Hard Groundwater Research Articles

Drinking and irrigation quality and pollution assessments of the groundwater resources from Alappuzha in Kerala (India) through an integrated approach using WQI and GIS

Groundwater in coastal areas, with surging population and growing settlements, is constantly at risk of pollution. Alappuzha is one of the most well-developed coastal districts in the southwestern Indian state of Kerala and employing various physico-chemical parameters (pH, EC, TDS, alkalinity, hardness, and contents of sodium, potassium, calcium, magnesium, carbonate, bicarbonate, chloride, sulphate, nitrate, and fluoride), this study aims to evaluate the drinking and irrigation water qualities of its groundwater resources and present their spatial distributions using the GIS platform. In the moderately hard to very hard groundwater of Ca-Mg-SO4 type, the ions dominate with order Ca > Na > Mg > K and HCO3 > Cl > SO4 > CO3 > F. The water quality index (WQI) values (0.85–144, avg., 26.77) established the suitability of drinking water, revealing 53 % and 45 % of samples are lies under the categories of excellent and good, respectively. Only 2 % of the sample are in extremely poor water category. SAR, RSC, Na%, PI, KR and MH indices established that almost all of the groundwater can be used for agriculture, and the samples from northern coast showed vulnerability to contamination.

Swelling of sulfate-bearing soil: A case study of A1 highway pavement failure

Lime stabilization is one of the most commonly used methods for improving weak road subgrades, but it becomes very problematic in sulfate-bearing soils. This article presents results of a case study in which the sulfate attack was the most probable reason for a significant deformation of a highway pavement founded on lime-stabilized Doggerian clay. Macroscopic analysis revealed partial degradation of the concrete structure, a larger extent of stabilization than designed, and large gypsum crystals in the native soil. Chemical tests indicated a very high content of sulfates in the soil (> 10,000 mg/kg of SO4) and in the groundwater (> 3,000 mg/l of SO42-). The maximum free swelling strain (εvolmax = 3–6%) and the swelling pressure (pcmax = 56 kPa) of the clay, determined in the Wasiliew apparatus and the oedometer tests, were not large enough to be considered as the only cause of the pavement damage. Sand-cement and clay-lime mixtures, which simulated stabilized soil layers in the road profile, were observed for several months in oedometric tests, under various loading conditions. The swelling of Sa-Cem was negligible, but the Cl-Lim mixtures turned out to be much more expansive than the natural soil (εvolmax up to 21%, pcmax = 230 kPa) with a much longer duration of volume increase. The samples were flooded with distilled water or hard groundwater to clarify whether the constant access of the material to sulfates is important in the swelling process, but the results were unequivocal. X-ray diffraction revealed that the addition of lime resulted in the formation of secondary minerals: butlerite, portlandite, and ettringite. The presence and swelling of ettringite in the stabilized sub-base soil layers was eventually agreed to be the most probable reason for the pavement deformation. These results indicate the need to introduce an obligatory investigation of the level of sulfates in clayey subbase soils subject to lime stabilization.

Reductive debromination of bromo‐substituted C2 aliphatics using a biochar–iron(II) composite

AbstractBACKGROUNDTribromoethylene (TrBE), dibromoethylenes (DBEs) and 1,2‐dibromoethane (DBA) are widespread, toxic and persistent contaminants found in anaerobic soil and groundwater. The abiotic debromination of TrBE, DBEs and DBA using a layered iron(II)–iron(III) hydroxide (green rust, GR) with biochars acting as electron mediators was studied. A screening of biochar substrates was conducted. Reactive biochars were chosen for debromination of TrBE, DBEs and DBA in deionized water and groundwater. Post‐pyrolysis activation with CO2 was tested for reactivity enhancement.RESULTSBone meal (BM) and shrimp shell (SS) biochars resulted in 60% and 90% debromination of TrBE, respectively. The SS biochar catalyzed debromination by elimination reactions of TrBE and DBEs resulting in formation of acetylene, while DBA was reduced to ethylene. All debrominations in deionized water followed pseudo‐first‐order kinetics with half‐lives t1/2 of 5.1, 1.3, 2.6 and 9.5 h for TrBE, cDBE, tDBE and DBA, respectively. For similar experiments in moderately hard groundwater, removal t1/2 values were on average 2.6 times slower, but still considered fast. Compared to removal t1/2 in deionized water, post‐pyrolysis activation with CO2 of an acid‐treated SS biochar produced a t1/2 11 times shorter for removal of TrBE and two times shorter for DBA.CONCLUSIONSBiochars are efficient mediators of reductive debromination of TrBE, DBEs and DBA. TrBE, DBEs and DBA can be effectively debrominated in deionized water and groundwater samples using a GR–SS biochar composite. The mediating ability of the SS biochar can be further improved by post‐pyrolysis CO2 activation. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Characterisation and quality assessment of surface and groundwater in and around Lake Bosumtwi impact craton (Ghana)

