DEEPENING, CLEANING AND PROCESSINGSEDIMENT FROM THE MIAMI RIVER

ANCIL TAYLOR, JEFF McWILLIAMS, HARRY VAN DAM AND BASTIAAN LAMMERS

ABSTRACT

Located in an urbanised industrial setting inMiami, Florida, USA, the Miami River hadnot been dredged in 70 years, since itsconstruction in 1934. In 2004 the US ArmyCorps of Engineers awarded a maintenancecontract to the Joint Venture of WestonSolutions / Bean Environmental to execute thedredging, transportation, and processing of approximately 721,000 cubic yards ofcontaminated materials from a 5.5 milelong shipping channel in the river. To dealwith the range of material types andsignificant debris encountered over thisrelatively narrow and crowded waterway,the latest generation of equipment fordredging, sediment processing and de-watering was implemented. This includeda newly designed and built precision backhoedredger Barredor del Rio. In addition,Boskalis Dolman, a subsidiary of Bean’spartner Stuyvesant, built and operated a“portable” sediment processing system, the Mobile Soil Washing Plant (MSWP),alongside the Miami River. The processingof the sediment with this on-site installationreduced the amounts of contaminatedsediment to be disposed, provided cleansand for beneficial reuse, and significantlylessened the cost of the operation.

INTRODUCTION

The Miami River corridor was home to earlyNative American settlements, and in the early1900s it was dredged in order to assist indraining the Everglades, the subtropicalmarshland in southern Florida. As the cityof Miami developed, the river became amajor outlet for storm water and untreatedsewage. With the US Army Corps ofEngineers (USACE) deepening of the riverto 15 feet in 1934, the river became thefourth largest port area in the United Stateswith US$ 4M in trade annually. During WorldWar II, the port became a manufacturingcenter for the Navy’s PT Boats in WWII.

In 1990 the USACE recommended thatmaintenance dredging be done to removesediments impacting navigation. Impactedsediments from storm water run-off from69 square miles of urban and industrialisedareas complicated and delayed thisrecommended maintenance dredging. The sediments were contaminated withheavy metals, pesticides, sewage andpetroleum products which were clearlyunsuitable for ocean disposal. In 1998 the Miami River Commission (MRC) wasestablished and charged with focussing on areas including dredging, greenways,

the redevelopment of areas adjoining theriver and storm-water retrofitting. The MRCalso targeted the contaminated sedimentsdegrading the mouth of the Miami Riverwhich flows into Biscayne Bay. Soon after a Dredging Work Group was established as a Sub-Committee to MRC and theynegotiated a plan which shared thefinancial responsibility for the projectdividing it into 80% for the Federalgovernment and 20% non-Federal costs.

PROJECT OVERVIEW

The aim of the Miami River project was torestore the navigation channel to a depthof 15 ft. This involved the removal of atotal of about 750,000 cubic yards ofcontaminated sediments. The approachdecided upon was to transport the dredgedcontaminated sediment to an interimdisposal and processing area. At theprocessing area the contaminated sedimentwould be separated, washed anddewatered, creating a high percentage of clean sand. Thereafter the clean sandand residue would be transported to a

Above, Figure 1. The site of the Miami River Project with

the sediment processing plant on the left.

Deepening, Cleaning and Processing Sediment from the Miami River 23

permanent disposal area in a legal andresponsible manner (Figure 1).

In 2004 the US Army Corps of Engineersawarded a maintenance contract to theJoint Venture of Weston Solutions / BeanEnvironmental to execute the dredging,transportation, and processing ofapproximately 721,000 cubic yards of

contaminated materials from a 5.5 milelong section of the river. The contract wasawarded on a basis of Best Value, withtechnical proposals, past performance, and price being primary evaluation factors. The total original budget available forproject execution was US$ 74 million,which included funding from the Federal,State, City and County governments.

SITE REQUIRMENTS

Marine traffic control was an essentialelement in planning the project as theMiami River is an extremely narrowwaterway, with an active freight andpleasure boat traffic. Prior to the start ofwork, clear lines of communication had to be established with the shippingcompanies and local pilots.

Traffic control also had to be established onland, as the management and control ofland traffic was crucial to the safe disposalof the dredged material. Approximately2500 tonnes of dewatered sediment anddebris per day were transported by truck to disposal facilities. A well-executed landtraffic plan, managed by Weston Solutions,included: – advance planning for traffic control prior

to the start of work;– clearly designated truck (lorry) hauling

routes; – specified types and sizes of the truck

(lorry) fleet;– clear signage and flagmen for en route;

and– requisite manifests and bills of lading.

