Arsenic Control During Aquifer Storage Recovery Cycle Tests in the Floridan Aquifer

Implementation of aquifer storage recovery (ASR) for water resource management in Florida is impeded by arsenic mobilization. Arsenic, released by pyrite oxidation during the recharge phase, sometimes results in groundwater concentrations that exceed the 10 µg/L criterion defined in the Safe Drinking Water Act. ASR was proposed as a major storage component for the Comprehensive Everglades Restoration Plan (CERP), in which excess surface water is stored during the wet season, and then distributed during the dry season for ecosystem restoration. To evaluate ASR system performance for CERP goals, three cycle tests were conducted, with extensive water‐quality monitoring in the Upper Floridan Aquifer (UFA) at the Kissimmee River ASR (KRASR) pilot system. During each cycle test, redox evolution from sub‐oxic to sulfate‐reducing conditions occurs in the UFA storage zone, as indicated by decreasing Fe²⁺/H₂S mass ratios. Arsenic, released by pyrite oxidation during recharge, is sequestered during storage and recovery by co‐precipitation with iron sulfide. Mineral saturation indices indicate that amorphous iron oxide (a sorption surface for arsenic) is stable only during oxic and sub‐oxic conditions of the recharge phase, but iron sulfide (which co‐precipitates arsenic) is stable during the sulfate‐reducing conditions of the storage and recovery phases. Resultant arsenic concentrations in recovered water are below the 10 µg/L regulatory criterion during cycle tests 2 and 3. The arsenic sequestration process is appropriate for other ASR systems that recharge treated surface water into a sulfate‐reducing aquifer.     

The Effectiveness of Arsenic Remediation from Groundwater in a Private Home

Private wells are the source of drinking water for approximately 15% of households in the United States, but these wells are not regulated or monitored by government agencies. The well waters can contain arsenic, a known carcinogen that occurs in groundwater throughout the nation at concentrations that can exceed the Maximum Contaminant Level defined by the U.S. Environmental Protection Agency (10 ppb). In order to reduce arsenic exposure, homeowners can either rely on bottled water for drinking or install in-house water treatment systems for arsenic removal. Here, we document the arsenic levels associated with these options. We examined 24 different major bottled water brands and found that all have arsenic levels <1.5 parts per billion (ppb), and more than half have levels below our measurement detection limit of 0.005 ppb. For in-house treatment systems, we examined the performance of arsenic removal by point-of-use reverse osmosis filtration, and by whole-house and point-of-use filters containing granulated ferric oxide. Our results show that long-term (2 years) filtration with granulated ferric oxide reduced arsenic in well water from an initial concentration of 4 to 9 ppb down to <0.005 ppb, validating this technology as an effective form of arsenic remediation for private homes.     

Risk characterization for arsenic-impacted water sources, including ground-truthing

One of the most severe issues for water supply in Bangladesh is high arsenic concentrations. Widespread implementation of tubewells was determined to be highly problematic due to arsenic contamination in the groundwater. For substantial areas in Bangladesh, groundwater cannot be utilized for water supply without treatment to reduce arsenic levels. Thus, calculations for the incremental excess lifetime cancer risk are used to demonstrate that indeed, seeing elevated arsenicosis must be expected. By observing the correlations between arsenic and iron and the prevalence of arsenicosis patients, the relationships among the concentrations of arsenic and iron, and the percentage of contaminated wells are significant for determining the prevalence of arsenicosis. The results declare that high arsenic concentrations and high percentages of contaminated wells, as well as the lower iron concentrations, lead to a higher prevalence of arsenicosis patients. It demonstrates the validity of the risk calculation procedure and single arsenic concentrations cannot provide good prediction of arsenicosis risk. When the concentration of arsenic and iron are both high, the ratio of arsenic/iron will decrease, and the arsenicosis rates will lessen, as well. The findings indicate that co-precipitation of iron and arsenic can remove some of the arsenic before the groundwater is consumed.     

