Nitrate is often seen as an agricultural pollutant of groundwater and so is expected to be at higher concentrations in the groundwaters surrounding a city than in those beneath it. However the ...difference between rural and urban nitrate concentrations is often small, due to the non-agricultural sources of nitrogen that are concentrated in cities. This paper illustrates the source and significance of non-agricultural nitrogen for groundwater and presents a case study of nitrate loading in the city of Nottingham. Major sources of nitrogen in urban aquifers are related to wastewater disposal (on-site systems and leaky sewers), solid waste disposal (landfills and waste tips). The major sources of nitrogen in the Nottingham area are mains leakage and contaminated land with approximately 38% each of a total load of 21
kg
N
ha
−1
year
−1.
Factors regulating the occurrence of fluoride in groundwater were investigated using natural isotope tracers and geochemical data in the southeastern part of Korea where about 10% of the total public ...water-supply wells (
n
=
422) inspected in this study had fluoride levels exceeding the drinking water limit of Korea (1.5
mg/l). The F-rich public wells are mostly distributed along the major faults, especially in the terrain of the F-rich granitic rocks. The stable isotope analysis results provide substantial information for the relative ages of groundwaters. It is revealed that the F-rich groundwaters are deeply circulating paleogroundwaters and occur along the faults due to upward flow along the fault plane. While reacting with granitic rocks for a prolonged period, the F concentrations of groundwater are continuously enriched even after the groundwater reaches an equilibrium state with respect to fluorite (CaF
2) due to removal of Ca by precipitation of calcite (CaCO
3). These observations reflect that rock chemistry, groundwater age, well depth, and geologic structure are the important factors controlling the occurrence of high F groundwaters. However, high F groundwaters are rarely observed in the fault zones where the associated fractures are widely developed. Isotopic signature provides an evidence for deep penetration of recently recharged groundwater into the wide fault zone, indicating that the hydrologic condition of the fault is also an important factor controlling the occurrence of high F groundwaters.
Introduction of acetate into groundwater at the Rifle Integrated Field Research Challenge (Rifle, CO) has been used for biostimulation aimed at immobilizing uranium. While a promising approach for ...lowering groundwater-associated uranium, a concomitant increase in soluble arsenic was also observed at the site. An array of field data was analyzed to understand spatial and temporal trends in arsenic release and possible correlations to speciation, subsurface redox conditions, and biogeochemistry. Arsenic release (up to 9 μM) was strongest under sulfate reducing conditions in areas receiving the highest loadings of acetate. A mixture of thioarsenate species, primarily trithioarsenate and dithioarsenate, were found to dominate arsenic speciation (up to 80%) in wells with the highest arsenic releases; thioarsenates were absent or minor components in wells with low arsenic release. Laboratory batch incubations revealed a strong preference for the formation of multiple thioarsenic species in the presence of the reduced precursors arsenite and sulfide. Although total soluble arsenic increased during field biostimulation, the termination of sulfate reduction was accompanied by recovery of soluble arsenic to concentrations at or below prestimulation levels. Thioarsenic species can be responsible for the transient mobility of sediment-associated arsenic during sulfidogenesis and should be considered when remediation strategies are implemented in sulfate-bearing, contaminated aquifers.
Leachate and groundwater samples were collected from Gazipur landfill-site and its adjacent area to study the possible impact of leachate percolation on groundwater quality. Concentration of various ...physico-chemical parameters including heavy metal (Cd, Cr, Cu, Fe, Ni, Pb and Zn) and microbiological parameters (total coliform (TC) and faecal coliform (FC)) were determined in groundwater and leachate samples. The moderately high concentrations of Cl-, NO- ₃, SO²- ₄, NH⁺ ₄, Phenol, Fe, Zn and COD in groundwater, likely indicate that groundwater quality is being significantly affected by leachate percolation. Further they proved to be as tracers for groundwater contamination. The effect of depth and distance of the well from the pollution source was also investigated. The presence of TC and FC in groundwater warns for the groundwater quality and thus renders the associated aquifer unreliable for domestic water supply and other uses. Although some remedial measures are suggested to reduce further groundwater contamination via leachate percolation, the present study demand for the proper management of waste in Delhi.
