Existing Groundwater Monitoring Research Articles

Exact optimisation of spatiotemporal monitoring networks by p‐splines with applications in groundwater assessment

AbstractThis paper develops methods to optimise the sampling strategy for monitoring networks which have fixed locations with regular sampling but with only a proportion of these locations to be used on each sampling occasion. This creates the need for a dynamic spatiotemporal sampling design which makes optimal choices of the locations to be sampled on each occasion. This is a commonly occurring scenario in many environmental settings where there is an existing network of monitoring stations and sampling can be expensive. The particular context of optimisation of an existing groundwater monitoring network is discussed in the paper. The standard design criteria of integrated variance (IV) and variance of the integral (VI) are adapted to the spatiotemporal setting. p‐spline models are shown to allow exact computation of IV and VI, in the case of the additive errors, and a very good approximation of IV in the case of multiplicative errors. The speed of these exact computations allows the globally optimal sampling design to be identified efficiently. In the standard case of additive errors, the design criteria are able to exploit information across time. The only information needed is the location of sampling points, not the values sampled. This contrasts with the case of multiplicative errors where the design criteria are also influenced by the observed response data. Simulated and real examples are used to illustrate the results throughout.

Konieczność walidacji monitoringu wód podziemnych w rejonach starych składowisk na przykładzie składowiska fosfogipsów w Wiślince (Żuławy Gdańskie)

The necessity of validation of groundwater monitoring in the regions of old dumping sites – a case study of a phosphogypsum dump at Wiślinka (Vistula Delta Plain). A b s t r a c t. The phosphogypsum waste dump near Gdansk was located within the Vistula delta depression on alluvial and lacustrine deposits close to the Dead Vistula River in the early 1970s. More than 16 million tonnes of waste deposits was accumulated until 2009. The loam outcrop of the old brick-yard was used for phosphogypsum. The leachates from the waste deposits causes the migration of contaminants due to density and hydraulic gradients down to the Vistula delta aquifers. The leachate is characterised by low pH, very high concentrations of phosphates and sulphates, metal ions, and radioactive elements. The waste dump was ultimately closed in 2009. The dump’s surface has been covered with municipal sewage sludge, as the so-called biological reclamation reduces the dustiness of phosphogypsym and the quantity of leachate, but generated additional threat resulting from the chemical compounds of the sludge. The matter from the municipal sewage sludge, dumped on the surface of the phosphogypsum waste heap, contained hormone disruptive compounds (EDCs), nitrogen compounds, viruses, bacteria and other pathogens. The existing groundwater monitoring started in the mid-1970s and was projected and constructed in a very simple way. The observation wells and piezometers have been screened over a short distance at the bottom. Contaminants of different densities, liberated to the aquifers underneath, cannot be properly detected. The new analytical procedures are implemented in chemical laboratories and new methods of monitoring, e.g. low flow sampling, are now in practice. Also the climate changes and sea level rise along the Baltic coast require a new approach and validation of groundwater monitoring in the surroundings of the old waste dumps of chemical and mining industry.

Geostatistical analysis and optimization of the state hydrogheological monitoring network within the Pripyat river basin (Ukraine)

