How significantly risky a business is managing contaminated land

In this edited paper by Adam Czarnecki and Sarah Dack of GeoDelft Environmental, the application of risk assessment in the management of contaminated land is reviewed within the context of requirements of recently introduced regulations applying in England and Scotland.


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After formulation and consultation over the past ten years the Contaminated Land

Regulations (2000) together with its associated circular were introduced into

England on 1 April and Scotland on 14 July of last year. The new legislation requires

landowners, local authorities, property developers, contractors, professional

advisers, the Environment Agency together with allied service sectors (such as

lenders and insurers) to identify and remediate contaminated/special sites in

accordance with prescribed risk assessment procedures.

Environmental control within the new legislation is in essence not radically

different from previously existing water (Water Resources Act (1991), planning

legislation and guidance PPG23 Planning and Pollution Control (1994), law or

protection from common law. Similarly, the fundamental concepts of risk assessment

and the pollution linkages concept which are enshrined within the new legislation

have been undertaken by some pro-active practitioners in the UK for several

years. In the UK for example GeoDelft Environmental (www.geodelft.co.uk)

has been undertaking Quantitative Risk Assessments (QRA) as a means of identifying

and assessing potentially contaminated sites for the past eight years.

UK policy dictates that land development is undertaken in accordance with the

Framework for Contaminated Land (DoE, 1994) and states that existing contamination

which poses a threat to human health or the environment is controlled and treated

within the suitable for use approach. Prior to the new legislation the investigation,

management and reclamation of contaminated sites was undertaken within the planning

process. A more pro-active process has now been implemented with local authorities

now responsible for the identification and if necessary reclamation of contaminated

sites.

What is a Risk Assessment?

An excellent overview, Guidelines for Environmental Risk Assessment and Management

of the underlying principles of risk assessment, risk management and risk

communication was published by the DETR on 31 August 2000.

So what is a risk assessment? It is (and should be) a formalised, transparent

and reproducible framework by which we can identify whether or not contaminated

land presents an unacceptable level or risk to human health, controlled waters,

property or ecological targets.

Where unacceptable risks are identified (by use of Quantified Risk Assessments)

the modelling can derive site-specific clean up target values that will reduce

the risks to an acceptable level.

This is an important point as previous guidance on the evaluation of contaminated

land has been based upon generic non-site specific standards such as ICRCL 59/83,

Dutch Intervention Values or the GLC “Kelly” guidelines. These are

still reported as being used as land evaluation and reclamation standards today,

with R & D Technical Report P260 identifying (from a market survey) that

88% of people still use ICRCL trigger values in their work and even more worryingly

that 55% of respondents routinely use the former GLC “Kelly” standards.

Reluctance over risk assessment

Reluctance to the use of risk assessments in the UK probably stems from a lack

of formal training (now available at some UK universities) and recognising that

the undertaking of risk assessments requires a multi-disciplinary specialist

approach by use of a team of hydrogeologists, geologists, geotechnical engineers,

ecologists, biologists and toxicologists.

At the time of writing we are still awaiting extensive technical guidance on

the use of risk assessments from the DETR. The impending CLEA model which eventually

will be routinely used as a tool for evaluating risks to human health is at

present under development. For controlled waters (the relevant regulatory authority

being the Environment Agency) guidance has been published with Methodology

for the Derivation of Remedial Targets for Soil and Groundwater to Protect Water

Resources, R & D P20. This provides guidance on different levels (Tiers)

of risk assessment when evaluating potential risk to controlled waters, commencing

with the impact for soil contaminants on pore water, to risk to sensitive receptors

such as water courses and abstraction boreholes.

GeoDelft has also been involved in the development of the new standards for

the Environment Agency with a resultant publication of Technical Report P260

Land Contamination Risk Assessment Tools and is also currently engaged in

conducting a sensitivity analysis on a beta version of the CLEA2000 model and

producing technical guidance in its use.

Risk Assessment Procedures

Tier I Investigation

Any cost-effective investigation of a potentially contaminated site should start

with a preliminary phase where information is gained on existing and former

on-site (and neighbouring) land uses(s). This is normally a historical desk

study and a walk-over survey (often essential and neglected) together with a

collation of information relating to the general environmental setting, i.e.

geology, hydrogeology, mining activity, local abstractors (unlicensed and licensed),

location of controlled waters (springs, rivers, streams, canals, estuaries,

ponds), pollution incidents and proximity to active/closed landfill sites etc.

The Tier I investigation may also include a preliminary site investigation

in order to develop a Conceptual Site Model (CSM) for the likely areas of contaminated

material (Sources), potential pathways (or linkages) and potential receptors

(humans, controlled waters, building or ecology).

A Tier I Investigation normally integrates the collected information together

with information gained into the CSM. Elevated concentrations of certain elements/compounds

are compared with screening concentration values which are non-site specific.

For controlled waters the P20 Methodology either calculates pore water concentrations

from soil concentrations and derives a Tier I remedial target concentration

by multiplying the partitioning against a suitable water quality standard, or

directly compares leaching test concentrations against a suitable water quality

standard.

Suitable screening levels could be drinking water standards for groundwater

or Environmental Quality Standards (EQS) if a nearby surface water receptor

is identified. However other standards could be considered such as bathing water

standards or standards to protect irrigation or livestock.

