Method Statement – Contaminated Land Management
Over many years our industrialised society has allowed areas of land to become contaminated
through poor management and lack of environmental awareness. Contaminated land may
cause unacceptable risks to human health, pollution of water supplies and the wider
environment.
Contaminants, from a range of industries, typically include:
• Hydrocarbons.
• Heavy metals.
• Organic compounds.
• Mining materials.
• Soluble salts.
On 1 April 2000 contaminated land legislation came into force in England and Wales as an
extension to Part IIA of the Environmental Protection Act 1990.
The regime provides an
improved system for the identification and remediation of contaminated land.
The
Contaminated Land (England) Regulations 2000, made under Part IIA of the Environmental
Protection Act, resulted in a requirement for local authorities to set up registers of contaminated
land lying within their boundaries.
The management of contaminated land is an important issue that involves many stakeholders
including local government, regulatory bodies, the local community, industry and service
providers.
Contaminated land presents a potential environmental and economic liability for landowners.
However, in recent years management techniques have been developed in the areas of site
investigation, risk assessment, modelling and remediation.
MWH’s approach
MWH has the in-house technical expertise to offer a complete service in a cost effective manner
with a contaminated land management process that is consistent with UK Government guide
lines and is designed to meet clients’ business goal objectives. For each commission we can
quickly build up teams from within the organisation having the relevant technical and
managerial skills, as well as access our worldwide knowledge base, to deliver a first class
service to the client.
Supported by an active global knowledge community our local teams have access to expertise
developed globally, ensuring that innovation and lessons learned can be quickly applied. MWH
provides specialist services for the identification and remediation of contaminated land as both
a consultant and contractor, including:
• Feasibility studies.
• Desk studies.
• Environmental risk management databases.
• Environmental investigations.
• Geotechnical appraisals.
• Quantitative risk assessment for human health and the environment.
1
Method Statement – Contaminated Land Management
• Groundwater modelling of contaminant fate and transport.
• Remedial option studies.
• Remedial design and construct.
• Land quality statements.
• Landfill closure reports.
• PPC condition surveys.
• Acquisition and merger audits.
Benefits
We undertake environmental site assessment (ESA) to assess a site’s environmental sensitivity
in terms of hydrogeological and geological setting, determine the type and location of on-site
pollutant sources and evaluate potential on-site and off-site receptors. This evaluation of the
relationship between source, pathway and receptor forms the conceptual site model which is
the foundation for future decision making.
For property portfolios, MWH has also developed a risk management database to provide our
clients with initial assessments of liability associated with management of their land holdings.
The database is focused on environmental issues, but other asset management attributes may
be included if required. The database is a useful tool for prioritising areas for further
investigation and algorithms can be utilised to prioritise sites within a portfolio where pollution
links between sources, pathways and receptors have been identified.
We conduct investigations, designed to find solutions to assumptions made during the
environmental site assessment, such as direction of groundwater flow, depth to groundwater,
presence of non-aqueous phase liquids and the extent and magnitude of contamination in the
soils and groundwater underlying the site.
MWH can tailor these works to suit the time and finance available, and prioritise the levels of
information required.
Central to the Contaminated Land provisions within Section 57 of the Environmental Act 1995,
is the use of Quantitative Risk Assessment (QRA) to determine the existence of contaminated
land. The Contaminated Land Exposure Assessment (CLEA) Model was introduced by DEFRA
(2002) and provides standard use Soil Guideline Values (SGVs) for a limited number of
contaminants.
Due to the current lack of published toxicity values for common contaminants, MWH has
developed soil guideline values for priority human health contaminants. We undertake
quantitative risk assessments to develop site specific target levels for clean up. This is a
valuable tool that may be used for reducing conservative assumptions that can result in overly
stringent guideline values and unnecessary remedial works.
A systematic review of all remedial options ensures the right solution is selected for the project.
Option reviews are completed according to the following key criteria:
That the technique is reasonable in terms of the cost involved and the seriousness of the harm to
human health or pollution of waters to which it relates.
That it represents the best combination of practicability, effectiveness, durability and efficiency.
2
Method Statement – Contaminated Land Management
The benefits are maximised by working closely with all parties to ensure that the zoning/end
use of the site is adapted to accommodate any contamination at the site.
