Planning, Designing, Operating, and Regulating a Geologic Sequestration Repository as an Underground Landfill—A Review

ABSTRACT

Geologic sequestration appears to be a technically feasible method of storing carbon dioxide in underground aquifers in order to lower greenhouse gas emissions into the atmosphere. The overall feasibility of geologic sequestration is still in question and as such, has been the focus of intense research over the past decade. Researchers have looked to the oil/gas industry and water well industry for lessons learned and technical knowledge, however, a better industry to emulate may well be the waste industry. Viewing geologic sequestration repositories as underground landfills has a great many benefits. First, there is a plethora of existing research and investigations that are directly analogous to geologic sequestration projects. Second, the regulatory framework is rather mature and can be easily adapted to serve geologic sequestration. This paper conducts an extensive literature search of the environmental, waste, and geologic sequestration literature to ascertain planning, design, and operational methodologies, lessons learned, and concepts that are directly useful for geologic sequestration to improve the technical and regulatory framework. Lastly, the paper uses a hypothetical underground landfill geologic sequestration site (ULGSS) in Florida, USA to discuss some of the findings and implications from the literature. It is concluded that there are a number of literature findings from the waste and environmental arena that should be adapted for geologic sequestration.

IMPLICATIONS

Geologic sequestration is a promising solution for greenhouse gas control. This work supports that notion but suggests further improvements to the technical and regulatory framework based upon an extensive review of the waste management and environmental literature. The improvements include suggestions in the areas of permitting, site selection, operations, cost accounting, and special waste handling. Some of these improvements are discussed using a hypothetical project site in Florida, USA.

INTRODUCTION

Concerns regarding global climate change are becoming the catalyst for significant changes in the energy, utility, and industrial sectors of the world economy.1 Due to concerns regarding greenhouse gas emissions and increases to planetary temperatures, the continued use of fossil fuels is being reexamined.2 Governments across the world are promoting the use of non-fossil-fuel-based energy including nuclear and alternative energy (e.g., solar, wind, geothermal, biomass) as a viable alternative to the more emissions-heavy fossil-fuel-based methods. In reality, however, the use of fossil fuels such as coal, oil, and natural gas will continue for several decades. Utilities are looking at electricity dispatch of lower carbon fuels and other similar operating strategies.3 Fossil fuels supply over 85% of all primary energy; the rest is made up of nuclear, hydroelectricity, and renewable energy (commercial biomass, geothermal, wind, and solar energy).4

How can our strategically important fossil fuel resources continue to be utilized so heavily in this new world? The answer lies with a fast-developing technology called carbon capture and sequestration (CCS). The focus is on carbon dioxide as the primary greenhouse gas most commonly emitted by the combustion of fossil fuels. Capture and geological storage of carbon dioxide (CO₂) provide a way to minimize CO₂ emissions into the atmosphere, by capturing CO₂ from major stationary sources, transporting it, usually by pipeline, and injecting it into suitable deep geological formations.5 6 The concept of storing CO₂ intentionally to avoid emissions has been investigated for the last 20 or so years.7 9

Typical components of a CCS system include the following:

•	Capture—The separation of CO2 from an effluent stream and its compression to a liquid or supercritical state. In most cases today, the resulting CO2 concentration is greater than 99%, though lower concentrations may be acceptable.4
•	Transport—The transport of CO2 can be accomplished most efficiently and economically with conventional gas pipelines although transport via ship tanker, rail tanker, or truck tanker may be feasible.6 10
•	Injection—The liquid or supercritical CO2 is injected into underground storage repositories, mostly consisting of geologic media. CO2 is injected using traditional pumps and deep wells similar to technology used in the petroleum industry or for conventional water wells. Other potential reservoirs include the deep ocean, ocean sediments, or mineralization (conversion of CO2 to minerals).4
•	Monitoring and verification—The stored CO2 is monitored to ensure that a majority of it stays sequestered for 100s to 1000s of years in order to keep it from escaping back to the atmosphere. Monitoring includes both direct measurements using monitoring wells or similar and non-invasive techniques such as surface geophysics.6 11

There are three primary storage types identified in the literature, including saline aquifers, depleted oil and gas fields, and thin-unmineable coal seams.12 14 The capacity of each of these repository categories to sequester CO₂ varies considerably and must be evaluated through feasibility-level and pilot-level investigations of potential projects. Deep saline aquifers appear to offer the highest potential capacity of the three primary options.15 In addition, in regions such as Florida, USA, saline aquifers are the most likely storage option, since the estimated capacity of oil/gas fields is relatively small by comparison (e.g., 100 times less) according to the Department of Energy.16 Since saline aquifers represent the largest probable source of geologic sequestration capacity in the United States and Florida, they will be the focus of the remainder of this article.