Formulation of the problem. The State Hydrogeological Monitoring Network has to provide the necessary information to manage groundwater resources and prevent negative changes in the geological environment. Currently, there is a negative tendency to decrease the number of observation wells, loss of information about the space-time variability of the hydrogeological regime elements in Ukraine. In conditions of limited funding, an important task is to develop an effective strategy for reforming the hydrogeological monitoring system, taking into account international experience and based on modern geoinformation technologies. Particular attention has to be given to transboundary territories. One of them is the Pripyat River basin, which is characterized by the low level of the State Hydrogeological Monitoring Network representativeness, both in comparison with European Union standards and with the existing groundwater monitoring network of neighbouring Belarus. The purpose of the article is to evaluate the actual state of the hydrogeological observation wells network and optimize it within the territory of the Ukrainian part of the transboundary Pripyat watershed basin. Methodology and materials. The State Scientific and Production Enterprise "Geoinform of Ukraine" database of State Groundwater Monitoring System composition and functioning as well as zoning map under the conditions of water exchange formation in the upper water-bearing level were used for the study. For the studied territory of the water exchange basin of Pripyat, the analysis of density and uniformity of the observation points distribution as well as the variogram analysis of the spatial distribution of groundwater-level altitudes within the study area were carried. For the actual monitoring network, the expected error of the spatial modelling of the groundwater-surface was evaluated. Results. The obtained results of the geostatistical analysis made it possible to substantiate the project wells locations within the water exchange sub-basins to improve the quality of hydrogeological monitoring problem solutions. Scientific novelty. The method of the hydrogeological monitoring network optimization has been improved based on geoinformation and geostatistical approaches and implemented for the Ukrainian part of the Pripyat River basin, taking into account the hydrogeological conditions of the territory and the configuration of the existing network. Practical significance. Optimization and increment of the observation wells network, taking into account the obtained results, will provide the effective functioning of the hydrogeological monitoring system within the Ukrainian part of the Pripyat River basin and will have an economic effect, given that the cost of any measures to improve the groundwater quality and quantity is far more expensive than the monitoring system optimization.

The Campus Wells Program: preserving and re-tasking

I used existing groundwater monitoring wells in the Back Bay area of Boston, MA as an effective way to teach the applied aspects of integrating the natural world with the built environment. These wells were installed as part of engineering studies for construction and rehabilitation of campus buildings, and through their use in laboratory exercises, undergraduate students developed valuable, field-based insight into the physical meaning of environmental science, mathematical models of groundwater movement, and the practical knowledge of professional practice. I arranged ongoing permission to access these wells and prevent them from being plugged once construction was completed. I compiled the existing long-term well data from both the Northeastern University Physical Plant office and the geotechnical engineering firm who installed the wells, providing students with context for their field measurements in lab.This project gave undergraduate students in introductory and upper division environmental science courses an opportunity to learn about water quality issues, construction and excavation issues, architectural retrofitting, and historical water table changes through analysis of the data. Close proximity of the wells to the classroom made possible many independent student projects.Through the Campus Wells Program, I involved the working community - including the Physical Plant staff at multiple colleges, and professional geologists in the geotechnical engineering consulting firm - in the learning process. Students recognized that their class laboratory exercises contributed real data to a long-term study of the hydrogeology of the campus, giving students buy-in to the project. The Campus Wells Program is a virtually cost-free, practice-oriented teaching opportunity that any university undergoing construction or site cleanup can implement.

A computational assessment of representative sampling of soil gas using existing groundwater monitoring wells screened across the water table

Representative sampling is of great importance to decision making regarding contaminant site risks and remedial effectiveness. A focus here is whether existing groundwater monitoring wells screened across the water table can be sampled to yield representative indicators of soil gas composition. For the first time, we provide multi-phase, multi-component computational simulations to address this. We simulated high and low gas extractions rate strategies to sample the gas phase over short and extended screening intervals across the water table. We investigated the options against a field data set representative of typical hydrocarbon vapour profiles, inclusive of major gases, oxygen and carbon dioxide. We also evaluated the sampling options for uniform and non-uniform multi-component gasoline LNAPL distributions, including hazardous chemicals. Less sensitivity to the sampling option was observed for depth-wise increasing concentration profiles with a near-constant concentration across the screen. Significant discrepancy between the ratio of different compounds in the sample and in-situ (real) values was observed for high-rate gas extraction (particularly for an extended-screen). Low-rate gas extraction provided satisfactory results for all the scenarios. Shorter screening slightly improved the accuracy of this option. Graphical representations are provided to allow assessment of the applicability of each sampling option for various site conditions.

