Intermediate Aquifer Research Articles

Hydrogeochemistry of a strategic alluvial aquifer system in a semi-arid setting and its implications for potable urban water supply: The Lodwar Alluvial Aquifer System (LAAS)

Lodwar Municipality is one of the fastest-growing urban areas of Sub-Saharan Africa that depends mainly on groundwater for its municipal water supply. Most of the groundwater sources are located within the riparian zones of the Turkwel River. With limited understanding of its aquifers, the groundwater of Lodwar may be at risk of natural processes and anthropogenic activities. Statistical techniques and geochemical methods were applied to determine the aquifer hydrogeochemistry. Three distinct aquifers, which we collectively refer to as the Lodwar Alluvial Aquifer System, underlie Lodwar and its environs, the shallow alluvial, intermediate, and deep aquifers which are the main source of fresh water. A fourth, the shallow aquifer of the Turkana grit, is highly saline and with fluoride contamination. Just as the Turkwel River, the shallow alluvial aquifer (SAA) was dominated by Ca–HCO3 water type, while the TGSA was Na–Cl water type and became Na–HCO3 near the Holocene sediments. The intermediate aquifer (IA) was Na–HCO3water type. Pockets of Mg–HCO3 water occurred in the shallow alluvial and intermediate aquifers. The natural processes in the SAA include rock-water interaction, recharge by surface water, and oxidation reactions, while evaporation and dissolution are the major factors controlling the chemistry of the TGSA. Ion exchange, dilution, and dissolution are the major processes in the IA. Elevated levels of NO3− and SO42− during the wet season within the SAA and the IA reflects their vulnerability to pollution. Saline intrusion into the shallow and intermediate aquifers from the Turkana grit aquifers is likely to occur.

Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping.

Across South Asia, millions of villagers have reduced their exposure to high-arsenic (As) groundwater by switching to low-As wells. Isotopic tracers and flow modeling are used in this study to understand the groundwater flow system of a semi-confined aquifer of Pleistocene (>10 kyr) age in Bangladesh that is generally low in As but has been perturbed by massive pumping at a distance of about 25 km for the municipal water supply of Dhaka. A 10- to 15-m-thick clay aquitard caps much of the intermediate aquifer (>40- to 90-m depth) in the 3-km2 study area, with some interruptions by younger channel sand deposits indicative of river scouring. Hydraulic heads in the intermediate aquifer below the clay-capped areas are 1-2 m lower than in the high-As shallow aquifer above the clay layer. In contrast, similar heads in the shallow and intermediate aquifer are observed where the clay layer is missing. The head distribution suggests a pattern of downward flow through interruptions in the aquitard and lateral advection from the sandy areas to the confined portion of the aquifer. The interpreted flow system is consistent with 3H-3He ages, stable isotope data, and groundwater flow modeling. Lateral flow could explain an association of elevated As with high methane concentrations within layers of gray sand below certain clay-capped portions of the Pleistocene aquifer. An influx of dissolved organic carbon from the clay layer itself leading to a reduction of initially orange sands has also likely contributed to the rise of As.

Engineering Subsoil Characterization for Shallow Foundation Design in Ode Irele Area of Ondo State, Southwestern Nigeria

