Dealing with Contaminated Sites

Over thousands of years, contaminants have been added to the world’s upper soil layers and have led to contamination of the soil and the groundwater. However, it was not until the late 1970s that several notorious cases of contaminated sites led to a sudden awareness to the general public. Today, in most developed countries, the number of potentially contaminated sites has grown to six or seven digits. This chapter describes the basic principles of contaminated site management. It focuses on risks and Risk Assessment, that is, quantifying the risks from contaminated sites on the basis of chance (exposure) and effects. This process is widely accepted today as offering the best balance between a sound scientific basis and practical implementation for appraisal of contaminated sites. Moreover, this chapter describes Risk Management, this is the process that brings contaminated sites back into beneficial use. The four major protection targets are human health, the soil ecosystem, the groundwater and Food Safety. Specific attention will be given in this chapter to a wide variety of topics including public and political awareness, soils, local and diffuse contaminated sites, contaminants, background concentrations, emissions to soil, site characterisation, land use, Soil Quality Standards, Brownfields, cost-benefit analyses, Risk Perception and Risk Communication, sustainability, and the actors involved in contaminated site management. Finally, several approaches to contaminated site assessment and management will be described, including the Fitness-for-Use approach, and Risk-based Land Management. In doing so, specific attention will be given to practical aspects such as effective use of financial resources and integration of contaminated site management (e.g., with regard to spatial planning, socio-cultural issues, economics and other factors).

This chapter deals with soils that have been contaminated by human activities and soils that have inherent contamination due to natural causes, as well as soils that may be thought of as contaminated, but where the contaminants are part of the natural geochemistry, they are completely inert and unlikely to cause any significant risk to life. Contaminated soils have figured greatly in the mind of the public since a number of dramatic, highly publicised events occurred in which residential developments on former landfills caused serious health problems for the inhabitants. Logically, the primary focus of studies and inventories of soil contamination were the industrial lands, from medieval metal processing to modern day manufacturing and storage, war zones and battle grounds. Besides, other factors impacting contamination potential have to be taken into account, e.g. flood occurrences and ubiquitous atmospheric deposition. There was a need to define background levels of all contaminants that can occur naturally in the land or could have been added by humans. Likewise, a need to discover the mobility and toxicity of the contaminants was required to develop Risk Assessment. Finally, chemical affinities and solubilities of several contaminant groups are discussed.

Given the volume of work and costs related to soil investigations, strategies and techniques for the investigation of potentially contaminated sites have been developed and have been standardized, both on a national as well as on an international level. Investigating soil contamination is not an easy task, since contaminants are generally distributed highly heterogeneous in the soil. It is important to focus on the objectives for site investigations. In this chapter three kinds of investigation phases have been described, these are the Preliminary Investigation, the Exploratory Investigation and the Main Investigation. The Preliminary Investigation, this is the most essential phase of the whole investigation, is a desk study combined with a site visit. A Preliminary Investigation can be performed both for sites where contamination is expected and for sites that are probably uncontaminated. The main objective of the Exploratory Investigation is to proof that the assumptions made in the Preliminary Investigation are indeed correct. The goal of the Main Investigation is to provide the necessary information to deal with the contamination on a cost-efficient basis. The Main Investigation is an iterative process, where after each step the question has to be answered if the available information is ‘fit for purpose’. Moreover, different sampling patterns and techniques are discussed in this chapter.

Exposure of humans to contaminated sites may result in many types of health damage ranging from relatively innocent symptoms such as skin eruption or nausea, on up to cancer or even death. Human health protection is considered as a major protection target, both by decision-makers as well as by the general public. The first step in Human Health Risk Assessment is definition of the problem (issue framing). In this stage, the scope of Human Health Risk Assessment must be clearly defined and the various stakeholders need to be actively involved. It is important to define the timeframe for which the Risk Assessment is applicable, since the effects depend on the duration of exposure and factors that impact human health risk will change over time. Subsequently, Exposure Assessment and Hazard Assessment must be performed. Ideally, the Exposure Assessment covers a smart combination of calculations, using exposure models, and measurements in contact media and body liquids and tissue (Biomonitoring). Hazard Assessment, which is different for contaminants with or without threshold effects, results in a Critical Exposure (aka: Toxicological Reference Value). In a final step, Risk Characterisation provides a risk appraisal calculated on the basis of exposure and hazard. Specific attention is given in this chapter to phenomena such as public perception, probabilistic Human Health Risk Assessment, Physiologically-Based PharmacoKinetic modelling, background exposure, sensitivity and uncertainty analyses, human health-based Soil Quality Standards, site-specific Human Health Risk Assessment on the basis of a tiered approach and ethical issues in regard to testing of human beings.