The representativity index of a simple monitoring network with regular theoretical shapes and its practical application for the existing groundwater monitoring network of the Tychy-Urbanowice landfills, Poland

The representativity index R u is a measure used in assessing the chemical status of groundwater based on monitoring studies. This index is designed to describe the spatial homogeneity of the monitoring network. The general formula for calculating the index R u includes the following parameters: average distance to the nearest monitoring point, number of monitoring points, and size of the test area. Calculations to determine the representativity index for four different shapes of the theoretical test study with the same area and the same number of monitoring points have been done. These calculations suggest that the index value depends on the shape and the position of these points, and it is less dependent on the size of the surface. An assessment of the representativeness of the monitoring network for the different numbers and configurations of the piezometers around the Tychy-Urbanowice landfills based on the mentioned index has been done as well. The best and the worst configurations of the monitoring network for these landfill sites in mathematical terms have been presented in this paper. The results are surprising: the highest index value is obtained with a single measurement point. The calculations were performed with the area of landfill and the area limited by the range of piezometers as the exclusive test area. To choose the optimal test area, representativity indicator was calculated also for the monitoring network around waste landfills, including the buffer network behind the piezometers. The difference in the values of the representativity indicator for subsequent variants is astounding. The representativity index for the same monitoring network is about 20 % higher if we consider the test area limited by external piezometers, and higher by another 20 %, taking into account the 95-m buffer zone behind piezometers. Due to increase of the representativity index value with a different width of buffer zone, the mathematical calculations of the monitoring network’s representativeness should be supported by an analysis of the geological structure and hydrogeological conditions occurring in the analyzed area.

In‐Situ Sonication for Enhanced Recovery of Aquifer Microbial Communities

Sampling methods for characterization of microbial communities in aquifers should target both suspended and attached microorganisms (biofilms). We investigated the effectiveness and reproducibility of low-frequency (200 Hz) sonication pulses on improving extraction efficiency and quality of microorganisms from a petroleum-contaminated aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.65, 0.9, and 1.1 kW) were applied to three different groundwater monitoring wells. Groundwater samples extracted after each pulse were compared with background groundwater samples for cell and adenosine tri-phosphate concentration. Turbidity values were obtained to assess the release of sediment fines and associated microorganisms. The bacterial community in extracted groundwater samples was analyzed by terminal-restriction-fragment-length polymorphism and compared with communities obtained from background groundwater samples and from sediment cores. Sonication enhanced the extraction efficiency up to 13-fold, with most of the biomass being associated with the sediment fines extracted with groundwater. Consecutive pulses at constant power were decreasingly effective, while pulses with higher power yielded the best results both in terms of extraction efficiency and quality. Our results indicate that low-frequency sonication may be a viable and cost-effective tool to improve the extraction of microorganisms from aquifers, taking advantage of existing groundwater monitoring wells.

The Optimization of Groundwater Dynamic Monitoring Network – An Example of the North Ordos Basin

Groundwater management is base on an sufficient dynamic monitoring network of groundwater depth and quality. Whil the monitoring network in Ordos Bain is insufficient due to the network is not been finished yet. Thus, in this paper, the dynamic type mapping method of groundwater based on GIS developing is used to optimize the distribution of dynamic monitoring positions. The purpose of the optimization is to observe reginal dynamics of groundwater with less monitoring wells. The reginal groundwater depth has a impact of hydroecology. Thus the optimization also consider the distribution of vegetations which are closely related with groundwater. The optimization shows that at least 28 new monitoring wells are needed depend on the existing groundwater monitoring network. The monitoring positions of 28 new wells are also estimated by the method.

Evaluation of Efficacy of Groundwater Level Monitoring Network by Graphical and Multivariate Statistical Techniques

Knowledge of spatial and temporal patterns of groundwater levels is useful to evaluate efficacy of existing groundwater monitoring network. Present study demonstrates application of graphical and multivariate statistical techniques to evaluate monitoring network of 50 sites in hard-rock aquifers of Ahar River catchment of Udaipur, Rajasthan. The graphical analysis included plotting of time plots and box-whisker plots for monthly groundwater levels for three years (May 2006-July 2009). The result revealed that temporal pattern of the groundwater level was almost similar for majority of the sites. Box-whisker plots revealed that the spatial variations of the groundwater levels were smaller in post-monsoon compared to that in the pre-monsoon season. Furthermore, principal component analysis (PCA) of the groundwater levels revealed that the first two principal components (PC) characterized as ‘hydraulic connectivity factor’ and ‘rainfall factor’ explained more than 75% of the total variance. Based on the PCA, the monitoring sites were classified into five groups according to behavior or