Manifests/Bills of Lading

ENVIRONMENTAL PROTECTION

Environmental protection was a top priorityat the Miami River and covered a widevariety of issues. Water quality was animportant consideration, and monitoringwas performed for turbidity, dissolvedoxygen, lead, arsenic, copper arsenic andcopper throughout construction. The presence of animals which are listed as “Endangered Species”, such as themanatees, are of great concern in Florida andtheir protection is mandated. In addition,submerged archeological resources neededto be safeguarded. And last, but certainlynot least, air quality while dredging had tobe monitored for noise, odor, air emissionsand the effects on birds.

Figure 2. Aerial view of the newly built precision

backhoe dredger, Barredor del Rio at work in the

narrow, well-trafficked river.

Deepening, Cleaning and Processing Sediment from the Miami River 25

EXECUTION OF THE PROJECT AND THEMOBILE SOIL WASHING PLANT

In order to meet the demands of the MiamiRiver clean-up project, Bean designed andbuilt the new precision backhoe dredger,Barredor del Rio (Figures 2 and 3). The Barredor del Rio is equipped with RTK-GPS and Bean’s in-house CraneMonitoring System (CMS) to provide real-time, heads up display to the operatorof the precise dredger and bucket locationin relation to the dredge plan and targetelevation. The measured system dredgingaccuracy is better than 6 inches in X, Y, and Z planes.

Another essential part of the clean-upoperation was the Mobile Soil WashingPlant (MSWP), built and operated byBoskalis Dolman. This is a “portable” highcapacity sediment processing system whichwas sited within the project area along thebanks of Miami River. Boskalis Dolman had

became involved in the Miami River projectbefore the tender procedure was initiated,during which time the dredging andsediment processing was studied as anIntegrated Approach, to define the mostappropriate and cost-effective method.

The Boskalis Dolman soil washingoperations were developed in the 1980s inresponse to stricter environmentalregulations and the need to find solutionsfor the disposal of contaminated soil andsediment. They have been used in theNetherlands at both temporary andpermanent locations for over twenty years.The concept of the “portable” highcapacity plant is a recent development. It allows the processing plant to bedelivered to project sites anywhere in theworld, rather than the client needing tobring the contaminated sediment to theplant. And it also eliminates the need todeal with the low processing capacity thatnormally comes with a portable plant.

ANCIL S. TAYLOR, JR.

Ancil Taylor is Vice President/General

Manager of Operations, Estimating,

& Production, Bean Stuyvesant, L.L.C.

and Senior Technical Advisor, Bean

Environmental, L.L.C. He has over 28 years

of experience in the dredging and marine

industries, all with Bean. Currently he

oversees projects for Bean Stuyvesant

involving a chartered dredger fleet of

hopper, hydraulic/pipeline, and hydraulic

excavator dredgers.

JEFFREY MCWILLIAMS

Jeffrey McWilliams has over 17 years of

experience in dredging and marine

construction on the US east, west,

and Gulf coasts and overseas. He has

supervised, managed, or participated

in over 40 diverse dredging, coastal

protection, port construction, and land

reclamation projects for both public and

private sector clients. He holds degrees

in both ocean and civil engineering from

Texas A&M University.

BASTIAAN LAMMERS

Bastiaan Lammers started in 2002 as assistant

superintendent within Boskalis Dolman,

working at the Soil Washing Centre in

Groningen, the Netherlands and at tender

preparations on international projects. Since

September 2004, he is Boskalis Dolman

representative in the USA to identify potential

projects in cooperation with the USA-based

dredging company Bean Environmental. In this

function, he operated as Project Manager on

the Miami River Sediment processing project.

HARRY VAN DAM

Harry van Dam started in 1990 as junior

environmental engineer at the Hydronamic

Engineering Department of Royal Boskalis

Westminster (RBW) and was involved in

several projects at RBW subsidiary Boskalis

Dolman bv. In 1992 he went to work for an

innovative Dutch in-situ remediation

company, returning to RBW in 1994 as a

Project Engineer directly for Boskalis Dolman.

He helped establish the Boskalis Dolman Soil

Washing Centres in 1995. For the past

12 years, he has been involved in all large

international Boskalis Dolman projects.

Figure 3. A close-up of the Barredor del Rio.

26 Terra et Aqua | Number 103 | June 2006

In the case of this project, the MSWP wasbeing used in southeastern England whenthe need arose for the Miami River project.Upon completion of the UK project, theMSWP was disassembled, packed up andmobilised by ship across the Atlantic.During mobilisation several adjustmentswere made to increase plant capacity from100 up to 150 tonnes per hour, in order tomeet the demands of the US job, that is, to be able to process more than 10,000 m3

situ sediment per week. This requiredadditional plant which was transported byAntonov airplane from the Netherlands tothe Miami site (Figure 4). Within threeweeks, this MSWP was reassembled alongthe banks of the Miami River and was upand running (Figure 5).