For the most part, national governments or large energy companies have pursued geologic sequestration.17 But, if the definition of waste was expanded to include greenhouse gases and carbon dioxide emissions, a large, integrated waste management company may be well positioned to serve the market need similar to how the same companies manage solid waste landfills around the world. Such an entity, if it were to undertake such a project, could use many planning, design, and operational concepts developed in the waste management and environmental fields to fully develop an underground geologic sequestration site; it could be planned, permitted, and regulated as an underground landfill. In addition, the regulatory framework developed for solid waste landfills over the last 30 years can be easily adapted and combined with regulatory schemes currently under consideration from the Safe Drinking Water Act, Underground Injection Control (UIC) program (http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm), to create more complete geologic sequestration guidance. This is important, as regulators across the world and in the United States are struggling to develop a coherent and technically defensible approach.18 Proper regulations for CO₂ storage are needed to reduce the current uncertainty associated with the economics of CO₂ storage and to accelerate the deployment of CCS technology.19 There is a growing consensus in some regulatory areas, but significant disagreement remains in regards to composition of the CO₂ pipeline stream, the size of the area of review, reservoir performance goals, and management of risks other than those to groundwater, including leakage from the storage zone or overall cost of commercial-scale projects.18 Key gaps are also evident, including actual ownership of the subsurface pore space, the overall greenhouse gas accounting methodology, and long-term postclosure management.¹⁸ Besides these identified gaps in the regulatory regime, the authors of this paper note that limited consideration has yet been given to so-called “local host” issues. It is obvious that local host and postclosure issues need to be resolved in order for geologic sequestration projects to be successful. Luckily, many of these same issues have already been intensively studied by waste management and environmental researchers and this knowledge can be transferred to the geologic sequestration technical area.

This paper uses existing waste regulations and research to develop a list of planning, design, operational, and regulatory improvements that could be incorporated into the geologic sequestration technical arena. First, this paper outlines and summarizes key components of solid waste management regulations that could be adapted for geologic sequestration sites; State of Florida regulations are used for comparison purposes. Then, through a review and evaluation of pertinent waste management, environmental, and geologic sequestration literature, the paper outlines technical approaches, methodologies, lessons learned, and conclusions that could be useful to furthering development of an improved geologic sequestration technical framework without “reinventing the wheel”. Finally, key technical and cost implications as determined from the literature are illustrated using a hypothetical underground landfill geologic sequestration site (ULGSS) in Florida, USA.

METHODOLOGY

Evaluation of a geologic sequestration repository as an underground landfill permits the designer to take advantage of above-ground landfill examples in regards to planning, design, subsurface investigations, monitoring, operations, site closure, and postclosure. Chapter 62–701 of the Florida Administrative Code (FAC) provides specific requirements and regulatory guidelines for solid waste management facilities in Florida (http://www.flrules.org/gateway/ChapterHome.asp?Chapter=62-701).20 These rules cover a wide array of solid waste management facility issues and cover typical sanitary landfills as well as hazardous industrial waste disposal areas and construction debris landfills. The rules that govern the regulation of sanitary landfills provide one focus of this paper. Many of the sanitary landfill rules are directly analogous to ULGSS and could be utilized to improve the overall regulatory and technical framework for ULGSS projects. Table 1 provides the FAC section along with the title of the section most pertinent to ULGSS where existing landfill guidance can be used to improve the geologic sequestration technical framework. Other existing FAC items relating to hydrogeological and geotechnical investigations, water quality monitoring, and site construction have been investigated in great detail by other researchers already and are not discussed further in this paper. These include

Table 1. Sanitary landfill requirements pertinent to geologic sequestration planning, design and operation reviewed in this paper

FAC Section	Section Title	Analogous Item for ULGSS
62–701.330	Landfill Permit Requirements	Geologic sequestration permits
62–701.340	General Criteria For Landfills	Site selection
62–701.500	Landfill Operation Requirements	Geologic sequestration site operation requirements
62–701.520	Special Waste Handling	Waste stream composition

1.	Waste disposal needs assessment including location of primary generators of CO2 [5,8]
2.	Identification of potential geologic sequestration repositories21
3.	Completion of feasibility-level assessment of most suitable geologic sequestration repositories to include injectivity, storage capacity, storage zone security/permanence, brine water management, and leakage sources (e.g., faults, fractures, and abandoned wells)22 24
4.	Development of estimates of CO2 transportation and disposal costs for each suitable geologic sequestration repository10 25 27
5.	Completion of site design and pilot testing28

The additional landfill planning, operation, and technical areas listed in Table 1 offer fresh insight for ULGSS projects and will be the remaining focus of this paper. These existing Florida solid waste regulations will provide a convenient way to organize the research presented in this paper. The research review presented herein will focus upon permit requirements, general site selection criteria, operational requirements, and special waste. These areas are discussed further below.

