Contrasting Influence of Geology on E. coli and Arsenic in Aquifers of Bangladesh

Arsenic in groundwater has been a concern in South and Southeast Asia for more than a decade. We explore here the possibility that hydrogeologic factors recently shown to influence the distribution of arsenic might also affect the level of contamination of shallow (<20 m) wells with microbial pathogens. A total of 96 shallow tube wells in two nearby villages of Bangladesh were surveyed during the wet and dry seasons, along with 55 deeper wells in neighboring villages. One of the two villages is located in a particularly sandy environment where recharge is rapid and shallow wells contain little arsenic. Shallow aquifers in the other village are capped with an impermeable clay layer, recharge is an order of magnitude slower, and arsenic levels are high. The fecal indicator E. coli was detected in 43% of shallow wells, compared with 12% of deeper wells. More shallow wells contained E. coli during the wet season (61%) than during the dry season (9%). In the wet season, a higher proportion of shallow wells in the village with low arsenic levels (72%) contained E. coli compared with the village having high arsenic levels (43%). Differences in arsenic and E. coli distributions between the two sites are likely due to the differences in permeability of near‐surface sediments although differences in average well‐depth between the two villages (9 ± 4 vs. 15 ± 3 m) may play a role as well. Hydrogeologic conditions that favor high levels of fecal contamination but low levels of arsenic in shallow groundwater should be taken into account during arsenic mitigation throughout South and Southeast Asia.     

Statistical characterization of arsenic contamination in shallow tube wells of western Bangladesh

A regional assessment of the arsenic (As) contamination scenario in shallow tube wells (depth < 150 m) of western Bangladesh is presented. Comparisons are made in light of bulk geological differences (Pleistocene versus Holocene deposits/northwest versus southwest) and As measurement protocols (field kit (FK) versus atomic absorption spectroscopy (AAS)). Our As database comprised the following: (1) the nationwide As survey completed in 1999 by the British Geological Survey in collaboration with the Department of Public Health Engineering (DPHE); and (2) a regional As survey conducted in southwest Bangladesh by the Japan International Cooperation Agency in collaboration with DPHE in 2002. First, we characterize the error structure of the semi‐quantitative FK As measurements using collocated AAS As measurements as reference from a set of 307 wells located in southwest Bangladesh. The depth distribution of As is identified using a very dense cluster of 2963 wells over a 560 km² domain. The probability of the FK method for successful detection of a well sample as unsafe (safe) was found to be 96·9% (34·1%) and 95·2% (80·3%) for the World Health Organization (WHO) and Bangladesh safe limits, respectively. Similarly, the probability of false alarms and false hopes for WHO (Bangladesh) safe limits were found to be 3·1% (4·8%) and 87·5% (19·7%), respectively. The depth at which the highest fraction of wells exceeding a given safe limit occurred could still be inferred correctly by FK measurements. A simple bias adjustment procedure on FK As data did not result in a more accurate characterization of depth distribution of As. This indicated that simple error statistics are inadequate for advancing the utility of FKs; rather, an understanding of the complex and multidimensional error structure is required. Regional anisotropy in the spatial dependence of As for the northwest was found to be stronger than the southwest. The correlation length for As concentration in the east–west direction of northwest Bangladesh (i.e. across major river floodplains) was found to be almost twice (158·80 km) that of the north–south direction (along the major axis of Pleistocene deposits) (78·21 km). For the southwest region, the ratio of east–west to north–south correlation lengths ranged from 1·40 to 1·51. For the northwest region, because it is well known to have the lowest concentrations of As countrywide, knowledge of this anisotropy appears to suggest the need for drilling twice as many remediation deep wells in the proximity of an unsafe shallow well in the north–south direction than in the east–west direction. Findings from this study are potentially useful in setting priority areas for emergency testing, distributing remediation resources equitably and formulating a regional water resources strategy for western Bangladesh. Copyright © 2005 John Wiley & Sons, Ltd.     

