MSW Management | Expecting the Unexpected

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Peer-Reviewed Feature Article

By Robert J. Schoenberger

Typically, in post closure, the labor and cost requirements are significantly reduced, and such continuing responsibilities as monitoring well sampling, leachate, and disposal, as well as vegetation management become minimal time requirements. However, this paper discusses two catastrophic events that completely altered the responsibility, costs and emergency responses needed during post closure.

The first guidelines defining the practice of “sanitary landfilling” only date back to the first half of the 20th century. The evolution of regulatory requirements expanded rapidly and changed direction frequently after the enactment of the Solid Waste Management Act (PL 89-272, 1965). Among those earliest documents that described appropriate landfill practice, Spencer (1943) proposed techniques that were used in wartime for the disposal of refuse. From these World War II and earlier guidelines evolved a plethora of documents that built upon these “dumps” to sanitary practice recommendations. The American Society of Civil Engineers (1959), Weaver (1952), Bevan (1967), American Public Works Association (1966), American City (1961), and Black (1961) all wrote synopses of these earlier recommendations. These early documents emphasized operation techniques such as compaction, daily cover, no open burning, and site selection. The issue of closure and post closure was mostly limited to settlement (Merz and Stone 1963) and gas management ( Merz and Stone, 1964; Eliassen et al, 1957). Other writers such as Basgall et al (1954) addressed the issue of post closure on the front end through site selection. By choosing a site that could be reclaimed for community use or development, landfilling could be turned into a positive infrastructure. While Basgall addressed site selection cautiously, such as discouraging the use of wetlands, post closure practices were much slower to become incorporated into permitting regulations.

Post Closure in Pennsylvania
The Commonwealth of Pennsylvania was little different from the other 49 states in the 1960s, when solid waste disposal was not actively managed. No written regulations had been promulgated, and an Operating Permit was not required to operate a landfill. This changed after the passage of the state’s first Solid Waste Management Act (Pennsylvania 1968). Evolving from the 1968 Act were regulations that became effective in 1972, and operating landfills were required to register with the Commonwealth. Once the state compiled a list of all landfills, a process to evaluate and issue interim permits began. Registration of more than 2,800 operating landfills clearly identified the magnitude of the evaluation process in Pennsylvania. This situation was not significantly different from other states.

In the 1972 regulations, Pennsylvania defined a sanitary landfill as, “A land site on which engineering principles are utilized to bury deposits of solid waste without creating public health or safety hazardous or nuisances.” The resulting regulations did not recognize post closure as a continuing responsibility other than for managing surface vegetation and gas should the need arise. Active gas management was not required unless subsequent problems occurred after closure.


	Table 1

Pennsylvania updated its regulations in 1977, and for the first time the issue of post closure was specifically identified. Summaries of the closure requirements are given in Table 1.

The Federal Role
The federal government was not actively engaged in solid waste management prior to the enactment of PL 94-580 in 1965. This act provided guidance and financial resources to define the scope of impact by Solid Waste Management. This act also allowed the federal government to investigate and fund demonstration projects using innovative technologies. The federal role was further expanded when Subtitle D of the Resource Conservation and Recovery Act (PL-94-580 ,1976) was established. However, regulations pursuant to this section did not become effective for more than a decade after passage of the law.

History of Knickerbocker Landfill
Knickerbocker Sanitary Landfill began operation in the mid-1950s, when several exhausted quarries on property owned by the Martin Marietta Corp. were sold to a corporation that ultimately developed and operated the Knickerbocker landfill. Small quarries were present throughout the site and filling operations moved from one location to another as the quarries were filled. The quarries varied in size from several thousand tons to large excavations from which millions of tons of limestone were removed. The USGS quadrangle shows one large quarry immediately adjacent to the site where a major slope failure occurred.

The quarries were the result of mining dolomitic limestone in the narrow central valley between two nondolomitic formations. Valley Creek flows through the central valley in a generally east-west direction for a distance of about 20 miles and discharges into the Schuylkill River at Valley Forge National Historical Park. There was concern for the impact of the water quality at Valley Forge as the creek has the highest water quality required by the state of Pennsylvania. Valley Creek is a coldwater habitat of the native brook trout. Any disturbance of the creek through either construction or surface discharge is tightly monitored and controlled by the state of Pennsylvania.

