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Most waste management techniques—including stabilization/solidification, soil washing, and precipitation/filter press—take more of a trial-and-error approach to environmental cleanups, failing to exploit the waste's fundamental chemical behavior. The result is scientifically inferior processes, wasted time and resources, and recurrence of the same old problems at treated sites. This column defines some of the principal problems of waste management technologies and recommends a prudent approach to their resolution. Several of the author's personal experiences are used to support his arguments. The technologies cited here were selected based on their widespread use, their cost-effectiveness, their ease of application, and their intrinsic limitations.     

Geographical analysis of tourism sites in Andaman Archipelago (India) and ecotourism development for Smith Island of North Andaman

This paper applies the nearest-neighbour analysis to analyse the clustering of tourist attractions in Andaman region and suggests ecotourism development for Smith Island of North Andaman using remote sensing techniques. The results indicated that present tourism sites are distributed in clusters in three regions (Port Blair, Mayabunder and Diglipur). To avoid concentration of tourism sites and population pressure in one particular area, there is a need to promote tourism to other locations as well. The study provided suggestions for ecotourism development in Smith Island after analysing its various ecological features to support the Andaman Administration’s vision to promote ecotourism.     

The impact of high level gamma radiation on immobilized waste forms in polymeric matrices

A new polymer-based composite binder was developed for the containment/immobilization of radioactive waste forms. This material was subjected to a variety of physicochemical tests to determine its suitability for this purpose. It appears that this composite material possesses superior qualities in terms of resisting radiation damage, retaining the radio isotopes after radiation exposure, and resisting biodegradation. Further, a combination of chemical fixation/immobilization technology with the radiation-resistant binder was studied. Our evaluation procedures, the results, and its potential applications based on our conclusions are presented in this article.     

Physicochemical mechanisms controlling the periodic release of flammable gases from hanford tanks

Hanford tanks contain more than 60 million gallons of high-level wastes produced by decades of extracting plutonium from irradiated uranium fuel. The wastes were concentrated to a thick slurry consistency by evaporation prior to storage to minimize space. The resulting concentrated waste properties introduced unanticipated, detrimental conditions affecting workers' and the public's health and safety and involving the release of potentially flammable gases. The released gases consist primarily of hydrogen, nitrous oxide, and ammonia. Dilution and sluicing were initially proposed to mitigate the flammable gas safety conditions. As a result of evaluations, the mechanisms and conditions that are thought to control the accumulation and spontaneous release of flammable gases were identified and confirmed. The technical rationale was established for developing operational approaches to mitigate the periodic generation of flammable gases in existing tanks and to avoid any reoccurrence of this serious safety problem during future waste management activities. The chemistry of the two highest risk tanks was examined to test the potential for reversing the conditions causing gas buildup and the consequences of sluicing without appropriate chemical conditioning. The identified mechanisms apply equally to the remaining flammable gas tanks at Hanford as well as to other waste tanks in the DOE complex, particularly those at Savannah River. Passive means of mitigating the flammable gas condition require less than 1:1 dilution, and sluicing wastes from tank 106-C can be accomplished without creating a flammable gas condition. Carbonate equilibria reactions and their effect on aluminum speciation are largely overlooked and provided the key for explaining the episodic release of flammable gases from tank wastes. The reaction of atmospheric carbon dioxide with a sodium hydroxide-rich waste solution produces carbonate precipitates. More importantly, this reaction lowers the pH of the waste and precipitates aluminum hydroxide as a gel. The wastes contain substantial amounts of complexing agents such as ethylene diamine tetraacidicacid (EDTA), hydroxy ethylene diamine triacidic acid (HEDTA), and their degradation products. These complexing agents stabilize the aluminum hydroxide gel together with chromium, manganese and iron hydroxides, and oxybydroxides under the resulting pH conditions. These complex species may coprecipitate and accumulate as a metastable layer in the middle and lower levels of th tank. The complexed aluminum hydroxide acts as a binding agent trapping other particulates in a microcrystalline mat. Microcrystalline particles such as sodium nitrite provide the structural strength for the mat. Once the gas accumulation below the gel layer achieves a critical buoyancy sufficient to rupture the microcrystalline mat, a gas release event occurs. The cycle of gas buildup and release continues each time the buoyancy of the trapped gas exceeds the hydrostatic pressure and the gels' plasticity modulus. Stokes Law predicts a particle settling rate in the tank of less than 50 days, well within the bistorical periodicity of GREs. Laboratory tests, forming the basis of a recent patent application, verify that large quantities of complexed aluminum hydroxide gel are produced by passing carbon dioxide through simulated waste solutions (Hobl, 1993) equivalent to those found in tank 101-SY. It was confirmed that a simple adjustment of pH witll redissolve the gel, thereby reducing viscosity and safely facilitating continuous flammable gas release. Additional experiments were undertaken to provide a basis for understanding the role of complexed aluminum hydroxides in the CO₂/NaOH/Al(OH)₃ (complexing agents)/NaAlO₂ system. This article examines a plausible mechanism for the periodic release of flammable gas and considerations for: (1) remediating existing flammable gas tanks through a combination of chemical treatment and mixer pumps; (2) diluting, combining, retrieving, and storing wastes; (3) preventing clogging of transfer lines; (4) sludge and soil washing; and (5) cribs, ponds, basins, and ground-water cleanup. This study provides a singificant breakthrough for tank waste management by explaining key mechanisms controlling episodic release of flammable gases. The breakthrough provides the bases for removing the tanks classified as flammable gas from the wathclist and has broad operational applications with a potential for billions of dollars in cost savings.