European achievements in soil remediation and brownfield redevelopment

With the aim of sharing best practices of soil restoration and management of contaminated sites among European countries and to raise awareness of the enormous efforts made to succeed in such difficult commitment, the experts of the EIONET Soil working group on contaminated sites and brownfields agreed to gather their country's interesting cases and successful stories of recovery of contaminated areas. This second edition of the monograph presents seventeen new cases from eight European countries and its Regions of how polluted sites and brownfields have been remediated like new methodologies of sustainable restoration of the subsoil, development of innovative technologies, and funding mechanisms etc. These stories have been compiled to present what national, regional or local governments are doing to improve the quality of the environment and the living conditions of their population. A second aim is the promotion of best practices among industry, consultancies and business operators.JRC.D.3-Land Resource

An alternative screening model for the estimation of outdoor air concentration at large contaminated sites

Simplified analytical solutions of fate and transport models are often used to carry out risk assessment on contaminated sites, to evaluate the long-term air quality in relation to volatile organic compounds in either soil or groundwater. Among the different assumptions employed to develop these solutions, in this work we focus on those used in the ASTM-RBCA \ue2\u80\u9cbox model\ue2\u80\u9d for the evaluation of contaminant dispersion in the atmosphere. In this simple model, it is assumed that the contaminant volatilized from the subsurface is dispersed in the atmosphere within a mixing height equal to two meters, i.e. the height of the breathing zone. In certain cases, this simplification could lead to an overestimation of the outdoor air concentration at the point of exposure. In this paper we first discuss the maximum source lengths (in the wind direction) for which the application of the \ue2\u80\u9cbox model\ue2\u80\u9d can be considered acceptable. Specifically, by comparing the results of \ue2\u80\u9cbox model\ue2\u80\u9d with the SCREEN3 model of U.S.EPA we found that under very stable atmospheric conditions (class F) the ASTM-RBCA approach provides acceptable results for source lengths up to 200 m while for very unstable atmospheric conditions (class A and B) the overestimation of the concentrations at the point of the exposure can be already observed for source lengths of only 10 m. In the latter case, the overestimation of the \ue2\u80\u9cbox model\ue2\u80\u9d can be of more than one order of magnitude for source lengths above 500 m. To overcome this limitation, in this paper we introduce a simple analytical solution that can be used for the calculation of the concentration at the point of exposure for large contaminated sites. The method consists in the introduction of an equivalent mixing zone height that allows to account for the dispersion of the contaminants along the source length while keeping the simplistic \ue2\u80\u9cbox model\ue2\u80\u9d approach that is implemented in most of risk assessment tools that are based on the ASTM-RBCA standard (e.g. RBCA toolkit). Based on our testing, we found that the developed model replicates very well the results of the more sophisticated dispersion SCREEN3 model with deviations always below 10%. The key advantage of this approach is that it can be very easily incorporated in the current risk assessment screening tools that are based on the ASTM standards while ensuring a more accurate evaluation of the concentration at the point of exposure

Human Health Risk Assessment

The focus of this chapter is human health risk assessment, which quantifies the human or environmental toxicological effects deriving from the release of a contaminant at a source and its migration towards exposed receptors. Essentially, this entails a quantitative description of the relations in the system “source—pathway—receptor”. The procedure of risk assessment consists in a sequence of steps, starting from site assessment investigations, through the definition of a conceptual model (i.e., identification of potential receptors and migration and exposure pathways, selection of constituents of concern), the determination of concentrations at the point of exposure, actual risk calculation, to a risk management decision making stage (i.e., uncertainty assessment, risk acceptability evaluation, determination of the maximum acceptable concentration levels at the source and the selection of appropriate interventions). The risk assessment itself can be carried out at an increasing degree of detail, through a tiered approach, illustrated in the chapter. A relevant focus of this chapter is the calculation of the concentration at the point of exposure via the determination of the natural attenuation factor. This factor is the cumulative result of the contaminant concentration attenuation in the course of its migration from the source to the point of exposure (e.g., partitioning between environmental components, attenuation in the unsaturated medium, dilution in the aquifer or in rivers, volatilization). Having determined the concentration at the point of exposure, the calculation of the rate of exposure is presented. With these two parameters it is then possible to calculate the risk deriving the exposure to carcinogenic or threshold compounds, following a contamination event. The carcinogenic risk is quantified by the incremental lifetime cancer risk, which is a function of the slope factor (defined in Chap. 9); the non-carcinogenic risk, instead, is quantified by the hazard quotient, which is a function of the reference dose (also defined in Chap. 9). Once the risk has been calculated, its acceptability can be evaluated according to the local legislation, and measures to manage it can be put into place

