W. L. Daniels

Beneficial Use of Dredge Materials for Soil Reconstruction and Development of Dredge Screening Protocols

Upland placement of dredge sediments has the potential to provide beneficial reuse of suitable sediments for agricultural uses or urban soil reconstruction. However, the use of many dredge materials is limited by contaminants, and most established screening protocols focus on limiting major contaminants such as heavy metals and polycyclic aromatic hydrocarbons and generally ignore fundamental agronomic parameters. Since 2001, we have placed over 450,000 m of Potomac River fresh water dredge materials and 250,000 m of saline materials from various locations into monitored confined upland facilities in Charles City, VA, and documented their conversion to agricultural uses. Groundwater and soil quality monitoring has indicated no adverse effects from material placement and outstanding agricultural productivity for the freshwater materials. Once placed, saline materials rapidly leach and ripen with quick declines in pH, electrical conductivity, and sodicity, but potentials for local groundwater impacts must be considered. Our experience to date indicates that the most important primary screening parameter is acid-base accounting (potential acidity or lime demand), which should become a mandatory analytical requirement. Our second level of acceptance screening is based on a combination of federal and state residual waste and soil screening standards and basic agronomic principles. High silt+clay and total organic C may also limit rapid use of many dredge materials due to extended dewatering times and physical limitations. This dredge material screening system separates potential upland placement candidates into three soil quality management categories (unsuitable, suitable, and clean fill) with differing monitoring requirements. Similar use of these sediments in urban soil reconstruction is also recommended.

Oxidation Rate of Pyrite from Brazilian Coal as Affected by CaCO3, Oxygenation, and Crystal Size

This study evaluated the effects of crystal size, CaCO3 and H2O2 simulated oxygenation doses on the kinetics of pyrite (FeS2) oxidation in order to better predict the potential behavior of pyrite in various mine backfill settings in Brazil. As expected, oxidation rate decreased with increasing crystal size and was slower at higher doses of CaCO3, except for the finest grains, where a liming effect was not evident. These results suggest microencapsulation via precipitation of Fe onto surfaces of the pyrite crystals leading to decreasing oxidation rates. Higher doses of CaCO3 were necessary to stabilize pyrite at the lowest oxygenation levels, but the reaction efficiency of CaCO3 was decreased at higher concentrations of H2O2. These data point out the importance of understanding the fundamental interactions of pyrite grain size, oxygenation, and the potential for Fe-oxide armoring when liming pyritic materials.

Application of Sludges for Remediation of Contaminated Soil Environment

In the past ten years about 3000 waste-water treatment plants have been built in Poland. The result of this development has been a massive increase in overall sludge production. According to data supplied by the Ministry of Environmental Protection, 400,000 dry tons of sludge are generated every year in Poland [1]. Still it is difficult to estimate the amount of sludge which is used in agriculture or for reclamation purposes. However, it can be assumed that this comes to no more than 10 percent of all sludge produced in Poland on a yearly basis.