Nine arsenic (As)-resistant bacterial strains isolated from As-rich groundwater samples of West Bengal were characterized to elucidate their potential in geomicrobial transformation and ...bioremediation aspects. The 16S rRNA gene-based phylogenetic analysis revealed that the strains were affiliated with genera Actinobacteria, Microbacterium, Pseudomonas and Rhizobium. The strains exhibited high resistance to As Minimum inhibitory concentration (MIC) ≥ 10 mM As
3+
and MIC ≥ 450 mM As
5+
and other heavy metals, e.g., Cu
2+
, Cr
2+
, Ni
2+
, etc. (MIC ≥ 2 mM) as well as As transformation (As
3+
oxidation and As
5+
reduction) capabilities. Their ability to utilize diverse carbon source(s) including hydrocarbons and different alternative electron acceptor(s) (As
5+
, SO
4
2−
, S
2
O
3
2−
, etc.) during anaerobic growth was noted. Growth at wide range of pH, temperature and salinity, production of siderophore and biofilm were observed. Together with these, growth pattern and transformation kinetics indicated a high As
3+
oxidation activity of the isolates Rhizobium sp. CAS934i, Microbacterium sp. CAS905i and Pseudomonas sp. CAS912i. A positive relation between high As
3+
resistance and As
3+
oxidation and the supportive role of As
3+
in bacterial growth was noted. The results highlighted As
3+
oxidation process and metabolic repertory of strains indigenous to contaminated groundwater and indicates their potential in As
3+
detoxification. Thus, such metabolically well equipped bacterial strains with highest As
3+
oxidation activities may be used for bioremediation of As contaminated water and effluents in the near future.
•Urban groundwater (GW) contaminated by carbamazepine (CBZ) and 5 metabolites (MET).•High concentrations are found when the aquifer is infiltrated by a polluted river.•The fate of CBZ and METs ...appeared to be dependent on the GW redox conditions.•Residence time could also play a major role in controlling their fate in aquifers.
This paper deals with urban groundwater contaminated with carbamazepine (CBZ) and five of its human metabolites in Barcelona. Groundwater samples were accordingly collected in the aquifers of Poble Sec and Besòs River Delta. Higher concentrations and more compounds were found in the Besòs River Delta aquifer, which is recharged by a river contaminated with treated effluent from numerous treatment plants. By contrast, the urban area of Poble Sec presented lower concentrations and fewer compounds. The results showed that CBZ could be attenuated in the Poble Sec aquifer since concentrations in groundwater were lower than those evaluated from mixing of the recharge sources. Conversely, CBZ and its human metabolites were not removed under the reducing conditions of the Besòs River Delta aquifer probably because of the short residence time in this aquifer.
To evaluate the potential for in situ bioremediation of U(VI) to sparingly soluble U(IV), we constructed a pilot test facility at Area 3 of the U.S. Department of Energy Natural and Accelerated ...Bioremediation Research (NABIR) Field Research Center (FRC) in Oak Ridge, TN. The facility is adjacent to the former S-3 Ponds which received trillions of liters of acidic plating wastes. High levels of uranium are present, with up to 800 mg kg-1 in the soil and 84−210 μM in the groundwater. Ambient groundwater has a highly buffered pH of ∼3.4 and high levels of aluminum (12−13 mM), calcium (22−25 mM), and nitrate (80−160 mM). Adjusting the pH of groundwater to ∼5 within the aquifer would deposit extensive aluminum hydroxide precipitate. Calcium is present in the groundwater at levels that inhibit U(VI) reduction, but its removal by injection of a high pH solution would generate clogging precipitate. Nitrate also inhibits U(VI) reduction and is present at such high concentrations that its removal by in situ denitrification would generate large amounts of N2 gas and biomass. To establish and maintain hydraulic control, we installed a four well recirculation system parallel to geologic strike, with an inner loop nested within an outer loop. For monitoring, we drilled three boreholes perpendicular to strike across the inner loop and installed multilevel sampling tubes within them. A tracer pulse with clean water established travel times and connectivity between wells and enabled the assessment of contaminant release from the soil matrix. Subsequently, a highly conductive region of the subsurface was prepared for biostimulation by removing clogging agents and inhibitors and increasing pH. For 2 months, groundwater was pumped from the hydraulically conductive zone; treated to remove aluminum, calcium, and nitrate, and supplemented with tap water; adjusted to pH 4.3−4.5; then returned to the hydraulically conductive zone. This protocol removed most of the aqueous aluminum and calcium. The pH of the injected treated water was then increased to 6.0−6.3. With additional flushing, the pH of the extracted water gradually increased to 5.5−6.0, and nitrate concentrations fell to 0.5−1.0 mM. These conditions were judged suitable for biostimulation. In a companion paper (Wu et al., Environ. Sci. Technol. 2006, 40, 3978−3987), we describe the effects of ethanol addition on in situ denitrification and U(VI) reduction and immobilization.