Integrated geophysical and geotechnical investigations for foundation design have proved to be good veritable tools in effective foundation design and construction. Geophysical and geotechnical methods involving electrical resistivity and cone penetration test have been carried out to investigate the foundation soil conditions of Ode Irele, southwestern Nigeria. Six vertical electrical sounding (VES) were carried out along two traverses; which is complemented by two cone penetration tests with seven trial tests at different subsurface depths. The geotechnical results showed that the soils are sand and silt dominated. All the tested parameters fall within the Nigeria federal ministry of works and housing specification with liquid limit (< 50%), plastic limit (< 30%), plasticity index (< 20%). The geoelectric sections identified maximum of six geoelectric/geologic subsurface layers comprising the topsoil (red sand), weathered layer (made up of coastal sand/white sand), clayey sand (which is the major aquitard in the area), intermediate sand aquifer unit. However the coastal sand layer has moderately high resistivity at shallow depth to sustain foundation load with thickness greater than 2 m. The groundwater level measured from existing borehole records 17.5 m which may not or seriously affect the bases of the foundation footing. Consequently an average allowable bearing capacity of 150 KN/m2 (ultimate bearing capacity of 450 KN/m2) would be appropriate for design of shallow foundation in the area, at a depth not less than 1.6 m in Ode Irele and 0.8 m at Ajagba. The foundation width of 0.6 m would produce minimum bearing settlement less than 25 mm. The appropriate (recommended) ultimate bearing and allowable bearing capacity for strip and square footings at depth levels of 0.6 – 1.2 m vary from 1486 – 1842 KN/m2 and 495 - 614 KN/m2; and 2056 – 2489 KN/m2 and 685 - 830 KN/m2 respectively.

Monitoring groundwater heads and estimating recharge in multi-aquifer systems illustrated by an irrigated area in north-west Bangladesh

The impact of groundwater abstraction in multi-aquifer systems can be identified by monitoring variations of groundwater heads with depth and with time. Equally important are estimates of recharge to the groundwater system including contributions from irrigation. A case study from the Rajshahi Barind in Bangladesh illustrates the methodologies. Abstraction of groundwater from deep tubewells has resulted in substantial increases in agricultural production but also significant falls in groundwater heads in the aquifers. Monitoring of the groundwater heads at different depths and relating these to the lithology has indicated the formation of an additional water table in an intermediate aquifer; this leads to the conceptualisation of the aquifer system as two Units, Upper and Lower. Estimates of the potential recharge to the aquifer system are obtained from a daily soil water balance which is enhanced to include the representation of recharge from standing water in flooded ricefields. Detailed fieldwork, over a period of more than 2 years, includes daily records of groundwater heads, rainfall, temperature and hours of pumping for irrigation; information about the crops grown in the command area is also collected. Individual, but interconnected, conceptual and computational models for the two Units are developed. The outputs of the computational models show good agreement with measured groundwater head fluctuations. Using information from the computational models, the sustainability of the current abstraction patterns is considered.

Effectiveness of Different Approaches to Arsenic Mitigation over 18 Years in Araihazar, Bangladesh: Implications for National Policy.

About 20 million rural Bangladeshis continue to drink well water containing >50 μg/L arsenic (As). This analysis argues for reprioritizing interventions on the basis of a survey of wells serving a population of 380,000 conducted one decade after a previous round of testing overseen by the government. The available data indicate that testing alone reduced the exposed population in the area in the short term by about 130,000 by identifying the subset of low As wells that could be shared at a total cost of <US$1 per person whose exposure was reduced. Testing also had a longer term impact, as 60,000 exposed inhabitants lowered their exposure by installing new wells to tap intermediate (45–90 m) aquifers that are low in As at their own expense of US$30 per person whose exposure was reduced. In contrast, the installation of over 900 deep (>150 m) wells and a single piped-water supply system by the government reduced exposure of little more than 7000 inhabitants at a cost of US$150 per person whose exposure was reduced. The findings make a strong case for long-term funding of free well testing on a massive scale with piped water or groundwater treatment only as a last resort.

Impact des Processus Hydrochimique sur la Qualité des Eaux souterraines de la Ville de N’Djaména-Tchad

