Looking Up

WHEN OPERATORS LOOK TO EXPAND a landfill, physical restrictions can be problematic. This was the case with the Hoffman Road Landfill in Toledo, Ohio, which planned to expand in 2003. Although the city had received approval from the Columbus-based Ohio Environmental Protection Agency for a horizontal and vertical expansion, the expansion area was boxed in and there was simply no room for the additional sedimentation pond that was needed. Project engineers needed a solution — and they decided there was nowhere to go but up.

The landfill expansion was necessary because the landfill is licensed to receive 1,500 tons per day and needed additional room to keep up with incoming waste. Part of the expansion process required installing an additional sedimentation pond in the southernmost portion of the landfill next to the wetland area. This would augment the existing system of settling ponds and enhance the landfill's ability to comply with the federal National Pollution Discharge Elimination System (NPDES) permit requirements.

However, the landfill operators were having problems locating the pond. The landfill is bounded on the east by a pair of overhead high-voltage transmission lines, a railroad repair yard and Interstate 75. To the west, there is a pair of high-pressure petroleum pipelines, a railroad switching yard and a major automobile manufacturing plant. To the north, there is the Ottawa River and Mudd Creek. A wetland area borders the south side of the landfill. Simply put, there was nowhere for the needed pond to go.

At first, it seemed that encroaching on the existing wetlands was the only expansion solution. Before the expansion permit was issued, the landfill had completed an extensive wetland delineation study. Because the wetland boundary was marked with signposts identifying the perimeter during the study, project engineers knew the physical restrictions they were facing. With the southern portion of the landfill dropping off rapidly into the wetland area and the Mudd Creek drainage area, they knew it would be necessary to build up the embankment area to retain water for the settling pond. Although the footprint of the sedimentation pond was outside the wetland area, the outermost four-to-one slopes required in conventional construction would encroach upon the wetland area.

The city then faced potentially long construction delays to file the appropriate permits to encroach upon the wetlands and to negotiate the required offsets. Project engineers decided that there was a better solution — using vertical construction for the perimeter wall.

After costing-out several options, including a conventional concrete retaining wall, they used a wire-formed retaining wall system manufactured by Atlanta-based Tensar Earth Technologies Inc. The system consists of welded wire baskets with an attached geogrid and backfilled with stone. There is a mechanical connection between each unit. Given the plasticity of the soils near the wetland area, engineers thought this system would better withstand the differential settlement likely to occur. The positive connection also served as a visual quality control check during the construction process.

By using the vertical construction of the perimeter wall, the footprint and volume of the sedimentation pond remained unchanged, providing sufficient design volume to meet the landfill's regulatory requirements. As an additional enhancement, the landfill added a Faircloth Skimmer, which consists of a perforated floating skimmer ring connected to a valve located at the invert of the primary discharge pipe. That allows systematic drainage of the sedimentation basin once the pond has stabilized after it rains. Also, additional retention time is allowed during the next rain storm as the pond refills to its design capacity.

Construction started on Feb. 8, 2003, and was on a tight schedule because the landfill's permit required the pond to be completed before to the start of the wetland growing season on March 31. Good weather permitted the project to be completed on schedule with minimal effects to the adjacent wetland area.

Overall, the landfill operators thought they had been backed into a corner, but with a little creativity, they soon realized things were looking up.

David Leffler
Division of Solid Waste
Toledo, Ohio