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Evaluation of Subtitle D Covers and Exposed
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To cite this article: J K Janga and K R. Reddy 2024
IOP Conf. Ser.: Earth Environ. Sci.
1337 012044
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GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
1
Evaluation of Subtitle D Covers and Exposed Geomembrane
Cover for Landfills: Sustainability and Resiliency
J K Janga1, and K R. Reddy1, *
1University of Illinois Chicago, Department of Civil, Materials, and Environmental
Engineering, 842 West Taylor Street, Chicago, Illinois 60607, USA.
*Corresponding author: kreddy@uic.edu
Abstract. Exposed geomembrane covers (EGMs) are considered as suitable alternatives to
traditional subtitle D soil covers with compacted clay layers (CCL) for landfill cover applications.
Compared to CCLs, which comprise various layers, including vegetation, erosion soil layers,
and barrier liners, EGMs offer benefits such as reduced resource use. There are several risks
associated with cover systems, ranging from climate-related shocks or stressors such as
earthquakes, droughts, and floods to local shocks such as excessive differential settlement due
to the uneven degradation of waste mass. Hence, their resilience and sustainability must be
analyzed, particularly considering the escalating impact of climate change and the growing need
to integrate resilience and sustainability principles into engineering designs and operations. This
study comparatively assessed the resilience and sustainability of three cover systems: EGM, soil
cover with geomembranes, and soil cover without geomembranes. A ((tiered quantitative life
cycle assessment of sustainability and resilience) framework was employed. The resilience
assessment was performed using a rating system, considering the technical performance of the
cover systems, along with the environmental, economic, and social implications of the failures.
Subsequently, a comprehensive sustainability assessment encompassing environmental,
economic, and social dimensions was conducted. A life-cycle assessment of all cover systems
was performed to evaluate environmental sustainability, and a cost-benefit analysis was
employed to compare their economic aspects. Social sustainability was evaluated using a rating
system. The assessments were combined to develop an integrated sustainability and resiliency
index. EGM was the most resilient and sustainable alternative for landfill cover systems
compared to traditional soil covers. These insights enable an objective comparison of resilience
and sustainability, facilitating informed decision-making.
1. Introduction
Any solid waste landfill requires a final cover system after it reaches its capacity, primarily to
minimize leachate generation and isolate waste from the surroundings [1]. To meet the design criteria,
federal regulations under RCRA subtitle D state that the final cover of a municipal solid waste landfill
must comprise an erosion layer underlain by a barrier layer. According to the requirements of Subtitle
D, the barrier layer should be a minimum of 18 inches of earthen material that with a permeability less
than or equal to the that of any bottom liner system or natural subsoil present, or a permeability not
greater than 1 x 10-5 cm/s (whichever is less). The erosion layer should have a minimum of 6 inches of
earthen material capable of sustaining native plant growth. An exposed geomembrane cover (EGM) can
be considered an alternative to the subtitle D cover system, as it can fulfill the main purpose of the
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
2
traditional cover system. Compared with the traditional cover system, a geomembrane cover is easy to
install, maintain, and replace, if required. The EGM can also have cost benefits over traditional landfill
covers because it eliminates the compaction efforts required for the soil layers in the subtitle D cover
system [2]. However, additional factors must be considered when designing an EGMs. These include
the provision of anchorage to resist wind forces, management of intense storm water runoff, and
management of penetration through the cover system [3]. In addition, it is important to consider the
resilience and sustainability of the proposed system when making final decisions regarding the same.
Resilience assessment is important when considering the resilience of the proposed cover system
compared with conventional systems. Sustainability assessment is important for understanding the
relative social, environmental, and economic benefits of each system [4]. This study assessed and
compared the sustainability aspects of the subtitle D cover system, with and without geomembranes,
and exposed geomembrane cover systems for landfills.
