Landfill Economics Part 3: Closing Up Shop

The first article examined a hypothetical landfill’s market and potential for waste receipt; as well as its site investigation, engineering, design and permitting costs.

The second article examined the cost of construction for site facilities and for each landfill cell. Additionally, the operating cost and disposal volume of each cell was described to show how cash flow will change over the operating life of the landfill.

This last article looks at the costs of landfill capping and closure, installation of gas management systems, and post closure care and maintenance costs (and how to plan ahead and provide financial assurance for each).

The Hypothetical Landfill
As described in the first article, we are using a hypothetical landfill to illustrate the financial aspects of landfill operations. This landfill has the following characteristics:

• Total landfill volume is approximately 4-million cubic yards.
• The landfill’s footprint is square, having dimensions of 1,200 feet, and is a little over 33 acres.
• The final surface grades needing cap and cover are approximately 34.0 acres.
• The area of the bottom of the landfill needing a cap and leachate system is 33.5 acres.
• Total acres of landfill construction (cap and cap) is 67.5 acres, giving a ratio of volume to construction area of almost 60,000 cubic yards per constructed acre.

The landfill is located in an eight-county area and services all or part of the waste-disposal needs of each of the counties. The local waste disposal market can be described as follows:

• a total waste disposal market of approximately $29 million dollars per year;
• an average tipping fee of approximately $40.00 per ton;
• of this amount, the landfill has an annual disposal rate of approximately 200,000 tons per year; and
• its projected annual gross revenues would be $4.4 million.

The landfill construction and operations will occur in the following stages, with their associated costs:

• the landfill will utilize approximately 363,000 cubic yards of airspace per year;
• its projected operational lifetime is 11 years;
• the landfill will construct an average of 3 acres of lined cells and/or final cover each year;
• support facilities and ancillary structures, which are constructed first, will cost about $1.2 million;
• the landfill’s cost of construction per lined acre will be approximately $350,000; and
• total annual operating costs will be $600,000 (equivalent to $3 per ton, or 7.5% of the tipping fee).

Landfill Closure Costs
The first step in landfill closure is the surveying of the surface to receive final cap and cover. Surveying is performed throughout the operational lifetime of the landfill and its individual disposal cells to track airspace utilization and ensure that minimum and maximum slopes are adhered to. These activities are best included with the costs of landfill operations (as described in the second article). However, as the landfill or cell reaches its final development grades a formal survey is performed to ensure that actual grades and elevations do not exceed those in the permit design. Usually, this final survey is performed at 100-foot grid points and at 100-foot intervals along major breaks in the slope line. This is fewer survey points than is typically required to establish grades for cell and cap construction, so the cost per acre is less expensive. The cost of final grade surveying can run from $3,000 to $6,000 per acre with $5,000 being typical.

Once the final waste grades have been certified by the surveyor to be at final design grades, construction can begin on the final cap and cover. The first layer to be installed in the final cover system is the gas management layer. This is usually a loose layer of soil spread into place to allow the free migration of landfill gas under the cap and prevent the accumulation of gas pockets. Extreme care has to be used when choosing and placing this material. Purely cohesionless soil, such as sand, may not have the internal strength required to repent the slippage failure of the overlying cap. Cost per cubic yard will vary from $15.00 to $20.00. The cost per acre of gas management layer construction will vary from $24,000 to $32,000. Sometimes a geocomposite blanket is used instead of loose soil, but this tends to clog over time.

A compacted clay cap is then constructed over the gas management layer. The construction of a clay cap is stringent in terms of material specifications, construction effort, and quality assurance. The effort is made more complicated by the fact that the clay is often being compacted over an unstable or soft trash surface. The required in-place density and moisture content will be determined by Proctor curves and tested by Boutwell test pads to assure that the maximum allowable permeability is achieved (usually 1 x 10ee–5 cm/sec). The results of these analyses and field tests will determine the weight of the compacting equipment, the penetrating length of the compactor’s sheepsfoot pad, the number of passes required to achieve compacted density and the field moisture content required for the construction effort. The cost of a clay cap runs from $8.00 to $16.00 per cubic yard (depending on the ready availability and quality of the clay). State agencies require clay caps with a minimum thickness of 2 feet, resulting in the need for 3,200 cubic yards per acre. The cost per acre of clay cap construction will vary from $26,000 to $51,000. A well-chosen landfill site with sufficient good clay onsite will tend to have lower costs.

After the clay cap has been constructed and certified, work can begin on the geosynthetic components of the final cap. A composite cap system consists of the clay cap overlain by a high density polyethylene (HDPE) geomembrane. As with any other plastic, the cost of geomembrane can vary wildly depending on the current price of oil. This price may even change during the course of a single construction season if a summer time gas shortage increases the price of oil (yet, strangely, the cost of geomembrane never seems to fall as the result of a sudden gas glut). The thickness of the geomembrane used in cap systems is typically 40 mil. Smooth geomembrane is used on the flat final grades of the landfills while roughened geomembrane with a textured surface is used on the 25% slopes and terraces. The cost of smooth geomembrane can vary from $0.40 per square foot to $0.50 per square foot. Textured geomembrane will tend to cost $0.15 per square foot more than the smooth variety. Often very low-density polyethylene (VLDPE) geomembrane may be used in the cap instead of HDPE.