The problem of access to water in quality and quantity is a major challenge, because it strongly influences the socio-economic conditions of populations in developing countries. The water of the basement of the city of N'Djamena is not sheltered from the risk of pollution. She disposes very little functional wastewater disposal system because the collection networks are almost non-existent, moreover there is a lack of infrastructures for evacuation of household waste, as well as the solid waste treatment units. In addition, under the town of N'Djamena there are two main aquifers located respectively at about 10 and 60 m depth, and the presence of an intermediate aquifer about 30 m deep was also noted. Like all urban cities, these aquifers are not immune to the risks associated with human activities. In order to highlight the influence of the hydrochemical process on the groundwater quality of the city of N'Djamena, a study was conducted on a sample of well water and borehole. In total, 20 open wells and 16 boreholes were sampled and analyzed. The pH and the temperature were measured in situ using the pH 323 / Set B mixed electrode and the conductivity using the Lf 318 / Set electrode. It is the same for the alkalinity which is determined by titrimetry, using a HACH / 16900 brand digital titrator. The analysis of major ions was carried out at the Laboratory of Hydrogeology of the University of Avignon. the anions (Cl - , SO42- , NO3 - ) were analyzed using a Dionex ion chromatograph, and the cations (Ca2+ , Mg2+ , Na+ , K + ) using an atomic absorption spectrometer for with a relative uncertainty of 5%. The results of the in-situ parameters have shown that the waters have a pH which is around 6.85 in the wells and 7.24 in the boreholes and the measured temperature is close to the ambient temperature of the air which is 28 ° C. The mineralization of the waters is sometimes high and this results in values of conductivities that can reach 1253 μS / cm), especially in the wells. This increase in conductivity is accompanied by an increase in Cl - and NO3 - ions in the water. Groundwater has a wide variety of chemical facies, among which mention may be made of calciumbicarbonate-type water, sometimes nitrated, sodium bicarbonate and potassium and nitrate, which may have high chloride contents and bicarbonate and chloride and nitrate calcium or sodium. Principal Component Analysis (PCA) has shown that the main processes influencing groundwater chemistry are hydrolysis of silicates, cation exchange between groundwater and clayey minerals, evaporation and the impact of human activities.

Hydrogeochemistry and groundwater quality assessment of the multilayered aquifer in Lower Kelantan Basin, Kelantan, Malaysia

Continual expansion of population density, urbanization, agriculture, and industry in most parts of the world has increased the generation of pollution, which contributes to the deterioration of surface water quality. This causes the dependence on groundwater sources for their daily needs to accumulate day by day, which raises concerns about their quality and hydrogeochemistry. This study was carried out to increase understanding of the geological setup and assess the groundwater hydrogeochemical characteristics of the multilayered aquifers in Lower Kelantan Basin. Based on lithological data correlation of exploration wells, the study area can be divided into three main aquifers: shallow, intermediate and deep aquifers. From these three aquifers, 101 groundwater samples were collected and analyzed for various parameters. The results showed that pH values in the shallow, intermediate and deep aquifers were generally acidic to slightly alkaline. The sequences of major cations and anions were Na+ > Ca2+ > Mg2+ > K+ and HCO3− > Cl− > SO42− > CO32−, respectively. In the intermediate aquifer, the influence of ancient seawater was the primary factor that contributed to the elevated values of electrical conductivity (EC), Cl− and total dissolved solids (TDS). The main facies in the shallow aquifer were Ca–HCO3 and Na–HCO3 water types. The water types were dominated by Na–Cl and Na–HCO3 in the intermediate aquifer and by Na–HCO3 in the deep aquifer. The Gibbs diagram reveals that the majority of groundwater samples belonged to the deep aquifer and fell in the rock dominance zone. Shallow aquifer samples mostly fell in the rainfall zone, suggesting that this aquifer is affected by anthropogenic activities. In contrast, the results suggest that the deep aquifer is heavily influenced by natural processes.

The long-term impacts of anthropogenic and natural processes on groundwater deterioration in a multilayered aquifer

In many regions around the world, there are issues associated with groundwater resources due to human and natural factors. However, the relation between these factors is difficult to determine due to the large number of parameters and complex processes required. In order to understand the relation between land use allocations, the intrinsic factors of the aquifer, climate change data and groundwater chemistry in the multilayered aquifer system in Malaysia's Northern Kelantan Basin, twenty-two years hydrogeochemical data set was used in this research. The groundwater salinisation in the intermediate aquifer, which mainly extends along the coastal line, was revealed through the hydrogeochemical investigation. Even so, there had been no significant trend detected on groundwater salinity from 1989 to 2011. In contrast to salinity, as seen from the nitrate contaminations there had been significantly increasing trends in the shallow aquifer, particularly in the central part of the study area. Additionally, a strong association between high nitrate values and the areas covered with palm oil cultivations and mixed agricultural have been detected by a multiple correspondence analysis (MCA), which implies that the increasing nitrate concentrations are associated with nitrate loading from the application of N-fertilisers. From the process of groundwater salinisation in the intermediate aquifer, could be seen that it has a strong correlation the aquifer lithology, specifically marine sediments which are influenced by the ancient seawater trapped within the sediments.

