Intrinsic Aquifer Vulnerability Research Articles

Assessment of alluvial aquifer intrinsic vulnerability by a generic DRASTIC model: a discussion on data adequacy and pragmatic results

Assessment of alluvial aquifer intrinsic vulnerability by a generic DRASTIC model: a discussion on data adequacy and pragmatic results

Assessment of Intrinsic Vulnerability Using DRASTIC vs. Actual Nitrate Pollution: The Case of a Detrital Aquifer Impacted by Intensive Agriculture in Cádiz (Southern Spain)

The degradation of groundwater quality due to nitrate is a widespread issue in heavily agricultural areas and a major concern for public health. Improving knowledge of the intrinsic vulnerability of aquifers with respect to the actual contamination is crucial for adequate water management and for complying with the European directives aimed at protecting this valuable resource. In this study, we applied the well-established DRASTIC method to assess the intrinsic vulnerability of the Benalup aquifer, a detrital aquifer located in the southern Iberian Peninsula that supports important agricultural activity. The model was compared with in situ measurements of this ion, evidencing a lack of agreement between the most vulnerable zones and those that display higher nitrate concentrations. This fact should not be interpreted as an inadequacy in the vulnerability model, but as a result of several factors such as (i) the marked heterogeneity in land uses and the spatial variability in contaminant sources, (ii) the construction and exploitation characteristics of the water boreholes, (iii) the sampling procedure and depth to the water table, and (iv) transport and degradation processes within the porous medium. All these aspects can lead to discrepancies between the actual distribution of contamination and vulnerability models such as DRASTIC. All these factors should be carefully considered in the design of a sampling network in order to achieve a representative picture indicating the extent of contamination and the overall chemical quality of the system.

Extending the Overlay and Index: A Simple Method for Assessing Aquifer Vulnerability in a Combined Vadose Zone—Groundwater Flow System

This work extends the overlay and index methods for intrinsic groundwater vulnerability, that typically involve the soil surface and the vadose zone, to groundwater (saturated) transport. The method is “hybrid” as it combines the standard overlay and index methods with a simplified process-based approach for the groundwater component. For the latter, we make use of concept and methodologies based on geomorphological analysis, employing tools that are generally implemented in Geographic Information Systems (GIS). The proposed method is based on a simple probabilistic analysis, in which the overlay and index method (that can be any) provides the probability that the contamination reaches the groundwater through the vadose zone, while the probability that the contaminant reaches a generic location in the groundwater system is determined by analyzing the groundwater streamlines. The analysis leads to the definition of the combined vulnerability index υ, that takes care of both transport in the vadose zone and the aquifer. The method is applied to a groundwater catchment in the Campania region, Southern Italy. The method is simple and effective in assessing aquifer vulnerability in a combined vadose zone—groundwater flow system, useful for preliminary, screening analysis of the intrinsic aquifer vulnerability.

Combining the classic vulnerability index and affinity propagation clustering algorithm to assess the intrinsic aquifer vulnerability of coastal aquifers on an integrated scale

In the northern plains of Laizhou City, groundwater quality suffers dual threats from anthropogenic activities: seawater intrusion caused by overextraction of fresh groundwater, and vertical infiltration of agricultural pollutants. Groundwater management requires a comprehensive analysis of both horizontal and vertical pollution in coastal aquifers. In this paper, Intrinsic Aquifer Vulnerability (IAV) was assessed on an integrated scale using two classic IAV models (DRASTIC and GALDIT) separately based on a GIS database. Hydrogeological parameters from two classic IAV models were clustered using affinity propagation (AP) clustering algorithm, and silhouette coefficients were used to determine the optimal classification result.In our application, the objects of the AP algorithm are 3320 units divided from the whole study area with 500 m*500 m precision. A comparison of all four outputs in AP-DRASTIC shows that the clustering results of the 4-classification yielded the best silhouette coefficient of 0.406 out of all four. Cluster 4, which comprises 21% of the area, had relatively low level of groundwater contamination, despite its high level of vulnerability as indicated by the classic DRASTIC index. In the second level of vulnerability Cluster 3, 53.8% of all water samples were found to be contaminated, indicating a greater level of nitrate contamination. With respect to AP-GALDIT, the silhouette coefficient for result 7-classification reaches the highest value of 0.343. There was a high level of vulnerability identified in Clusters 2, 4 and 5 (34.7% of the study area) relating to the classic GALDIT index. The concentration of chloride in all water samples obtained in these areas was extremely high. Groundwater management should be addressed by AP-DRASTIC results on anthropogenic activity/contamination control, and by AP-GALDIT results on groundwater extraction limitation. Overall, this method allows for the evaluation of IAV in other coastal areas on an integrated scale, facilitating the development of groundwater management strategies based on a better understanding of the aquifer's essential characteristics.

