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Risk Assessment of Geologic Carbon Capture and Storage

Groundwater Contamination Study

1.	Introduction Carbon dioxide (CO2) has been recognized by an interdisciplinary community of scientists as one of the main drivers of global climate change (IPCC, 2005). Consequently, several ways to reduce atmospheric CO2 have been identified (Pacala and Socolow 2004). The options include reducing the amount of emissions produced from anthropogenic sources globally, carbon capture and storage, cap and trade legislation, etc. Carbon capture and storage (CCS) is a viable yet controversial combatant against anthropogenic increases in atmospheric CO2 (De Figueiredo et al., 2005). The idea of carbon sequestration through geologic carbon capture and storage is a technological relict of the oil and gas industry where CO2 input is used to increase product yields from reservoirs. There are currently three “commercial-scale” geologic carbon sequestration projects: Weyburn CO2 flood project (Canada), Sleipner (Norway), and In Salah (Algeria) (EPA, 2012). There are three main steps associated with CCS. (1) Capture (2) Transport and (3) Storage, each with its own risks. Site selection is a key component for geologic CCS. In order to acceptably store the carbon there must be an impermeable cap rock above a site that has limited flow potential as well as limited disturbance (i.e. faults, fractures, or abandoned wells). There are four environments suitable for CCS (1).Active and depleted oil fields (2)Active and depleted natural gas reservoirs (3)Deep saline (brine) formations and (4) Deep coal seams or coal beds. Included below is a list of sights in the varying environments (IPCC, 2005). There are risks associated with each step of the CCS process. In this analysis, we will focus on the possibility of leakage of stored CO2 from storage areas and the associated impacts on human health. If CO2 leaks from storage areas into groundwater/aquifers it has the potential to decrease aquatic pH levels and impact the solubility of metals, especially dangerous heavy metals. 2.	Problem Formulation 2.1.	Problem Statement Recent developments allow for the capture and storage of carbon dioxide emissions as a way to combat rising CO2 atmospheric concentrations. Geologic carbon capture and storage (CSS) is one means of sequestering CO2 emissions. There are several geologic environments that are suitable for the injection of compressed CO2 (IPCC, 2005). These geologic environments suitable for CCS have inherent risks associated with them (Apps, et al., 2010). Continental geologic CCS environments can leak CO2 into groundwater/aquifer regions, decreasing pH and increasing concentrations of trace metals (Apps, et al., 2010). Aquifers have been used as sources of potable water around the world since ancient civilizations (Shah, et al., 2007). Nowadays groundwater is used intensively not only in agriculture but also as a source of drinking water (Shah et al., 2007). However these intensive uses can be imperilled by the leakage of CO2 as a result of geologic carbon sequestration. Geologic carbon sequestration can change the water quality drastically (Keating et al. 2010, Lemiaux 2011,Wang & Jaffe 2004,). The impact can be caused not only by the direct release of CO2  at the surface e.g. well blow-out (Keating et al., 2010) but also by the dissolution of CO2 in the water that produces an increase in the acidity (decrease of the pH). This acidity facilitates the dissolution of minerals which include hazardous trace elements. The hazardous elements that can impact groundwater quality are mercury, uranium, lead, arsenic, chromium, cadmium, molybdenum, selenium, vanadium (Keating et al. 2010). For the purpose of the present Risk Assessment we are going to focus in the human health effects of two elements: Arsenic (As) and lead (Pb) that would exceed permitted concentrations at the Kevin Dome site. 2.2.	Conceptual Model and Focal Pathway In this risk analysis we will be focussing primarily on the risks associated with storage of carbon dioxide and its potential to affect groundwater. Stored CO2 has the potential to leak from the storage site into a nearby groundwater aquifer through a permeable cap rock, fractured or faulted rock, or through an abandoned well. Once this CO2 reaches groundwater it decreases pH and causes the increases dissolution of minerals, some of which contain hazardous trace metals. 2.3.	Kevin Dome, MT Kevin Dome, MT (Figure 1) is one of the sites in the United States that has been classified as suitable for CO2 storage. Geologically it is a natural storage site of CO¬2 with the typical impermeable cap rock (Big Sky Carbon Partnership, 2010). There is intention of storing 1 million tons of CO2 in the Kevin Dome site.