2. Methodology
Three systems were considered to assess resilience and sustainability: (1) cover system without
geomembrane (18 in thick compacted clay layer and 6 in thick erosion layer above waste (CCL)), (2)
cover system with geomembrane between the erosion layer and compacted clay layer (CCL-GM), and
(3) exposed geomembrane cover system (EGM) over the waste. The schematics of the three systems
considered in this study are presented in figure 1.
Figure 1. Schematics of different cover systems considered for the sustainability and resiliency
assessment
Although the terms "resiliency" and "sustainability" have been definitively defined by diverse agencies
and professional bodies, the challenge lies in effectively quantifying and incorporating these dimensions
into engineering designs. Reddy et al. [5] introduced a tiered quantitative assessment of life cycle
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
3
sustainability and resilience) framework [5]. This framework serves as a tool for quantifying the
dimensions of resiliency and sustainability in relation to products, systems, processes, and structures,
ultimately facilitating their integration for informed decision-making. In the context of the present study,
this framework was utilized to conduct a comparative assessment of the three landfill cover systems.
Resiliency assessment: To assess the resiliency of each cover system, each cover system is first rated
for its technical performance based on expert judgement and literature according to market research.
The assessment also includes the environmental, economic, and social impacts that could result from
the failure of cover systems. The scores are then summed and averaged to obtain the final resilience
index.
Integrated resiliency and sustainability assessment: The TQUALICSR framework outlines a
comprehensive sustainability analysis process for designs considering the triple bottom-line aspects. It
begins by categorizing design-related variables into requirements, criteria, and indicators. The
requirements cover environmental, economic, and social sustainability, which are broken down into
specific criteria. These criteria are associated with various indicators. The sustainability assessment was
performed as follows:
Sustainability assessments were conducted for a landfill covering an area of one acre. The Zion
landfill at 701 Green Bay Rd, Zion, IL, was considered for the landfill location, and MPC containment
systems at 4834 S. The geomembrane was supplied by Oakley Avenue Chicago, IL. The soil required
for the subtitle D cover system was collected from the surrounding areas within a distance of 5 km.
Many simple, complex, qualitative, and quantitative tools are available for sustainability analysis.
The available tools include monetary valuation tools, ecological footprint analysis, and composite
indicator tools [6- 8]. Sustainability analysis considers environmental, social, and economic
sustainability. A quantitative environmental sustainability analysis of the three systems considering their
life cycles was performed using SimaPro (Version 8.0), which is a specialized life cycle assessment
computer program. SimaPro has a general system that is applicable to any business, allowing life cycle
assessment trough out the life of the product or process. It is a well-known, internationally accepted,
and validated tool for sustainability assessments. Different methods are available in SimaPro to analyze
the environmental impacts of a product. The Tool for the Reduction and Assessment of Chemical and
Other Environmental Impacts (TRACI) was also used in the current study. TRACI is an LCA
methodology developed by the U.S. Environmental Protection Agency (USEPA) specifically for the US
and uses input parameters consistent with locations. TRACI compares the percentage contribution of
each system to ozone depletion, global warming, smog, acidification, eutrophication, production of
carcinogens and non-carcinogens, respiratory effects, ecotoxicity, and fossil fuel depletion.
An economic sustainability assessment was conducted based on the present costs of the materials
and processes involved in the construction of the cover systems. A social sustainability analysis was
performed considering the parameters given by Benoit-Norris et al. [9] and points were assigned based
on qualitative judgment. Their methodological sheet was developed based on the guidelines for the
social life cycle assessment of products launched at the International Organization for Standardization
(ISO) 26000 (social responsibility) meeting in Quebec City, Canada. These guidelines provide a
framework for assessing the social impact of a product across its lifecycle. The methodological sheets
contained indicators and subcategories of assessment that were defined to consider the socioeconomic
concerns of all impacted groups.
