Michael Finkel

Designing sustainable and economically attractive brownfield revitalization options using an integrated assessment model

We describe the development of an integrated assessment model which evaluates redevelopment options of large contaminated brownfields and we present the application of the model in a case study. Aiming to support efficient and sustainable revitalization and communication between stakeholders, the presented assessment model integrates three pinnacles of brownfield revitalization: (i) subsurface remediation and site preparation costs, (ii) market-oriented economic appraisal, and (iii) the expected contribution of planned future land use to sustainable community and regional development. For the assessment, focus is set on the early stage of the brownfield redevelopment process, which is characterized by limited data availability and by flexibility in land use planning and development scope. At this stage, revealing the consequences of adjustments and alterations in planning options can foster efficiency in communication between the involved parties and thereby facilitates the brownfield revitalization process. Results from the case-study application indicate that the integrated assessment provides help in the identification of land use options beneficial in both a sustainable and an economical sense. For the study site it is shown on one hand that brownfield redevelopment is not automatically in line with sustainable regional development, and on the other hand it is demonstrated that additional contributions to sustainability are not intrinsically tied to increased costs.

Uncertainty and data worth analysis for the hydraulic design of funnel-and-gate systems in heterogeneous aquifers

[1] Hydraulic failure of a funnel-and-gate system may occur when the contaminant plume bypasses the funnels rather than being captured by the gate. We analyze the uncertainty of capturing the plumes by funnel-and-gate systems in heterogeneous aquifers. Restricting the analysis to two-dimensional, steady state flow, we characterize plume capture by the values of the stream function at the boundaries of the plume and the funnels. On the basis of the covariance of the log conductivity distribution we compute the covariance matrix of the relevant stream function values by a matrix-based first-order second-moment method, making use of efficient matrix-multiplication techniques. From the covariance matrix of stream function values, we can approximate the probability that the plume is bypassing the funnels. We condition the log conductivity field to measurements ofthe logconductivity and the hydraulic head. Prior to performing additional measurements, we estimate their worth by the expected reduction in the variance of stream function differences. In an application to a hypothetical aquifer, we demonstrate that our method of uncertainty propagation and our sampling strategy enable us to discriminate between cases of success and failure of funnel-and-gate systems with a small number of additional samples. INDEX TERMS: 1829 Hydrology: Groundwater hydrology; 1869 Hydrology: Stochastic processes; 1832 Hydrology: Groundwater transport; KEYWORDS: conditioning, data worth, funnel-and-gate systems, heterogeneous aquifers, stream function, uncertainty propagation

Integrated planning and spatial evaluation of megasite remediation and reuse options.

Redevelopment of large contaminated brownfields (megasites) is often hampered by a lack of communication and harmonization among diverse stakeholders with potentially conflicting interests. Decision support is required to provide integrative yet transparent evaluation of often complex spatial information to stakeholders with different areas of expertise. It is considered crucial for successful redevelopment to identify a shared vision of how the respective contaminated site could be remediated and redeveloped. We describe a framework of assessment methods and models that analyzes and visualizes site- and land use-specific spatial information at the screening level, with the aim to support the derivation of recommendable land use layouts and to initiate further and more detailed planning. The framework integrates a GIS-based identification of areas to be remediated, an estimation of associated clean-up costs, a spatially explicit market value appraisal, and an assessment of the planned future land uses contribution to sustainable urban and regional development. Case study results show that derived options are potentially favorable in both a sustainability and an economic sense and that iterative re-planning is facilitated by the evaluation and visualization of economic, ecological and socio-economic aspects. The framework supports an efficient early judgment about whether and how abandoned land may be assigned a sustainable and marketable land use.

Modelling surfactant-enhanced remediation of polycyclic aromatic hydrocarbons

Abstract Within the framework of a comprehensive investigation concerning the use of surfactants to enhance the in situ remediation of polycyclic aromatic hydrocarbons (PAH) contaminations in the subsurface, SMART (Streamtube Model for Advective and Reactive Transport), a multicomponent transport model, was developed to study the processes (interactions) taking place when surfactants and PAH migrate through porous media as solutes. The model is an adaption of a Lagrangian method allowing for separate treatment of conservative transport and reactive processes. It accounts for the hydraulic as well as physico-chemical heterogeneity of porous aquifers. The system of processes implemented in the model has been shown to be able to represent the behaviour of PAH and surfactants in porous media at the laboratory scale. Here the transport model is applied to a simplified two-dimensional remediation scenario (field scale). It is shown how surfactants may influence the clean-up of PAH contaminated aquifers. Emphasis is put on the effect of hydraulic and physico-chemical aquifer properties on the coupled transport of PAH and surfactants.