The current chapter discusses soil and dust ingestion, a potentially important pathway for non-dietary oral exposure, especially for children. Starting from clear definitions on what is meant by soil and dust and how they interrelate, it explores the several approaches that have been used to derive estimates of soil and dust ingestion rates. It concludes that tracer methodology studies, with all their limitations and uncertainties, probably provide the most adequate estimates of soil ingestion rates. However, these studies are limited to short-term estimates and do not distinguish between soil and dust. Hand-loading studies can be designed so that information is collected for the micro-environments we are interested in, but the interpretation requires assumptions about transfer parameters, which may introduce substantial uncertainty. Biokinetic modelling studies only provide rough estimates or ranges of estimates, but are nevertheless useful as a complementary line of evidence. From a comparison of these approaches it is concluded that average soil and dust ingestion rates for children are below 100 mg/d and most likely around 50 mg/d, a conclusion that is confirmed by the most recent evaluations published in literature. Still, good estimates of site-specific soil and dust ingestion rates for Europe are lacking due to paucity of data on age-related time activity patterns, transfer factors and intrinsic differences in children’s behaviour.

Soil ingestion is a key exposure pathway in Human Health Risk Assessment for contaminants in soil. The theory and mechanisms of how contaminants in a soil enter the human body through the gastrointestinal tract are outlined. The methods available for measuring human exposure using human, animal and validated in-vitro laboratory methods are described and contrasted. The role of the physico-chemical properties of the soils that control the bioavailability of contaminants are summarised. Finally, examples of how bioavailability/bioaccessibility studies of soils from both anthropogenic and geogenic origin are discussed along with the criteria required for deciding whether bioavailability data should be used in a Human Health Risk Assessment.

The consumption of locally-produced vegetables by humans may be an important exposure pathway for soil contaminants in many urban settings and for agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables from contaminated soils is an important part of the Human Health Risk Assessment procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium) in contaminated soils depends to a large extent on the intrinsic charge, valence and speciation of the contaminant ion, and soil properties such as pH, redox status and contents of clay and/or organic matter. However, chemistry and behaviour of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake, root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmosphere, and plant partitioning are important processes that ultimately govern the accumulation of metals and metalloids in edible vegetable tissues. Mechanistic models to accurately describe all these processes have not yet been developed, let alone validated under field conditions. Hence, to estimate risks by vegetable consumption, empirical models have been used to correlate concentrations of metals and metalloids in contaminated soils, soil physico-chemical characteristics, and concentrations of elements in vegetable tissues. These models should only be used within the bounds of their calibration, and often need to be re-calibrated or validated using local soil and environmental conditions on a regional or site-specific basis.

Contaminants may enter vegetables and fruits by several pathways: by uptake with soil pore water, by diffusion from soil or air, by deposition of soil or airborne particles, or by direct application. The contaminant-specific and plant-specific properties that determine the importance of these pathways are described in this chapter. A variety of models have been developed, specific for crop types and with steady-state or dynamic solutions. Model simulations can identify sensitive properties and relevant processes. Persistent, polar (log K _OW < 3) and non-volatile (K _AW < 10^–6) contaminants have the highest potential for accumulation from soil, and concentrations in leaves may be several hundred times higher than in soil. However, for most contaminants the accumulation in vegetables or fruits is much lower. Lipophilic (log K _OW > 3) contaminants are mainly transported to leaves by attached soil particles, or from air. Volatile contaminants have a low potential for accumulation because they quickly escape to air. Experimental data are listed that support these model predictions, but underline also the high variability of accumulation under field conditions. Plant uptake predictions are uncertain, due to the immense variation in environmental and plant physiological conditions. Uptake of organic contaminants into vegetables and fruits may lead to human health risks, but it may also be used to delineate subsurface plumes and monitor Natural Attenuation. Most models mentioned in this chapter are freely available from the authors.

