Risk Of Groundwater Pollution Research Articles

Spatio-temporal Evolution of Groundwater Vulnerability Based on Spatial Autocorrelation

The distribution patterns of human activities affecting groundwater vulnerability vary with time. Studying the temporal and spatial changes in groundwater vulnerability, exploring the distribution characteristics of each period, and predicting the trends of development are important to formulate an effective development plan and reduce the risk of groundwater pollution at the same time. Based on the hydrogeological data as well as humanities and social data for 2004, 2010, and 2016 for the Chaoyang District of Beijing, a comprehensive evaluation model considering the human factors such as the land use types was established using the DRASTIC model. The spatiotemporal pattern of groundwater vulnerability was quantitatively characterized by calculating the Global Moran's Ⅰ and Getis-Ord Gi* index, and the distribution characteristics and variations in groundwater vulnerability were analyzed by the centroid of the G index and the standard deviation ellipse of the study area. The results indicate that in 2004, 2010, and 2016, the areas of high vulnerability have gradually reduced. The groundwater vulnerability in the study area shows a strong spatial aggregation; high concentration areas are mainly distributed in the northeast and southwest regions. The vulnerability of the northeast region has been decreasing each year, while the vulnerability of the northwest region has not changed much. The main reasons are the land use changes and the reductions in fertilizer use.

Pollution risk evaluation of regional groundwater based on sources apportionment of pollution

Abstract Pollution sources are determined by source apportionment, and are used as human-influenced factors to calculate the pollution risk of regional groundwater. In this case study, 266 samples of shallow groundwater were collected from the Lower Liaohe River Plain in northeastern China. Hydrochemical indexes of NH4+, Ca2+, Cl−, F−, HCO3−, Pb, Mg2+, NO3−, NO2−, K+, Na+, SO42−, total Cr, chemical oxygen demand, total dissolved solids, and total hardness of each sample were determined. Factor analysis method was used to identify potential pollution sources. Five common factors (agricultural activities, groundwater extraction, industrial activities, river pollution, and sewage discharges) represented 77.10% of the total variance. The results showed that the relatively high pollution risk mainly occurred in the west, with 19.91% of the area. The southeastern area showed a low risk of pollution, covering only 1.07% of the study area. Clearly, human activities have significantly changed the distribution of regional groundwater pollution risk in the study area.

Distribution, genesis, and pollution risk of ammonium nitrogen in groundwater in an arid loess plain, northwestern China

Nitrogenous pollutants from intense human activities have become serious environmental and health problems worldwide, particularly in groundwater source areas used for public water supply. To investigate the genesis and pollution risks associated with elevated concentrations of ammonium nitrogen in a groundwater source area, investigations were undertaken in the Jinji groundwater source area, located in an arid loess plain in northwestern China where 16 groundwater samples were collected from an aquifer used for water supply. The investigation indicated that high concentrations of ammonium nitrogen originated mainly from: infiltration of water from the Yellow River; livestock; and the discharge of industrial wastes. Measured parameters including pH, the permanganate index and the oxidation reduction potential could be used as important indicators of the genesis of ammonium nitrogen. A modified DRTCLN model was applied to the observed distribution of ammonium nitrogen to assess pollution risk of regional groundwater. The model was optimized by rebuilding the index system, and the analytic hierarchy process was used to calculate the rating scale of each index. A Monte Carlo simulation was performed to analyze the uncertainty of results of the risk assessment. The result showed that the risk value is relatively low in most areas of the groundwater source area. Only an industrial area in the southwestern part of the groundwater source area was classified as high risk; it should be the key factor of pollution control.

Relationship between trace elements and depositional environments in shallow sediments: a case study from Southern Kanto Plain, Central Japan

