Neil J. Hutzler

Vapor transport in unsaturated soil columns: Implications for vapor extraction

A mathematical model was derived to examine the impact of gas advection, gas diffusion, gas-water mass transfer, gas-water partitioning, sorption, and intraaggregate diffusion on subsurface movement of organic vapors. Laboratory experiments were performed to determine the validity of the model and to investigate the impact of the various mechanisms on vapor transport. Columns were packed with a uniform Ottawa sand and an aggregated porous soil material (APSM) to compare transport in different soil structures. Toluene vapor transport was observed in the sand under dry and wet (27% water saturation) conditions. The experiments with the APSM were performed dry and at 67% water saturation. In all the sand and the dry APSM experiments, gas advection and diffusion had the greatest impact. In a wet APSM experiment, intraaggregate (liquid) diffusion was also important to consider for gas velocities greater than approximately 0.05 cm s−1. For both soil materials, sorption of toluene vapors occurred for dry conditions, while vapor sorption was negligible when liquid water was present. These findings imply that vapor extraction performance in moist, aggregated soils will be affected by nonequilibrium transport. Therefore models that are developed for predicting the complete removal of contaminants by vapor extraction must account for nonequilibrium.

Wastewater disinfection and infectious disease risks

Under certain conditions, direct exposure to wastewater effluents during swimming or indirect exposure via consumption of shellfish taken from contaminated waters or drinking water produced from contaminated supplies may cause human infectious disease. Prior data on outbreaks associated with such cases will be reviewed along with relevant epidemiological and dose‐response studies. The relationship between these data and policy setting for microbial effluent criteria will be discussed.

Quantitative Mineral Determinations of Industrial Coal Ash

The majority of coal ash generated by electric utilities and power plants of industrial manufacturers is disposed of in landfills; the remainder is used primarily as admixtures in construction materials. Predictive computer models used to assess the environmental impact of disposal or utilization need quantitative information on ash composition and mineralogy. Typically, compositions are reported as elemental concentrations, but this data does not indicate the mineral or glass (amorphous) phases in which the elements are contained. Such phases affect the leaching mechanisms and rates. X-ray diffraction and scanning electron microscopy combined with energy dispersive X-ray spectrometry, common methods for qualitative mineral identification and particle characterization, were used to quantify coal ash mineral compositions. Samples of industrial coal ash from a stoker boiler and a fluidized bed combustion (FBC) system were analyzed and the results were compared to those for a standard sample of coal ash from...