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Dilute and disperse landfills: evidence for natural attenuation. Brian Bone Environment Agency Science Group G.M. Williams, J.K. Trick, D.J. Noy, R.D. Ogilvy (all British Geological Survey) and T.H.E. Heaton (NERC Isotope Geology Laboratory). Study of dilute and disperse sites. - PowerPoint PPT Presentation
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Dilute and disperse landfills: Dilute and disperse landfills: evidence for natural attenuationevidence for natural attenuation
Brian Bone
Environment Agency Science Group
G.M. Williams, J.K. Trick, D.J. Noy, R.D. Ogilvy (all British Geological Survey) and
T.H.E. Heaton (NERC Isotope Geology Laboratory)
Study of dilute and disperse sitesStudy of dilute and disperse sites• 1974 IGS/DoE survey of landfill sites
– 56 of 3,000+ sites with potential to seriously pollute surface or ground water
• 1973-1978 DoE “Brown Book” study– The Behaviour of Hazardous Wastes in Landfill Sites
• 1980s continued investigation of some Brown Book sites
• 1990s NRA (now EA) desk study to identify potentially polluting landfills– Thriplow selected for study 1996-2002
Phase Ioperated 1957 - 1977household and some commercial/industrial waste7.2ha, filled to 3 - 9 m bglthin soil cover
Phase IIoperated 1981 - 1987household, commercial & industrial waste4ha, filled to 1.8 - 9 m bglcontoured “clay” cap
Thriplow landfill site
Study objectivesStudy objectives
• Characterise plume/s of contaminated groundwater from the landfill
• Identify controls on leachate migration and attenuation
• Develop a well-constrained model for groundwater flow and mass transport
• Provide facilities for long-term monitoring to determine NA processes and test model predictions
Desk studyDesk study
• Previous investigations
• Groundwater monitoring data from existing boreholes
• Environment Agency/local authority archives (disposal history)
• Aerial photographs
• Meteorological data
Preliminary conceptual modelPreliminary conceptual model
Landfills previously gravel pits, up to 9 m deep
Leaching may vary seasonally
Contamination identified in BHs to west
Regional gw flow to NW
Vertical flow possibly limited by Plenus Marls
UncertaintiesUncertainties
• Borehole construction and quality of previous monitoring data
• Borehole coverage
• Waste characteristics and leachate quality
• Hydraulic continuity between Middle and Lower Chalk
• Direction, depth and extent of leachate plume
Site investigations 1996 - 97Site investigations 1996 - 97
• CCTV and sampling from 7 of the 11 previously drilled boreholes (1976 - 1993)
• Landfill characterisation (5 new BHs in waste)
– waste, leachate, porewater, BMP, gas, infiltration
• Surface resistivity imaging (2D)
• Characterisation of Chalk aquifer (1 new BH)
• Groundwater sampling
• Preliminary modelling
Waste characterisationWaste characterisation
Significant findingsSignificant findings• Some BH depths at variance with those recorded
• Some BH completions in both Middle and Lower Chalk - distortion of groundwater flow & dilution of leachate?
• Waste in Phase I was more degraded than waste in Phase II (function of age and cover thickness)
• Landfill resistivity appears to reflect leachate front rather than waste - Chalk interface, artefacts below ~ 20 m
• Elevated TOC, Cl and NH4-N in groundwater downgradient of landfills
• Perimeter resistivity surveys indicate distinct plumes (but one anomaly drilled did not intercept leachate - poor resolution of formation resistivity below 30 m bgl)
UncertaintiesUncertainties
• Drift thickness - geometry of buried channel along western perimeter
• Aquifer properties
• Seasonal variation in groundwater flow
• Calibration of resistivity surveys
• Leachate release from landfill
• Evidence for natural attenuation
Site investigations 1998 - 2002Site investigations 1998 - 2002
• 3D resistivity survey of landfill phases
• 6 (No.) BHs in waste/Chalk
• 3 (No.) BHs north of landfill
• Downhole resistivity arrays in new BHs
• Sampling– waste, porewater, leachate, groundwater, gas
• Trace organics analyses
• Stable isotope analyses
3D resistivity tomography3D resistivity tomography
Porewater chemistry below wastePorewater chemistry below waste
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T P 1 3 A A m m o n i u m ( m g / l )
Dep
th (
mbg
l)
S o i l
S a t u r a t e d Z o n e ( 1 0 / 1 1 / 9 9 )
A l t e r e d C h a l k
C h a l k
W a s t e
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TP10 Ammonium (mg/l)
Dep
th (
mbg
l)
Soil
Waste
Chalk
Saturated Zone (10/11/99)
Soil Fill
Waste
