VOLUME REDUCTION ESTIMATING

ERDC TN-DOER-C27

July 2002

disposal, and quantity suitable for beneficial use. Methods for estimating recoverable and

residual volumes follow in the section titled "Volume Reduction Estimating."

b. Calculate interest during construction (IDC).

IDC must be calculated for each

construction (new work) year using Equation 1.

c. Calculate initial investment. The initial construction cost will equal the sum of all

construction costs and IDC for each construction year.

d. Develop maintenance dredging cycle and associated costs, including mobilization/

demobilization, dredging, dewatering, separation, transportation, and placement.

Sufficient placement capacity (either CDF or offsite) must be available to accommodate

all residual maintenance material for the entire period of analysis. All associated

placement costs for the disposal alternative, such as CDF construction or expansion,

facility maintenance costs, and transportation and unit disposal costs, must be developed

and included. Timing for future costs must be established.

e. Calculate net present value (NPV). Determine NPV of all costs, including construction

costs, IDC, and anticipated future expenditures. These calculations are completed using

Equation 2.

f. Compute the AAEV for each alternative using Equation 3.

g. Select the separation alternative. If more than one separation alternative is being

considered, these steps must be completed for each alternative. The least costly

alternative that accommodates all future maintenance material, including initial

investment, IDC, and future maintenance costs, is the selected separation option. The

selected plan will have the lowest AAEV.

IV. Calculate Benefits from Separation. The benefit to separation is the savings between the

annualized base condition costs and the annualized selected separation alternative costs. If

separation is not more efficient than the base plan, the benefits from separation will be negative.

Among separation alternatives with comparable benefits, intangible benefits, such as reduced

contaminant emissions or habitat creation, may be factored into the final selection.

VOLUME REDUCTION ESTIMATING: Economic analysis requires estimation of in situ

sediment volumes and relative volumes of recoverable materials and residuals requiring disposal.

Procedures for estimating the percent material by mass meeting BU specifications (recoverable

materials) were presented in Olin-Estes and Palermo (2000a). Mass and volume percentages are

not equivalent, however, and this is central to the concept of volume reduction. The volume

represented by a given mass percent of sand, for example, is a function of the specific gravity of

the relative sediment fractions and the void ratio of the material. The relative proportions and

specific gravity of the principal sediment fractions (sand, fines, organics) and in situ void ratio can

be determined from bench-scale characterization of the material to be processed. Nomographs were

developed for a hypothetical material to illustrate the variation in percent sand by volume versus

percent sand by mass (Figure 5). Similar nomographs can be developed using site-specific

information and the mathematical and geotechnical relationships describing the sediment fractions

for a unit mass of sediment. By bounding the analysis within a range of values representative of