Environmental impact of an urban landfill on a coastal aquifer (El Jadida, Morocco)

The El Jadida landfill is one among many uncontrolled dumping sites in Morocco with no bottom liner. About 150 tons/day of solid wastes from mixed urban and industrial origins are placed directly on the ground. At the site of this landfill, the groundwaters circulate deeply (10–15 m) in the Cenomanian rock (calcareous–marl), which is characterised by an important permeability from cracks. The soil is sand–clay characterized by a weak coefficient of retention.The phreatic water ascends to the bottom of three quarries, which are located within the landfill. These circumstances, along with the lack of a leachate collection system, worsen the risks for a potential deterioration of the aquifer.To evaluate groundwater pollution due to this urban landfill, piezometric level and geochemical analyses have been monitored since 1999 on 60 wells. The landfill leachate has been collected from the three quarries that are located within the landfill. The average results of geochemical analyses show an important polluant charge vehiculed by landfill leachate (chloride = 5680 mg l⁻¹, chemical oxygen demand = 1000 mg l⁻¹, iron = 23 000 μg l⁻¹). They show also an important qualitative degradation of the groundwater, especially in the parts situated in the down gradient area and in direct proximity to the landfill. In these polluted zones, we have observed the following values: higher than 4.5 mS cm⁻¹ in electric conductivity, 1620 and 1000 mg l⁻¹ respectively in chlorides and sulfate (), 15–25 μg l⁻¹ in cadmium, and 60–100 μg l⁻¹ in chromium. These concentrations widely exceed the standard values for potable water.Several determining factors in the evolution of groundwater contamination have been highlighted, such as (1) depth of the water table, (2) permeability of soil and unsaturated zone, (3) effective infiltration, (4) humidity and (5) absence of a system for leachate drainage. So, to reduce the pollution risks of the groundwater, it is necessary to set a system of collection, drainage and treatment of landfill leachates and to emplace an impermeable surface at the site of landfill, in order to limit the infiltration of leachate.     

Hydrogeological studies on the mechanical behavior of landfill gases and leachate of the Nanjido Landfill in Seoul, Korea

 The Nanjido Landfill is the largest uncontrolled landfill in Korea and it causes various kinds of environmental problems. Landfill gases and leachate are recognized as the most serious environmental problems associated with the landfill. This study employs a series of numerical models and uses test data to interpret the distribution and flow of landfill gases and leachate. Leachate seepage appears about 40–60 m higher than the estimated basal groundwater table. Thus, seepage data indicate that perched or floating leachate layers are formed in the unsaturated zone of the landfill. The leachate production rate is estimated using infiltration test data and a model for unsaturated groundwater flow. Geochemical data indicate that the landfill leachate degrades the basal groundwater quality along the downgradient zone. The environmental impact of the leachate on river water is estimated. Received: 17 June 1996 · Accepted: 2 October 1996     

Sorption and anaerobic biodegradation of soluble aromatic compounds during groundwater transport. 1. Laboratory column experiments

. This paper deals with sorption and anaerobic biodegradation of the soluble aromatic fraction of jet fuel and how it is influenced by pore-water velocity during transport in a groundwater aquifer. The study was carried out as controlled laboratory column experiments. A binary mixture of toluene and 1,2,4-trimethylbenzene with a concentration ratio of 2:1 was used through the entire investigations. The column experiments were conducted with contaminated sediments and groundwater, taken from wells at a field research site. The columns were operated anaerobically under continuous-flow conditions at 10 °C in a temperature-controlled refrigerator. Two percent sodium azide was added to the injection solution of two of the columns to prevent biodegradation of the studied organic mixture. Chloride was used as a conservative tracer to characterize the hydrodynamic parameters such as dispersivity and porosity of the columns. The results showed that both compounds in the mixture were attenuated because of sorption and biodegradation processes in the columns. 1,2,4-trimethylbenzene was attenuated more significantly than toluene. Biodegradation of toluene was coupled mainly with the microbial reduction of ferric iron, whereas 1,2,4-trimethylbenzene, in contrast, was mostly sorbed. Their sorption and biodegradation were studied with different pore-water velocities, and a mass balance approach was applied to calculate biodegradation rates. The biodegradation rates of toluene were –0.16, –0.21, and –0.26 (unit: mM day^–1) for pore-water velocities of 96, 82.4, and 54.9 (unit: cm day^–1), respectively. This indicates that a decrease in the pore-water velocity significantly enhanced the biodegradation of toluene, consistent with other reports in the literature. For 1,2,4-trimethylbenzene the biodegradation rates were –0.05, –0.13 (unit: mM day^–1) for pore-water velocities of 96 and 82.4 (unit: cm day^–1), respectively. The biodegradation rate of 1,2,4-trimethylbenzene did not increase at the lowest pore water velocity as expected. This might be a result of substrate competition.     