The hypothetical landfill has a total lined area of 34 acres divided into 4 acres of flat grades and 30 acres of steep slopes. An average lined acre will have approximately 90% smooth geomembrane and 10% textured geomembrane resulting in a cost of installed geomembrane varying from $18,000 to $23,000 per acre. The actual cost per acre will vary based on the geometry of the landfill and the location of the cell being constructed.

To prevent the build-up of percolating precipitation on the impermeable geomembrane cap, a geocomposite drainage layer is installed. This layer will window out somewhere downslope at discreet points to vent percolation back to the surface as runoff. The geocomposite consists of a factory-bonded three-layer sandwich: nonwoven geotextile bottom cushion, geonet drainage medium, and a top geotextile filter. The costs of two-sided geocomposites with 8-ounce-per-square-yard nonwoven geotextile layers will vary as with the geomembranes, with a typical price range from $0.75 to $1.00 per square foot. The total cost per acre of geocomposite varies from $33,000 to $44,000.

Above the geocomposite is a layer of protective cover soil thick enough and fertile enough to support a thick growth of vegetation, and to provide enough protection against frost penetration. Typically, a minimum thickness of 2 feet is required, resulting in a total granular volume of 3,200 cubic yards per acre. The cost of cover soil, like the cost of clay, will vary widely depending on local availability and quality. The cost of cover soil can range from $4.00 to $8.00 per cubic yard, resulting in a per acre cost of $13,000 to $26,000.

Once final cover soil has been placed, its surface is to be hydroseeded and fertilized to grow a grass cover for protection against erosion and gullying. A layer of mulch is applied to hold the seed in place until it germinates. Cost for seeding, mulch, and fertilizer varies from $1,000 to $2,000 per acres.

Installed through the final cap and cover are the collection wells, header pipes and fittings, and condensate drip legs of the landfill gas management system. Each landfill also has at least one blower flare assembly for safe destruction of the extracted gas (usually one flare per 100 acres of landfill). The pricing of each component is unique, but can be roughly prorated on a per acre basis.

• Gas probes typically cost $6,000 to $8,000 each and are installed at a rate of one per 10 acres. Cost per acre would be between $600 and $800.
• Gas extraction wells and associated fittings cost between $8,000 and $10,000 each, depending on their depth. At a rate of one per acre, the costs per acre would be between $8,000 and $10,000.
• Assuming about a 200-foot average spacing interval, header pipelines are installed at a rate of 200 feet per acre. Costing $100 to $120 to install, their cost per acre varies from $20,000 to $24,000.
• A gas collection blower and flare assembly connected to the extraction well field by the header pipes will cost from $40,000 to $50,000 each. At an installation rate of one per 100 acres, per acre cost would be between $400 and $500.

The total cost per acre of the landfill gas management system would be between $29,000 and $35,000.

Installed over the final cap and cover are the swales, discharge channels, and culverts of the surface water run-off control system. Each landfill also has at least one sedimentation retention pond for the extraction of sediment and reduction of off-site run-off discharges. The pricing of each can be roughly prorated on a per acre basis:

• Assuming about a 200-ft. average spacing interval, collection swales and discharge channels are installed at a rate of 200 feet per acre. Costing $10 to $15 to install, their cost per acre varies from $2,000 to $3,000.
• Assuming culverts are installed at a rate of 100 feet per acre, and with the cost varying from $25 to $30 per linear foot (depending on the culvert type and diameter), the cost per acre would be from $2,500 to $3,000.
• A sedimentation basin will cost from $50,000 to $100,000 each. At an installation rate of one per 100 acres, per acre cost would be between $500 and $1,000.

The total cost per acre of the surface water runoff control system would be between $5,000 and $7,000.

In addition to the physical acts of construction and installation, management and quality oversight is required. This is typically done by independent third-party consultants and breaks down as follows:

• geomembrane cap construction management costs from $18,000 to $20,000 per acre;
• clay cap construction management costs from $2,000 to $4,000 per acre;
• overall project management costs from $12,000 to $16,000 per acre;
• construction surveying and drawing costs from $6,000 to $10,000 per acre;
• earthwork (structural fill and excavation) QA/QC costs from $15,000 to $20,000 per acre;
• liner (clay and geomembrane) QA/QC costs from $16,000 to $20,000 per acre; and
• leachate management system installation QA/QC costs from $6,000 to $9,000 per acre.

Total overhead and quality control would therefore range from $75,000 to $100,000 per acre.

Table 1 summarizes the above closure costs and the typical cost per acre of landfill closure.The cost of closing a landfill can range from $227,000 to $326,000 per acre, with the main cost difference due to the cost of clay and cover soil. For the purposes of this study, the hypothetical landfill will be assumed to have a closure cost of approximately $250,000 per acre.