Conventional graphical methods have been used to classify water in Lake Bosumtwi and groundwater around the lake. The study also assessed the suitability of these water resources for agricultural use. Results indicate slightly acidic, moderately hard to very hard groundwater with alkaline earth concentrations exceeding alkali metals. In contrast, the lake water is alkaline, showing alkalis in excess over alkaline earth metals. Weak acids exceed strong acids in both lake/groundwater. Rock weathering largely controls groundwater and lake water chemical compositions, resulting mainly in Ca–Mg–HCO3 groundwater and Na–HCO3 lake water types. Thus, suggesting that there is no apparent incipient relationship, which benefits the primary aquifer system in terms of recharge. Water quality indices suggest groundwater of good to excellent quality for human consumption and other domestic use. An evaluation of lake/groundwater based on salinity, sodicity and bicarbonate hazard reveals that the groundwater is generally suitable for irrigation whiles the lake water is not suitable for irrigation. However, the lake water may be used in generous amounts on highly permeable soils and salt-tolerant crops under special soil and water management practices.

Mapping groundwater hardness in wells as a source of drinking water for the people

Herce Farida Solossa 20.2018.2.00117 Mapping of Groundwater Hardness Distribution of Drinking Water for Bangkalan District Community, in 2019. Thesis, Department of Environmental Engineering, Faculty of Civil Engineering and Planning, Adhi Tama Institute of Technology Surabaya, Advisor Dr. Yulfiah, ST., Msi. Water hardness is the content of certain minerals in water, generally calcium (Ca) and magnesium (Mg) ions in the form of carbonate salts and this content if it exceeds quality standards can have an impact on human health. The purpose of this study is to map the distribution of groundwater hardness as a source of water supply in Kab. Bangkalan. The sample of this study is shallow wells with a depth not exceeding 20 m. This type of research is a descriptive study with a qualitative and quantitative approach. The research sample was taken as many as 18 following the number of subdistricts in Kab. Base Samples taken are water source wells used by the community. Sampling time is the dry season. Samples taken are stored in bottles and immediately taken to the laboratory for examination. Sampling locations are made in the form of maps with the ArcGis application. The conclusion of this research is that the level of hardness in groundwater in Kab. Base has moderate value - maximum. The distribution of hard water is also evenly distributed throughout the Kab. Base with the maximum distribution from east-west to east and east-east while the hardening is starting from north and northeast to south, southwest and west. This suggestion that can be made is that residents who use shallow wells should use a filter and cook it first for drinking needs. Keywords: Mapping, hard groundwater, drinking water sourcesKeywords: Mapping, hard groundwater, drinking water sources.

Assessing the ground waters of Bulgaria using a Water Quality Index

The study focuses on the quality of shallow groundwater in Bulgaria based on the content of major ions. To be safe for drinking purposes, their concentrations must not exceed the respective thresholds. The groundwater quality is assessed in terms of health hazard by a groundwater quality index (GWQI or WQI), and the respective map is presented. The results show that for the territory of Bulgaria, this index varies from 13 to 92. The highest values of this index (related to health hazard) are typical for the lower hypsometric zone of the country. The shallow groundwater in the zone of active water exchange is distributed as follows: waters of excellent quality, waters of good quality, waters of poor quality, and waters of very poor quality, covering 3%, 39%, 22%, and 31% of the whole area of the country, respectively. In this study, no estimates have been made for 5% of the territory of Bulgaria, which is characterized by the presence of very hard groundwater.

