Local Pollution Sources Research Articles

Spatial and temporal distribution characteristics and influencing factors analysis of particulate matter pollution in Jinan City

With the development of economy, PM2.5 and PM10 have already become primary air pollutants that seriously affect people’s life and health. As the capital city of Shandong Province, Jinan’s atmospheric environment quality is not optimistic. In the work, hourly PM2.5 and PM10 data were collected in Jinan from 2017 to 2019 to reveal the temporal and spatial variation of local particulate matter and its influencing factors. From 2017 to 2019, the average concentrations of PM2.5 and PM10 decreased by 17.61% and 15.87%, respectively, indicating the effects of efficient control measurements during this period, but which still exceeded the annual limit of the grade II standard. The concentrations of PM2.5 and PM10 were highest in winter and lowest in summer. In addition, the diurnal variation pattern of PM2.5 and PM10 was consistent, which was double peak and double trough pattern. Correlation analysis showed that PM2.5 and PM10 were negatively correlated with temperature and positively correlated with atmospheric pressure, NO2, SO2, and CO, indicating that both meteorological factors and secondary aerosol generation had a strong impact on local particulate pollution. In terms of spatial distribution, both of them showed a general trend that was higher in the north and lower in the south, which was closely related to the distribution of local pollution sources. The results of wavelet analysis showed that PM2.5 and PM10 expressed alternate fluctuation on 34, 69, and 172 days time scales. Long-distance transmission had certain contribution to the local particulate matter concentration, and its potential contribution was mainly from the northern, northwestern, and southwestern areas of Jinan. Through the analysis of atmospheric particulate matter in Jinan city, the results shown herein provide a scientific insight into the impact factors of air pollution in Jinan city.

Real-time location algorithms of drinking water pollution sources based on domain knowledge.

The real-time location of pollution sources is the process of inverting pollution sources based on the dynamic optimization model constructed by the time-varying pollution concentration detected by the water quality sensor. Due to the vast quantities of the water supply networks, the water quality sensors will only be placed on critical nodes, resulting in multiple solutions. However, the increased monitoring data enhances the uniqueness of the solution. Combined with the real-time location of pollution sources, this work proposed a multi-strategy dynamic multi-mode optimization algorithm based on domain knowledge, which could guide the population search and avoid trapped into local optimal. The merging mechanism was used to keep the diversity of the population and prevent sub-population clustering on the same optimal solution. The simulation results showed that the algorithm could effectively solve the real-time location problem of pollution sources in different pipe networks and pollution scenarios.

Vertical characterization and potential sources of aerosols in different seasons over the Yangtze River Delta using ground-based MAX-DOAS.

Assessing the vertical distribution of aerosols in the atmosphere can elucidate the regional sources of accumulated pollutants at different altitudes. Although studies in Hefei have mainly focused on aerosols in the near-surface atmosphere, few studies have assessed the vertical variability in aerosol concentrations. In this study, the vertical aerosol distribution in Hefei was analyzed continuously for one year (from March 2018 to February 2019) using multi-axis differential optical absorption spectroscopy. The aerosol extinction coefficient was the highest in winter (0.94km-1), followed by autumn (0.63km-1), spring (0.57km-1), and summer (0.47km-1). Local pollution caused the accumulation of aerosols near the surface. The rate of decrease of the aerosol extinction coefficient was higher in autumn and winter than in spring and summer. The diurnal variations of aerosol extinction coefficient in the different seasons were affected by the planetary boundary layer height, and we observed notable high-altitude transport of aerosols in autumn. We assessed the vertical distribution of the aerosol extinction coefficient under different pollution concentrations and identified peak values mainly below a height of 0.5km. With increasing height, the extinction coefficient decreased linearly and slowly under low PM2.5 concentrations, whereas decreased more rapidly under high PM2.5 concentrations. Clustering analysis, the weight potential source concentration function, and the concentration weighted trajectory model inferred different seasonal characteristics in the potential source areas of aerosols at different heights. In addition to local pollution sources, Jiangsu Province was found to be the main source of pollution in Hefei at a height of 0.4km, whereas Hubei Province was the main source of pollution at a height of 2km.

