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|Title:||Design of an improved column leaching apparatus for sediments and dredged material|
|Authors:||Louisiana State University (Baton Rouge, La.). Laboratory for Wetland Soils and Sediments|
Louisiana Water Resources Research Institute.
Long-Term Effects of Dredging Operations Program (U.S.)
Myers, Tommy E.
Gambrell, Robert P.
Tittlebaum, Marty E.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: This report describes a new column design for investigating contaminant leaching from sediments and dredged material. Improved sampling and sample preservation procedures are also described. A review of the literature on column leaching studies is also provided. Three types of columns were reviewed: (A.) soil columns, (B.) solid waste columns, and (C.) sediment and dredged material columns. The review focused on column design and operating parameters, not data interpretation. The literature review showed that the soil column literature is much more extensive than the column literature for either solid wastes or sediments and dredged material. A wide variety of column designs have been used, but nearly all involve a vertical column with a small diameter-to-length ratio, and percolation of water either upward or downward. Information from selected studies on material used to fabricate columns, column dimensions, hydraulic flux, direction of flow, type of soil, waste, or sediment tested, and chemical(s) applied is tabulated and discussed, including advantages and disadvantages of various column designs. The column literature on sediments and dredged material indicated that the performance of column designs based on the type of column used in most soil and solids waste studies is not satisfactory for sediments and dredged material, primarily due to insufficient flow. Based on the literature review and recommendations from a workshop held to review sediment leaching studies, a thin-layer leaching column was designed. The thin-layer column design has a large diameter-to-length ratio (25.4/4 cm) that provides a short travel length and a large cross-sectional flow-through area. The short travel length allows a greater number of pore volumes to be eluted relative to previous designs, while the large cross-sectional flow-through area provides sufficient volume of sample for chemical analysis. The improved design includes upflow mode with distribution disks at both the top and bottom of the column. Pore water velocity is controlled to be less than 1 E-05 cm/sec using a constant volume pump. Improved sample collection and preservation are incorporated into the column design. However, separate columns for investigating metals and organics are required. For metals, an adaptation of the apparatus commonly used to study the chemistry of soil and sediment suspension under controlled redox potential and pH conditions is attached to the column outlet tube. This system collects and preserves metals continuously by maintaining pH below 2.8 as the sample is eluted. For organics, an adaptation of a Neilson-Kryger steam distillation apparatus is attached to the column outlet tube. This system collects and preserves organics continuously by use of a trapping solvent through which the sample passes.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|