Arsenic in glacial drift aquifers and the implication for drinking water--lower Illinois River Basin

The lower Illinois River Basin (LIRB) covers 47,000 km2 of central and western Illinois. In the LIRB, 90% of the ground water supplies are from the deep and shallow glacial drift aquifers. The deep glacial drift aquifer (DGDA) is below 152 m altitude, a sand and gravel deposit that fills the Mahomet Buried Bedrock Valley, and overlain by more than 30.5 m of clayey till. The LIRB is part of the USGS National Water Quality Assessment program, which has an objective to describe the status and trends of surface and ground water quality. In the DGDA, 55% of the wells used for public drinking-water supply and 43% of the wells used for domestic drinking water supply have arsenic concentrations above 10 micrograms/L (a new U.S. EPA drinking water standard). Arsenic concentrations greater than 25 micrograms/L in ground water are mostly in the form of arsenite (AsIII). The proportion of arsenate (AsV) to arsenite does not change along the flowpath of the DGDA. Because of the limited number of arsenic species analyses, no clear relations between species and other trace elements, major ions, or physical parameters could be established. Arsenic and barium concentrations increase from east to west in the DGDA and are positively correlated. Chloride and arsenic are positively correlated and provide evidence that arsenic may be derived locally from underlying bedrock. Solid phase geochemical analysis of the till, sand and gravel, and bedrock show the highest presence of arsenic in the underlying organic-rich carbonate bedrock. The black shale or coal within the organic-rich carbonate bedrock is a potential source of arsenic. Most high arsenic concentrations found in the DGDA are west and downgradient of the bedrock structural features. Geologic structures in the bedrock are potential pathways for recharge to the DGDA from surrounding bedrock.     

Arsenic Management Through Well Modification and Simulation

Arsenic concentrations can be managed with a relatively simple strategy of grouting instead of completely destroying a selected interval of well. The strategy of selective grouting was investigated in Antelope Valley, California, where groundwater supplies most of the water demand. Naturally occurring arsenic typically exceeds concentrations of 10 µg/L in the water produced from these long-screened wells. The vertical distributions of arsenic concentrations in intervals of the aquifer contributing water to selected supply wells were characterized with depth-dependent water-quality sampling and flow logs. Arsenic primarily entered the lower half of the wells where lacustrine clay deposits and a deeper aquifer occurred. Five wells were modified by grouting from below the top of the lacustrine clay deposits to the bottom of the well, which reduced produced arsenic concentrations to less than 2 µg/L in four of the five wells. Long-term viability of well modification and reduction of specific capacity was assessed for well 4-54 with AnalyzeHOLE, which creates and uses axisymmetric, radial MODFLOW models. Two radial models were calibrated to observed borehole flows, drawdowns, and transmissivity by estimating hydraulic-conductivity values in the aquifer system and gravel packs of the original and modified wells. Lithology also constrained hydraulic-conductivity estimates as regularization observations. Well encrustations caused as much as 2 µg/L increase in simulated arsenic concentration by reducing the contribution of flow from the aquifer system above the lacustrine clay deposits. Simulated arsenic concentrations in the modified well remained less than 3 µg/L over a 20-year period.     

Recommended Sampling Intervals for Arsenic in Private Wells

Geogenic arsenic in drinking water is a worldwide problem. For private well owners, testing (e.g., private or government laboratory) is the main method to determine arsenic concentration. However, the temporal variability of arsenic concentrations is not well characterized and it is not clear how often private wells should be tested. To answer this question, three datasets, two new and one publicly available, with temporal arsenic data were utilized: 6370 private wells from New Jersey tested at least twice since 2002, 2174 wells from the USGS NAWQA database, and 391 private wells sampled 14 years apart from Bangladesh. Two arsenic drinking water standards are used for the analysis: 10 µg/L, the WHO guideline and EPA standard or maximum contaminant level (MCL) and 5 µg/L, the New Jersey MCL. A rate of change was determined for each well and these rates were used to predict the temporal change in arsenic for a range of initial arsenic concentrations below an MCL. For each MCL and initial concentration, the probability of exceeding an MCL over time was predicted. Results show that to limit a person to below a 5% chance of drinking water above an MCL, wells that are ½ an MCL and above should be tested every year and wells below ½ an MCL should be tested every 5 years. These results indicate that one test result below an MCL is inadequate to ensure long-term compliance. Future recommendations should account for temporal variability when creating drinking water standards and guidance for private well owners.     

