Guidelines for Developing National Strategies to Use Monitoring of Local and Diffuse Soil

Contamination as Environmental Policy Tools

Professor Mark Kibblewhite(mark@mksoilscience.eu)

INTRODUCTION

• Local soil contamination from historic and present misuse, disposal and spillage of materials may present an unacceptable risk of harm to especially humans and water resources. • Diffuse soil contamination occurs over wide areas, generally at lower

levels than local soil contamination; it may present risk of chronic harm to the soil system itself, humans, water resources and biodiversity.

Monitoring of local and diffuse soil contamination requires different approaches and these are considered separately.

LOCAL SOIL CONTAMINATION

Strategy for local soil contamination

• Define unacceptable risk from local soil contamination• Prioritize resources to sites presenting most risk to humans,

surface and ground waters and ecosystems• Implement and monitor effectiveness of policy actions with

targets to assess and drive progress

How much contamination is acceptable?

• It is better to adopt a risk and not hazard-based approach. In this case:• the mere presence of a hazardous contaminant at any level does not in itself

indicate unacceptable contamination• acceptability should be assessed in relation to risk of harm to specific

receptors (e.g. humans, natural waters, ecosystems).

• A risk-based approach allows site-specific decision-making and avoids land being designated as having unacceptable local soil contamination, when there is no unacceptable risk arising under its current or planned use.

Ingestingdust

Ingestingsoil

Inhalingvapour

Inhaling vapour

Eating contaminatedvegetables and

ingesting soil

Skin contactwith dust

Skin contactwith soil

Soil transferFrom gardenTo house

Rising vapour

Rising vapour

Wind blown dust

Plant uptake

Possible Source-Pathway-Receptor linkages

Illustration of human exposure from contaminated garden soil

Defining unacceptable risk from local soil contaminationUnacceptable risk of harm requires the definition of both unacceptable harm and an unacceptable probability of exceeding this harm This is achieved in a four steps.1. Identification of the subject that is at risk of

harm (the receptor)2. Identification of the type of harm that may be

caused by exposure of the receptor 3. Definition of a quantitative measure of risk of

this harm4. Definition of the unacceptable level of risk of

harm.

EXAMPLE1. The risk of harm to human health from a

contaminant X could be assessed in relation to risk of harm to a 6 year old female child

2. The type of harm that may result from exposure to contaminant X could be disease Y

3. The measure of risk of harm could be the lifetime chance of such a child contracting Y, relative to that for the wider population of non-exposed children

4. A policy decision might be made that any increase in the incidence of the disease with a probability of more than 1 in 100,000 is unacceptable.

Managing local soil contamination

Sequential steps (at individual sites)

1. preliminary studies 2. preliminary investigation3. main investigation4. options appraisal5. implementation of

remediation strategyTargets should refer to the number / percentage of sites at which these steps are completed

MetricTotal number of sites undergoing risk assessment or risk management (i.e. all sites within inventories)

Number of sites with preliminary studies in progressPercentage of total number of sites with preliminary studies in progressNumber of Potentially Contaminated SitesPercentage of the total number sites currently identified as Potentially Contaminated Sites

Number of Contaminated SitesPercentage of the total number sites identified as Contaminated SitesNumber of sites where a remediation strategy is being implementedPercentage of the total number of sites where a remediation strategy is being implemented

Number of sites incurring costs within expenditure categories

Metrics for monitoring local soil contamination

Monitoring local soil contamination

• Designate a single coordinating institution• Implement data collection exercises at intervals of no less

than five years using an unchanging questionnaire• Establish a central inventory of data on sites of local soil

contamination

Actors

Activities Outputs (Examples)

Central Government (responsible Ministers and their officials)

Setting an overarching policy framework

Key policies, e.g.:1. Avoid new contamination2. Risk-based approach, focusing resources on higher risk sites3. Polluter pays principle applies, but with financial and legal incentives to

encourage site assessment and management4. Local-level regulation to encourage integrated actions by land owners /

managers / developers and regulatory authorities

Legislature Designing and enacting a national legislative regime

Legislation and statutory regulations, e.g.:1. Legal definitions e.g. of “contaminated site”2. Responsibilities3. Liability

Central Agency (e.g. Environmental Protection Agency)

Developing and maintaining technical guidance; monitoring progress

1. Regulatory and technical procedures for assessing and managing sites of local soil contamination

2. Definition and publication of intervention values for contaminants3. Technical expertise for ‘difficult’ sites4. Operation of national monitoring system for local soil contamination

