Contaminated Land
Throughout the UK there are thousands of sites which have been contaminated by previous
industrial use, often associated with traditional processes which are now obsolete, which may
present a hazard to the general environment, but for which there is a growing requirement for
reclamation and redevelopment.
Recent targets set by the Government demand that 60% of all new houses should be built on
"Brownfield" sites to relieve the pressure on greenfield sites and preserve the countryside. The
Environment Agency estimates that some 300,000+ hectares of land are affected, covering
between 5,000 and 20,000 "problem sites". The problems of contaminated land have been
tackled almost exclusively in the context of redevelopment where there was the objective of
economic benefit linked to environmental enhancement.
The Environmental Protection Act 1990 Part IIA (inserted by Section 57 of the
Environment Act, enacted April 2000) defines Contaminated land as
“Any land which appears to the local authority in whose are it is situated to be in
such a condition, by reasons of substances in, on or under the land, that
(a) significant harm is being caused, or there is a significant possibility of such
harm being caused, o
(b) pollution of controlled waters is being, or is likely to be caused.”
In practice less that 15% of redevelopment land will come under this definition within the UK.
However with Government initiatives to reuse derelict industrial land (brown field sites) for
housing and offices, many sites will be contaminated to such a level that planning restrictions
will be placed on the land although it does not fit the legal definition of contamination. Many
sites will contain contamination levels above published guidelines that need cleaning up in order
to build upon, but are not causing, or likely to cause “significant harm”. Such sites will form 85%
of land requiring remedial works for contamination and will be dealt with by standard planning
procedures with no recourse to the Environment Act.
Types of Contamination
Potential hazards
This list is by no means exhaustive, but it gives a flavour of the different classes of potential hazards.
Toxic, flammable and explosive gases
 acetylene
 hydrogen cyanide
 hydrogen sulphide
Flammable liquids and solids
 fuel oils
 solvents
Combustible materials
 timber
 ash
 coal residues
Corrosive substances
 acids
 alkalis
Toxic substances
 phytotoxic heavy-metals
 hydrocarbons
 inorganic salts
 asbestos
Substituted Aromatic compounds
 PCBs
 dioxins
 furans
Biological agents
 anthrax
 tetanus
 BSE
 Genetically Modified Organisms
 Genetically Modified Pollens
UK Approach
The problems of contaminated land in the UK have been tackled almost exclusively in the
context of redevelopment where there was the objective of economic benefit linked to
environmental enhancement. This has lead to an approach based around the ‘suitability
for use’ concept and evaluated in terms of risk assessment.
Section 57 of the 1995 Environment Act endorses the risk based approach for managing
contaminated land and adopts a rationale based on international definitions
toxicity – potential of a material to harm biological systems
hazard - the nature of the adverse effect posed by the compound
risk – the probability of suffering harm or loss under specific circumstances.
A risk therefore only exists where there is a
Contaminant or Source
which can reach a Receptor
via a Pathway
This can be done in a QUALITATIVE or QUANTITATIVE way
Sources of Contamination
Gasworks Coal tar creosote Phenols phenol Cyanide free / complex Sulphur sulphide /
sulphate
Iron + Steel works Metals copper, nickel, lead Acids sulphuric, hydrochloric Mineral oils Coking works residues (as for gasworks )
Metal finishing Metals cadmium, chromium, copper, nickel, zinc Acids sulphuric,
hydrochloric Plating salts cyanide Aromatic hydrocarbons benzene Chlorinated
hydrocarbons 1,1,1-Trichloroethane
Non ferrous metal processing Metals copper, cadmium, lead, zinc Impurity metals
antimony, arsenic Other wastes battery cases, acids
Oil refineries Hydrocarbons various fractions Acids, alkalies sulphuric, caustic soda
Lagging, insulation asbestos Spent calalysts lead, nickel, chromium Paints Metals lead,
cadmium, barium Alcohols toluol, xylol Chlorinated hydrocarbons Methylene Chloride
Fillers, extenders silica, titanium dioxide, talc
Petrochemical plants Acids, alkalies sulphuric, caustic soda Metals copper, cadmium,
mercury Reactive monomers styrene, acrylate, VCM Cyanide toluene di-isocyanate
Amines analine Aromatic hydrocarbons benzene, Toluene
Petrol stations Metals copper, cadmium, lead, nickel, zinc Aromatic hydrocarbons
benzene Octane boosters lead, MTBE Mineral oil - Chlorinated hydrocarbons
trichloroethylene Paint, plastic residues barium, cadmium, lead
Rubber processing Metals zinc, lead Sulphur compounds sulphur, thiocarbonate Reactive
monomers isoprene, isobutylene Acids sulphuric. hydrochloric Aromatic hydrocarbons
xylene, Toluene
Pathway
Pathways can exist via air, water and soil. This can be by ingestion, inhalation, eye
contact, absorption through skin, contamination of plants and animals, uptake by
vegetation, drinking water contaminated or migration through permeable strata.
