LAKE OSBORNE MUCK DREDGING PROJECT

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LAKE OSBORNEMUCK DREDGING PROJECT
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Presentation Overview

• What are the Chain of Lakes?
• How have the lakes become degraded?
• Palm Beach Countys Involvement
• - State of the Lakes Plan
• What is Muck?
• - How does muck develop?
• How much muck is in the lake and how do we know?
• - Surveys
• What is the Countys plan?
• - Lake Osborne Muck Dredging Project
• Lake Osborne Muck Dredging Project
• Brennan Marine Professionals
• Dredging Equipment
• Dewatering Plant
• Drying Methods
• Disposal of Muck

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CHAIN OF LAKES

• Part of a natural lake system that, at one time,
  extended from West Palm Beach to Delray Beach
• The E4 canal connects Pine Lake, Lake Clark, Lake
  Osborne, Lake Eden, Lake Ida
• Freshwater lakes
• provide habitat for native flora fauna
• replenish drinking water supplies
• store and filter storm water
• provide recreational opportunities
• aesthetically appealing

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Degradation of a System

• Historical dredge fill activities, urban
  encroachment discharge from canals.....

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South Lobe of Lake Osborne (1986)

• ...lead to the lakes waters becoming
  overloaded with nutrient-rich organics

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As a result, excessive plant life (algal blooms)
develops throughout the Chain of Lakes causing a
decrease in water quality reduction in oxygen
levels
HYDRILLA
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STATE OF THE LAKES PLANThe lakes decreasing
quality prompts Palm Beach Countys Department of
Environmental Resources Management to commission
a report in 1997 to address how to enhance and
improve the freshwater system and its management
The plan focuses on the following goals

• Restore and Protect Wetland Habitats
• Protect Improve Water Quality
• Control Exotic Vegetation
• Maintain Enhance Fisheries
• Enhance Public Participation Environmental
  Awareness

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MUCK

• What is MUCK?
• Muck is organic and inorganic sediments,
  sands, silt, debris and other materials
• How does MUCK form?
• Muck is a result of the excess nutrients in
  the water. Excess nutrients are attributed to
• -Lakes extensive development
• -Herbiciding of non-native
• vegetation
• -Discharge of several canals
• How long has MUCK been
• accumulating throughout the lakes?
• -50 plus years

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Photo Credit SFWMD (Know the
Flow Poster)
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Method of Measurement dual frequency
transducer Transducer captures the top
of the muck layer and natural sandy lake
bottom to determine mucks thickness
In 2002, the County contracts with the survey
company, Morgan Eklund, INC., to measure the
amount of muck throughout Lake Osborne
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LAKE OSBORNE MUCK DREDGING PROJECT

• Surveys reveal 700,000 CY of muck cover the
  sandy lake bottom
• In response, Palm Beach County develops the Lake
  Osborne Muck Dredging Project
• County divides the dredging of
• the southern lobe into phases
• Phase I removal of approximately 20,000 cubic
  yards of muck, in situ, from a 199,241 square
  foot section
• Phase II removal of approximately 85,000 cubic
  yards of muck, in situ from a 1,015,010 square
  foot section

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LAKE OSBORNE MUCK DREDGING PROJECT

• County decides to pay selected contractor by the
  square footage vs. cubic yard because of the
  consistency of the material
• Muck is difficult to measure volumetrically
  because there is no defined top layer
• 1.2 million square feet (approximately 28 acres)
  throughout the project site
• 1.12 per square foot
• Total project cost for Phase I II 1.4 million
  dollars

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• County awards Brennan Marine Professionals Phase
  I of the contract in March 2004
• Brennan receives Phase II of the project if they
  are able to meet project deliverables complete
  work within allotted time frame for Phase I
• Project Time Frames
• Phase I - 45 days from Notice to
  Proceed to mobilize all equipment (no
• payment for
  mobilization)
• 70 calendar days after
  mobilization to complete dredging and
• dewatering of material
  from Phase I
• Phase II 300 calendar days from
  issuance of the second Notice To
• Proceed to complete
  Phase II

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• Spring 2004 Brennan receives Notice to Proceed
• in March and begins to mobilize equipment in
  April

Mobilization at Melear Park April 22, 2004
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Fusing placement of polyethylene plastic pipe
Mobilization April 22, 2004
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Eight (8) inch intake pipeline transports muck
(slurry) to the dewatering plant
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Buoys signage along the pipelines warn
recreational users of the pipes presence
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Dredging Equipment