Aquifer Treatment of Sea Water to Remove Natural Organic Matter Before Desalination

An investigation of a sea water reverse osmosis desalination facility located in western Saudi Arabia has shown that aquifer treatment of the raw sea water provides a high degree of removal of natural organic matter (NOM) that causes membrane biofouling. The aquifer is a carbonate system that has a good hydraulic connection to the sea and 14 wells are used to induce sea water movement 400 to 450 m from the sea to the wells. During aquifer transport virtually all of the algae, over 90% of the bacteria, over 90% of the biopolymer fraction of NOM, and high percentages of the humic substance, building blocks, and some of the low molecular weight fractions of NOM are removed. Between 44 and over 90% of the transparent exopolymer particles (TEP) are removed with a corresponding significant reduction in concentration of the colloidal fraction of TEP. The removal rate for TEP appears to be greater in carbonate aquifers compared to siliciclastic systems. Although the production wells range in age from 4 months to 14 years, no significant difference in the degree of water treatment provided by the aquifer was found.     

A Leaky Aquifer below Champlain Sea Clay: Closed‐Form Solutions for Natural Seepage

Closed‐form solutions are proposed for natural seepage in semiconfined (leaky) aquifers such as those existing below the massive Champlain Sea clay layers in the Saint‐Lawrence River Valley. The solutions are for an ideal horizontal leaky aquifer below an ideal aquitard that may have either a constant thickness and a constant hydraulic head at its surface, or a variable thickness and a variable hydraulic head at its surface. A few simplifying assumptions were needed to obtain the closed‐form solutions. These have been verified using a finite element method, which did not make any of the assumptions but gave an excellent agreement for hydraulic heads and groundwater velocities. For example, the difference between the two solutions was smaller than 1 mm for variations in the 5 to 8 m range for the hydraulic head in the semiconfined aquifer. Note that fitting the hydraulic head data of monitoring wells to the theoretical solutions gives only the ratio of the aquifer and aquitard hydraulic conductivities, a clear case of multiple solutions for an inverse problem. Consequently, field permeability tests in the aquitard and the aquifer, and pumping tests in the aquifer, are still needed to determine the hydraulic conductivity values.     

Long-term disturbance of ground water chemistry following well installation

Ground water samples collected from a multilevel sampler shortly after its construction showed significantly higher alkalinity and concentrations of calcium and magnesium than those from nearby wells installed 10 years earlier. The sampler was drilled using a conventional hollow-stem power auger in a sandy, silicate aquifer lying beneath an isthmus between two lakes in northern Wisconsin. Ground water in the study area is of low ionic strength and its chemistry is dominated by silicate mineral weathering. Periodic sampling over two years following installation of the sampler showed that the higher solute concentrations had subsequently decreased. Oxygen isotope signature and other solute species, such as sulfate and chloride, were comparable to those of older wells and did not show any notable trends over time. Independent variation of other chemical species that cannot be derived from aquifer minerals, and the similarly high concentrations in older wells shortly after their installation, suggest that rapid dissolution of fresh mineral surfaces and hyperfine particles generated during drilling has induced the enhanced concentrations. This observation is consistent with the field equivalent of laboratory mineral dissolution experiments that show initially increased dissolution rates that decay over time. Well installations for geochemical sampling in dominantly silicate material may require longer times to reach an equilibrium state than has been previously thought.     

In-Well Degassing Issues for Measurements of Dissolved Gases in Groundwater

Measurement of dissolved gases in groundwater is becoming increasingly common and important. Many of these measurements involve monitoring or sampling within wells or from water pumped from wells. We used total dissolved gas pressure (TDGP) sensors placed in the screened section of various wells (4 to 72 m deep) to assess the dissolved gas conditions for open wells compared to the conditions when sealed (i.e., isolated from the atmosphere) with a hydraulic packer (one well) or when pumped. When the packer was installed (non-pumping conditions), TDGP rose from <1.7 to >3.1 atm (<172 to >314 kPa), with declines noted when the packer was removed or deflated. While pumping, TDGP measured in many of the wells rose to substantially higher levels, up to 4.0 atm (408 kPa) in one case. Thus, when groundwater is gas charged, the background aquifer TDGP, and likewise the dissolved gas concentrations, may be substantially higher than initially measured in open wells, indicating significant in-well degassing. This raises concerns about past and current methods of measuring the dissolved gases in groundwater. Additional procedures that may be required to obtain representative measurements from wells include (1) installing in-well hydraulic packers to seal the well, or (2) pumping to bring in fresh groundwater. However, observed transient decreased TDGPs during pumping, believed to result from gas bubble formation induced by drawdown in the well below a critical pressure (relative to TDGP), may disrupt the measurements made during or after pumping. Thus, monitoring TDGP while pumping gas-charged wells is recommended.     