Underground developments such as subways and shopping facilities have been increasing in number and magnitude in the relatively shallow subsurface of many urban areas where the earth materials commonly are composed of marine sediments. Marine sediments can contain significant amounts of toxic trace elements such as arsenic, boron, and lead. Changes in the subsurface environment caused by excavation and construction in underground developments could potentially cause these toxic elements to be dissolved into pore water of the sediments, which might lead to groundwater pollution. The purpose of this study is to investigate correlations among chemical properties of marine sediments, such as pH and electrical conductivity (EC), concentrations of toxic trace elements, and stratigraphic characteristics of the sediments. We selected three sites with different stratigraphic settings in the southern Kanto Plain around the Tokyo Metropolis. We collected core samples from shallow strata at a site in the Arakawa Lowland, southern Saitama, and at two sites in the Musashino Upland, Middle Tokyo. All sites have both marine and non-marine sediments up to 50–60 m in thickness. We determined trace element concentrations in the pore water, pH, EC, and loss on ignition. The results show that (1) the marine sediments tend to have low pH, high EC, and high sulfur concentration compared to the non-marine sediments (2) the concentration of most of the soluble heavy metals vary depending on the concentration of sulfate, the pH, and the formation processes of the strata, (3) the arsenic concentration is not related to sulfur concentration but apparently to Fe and Al concentrations, (4) the boron concentration is not related to any other properties implying that the boron level is independent of and cannot be predicted by common chemical properties, and (5) for all three sites, concentrations of most of the trace elements, EC, pH, and sulfate concentration were correlated with each other. This study shows that the concentration and potential mobilization of many toxic trace elements in marine sediments could be predicted by easily measurable pore water chemical properties such as pH and EC. This could be useful for predicting and avoiding the risk of groundwater pollution during underground development projects.

A modified SINTACS method for groundwater vulnerability and pollution risk assessment in highly anthropized regions based on NO3− and SO42− concentrations

Groundwater vulnerability and risk assessment are worldwide tools in supporting groundwater protection and land planning. In this study, we used three of these different methodologies applied to the Campanian Plain located in southern Italy: SINTACS, AVI and LOS. However, their capability to describe the observed chemical pollution of the area has resulted quite poor. For such a reason, a modified SINTACS method has been then implemented in the area in order to get a more reliable view of groundwater vulnerability. NO3− and SO42− from more than 400 monitoring wells were used for specific vulnerability assessment. Land use was chosen as key parameter to infer the risk of groundwater pollution in our area. The new methodology seems to show a higher correlation with observed NO3− concentrations and a more reliable identification of aquifer's pollution hot spots. The main sources of NO3− were found in sub-urban areas, where vulnerability and risk are higher than in other areas. Otherwise due to reducing conditions triggered by the presence of elevated sedimentary organic matter and peat, concentrations below agricultural areas were lower than in sub-urban areas. The SO42− specific vulnerability map showed a positive correlation with observed concentrations, due to geogenic and anthropogenic SO42− sources present in the area. The combination of both NO3− and SO42− derived risk maps becomes essential to improve the conceptual model of aquifer pollution in this severely anthropized area. The application of this new and original approach shed light on the strengths and weaknesses of each of the described previous methods and clearly showed how anthropogenic activities have to be taken into account in the assessment process.

Performance of Applying Scale Permeable Pavements for Control of Runoff Pollution in an Area with High Groundwater Level

The purpose of this article was to study the effect of permeable pavements on runoff pollution control and its possible influence on groundwater quality in the area with high groundwater level. Three experimental permeable parking lots and one impermeable parking lot were built in urban Shanghai in order to monitor their quality of influent and effluent water under actual precipitation conditions, in order to investigate the performance of pollutant control effects and to evaluate the possibility of the pollution of groundwater. The results showed that all the three facilities could effectively remove TP, TSS, COD, Cr, Mn, Cu, Zn, Pb and O&G, but imposed poor removal efficiency on TN. Obvious release of NO3--N occurred in all three pavements. The permeable interlocking concrete pavement using cement stabilized crushed stones as base course and the one using crushed stones as base course had a better removal efficiency on NH4+-N than the previous concrete one. The quality of effluent water from different permeable pavements had no significant difference except NH4+-N. The in-situ groundwater quality was generally worse than background values of groundwater in Shanghai. Effluent water quality of three permeable pavements was generally worse than that of the in-situ groundwater, and a number of indicators belonged to or were close to groundwater class V standard. In the area with high groundwater level, there was risk of groundwater pollution caused by permeable pavements without liners.

Assessment of groundwater vulnerability to pollution using the Kherici’s method in the Talezza plain, Collo region (NE Algeria)

Abstract The intrinsic vulnerability of groundwater aquifers refers to their sensitivity to all contamination coming from soil surface irrespective of the nature of the polluting. In order to improve the protection of groundwater, there must be a reduction in the infiltration of contaminants towards the reservoir through the impacting factors determination of this phenomenon by means of research. There are collected models that include particular number of factors which allow the determination of a sign of groundwater vulnerability of all superficial pollutions. The goal of the study centers on ascertaining the state of vulnerability and the risk of groundwater pollution of the Collo region with a new proposed method by Kherici. Generally, assessment methods of vulnerability and the danger of groundwater pollution employ parametric systems with numerical quotation, cartographic superposition where the analytical methods are based on equations. In this study, we consider the combination of criteria dependent on natural factors (thickness of the unsaturated zone, geologic facies, degree of auto-purification) and the causes of groundwater vulnerability to man-made pollution (anthropogenic factors).

