INSTALL AN OVERLINER OR EXCAVATE AS PART OF LANDFILL MINING PROJECT: BEST APPROACH FOR A LANDFILL EXPANSION OVER AN UNLINED LANDFILL

Transcription

1 INSTALL AN OVERLINER OR EXCAVATE AS PART OF LANDFILL MINING PROJECT: BEST APPROACH FOR A LANDFILL EXPANSION OVER AN UNLINED LANDFILL Patrick M. Bell Cornerstone Environmental Group, LLC Middletown, New York Derek T. Long Cornerstone Environmental Group, LLC Middletown, New York Martin L. Ryan Ocean County Landfill Corporation Manchester, New Jersey Prentiss A. Shaw Cornerstone Environmental Group, LLC Middletown, New York OVERLINER OR EXCAVATE: BEST APPROACH FOR A LANDFILL EXPANSION OVER AN UNLINED LANDFILL Many landfills currently operating have an old unlined landfill area that was operated more than 30 years ago and is now closed and capped. In many cases, these unlined landfills occupy a significant portion of the overall solid waste footprint and, due to settlement over the years, these areas represent a large volume of unused airspace above the current cap elevation. When sites are constrained from expanding laterally one viable option is to expand using the footprint of these old landfills. This paper/presentation explores two approaches to capture this available airspace. 1. Install an overliner system on top of the old landfill and piggyback onto the adjacent landfill areas. 2. Mine (excavate) the waste from the old landfill and install a traditional base liner system within the permitted footprint. Every landfill facility has its unique characteristics and special conditions that must be accounted for when deciding what to do with old unlined landfills. However, before deciding on how to proceed with a design an evaluation of the best fit for a specific facility should be completed. Any such evaluation should include a cost benefit analysis that takes into consideration the different design elements, the environmental concerns, and improvements and costs of each design approach. This presentation will share the key components of one such evaluation that recently led a landfill owner to choose the landfill mining (excavation) option. The table below summarizes some pivotal decision making criteria considered that drove the project toward the particular expansion approach. Each will be discussed in detail during the paper/presentation. Key Criteria Overliner System Landfill Mining (excavation) Airspace gain Less due to fill material More due to soil recovery and increased densities Geotechnical evaluation Differential settlement evaluation is critical Stability of adjacent cells is critical Base grade configuration More complicated configuration due to differential loading and post-settlement requirements Generally a more traditional configuration Reclaimed daily cover None Up to 50% or more Construction costs Source of fill material is driver Mining and screening is driver Base/Overliner costs Higher due to subgrade gas collection system More traditional May require temporary caps on adjacent cells Air permitting process Traditional approach Addition of screening equipment Length of construction Consider lead time for fill material Longer lead time necessary for excavation activity TABLE PROJECT DECISION MAKING Bell, P. 1

2 SECTION 1 INTRODUCTION Active landfill facilities with unlined cell(s) on site may benefit from a landfill expansion, either through installation of an overliner or excavation of waste (known as landfill mining) and installation of a new baseliner. Both approaches allow landfill facilities to expand and accept new wastes on an existing footprint that has already been used for waste disposal. Disposing of new wastes in an existing waste disposal footprint is a sustainable approach to landfilling. Accepting additional wastes at a site results in additional revenue and extends landfill life, directly reducing the need for a new replacement landfill facility. The big question landfill owners must ask themselves is: Is an unlined landfill cell expansion practical at my facility, and which approach makes more sense for my site? The answer can have a huge impact, since there are more than 3,500 active municipal landfills in the United States, many of which began operations before landfill liner regulations were in effect (EPA, 1995). Therefore, it is likely that many active landfill facilities have an unlined cell on the property. If only 5 percent of these sites turn out to have unlined cells suitable for redevelopment, that means that more than 175 active municipal landfills may be missing out on potential airspace gained from landfill expansion over an unlined landfill cell. If one assumes that these 175 landfills with unlined cells could expand vertically an additional 50 feet over a 30-acre area, this would the equivalent of gaining more than 400 million cubic yards of airspace without a single facility expanding from the currently permitted landfill area. Construction Approaches Overlining an existing unlined landfill cell involves the construction of a baseliner system on top of an existing cell and filling the cell to existing permitted final grades for the landfill as a whole. This approach is discussed in detail in Section 2. LF mining involves excavating existing waste and soils in an unlined landfill cell. Upon completion of the excavation, a new baseliner system can be constructed within the footprint of the existing cell. This approach is discussed in Section 3. Every landfill facility is unique and it is hard to generalize on which approach is better. Deciding which approach to use at a particular site can be difficult and there are many specific design, operational, and environment considerations for both overlining and LF mining. One site that has made a decision between overlining and LF mining is Ocean County Landfill (OCLF), a privately owned and operated sanitary landfill located in Manchester Township, New Jersey. Section 4 presents the process that OCLF went through in deciding between completing an overliner or an LF mining project at their site. Section 5 presents the factors that a site should use to evaluate completing an overliner or LF mining project. These factors can help identify the site-specific criteria that will ultimately dictate which approach is better suited for a particular site. Examples of Successful Expansions Examples of various landfill facilities around the United States that have taken advantage of the unused airspace above unlined landfill cells include: A landfill facility near Kansas City has overlined approximately 75 acres of waste and has plans to construct overliner on an additional 65 acres in the near future. By the end of this construction project, the facility will have taken in an additional million cubic yards (CY) of waste. An overliner construction project is scheduled to take place next year at a landfill outside of Detroit, which will increase the landfill site capacity by 7 million CY of waste. An existing landfill facility in Kentucky has an area of unlined landfill of approximately 18 acres that currently holds almost 1 million CY of material. A LF mining or overliner construction project at this facility has the potential to gain an estimated additional 2 million CY of airspace, almost tripling the capacity of the existing cells. The owner of the facility is just now beginning to look into the potential of these existing unlined cells. At a landfill facility in New York, the original grading of an unlined landfill was so poor that an estimated 300,000 CY of additional waste had to be brought in just to get the slopes to final grades so the site could be capped. Even if landfill expansion is out of the question at this site, there is still airspace potential in getting landfill cells to permitted grades for more effective stormwater management. Bell, P. 2