Permit Requirements

For sanitary landfills, FAC requires owners to secure multiple landfill permits, including one for construction, operation, modification, and closure. Typically, the construction permit is confined to a maximum of 5 years, whereas the operation permit is granted for 10-year durations that can be renewed periodically. Significant changes to the landfill size, height, waste input, or waste type accepted require a permit modification to be approved. A closure permit is required when a landfill has ceased to accept solid waste and is preparing to go into long-term care. For geologic sequestration repositories, a similar permitting scheme is under consideration by the U.S. Environmental Protection Agency (EPA) UIC Program (http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm). Bayer and Kobelski discuss the proposed rule at length and present the requirements.29 The proposed rule puts forth technical criteria and guidelines for geologic site characterization, area of review evaluation, well construction and operation, mechanical integrity testing, monitoring, financial responsibility, injection well plugging, postinjection site care, and site closure. The basic requirements29 include the following:

•	Geologic site characterization to ensure that geologic sequestration wells are appropriately sited.
•	Requirements to construct wells with injectate-compatible materials and in a manner that prevents fluid movement into unintended zones.
•	Periodic reevaluation of the area of review around the injection well to incorporate monitoring and operational data and verify that the CO2 is moving as predicted within the subsurface.
•	Testing of the mechanical integrity of the injection well, ground water monitoring, and tracking of the location of the injected CO2 to ensure protection of underground sources of drinking water (USDWs).
•	Extended postinjection monitoring and site care to track the location of the injected CO2 and monitor subsurface pressures.
•	Financial responsibility requirements to ensure that funds will be available for well plugging, site care, closure, and emergency and remedial response.

Under the UIC program, the owner will be required to secure a construction permit and an operation permit although construction and testing may be permitted for more than 5 years prior to obtaining the operation permit. The closure permit used in landfill regulation could be adopted for ULGSS. Also, the postclosure period for landfills, usually 30 years, could be the minimum postclosure period for ULGSS projects. The postclosure period should focus upon the time period when CO₂ is a separate-phase fluid and most highly mobile which still may be on the order of several hundred years or more.30 Permit considerations also need to address the enormous scale of potential ULGSS projects. Infrastructure for injecting carbon dioxide will need to be an order of magnitude larger than current pilot-scale CCS projects.31 Also it should be noted that in most cases, the CO₂ injection scheme will consist of multiple wells, potentially including wells for monitoring and pressure control.31 Therefore, postclosure monitoring will be critical to control of large ULGSS projects.32

General Criteria

For sanitary landfills, FAC requires owners to provide information regarding landfill site selection, setback distances, and siting prohibitions (e.g., cannot be in 100-year flood plain). For ULGSS similar considerations are equally important. Ideally situated repositories should be in close proximity to major sources of emissions as well as “over” a suitable storage zone. Other general siting criteria to be considered include social and environmental considerations as well as “host” county concerns. An optimal location will enable efficient collection of CO₂ waste through a pipeline network while maximizing underground storage efficiency and minimizing social, environmental, and institutional impacts. Considerable research has already been completed regarding the optimal site selection of numerous facilities, including noxious or “unwanted” projects. Multiple researchers have studied site selection considerations of negative perception projects such as power plants, landfills, transportation projects, hazardous waste treatment plants, or radioactive waste disposal sites using automated models and geographic information systems (GIS).33 39 The models, experience, and lessons learned from these studies are directly applicable to the siting of geologic sequestration repositories.

Previously, researchers developed a site suitability analysis to identify locations for energy facilities that were acceptable across a range of engineering, economic, environmental and socioeconomic criteria, although they note that the application of the analysis can be biased by users.33 An analytic hierarchy process (AHP) was utilized to site a sanitary landfill in Edmonton, Alberta, Canada.35 A great advantage of this methodology is that it is very quantitative and less subject to political or emotional bias. The researchers argue that it should be useful to public sector decision makers to locate obnoxious facilities like landfills. The siting of an ULGSS would certainly be subject to similar special interest bias, especially given the size of CO₂ plumes may be tens of square kilometers in size.40 Delgado et al. used a GIS-based model to evaluate site selection of a large inter-municipal landfill in Mexico.39 Both environmental (biophysical) and socioeconomic data were processed in one of three GIS models that differed in their complexity and restrictiveness; these included a Boolean logic model, a binary data model, and an overlapping index model. They found that the Boolean logic model was easier to apply and more restrictive than the other two, because it is based on the assessment of single attributes, whereas the other two methods relied upon weighting of multiple attributes. The site screening results showed that the most suitable areas covered only 1.5% to 5% of the available study area. Similar GIS approaches should be standard practice when locating optimum sites for ULGSS. Also, when considering various geologic sequestration site selection factors (e.g., emissions location, suitable geology, minimal social impacts, minimal environmental impacts, costs), it would not be surprising that less than 5% of the study area would meet criteria for optimality.