Analysis of temporal and spatial variations in groundwater nitrate and development of its pollution plume: a case study in Karaj aquifer

Considering the importance of groundwater resources in water-supply demands in arid and semiarid areas such as Iran, it is essential to investigate the risk of groundwater pollution. Nitrate is one of the main pollutants that penetrate into the groundwater from various sources such as chemical fertilizers, pesticides, and domestic and industrial sewage. Unfortunately currently, nitrate contamination of the aquifers is a serious problem in Iran. The Karaj aquifer is not exempted, and the nitrate pollution zone, with concentrations far beyond the permitted limit (50 mg/L), expands fast. In this paper, the long-term groundwater-quality data (from 2000 to 2013) collected from Alborz Province Water and Wastewater Company were analyzed using ArcGIS10 and statistical software, and the spatial and temporal patterns of nitrate pollution in drinking-water wells in the Karaj plain and effective parameters (such as depth to groundwater level, hydraulic gradient, land use, precipitation, and urban, agricultural and industrial wastewater) were investigated. The authors also investigated the status of nitrate concentration variation using the concepts of geostatistics, based on determinations from 62 to 194 surveyed wells with a suitable distribution across the plain. With respect to the relationship between quality parameters, hydrogeological status of the aquifer and land usage, causes of the increase in the concentration of nitrate in the water and its trend were investigated as well. Results revealed that the nitrate levels in the northern portion of the study area were the highest with maximum concentrations of 181.7 mg/L from 2000 to 2013. Based on nitrate concentration distribution maps, the levels of nitrate increased from 2006 onwards to 26–100 mg/L. Unfortunately from 2008 to 2012, a pollution zone with a nitrate water concentration of 101–150 mg/L has been observed and even a concentration of 180 mg/L has been determined. In 2000, the entire aquifer area has been drinkable but with the increase in nitrate concentration, the area with undrinkable water has expanded to 21% in 2003, 24% in 2005, 33% in 2007, 39% in 2009, 43% in 2011 and 44% in 2013. The results of this study could provide valuable information with on the status of nitrate water concentrations in the Karaj plain which demands proper strategies and qualitative approaches in the future.

Aquifer vulnerability and potential risk assessment: application to an intensely cultivated and densely populated area in Southern Italy

The use of indices, describing aquifer vulnerability and the risk of groundwater pollution, is a basic tool for the implementation of a sound water management plan, especially in densely populated and intensely cultivated areas. In this study, the groundwater contamination risk of the Caserta Plain (Southern Italy) was assessed through the integration of hazards defined on the basis of the different land uses, of the intrinsic vulnerability calculated by applying the SINTACS model and of the groundwater value evaluated by considering water wells density. In order to evaluate the evolution of the risk of groundwater pollution, the proposed methods were applied in the study area for both 2001 and 2009. The resulting specific vulnerability (SINTACS-L) and the risk (GRA) maps, created in a GIS environment, were validated by the comparison with the nitrate concentration distribution. The application of the proposed approach to the study area highlighted the strengths and weaknesses of each method and, at the same time, showed that their combination can provide an overall view of the threats posed to groundwater resources by the human activities affecting the territory. Considering both the benefits and the issues of the proposed approach, overall, the groundwater risk map is thought to be a robust tool to support water managers in defining future plans for water resources exploitation and land use.

Landfill Site Selection Using Pollution Potential Zoning of Aquifers by Modified DRASTIC Method: Case Study in Northeast Iran

Nowadays, with the ever-increasing growth of the population and the development of various industries, we are experiencing an increase in man-made leachates such as urban solid wastes, chemicals, and wastewater. Generally, the groundwater in aquifers is contaminated by these pollutants seeping through the above-ground sediment. The vulnerability of groundwater to contaminants can be assessed, which means those areas with lower vulnerability can be distinguished from those areas with high vulnerability. Hydrogeological parameters are presented in a modified DRASTIC method which assesses depth to groundwater surface (D), recharge (R), soil media (S), topography (T), impact of vadose zone (I), conductivity of aquifer, hydraulic capabilities (C), and the effect of land use activity (L). This study aims at zoning the pollution potential of the Mashhad aquifer by using the modified DRASTIC method and GIS to assess the old and new landfill sites. The results show that new and existing (old) landfill sites for solid waste disposal in Mashhad site selections should be closed down due to their location in high vulnerability zones where the risk of groundwater pollution is high.

