Dolomite Aquifer Research Articles

Quantitative classification of carbonate aquifers based on hydrodynamic behaviour

A quantitative classification of carbonate aquifers based on hydrodynamic behaviour is introduced. This type of classification is necessary to understand the physical functioning of carbonate hydrogeological systems and to provide a realistic interpretation of field data. Carbonate aquifers are generally considered as karst systems; however, geomorphology and aquifer geology alone are insufficient for determining hydrodynamic behaviour. Analysis of spring and well hydrographs based on analytical solutions is applied to establishing a quantitative classification. A base-flow recession coefficient is used as an indicator of hydrodynamic behaviour. Detailed numerical analyses suggest that carbonate systems can be classified into two distinct groups based on hydrodynamic behaviour. The physical processes depend on a combination of hydraulic and geometric parameters, and their functional relationships can be quantitatively determined. The proposed classification methodology involves making an assumption about aquifer type, estimating aquifer properties from hydrograph data, and comparing the results with field observations. The proposed classification methodology was applied to aquifers representing the two groups of carbonate systems. In both cases, the applied methods revealed crucial information about hydrodynamic functioning of the investigated systems. While the studied limestone aquifer showed karstic hydrodynamic behaviour, the investigation of a dolomite aquifer disproves a priori assumptions on karstic flow conditions. Dolomite aquifers represent an ambiguous group of carbonates and require caution in the selection of investigation tools and interpretation of hydrogeological data. The introduced methodology provides a reliable means of determining the hydrodynamic functioning of an aquifer and supports the quantitative classification of carbonate hydrogeological systems.

A Systemic Analysis of the Environmental Impacts of Gold Mining within the Blyde River Catchment, a Strategic Water Area of South Africa

Exploratory modelling of the impact of gold mining on groundwater in a strategic water area of South Africa was undertaken. A systems dynamics (SD) model was developed to simulate the impact of gold mining on water quality, focusing on groundwater contamination risk, within the context of competing developmental priorities around water resource development and the socio-economic gains from gold mining. The model also identified interventions to minimise the impacts by the year 2040. The study area was the Blyde River Catchment (BRC), which is part of the Olifants Water Management Area in South Africa. This area is an important contributor, currently and in the future, to freshwater flows and groundwater in the Olifants River Catchment, which is one of South Africa’s most economically important catchments. The model development process included a causal loop diagram­–based problem conceptualisation, followed by the drawing of stock-flow diagrams and the determining of model parameters based on a combination of background literature, data from environmental impact assessments, and from the national Department of Water and Sanitation. The model showed the potential environmental risks of gold mine wastewater production and interventions to minimise these risks. The most effective intervention identified to reduce the risk of groundwater contamination was the development and use of synthetic-lined tailings dams. The baseline simulation result of sulphate loading of 5430 t/year can be reduced by 3070 t/year to give a simulated sulphate load of 2270 t/year in 2040 using this intervention. In comparison, the simulated wastewater recycling intervention only reduced the sulphate load to 4630 t/year and the wastewater treatment interventions to 3420 t/year. This project contributes to the exploratory modelling of an understudied region of the Olifants River Catchment that is a crucial provider of freshwater flows to the Olifants, which is threatened by increasing gold mining in the upper BRC. The SD model highlighted the importance of protecting the dolomitic aquifers in the BRC for the long term sustainability of the catchment, which is particularly important if groundwater development occurs.

Drinking Water Quality and Provision in Six Low-Income, Peri-Urban Communities of Lusaka, Zambia.

Lusaka, Zambia, is a rapidly growing city located on a vulnerable karstic dolomite aquifer that provides most of the city's drinking water. Over 65% of residents live in peri‐urban communities with inadequate sanitation leading to widespread groundwater contamination and the spread of waterborne diseases such as cholera. To fill the water service gap, Water Trusts were created: public/private partnerships designed to provide clean water to peri‐urban community residents. Water Trusts extract groundwater via boreholes, treat it with chlorine, and distribute it to residents via public kiosks. We investigated the efficacy of drinking water provision to residents in six of Lusaka's peri‐urban communities with Water Trusts. Water samples were collected from Water Trust boreholes and kiosks, privately owned boreholes, and shallow wells during four sampling efforts. To assess potential risk to human health, water samples were analyzed for Escherichia coli (E. coli) and nitrate. Shallow wells were significantly more contaminated with E. coli than Water Trust boreholes, kiosks, and private boreholes (Tukey‐adjusted p values of 9.9 × 10−6). Shallow wells and private boreholes had significantly higher nitrate‐N concentrations (mean of 29.6 mg/L) than the Water Trust boreholes and kiosks (mean of 8.8 mg/L) (p value = 1.1 × 10−4). In 2016, a questionnaire was distributed to Water Trust managers to assess their ability to meet demands. In the six communities studied, Water Trusts served only about 60% of their residents. Water Trusts provide a much safer alternative to shallow wells with respect to nitrate and E. coli, but they struggle to keep pace with growing demand.