Algal softening followed by ozonation: The fate of persistent micropollutants and natural organic matter in groundwater

A proof-of-concept study evaluates the performance of a novel strategy using photosynthetic microorganisms to soften groundwater instead of using caustic chemicals. The microalga Scenedesmus quadricauda was used to increase the pH of the groundwater via natural photosynthesis. This work applied softening as a pretreatment to ozonation of hard groundwater and mainly focused on investigating the multiple effects of algal softening on the degradation of persistent micropollutants upon subsequent ozonation. The algae-induced alkaline conditions (pH > 10) were favorable to catalyze the formation of OH radicals directly from O3 molecules. Moreover, algal softening removed the strong radical-scavenging carbonate species (HCO3− and CO32−) to a much greater extent than that achieved by chemical softening, which was attributed to the combination of mineral carbonation and metabolic CO2 reduction. The fate of the natural organic matter (NOM) was characterized with spectroscopy, chromatography, and bioassay, which indicates that algal treatment decomposed the NOM to be less susceptible to attack by OH radicals. Consequently, the ozonation of alkaline groundwater achieved a better removal of the micropollutant residues in groundwater. Carbamazepine and diclofenac were used as model chemicals of persistent groundwater contaminants and were almost completely removed with an addition of 1.25 mg O3 L−1 (0.63 mg-O3 mg-C−1).

Activity and stability of the catalytic hydrogel membrane reactor for treating oxidized contaminants

The catalytic hydrogel membrane reactor (CHMR) is an interfacial membrane process that uses nano-sized catalysts for the hydrogenation of oxidized contaminants in drinking water. In this study, the CHMR was operated as a continuous-flow reactor using nitrite (NO2−) as a model contaminant and palladium (Pd) as a model catalyst. Using the overall bulk reaction rate for NO2− reduction as a metric for catalytic activity, we evaluated the effect of the hydrogen gas (H2) delivery method to the CHMR, the initial H2 and NO2− concentrations, Pd density in the hydrogel, and the presence of Pd-deactivating species. The chemical stability of the catalytic hydrogel was evaluated in the presence of aqueous cations (H+, Na+, Ca2+) and a mixture of ions in a hard groundwater. Delivering H2 to the CHMR lumens using a vented operation mode, where the reactor is sealed and the lumens are periodically flushed to the atmosphere, allowed for a combination of a high H2 consumption efficiency and catalytic activity. The overall reaction rate of NO2− was dependent on relative concentrations of H2 and NO2− at catalytic sites, which was governed by both the chemical reaction and mass transport rates. The intrinsic catalytic reaction rate was combined with a counter-diffusional mass transport component in a 1-D computational model to describe the CHMR. Common Pd-deactivating species [sulfite, bisulfide, natural organic matter] hindered the reaction rate, but the hydrogel afforded some protection from deactivation compared to a batch suspension. No chemical degradation of the hydrogel structure was observed for a model water (pH > 4, Na+, Ca2+) and a hard groundwater after 21 days of exposure, attesting to its stability under natural water conditions.

A nitrogen dynamic hydroponic culture on performance and quality of water spinach (Ipomoea aquatica)

In view of the unreasonable application of chemical fertilizers in agriculture and the groundwater pollution caused by nitrogen (N) leaching, a nitrogen dynamic hydroponic culture was used to simulate the dynamics variation of ammonium nitrogen (NH4-N) and nitrate nitrogen (NO3-N) in the leaching loss soil. Solutions with different ratio of NO3-N and NH4-N (100:0, 70:30, 50:50, 30:70 and 0:100) were prepared as well as the same solutions that not containing NO3-N .Water spinach was chosen to culture in the two solutions that differ from NO3-N every two (E2) or five days (E5) to observe the growth, quality and nutrient solution uptake. In terms of the growth, uptake of N source, N use efficiency and the chemical indicators, plants grown in the balanced solution all showed the best results. The nitrogen dynamic hydroponic culture showed some differences between E2 and E5 in some aspects. Under the same N source level, plants in E2 showed a better growth and higher NO3-N uptake than E5. On the other hand, the uptake of NH4-N seemed to be affected significantly by the interchanged frequency, which showed the same variations of glutamine synthetase activity. The activity of nitrate reductase and glutamine synthetase showed the coexist of NO3-N and NH4-N could play synergistic effect. It is not recommended to supplement NO3-N frequently in the case of N leaching loss, which has little impact on the growth and may lead to the hard taste and groundwater pollution.

