1. Greenwich Peninsula

2. The Site 300 Acres East London
Now the location of the Dome and the millennium village

3. Site History Heavy industrial use Ordnance factory Power station
Bronze foundry
Lime works
Largest gasworks in Europe
Built in 1884
Production ended in 1977
Tar distillation
Benzol plant
Chemical works
Power station
Steel processes plant
Domestic waste landfill

4. Contaminants Present Coal tars Polyaromatic hydrocarbons Phenols
Benzene and other VOC’s
Cyanides and heavy metals
Sulphur compounds
Ammonia
Structural debris
130 underground tanks upto 36m diameter, 8m depth

5. Spread of Contaminants
Increasing levels of industrial pollution further north
Abandoned industrial structures
‘Hotspots’ across the site
Tar well
36m diameter, 8m deep
full and capped
BTEX, cyanide and PAH also present
Several remediation methods used

6. Remediation Began in 1996 Scale of the work 4 Years, total cost £202 m
Site was designated as the area for the national millennial exhibition
British Gas required to undertake statutory remediation
clear target contaminants that would pollute 3rd party land and aquifers
English Partnerships followed with development remediation
Scale of the work
“probably the largest single remediation of a single site undertaken in this country”(ICE newsletter for the north western local assoc, 1998)
4 Years, total cost £202 m

7. Remedial Techniques Off-site disposal Containment
Dry processing
Containment
laterally and vertically
Soil & Gravel washing
Soil vapour extraction
Groundwater treatment

8. Off-site Disposal & Dry Processing
m3 removed to landfill
To minimise disposal m3 dry-screened
Courser fractions tend not to contain contaminant
Only contaminated fines were landfilled

9. Soil & Gravel Washing Theory Ex-situ process Principal processes:
mechanical separation/aqueous leaching, to remove contaminants from sediment
Principal processes:
removal of surface bound and absorbed contaminants into a treatable aqueous medium
separation of contaminated particles from the soil matrix for treatment/disposal
exploits tendency for contaminants to absorb on to silts and clays

10. Soil & Gravel Washing 22 000 m3 contaminated soil processed
65% reused
Cutoff size 2mm diameter
Material < 2mm put through washing process
Material > 2mm relatively clean so was reused without further treatment
Material processed
Material excavated
Products from on-site crushing of old foundations

11. Soil Vapour Extraction
Theory
in-situ technique
induce airflow through soil to enhance the volatilisation and aerobic biodegradation of contaminants
The problem
VOCs were concentrated mainly in made ground of 1-4m depth
spread laterally on contact with underlying clays
The solution
300 wells sunk and pumps set to work
Measurements showed a 90% reduction in contamination

12. Containment The Problem
Impossible to remove all contamination from the site
Necessary to ensure that remaining contaminant could not effect…
River Thames
Underlying aquifer
People using the site
Therefore barriers constructed to stop lateral and vertical migration

13. Containment Tar well River Thames
Shallow bentonite slurry cut-off wall, 100m diameter, keyed into clay, constructed around well.
Contents removed & hydrocarbon plume extracted
This groundwater was treated before discharge into public sewers
50 000m3 contaminated water treated across the site
River Thames
Bentonite slurry wall constructed 15m back from the river

14. Containment Upward Migration
orange plastic layer installed as a visual aid to limit of contaminated zone
200mm capillary breaking layer of crushed rock
layer of low permeability London clay
1.5m clean soil

15. The Result Remedial work has now finished
English Partnerships and Bovis Lendlease are continuing to regenerate the site
A third commercial centre for London?
A key drive for the transformation of the Thames Gateway