Investigation on potential groundwater impacts and influence of local hydrogeology on natural attenuation of leachate at a municipal landfill

The influence of local hydrogeology on natural attenuation of contaminants from landfill leachates in shallow aquifer underlying the active Olusosun landfill base in Lagos was investigated. In addition, the level of groundwater contamination in the vicinity of the landfill and of leachate migration pattern in groundwater down gradient of the landfill base was equally assessed. Landfill leachate and groundwater samples were collected and analyzed and characterized. Physico-chemical analyses of sampled water followed standard analytical methods. Analytical results showed a measurable impact of leachate outflows on groundwater quality. Elevated levels of anions: nitrate, chloride and sulphate in the groundwater body and heavy metals: Cr₃. Cd and Cu, were detected at measurable levels in groundwater down gradient of the landfill location without any particular attenuation pattern. The migration pattern and dispersion of leachates down gradient, 750 m away from the landfill location are irregular and difficult to predict as depicted by levels of contaminants present in groundwater. The study highlighted the importance of soil stratigraphy beneath the landfill base as an important factor in the natural attenuation of leachate constituents in the groundwater body.     

Tunisian landfill leachate treatment using <Emphasis Type="Italic">Chlorella</Emphasis> sp.: effective factors and microalgae strain performance

The potential of the autoclaved Tunisian landfill leachate treatment using microalgae (Chlorella sp.) cultivation was investigated in this study. Landfill leachate was collected from Borj Chakir landfill, Tunisia. A full factorial experimental design 2² was proposed to study the effects of the incubation time and leachate ratio factors on the organic matter removal expressed in chemical oxygen demand (COD) and ammoniacal nitrogen (NH₄─N) and on the biological response of Chlorella sp. expressed by the cell density and chlorophyll content. All experiments were batch runs at ambient temperature (25 ± 2 °C). The Chlorella sp. biomass and chlorophyll a concentrations of 1.2 and 5.32 mg L^?1, respectively, were obtained with 10% leachate spike ratio. The obtained results showed that up to 90% of the ammoniacal nitrogen in landfill leachate was removed in 10% leachate ratio spiked medium with a residual concentration of 40 mg L^?1. The maximum COD removal rate reached 60% within 13 days of incubation time indicating that microalgae consortium was quite effective for treating landfill leachate organic contaminants. Furthermore, with the 10% leachate ratio spiked medium, the maximum lipid productivity was 4.74 mg L^?1 d^?1. The present study provides valuable information for potential adaptation of microalgae culture and its contribution for the treatment of Tunisian landfill leachate.     

Riverine organic carbon in the Xijiang River (South China): seasonal variation in content and flux budget

. Riverine water samples were collected from the lower reach hydrometric station Makou of the Xijiang River, in four hydrological seasons during 1997 and 1998. The samples were analyzed for their particulate and dissolved organic carbon. The contents of riverine particulate and dissolved organic carbon changed synchronously during different hydrological processes. The contents of organic carbon and total suspended substances in the riverine water increased with increasing discharge. The mass of organic carbon in the total suspended substances decreased logarithmically with increasing total suspended substances. The transported flux of organic carbon in the Xijiang River drainage is about 10.18᎒⁶ g of C km^–2 year^–1, which is two to three times larger than that of the average value in other river systems. Particulate organic carbon is the main component of riverine organic carbon, with a flux of about 8.30᎒⁶ g of C km^–2 year^–1.     