The role of bromide and iodide ions in the salinization mapping of the aquifer of Glafkos River basin (northwest Achaia,Greece)

Seawater intrusion causes many problems for groundwater quality, whereas natural remediation is time consuming. However, in cases where groundwater replenishment is feasible, groundwater quality remediation is possible and rapid. The alluvial aquifer in the lowland of the Glafkos River basin, which extends south of Patras city, was for over 30 years the major water source supplying the broader area. Groundwater quality has been degraded due to seawater intrusion, caused by overpumping and generally by inappropriate groundwater management. During the last decade, groundwater quality has been remedied due to diminished groundwater abstractions. The remediation rate was further higher because of rapid discharge of the brackish groundwater, through wells with freely flowing water in the coastal area, where, however, groundwater quality remains low. This paper deals with the hydrogeochemical processes that take place in the area. It is ascertained that ion exchange and mineral dilution processes are dominant. The ion relations between chloride, bromide and iodide, as well as the distribution maps of their concentrations, were used to determine the spatial distribution of the seawater intrusion front. In the lower part of the area in a distance from 1000 and 1500 m from the coast, the rBr^?/rCl^? ratio showed low values (<2·5 × 10^?3) similar to those of seawater. The rI^?/rCl^? ratio also presented low values (<7 × 10^?5), with the lowest one (2·7 × 10^?5) detected along the coastline. In the upper part of the area, a gradual change of those ratios was observed upstream, until they receive values similar to those of the surface waters of Glafkos River. Copyright © 2007 John Wiley & Sons, Ltd.     

Evaluating the interactions between surface water and groundwater in the arid mid-eastern Yanqi Basin,northwestern China

The environment of Bosten Lake in the Mid-Eastern Yanqi Basin (MEYB), an arid inland area in northwest China, has deteriorated greatly due to increasing groundwater exploitation and changes in the interactions between groundwater and surface water. This study intended to simulate the spatio-temporal variability of groundwater and surface water across the entire MEYB over the period 2000–2013. The applicable groundwater flow model and mass balance calculation method for river water were constructed to evaluate the change in groundwater recharged by and discharged to different segments of the Kaidu River. Simulation results show that the entire river seepage in the MEYB increased from 1.05 to 6.17 × 10⁸ m³/year between 2000 and 2013. The increasing river seepage, induced by increasing groundwater exploitation, plays the most important role in the water level decline in the downstream reaches of the Kaidu River and in Bosten Lake. This implies that the current utilization of groundwater resources in the MEYB is unsustainable.     

Cancer risk estimation from dietary arsenic,a new approach from longitudinal cohort study

Inorganic arsenic is a carcinogen and consumption in low dose may lead to cancer. We estimated the cancer risk of the participants from arsenic endemic regions of West Bengal, India. The probable cancer risk was estimated following the assessment of daily inorganic arsenic intake through drinking water and diets of 20 participants for three consecutive years who had been using low arsenic water in the Indian context (median arsenic concentration in the study Years-I, II and III were 22, 16, 13 µg/l respectively). Probable cancer risk of the population was 2.80 × 10^?4, 2.94 × 10^?4, 3.12 × 10^?4 in the three respective study years (Year-I, II and III); just higher than the US EPA risk level of concern. The arsenic species content of the paired raw, cooked rice and urine was estimated in the as is taken basis. The major diet component, rice contained 72–86% inorganic arsenic whereas urine contains 70% organic arsenic on an average. The cancer risk assessment has been proposed to be modified by inclusion of urine arsenic release, considering the fact of arsenic release through urine. The risk became 1.28 × 10^?5, 1.13 × 10^?5, 1.01 × 10^?5 in the study Year-I, II and III respectively, considering urinary arsenic release, attributed the consideration of urine arsenic release into probable cancer risk estimation.     

Genesis of arsenic in groundwater of North Bengal Plain using PCA: A case study of English Bazar Block,Malda District,West Bengal,India