3 In the past, there had been somewhat of a preconceived notion that it is best not to disturb an existing unlined landfill cell due to its lack of proper containment. However, with land at a premium in some areas, and the predictable push back of new landfill facility construction projects, remaining at an existing landfill site for as long as possible is a main priority of all landfill owners. Therefore, conducting responsible construction activities that improve the containment of existing and future wastes is truly a win-win for all involved. SECTION 2 OVERLINER DEVELOPMENT APPROACH Overliner and Piggyback Depending upon the region, the terms overliner and piggyback may vary. For this discussion the terms are defined as follows: As depicted in Figure 2-1, an overliner is a base containment system constructed over in-place waste prior to placing additional waste up to some defined elevation. As depicted in Figure 2-2, a piggyback approach is a method of connecting two adjacent cells to capture all the airspace between the two cells. Typically there is a cell already filled and as waste is placed in the new cell it is piggybacked on top of the previously filled cell. Why an Overliner is Necessary: Airspace is king in the landfill business and finding avenues to effectively maximize this asset within a facility footprint is a priority. Therefore, filling the entire landfill footprint up to a permitted final grade is the goal. However, many sites that have been operating for decades may have a variety of baseliner systems within the landfill footprint, ranging from no baseliner (at a very old site) to a pre subtitle D liner system. Also, many of these areas have settled, which means there may be potential airspace. However, regulations prevent filling in these cells, because the containment system is substandard. Therefore, to capture the airspace and place additional waste in this portion of the landfill footprint (piggyback), an overliner system is necessary. The Overliner System: Similar to a baseliner system, an overliner system needs to meet certain performance criteria. Subtitle D regulations do not define an overliner system and this lack of definition also exists in many state regulations. With overliner components not defined, many designers use the baseliner regulations as the design criteria. In some states this means that a double composite liner is required, while in others it means a single composite system. There are some regulators that may allow the components making up the existing baseliner to count toward meeting the overall containment system (See Figure 2-3). For instance, if a cell had a clay baseliner in place this containment component may eliminate the need for clay in the proposed composite overliner system. There are also cases in which cells may have a temporary or final cap in place, and, if the settlement analysis is favorable and the grades are adequate, this cap system may be retained and its components counted toward achieving an adequate overliner system as illustrated in Figure 2-4. Design Challenges of an Overliner/Piggyback System There are always site specific challenges associated with landfill design but designing an overliner subgrade system adds a few additional challenges, including these factors that should be considered for the development of the subgrade layout for an overliner system: Accessibility to existing features associated with adjacent cells (manholes, cleanouts, gas headers, leachate headers, utilities, etc.) Leachate flow lengths Subgrade gas collection Post-settlement grades Cut and fill volume requirements Maximization of airspace Tie-ins with adjacent cells Subgrade Design (grading): The differential settlement analysis, discussed below, generally drives the necessary design grades and slopes. To achieve the proposed grades (see Figure 2-5) that maximize the potential airspace, the subgrade design takes into consideration the design criteria listed above, and generally involves a combination of both cut and fill rather than all fill or all cut. All landfill designs require an analysis of settlement but for a baseliner design it is more critical for the final cover rather than the subgrade, unless there are questionable underlying soils. In the case of an overliner system, the differential settlement analysis is a critical design task in achieving an optimal subgrade design that Bell, P. 3

4 accounts for waste decomposition throughout the life of the landfill. Similar to a baseliner design, the post-settlement grades must meet the regulated slope requirement for both the leachate collection lines and cross flow slope. Maintaining a positive slope on the leachate collection lines despite encountering differential settlement is imperative, as depicted in Figure 2-6. There are a number of considerations for this type of analysis associated with an overliner system: Uncertainty of existing waste composition extent and age. Varying subgrade condition, including heterogeneous underlying waste, and fill consisting of recompacted excavated waste and/or clean fill. Varying overburden pressure along collection pipes combined with changes in underlying waste depths create a critical analysis point where the collection pipe penetrates the liner system (if using manholes). Subgrade LFG collection: A gas collection system needs to be incorporated when proposing a containment system over waste, whether for a temporary or final cap system or an overliner. However, with a cap many LFG collection systems include placement of vertical wells that penetrate the cap geomembrane and a network of transmission lines above the geomembrane that convey the gas to perimeter LFG headers. Vertical wells are not ideal for an overliner system because they need to penetrate the containment system and continually be raised as waste operations progress up to final grade. A horizontal system (see Figure 2-7) is an alternative to vertical wells, but this too has its challenges, including: Differential settlement, as discussed earlier. Penetration of containment system at the perimeter since the system is below the overliner. Accessibility of valves. Condensate management. Tie-in to Adjacent Liner Systems (Cap or Baseliner): Ideally the overliner components should tiein to the adjacent cells baseliner system to provide a sealed containment system, as depicted in Figure 2-8. Therefore it is important to have access to as-built information for all adjacent cells. There may be instances where the baseliner anchor trench is not easily accessible and alternative designs may be warranted. Leachate Management System: The leachate management system design for an overliner is quite similar to a baseliner design in that the existing system elements must include adequate capacity in the headers, pump stations, storage and treatment facilities. However, there are a few design elements that can be challenging with overliner designs, including relocating utilities between the adjacent cells as depicted in Figure 2-9 and ensuring access to proposed cleanouts as shown in Figure Construction Challenges of an Overliner/Piggyback System Cell Sequence to Balance Cut/Fill to Limit Double Handling: One item that can drive up the cost of any construction project is how many times materials must be handled. Many overliner designs require both cut and fill to meet the proposed subgrades. Therefore the ideal construction sequence would result in a balance of cut and fill material. Any material cut could be used as fill in the same phase. An excess of either results in double or triple handling and additional costs as illustrated in Figure A design requiring additional fill at a facility that is dirtpoor requires the importation of material. Generally this imported material must be stockpiled due to space constraints within the overliner footprint and the quantity required to meet production rates when construction begins. A design resulting in excess cut needs to be disposed of at an operational landfill. Typically the volume being cut is not large enough to warrant screening the material; therefore, the entire volume of cut, which may include significant percentages of soil, is using valuable permitted airspace. Varying Subgrade Conditions: When constructing an overliner system the subgrade materials can vary from underlying waste, re-compacted waste and/or clean fill as shown in Figure It is difficult enough to grade soils at a 1 percent slope; grading waste or soils on top of exposed waste to exact design grades is even more challenging. The workability and compaction differences need to be taken into account when developing construction costs and schedules. Delineated Waste Excavation Instead of Mass Excavation: Overliner designs may require some excavation into the existing waste mass, but unlike a mass excavation, the limits of excavation (meeting the design grades) are critical to avoid over-excavating, which would then require additional backfill material. In Bell, P. 4