The use of strontium and lead isotopes to identify sources of water beneath the Fresh Kills landfill,Staten Island,New York,USA

A study was undertaken to explore whether the isotopic compositions of Pb and Sr are useful to distinguish mixtures of uncontaminated groundwater, seawater, and landfill leachate at the Fresh Kills landfill, Staten Island, New York. Ratios of ⁸⁷Sr/⁸⁶Sr ranged from 0.7088 to 0.7137 and could be used to distinguish Sr that was derived from seawater from that in uncontaminated groundwater. Lead isotopic abundances did not vary systematically among the different water sources. Plots of ⁸⁷Sr/⁸⁶Sr versus dissolved organic C, B, and NH₄⁺ defined perpendicular trends, documenting where leachate or sea water mixed with uncontaminated groundwater, and demonstrating that leachate has not contaminated groundwater in aquifers beneath the landfill.     

Direct current (DC) resistivity measurements in long-term groundwater monitoring programmes

. Effective leak detection systems are most often needed to enable early warnings of groundwater contamination from landfill areas. In order to monitor the groundwater chemical changes over time direct current (DC) resistivity measurements have been used, since variation in groundwater ion concentration give changes of the electrical potential field. A simple, low-cost system for long-term monitoring has been developed and used for 4 years at an existing operational landfill in central Sweden. The paper describes the construction and operation of the geoelectrical monitoring system based on a fixed electrode Wenner array, situated in a glaciated terrain. The simplicity of the system enables non-experts in geophysics to run the system and evaluate the results. The lateral resistivity variations (up to 10,000% from the mean lateral value) clearly reflect strongly different natural geological conditions, whereas the variations over time (15% from the mean value at each specific point) reflect mainly the seasonal soil humidity and groundwater level variations. Leachates from the landfill have a low resistivity (about 1 ohmm) and the moderate seasonal variations in electrical resistivity favour the possibilities for identification of leakage from the landfill. Evaluation of resistivity data comprises modified double mass calculations versus data from reference measurement sites, which enables detection of contamination although it influences the resistivity less than the natural seasonal variations.     

Hydrogeophysical approach for contamination assessment in NamSon landfill,Hanoi, Vietnam

Self potential (SP) and electrical resistivity tomography (ERT) methods are used together with the results of groundwater samples hydrogeochemical analysis to assess the impact of the water leak from the landfill garbage site at NamSon located in Northern Hanoi on causing pollution to the surrounding environment and affecting geological structure. Selected survey area covers an area of 180 × 300 m lying in the low land of the NamSon site with a slope ranging about 8 m in direction NW–SE. There are three geophysical measurements lines denoted as T1, T2 and T3. Processing 180 SP data points has allowed to draw maps of equipotential epoch in the two periods in 2015 and 2016. The maps show four zones of SP positive anomalies with maximum amplitudes of about +20 mV where the groundwater flow direction is downward and five zones of SP negative anomalies with minimum values in a range from ?180 to ?260 mV where the groundwater flow direction is upward. Resistivity values of the subsurface layers of soils and rocks have been aquired from 2D inverse model for measuring ERT in March 2015 and March 2016. The results of the ERT allowed to define the low resistivity in the range 15–20 Ωm related to leachate plume from NamSon landfill site. Results of the physico-chemical analysis of groundwater samples from the existing six boreholes show increases in concentration of the measured pollutant parameters indicating contamination of the groundwater as a result of solid waste leachate accumulation. This result is affirmative evidence for the survey results by geophysical technique. The rapid decrease in quality of groundwater over the last year is probably due to the influence of the leachate from the NamSon landfill site.     

18OSO4 and 18OH2O as prospective indicators of elevated arsenic in the Goose River ground-watershed, Maine

Anomalous geogenic arsenic occurs in drinking water from the Goose River crystalline ground-watershed in mid-coastal Maine. Isotope investigations were useful in understanding release areas of arsenic into affected water wells. The isotope composition of sulfate associated with probable arsenian pyrite oxidation is described. Correlation of '¹⁸O_SO4 enrichment [+4.57 to +7.46‰ Vienna Standard Mean Ocean Water (VSMOW)] is discussed with specific and recurring areas of elevated arsenic (10-52 µg l^-1). Although arsenic concentrations were highly variable over 2 years per well, '¹⁸O_SO4 values were always consistent and suggested a specific and consistent risk for elevated arsenic occurrences for each well. The '¹⁸O values in the water molecule (-12.07 to -8.81‰ VSMOW) and the '¹⁸O_SO4 values may serve as prospective indicators of prominent zones of aeration at depth in discrete fracture zones. The '¹⁸O values in the water molecule and sulfate ion appear to indicate that more than 60% of O₂ incorporated into the SO₄^2- ion are from dissolved oxygen and belong to distinct fractured areas. These aeration zones or oxidation fronts, as outlined by oxygen isotopes, are sentinels for high arsenic risk in groundwater.     

