Calculation of MRP

ERDC TN-DOER-C13

July 2000

Substances Control Act (TSCA). Cost to manage such materials must be considered in the

economic analysis if the potential to produce them exists. Preliminary chemical characterization

will be important in this regard.

Screening criteria can be applied for the entire sediment mass within a waterway or to specific

reaches within the waterway if such reaches define areas with similar characteristics, or if the reaches

will be separately handled. Similarly, the screening criteria can be applied to the entire dredged

material mass within the CDF for proposed reclamation or to separate zones, such as areas with

materials having higher coarse fractions (such as mounds near inflow points). Compositing of

samples during characterization should be done carefully, however. If separation is planned,

samples should not be composited unless materials will be blended in a similar manner for

processing (Olin et al. 1999).

Calculation of MRP. The calculation of MRP is derived from a comparison of the GSD of the

material to the BU specification (assuming COC levels are acceptable) and an estimate of the tons

dry weight of material available. Assuming that the available GSD and contaminant data point to

separation as a possible management approach, the MRP following separation must be determined.

The definition of MRP is expressed in terms of tons dry weight of product for two reasons. First,

volumes and wet weights may change with the relative gain or loss of water during separation or

dewatering processes, but the dry weight of product is essentially constant. Second, project

requirements for a product derived from separation would usually be expressed on a dry weight

basis. This is especially true for products such as fine aggregates or manufactured soil products.

Following separation, the product intended for BU and the residual material will have different grain

size distributions compared to the bulk material distribution prior to separation. Figure 4 illustrates

the typical case in which the desired product is specified as having a coarser grain size distribution

than the initial material prior to separation. The specifications for an acceptable product will usually

include a range of grain sizes, and this is illustrated by the band of distributions shown in the figure.

The recommended method for calculating MRP is as follows:

i=n

∑ Psi Wsi

MRP =

(1)

i=0

where

MRP = material recovery potential, tons

Psi = percentage by weight of sample grain size meeting the BU material specification

for sample i (as a decimal)

Wsi = dry weight of material represented by sample i, tons

n = number of samples considered