Recharge, élévation retardée du niveau des eaux souterraines et rendement spécifique au sein de l’aquifère karstique du Trias de la montagne Kopa, dans les Carpates occidentales, Slovaquie

Notable delay of more than 1 year (12.5–15.9 months) between precipitation recharge and groundwater-level upturn was recorded in the Triassic karstic aquifer of the Kopa Mt. (1,187 m asl) in the middle of the West Carpathians in Slovakia. The velocity of recharge transit (0.24–0.70 m/day) was affirmed by borehole hydrographs. The groundwater level here is deep (113–300 m below ground surface) but approximately evenly distributed at the same elevation (~467 ± 10 m asl). Dolomites extend over 78% of the surface area of the karstic reservoir, with a Cretaceous marly aquitard boundary on the perimeter and on its base. The whole area is recharged merely by precipitation and entirely discharged by springs and small surface streams. The water balance between recharged and discharged water, and the groundwater-level fluctuation (shift in time), enabled calculation of stored groundwater volumes. The estimated specific yield of the Triassic dolomitic aquifer was unusually high (7.6–23.4%, mean 16.1%). Karstic cavities were also widely found in the borehole logs of nine boreholes that were 87–490-m deep and drilled in Triassic dolomites and limestones along the axis of a planned highway tunnel. Groundwater level monitoring took place over 40 months, between June 2014 and October 2017. Typical seasonal water-level oscillations were absent in the karstic reservoir, but water-level change was relevant to delayed past recharge events. In a borehole situated in the Cretaceous marly aquitard, good seasonal correlation with effective precipitation and also tidal response was observed.

Assessing the Karst Groundwater Quality and Hydrogeochemical Characteristics of a Prominent Dolomite Aquifer in Guizhou, China

Karst groundwater is one of the primary water resources in most provinces of Southwestern China where karst topography is strongly featured. In Guizhou Province, a prominent geologic sedimentary formation is the dolomite stratum which exists as the restricted platform facies and potentially provides a large reservoir for drinking water. A proper understanding and evaluation of its hydrogeochemical characteristics and water quality is the key to ensuring the drinking water safety. In the present study, groundwater samples were collected from 25 locations of the dolomite aquifer across Guizhou to determine their major chemical compounds, including the cations (K+, Na+, Ca2+, Mg2+) and the anions (HCO3−, F−, Cl−, NO3−, SO42−), as well as the pH, total hardness, and total dissolved solids. HCO3− and Ca2+ were found to be the dominant anion and cation, respectively, which is characteristic of typical karst groundwater and supports the overall observation of a slightly weak acid to weak alkaline environment in the studied groundwater, as the pH measurements ranged from 6.80 to 8.37. Fuzzy comprehensive evaluation method is used to evaluate the groundwater quality based on typical drinking water safety standard. The results show that the groundwater in most of the studied aquifers is of reasonably good quality. However, in some aquifers, concentrations of NO3− and/or SO42− were found to be excessively high. Overall, the studied dolomite aquifer in its natural environment as investigated in the present study can be considered as a potential geological stratum for water resources exploitation in Guizhou.

In-depth prospection of Avène Thermal Spring Water reveals an uncommon and stable microbial community.