The literature makes a strong case for further direct involvement of multiple stakeholders during site selection screening.³⁴ Other researchers used complicated decision-making approaches (e.g., Markov chains) to evaluate models of possible future human actions during the long-term postclosure period of a radioactive waste repository.³⁶ This is certainly important in the case of nuclear waste repositories where waste may be radioactive for 10,000 years and future actions of humanity that far into the future are unknown. Similarly, this model approach may be applicable to ULGSS, since it may take 1000s of years for separate phase CO₂ to fully dissolve into native brines.¹²

Cram et al. used multicriteria screening of 12 different vegetation types in Mexico's Tamaulipas State to help select potentially suitable sites for hazardous waste treatment plants.38 They included evaluations of species richness, spatial distribution, and uniqueness as the criteria for estimating a vegetation type's suitability to host the hazardous waste treatment plants. Similarly, sensitive environmental areas should be avoided when conducting site selection activities for ULGSS. Several researchers considered the environmental justice implications of transportation plans and policies in the United States.37 Chakraborty found that despite several administrative orders and federal mandates, few specific guidelines exist for assessing the disproportionate effects of transportation projects and implementing environmental justice principles in the transportation planning process.[37] The indices he developed were formulated on the basis of readily available census data and tools available within basic GIS software. Certainly, considerations for environmental justice issues should be taken into account for geologic sequestration sites too. Too often, lower-income communities take the brunt of noxious projects.

For instance, it has been found that certain community types were more likely to be located near a National Priorities List (NPL) or Superfund remediation site than others.41 The researchers examined patterns of neighborhood type based on NPL site classification by activity and waste type (e.g., manufacturing, mining). Overall, block groups described as “Military Quarters” had the highest risk of being located near an NPL site. Lower-income areas are also more likely to be near NPL sites than affluent neighborhoods. This study utilized 1999 census block group population estimates as well as neighborhood descriptors in the United States. In a similar siting study,42 investigators presented research regarding the factors influencing community responses to municipal incinerators. These factors range from those about which experts and lay people may readily agree, such as the years of service remaining in an existing landfill, to issues that are more likely to engender disagreement, such as community perceptions of environmental risks, “environmental equity”, and other economic and political concerns.

Besides neighborhood-specific studies of possible project locations, general “host community” considerations are also important given the expected enormous size of underground CO₂ plumes. Host governments are likely to be on the scale of a U.S. county or city or perhaps multiple counties. Hosts of noxious facilities often suffer from a “stigmata” that affects area desirability.43 The host community may experience decrease in property values44 or loss of amenity value,45 although the long-term impact to the community in the case of ULGSS is unknown but expected to be small. In order to avoid, reduce, or address actual or potential impacts caused by siting of noxious facilities in a host community, the project proponent should utilize multiple measures and approaches as part of the site selection task. Zeiss and Lefsrud presented a comprehensive study and review regarding key principles and elements of effective siting packages for host communities.43 They note that it is in the best interest of the host community as well as the facility proponent to select and negotiate the most effective measures for a siting package and properly sequence the measures to reduce overall time and resources required to negotiate agreements. The key principles and elements of host community siting packages should include:

•	Need identification
•	Technical and site optimality
•	Waste stream control
•	Impact reduction management
•	Benefits, compensation, and incentives
•	Process management

Their analysis of reported siting cases showed that need justification, technology and site choice, and waste stream controls are infrequently used, whereas compensation benefits are often used in conjunction with process management and impact reduction. The article concludes that creative use of need identification, technology selection, and waste stream control may improve siting agreement success, shorten the negotiation process, and result in less costly agreements.43 The key elements of host community siting packages should be considered for ULGSS as well as other similar projects such as new natural gas wells where hydrofracturing is proposed.

