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CASE STUDIES ON THE USE OF ENVIRONMENTAL CLAMSHELL BUCKETS FOR REMEDIATION OF CONTAMINATED SEDIMENTS Application of Environmental Dredging Tips Lessons.

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Presentation on theme: "CASE STUDIES ON THE USE OF ENVIRONMENTAL CLAMSHELL BUCKETS FOR REMEDIATION OF CONTAMINATED SEDIMENTS Application of Environmental Dredging Tips Lessons."— Presentation transcript:

1 CASE STUDIES ON THE USE OF ENVIRONMENTAL CLAMSHELL BUCKETS FOR REMEDIATION OF CONTAMINATED SEDIMENTS Application of Environmental Dredging Tips Lessons learned from more than 10 years of completing dredging projects with environmental clamshell buckets Presented by Darrell Nicholas, P. E. Cable Arm Professional Services

2 Clamshell Advantages - Rapid mobilization with usually lower costs - Equipment and labor readily available in most markets - Handles deep water greater than 40 feet - Some rock and debris handling capability - Much lower water treatment costs Clamshell Disadvantages - Lower production rates usually vs. cutterhead - Need for onshore unloading/transfer facilities, trucks - Loss of volatile organic compounds from open barges - Need for secondary spill containment at transfer points Cable Arm, Inc. June 2005 – p2

3 Comparison of Water Treatment Needs Environmental Clamshell vs. Cutterhead Cutterhead dredging typically produces 4 to 14 times more water to be treated than clamshell dredging in environmental applications. Cable Arm, Inc. June 2005 – p3

4 ENVIRONMENTAL CLAMSHELL BUCKET FEATURES

5 St. Lawrence River Remediation Project April – November 2001 Contaminant – PCBs Concentration Range: 1 to >1000 ppm Area Remediated: 22 acres Volume Removed: 86,400 cubic yds Water Depth: 0 to 30 ft Current: 0 to >4 ft per second Tidal range: 0 to 3 ft (ship traffic) Secondary Turbidity Control: Sheetpile Obstructions: Cobbles, dredge spoil, driftwood, old dock Operations Software: WINOPS Clean-up Goal: 1 ppm Cable Arm, Inc. June 2005 – p5

6 St. Lawrence River Remediation Project Removal of 86,600 cy of sediment containing 20,200 lbs of PCBs 98.6% reduction in PCB contaminant levels 4% of the area remained above 10 ppm and was capped. Source: SLRPP Completion Report, Bechtel, Cable Arm, Inc. June 2005 – p6

7 St. Lawrence River Remediation Project – Lessons Learned Source: SLRPP Completion Report, Bechtel, Sections on 25 to 50 ft centers aren’t good enough. Sonar depth positioning wasn’t fast enough to provide on-the-fly updates in production mode. Need a survey point within 1 bucket width of every bite. Cable Arm, Inc. June 2005 – p7

8 St. Lawrence River Remediation Project – Lessons Learned Accurate starting elevation essential. Real time xy and z positioning required under production conditions. Update bottom elevations as material is removed. Real time operator display of current bucket depth, current bottom depth, and target depth needed. Cable Arm, Inc. June 2005 – p8

9 Lessons Learned - Contracting Make sure your contract rewards the right things Retain the ability to reject a bid if the contractor cannot demonstrate 100% compliance with the specifications. Don’t be afraid to use a hybrid contracting system that mixes lump sum items with time and material items. Identify and spell out testing and reporting requirements. Provide separate pay items for health and safety support and quality assurance work Don’t under estimate budget and schedule impacts for interfacing with the public and regulators. Include a pay item for contractor support with these issues. Provide a start-up period for training and working out the kinks. Require dry runs and trials of equipment before starting production, particularly with complicated procedures and/or difficult interfaces. Cable Arm, Inc. June 2005 – p9

10 White Lake, Michigan – Summer 2003 Contaminant – PCBs Concentration Range: 1 to 150 ppm Area Remediated: 2 acres Volume Removed: 8,000 cubic yds Water Depth: 40 to 60 ft Current: negligible Tidal range: negligible Secondary Turbidity Control: Floating cell w/ short curtain skirt Obstructions: Timber Operations Software: Clamvision – 1 st field application Clean-up Goal: 2 ppm Cable Arm, Inc. June 2005 – p10

11 White Lake, Michigan – Summer 2003

12 White Lake, Michigan - Summer 2003 Lesson Learned and Applied – Obtain a highly accurate survey with no more than a bucket width spacing between sections. Cable Arm, Inc. June 2005 – p12

13 White Lake, Michigan - Summer 2003 Lesson Learned and Applied – Evaluate Survey Accuracy & Precision Before Dredging - Provided independent QA/QC of surveys for precision and accuracy. - Performed 3 independent surveys on 3 different days. - Evaluated 15 profiles. All profiles fell within an 8-inch vertical band. Cable Arm, Inc. June 2005 – p13

14 White Lake, Michigan - Summer 2003 Lesson Learned and Applied – Update bottom elevations as dredging progresses Cable Arm, Inc. June 2005 – p14