This relates to several factors, such as:



the nature of the site (physical layout and geology).
the nature of the use and exposures
the nature of the pollutants
The nature of the pollutants can include:
Pollutant solubility: will determine how much dissolves into water
Pollutant volatility: will determine how much passes into the air.
Pollutant partitioning and adsorption: will determine how strongly it is held to solids.
This can mean that a site with, for example, a range of organic pollutants may have a
variety of different pathways.
Transport Properties of Selected Organic Contaminants
Compound
Benzene
Phenol
Hexachlorodibenz
ene-p-dioxin
Benzo[a]pyrene
Aqueous Solubility
(mg/l)
1780
8.2x104
1.3x10-4
Vapour pressure
(Pa)
1.3x104
71
1.9x10-6
Koc*
65
14
2.6x107
Dominant partition
medium
Air
Water
Soil
3.8x10-3
7.3x10-7
5.5x106
Soil
* partitioning coefficient organic carbon-water
Receptors and Targets
The receptors can be:
People
Water Resources
Flora and Fauna
Buildings
adults, children, site workers, residents, visitors, neighbours
surface, ground
SSSIs, livestock, wild animals, birds, landscaping
foundations, services, structures
Defined in EPA 1990
Sensitivity of use:
Domestic Gardens
Allotments
Parks
Landscaped Areas
Buildings (no gardens)
Hard Covered Areas
Most Sensitive
Least Sensitive
Risk Assessment
see handout
Standards
Once a risk has been identified, it needs to be quantified.
Inter Departmental Committee on the Reuse of Contaminated Land
ICRCL 59/83 Trigger Concentrations
Contaminant
Planned Use
Group A (may pose hazards to health)
Arsenic
Domestic gardens, allotments
Parks, playing fields, open space
Cadmium
Domestic gardens, allotments
Parks, playing fields, open space
Domestic gardens, allotments
Chromium
(hexavalent) (1)
Parks, playing fields, open space
Domestic gardens, allotments
Chromium
(total)
Parks, playing fields, open space
Lead
Domestic gardens, allotments
Parks, playing fields, open space
Mercury
Domestic gardens, allotments
Parks, playing fields, open space
Selenium
Domestic gardens, allotments
Parks, playing fields, open space
Group B (Phytotoxic - but not normally hazardous to health)
Boron
Any uses where plants are grown (2) (6)
(water-soluble) (3)
Copper (4) (5)
Any uses where plants are grown (2) (6)
Nickel (4) (5)
Any uses where plants are grown (2) (6)
Zinc (4) (5)
Any uses where plants are grown (2) (6)
Group C - (Organic contaminants)
Domestic gardens, allotments, play areas
Polyaromatic
hydrocarbons (7) (8)
Landscaped areas, buildings, hard cover
Phenols
Domestic gardens, allotments,
Landscaped areas, buildings, hard cover
Cyanide
Domestic gardens, allotments, landscaped
(free)
areas
Buildings, hard cover
Cyanide
Domestic gardens, allotments
(complex)
Landscaped areas
Buildings, hard cover
Thiocyanate
All proposed uses
Sulphate
Domestic gardens, allotments, landscaped
areas
Buildings (9)
Hard cover
Sulphide
All proposed uses
Sulphur
All proposed uses
Acidity
Domestic gardens, allotments, landscaped
areas
Buildings, hard cover
Trigger Values
(mg / kg air-dried soil)
Threshold Action
10
40
3
15
25
No Limit
No Limit
600
1,000
500
2,000
1
20
3
6
Threshold Action
3
130
70
300
Threshold Action
50
500
1,000
10,000
5
200
5
1,000
25
500
100
250
250
250
50
500
1,000
5,000
No Limit
No Limit
2,000
10,000
2,000
2,000
250
5,000
50,000
No Limit
1,000
20,000
pH<5
pH<3
No Limit
No Limit
The New Dutchlist
Contaminant
Metals
Arsenic
Barium
Cadmium
Chromium