Avène Thermal Spring Water (TSW) exhibits therapeutic properties in the treatment of skin pathologies. Arising from a dolomitic aquifer system, its physico-chemical properties are well-established and its bacteriological quality regularly monitored. The microbiota of this aquifer have been characterized. We aimed to describe the structure of the bacterial community inhabiting the deep aquifer and to examine its dynamics over time. The Avène TSW was collected at the catchment point and filtered through 0.1µm pore size filters. The sampling was carried out every 3months to generate a 4-year time series. The DNA extracted from filters was analysed using high-throughput 16S rRNA gene amplicon sequencing, and the microorganisms and their contribution were characterized by the taxonomic assignment of sequence variants generated from each sample. Bacteria were distributed into 39 phyla. Nitrospirae and Proteobacteria were the most prevalent, accounting for 38% and 23% of the total community on average, respectively. A stable pattern was observed throughout the study. A few bacterial species were always detected, forming a core community of likely chemolithoautotrophic organisms which might use energy sources and nutrients produced from water-bedrock interactions. Most of the species were distantly related to organisms described to date. Avène TSW provided by the deep aquifer system harbours a unique microbial community, shaped by the physico-chemical characteristics of the deep environment. Its remarkable stability over time has revealed a high level of confinement of the water resource.

Assessment of water resources quality of a karstic aquifer in the Southwest of Iran

In this study, the pollution risks related to arsenic, fluorine, iron, physicochemical parameters, and various indices have been investigated in the Bazoft dam site. The proposed dam is a double-curvature arch dam with a height of 211 m in order to produce hydroelectric energy and the supply of agricultural and drinking water in the west of Iran. Chemical analysis of water samples obtained from springs, river, and boreholes in the dam site was conducted. Anions such as HCO3, Cl, SO4, CO3, and NO3, and cations including Ca, Na, Mg, K, F, Fe, and As had the highest amounts, respectively. The concentration of assessed variables was lower than the WHO permissible limit. The results of the principal factor analysis (PCA) showed that four factors control 82% of the water quality variations. The factors such as EC, TDS, Na, K, SO4−, CO3, HCO3, total hardness, and alkalinity with 43.10% were the most important factors in the dam site. The heavy metals of iron and arsenic have no meaningful relationship with any of the ions. The accuracy of the relations was investigated based on different statistical criteria. The main processes in controlling the water quality are weathering and the dissolution of the carbonates caused by the interaction of water and rock. Ionic ratios indicated that the water origin of the springs is the dolomitic aquifers and the main source of magnesium is carbonate dissolution. The water resources of the dam site are corrosive, and all indices indicate the appropriate quality of water for irrigation and drinking purposes. Filed studies and boreholes water level variations showed that karstification is limit in the dam site.

Reactive transport modeling of produced water disposal into dolomite saline aquifers: Controls of barium transport

Experimental results on barium transport in dolomite are used to formulate, calibrate, and validate a reactive transport model of produced water disposal into dolomite saline aquifers. The model accounts for sorption, dissolution/precipitation reactions of minerals (dolomite, calcite, barite, gypsum, and witherite) and complexation and acid-base reactions of most abundant ionic species (H+, HCO3−, SO42−, Ca2+, Mg2+, and Cl−) in produced waters including Ba2+ which is the most common and abundant heavy metal present in produced water from oil and gas reservoirs. The model is applied to determine the chemical controls of barium transport in Arbuckle dolomite aquifers. The simulated scenario corresponds to produced water disposal through a Class II injection well located near an abandoned well that can facilitate the transport of barium to underground sources of drinking water (USDW). Simulation results reveal that most suitable dolomite aquifers to prevent the contamination of USDW by barium are dolomite aquifers of high SO42− content (>1000 mg/L). The mobility of barium which is promoted by the formation of Ba(Cl)+ and competition of cations (Ca2+ and Mg2+) for hydration sites of dolomite can be suppressed by the precipitation of barium as barite in dolomite saline aquifers of high SO42− content. A sensitivity analysis conducted using a two-level factorial design of experiments indicates that barium transport can be controlled by the initial concentration of a single ionic specie (mostly SO42−) or the concentration of various ionic species (e.g., SO42−, Cl−, and Mg2+). This depends on the chemical composition of both the dolomite saline aquifer and injection produced water. This work highlights the potentiality of a reactive transport simulation approach to conduct compatibility analysis of dolomite saline aquifers and produced waters to select dolomite aquifers and/or decide on treatment methods to prevent the contamination of USDW by barium.