Possible links between groundwater geochemistry and chronic kidney disease of unknown etiology (CKDu): an investigation from the Ginnoruwa region in Sri Lanka

Since at least two decades, Chronic Kidney Disease of Uncertain Etiology (CKDu) has become an increasingly discussed health issue in Sri Lanka and as well as in other tropical regions. Areas that are particularly affected with the disease are mostly located in the dry zone of Sri Lanka. The disease is more prominent among communities that consume groundwater as their main source of drinking water. Hydrogeochemical investigations were carried out in the Ginnoruwa area, a known hotspot of CKDu. It revealed possible links between drinking water chemistry and the spreading of the disease. This work compares hydrogeochemical data of drinking water sources of wells whose consumers are affected by CKDu and other nearby wells whose consumers were not affected by the disease. A total of 63 groundwater samples were collected from selected wells. About one-third of these samples (i.e., 19) were collected from wells used by CKDu patients. Significantly higher values of pH, total hardness, electrical conductivity, Ca2+, Mg2+, F−, Cl−, PO43−, and SO42− were found in wells that were used by CKDu patients. Mean contents of Na+, Ca2+, and Mg2+ in CKDu affected wells were 33.8 mg/L, 30.1 mg/L, and 14.9 mg/L, respectively, compared to 23.1 mg/L, 26.7 mg/L, and 9.65 mg/L in non-CKDu wells. Differences in major ion geochemistry in groundwaters are possibly governed by variable time periods of water storage in fractured hard rock aquifers in this region. Hydrogeochemical parameters were statistically compared by a Mann–Whitney U test and indicated significant differences in total dissolved solids (TDS) (p = 0.016), SO42− (p = 0.005), PO43− (p = 0.030), F− (p = 0.048), Na+ (p = 0.008), and Mg2+(p = 0.008) between non-CKDu and CKDu wells at p = 0.050 level. Other suspected solutes such as nephrotoxic trace elements including As, Cd, and Pb were similar in both types of wells. They were also lower than the accepted guideline limits of the World Health Organization (WHO). Results of this study suggest that fluoride in drinking water in combination with water hardness may be one of the responsible factors for kidney damage and progression of the disease. This may be particularly the case when elevated amounts of Mg2+ are present in hard groundwater.

Hybrid Hollow Fiber Nanofiltration-Calcite Contactor: A Novel Point-of-Entry Treatment for Removal of Dissolved Mn, Fe, NOM and Hardness from Domestic Groundwater Supplies.

Groundwater (GW) is one of the main potable water sources worldwide. However, the presence of undesirable compounds and particularly manganese (Mn) and iron (Fe) (mainly co-existing in GWs) are considered as objectionable components of potable water for both health and aesthetic issues. As such, individual dwellings supplied by domestic wells are especially threatened by these issues. Current domestic treatment technologies are complicated to operate and even dangerous if improperly maintained (e.g., catalytic filtration) or consume salts and produce spent brine which pollutes the environment (i.e., ion exchange resins). Therefore, it is of prime importance to design a simple and compact, yet robust, system for Mn and Fe control of the domestic GW sources, which can reliably guarantee the desired Mn limit in the finished water (g/L). In the course of this study, we demonstrated, for the first time, that a hybrid hollow fiber nanofiltration (HFNF)–calcite contactor process is a promising alternative for treating domestic GWs with elevated levels of Mn, Fe, natural organic matter (NOM) and hardness. The efficacy of the HFNF membranes in terms of removal of Mn, Fe, NOM and fouling was compared with commercially available NF270 and NF90 membranes. The results revealed that HFNF (100–200 Da) and NF90 maintained considerably high rejection of Mn, Fe and NOM due to their dominant sieving effect. In contrary, the rejections of the above-mentioned components were decreased in the presence of high hardness for the looser HFNF (200–300 Da) and NF270 membranes. No membrane fouling was detected and the permeate flux was stable when the hard GW was filtered with the HFNF membranes, regardless of their molecular weight cut-off and transmembrane pressure, while the permeability of the NF270 and NF90 membranes steadily decline during the filtration. Integrating a calcite contactor, as a post filtration step, to the HFNF process yielded further Mn, Fe and NOM removals from the HFNF permeate and adjustment of its hardness level. The best performance was achieved when a blend of Calcite–CorosexTM () was used as a post-treatment to the tight HFNF (100–200 Da).

