Modeling ground-water flow by means of a hybrid trajectory image, boundary integral equation method

The trajectory image method (TIM), a new modeling technique based on image theory, can be used to find head, gradients, velocities, and flow directions. TIM derives from the idea that particles emitted by sources or adsorbed by sinks may be reflected by impermeable boundaries, or they may be partially absorbed, reflected, and partially transmitted by boundaries of differing hydraulic conductivities but with abrupt changes in their hydraulic heads. Particles move until their changes in head become negligible. Each reflection represents an image in terms of the boundaries where the trajectories are reflected, thus a great number of imaginary points, depending on accuracy desired after projection, are generated. The traveling distances of particles are measured from sources or sinks to the current ray-boundary intersections. Then the total head and gradients at each observation point are found by superposing heads and gradients of particle trajectories that pass through or close to the observation point. The number of reflections for each trajectory depends on the geometry of the boundary. TIM offers the following advantages for modeling ground-water flow with point or line sources and sinks: (1) Unlike finite difference and finite element methods, TIM does not magnify errors near sources or sinks; (2) Unlike the boundary integral equation method (BIEM), near-boundary computations are very accurate, and complicated integrations are avoided under unsteady-state condition; (3) Only zones with differing hydraulic conductivities have to be discretized; (4) Ease in modeling flow through anisotropic media without requiring that principal directions be parallel to coordinate directions or be transformed into other coordinate systems; and (5) Problem setup is much easier than in above methods. Although TIM requires considerably more computing time with standard mainframes, run times were reduced by an order of magnitude with a supercomputer. Also a combination of TIM and BIEM (TIMBIE) can reduce time requirements because of elimination of interpolation at internal accounting points. This testing procedure is rather reliable and convenient in comparing the values at all interior points, because both methods are completely independent of each other at accounting points (nodes). (Abstract shortened with permission of author.

Variations in Tectonic Activities of the Central and Southwestern Foothills, Taiwan, Inferred from River Hack Profiles

A longitudinal profile of a river under static equilibrium shows no degradation or aggradation and can be ideally described as a straight line on a semi-logarithmic graph. This type of profile is called a “Hack profile”. If a river runs across uprising active structure systems, its Hack profile becomes convex. Accumulated tectonic strain varies positively with the intensity of the upwarping in Hack-profile convexity. In this paper, we compare curvature changes in Hack profiles of a series of rivers running through faults in the central and southwestern Foothills of Taiwan. Longitudinal profiles of these rivers were derived from two versions of topographic maps (1904 and 1985) and recent DTM data (2000). Prior to comparisons, we calibrated the 1904 topographic map, named “Taiwan Bautu”, by “offsetting” horizontal coordinates north and westward approximately 440 m and then “linear transforming ” the elevation values. The Tungtzchiau fault of the central Foothills has remained inactive since 1935. Here relatively hig

Sources and controls for the mobility of arsenic in oxidizing groundwaters from loess-type sediments in arid/semi-arid dry climates - Evidence from the Chaco-Pampean plain (Argentina)