1. Land owners / managers / developers

2. Regional / municipality departments for development control (spatial planning) and environmental protection

3. Technical experts and specialized contractors

4. Citizens and stakeholder organizations

Identifying sites; assessing risks; defining site management plans (according to regulations defined by central agency)

1. Systematic identification of possible sites of unacceptable local soil contamination

2. Preliminary studies / preliminary investigations of candidate sites3. Main investigations of sites where required4. Designation of sites as ‘contaminated land’ (by regional / municipal

authorities)Implementing and signing-off site remediation(according to regulations defined by central agency)

1. Evaluating options for management of contaminated sites and agreeing detailed plans

2. Completing and confirming success of site plans.

DIFFUSE SOIL CONTAMINATION

• Diffuse soil contamination is widespread and results from the transfer of contamination from other environmental compartments, such as air and water, as well as the use of chemicals on land and the spreading of organic and other wastes. • A precautionary policy position is

that diffuse soil contamination should be minimized where feasible and economics allow.

Purpose of monitoring diffuse soil contamination• Is diffuse soil contamination an

actual or potential risk (e.g. to food production and / or water quality)?

Strategy for diffuse soil contamination

• Define priority contaminants• Inform decisions by

assessing the spatial distribution and temporal trends in contamination• Integrate decisions with

wider environmental policy to assess where to focus control

Type of contaminant Examples (potential priority contaminants)

Heavy metals Cadmium, Chromium, Copper, Lead, Mercury Nickel, Zinc.

Metalloids Arsenic, Antimony, Selenium

Persistent Organic Pollutants

Poly-Chlorinated Biphenyls (PCBs), Poly-Aromatic Hydrocarbons (PAHs), Dioxins, Furans, banned pesticides

Operational steps for monitoring

• Designate a single coordinating institution • Define quantitative

performance requirements• Confirm that the chosen

design is fit for purpose

• Adopt formal procedures and protocols •Maintain a central

database and sample archive

Technical approach to monitoring diffuse soil contamination• Sampling soil over large areas

followed by testing of samples for priority contaminants

Measurement performance specification• Absolute detection limit i.e. the minimum level of the contaminant

that can be detected (mg kg-1); • Dynamic range over which measurement of levels of the contaminant

are required (mg kg-1); • Maximum error allowable e.g. specified as the standard deviation of

measurements of level of contaminant at 80% of the dynamic range (mg kg-1);• Detection limit for a change in level of contaminant at e.g. 50% of the

dynamic range, over a specified period (mg kg-1y-1).

Design of sampling network

• Invest in a thorough investigation of the expected measurement performance of options using statistical modeling.• A model approach locates sampling sites e.g. at the nodes of a regular

grid. A classical approach selects sites randomly from within strata (categories of possible sampling sites) representative of e.g. different land use / cover, geology, etc. • On balance, it is recommended that countries establish systems based

on regular grids as these are more flexible to meet future needs. A European-wide project aiming to develop a continental scale soil monitoring system (ENVASSO) recommended a minimum sampling density of 1 site per 300 km2.

Sampling and testing

• Large variations in levels of diffuse contamination of soils are observed at field scales (1-10m) and it is essential to sub-sample an adequate area at each location. • Archive samples so that they can be re-tested or tested for additional

contaminants at a later date• Standard ISO testing methods should be used.• Laboratories should meet international performance standards by

having auditable traceability of measurements, quality control systems incorporating standard reference materials, and participation in inter-laboratory comparability exercises.

At what level does diffuse soil contamination present unacceptable risk?

• If the contaminant does not occur naturally then its level should be as ‘low as practicable’• If the contaminant occurs

naturally then account has to be taken of background “contamination” . For example, a ‘level of concern’ could be set at two times the 90th percentile of the non-urban background level.

Land cover Soil-forming material

Metal Mean +/- 2 standard deviations

Median +/- median absolute deviations

10th to 90th percentiles

Urban All Cd 0.1-2.3 0.2-2.0 0.2-1.4Pb 11-370 17-210 28-140

Agriculture Mudstone Cd 0.3-1.9 0.4-1.5 0.4-1.4Pb 14-110 17-74 23-89

Chalk till Cd 0.2-1.3 0.2-1.1 0.3-1.0Pb 9-65 11-48 13-42

Sandstone / Mudstone / Shales

Cd 0.3-2.3 0.2-1.8 0.2-1.4Pb 14-320 18-220 28-240

Background “contamination”

Concluding reflections

Soil monitoring systems are an essential part of integrated environmental management

The specification of soil monitoring systems should be carefully developed and design options fully evaluated before implementation

Establishing a permanent central secretariat is critical to the efficiency and enduring good performance of soil monitoring systems