Vapor intrusion is a pathway of potential exposure to volatile and semi-volatile contaminants (collectively referred to here as VOCs or vapors) that migrate from the subsurface to the air inside occupied buildings. Soil vapor intrusion to indoor air can occur regardless of whether a building has a basement, slab-on-grade or crawlspace design. As a basis for a mathematical model a conceptual model is needed, which describes the movement of contaminants from the source to the building, vapor migration barriers and receptors. It also provides a framework for interpreting the processes influencing the fate and transport of contaminants as they move from a source to a receptor. The approach for assessing vapor intrusion will vary from site-to-site, but there are certain elements that are appropriate in most cases. In this chapter the relevant processes have been described, like phase partitioning, biodegradation, advection and dilution within the building due to ventilation. Moreover, the presence of NAPLs, available vapor intrusion models, sampling and analysis procedures and subsurface vapor mitigation have been discussed.

Depending on land use and corresponding human activities, a number of exposure pathways are relevant for human exposure. In this chapter, six important pathways are described, i.e., exposure through consumption of vegetables, consumption of animal products, consumption of domestic water, inhalation of vapours outdoors, inhalation of dust particles (indoors and outdoors) and dermal uptake via soil material (outdoors and indoors). Note that these exposure pathways follow different exposure routes to enter the human body, i.e., oral, inhalation and dermal routes, respectively. Human exposure through all oral and inhalative exposure pathways described in this chapter (so excluding the dermal uptake exposure pathway), follow a similar pattern. This pattern includes three steps. Firstly, the transfer of contaminants from one of the mobile phases of the soil (pore water or soil gas) into a so-called contact medium. Secondly, the intake of that contact medium by human beings. And thirdly, the uptake of part of the contaminants from the contact medium into the blood stream and target organs and the corresponding excretion of the remaining part of the contaminants. For each of the pathways the significance, conceptual model, an example of mathematical equations and of the input parameters is described in this chapter, in detail. Moreover, attention is given to the reliability and limitations of the calculations.

Hazard Assessment is a key component of Human Health Risk Assessment and is comprised of the steps of Hazard Identification and Dose-response Assessment. Hazard Identification examines the capacity of a contaminant to cause adverse health effects in humans and other animals using data from a range of toxicological and epidemiological sources. Dose-response Assessment considers both qualitative and quantitative toxicological and epidemiological information to estimate the incidence of adverse effects occurring in human populations at different exposure levels. The conclusions from Hazard Assessment are assessed with those from Exposure Assessment to enable Risk Characterisation. This chapter provides an overview of the toxicological and epidemiological tools used for Hazard Assessment to enable a broader understanding of the Risk Assessment of contaminated sites and the principles underlying the development of risk-based policy and Soil Quality Standards.

The topsoil is the most biologically diverse part of the earth, harbouring more than one billion organisms per square meter. These soil organisms live in extremely complex mutual interaction and, additionally, in similarly complex interactions with their physical and chemical environment. Although not always acknowledged by the general public, the soil ecosystems perform so-called Ecosystem Services which are very important for society. Some of these Ecosystem Services, described in detail in this chapter, are soil structuring, humus formation, nutrient supply, cleaning function, disease control, and – only recently recognised – energy-related processes. The conclusion to be drawn is that intensive communication about Ecological Risk Assessment is a necessity, both to guarantee that appropriate ecological protection is on the political agenda and to justify protection of the soil ecosystem and the costs involved for the tax payer. Soil contamination has a big impact on the soil ecosystem. Ecological Risk Assessment is an extremely useful process for supporting the decisions taken concerning contaminated sites. The general target for Ecological Risk Assessment is Ecological Health (the preferred state) rather than the Ecological Integrity (the unimpaired condition), and this ideally at the level of a whole ecosystem. The important factors that relate to ecological effects in soil will be introduced in this chapter, factors such as bioavailability, food supply, sealing, resilience and recovery, adaptation, land use, secondary poisoning, the food web approach, wildlife protection, scale and contaminant pattern, and spatial planning. Finally, insight will be provided as to how Ecological Risk Assessment actually works in practice.