The study area is located on the western part of the alluvium‐filled gap between the Rajmahal hills on the west and the Garo hills on the east. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Three hydrochemical facies with distinct characteristics have been identified which are dominated in general by alkaline earths and weak acids. The major‐ion chemistry of the area is controlled by weathering of silicate minerals, rainfall recharge, ion‐exchange processes and anthropogenic activities such as irrigation return flow and the application of inorganic fertilizers and pesticides. A stoichiometric approach suggests that mineral dissolution and anthropogenic activities contribute 79% and 21% of the total cations dissolved in groundwater. Principal component analysis (PCA) of 42 groundwater samples using 13 chemical parameters indicates that the combined processes of recharge of groundwater from rainfall, sediment water interaction, groundwater flow, infiltration of irrigation return water (which is arsenic rich due to the use of arsenic‐bearing pesticides, wood preservatives, etc. and the pumping of arsenic‐rich groundwater for agriculture purpose), oxidation of natural or anthropogenic organic matter and the reductive dissolution of ferric iron and manganese oxides play a key role in the evolution of groundwater in the study area. Factor 2 scores, associated with the infiltration of irrigation return water and spatial distribution of arsenic concentration reveal that the groundwater of the municipal area will not be affected by arsenic in the future in spite of heavy groundwater abstraction. Another PCA with geologic, geomorphic, anthropogenic, geochemical and landuse factors indicates that arsenic concentration in groundwater increases with increasing area of mango orchards, sand lithofacies and nitrate and decreases with increasing distance of paleochannel from the monitored well and depth of bore wells. High loading on nitrate may be attributed to the use of fertilizer, pesticides, etc. in mango orchards and agricultural land. High loadings on log pCO₂, mango orchards (with negative sign) and phosphate (with positive sign) indicate that mango orchards provide the organic waste material which is decomposed to form organic carbon. The organic carbon undergoes oxidative carbon degeneration by different oxidants and increases the concentration of CO₂ in the aquifer. The reducing condition thus developed in the aquifer helps to dissolve the arsenic adsorbed on iron hydroxide or oxy‐hydroxide coated margins of sand, iron rich heavy mineral grain margins, clay minerals and Fe–Mn concretions present in the aquifer matrix. Copyright © 2007 John Wiley & Sons, Ltd.     

Arsenic Remediation Field Study Using a Sulfate Reduction and Zero‐Valent Iron PRB

Toxic and carcinogenic effects of arsenic in drinking water continue to impact people throughout the world and arsenic remains common in groundwater at cleanup sites and in areas with natural sources. Advances in groundwater remediation are needed to attain the low concentrations that are protective of human health and the environment. In this article, we present the successful use of a permeable reactive barrier (PRB) utilizing sulfate reduction coupled with zero‐valent iron (ZVI) to remediate the leading edge of a dissolved arsenic plume in a wetland area near Tacoma, Washington. A commercially available product (EHC‐M®, Adventus Americas Inc., Freeport, Illinois) that contains ZVI, organic carbon substrate, and sulfate was injected into a reducing, low‐seepage‐velocity aquifer elevated in dissolved arsenic and iron from a nearby, slag‐containing landfill. Removal effectiveness was strongly correlated with sulfate concentration, and was coincident with temporary redox potential (Eh) reductions, consistent with arsenic removal by iron sulfide precipitation. The PRB demonstrates that induced sulfate reduction and ZVI are capable of attaining a regulatory limit of 5 µg/L total arsenic, capturing of 97% of the arsenic entering the PRB, and sustaining decreased arsenic concentrations for approximately 2 years, suggesting that the technology is appropriate for consideration at other sites with similar hydrogeochemical conditions. The results indicate the importance of delivery and longevity of minimum sulfate concentrations and of maintaining sufficient dissolved organic carbon and/or microscale ZVI to precipitate FeS, a precursor phase to arsenic‐bearing pyrite that may provide a stable, long‐term sink for arsenic.     

Characterizing replenishment water,lake water and groundwater interactions by numerical modelling in arid regions: a case study of Shahu Lake

In order to maintain the scenic and eco-environmental values of a lake, we need to characterize its water interactions. Shahu Lake was used as a case study to show the interactions among replenishment water, lake water and groundwater in an arid region. Shahu Lake is located in the Ningxia Hui Autonomous Region of northwest China and has an area of 13.96 km² and an average depth of 2.2 m. The groundwater modelling software MODFLOW was used. The analysis results show that hydraulic connectivity among replenishment water, lake water and groundwater is the crucial driving factor that affects the water level in Shahu Lake. The lake water level is highly sensitive to the volume of replenishment water. The groundwater is of great importance in balancing the water level in the lake and preventing it from drying up. It was determined that 13.8 × 10⁶ m³/yr is the optimal volume of replenishment water for Shahu Lake in order to maintain the lake level at its normal state and also to make the best use of available water resources on a long-term basis. Understanding of the water interactions can promote effective management of water resources in Shahu Lake.