Palaeosol Control of Arsenic Pollution: The Bengal Basin in West Bengal,India

Groundwater in the Bengal Basin is badly polluted by arsenic (As) which adversely affects human health. To provide low‐As groundwater for As mitigation, it was sought across 235 km² of central West Bengal, in the western part of the basin. By drilling 76 boreholes and chemical analysis of 535 water wells, groundwater with <10 µg/L As in shallow aquifers was found under one‐third of a study area. The groundwater is in late Pleistocene palaeo‐interfluvial aquifers of weathered brown sand that are capped by a palaeosol of red clay. The aquifers form two N‐S trending lineaments that are bounded on the east by an As‐polluted deep palaeo‐channel aquifer and separated by a shallower palaeo‐channel aquifer. The depth to the top of the palaeo‐interfluvial aquifers is mostly between 35 and 38 m below ground level (mbgl). The palaeo‐interfluvial aquifers are overlain by shallow palaeo‐channel aquifers of gray sand in which groundwater is usually As‐polluted. The palaeosol now protects the palaeo‐interfluvial aquifers from downward migration of As‐polluted groundwater in overlying shallow palaeo‐channel aquifers. The depth to the palaeo‐interfluvial aquifers of 35 to 38 mbgl makes the cost of their exploitation affordable to most of the rural poor of West Bengal, who can install a well cheaply to depths up to 60 mbgl. The protection against pollution afforded by the palaeosol means that the palaeo‐interfluvial aquifers will provide a long‐term source of low‐As groundwater to mitigate As pollution of groundwater in the shallower, heavily used, palaeo‐channel aquifers. This option for mitigation is cheap to employ and instantly available.     

Effects of water use on arsenic release to well water in a confined aquifer

Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole.     

Investigation of Possible Contamination of Shallow Ground Water by Deeply Injected Liquid Industrial Wastes

The objective of this study was to assess the possible impact of deep well disposal operations, conducted between 1958 and 1974, on the ground water quality in a shallow fresh water aquifer beneath Sarnia, Ontario, Canada. Because of the breakout of formation fluids in Sarnia and Port Huron, Michigan, in the early 1970s, it had been hypothesized that liquid waste from the disposal zone in bedrock had leaked through numerous abandoned oil, gas, and salt wells in the area up to the shallow fresh water aquifer and from there to the surface.
A monitoring well network of 29 5cm (2 inch) diameter piezometers was established in the thin sand and shale aquifer system, which exists between 30 and 70m (100 and 230 feet) below ground surface. In addition, a 300m (1000 foot) deep borehole was drilled and instrumented with a Westbay multilevel casing, which permitted sampling of the disposal zone.
Ground water samples from the shallow monitoring wells and the Westbay multilevel casing were analyzed for volatiles by GC/MS. Those volatile aromatics that were conspicuously present in the deep disposal zone, e.g., ethyl toluenes and trimethyl benzene, were not detected in the shallow monitoring wells. Thus, if contaminants from the disposal zone did indeed migrate to the shallow aquifer, contamination was not widespread and probably consisted mostly of displaced chloride-rich formation waters.     

Sustainability of groundwater usage in northern China: dependence on palaeowaters and effects on water quality,quantity and ecosystem health