Ecological Risk Assessment related to soil contamination requires a conceptual framework and practical tools to support Risk Management. The conceptual framework is provided by the Risk Assessment paradigm, which means that risks are assessed based on an Exposure Assessment and an Effect Assessment step. Current practical tools to appraise soil quality by Ecological Risk Assessment are: (1) comparison of soil contaminant concentrations to ecological Soil Quality Standards; (2) quantification of ecological risks by modeling; (3) quantification of impacts in bioassays or in field monitoring; and (4) quantification of ecological risks by weight-of-evidence approaches. The present chapter concerns the theory and practices of Effect Assessment and risk modeling using Species Sensitivity Distributions (SSDs), and similar Functional Sensitivity Distributions (FSDs). SSD- and FSD-based Risk Assessment outputs are used for the appraisal of soil quality, soil protection and the management of (slightly and highly) contaminated sites, for both the upper soil and the groundwater. For the appraisal of soil and soil protection, one can derive Hazardous Concentrations (HCs) for individual contaminants, which are estimates of the concentration of a chemical that would affect a defined fraction of species. Likewise, one can derive Hazard Potentials (HPs) for contaminated soil samples, which represent effects levels for a certain fraction of the tested soil species when exposed in such a soil. This chapter introduces the theory of SSDs and illustrates the types of practical applications of SSD-based effect and risk models in all four of the aforementioned types of tools. Since Risk Assessment requires assessments of exposure as well as effects, the chapter also discusses Exposure Assessments for SSDs. Practical software models and database tools are described, to support easy application of SSDs in practice. Through the examples, the reader is informed on a multitude of useful options for SSD-based assessment. SSD-modeling is versatile, and can be of use to a range of soil contamination problems, from diffuse contamination in large areas to local contamination hot spots.

In many countries, soil quality is expressed in chemical concentrations as Soil Quality Standards to address the potential ecological risks in a first tier of an Ecological Risk Assessment (ERA). In cases where application of these standards do not provide satisfactory results, additional tools are required. In this chapter the focus is on these tools, i.e. ERA taking into account the complete mixture of contaminants and the integration of data from bioassays and field ecological observations according to a weight of evidence approach. A straightforward Triad framework, combining three lines of evidence, was introduced in the Netherlands in 2007 and is presented here.

In this chapter we review and discuss the commonly used phrase or concept “bioavailability”. This concept is key to Risk Assessment as it assesses what proportion of a contaminant present at a contaminated site is available for uptake by organisms and is thus potentially able to cause harm. Whilst this is a relatively straightforward concept the reader will discover that in reality life is not that simple. We start by reviewing the different definitions of bioavailability currently in use. We go on to discuss how soil properties impact on the bioavailability of both metal, metalloid and organic contaminants. Next we review the different methods people currently use to determine bioavailability, concentrating on chemical extractions, but also covering modelling approaches. We conclude that a precise definition of bioavailability equally applicable to all different contaminated sites, contaminants and organisms is unlikely to be achieved. Similarly, a single chemical extraction is unlikely to give a universal measure of bioavailability. However, the message is not all doom and gloom. On a contaminant by contaminant or species by species level chemical extractions and other measurement techniques can accurately predict bioavailability. Modelling techniques are constantly improving and offer hope for the future in terms of predicting bioavailability. At present however, the best method of determining the amount of contaminant available for uptake by an organism is to measure the concentration of the contaminant in the organism. Even this method, however, is open to question as organisms can and have evolved methods of regulating metal uptake.

Groundwater includes the pore water in the water-unsaturated upper soil layer as well as water usually referred to as groundwater, that is, the water in the water-saturated zone. Groundwater contains contaminants of natural and anthropogenic origin. It is generally recognised by all segments of society that fresh water is an immensely important resource. From a Risk Assessment point of view, groundwater needs to be approached from two different perspectives, namely, as an important protection target and as a means of transport (a pathway) for contaminants. For human beings the primary use for groundwater is as a source of drinking water. Although often underestimated, the water-saturated deeper soil layer is also a habitat for many organisms. For decades, there has been an on-going and interesting discussion concerning the intrinsic value of groundwater, sometimes including spiritual and even supernatural or religious arguments. Generally speaking, the transport of water and contaminants is much faster in the groundwater zone than in the water-unsaturated upper soil layer. Specific attention will be given in this chapter to the impact that a revised quantitative groundwater regime, the presence of heterogeneous soils or aquifers, surface water bodies, anthropogenic subsurface processes and structures, and heterogeneous soils and aquifers all have on groundwater quality. Additional attention will be paid to sustainable protection of groundwater resources, Conceptual Models, mathematical (numerical) models, Risk Management (including Natural Attenuation and regional approaches), sampling and monitoring, lysimeters and column experiments, the impact of climate change, mingling groundwater plumes, risk perception and communication, and the European Water Framework Directive.