5 addition, mass excavation can usually be accomplished with larger equipment and excavation continues until virgin ground is encountered. Both result in high production rates. Environmental Perceptions: Overliner projects are always on lands that have already been approved for solid waste management purposes, and previously used for waste disposal, and this can generate a very positive green perception of the project. In addition, many of the typical potential environmental impacts analyzed for expansions have already been addressed. While there are environmental perception challenges with any landfill design, there are a few distinctive perceptions associated with piggyback and overliner designs that should be considered. For each of these concerns, answers should be planned in advance to address the issues. Loading Existing Waste Mass Squeezing It : The general perception is that all the new waste is going to load the existing waste mass onto a non-compliant containment system, squeeze out remaining leachate and contaminate the surrounding properties. A variety of predesign studies can be conducted to address this issue, including test-pits, waste characterization, groundwater modeling. Additional design elements can be incorporated. Unlined Landfill Cell Still in Place at Facility: Constructing an overliner system still results in an area of the landfill that has a substandard liner system and can be viewed as an environmental liability. A variety of environmental controls can be incorporated to address this issue. Disturbing a Capped Cell Will Release Odors: The general perception is that once the cap is removed and the underlying waste is exposed the site and surrounding properties are going to be inundated with methane and odor. Understanding the waste composition state through test pits and biochemical methane potential (BMP) testing is well worth the investment. A thorough test pit program at a range of depths provides relevant design parameters to allow sufficient controls to be incorporated and provides answers to this question. SECTION 3 LANDFILL MINING AND BASELINER DEVELOPMENT APPROACH LF mining has been defined as the excavation and mechanical processing of previously landfilled materials to recover resources (such as land) and to mitigate environmental impacts. As presented in the EPA s Landfill Reclamation Fact Sheet, there are three (3) steps to follow in completing a LF mining project; excavation, screening, and processing for reclamation of recyclable material or disposal. (EPA, 1997) Excavation entails excavating and placing material in manageable stockpiles and separating out any bulky materials in the waste (for example, appliances). Screening entails using a trommel or vibrating screens to separate the waste and soil in the excavated material. (a 2-1/2-inch screen would be used for recovery of daily cover). Processing would include using the recovered soils at the landfill and processing the waste for commodities (copper or steel) or sending it a municipal waste combustor for energy production. (EPA, 1997) While LF mining may provide revenue through the recovery of commodities, for many landfills, airspace and soil are the most valuable things recovered. Cover soil recovery could result in large cost savings for a site required to import soils for this purpose. The recovery of airspace will be realized if a new Subtitle D baseliner is installed in the excavated footprint when the LF mining is complete (see Figure 3-1). During the duration of the LF mining project, the excavated waste will need to be relocated, which will consume airspace in the active area. However, the waste will be placed at a higher compaction density than when it was originally placed. To ensure that a LF mining project is feasible a site must confirm that they have enough available airspace to handle both the incoming waste and the waste that will be relocated. Additionally, excavating an unlined landfill and installing a Subtitle D baseliner will reduce a site s environmental exposure by removing a potential source of contamination. While completing a LF mining project and subsequent baseliner installation may have numerous enticing aspects, there are many design and construction challenges to be aware of prior to moving forward, discussed below. Design Challenges - Baseliner An advantage associated with completing a LF mining project is the ability to install a baseliner that follows accepted design standards (0.5 percent pipe slope, cell floor cross slope of 2 percent, and 3:1 side slopes, etc.) after the excavation is complete. The horizontal limits of the new baseliner will likely be based on the permitted limit of waste associated with unlined landfill (even if the waste is discovered to be Bell, P. 5