Vulnerability mapping as a tool to foster groundwater protection in areas subject to rapid population expansion: The case study of Abuja Federal Capital Territory (Nigeria)

Study regionAbuja Federal Capital Territory (FCT; Nigeria). Study FocusRapid population growth has led to significant land use changes, with potential negative impacts on groundwater quality. However, the lack of understanding of hydrogeological settings, often due to limited data availability, is one of the main obstacles to sound planning in rapidly changing environments. To assess the specific groundwater vulnerability to nitrate, a DRASTIC-LU model was applied, combining the land use data from the last 20 years with the intrinsic aquifer vulnerability. This study represents the first attempt to assess aquifer vulnerability in the region. New hydrogeological insights for the regionResults show that the Abuja FCT has been affected by a dramatic change in land use with an increase in urbanized and agricultural areas and may induce nitrate contamination in groundwater. Currently, several wells in the region are showing nitrate concentrations that exceed the statutory limit for drinking purposes. The comparison of DRASTIC-LU results with nitrate concentrations shows that the highest concentrations are found in urban/peri-urban areas. Although fertilizers are generally considered to be the main source of nitrate contamination, these results suggest a possible mixed (urban and agricultural) pollution origin. This investigation therefore represents a starting point for future nitrate monitoring assessments and for supporting decision makers with adequate information for urban planning in view of the expected population growth in the area.

Assessment of intrinsic aquifer vulnerability at continental scale through a critical application of the drastic framework: The case of South America

An assessment of the intrinsic aquifer vulnerability of South America is presented. The outcomes represent the potential sensitivity of natural aquifers to leaching of dissolved compounds from the land surface. The study, developed at continental scale but retaining regionally a high resolution, is based on a critical application of the DRASTIC method. The biggest challenge in performing such a study in South America was the scattered and irregular nature of environmental datasets. Accordingly, the most updated information on soil, land use, geology, hydrogeology, and climate at continental, national, and regional scale were selected from international and local databases. To avoid spatial discrepancy and inconsistency, data were integrated, harmonized, and accurately cross-checked, using local professional knowledge where information was missing. The method was applied in a GIS environment to allow spatial analysis of raw data along with the overlaying and rating of maps. The application of the DRASTIC method allows to classify South America into five vulnerability classes, from very low to very high, and shows an overall medium to low vulnerability at continental scale. The Amazon region, coastal aquifers, colluvial Andean valleys, and alluvial aquifers of main rivers were the areas classified as highly vulnerable. Moreover, countries with the largest areas with high aquifer vulnerability were those characterized by extended regions of rainforest. In addition, a single parameter sensitivity analysis showed depth to water table to be the most significant factor, while a cross-validation using existing vulnerability assessments and observed concentrations of compounds in groundwater confirmed the reliability of the proposed assessment, even at regional scale. Overall, although additional field surveys and detailed works at local level are needed to develop effective water management plans, the present DRASTIC map represents an essential common ground towards a more sustainable land-use and water management in the whole territory of South America.