Analytical model for the design of in situ horizontal permeable reactive barriers (HPRBs) for the mitigation of chlorinated solvent vapors in the unsaturated zone

In this work we introduce a 1-D analytical solution that can be used for the design of horizontal permeable reactive barriers (HPRBs) as a vapor mitigation system at sites contaminated by chlorinated solvents. The developed model incorporates a transient diffusion-dominated transport with a second-order reaction rate constant. Furthermore, the model accounts for the HPRB lifetime as a function of the oxidant consumption by reaction with upward vapors and its progressive dissolution and leaching by infiltrating water. Simulation results by this new model closely replicate previous lab-scale tests carried out on trichloroethylene (TCE) using a HPRB containing a mixture of potassium permanganate, water and sand. In view of field applications, design criteria, in terms of the minimum HPRB thickness required to attenuate vapors at acceptable risk-based levels and the expected HPRB lifetime, are determined from site-specific conditions such as vapor source concentration, water infiltration rate and HPRB mixture. The results clearly show the field-scale feasibility of this alternative vapor mitigation system for the treatment of chlorinated solvents. Depending on the oxidation kinetic of the target contaminant, a 1 m thick HPRB can ensure an attenuation of vapor concentrations of orders of magnitude up to 20 years, even for vapor source concentrations up to 10 g/m3. A demonstrative application for representative contaminated site conditions also shows the feasibility of this mitigation system from an economical point of view with capital costs potentially somewhat lower than those of other remediation options, such as soil vapor extraction systems. Overall, based on the experimental and theoretical evaluation thus far, field-scale tests are warranted to verify the potential and cost-effectiveness of HPRBs for vapor mitigation control under various conditions of application

Laboratory investigation and LNAPL saturation and dissolution kinetics in different heterogeneous porous media

The presence of residual LNAPL (light non aqueous phase liquid) in the subsurface is a key environmental issue in most of sites contaminated by hydrocarbon compounds. Residual LNAPL indeed remains in the soil after mobile LNAPL is recovered and can serve as a long-term source of dissolved hydrocarbon plumes. The aim of this work is to assess the dissolution behavior of residual LNAPL entrapped in different porous media. To this end, lab-scale column tests (12.7 x 2.9 cm) with soils artificially-contaminated by toluene were carried out. Specifically, two types of soil, composed of medium-fine sands with different percentage of silt (9% and 14%) and clay (1% and 2%), characterized by a total porosity of about 38-39% and a total organic carbon of about 0.2%, were used. Furthermore, control tests with columns packed with glass spheres of 6 mm diameter were also carried out. In each experiment, columns were first saturated with demineralized water from the bottom and then with toluene from the top to maintain stable displacement. The column saturated with toluene was then flushed with water at different flow rates (0,5–1 ml/min) in order to displace the free phase of toluene. The residual toluene saturation in the column was then calculated as difference between the volume of toluene injected and the one displaced. Afterwards, to assess the dissolution kinetics of toluene from the residual phase entrapped in the column, demineralized water was flushed in the column at different flow rates (0.2–2 ml/min) and the effluent samples were collected in vials and measured by HSS-GC-MS analysis. The obtained results revealed, as expected, that the residual saturation of the two tested soils was significantly higher than the one observed for the column packed with the glass spheres. The time-series dissolution profiles for toluene, expressed as a function of the pore volume flushed in the column, highlighted initially high aqueous contaminant concentrations (in the order of the solubility values) which were followed by a period of rapid decline and an asymptotic time when concentrations declined very slowly. The dissolution profiles were also described by a modified first order kinetic model allowing to identify the dissolution rates for the tested different porous media and to provide some insights about the long-term impacts of residual LNAPL