Cobalt
Soil Sediment(mg/kg dry
weight)
optimum
action
29
200
0.8
100
20
Groundwater(µg/l)
optimum
55
625
12
380
240
action
10
50
0.4
1
20
60
625
6
30
100
Copper
Lead
Molybdenum
Nickel
Mercury
Zinc
Cyanides
Free
Complex (pH<5) (1)
Complex (pH>5) (1)
Thiocyanate
Aromatics
Benzene
Ethylbenzene
Phenol
Toluene
Xylene
Cresol
Catechin
Resorein
Hydroquinone
Polycyclic Aromatic Hydrocarbons (PAH)
Anthracene
Benzo(a)pyrene
Fluoroanthrene
Naphtalene
Phenanthrene
Benzo(a)anthracene
Chrysene
Benzo(a)fluoranthrene
Benzo(k)fluoranthrene
Benzo(g,h,i)perylene
Indenol(1,2,3-c,d)pyrene
Total PAH (2) (10)
Chlorinated Hydrocarbons
1,2 Dichloroethane
Dichloromethane
Tetrachloromethane
Tetrachloroethane
Trichloromethane
Trichloroethene
Vinylchloride
Monochlorobenzene
Dichlorobenzol (total)
Trichlorobenzol (total)
Tetrachlorobenzol (total)
Pentachlorobenzene
Hexachlorobenzene
Chlorobenzenes (3) (10)
Monochlorophenol
Dichlorophenol
Trichlorophenol
Tetrachlorophenol
Pentachlorophenol
Chlorophenols (total) (4) (10)
Chloronapthylene
PolyChloroBiphenyls (total)(5) (10)
Pesticides
DDT/DDD/DDE (total) (6)
Aldrin
Dieldrin
Endrin
Drins (total)
alpha HCH
36
85
10
35
0.3
140
optimum
190
530
200
210
10
720
action
1
5
5
-
optimum
20
650
50
-
optimum
action
0.05[d]
0.05[d]
0.05[d]
0.05[d]
0.05[d]
optimum
action
---1
optimum
action
[d]
0.001
0.01
0.001
0.001
[d]
0.01
0.01
0.01
0.0035
0.0025
0.0025
0.003
0.001
0.001
0.002
0.02
optimum
75
75
300
75
0.3
800
action
5
10
10
20
optimum
2
50
40
130
25
5[d]
20
10
10
1500
1500
1500
1500
action
0.2
0.2
0.2
0.2
0.2
-
4
20
1
4
10
60
0.1
30
5
10
10
1
4
[d]
4
-
action
0.02
0.001
0.005
0.1
0.03
0.002
0.002
0.003
0.001
0.0002
0.0004
optimum
action
30
150
2000
1000
70
200
1250
600
800
optimum
40
action
0.0025
0.0025
0.0005
0.001
0.0025
15
15
5
15
0.05
65
5
0.5
1
70
5
0.5
0.05
0.5
0.05
0.05
0.05
-
0.01[d]
400
0.01[d]
1000
0.01[d]
10
0.01[d]
40
0.01[d]
400
0.01[d]
500
0.7
0.01[d]
180
0.01[d]
50
0.01[d]
10
0.01[d]
2.5
0.01[d]
1
0.01[d]
0.5
0.25
100
0.08
30
0.025
10
0.01
10
0.02
3
6
0.01
0.01[d]
optimum
action
[d]
0.01
[d]
0.02ng/l
0.1
[d]
-
beta HCH
gamma HCH
HCH combined (7)
Carbaryl
Carbofuran
Maneb
Atrazin
Miscellaneous
Tetrahydrofuran
Pyridine
Tetrahydrothiophene
Cyclohexanone
Styrene
Mineral Oil (9)
Phthalates (total)
0.001
0.05 µg/l
0.05 µg/l
optimum
action
0.1
0.1
0.1
0.1
0.1
50
0.1
2
5
2
35
6
0.4
1
90
270
100
5000
60
[d]
0.2 ng/l
1
0.01[d]
0.1
0.01[d]
0.1
[d]
0.1
0.0075
150
optimum
action
0.5
1
0.5
3
0.5
30
0.5
15000
0.5
300
50
600
0.5
5
Kelly Indices (Former GLC) Guidelines for Contaminated Soils specifically developed for gasworks sites in
London: Suggested Range of Values (mg/kg on air-dried soils, except for pH)
Uncontamin
ated
pH (acid)
6-7
pH (alkaline)
7-8
Antimony
0-30
Arsenic
0-30
Boron (available)
0-2
Barium
0-500
Beryllium
0-5
Cadmium
0-1
Chromium
0-100
Copper
0-100
(available)
Cyanide (free)
0-1
Cyanide
0-5
Ferricyanide
0-100
Lead
0-500
Lead (available)
0-200
Mercury
0-1
Manganese
0-500
Magnesium
0-500
Nickel
0-20
(available)
PAHs (Coal Tar)
0-500
Phenol
0-2
Selenium
0-1
Sulphate
0-2000
Sulphur (free)
0-100
Sulphide
0-10
Thiocyanate
0-10
Toluene extract
0-5000
Vanadium
0-100
Zinc (available)
0-250
Zinc (equivalent)
0-250
Parameter
Slight
Contamin
Heavy
Contamination
ated
Contamination
5-6
4-5
2-4
8-9
9-10
10-12
30-50
50-100
100-500
30-50
50-100
100-500
2-5
5-50
50-250
500-1000 1000-2000
2000-1.0%
5-10
10-20
20-50
1-3
3-10
10-50
100-200
200-50
500-2500
100-200