Phase I Phase II
Time-lapse Monitoring of landfill boreholes to Time-lapse Monitoring of landfill boreholes to detect transient leachate plumesdetect transient leachate plumes
Electrode sensors have been permanently installed in landfill boreholes.Monthly monitoring helps to detecttransient plumes and seasonal variations in leachate distribution within landfill
Electrodes on outsideof PVC casing ensures electrical contact withsurrounding materialirrespective of watertable
2D inversion results for prism model2D inversion results for prism model
X(m)X(m)
Z(m
)
BOR EHOLE BOREHOLE
50 Ohm-m
50 Ohm-m
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Resist ivity(ohm-m)
N separat ion
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BOREHOLE
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ApparentResistivity(ohm-m)
GROUND SURFACE AT Z=0m
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(a) (b) (c)
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Fig. 8
ERT inversion images for Borehole TP09ERT inversion images for Borehole TP09
1 2
Se arch radius (m)
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TP09
Bor
ehol
ede
pth
(m)
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ehol
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pth
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ehol
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pth
(m)
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Bor
ehole
dept
h(m
)
Log Res istivity(ohm.m)
1 2
Se arch radi us (m)
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TP09
Bor
ehol
ede
pth
(m)
1 2
Search Radius (m)
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TP09
Bore
hol
ede
pth
(m)
Dec. 1999
1 2
Search radius (m)
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hole
dept
h(m
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dept
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Bore
hole
dept
h(m
)
W.T
Chalk
W.T
W.TW.T W.T
W.T
W.T
W.T
W.T= 11.91m
Chalk
Chalk
Chalk Chalk
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Chalk ChalkChalk
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Chalk
W.TMissing Data
W.T
Jan. 2000 Feb. 2000 Mar. 2 000 Apr. 2000 May 2000
Jul. 2000Jun. 2000 Aug. 2000 Sept. 2000 Oct. 2000 Nov. 2000
W.T
Cl = 41.9 mg/l
Cl = 35.8 mg/l Cl = 36.9 mg/l
Plume?
Plume ?
Plume?
Plume?
Plume?
Chalk
TP09
Fig. 10
Plume?
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So, with a better (although not perfect) idea of the waste
characteristics, groundwater flow, leachate distribution and flow, is
there any evidence for natural attenuation?
Conventional chemistryConventional chemistry
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Distance ( m)
TO
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l
TP12
BH3
TR4 TR12
TR13TR14
TOCCl
1 year1 year
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Distance ( m)
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TP12
BH3
TR4 TR12
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TOCCl
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Distance ( m)
TO
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l
TP12
BH3
TR4 TR12
TR13TR14
TOCCl
0.00
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Distance ( m)
TO
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l
TP12
BH3
TR4 TR12
TR13TR14
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0 50 100 150 200 250 300 350 400
Distance ( m)
TO
C:C
l
TP12
BH3
TR4 TR12
TR13TR14
TOCCl
1 year1 year1 year1 year
Stable isotope findings ( S & N)Stable isotope findings ( S & N)
100 metres
Methanogenesis
Sulphate reduction
Nitrificaton
Denitrification
Enantiomeric forms of MecopropEnantiomeric forms of Mecoprop
H3CO
Cl
HOOC
CH3H
H3CO
Cl
COOH
H C3 H
2-(4-chloro-2-methyl phenoxy) - propionic acid2-(4-chloro-2-methyl phenoxy) - propionic acid
(R) - Rectus(R) - Rectus (S) - Sinister(S) - Sinister
Biodegradation of mecopropBiodegradation of mecoprop
Redox R-mecoprop S-mecoprop
Methanogenicsulphate red.
NO NO
Nitrate red. YES NO
Aerobic YES YES (faster)
Redox zonesRedox zones
MMeetthhaannooggeenniicc zzoonnee
NNiittrraattee rreedduucciinngg zzoonnee
225500 mm
SSuullpphhaattee rreedduucciinngg zzoonnee
Conceptual model (latest)Conceptual model (latest)
Uncertainties/challengesUncertainties/challenges
• Access
• Spatial data
• Source term evolution with time
– a decade of missing data!
• Significance and frequency of pulsed release of leachate
• Any more plumes?
SuccessesSuccesses
We found a plume!
Development and refinement of tools
Greater awareness of leachate release
Established lines of evidence to support NA