Regulating the ultimate sink: managing the risks of geologic CO2 storage

Prediction of long-term heavy metal leaching from dredged marine sediment applied inland as a construction material

Column leaching studies have been suggested as a reference for site-specific prediction of the long-term leaching characteristics of trace constituents in granular materials used as construction materials. In this study, the concept of the long-term leaching prediction using column studies is applied for dredged marine sediment impacted by heavy metals. The column studies show tailing of the liquid to solid ratio-dependent heavy metal leaching for sediment after heavy metal treatment by acid washing. A dual-mode first-order decay model, applied for the first time in this study for column leaching studies, is able to reproduce the leaching characteristics observed. A procedure for long-term leaching prediction using the dual-mode model is developed and applied to a virtual field scenario for which the sediment is beneficially used as a construction material. The prediction results show that by more accurately reproducing the column study results, the dual-mode model generally predicts greater long-term heavy metal loading to the underlying soil layer and longer duration of leaching than the single-mode model. The heavy metal leaching observed in the columns does not show any correlation with the sequential extraction procedure and toxicity characteristic leaching procedure (TCLP) results, suggesting that the column leaching test should be considered to be independent of such batch test procedures.

Genomic resolution of a cold subsurface aquifer community provides metabolic insights for novel microbes adapted to high CO2 concentrations

As in many deep underground environments, the microbial communities in subsurface high-CO₂ ecosystems remain relatively unexplored. Recent investigations based on single-gene assays revealed a remarkable variety of organisms from little studied phyla in Crystal Geyser (Utah, USA), a site where deeply sourced CO₂ -saturated fluids are erupted at the surface. To provide genomic resolution of the metabolisms of these organisms, we used a novel metagenomic approach to recover 227 high-quality genomes from 150 microbial species affiliated with 46 different phylum-level lineages. Bacteria from two novel phylum-level lineages have the capacity for CO₂ fixation. Analyses of carbon fixation pathways in all studied organisms revealed that the Wood-Ljungdahl pathway and the Calvin-Benson-Bassham Cycle occurred with the highest frequency, whereas the reverse TCA cycle was little used. We infer that this, and selection for form II RuBisCOs, are adaptions to high CO₂ -concentrations. However, many autotrophs can also grow mixotrophically, a strategy that confers metabolic versatility. The assignment of 156 hydrogenases to 90 different organisms suggests that H₂ is an important inter-species energy currency even under gaseous CO₂ -saturation. Overall, metabolic analyses at the organism level provided insight into the biochemical cycles that support subsurface life under the extreme condition of CO₂ saturation.

Integrated Framework for Assessing Impacts of CO₂ Leakage on Groundwater Quality and Monitoring-Network Efficiency: Case Study at a CO₂ Enhanced Oil Recovery Site

This study presents a combined use of site characterization, laboratory experiments, single-well push-pull tests (PPTs), and reactive transport modeling to assess potential impacts of CO2 leakage on groundwater quality and leakage-detection ability of a groundwater monitoring network (GMN) in a potable aquifer at a CO2 enhanced oil recovery (CO2 EOR) site. Site characterization indicates that failures of plugged and abandoned wells are possible CO2 leakage pathways. Groundwater chemistry in the shallow aquifer is dominated mainly by silicate mineral weathering, and no CO2 leakage signals have been detected in the shallow aquifer. Results of the laboratory experiments and the field test show no obvious damage to groundwater chemistry should CO2 leakage occur and further were confirmed with a regional-scale reactive transport model (RSRTM) that was built upon the batch experiments and validated with the single-well PPT. Results of the RSRTM indicate that dissolved CO2 as an indicator for CO2 leakage detection works better than dissolved inorganic carbon, pH, and alkalinity at the CO2 EOR site. The detection ability of a GMN was assessed with monitoring efficiency, depending on various factors, including the natural hydraulic gradient, the leakage rate, the number of monitoring wells, the aquifer heterogeneity, and the time for a CO2 plume traveling to the monitoring well.

A first principles study of CO2 adsorption on α-SiO2(001) surfaces

CO₂ interaction with cleaved and reconstructed α-SiO₂(001) surfaces is studied using first principles calculations.

Ground gas monitoring: implications for hydraulic fracturing and CO2 storage

Understanding the exchange of carbon dioxide (CO2) and methane (CH4) between the geosphere and atmosphere is essential for the management of anthropogenic emissions. Human activities such as carbon capture and storage and hydraulic fracturing ("fracking") affect the natural system and pose risks to future global warming and to human health and safety if not engineered to a high standard. In this paper an innovative approach of expressing ground gas compositions is presented, using data derived from regulatory monitoring of boreholes in the unsaturated zone at infrequent intervals (typically 3 months) with data from a high frequency monitoring instrument deployed over periods of weeks. Similar highly variable trends are observed for time scales ranging from decades to hourly for boreholes located close to sanitary landfill sites. Additionally, high frequency monitoring data confirm the effect of meteorological controls on ground gas emissions; the maximum observed CH4 and CO2 concentrations in a borehole monitored over two weeks were 40.1% v/v and 8.5% v/v respectively, but for 70% of the monitoring period only air was present. There is a clear weakness in current point monitoring strategies that may miss emission events and this needs to be considered along with obtaining baseline data prior to starting any engineering activity.