In oxidizing aquifers, arsenic (As) mobilization from sediments into groundwater is controlled by pH-dependent As desorption from and dissolution of mineral phases. If climate is dry, then the process of evaporative concentration contributes further to the total concentration of dissolved As. In this paper the principal As mobility controls under these conditions have been demonstrated for Salí River alluvial basin in NW Argentina (Tucumán Province; 7000 km2), which is representative for other basins or areas of the predominantly semi-arid Chaco-Pampean plain (1,000,000 km2) which is one of the world's largest regions affected by high As concentrations in groundwater. Detailed hydrogeochemical studies have been performed in the Salí River basin where 85 groundwater samples from shallow aquifers (42 samples), deep samples (26 samples) and artesian aquifers (17 samples) have been collected. Arsenic concentrations range from 11.4 to 1660 μg L-1 leaving 100% of the investigated waters above the provisional WHO guideline value of 10 μg L-1. A strong positive correlation among As, F, and V in shallow groundwaters was found. The correlations among those trace elements and U, B and Mo have less significance. High pH (up to 9.2) and high bicarbonate (HCO3) concentrations favour leaching from pyroclastic materials, including volcanic glass which is present to 20-25% in the loess-type aquifer sediments and yield higher trace element concentrations in groundwater from shallow aquifers compared to deep and artesian aquifers. The significant increase in minor and trace element concentrations and salinity in shallow aquifers is related to strong evaporation under semi-arid climatic conditions. Sorption of As and associated minor and trace elements (F, U, B, Mo and V) onto the surface of Fe-, Al- and Mn-oxides and oxi-hydroxides, restricts the mobilization of these elements into groundwater. Nevertheless, this does not hold in the case of the shallow unconfined groundwaters with high pH and high concentrations of potential competitors for adsorption sites (HCO3, V, P, etc.). Under these geochemical conditions, desorption of the above mentioned anions and oxyanions occurs as a key process for As mobilization, resulting in an increase of minor and trace element concentrations. These geochemical processes that control the concentrations of dissolved As and other trace elements and which determine the groundwater quality especially in the shallow aquifers, are comparable to other areas with high As concentrations in groundwater of oxidizing aquifers and semi-arid or arid climate, which are found in many parts of the world, such as the western sectors of the USA, Mexico, northern Chile, Turkey, Mongolia, central and northern China, and central and northwestern Argentina

Investigation of intercalation of diphenhydramine into the interlayer of smectite by XRD, FTIR, TG-DTG analyses and molecular simulation

Diphenhydramine (DPH) is one of the pharmaceuticals commonly found in the effluent stream after wastewater treatment, and the cause of its environmental persistence needs to be addressed urgently. Smectite minerals are common soil components with large surface area, expandable interlayer, and high cation exchange capacity (CEC), thus are capable of adsorbing or intercalating inorganic or organic cations on the surface or in the interlayer. In this study the intercalation of DPH in the interlayer of a Ca-smectite was characterized by X-ray diffraction, infra-red, and thermogravimetric analyses supported by molecular dynamic simulation. At the low (0.2–0.3 CEC) and high (0.6–0.7 CEC) adsorption levels, the intercalated DPH might take a horizontal monolayer or a bilayer configuration, resulting in a d001 expansion to 15 or 17 Å, respectively. As the amount of DPH intercalation increased, a gradual, yet systematic, dehydration due to removal of hydrated inorganic cation Ca2+ from the interlayer was observed. In addition, the intercalated DPH had a slightly higher thermal stability due to the shield effect of the host mineral smectite against heat. The uptake of DPH by the smectite was attributed to both electrostatic interactions between the negatively charged mineral surfaces and the positively charged tertiary amine and cation exchange interactions between DPH+ and hydrated Ca2+. Thus, smectite minerals could serve as a sink to remove dissolved DPH from water on the one hand, and as a carrier to transport intercalated DPH in the environment on the other hand

Potential Antifreeze Compounds in Present-Day Martian Seepage Groundwater

Is the recently found seepage groundwater on Mars pure H2O, or mixed with salts and other antifreeze compounds? Given the surface conditions of Mars, it is unlikely that pure water could either exist in its liquid state or have shaped Mars¡¦ fluid erosional landforms (gullies, channels, and valley networks). More likely is that Mars¡¦ seepage groundwater contains antifreeze and salt compounds that resist freezing and suppress evaporation. This model better accounts for Mars¡¦ enigmatic surface erosion. This paper suggests 17 antifreeze compounds potentially present in Martian seepage groundwater. Given their liquid state and physical properties, triethylene glycol, diethylene glycol, ethylene glycol, and 1,3-propylene glycol are advanced as the most likely candidate compounds. This paper also explores how a mixing of glycol or glycerol with salts in the Martian seepage groundwater may have lowered water¡¦s freezing point and raised its boiling point, with consequences that created fluid gully and channel erosion. Ethylene glycol and related hydrocarbon compounds have been identified in Martian and other interstellar meteorites. We suggest that these compounds and their proportions to water be included for detection in future explorations

Depth-resolved abundance and diversity of arsenite-oxidizing bacteria in the groundwater of Beimen, a blackfoot disease endemic area of southwestern Taiwan