Unusually Heavy
Contamination
<2
> 12
> 500
> 500
> 250
> 1.0%
> 50
> 50
> 2500
200-500
500-2500
> 2500
1-5
5-50
5-25
25-250
100-500 500-1000
500-1000 1000-2000
200-500 500-1000
1-3
3-10
500-1000 1000-2000
500-1000 1000-2000
50-100
250-500
1000-5000
200-10,000
1000-5000
10-50
2000-10,000
2000-1.0%
> 100
> 500
> 5000
> 10,000
> 5000
> 50
> 10,000
> 1.0%
50-200
200-1000
> 1000
500-1000 1000-2000
2-5
5-50
1-3
3-10
2000-5000 5000-1.0%
100-500 500-1000
10-20
20-100
10-50
50-100
5000-1.0% 1.0-5.0%
100-200
200-500
250-500 500-1000
250-500 500-2000
2000-1.0%
50-250
10-50
1.0%-5.0%
1000-5000
100-500
100-500
5.0-25.0%
500-2500
1000-5000
2000-1.0%
> 1.0%
> 250
> 50
> 5.0%
> 5000
> 500
> 500
> 25.0%
> 2500
> 5000
> 1.0%
20-50
Contaminated Land Research Programme
On the 14th of March 2002, the first result of a 10-year project to create standard
procedures for risk assessment in the UK were released by the EA and DEFRA in a series
of documents. This included a mathematical model for Contaminated Land Exposure
Assessment (CLEA). This also included the first 7 (out of 55) of the Tox series of reports
were released giving Soil Guideline Values for Arsenic, Cadmium, Chromium, inorganic
Mercury, Nickel, Selenium and Lead. These have only been available since 22nd of April
and can be found for download at http://www.defra.gov.uk/.
Sampling
Sampling of contaminated sites has always been difficult because of the potential for ‘hot
spots’ giving an uneven spread of pollution. As certain chemical analyses can be quite
expensive there has always been a trade off between the number of samples and the
probability of finding a randomly located source. This can be explained statistically by
assuming the distribution of pollution is random according to a frequency distribution.
Sampling is usually arranged in a grid (effectively stratified random sampling)
BS DD175: Guidance on the Number of Sampling Points
Area
(Ha)
of
Site Recommended Number
Sampling Points
0.5
1.0
5.0
15
25
85
of Implied Spacing
18 m
20 m
24 m
Area (m2) of contamination to
give
detection
(95%
confidence)
905
1129
1732
BS DD171 also recommends that samples are taken at 3 depths (surface, max excavation
+ 1 intermediate) or every 0.5 m.
ICRCL recommends that at small sites a 10-15 m grid is used and on large sites a 2550m. The grid represents the are of contamination which could be handled without
difficulty if not found during the investigation.
Further statistical guidance has been issued as part of the Contaminated Land Exposure
Assessment document series.
Soil, water and air samples can be taken for analysis as required from boreholes or trial
pits.
If the previous use has been well documented, sampling can be targeted at known
problem areas, such as tar storage areas
Stages of Site Investigation
Phased investigation.
I.
II.
III.
Phase 1 investigation. Gathering existing information. identify sources, receptors
and pathways
Phase 2 – risk estimation and evaluation. Estimation involves quantifying the
nature and extent of exposure of the receptors and the magnitude of effects should
exposure occur. This requires a physical investigation of the site and the pollutant
levels. The compounds, their concentrations and receptors are identified and are
usually related to the ICRCL or Dutch environmental standards. The evaluation of
this risk is then made against the probability and consequence of the exposure to
decide how the risk will be managed.
