LANDFILL ODOURS: ASSESSMENT AND MITIGATION MEASURES 7th European Biosolids Conference Dr Peter McKendry 18 November 2002

Contents Background Monitoring Modelling & Sensitivity Analysis Results Prioritisation of Management Activities

Background

Introduction – Study Funding Funded by Landfill Tax Credit Scheme Viridis SITA Trust SITA Millennium Science & Engineering Ltd

Introduction – Study Objectives Assist site designers and managers to identify and assess management techniques for odour control Guidance on odour management and control by identifying key parameters associated with odour production and its management Prioritisation of odour control techniques and practices in terms of effectiveness

Introduction – Study Format Study comprised four elements: public questionnaire on odour field measurement of methane emissions (as proxy for odorous emissions) from landfill sources air dispersion modelling using field data prioritising management options based on modelling results

Monitoring

Methodology - Questionnaire Odour complaints should be seen in a positive light EA inspections provide snap-shot Local residents most likely to complain as potential exposure period up to 100% of the year Use of historical data inhibited by accuracy, lack of completeness or total absence of data

Methodology - Questionnaire Letter mailshot to residents General response good (40%) Lowest return rate for site with least current and historical complaints Highest return rate for site with active site-liaison committee

Methodology - Questionnaire Overview of findings: Short term event (few hours duration) Frequency once per week or greater Usually a longstanding issue, commencing at site opening Worst time of day mornings and/or evenings Odours usually detected under still/foggy conditions Odour strength typically ‘moderate/strong’ Generally rotten food/putrid/pungent Most people do not complain about odours

Methodology – Monitoring Programme FID used to monitor CH4 Site-boundary survey Identification of off-site odours Site survey Identification of on-site odour sources Flux-box (tent/bin/bag) Monitoring on-site source emission rates Meteorological assessment

Methodology – Flux-box monitoring device Trench dug around perimeter of the flux-box Flux box located with edge placed in trench, back filled and compressed Monitoring point connected to FID Monitoring concentration within flux-box until no change in concentration detected

Methodology – Site Descriptions 6 Sites included within study Classified into 3 generic landfill types Hill on a plain (P1-P3) Hill on a hill (H1) Hill in a valley (V1-V2)

Methodology – Site Design Characteristics P1 P2 P3 H1 V1 V2 Domestic  Non-hazardous Commercial / Industrial Special / Hazardous Liquids / Sludges Other Annual Input (m3) 350,000 430,000 200,000 130,000 140,000 80,000 Total Site Area (ha) 50 140 26 27 21 9

Methodology – Monitored and Reported CH4 Surface Emission Rates Odour Source Methane Flux Rates (mg m-2 s-1 – areas, or mg s-1 – point sources) Current Study Range (Average) Range of Reported Values (Bond et al, 2000) Active working area n/a 4.2x10-2 Daily cover 3.1x10-1 Flank –temporary cover (Sandy) 1.2x10-2 – 2.4x10-1 Flank –temporary cover (Clayey Soil) 1.0x102* 5.0x10-3 Temporary Cap (Sandy) 6.0x10-2 Temporary Cap (Soil) 6.2x100 5.0x10-2 1.0x100 Restored (Capped) 0.0 4.0x10-3 5.0x10-5 4.1x10-2 Freely venting gas well 2.2x103 4.0x103 Man-hole cover over 1.2m diameter leachate chamber* 4.6x10-2 * Single observation: not to be regarded as typical

Methodology – Monitoring Comments 1 Monitored emission rates comparable to other literature reported values Difference of emission rates between sandy and clayey soils attributable to differences in homogeneity Sandy soils may be more coarse but are more homogeneous than insufficiently compacted clay soils

Methodology – Monitoring Comments 2 Odour with particular characteristics noted consistently at distinct thresholds at different sites Leachate source 25ppm* LFG Source 50-75ppm* Note: ppm CH4 measured using FID

Modelling and Sensitivity Analysis

Modelling & Sensitivity Analysis Data input: Odorant emission rate: 5x10-5 gs-1 Point Source: Ø35.68m (1000m2) Input values constant for all runs, excluding sensitivity analysis

Sensitivity Analysis Parameter Analysis Result Terrain Inclusion vs Exclusion Clear demonstration of the requirement for including DTM Grid Resolution (32x32 vs 64x64) Greater resolution grid results in improved definition of output Fluctuations Fluctuation Period (1s, 1min, 2min, 5min, 15 min) Shorter fluctuation periods result in an increased area potentially impacted. Marginal difference for fluctuation periods of <5min Surface Roughness Surface Roughness (0.2m, 0.3m, 0.5m, 1.0m) Output decreases in aerial extent as roughness increases

Sensitivity Analysis Parameter Analysis Result Wind Speed Wind speed variation from 0.8ms-1 – 10ms-1 Complex output: P3, Output decreases in area as wind speed increases H1, ADMS 3.1 does not model accurately at wind speeds <1.5ms-1 given H1 parameters At V2, output increases in extent as wind speed increases to ~2.5ms-1, then decreases as wind speed increases further Emission Rates 5x10-5 gs-1 Output covers a greater area emission rate increases Odour Detection Threshold Variation in ODT 3x10-5, 3x10-6 & 3x10-7 Lower ODT results in a greater aerial extent covered by output

Results

Surface Roughness Output decreases in size as roughness increases. More turbulence and mixing results in dilution Animation

Fluctuations .... 1sec _ _ 5min __ 15min

Wind Speed Wind speed increase results in increased dispersion & dilution Output aerial extent decreases Animation

Wind Direction Identical output Rotation about central point Animation

Complex Terrain Interactions 1 H1 V2 6 5 4 3 2 1 1 2 3 4 5 6

Complex Terrain Interactions 2 Terrain is vital factor in determining dispersion of odours The output not always as expected Animation 1 (2D) H1 Animation 2 (3D) H1 Animation 3 (3D) V2 Wind Speed Animation 4 (3D)V2 Wind Direction

Odour Rose 1 Probability analysis of meteorological conditions and terrain interactions

Odour Rose 2: % probability of odour event Controlling Factor Site P3 H1 V2 Wind Direction 8.5 7.5 5.3 58.3 37.7 26.7 55.9 50.6 35.8 Wind Speed Receptor Availability

Prioritisation of Management Activities

Prioritisation of Management Activities Initial Site Risk Assessment Location of Potential Receptors Terrain Minimisation of: Number of Sources Types of Sources Emission Area

Practical Examples Delivery vehicle routing Prohibition of specific wastes Waste Cover type / depth Size of operational cells Excavation of deposited wastes Minimisation of cell flank areas Minimisation of uncapped areas Pollution control infrastructure LFG system Leachate collection disposal