DETERMINATION OF VACUUM SPHERE OF INFLUENCE SURROUNDING BIOGAS EXTRACTION WELLS BY A LOW EXPENSIVE IN SITU METHODOLOGY USING A TRACER GAS Tommaso Pandolfi Raffaele Isolani Società Certificata ISO 9001:2008 Sardinia 2011 Thirteenth International Waste Management and Landfill Symposium October 2011 S. Margherita di Pula (Cagliari), Sardinia, Italy Session G15 – Workshop

INTRODUCTION DETERMINATION OF THE ZONES OF VACUUM Planning upgrade in biogas collection system Planning upgrade in landfill coverage Checking the efficiency of both Biogas extraction system design MATHEMATICAL MODELS DIRECT MEASUREMENTS VS Experimental method to determine the vacuum sphere of influence and pressure profile around an extraction well and to describe biogas behaviour in the migration process realized by vertical wells and sub-horizontal drainage using a tracer gas

MATERIAL AND METHODS GEOTECHNICAL PROBES Permit injection of tracer gas Allow reading of pressure levels Removable and replaceble in landfill body Bear pounding procedures SUB-HORIZONTAL DRAINAGE PROBE VERTICAL EXTRACTION WELL PROBE

MATERIAL AND METHODS TRACER GAS Not dangerous, flammable or explosive Not toxic for humans or environment Keep inert and non reacting in landfill body Not present in landfill biogas Appropriate molecular weight TETRAFLUOROETHANE R134A OZONE DEPLETION POTENTIAL ODP = 0.28 WITH ODP CO 2 = 1.0 Car air-conditioning 1.0 kg non-refillable gas cylinders Not toxic Not flammable

MATERIAL AND METHODS PORTABLE GAS ANALYZER Semiconductor technology Electrochemical reaction cell Non Dispersive InfraRed (NDIR) Not affected by cross-sensitivity Sensor range is 0 ÷ 775 ppm with 30 ppm precision Can work up to – 15 mbar depression Data logging available on internal memory

FIELD SURVAY FIRST PHASE Vacuum sphere of influence and pressure profile surrounding an extraction well while changing the strength of the exerted vacuum SUB-HORIZONTAL DRAINAGE (HORIZONTAL LAYER) VERTICAL WELL (HORIZONTAL LAYER) VERTICAL WELL (VERTICAL PROFILE)

FIELD SURVAY FIRST PHASE Landfill body Landfill scarp Sub-horizontal drainage Control valve Sampling point Geotechnical probes 1. CLOSE VALVE EXCLUDE EXTRACTION 2. TIME LAPSE 3. START MEASURING POSITIVE PRESSURES +2.1 mbar +3.4 mbar +1.8 mbar 4. OPEN VALVE EXACT DEPRESSION LEVEL (-1.5 mbar; -2.5 mbar) +0.8 mbar +1.9 mbar +1.1 mbar D -1.3 mbar -1.5 mbar -0.7 mbar CH 4 = 38.5 % CO 2 = 25.3 % O 2 = 2.1 % SUB-HORIZONTAL DRAINAGE HORIZONTAL LAYER

FIELD SURVAY FIRST PHASE Landfill body Landfill scarp Vertical extraction well Control valve Sampling point Geotechnical probes 1. CLOSE VALVE EXCLUDE EXTRACTION 2. TIME LAPSE 3. START MEASURING POSITIVE PRESSURES 4. OPEN VALVE EXACT DEPRESSION LEVEL (-1.5 mbar; -2.5 mbar) VERTICAL EXTRACTION WELL HORIZONTAL LAYER

FIELD SURVAY FIRST PHASE Landfill body Landfill scarp Vertical extraction well Control valve Sampling point Geotechnical probes 1. CLOSE VALVE EXCLUDE EXTRACTION 2. TIME LAPSE 3. START MEASURING POSITIVE PRESSURES 4. OPEN VALVE EXACT DEPRESSION LEVEL (-1.5 mbar; -2.5 mbar) VERTICAL EXTRACTION WELL VERTICAL PROFILE

RESULTS AND DISCUSSION FIRST PHASE SUB-HORIZONTAL DRAINAGE HORIZONTAL LAYER

RESULTS AND DISCUSSION FIRST PHASE VERTICAL EXTRACTION WELL HORIZONTAL LAYER

RESULTS AND DISCUSSION FIRST PHASE VERTICAL EXTRACTION WELL VERTICAL PROFILE

FIELD SURVAY SECOND PHASE 1. CLOSE VALVE EXCLUDE EXTRACTION 2. TIME LAPSE 3. START INJECTION OF TRACER GAS 4. OPEN VALVE TO A GIVEN VALUE AND START DATA LOGGING SUB-HORIZONTAL DRAINAGE Describe biogas behaviour in the migration process realized by different type of extraction system

FIELD SURVAY SECOND PHASE 1. CLOSE VALVE EXCLUDE EXTRACTION 2. TIME LAPSE 3. START INJECTION OF TRACER GAS 4. OPEN VALVE TO A GIVEN VALUE AND START DATA LOGGING VERTICAL EXTRACTION WELL

RESULTS AND DISCUSSION SECOND PHASE SUB-HORIZONTAL DRAINAGE

RESULTS AND DISCUSSION SECOND PHASE VERTICAL EXTRACTION WELL

CONCLUSIONS Waste in landfill are disposed in piled up compacted sub-horizontal layers Preferential migration paths that enable vertical extraction well to reach higher extraction efficiency 50 meters radial distance vacuum sphere of influence with cylindrical volume shape concentric to the well axis 100 m Exerting a higher depression level we obtain greater pressure differentials taken from a contraction of the vacuum sphere of influence. Migration process produced by vertical extraction well is extremely effective, collecting large quantities of biogas at wide distances.

CONCLUSIONS 15 meters radial distance vacuum sphere of influence Length of the drainage seems not to influence extraction capability Produces horizontal vacuum layer without pushing its effect deeper in the landfill body 30 m As shown for vertical well, exerting a higher depression level on the drainage we obtain greater pressure differentials taken from a contraction of the vacuum sphere of influence. Migration process produced by sub-horizontal drainage is similar to a slow biogas dragging. Represents a good barrier against biogas dispersion in atmosphere

DETERMINATION OF VACUUM SPHERE OF INFLUENCE SURROUNDING BIOGAS EXTRACTION WELLS BY A LOW EXPENSIVE IN SITU METHODOLOGY USING A TRACER GAS Tommaso Pandolfi Raffaele Isolani Società Certificata ISO 9001:2008 Sardinia 2011 Thirteenth International Waste Management and Landfill Symposium October 2011 S. Margherita di Pula (Cagliari), Sardinia, Italy Session G15 – Workshop