Geothermische Nutzung eines alpinen Aquifers – Pilot Studie Davos

Topographically induced Alpine regional groundwater flow systems below the unconsolidated valley fillings constitute a substantial unused geothermal resource. Within the framework of the INTERREG VB project GRETA (shallow geothermal energy in the Alpine region), we developed a method to quantify the groundwater flux of complex alpine aquifers. The basis of the study is a regional-scale hydraulic groundwater model, which is based on a 3D tectonic model of the Davos region in Switzerland. Based on data from a large pumping test, we were able to calibrate the hydraulic model and to calculate basics for various usage scenarios of energetic exploitation for the Arosa Dolomite aquifer. Favourable conditions for an energetic exploitation are related to large-scale topography differences between groundwater recharge and potential exfiltration areas in the valleys, thanks to the 3D geometry of the large-area tectonic nappe units with their root zone located within river valleys. In general, the proposed concept could be applied to manifold similar geological and hydrogeological settings of the Alpine belt.

Hydrogeochemical controls on aquifers of northwestern Illinois’ Driftless Area, USA

Groundwater in the Driftless Area of northwestern Illinois is a very hard Ca–Mg-bicarbonate-type water that reflects the dolomite aquifer material in this karst region. Groundwater in shallow aquifers has a short residence time and is susceptible to surface-borne contaminants. Deeper aquifers have distinct chemistry indicating longer flowpaths, most clearly indicated by low tritium values and elevated potassium and fluoride concentrations. Thirty water samples were collected from springs from across Jo Daviess County in northwestern Illinois between 2015 and 2016. The groundwater samples collected from what were initially identified as springs were found to be of two types: (1) natural springs that are stratigraphically controlled and discharging from crevices and bedding planes, especially where the underlying Galena Dolomite or overlying Silurian dolomite aquifer intersects the Maquoketa Shale; and (2) abandoned flowing-artesian wells, often with no identifiable well casing at the surface, that had been mistaken for springs. Background concentrations of eight water-quality parameters were calculated to determine pre-settlement and present-day background thresholds. The background concentrations, overall chemical compositions, tritium concentrations, and F/Cl and K/Cl ratios were used to characterize and group groundwater within the study area. The results of this investigation combined with recent work by the authors [Panno et al. (IL State Geological Survey Circular 586, 2017)] were used to determine the geologic, hydrogeologic, and geochemical controls on springs in this part of the Driftless Area. The results of this investigation revealed the susceptibility of the Galena Dolomite and Silurian dolomite aquifers to surface-borne contaminants. In addition, this work has developed a means, using ion ratios and spring location relative to bedrock geology to identify discharge from abandoned wells.

Hydrochemical and isotopic approach to dynamic recharge of a dolomite aquifer in South Africa

The dolomite aquifer is the largest water source in northern South Africa. The flow dynamics of the dolomite aquifer is investigated by using analyses of the hydro-chemical parameters and isotopes (3H, δ2H, δ18O, δ13C-DIC and 14C-DIC) of spring samples. Recharge areas of the dolomite aquifer are confirmed through interpretation of the hydro-geochemical types of the spring samples. The important role of rainfall in groundwater recharge is suggested by low Na+ and Cl− concentrations and by the δ2H and δ18O values of the spring samples. Groundwater mean residence time (MRT) and its temporal and spatial distributions within the young dolomite spring system can be analyzed using an improved lumped-parameter model based on the time series of 14C-DIC, initial 14C activities and δ13C-DIC values of the spring samples collected during the 1970s and 2000s. The results show that the spring samples have about 50–80% of the initial 14C activities and the MRTs of the dolomite spring system range from ≤10–51 years. At five spring sites, the temporal distributions of groundwater MRTs are identified to be significantly influenced by the variability of the local rainfall. At the Kuruman sites only, an increasing trend of the groundwater MRTs and the evolution of the [Ca2+]/[Mg2+] ratio along the flow direction indicate an important role of deep groundwater inflow to the spring flow. The results provide basic scientific information required for sustainable management of the dolomite aquifer.

Using Hydrogeophysical Techniques to Characterise and Map Sea Water Intrusion and Preferential Flow Paths in Howards East Aquifer, Darwin Rural Area, Northern Territory

In the Howards East Aquifer (HEA) in Darwin’s Rural District, groundwater resources in a dolomitic and karstic aquifer system provide important water security for Darwin and a large horticultural i...

Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area, South Africa

Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ18O and δ2H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m3 from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO2 as a dominant source of carbon (δ13C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.

Automated Time Series Measurement of Microbial Concentrations in Groundwater-Derived Water Supplies.