Groundwater contamination risk assessment using a modified DRATICL model and pollution loading: A case study in the Guanzhong Basin of China

Groundwater contamination risk assessment is not only the basis for groundwater management, but also an effective tool for groundwater pollution control and prevention. However, only groundwater vulnerability assessment is not enough to prove the risk of groundwater contamination. Therefore, this study describes an evaluation method combining aquifer intrinsic vulnerability and pollution source loading to evaluate groundwater contamination risk in Guanzhong Basin on a macro scale. A modified DRATICL model was introduced to evaluate the intrinsic vulnerability, and the analytic hierarchy process (AHP) and the entropy weight method were combined to determine the weight of each evaluation factor. Pollution loading was evaluated by quantifying the characteristics of potential pollution sources, mainly including pollutant toxicity, pollutant release possibility and potential pollutant release amount. Finally, total iron, Cl−, SO42−, F−, COD (Chemical Oxygen Demand), NO3−, NO2− and TDS (Total Dissolved Solids) are used to calculate the water quality index and verify the model results. The results showed that industries were the most harmful potential pollution sources in the study area, followed by landfills. Very high vulnerability areas were mainly situated around Huazhou District, Huayin and Dali County, as well as the low terraces around Zhouzhi County and Hu County, which are mainly caused by shallow groundwater depth and high net recharge. The final groundwater contamination risk results showed the high groundwater contamination risks are detected around Xi'an City, Xianyang City, Hancheng City and Dali County. Both high vulnerability and high pollution loading were present at the Jingwei District in the north of Xi'an City, where a priority attention should be given.

CC-PESTO: a novel GIS-based method for assessing the vulnerability of karst groundwater resources to the effects of climate change

The new GIS-based CC-PESTO method is shown to successfully assess and map the vulnerability/resilience of karst aquifers to effects of climate change. Karst aquifers were chosen due to their importance at the global level and widespread utilisation in potable water supply and irrigation, but also because of their hydrogeological complexity. The method was developed to assess the intrinsic vulnerability of aquifers, without considering the direct impact of variable climate factors, but considering the adaptive capacity of aquifers in response to expected climate extremes (floods and prolonged droughts). The procedure includes a subdivision of aquifer systems and an assessment of four main attributes: permeability, storativity, the discharge regime and the slope of each of the subdivided segments. CC-PESTO was tested in three study areas located in the highly developed karst of Montenegro and Serbia. In Mt. Durmitor (Montenegro), four out of 21 subunits were found to belong to the category of ‘low vulnerability’ and to have a good prospect for further development. Two subunits in the Babine and Bogovina study areas (Serbia) were defined as less vulnerable than others. The results obtained should help water managers and spatial planners to safeguard and reserve these areas as alternative or supplementary water sources that might be able to reduce the shock on groundwater-dependent ecosystems caused by expected extended droughts. The CC-PESTO method is flexible, and its application is possible in other karstic terrains such as platform or tropical karst. Indexation of the main attributes and their subcomponents could be adapted to local circumstances.

A high-resolution nitrate vulnerability assessment of sandy aquifers (DRASTIC-N)

Groundwater protection against agricultural diffuse nitrate pollution is of paramount importance for safeguarding groundwater-dependent aquatic ecosystems and protecting human health by securing clean groundwater for drinking water production. Nitrate vulnerability assessment of aquifers is the core of a scientifically sound strategy for management and protection of groundwater by authorities. A multitude of methods exists for assessing intrinsic aquifer vulnerability. The objective of this paper is to develop a nitrate-specific groundwater vulnerability assessment method based on the globally recognized DRASTIC method, which was developed by the US Environmental Protection Agency in the 1980s. We propose a new method “DRASTIC-N″ for assessing aquifer nitrate vulnerability, which for the first time expands the seven original geological and hydrogeological parameters with a geochemical parameter for redox condition. The development of DRASTIC-N is based on the longstanding Danish practice of performing detailed groundwater mapping based on dense sampling of geophysical, geological, and geochemical data. DRASTIC-N is compared to the widely used and documented Danish nitrate vulnerability assessment method SCANVA in a study area where the primary aquifer used for drinking water production is composed of heterogeneous sandy glacial deposits. Both SCANVA and DRASTIC-N result in vulnerability maps, which show similar patterns of nitrate vulnerability with a fair overall agreement of 71%. DRASTIC-N provides a framework for systematic and transparent application, which can facilitate stakeholder involvement and help authorities in groundwater protection and decision-making with regards to nitrate pollution. DRASTIC-N is suitable for nitrate vulnerability assessments of glacially deposited sandy aquifers, an abundant and important water resource worldwide, potentially threatened by nitrate pollution from anthropogenic activities.