As part of comprehensive regulations for ULGSS, consideration should be given to the sum of all of the environmental and social impacts on the host community. The cumulative impacts from ULGSS projects have not really been studied in any detail as of yet. Cumulative impacts are the sum of individual impacts plus or minus interaction of the individual impacts.46 Others found that cumulative assessments were infrequently completed or addressed in detail.47 Of 50 Environmental Impact Statements (EISs) reviewed in the study, only 24 EISs (48%) mentioned the term “cumulative effects/impacts” and only 9 EISs (18%) provided a discussion, which were mostly qualitative in nature.48 A key finding of the study was that where cumulative effects were considered in the scoping stage, further discussion or analysis of these effects was generally undertaken. Atkinson and Canter suggest methodology using GIS technology to complete such an assessment.48 One research team has provided a useful checklist of items to assess for cumulative impacts that could be adopted by ULGSS.46 They included the following general categories necessary for thorough evaluation:

•	Physical environment landform
•	Air/climatology
•	Water
•	Solid waste
•	Noise
•	Hazardous waste
•	Biological environmental flora
•	Biological environment fauna
•	Socioeconomic environment landuse
•	Recreation
•	Aesthetics
•	Archeological sites
•	Health and safety
•	Cultural patterns
•	Local services
•	Public utilities
•	Population
•	Economic
•	Transportation
•	Natural resources
•	Energy

Operational Requirements and Considerations

For sanitary landfills, there are a number of important issues to deal with regarding site operations and regulatory reporting. Many of these items are specifically identified in the FAC including operating personnel, operations plans, required site equipment, and recordkeeping/reporting. All of these items are also important at ULGSS and should be considered during the planning process and as part of a final regulatory framework for projects. The number present and overall training requirements for onsite operators of ULGSS is an important operational detail. Conventional landfill operations include a minimum of one trained operator and one waste spotter whose role is to identify unauthorized waste from being placed in the landfill. The trained operator must understand all of the various components of the landfill. The operator must also understand how to handle emergencies that may occur. For ULGSS, the operator training is also important. The site operator has to understand the meaning of complicated site instrumentation data as well as operation of site compressors, pipelines, injection wells and other site infrastructure. The ULGSS operator also has to understand what type emergencies might occur at a typical project site. For example, what needs to be done if a large CO₂ leak is identified within the project operational area? Many of these questions could be simplified by adoption of site operation plans similar to those required for aboveground landfills. As noted by Price and Oldenburg, it is certainly easier to avoid failure as part of site selection but failures are likely to occur none the less.49 The overall response to such an emergency should be outlined as part of the site operations plan. The conventional landfill regulations also lay out requirements for backup and “reserve” or redundant site equipment and critical infrastructure. These can be located onsite or they must be available within 24 hours through a contractual arrangement. This practice seems very prudent and should be adopted for ULGSS projects. Certainly, items such as redundant communications, standby generators, or a well tender truck/crane should be considered at a ULGSS project. Lastly, recordkeeping and reporting are important issues that need further consideration by regulators. How will waste placed in the ULGSS be measured and tracked? How will the remaining capacity of the ULGSS be assessed annually as is required for conventional landfills? Obviously, monitoring of the stored CO₂ will need to be completed along with other storage zone conditions including temperature, pressure, and brine water quality. Without these data, determining the remaining site capacity will be difficult.

In addition, the operation of the ULGSS may change over time based upon waste flows and overall site economics. As site capacity fills up, owners may opt to implement “pay-as-you-throw” programs to encourage customers to reduce waste streams or they could provide incentives to reduce waste impurities. The International City-County Management Association has noted that Pay-As-You-Throw (PAYT), also known as variable-rate or unit-based pricing, provides a direct economic incentive for customers to reduce the amount of waste they generate.50 Under this system, consumers are charged based on how much service they use, just as they are charged for other utilities, such as water or electricity, and are therefore motivated to generate less waste. This approach may extend the useful life of the ULGSS project.

An important operational consideration is the operational cost and source of project revenue. A private owner of an ULGSS will likely want to charge a waste tipping fee similar to conventional landfills. Conventional tipping fees are in the range of $20 to $40 per ton. In 1996, the average tipping fee at Virginia municipal waste landfills was $34.91 per ton.51 Davila et al. found tipping fees between $20 and $30 per ton in Texas.52 The tipping fee is also a way to control the overall waste stream entering the ULGSS. As tipping fees increase, waste generators may opt to change their waste management alternative. What to include in the tipping fee is also important. According to one investigator, many landfill owners significantly underestimate the total cost of landfill disposal by considering only land and operating costs, ignoring external physical and social costs associated with landfills.53 FAC landfill regulations require full cost accounting of the landfill including the components of the tipping fee. FAC also dictates that landfill owners provide proof of financial assurance in the amount of the estimated closing and long-term care costs. Based upon an extensive literature review, in order to develop an ULGSS, the tipping fee would need to include the following components:

•	Pipeline transportation capital costs
•	Pipeline transportation annual operating costs
•	ULGSS construction capital costs
•	ULGSS annual operating costs
•	Local host costs during operation
•	Local host costs during postclosure period
•	Costs of pore space used
•	Postclosure costs for monitoring, verification, and possible remediation

It is assumed that capture costs would be the responsibility of the ULGSS customer and this would be completed at the emissions source. The overall range of costs for each of these components is fairly large based upon the existing literature. Table 2 lists each potential ULGSS cost component, the estimated cost per tonne of CO₂ per year, and the reference source for the data.