The role of arsenite oxidizers in natural attenuation of arsenic pollution necessitates studies on their abundance and diversity in arsenic-contaminated aquifers. In this study, most probable number-polymerase chain reaction (MPN-PCR) and denaturing gradient gel electrophoresis (DGGE) was applied to monitor depth-wise abundance and diversity of aerobic arsenite oxidizers in arsenic-enriched groundwater of Beimen, southwestern Taiwan. The results revealed that the abundance of arsenite oxidizers ranged from 0.04 to 0.22, and the lowest ratio was observed in the most arsenic-enriched and comparatively more reduced groundwater (depth 200m) of Beimen 1. The highest ratio was observed in the less arsenic-enriched and less reduced groundwater (depth 60m) of Beimen 2B. DGGE profiles showed a shift in diversity of arsenite oxidizers, consisting of members of the Betaproteobacteria (61%), Alphaproteobacteria (28%) and Gammaproteobacteria (11%), depending on mainly arsenic concentration and redox level in groundwater. Groundwater with the lowest arsenic and highest dissolved oxygen at Beimen 2B harbored 78% of the arsenite oxidizers communities, while groundwater with the highest arsenic and lowest dissolved oxygen at Beimen 1 and Beimen-Jinhu harbored 17 and 22% of arsenite oxidizers communities, respectively. Pseudomonas sp. was found only in groundwater containing high arsenic at Beimen 1 and Beimen-Jinhu, while arsenite oxidizers belonging to Alpha- and Betaproteobacteria were dominated in groundwater containing low arsenic

Hydrogeochemistry of Groundwater and Arsenic Adsorption Characteristics of Subsurface Sediments in an Alluvial Plain, SW Taiwan

Many studies were conducted to investigate arsenic mobilization in different alluvial plains worldwide. However, due to the unique endemic disease associated with arsenic (As) contamination in Taiwan, a recent research was re-initiated to understand the transport behavior of arsenic in a localized alluvial plain. A comprehensive approach towards arsenic mobility, binding, and chemical speciation was applied to correlate groundwater hydrogeochemistry with parameters of the sediments that affected the As fate and transport. The groundwater belongs to a Na-Ca-HCO3 type with moderate reducing to oxidizing conditions (redox potential = −192 to 8 mV). Groundwater As concentration in the region ranged from 8.89 to 1131 μg/L with a mean of 343 ± 297 μg/L, while the As content in the core sediments varied from 0.80 to 22.8 mg/kg with a mean of 9.9 ± 6.2 mg/kg. A significant correlation was found between As and Fe, Mn, or organic matter, as well as other elements such as Ni, Cu, Zn, and Co in the core sediments. Sequential extraction analysis indicated that the organic matter and Fe/Mn oxyhydroxides were the major binding pools of As. Batch adsorption experiments showed that the sediments had slightly higher affinity for As(III) than for As(V) under near neutral pH conditions and the As adsorption capacity increased as the contents of Fe oxyhydroxides as well as the organic matter increased

Arsenic-enriched aquifers: occurrences and mobilization of arsenic in groundwater of Ganges Delta Plain, Barasat, West Bengal, India

Hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for As-enrichment in part of the Gangetic plain (Barasat, West Bengal, India). Analysis of water samples from shallow tubewells (depth 24.3-48.5m) and piezometer wells (depth 12.2-79.2m) demonstrate that the groundwater is mostly the Ca-HCO3 type and anoxic in nature (mean EhSHE=34mV). Arsenic concentrations ranged from <10-538μg/L, with high concentrations only present in the shallow to medium depth (30-50m) of the aquifer along with high Fe (0.07-9.8mg/L) and relatively low Mn (0.15-3.38mg/L) as also evidenced in core sediments. Most groundwater samples contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V), exhibiting the reducing condition. Results show lower concentrations of NO3, SO4 and NO2 along with higher values of DOC and HCO3, indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of As from sediments into groundwater. Positive correlations of As with Fe and DOC were also observed. The presence of DOC may actively drive the redox processes. This study revealed that reduction processes of FeOOH was the dominant mechanism for the release of As into the groundwater in this part of the Ganges Delta plain