Chemical changes and leachate mass balance of municipal solid waste bottom ash submitted to weathering.

A study on the chemical stability of municipal solid waste (MSW) bottom ash submitted to weathering was carried out in order to identify and quantify the physico-chemical maturation mechanisms in a large heap (375 tonnes) over a period of about 18 months. The mineralogy and chemical composition of MSW bottom ash were analysed on fresh and maturated material. Calcite is the predominant newly formed mineral during bottom ash maturation, combined with aluminium hydroxides and various sulphates. Lead and zinc are trapped primarily by newly formed carbonates. Monitoring of the pore water and the outlet leachates revealed a marked contrast in the physico-chemical conditions within the heap and at the outlet. The salinity of the fluids peaked at around 16 g/l within the first few weeks and then progressively decreased to fluctuate between 5 and 8 g/l. Due to the high pH of the pore water, the average concentrations of heavy metals in the heap are high: 42.7, 9.6 and 0.8 mg/l for Cu, Pb and Zn. At the heap outlet, however, the leachates are buffered by carbonate precipitation due to equilibration with atmospheric CO2. Copper complexed as a chloride at the outlet remains at a relatively high concentration (10.2 mg/l), whereas Pb and Zn concentrations are below the limit of detection (<25 microg/l). A mass balance carried out over the 18 months of monitoring indicated that 86% of remobilized material within the heap is evacuated from the system. Within the heap, carbonation trapped 43 and 54% of the calcium and bicarbonate flux. The copper, lead and zinc flux at the heap outlet represent only 34, 18 and 19% of the actual remobilized mass of heavy metals.

Radon (222Rn) level variations on a regional scale: influence of the basement trace element (U, Th) geochemistry on radon exhalation rates.

The approach proposed in this study provides insight into the influence of the basement geochemistry on the spatial distribution of radon (222Rn) levels both at the soil/atmosphere interface and in the atmosphere. We combine different types of in situ radon measurements and a geochemical classification of the lithologies, based on 1/50,000 geological maps, and on their trace element (U, Th) contents. The advantages of this approach are validated by a survey of a stable basement area of Hercynian age, located in South Brittany (western France) and characterized by metamorphic rocks and granitoids displaying a wide range of uranium contents. The radon source-term of the lithologies, their uranium content, is most likely to be the primary parameter which controls the radon concentrations in the outdoor environment. Indeed, the highest radon levels (> or = 100 Bq m-3 in the atmosphere, > or = 100 mBq m-2 s-1 at the surface of the soil) are mostly observed on lithologies whose mean uranium content can exceed 8 ppm and which correspond to peraluminous leucogranites or metagranitoids derived from uraniferous granitoids.

Diffuse volcanic emissions of carbon dioxide from Vulcano Island, Italy.

RECENT investigations on Mount Etna (Sicily)(1-3) have revealed that volcanoes may release abundant carbon dioxide not only from their active craters, but also from their flanks, as diffuse soil emanations. Here we present analyses of soil gases and air in water wells on Vulcano Island which provide further evidence of such lateral degassing. Nearly pure carbon dioxide, enriched in helium and radon, escapes from the slopes of the Fossa active cone, adding a total output of 30 tonnes per day to the fumarolic crater discharge ( 180 tonnes CO(2) per day). This emanation has similar He/CO(2) and (13)C/(12)C ratios to those of the crater fumaroles (300%ndash;500 degrees C) and therefore a similar volcanic origin. Gases rich in carbon dioxide also escape at sea level along the isthmus between the Fossa and Vulcanello volcanic cones, but their depletion in both He and (13)C suggests a distinct source. Diffuse volcanic gas emanations, once their genetic link with central fumarole degassing has been demonstrated, can be used for continuous volcano monitoring, at safe distances from active craters. Such monitoring has been initiated at Vulcano, where soil and well emanations of nearly pure CO(2) themselves represent a threat to the local population.