Experience
Site Investigations
MWH has an ongoing contract to carry out environmental site investigations at former gas
manufacturing plants throughout the UK. To date we have conducted over 70 site history
reviews and intrusive site investigations for a UK national gas company. A typical scope of
works involves a site visit, collation of all available information (including information from the
regulatory authorities), a site history review, a topographical survey and a qualitative risk
assessment. This work is followed by an intrusive soil and groundwater investigation,
laboratory analysis, human health and environmental risk assessment and recommendations for
remedial action which include cost estimates to address statutory and non-statutory liabilities.
Typical contaminants include poly-aromatic hydrocarbons, phenols, cyanides and heavy metals.
Several projects have been taken to full remedial design, including all negotiation with
regulators and statutory bodies, construction management, environmental supervision and
closure reporting.
MWH has conducted gap analysis on a site investigation carried out by another consultant on a
former gas-manufacturing site, with subsequent additional groundwater sampling and
monitoring.
Results of the site investigation and groundwater monitoring indicated
concentrations of chemicals in excess of the Tier 1 Screening Criteria. A human health risk
assessment was used to quantify the impact of hazards on receptors and to identify options for
managing or mitigating those risks.
Site specific screening criteria for chemicals were generated using the Environment Agency’s
CLEA model. These took into account the ground conditions of the site (soil type, soil pH and
organic matter content), proposed end use of the site, route of exposure (e.g. ingestion or
inhalation) and the most sensitive receptor selected for the site. In addition, the US Johnson
and Ettinger model (2003) was used to assess volatile contaminants. Results from the risk
assessment were used to define areas of the site that required remedial action, isolating those
areas considered not to pose a significant risk to future site users and to put forward
management options.
MWH is undertaking a long term monitoring and natural attenuation study, carrying out
groundwater monitoring and sampling at the United States Air Force (USAF) base at RAF
Mildenhall under the DE USF term commission hazardous material spill assessment contract
awarded to MWH in 1999. MWH’s team of hydrogeologists and modellers, with support from
3
Method Statement – Contaminated Land Management
colleagues in other countries, has developed a calibrated model capable of simulating
groundwater conditions beneath base.
The development of a robust model will enable technically sound, defendable fate and transport
models for contaminants of concern to be developed. The development of predictive plume
maps using industry leading software will provide the base with a powerful management tool to
assess and prioritise remedial actions and clean-ups. Spill scenario plans using RT3D for
chlorinated solvents and MT3DMS for petroleum hydrocarbon have been developed.
Remediation
MWH was commissioned by a major gas company to undertake Phase 1 (Desk Study), Phase 2
(Site Investigation) and Phase 3 (Remediation) services relating to the remediation of a former
town-gas site in Cumbria. Groundwater and surface water monitoring was carried out prior to
the works commencing and post remediation. Our Phase 3 services included remediation
design, provision of remediation works contract tender documents and provision of the
remediation specification, validation reporting and full liaison with the local authority and
Environment Agency (North West Region) during the works. A MWH environmental engineer,
acting in the capacity of Resident Engineer carried out supervision of the contract. The
remedial works were carried out during a 10 week period and involved the removal of the
contents of three tar tanks and surrounding localised areas containing tar. Approximately 10,
000 tonnes of contaminated material were removed from the site by the principal contractor
and subsequently disposed to a suitably licensed landfill facility. The site was fully restored
utilising backfill material, subsoils and topsoil. The site was seeded with grass and is currently
used as a recreational area for the general public.
MWH was commissioned to undertake the detailed design, installation, commissioning and
subsequent operation of an emergency remedial system that was required to ensure recovery
and containment of free phase hydrocarbons migrating within an operational railway depot’s
surface water drainage network. The uncontrolled release of hydrocarbons from the site’s
drainage system was causing pollution of a fresh water lake located within a high amenity,
public recreation area.
As part of the United States Forces clean-up programme at RAF Mildenhall, MWH was
commissioned to design a remedial programme to remove lead impacted soils from a disused
small arms range at the base. X-ray fluorescence was utilised for on-site validation to confirm
that targets were met, eliminating the need to wait for laboratory analytical results before back
filling. This approach enabled the programme to be accelerated and significant cost savings to
be passed on to the client. Approximately 1,000m 3 of impacted soil was removed from site and
the land was returned to beneficial use
Summary
The challenge for the future is to ensure that the management of contaminated land sits within
a framework of sustainability. MWH has the flexibility and depth of experience to undertake
remediation work in a number of ways. We can act as consultant, prime contractor or provide
a complete design, bid, build and operate solution to the problems of contaminated land
management. Our approach allows our clients to achieve their goals in a safe, timely and costeffective manner.
4