Flow and water quality data are obtained from a USGS gauging station about two miles downstream from the landfill. The total drainage area of Valley Creek is 23 square miles. Drainage area at the gauging station is 20.8 square miles and the drainage area at the point of failure is 5.37 square miles.

In 1972 the Commonwealth of Pennsylvania required all landfills to obtain a permit to continue operation. These regulations required all landfills in mines and quarries to be constructed and operated with an impermeable liner system. In addition, landfills in karst topography were forbidden. As a result, all Knickerbocker operations in non-lined areas were closed and a new lined landfill area was constructed on the north side of Valley Creek. They were constructed with an asphaltic impermeable liner that had leachate collection and treatment systems. All non-lined landfills were closed when filling operations moved to new areas on the north side. The area of slope failure was the last unlined portion of the landfill to be closed.

The lined areas operated until Subtitle D regulations become effective, because the single asphaltic liner did not meet Subtitle D criteria. Therefore, the landfill closed and ceased receiving refuse. Closure was partly driven by the regulations; however the asphalt lined portions of the landfill had reached final elevations. Any new expansion would have required compliance with Subtitle D regulations. Expansion approval was considered to be unlikely given the location of the landfill, a highly populated upper middle class region and in karst topography.

Closure Requirements
Operation of landfill sites on the Knickerbocker property over four decades and under various regulatory scenarios often created confusion when identifying the pertinent regulatory requirements. Landfill operations completed before 1972 were not subject to any specific closure and post closure requirements other than to cover the waste with an acceptable final cover material and to provide surface vegetation that controlled runoff and erosion. The portion of the landfill opened in 1972 was subject to permit requirements at the time of issue. Landfill expansions after 1977 imposed requirements based on new regulations approved that year. Since Pennsylvania did not implement impermeable cap requirements until Subtitle D became effective, no portion of the landfill was required to install an impervious closure cap. Only a soil cover of 24-inch depth that would support vegetation was required. However, the lined part of the landfill was still required to collect and treat leachate and to prevent any contaminated runoff from reaching Valley Creek. The location of the leachate treatment plant, pumping stations, and equalization lagoon was on the north side of Valley Creek. The only access to the treatment plant and monitoring wells was from the south over a pipe culvert bridge installed in the 1950s. The landfill operated for more than 40 years while the population of the drainage area of the landfill increased by more than 300% during its operating life. The development of residential and commercial buildings increased the impervious area and provided higher stormwater runoff peaks.

The Unexpected—A Hurricane
On September 16, 1999, Hurricane Floyd raced across South Carolina, North Carolina, Virginia, and into central Pennsylvania depositing nearly 10 inches of rain in less than 12 hours. The existing pipe-bridge system that had provided access to the site for more than 50 years was swept away by the runoff in Valley Creek. This left a 40-foot-wide-by-30-foot-deep void where the pipe bridge formerly stood. The result was the need for a bridge to access the north side of the landfill across a 40-foot span above 30 feet.

The peak flow of flood runoff resulting from the Hurricane Floyd was 6,200 cubic feet per second as measured at the downstream USGS gauging station. The second highest peak flow was 2,100 cubic feet per second, approximately one-third of Hurricane Floyd’s driven flow. The peak flow from Hurricane Floyd exceeded the average flows by a margin so great that the average peak flow was 95.5 cubic feet per second for September 1999, as compared to the 20-year average of 29.3 cubic feet per second including the 1999 data.

This bridge failure posed an immediate emergency situation; it was the only means of access to the leachate management system and monitoring wells. Closure requirements mandate that the approved monitoring wells be sampled and analyzed quarterly. September was the end of a calendar quarter and monitoring well sampling was required. While vehicle access was not possible, sampling could be performed by physically carrying all equipment and supplies needed for well sampling onto the site. However, delivery of chemicals to the leachate treatment plant was not possible and presented an immediate problem. Since the leachate plant had a 0.75 million gallon effluent lagoon, 3–6 months was the time window required before access would become critical.