Effect of overpumping and irrigation stress on hydrochemistry and hydrodynamics of a Saharan oasis groundwater system

ABSTRACTStepwise hydrochemical and isotope-based methodology was adopted to identify mineralization processes, assess the impact of resources overexploitation and flood irrigation, and conceptualize groundwater hydrodynamics in the Djérid aquifer system, Tunisia. The study demonstrates that the main processes controlling groundwater geochemistry are dissolution of evaporates and phosphate-bearing rocks, cation exchange, mixing between high and low TDS end-members, and irrigation return flow. Interpretation of isotope data demonstrates that the deep aquifer was mostly recharged by late Pleistocene palaeowater, while the shallow aquifer is entirely recharged by return flow. The intermediate aquifer groundwater is actually a mixing of early to middle Holocene palaeowater, late Pleistocene deep aquifer palaeowater and return flow waters. The established conceptual model shows that deep and shallow groundwater leakages into the intermediate aquifer are enhanced by the presence of deep faults, the high hydraulic head of the deep aquifer, the overexploitation of the intermediate aquifer, and the long-term flood irrigation.

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer, Sfax, southeastern Tunisia

Major element concentrations and stable (δ18O and δ2H) and radiogenic (3H and 14C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ18O and δ2H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO4 and Ca-Na-Cl-SO4. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ18O and δ2H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

Hydrogeochemistry of Groundwater from Different Aquifer in Dimbhe Command Area of Ghod River, Maharashtra India

The groundwater geochemistry of Dimbhe command area of Ghod River basin was evaluated based on major ions characteristic to decide its suitability for drinking, domestic use, and irrigation. Groundwater samples from different depth (shallow and deep) aquifer were collected and investigated for pH, electrical conductivity (EC), total dissolved solid (TDS), Ca, Mg, Na, K, Cl, SO4, CO3, HCO3, NO3, Fe, and Mn. The results show that the shallow groundwater is dominated by Ca-HCO3 and Na-HCO3 and deep aquifer by Na-HCO3 water facies. The sodium adsorption ratio (SAR) and salinity hazard indicate that the groundwater from the shallow and deep aquifer is suitable for irrigation purposes, and part of the intermediate aquifer is not suitable for crop irrigation. Groundwater from the shallow and deep aquifer is regarded as fresh water and suitable for drinking, domestic and agricultural irrigation use.

The influence of subsurface flow on lake formation and north polar lake distribution on Titan

Observations of lakes, fluvial dissection of the surface, rapid variations in cloud cover, and lake shoreline changes indicate that Saturn's moon Titan is hydrologically active, with a hydrocarbon-based hydrological cycle dominated by liquid methane. Here we use a numerical model to investigate the Titan hydrological cycle – including surface, subsurface, and atmospheric components – in order to investigate the underlying causes of the observed distribution and sizes of lakes in the north polar region. The hydrocarbon-based hydrological cycle is modeled using a numerical subsurface flow model and analytical runoff scheme, driven by a general circulation model with an active methane-cycle. This model is run on synthetically generated topography that matches the fractal character of the observed topography, without explicit representation of the effects of erosion and deposition. At the scale of individual basins, intermediate to high permeability (10−8–10−6cm2) aquifers are required to reproduce the observed large stable lakes. However, at the scale of the entire north polar lake district, a high permeability aquifer results in the rapid flushing of methane through the aquifer from high polar latitudes to dry lower polar latitudes, where methane is removed by evaporation, preventing large lakes from forming. In contrast, an intermediate permeability aquifer slows the subsurface flow from high polar latitudes, allowing greater lake areas. The observed distribution of lakes is best matched by either a uniform intermediate permeability aquifer, or a combination of a high permeability cap at high latitudes surrounded by an intermediate permeability aquifer at lower latitudes, as could arise due to karstic processes at the north pole. The stability of Kraken Mare further requires reduction of the evaporation rate over the sea to 1% of the value predicted by the general circulation model, likely as a result of dissolved ethane, nitrogen, or organic solutes, and/or a climatic lake effect. These results reveal that subsurface flow through aquifers plays an important role in Titan's hydrological cycle, and exerts a strong influence over the distribution, size, and volatile budgets of Titan's lakes.