Applying a multi-criteria genetic algorithm framework for brownfield reuse optimization: Improving redevelopment options based on stakeholder preferences

The reuse of underused or abandoned contaminated land, so-called brownfields, is increasingly seen as an important means for reducing the consumption of land and natural resources. Many existing decision support systems are not appropriate because they focus mainly on economic aspects, while neglecting sustainability issues. To fill this gap, we present a framework for spatially explicit, integrated planning and assessment of brownfield redevelopment options. A multi-criteria genetic algorithm allows us to determine optimal land use configurations with respect to assessment criteria and given constraints on the composition of land use classes, according to, e.g., stakeholder preferences. Assessment criteria include sustainability indicators as well as economic aspects, including remediation costs and land value. The framework is applied to a case study of a former military site near Potsdam, Germany. Emphasis is placed on the trade-off between possibly conflicting objectives (e.g., economic goals versus the need for sustainable development in the regional context of the brownfield site), which may represent different perspectives of involved stakeholders. The economic analysis reveals the trade-off between the increase in land value due to reuse and the costs for remediation required to make reuse possible. We identify various reuse options, which perform similarly well although they exhibit different land use patterns. High-cost high-value options dominated by residential land use and low-cost low-value options with less sensitive land use types may perform equally well economically. The results of the integrated analysis show that the quantitative integration of sustainability may change optimal land use patterns considerably.

Field scale characterization and modeling of contaminant release from a coal tar source zone

A coal tar contaminated site was characterized using traditional and innovative investigation methods. A careful interpretation of hydrogeological and hydrogeochemical data allowed for the conceptualization of the heterogeneous coal tar distribution in the subsurface. Past and future contaminant release from the source zone was calculated using a modeling framework consisting of a three-dimensional steady-state groundwater flow model (MODFLOW) and two hydrogeochemical models (MIN3P). Computational time of long-term simulations was reduced by simplifying the coal tar composition using 3 composite and 2 individual constituents and sequential application of a 2D centerline model (for calibration and predictions) and a 3D model (only for predictions). Predictions were carried out for a period of 1000 years. The results reveal that contaminant mass flux is governed by the geometry of zones containing residual coal tar, amount of coal tar, its composition and the physicochemical properties of the constituents. The long-term predictions made using the 2D model show that even after 1000 years, source depletion will be small with respect to phenanthrene, 89% of initial mass will be still available, and for the moderately and sparingly soluble composite constituents, 60% and 98%, respectively.

A system dynamics model for the screening-level long-term assessment of human health risks at contaminated sites

For the design of sustainable and cost-effective management strategies for contaminated sites, decision makers need appropriate tools, i.e. environmental decision support systems to assist them in the planning, assessment, selection and optimisation of possible alternatives. We propose a novel system dynamics model, CARO-PLUS (Cost-efficiency Analysis of Remediation Options), which provides estimates of current and future risks originating from soil and groundwater contamination. Utilising a source-pathway-receptor concept, the model particularly addresses the presence of multi-compound non-aqueous phase liquids in porous media, which have been identified as major sources of groundwater contamination at many of these sites. Simplified approaches for the description of contaminant release and transport, as well as of exposure pathways for human health risk assessment, allow for a fast and effective screening model, which is particularly qualified to support early decisions within a tiered management approach at contaminated sites. CARO-PLUS is applied to assess the long-term risks originating from a kerosene contamination at a former military airfield in Germany. Monte Carlo simulations are performed to account for the large uncertainty in model parameters at early decision levels. The results of the application show that the implementation of monitored natural attenuation might be a feasible management strategy for the site, and provide guidance for additional, more detailed investigations. Highlights� Screening-level model allows to quickly assess human health risks at contaminated sites. � System dynamics approach links interdisciplinary systems research with policy assessment. � Reliable results through evaluation of uncertainty and variability using Monte Carlo simulation. � EDSS CARO-PLUS supports early decisions within a tiered management approach.