A New Screening Method for Methane in Soil Gas Using Existing Groundwater Monitoring Wells

Methane in soil gas may have undesirable consequences. The soil gas may be able to form a flammable mixture with air and present an explosion hazard. Aerobic biodegradation of the methane in soil gas may consume oxygen that would otherwise be available for biodegradation of gasoline hydrocarbons. The consumption of oxygen by methane may increase the chance of completing a vapor intrusion pathway for benzene. A protocol was developed to sample soil gas from conventional groundwater monitoring wells that had some portion of their screen in the vadose zone. This protocol was applied at 12 gasoline stations in Oklahoma. The soil gas as collected from the monitoring wells was not flammable, due to low concentrations of oxygen. However, soil gas at five of the 12 sites could form flammable mixtures in air. To allow a simple comparison of the possible effect of methane on vapor intrusion of benzene, characteristics of the sites were matched to computer simulations published by others. At three of 11 sites, the methane in the soil gas might cause unacceptable concentrations of benzene in a hypothetical receptor. Ethanol is readily fermented to methane. The increased use of ethanol in gasoline raises concerns about methane at gasoline spill sites. At five sites with high concentrations of methane, the concentration of 14C in methane was used to determine the source of the methane. At four sites, the majority of the methane was produced from anaerobic biodegradation of petroleum, and not from ethanol or another biofuel. At three sites, the maximum possible contribution of methane from ethanol or another biofuel was 5.1% of total methane. At a fourth site, the maximum contribution of ethanol or another biofuel to methane was 31% of the total methane. At the fifth site, the methane came from a leak of natural gas.

The groundwater monitoring in the Novogorod region in the system of regional nature management

80 This article examines the current state of the groundwater system monitoring in the Novgorod region. The groundwater monitoring observations serve as the basis for prediction assessment of water resources. The efficiency of water resource management largely depends on the comprehensiveness and reliability of information on the groundwater condition. The existing groundwater monitoring system has proven to be incapable of fully implementing its functions. It requires a fundamental reorganization and further development at the contemporary scientific and technical level, since groundwater resource management is impossible without a quantitative forecast of groundwater condition and properties. From the perspective of rational Nature management, the leading ecological function of underground hydrosphere is carried out by fresh underground waters. Rational Nature management underlies the sustainable development of the Northwest region, which is economically viable for the European territory of the country.

Groundwater in the Urban Environment: Management Needs and Planning Strategies

Problem statement: Over the past thirty years urban transformations, such as urbanization, suburbanization, dis-urbanization and re-urbanizati on processes, have modified the subsurface conditions of Torino (NW Italy). In order to contri bute to the solution of the problems concerning groundwater the conceptual model for the groundwater flow system, the schematization of the aquifers boundaries and the estimation of basic hydrogeologi cal parameters are among the main issues which should be investigated. This study was mainly aimed at illustrating (i) a new interpretation for the Torino urban area hydrogeological setting (ii) high lighting the current groundwater criticisms and (ii i) emphasizing the priority actions to implement a goo d urban groundwater management system. Approach: Starting from the analysis of the existing subsurf ace data, a comprehensive description of the general geological setting had been performed, three main (hydro) stratigraphical Units had been described and their reciprocal relationships had be en detected. On the basis of the available data, th e unconfined groundwater natural seepage had been reconstructed, a hydrogeological map and a cross section illustrating the units characteristics had been produced. Results: The analysis highlighted three main groundwater criticisms: A natural unconfined groundwater level uplifting in the quaternary unit 1, a widespread inorganic pollution under abandoned industrial areas and many interference problems with the groundwater in unit 1 caused by the new tr ansport infrastructures. Another important problem was the scarce geographical density of the existing groundwater monitoring network operating in the urban area. Conclusion: Solutions to specific, local problems can give the opportunity to transform some of the above mentioned problems into useful resources for the territorial development. The expansion of the groundwater observation network clearly appeared to be the main action to be implemented by the public authorities. Other succes sive actions could be the construction of a multi- purpose interactive real-time mathematical model of groundwater movement in the urban area and the development of improved methods for predicting changes of hydrogeological conditions.