Connectivity to the surface determines diversity patterns in subsurface aquifers of the Fennoscandian shield.

Little research has been conducted on microbial diversity deep under the Earth's surface. In this study, the microbial communities of three deep terrestrial subsurface aquifers were investigated. Temporal community data over 6 years revealed that the phylogenetic structure and community dynamics were highly dependent on the degree of isolation from the earth surface biomes. The microbial community at the shallow site was the most dynamic and was dominated by the sulfur-oxidizing genera Sulfurovum or Sulfurimonas at all-time points. The microbial community in the meteoric water filled intermediate aquifer (water turnover approximately every 5 years) was less variable and was dominated by candidate phylum OD1. Metagenomic analysis of this water demonstrated the occurrence of key genes for nitrogen and carbon fixation, sulfate reduction, sulfide oxidation and fermentation. The deepest water mass (5000 year old waters) had the lowest taxon richness and surprisingly contained Cyanobacteria. The high relative abundance of phylogenetic groups associated with nitrogen and sulfur cycling, as well as fermentation implied that these processes were important in these systems. We conclude that the microbial community patterns appear to be shaped by the availability of energy and nutrient sources via connectivity to the surface or from deep geological processes.

Geogenic As and Mo groundwater contamination caused by an abundance of domestic supply wells

Lacking a connection to a municipal water supply, each household in the municipality of Lithia, approximately 30 km southeast of Tampa, Florida (USA), is responsible for its own supply of drinking water, causing a high-density of private domestic supply wells (DSW) in this area. There, a multilayered aquifer system exists, which can be subdivided into three distinct hydro stratigraphic units, which are, from the top down: the Surficial Aquifer System (SAS), the Intermediate Aquifer System (IAS), and the Upper Floridan Aquifer System (UFA). Despite the relatively small area, the geochemical and hydrogeological setting in Lithia is complex, consisting of: i) extensive cyclical pumping in a municipal well field to the west, ii) large seasonal changes in hydraulic head, ii) multiple aquifers with different hydraulic heads, and iv) a large density of domestic supply wells (DSW). Within the zone of highest As concentrations, there are approximately 100 wells in an area of 2.5 km × 1.5 km. Most of these wells have large open screened intervals, often open to all three aquifers, allowing the downward flow of oxygenated and upward flow of anoxic groundwater. A survey of groundwater quality found that As and Mo concentrations in the DSW were up to 371 μg/L and 4740 μg/L, respectively. To obtain information about the individual aquifers, 5 well clusters with 4 monitoring intervals (approximately 50 m, 65 m, 80 m and 95 m below surface) and 8 push core wells (approximately 9 m below surface) were installed and sampled. In those wells, As and Mo were only elevated in a permeable layer within the IAS at a depth of 50 m. Values were up to 195 μg/L for As and up to 5050 μg/L for Mo. Using the tritium-helium (3H–3He) method, the ages of those samples high in As and Mo were determined to be 40, 30 and 30 years, respectively, while all other samples had ages older than 50 years. This indicated that mixing between young and old groundwater could be responsible for the high As and Mo concentrations. A good negative correlation for the whole data set was also observed between the concentration 3H and δ18O values, which together with hydrogeological modeling confirmed that the increased permeability created by the high density of DSW resulted in flow paths that permitted the perpetual mixing of shallow and deep groundwater. The release of the As and Mo appeared to be a consequence of changes to the physicochemical conditions in the aquifer, either via the introduction of oxygen-rich fluids into the IAS or the mixing of different fluids in the IAS or the introduction of oxygen-depleted fluids into the IAS. While the mobilization of geogenic trace metals is often associated with pumping-induced hydraulic gradient changes, we found that a certain density of multi-aquifer wells can be sufficient to alter hydrologic flow paths and induce the mobilization of geogenic trace metals even in the absence of significant pumping. In Lithia, the DSW effectively increased the local scale permeability of the aquifer, causing the mixing of oxygen-rich surface and deeper anoxic groundwater across a confining unit. Because the alteration to the hydrologic flow paths was a consequence of changes to the physical structure of the aquifer system rather than due to pumping, the alteration is not easily reversible, thus significantly complicating site remediation. Our results provide a cautionary warning of the risks of undue private DSW development in rapidly growing communities.