EDITOR D. Koutsoyiannis

ASSOCIATE EDITOR D. Hughes     

Environmental isotopic and hydrochemical characteristics of groundwater systems in Daying and Qicun geothermal fields,Xinzhou Basin,Shanxi, China

The conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad‐scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO₄‐Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (>0·8 g/l) and Sr contents, but relatively low Ca, Mg and HCO₃ contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and ¹⁴C activities indicate that deep non‐thermal groundwater (130–160 m) in the Daying region range from modern (post‐1950s) in the piedmont area to more than 9·4 ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active ¹⁴C, indicating long residence times (>50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = ? 23·8 × δ²H (‰ ) ? 121·3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 10³ and 4107 × 10³ m³/a, respectively. The variable ⁸⁶Sr/⁸⁷Sr values in the thermal and non‐thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water‐rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water‐rock interaction processes that occur under different scenarios. Copyright © 2010 John Wiley & Sons, Ltd.     

A combined methodology for estimating the potential natural aquifer recharge in an arid environment

ABSTRACT

An innovative methodology that combines an indirect physiography-based method for determining the runoff coefficient at a sub-basin scale and a water balance model applied on a daily time scale was developed to calculate the natural groundwater recharge in three watersheds within the Oum Zessar arid area, Tunisia. The effective infiltration was calculated as part of the water surplus by considering the average available water content (AWC) of soil and an average runoff coefficient for each sub-basin. The model indicates that the sub-basins covered mainly by the “artificial” soils of tabias and jessour, characterized by average AWC values greater than 150 mm, did not contribute to natural groundwater recharge over the 10-year period (2003–2012) considered. The estimated volume for the Triassic aquifer amounted to about 4.5 hm³ year^?1, which is consistent with previous studies. For the Jurassic and Cretaceous aquifers, the estimated volumes amounted to about 200 dm³ year^?1.     

Electrical resistivity imaging and hydrochemical analysis for groundwater investigation in Kuala Langat,Malaysia

ABSTRACT

Integrated two-dimensional electrical resistivity imaging (ERI) and hydrochemical surveys were used to investigate the groundwater alluvial aquifer in Kuala Langat, Malaysia. The study in the Langat basin considered the thickness of the aquifer, the depth of the bedrock, the regions influenced by seawater intrusion, and the monitoring of water levels. The resistivity imaging results show that the upper layer consists of clay, while the second layer is an aquifer whose thickness varies mostly in the range of 10–30 m, and in some cases extends to 40 m. The bedrock depth varies from 30 to 65 m. The chemical analyses were carried out on groundwater samples from nine boreholes collected between 2008 and 2012. The analyses indicate that the total dissolved solids (TDS) exceed 1000 mg L^-1 near the coastal area and are often less than 500 mg L^-1 further inland. The ERI and hydrochemical analyses reveal that groundwater in the study area, especially towards the coast, is a mixture of brackish and fresh waters.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR M.D. Fidelibus     

Estimating groundwater recharge using the chloride mass-balance method in the West Bank,Palestine

Abstract

The quantification of natural recharge rate is a prerequisite for efficient and sustainable groundwater resources management. Since groundwater is the only source of water supply in the West Bank, it is of utmost importance to estimate the rate of replenishment of the aquifers. The chloride mass-balance method was used to estimate recharge rates at different sites representing the three groundwater basins of the Mountain Aquifer in the West Bank. The recharge rate for the Eastern Basin was calculated as between 130.8 and 269.7 mm/year, with a total average replenishment volume of 290.3 × 10⁶ m³/year. For the Northeastern Basin, the calculated recharge rate ranged between 95.2 and 269.7 mm/year, with a total average recharge volume of 138.5 × 10⁶ m³/year. Finally, the recharge rate for the Western Basin was between 122.6 and 323.6 mm/year, with a total average recharge volume of 324.9 × 10⁶ m³/year. The data reveal a replenishment potential within the estimated replenishment volumes of previous studies for the same area. Also, the range was between 15 and 50% of total rainfall, which is still within the range of previous studies. The geological structure and the climate conditions of the western slope were clearly play an important role in the increment of total volume. In some cases, such as the geological formations in the Northeastern Basin, the interaction between Eocene and Senonian chalk formations result in minimum recharge rates.