A synthesis of groundwater ages, recharge rates and information on processes affecting groundwater quality in northern China highlights the major challenges faced for sustainable management of the region's groundwater. Direct recharge rates range from hundreds of millimetres per year in the North China Plain, to tens of millimetres per year in the Loess Plateau to less than 4 mm/year in the arid northwest. Recharge rates and mechanisms to deep semiconfined and confined aquifers are poorly constrained; however, on the basis of available data, these are likely to be mostly negligible. Severe groundwater level declines (0.5–3 m/year) have occurred throughout northern China in the last three to four decades, particularly in deep aquifers. Radiocarbon dating, stable isotope and noble gas data show that the most intensively extracted deep groundwater is palaeowater, recharged under different climate and land cover conditions to the present. Reservoir construction has reduced surface runoff in mountain‐front areas that would naturally recharge regional Quaternary aquifers in many basins. In combination with intensive irrigation practices, this has resulted in the main recharge source shifting from surface runoff and mountain‐front recharge to irrigation returns. This has reduced infiltration of fresh recharge at basin margins and rapidly increased nitrate concentrations and overall mineralisation in phreatic groundwater over wide areas (in some cases to >400 mg/l and >10 g/l, respectively). In some basins, there is evidence that poor quality shallow water has leaked into deep layers (>200 m) via preferential flow, mixing with palaeowaters stored in semiconfined aquifers. High concentrations of naturally occurring fluoride and arsenic (locally >8.5 and >4 mg/l, respectively) have recently lead to the abandonment of numerous supply wells in northern China, creating further pressure on stressed water resources. Increasing water demand from direct and indirect consumption poses major challenges for water management in northern China, which must consider the full water cycle. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrogeological Investigation of Hydrocarbon Contamination of Ground Water in Albolote (Granada, Spain)

In July 1988, hydrocarbons were detected in wells in the urban area of Albolote, near Granada, Spain, near the border of the "Vega de Granada" alluvial aquifer. According to available hydrogeological data, the contamination was attributed to leaks in the underground pipelines of a nearby (300m) industrial factory, where the loss of 40,000 to 50,000 liters of gasoline had been detected some weeks before. A complete hydrogeological investigation was then undertaken, involving, among other techniques: (a) an inventory of the existing wells in the area; (b) the preparation of piezometric maps; (c) the application of electrical geophysical methods; (d) the drilling of piezometers and new pumping wells between the urbanized area and the leak point; (e) the improvement of the pluviometric and piezometric control by the installation of a pluviograph and several limnigraphs; (f) the sampling, initially daily and finally weekly, in a 20-well observation network, also used for piezometric control; and (g) the geostatistical study of the analytical data. The contamination plume, extended in the direction of the flow lines, has a length of 500m and a width of less than 50m, and appears to have occurred mainly in a paleochannel. Hydrocarbons (1600 liters) were recovered by pumping and by using absorbent blankets, as well as by a gas and liquid suction method. Hydrocarbon concentrations have continuously decreased. However, sporadic increases, associated with rainfall, have been observed suggesting the presence of retained hydrocarbons in the unsaturated zone. The rate of decrease in hydrocarbon concentrations has currently slowed, particularly in the less affected zone. As a means of activating the cleaning up of the unsaturated zone, an artificial recharging method has been designed.     

Electromagnetic‐Induction Logging to Monitor Changing Chloride Concentrations

Water from the San Joaquin Delta, having chloride concentrations up to 3590 mg/L, has intruded fresh water aquifers underlying Stockton, California. Changes in chloride concentrations at depth within these aquifers were evaluated using sequential electromagnetic (EM) induction logs collected during 2004 through 2007 at seven multiple‐well sites as deep as 268 m. Sequential EM logging is useful for identifying changes in groundwater quality through polyvinyl chloride‐cased wells in intervals not screened by wells. These unscreened intervals represent more than 90% of the aquifer at the sites studied. Sequential EM logging suggested degrading groundwater quality in numerous thin intervals, typically between 1 and 7 m in thickness, especially in the northern part of the study area. Some of these intervals were unscreened by wells, and would not have been identified by traditional groundwater sample collection. Sequential logging also identified intervals with improving water quality—possibly due to groundwater management practices that have limited pumping and promoted artificial recharge. EM resistivity was correlated with chloride concentrations in sampled wells and in water from core material. Natural gamma log data were used to account for the effect of aquifer lithology on EM resistivity. Results of this study show that a sequential EM logging is useful for identifying and monitoring the movement of high‐chloride water, having lower salinities and chloride concentrations than sea water, in aquifer intervals not screened by wells, and that increases in chloride in water from wells in the area are consistent with high‐chloride water originating from the San Joaquin Delta rather than from the underlying saline aquifer.     