Fecal contamination by human and animal pathogens, including viruses, bacteria, and protozoa, is a potential human health hazard, especially with regards to drinking water. Pathogen occurrence in groundwater varies considerably in space and time, which can be difficult to characterize as sampling typically requires hundreds of liters of water to be passed through a filter. Here we describe the design and deployment of an automated sampler suited for hydrogeologically and chemically dynamic groundwater systems. Our design focused on a compact form to facilitate transport and quick deployment to municipal and domestic water supplies. We deployed a sampler to characterize water quality from a household well tapping a shallow fractured dolomite aquifer in northeast Wisconsin. The sampler was deployed from January to April 2017, and monitored temperature, nitrate, chloride, specific conductance, and fluorescent dissolved organic matter on a minute time step; water was directed to sequential microbial filters during three recharge periods that ranged from 5 to 20 days. Results from the automated sampler demonstrate the dynamic nature of the household water quality, especially with regard to microbial targets, which were shown to vary 1 to 2 orders of magnitude during a single sampling event. We believe assessments of pathogen occurrence and concentration, and related assessments of drinking well vulnerability, would be improved by the time‐integrated characterization provided by this sampler.

Assessing groundwater recharge in crystalline and karstic aquifers of the Upper Crocodile River Basin, Johannesburg, South Africa

Groundwater recharge and flow conditions were assessed in the Upper Crocodile River Basin, Johannesburg South Africa. This study revealed high elevation recharge from rainfall that is depleted in stable isotopes of water molecule (δ18O and δ2H) occurring prior to extreme evaporation. The effective recharge occurs from rainfall of varying moisture source and humidity conditions. The δ13C (‰) value in groundwater indicates both open and closed system carbon evolution. Open system was observed in shale, andesite and granitic gneiss aquifers indicating that soil CO2 is a dominant source of carbon in bicarbonate. Enriched δ13C observed in Malmani dolomite aquifers deduced the presence of carbonate dissolution, which indicates a closed system carbon evolution. Mixing of water from open and closed systems, or evolution from closed to open system is also observed in groundwater samples that had intermediate δ13C (‰) values, particularly groundwater samples that are positioned at the periphery of the Basement Complex granitic gneiss near the Malmani dolomite aquifers. The integrated mean annual recharge estimates obtained from BFS for the UCRB is 6.7% while the distributed point recharge estimates in the Malmani dolomite obtained from application of WTF on 43 individual boreholes ranged between 2.5% and 39% with an average of 15% as a percentage of MAP. A comparison between estimated recharge and groundwater abstractions conducted for each sub-catchment revealed that there is an excess of groundwater recharge over groundwater use in most sub-catchments. The CMB point recharge estimates obtained from the Albert Farm spring and the Malmani dolomite springs are 2.5% and 27.8% of MAP, respectively. The low CMB recharge estimates in the shale and quartzite has been attributed to possible anthropogenic chloride sources such as leakage of chlorinated potable water in the pipelines of the city of Johannesburg, which elevate chloride concentrations in groundwater.

An updated water balance for the Grootfontein aquifer near Mahikeng

The Grootfontein Aquifer, part of the important North West dolomite aquifers, supplies about 20% of Mahikeng’s domestic water needs. Over-abstraction caused the large natural spring draining the aquifer to disappear in 1981, and groundwater levels have since fallen nearly 30 m in the vicinity of the former spring. Analysis of water levels and a water balance using recent assessments of groundwater abstractions confirm past work describing the hydrogeological functioning of the aquifer, and suggest that current abstractions need to fall by between 19 and 36 ML/day (7 and 13 Mm3/a) to bring the aquifer back into longterm balance. Continued over-abstraction at Grootfontein implies increasing risk to Mahikeng’s water supply, and illuminates the larger challenge of ensuring groundwater use in the North West dolomites that is sustainable and in the public interest.

