 |
 |
 |
 |
 |
 |
 |
 |
 |
|
What do you do when storm debris threatens to overwhelm your landfill expansion project? By Dennis Davis, George Reinhart, and Brooks Stayer Polk County, FL, is situated just south of Interstate 4 halfway between Tampa and Orlando. Just over half a million residents are spread out over 2,000 square miles of land that’s dotted with over 550 lakes. The income from the area comes from cattle ranching, phosphate mining, and agriculture, with citrus being the cash crop. Waste in the county is taken to the North Central Landfill (NCLF) for disposal. The 2,200-acre disposal facility includes a progression of Class I and Class III landfill cells that have already been closed and those that are operating and accepting waste. Also onsite are waste-tire and household-hazardous-waste disposal facilities, an administration building, a bioreactor, and a connection to a gas-to-energy facility that uses methane from the landfills to generate electricity. It’s a busy and progressive facility that rarely shows up on the regulators’ or meteorologists’ radar. But when the 2004 hurricanes blew through, Polk County got some notice. In just over six weeks, Hurricanes Charley, Jeanne, and Frances barreled through Florida, the paths of all three crossing through Polk County. With winds exceeding 100 miles per hour, damage was extensive across the county. Trees were felled and buildings destroyed. Cleanup lasted for months, with residents and outsiders pulling to put the county back together. At the time the storms hit, the county was using its 45-acre Class I landfill (Phase II) at the NCLF for disposal of residential garbage. It had been in service since 2000 and was nearing capacity. Based on the amount of waste coming in, Phase II had approximately three years of capacity remaining. The design, permitting, and construction of another landfill, Phase III, were under way. A three-year time frame was tight but doable. But this schedule would soon seem like a vacation. Storm Damage and More If the Phase III area wasn’t completed before the Phase II area filled up, the county would have to find other alternatives for disposing of its waste. Even though tonnage rates had begun to return to their normal range, this was a still a considerable amount of garbage to dispose of. Landfills are permitted for specific tonnage rates, and an additional thousand or so tons is not something most facilities are capable of handling. The nearest facility capable of handling this additional volume was over 70 miles away from Polk County. The projected cost of hauling waste to this facility was calculated to be over $100,000 a day. Not only was this an exorbitant amount of money, but 70 miles was too great a distance; it would take too long and cause too much wear and tear on the trucks. With this cost hanging over the county’s head, everyone knew the Phase III area had to be completed before the Phase II area was filled. The project team, the Polk County Solid Waste Department and consulting engineers Jones Edmunds & Associates Inc., looked hard at alternatives to compress the design, permitting, and construction schedule. The most straightforward way to speed up the process was to divide the work into sequenced phases: site preparation and then construction. Normally, both tasks would be included in the same contract, but by separating them work could begin on the site while the final design was being completed and permitted. Keep on Trucking
On a typical day at the NCLF, before the storms of 2004, approximately 700 trucks hauled waste in and out every day. This equates to one truck every minute during a 12-hour workday. The normal route for the haul trucks is a two-lane road that runs from the Polk Parkway and State Road 570. As trucks enter the site they stop at the scalehouse, where they are weighed. If tare weights for the trucks are not on hand at the scalehouse, the trucks are also measured on the way out to determine the weight of the waste. This is required not just for billing but to meet solid waste permit conditions. The schedule allowed for six months to clear and grub 100 acres and bring in more than half a million cubic yards of soil. Transporting an additional 600,000 cubic yards of soil to the site in such a short time meant an additional 300–600 trucks were now entering the landfill. It was unrealistic for the scalehouse to weigh trucks bringing soil to the site: The facility wasn’t big enough, and it would interfere with the schedules of the trucks hauling waste. The soil trucks initially bypassed the scalehouse, but because the Phase III area is next to the active Phase II area, truckers used the same road as the waste haulers. This doubled the onsite truck traffic and disrupted solid waste and construction activities at the site. The main access road couldn’t be expanded as it ran under a four-lane highway overpass. Because of the site layout, the highway on the east side of the site, and a creek to the west, building an additional site entrance wasn’t an option. This meant construction vehicles and garbage trucks would continue to share the entrance and exit of the landfill property, but while onsite they didn’t need to travel the same route. A limestone road ended up being about 8,000 feet (1.5 miles) long, and construction started just inside the landfill property. It allowed construction traffic to turn off of the main road passing by the administration building before driving off the asphalt onto the new limerock road. This left the main road available for trucks hauling garbage to the Phase II area.