Mercury concentrations in environmental media at a hazardous solid waste landfill site and mercury emissions from the site

Mercury (Hg) concentrations in air, effluent water, landfill gas, leachate, groundwater, and soil at a hazardous solid waste landfill site in Korea were measured along with air–soil surface Hg exchange fluxes at the site. The concentrations and fluxes were considerably higher than have been found elsewhere in Korea. Gaseous Hg concentrations in the air peaked during the day, coinciding with Hg being released from the landfill surface. This suggests that air–soil exchange increased the Hg concentrations in the atmosphere. The air–soil exchange flux increased abruptly when solar radiation reached the soil surface. The Hg flux peaked about 3 h before the solar radiation peaked, possibly because reducible Hg was abundant at the soil surface. The Hg emission flux activation energy (E _a) was low, indicating that the Hg species present and Hg–soil binding were probably not as important (because of the high Hg content of the soil) as in previous studies. The methylmercury to total Hg ratios in the discharged effluent, groundwater, and leachate was clearly higher than typically found in coastal water and freshwater, suggesting bacteria caused active methylation to occur under the reducing conditions in the anaerobic landfill. The results suggested that considerable amounts of Hg are probably transported from the landfill to nearby environmental media and that this will continue if waste with a high Hg content continues to be added to the landfill without being pretreated.     

Arsenic pollution in groundwater from Hetao Area,China

. Hetao Area, China is a district where arsenic concentrations in drinking water are elevated. The 180,000 people that inhabit the 6,100 km² of the seven counties in the area show symptoms of arsenic poisoning. In this paper, the distribution and origin of arsenic in groundwater were studied. The results demonstrate that the affected district boundaries encompass an area with high contents of As in well water, which the local inhabitants drink and use in daily life. This district is labeled as a population pathological change area. The isotope ratios of ⁸⁷Sr/⁸⁶Sr (0.7100–0.7164), ²⁰⁶Pb/²⁰⁴Pb (18.3817–19.1871), and ²⁰⁷Pb/²⁰⁴Pb (15.7581–15.9578) in groundwater of the population pathological change area are close to the ratios measured in water from mine areas (⁸⁷Sr/⁸⁶Sr=0.7196, ²⁰⁶Pb/²⁰⁴Pb=19.1940, ²⁰⁷Pb/²⁰⁴Pb=15.9574), and are somewhat close to ratios in Yellow River, water which is used to irrigating in Hetao Area (⁸⁷Sr/⁸⁶Sr=0.7168, ²⁰⁶Pb/²⁰⁴Pb=18.3495, ²⁰⁷Pb/²⁰⁴Pb=15.5969). The average content of As in the drinking water is as high as four times more than the environmental standard of As in drinking water. The study suggests that the origin of the As in groundwater of the population pathological change area in Hetao Area is transported from higher elevations where mineral deposits exist. Mining of some of the deposits has occurred for a long time. Mining practices can result in release of toxic elements, which can then be transported from the mining district down gradient.     

Electrical geophysical and hydrogeological investigations of groundwater aquifers in Ruseifa municipal landfill, Jordan

The effect of the Ruseifa municipal landfill on the shallow groundwater aquifers in the area was investigated in two separate sites. The first one was not used since 1994, whereas the other is still being used for dumping. Fourteen electrical resistivity soundings were performed to detect the leachate and its effect on the quality of the groundwater. Results indicated that the solid waste thickness of the landfill was ranged from 3 to 20 m with resistivity value less than 10 Ω m. Based on the resistivity decreases of values less than 5 Ω m, the leachate was detected in the landfill sites at depths ranged from 10 to 50 m. However, the flow direction of the leachate at depth ranging 10–20 m in the terminated site was toward north, whereas the flow direction of the leachate in the site still used for dumping was toward east–northeast which causes the major source of groundwater pollution.     