In this chapter the water flow and contaminant transport processes in the unsaturated or vadose zone are described. These processes include water retention and hydraulic conductivity, evapotranspiration, preferential flow, root water uptake (water flow) and diffusion, dispersion, advection and volatilization (contaminant transport). The equation governing transport of dissolved contaminants in the vadose zone is obtained by combining the contaminant mass balance with equations defining the total concentration of the contaminant and the contaminant flux density. Further attention is this chapter is given to nonequilibrium transport, stochastic models, multicomponent reactive solute transport, multiphase flow and transport. Mathematical models should be critical components of any effort to understand and predict site-specific subsurface water flow and contaminant transport processes. Generally, models range from relatively simple analytical approaches for analyzing contaminant transport problems during one-dimensional steady-state flow, to sophisticated numerical models for addressing multi-dimensional variably-saturated flow and contaminant transport problems at the field scale. An overview is given of several existing analytical and numerical models. Moreover, several applications to unsaturated flow and geochemical transport modeling are presented in this chapter.

Understanding the complex, interacting processes that determine the fate and transport of contaminants in groundwater is a major challenge for evaluating and predicting risks to clean water, human and ecological receptors and for designing effective remediation plans. Different physical and biogeochemical processes including advection, hydrodynamic dispersion, dissolution, sorption and biodegradation affect the migration of contaminants in saturated porous media like a groundwater system. In this chapter an overview of these processes is presented together with the basic theory on contaminant transport modeling, which represents an essential tool for a quantitative description of contaminant migration in the subsurface. Numerical simulations of typical contamination scenarios are presented, with the main goal of identifying the influence of different parameters on contaminant fate and transport such as transverse dispersivity, thickness and strength of the contamination source, recharge, biodegradation rates and mixing enhancement through flow focusing in high permeability zones. These numerical simulations are complemented by two examples, i.e. the reactive transport of toluene from a LNAPL source and a field study, where ammonium is continuously released from a leaking landfill to the underlying aquifer. The principal processes at the landfill site have been quantitatively integrated into the framework of a two-dimensional reactive transport model.

A summary of two decades of developments of In Situ remediation is presented in this chapter. The basic principles of In Situ technology application are addressed, such as equilibrium relations between contaminant phases, factors controlling biological and geochemical processes, contaminant characteristics affecting reductive and oxidative conversion parameters and chemical and biological availability. A wide range of In Situ technologies are discussed within the framework of Risk Management. Technologies can be oriented at contaminant sources, migration pathways or at the receptors. Integration of In Situ technologies in sustainable Risk Management approaches is further evaluated relating to the latest concepts and frameworks. Examples are given of application of In Situ technologies in Risk Management approaches, including those for large scale contaminated Megasites. In the future, one can foresee the rise of combined sustainable technologies for soil, groundwater, surface water and energy.

Natural Attenuation (NA) has emerged during the last 10–15 years as a useful and cost-efficient alternative approach for contaminated site management. It refers to the naturally occurring processes like dispersion, diffusion, sorption, volatilization, degradation and transformation, all of which can substantially decrease contaminant concentration, mass, toxicity and/or mobility within soil and groundwater. The efficiency of Natural Attenuation processes depends to a large extent on site-specific conditions, primarily on the type of contaminants present at the site. Proving and evaluating the efficiency of Natural Attenuation processes is a prerequisite for accepting them as the sole or additional remediation alternative. The implementation of Natural Attenuation as a remediation alternative, i.e. the monitoring that assures sustainability of Natural Attenuation processes over time, is called Monitored Natural Attenuation (MNA). This chapter presents an overview of the history and political acceptance of Natural Attenuation and the principles on which it was built. Specifically, it describes how the different processes act on contaminant plume development and explores methods of evaluating Natural Attenuation processes and proving their effectiveness. A stepwise approach to assess and implement Natural Attenuation is presented, followed by three sections on the most frequently found contaminant groups for which Monitored Natural Attenuation is being applied. These are petroleum hydrocarbons, chlorinated hydrocarbons and tar oil contaminants. Characteristics of these contaminant groups, the resulting contaminant-specific potential for implementation of Natural Attenuation and the challenges to be expected, are elucidated and discussed.