6 placed beyond this limit) and the limits of any adjacent lined landfill cells. The depth of the existing waste should be identified by completion of a test pit and boring program, though it is probable that deeper pockets of waste will be discovered as the excavation proceeds. A site should consider taking a conservative approach and establish the baseliner grades using the minimum separation distance between groundwater (or bedrock) and the baseliner. This approach provides a minimum excavation volume and maximum airspace volume which could be used in determining if the project is economically feasible. Due to the unknowns, a site should include a contingency to account for the possibility of waste excavation below the established baseliner grades or outside the permitted limits of waste. After establishing the limits of waste excavation and baseliner installation, an evaluation of the following design criteria should be completed, including: Stability Analysis Baseliner Configuration Leachate Containment Stability Analysis: Similar to any new baseliner construction requirements, the baseliner design should include a stability analysis to ensure the long term stability for both the baseliner and adjacent cells. Additionally, a stability analysis should be completed to ensure that the LF mining activities will not adversely impact the site in any way. To maximize excavation volume and limit the excavation footprint, the use of an excavation slope of greater than 2:1 may be acceptable for excavating the waste along the perimeter of excavation. In the areas of excavation along adjacent cells, the stability analysis should be used to establish a buttress to prevent a failure of the adjacent cell. Depending on the size and configuration of the buttress it may not be possible to excavate all of the inplace waste in these areas. Baseliner Configuration: Due to the impact the waste relocation may have on a site s available airspace it may be necessary to construct the new baseliner in a phased approach. This may also help a site offset the excavation project s economic burden by gaining revenue from landfilling in the area where the portion of the baseliner is being constructed. The phased approach would allow the site to operate the leachate collection system for each phase independently. Having separate systems would allow flexibility in the design of future cells if warranted due to the LF mining project (see Figure 3-2). Leachate Containment: To ensure leachate containment the new baseliner will either need to be directly connected with the baseliner of the adjacent cells (see Figure 3-3) or, if warranted by site conditions, a portion of the new baseliner should be installed as an overliner onto an adjacent cell. If an overliner system is installed an evaluation must be conducted to determine the limit of the overliner to ensure leachate containment. Due to the changing design standards for baseliner construction over the past 30 years, the type of baseliner systems may vary widely in the adjacent cells. Sites contemplating an LF mining and baseliner project should complete an evaluation of the existing site infrastructure to determine additional improvements that may be needed outside the area of construction. The old unlined landfill was most likely never included in long term planning for the site. It may therefore have limited existing infrastructure in close proximity to the new baseliner area, or infrastructure not sized properly to handle the addition of the new baseliner area. An evaluation of the existing infrastructure should include: Leachate Collection and Conveyance System Leachate Handling System Gas Collection and Control System (GCCS) Leachate Collection and Conveyance System: Within the new baseliner area the leachate collection system will most likely consist of a pipe and stone system. The required excavation associated with LF mining may ultimately result in a thick waste wedge in the new baseliner and a pipe loading calculation should be completed to ensure long term pipe integrity. Due to the depth of the baseliner grades, the type of leachate conveyance system a site uses may need to be changed. A site may need to move from liner penetrations and gravity headers to a sump and sideriser design due to constructability issues. Leachate Handling System: There may not be an adequate leachate handling system in close proximity for use with the new baseliner. As a consequence, a site s handling system may require improvements, including force main or gravity header installation, addition or Existing Landfill Bell, P. 6

7 upgrades to pumps to ensure proper handling of the leachate at the site. Or the opposite may occur, in which the site s existing leachate handling system may be within the footprint of the LF mining excavation and the site might be required to temporarily or permanently relocate its handling system to allow the excavation to occur (see Figure 3-4). An evaluation of the handling system should also include analyzing the disposal point of the leachate (on-site treatment plant, or on-site storage with discharge to a POTW) to ensure it can handle the additional flow associated with the development of the old unlined landfill area. Gas Collection and Control System (GCCS): Similar to the leachate handling system, the evaluation of the site s GCCS should determine if provisions for collection are in close proximity and if it s large enough to handle the flow, if there will be an impact on existing infrastructure, and if the site s existing end point (LFGTE facility or flare) is large enough to handle the anticipated flow. In addition, there should be provision for collecting subgrade gas from waste left in place under the baseliner. Most likely horizontal collectors would provide the most adequate gas collection for these areas, but this should be evaluated based on the individual site. Design Challenges LF Mining After setting the overall design parameters for the baseliner project the design parameters for the LF mining can be completed. This should include addressing the following: Excavation Grading Interim Gas Collection Temporary Capping Stormwater Control Excavation Grading: The excavation grading for a LF mining project should incorporate the following key design detail: Overall excavation and phasing Identify the entire area of excavation and identify potential areas of impact from the excavation. Excavation along the perimeter Area of excavation will ultimately become the outside limit of baseliner so area should be left with a 3:1 slope. Area may require excavation slope greater than 2:1 to maximize waste removal. Excavation depth Should be based on the assumed depth of waste but additional parameters should be included to identify the procedure for excavating beyond the assumed depth. Excavation near adjacent cells Existing waste may need to be left in place to ensure stability. Interim Gas Collection: If a site has active gas collection in the old unlined landfill, provisions must be made not to interrupt the gas collection system outside the area being excavated. It may be beneficial to phase the excavation to keep the existing system functioning as long as possible. Temporary Capping: In the excavation areas near adjacent cells waste may need to be left in place to ensure stability. In the interim between LF mining activities and baseliner installation a temporary cap should be installed to limit a site s environmental exposure. Since this is a temporary condition, exposed geomembrane could be used but there must be provisions for handling stormwater runoff. Stormwater Control: During LF mining the area of excavation must be protected from stormwater run-on to minimize creating leachate in the area of waste excavation. Stormwater diversion berms and cut-off swales should be constructed as excavation progresses to eliminate the exposure of waste. Provisions should be made for removal of leachate in the area of the active waste excavation. Construction Challenges LF Mining Once the LF mining begins there will be construction challenges faced and a site should be prepared to address the following: Excavation and processing rate Odor control Hazardous waste materials On-site traffic Excavation and Processing Rate: To manage the need for cover soils, available airspace, and baseliner construction, a site will need to establish an excavation and processing rate that is optimal for their needs. The use of a low rate may result in a deficit of available cover soils, while the use of a high rate may consume too much of the available airspace. Bell, P. 7

