Dredging

ERDC TN-DOER-C27

July 2002

Dredging. Dredging costs are included as part of the economic analysis. Where physical

separation is employed, the type of dredge or processing rates may be determined by separation

plant capacity and slurry feed requirements. Dredging costs may be impacted by this factor. These

costs typically include a substantial mobilization/demobilization cost, and unit costs incremented

based on the volume to be dredged. Costs may differ substantially between regions, and be strongly

influenced by the distance the contractor has to travel to the site. The level of contamination of the

sediment will typically influence unit costs as well.

Reported costs for mechanical dredging of clean sediment in the north-central region of the United

States range from $3.53 to $10.46/m3 ($2.70/yd3 to $8/yd3), with costs incremented downward

above a specified volume threshold that varies from 11,475 to 114,750 m3 (15,000 to 150,000 yd3).

Mobilization/demobilization and bond costs for this region ranged from 2 to 38 percent of the total

contract cost. Mobilization/demobilization costs in excess of $1 million are not uncommon.

McCorquodale, Selvidge, and Bennett (2000) provide a useful summary comparison of cost and

suitability of dredging equipment developed for the Great Lakes area. Based on that report,

clamshell, conventional excavation, portable hydraulic, and plain suction dredges all fall within a

low cost range. Cutterhead and airlift dredges are classified as moderate in cost, and cable-arm

dredges as high cost. Cost ranges of approximately $15-$40/m3 ($12-$31/yd3) were cited, with

lower unit costs associated with high-volume projects (over 50,000 m3 (65,400 yd3).

Excavation. Cost estimates for hydraulic excavation of existing dredged material stockpiles were

obtained for a site in the north-central region (U.S. Fiscal Year (FY) 2000). Costs included

redredging, transferring, and disposing of uncontaminated dredged material from two dredged

material stockpile areas. Mobilization, demobilization, and bond costs were additional. Costs

ranged from $2.10 to $8.00 per cubic yard for a 60,000-yd3 (45,873-m3) site and $1.62 to $11.00

for a 500,000-yd3 (382,277-m3) site. The effort was completed over a period of 2 years.

A small volume of dredged material (approximately 382 m3 (500 yd3) was mechanically excavated

from a Great Lakes CDF using a large backhoe. Unit costs for this effort were approximately

$2.25/yd3. The effort required approximately one-half day in the field to complete.

Separation/Dewatering. Overall project costs expressed on a unit basis ranged from $18 to

$410/yd3 for 10 case studies reported in the literature, utilizing separation and mechanical dewater-

ing (Wisconsin Department of Natural Resources 2002; Sevenson Environmental Services 2002a,

2002b, 2002c; USEPA 2002a, 2002b, 2002c; USEPA 1992). Project costs appear to have been

influenced by level of contamination, total project volume, offsite transportation and disposal costs,

real estate and permitting costs, water treatment requirements, and public relations efforts. A range

of $18 to $60/yd3 appears to be representative of the separation and dewatering cost component,

when isolated from other project costs, for project volumes of 191,139-573,416 m3 (250,000-

750,000 yd3). The lowest unit cost is exclusive of a mobilization/demobilization cost. Unit costs

for smaller volume projects would likely be higher.

Transportation/Off-site Disposal. Transportation and offsite disposal costs may be on a unit

volume distance or a unit weight distance basis. River transportation costs reported in the

northeastern region ranged from $0.65/cubic yard mile to $1.00/cubic yard mile, with the higher

costs reflecting distances greater than 8 river miles. Overland transport over distances up to