Using spatial statistics to identify the uranium hotspot in groundwater in the mid-eastern Gangetic plain,India

The occurrence of uranium in groundwater is of particular interest due to its toxicological and radiological properties. It has been considered as a relevant contaminant for drinking water even at a low concentration. Uranium is a ubiquitously occurring radionuclide in the environment. Four hundred and fifty-six (456) groundwater samples from different locations of five districts of South Bihar (SB) were collected and concentrations of uranium (U) were analyzed using a light-emitting diode (LED) fluorimetric technique. Uranium concentrations in groundwater samples varied from 0.1 µg l^?1 to 238.2 µg l^?1 with an average value of 12.3 µg l^?1 in five districts of Bihar in the mid-eastern Gangetic plain. This study used hot spot spatial statistics to identify the distribution of elevated uranium concentration in groundwater. The hypothesis whether spatial distribution of high value and low value of U is more likely spatially clustered due to random process near a uranium hotspot in groundwater was tested based on z score and Getis-Ord Gi* statistics. The method implemented in this study, can be utilized in the field of risk assessment and decision making to locate potential areas of contamination.     

Use of chemical tracing to study acquisition modalities of the mineralization and behaviour of unconfined groundwaters under a semi-arid climate: the case of the Souss plain (Morocco)

The chemical content of the Souss unconfined groundwater displays spatial variations in conductivity (between 400 and 6,000 µS cm^-1). The chemical tracers (Cl^-, SO₄^2-, Sr²⁺, Br^-), which characterize the different components of the groundwater, allowed the determination of the origin of water salinity. Cl^- and SO₄^2-, reaching respectively 2,000 and 1,650 mg L^-1, display localized salinity anomalies. Br^-/Cl^- ratio distinguishes marine-influenced impoverished zones versus the oceanic domain. Thus, salinity anomalies can be attributed: (1) downstream, to a currently existing salt-encroachment (with added waste water) and sedimentary palaeosalinity, (2) in the middle-Souss, to High Atlas evaporites and to irrigation water recycling. Sr²⁺/Ca²⁺ ratio (evaporites if >1‰), confirms the evaporitic origin of the anomalies along the right bank of oued Souss. Furthermore, it facilitates the distinction between the different aquifer contributions (Cretaceous, Jurassic and Triassic), and it highlights leakage from deep Turonian limestones in the groundwater recharge system. To the south, recharge is from the Anti Atlas (evaporite-free) waters. Oxygen-18 measurements confirm the groundwater recharge from the High and Anti Atlas as piezometric maps and chemical tracers suggested, plus from leakage from the Turonian and the marine aquifers.     

甘肃某生活垃圾填埋场地下水污染特征及污染途径分析

依据实际调查数据,采用单因子污染指数分析法确定了生活垃圾填埋场地下水中主要污染物、污染程度和污染范围,并进行了土壤和地下水污染耦合性分析,研究结果表明：该生活垃圾填埋场地下水污染物主要为氨氮、总氮、高锰酸盐、锰、挥发酚和氟化物,其污染指数最大值分别为1 407.24、745.00、137.12、97.50、3.60和1.68,污染区总面积0.168 km²;填埋场下游沟谷纵向上,总氮、锰两项指标在土壤中的含量与地下水中浓度变化趋势一致;其污染途径主要为库区防渗层破损,渗滤液垂向沿基岩风化裂隙进入地下含水层,以连续渗漏的方式不断污染地下水,污染物在地下水径流作用下向拦挡坝下游不断迁移。     

Analysis of the distribution of inorganic constituents in a landfill leachate-contaminated aquifer: Astrolabe Park,Sydney, Australia

An investigation was conducted at Astrolabe Park landfill, a decommissioned municipal landfill in Sydney, Australia, to assess the physical and chemical processes affecting the distribution of inorganic constituents in the leachate plume. The plume is migrating from the landfill towards a groundwater-fed pond into which leachate-impacted groundwater discharges. Borehole geophysical logging and depth-discrete groundwater sampling were used to delineate the distribution of the leachate plume along two groundwater flow paths between the landfill and the shore of the pond. Borehole geophysical logs indicate a strong correlation between bulk and fluid electrical conductivity (EC) values, and help to identify small-scale heterogeneities that comprise a major constraint on contaminant transport within the aquifer. Variations in the distribution of several indicator parameters (EC, HCO₃^–, pH, Eh, NH₄⁺/NO₃^–, S^2–/SO₄^2–) are used to assess the dominant processes affecting contaminant distribution along the flow path, including mixing of fresh and contaminated groundwater, oxidation/reduction reactions and ion exchange.     