Environmental Aspect of the Cement Manufacturing in the Świętokrzyskie Mountains (Southeastern Poland)

The research area located in south-eastern Poland is exposed to alkaline pressure from a cement plant in Nowiny, which has been operating there since 1960. Both biotic and abiotic components of the natural environment remain in the zone of the plant’s negative impact. Their reaction, described according to the concept of geo- and bioindicators, provides valuable information on the state of the natural environment in this area. In 2016–2018, the properties of precipitation were being investigated by determining its pH, EC (specific electrolytic conductivity), and chemical composition in terms of the presence of selected heavy metals. Additionally, the chemical composition of samples of two-year-old pine needles, bark, and wood, as well as soil taken from the immediate vicinity of the cement plant, was analyzed. The analysis performed using the Inductively Coupled Plasma-Mass Spectrometer-Time-of-Flight (ICP-MS-TOF) showed the presence of heavy metals. The highest contents were recorded in soils (Pb 123 mg·kg−1; Cr 138 mg·kg−1; Cu 18 mg·kg−1; Zn 699 mg·kg−1), while the lowest ones were found in the wooden cores of drilled trees (Pb 0.1 mg·kg−1; Cr 1 mg·kg−1; Cu 0.1 mg·kg−1; Zn 4.1 mg·kg−1). On the basis of the research conducted on precipitation, it was found that the pH and EC values were increased, and the presence of heavy metals (Pb, Cr, Ni, and Cu) indicating a local source of pollution was indicated.

The Micrometeorology of the Haifa Bay Area and Mount Carmel during the Summer

The Haifa bay area (HBA), which includes Mount Carmel and the Zevulun valley is the third largest metropolitan area in Israel. It is also a centre of heavy industry and an important transportation hub which serve as sources of local anthropogenic pollution. Such sources are associated with adverse health effects. In order to estimate the possible exposure of the inhabitants in such heterogeneous orographic area, a detailed atmospheric transport and dispersion modelling study is required, which in turn must take into account the local micrometeorology. The aim of this study is to conduct a spatio-temporal analysis of the flow field in the HBA in order to identify the common patterns of the average wind and characterize the statistical parameters of turbulence in this area, essential for detailed pollutants dispersion modelling. This study analyses data collected during four months of summer in a network of 16 weather stations which extend across Mount Carmel and the Zevulun valley. It was found that, during the evening and night time on Mount Carmel, different flow patterns may develop on each side, separated by the watershed line. When such conditions do not develop, as well as during the daytime, the wind field, both on Mount Carmel and the Zevulun valley is approximately homogenous. The analysis of the Monin–Obukhov similarity theory functions for the velocity standard deviations show a distinct difference between Mount Carmel and the Zevulun valley, as well as between strong and weak winds. This difference can be clearly seen also in the diurnal hourly distribution of atmospheric stabilities which exhibit higher proportions of unstable conditions in the Zevulun valley during day time and higher proportion of stable stratifications at the Mount Carmel during night-time.

Characterization of 56 airborne persistent organic pollutants (POPs) in gas-phase and particle-phase

A systematic investigation was conducted on 56 persistent organic pollutants (POPs) in the atmosphere at seven functional regions of Jinan, China. The POPs included 16 polycyclic aromatic hydrocarbons (PAHs), 6 phthalic acid esters (PAEs), 17 polychlorinated biphenyls (PCBs), and 17 organochlorine pesticides (OCPs). The concentrations in gas-phase and particle-phase were monitored and analyzed to assess the contamination status and to identify the pollution sources according to the mass ratios between POP congeners and the distribution among the sampling regions and periods. The results show that the pollution level at a recreational area was lower than that in other regions of the city and it was higher in winter than in summer for all the 7 sampling sites. Sixteen polycyclic aromatic hydrocarbons (PAHs) were evenly distributed between gas-phase and particle-phase. The total concentration of phthalic acid esters (∑PAEs) in particle-phase was 96.4% larger than that in gas-phase, which was possibly derived from artificial plastics. PCB-126 was one of the major pollutants of the 17 polychlorinated biphenyls (PCBs) in the atmosphere. High-Cl PCBs favored adhering to airborne particles, while low-Cl PCBs tended to stay in gas-phase. The total concentration of 17 organochlorine pesticides (∑OCPs) in gas-phase accounted for 68.0%, while methoxychlor, dieldrin, and endrin aldehyde preferred to particle-phase. Additionally, the preliminary investigation suggests that local pollution sources contributed to most PAHs in urban sites, while the sources could be complex for the suburban area and adjacent towns in winter. Residues of some OCPs could also come from long-distance transportation.

