ADCs Conserve Space By Reusing Disposed Material

Curt Holman

Landfill owners from coast to coast are discovering the benefits of segregating some of their waste materials to use as alternative daily covers (ADCs).

Most landfills have mandates to use approximately six inches of soil daily to cover solid waste. When disposed materials are used as daily covers, however, they often can save space, extend landfill life and, in some cases, cut costs.

"Alternative daily covers are the items that could have the most im-pact on reducing landfill costs," Juan Vargas, senior project manager, HDR Inc., El Dorado Hills, Calif., told World Wastes. He said that ADCs have yet to find wide-spread use, which he attributes to technical limitations.

Paul Emond, environmental en-gineer for the Massachusetts Di-vision of Solid Waste Management, Boston, added, "There is an in-creased interest in alternative daily cover materials, mostly in residuals from recycling facilities."

Emond said that his division has approved ADCs including compost, sludge, wood ash, modified construction and demolition debris and treated soil that had been contaminated with oil. "Nobody's using foams or fabric covers here yet, but we get frequent inquiries for ap-proval," he said.

He added that for many materials, reducing cover thickness isn't the point. "These materials have to be used in the same thickness as soil. The advantage is that these are materials being thrown away that don't have to be covered. They can be the cover."

Emond cited the example of Browning-Ferris Industries' (BFI) East Bridgewater Landfill in Fall River, Mass., which has been testing a cover material derived from automobile shredder residue (ASR) since March 1992. Richard Marti-ni, district manager for BFI North-ern Disposal, explained that the material comes from ground, nonmetallic automobile scrap (from the dashboard, seats, etc.) that is combined with cement. According to Martini, the modification makes the material heavier than ASR "fluff" and thus more suitable as a landfill cover.

BFI's test is scheduled for completion this November. "After the test is over we'll apply for unrestricted use. Currently we're using [the material] on half the landfill face and dirt on the other half," he said. "I see no problem with its use as top cover. In terms of workability, odor control, seagull control and things like that, it seems equal to soil."

Yolo County, Calif., found savings of another sort by using chipped green waste as an ADC. Tamara Bowcutt, assistant director of public wastes and transport for Yolo County Public Works, spoke highly of the material. "There's seasonal variation in the quality of the material itself, but not in its performance. In the fall, when yard waste is primarily leaves instead of grass, we put in a thicker layer of material, because leaves are lighter."

For the Yolo landfill, finding a replacement for soil was a matter of necessity. "We are short of cover, period. We're dirt-poor. We don't have enough on-site cover material to last through 2021 - the life of the landfill - which was the impetus for finding an alternative."

The landfill, located near Sac-ramento, still uses soil, but in smaller amounts. With green waste as a cover material, the solid waste to soil ratio has been increased from 3:1 to 7:1. "I can't put a target figure on the financial savings, but we are saving," she said.

By using less soil, the site reportedly saves hauling costs and time. The site's compactor can spread and compact the chipped green waste more easily than soil.

Bowcutt said, "I can't say it would be fine for all landfills, but as much as our landfill's representative of any other, I think it would work." She added that the county recently received a grant to test shredded tires as cover material.

Other ADCs include recycled newspaper slurry, which Newaste-con Inc. of Toledo, Ohio, markets in a spray form called ConCover, and stabilized fly ash, which Energy Answers Corp., Rochester, N.Y., is currently testing to cover landfilled incinerator ash (see story on p.12).

Johannes Graven and Fred Pohland of the University of Pitts-burgh warn that before an ADC can be approved, operators must ensure that it doesn't cause problems such as excessive vectors, odors, moisture infiltration, combustibility, dust or litter. In their paper Developments in Alternative Cover Materials for Landfill Appli-cation, they caution that the suitability of an indigenous material (a locally available waste product) often depends on site-specific conditions.