A methodological approach to assess the dissolution of residual LNAPL in saturated porous media and its effect on groundwater quality. Preliminary experimental results

In this paper, we present a simple methodological approach to assess the dissolution behaviour of residual light nonaqueous phase liquid (LNAPL) sources entrapped in saturated porous media and to estimate the actual risk to human health by water ingestion related to their presence in the subsurface. The approach consists of collecting experimental data on the release kinetics through lab-scale column tests and including these data in a modified version of the analytical model used to describe the groundwater ingestion pathway in risk analysis. The approach was applied to different test scenarios using toluene as a model compound and three types of porous media, i.e. glass beads and two sandy soils with slightly different textures. The experimental results showed that the concentration of toluene in the eluted water was far from the solubility value after a limited number of pore volumes. Furthermore, different behaviour was observed for the three types of porous media. In particular, higher residual saturation and a slower dissolution rate were observed for the soil characterized by the finest texture. This behaviour suggests that the release rate is inversely proportional to the total residual saturation due to the reduction in the porosity available for water flow and the permeability of the porous media. Using these data in a modified risk-based model showed that a remarkable reduction of the hazard index related to the water ingestion pathway can be achieved for a relatively high groundwater velocity and a small contamination source

The fate of MtBE during Fenton-like treatments through laboratory scale column tests

In Situ Chemical Oxidation (ISCO) based on the Fenton's process is a proven technology for the treatment of groundwater contaminated by organic compounds. Nevertheless, the application of this treatment process to methyl tert-butyl ether (MtBE) is questioned, as there are concerns about its capacity to achieve complete mineralization. Many existing studies have focused on water contaminated by MtBE and are thus not representative of in situ treatments since they do not consider the presence of soil. In this work, the effectiveness of a Fenton-like process for MtBE treatment was proven in soil column tests performed at operating conditions (i.e., oxidant and contaminant concentration and flow rates) resembling those typically used for in situ applications. No MtBE by-products were detected in any of the tested conditions, thus suggesting that the tert-butyl group of MtBE was completely degraded. A mass balance based on the CO2 produced was used as evidence that most of the MtBE removed was actually mineralized. Finally, the obtained results show that preconditioning of soil with a chelating agent (EDTA) significantly enhanced MtBE oxidation

Analytical model for the design of in situ horizontal permeable reactive barriers (HPRBs) for the mitigation of chlorinated solvent vapors in the unsaturated zone

In this work we introduce a 1-D analytical solution that can be used for the design of horizontal permeable reactive barriers (HPRBs) as a vapor mitigation system at sites contaminated by chlorinated solvents. The developed model incorporates a transient diffusion-dominated transport with a second-order reaction rate constant. Furthermore, the model accounts for the HPRB lifetime as a function of the oxidant consumption by reaction with upward vapors and its progressive dissolution and leaching by infiltrating water. Simulation results by this new model closely replicate previous lab-scale tests carried out on trichloroethylene (TCE) using a HPRB containing a mixture of potassium permanganate, water and sand. In view of field applications, design criteria, in terms of the minimum HPRB thickness required to attenuate vapors at acceptable risk-based levels and the expected HPRB lifetime, are determined from site-specific conditions such as vapor source concentration, water infiltration rate and HPRB mixture. The results clearly show the field-scale feasibility of this alternative vapor mitigation system for the treatment of chlorinated solvents. Depending on the oxidation kinetic of the target contaminant, a 1 m thick HPRB can ensure an attenuation of vapor concentrations of orders of magnitude up to 20 years, even for vapor source concentrations up to 10 g/m3. A demonstrative application for representative contaminated site conditions also shows the feasibility of this mitigation system from an economical point of view with capital costs potentially somewhat lower than those of other remediation options, such as soil vapor extraction systems. Overall, based on the experimental and theoretical evaluation thus far, field-scale tests are warranted to verify the potential and cost-effectiveness of HPRBs for vapor mitigation control under various conditions of application