Date of Award

6-2019

Degree Name

MS in Civil and Environmental Engineering

Department/Program

Civil and Environmental Engineering

Advisor

James Hanson

Abstract

Comprehensive and systematic aerial and field investigations were conducted at representative California landfills to quantify emissions of methane and nitrous oxide. Landfills are highly engineered; however, they are one of the largest anthropogenic sources of greenhouse gases, causing human health and safety concerns. Methane (CH4) and nitrous oxide (N2O) are significant greenhouse gases with high global warming potentials that are generated in a landfill environment.

For site selection, sites were evaluated based on waste in place, climate zone, faults and oil and gas operations, population density, cover conditions and percentage of cover types, age of waste, waste profile, landfill style and configuration, and disposal of waste tires. Fifteen representative sites were chosen for the aerial portion of testing, and of those fifteen, five sites were selected for extensive ground testing using the static flux chamber method, conducted over a year-long time period. At the five sites for ground testing, between five and seven cover systems were tested at each site during the wet and dry season. Daily, intermediate, and final covers were tested to obtain representative and comparative measurements during the wet and dry season to account for seasonal variation. In addition to the flux chamber testing, geotechnical characterization of cover materials was conducted.

CH4 flux values exhibited higher variability in the dry season (102 g/m2/d to -101 g/m2/d) than the wet season (102 g/m2/d to 10-1 g/m2/d). N2O flux values exhibited slightly higher variability in the wet season (10-1 g/m2/d to -10-3 g/m2/d) than the dry season (10-1 g/m2/d to -10-3 g/m2/d). The measured flux value for CH4 was generally greater than the measured flux value for N2O across both seasons. N2O flux values (10-1 g/m2/d to -10-3 g/m2/d) exhibited less variability than CH4 flux values (102 g/m2/d to -10-1 g/m2/d). Relationships were developed between aerial emissions and areal coverage, throughput, waste column height, and waste in place. All correlations were positive. Relationships were also developed between flux values and geotechnical properties of covers, including density and cover thickness. Most geotechnical parameters yielded limited correlation.

The surface flux values from the field investigation were scaled up to estimate facility-wide surface emission values. The methane surface emissions ranged from 10-1 to 103 and from 100 to 102 tonnes/year in the wet season and dry season. The nitrous oxide surface emissions ranged -10-2 to 100 and from 10-2 to 10-1 tonnes/year in the wet season and dry season, respectively. Emissions were converted to CO2 equivalent (CO2 E) to allow for comparison between methane and nitrous oxide. The methane surface emissions in CO2 E terms ranged from 101 to 104 tonnes/year in both the wet season and dry season, respectively. The nitrous oxide surface emissions in CO2 E terms ranged from -100 to 102 and from 101 to 102 tonnes/year in the wet season and dry season, respectively. Aerial and ground emissions were compared, with aerial results being higher at all five ground sites. This study provides systematic and comprehensive field emissions testing comparing climate and waste in place, among other parameters, that demonstrate the complicated nature of the landfill environment.

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