Table 2. ULGSS cost components

Cost Component	Cost $/tonne CO2/year	Data Source
Pipeline transportation capital costs	$1.37 to $3.71 $3.78 (for 100 km) $0.38 to $1.28	27 54^b 55^b
Pipeline transportation O&M^a costs	$0.92 to $2.47	27
ULGSS construction capital costs	$0.47 to $0.70 $0.81 $0.25 to $6.20	55^c 56 6^c
ULGSS O&M costs	$2.60	56
Local host costs during operation phase	$0.13 to $7.70	43
Local host costs during postclosure	Unknown
Costs to purchase or lease pore space	$0.04 to $11.00	40
Postclosure costs for monitoring, verification, and possible remediation	$0.13 $0.27 to $0.30	56 6
Notes: ^aO&M = operation and maintenance. ^bZhang et al. nor Keating et al. separate out transportation costs into capital and O&M. ^cIPCC nor Keating et al. separate out storage costs into capital and O&M.

Based upon the recent literature, the cost to develop the ULGSS will range from $0.93 to $28.98 per tonne CO₂ per year, not including any local host costs required during the postclosure period that are unknown at this time. Using the average of this range, the estimated cost would be about $15/tonne CO₂/year.

In order for the owner of an ULGSS to make a profit from the operation, a tipping fee model could be useful. Ready and Ready developed a general model for pricing a replaceable, depletable asset, focusing on the problem of determining an optimal tipping fee for a landfill site.57 Their model could be adapted for ULGSS projects to determine the optimal tipping fee to be charged by an owner. Depending upon assumptions made and operational period length of the model, the tipping fee would have to start at $15/tonne CO₂ and increase to as much as $29/tonne over a 25-year period based upon costs identified in the literature. A key component of the tipping fee should be an item that grows at the real interest rate as space in the landfill is depleted. A complete cost estimate of the “total cost” of the ULGSS is important and should certainly include appropriate social, environmental, and engineering cost components. The estimated costs for closure and postclosure activities should be included in the tipping fee during the operational period. So if the postclosure period is mandated to be 30 years, all of the estimated costs to be expended during that time need to be collected during ULGSS operation and placed into escrow. Depending upon who pays for geologic sequestration and how those costs are recouped, the overall “willingness to pay” may have to be studied, especially if citizens from poor or socially disadvantaged areas cannot afford the initial costs. The potential to close the apparent willingness-to-pay gap through state or federal subsidies may have to be assessed.58 Where grant or subsidy programs are insufficient to bridge the gap, and local officials are reluctant to impose costs that are not publicly supported, public education efforts will be needed to increase the value residents ascribe to the nonexclusive positive externalities and local nonmarket benefits of reducing greenhouse gas pollution.58

Research has been conducted regarding “fair fund” distribution related to siting of municipal incinerators in Taiwan.59 A fair fund is a compensation fund to support the welfare of those citizens who suffer lost amenity. According to Chang et al., public reluctance with regard to accepting the incinerators as typical utilities often results in an intensive debate concerning how much welfare is lost for those residents living in the vicinity of those incinerators. The researchers conclude that involving all stakeholders and using democratic procedures is the best way for determining the use and distribution of the fair fund. Usually, some type of multiobjective screening criteria is used involving political, socioeconomic, technical, environmental, public health, and industrial aspects. Distribution of similar fair funds should be part of the planning and operation of the ULGSS. Examples of fair fund compensation could be property value guarantees, improved infrastructure, property tax payments either to the community or to land owners, insurance costs, closure, and clean-up funds.43 Compensation can be structured as (1) ex-ante to address fairness, (2) interim to protect against tangible losses, and (3) ex-post compensation to defray losses from future events or losses (e.g., accidents, closure, leaks, remediation).⁴³

Eldredge suggests some basic rules for good public relations between the landfill owner/operator and the community neighbors.44 He suggests the use of an experienced and knowledgeable consultant engineer to design and monitor construction; good recordkeeping; use of an objective project review panel including neighbors of the site; making the project environs attractive; and appointing a spokesperson and developing good relations with the news media. Again, Eldredge also mentions the use of a compensation fund to support impacted residents.

Special Waste Handling and Screening

The waste streams converging on the ULGSS may be different or contain various impurities. Other investigators have found that key impurities in CO₂ waste streams include sulfur dioxide (SO₂), nitrogen dioxide (NO₂), hydrogen chloride (HCl), and mercury (Hg).60 Others have noted that low-rate leakage from a CCS injection well into a groundwater aquifer could lead to complex geochemical reactions such as carbonate dissolution, mobilization of trace metals, or other changes.61 The potential risk from CO₂ leakage could be reduced by controlling the impurity levels in the upstream carbon separation at the coal-fired power plants.