The indicators obtained from the environmental, economic, and social assessments were standardized
using a value function ranging as 0–1. This normalization facilitates easier comparison and integration
of diverse indicator values. Based on the specific form of the value function determined by the trends
(increasing or decreasing), curve shape (convex, concave, linear, or S-shaped), and maximum and
minimum satisfaction points (Smax and Smin), the value function is expressed as follows [10]:
(1)
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
4
(2)
where Vi represents the value function, B is a factor that maintains the values of Vi within the range of
0–1, S is the indicator value derived from the analysis, and Pi is a shape factor dictating the shape of the
curve (concave, Pi<1; convex or S-shaped, Pi > 1; linear, Pi ~ 1). Further, Ci denotes the x-coordinate
of the inflection point in the curves with Pi > 1 and Ki determines the y-coordinate of the inflection point.
These parameters were customized based on variable types and the definition of value curves, ensuring
the normalization of each indicator value within the range of 0–1. Moreover, it is crucial to incorporate
the environmental, economic, and social resilience scores acquired from resilience assessments as
additional indicators in an integrated evaluation. This holistic approach ensures the consideration of
resilience factors and contributes to the development of a comprehensive resilient sustainability index
that can be used as an objective value to simplify decision-making processes.
Once all indicators have been quantified, the next task involves assigning appropriate weights to each
indicator, criterion, or requirement. This weighting process relies on both the quality and quantity of
available data, and the relative significance of each variable compared to the others. In this study, the
specialized framework employed a multicriteria decision analysis tool known as MIVES [11]. Using
this method, the values of the acquired indicators can be effectively integrated. Consequently, the values
for the criteria, requirements, and final integrated resilient-sustainability index (RSI) were calculated
using the following formulas:
(3)
(4)
(5)
where Vind, Vcr, and Vreq represent the values of individual indicators, criteria, and requirements,
respectively, and Wind, Wcr, and Wreq denote their weights, respectively. Vfinal yields the ultimate resilient
sustainability index (RSI) based on a analysis. Notably, the weights of various requirements, criteria,
and indicators can be adjusted according to stakeholder preferences. This flexibility facilitates the
conduction of sensitivity analysis, thereby enabling the identification of important variables that affect
the RSI of the system. The resulting RSI values provide valuable insights for practitioners, stakeholders,
and decision-makers, guiding them in choosing the most optimal option among the analyzed alternatives.
The current study considers equal weights for all indicators; however, a more comprehensive assessment
can include an analytical hierarchy process (AHP) to determine the weights of each indicator, criterion,
and requirement to further improve the comprehensiveness of the assessment [12].
3. Results and discussion
3.1. Resilience Assessment
To perform the resilience assessment, a rating scale of -2 to +2 (worst to best, high negative impact to
low negative impact, high costs to low costs, etc.) was adopted. A resilience assessment was performed
considering the technical, environmental, economic, and social aspects of resilience.
The first phase of the resilience assessment considered the technical aspects of all three cover
materials. The permeability, service life, tensile strength, and landfill compatibility were identified as
the major indicators of the resilience of each cover system [13]. Ratings were provided for the CCL and
EGM based on the values for each of these aspects for the clay and HDPE geomembrane as provided
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
5
by Zhang et al. [13]. However, for the CCL-GM, the values were provided on a judgement basis,
depending on the relative performance compared with the other two systems.
The environmental, economic, and social implications of a failure, that is, the impacts on the triple
bottom line aspects if a cover system fails are rated on the same scale (-2 to +2), as shown in table 1.
The overall scores obtained for each system indicated that the CCL-GM and EGM were more resilient
than the CCL. In addition, the environmental, economic, and social resilience values obtained from this
assessment were used as indicators of environmental, economic, and social sustainability assessments
while developing the integrated RSI values to truly consider the resilience in the overall assessment.
