Luís Ribeiro

OPTIMAL SPACE-TIME COVERAGE AND EXPLORATION COSTS IN GROUNDWATER MONITORING NETWORKS

A method to determine the optimal subset of stations from a reference level groundwater monitoring network is proposed. The method considers the redundancy of data from historical time series, the times associated with the total distance required to run through the entire monitoring network, and the sum of the times for each monitoring station. The method was applied to a hypothetical case-study consisting of a monitoring network with 32 stations. Cost-benefit analysis was performed to determine the number of stations to include in the new design versus loss of information. This optimisation problem was solved with simulated annealing. Results showed that the relative reduction in exploration costs more than compensates for the relative loss in data representativeness.

Survey paper: Re-thinking diagnosis for future automation systems: An analysis of current diagnostic practices and their applicability in emerging IT based production paradigms

With the advent of the Internet and the progressive development and consolidation of a wide range of web standards and technologies as well as the advances in distributed artificial intelligence (DAI), namely the multi agent system concept, new opportunities have emerged for conceiving, modelling and enhancing shop floors performance and response. Modern IT-supported production paradigms denote a common concept where the shop floor is a lively entity composed by interacting intelligent modules whose individual and collective function adapts and evolves ensuring the fitness and adequacy of the organization, owning the system, in tackling profitable but volatile business opportunities. The self-organizing and peer to peer nature of these systems renders a collective behaviour and dynamics that are fundamentally new. Conventional diagnostic methods and tools have not been designed targeting the envisioned systems therefore lack the required support. In this paper the emerging IT-based production paradigms are surveyed as well as the existing diagnostic methods whose adequacy is analysed. The resulting requirements and characteristics are exposed to stress the need for rethinking current diagnostic practices in future automation systems.

Optimization of the Operation of Large-Scale Multisource Water-Supply Systems

This paper describes a simulation-optimization model aimed at helping water utilities determine the best way to operate large-scale multisource water-supply systems. The operation of water systems is optimized taking into account the principal planning objectives defined for interventions that include reducing operating costs, satisfying demand, delivering water of appropriate quality, and not prompting the use of emergency sources. The model allows that these planning objectives may not be completely fulfilled in critical circumstances (e.g., droughts) when goals have to be prioritized by the water utilities. The model is a highly nonlinear programming problem and is solved with the general algebraic modeling system (GAMS), using the MINOS algorithm (GAMS/MINOS). The application of the model to the multimunicipal urban water-supply system of the Algarve shows its capabilities for optimizing the operation considering economic and noneconomic goals included in the objective function and to cope with future...

Nitrate probability mapping in the northern aquifer alluvial system of the river Tagus (Portugal) using Disjunctive Kriging

The Water Framework Directive and its daughter directives recognize the urgent need to adopt specific measures against the contamination of water by individual pollutants or a group of pollutants that present a significant risk to the quality of water. Probability maps showing that the nitrate concentrations exceed a legal threshold value in any location of the aquifer are used to assess risk of groundwater quality degradation from intensive agricultural activity in aquifers. In this paper we use Disjunctive Kriging to map the probability that the Nitrates Directive limit (91/676/EEC) is exceeded for the Nitrate Vulnerable Zone of the River Tagus alluvium aquifer. The Tagus alluvial aquifer system belongs to one of the most productive hydrogeological unit of continental Portugal and it is used to irrigate crops. Several groundwater monitoring campaigns were carried out from 2004 to 2006 according to the summer crops cycle. The study reveals more areas on the west bank with higher probabilities of contamination by nitrates (nitrate concentration values above 50mg/L) than on the east bank. The analysis of synthetic temporal probability map shows the areas where there is an increase of nitrates concentration during the summers.

Exposure assessment of pesticides in a shallow groundwater of the Tagus vulnerable zone (Portugal): a multivariate statistical approach (JCA).