Citation Marei, A., Khayat, S., Weise, S., Ghannam, S., Sbaih, M. & Geyer, S. (2010) Estimating groundwater recharge using the chloride mass-balance method in the West Bank, Palestine. Hydrol. Sci. J. 55(5), 780–791.     

Arsenic and other water‐quality issues affecting groundwater,Indus alluvial plain,Pakistan

Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain in southern Sindh Province, concentrations of As exceeded the WHO guideline value for drinking water of 10 μg/L in 38%, with 22% exceeding 50 μg/L, Pakistan's guideline value. The As pollution is caused by microbially‐mediated reductive dissolution of sedimentary iron oxyhydroxides in anoxic groundwaters; oxic groundwaters contain <10 μg/L of As. In the upper Indus River plain, in Punjab Province, localized As pollution of groundwater occurs by alkali desorption as a consequence of ion exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion exchange in the aquifer and so has values >0 for residual sodium carbonate. In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (electrical conductivity up to 6 mS/cm). High salinities result from local inputs of waste water from unsewered sanitation but mainly from evaporation/evapotranspiration of canal water and groundwater used for irrigation. The process does not concentrate As in the groundwater owing to sorption of As to soils. Ion exchange exerts a control on concentrations of Na, Ca, and B but not directly on As. High values of Cl/Br mass ratios (most ?288, the marine value) reflect the pervasive influence on groundwater of sewage‐contaminated water from irrigation canals through seepage loss and deep percolation of irrigation water, with additional, well‐specific, contributions from unsewered sanitation.     

Groundwater recharge and discharge in a hyperarid alluvial plain (Akesu,Taklimakan Desert,China)

Groundwater recharge and discharge in the Akesu alluvial plain were estimated using a water balance method. The Akesu alluvial plain (4842 km²) is an oasis located in the hyperarid Tarim River basin of central Asia. The land along the Akesu River has a long history of agricultural development and the irrigation area is highly dependent on water withdrawals from the river. We present a water balance methodology to describe (a) surface water and groundwater interaction and (b) groundwater interaction between irrigated and non‐irrigated areas. Groundwater is recharged from the irrigation system and discharged in the non‐irrigated area. Uncultivated vegetation and wetlands are supplied from groundwater in the hyperarid environment. Results show that about 90% of groundwater recharge came from canal loss and field infiltration. The groundwater flow from irrigated to non‐irrigated areas was about 70% of non‐irrigated area recharge and acted as subsurface drainage for the irrigation area. This desalinated the irrigation area and supplied water to the non‐irrigated area. Salt moved to the non‐irrigation area following subsurface drainage. We conclude that the flooding of the Akesu River is a supplemental groundwater replenishment mechanism: the river desalinates the alluvial plain by recharging fresh water in summer and draining saline regeneration water in winter. Copyright © 2007 John Wiley & Sons, Ltd.     

A water balance model to estimate climate change impact on groundwater recharge in Yucatan Peninsula,Mexico

ABSTRACT

The aim of this paper is to estimate the effect that climate change will have on groundwater recharge at the Yucatan Peninsula, Mexico. The groundwater recharge is calculated from a monthly water balance model considering eight methods of potential and actual evapotranspiration. Historical data from 1961–2000 and climate model outputs from five downscaled general circulation models in the near horizon (2015–2039), with representative concentration pathway (RCP) 4.5 and 8.5 are used. The results estimate a recharge of 118 ± 33 mm·year^–1 (around 10% of precipitation) in the historical period. Considering the uncertainty from GCMs under different RCP and evapotranspiration scenarios, our monthly water balance model estimates a groundwater recharge of 92 ± 40 mm·year^–1 (RCP4.5) and 94 ± 38 mm·year^–1 (RCP8.5) which represent a reduction of 23% and 20%, respectively, a result that threatens the socio-ecological balance of the region.     

