Contracted by the City of Tucson and its Environmental Management Department, Hydro Geo Chem, Inc. has completed Phase I of a Landfill Stabilization Program that is designed to achieve a breakthrough concept in landfill waste management: enhanced aerobic degradation of landfill wastes. Test results and theoretical considerations indicate that the promise of substantially reducing the time and money spent on maintaining closed landfills and turning unproductive land into an asset may become a reality.

Wastes in most landfills slowly decompose anaerobically, that is, in the absence of air. Anaerobic microbes are both sluggish and inefficient; we have estimated that inactive landfills in the arid West may take s150 years to reach a point where decomposition is negligible. During this time anaerobic microbes produce copious amounts of methane, an explosive gas that may migrate beyond its source into houses and utility vaults, sometimes with deadly consequences. It is also apparent that methane and other landfill gases enhance the migration of other harmful volatile organic chemicals into groundwater supplies. Furthermore, methane is a greenhouse gas, having twenty times the effect of an equal volume of carbon dioxide.

However, in the presence of the correct mixture of air and water, anaerobic microbes give way to their more energetic cousins, the aerobes, which theoretically can reduce the same wastes up to 50 times faster, without generating harmful quantities of methane. Active aerobic decomposition consists of managing the air and water flows through the landfill to achieve optimal rates of waste reduction. Thus, a short period of proactive management replaces an indefinite period of reactive monitoring. Details of the concept to be applied to the Rio Nuevo Redevelopment in Tucson, Arizona, can be found in the November edition of BioCycle (www.biocycle.net). The pilot test is underway and will be completed by fall of 2001.