大井间距井间地震观测试验

介绍了井间地震数据采集方面取得的最新进展．为了使我国井间地震技术实用化,开展了大井间距井间地震数据采集试验．通过地面浅井激发深井接收、深井激发深井接收、不同炸药量、不同传播距离试验,确定了井间地震观测参数．应用改进后的井中安全炸药震源、一个三分量井中检波器和常规数据记录系统,在陕北顺宁油田的顺3井、顺4井和顺5井3口生产井中成功采集到两对大井间距、深井、油井中的井间地震资料,两对井的井距分别为307．92m和470．36m,采集井段为904．31-1272．32m．共设计了4种观测方式,采集到800多炮井间地震记录,对油井无损害．改进型井中安全炸药震源在使用效率和寿命方面有显著提高,可用于商业性并间地震数据采集．     

In Situ Vertical Circulation Column: Containment System for Small-Scale DNAPL Field Experiments

The in situ vertical circulation column (ISVCC) is a cylindrical containment system consisting of an instrumented steel cylinder used for experimental ground water studies in sandy aquifers. Vertical flow is imposed inside the ISVCC. Although vertical wells are an option, the ISVCC installed in the Borden Aquifer is instrumented with horizontal wells and monitoring ports to avoid creating vertical preferential flow paths. The cylinder was driven downward into the aquifer using a small backhoe equipped with a vibrating plate. The ISVCC penetrates the 2.3-m-thic sand aquifer and is keyed 20 cm into the underlying clay aquitard. The cylinder was installed inside a 2 m X 2 m steel sheet pile enclosure so that the enclosed segment of aquifer could be conveniently dewatered and then excavated to allow installation of the horizontal wells. The dispersivity of the column was comparable to literature values for long sand-packed laboratory columns.
Pure phase DNAPL (tetrachloroethene and 1,1,1-trichloroethane) was slowly pumped into two ports in the center of the column. Following this DNAPL injection, an aqueous solution of vitamin B₁₂ and reduced titanium was circulated through the column to promote degradation of the solvents. Processes observed in the ISVCC included DNAPL distribution, dissolution, and degradation, and geochemical evolution of the aquifer.
The ISVCC provides a convenient means for testing in situ technologies in the experimental stage or for selection of proven technologies to find the most effective at a specific site. It is inexpensive, easy to install, and maximizes control over flow distribution in a heterogeneous aquifer. Its application will be restricted where low hydraulic conductivity beds are present in the aquifer.     

A Method for Installing Miniature Multilevel Sampling Wells

Abstract. A method has been developed to install miniature multilevel ground-water sampling wells in shallow, unconsoli-dated aquifers at sites without truck access. An advantage of these wells over the traditional bundle-type multilevel is that this type of installation causes minimal aquifer disturbance. Thus, miniature multilevels can be installed while a tracer test is in progress. Furthermore, only hand tools are needed in the field, and equipment and materials are easily obtained and inexpensive. The time required for installation is comparable to other methods.     

Characteristics and role of groundwater dissolved organic matter on arsenic mobilization and poisoning in Bangladesh

The fluorescence and molecular weight characteristics of dissolved organic matter (DOM) in groundwater of Bangladesh were investigated to evaluate its multiple roles on arsenic (As) mobilization and poisoning. Fluorescence properties of DOM were measured in groundwater samples collected from two As contaminated areas of Bangladesh (Faridpur at the Ganges floodplain and Sonargaon at the Meghna floodplain) from different locations and depths. The three dimensional excitation–emission matrix (3DEEM) fluorescence spectra of groundwater samples showed two characteristic peaks around Ex/Em = 335–365 nm/435–480 nm for fulvic-like peaks and peak at around Ex/Em = 275–290 nm/310–335 nm for the protein-like materials. The similarity of fluorescence spectra of groundwater and surface water of both the study areas with high intensity of fluorescence and its strong correlation with DOC reflect the in situ generation of fluorescent DOM from sedimentary organic matter (SOM) and recent recharge of terrestrial labile organic carbon into shallow aquifer. High performance size-exclusion chromatography (HPSEC) analysis of DOM shows positive correlations between fluorescence intensities (FI) of small molecular fractions (0.65 kDa) and As concentrations, with the signatures of protein-like peaks of DOM in groundwater. This result provides new evidence that small molecular weight fraction of DOM in groundwater of Bangladesh can play an important role on As mobilization and toxicity. In addition, high concentration of fluorescence materials in DOM of As contaminated groundwater of Bangladesh may pose a threat to public health.