8 Odor Control: Due to the age of the waste odors from the waste may be minimal and if so, recovered soils can be used as cover in the excavation area. Even with an older waste there is the possibility of releases of gases that could cause odor and safety issues at the site so safety procedures should be in place to address this potential. Hazardous Waste Materials: Due to the age of waste there may be hazardous waste that is uncovered during the LF mining. The site should have proper hazardous waste material identification and handling procedures in place. On-site Traffic: Due to the need to relocate waste from the LF mining there will be an increase in on-site traffic, which can be mitigated by the use of separate haul roads for waste excavation traffic and the incoming waste traffic. Additional measures may include setting up a second working face to handle the relocated waste. Construction Challenges Baseliner Upon completion of the LF mining, the baseliner will be installed. Since the installation of a baseliner is typical activity at a landfill construction challenges should be minimal. However there are still some challenges and a site should be prepared to address the following: Baseliner installation over existing waste Baseliner connection Infrastructure improvements Baseliner Installation over Existing Waste: To install a baseliner over in-place waste, measures will be required to prevent any penetrations of the subgrade gas collection system into the baseliner system. This may include the installation of a geosynthetic material below the secondary liner to provide an added level of protection. Baseliner Connection: When the new baseliner is installed it will require detailed work to expose the limits of the existing baseliner and allow for the connection of the components from the two baseliners. Additional construction challenges may be discovered in the field if the components of the existing baseliner don t reflect what was used as the design basis Infrastructure Improvements: While improvements are not uncommon with the addition of any new baseliner at a site those required in this instance may be extensive since this area may not have been part of the site s long term plan. Environmental Perceptions The completion of a LF mining and baseliner installation project may carry with it some environmental perceptions that a site should be prepared to address are: Increased Site Emissions Increase to Total Site Volume. Increased Site Emissions: The perception may exist that the activities related to LF mining will increase the total emissions created by a site. While there will be additional equipment on-site required to complete this should be offset by the decrease in off-site traffic for the delivery of soils to the site. Increase to Total Site Volume: Due to the relocation and re-compaction of waste, there may be a perception that an LF mining project is adding airspace; however, while the relocation and re-compaction of waste may provide a higher compaction rate than when originally installed, the overall permitted airspace for a site would not be increased. SECTION 4 - OCEAN COUNTY LANDFILL CASE STUDY Introduction Ocean County Landfill (OCLF) is a privately owned and operated sanitary landfill located in Manchester Township, New Jersey, approximately 50 miles east of Philadelphia, and 70 miles south of New York City. The landfill serves the 33 municipalities comprising the County of Ocean, with an area of 915 square miles, and a population of 580,000. Early Analysis of Landfill Reutilization OCLF has served the waste disposal needs of the County of Ocean in a public/private partnership for many decades. Siting another landfill in the County would be extremely difficult due to strict regulations imposed by the Pinelands National Preserve in the western areas of the County, and State of New Jersey coastal development regulations in eastern areas. As such, it is imperative that the capacity available at OCLF be utilized as efficiently as possible to extend the lifespan of the facility. OCLF began an evaluation of possible alternatives for a capacity expansion of the facility. In the early 2000 s, an analysis concluded that a lateral expansion of the landfill footprint is not feasible due to the proximity of surrounding neighborhoods and wetlands located in the facility s buffer areas. Bell, P. 8

9 A vertical expansion of the landfill would also be challenging due to height restrictions imposed by the New Jersey Department of Environmental Protection (NJDEP), with a focus on sensitivity to the surrounding community, as well as engineering design constraints. The current maximum approved elevation is 175 above mean sea level (amsl). (Existing grade at the site ranges from amsl.) The focus for expansion then shifted to a 60-acre parcel known as the Existing Landfill, as illustrated in Figure 4-1, an unlined portion of the site where waste placement occurred from 1972 until the early 1980s. The Existing Landfill was capped in the mid-1980s with HDPE, and has an active landfill gas collection system. Current elevations of this area range from amsl. The facility s engineering design consultants, Cornerstone Environmental Group, LLC (Cornerstone), saw an opportunity for additional waste placement in this area without the need for a horizontal footprint expansion or a vertical expansion beyond the currently approved maximum elevation for the site. Test Pit Program In 2006, Cornerstone prepared an application on behalf of OCLF for a Waste Disruption Permit for the Existing Landfill to obtain waste characterization, condition, and stage of decomposition data, as well as average thickness of cover soils above and below the HDPE geomembrane. It should be noted that at this time LF mining was not contemplated, so overall depth of the waste was not evaluated, but is assumed to be approximately 50 feet. The Waste Disruption Permit was issued in February 2007 and test pits were excavated in July Twenty test pits were excavated, of which 11 were shallow test pits that did not penetrate the geomembrane, while 9 were deep test pits at an average depth of 23 feet for purposes of waste characterization. A Report of Findings was prepared and submitted to NJDEP in September 2007 and this information was later used to evaluate Original Landfill redevelopment design alternatives, which came to be known as the Sustainable Landfill Project (SLP). Biochemical Methane Potential (BMP) tests were used to determine the amount of methane that could be produced from remaining organic matter, by calculating the methane yield as a percentage of volatile solids. This analysis is useful for assessing the stage of decomposition of the organics in the waste. BMP testing showed that the waste material was largely decomposed, minimizing the potential for fugitive landfill gas emissions and odor. Cover soils above and below the liner were generally thicker than anticipated. Consistent with the recollection of site personnel present at the time of the operational stage of the Original Landfill, a large amount of daily cover soil was used during waste placement operations. No perched leachate was encountered. Overliner Design Based on these findings, OCLF decided to pursue redeveloping the Original Landfill using an overliner/piggyback cell. This option was viewed at the time as the most efficient way to redevelop the area without large scale disruption of the existing waste. After evaluating several design options, OCLF and Cornerstone requested a pre-application meeting with NJDEP to present preliminary concepts and to obtain initial feedback on the project. The overfill area encompassed approximately 72 acres, including areas overlapping on cells adjacent to the Original Landfill. Although NJDEP agreed that the project fit well with sustainable initiatives being promoted to maximize existing landfill capacity in the State, they ultimately required a major modification to OCLF s Solid Waste Facility Permit because the project would provide an additional 6,000,000 CY of airspace. After finalizing the challenging subgrade design and infrastructure requirements, a permit modification for the SLP project was filed with NJDEP in September A detailed differential settlement analysis was performed, using data obtained from the Test Pit Program. There were a number of key differences in the SLP design compared to that of the typical OCLF baseliner, including: Steeper slopes of leachate collection lines to ensure positive drainage of the overliner. Typical OCLF leachate collection lines have been installed with percent typical slopes, while the overliner used a two-stage design with 4.5 percent in interior portions of the cell, and 6 percent closer to the liner penetrations to the collection manholes. A rather complex subgrade design with leachate laterals draining the subcells south to north, and west to east in areas. Installation of subgrade gas collectors in the Original Landfill waste remaining in place. A construction staging plan with a goal of balancing and timing the cuts to fills to the greatest extent possible. Bell, P. 9