• 8 Swinging Ladder Rotating Cutter Head Suction
  Dredge
• - 3 Spud System
• - Hydraulically Actuated Spud Frame enables
  dredge to
• walk along the lake bed

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CUTTER HEAD
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Interface between the dredge operator field
conditions
Dredge Operator Booth
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High Tech Instrumentation on the Dredge Includes

• RTK Global Positioning System
• RTK Positioning System provides sub-centimeter
  accuracy for position of dredge and cutter head

• DREDGEPACK Software
• Uses county surveys that designate dredge depths
• Screen displays operator position amount of
  material being removed
• Tracks recalculates the amount of material to
  be excavated
• Displays new calculations on the screen until
  achieving designated dredge depth

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Pay Survey Deliverable
Dredge Track Lines demonstrate where the
dredges cutter head is working throughout the
day
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Dewatering Plant
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Underflow (slurry) entering dewatering plant
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SAND WHEEL (used initially)
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Wheel removes sand from slurry
Contains 200-mesh (.074 mm) screens
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SCALPER Removes debris organics by gravity
feeding slurry through a belt screen
FRAC TANK Slurry homogenizes in frac tank (Only
minus 200-mesh /.074 mm solids remain)
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VIBRATORY SCREEN

• Material travels over a 5 x 7 vibrating screen
  (35-mesh/0.5 mm)
• Vibration causes the sands larger material to
  move toward the discharge end of the screen where
  it is placed on the radial stacker
• Material finer than 35-mesh/0.5 mm drops through
  the screen into a sump

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HYDROCYCLONES(now in use)

• Slurry collecting in sump is pumped and delivered
  to two cyclonic separators
• The cyclonic separators perform like a
  centrifuge, using 320-mesh screens to further
  separate the slurry

• Finer material spins out the top of the
  separators moves toward the frac tank

• Larger material falls to the bottom of the
  separators passes over the dewatering screen
  for a second time

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Dewatering Screen
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Radial Stacker

• Material passing over the dewatering screen
  falls onto the radial stacker

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FRACTANK
Fine material leaves via top of cyclone

• Slurry now contains only 320-mesh solids
• First injection of chemical Aluminum-Chloride-Hyd
  roxide (a coagulant)
• Slurry homogenizes in the tank

Slurry flows into frac tank
Flow regulator (injects chemical into tank at a
controlled rate)
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THICKENER
Twin Clarifier Tanks
Concentrated deflocculent
2 Solution
Inflow
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Flocculent Mixture

• Second chemical injected
• FLOC NALCO 83906
• Optimer Plus
• Chemical mixes with water pumped from an
  underground well
• Solution added to the slurry contains 1-3 of
  chemical
• Injection of chemical into the slurry is computer
  controlled and based upon the consistency of the
  material
• Opitmer Plus (flocculent) helps the organics
  organize into a semi-solid mass

Control Panel
Well Water
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Chemical slurry mix together in the flocculent
injection tank
Slurry separates into the twin clarifiers
Return water flows to the top exits via the
overflow pipe
Overflow Pipe
Makeup Well Water
Generator
Underflow Pipe
Well
Fuel
Auxiliary Pump
Slurry sinks to the bottom of the clarifiers and
exits via the underflow pipe
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End ResultsOverflow

• Return water is diverted back to Lake Osborne via
  the 11.5 overflow pipe
• Return water can not exceed 29 NTUs
  (Nephelometric Turbidity Units) above lakes
  background level
• Overflow is monitored for high turbidity levels
  twice a day at the overflow tank using a
  nephelometer

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Overflow Tank
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End ResultsUnderflow

• Underflow exits the dewatering plant and is
  pumped into a drying bed
• The processed muck remains within the bed for a
  week for further dewatering

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MANIFOLD
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GEO BAGS

• First dewatering method
• Allows for further concentration of slurry for
  hauling
• Contractor assembled five bags in total (500 CY
  per bag)

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Drying Beds (now in use)
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MUCK REMOVAL

• Muck remixes with sand from the radial stacker
• Parks Department uses mixture as a soil amendment
  throughout various County parks and at the site
  of a future County golf course

• Processed Material
• Output 600 CY per day

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• Anticipated Benefits
• Improved water quality environment
• Enhanced boating fishing
• Re-establishment of native benthic vegetation
• Increased property value
• Enriched top soil for use in public parks

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The Projects Future

• South Florida Water Management District (SFWMD)
  dedicates 200,000 in matching grant funding for
  the continued excavation of muck from Lake Osborne

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Proposed Dredge Areas for Phase III