Figure 5. The sediment processing Mobile Soil Washing Plant and transloading operations were situated along the banks of the river.

The sand separation unit (hydrocyclones and counter current washer) is in the middle.

Figure 4. Additional components of the Mobile Soil

Washing Plant were shipped by Antonov airplane,

shown here at Miami International Airport.

PRIMARY SYSTEM COMPONENTS

The MSWP combines coarse fractionseparation via a stationary grizzly screen,rotating sieve drums, vibrating shakerscreens and hydrocyclones, and mechanicalde-watering of the fine fraction through apre-thickener tank and a series of belt filterpresses (Figures 6 and 7). Different types andsizes of debris require different treatment.Oversized debris, including car bodies,motorcycles, boats and heavy industrialdebris were removed and separated outover a stationary Input Grizzly. The coarsedebris, composed of rock, trash and rockswith a particle size of from 1 m to 3 cm,passed the grizzly and was placed in arotating wash and sieve drum (Figure 8).This fraction will typically be over 90percent dry solids content. The passing finedebris (Figure 9), that is particles of lessthan a centimetre, also typically over 90percent dry solids content, are then placedthrough vibrating shaker screens. Anotherprocessing step can be added as necessary.

At this point the sand separation processbegins using hydrocyclones and counter-current washing. The sand particles (Figure 10) are 3 mm to 63 µm, with a dry solids content typically over 70 percent.The de-sanded sediment is then putthrough a mechanical de-watering processwhere flow and density measurements areconducted and automated polymer dosingoccurs. This results in the pre-conditioningof fines of 20 percent dry solids in a pre-thickener tank. The mechanical de-watering table uses belt filter presseswhich reduces the remaining dry solidscontent by about 50 percent. The MSWPutilised the 2 metre Andritz CPF 2200 S8belt filter presses. The final design of thesepresses was done in-house with specialsafety features engineered into the pressdesign.

Figure 6. A closer view of the Mobile Soil Washing Plant.

Figure 7. The hydrocyclone and counter

current washer stack.

28 Terra et Aqua | Number 103 | June 2006

The MSWP has a fully automatedprogrammable logic control (PLC) withwhich all fluid levels and flows aremonitored and controlled. The MSWP alsohas a built-in maintenance schedule, andtechnical support can be achieved bytelemetry. This permits the plant to beoperated efficiently with limited personnel:two process operators control the plant andto check the results, one loader operatorand two deckhands for housekeepingresponsibilities (Figure 11).

The production capacity on most fixedinstallation soil processing plants aretypically 40 to 50 tonnes per hour. The MSWP can realise up to 140 tonnesper hour or over 2200 m3 per day. During the Miami River operation theaverage production rate was approximately1300 m3 per day.

The production capacities of the dredgingand processing operations were wellbalanced on the project and resulted in the breakdown of fractionated products as shown in Table I.

More than 50 percent of the dredgedsediment was processed clean (coarse)fractions which could be beneficially usedin the community at little to no cost to the project; and around one quarter wasdewatered filtered cake which wastransported by truck for ultimate disposal at one of three licenced landfills.

Figure 8. Coarse debris output, composed of trash and rocks with a particle size of from 2 cm to 30 cm,

pass the grizzly and are placed in a rotating wash and sieve drum.

Figure 9. Fine debris output,

particles 3 mm to 2 cm.

Table I. Breakdown of fractionated products.Product Size Material Mass Balance Dry Solid Content

Trommel Coarse material 30 cm – 20 mm Rock, trash 19% 90 – 95%Shaker Screen Fine material 20 mm – 3 mm Fine gravel 5% 90 – 95%Hydro-cyclone Sand 3 mm – 63 µm Sand 52% 75 – 85%Hydro-cyclone Fines (sludge) <63 µm Fines to be dewatered 24% up to 54% after dewatering

on belt filter presses with belt filter presses

Deepening, Cleaning and Processing Sediment from the Miami River 29

CONCLUSIONS

The challenges of dredging the Miami Riverare derived primarily from the presence of a constant stream of water-basedtransportation, the need to proceed understrict ecological guidelines, and specificenvironmental legislation regarding thedisposal of contaminated dredgedmaterials.

The high production levels of the MobileSand Washing Plant coupled with the needfor a limited number of operators made the operation extremely cost-efficient. In addition, the processed clean (course)fractions could be beneficially used in thecommunity at little to no cost to theproject. The tremendous decrease incontaminated volume achieved throughimplementation of the MSWP offered anenvironmentally sound practice fordredging in difficult contaminated waters.

Figure 11. Right, operator in

the control room of the MSWP.

Below, close-up of one of the

control screens.

Figure 10. Separated sand output.