The in-situ remediation of a lead-contaminated soil (silt loam, K-H = 5 x 10(-8) cm/s, soil Pb = 1,000 mg/kg) by electrokinetic (EK) soil flushing [60 V (DC)] was studied. Research focused on the chemical conditioning of the electrode reservoirs with either 500 mu S/cm (as NaNO3, baseline behavior), acetic acid (HAc), HCl, or EDTA. For baseline tests there were significant amounts of lead transported through the soil, but the Pb precipitated or was readsorbed on the soil adjacent to the cathode because of the high soil pH in that region. The addition of 1 M HAc to the cathode reservoir prevented the formation of the basic conditions in the soil, and about 65% of the Pb was transported into the cathode. When HCl was added to the anode and HAc was added to the cathode, more than 75% of the lead resided in the cathode. Pb removals in the EDTA-experiments were greater than those observed in the baseline experiments and were similar to those observed in the HCl-HAc experiments. A low anode reservoir pH resulting from a high current was the most likely reason.
Using a three-dimensional stochastic model of radionuclides in forests developed in Part I, this work simulates the long-term behavior of Cs-137 in forest soil. It is assumed that the behavior of Cs-137 in soils is driven by its advection and dispersion due to the infiltration of the soil solution, and its sorption to the soil matrix. As Cs-137 transport through soils is affected by its uptake and release by forest vegetation, a model of radiocesium behavior in forest vegetation is presented in Part III of this paper. To estimate the rate of infiltration of water through the soil, models are presented to estimate the hydrological cycle of the forest including infiltration, evapotranspiration, and the root uptake of water. The state transition probabilities for the random walk model of Cs-137 transport are then estimated using the models developed to predict the distribution of water in the forest. The random walk model is then tested using a base line scenario in which Cs-137 is deposited into a coniferous forest ecosystem.
To understand the behavior of radionuclides in forests, we require information on the processes which govern the interaction of elements in these ecosystems. The basic questions we ask are: (1) What is the residence time of any element in a forest? (2) What are the dominant rate determining processes responsible for uptake? (3) What are the important radionuclide pathways through the forest to man? (4) How long does the contamination remain a risk to man? (5) What chemical complexing species are responsible for element uptake by the roots. Such questions must be answered to define better the processes which are responsible for the distribution and fate of trace elements and radionuclides in forest and natural ecosystems, and to develop predictive models for radiological assessment purposes.
To understand the behavior of radionuclides in forests, we require information on the processes which govern the interaction of elements in these ecosystems. The basic questions we ask are: (1) What is the residence time of any element in a forest? (2) What are the dominant rate determining processes responsible for uptake? (3) What are the important radionuclide pathways through the forest to man? (4) How long does the contamination remain a risk to man? (5) What chemical complexing species are responsible for element uptake by the roots. Such questions must be answered to define better the processes which are responsible for the distribution and fate of trace elements and radionuclides in forest and natural ecosystems, and to develop predictive models for radiological assessment purposes.