Source apportionment of polycyclic aromatic hydrocarbons and n-alkanes in the soil-sediment profile of Jianghan Oil Field, China.

Surface soil in oil exploration area always contains high contents of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. To investigate the migration possibility of PAHs and n-alkanes from surface through aquitard and aquiclude to aquifer, the distribution, together with the source apportionment using several indicators, such as composition pattern, fluoranthene/(fluoranthene+pyrene) (Flt/(Flt+Pyr)), anthracene/(anthracene+phenanthrene) (Ant/(Ant+PA)), and the carbon preference index (CPI) of n-alkanes, in a 30-m-deep soil-sediment profile were studied. Results showed that there were considerable PAHs and n-alkanes not only in surface soil but also in aquitard, aquiclude, and aquifer sediments. The PAHs and n-alkanes in surface soil strongly suggested petroleum pollution. The high molecular weight PAHs and the n-alkanes with both long and short chains could not migrate into deep sediments as their sources in surface soil and deep sediment were different. Whereas the aquitard and aquiclude had significant input of low molecular weight PAHs (LMWPAHs) from petroleum sources, the LMWPAHs in confined aquifer suggested pyrogenic sources. Therefore, LMWPAHs migrated from surface to aquitard and aquiclude, but did not cause aquifer pollution in Jianghan Oil Field. However, the high mobility of LMWPAHs from surface to aquitard and aquiclude suggested that the long-term risk of groundwater pollution from oil exploration should be concerned.

Stream network pollution by olive oil wastewater risk assessment in Crete, Greece

Discharge of olive mill wastewater (OMWW) into rivers system in Crete had led to heavy organic pollution and several drastic environmental impacts. The current research study aims to map and evaluate the environmental hazards initiated by olive mill wastewater pollution discharged into surface stream network of Kolymvari agricultural area located in western Crete, Greece. Implemented methodology is based on locating source points of pollution and determining pollutant surface flow paths under GIS environment. Hydrological features of the area were delineated in the GIS environment using basically elevation data provided by the Ministry of Agriculture. On a microscale, it was proved that the implementation of MCA can quantify the environmental risk to surface water resources caused by OMWW. On a macroscale, risk mapping was implemented by establishing a spatial connection between the source points of pollution and the possible sedimentation areas. Furthermore, mapping of olive mill waste tanks will positively improve the exercised methodology in term of assessing the potential risks of soil and groundwater pollution.

A GIS-based LVF model for semiquantitative assessment of groundwater pollution risk: A case study in Shenyang, NE China

ABSTRACTGroundwater pollution risk assessment is a useful tool to prevent and control groundwater pollution, but its quantitative research is still relatively immature. In this study, a geographic information system based LVF model for a semiquantitative assessment of groundwater pollution risk is established, based on the groundwater pollution source load (L), groundwater vulnerability (V), and groundwater function value (F). Further, the pollution source load is characterized by seven specific pollution sources, the vulnerability is calculated by the modified DRASTIC method, and the groundwater function value is evaluated with the water quality and quantity. The model was used to assess the risk of shallow groundwater pollution in Shenyang city, Northeast China, with an area of 8,263 km2. The results show that highest risk areas account for 16.3% of the study area and are mainly distributed in the east of the study area. High risk areas are significantly affected by a shallow buried depth of groundwater and many types of harmful pollutants from industrial, agricultural, and domestic pollution sources. The evaluation results reflect the risk of groundwater pollution in the Shenyang area, which is relevant to the management and sustainable use of groundwater resources in the area.

Model-based assessment of groundwater vulnerability for the Dalyan Region of southwestern Mediterranean Turkey

The Dalyan Region that drains into a complex lagoon system is located on the Mediterranean Sea coast of southwest Turkey. There are no large streams in the area, indicating that a considerable amount of freshwater draining into the lagoon is expected to be based on groundwater inflows and that groundwater quality is an important issue for the lagoon ecosystem. Since the lagoon and its watershed are within an environmental special protection area, planning preventive and mitigative measures toward water quantity and quality, including groundwater, is crucial. Since an important step in such a study is the generation of vulnerability map of groundwater pollution, this study aims at the generation of an intrinsic groundwater vulnerability map and its assessment for the first time in the study area based on the DRASTIC method. Since the DRASTIC method requires recharge rates for the calculation of groundwater pollution potential index, these were obtained from a previous modeling study conducted in the same area, where SWAT model was used. The intrinsic vulnerability maps generated were overlaid with current land-use maps to evaluate actual groundwater pollution risk. Our analyses showed that 46% of the study area is under the high risk of groundwater pollution, where 62% of the vulnerable high-risk area is agricultural land.