Geologic storage may involve injection of impure carbon dioxide (CO₂) streams in order to lower capture costs.62 Unless waste streams are standardized via regulations, it will be up to the owner and operator of the ULGSS to develop a standard system to assess the purity of the waste stream. Verma et al. studied the implications of various contaminants in the purified CO₂ stream and concluded that they depend on the type of power plant and the capture scheme.62 Due to the possible contaminants present, the waste stream itself may be a concern to the local host community as well.

It has been noted that limitations on waste type, quantity, toxicity, sources, and source areas are occasionally identified as relevant components for site selection considerations.63 The investigators further noted that the exclusion or monitoring of specific wastes might be considered and discussed with a local host community prior to project construction and operation. Limiting waste streams or controlling waste impurities as part of ULGSS projects may prevent certain impacts as well as contributing to fairness to host community concerns.[43,48] as well as contributing to fairness to host community concerns.⁴³ It has also been noted by several researchers that some of the impurities in the CO₂ stream, when mixed with water vapor, can lead to possible corrosion of the transport pipelines, injection well steel casing, or weakening of well construction components like cement bond.64 66

DISCUSSION

This paper has included an extensive review of the waste management, environmental, and geologic sequestration literature for the purpose of gaining new insight into future underground landfill geologic sequestration sites or ULGSS. Considerable research is ongoing regarding geologic sequestration, but this paper clearly indicates that previously conducted work related to waste sites is very much pertinent to the current discussion. In addition, the regulatory framework provided by existing solid waste management regulations provides opportunities to improve the proposed geologic sequestration guidance.²⁹

A number of key considerations for future ULGSS have been revealed as a result of this paper. These include considerations for ULGSS permitting, site selection, impact evaluation, operations, cost, and waste stream make-up. The critical key considerations that should be incorporated into the geologic sequestration technical and regulatory framework include

•	Closure permit requirements
•	Postclosure duration of at least 30 years
•	Site suitability screening criteria
•	Stakeholder involvement
•	Environmental justice evaluation during site selection
•	Local host acceptance and compensation
•	Distribution of fair fund compensation
•	Assessment of cumulative impacts
•	Operator training requirements
•	Development of operation manuals
•	Full cost accounting of all components
•	Willingness to pay surveys or assessment
•	Waste stream volume reduction or toxicity reduction

In order to illustrate the implications of some of these items for an ULGSS, consider a hypothetical regional system of emission sources and possible ULGSS locations in Florida, USA. The top 40 primary power plants in Florida emitted almost 123,000,000 tonnes CO₂ (or 123 Mt CO₂) in 2007.67 These 40 sources account for over 86% of the 2007 total CO₂ emissions for Florida. The 40 primary emission sources, along with map identification number, location in UTM 1983 (meters) horizontal grid coordinates, and the respective annual CO₂ emissions, is shown on Table 3. These 40 primary emission sources along with possible geologic sequestration repositories identified in previous studies are shown on Figure 1. ^27,68

Table 3. Forty primary CO₂ emission sources in Florida in 2007

Map ID	Plant/Facility Name	Northing	Easting	Annual CO2 Emissions (Mt)
1	Crystal River	3204678.076	334313.2099	14.53
2	Big Bend	3075217.213	361725.5861	9.50
3	St Johns River Power Park	3366685.069	447107.3266	9.38
4	Seminole	3289401.62	438698.3555	8.95
5	Martin	2992447.195	543356.5439	8.02
6	Crist	3398084.815	−97895.92908	6.62
7	Stanton Energy Center	3150786.692	483497.4057	5.89
8	Manatee	3054258.698	367211.8689	5.21
9	Sanford	3190513.232	468238.3524	4.77
10	Northside Generating Station	3365145.497	446936.553	4.46
11	Fort Myers	2953081.892	422095.7715	3.77
12	Turkey Point	2813351.315	567289.7214	3.45
13	Lansing Smith	3357948.163	47642.89122	3.44
14	C D McIntosh Jr	3106509.925	409058.5118	3.14
15	H L Culbreath Bayside	3087736.668	359949.3805	3.03
16	Hines Energy Complex	3074087.837	414350.2864	3.01
17	Anclote	3118924.345	324414.8847	2.80
18	Lauderdale	2883472.057	580187.5679	2.22
19	Port Everglades	2885457.177	587476.496	2.20
20	Indiantown Cogeneration LP	2990880.875	548162.4763	1.86
21	Polk	3067530.65	402444.7148	1.85
22	Deerhaven Generating Station	3292844.025	365772.0841	1.58
23	Cape Canaveral	3149224.638	523083.2452	1.47
24	P L Bartow	3082867.637	342353.2147	1.43
25	Riviera	2960791.066	594173.507	1.37
26	Cedar Bay Generating Company LP	3365693.624	441618.5065	1.28
27	Curtis H Stanton Energy Center	3151285.066	483605.7691	1.03
28	Osprey Energy Center	3103281.61	420562.9754	0.91
29	Central Power & Lime	3162445.126	360123.38	0.77
30	Wheelabrator North Broward	2907830.005	584050.8789	0.72
31	Wheelabrator South Broward	2883538.323	580157.1517	0.71
32	S O Purdom	3341056.505	191654.8001	0.64
33	Brandy Branch	3354692.44	408803.1779	0.63
34	Shady Hills Generating Station	3138790.319	347216.719	0.60
35	Cane Island	3127936.412	447728.0046	0.60
36	Intercession City	3126436.614	446191.2344	0.54
37	Arvah B Hopkins	3373808.201	173480.9335	0.52
38	Scholz	3399359.385	127519.093	0.52
39	Putnam	3277742.366	443310.436	0.50
40	Miami Dade County Resource Recovery	2857602.486	564510.4052	0.46