Fuzzy-Probabilistic Model for a Risk Assessment of Groundwater Contamination: Application to an Urban Zone in the City of Belém, Pará, Brazil

This study proposes a fuzzy-probabilistic modelling approach for groundwater contamination risk assessment (FPM-risks) regarding underground fuel storage tanks (UFST). Considering the subjective measures of hydrogeological parameters, a fuzzy inference system is proposed to assess the intrinsic vulnerability of aquifers (Y). Measurement of the UFST hazard degree (H) and natural groundwater quality (Q) is considered as a pattern framing issue, such that they were quantified by fuzzy-analytic hierarchy process (AHP) of the recognizing patterns model. Though the association among Q and the probability of using groundwater reserves (G), estimated by the Monte Carlo method, the consequences of contamination (C) were measured. Associating Y, H, and C, the basic and value-weighted risk assessment of groundwater contamination was performed in the urban zone of Belém city, Pará state, Brazil. The results showed that the majority of UFSTs concentrated in the more urbanized zone were classified by FPM-risks as high basic risk and very high value-weighted risk of groundwater contamination. Although the risk assessment should be updated regularly because of the dynamic characteristics of hazards from the USFTs, the FPM-risks was shown as a tool to be considered for managing groundwater resources, as these models overcome subjectivities and address uncertainties, thereby providing a higher level of accuracy than usual risk methods and possibly become a decision-making way.

Avaliação do Potencial Hídrico Não-Potável em Aquíferos do Município de Salvador, Bahia, com Base no Mapa de Vulnerabilidade GOD

Este trabalho avaliou o potencial hídrico não-potável dos aquíferos do município de Salvador, Bahia, com base no mapa de vulnerabilidade GOD. Os aquíferos de Salvador apresentam características de aquífero fissural, nos domínios do Complexo Cristalino, e de aquífero granular, no domínio das rochas sedimentares. O método GOD calcula a vulnerabilidade intrínseca do aquífero através da avaliação numérica dos parâmetros hidrogeológicos do sítio associados ao tipo de aquífero (de confinado à não confinado), ao tipo de solo (de argila à areia) e da profundidade até o topo do aquífero. A metodologia GOD revelou que a vulnerabilidade natural dos aquíferos da cidade de Salvador se classifica de baixa à insignificante, nos trechos mais argilosos e de topografia elevada da cidade; e, de alta à extrema, nos trechos mais arenosos dos vales e baixadas. Construindo o mapa das classes de vulnerabilidade e delineando os trechos de alta à extrema vulnerabilidade, foi possível avaliar o potencial de água subterrânea classificada como não potável, face ao risco de contaminação por atividades antrópicas nelas instaladas ou, por instalar. Tomando-se a área desses trechos e as características hidrogeológicas do aquífero, foi quantificado um volume hídrico não potável de aproximadamente 20 milhões de m3, com recarga anual de aproximadamente 9 milhões de m3, baseada numa taxa anual de recarga de 12% das precipitações pluviométricas sobre as áreas mapeadas como vulnerabilidade GOD alta e extrema. Assim sendo, o mapa de vulnerabilidade favorece uma explotação ambientalmente adequada dos recursos hídricos subterrâneos de uma região.