The objective of this work is to facilitate a sustainable regional planning of water resources in karst areas by providing a conceptual framework for an integrative vulnerability assessment. A ...combined mapping and modeling approach is proposed, taking into account both spatial and temporal aspects of karst groundwater vulnerability. The conceptual framework comprises the delineation of recharge areas, vulnerability mapping, numerical flow and transport modeling and the integration of information into a combined vulnerability map and time series. The approach is illustrated at a field site in northwest Switzerland (Gempen plateau). The results show that the combination of vulnerability mapping and numerical modeling allows the vulnerability distribution, both in the recharge and discharge areas, to be identified, and at the same time, the time dependence of karst groundwater vulnerability to be assessed. The combined vulnerability map and time series provide a quantitative basis for drinking water management and for regional planning.
Alluvial aquifers serve as one of the main water sources for domestic, agricultural, and industrial purposes globally. Groundwater quality, however, can be threatened by naturally occurring and ...anthropogenic metal contaminants. Differing hydrologic and biogeochemical conditions between predominantly coarse-grained aquifer sediments and embedded layers or lenses of fine-grained materials lead to variation in metal behavior. Here, we examine processes controlling Zn partitioning within a dual-pore domain-reconstructed alluvial aquifer. Natural coarse aquifer sediments from the Wind River-Little Wind River floodplain near Riverton, WY, were used in columns with or without fine-grained lenses to examine biogeochemical controls on Zn concentrations, retention mechanisms, and transport. Furthermore, following the introduction of Zn to the groundwater source, Zn preferentially accumulated in the fine-grained lenses, despite their small volumetric contributions. While the clay fraction dominated Zn retention in the sandy aquifer, the lenses supported additional reaction pathways of retention—the reducing conditions within the lenses resulted in ZnS precipitation, overriding the contribution of organic matter. Zinc concentration in the groundwater controlled the formation of Zn-clays and Zn-layered double hydroxides, whereas the extent of sulfide production controlled precipitation of ZnS. Our findings illustrate how both spatial and compositional heterogeneities govern the extent and mechanisms of Zn retention in intricate groundwater systems, with implications for plume behavior and groundwater quality.
Experimental investigations were carried out on removal of arsenic from contaminated groundwater by employing a new flat-sheet cross flow membrane module fitted with a hydrophobic ...polyvinylidenefluoride (PVDF) microfiltration membrane. The new design of the solar-driven membrane module in direct contact membrane distillation (DCMD) configuration successfully produced almost 100 per cent arsenic-free water from contaminated groundwater in a largely fouling-free operation while permitting high fluxes under reduced temperature polarization. For a feed flow rate of 0.120
m
3/h, the 0.13
μm PVDF membrane yielded a high flux of 74
kg/(m
2
h) at a feed water temperature of 40
°C and, 95
kg/m
2
h at a feed water temperature of 60
°C. The encouraging results show that the design could be effectively exploited in the vast arsenic-affected rural areas of South-East Asian countries blessed with abundant sunlight particularly during the critical dry season.
Solar-driven membrane distillation has the potential of removing arsenic from contaminated groundwater.
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