Oxidation and emission of methane in a monomictic lake (Rotsee, Switzerland)

The build-up of methane in the hypolimnion of the eutrophic Lake Rotsee (Lucerne, Switzerland) was monitored over a full year. Sources and sinks of methane in the water column were characterized by measuring concentrations and carbon isotopic composition. In fall, high methane concentrations (up to 1 mM) were measured in the anoxic water layer. In the oxic layer, methane concentrations were much lower and the isotopic composition shifted towards heavy carbon isotopes. Methane oxidation rates peaked at the interface between oxic and anoxic water layers at around 8–10 m depth. The electron balance between the oxidants oxygen, sulphate, and nitrate, and the reductants methane, sulphide and ammonium, matched very well in the chemocline during the stratified season. The profile of carbon isotopic composition of methane showed strong indications for methane oxidation at the chemocline (including the oxycline). Aerobic methane oxidizing bacteria were detected at the interface using fluorescence in situ hybridization. Sequencing the responsible organisms from DGGE bands revealed that aerobic methanotrophs type I closely related to Methylomonas were present. Sulphate consumption occurred at the sediment surface and, only towards the end of the stagnation period, matched with a zone of methane consumption. In any case, the flux of sulphate below the chemocline was not sufficient to oxidize all the methane and other oxidants like nitrate, iron or manganese are necessary for the observed methane oxidation. Although most of the methane was oxidized either aerobically or anaerobically, Lake Rotsee was still a source of methane to the atmosphere with emission rates between 0.2 mg CH₄ m^?2 day^?1 in February and 7 mg CH₄ m^?2 day^?1 in November.     

Risk-based assessment of arsenic-affected aquacultural water in blackfoot disease hyperendemic areas

This work explored a risk-based arsenic (As) regulation in farmed pond water by ingesting tilapia (Oreochromis mossambicus) in blackfoot disease hyperendemic areas and discussed a rational As regulation in pond water. Monte Carlo analysis was used to propagate the parameter uncertainty and to assess probabilistically regulation risks. A dynamic scheme of groundwater management was proposed that curves of utilization ratios against As concentrations in groundwater were established based on the risk-based regulation. The 5th to 95th percentiles of risks range from 3.5 × 10⁻⁷ to 6.0 × 10⁻⁵ via ingesting the farmed tilapia under the current As regulation in farmed pond water in Taiwan, 50 μg/L. To compare to inorganic As regulation in drinking water, the current As regulation in farmed pond water does not pose a great threat to human health, but it is unsafe. Therefore, this study suggests that the regulation of As in farmed pond water is revised to be 25 μg/L.     

Uranium and boron distributions in some oceanic ultramafic rocks

From mica fission-track maps the serpentinized and weathered portions of four ultramafic rocks from oceanic ridge systems contained 0.5 to 2.4 ppm U compared to only 2.5 ppb in clinopyroxene, 0.6 ppb in chromite and less than 7.0 ppb in olivine. Orthopyroxene grains contained 0.4 ppb U which is three orders of magnitude lower than had previously been reported.Long thin tracks from (n, α) reactions with boron were recorded in cellulose nitrate plastic and were counted like fission tracks. The track density from boron was 2×10⁴ times higher than that from uranium fission alone. Boron in serpentine was variable on a 50-μm scale attaining 155 ppm concentrations. Orthopyroxene grains, in contrast, had maximum concentrations of 0.8 ppm.Most of the uranium and boron in the rocks is believed to have been introduced during serpentinization. From known crystal-melt partitioning ratios the uranium and boron distributions are consistent with the ultramafic rocks being cumulates or residues from partial melting events.     

An integrated water balance model for assessing water scarcity in a data-sparse interfluve in eastern India

Abstract

The objective of this study is to measure the balance of water demand versus water resource availability in an interfluve of West Bengal, India to support water resource planning, particularly of inter-basin transfers. Surface water availability was modelled using the US Soil Conservation Service curve number (SCS-CN) approach, whilst groundwater availability was modelled based on water-level fluctuations and the rainfall infiltration method. Water use was modelled separately for the agricultural, industrial, and domestic sectors using a predominantly normative approach and water use to availability ratios calculated for different administrative areas within the interfluve. Overall, the approach suggested that the interfluve receives 327 × 10⁶ m³ year^-1 of excess water after satisfying these sectoral demands, but that the eastern part of the study area is in deficit. However, a sensitivity analysis carried on the approach to several assumptions in the model suggested changed circumstances would produce surplus/deficit ranging from ?215 × 10⁶ to 435 × 10⁶ m³ year^-1 . The approach could have potential for localised water balance modelling in other Indian catchments.

Editor D. Koutsoyiannis; Associate editor D. Hughes