The potential evaluation of groundwater pollution based on the intrinsic and the specific vulnerability index

Assessment of groundwater pollution vulnerability is imperative and undeniable for appropriate and sustainable management of aquifer, especially in arid regions like Iran. This study aim was to evaluate the intrinsic and the specific vulnerability rate of Nehbandan aquifer groundwater vis-à-vis contamination propagation using the three weighting models; DRASTIC, SINTACTS AND modified FUZZY-DRASTIC. Considering the two DRASTIC and SINTACS models only study the intrinsic vulnerability, the fuzzy method was modified DRASTIC to determine the specific vulnerability. The results showed that the best method to estimate the area's vulnerability was the modified FUZZY-DRASTIC model that had a correlation coefficient of 0.79 with nitrate points. This amount is 0.38 and 0.5 respectively for DRASTIC and SINTACS. Besides, it was observed that only 2% of the area in DRASTIC, 6% in SINTACS and 4% in modified FUZZY-DRASTIC were located in a very high vulnerable situation and the most area was not vulnerable. The outputs of applied methods in the case study area exhibited the intrinsic vulnerability of aquifer and even can be used as a preliminary tool in the development and management of water resources in the future.

Evaluating the suitability of urban groundwater resources for drinking water and irrigation purposes: an integrated approach in the Agro-Aversano area of Southern Italy.

Deterioration of groundwater quality due to the introduction of pollutants from natural and anthropic sources has become a major environmental issue. We tested three methodologies in assessing groundwater quality and intrinsic aquifer vulnerability in the Agro-Aversano area (Southern Italy). A geographic information system (GIS)-based groundwater quality index (GQI) was realized to assess groundwater quality for drinking and irrigation use and, in parallel, standard SINTACS was applied to evaluate the intrinsic vulnerability of the aquifer. Nitrate concentrations and sodium absorption ratio (SAR) in groundwater samples were used to verify the reliability of vulnerability data. GQI analysis pointed to a general poor quality of groundwater both for drinking and irrigation use, especially in sub-urban areas. The spatial pattern of water quality from GQI analysis was positively related to nitrate and fluoride concentrations for drinking use and to bicarbonate and sodium concentrations for irrigation use, whose levels exceeded the WHO and FAO recommended thresholds, respectively. Standard SINTACS was found to be inadequate for describing the aquifer state, its results showing no correlation with nitrate concentration or SAR. Because of this inconsistency, we tested a novel approach combining GQI with SINTACS analysis. Results showed positive correlation with nitrate (r = 0.63) and SAR (r = 0.64) contents, thus pointing to combined SINTACS-GQI as a more reliable approach than standard methodologies.

Modeling intrinsic vulnerability of complex karst aquifers: modifying the COP method to account for sinkhole density and fault location

This study investigates a method of karst-aquifer vulnerability modeling that modifies the concentration-overburden-precipitation (COP) method to better account for structural recharge pathways through noncarbonate rocks, and applies advancements in remote-sensing sinkhole identification. Karst aquifers are important resources for human and agricultural needs worldwide, yet they are often highly complex and have high vulnerability to contamination. While many methods of estimating intrinsic vulnerability of karst aquifers have been developed, few methods acknowledge the complication of layered karst aquifer systems, which may include interactions between carbonate and noncarbonate rocks. This paper describes a modified version of the COP method applied to the Kaibab Plateau, Arizona, USA, the primary catchment area supplying springs along the north side of the Grand Canyon. The method involves two models that, together, produce higher resolution and greater differentiation of vulnerability for both the deep and perched aquifers beneath the Kaibab Plateau by replacing the original sinkhole distance parameter with sinkhole density. Analyses indicate that many karst regions would benefit from the methodology developed for this study. Regions with high-resolution elevation data would benefit from the incorporation of sinkhole density data in aquifer vulnerability assessments, and deeper semi-confined karst aquifers would benefit greatly from the consideration of fault location.

Fuzzy-based assessment of groundwater intrinsic vulnerability of a volcanic aquifer in the Chilean Andean Valley.