A review of the National Groundwater Monitoring Network in Korea

AbstractThe drastic expansion of cities and the rapid economic growth in Korea have caused dramatic increases to demand from groundwater supplies for drinking, domestic, agricultural and industrial water usage. The Ministry of Construction and Transportation and the Korea Water Resources Corporation have constructed and operated the National Groundwater Monitoring Network (NGMN) throughout the country since 1995. The NGMN, an official project establishing a total of 320 groundwater monitoring stations, was completed in 2005. Each national groundwater monitoring station serves as a baseline and primary station to monitor long‐term general trends in water‐level fluctuations and in groundwater quality. The present NGMN and its monitoring capabilities were evaluated to enhance the efficiency of groundwater monitoring and to meet the new societal conditions. Based on reviews and evaluations, some suggestions and recommendations are made with regard to improvements of the national network, including the installation of rainfall gauges in groundwater monitoring stations, gathering groundwater data every hour instead of every 6 h as at present, involving major cations and anions in the regular and periodic chemical analyses, regular periodic analyses of collected groundwater data, and construction of 199 additional groundwater monitoring stations to supplement the existing groundwater monitoring network. Copyright © 2006 John Wiley & Sons, Ltd.

Flux-based assessment at a manufacturing site contaminated with trichloroethylene

Groundwater and contaminant fluxes were measured, using the passive flux meter (PFM) technique, in wells along a longitudinal transect passing approximately through the centerline of a trichloroethylene (TCE) plume at a former manufacturing plant located in the Midwestern US. Two distinct zones of hydraulic conductivity were identified from the measured groundwater fluxes; a 6-m-thick upper zone (∼7 m to 13 m below the ground surface or bgs) with a geometric mean Darcy flux ( q 0) of 2 cm/day, and a lower zone (∼13 m to 16.5 m bgs) with a q 0 ∼ 15 cm/day; this important hydrogeologic feature significantly impacts any remediation technology used at the site. The flux-averaged TCE concentrations estimated from the PFM results compared well with existing groundwater monitoring data. It was estimated that at least 800 kg of TCE was present in the source zone. The TCE mass discharge across the source control plane (85 m × 38 m) was used to estimate the “source strength” (∼365 g/day), while mass discharges across multiple down-gradient control planes were used to estimate the plume-averaged, TCE degradation rate constant (0.52 year − 1 ). This is close to the rate estimated using the conventional centerline approach (0.78 year − 1 ). The mass discharge approach provides a more robust and representative estimate than the centerline approach since the latter uses only data from wells along the plume centerline while the former uses all wells in the plume.

In Situ Assessment of Biodegradation Potential Using Biotraps Amended with 13C-Labeled Benzene or Toluene