Elucidating local pollution and site representativeness at the Jungfraujoch, Switzerland through parallel aerosol measurements at an adjacent mountain ridge

Many long-term air pollution and climate monitoring stations face the issue of increasing anthropogenic activities in their vicinity. Furthermore, the spatial representativeness of the sites is often not entirely understood especially in mountainous terrain with complex topographic features. This study presents a 5-year comparison of parallel aerosol measurements (total particle number concentration and equivalent black carbon mass concentration) at the Jungfraujoch in the Swiss Alps (JFJ, 3580 m a.s.l.), and an adjacent mountain ridge, the Jungfrau East Ridge (JER, 3705 m a.s.l.), in 1000 m air-line distance to the main site. The parallel aerosol measurements reveal characteristic differences in the diurnal variations between the two sites under certain specific meteorological conditions. Our analysis estimates that on 20%–40% of the days local activities at the Jungfraujoch have a clear influence on the measured time series of the total aerosol number concentration and the equivalent black carbon mass concentration. This influence is mainly seen in form of strong isolated spikes rather than by an increase in the on-site background concentration. They can thus be flagged during the data quality assurance process and filtered from those measurement parameters available at high time resolution. Removing the spikes from the original time series results in daily mean values for the total aerosol number concentration and equivalent black carbon mass concentration that are 5%–10% lower compared to the original signals. During nighttime with hardly any local pollution sources that cause spikes this percentage decreases towards 0%. The signal baselines at the Jungfraujoch and Jungfrau East Ridge correlate well during more than 50% of the days.

Characteristics and source attribution of PM2.5 during 2016 G20 Summit in Hangzhou: Efficacy of radical measures to reduce source emissions

A field campaign was conducted to study the PM2.5 and atmospheric gases and aerosol's components to evaluate the efficacy of radical measures implemented by the Chinese government to improve air quality during the 2016 G20 Summit in Hangzhou China. The lower level of PM2.5 (32.48 ± 11.03 µg/m3) observed during the control period compared to pre-control and post-control periods showed that PM2.5 was alleviated by control policies. Based on the mass concentrations of particulate components, the emissions of PM2.5 from local sources including fossil fuel, coal combustion, industry and construction were effectively reduced, but non-exhaust emission was not reduced as effectively as expected. The accumulation of SNA (SO42−, NO3−, NH4+) was observed during the control period, due to the favourable synoptic weather conditions for photochemical reactions and heterogeneous hydrolysis. Because of transboundary transport during the control period, air masses from remote areas contributed significantly to local PM2.5. Although, secondary organic carbon (OCsec) exhibited more sensitivity than primary organic carbon (OCpri) to control measures, and the increased nitrogen oxidation ratio (NOR) implied the regional transport of aged secondary aerosols to the study area. Overall, the results from various approaches revealed that local pollution sources were kept under control, indicating that the implementation of mitigation measures were helpful in improving the air quality of Hangzhou during G20 summit. To reduce ambient levels of PM2.5 further in Hangzhou, regional control policies may have to be taken so as to reduce the impact of long-range transport of air masses from inland China.

Significance of the long-term biomonitoring studies for understanding the impact of pollutants on the environment based on a synthesis of 25-year biomonitoring in the Holy Cross Mountains, Poland.

This review presents compiled results of complex biomonitoring studies that have been conducted in the Holy Cross Mountains, south-central part of Poland, since the 1990s. The significance of these studies results from several aspects: (i) a number and a variety of plant organisms used, e.g., mosses, lichens, coniferous and deciduous trees, and their tissues (wood, bark, needles, leaves, the aboveground parts of several vascular plants); (ii) applications of a broad scope of instrumental methods aiming at determining major and trace elements (including rare earth elements), organic compounds (PAHs, PCBs, phenols), and stable sulfur isotopes (δ34S); and (iii) different methodological and environmental issues addressed. The comparison and interpretation of results derived from seventeen sampling campaigns carried out between 1994 and 2017 are a valuable source of information on the following: (i) bioaccumulative properties of organisms used in air quality monitoring, (ii) identification and variations of local and regional pollution sources and geochemical landscape patterns and processes over years, and (iii) establishing environmental factors that variously affected chemical composition of plants growing under physiological stress, including roadside vegetation and plants from acid mine drainage areas.