Assessment of hydrochemical processes and groundwater hydrodynamics in a multilayer aquifer system under long-term irrigation condition: A case study of Nefzaoua basin, southern Tunisia

The hydrochemical and isotopic investigation of the Nefzaoua aquifer system demonstrates that groundwater mineralization in is controlled by natural and anthropogenic processes including water-rock interaction and irrigation return flow. It identifies all of the water bodies that flow within the aquifer system and their circulation patterns. The isotopically depleted paleowaters, identified within the deep and intermediate aquifers, undergo significant enrichment by evaporation during irrigation and recharged the shallow aquifer by return flow. Subsequently, they infiltrate to the intermediate aquifer which receives also rainfall modern recharge.

Remarks on the hydrogeological setting of S. Eufemia Lamezia plain through the development of the top surface of the intermediate confined aquifer (central Calabria)

The S. Eufemia Lamezia plain, located in central Calabria, is characterized by the presence of a multi-layered aquifer. In particular, it was studied the intermediate artesian aquifer, content in the Pliocene sands and sandstones. The collection of new lithostratigraphic data, related to drilling for water supplies, allowed to draw the map of the top of intermediate artesian aquifer underlying in the study area. The top surface of sands and sandstones map, presented here, seems to confirm the structural-geological data of the surface showing, also in depth, the conditioning of tectonics on the study area and on the groundwater flow. The analysis of the selected stratigraphic data shows that the studied aquifer is constituted by Pliocene deposits of sand and sandstones, confined to the top by Pliocene clay. Therefore locally hydraulic connections with the shallow aquifer for leackage phenomena are possible. The supply of the studied aquifer happens mainly for lateral recharge because the clay horizon that borders with the top of the aquifer prevents direct transfer of rainfall recharge. However, a reduced recharge rate is due to the meteoric recharge, which is possible in limited parts of the territory to the east of the study area and over. Therefore, this study aims to implement the knowledge of the groundwater flow of S. Eufemia plain by returning the top intermediate confined aquifer map which, is little studied but strongly exploited because, respect to the shallow aquifer, is more productive and more protected by potential contamination due to the presence of the aquiclude/aquitard which isolates it by the top.

Long-term Investigation of Sr- Isotope and Rare Earth Element Fractionation Processes Within Three Major Aquifers in the Äspö Hard Rock Laboratory (Sweden)

The 450 m deep Äspö Hard Rock Laboratory (Äspö HRL) provides a unique opportunity to access different aquifer systems within the Precambrian granodioritic basement of the Baltic Shield. In this study, emphasis will be placed on systematic variations of the isotopic and chemical composition including fractionation patterns of rare earth elements (REE) of three different aquifers. The aim is to identify end-member groundwater compositions and increase the knowledge and understanding of the groundwater evolution, and water rock interaction, parameters which are important for the subsurface microbial activity in the Äspö HRL. Groundwaters at the shallow and intermediate aquifers were influenced most from Baltic Sea water and meteoric water. The analyses of Sr-data and REE show especially long-term groundwater-rock interaction and δ18O values indicate the presence of glacial meltwater in the deep aquifer. During the 5 years of investigation, significant chemical changes caused by internal mixing processes or present microbial activity were not observed.