A fuzzy logic approach has been proposed to face the uncertainty caused by sparse data in the assessment of the intrinsic vulnerability of a groundwater system with parametric methods in Las Trancas Valley, Andean Mountain, south-central Chile, a popular touristic place in Chile, but lacking of a centralized drinking and sewage water public systems; this situation is a potentially source of groundwater pollution. Based on DRASTIC, GOD, and EKv and the expert knowledge of the study area, the Mamdani fuzzy approach was generated and the spatial data were processed by ArcGIS. The groundwater system exhibited areas with high, medium, and low intrinsic vulnerability indices. The fuzzy approach results were compared with traditional methods results, which, in general, have shown a good spatial agreement even though significant changes were also identified in the spatial distribution of the indices. The Mamdani logic approach has shown to be a useful and practical tool to assess the intrinsic vulnerability of an aquifer under sparse data conditions.

The Spatial and Temporal Variability of Groundwater Vulnerability and Human Health Risk in the Limin District, Harbin, China

This study aimed to analyze the variations in groundwater quality, vulnerability and potential health risk from 2006 to 2016 in the Limin District, Harbin, China. Groundwater geochemical characteristics were described using statistical analysis and Piper diagrams. A modified DRASTIC model that combined factors of intrinsic aquifer vulnerability and land use was applied to assess groundwater vulnerability. The weights of parameters were adjusted by using the analytic hierarchy process (AHP) to optimize the model. The non-carcinogenic health risk was estimated by the Unites States Environmental Protection Agency (USEPA) model. Results suggested that concentrations of NH4-N, Fe and Mn in groundwater exceeded the limits both in 2006 and in 2016. The concentration of Fe in the groundwater showed more significant variation between 2006 and 2016 than the other parameters. Very high vulnerability zones increased from 6.3% in 2006 to 16.9% in 2016, and distributed on agricultural land, indicating that agriculture was still a major source of pollution. Mn and NO3-N contributed the most to human health risks in 2006 and 2016, respectively. This study highlights the influence of groundwater quality variation in decadal exploitation on human health.

Groundwater Vulnerability to Pollution Map for Karst Aquifer Protection (Ziria Karst System, Southern Greece)

In recent years vulnerability maps have been used as a tool to highlight the areas with the greatest potential for groundwater pollution based on the hydrogeological conditions and their respective human impacts. Several regions of Greece depend completely or partially on drinking water from karst aquifers; thus, the production of vulnerability maps for such karstic areas is considered essential. In the present study, an assessment of aquifer intrinsic vulnerability has been conducted applying the COP method in the Ziria karst system. The latter is located at the Northeast part of Peloponnese in South Greece and is used as a public resource for drinking water. This method, which has been developed for carbonate (karst) aquifers, uses the properties of the overlying layers above the water table (O factor), the concentration of flow (C factor) and the precipitation regime (P factor) over the aquifer. The COP method considers karstic landforms as factors that decrease the natural protection provided by the overlying layers of a karst aquifer. With the use of GIS tools, vulnerability maps were produced highlighting the different degrees of intrinsic vulnerability in the karst system of Ziria.

A Tier-I leaching risk assessment of three anticoagulant compounds in the forested areas of Hawai'i