Risk assessment of groundwater with multi-source pollution by a long-term monitoring programme for a large mining area

Environmental problems caused by mineral exploitation have increased significantly, a situation that has serious effects on the surrounding groundwater quality, especially with respect to the descent of the groundwater table caused by deep mining and multi-source pollution produced by auxiliary projects. Therefore, the study of groundwater risk assessment from multi-source pollution and the development of a long-term monitoring programme to manage such problems are essential. A copper-molybdenum opencast mine was the target of this study. Based on an analysis of the hydrogeological conditions of the mining area, aquifer parameters were obtained through field drilling and pumping tests. A finite element subsurface flow (FEFLOW) system was utilized to construct a numerical model that can analyse and predict the migration of multi-source pollutants during groundwater pumping and drainage in the mining area. The migration of pollutants is controlled not only by natural groundwater flow, but it is also strongly influenced by water drainage during deep mining, an activity that causes the multi-source pollutants to migrate to the mining centre. Therefore, both influencing factors should be considered when assessing the risk of groundwater pollution by multi-source pollutants. A reasonable groundwater monitoring programme that considers the migration direction and the distance of the pollutants from the groundwater movement in a non-natural flow field under the influence of a groundwater funnel during deep mining is also necessary.

Leachate Properties and Cadmium Migration Through Freeze-thaw Treated Soil Columns.

Soil column leaching experiments were conducted to study the effects of multiple freeze-thaw cycles on the vertical migration of cadmium (Cd). Three Cd-spiked leaching solutions of different properties were derived from snowmelt, sludge, and straw, designated as B, W and J, respectively. The leaching solutions varied in dissolved organic matter (DOM) concentrations in the order of J > W > B. Changes in leachate properties and Cd concentration were observed. The results showed that pH values of all the leachate solutions through freeze-thaw treated soil columns were higher than those of leachates through unfrozen soils. However, electrical conductivity (EC) values decreased compared with leachates in unfrozen treated soil columns. Although the concentrations of DOM in leachate solutions had no evident differences between the freeze-thaw and unfrozen treated soil columns, the concentrations of DOM in the leachate solutions B, W and J were different. Freeze-thaw cycles resulted in increased concentrations of Cd in the leachate solutions in the order J > W > B, and promoted a deeper migration of Cd in the soil columns. Thus, it was shown that freeze-thaw cycles may increase the risk of groundwater pollution by Cd.

Assessing groundwater vulnerability in the Kinshasa region, DR Congo, using a calibrated DRASTIC model

This study assessed the vulnerability of groundwater against pollution in the Kinshasa region, DR Congo, as a support of a groundwater protection program. The parametric vulnerability model (DRASTIC) was modified and calibrated to predict the intrinsic vulnerability as well as the groundwater pollution risk. The method uses groundwater body specific parameters for the calibration of the factor ratings and weightings of the original DRASTIC model. These groundwater specific parameters are inferred from the statistical relation between the original DRASTIC model and observed nitrate pollution for a specific period. In addition, site-specific land use parameters are integrated into the method. The method is fully embedded in a Geographic Information System (GIS). Following these modifications, the correlation coefficient between groundwater pollution risk and observed nitrate concentrations for the 2013–2014 survey improved from r = 0.42, for the original DRASTIC model, to r = 0.61 for the calibrated model. As a way to validate this pollution risk map, observed nitrate concentrations from another survey (2008) are compared to pollution risk indices showing a good degree of coincidence with r = 0.51. The study shows that a calibration of a vulnerability model is recommended when vulnerability maps are used for groundwater resource management and land use planning at the regional scale and that it is adapted to a specific area.