Impact of heterogeneous properties of soil and LNAPL on surfactant-enhanced capillary desaturation

This paper investigates low-concentration (<1wt%) surfactant flushing when used as a follow-up technology for multiphase vacuum extraction on heterogeneous sites. Challenges posed by soil permeability, pore-size distribution, mineralogy, light non-aqueous phase liquid (LNAPL) weathering and groundwater hardness were quantified through batch and soil column tests. Compatibility issues between the mixed mineralogy soils, hard groundwater, mixed LNAPL and usual anionic surfactants were observed. The selected solution was a Winsor type I system promoting an interfacial tension of 0.06mN/m between the site LNAPL and the amphoteric surfactant CAS in aqueous solution at pH12. Surfactant loses to adsorption and pore media plugging were observed in the fine soil fraction. The capillary desaturation curves (CDC) obtained with the column tests suggested mixed-wettability behavior. The soil permeability strongly influenced LNAPL recovery, as expressed by the relationship obtained between capillary numbers (NCa) and hydraulic gradients. In this case, the critical NCa, marking the onset of capillary desaturation, could only be obtained with realistic hydraulic gradients in the coarse soil fraction. At those gradients, potential LNAPL recovery was 30% at the most. Unlike previously published CDCs, the relationship between NCa (log-scale) and LNAPL recovery was not linear but dependant on residual LNAPL saturation.

Single and combined effects of phosphate, silicate, and natural organic matter on arsenic removal from soft and hard groundwater using ferric chloride

In order to assess the effects of phosphate, silicate and natural organic matter (NOM) on arsenic removal by ferric chloride, batch coprecipitation experiments were conducted over a wide pH range using synthetic hard and soft groundwaters, similar to those found in northern Vietnam. The efficiency of arsenic removal from synthetic groundwater by coprecipitation with FeCl3 was remarkably decreased by the effects of PO4 3−, SiO4 4− and NOM. The negative effects of SiO4 4− and NOM on arsenic removal were not as strong as that of PO4 3−. Combining PO4 3− and SiO4 4− increased the negative effects on both arsenite (As3+) and arsenate (As5+) removal. The introduction of NOM into the synthetic groundwater containing both PO4 3− and SiO4 4− markedly magnified the negative effects on arsenic removal. In contrast, both Ca2+ and Mg2+ substantially increased the removal of As3+ at pH 8–12 and the removal of As5+ over the entire pH range. In the presence of Ca2+ and Mg2+, the interaction of NOM with Fe was either removed or the arsenic binding to Fe−NOM colloidal associations and/or dissolved complexes were flocculated. Removal of arsenic using coprecipitation by FeCl3 could not sufficiently reduce arsenic contents in the groundwater (350 μg/L) to meet the WHO guideline for drinking water (10 μg/L), especially when the arsenic-rich groundwater also contains co-occurring solutes such as PO4 3−, SiO4 4− and NOM; therefore, other remediation processes, such as membrane technology, should be introduced or additionally applied after this coprecipitation process, to ensure the safety of drinking water.