Groundwater potential of the eastern Kalahari region of South Africa

Abstract An integrated approach involving geological, borehole data, hydrogeochemical and environmental isotope analyses was used to determine the groundwater potential of the eastern Kalahari region of South Africa, an area to the west of Mahikeng that stretches northward from the Orange River into Botswana. The total groundwater resource potential for the eastern Kalahari region of South Africa is estimated at 10127 Mm3/a, with the Kalahari Group aquifer showing the greatest potential, comprising 51% of the total resource. The storage capacity of the Kalahari Group aquifer (7130 Mm3) is also impressive, estimated to be more than twice that of the dolomite aquifer (2728 Mm3). Despite having such great potential, the aquifer is not actively recharged and is often associated with very saline water that is not suitable for human and livestock consumption. The limestone and dolomite aquifers of the Campbell Rand Subgroup, as well as the weathered granitic rocks of the Archaean basement, are considered as the most prospective water bearing formations, with a groundwater resource potential estimate of 1981 Mm3/a and 1845 Mm3/a, respectively. Aquifers with the least potential in the project area comprise the fractured basement rocks of the Kraaipan - Amalia greenstone belt, with a groundwater resource potential of 26 Mm3/a, and the fractured sedimentary rocks of the Asbestos Hills Subgroup, with a groundwater resource potential of 108 Mm3/a. The calculated groundwater storage and resource potential in the eastern Kalahari region of South Africa satisfies a large proportion of the water demand in the region.

EVALUATION OF GROUNDWATER QUALITY OF SIWA OASIS

In discussing the water quality evaluation for use in different purposes, the author will briefly examine some of the major important water quality standards. These standards serve as a basis for appraisal of the results of chemical water analysis in terms of suitability of the water for various intended uses. According to total dissolved salts (TDS), major ions as cations ( Ca2+, Mg2+, Na+, K+), anions (CO₃2⁻, HCO₃⁻ ,SO₄2⁻, Cl⁻), with some heavy metals such as Al3+, B3+ , Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mn2+, Mo2+, Ni2+, Pb2+, Sr2+, V2+ and Zn2+ The results indicate that the samples of Nubian sandstone aquifer is suitable for drinking of human and livestock , suitable for laundry purposes and for irrigation. While the samples of Fractured dolomite limestone aquifer are unsuitable for drinking and irrigation.

Compound-Specific Isotope Analyses to Assess TCE Biodegradation in a Fractured Dolomitic Aquifer.

The potential for trichloroethene (TCE) biodegradation in a fractured dolomite aquifer at a former chemical disposal site in Smithville, Ontario, Canada, is assessed using chemical analysis and TCE and cis-DCE compound-specific isotope analysis of carbon and chlorine collected over a 16-month period. Groundwater redox conditions change from suboxic to much more reducing environments within and around the plume, indicating that oxidation of organic contaminants and degradation products is occurring at the study site. TCE and cis-DCE were observed in 13 of 14 wells sampled. VC, ethene, and/or ethane were also observed in ten wells, indicating that partial/full dechlorination has occurred. Chlorine isotopic values (δ37 Cl) range between 1.39 to 4.69‰ SMOC for TCE, and 3.57 to 13.86‰ SMOC for cis-DCE. Carbon isotopic values range between -28.9 and -20.7‰ VPDB for TCE, and -26.5 and -11.8‰ VPDB for cis-DCE. In most wells, isotopic values remained steady over the 15-month study. Isotopic enrichment from TCE to cis-DCE varied between 0 and 13‰ for carbon and 1 and 4‰ for chlorine. Calculated chlorine-carbon isotopic enrichment ratios (ϵCl /ϵC ) were 0.18 for TCE and 0.69 for cis-DCE. Combined, isotopic and chemical data indicate very little dechlorination is occurring near the source zone, but suggest bacterially mediated degradation is occurring closer to the edges of the plume.

Karst aquifer characterization using storm event analysis for Black Dragon springshed, Beijing, China

Beijing is a megacity suffering from acute water shortage. The characterization of karst aquifers in Beijing's outlying districts is critical to inform sustainable policies and practices in groundwater development. We captured spring hydrogeochemical dynamics during an intense storm event (721 Storm) by installing a data logger in the weir, which presents an opportunity for defining and characterizing the recharging sources of discharge from Black Dragon (BD) springshed. Multivariate techniques (including PCA, 2D-HCA heat map, and piper diagram) were used to characterize the waters and investigate their geochemical evolution. The results in combination with hydrological evidence suggest BD Spring was dominated by interaction with dolomite host limestone rock during dry season, whereas it was fed by a second water supply (dolomite aquifer) during storm events. The infiltration coefficients were calculated based on the water balance model, and it was found that the 721 Storm has resulted in less infiltration due to the high rainfall intensity. We presented a novel methodology, combining high-frequency data sets and routine manual flow measurements with traditional geochemical sampling techniques. This methodology appears to be very efficient at characterizing a karst aquifer and seems to be potentially applicable to other karst aquifers.