Clean Closure and the Small Landfill
In many cities across the United States, there are old landfills on prime property that are out of sync with general plans and shifting demographics.
Saturday, April 30, 2011
By Guy J Graening
At the end of a landfill’s useful life, capping is the traditional approach for closure. This is primarily because modern landfill cover systems are reliable, many contractors are available for installation, and permitting is relatively straightforward. However, the landfill owner incurs significant capital costs for cap installation and indefinite recurring costs for cap maintenance and monitoring. Future development or use of the property is severely restricted, if not prohibited. For small landfills, a better long-term solution may be a “clean closure” where the fill and any impacted soil are removed. Although capital costs are considerably more than capping, clean closure results in eliminating regulatory oversight and the associated recurring costs for complying with the closure permit. In addition, the property is ready for unrestricted sale and development, which can offset the capital costs and improve the land use. The various aspects of this type of closure are illustrated by the city of Folsom’s recent clean closure of its corporation yard landfill.
In Folsom’s Historic District
Folsom is a city rich in California pioneer history and has grown rapidly in the last quarter century. Situated next to the American River about 25 miles downstream of Sutter’s Mill, much of Folsom was dredged for gold, leaving towering rows of river cobbles, or “Folsom potatoes.” By the 1950s the city was outgrowing its existing infrastructure, and a wastewater treatment plant was built on the dredge tailings adjacent to the river. After operating the plant for 20 years, the city demolished the head works to make room for a corporation yard and began using the 3-acre settling ponds as a Class III landfill in 1974. Various city departments used the landfill for disposing around 50,000 cubic yards of excess soil, greenwaste, tires, and such construction and demolition debris as asphalt, concrete, lumber, plastic, and scrap metal. Illicit dumping of MSW by unknown parties occurred in a 1-acre area adjacent to the permitted landfill. In 1996, the landfill was capped with about 20,000 cubic yards of import material to create a 4-foot thick cover system of native grasses, topsoil, clay, and foundation soil.
The city’s general plan includes ambitious plans to revitalize and develop the historic downtown area. The 4-acre landfill was situated in the middle of eight undeveloped acres on the edge of the historic district. With a fantastic view of the American River, the property without the landfill was worth about half a million dollars an acre. The landfill cap maintenance and monitoring was costing the city about $60,000 a year and the only beneficial use of the entire property was a small employee parking lot on top of the landfill cap. It was time to consider clean closure.
Considering Clean Closure
Candidates for clean closure are typically small landfills fewer than 10 acres in size with mostly nonhazardous fill—which probably excludes burn dumps. From a purely economic standpoint, the cost of landfill clean closure needs to be less than or equal to the costs of cap construction and long-term monitoring. Today, capping a 4-acre landfill with a synthetic liner and cover soil would cost around $1.5 million. Maintaining and monitoring this landfill cap for 30 years at $60,000 annually would cost around $1 million (based on a present value analysis at a 4% interest rate) to bring the total cost for capping at $2.5 million. Initial cost estimates for clean closure of the 4-acre, 70,000-cubic yard Folsom landfill ranged from $2.5 million to $3.5 million depending upon how much segregated material could remain on site. It would appear that capping is a more economical closure option than clean closure, at least for a 30-year period. However, there is another element to the equation. Clean closure results in a property that is unencumbered from environmental regulation and potentially worth full market value for future development. Clean closing the Folsom landfill would free up the surrounding acreage and an initial appraisal valued the 8-acre property at $4 million to $5 million. The property could then be developed to fit in with the flavor of the gold-rush era historic district. Clean closure, in essence, was a good investment for Folsom’s future.
New Regulatory Waters
Folsom soon found out that theirs would be the first landfill clean closure in California’s Central Valley region. Thousands of pages in the California solid waste regulation provide detailed requirements on how to conventionally close (i.e., cap) a landfill; clean closure requirements occupy only about three pages—normally a good situation. However, the uniqueness of clean closure in the Central Valley meant the regulators had to work out who had jurisdiction, who would provide the permit, who would conduct inspections, and who would certify completion.
