Determining Recovery Potential of Dredged Material for Beneficial Use Soil Separation Concepts

ERDC TN-DOER-C13

July 2000

Determining Recovery Potential

of Dredged Material for Beneficial

Use Soil Separation Concepts

PURPOSE: This is the first of three technical notes providing guidance in evaluating dredged

material recovery potential. This technical note provides an overview of physical separation (soil

washing) concepts, and methods for calculating volumes of recoverable material meeting beneficial

use (BU) requirements. The other technical notes address data acquisition for volume estimation.

The second (Olin-Estes and Palermo 2000) outlines a prescriptive approach, using existing infor-

mation obtained from limited sampling, to estimate volumes meeting BU requirements. The third

(Olin-Estes 2000) introduces statistical methods for developing a more extensive sampling plan,

and methods of organizing and interpreting data.

BACKGROUND: Contaminated dredged material is often placed in confined disposal facilities

(CDFs), but as land development and acquisition costs continue to rise, there is a growing shortage

of CDF storage capacity. Several options can be considered to increase capacity, including restricted

disposal (that is, storage of only the most contaminated sediments), dredged material dewatering

and densification, and, more recently, reclamation and reuse of materials from the CDF. Physical

separation (soil washing) is a management approach that has been applied at several projects and

holds promise as a potentially low-cost method to recover materials for BU and to restore CDF

capacity.

Physical separation or soil washing in this context refers to the process of classifying or separating

sediment into fractions according to particle size or density. Separation may be accomplished by

screening, gravity settling, flotation, or hydraulic classification using devices such as hydrocyclones

(Averett et al. 1990; Allen 1994; U.S. Environmental Protection Agency (USEPA) 1994b; Olin et

al. 1999). Equipment for physical separation is widely available, and the concept has been

demonstrated for sediments in both the United States and Europe (USEPA 1994a; Zwakhals, Deibel,

and van Rijt 1995; Detzner, Kitschen, and Weimerskirch 1995; Granat 1998). Additionally, various

site design and operational approaches can be effective in achieving separation during placement

of dredged material in a conventional CDF (Olin and Bowman 1996; Zwakhals, Deibel, and van

Rijt 1995). However, methods to evaluate the feasibility of separation for a given dredged material

or for a given CDF site, considering environmental, logistical, and economic factors, are not yet

well established (Olin and Bowman 1996).

The feasibility of separation as a management approach is dependent on several factors, including the

ability to identify distinct fractions within the material meeting BU criteria, the ability to separate suitable

fractions, and the material recovery potential (MRP) as determined by available volumes of suitable

material. This technical note introduces the technical considerations of physical separation as applied to

dredged material and provides a framework for evaluation of physical separation. Olin-Estes (2000) and

Olin-Estes and Palermo (2000) address data acquisition and utilization for evaluating MRP. The

information contained in those technical notes is applicable to MRP determination, not only for physical

separation feasibility evaluation, but for BU recovery in general.