Bioaugmentation and Propane Biosparging for In Situ Biodegradation of 1,4-Dioxane

Propane biosparging and bioaugmentation were applied to promote in situ biodegradation of 1,4-dioxane at Site 24, Vandenberg Air Force Base (VAFB), CA. Laboratory microcosm and enrichment culture testing demonstrated that although native propanotrophs appeared abundant in the shallow water-bearing unit of the aquifer (8 to 23 ft below ground surface [bgs]), they were difficult to be enriched from a deeper water-bearing unit (82 to 90 feet bgs). Bioaugmentation with the propanotroph Rhodococcus ruber ENV425, however, supported 1,4-dioxane biodegradation in microcosms constructed with samples from the deep aquifer. For field testing, a propane-biosparging system consisting of a single sparging well and four performance monitoring wells was constructed in the deep aquifer. 1,4-dioxane biodegradation began immediately after bioaugmentation with R. ruber ENV425 (36 L; 4 × 109 cells/mL), and apparent first-order decay rates for 1,4-dioxane ranged from 0.021 day−1 to 0.036 day−1. First-order propane consumption rates increased from 0.01 to 0.05 min−1 during treatment. 1,4-dioxane concentrations in the sparging well and two of the performance monitoring wells were reduced from as high as 1090 µg/L to <2 µg/L, while 1,4-dioxane concentration was reduced from 135 µg/L to 7.3 µg/L in a more distal third monitoring well. No 1,4-dioxane degradation was observed in the intermediate aquifer control well even though propane and oxygen were present. The demonstration showed that propane biosparging and bioaugmentation can be used for in situ treatment of 1,4-dioxane to regulatory levels.

Hydrogeochemistry of Groundwater from Different Aquifer in Lower Kelantan Basin, Kelantan, Malaysia

The groundwater geochemistry of Lower Kelantan Basin was evaluated based on major ions characteristic to determine its suitability for drinking, domestic use and irrigation. Groundwater samples from different aquifer layers (shallow, intermediate and deep) were collected and analysed for pH, electrical conductivity (EC), total dissolved solid (TDS), Ca, Mg, Na, K, Cl, SO4, CO3, HCO3, NO3, Fe and Mn. The results show that the shallow groundwater is dominated by Ca-HCO3 and Na-HCO3 while intermediate is dominated by Na-Cl and Na-HCO3, and deep aquifer by Na-HCO3 water facies. The sodium adsorption ratio (SAR) and salinity hazard indicate that the groundwater from shallow and deep aquifer is suitable for irrigation purposes, and part of intermediate aquifer is not suitable for crop irrigation. Groundwater from shallow and deep aquifer is regarded as fresh water and suitable for drinking, domestic and agricultural irrigation use while groundwater from intermediate aquifer is slightly brackish water particularly closed to coastal area.

Hydrogeochemistry of high-fluoride groundwater at Yuncheng Basin, northern China

Hydrogeochemical and environmental isotope methods were integrated to delineate the spatial distribution and enrichment of fluoride in groundwater at Yuncheng Basin in northern China. One hundred groundwater samples and 10 Quaternary sediment samples were collected from the Basin. Over 69% of the shallow groundwater (with a F− concentration of up to 14.1mg/L), 44% of groundwater samples from the intermediate and 31% from the deep aquifers had F− concentrations above the WHO provisional drinking water guideline of 1.5mg/L. Groundwater with high F− concentrations displayed a distinctive major ion chemistry: Na-rich and Ca-poor with a high pH value and high HCO3− content. Hydrochemical diagrams and profiles and hydrogen and oxygen isotope compositions indicate that variations in the major ion chemistry and pH are controlled by mineral dissolution, cation exchange and evaporation in the aquifer systems, which are important for F− mobilization as well. Leakage of shallow groundwater and/or evaporite (gypsum and mirabilite) dissolution may be the major sources for F− in groundwater of the intermediate and deep aquifers.