The next stage is the remediation or site management
IV.
Final - check levels following clean up. Generally to be below Target or Threshold
value.
Design details can be found in Cairney and Hobson, 1998
Remediation Options
Technologies to control remediate contaminated sites depend on the type of pollutant and
site. Biodegradable pollutants organic can be removed by breakdown by microorganisms. Other pollutants can be selectively removed from the soil and others can be
immobilised.
This can include:
Removal of material for treatment and disposal as a hazardous waste
Containment: this limits the mobility of material and blocks the pathway to the receptor.
Treatment: biological, chemical and physical processes to treat the contamination.
Excavation and Disposal
Traditionally this was the most common method of remediating contaminated sites with
about 1x106 m3 of contaminated soil being buried per year. However, new landfill
regulations and the landfill tax have limited this option.
Containment
Cover Systems: a layer (or layers) are used to cover the contamination. This can be to
just put distance between with contamination and the surface, or an impermeable material
to seal the site from water (i.e. to stop precipitation contaminating groundwater) or protect
occupants from gas venting. This can be used for a wide range of contamination.
Designs are made on a site specific basis and are usually made up of gravel, geotextiles
and clays of specified engineering properties.
In-Ground Barriers: these isolate a contaminated mass of ground from the environment.
This can be above, below or around the material. Materials include clays, clay-bentonite
slurry walls, membranes and sheet piles.
The design of in ground barriers depends on the site conditions and the phase of the
contamination.
gas
water
aquiclude
a) standard cut-off
water
aquiclude
b) membrane barrier
gas
water
aquiclude
c) gas / leachate barriers
organics
water
d) light organics barrier
Bioremediation
Bioremediation: this uses biological processes (mainly micro-organisms) to degrade
organic pollutants. This of course needs the right ‘bugs’ in the right conditions.
Phytoremediation involves growing plants on the site to either promote rhizosphere
degradation processes or promote uptake of compounds such as heavy metals.
This can be done ex-situ, where the material is dug and then either placed in a bioreactor
or in windrows to promote aeration. It is estimated that about 100-200 sites have been
remediated in this way in the UK. In-situ bioremediation has been applied to about 30
sites in the UK. It involves stimulating degradation by seeding with microbes and/or
modifying physical conditions in the ground. This can be as in bio-venting where air is
introduced to promote biological activity or by adding nutrients and/or substrates to
stimulate biological activity.
See Handout.
Physical Processes
Vapour extraction/air sparging can be used to remove volatile compounds from the vapour
space in soils. Various techniques have been applied to achieve this at about 400 sites in
the UK. Air flow is stimulated by withdrawing or introducing air into the soil causing
volatile compounds to pass into the vapour phase
Dual Phase extraction: this involves removing air and water from the site to extract volatile
and water soluble compounds.
Soil washing involves extracting the soil and washing it with water or other chemicals. It
has been applied to organic and heavy metal contamination.
Cement fixation, this involves fixing pollutants (particularly heavy metals) with cement or
other compounds which bind up the material. 10 projects in the UK have used this
technology, either by injecting material into the ground or by extracting the soil and mixing
with cement on the surface. This effectively ‘locks’ up the contaminants and prevents a
pathway to a receptor being established.
See Handout
Case Studies
Lumsden Road, Portsmouth 120 families rehoused after houses, built in the 1950s and
1960s, were found to be on an old RN waste site contaminated with asbestos and heavy
metals. The rehousing, medical screening, demolition, remediation and rebuilding cost
£6.12m.
Clarke Avenue, Loscoe, Derbyshire bungalow demolished and occupants injured by
exploding landfill gas £350k
Ilford Essex, late 1980s, low level radiation found on former chemical works being
redeveloped for housing. Remediation and delays cost £10m.
http://www.contaminatedland.co.uk/case-stu/erg-finy.htm
References
Cairney, T and Hobson, D.M. 1998. Contaminated Land, problems and solutions. E and
FN Spon
Evans, D., Jefferies, S.A, Thomas and Cui, S. 2001. Remedial processess for
Contaminated Land. CIRIA Report C549, CIRIA London.
Rudland, D.J., Lancefield, R.M. and Mayell, P.N. 2001. Contaminated Land Risk
Assessment. CIRIA Report C552, CIRIA, London.
Hester, R.E. and Harrisson, R.M. 1997. Contaminated Land and its Reclamation. Royal
Society of Chemistry, London.
Web sites
DETR
EA
+ various