Diffusive-Gas Transport of Volatile Organic Carbons from a Source in an Unsaturated (Vadose) Zone
Journal Title: IOSR Journal of Environmental Science, Toxicology and Food Technology (IOSR-JESTFT) - Year 2019, Vol 13, Issue 1
Abstract
In the absence of pressure gradients, conditions prevalent in the batch experiments, gas –phase diffusion dominates migration of volatile pollutants in the unsaturated zone. Gas –phase diffusion in the unsaturated zone is affected by partitioning into soil-water, onto air-water and into or onto solid. The process spreads only the contaminants in the gas phase where contaminants with low mass fraction fa in the soil gas diffuse more slowly depending on the soil and chemical properties on the diffusing substance. This study shows Non-aqueous phase liquids (NAPL) compounds with higher mass fraction (Isooctane (0.82), n-hexane (0.78), methylcyclopentane (0.54)) diffuse to a longer distance (1.75m, 1.30m, 1.50m) than those with low mass fraction (toluene (0.04), m-xylene (0.04), octane (0.09), (60m, 60m and 51 m respectively) from a source zone. The diffusion coefficient D’ calculated was also higher for these compounds; 0.05, 0.05, 0.05 and 0.00, 0.00 and 0.001 respectively. At transient diffusion described by the sorption- affected diffusion coefficient, compounds with higher vapour pressure as Isooctane, n-hexane, methylpentane showed higher mass fraction in soil gas, a phenomena that accounts for their higher diffusion rate hence longer distance attained before attenuated. The results obtained shows isooctane travel the most distance (1.3 m) before been attenuated to 1 % of the original concentration of a source zone, a reason attributed to it recaltricant and slow degradation nature.
Authors and Affiliations
Edward Membere, Emmanuel Johnson
Keywords
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- EP ID EP443098
- DOI 10.9790/2402-1301011118.
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