The Alternative Cover Assessment Program: In Search of a Better Way to Take Out the Trash

Last year, the United States generated more than 220 million tons of solid municipal waste. While some of that waste was recycled or burned, most of it made its way to one of the more than 3,000 landfills scattered across the nation, where big money is being spent to keep it out of sight and out of mind. Let's face it, safely containing all that stuff we throw away is a dirty job-one of those jobs that "somebody" has to do. As a key player in ACAP, the Alternative Cover Assessment Program, DRI hydrogeologist Bill Albright not only doesn't mind being that "somebody," he's downright enthusiastic about it.

"This is a really great program because it's truly collaborative," says Albright. "The waste site operators, the regulators, the scientists, we're all working together on this, and we're all going to benefit from it." Albright, along with DRI's Brad Lyles, Glendon Gee of Pacific Northwest National Laboratory, Craig Benson of the University of Wisconsin, Madison, and Steve Rock of the Environmental Protection Agency (EPA) in Cincinnati created ACAP to help landfill operators, regulatory agencies, and engineers design, test, and put to use innovative and cost-effective new landfill covers, the caps that are placed atop closed landfills. The benefits Albright speaks of will include big savings for landfill owners, reliable data on cover performance for regulatory agencies, and lots of good basic hydrologic data for scientists.

But what brought Albright, a water guy with years of experience studying the hydrology of the southern Nevada desert, into the wonderful world of municipal waste? "Actually, it's not a waste issue, it's a water issue," says Albright of the key to containing a landfill or other hazardous materials site. He goes on to explain that, assuming your waste material is physically confined as in a landfill, the most likely means for the spread of landfill contaminants is via water. Precipitation that is allowed to percolate through waste can contaminate groundwater. And, since the fate of fallen water-and what it might carry with it-has been the primary focus of Albright's previous years of work on the Nevada Test Site, the transition was a natural one.

"As that work began winding down, I started looking around for other hazardous or radioactive waste sites that might need the kind of expertise we'd gained over the years," Albright says. "Most of those places already had their own set of experts, so I got it into my head to look at municipal sites and, specifically, do some cover work."

In light of Albright's previous experience, covers were the obvious place to focus. A landfill cover's primary purpose is to keep water away from the waste. Prescribed covers-those designs that currently carry the approval of regulatory agencies-traditionally do this with layers of compacted clay and/or a synthetic membrane to create a waterproof barrier between the world and the waste.

"It's a raincoat approach," says Albright. Sounds simple, but there are problems with these "raincoats." There is the potential of cracking in the clay, root penetration of the barriers, and the possible adverse effects of freezing. Then there is the cost, which Albright points out is considerable. "A typical membrane cover costs between $65,000 and $75,000 per acre. A fancier one could be up to $150,000 per acre, and most of that cost comes from trucking in the huge amounts of soil you need to make the clay barrier."

But according to Albright, the core problem with prescribed covers-and the reason they are costly when they don't necessarily need to be-is that they rely on material specifications (in this case, low permeability) instead of the soil-plant-atmosphere system as a whole. As a result, a single prescriptive cover design can be applied in any location without regard to the physical environment. In arid Arizona or watery Washington, landfill cover design is essentially the same. Without field data on alternative cover performance, it was difficult for landfill operators to use less costly approaches that might work just as well, or better than the prescriptive designs. And that's where Albright saw the opportunity to develop an interdisciplinary design methodology and a program to objectively test alternative covers and compare their effectiveness to traditional ones. Without the data to back them up, regulators simply couldn't give alternative covers the okay. "The philosophy of ACAP," says Albright, "is to replace these prescriptive covers with descriptive covers-covers that reflect the specific environmental conditions at each site. We want to do away with the one-size-fits-all approach."

The basic idea of most alternative covers is to avoid the use of unnatural physical barriers and instead incorporate native soils and plant communities to do the job, eliminating the huge expense of installing geomembranes and trucking in soil. Properly combined soil layers, native trees, shrubs, and grasses can contribute greatly to creating an effective water barrier. Plant roots take up water from the soil before it can penetrate deeply, and leaves return it to the atmosphere through transpiration.

To prove that alternative covers can do the job in a variety of climates, the ACAP team, in close cooperation with the EPAand site operators and engineers, has set up a network of twelve test sites at landfills across the country (http://www.dri.edu/Projects/EPA/boston-brochure2.html). Here they've built both prescribed and alternative covers in 10-meter by 20-meter test pads, carefully designed, instrumented, and monitored to provide hard data on how well they perform. Each test site is fully contained, somewhat like a swimming pool, by a tough waterproof membrane. Each lift, or layer of soil, has been carefully planted with instrumentation to measure its moisture content. Any surface runoff and recharge (water that makes it through the cover layers to the containing membrane) is collected and measured. The sites are topped with the chosen vegetation (i.e., hybrid poplars in Albany, Georgia; native grasses and oleander shrubs in Sacramento, California), and climate conditions like rainfall, snowfall, air temperature, solar radiation, and humidity are monitored and recorded.

With construction of all the test pads completed in November of 2000, the researchers are now eagerly tracking the performance of each site as data is continuously uploaded. "We'll probably collect data for about five years," says Albright. "The plant communities need time to mature and get their roots through the entire soil profile, and we need to see some variety in seasonal rainfall."

Those data eventually are going to make a difference in how we handle our municipal waste by improving computers models used to design and predict the performance of landfill covers. But, if Albright sees it right, that's not the only use for the data. "One of the most attractive things about this project, from a scientific perspective, is that even though it's being applied directly to the issue of waste management right now, the data we're gathering and the facilities we've built have the potential to contribute to a lot of other areas-recharge investigation, plant physiology, snow-melt process, flood control. We can benefit from ACAP in a lot of ways."

And that sounds like a pretty fresh way to handle a dirty job.