Application of a Numerical-Asymptotic Approach to the Problem of Restoring the Parameters of a Local Stationary Source of Anthropogenic Pollution

Application of a Numerical-Asymptotic Approach to the Problem of Restoring the Parameters of a Local Stationary Source of Anthropogenic Pollution

Investigation and Water quality Analysis of Agricultural nonpoint Source pollution in Tanxia Town

Taking the small watershed in Tanxia town as an example, the classified investigation of agricultural non-point source pollution in the tributaries of Lijiang River was carried out, the sources of local agricultural non-point source pollution were analyzed, and the surface water environmental quality standard and Nemero index method were used to evaluate the water quality of the basin. The results show that the water quality of the basin is poor and the pollution exceeds the standard all the year round, and the source of agricultural non-point source pollution mainly depends on the pollution of agricultural chemical fertilizer. Improving the use of local chemical fertilizer and rational application of chemical fertilizer are the key factors to improve local agricultural non-point source pollution.

Equidistributed Search+Probability Based Tracking Strategy to Locate an Air Pollutant Source With Two UAVs

As the atmospheric pollution becomes an increasingly serious problem, finding accurately the location of pollutant sources is still challenging. In the present work, a probability-based tracking strategy is proposed for guiding two cooperative unmanned aerial vehicles (UAVs) within a quest area to find an atmospheric pollutant source. This tracking strategy implies deploying algorithmically two phases: exploration and exploitation. During the exploration phase each vehicle follows a trajectory based on plane coordinates generated from a Hammersley sequence. The overlapping between UAVs’ trajectories is avoided by splitting guidance points into two groups by using the k-means algorithm. The navigation trajectories are smoothed by an TSP solver and a cubic spline planning algorithm. The exploitation phase redirects the search to specific locations where the probability of finding the source is higher. This is achieved by considering the quest area as a mesh, where each cell is assigned a probability computed with information collected by the UAVs measurement system. Every time a high concentration is found, the probabilities are recalculated, and flight trajectories are adjusted. The trajectories are semicircular, and the radius is decreased when a new high concentration is found. Simulation data of the proposed tracking strategy shows promising results on the accuracy achieved in the finding of the pollutant source, in comparison with three other tracking strategies: leader-follower, random walk with particle swarm optimization, and a hill climb traceability algorithm.

Оценка пирогенного загрязнения почвенно-растительной системы на основе геохимических маркеров для локальной модели транспортной нагрузки

The choice of informative indicators for local estimates of the transport pressure on urban soil-plant systems is a serious problem of preserving green spaces. The spatial variations of the characteristics of the flows of marker compounds (polycyclic aromatic hydrocarbons (PAHs) acting as geochemical markers), the integral characteristics of the toxicity of soil pollutants, roots and aerial parts of plants TEQ, as well as the values of indicator ratios based on the concentrations of PAHs in the media are considered. The object of local research is the RUDN University campus (Moscow, Russia) with an adjacent forest park area. The territory is located in the zone of influence of heavy traffic flows and is experiencing an intense load from emissions. The state of the territory is monitored at 33 points according to a unique monitoring program. Pollution indicators showed different informativeness for constructing transport pressure models. Various modes of pollution in 3 functional zones of the territory are revealed; the zones of influence of the main sources of pollution are justified. The indicator ratios confirmed the leading source of pollution –pyrogenic emissions of transport, but they are to varying degrees sensitive to the activity of local pollution sources. Priority routes of PAH intake and accumulation in the components of the soil and plant system were identified. For the first time, a correlation between a number of ratios and indicators of polyarene contamination toxicity (TEQ) was established.

Identification of clandestine groundwater pollution source locations and their release flux history

Large numbers of untreated toxic wastes are often buried underground, as a method of disposal. Such methods of clandestine disposal have led to widespread pollution of groundwater resources. These methods of wastes disposal are often adopted to avoid the cost incurred in proper treatment of the waste and untraceability of such clandestine disposals. However, the effect of such disposals manifests in form of groundwater pollution, which if left unchecked would potentially pollute the entire aquifer. Such polluted aquifers need to be reclaimed by implementing proper remediation techniques. However, the effectiveness of any remediation technique would depend on the precise knowledge of the unknown pollutant source/s characteristics, in terms of their Numbers, their Locations and their Release Flux history referred to as NLRF. This study presents a noble technique for simultaneously estimating the unknown number of clandestine pollutant sources, their locations along with their release flux history. Simulated Annealing (SA) is used in Linked Simulation Optimization (LSO) based framework. In this developed methodology, the number of sources and their respective locations and release flux histories are treated as unknown decision variables, and are estimated simultaneously along with the source release flux history.

