Contaminated Land Investigation, Assessment and Remediation

Site Investigation

Environmental risk assessment and assessment of health hazards

Source-pathway-receptor linkages

Analysis, design and interpretation reporting

Remedial works and site redevelopment proposals

Environmental audit, due diligence and compliance

Assessment for property acquisition and disposal

Acquisition and liability audits

The desk study and/or intrusive ground investigation is typically carried out in accordance with the requirements of BS5930 and BS10175.  In relation to contamination the desk study is referred to as the preliminary investigation in BS10175 and the intrusive ground investigation is referred to as the Exploratory Investigation.  This appendix briefly describes the nature of the work carried out and explains the standards against which contamination data has been assessed.  The nature of any contamination investigation is such that only a small percentage of the ground, and therefore potential contamination, is sampled.  Consequently variations in both ground conditions and contaminant levels can occur between any two sampling positions.  The contamination investigation is designed to minimise such risks, but they cannot be eliminated. 

REVIEW OF CONTAMINATION ISSUES

Part 2A of the Environmental Protection Act 1990 created a new regime for the identification and remediation of contaminated land.  It introduced a definition of contaminated land described in Section 78A (2) of the Act of:

"any land which appears to the local authority in whose area it is situated to be in such a condition, by reason of substances in, on or under the land, that 

significant harm is being caused or there is a significant possibility of such harm being caused; or 

significant pollution of controlled waters is being caused or there is a significant possibility of such pollution being caused: 

Both Part 2A and the planning regime embrace the "suitable for use" approach.  In the context of Part IIA, action is necessary only where there are unacceptable risks to health or to the environment, taking into account the current use of the land and its environmental setting. 

For humans, significant harm is defined as "death, disease, serious injury ".  Specifically, disease is taken to mean an unhealthy condition of the body or part of it.  "Significant possibility of significant harm" is described as health effects arising from the intake of a contaminant or other direct bodily contact with the contaminant where the intake or exposure is unacceptable.  The assessment should also take into account the total intake from all sources, the relative contribution of the pollutant linkage in question, and the duration of intake or exposure.  The various statutory definitions are given overleaf. 

The presence of unnatural substances does not automatically constitute a risk unless there is a link or pathway between the contamination (the hazard) and the receptor (the target) be it humans, the environment or property.  Therefore the assessment needs to determine whether a hazard is present and whether the necessary pathway exists the so-called "pollution linkage" or “conceptual site model”. 

The effect of any hazard on a site depends primarily on the site use and groundwater conditions since these determine who and what may be at risk and the routes by which they may be exposed to the hazard.  Site uses can include allotments, domestic gardens on residential developments, amenity and recreational areas, public open space and industrial and commercial buildings.  On any site, the potential contaminants have to be identified together with the potential receptors.  The pathway for that contaminant to reach its target has then to be considered.  

PRELIMINARY INVESTIGATION

The report will summarise the findings and also relate our opinions to the potential for a site to be geoenvironmentally impaired, at levels likely to warrant mitigation or further consideration appropriate to the current or future use. 

Findings are based on information obtained and described during the desk study and site inspection without intrusive ground investigation.  It is possible that further information exists.  The absence of indicators of impairment does not mean that such impairment does not exist.  Additional investigation including intrusive methods can reduce the risks but cannot eliminate them and may not be cost effective.  We can advise on the additional research opportunities, their cost and their possible impact on mitigating risk.  Recommendations are normally given based on the redevelopment proposals for the site.

INTRUSIVE INVESTIGATION

BS10175 describes this as an exploratory investigation.  Intrusive ground investigation is described in Standard Appendix A.  During the investigation representative or indicative samples are obtained for testing by an accredited laboratory.  The aim is to determine (with a degree of confidence appropriate to the objectives), the presence, concentration and distribution of contaminants in respect of those points investigated.  The extent of any necessary intrusive investigation will depend on the size of the site and any hazards, either known or suspected. 

ASSESSMENT OF CONTAMINATION

The assessment of contaminated land under the terms of Part II A of the Environmental Protection Act 1990 is based upon pollution linkage (source - pathway - receptor model). 

The Contaminated Land Report (CLR) series of documents have been produced by the Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency, to provide regulators with "relevant, appropriate, authoritative and scientifically based information and advice on the assessment of risk from contamination in soils". 

The Environment Agency has issued a number of Soil Guideline Values (SGVs), which whilst non-binding, may be used as guidance in the assessment of land and in setting remediation targets.  They should only be applied to human health assessments. 

The SGVs have been derived using the Contaminated Land Exposure Assessment Model (CLEA) and are based on assumptions relating to soil conditions, pollutant type and behaviour, land use patterns and the availability of receptors.  SGVs are also subject to statistical assessment.  The CLR documentation requires that the results of laboratory testing are subject to statistical analysis to remove uncertainty over a so-called 'averaging area'.DEFRA have issued the “Outcome of the Way Forward Exercise on Soil Guideline Values”.  This document is intended to provide guidance to determine if there is a Significant Possibility of Significant Harm (SPOSH) i.e. whether land meets the legal trigger of being contaminated land. 

The CLEA model has been revised.  SGV values are also currently being revised and further SGVs are to be issued shortly.  The older SGVs have been withdrawn in the light of this.  However, since the toxicological data has not been revised, this practice believes that the older SGVs can continue to be used for general guidance where new SGVs have not been published.  In other words they can be considered generic assessment criteria to assess the minimal risk to health. 

In the context of Part 2A, a risk assessor using and SGV can conclude the following (DEFRA, 2008). 

At a representative average soil concentration at or below an SGV, it is very unlikely that there be the significant possibility of significant harm

At a representative average soil concentration above an SGV, there might be a significant possibility of significant harm with the significance linked to the margin of exceedance, the duration and frequency of exposure, and other site-specific factors that the enforcing authority may wish to take into account.  Further investigation and / or detailed evaluation will usually be required. 

The guideline values for so-called non-threshold substances may change considerably, as a result of the current   review perhaps by a factor of 10.  In addition, the effect of naturally occurring metal-rich soils may also have to be taken into account.  A pragmatic approach has therefore been adopted by this practice. 

It should be stressed that where there is any uncertainty as to whether or not there is a SPOSH, it is the policy of this practice to adopt a conservative approach, particularly in the adoption of clean cover systems.

GEOENVIRONMENTAL RISK ASSESSMENT 

Potential Hazard Sources.  Ground contamination can occur through several causes, particularly from historical use of the site and is often linked to the processes of waste disposal, underground storage, open storage, process pipework, leaks, spillages, tanks, site filling and various other reasons.  The contamination can either arise from site sources or be the result of migration from other sources off site. 

Potential Migratory Pathways.  The primary pathways are considered to be laterally or vertically downward through underlying strata or upward to the ground surface.  Such pathways also provide the potential for contaminants to migrate towards local watercourses and groundwater. 

Potential Targets at Risk.  Potential environmental liabilities related to current legislation associated with contaminated land with regard to existing ownership and redevelopment are summarised. 

The probability of a hazard, linked with its consequences, can be used to assess risk in accordance with the tables below for use in decision making.

Evaluation of contaminated and marginal land for its safe remediation and development, including a staged approach comprising phase 1 and 2 assessments.

Associated issues

Waste Management Licensing

Waste Acceptance Criteria (WAC)

Clean Cover Systems

Asbestos in Soil

Client's Guide to Phase 1 Geoenvironmental Risk Assessment