issue in the field of geography. Using the limited areas of Koh Chang in Thailand as the research case, this study analyzed the simulation of its spatial evolution from a multi-scenario perspective on the basis of the 1900–2020 thematic mapper/operational land imager (TM/OLI) remote sensing data obtained through the transfer matrix model, and modified LUC and the dynamic land-use change model (Dyna-CLUE). Over the past 30 years, the expansion of recreation areas and urban and built-up land has been very high (2944.44% and 486.99%, respectively) along the western coast of Koh Chang, which replaced the original mangrove forests, orchards, and communities. Logistic regression analysis of important variables affecting LUC revealed that population density variables and coastal plain topography significantly affected LUC, which showed strong β coefficients prominently in the context of a coastal tourist city. The results of the LUC and logistic regression analyses were used to predict future LUCs in the Dyna-CLUE model to simulate 2050 land-use in three scenarios: (1) natural evolution scenario, where a large patch expansion of agricultural land extends along the edge of the entire forest boundary around the island, particularly the southwestern areas of the island that should be monitored; (2) reserved area protection scenario, where the boundary of the conservation area is incorporated into the model, enabling forest preservation in conjunction with tourism development; and (3) recreation area growth scenario, where the southern area is the most susceptible to change at the new road crossing between Khlong Kloi village to Salak Phet village, and where land-use of the recreation area type is expanding. The model-projected LUC maps provide insights into possible changes under multiple pathways, which could help local communities, government agencies, and stakeholders jointly allocate resource planning in a systematic way, so that the development of various infrastructures to realize the potential impact on the environment is a sustainable coastal tourist city development

Risk assessment of arsenic from contaminated soils to shallow groundwater in Ong Phra Sub-District, Suphan Buri Province, Thailand

Study region: The Arsenic (As) concentrations found in Ong Phra sub-district, Dan Chang district, and Suphan Buri province are approx. 20 times higher than the average concentration of As in agricultural soils of Thailand. Study focus: The objectives of this current study were to investigate the As contamination in soil and groundwater and further develop the risk assessment map of As from contaminated soils releasing to shallow groundwater by combining DRASTIC method with contamination factor (CF) and mobility factor (MF). New hydrological insights for the region: According to the sequential extraction result, the concentrations of total As in 39 soil samples ranges from 4.8 to 1070.4 mg/kg. The highest As concentration in shallow groundwater was found at well number 3, located within 130). The high vulnerability area, found along the waterway, is approximately 35 km2 (18.65% of the study area). Interestingly, the DRASTIC index of the old tin mine is indicated as the zone of moderate and high vulnerability. The findings in this study reveal that the integration of the DRASTIC risk map with CF can well elucidate As contaminated in shallow groundwater. Keywords: Arsenic, Contaminated soil, Groundwater, Old tin mine, Sequential extractio

Experimental and modelling investigations of tracer transport in variably saturated agricultural soil of Thailand: Column study

Tracer (Bromide) movement through the unsaturated agricultural soil was investigated in soil columns. Two tracer column experiments, with a diameter of 7 cm and a depth of 25 cm, were vertically homogeneous packed with sandy loam and then carried out to investigate bromide (Br−) transport under different water contents (at steady flow condition). One soil column (Column 1) represents the unsaturated agricultural soil in dry season (with water content ranging from 0.23 to 0.26) and the other (Column 2) represents the soil in wet season (water content from 0.24 to 0.35). Bromide samples were periodically collected by vacuum tubes inserted at 6.25 cm equally spaced intervals (e.g., 6.25, 12.5, 18.75 and 25 cm) along the length of the column and the effluent collected at the end of the column. The observed breakthrough curves (BTCs) of bromide in both columns represented a relative smooth and sigmodal curves at different distances (sampling ports). Dispersivity (α, cm) for sandy loam at different locations was numerically estimated by curve fitting the experimental data with HYDRUS-1D. The α can be well described by the convection–dispersion equation and these values derived from Column 1 (ranging from 0.37 to 0.98 cm) are more than those from Column 2 (0.25–0.59). Moreover, the α in both columns increases with the travel distance due to the scale-dependent effect. Furthermore, the α values were plotted on a log–log scale against travel distances and they yield empirical power law relationships with an excellent correlation (α = 0.102 (L)0.697, R2 = 0.999 and α = 0.086 (L)0.579, R2 = 0.963 for Column 1 and 2, respectively)