Groundwater hydrogeochemical characteristics in rehabilitated coalmine spoils

The investigation aims to identify and describe hydrogeochemical processes controlling the evolution of groundwater chemistry in rehabilitated coalmine spoils and their overall influence on groundwater quality at a study area located in the Karoo basin of South Africa. A good understanding of the processes that controls the evolution of the mine water quality is vital for the planning, application and management of post-mining remedial actions. The study utilises scatter plots, statistical analysis, PHREEQC hydrogeochemical modelling, stoichiometric reaction ratios analysis, and the expanded Durov diagram as complimentary tools to interpret the groundwater chemistry data collected from monitoring boreholes from 1995 to 2014. Measured pH ranging between 6–8 and arithmetic mean of 7.32 shows that the groundwater system is characterised by circumneutral hydrogeochemical conditions period. Comparison of measured groundwater ion concentrations to theoretical reaction stoichiometry identifies Dolomite-Acid Mine Drainage (AMD) neutralisation as the main hydrogeochemical process controlling the evolution of the groundwater chemistry. Hydrogeochemical modelling shows that, the groundwater has temporal variations of calcite and dolomite saturation indices characterised by alternating cycles of over-saturation and under-saturation that is driven by the release of sulphate, calcium and magnesium ions from the carbonate-AMD neutralization process. Arithmetic mean concentrations of sulphate, calcium and magnesium are in the order of 762 mg/L, 141 mg/L and 108 mg/L. Calcium and magnesium ions contribute to very hard groundwater quality conditions. Classification based on total dissolved solids (TDS), shows the circumneutral water is of poor to unacceptable quality for drinking purposes. Despite its ability to prevent AMD formation and leaching of metals, the dolomite-AMD neutralisation process can still lead to problems of elevated TDS and hardness which mines should be aware of when developing water quality management plans.

HARD WATER REGIMES DURING PRE-MONSOONAL PERIOD IN RAJNAGAR BLOCK, ODISHA, INDIA: A GEOSPATIAL ANALYSIS BY GEOGRAPHIC INFORMATION SYSTEM

From the hydrochemical analysis of 53 representative groundwater samples along coastal Kendrapara district, Odisha, the current research establishes widespread occurrences of moderately hard to hard groundwater within the subsurface water bearing horizons. There exists a distinct belt of moderately hard ground water in the Rajnagar block of the district whereas soft water occurrence is practically absent in the study area. The analysis also points to no specific interrelationship between the hardness of groundwater to that of the physical parameters including pH and electrical conductance.

Use MODIS satellite data to study new phenomena of underground fire in the Al Ruhban oasis in Al Najaf city, Iraq

On 15 August 2010, a phenomenal underground fire was experienced for the first time in the western province of Al Najaf in Iraq. During the incidence, longitudinal cracks and small holes were observed in the ground emitting white smoke. These cracks and emitted smoke extended and were observed up to over 5,000 m2 of space. These observations continued from 15 August to 30 October 2010. In this study, the authors investigated the possibility of thermal jump in the studied area during the observation period using MODIS data. Here, MODIS data detected two significant thermal activity jumps in the study area from 15 August 2010 to 27 September 2010. The result further indicated that the combustion process in the Al-Ruhban area is likely due to natural causes, combustion of hydrocarbon gases emitted or leaked from oil pools; and these fires may continue to incandescent and slow creep until the end of the source material causing fire or facing hard groundwater levels.

Effect of water hardness and pipe material on enhanced disinfection with UV light and chlorine

Limited studies have been conducted to evaluate synergistic benefits between disinfectants, although promise has been shown between ultraviolet (UV) light and chlorine-based disinfectants. This research aimed to determine drinking water quality factors that affect potential for enhanced removal of heterotrophic bacteria due to synergy between UV light and free chlorine. An additional goal was to determine the impact of pipe material on the formation of biofilm and the effectiveness of combined disinfection in controlling it. Annular reactors (ARs) containing polycarbonate or cast iron coupons were used to simulate typical drinking water distribution systems. Two experiments were conducted with untreated hard groundwater and groundwater treated with ion exchange to remove hardness, each comparing chorine alone to chlorine with UV pre-treatment. Results show that enhanced removal of heterotrophic plate count (HPC) bacteria existed with hard water when UV preceded chlorine, but synergistic benefits were not consistently observed. Under softened water conditions, no enhanced reduction or synergy was observed. Cast iron ARs supported biofilm HPC bacteria that were unaffected by any disinfection scheme regardless of source water, while bulk HPC bacteria were more resistant to disinfection in polycarbonate than cast iron ARs. Results indicate that disinfection synergy between UV and chlorine is limited in groundwater sources.