Interaction effect of nitrogen and vermicompost in the presence of herbicide (Clodinafop propargyl) on nitrogen transformation in a sandy soil

A laboratory experiment with three levels of nitrogen (0, 100 and 200 mg kg-1), two levels of vermicompost (0 and 1 % on dry wt. basis) and two levels of herbicide (0 and 60 g a.i. ha-1) was conducted with sandy soil of Hisar to study the interaction of nitrogen and vermicompost in the presence of herbicide (clodinafop propargyl) on nitrogen transformation during 2014. NH4+-N contents increased upto the 14th day in soil and then declined up to 56th day under control. NO3--N content in soil increased significantly throughout the incubation study under control. With con-junctive use of nitrogen along with vermicompost, NH4+-N contents increased significantly in the soil upto 14th day of incubation with an increase from 44.49 to 73.22 mg kg-1 and 64.00 to 102.87 mg kg-1, whereas NO3--N content in soil significantly increased throughout the incubation study over control and the increase was from 13.68 to 101.36 mg kg-1 and 23.19 to 115.48 mg kg-1. However, NH4+-N and NO3--N decreased significantly at all incubation periods with the application of herbicide alone and in presence of nitrogen as well as vermicompost. The study revealed that judi-cious use of N, leads to more availability of N to crop and prevents the environmental pollution. Higher levels of N application may increase the risk of ground water pollution due to more availability of NO3- ion which can be sub-jected to leaching losses. Vermicompost proved to be the important source of nutrients as it has narrow C:N ratio and decompose more quickly than other organic manures such as FYM etc. Among commonly used herbicides, clodinafop propargyl is most commonly used herbicide and may have negative impact on the microbial population and thus may hinder the transformation processes particularly in sandy soils which have low organic matter content and thereby affecting the availability of nutrients to crop and play decisive role in crop yields.

Preferential Transport in Macropores is Reduced by Soil Organic Carbon

Core Ideas Soils of larger SOC content showed weaker preferential transport. These soils also had larger volumes of pores <600 μm in size. Results suggest a threshold SOC content above which effects were negligible. It has been suggested that some management practices and farming systems that promote C sequestration may exacerbate the risk of groundwater pollution due to fast preferential transport in soil macropores. However, soil organic C (SOC) may also impact the soil pore structure at scales smaller than the macropore scale, where complexes of SOC and clay form microaggregates that may increase pore volumes in the micrometer size range. These effects of SOC per se on pore network architecture, water flow, and solute transport have hardly been investigated. Therefore, to investigate this question, we measured tracer transport through soil cores sampled along a transect on a field under grass–clover ley with a natural gradient in SOC content. The strength of preferential transport was characterized at two flow rates (2 and 5 mm h−1) and related to the volume, size distribution, heterogeneity, and connectivity of pore networks quantified by X‐ray tomography. The results showed that soils with a larger SOC content had larger volumes of pores in the smallest imaged size range (200–600 μm) that were also more uniformly distributed. These effects of SOC on the imaged pore networks were only apparent up to a threshold value of the ratio between clay and SOC of 10:1, which is assumed to correspond with the amount of SOC needed for C saturation of the clay fraction. The increased flow capacity of these smaller macropores in soil columns with larger SOC contents prevented flow from being activated in larger pores, which significantly reduced the strength of preferential transport.

Detoxification of sewage sludge by natural attenuation and implications for its use as a fertilizer on agricultural soils

Sewage Sludges (SS) from wastewater treatment systems constitute a potential alternative to agricultural fertilizers. However, their use is limited by the presence of toxic substances that may represent significant hazards for the environment and for human health. To test the potential of natural processes to attenuate their putative toxic activities, actual SS samples from domestic sewage were buried in holes in a pollution-free environment for different periods of time, up to one year. Aqueous and organic extracts were obtained after each period of natural attenuation, and their respective toxicity was tested for estrogenic and dioxin-like activity by yeast-based bioassays (ER-RYA and AhR-RYA, respectively) and for general toxicity and teratogenicity in zebrafish embryos. Dioxin-like activity was also tested in zebrafish embryos by monitoring the induction of the marker gene cyp1a. Whereas the results showed essentially no estrogenic activity, both dioxin-like activity and embryotoxicity were observed in the initial samples, decreasing significantly after six months of attenuation. Chemical analysis of toxic SS samples showed the presence of low levels of dioxins and furans, and relatively high levels of m- and p-cresol, at concentrations that only partially justify the observed biological effects. Our data indicates the presence of largely uncharacterized hydrophilic compounds with high biological activity in SS, constituting a potential risk of groundwater pollution upon their disposal into the environment. It also shows that this potential impact may be significantly mitigated by attenuation protocols, as the one presented here.