Identifying the Presence of AMD-Derived Soil CO₂ in Field Investigations Using Isotope Ratios

Recent incidents of hazardous accumulations of CO2 in homes on or adjacent to reclaimed mine land have been shown to be linked to neutralization reactions between acidic mine drainage and carbonate material. An efficient and economic method is necessary to identify the presence of acid mine drainage- (AMD-) derived CO2 on reclaimed mine land, prior to construction. One approach to identify the presence of AMD-derived CO2 is to characterize stable carbon isotope ratios of soil CO2. To do so, a viable method is necessary to acquire soil gas samples for isotope ratio analysis. This paper presents preliminary investigations of the effectiveness of two methods of acquiring gas samples (sampling during soil flux measurements and using slam bar) for isotope analysis. The results indicate that direct soil gas sampling is cheaper and provides better results. Neither method is adequate without accounting for temporal effects due to changing gas transport mechanisms. These results have significant implications for safe post-mining land uses and future investigations of leakages from geologic carbon sequestration sites

Spatial variation of AMD related CO₂ emissions on reclaimed mine spoil

Carbon dioxide (CO₂) from acid mine drainage (AMD)-carbonate neutralization reactions in reclaimed mine spoils, can intermittently invade homes and structures constructed on or adjacent to these spoils in hazardous and even lethal concentrations (\u3e15%) and rendering them uninhabitable. This phenomenon is beginning to be recognized as an emerging environmental, safety and health threat with potential environmental and financial liability for mine operators, developers and owners. Like in natural soils, soil temperature and moisture, and possibly elevation are likely to influence CO₂ emissions from reclaimed mine spoils. However, mine spoil soils are heterogeneous and have significant convective transport due to exothermic AMD reactions. Therefore, assumptions made for natural soils may not hold. The aim of this study was to foster further understanding of the processes controlling the efflux of CO₂ from reclaimed mine spoils and evaluate the effectiveness of accumulation chamber (AC) flux measurement in identifying and delineating this hazard. AC measurements, isotope ratio mass spectroscopy, and statistical techniques were applied to three reclaimed mine sites in the United States of America. Among the study findings are that: (i) there is correlation between CO₂ flux and elevation, soil temperature and moisture; (ii) CO₂ fluxes are not always random but spatially autocorrelated; (iii) AMD-derived CO₂ emissions are normally too low to successfully be used to delineate hazards. This pioneering effort also makes recommendations for future work that could make AC flux measurement more effective for this emerging hazard --Abstract, page iii

Spatial Autocorrelation of Soil CO₂ Fluxes on Reclaimed Mine Land

Recent evidence has shown that CO2 emissions from reclaimed mine soil with acid mine drainage and carbonate material is an emerging geohazard. Surface CO2 flux measurements can be a cheap and effective way to delineate such hazards and avoid residential and commercial real-estate development on high-risk zones. Very little work has been done to ascertain whether or not such fluxes are spatially correlated, which has significant implications on the choice of statistical methods for analysis. The objective of this study was to understand the extent to which CO2 fluxes on a reclaimed mine spoil, with CO2 from carbonate neutralization of acidic drainage, are spatially autocorrelated. CO2 fluxes from three reclaimed surface coal mine sites were measured and used in statistical analysis to test the research hypothesis. The results show that the spatial variability of fluxes is not always random but can show significant (p \u3c 0.0001) spatial autocorrelation. This result implies that classical statistical analysis of CO2 fluxes from reclaimed mine land may lead to wrong inferences, since such analysis ignores the spatial correlation. It appears spatial autocorrelation in CO2 fluxes may be related to spatial autocorrelation in soil temperatures, suggesting a common underlying phenomenon. Significant contribution of CO2 from exothermic acid mine drainage to soil CO2 flux is suggested as a possible explanation

Delineating Hazardous CO₂ Fluxes from Acid Mine Drainage

Incidents of hazardous accumulations of CO2 in homes built on or near reclaimed mine land, in the last decade, have been shown to be linked to neutralization reactions between acidic mine drainage and carbonate material. Recent research has shown that CO2 fluxes on reclaimed mine land with this hazard are, sometimes, spatially autocorrelated (i.e., the spatial variability is not random). This result implies geostatistics can be used to delineate hazardous areas where fluxes are likely to exceed established thresholds. This study applies sequential Gaussian simulation to delineate this emerging hazard on a site in southwestern Indiana, USA. Due to lack of regulatory threshold limits for CO2 flux at the current time, the authors conduct a sensitivity analysis of the threshold limit using the 75th, 90th and 95th percentiles of the measured fluxes for the first day of monitoring. These limits are used to produce hazard maps, which are validated with the known hazard at the site. This work further shows the potential of surface CO2 flux monitoring as a cheap and effective strategy to monitor and delineate such hazards to avoid residential and commercial real estate development in high risk zones

Identifying the Presence of AMD-Derived Soil CO2 in Field Investigations Using Isotope Ratios

Recent incidents of hazardous accumulations of CO2 in homes on or adjacent to reclaimed mine land have been shown to be linked to neutralization reactions between acidic mine drainage and carbonate material. An efficient and economic method is necessary to identify the presence of acid mine drainage- (AMD-) derived CO2 on reclaimed mine land, prior to construction. One approach to identify the presence of AMD-derived CO2 is to characterize stable carbon isotope ratios of soil CO2. To do so, a viable method is necessary to acquire soil gas samples for isotope ratio analysis. This paper presents preliminary investigations of the effectiveness of two methods of acquiring gas samples (sampling during soil flux measurements and using slam bar) for isotope analysis. The results indicate that direct soil gas sampling is cheaper and provides better results. Neither method is adequate without accounting for temporal effects due to changing gas transport mechanisms. These results have significant implications for safe post-mining land uses and future investigations of leakages from geologic carbon sequestration sites

Influence of Elevation, Soil Temperature and Soil Moisture Content on Reclaimed Mine Land Soil CO₂ Fluxes

Recently, incidents of hazardous accumulations of CO2 in homes built on or near reclaimed mine land have been shown to be linked to neutralization reactions between acidic mine drainage and carbonate material. Surface CO2 flux measurements have been proposed as a potentially cheap and effective strategy to monitor and delineate such hazards to avoid residential and commercial real-estate development on high risk zones. For this strategy to work, more work is needed to understand the strength of association between CO2 fluxes on reclaimed mine land and relevant covariates (e.g. sample elevation, soil temperature and soil moisture) to ensure comprehensive monitoring. The objective of this study was to understand the extent to which CO2 fluxes on reclaimed spoil are affected by sample elevation, soil temperature and soil moisture. Specifically, the work tested the hypothesis that CO2 fluxes are correlated to elevation, soil temperature and soil moisture. Carbon dioxide fluxes from three study sites were measured and used in statistical analysis to test the research hypothesis. The results show statistically significant (p \u3c 0.05) positive but monotonic correlation between CO2 fluxes and soil temperature, while fluxes and elevation are negatively correlated, monotonically in a similar manner. Where significant, correlation between fluxes and soil moisture was observed to be negative. This result implies that flux surveys on reclaimed mine land need to measure elevation, soil temperature and soil moisture at survey points