Positive and negative impacts of five Austrian gravel pit lakes on groundwater quality

Groundwater-fed gravel pit lakes (GPLs) affect the biological, organic, and inorganic parameters of inflowing groundwater through combined effects of bank filtration at the inflow, reactions within the lake, and bank filtration at the outflow. GPLs result from wet dredging for sand and gravel and may conflict with groundwater protection programs by removing the protective soil cover and exposing groundwater to the atmosphere.We have investigated the impact on groundwater of five GPLs with different sizes, ages, and mean residence times, and all having low post-excavation anthropogenic usage. The results revealed highly active biological systems within the lake water, in which primary producers significantly reduced inflowing nitrate concentrations. Decalcification also occurred in lake water, reducing water hardness, which could be beneficial for waterworks in hard groundwater areas. Downgradient groundwater nitrate and calcium concentrations were found to be stable, with only minor seasonal variations. Biological degradation of organic material and organic micropollutants was also observed in the GPLs. For young GPLs adequate sediment deposits may not yet have formed and degradation processes at the outflow may consequently not yet be well established. However, our results showed that within 5years from the cessation of excavation a protective sediment layer is established that is sufficient to prevent the export of dissolved organic carbon to downgradient groundwater.GPLs can improve groundwater quality in anthropogenically (e.g., pesticides and nitrate) or geologically (e.g., hardness) challenging situations. However, post-excavation usage of GPLs is often dominated by human activities such as recreational activities, water sports, or fish farming. These activities will affect lake and groundwater quality and the risks involved are difficult to predict and monitor and can lead to overall negative impacts on groundwater quality.

Field deployable method for arsenic speciation in water

Contamination of drinking water supplies by arsenic is a world-wide problem. Total arsenic measurements are commonly used to investigate and regulate arsenic in water, but it is well understood that arsenic occurs in several chemical forms, and these exhibit different toxicities. It is problematic to use laboratory-based speciation techniques to assess exposure as it has been suggested that the distribution of species is not stable during transport in some types of samples. A method was developed in this study for the on-site speciation of the most toxic dissolved arsenic species: As (III), As (V), monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA). Development criteria included ease of use under field conditions, applicable at levels of concern for drinking water, and analytical performance. The approach is based on selective retention of arsenic species on specific ion-exchange chromatography cartridges followed by selective elution and quantification using graphite furnace atomic absorption spectroscopy. Water samples can be delivered to a set of three cartridges using either syringes or peristaltic pumps. Species distribution is stable at this point, and the cartridges can be transported to the laboratory for elution and quantitative analysis. A set of ten replicate spiked samples of each compound, having concentrations between 1 and 60 μg/L, were analyzed. Arsenic recoveries ranged from 78% to 112% and relative standard deviations were generally below 10%. Resolution between species was shown to be outstanding, with the only limitation being that the capacity for As (V) was limited to approximately 50 μg/L. This could be easily remedied by changes in either cartridge design, or the extraction procedure. Recoveries were similar for two spiked hard groundwater samples indicating that dissolved minerals are not likely to be problematic. These results suggest that this methodology can be use for analysis of the four primary arsenic species of concern in drinking water supplies.

Discussion on Tunis Soft Soil Sensitivity

In Tunis City, the sensitivity of the marine deposits at shallow depth (z = 0–20 m) varies significantly. The influence of the process of the leaching out of Tunis soft soil on its geotechnical parameters is a focal point in this research. This process leads finally to moderate levels of sensitivity for Tunis clays since it appears to happen in a two steps with increasing sensitivity. The “hard water” leaching out and the dispersive action of organic matter (humus) lead unexpectedly to higher but still moderate level of sensitivity as measured on many Tunis sites. These sensitivity variations result from the combination of leaching out with hard ground water and high content of organic matter. This sensitivity attracted our attention and remains of high interest for the study of the behaviour of the Tunis soft clay.