Because time was a critical concern to assure that emergency and routine maintenance of the closed landfill could be conducted, various construction alternatives were evaluated. Three construction alternatives were considered:

Construct in-place using concrete abutments and steel or concrete stringers with wooden
decking.
Install a pre-cast concrete culvert with stone/soil fill.
Install steel pipe arch bridge with stone/soil overfill.

The two-pipe system that was removed in the flood consisted of one 60-inch and one 72-inch diameter pipe. The maximum flow of the 60-inch pipe was calculated to be 140 cubic feet per second, while the flow of the 72-inch pipe was calculated to be 230 cubic feet per second. Negotiations were conducted with the Pennsylvania regulatory agencies to define the design flow. Since the peak flow at the gauging station was slightly more than 6,000 cubic feet per second, and the drainage area was 25% of the area at the gauging station a bridge passage of 2,200 cubic feet per second was the design criteria.

This design flow criteria was calibrated using the capacity of a box culvert bridge 0.25 miles below the landfill bridge. The box culvert consisted of three parallel sections each having a cross section of 4 feet by 10 feet. That was calculated to allow 1,800 cubic feet per second to pass in the culverts.

After evaluation of the time frame needed to construct the replacement bridge, it was decided to use a steel arch concept. The bridge could be fabricated and shipped within six weeks, and erection could be completed in two weeks if foundations were completed prior to start of erection.

Because of the Exceptional Quality stream classification, construction of the foundations was closely monitored. No equipment was allowed to function in the water to perform tasks needed for footer installation. Therefore, a cofferdam was constructed upstream from the bridge construction site. Water from the dam was piped around the construction zone.

Erection of the bridge began in early December 1999. The sections of the arch were bolted into position until the arch was completed. When the steel was installed, 6 feet of compacted soil was placed over the completed pipe arch. The final bridge was completed with compacted soil with Jersey barrier sidewalls and gabion protection at the access and exit of the pipe arch bridge.

Construction was completed on December 30, about 15 weeks after Hurricane Floyd.

The Unexpected—The Power of Water
Unlike the extreme event of a hurricane, sometimes the natural processes of geomorphology lead to unanticipated failures. Valley Creek flows through stream reaches defined by pools and riffles. The creek flows through a series of curves that border steep slopes of the landfill on both the north and south side. At these narrow locations no flood plain exists to assist in containing velocity scour of the side slopes. For reaches of the stream that are not linear, the result is continual erosion of the base landfill slope as the stream centerline meanders orthogonally into the eroding slope.

The increased peak runoff of stormwater in the absence of a defined flood plain increases side slope erosion during the peak events. From the time of closure in 1972 erosion had been undercutting the south embankment of the landfill and causing the centerline of the stream to migrate in that direction. After a shift of about 50 feet, the sidewall was essentially vertical, and when the surface mass of refuse became saturated, a slope failure occurred. Not only did the slope failure expose previously buried waste, but several tons of waste were discharged into Valley Creek and carried downstream by the high water.

To permanently correct the erosion, it was necessary to move the stream centerline 50 feet to its channel at the time when the initial landfill was closed. As with the bridge, no stream encroachment was allowed and a stream bypass was required. An initial barrier system was put in place to prevent further failure of the unstable slope. Since the failure occurred in December, the time needed to gain emergency approval from the Pennsylvania Department of Environmental Protection, the Corps of Engineers, and the Chester County Conservation District for a stream encroachment would not allow construction to begin until spring.

The next construction step was to install a new barrier system that would be the base of the slope of the new stream channel that was moved 50 feet to the north. A new set of barriers was installed to divert the stream through three pipes that would provide a temporary bridge for construction vehicles to cross the stream and supply the soil for the repaired bank. Because of the time involved, flow capacity of the temporary diversion bridge was of concern. Since work was being conducted in the spring the probability of a significant storm event was high. It was estimated that the three-pipe temporary bridge could allow 600 cubic feet per second to pass. The stream was contained within two sets of barriers until diverted through the pipes. Then the original set of barriers would be moved 50 feet to define the base of the reconstructed slope. Even with a new stream channel, the need to minimize future erosion was present. At the upstream reach of the reconstructed stream a jetty was placed to divert water away from the base. After the slope was reconstructed it was hydro-seeded before removal of the temporary bridge and return of the channel to original centerline.