Living conditions and respiratory health in Walmer Township and Wells Estate, Port Elizabeth, South Africa.

Many impoverished communities in South Africa (SA) simultaneously face multiple preventable socioenvironmental hazards associated with elevated burdens of ill health. One such hazard is failure to institute effective buffer zones between human settlements and point sources of pollution such as airports and industrial zones. To gather information on living conditions, housing quality and health status in two poor communities in the SA coastal industrial city of Port Elizabeth. The study was undertaken in Walmer Township, situated in close proximity to Port Elizabeth International Airport, and Wells Estate, which borders two industrial sites. Approximately 120 households were randomly selected from each study site. Following written informed consent, information on the neighbourhood environment and housing conditions was collected through administration of a structured questionnaire. The two study sites were similar in respect of household language, income, education, high levels of debt servicing and high reliance on social grants. Relative to Walmer Township, higher levels of indoor dust and bad odours in the neighbourhood were reported in Wells Estate, as were higher rates of selected respiratory ill-health symptoms. Upper respiratory tract symptoms were significantly associated with reports of high levels of indoor dust, while lower respiratory tract symptoms were significantly associated with low income, overcrowding, and having a young child in the household. The study highlights a scenario of a triple environmental hazard to health in the study communities: (i) poverty; (ii) poor-quality housing; and (iii) lack of an effective buffer zone between the study communities and local point sources of pollution. Respiratory ill-health conditions were significantly associated with poverty, household composition and living conditions.

Simultaneous identification of groundwater pollution source location and release concentration using Artificial Neural Network

Groundwater pollution source identification problem plays an important role in designing the groundwater remediation measures. This study aims at identifying the groundwater pollutant source location and its strength given a set of concentration breakthrough curves at different locations. Feed forward three layered artificial neural network (ANN) has been used to identify these two source parameters: location, i.e., the distance of source from the observation point and strength, i.e., the release concentration. A simplified ANN architecture is achieved by presenting the available concentration breakthrough curves in a specific manner as input to the model. The database of 1750 patterns for training and testing of the model is generated employing analytical solution of one dimensional steady flow and transient contaminant transport in a homogeneous aquifer. The performance of the ANN model was evaluated using standard statistical methods. A network with architecture 22-16-2 was found to be optimum and resulted in a normalized root mean square error (NRMSE) of 0.014 for identifying the source location and NRMSE of 0.044 for identifying the source release concentration. The results show that ANN can be a very efficient tool for locating pollution sources and estimating the release concentration at source. A good ANN model performance was obtained even with a simple architecture and with a small number of input variables.

Impact of low-level fine particulate matter and ozone exposure on absences in K-12 students and economic consequences

High air pollution levels are associated with school absences. However, low level pollution impacts on individual school absences are under-studied. Understanding the variability of pollution at individual schools within an urban region could improve school recess decisions, better identify local pollution sources, and improve local economic impact assessments by providing granular information relevant to specific schools. We modelled PM2.5 and ozone concentrations at 36 schools from July 2015 to June 2018 using data from a dense, research grade regulatory sensor network. We determined exposures and daily absences at each school. We used a generalized estimating equations model to retrospectively estimate rate ratios for association between outdoor pollutant concentrations and school absences. We estimated lost school revenue, productivity, and family economic burden. PM2.5 and ozone concentrations and absence rates vary across the School District. Pollution exposure was associated with a rate ratio as high as 1.02 absences per μg m−3 and 1.01 per ppb increase for PM2.5 and ozone, respectively. Significantly, even PM2.5 and ozone exposure below the air quality index breakpoints for good air quality (<12.1 μg m−3 and <55 ppb, respectively) was associated with positive rate ratios of absences: 1.04 per μg m−3 and 1.01 per ppb increase, respectively. Granular local measurements enabled demonstration of air pollution impacts that varied between schools and were undetectable with averaged pollution levels. Reducing pollution by 50% would save $426 000 per year districtwide. Pollution reduction benefits would be greatest in schools located in socioeconomically disadvantaged areas. Heterogeneity in exposure, disproportionately affecting socioeconomically disadvantaged schools, points to the need for fine resolution exposure estimation. The economic cost of absences associated with air pollution is substantial even excluding indirect costs such as hospital visits and medication. These findings may help elucidate the differential burden on individual schools and inform local decisions about recess and regulatory considerations for localized pollution sources.