Soil and groundwater element/compound concentrations should be compared with

the

most relevant (and defendable!) screening levels. If there are no exceedances,

the site or individual areas of the site can be assumed to not pose an unacceptable

risk. If there are exceedances then a following stage of investigatory work

is warranted.

Tier II Investigation

A Tier II Investigation usually involves investigatory work based on amended

likely pollutant linkages identified within Tier I.

GeoDelft uses a number of models to carry our Tier II Investigations. These

include RBCA (based upon the ASTM standard E-1739) produced by Groundwater Services

Inc which models both human health exposure pathways and groundwater migration

pathways. The model incorporates a large chemical and toxicological database

that is continuing to be revised and expanded. GeoDelft has modified RBCA to

become more UK focused than the original model. This model has been routinely

used on over 300 sites in the past two years. For controlled waters the “P20

method” is also routinely used.

Risc-Human v.3.0 developed by the Dutch Institute for Public Health and the

Environment and based upon the CSOIL model can at present only be used for human

health exposures.

Information required for a Tier II human health risk assessment include site-specific

geological information, physical and chemical properties of the unsaturated

and zones, site-specific human health exposure parameters such as ingestion

rates or breathing rates. The estimated quantity of contaminant inhaled, adsorbed

or ingested is compared against acceptable daily intake values.

For controlled waters the assessment again requires site-specific soil and

groundwater parameters for inclusion in simple groundwater fate and transport

algorithms based on the Domenico equation. These algorithms model the movement

of contaminants in the saturated and unsaturated zones to identified receptors

such as aquifers, abstraction wells or surface water bodies. Concentrations

predicted at the various receptors are compared against target values such as

Drinking Water Standards or Environmental Quality Standards.

Groundwater modelling may include conservative biodegradation half-lives in

order to account for biodegradation, degradation and attenuation processes occurring

in the aquifer.

If the contaminant is above the acceptable intake value for any identified

receptor it is assumed that there is a potential for an unacceptable level of

risk to exist and risk-based site-specific target levels SSTL’s are calculated

for the site. The site can either be remediated on the basis of the SSTL’s or

an additional investigation instigated in order to facilitate a Tier III risk

assessment. The extra cost of data collection within the Tier III investigation

is most likely to be offset by the reduced conservatism and uncertainty in the

resulting remediation targets.

Tier III Investigation

A Tier III investigation and risk assessment involves a further reduction in

the level of uncertainty of the risk estimates by obtaining more site-specific

data for each exposure pathway that has been determined to exceed acceptance

criteria at the Tier II stage.

A Tier III risk assessment involves more sophisticated fate and contaminant

transport modelling and the use of probabilistic risk assessment techniques.

Additional site-specific information required for the assessment may include

three dimensional source characterisation, unsaturated zone porosity, review

of building design, hydraulic conductivity and organic carbon data etc.

Other models may well be used in order to take into consideration of surface

water dilution at a receiving water body, modelling of biodegradation processes

(with use of Biochlor or Bioscreen) or a re-assessment of the degradation half-lives

and exposure duration’s used in the Tier II investigation.

Summary

The Royal Institution of Chartered Surveyors predicted in 1997 that the new

Contaminated Land Regulations (2000) would be the single most important piece

of legislation to impact on the property industry.

The development of brownfield or contaminated land has now achieved a degree

of maturity, with sophisticated scientific methods required to quantify risk

for human health, controlled waters, buildings and in some cases ecological

receptors. Practitioners and regulators will need to respond to this new regime,

staff training in risk assessment techniques will be necessary, site investigations

should will become more sophisticated, environmental insurance policies will

become more common and inevitably legal opinion on the designated status of

sites will become increasingly necessary.

A report by the Urban Task Force entitled Towards an Urban Renaissance (DETR,

1999) proposes that all polluted sites should be restored by the year 2030.

Our question is, how many sites have been unnecessarily reclaimed because no

site-specific risk assessment was ever performed? Even more worryingly how many

contaminated sites that have been developed have not identified all the potential

sources or pollutant linkages and therefore still pose a risk to human health

and the environment?

Only time will tell.

Risk Assessment Workshops

In order to assist local authorities in the undertaking of their new duties

GeoDelft Environmental has developed a Risk Assessment Workshop (first to be

run on 15-16 October 2001) that aims to give relevant staff practical experience

in the development/verification of qualitative/quantitative risk assessments

for potentially contaminated sites.

Demonstrations will be given on the development of appropriate risk models

from information gained by desk studies, intrusive/non-intrusive surveys and

chemical testing by using different propriety software packages and best-practice

guidelines.

Case studies will be presented in the form of a series of different geological/hydrogeological

settings; existing site uses together with proposed end use scenarios. Delegates

will be assisted in their development of a Conceptual Site Model, and an initial

Tier 1 Risk Assessment together with a prioritisation model for screening of

multiple sites.

A more sophisticated Tier 2 model would be developed by the delegates from

information gained from a series of different types of site investigations,

chemical testing and after choosing and deciding upon appropriate toxicological

and exposure parameters. Output from the different models would be examined

for the different pathways, receptors and contaminants of concern.

Risk Assessment Bureau Service

GeoDelft Environmental has been in consultation with several local authorities

over the past six months in the development of a dedicated Risk Bureau Service.

Delegates to each workshop will be given a unique opportunity to participate

in a service that will initially provide a dedicated telephone help-line and

web-based information knowledge base.

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