Ocean County Landfill Corp.’s landfill mining project is helping preserve capacity while allowing operators to repurpose cover soil.
Preserving landfill capacity is a foremost objective for today’s landfill operators thanks to increasing complications with both permitting of new sites and expansion of existing ones.
In an effort to maximize the capacity at its 300-acre landfill in Manchester, New Jersey, Ocean County Landfill Corp. began to look at options in the mid-2000s for preserving space at the site.
The company first looked at redeveloping an older, unlined portion of its landfill built between 1972 and 1985, which comprised around 60 acres. The original goal was to expand capacity and extend the lifespan without requiring a horizontal or vertical expansion beyond what the landfill was presently permitted for.
“The footprint of the landfill is pretty well-established, and we don’t really have the luxury of going out any farther without encroaching on neighborhoods and wetlands and things like that,” explains Martin Ryan, vice president of engineering at Ocean County Landfill Corp. “So, as we were looking at the lifespan of our facility and trying to figure out ways to squeeze a little more time out of it, we thought that certainly a vertical expansion was something that was a possibility, but that’s not a definite thing that will get approved by the regulators. Also, I think there’s some sensitivity to the surrounding community, as well. You don’t want to have this huge mountain of garbage sticking up out of the pine trees [that surround the landfill], so we had kind of settled on our final elevation with some sensitivity to the surrounding community.”
Ryan says the company first discussed an overliner design where new waste could be placed on top of the existing capped areas within the vertical limits the site was approved for. In order to assess the viability of this, Ocean County Landfill Corp. had waste composition tests performed. The primary goals were to gauge the thickness of cover soils and to obtain waste characterization, condition and stage of decomposition data.
“The firm we hired did a biomethane potential (BMP) test, which basically said that the waste was largely ‘cooked,’ for lack of a better word,” Ryan says. “This meant it was largely decomposed. The testing also found the mass should be stable and not prone to a lot of settlement, while simultaneously showing that there was quite a bit of cover soil there.”
Ryan says, at the time, the landfill was importing almost every yard of soil it was using for cover and capping construction. Between the desire to minimize the height of waste at the landfill and the ample supply of cover soil that would eliminate the need to outsource from third parties, Ocean County Landfill Corp. decided that landfill mining, not installing an overliner, was the best course of action.
Ryan says that, at the time, no landfill mining project of the scale the company was proposing had been undertaken in New Jersey. This necessitated both ample planning and time needed to secure permitting.
“We were looking at mining basically all of the waste that’s in that old, 60-acre part of the landfill, but we looked at it as a win-win because we would be keeping our construction crews busy with mining during times in between building baseliners and caps, we would create a lot of cover soil for us to help offset the need to then import all that soil, and then we’d also develop a new area for future landfilling, which we hope will allow us to operate until around 2036 or 2037, [beyond the original estimated close date of 2024],” Ryan says.
Mining for opportunity
After going through all the regulatory hurdles to be approved by the state, Ryan says that they began screening operations in 2014. They developed a plan for phased excavation and base liner construction that constituted three phases, which would stretch out over approximately 15 years.
Lawrence Kiesel, vice president of construction at Ocean County Landfill, says before commencing operations, the company evaluated several different types of screens for the project. The company demoed both shaker deck-type screens where waste was placed in the top and fines and dirt filtered out the bottom as well as trommel screens that spun to accomplish the same goal.
Ocean County ultimately settled on a Doppstadt SM720K trommel screen since the circular rotation was able to better separate the dirt from the waste. Kiesel notes that the company uses an excavator to dig to a depth of around 40 to 45 feet. The excavator then transfers the waste to an off-road end-dump truck so the material can be moved from the area that is being mined to a separate screening station, where another excavator feeds the hopper of the trommel screen. A wheel loader is then used to load the resulting material into off-road end-dump trucks, which transport the 2-inch-minus cover soil and over 2-inch waste materials, respectively, back to the site’s active landfill cell.
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