Table 1. Summary of resilience assessment performed for all three cases
Resilience aspect
CCL
CCL-GM
EGM
Technical Resilience
Permeability
-1
1
0
Service life
-1
1
1
Tensile strength
-1
1
1
Compatibilitya
-1
1
0
Environmental Resilience
(Environmental implications of a failure)
Emissions due to failure
-1
-1
-2
Environmental impact of replacement
-2
-2
0
Impact on surrounding wildlife
-1
-1
-2
Environmental impacts of waste generated due to failure
-1
-1
0
Economic Resilience
(Economic implications of a failure)
Direct cost of replacement
-1
-2
-1
Indirect cost of replacement
(environmental costs, loss of labor, etc)
-1
-2
-1
Income from recycled waste (waste generated by failure)
0
1
1
Social Resilience
(Social implications of a failure)
Impact on quality of life of surrounding communities
-1
-1
-2
Health impacts to people working at landfill
-1
-1
-2
Total score
-13
-7
-7
aLandfill compatibility refers to the capacity of the cover system to withstand structural changes induced
by landfill content and its adaptability under varying landfill conditions. The material within the landfill
significantly influences the cover, particularly in terms of its ability to adapt to varying temperatures
and to resist punctures/cracks and aging.
3.2. Environmental Sustainability
Table 2 lists the input parameters used for the SimaPro analysis. As per the environmental impacts of
SimaPro using the TRACI method, the percentage contributions under most of the categories
considered- ozone depletion, global warming, smog, acidification, eutrophication, production of
carcinogens, production of non-carcinogens, respiratory effects, and ecotoxicity – were highest in CCL-
GM, followed by CCL and EGM, as shown in figure 2.
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
6
Table 2. Inputs for SimaPro
System
Material
Density (kg/m3)
Weight (kg)
Transport Distance (km)
CCL
Clay (18”)
1200
2220000
5
Silty loam (6”)
1300
802100
5
CCL-GM
Clay (18”)
1200
2220000
5
Silty loam (6”)
1300
802100
5
HDPE (60 mil)
940
5706
100
EGM
HDPE (60 mil)
940
5706
100
Figure 2. Relative environmental impacts of all the three systems analyzed using TRACI method
The EGM had a considerably lower contribution in all the categories considered compared to the
other two systems. Higher values for CCL-based covers were attributed to the emissions and effects
associated with the handling and transportation of soil used for the infiltration and vegetative cover
layers. The fossil fuel depletion was comparatively higher for EGM because of the energy consumed
during the manufacturing of HDPE, as considered by SimaPro (SimaPro uses the eco-profile dataset
created by Plastics Europe to quantify the life-cycle environmental impacts of HDPE Resin E) [14].
Although the distance between the vendor and the site was longer at 100 km in this case, the impact on
fossil fuel depletion was minimal compared to the impact of manufacturing HDPE geomembranes.
CCL-GM exerted a greater impact in all categories because it contained a combination of materials from
CCL and EGM. Fossil fuel depletion was the only category wherein the exposed geomembranes resulted
in considerable damage compared to the CCL. The production of carcinogens, respiratory organics,
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
IOP Publishing
doi:10.1088/1755-1315/1337/1/012044
7
respiratory inorganics, climate change, radiation, ozone layer effects, ecotoxicity,
acidification/eutrophication, and land-use damage were considerably higher for CCL and CCL-GM than
for EGM. Under most impact categories, the Subtitle D cover systems exhibited more environmental
impact than the exposed geomembrane cover system. While analyzing the results, it is important to
consider that the results obtained here are dependent on the location of the project and the location of
material suppliers for the project. The results can vary if on-site soil is used for the subtitle D cover
materials or if a geomembrane supplier is located at a different distance from the site considered.
3.3. Economic Sustainability
For economic sustainability analysis, a cost comparison of both cover systems was performed
considering the material, transportation, and placement costs, including the life cycle costing of all the
materials involved. The factors considered are listed in table 3. The material and process costs
considered for the clay layer included excavation, loading on trucks, transport, hauling from stockpiles,
spreading, and compaction, while the costs considered for silty loam for the vegetative cover layer
included excavation, loading on trucks, transport, hauling from stockpiles, and spreading [2]. Material
and transportation costs were considered for the geomembrane. The economic analysis results in table
3 indicate that CCL and EGM incurred similar costs; however, CCL-GM incurred a considerably higher
cost because it added up the costs of clay, silty loam, and the geomembrane.