This chapter focuses on application of scientific knowledge in dealing with contaminated sites within the broader context of policies and regulations. It reviews the development of strategies in industrial countries and describes the current understanding of how to tackle the problem of contaminated sites in a sustainable manner. Since the first discovery of contaminated sites at the end of the 1970s, public and political perception has changed and the understanding of the nature of the problem has increased considerably. Consequently, strategies for managing these problems have been further developed and improved. Three generations of contaminated sites policy are identified and described in this chapter; from early command-and-control regulations at a national level towards more flexible, site-specific and incentive-driven management approaches at the local level. Today, contaminated sites policy needs to address environmental and spatial planning aspects. It is important to explore and promote solutions in a multi-stakeholder environment that satisfy both environmental and social-economic needs of the society. Internationally accepted concepts that could lead to better problem solutions have been developed jointly in multinational partnerships, like the Risk-Based Land Management (RBLM) Concept of the European Union (EU) network CLARINET. Furthermore, the chapter briefly introduces the general soil protection policy currently under development in the EU. Contamination is one of the identified soil threats in the EU Thematic Strategy for Soil Protection and prevention of new soil contamination should be the key aim for the future in order to provide an added value to already existing national regulations.

NICOLE, the Network for the management of Industrially Contaminated Land in Europe is a leading forum on this matter in Europe, promoting co-operation between industry, academia and service providers. NICOLE’s goal is to enable European industry to identify, assess and manage industrially contaminated land efficiently, cost effectively and within a framework of sustainability. This chapter provides an introduction to NICOLE’s philosophy and addresses a number of topics that are relevant to NICOLE’s industrial members throughout the EU. Topics range from consideration about consistency in legislation to innovative, risk-based and sustainable approaches for the management of operational sites, megasites and Brownfields. The chapter outlines the existing concerns and constraints that may hinder cost-effective contaminated land management, proposes solutions and provides examples of promising and proven methods or best practice. NICOLE’s industrial members have developed and put into practice a range of techniques and methods to reduce, alleviate and prevent contamination of soil, surface water and groundwater. A greater knowledge and understanding of the forms and nature of contamination has allowed the refinement and improvement of remediation approaches used. NICOLE and its members advocate the view that remediation should be sustainable, i.e. that there be an acceptable balance between the effects of undertaking remediation activities and the benefits the same activities will deliver, in terms of environmental, economic and social indicators.

Sustainable Brownfield regeneration involves making abandoned, underused, derelict and, only occasionally contaminated, land fit for a new long-term use in order to bring long-lasting life back to the land and the community it lies within. Brownfields sites have been affected by former uses of the site or surrounding land; are derelict or underused; are mainly in fully or partly developed urban areas; may have real or perceived contamination problems; and require intervention to bring them back to beneficial use. While Brownfields do not have to be contaminated, contaminated sites are the focus of this book so it is important to point out that risk based contaminated land management is an essential prerequisite to ensuring efficient deployment of resources to deliver land that is fit for use. Vision and strong leadership are needed to build up and maintain momentum during the long time for remediation, reclamation and redevelopment and before regeneration can begin. Brownfields occur throughout the world and, while local definitions of Brownfield may vary, there is growing consensus on the opportunity they offer and great benefit on sharing experiences of and good practice in their regeneration. Specialist Brownfield regeneration process managers are needed to help deliver more successful projects. Suitable enabling policy and facilitating public sector finance usually lag behind the structural change that causes Brownfields yet must respond quickly if regions are to survive and deliver the stability and opportunity their citizens have come to expect.