M6 PM Fate and Transport of Pollutants from Dredging and Placement
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 324-326

(THI-1117-833308) PAH volatile emissions from dredged material-1. Windtunnel measurements and results.

thibodeaux, l¹, fountain, k¹, price, c², ravikrishna, r¹, valsaraj, k¹, ¹ louisiana state university² us army corp of engineers

ABSTRACT- Flux measurements to air were made on naphthalene, methyl naphthalene and phenanthrene using 2.3 cubic meters of dredged material from Indiana Harbor and Canal, Chicago Il. The DM was extracted by a mechanical dredge, placed in drum containers, shipped and held in a refrigerated truck prior to mixing and placement in the pilot-scale size windtunnel. Atmospheric air at ambient temoeratures and humidities was drawn through the device. Three experiments were performed over a three month period from November '03 to January '04. Re-working and re-watering was done between experiments. The windtunnel was a rectangular shaped box positioned above a 1.2 meter wide by 4.6 meter long lysimeter. A constant 1.2 m/s(2.6 mi/hr) wind speed was maintained. The soil loadings were 2.7, 1.2 and 4.3 mg/kg dry for NAPH, M-NAPH and PHEN respectively. The maximum fluxes observed were 50, 25 2.0 ng/sq cm/hour respectively. They occured several hours into the experimental runs! All three chemicals displayed this very unusual flux-vs-time pattern. Numerous previous flux experiments using small laboratory-scale size evaporation surfaces all displayed the maximum flux at time zero followed by a decreasing flux which decayed exponentially with time. Based on water saturation measurements in the windtunnel soil it was concluded that the moisture vs time behavior was key to interpreting the unusual flux pattern. Initially for a short time-period the flux was near zero. This was followed by a dramatic period of increasing flux with increasing time till a maximum was achieved. Afterwards the flux decreased in the usual exponential decay fashion. A 3-regime water dominated process is proposed to explain the flux pattern. During Regime-1 a layer of water or "soupy" fluid mixture covers much of the soil surface. A small flux occurs but quickly disappears because of non detectable concentrations in air. Regime-2 occurs as the surface soil porespaces become progressively air-filled. Volatilization rate increases as these "dry patches" increasingly form on the surface with time. When the entire surface becomes dry, in the sense that all surface porespaces are air filled, the maximun flux occurs. Regime-3 is characterized by decreasing fluxes as chemical depletion occurs in the surface layers slowing the chemical emission process.

Key words: transport chemodynamics, dredge material storage, sediment remediation, air toxics