Project Activities

presently equipped. One advantage to the configuration was the potential for

making the sand/silt separation on the screen, followed by a finer cut at the

hydrocyclones, thus addressing both size separations of principal interest with

one unit. Tri-Flo also manufactures a mud pump that could be useful for

excavating and slurrying consolidated material. The mud pump is equipped with

an integral screen that prevents the pump from picking up oversize particles.

Principal limitations of the equipment were the potential for blinding of the

screens, the inability of screens to separate coarse organic materials from coarse

minerals, and the fact that this equipment has not been demonstrated for dredged

material or sediments.

MetPro Supply manufactures a self-contained maximum density separator

(MDS) consisting of a trailer-mounted sump, slurry pump, and MDS. Both 0.15-

and 0.3-m (6- and 12-in.) MDS have been demonstrated on sediments in the U.S.

Army Engineer District, Jacksonville. Based on previous testing, MetPro

recommended a 0.61-m (24-in.) MDS to produce a coarse fraction with less than

10 percent fines entrained. A 0.61-m (24-in.) MDS has a throughput of

approximately 4.5 cu m (1,200 gal) per minute (approximately 68,039 kg

(75 tons) solids per hour), and can accept particles up to 25-38 mm (1 1-1/2 in.)

in diameter, thus simplifying prescreening. Dry or slurried material could be fed

to the sump, with adjustments to the volume of makeup water supplied. The

MDS differs from a conventional hydrocyclone in that a flexible sleeve is

attached to the apex of the cone, and a vacuum is applied to the overflow line,

thus restricting discharge of underflow until sufficient weight accumulates to

force discharge. This reportedly results in a higher solids underflow.

Because of the potential variability in feed requirements, the offerors were

tasked with providing the necessary auxiliary equipment to support the proposed

separation unit, in effect developing a compatible treatment train. Mechanical

excavation and prescreening were to be handled by the Detroit District.

Auxiliary equipment was located in the Green Bay/Milwaukee area. A

powerscreen for prescreening material; water supply pump; flexible, quick-

coupling water hoses; and generator were available and obtained as short-term

rentals.

Because the target separation of the proposed equipment was 75 m, it was

necessary to locate material containing sufficient sand to permit evaluation of the

efficiency of the equipment in making this separation. Based on anecdotal

information, Cell 5 was initially identified as containing sandy material from the

outer harbor. Core and near-surface bulk samples were taken from Cell 5 for

evaluation. However, finer material had apparently been placed over the target

material, and the near-surface dredged material contained little sand. Additional

samples were therefore taken for evaluation from Cell 4, where additional coarse

material had recently been placed. (This material was from an inner harbor

dredging project, and may not be representative of outer harbor sandy sedi-

ments).1 Sampling, sample handling, and bench-scale testing are further detailed

in subsequent sections of this report. Approximately 380 cu m (500 cu yd) were

Dean Haen, Personal Communication, 5 November 2001, Port Manager, Brown County

Port and Solid Waste Department (Port of Green Bay), Green Bay, WI.

Chapter 2 Project Description