PurposeTo assess groundwater exposure to pesticides, in agricultural areas of ‘Ribatejo’ region (Portugal), and the influence of some key factors in that exposure, field, laboratory and modelling studies were carried out.MethodsThe study was performed in maize, potato, sugar beet, tomato and vegetables agricultural areas, located in a shallow aquifer, with pesticides use and, in most cases, with irrigation practices. Pesticides used in the studied agricultural areas and having leaching potential were selected, being considered also other pesticides included in priority lists, defined in Europe. Evaluation of groundwater exposure to pesticides was carried out by successively: (1) groundwater sampling in seven campaigns over the period 2004–2006; (2) pesticide analysis [including isolation and concentration from the groundwater samples and further determination by gas chromatography–mass spectrometry (GC–MS) of 14 herbicides, four insecticides and two metabolites]; and (3) analysis and discussion of the results by applying joint correspondence analysis (JCA).ResultsFrom the 20 pesticides and metabolites selected for the study, 11 were found in groundwater. Pesticides and metabolites most frequently detected were atrazine, alachlor, metolachlor, desethylatrazine, ethofumesate, α-endosulfan, metribuzine, lindane and β-endosulfan. The results showed that groundwater exposure to pesticides is influenced by local factors—either environmental or agricultural, as precipitation, soil, geology, crops and irrigation practices. Spring and autumn were more associated with the detection of pesticides being more likely to observe mixtures of these compounds in a groundwater sample in these transition seasons.ConclusionsThis work evidences the importance of models, which evaluate pesticides environmental behaviour, namely their water contamination potential (as Mackay multicompartimental fugacity model) and, specially, groundwater contamination potential (as GUS and Bacci and Gaggi leaching indices), in pesticide selection. Moreover, it reveals the importance to adapt proper statistical methods according to level of left-censored data. Using JCA was still possible to establish relations between pesticides and their temporal trend in a case study where there were more than 80% of data censored. This study will contribute to the Tagus river basin management plan with information on the patterns of pesticide occurrence in the alluvial aquifer system.

Major Issues Regarding the Efficiency of Monitoring Programs for Nitrate Contaminated Groundwater

Major issues regarding the efficiency of moni toring programs for nitrate contaminated groundwater are analyzed in this paper: (i) representativeness of monitoring networks; (ii) correct interpretation of the monitoring data and resulting time series and trends; and (iii) differentiation among the different sources of nitrates in groundwater. Following an overview of the nitrate contamination problem and possible solutions, as well as some of the difficulties found, a relatively straightforward method for assessing monitoring network representativity is presented, namely interpolation standard error assessment. It is shown how nitrate-concentration time series resulting from periodic observations can be corrected with a conservative tracer, in order to avoid misinterpretation and confirm or correct apparent trends. Finally, coupled ¹⁵N and ¹⁸O isotope signatures of nitrate (NO₃⁻) in groundwater are used to differentiate among nitrogen (N) sources, to ensure correct targeting of restoration measures. The case study regards a Nitrate Vulnerable Zone in the south of Portugal, designated in compliance with the European Nitrates Directive, where coastal discharge of nutrient-rich groundwater threatens the good qualitative and ecological status of the Ria Formosa coastal lagoon. Results show that mineral fertilizer is the main source of N in groundwater, and that increases in N load can be masked by dilution phenomena.

Combining natural background levels (NBLs) assessment with indicator kriging analysis to improve groundwater quality data interpretation and management.

The natural background level (NBL) concept is revisited and combined with indicator kriging method to analyze the spatial distribution of groundwater quality within a groundwater body (GWB). The aim is to provide a methodology to easily identify areas with the same probability of exceeding a given threshold (which may be a groundwater quality criteria, standards, or recommended limits for selected properties and constituents). Three case studies with different hydrogeological settings and located in two countries (Portugal and Italy) are used to derive NBL using the preselection method and validate the proposed methodology illustrating its main advantages over conventional statistical water quality analysis. Indicator kriging analysis was used to create probability maps of the three potential groundwater contaminants. The results clearly indicate the areas within a groundwater body that are potentially contaminated because the concentrations exceed the drinking water standards or even the local NBL, and cannot be justified by geogenic origin. The combined methodology developed facilitates the management of groundwater quality because it allows for the spatial interpretation of NBL values.