10 This permit modification was subsequently approved by NJDEP in September Related Project Highlights Benefits of Landfill Mining While the SLP overliner project was being designed and permitted, OCLF and Cornerstone pursued an LF mining-related initiative on an adjacent parcel that contained the Manchester Township Landfill, which operated from the 1940s to the 1970s. This unlined landfill had never been properly closed and OCLF had agreed to acquire it from the Township of Manchester and relocate the waste to the lined cells at OCLF. A Waste Disruption Permit Application was filed with the NJDEP in July 2008, and approved later that year. Excavation activities commenced in January 2009 and ended in April 2010, during which more than 600,000 CY of material was excavated. Many valuable lessons were learned, including: Odor from the excavation activities was negligible. Extensive air monitoring revealed no health and safety concerns. Leachate and stormwater issues were easily managed by proper construction staging. No extensive nuisance control measures were necessary for issues such as vectors, dust or litter. A large quantity of cover soil was used during the landfilling operations, some of which was able to be recovered for reuse at OCLF. In light of the positive experience and lessons learned from the Manchester Landfill excavation, the management of OCLF reevaluated the design of the SLP as an overliner, and began to reconsider mining the Original Landfill. Of particular interest was the potential to generate a large quantity of soil available for reuse as daily and intermediate cover. OCLF uses more than 200,000 CY of soil each year for cover material purposes alone, not including soils required for construction of cell baseliner or capping systems. The vast majority of these materials are imported, as most of the onsite borrow areas have been exhausted. The SLP in its current overliner configuration would have added to the soil import needs, since more than 650,000 CY of fill material would be necessary to establish the subgrade design. OCLF then made the decision to explore landfill mining options, and Cornerstone evaluated several scenarios, ranging from partial excavation with the goal of balancing the overall cuts and fills for the SLP, to a complete excavation to elevation 45 amsl +/- to remove all waste down to the cell floor. This assumed depth of waste was based on groundwater elevations, and base elevations of adjacent cells and the Manchester Landfill excavation project. It was not deemed necessary to excavate additional test pits or borings, but instead a worst case waste quantity was used for the purposes of the evaluation. Besides the engineering and construction challenges of a project of this size and nature, financial constraints had to be considered. OCLF pays for all construction activities and closure/post closure requirements from escrow accounts funded from the facility s tipping fees. Cornerstone spent considerable time preparing construction phasing and filling sequence models to enable a detailed analysis of the impact of a landfill mining project of this magnitude on OCLF s financial plan. Ultimately, OCLF selected a plan that calls for a waste excavation and baseliner construction sequence broken up into 3 phases stretching out over 15 years (see Figure 4-2). The phasing plan balanced the anticipated need for having cells available for waste placement with the minimization of impacts to the facility s funding requirements for construction and closure/post closure. Over 4,000,000 CY of waste will be excavated and relocated to lined cells. All waste will be removed down to the cell floor, but for safety and stability reasons, and to protect the integrity of other cell baseliners, some waste will remain on slopes adjacent to other cells. The waste excavated will be screened to recover soil material for use as daily/intermediate cover. Industry data suggests 50 percent or more of the excavated material may be comprised of in-place cover soils and decomposed fine organic waste which could be reclaimed for cover material. As such, the project could generate 2,000,000 CY or more of cover soil for OCLF s reuse, meeting the facility s needs for approximately 10 years, and offsetting the need to purchase and import this material. A complete excavation will also enable OCLF to construct a double composite liner system in an area that is currently unlined. This will result in additional leachate containment and mitigate the potential liability associated with an unlined landfill, which would largely remain if an overliner were to be constructed. It also allows a much more typical cell subgrade design, Bell, P. 10

11 featuring standard leachate collection line slopes. Minimizing seams and scrap material associated with irregular HDPE panel layouts will also facilitate baseliner construction. Excavating the Original Landfill will also enable more efficient landfilling in this airspace using modern techniques and compaction equipment, as well as more efficient use of cover soils. It is estimated that this option could allow for an additional 1,250,000 CY of waste to be placed in the same envelope of airspace, which equates to approximately 1.5 years of additional site life, based on predicted waste acceptance rates and effective densities (see Figure 4-3). Cost per Cubic Yard When deciding between overlining and LF mining one of the biggest and most influential deciding factors is cost. The most telling cost for comparison is the construction cost per cubic yard of airspace gained. While one approach s capital cost may be higher than the other, the cost per cubic yard of airspace the construction creates is a better gauge as to which approach is better financially. Since the Ocean County Landfill has considered both options, there is some representative cost data available. The construction cost of an overliner at Ocean County Landfill is $16.51 per cubic yard while the construction cost of LF mining is $13.99 per cubic yard. These costs include both the earthwork costs and the materials and installation of the infrastructure and baseliner necessary for each approach. The added airspace gained by landfill mining also creates additional benefits that go beyond the incentive of having a lower cost per cubic yard of airspace gained. The ability to accept additional waste allows for the opportunity for additional funding to escrow accounts, as well as keeping the facility open for an additional amount of time. Keeping the facility open for an additional amount of time creates many added benefits to the local economy, the biggest being keeping disposal rates consistent. Having to dispose of waste in a facility farther away or constructing a new facility both would lead to higher disposal rates. Keeping the facility in operation for additional time delays these impacts to disposal costs. Due to the perceived advantages of the LF mining option versus the overliner option, OCLF management asked Cornerstone to pursue a permit modification for the SLP redevelopment. A pre-application meeting was held with NJDEP in June 2012 and the agency embraced the concept of eliminating an unlined landfill, and replacing it with a modern double composite liner system. Since the redevelopment was taking place within the existing footprint of the landfill, and not exceeding the existing maximum elevations, many of the submittals that would ordinarily be required for a lateral expansion were not required. That being said, the excavation of 4,000,000 CY of solid waste was unprecedented in the State of New Jersey, and NJDEP asked for a detailed plan of how this would be accomplished. OCLF agreed to submit a Waste Disruption Permit Application, followed with a Solid Waste Facility Permit Modification Application to address the reconfigured baseliner design of the SLP. The Waste Disruption Permit Application was submitted to NJDEP by Cornerstone in September 2012, incorporating techniques and valuable lessons learned from the Manchester Landfill excavation project, albeit on a much larger scale. NJDEP issued the disruption permit in March 2013, with some minor modifications incorporated in June 2013, and authorized the complete excavation of the Original Landfill. The permit will require OCLF to provide extensive monitoring, progress reports, and post excavation sampling to NJDEP throughout the waste excavation process. A Solid Waste Facility Permit Modification Application was submitted to NJDEP by Cornerstone in February This application included plans for the redesigned SLP baseliner, as well as changes to OCLF s operational filling sequence to accommodate the timeframe necessary for waste excavation and cell construction in the SLP area. OCLF also requested the option to use a GCL in the primary liner system, due to the lack of availability of suitable clay for such a large baseliner system. NJDEP agreed to process these elements as a minor permit modification since the capacity increase associated with the SLP area had already been permitted with the overliner configuration in This application was subsequently approved in November 2013, and also incorporated the requirements and conditions associated with the previously approved Waste Disruption Permit. Status of SLP Redevelopment OCLF and Cornerstone are currently finalizing construction plans for Phase 1 of the Waste Excavation Project, which entails excavation and screening of approximately 1,500,000 CY, and incorporating temporary capping of exposed slopes, interim gas collection, and necessary stormwater controls. OCLF has also filed a permit modification to the facility s Title V Air Operating Permit, to authorize the large scale screening operation that will occur during the waste excavation activities. It is anticipated that excavation Bell, P. 11