Examining the role of carbon capture and storage through an ethical lens

The risk posed by anthropogenic climate change is generally accepted, and the challenge we face to reduce greenhouse gas (GHG) emissions to a tolerable limit cannot be underestimated. Reducing GHG emissions can be achieved either by producing less GHG to begin with or by emitting less GHG into the atmosphere. One carbon mitigation technology with large potential for capturing carbon dioxide at the point source of emissions is carbon capture and storage (CCS). However, the merits of CCS have been questioned, both on practical and ethical grounds. While the practical concerns have already received substantial attention, the ethical concerns still demand further consideration. This article aims to respond to this deficit by reviewing the critical ethical challenges raised by CCS as a possible tool in a climate mitigation strategy and argues that the urgency stemming from climate change underpins many of the concerns raised by CCS.

Carbon dioxide concentration dictates alternative methanogenic pathways in oil reservoirs

Deep subsurface formations (for example, high-temperature oil reservoirs) are candidate sites for carbon capture and storage technology. However, very little is known about how the subsurface microbial community would respond to an increase in CO₂ pressure resulting from carbon capture and storage. Here we construct microcosms mimicking reservoir conditions (55 °C, 5 MPa) using high-temperature oil reservoir samples. Methanogenesis occurs under both high and low CO₂ conditions in the microcosms. However, the increase in CO₂ pressure accelerates the rate of methanogenesis to more than twice than that under low CO₂ conditions. Isotope tracer and molecular analyses show that high CO₂ conditions invoke acetoclastic methanogenesis in place of syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis that typically occurs in this environment (low CO₂ conditions). Our results present a possibility of carbon capture and storage for enhanced microbial energy production in deep subsurface environments that can mitigate global warming and energy depletion.

Deep subsurface formations are potential sites for carbon capture and storage but how subsurface microbial communities may respond to this is not clear. Here, Mayumi et al. construct microcosms and show that increasing CO₂ partial pressure via carbon capture and storage more than doubles the rate of methanogenesis.

Ocean acidification in a geoengineering context

Fundamental changes to marine chemistry are occurring because of increasing carbon dioxide (CO(2)) in the atmosphere. Ocean acidity (H(+) concentration) and bicarbonate ion concentrations are increasing, whereas carbonate ion concentrations are decreasing. There has already been an average pH decrease of 0.1 in the upper ocean, and continued unconstrained carbon emissions would further reduce average upper ocean pH by approximately 0.3 by 2100. Laboratory experiments, observations and projections indicate that such ocean acidification may have ecological and biogeochemical impacts that last for many thousands of years. The future magnitude of such effects will be very closely linked to atmospheric CO(2); they will, therefore, depend on the success of emission reduction, and could also be constrained by geoengineering based on most carbon dioxide removal (CDR) techniques. However, some ocean-based CDR approaches would (if deployed on a climatically significant scale) re-locate acidification from the upper ocean to the seafloor or elsewhere in the ocean interior. If solar radiation management were to be the main policy response to counteract global warming, ocean acidification would continue to be driven by increases in atmospheric CO(2), although with additional temperature-related effects on CO(2) and CaCO(3) solubility and terrestrial carbon sequestration.

Regulating geologic sequestration in the United States: early rules take divergent approaches

Regulations for geological sequestration (GS) of carbon dioxide (CO2) have been adopted in the state of Washington and proposed by the state of Kansas and the U.S. Environmental Protection Agency (EPA) Underground Injection Control (UIC) Program. These three sets of rules take significantly different approaches to regulating GS of CO2. This paper compares these rules, focusing on elements where their differences highlight the choices that must be made to create a regulatory framework for GS in the United States. Consensus is emerging in some areas, but there is still substantial disagreement regarding the allowable composition of the CO2 stream, the size of the area of review, reservoir performance goals, and management of risks other than those to groundwater. Gaps include issues related to ownership of subsurface pore space, greenhouse gas accounting, and long-term stewardship. The divergent approaches of these rules raise two overarching questions: (1) Should policy makers create GS regulations by modifying and supplementing UIC rules or through new enabling legislation? (2) What should be the relative roles of state and federal governments in GS regulation? We outline trade-offs between the consistency and coordination that federal involvement could offer and the reality that states need to be heavily involved with implementation of GS regulations. We conclude that federal involvement above and beyond the proposed EPA Class VI rules is needed to create effective GS regulation in the United States.