Exposure-time based modeling of nonlinear reactive transport in porous media subject to physical and geochemical heterogeneity

Transport of reactive solutes in groundwater is affected by physical and chemical heterogeneity of the porous medium, leading to complex spatio-temporal patterns of concentrations and reaction rates. For certain cases of bioreactive transport, it could be shown that the concentrations of reactive constituents in multi-dimensional domains are approximately aligned with isochrones, that is, lines of identical travel time, provided that the chemical properties of the matrix are uniform. We extend this concept to combined physical and chemical heterogeneity by additionally considering the time that a water parcel has been exposed to reactive materials, the so-called exposure time. We simulate bioreactive transport in a one-dimensional domain as function of time and exposure time, rather than space. Subsequently, we map the concentrations to multi-dimensional heterogeneous domains by means of the mean exposure time at each location in the multi-dimensional domain. Differences in travel and exposure time at a given location are accounted for as time difference. This approximation simplifies reactive-transport simulations significantly under conditions of steady-state flow when reactions are restricted to specific locations. It is not expected to be exact in realistic applications because the underlying assumption, such as neglecting transverse mixing altogether, may not hold. We quantify the error introduced by the approximation for the hypothetical case of a two-dimensional, binary aquifer made of highly-permeable, non-reactive and low-permeable, reactive materials releasing dissolved organic matter acting as electron donor for aerobic respiration and denitrification. The kinetically controlled reactions are catalyzed by two non-competitive bacteria populations, enabling microbial growth. Even though the initial biomass concentrations were uniform, the interplay between transport, non-uniform electron-donor supply, and bio-reactions led to distinct spatial patterns of the two types of biomass at late times. Results obtained by mapping the exposure-time based results to the two-dimensional domain are compared with simulations based on the two-dimensional, spatially explicit advection-dispersion-reaction equation. Once quasi-steady state has been reached, we find a good agreement in terms of the chemical-compound concentrations between the two approaches inside the reactive zones, whereas the exposure-time based model is not able to capture reactions occurring in the zones with zero electron-donor release. We conclude that exposure-time models provide good approximations of nonlinear bio-reactive transport when transverse mixing is not the overall controlling process and all reactions are essentially restricted to distinct reactive zones.

Modelling surfactant influenced PAH migration

Abstract Within the framework of a comprehensive investigation concerning the use of surfactants to enhance the remediation of PAH contaminations in the subsurface, a multicomponent transport model was developed to study the processes (interactions) taking place when surfactants and PAH migrate through porous media as solutes. Based on a close co-operation with the laboratory investigations during model development only those processes that could be identified within laboratory experiments have been implemented in the model: (i) surfactant-micellization, (ii) surfactant sorption (formation of hemi- and admicelles), (iii) intra-particle diffusion of PAH, (iv) PAH sorption on hemi- or into admicelles, (v) solution of PAH within micelles. Furthermore, process-oriented descriptions are used to guarantee that only measurable parameters are needed as model input. In a first step column experiments with phenanthrene and the surfactant Terrasurf G50 (Danzer and Grathwohl, 1997, this issue) have been simulated by pure forward modelling in order to validate the conceptual model. Using independently measured parameters only the model is able to reproduce the breakthrough curves of both phenanthrene and Terrasurf G50 very well. Furthermore, the modelling results provide evidence that not only PAH sorption but also the sorption of surfactants may be limited by diffusion. Based upon these results a new conceptual model of the processes involved in the coupled transport of PAH and surfactants has been developed.

Using travel times to simulate multi-dimensional bioreactive transport in time-periodic flows

In travel-time models, the spatially explicit description of reactive transport is replaced by associating reactive-species concentrations with the travel time or groundwater age at all locations. These models have been shown adequate for reactive transport in river-bank filtration under steady-state flow conditions. Dynamic hydrological conditions, however, can lead to fluctuations of infiltration velocities, putting the validity of travel-time models into question. In transient flow, the local travel-time distributions change with time. We show that a modified version of travel-time based reactive transport models is valid if only the magnitude of the velocity fluctuates, whereas its spatial orientation remains constant. We simulate nonlinear, one-dimensional, bioreactive transport involving oxygen, nitrate, dissolved organic carbon, aerobic and denitrifying bacteria, considering periodic fluctuations of velocity. These fluctuations make the bioreactive system pulsate: The aerobic zone decreases at times of low velocity and increases at those of high velocity. For the case of diurnal fluctuations, the biomass concentrations cannot follow the hydrological fluctuations and a transition zone containing both aerobic and obligatory denitrifying bacteria is established, whereas a clear separation of the two types of bacteria prevails in the case of seasonal velocity fluctuations. We map the 1-D results to a heterogeneous, two-dimensional domain by means of the mean groundwater age for steady-state flow in both domains. The mapped results are compared to simulation results of spatially explicit, two-dimensional, advective-dispersive-bioreactive transport subject to the same relative fluctuations of velocity as in the one-dimensional model. The agreement between the mapped 1-D and the explicit 2-D results is excellent. We conclude that travel-time models of nonlinear bioreactive transport are adequate in systems of time-periodic flow if the flow direction does not change.