The length of slope reconstruction project was over 210 feet and required 225 truck loads (approximately 22 tons per load) of soil. Construction was completed in 15 days after the diversion barrier was completed and the stream diverted.


	Table 2

Costs
Table 2 is a breakdown of costs for the bridge replacement project, including the cost estimates for the two scenarios that were not selected.

Reviewing the costs and estimates to complete the bridge replacement, the actual costs are influenced by work that is either undertaken by the landfill ownership or reflects negotiated costs with contractors during a winter construction season. Some materials such as soil needed for the projects were supplied from on-site sources.


	Table 3

Table 3 is the cost for reconstruction of the side slopes. The time required to complete the work scope was 20 days during the spring construction season.

Summary
Landfills that are closed to active filling may encounter events that are unexpected. The case study presented in this paper required the landfill to address remediation tasks that may be unexpected at most landfills. However, slope failure and access to closed landfills may be caused by different circumstances, but the possibility does exist that these or other events may occur.

The regulatory problems at Knickerbocker Landfill were both helped and hindered by the location in high population suburbs on a stream that has the highest water classification in Pennsylvania. Because of the classification of the stream, there was unqualified cooperation among the various agencies and local environmental groups including the Valley Creek Coalition and Trout Unlimited. All parties agreed that the objective was to eliminate future problems in the shortest possible time frame. In both events emergency permits were issued within two weeks, and this cooperation allowed the projects to be completed in a timely manner.

References
Spencer, C.C. “Recommended Wartime Refuse Disposal Practice: With Particular Reference to Sanitary Landfill Method of Disposal for Mixed Waste”. Public Health Reports, Supplement 173, U. S. Government Printing Office, Washington, D.C. 1943.

American Society of Civil Engineers, “Manual of Practice No. 39” ASCE, New York, 1959.

Weaver, Leo and D. Keagy. “Sanitary Landfill Method of Refuse Disposal in Northern States”. U. S. Public Health Service, Publication No 226, U. S. government Printing Office, Washington, D.C. 1952.

Bevan, R.E. “Notes on the Science and Practice of Controlled tipping of Refuse”. London 1967.

Black, R. J. “Suggested landfill Standards and Methods”. Refuse Removal Journal, October 1961.

American City Magazine. “Sanitary Landfill-How it operates”. Part I, February 1961. Part II, March 1961. Part III, April 1961.

American Public Works Association. “Municipal Refuse Disposal”. Public Administration Service, Chicago 1966.

Merz, R. C. and Ralph Stone. “Gas Production in a Sanitary Landfill”. Public Works, February 1964.

Merz, R. C. and Ralph Stone. “Landfill Settlement rates”, Public Works, September 1962.

Eliassen, Rolf, F. N. O’Hara and E.C. Monahan. “Sanitary Landfill Gas Control: How Arlington, Mass. Discovered and Corrected a Danger Spot in its Sanitary landfill”. American City, December 1957.

Basgall, V. A., W. F. Johnson and C. F. Schwalm. “Sanitary landfill Series-Trench Type: Civic Pride, One-man, one machine; Do you Realize that a City’s garbage can Turn Wasteland into a Beautiful Playground?”. American City, February 1954.

Pennsylvania, Commonwealth of. “Act 241-Solid Waste Management Act”. Pennsylvania Department of Health, July 1968.

Pennsylvania, Commonwealth of. “Title 25, Chapter 75, Solid Waste Management”. Pennsylvania Department of Environmental Resources, Harrisburg 1971.

Pennsylvania, Commonwealth of. “Department of Mines and Mineral Industries-Rules and Regulations for the Operation and Maintenance of Licensed Waste Disposal Areas, Harrisburg, PA 1967.

US Congress, PL 94-580, “Resource Conservation and Recovery Act” October 21, 1976.

Robert J. Schoenberger is chairman of the Chester County Solid Waste Authority, Division Highway, in Narvon, PA.

MSW - May/June 2008