The secondary road served its purpose, but not without complications. Its path ran in front of the administration building, where the speed limit was 10 miles per hour. Truckers, however, were paid by the trip, making exceeding the speed limit too tempting. The county took several measures to deter the speeders. Oversized speed bumps were placed in the road. A digital speed-monitoring device was put alongside the road. After the excessive speeds began to cost jobs, the other drivers began to slow down. Even at slow speeds, driving large trucks on the road took its toll. Portions of the asphalt broke under the strain, but repairs waited until after the project was complete. Work was progressing at the site. As crews continued to clear and grub and transport fill dirt to the site, the engineers back in the office worked to complete the design and acquire the necessary permits. Another Hurricane Season Materials were hard to come by and transportation prices skyrocketed. Fill dirt was being shipped off to the Gulf Coast, tightening the demand in Florida and other parts of the country. Because Florida was in the midst of a housing boom, Polk County found itself competing with desperate contractors. Because of damage to oil derricks in the Gulf, fuel costs jumped, increasing 12% in just a month. Trucking companies dispatched entire fleets to the affected areas, leaving few available in the southeast. Even if material was available, getting it to the site was a challenge. The cost for completing the project was growing. Escalations in project costs were most affected by the increase in the price of fill dirt. The original estimate for landfill construction, before the 2004 and 2005 hurricane seasons, included a cost to import soil of $4 per cubic yard. After the hurricanes the price rose to $10 per cubic yard, increasing the project cost by $3.6 million. Again, the county and its consultants looked for remedies—and they found one. When the final design was completed, it was determined that landfill liner could be lowered 1.5 feet, reducing the amount of soil needed to construct the landfill footprint. While residents of the Florida peninsula had reason to celebrate the mildness of the hurricane season, rain still fell. The summer months are typically the rainy season in Florida, and June and July 2005 were no different. The road to the stockpile area was limerock, and the rain turned it into a mud bath. On-road vehicles drove through white mud, making their way slowly through the site and back to the stockpile area. Crews maintained and graded the access road almost continually just to keep it passable. Measurement and Payment As the material was brought onsite, it was stored in five stockpiles. This meant the dirt had to be handled twice: once to unload it and then again to push it into place. This wasn’t the most efficient handling practice, but with the critical time constraints it was the only alternative.
It was decided that surveying would be the best method to determine the size of the stockpiles and verify the quantity of soil. First the cleared and grubbed ground where soil would be stored was surveyed to get an initial elevation. After the completed stockpile was in place, the area was surveyed again and the differing volume calculated. Looking across the site, the stockpiles were hard to miss. With dimensions of approximately 500 feet by 500 feet by 20 feet high they were impressive. Each stockpile came in at about 110,000 to 130,000 cubic yards, and the specific volumes were used to determine payment for the contractor. From the Stockpile To prepare the base of the landfill, soil was placed on the bottom of the 80-acre footprint in lifts, each being 1-foot thick. Specifications required that a minimum modified proctor density of 95% be achieved on each lift before the next lift could be placed. Lifts began at an elevation of 105 feet and continued upward to 119 feet. With a frequency of one test every 20,000 square feet, this resulted in approximately 1,200 density tests for the entire project. Locations where density tests failed were added to the queue for the next testing round. All testing was performed by an outside party and was scheduled by the engineer. The testing company had a person onsite every day during earthwork operations to ensure a smooth and efficient operation and that work would not be held up waiting for testing and results. Soil was also moved from the stockpiles and used to fill the 30-foot-deep finger lake. But before backfilling, the lake had to be drained and the muck scraped out. Using a diesel centrifugal that ran continuously for over a week, water was pumped to the surrounding stormwater system. Once water levels were brought down, approximately 5,000 cubic yards of muck were removed. Because the lake was formed by phosphate mining, there was concern that it would contain clay slimes, a wet clayey material left over from pumping the phosphate slurry. Fortunately, only insignificant amounts of clay slimes were encountered during the course of backfilling operations. Since the haul trucks were not suited for hauling wet muck, costly fill material was wedged against the truck gate to absorb the liquid muck and prevent it from being scattered during hauling. The muck was stockpiled onsite, allowed to dry, and used for daily cover for the active landfill. In the Dark
While nighttime work is relatively common for roadwork where the public is likely to be inconvenienced by daytime operations, it’s rarely done at landfills. Lighting was installed in the areas where dirt was to be moved from the stockpiles to the landfill footprint. While lifts were placed at night and initial compaction performed, construction quality assurance testing was done only during daylight hours. During night work, the contractor was given access codes to the front gate and comings and goings were logged by the NCLF’s security system. Because the NCLF is in a rural area, there were no surrounding residents to be bothered by the nighttime work. Show’s Over Polk County and Jones Edmunds learned a lesson during the 2004 and 2005 hurricane seasons. Even the best plans can be turned upside down within six short weeks. And by thinking outside the usual scopes of work and routine, people really can move mountains—quickly. Dennis Davis, P.E., and George Reinhart, Ph.D., E.I., both work for Jones Edmunds & Associates Inc. in Gainesville, FL. Brooks Stayer is the solid waste director for Polk County, FL. MSW - September/October 2007
|
|
||||||||||||||||||||||||||||||
 |
Home | Search | Subscribe | About | News | Advertise | Register | Services | Industry Events Copyright FORESTER COMMUNICATIONS, INC
|