Table 3. Calculated costs of the all systems of covers under consideration
System
Material
Volume (m3)
Cost ($)
Distance (km)
Total cost ($)
CCL
Clay (18”)
1850
14793
5
19684
Silty loam (6”)
616
4543
5
CCL-GM
Clay (18”)
1850
14793
5
39383
Silty loam (6”)
616
4543
5
HDPE (60 mil)
6
19662
100
EGM
HDPE (60 mil)
6
19662
100
19699
3.4. Social Sustainability
A social sustainability assessment was performed using a binary system [9]. The guidelines provide a
framework for assessing the social impacts across product life cycles. An assigned value of ‘0’
corresponds to no negative impact and an assigned value of ‘1’ corresponds to a negative social impact.
A higher total value implied a more negative social impact. Assessments are subjective and can vary
according to the assessor’s perspective. For example, more working hours are considered in the case of
the subtitle D cover system, considering the placement and compaction of the soil material. Health and
safety aspects were also considered for the subtitle D cover system, considering particulate matter
inhalation and probable accidents during the placement and compaction of the soil. The transportation
involved and the probable emissions during transportation are also considered for public health and
safety. Delocalization and safety of the local community were also considered while transporting and
handling soil materials. The probability of employment for local people is considered greater for the
subtitle D system than for the geomembrane system, as the placement and compaction of soil is expected
to create more employment opportunities. A summary of the results of the social sustainability analysis
is presented in table 4. The results of the social sustainability analysis showed that the exposed
geomembrane cover may be a more socially sustainable option than both subtitle D cover systems.
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
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doi:10.1088/1755-1315/1337/1/012044
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Table 4. Summary of social impact analysis (SIA)
Stakeholder group
CCL
CCL-GM
EGM
Workers
2
2
0
Consumers
1
1
1
Local community
3
3
1
Society
0
0
0
Total SIA value
6
6
2
3.5. Integrated assessment
An integrated assessment was performed to calculate the final RSI values of all the three systems for an
objective comparison. The values of the indicators, as shown in tables 1, 3, and 4 (resilience, economic,
and social assessments) and figure 2 (environmental assessment), were normalized on a scale of 0–1
using equations 1 and 2 by assuming different shape functions depending on the nature of the variable.
The values of the indicators were used to calculate the final RSI using equations 3, 4, and 5. For this
study, the weights of all indicators were assumed to be of equal importance, and further calculations
were performed. The final RSI values obtained, as shown in figure 3, indicates that the EGM was the
most suitable landfill cover system.
Figure 3. Integrated resilient sustainability indices of all three systems
4. Conclusions
This study described the resiliency and sustainability assessment of the subtitle D landfill cover system
compared to an EGM system. The results suggest that EGM can be a better option than the Subtitle D
cover system from sustainability and resiliency perspectives. The resilience assessment indicated that
the EGM system was equally resilient to the subtitle D cover system with a geomembrane, considering
the technical, environmental, economic, and social aspects of resilience. Although the economic
sustainability analysis provided similar results for CCL and EGM, the environmental and social
sustainability assessments imply that EGM is a more sustainable option than the other two systems. The
importance of the current study lies in the assessment of resiliency and sustainability, as well as the
development of a comprehensive resilience–sustainability index that can be used as a metric to aid in
GeoShanghai 2024 – Volume 8
IOP Conf. Series: Earth and Environmental Science 1337 (2024) 012044
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doi:10.1088/1755-1315/1337/1/012044
9
decision making. Although the final RSI indicates that EGM is a better option than the other systems,
this analysis was project-specific; consequently, the results may change considerably based on the
location of the project and the distance of the raw materials from the site.
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