The anticoagulant rodenticides brodifacoum, chlorophacinone, and diphacinone have been proposed for broadcast application in some forested areas in Hawai'i to protect rare and endangered native bird species from introduced mice and rats. Groundwater resources in Hawai'i are prone to contamination due to the intrinsic aquifer vulnerability to leaching from the land surface. Because of the hydrogeologic complexity, Hawai'i uses a Tier-I leaching assessment tool, CLERS, to make registration decisions for new or existing chemicals. The CLERS tool uses soil and pesticide properties as well as water recharge through the soil profile in a GIS framework to estimate mass attenuation of the chemicals at a given depth and compares against this attenuation factor against those of a known leacher and a non-leacher. Disturbed soil samples were collected across the state of Hawai'i, including the islands of Hawai'i, Kaho'olawe, Kaua'i, Lana'i, Maui, Moloka'i, and O'ahu, with two sampling locations per island, except for Kaua'i which had three. As only limited information on chemical properties of these anticoagulants in soils is available, laboratory experiments were performed to determine the sorption capacity (Kd) and the degradation rate (T1/2) of brodifacoum, chlorophacinone, and diphacinone to construct a proper chemical database. Depending on the soil type, T1/2 values ranged between 37 and 248days for diphacinone, between 39 and 1000days for chlorophacinone, and between 72 and 462days for brodifacoum. These data were used in the CLERS tool to estimate leaching risks for these chemicals primarily in forested areas of the state where the chemicals are likely to be applied. The results from the CLERS tool indicate low risks of leaching of these three compounds into aquifers in five out of six major Hawaiian Islands. Diphacinone showed medium risk of leaching in a few remote areas in Maui.

Introducing a new framework for mapping subsidence vulnerability indices (SVIs): ALPRIFT

Proof-of-concept (PoC) is presented for a new framework to serve as a proactive capability to mapping subsidence vulnerability of Shabestar plain of approximately 500km2 overlaying an important aquifer supporting a region renowned for diversity of agricultural products. This aquifer is one of 12 in East and West Azerbaijan provinces, Northwest Iran, which surround the distressed Lake Urmia, with its water table declined approximately 4m in between 2004 and 2014. The decline of water table in aquifers undermines their soil texture and structure by exposure to pressures under their weight and thereby induce or trigger land subsidence. Inspired by the DRASTIC framework to map intrinsic aquifer vulnerability to anthropogenic pollution, the paper introduces the ALPRIFT framework for subsidence, which comprises the seven data layers of Aquifer media (A), Land use (L), Pumping of groundwater, Recharge (R), aquifer thickness Impact (I), Fault distance (F) and decline of water Table (T). The paper prescribes rates to account for local variations and weights for the relative importance of the data layers. The proof-of-concept for ALPRIFT is supported by the correlation of Subsidence Vulnerability Indices (SVIs) with measured subsidence values, which renders a value of 0.5 but improves significantly to 0.86 when using fuzzy logic. Similar improvements are suggested by the ROC/AUC performance metric.

Underground structures increasing the intrinsic vulnerability of urban groundwater: Sensitivity analysis and development of an empirical law based on a groundwater age modelling approach

In a previous paper published in Journal of Hydrology, it was shown that underground structures are responsible for a mixing process between shallow and deep groundwater that can favour the spreading of urban contamination. In this paper, the impact of underground structures on the intrinsic vulnerability of urban aquifers was investigated. A sensitivity analysis was performed using a 2D deterministic modelling approach based on the reservoir theory generalized to hydrodispersive systems to better understand this mixing phenomenon and the mixing affected zone (MAZ) caused by underground structures. It was shown that the maximal extent of the MAZ caused by an underground structure is reached approximately 20years after construction. Consequently, underground structures represent a long-term threat for deep aquifer reservoirs. Regarding the construction process, draining operations have a major impact and favour large-scale mixing between shallow and deep groundwater. Consequently, dewatering should be reduced and enclosed as much as possible. The role played by underground structures’ dimensions was assessed. The obstruction of the first aquifer layer caused by construction has the greatest influence on the MAZ. The cumulative impact of several underground structures was assessed. It was shown that the total MAZ area increases linearly with underground structures’ density. The role played by materials’ properties and hydraulic gradient were assessed. Hydraulic conductivity, anisotropy and porosity have the strongest influence on the development of MAZ. Finally, an empirical law was derived to estimate the MAZ caused by an underground structure in a bi-layered aquifer under unconfined conditions. This empirical law, based on the results of the sensitivity analysis developed in this paper, allows for the estimation of MAZ dimensions under known material properties and underground structure dimensions. This empirical law can help urban planners assess the area of influence of underground structures and protect urban strategic reservoirs.