Impacts of land-use changes on watershed discharge and water quality in a large intensive agricultural area in Thailand

<p>The objectives of this research were to evaluate the effect of land-use change on streamflow, sediment and water quality data along the Lower Yom River, Thailand, covering an intensively agricultural area of 14 613.6 km², and to assess the relative impact of point and non-point sources of pollution from multiple-land-use watersheds. Long-term calibration and validation of the SWAT (Soil and Water Assessment Tool) model was performed on data for 2000–2013. Land-use change led to a 13–49% increase in runoff in the basin and resulted in 37–427% increased sediment yield. The amount of NO₃-N load doubled in the upper and middle parts of the study area, while the increase in PO₄^3– ranged from 37 to 377%, reflecting the increase in agricultural lands and urban areas. It is concluded that the changed land use is closely associated with the quantity of runoff, sediment yield and the NO₃-N and PO₄^3– concentrations.</p

The risk assessment of arsenic contamination in the urbanized coastal aquifer of Rayong groundwater basin, Thailand using the machine learning approach

The rapid expansion of urbanization has resulted in an insufficient of groundwater resource. In order to use groundwater more efficiently, a risk assessment of groundwater pollution should be proposed. The present study used machine learning with three algorithms consisting of Random Forest (RF), Support Vector Machine (SVM), and Artificial Neural Network (ANN) to locate risk areas of arsenic contamination in Rayong coastal aquifers, Thailand and selected the suitable model based on model performance and uncertainty for risk assessment. The parameters of 653 groundwater wells (Deep=236, Shallow=417) were selected based on the correlation of each hydrochemical parameters with arsenic concentration in deep and shallow aquifer environments. The models were validated with arsenic concentration collected from 27 well data in the field. The model&apos;s performance indicated that the RF algorithm has the highest performance as compared to those of SVM and ANN in both deep and shallow aquifers (Deep: AUC=0.72, Recall=0.61, F1 =0.69; Shallow: AUC=0.81, Recall=0.79, F1 =0.68). In addition, the uncertainty from the quantile regression of each model confirmed that the RF algorithm has the lowest uncertainty (Deep: PICP=0.20; Shallow: PICP=0.34). The result of the risk map obtained from the RF reveals that the deep aquifer, in the northern part of the Rayong basin has a higher risk for people to expose to As. In contrast, the shallow aquifer revealed that the southern part of the basin has a higher risk, which is also supported by the location of the landfill and industrial estates in the area. Therefore, health surveillance is important in monitoring the toxic effects on the residents who use groundwater from these contaminated wells. The outcome of this study can help policymakers in regions to manage the quality of groundwater resources and enhance the sustainable use of groundwater resources. The novelty process of this research can be used to further study other groundwater aquifers contaminated and increase the effectiveness of groundwater quality management

Factors controlling the release of metals and a metalloid from the tailings of a gold mine in Thailand

Concentration of metals and As leached from the sulphide mixing and oxide zones at differing pH

Detection of arsenite-oxidizing bacteria in groundwater with low arsenic concentration in Rayong province, Thailand

As contamination in groundwater has become one of the global problems. It has been reported that million people around the world get adverse effects on their health by direct and indirect As-contaminated groundwater consumption. In groundwater, the most abundant As species are arsenite (As3+) and arsenate (As5+). Arsenite is more toxic and mobile than arsenate. Consequently, arsenite oxidation is considered as an important process in groundwater As bioremediation. It has been reported that arsenite-oxidizing bacteria play an important role in reducing As toxicity in contaminated groundwater environment. A functional gene involved in arsenite oxidation is aioA gene. The key objective of this study was to investigate the arsenite-oxidizing bacteria in groundwater with low arsenic concentration in Rayong province, Thailand. The results showed that the arsenite-oxidizing bacteria were detected in groundwater with low arsenic concentration. Phylogenetic analysis revealed that they were closely related to Rhizobium sp., Bradyrhizobiaceae sp., Hydrogenophaga sp., and Stenotrophomonas sp. The knowledge gained from this study will help better understand the distribution of arsenite-oxidizing bacteria in groundwater with low As concentration