15 Lesson Learned and Applied Correlate turbidity measurements with operational practices Result - 100% Compliance with Turbidity Limits Cable Arm, Inc. June 2005 – p15

16 White Lake, Michigan - Summer 2003 A very simple pie chart – 100% successfully remediated Apparently the first clean closure of a site with PCB contaminated sediment in the Great Lakes region. Cable Arm, Inc. June 2005 – p16

17 Contaminant – Coal tar, creosote Navigational with environmental handling of sediments Volume Removed: 5,000 cubic yds Water Depth: 15 to 45 ft Current: reversible, up to 3 knots Tidal range: 3 ft Secondary Turbidity Control: Floating cell w/ short curtain skirt Obstructions: Poles, tires, etc. Operations Software: Clamvision Clean-up Goal: Reach target depth Cable Arm, Inc. June 2005 – p17 Jacksonville, Florida – Summer 2004

18 Jacksonville, Florida - Summer 2004

19 Jacksonville, Florida – Summer 2004 Lesson Learned and Applied – Use wash tank, drip pan, dredge cell, and underwater spill containment to reduce sediment resuspension.

20 Jacksonville, Florida – Summer 2004 Lesson Learned and Applied - Work from high to low where possible. Cable Arm, Inc. June 2005 – p20

21 Lesson Learned and Applied Perform Quality Control Checks on All Survey Data No dredging has taken place, yet comparing two independent pre-dredge surveys indicates more than one ft of cut or fill in portions of the site!! The alignment of high and low spots was found to be caused by a failure to adjust for sonar latency on one survey. In flat areas, this failure made little difference. On steep side slopes, the difference was significant. Always make and compare at least two surveys. Cable Arm, Inc. June 2005 – p21

22 Lesson Learned and Applied – Be Prepared to Handle Rock, Debris, and Excess Water on Every Job Cable Arm, Inc. June 2005 – p22

23 Contaminant – Coal tar Removal of up to 9 ft of contaminated sediment Volume Removed: 4,000 cubic yds Water Depth: 15 to 45 ft Current: Less than 1 fps Tidal range: 5 ft Secondary Turbidity Control: Silt curtain Obstructions: Scrap metal Operations Software: Clamvision Clean-up Goal: Reach target depth Cable Arm, Inc. June 2005 – p23 Hudson River – Fall 2004

24 Cable Arm, Inc. June 2005 – p24

25 Lesson Learned and Applied - Triple check coordinate transforms, datum conversions, and tide settings in the software; these are the most frequent sources of errors. Cable Arm, Inc. June 2005 – p25

26 Lesson Learned and Applied - Verification by Independent Methods Builds Confidence in Regulators and Public. Cable Arm, Inc. June 2005 – p26

27 Contaminant – PCBs Concentration – 1 to <50 ppm Approx. 1 acre site Removal of 14 inches of contaminated sediment Volume Removed: <2,000 cubic yds Water Depth: 0 to 20 ft Current: negligible Tidal range: 4 ft Secondary Turbidity Control: Silt curtain Obstructions: Cobbles, boulders, driftwood Operations Software: Clamvision Clean-up Goal: 1 ppm Cable Arm, Inc. June 2005 – p27 Sherman Reservoir, Massachusetts – Fall 2004

28 Lesson Learned and Applied: Precision dredging requires a crane in top mechanical condition. Precision instrumentation can be wasted on a poorly functioning crane or uncooperative operator. Cable Arm, Inc. June 2005 – p28

29 Lesson Learned and Applied Have a plan for handling debris and obstructions. Cable Arm, Inc. June 2005 – p29

30 Lesson Learned and Applied Use a differential global positioning system, bucket and crane instrumentation, tide gauge, and dredging software to track bucket location in 3-D. Don’t swing across clean areas. Cable Arm, Inc. June 2005 – p30

31 Lesson Learned and Applied For comparability, sample & test sediments using the same methods before & after dredging. Determine sampling locations & depths precisely, before & after. Unless comparable methods are used in the same x-y location, dredging effectiveness cannot be accurately evaluated. Cable Arm, Inc. June 2005 – p31

32 Lessons Learned and Applied Provide time in the project schedule to train crane operators to use new instrumentation and procedures for precision dredging. Cable Arm, Inc. June 2005 – p32

33 Lesson Learned and Applied Involve the crew. Track project status on a real-time basis and provide daily updates. Provide feedback that includes both successes and areas for improvement. Establish realistic performance expectations. Cable Arm, Inc. June 2005 – p33

34 Sherman Reservoir – Fall 2004 Another Site 100% Successfully Remediated Applying the lessons learned from past environmental dredging experience can produce results that are easy to explain to your clients, to the public and to the regulators. Cable Arm, Inc. June 2005 – p34

35 Structure your contract to procure the right equipment operated by well-qualified personnel using the correct techniques by rewarding safe, efficient, high quality performance that achieves your well-defined project goals. Cable Arm, Inc. June 2005 – p35 To Summarize the Lessons Learned


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