Stable isotope fractionation analysis of an aquifer heavily contaminated with benzene (up to 850 mg L(-1)) and toluene (up to 50 mg L(-1)) at a former hydrogenation plant in Zeitz (Saxonia, Germany) has suggested that significant biodegradation of toluene was occurring. However, clear evidence of benzene biodegradation has been lacking at this site. Determining the fate of benzene is often a determining factor in regulatory approval of a risk-based management strategy. The objective of the work described here was the demonstration of a new tool that can be used to provide proof of biodegradation of benzene or other organics by indigenous microorganisms under actual aquifer conditions. Unique in situ biotraps containing Bio-Sep beads, amended with 13C-labeled or 12C nonlabeled benzene and toluene, were deployed at the Zeitz site for 32 days in an existing groundwater monitoring well and used to collect and enrich microbial biofilms. Lipid biomarkers or remaining substrate was extracted from the beads and analyzed by mass spectrometry and molecular methods. Isotopic analysis of the remaining amounts of 13C-labeled contaminants (about 15-18% of the initial loading) showed no alteration of the 12C/13C ratio during incubation. Therefore, no measurable exchange of labeled compounds in the beads by the nonlabeled compounds in the aquifer materials occurred. Isotopic ratio analysis of microbial lipid fatty acids (as methyl ester derivatives) from labeled benzene- and toluene-amended biotraps showed 13C enrichment in several fatty acids of up to delta (13C) 13400%o, clearly verifying benzene and toluene biodegradation and the transformation of the labeled carbon into biomass by indigenous organisms under aquifer conditions. Fatty acid profiles of total lipid fatty acids and the phospholipid fatty acid fraction and their isotopic composition showed significant differences between benzene- and toluene-amended biotraps, suggesting that different microbial communities were involved in the biodegradation of the two compounds.

Quantifying uncertainty of the semivariogram of transmissivity of an existing groundwater monitoring network

AbstractA method is presented for quantifying the uncertainty of the semivariogram of transmissivity and determining the required number of measurements. In this method, the estimated semivariogram and its 95% confidence limits are first determined from a finite number of measurements. The uncertainty of the estimated semivariogram is then quantified using the random field simulation technique. For a given value of the quantitative index of uncertainty, the required number of measured data can finally be obtained. Actual transmissivity data of an existing groundwater monitoring network are used in the application of the proposed method. The required numbers of measurements of transmissivity for four different values of the quantitative index of uncertainty are provided, from which reliable semivariograms of the transmissivity can be obtained. Copyright © 2004 John Wiley & Sons, Ltd.

Groundwater monitoring plans at small-scale sites--an innovative spatial and temporal methodology.

An innovative methodology for improving existing groundwater monitoring plans at small-scale sites is presented. The methodology consists of three stand-alone methods: a spatial redundancy reduction method, a well-siting method for adding new sampling locations, and a sampling frequency determination method. The spatial redundancy reduction method eliminates redundant wells through an optimization process that minimizes the errors in plume delineation and the average plume concentration estimation. The well-siting method locates possible new sampling points for an inadequately delineated plume via regression analysis of plume centerline concentrations and estimation of plume dispersivity values. The sampling frequency determination method recommends the future frequency of sampling for each sampling location based on the direction, magnitude, and uncertainty of the concentration trend derived from representative historical concentration data. Although the methodology is designed for small-scale sites, it can be easily adopted for large-scale site applications. The proposed methodology is applied to a small petroleum hydrocarbon-contaminated site with a network of 12 monitoring wells to demonstrate its effectiveness and validity.

A multiobjective approach to cost effective long-term groundwater monitoring using an elitist nondominated sorted genetic algorithm with historical data

This study presents a methodology for quantifying the tradeoffs between sampling costs and local concentration estimation errors in an existing groundwater monitoring network. The method utilizes historical data at a single snapshot in time to identify potential spatial redundancies within a monitoring network. Spatially redundant points are defined to be monitoring locations that do not appreciably increase local estimation errors if they are not sampled. The study combines nonlinear spatial interpolation with the nondominated sorted genetic algorithm (NSGA) to identify the tradeoff curve (or Pareto frontier) between sampling costs and local concentration estimation errors. Guidelines are given for using theoretical relationships from the field of genetic and evolutionary computation for population sizing and niching to ensure that the NSGA is competently designed to navigate the problem's decision space. Additionally, both a selection pressure analysis and a niching-based elitist enhancement of the NSGA are presented, which were integral to the algorithm's efficiency in quantifying the Pareto frontier for costs and estimation errors. The elitist NSGA identified 34 of 36 members of the Pareto optimal set attained from enumerating the monitoring application's decision space; this represents a substantial improvement over the standard NSGA, which found at most 21 of 36 members.