Water Quality Assessment of the Mining-Impacted Elqui River Basin, Chile

Multivariate data analysis techniques were used to identify the interrelationships between the physical–chemical analyses of 22 parameters sampled monthly from 1991 to 2007 at 16 monitoring stations along the Elqui river and its tributaries to characterize the scale of the geogenic and anthropogenic impacts on the river’s water quality. Principal component analysis was used to identify the differences and similarities between variables in the watershed. Factorial indices, computed to highlight the sections of the river and tributaries more influenced by hydrothermal, mining or agricultural activities, made it possible to synthesize groups of parameters with similar characteristics into a single value.ZusammenfassungVon 1991 bis 2007 wurden an 16 Beobachtungstationen entlang des Elqui-Flusses und seinen Zuflüssen monatlich 22 physiko-chemische Parameter gemessen. Der Grad geogener und anthropogener Einflüsse auf die Wasserqualität wurde mit multivariaten Analysen untersucht. Hauptkomponentenanalyse wurde angewendet, um Unterschiede und Ähnlichkeiten zwischen Variablen in dem Wassereinzugsgebiet zu identifizieren. Um Abschnitte des Flusses und seiner Zuflüsse mit stärkerem Einfluß hydrothermaler, bergaulicher oder landwirtschaftlicher Aktivitäten hervorzuheben, wurden faktorielle Kennzahlen berechnet. Damit war es möglich, Gruppen von Parametern ähnlicher Besonderheiten in einen Einzelwert zusammenzuführen.ResumenSe utilizaron técnicas de análisis multivariante para identificar las relaciones entre los análisis de 22 parámetros fisicoquímicos obtenidos mensualmente desde 1991 hasta 2007 en 16 estaciones de monitorio a lo largo del Río Elqui y sus tributarios, en función de caracterizar de la escala de los impactos geogénicos y antropogénicos sobre la calidad del agua del río. El análisis de componentes principales (PCA) fue usado para identificar las diferencias y similitudes entre variables de la cuenca. Los índices factoriales, estimados para destacar las zonas del río y sus tributarios más influida por las actividades minerales, hidrotérmicas o agrícolas, permitieron reunir grupos de parámetros con similares características dentro de un solo valor.抽象化学水质监测指标之间的关系,以研究地质成因和人类活动作用对流域水质的影响程度。利用主成分分析法(PCA)识别了流域内各变量之间的差异与相似性。利用因子分析突出了埃尔基河及其支流受热液、采矿和农业活动的影响程度,使具有相似特征的多元变量转化为单一变量成为可能。

Improving reservoir description by using geostatistical and multivariate data analysis techniques

In order to improve the reservoir description phase in extensively recognized oil fields, a methodology, combining geostatistics, multivariate data analysis, and appropriate geological reasoning, was developed. This methodology involves several steps: (i) Splitting the variable set available on each well into two subsets, with different intrinsic meaning—the “principal” and the “supplementary” variables. The former summarize oil-quality distribution, and supplementary variables are chosen to reproduce some geological/petrophysical characteristics of the reservoir. (ii) Application of Correspondence Analysis to the disjunctive table recoding all data in categorical form, using arbitrary class limits for quantitative variables. (iii) Selection of “final” class limits by visualization of supplementary projections onto the factorial plane and by contiguity analysis of groups in the well-location map. Groups of wells are arranged in decreasing order of their average oil-quality distribution, given by an index, which is the projection onto factor 1 of correspondence analysis. (iv) Establishment of Reservoir Quality Zones (RQZ), being a zone defined as a set of embedded groups, displaying spatial contiguity. The oil-quality index of a given zone is greater than a certain limit, which is related to fluids saturation, spatial distribution of net oil column and petrophysical characteristics of the zone. (v) Estimation of boundaries for each zone through Transitive Kriging of indicator data. (vi) Oil-in-place volume calculation for each zone, combining the geometrical estimation approach with Universal Kriging. Steps (i)–(iv) are applied interactively, using a case study for illustration purposes. Some consequences of horizontal zonation on production planning are discussed, focusing on the improvement of the reservoir description phase, brought by the proposed methodology.

Evaluating piezometric trends using the Mann-Kendall test on the alluvial aquifers of the Elqui River basin, Chile

Abstract Today, more than ever, there is a need to implement robust statistical methods to ensure the proper evaluation of water resources data to support decision makers in water resources planning and management. Graphing or mapping data for visualization is the easiest way to communicate trends, especially to a non-technical audience. This paper describes the use of an approach that combines the Mann-Kendall test, Sen slope test and principal component analysis to detect and map the monthly trends of piezometric time series and their magnitude in the period 1979–2008. The data were obtained in 23 shallow wells in the alluvial aquifers of the Elqui River basin in central Chile, an area characterized by scarce water resources and intense agricultural and mining activities. The results show significant downward trends at the majority of the wells. Because groundwater in these shallow wells is highly dependent on the water in the river and its tributaries, the reasons for these downward trends are mainly related to a decrease of streamflow observed in the Elqui River. The streamflow is derived from mountain snowmelt rather than from rainfall, which showed no flow trend during the same period.