Peter M. Czepiel's research while affiliated with University of New Hampshire and other places

Landfills are the largest source of anthropogenic methane (CH4) emissions to the atmosphere in the United States. However, few measurements of whole landfill CH4 emissions have been reported. Here, we present the results of a multi-season study of whole landfill CH4 emissions using atmospheric tracer methods at the Nashua, New Hampshire Municipal landfill in the northeastern United States. The measurement data include 12 individual emission tests, each test consisting of 5-8 plume measurements. Measured emissions were negatively correlated with surface atmospheric pressure and ranged from 7.3 to 26.5 m3 CH4 min(-1). A simple regression model of our results was used to calculate an annual emission rate of 8.4 x 10(6) m3 CH4 year(-1). These data, along with CH4 oxidation estimates based on emitted landfill gas isotopic characteristics and gas collection data, were used to estimate annual CH4 generation at this landfill. A reported gas collection rate of 7.1 x 10(6) m3 CH4 year(-1) and an estimated annual rate of CH4 oxidation by cover soils of 1.2 x 10(6) m3 CH4 year(-1) resulted in a calculated annual CH4 generation rate of 16.7 x 10(6) m3 CH4 year(-1). These results underscore the necessity of understanding a landfill's dynamic environment before assessing long-term emissions potential.

Methane emissions were measured at nine U.S. landfill sites using chamber and/or tracer flux techniques. These flux measurement methodologies were compared at two sites, and excellent agreement (<10% difference) was observed. Total methane emissions ranged from 540 to 30 100 L min-1. Expressed on an area basis, methane fluxes ranged from a low of 9.1 g of CH4 m-2 d-1 at a closed 20-ha site with active gas recovery to 130 g of CH4 m-2 d-1 at a 23-ha active site with no gas recovery. Methane emission factors [in units of m3 of CH4 min-1 (106 m3 waste-in-place)-1] were calculated for seven of the nine sites. The two sites with no active gas recovery exhibited the highest emission factors of 4.8 and 5.1. Values were significantly lower at three sites with partial gas recovery, ranging from 1.6 to 3.7. At the two closed sites with active gas recovery, emission factors were much lower still (0.4 and 1.1). It is evident that even partial gas recovery at active landfill sites can significantly reduce methane emissions, and gas recovery at closed, covered sites reduces methane emissions to the atmosphere by as much as a factor of 10.

The Harvard Forest research site located in central New England is influenced by numerous anthropogenic methane sources on a year-round basis. Methane is strongly correlated to other chemical species that have an anthropogenic component, including acetylene, propane, ethane, hexane, and additional short-lived nonmethane hydrocarbons. The correlation between methane and acetylene is due to the colocation of landfills and cities. The correlation between methane and other short-lived species implies that emissions from local and regional rather than distant sources are the primary cause of elevated events. Wind roses of chemical species are examined for annual and seasonal time periods with enhancements in anthropogenic species corresponding to the location of large cities and landfills. The southwest quadrant is subjected to the most severe pollution events and is impacted by outflow from nearby cities in that sector, including Northampton and Springfield, Massachusetts. Emissions from cities in other quadrants, including Boston and Worcester, Massachusetts, Providence, Rhode Island, and the close-by town of Petersham, Massachusetts, also affect the site, but to a lesser degree. Case studies are used to identify atmospheric conditions that lead to high concentrations of methane and other species. The co-occurrence of a persistent wind direction, light wind speed, and stable atmospheric conditions is the ideal scenario in which emissions from nearby cities and landfills are advected to the site. Emissions from local and regional, rather than distant sources, are the primary cause of elevated events.

Field, laboratory, and computer modeling methods were utilized to quantitatively assess the capability of aerobic microorganisms to oxidize landfill-derived methane (CH4) in cover soils. The investigated municipal landfill, located in Nashua, New Hampshire, was operating without gas controls of any type at the time of sample collection. Soil samples from locations of CH 4 flux to the atmosphere were returned to the laboratory and subjected to incubation experiments to quantify the response of oxidation in these soils to temperature, soil moisture, in situ CH 4 mixing ratio, soil depth, and oxygen. The mathematical representations of the observed oxidation reponses were combined with measured and predicted soil characteristics in a computer model to predict the rate of CH 4 oxidation in the soils at the locations of the measured fluxes described by Czepiel et al. (this issue). The estimated whole landfill oxidation rate at the time of the flux measurements in October 1994 was 20%. Local air temperature and precipitation data were then used in conjunction with an existing soil climate model to estimate an annual whole landfill oxidation rate in 1994 of 10%.

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4 min-1. Omnidirectional variograms displayed spatial correlation among CH4 fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4 min-1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4 flux. This resulted in a pressure-corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4 min-1.

The influence of organic matter and soil moisture on the spatial distribution of methane (CH4) oxidation was examined in temperate zone soils by laboratory incubations. CH4 oxidation in soil cores exhibited distinct vertical zonation with maxima at 3 to 6 cm. The kinetic parameters of CH4 oxidation were measured in soil composites. The maximum rate of CH4 uptake, Vmax, ranged from 6.8 to 7.4 nmol hr-1 g dry soil-1 and the apparent half saturation constant, Km, ranged from 17.4 to 19.9 (parts per million by volume) ppmv. Oxidation in random samples was observed to be influenced by both soil moisture and organic matter contents. The rate of oxidation in each sample increased to a maximum with increasing water content and decreased with additional water. Maximum oxidation rates ranged from 2.2 to 9.0 nmol hr-1 g dry soil-1 at sample moisture contents of 18 to 51%. Organic matter content appears to explain the spatial variability of methane oxidation at optimal soil moisture contents. The oxidation maximum at this site was coincident with an organic matter content of 14% by weight and a gravimetric moisture content of 33%.

Methane and carbon dioxide emissions from primary and secondary wastewater treatment processes were measured from mid-winter to summer conditions in Durham, NH. A statistically significant positive relationship between gas flux and wastewater temperature was determined for methane and carbon dioxide in both the aerated and nonaerated areas of the grit tanks. Statistical correlations to temperature measured in a secondary aeration tank were marginal for methane and insignificant for carbon dioxide. Emission factors derived from our measurements were 39 g of CH[sub 4] person[sup [minus]1] year[sup [minus]1] and 35 698 g of CO[sub 2] person[sup [minus]1] year[sup [minus]1] for primary and secondary activated sludge treatment processes. 14 refs., 4 figs., 2 tabs.