Post-Closure Care and Maintenance Costs
Most operators are required to care for and maintain their landfills for a minimum period of 30 years after final closure and cessation of landfill disposal operations. Post-closure costs can be divided into four broad categories, depending on their cost basis:

• site security maintenance (annual cost per 1,000 feet of perimeter);
• landfill cover and mechanical systems maintenance (annual cost per acre);
• monitoring wells and gas probes (annual cost per each); and
• environmental monitoring (annual cost monitoring associated with the landfill).

Site security maintenance consists of fence repair and replacement, sign replacement, and gate replacement. Fence replacement is performed annually and usually involves about 20 feet of perimeter fence per 1,000 feet of fence. The unit cost of replacement varies from $10.00 to $15.00 per foot of fence replaced. The hypothetical landfill has a 6,000- foot-long security fence, resulting in an annual repair effort of 120 feet, costing from $1,200 to $1,800. An average of one sign will be replaced each year at an incidental cost of $10.00 to $20.00 each. The main entrance gate will have to be replaced on average once every 10 years at a cost of $1,000 to $2,000, resulting in an average annual cost of $100 to $200. Over a 30-year post-closure care period, security maintenance will cost between $3,000 and $6,000. Since this hypothetical landfill has an area of 33 acres, these costs become $90 to $180 per acre

The landfill itself will also need tending to. Each year the landfill’s cover vegetation should be mowed at the cost of $20 to $30 per acre. The cover soil will probably need repair to a depth of 1 foot at an average rate of 0.03 acre per year, at a cost of $4.00 to $100 per cubic yard, resulting in an annual cost of $200 to $400 per acre. The same damaged cover soil areas will need reseeding at a rate of 0.03 acres per acre at a cost of $1,000 to $2,000 per acre, resulting in an annual cost of $30.00 to $60.00 per acre. Surface water runoff control structures will also need dredging and excavation at a rate of about 100 cubic yards per acre of landfill every five years, at a cost of $2.00 to $4.00 per cubic yard, resulting in an annual cost of $40.00 to $80.00 per acre. Total cover maintenance will cost from $290 to $570 per acre per year. Over a 30-year post-closure care period, cover maintenance will cost from $9,000 to $17,000 per acre.

Other per-acre site post-closure care costs include maintenance of the mechanical systems managing landfill gas and leachate extraction. Leachate maintenance of pipes should occur at a rate of 100 feet to 300 feet of pipe per acre, twice per year. This operation costs the equivalent of $100 to $300 per acre per year. Leachate extraction pumps and associated controls are usually replaced at a rate of one replacement every five years at a cost of $40,000 to $45,000. With a pump for every 10-acre cell, this works out to $800 to $900 per acre per year. Total leachate maintenance costs will vary from $900 to $1,200 per acre per year. Over a 30-year post-closure care period, leachate system management costs will vary from $27,000 to $36,000 per acre.

Landfill gas system maintenance can also be prorated on a per acre basis. Annual maintenance averages $50 to $70 per well, with an average of one gas well per acre. Maintenance of the header pipe lines and other appurtenances averages $2.00 to $2.50 per linear foot. At an average 200 linear feet of header pipeline per acre, the cost of maintaining the pipelines varies from $400 to $500 per acre. Total annual gas system costs per acre will be $450 to $570. Over a 30-year post-closure care period, leachate system management costs will vary from $13,500 to $17,100 per acre.

Groundwater monitoring wells and landfill gas probes will need replacement on occasion. Typically, this happens at an annual cost equal to 2% of the capital costs of either the monitoring wells or probes. If a site has 10 wells, the annual cost of well replacement and repair will be equal to the cost of installing one-fifth well. If a site has 50 probes the annual cost of well replacement and repair will be equal to the cost of installing one probe. The number of wells and probes are not directly related to the number of landfill acres. Each site typically has a minimum of four wells— one up-gradient and three down-gradient. Also, the minimum number of gas probes is four—one on each side of the landfill. At a unit cost of $7,000 per well and $3,000 per probe, total capital costs for a 4 x 4 system would be $40,000. The annual maintenance and repair cost for probes and wells would be $800. For a hypothetical 33-acre landfill, this is equivalent to $20 to $30 per acre. Over a 30-year post-closure care period, probe and well maintenance, and replacement costs will vary from $600 to $900 per acre.

Environmental monitoring must be performed throughout the post-closure care period. These sampling and analysis events are usually performed as follows:

• groundwater monitoring (two events per year) at a total annual cost of $3,000 to $4,000;
• surface water monitoring (two events per year) at a total annual cost of $2,500 to $3,000;
• leachate monitoring (one event per year) at a total annual cost of $2,500 to $3,000;
• landfill gas monitoring (four events per year) at a total annual cost of $800 to $1,200; and
• statistical analysis (annually) at a cost of $6,000 to $8,000.