1. Professor Mark Kibblewhite (mark@mksoilscience.eu)
Guidelines for Developing National Strategies to Use Monitoring of Local and Diffuse Soil Contamination as Environmental Policy Tools
Professor Mark Kibblewhite

2. 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.

3. LOCAL SOIL CONTAMINATION

4. 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

5. 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.

6. Possible Source-Pathway-Receptor linkages
Ingesting
soil
Inhaling
vapour
Ingesting
dust
Inhaling
vapour
Rising
vapour
Soil transfer
From garden
To house
Wind blown dust
Rising vapour
Eating contaminated
vegetables and
ingesting soil
Skin contact
with dust
Skin contact
with soil
Plant uptake
Illustration of human exposure from contaminated garden soil

7. Defining unacceptable risk from local soil contamination
Unacceptable 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.
Identification of the subject that is at risk of harm (the receptor)
Identification of the type of harm that may be caused by exposure of the receptor
Definition of a quantitative measure of risk of this harm
Definition of the unacceptable level of risk of harm.
EXAMPLE
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
The type of harm that may result from exposure to contaminant X could be disease Y
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
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.

8. Managing local soil contamination
Sequential steps (at individual sites)
preliminary studies
preliminary investigation
main investigation
options appraisal
implementation of remediation strategy
Targets should refer to the number / percentage of sites at which these steps are completed

9. Metrics for monitoring local soil contamination
Total number of sites undergoing risk assessment or risk management (i.e. all sites within inventories)
Number of sites with preliminary studies in progress
Percentage of total number of sites with preliminary studies in progress
Number of Potentially Contaminated Sites
Percentage of the total number sites currently identified as Potentially Contaminated Sites
Number of Contaminated Sites
Percentage of the total number sites identified as Contaminated Sites
Number of sites where a remediation strategy is being implemented
Percentage of the total number of sites where a remediation strategy is being implemented
Number of sites incurring costs within expenditure categories

10. 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

11. Actors Activities Outputs (Examples)
Activities
Outputs (Examples)
Central Government (responsible Ministers and their officials)
Setting an overarching policy framework
Key policies, e.g.:
Avoid new contamination
Risk-based approach, focusing resources on higher risk sites
Polluter pays principle applies, but with financial and legal incentives to encourage site assessment and management
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.:
Legal definitions e.g. of “contaminated site”
Responsibilities
Liability
Central Agency (e.g. Environmental Protection Agency)
Developing and maintaining technical guidance; monitoring progress
Regulatory and technical procedures for assessing and managing sites of local soil contamination
Definition and publication of intervention values for contaminants
Technical expertise for ‘difficult’ sites
Operation of national monitoring system for local soil contamination
Land owners / managers / developers
Regional / municipality departments for development control (spatial planning) and environmental protection
Technical experts and specialized contractors
Citizens and stakeholder organizations
Identifying sites; assessing risks; defining site management plans (according to regulations defined by central agency)
Systematic identification of possible sites of unacceptable local soil contamination
Preliminary studies / preliminary investigations of candidate sites
Main investigations of sites where required
Designation of sites as ‘contaminated land’ (by regional / municipal authorities)
Implementing and signing-off site remediation
(according to regulations defined by central agency)
Evaluating options for management of contaminated sites and agreeing detailed plans
Completing and confirming success of site plans.

12. 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.

13. Purpose of monitoring diffuse soil contamination
Is diffuse soil contamination an actual or potential risk (e.g. to food production and / or water quality)?

14. Strategy for diffuse soil contamination
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
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

15. 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

16. Technical approach to monitoring diffuse soil contamination
Sampling soil over large areas followed by testing of samples for priority contaminants

17. 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).

18. 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.

19. 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.

20. 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 Pb
11-370
17-210
28-140
Agriculture
Mudstone
14-110
17-74
23-89
Chalk till
9-65
11-48
13-42
Sandstone / Mudstone / Shales
14-320
18-220
28-240
Background “contamination”

21. 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