Stuyvesant was a subcontractor to the Weston - Bean Joint Venture performing the sediment processing and dewatering for the Miami River 15' Maintenance Dredging Project. The client for this project was the US Army Corps of Engineers, District Jacksonville.

Located in Miami, Florida, the Miami River project is an example of a successful full scale, ex-situ sediment management project. The project included the dredging, processing, and disposal of sediments from a 5.5 mile stretch of the Miami River. The total volume dredged was approximately 720,000 cubic yards. The sediments were contaminated with low levels of primarily arsenic. The project was divided into 15 acceptance areas. Areas 1 through 6 where dredged in 2004/2005. The second phase of the project started in February 2008 and was completed in November 2008.

The operational responsibility of Stuyvesant on this project included the unloading of barges, and sediment separation and mechanical dewatering. Further, Stuyvesant was heavily involved in the project design during the pre-proposal and technical development phase of the project. The project was ultimately implemented in accordance with the proven integrated approach where the focus is on the entire "project chain" of dredging, processing and transport & disposal.

Stuyvesant's work began with an intensive sediment sampling campaign. Based on the analyses of these samples, four (4) basic sediment types where determined, varying in fine-, solid and organic matter content and density.

Once the sediment types were characterized, the selection of equipment and system configurations was initiated. Production rates of the dredge, the processing plant and the transport and disposal were designed to match each other. The overall project design production rate was 1,750 in-situ cy per day, based on an operating schedule of 24 hours per day, 7 days per week, with a plant efficiency (uptime) of greater than 80%.

Based on the sediment data, and required production rates, Stuyvesant. Mobilized one of the company's Mobile Separation & Dewatering Plants (MSDP). A detailed description of these plants is given in MSDP section of this website. Each of these plants consists of three major process functions: (a) sediment pre-conditioning, (b) sand separation and (c) mechanical dewatering.

(a) Sediment Pre-Conditioning
Sediments were mechanically dredged with Bean's "Barrador del Rio", a precision hydraulic excavator (backhoe) dredge with mounted environmental bucket. Dredged sediments were transported by barge to the processing facility site on a waterfront property along the river. Here sediments were offloaded with a mechanical excavator from the barges into the input hopper of the processing plant. A stationary grizzly screen on top of the input hopper removed the oversized fraction (>1 foot) from the sediments. Material <1 foot was placed in a rotary trommel screen where process water was added to slurry the sediments. In this rotary screen, materials between 1" and 1' were separated and stockpiled for further handling. Material <1" was pumped to the shaker screen where materials between 1 inch and 1/8 inch were separated.

(b) Sand Separation
Material passing the shaker screen (<0.12mm) was pumped to the sand separation unit. The hydrocyclones separate the sand (63µm - 0.12") from the fines (<63 µm). The separated sand was deposited from the cyclones into the upflow classifier. This classifier washes out all the remaining fine and organic particles from the sand ensuring a clean sand fraction. The washed sand is deposited on a sand dewatering screen and stockpiled. The separated fine and organic particles are collected from the hydrocyclones and the upflow classifier in a slurry holding tank.

(c) Dewatering
Dewatering of the fines in the overflow of the hydrocyclone process were deposited in the slurry holding tank as the start of the dewatering process. The average density of the slurry mixture was measured on a continuous basis. From this tank, the slurry was pumped to the pre-thickener tank. Based on the flow to the pre-thickener tank and the density measurements, polymer demand was automatically calculated and adjusted. Polymer was injected in-line before the slurry enters the pre-thickener tank. The pre-thickener tank separated the sediments from the process water and increases the dry solids content to about 20%. From the pre-thickener tank the slurry was pumped to a series of belt filter presses, where polymer is added for a second time. The belt filter presses dewatered the slurry into a filter cake with a dry solids content of approximately 55%.

Separated water from the pre-thickener tank and the belt filter presses were collected in the process water tanks and re-used in the process. Surplus water was discharged from the process water tanks into the river after clarification through a series of sand filters.

Most of the water was recycled in the processing plant. The surplus water varied depending on the dredge area, sediment composition, bank thickness of removal and other factors. The processing plant was capable of buffering these fluctuations and to then discharge the surplus water in a controlled manner. Excess water was discharged after treatment and in accordance with the USACE and FDEP permit requirements.

After processing, the products including rock, sand, and filter cake, were ready for transportation by trucks to their final destinations. Since the materials could be transported directly from stockpiles, the required processing footprint was minimized. The trucking capacity met the production of the processing plant.

Based on the quality of the sand, a re-use determination was made and The the sand was transported to one of three landfills andfor use as intermediate cover (a beneficial reuse) or disposed. Sand was staged in batches of 1,000 tons and sampled. The requirements for re-use were based on the standards for residential re-use.

The following final mass balance on the Miami River project was achieved: 29% oversized, 34% sand and 37% dewatered filtercake (by weight).