Assessment of the effect of long-range transport on air pollution trends for different Russian regions

The features of the dynamics of long-range atmospheric pollution of the territories of the Russian Federation under current conditions, in the immediate and distant prospects (from 1980 to 2050) taking into account two scenarios of the changing climate in the 21st century were studied. To assess contribution and trends of long-range atmospheric pollution in Russian regions, a two-dimensional numerical model is constructed, which implements the solution of the coupled problem of transport and diffusion of impurities in spherical coordinates, as well as an improved method for identifying sources of transboundary and local air pollution. The results indicate general trends in the directions of the flow of pollutants to the Russian regions in 1980-2050 from zonal (western) to meridional (southern). Such dynamics is markedly expressed in the regions of Siberia and the Far East and slightly in the European territory of Russia and the Urals. In the climatic scenario RCP8.5, despite the general tendency towards the southern transport of impurities, a certain dispersion of directions from where the regions are polluted becomes noticeable. It indicates an increase in atmospheric pollution from the west in certain regions, mainly in the central part and in the south of the ETR. The greatest danger to long-range atmospheric pollution of the regions of Siberia and the Far East in the coming decades will be sources located south of these territories; of the regions of the ETR and the Urals – sources located to the west and south. These results are important for the development of proposals for ensuring the environmental safety of Russian regions and for planning economic development of the country’s territories that affect the pollution of the environment of ecologically significant zones.

Contrasting wet deposition composition between three diverse islands and coastal North American sites

This study examined spatial variations of precipitation accumulation and chemistry for six sites located on the West and East Coasts of the U.S., and one site each on the islands of Hawaii, Bermuda, and Luzon of the Philippines (specifically Manila). The nine coastal sites ranged widely in both mean annual precipitation accumulation, ranging from 40 cm (Mauna Loa, Hawaii) to 275 cm (Washington), and in terms of monthly profiles. The three island sites represented the extremes of differences in terms of chemical profiles, with Bermuda having the highest overall ion concentrations driven mainly by sea salt, Hawaii having the highest SO42− mass fractions due to the nearby influence of volcanic SO2 emissions and mid-tropospheric transport of anthropogenic pollution, and Manila exhibiting the highest concentration of non-marine ions (NH4+, non-sea salt [nss] SO42−, nss Ca2+, NO3−, nss K+, nss Na+, nss Mg2+) linked to anthropogenic, biomass burning, and crustal emissions. The Manila site exhibited the most variability in composition throughout the year due to shifting wind directions and having diverse regional and local pollutant sources. In contrast to the three island sites, the North American continental sites exhibited less variability in precipitation composition with sea salt being the most abundant constituent followed by some combination of SO42−, NO3−, and NH4+. The mean-annual pH values ranged from 4.88 (South Carolina) to 5.40 (central California) with NH4+ exhibiting the highest neutralization factors for all sites except Bermuda where dust tracer species (nss Ca2+) exhibited enhanced values. The results of this study highlight the sensitivity of wet deposition chemistry to regional considerations, elevation, time of year, and atmospheric circulations.

Water supply network pollution source identification by random forest algorithm

Abstract A novel approach for identifying the source of contamination in a water supply network based on the random forest classifying algorithm is presented in this paper. The proposed method is tested on two different water distribution benchmark networks with different sensor placements. For each considered network, a considerable amount of contamination scenarios with randomly selected contamination parameters were simulated and water quality time series of network sensors were obtained. Pollution scenarios were defined by randomly generated pollution source location, pollution starting time, duration of injection and the chemical intensity of the pollutant. Sensor layout's influence, demand uncertainty and imperfect sensor measurements were also investigated to verify the robustness of the method. The proposed approach shows high accuracy in localizing the potential sources of pollution, thus greatly reducing the complexity of the water supply network contamination detection problem.