Dilute and disperse Dilute and disperse landfills: evidence for landfills: evidence for natural attenuation 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)
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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.
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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
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
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
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Fig. 8
ERT inversion images for Borehole TP09ERT inversion images for Borehole TP09