The clean closure involved regulatory oversight from multiple state and county agencies. The California Regional Water Quality Control Board required the city to prepare an amended report of waste discharge prior to issuing a permit for clean closure. The California Integrated Waste Management Board required the city to prepare a clean closure work plan prior to starting fieldwork. The county of Sacramento acted as the local enforcement agency and conducted inspections. The city engaged the California Department of Toxic Substances Control to certify that the site would ultimately meet the human health risk standards for residential development. Although an air permit was not required, the city proactively developed a perimeter air-monitoring program and engaged the Sacramento Metropolitan Air Quality Management District. With the regulatory framework set, Folsom could begin designing the clean closure.
Designing the Clean Closure
The first design step was to determine what impacts the clean closure project would have on the environment as required by the California Environmental Quality Act. Land use adjacent to the landfill consisted of the active corporation yard, a veteran’s hall, a residential neighborhood, and recreation on the American River. To include public input into the environmental review, the city held a 30-day public comment period, hosted multiple neighborhood meetings, and created a project website. The study identified the need to protect oak trees and habitat for endangered species. The city implemented a dust-control plan and conducted perimeter air monitoring to protect neighbors from fugitive dust during construction.
The second design step was to fully characterize the landfill contents and extent, especially in the area where the illicit dumping occurred. An investigation was launched that involved surveying, digging test pits, drilling borings, and analyzing samples of soil and waste. Whenever possible, city equipment and operators were used to minimize investigation costs. The “pre-design” investigation provided accurate volumes of soil and waste and formed the basis for the construction drawings, specifications, and the engineer’s estimate of probable construction costs. It was important, however, to emphasize to the city decision-makers that any landfill project has the potential for hidden surprises.
Folsom’s use of the corporation yard landfill resulted in fill that was composed of about 85% soil and 15% waste—about the opposite proportion expected at an MSW landfill where minimal daily soil cover is applied over waste. From the start, the city realized that the key to keeping the cost of the clean closure down was to prevent hauling off the entire 50,000 cubic yards of fill and 20,000 cubic yards of cap material. Since most of the waste was inert material such as tree stumps, tires, asphalt, concrete, and lumber, onsite segregation had the potential to produce large volumes of refuse-free soil that could be left onsite. Clean closure regulations require that soil segregated from waste be chemically tested and cleared prior to backfilling, just as if it was imported. The Clean Closure Work Plan proposed chemical cleanup goals for soil to regulatory agencies. The stockpiles would have to be staged on the undisturbed portions of the landfill due to space restrictions in the remainder of the corporation yard. The crux to the project design came down to: 1) optimizing the segregation process; 2) determining how large the stockpiles should be before testing; and 3) figuring out how to sequence the work in a confined area.
Scheduling, Contracting, and Funding the Clean Closure
To keep the project schedule moving along, the permitting, design, and contracting phases overlapped. The permitting process required seven months, including the preparation of the planning documents. The design document package, consisting of drawings and specifications, took about three months to prepare and was completed by the time the clean closure permit was issued.
Prequalifying construction contractors during the permitting phase enabled the city to have six qualified bidders ready to bid upon completion of the design documents. The bid package consisted of the city’s front-end documents, the permit, the clean closure work plan, and design documents. The pricing sheets in the front-end documents included lump sum line items for activities such as excavation, segregation, backfilling, hauling, and offsite disposal based on volume estimates from the predesign investigation. For landfill projects there is always the element of the unknown; therefore, the contractors were required to provide unit pricing on all activities in case the design volumes were off. A monetary incentive was included in the contract to reward the contractor for segregating out asphalt, concrete, cobbles, and metal for recycling. In addition to the “green” benefits of recycling, eliminating these materials from stockpiles reduced the density considerably which in turn reduced the cost of hauling and off-site disposal. The contractor was allowed 12 months to complete the clean closure, which allowed for the typical three-month construction downtime due to winter rains.
The total project value was $4.1 million with $3.3 million for clean closure construction activities and the remainder for permitting, engineering design, bid assistance, and construction management. The construction contract included hauling soil containing chemical concentrations above the clean up goal to a Class II landfill. The city used existing MSW fleet resources to collect and haul waste generated from the project to a Class III landfill.
