INTRODUCTION - doerc130002

ERDC TN-DOER-C13

July 2000

INTRODUCTION: An overall approach to evaluate feasibility of separation as a management

option is illustrated in the flowchart in Figure 1. The need for recovery or preservation of CDF

capacity should first be evaluated based on available capacity and projected future needs, although

adequate long-term capacity need not rule out BU of dredged material. A screening examination

of proposed BU applications for the locale should be conducted to determine if the material can be

used without pretreatment. If available information is inadequate, at least limited sampling of the

material will be needed to make a preliminary determination. Preliminary sampling and data

acquisition are further discussed in Olin-Estes and Palermo (2000). If separation appears to be

necessary to meet material specifications for identified BU, an evaluation of MRP and a more

detailed sediment/site characterization and evaluation are needed. Extensive site sampling and data

interpretation are further discussed in Olin-Estes (2000). Material characterization, physical

separation processes and limitations, and determination of MRP are discussed in the following

sections.

MATERIAL CHARACTERIZATION: Material characterization is necessary both to determine

as-is suitability of material for BU and, when the material is found not suitable, to determine

feasibility of physical separation for recovering usable fractions. Preliminary material charac-

terization for BU screening generally includes a particle size distribution analysis and bulk

(unseparated) chemical contaminant analysis, since acceptable grain size and contaminant levels

are specified for most, if not all, BU. Other parameters may also be of interest, depending upon the

BU specifications, but might include clay content, liquid limit, plastic limit, and moisture content.

If bulk material is found to be unsuitable as is for identified BU, a more comprehensive charac-

terization is required. This typically implies a contaminant distribution, or fractionation, analysis

in which material is separated into different size and density fractions. Fractionation studies permit

evaluation of the quality of the respective size and density fractions of the material under

consideration. Anecdotal evidence suggests that separation of sandy materials results in a large

proportion of contaminants of concern (COC) remaining associated with the fine silt and clay

fraction (Olin and Bowman 1996; Allen 1994; Olin et al. 1999). Although coarse minerals, sand

size and larger, are typically relatively uncontaminated, in some cases efficient separation of coarse

and fine fractions may be difficult. A clean coarse product will therefore be difficult to produce,

or may require additional processing operations.

Organic materials of all sizes will typically have higher contaminant levels than any of the mineral

fractions, including the clays, particularly for hydrophobic organic contaminants. The contribution

of organic material to overall contaminant levels can be determined from a density fractionation

study. Collectively, contaminant distribution information is used to determine whether or not an

acceptable size or density fraction is likely to be recoverable from the material, what percentage of

the material this represents, and what unit operations are likely to be needed to achieve this

separation. Organically bound contaminants may be less available than mineralogically bound

contaminants. Bioavailability may ultimately determine whether this fraction must be removed to

produce a material suitable for beneficial use; this is typically a regulatory decision.

All samples should be physically tested prior to any chemical fractionation testing, since the physical

tests are fast and inexpensive, will yield data that may rule out separation as a viable approach, and

will indicate which samples should undergo chemical analysis. Chemical fractionation testing