12 activities will commence in Summer 2014, with the first phase of SLP baseliner construction projected for SECTION 5 DECISION PROCESS Every landfill facility has its unique characteristics and special conditions that must be accounted for when deciding how to capture potential airspace associated with an old unlined landfill. However, there are a few key criteria that should be considered when evaluating whether an overliner or mining approach would be a better fit for a particular facility. These criteria include: Remaining Permitted Site Life Historical Groundwater Compliance Existing Grades of Unlined Cell Age of Existing Waste In addition to these criteria the economics of the decision must be considered. Factors to be considered are discussed below. Remaining Permitted Site Life Greater Than 5 Years: For a site that has a site life of greater than 5 years it may be more beneficial for the site to complete a LF mining project and baseliner installation. A site life greater than 5 years should provide sufficient time to complete the required excavation and waste relocation associated with a LF mining project and the subsequent installation of new baseliner (either portion or the entirety) within the excavated footprint of the LF mining project. A site should complete an evaluation to determine how much airspace the relocated waste will take up in the active area to confirm that they can handle the anticipated waste relocation. Less Than 5 Years: For a site that has a site life of less than 5 years it may be more beneficial for the site to complete an overliner project rather than a LF mining project and baseliner installation. The installation of an overliner will not have an impact on the remaining permitted airspace as the relocation of waste to the active face would not be necessary. While excavation and filling operations may be necessary in preparation of an overliner, this work would be contained within in the footprint of the existing unlined landfill. Though an overliner project may not provide a site with as much additional airspace as would an LF mining project and baseliner installation, it would provide additional site life not otherwise obtainable. Groundwater Monitoring Compliance Good Compliance Record: If a site has had a strong compliance record with minimal or no exceedances in their groundwater monitoring, there is a strong case to be made for either construction option. Completing an overliner project would require minimal disruption of the existing waste and minimize any impact to their groundwater quality. However, with no history of exceedance, it is also likely that the existing waste is not impacting the groundwater quality. Therefore, excavating the waste would probably not put a site at risk with impacts to their groundwater. However, if this option is selected appropriate run-on and leachate controls should be implemented to prevent groundwater quality degradation. Poor Compliance Record: If a site has had a poor compliance record with a history of exceedances in their groundwater monitoring it may be beneficial for them to complete an LF mining project. The completion of the LF mining project would allow the site to relocate waste to a lined cell, which could lead to an improvement in future groundwater testing results. The completion of an LF mining would provide an avenue to improve a site s groundwater quality that might not otherwise be possible. Existing Grading of Unlined Cell Relatively Flat: A site that is evaluating an expansion in the area of a relatively flat unlined cell should probably first consider the LF Mining alternative. Due to the potential for differential settlement, an overliner design typically requires much steeper grading compared to a standard baseliner system, in order to ensure positive drainage of the leachate collection system. An LF mining project followed by the construction of a traditional baseliner system will avoid the need for a large expenditure for fill material and/or cuts and fills to establish the proposed grades required for an overliner constructed in a relatively flat area. Favorable Existing Grades: A site that is evaluating an expansion in the area of an unlined cell with slopes greater than 10 percent should be able to construct the grading necessary for an overliner system without the need for a large quantity of fill material and/or cuts and fills. A site-specific differential settlement analysis will determine the slopes necessary to maintain positive drainage of the leachate collection system, but in general, favorable grading of the existing unlined area will facilitate the construction of an overliner system. Age of Existing Waste Greater Than 20 Years: For a site where existing waste has been in place for greater than 20 years, it may Bell, P. 12