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Photo: Brown & Caldwell
Since most of the Folsom landfill’s waste was inert material such as tree stumps, tires, asphalt, concrete, and lumber, onsite segregation had the potential to produce large volumes of refuse-free soil that could be left onsite. |
Clean-Closing the Landfill
After facing intensive permitting, design, and contracting challenges, the city now had to figure out how to clean close the 4-acre landfill in only about five usable acres. The other three acres had restrictions on construction activity due to steep slopes, protection zones for oak trees and endangered species, and proximity to residential neighbors. Within the five usable acres, the contractor was required to excavate 70,000 cubic yards of material, segregate waste from soil, stockpile soil for chemical sampling and analysis, conduct confirmation sampling of the surface beneath the landfill, and backfill soil that met the chemical cleanup goals for the project.
The strategy for clean closing the landfill was to begin in the area of most uncertainty, the area where illicit dumping occurred, and work toward the permitted landfill area, which had definitive boundaries from the old wastewater treatment settling ponds. This was done with the hope that there would be fewer “surprises” regarding the landfill’s extent and contents as the project progressed. Another strategy component was to excavate the main landfill in vertical cuts rather than horizontal lifts so that the cap and parking lot could be used for staging stockpiles and equipment. This had the additional benefit of keeping rain from leaching through uncovered waste, which was prohibited in the permit. To keep from digging himself into a corner, the contractor conducted confirmation sampling immediately after clearing waste from a section of the landfill rather than waiting to sample the entire 4 acres at the end of the project. When the cleared section was confirmed to have met the chemical clean up goals, the contractor could immediately use the area to backfill soil that also passed the clean up goals. This in turn freed up space on the landfill cap for new stockpiles and the process continued.
A typical construction day consisted of one CAT 330D L excavator removing waste from the open face of the excavation at a rate of 1,500 cubic yards per day. Supporting the excavation operation were three 10-yard dump trucks and a CAT D6 bulldozer that built and staged the waste stockpile on an undisturbed portion of the landfill cap. During the same day, a second excavator transferred waste from the staged stockpile and placed it in a Warrior 1800 PowerScreen to mechanically screen waste from soil at a rate of 500 cubic yards per day. The mechanical screener incorporated a hopper, a shaker section with two screen sizes, and conveyor belts to screens waste into three piles: oversize, 4-inch plus, and 4-inch minus. Supporting the screening operation were a Bobcat 248 Skidster removing waste stockpiles and three laborers manually removing waste from the PowerScreen shaker section and fines pile. A Cat 950 front loader alternated from building waste stockpiles to building screened soil and cobble stockpiles.
The operations produced about 40 cubic yards of waste per day that was hauled off by the city in 20-yard roll-off bins to a Class III landfill. Regulated waste such as tires, transite pipe, and batteries as well as large pieces of concrete, asphalt, and metal were segregated and hauled offsite for recycling or specialized disposal. A 2,500-gallon water truck provided dust control for the entire operation. Once a day, a fuel/service truck arrived onsite to fuel and grease all equipment. When backfill operations were occurring, two additional laborers manually removed larger pieces of plastic and similar debris from the material that is being backfilled.
At the end of construction, the site was graded for proper drainage and seeded with native grasses. The permit required the submittal of a thorough Clean Closure Results Report to document the analytical testing results, final volumes and disposition of all materials, manifests from transportation, and weight tickets from disposal and recycling facilities.
Is Clean Closure Better?
The city of Folsom was faced with perpetually maintaining a capped landfill within 8 acres on the edge of the historic district near the American River. Clean closing the landfill required a significant and immediate investment of capital, intensive and lengthy permitting, and close regulatory agency coordination throughout the project. Neighbors had to endure nine months of construction activity. But the benefits are clear. Removal of the permitted landfill eliminates annual cap maintenance costs and brings the property to full value. The sparse waste in the landfill has been segregated from soil and the majority of the soil was chemically acceptable for backfill. Chemically impacted soil, regulated waste, and large pieces of concrete, asphalt, and metal were segregated and hauled offsite for recycling or specialized disposal. For the city of Folsom, clean closure is ultimately about the future: changing the land use from a perpetual landfill and monitoring requirement into a vibrant property within the historic district.
Author's Bio: Contributing author Guy Graening is a project manager with Brown and Caldwell. |
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