Net radiative forcing from widespread deployment of photovoltaics

If photovoltaics (PV) are to contribute significantly to stabilizing the climate, they will need to be deployed on the scale of multiple terawatts. Installation of that much PV would cover substantial portions of the Earth's surface with dark-colored, sunlight-absorbing panels, reducing the Earth's albedo. How much radiative forcing would result from this change in land use? How does this amount compare to the radiative forcing avoided by substituting PV for fossil fuels? This analysis uses a series of simple equations to compare the two effects and finds that substitution dominates; the avoided radiative forcing due to substitution of PV for fossil fuels is approximately 30 times largerthan the forcing due to albedo modification. Sensitivity analysis, including discounting of future costs and benefits, identifies unfavorable yet plausible configurations in which the albedo effect substantially reduces the climatic benefits of PV. The value of PV as a climate mitigation option depends on how it is deployed, not just how much it is deployed--efficiency of PV systems and the carbon intensity of the substituted energy are particularly important

Environmental bonds and the challenge of long-term carbon sequestration

The potential to capture carbon from industrial sources and dispose of it for the long-term, known as carbon capture and sequestration (CCS), is widely recognized as an important option to reduce atmospheric carbon dioxide emissions. Specifically, CCS has the potential to provide emissions cuts sufficient to stabilize greenhouse gas levels, while still allowing for the continued use of fossil fuels. In addition, CCS is both technologically-feasible and commercially viable compared with alternatives with the same emissions profile. Although the concept appears to be solid from a technical perspective, initial public perceptions of the technology are uncertain. Moreover, little attention has been paid to developing an understanding of the social and political institutional infrastructure necessary to implement CCS projects. In this paper we explore a particularly dicey issue--how to ensure adequate long-term monitoring and maintenance of the carbon sequestration sites. Bonding mechanisms have been suggested as a potential mechanism to reduce these problems (where bonding refers to financial instruments used to ensure regulatory or contractual commitments). Such mechanisms have been successfully applied in a number of settings (e.g., to ensure court appearances, completion of construction projects, and payment of taxes). The paper examines the use of bonding to address environmental problems and looks at its possible application to nascent CCS projects. We also present evidence on the use of bonding for other projects involving deep underground injection of materials for the purpose of long-term storage or disposal.

The United States Department of Energy's Regional Carbon Sequestration Partnerships program: a collaborative approach to carbon management

This paper reviews the Regional Carbon Sequestration Partnerships (RCSP) concept, which is a first attempt to bring the U.S. Department of Energy's (DOE) carbon sequestration program activities into the "real world" by using a geographically-disposed-system type approach for the U.S. Each regional partnership is unique and covers a unique section of the U.S. and is tasked with determining how the research and development activities of DOE's carbon sequestration program can best be implemented in their region of the country. Although there is no universal agreement on the cause, it is generally understood that global warming is occurring, and many climate scientists believe that this is due, in part, to the buildup of carbon dioxide (CO(2)) in the atmosphere. This is evident from the finding presented in the National Academy of Science Report to the President on Climate Change which stated "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, ...". In the United States, emissions of CO(2) originate mainly from the combustion of fossil fuels for energy production, transportation, and other industrial processes. Roughly one third of U.S. anthropogenic CO(2) emissions come from power plants. Reduction of CO(2) emissions through sequestration of carbon either in geologic formations or in terrestrial ecosystems can be part of the solution to the problem of global warming. However, a number of steps must be accomplished before sequestration can become a reality. Cost effective capture and separation technology must be developed, tested, and demonstrated; a database of potential sequestration sites must be established; and techniques must be developed to measure, monitor, and verify the sequestered CO(2). Geographical differences in fossil fuel use, the industries present, and potential sequestration sinks across the United States dictate the use of a regional approach to address the sequestration of CO(2). To accommodate these differences, the DOE has created a nationwide network of seven Regional Carbon Sequestration Partnerships (RCSP) to help determine and implement the carbon sequestration technologies, infrastructure, and regulations most appropriate to promote CO(2) sequestration in different regions of the nation. These partnerships currently represent 40 states, three Indian Nations, four Canadian Provinces, and over 200 organizations, including academic institutions, research institutions, coal companies, utilities, equipment manufacturers, forestry and agricultural representatives, state and local governments, non-governmental organizations, and national laboratories. These partnerships are dedicated to developing the necessary infrastructure and validating the carbon sequestration technologies that have emerged from DOE's core R&D and other programs to mitigate emissions of CO(2), a potent greenhouse gas. The partnerships provide a critical link to DOE's plans for FutureGen, a highly efficient and technologically sophisticated coal-fired power plant that will produce both hydrogen and electricity with near-zero emissions. Though limited to the situation in the U.S., the paper describes for the international scientific community the approach being taken by the U.S. to prepare for carbon sequestration, should that become necessary.