13 be more beneficial to complete an LF mining project and baseliner installation. Waste in place for more than 20 years has mostly decomposed and therefore will have minimal landfill gas production, so it is unlikely that waste excavation will cause landfill gas and odor issues. Such waste is also likely to be more uniform in composition, and therefore easier to excavate than younger waste. The ease of excavation would also support a landfill mining construction project. Less Than 20 Years: Where existing waste has been in place for less than 20 years, it may be more beneficial to complete an overliner project than a LF mining project and baseliner installation. Waste that has been in place for less than 20 years is likely to still be decomposing, so it has the potential to create landfill gas and odor issues if the cap is disturbed. The installation of an overliner will have a minimal impact on the existing cap and will mitigate the release of landfill gas and odors from the existing waste. This decomposing waste is likely to still lack uniformity, making it difficult to excavate, and would support the construction of an overliner. Economics Determining which option is more economical to capture the potential airspace associated with a particular unlined landfill requires consideration of a number of factors. It is important to realize that each of these factors can be influenced by the many of the other criteria discussed in this section. Therefore deciding the best-fit approach based on the economics requires an evaluation of each factor and how it may be influenced by the other criteria. The decision process discussed here is designed to determine a best fit for each approach and does not aim to provide a definitive answer on the economic viability of each approach but rather a comparison. Total Cost of Construction: The total cost of LF mining is generally higher due to the additional costs associated with excavation and screening. This cost can be substantially influenced by a few key factors, including s the depth of the landfill, waste composition, presence of hazardous waste, leachate level, and waste moisture content, environmental mitigation measures required, level of reprocessing undertaken and choice of technology. The overliner approach can be influenced by how much fill may be required to meet the proposed grades and whether this material is available on-site or needs to be purchased and hauled on-site. An important consideration associated with the total cost may be the cost of bonding a project when the upfront CAPEX is significantly higher. Cost per Cubic Yard of Airspace Gained: LF mining projects generating in excess of 50 percent recovered soils where due diligence on the waste composition has been completed, when compared to an overliner approach, will have a lower cost per CY of airspace gained. The additional capacity from LF mining comes from the recovery of recyclable and reusable materials that no longer need to occupy valuable airspace. Therefore, LF mining the waste rather than constructing an overliner above the unlined waste creates more available airspace despite having to re-landfill a portion of the excavated material. Revenue from Additional Airspace: The additional airspace gained from LF mining has value from several perspectives. Not only is more profit realized by each additional ton gained, but the closure/post-closure accounts receive more funding than the overliner approach for a similar final cap area. To defray post-closure costs, many facilities establish escrow accounts during the landfill s operational life and divert a portion of the tipping fee to this account. At the very least they fund a post-closure account as stipulated by the regulations. Consequently, the longer a landfill area can remain open due to increased airspace, the more money an escrow account will accrue. A robust escrow account ensures financial stability long after the landfill closes. Value of Recovered Soils: The value of the recovered soil from LF mining can be significant for a site that has limited or no remaining borrow areas and is importing material for daily cover. Recovered materials that will be used at the same facility has more leeway in terms of analytics and specifications than material intended to be sold for off-site use. Value of Recovered Recyclables: The recyclable materials recovered from LF mining may include ferrous metals, aluminum, plastic, and glass; however, the feasibility of recycling these materials depends on the contamination level, availability of sorting/processing operations within a reasonable proximity and end markets willing to accept and pay for the materials. Although there is opportunity for additional revenue a lot of advance due diligence and economic analysis is necessary. Avoided Costs: LF mining removes a potential or current liability if groundwater has already been compromised from the unlined landfill area. Removing the potential liability has value; however, it is more of an internal savings, not necessarily a real one, unless the environmental liability insurance carrier lowers the premium. Although there are unique design, operational and environmental issues to address with each approach, by considering these criteria and economic factors the path Bell, P. 13

14 chosen to capture the potential airspace will likely result in the most financially feasible. To summarize, the following table groups a number of factors that could push an owner toward one approach over the other. Factors that could push an owner towards an Overliner More immediate need for airspace Dirt-rich site Conducive grading of existing cell that would not require significant excavation to install overliner Contractual issues of a large scale, long term landfill mining project may be an issue for a public entity Financial considerations and results of cost/benefit analysis Regulatory/Permitting issues concern with disturbing existing cap/gccs, permitting for screeners Factors that could push an owner towards Landfill Mining Less immediate need for airspace sufficient existing airspace to relocate overs from screening operation to a lined cell, as well as normal incoming waste Dirt-poor site ability to reclaim a large quantity of soil Environmental issues, i.e., desire to mitigate/prevent GW issues from unlined landfill Concerns with differential settlement impacts on overliner Ability to excavate and screen with own forces Financial considerations and results of cost/benefit analysis Age/composition of waste BMP shows higher methane yield, greater potential for odor issues. Stability of baseliner and existing adjacent cells TABLE 5-1 SUMMARY OF FACTORS REFERENCES Innovative Waste Consulting Services, LLC, Landfill Reclamation Demonstration Project, Perdido Landfill, Escambia County, Florida, June 2009 United States Environmental Protection Agency, 1995 List of Municipal Solid Waste Landfills, Table 1. United States Environmental Protection Agency, 1997 Landfill Reclamation, EPA 530-F Westlake, K., 1995, Landfill Waste Pollution and Control, P. 42. Bell, P. 14

15 FIGURE 2-1 OVERLINER FIGURE 2-2 PIGGYBACK FIGURE 2-3 OVERLINER WITH EXISTING BASE CONTAINMENT FIGURE 2-4 OVERLINER WITH EXISTING CAP IN-PLACE Bell, P. 15

16 FIGURE 2-5 SUBGRADE DESIGN OPTIONS FIGURE 2-6 POST DIFFERENTIAL SETTLEMENT SLOPES Bell, P. 16

17 FIGURE 2-8 OVERLINER TIE-IN FIGURE 2-7 SUBGRADE GAS COLLECTION HORIZONTAL FIGURE 2-9 RELOCATING INFRASTRUCTURE FIGURE 2-10 CLEANOUT ACCESSIBILITY Bell, P. 17

18 FIGURE 2-11 COST IMPACTS FIGURE 2-12 VARYING SUBGRADE CONDITIONS FIGURE 3-1 AIRSPACE RECOVERY FROM LANDFILL MINING FIGURE 3-2 PHASED EXCAVATION AND BASELINER CONSTRUCTION OPTIONS Bell, P. 18

19 FIGURE 3-3 BASELINER TIE-IN FIGURE 3-4 IMPACTS TO INFRASTRUCTURE FIGURE 4-1 SITE PLAN Bell, P. 19

20 FIGURE 4-2 PHASING PLAN FOR SLP FIGURE 4-3 SUSTAINABLE LANDFILL PROJECT Bell, P. 20