Figure 1. Study area for illustrative example.

Past studies and ongoing work at the University of North Florida has identified that repository or disposal area number 4 on Figure 1 is near many primary sources and results in minimum pipeline transportation costs for all emission sources in Central Florida including sites numbers 1, 14–17, 20–24, 27–29, and 34–36.²⁷ As a result, up to 53.8 Mt CO₂ would be sent to area number 4 annually. Figure 2 details the emission sources and a Florida-wide pipeline network required to connect to a proposed ULGSS within area number 4. For planning purposes it is assumed that all of this mass would be injected down a single well into a 100-m-thick storage zone with a porosity of 20% and an irreducible brine saturation of 20%. Further assume that the CO₂ density in place was approximately 618 kg/m³ and the brine density was 1010 kg/m³. Based upon analytical solutions presented in the literature,⁴⁰ the CO₂ plume would have a maximum radius of approximately 21,500 m or 21.5 km after 25 years. Therefore, the conservative area of a CO₂ plume would be 1452 km². Three hypothetical CO₂ plumes are shown on Figure 3 to illustrate northern, central, or southern ULGSS placement. Certainly the overall configuration of the plume could be modified by using a large injection well field or a series of horizontal wells, but, the scale of the ULGSS would still be enormous and on a scale similar to that displayed on the figure. Several of the critical key considerations identified above would require careful evaluation.

Figure 2. Optimal pipeline network to Area No. 4 for illustrative example.

Figure 3. Estimated size of three CO₂ plumes for an illustrative example.

First, closure permitting and postclosure monitoring would have to be resolved. Although the plume would start at a size of 1452 km², this would increase substantially over time as the free phase CO₂ simultaneously translated down gradient and dissolved into the native brine. How many monitoring wells would be needed? What surface geophysics would be applicable to track the plume evolution? What communities are most concerned over time? During operation, the operations plan would have to account for possible leaks developing along any existing oil/gas well or other penetration. Luckily, in the case of Florida, this issue is probably less of a concern, as known oil and gas reserves are not located in Central Florida. As part of the detailed site selection within area number 4, site suitability studies using GIS would need to be conducted, including an evaluation of environmental justice concerns to pick northern, central, or southern site locations as final project site. Given the potential size of the CO₂ plume, once a site is finalized with the input of various stakeholder groups, the local host(s) siting package would need to be determined. For the example here, several different counties would be involved for any of the three site placements. If a fair fund compensation package was included, the actual distribution of the fund would need to worked out with host counties using a multicriteria decision or similar process. Lastly, the overall investment required to site, design, build, operate, and monitor the ULGSS would need to be determined. In this illustration, the annual cost would be approximately $807,000,000 if a tipping fee of $15/tonne CO₂ was utilized. If the high-end tipping fee of $29/tonne CO₂ was assumed, the annual cost of the ULGSS would be approximately $1,600,000,000. In either case, the working capital required to develop any ULGSS of reasonable commercial scale is very large. Therefore, the overall willingness to pay such a huge cost is very much an open question given that in Florida the per capita cost could be as much as $83 per year for these costs alone which do not include the additional cost of CO₂ capture.

ACKNOWLEDGMENTS

This paper was made possible by support of the University of North Florida (UNF) Academic Affairs summer scholarship grant. The authors also offer thanks to the UNF graduate program and the two anonymous reviewers whose comments significantly improved the original manuscript.