Deterioration of groundwater quality in the vicinity of an active open-tipping site in West Malaysia

There is an urgent need for characterization of leachate arising from waste disposal to ensure a corresponding effective leachate management policy. Field and laboratory studies have been carried out to investigate the impact of municipal landfill leachate on the underlying groundwater at a site in West Malaysia. The solid waste was disposed of directly onto an unprotected natural soil formation. This situation was made worse by the shallow water table. The hydrochemical composition of groundwater in the vicinity of the site (background) is a dilute mixed cation, bicarbonate water. The high ionic balance error of ~13.5% reveals that the groundwater body underneath the site was a highly contaminated leachate rather than contaminated groundwater. Elevated concentration of chloride (355.48 mg/L), nitrate (10.40 mg/L as NO₃), nitrite (14.59 mg/L), ammoniacal-N (11.61 mg/L), sodium (227.56 mg/L), iron (0.97 mg/L), and lead (0.32 mg/L) measured downgradient indicate that the contamination plume has migrated further away from the site. In most cases, the concentration of these contamination indicators, together with the ranges of sodium percentage (66.3–89.9%) and sodium adsorption ratio (10.1–19.7%), were found to be considerably higher than the limit values of safe water for both domestic and irrigation purposes, respectively.     

Hydrogeology and historical assessment of a classic sequential-land use landfill site,Illinois, U.S.A.

The Blackwell site in northeastern Illinois was a classic sequential-use project combining land reclamation, a sanitary landfill, and a recreational park. This paper adds a recent assessment of leachate generation and groundwater contamination to the site's unfinished record. Hydrogeological studies show that (1) the landfill sits astride an outwash aquifer and a till mound, which are separated from an underlying dolomite aquifer by a thin, silty till; (2) leachate leaks from the landfill at an estimated average rate between 48 and 78 m³/d; (3) the resultant contaminant plume is virtually stagnant in the till but rapidly diluted in the outwash aquifer, so that no off-site contamination is detected; (4) trace VOC levels in the dolomite probably indicate that contaminants have migrated there from the landfill-derived plume in the outwash. Deviations from the original landfill concepts included elimination of a leachate collection system, increased landfill size, local absence of a clay liner, and partial use of nonclay cover. The hydrogeological setting was unsuitable for the landfill as constructed, indicating the importance of detailed geological consideration in landfill and land-use planning.     

Experimental and Modelling Approaches for the Assessment of Chemical Impacts of Leachate Migration from Landfills: A Case Study of a Site on the Triassic Sandstone Aquifer in the UK East Midlands

Current risk-based methods for assessing the effects of landfill leachate migration on groundwater resources are conservative and generalised. Cost-effective and practical strategies are required which can robustly determine the potential for contaminant attenuation on a site-specific basis. In this paper laboratory column experiments and reactive transport modelling are evaluated as a combined approach for assessing the chem’ical impact of leachate migration in the Triassic Sandstone aquifer. The results are compared with field data for a landfill in the East Midlands. Columns of aquifer sandstone were flushed sequentially with groundwater, followed by acetogenic or methanogenic leachate to simulate chemical interactions occurring during leachate loading episodes. The key contaminants in leachate (NH₄, heavy metals, organic fractions) were attenuated by ion exchange, redox reactions, sorption and degradation. These processes produce a consistent hydrochemical signature which may help identify the extent of leachate migration in the aquifer. The laboratory results largely replicate those found in the field system, and the behaviour of inorganic contaminants during leachate flushing of the aquifer columns can be described by the reactive transport model. The experimental and modelling approach presented represents a powerful tool for risk assessment and prediction of leachate contaminant fate at unlined and lined landfills.