Environmental Dredging Productivity for Precision Excavator Dredges

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

ENVIRONMENTAL DREDGING PRODUCTIVITY FOR PRECISION EXCAVATOR DREDGES

Robert S. Webb1, Teal M. Dreher2, and Paul Fuglevand3 ABSTRACT This paper will discuss factors affecting environmental dredging productivity for precision excavator dredges. Actual performance data from environmental dredging is needed to estimate productivity and costs for environmental dredging during the feasibility study stage of a project. This paper will present actual environmental dredging productivity data for precision excavator dredges in relation to the following three factors: 1) Dredging Time. Dredging production rate is often expressed in terms of cubic yards (in-situ volume) per hour of dredging time. There are two components that make up the dredging time, the effective working time and the non-effective working time. The proportion between effective and non-effective time for environmental dredging is considerably different than for navigation dredging. The paper will present a discussion of these factors, present actual dredging time data for environmental dredging projects and provide recommendations for effective work time estimates during planning stages of projects. 2) Mechanical Dredging Production Rate. The production rate of a mechanical dredge is a function of the bucket size, the average filling rate of the bucket, the amount of time it takes the bucket to make a pass and place material in a barge, and the daily effective working time of the dredge. This paper will present a specific method for calculating the production rate of a precision excavator dredge. It will discuss the range of parameters considered appropriate for those estimates for environmental dredging with excavators. 3) Volume Estimate. The volume of sediment removed is a primary factor in estimating the cost of environmental dredging. During the early stages of a remediation project, the remedial investigation (RI) and feasibility study (FS), an initial estimate of dredging volume is made. The RI often establishes the extent of sediment contamination and the in-situ volume of impacted sediment. The FS estimates the volume of sediment that will be dredged in order to capture the in-situ volume of impacted sediment. This paper will present information on factors that influence actual dredging volumes generated in the process of removing the target material. It will present an example of a project with known actual dredging volumes and the RI estimate of the in-situ volume, and will discuss the use of scaling factors during the FS stage to estimate dredging volumes based on the RI estimate of in-situ volume.

Keywords: Production, remediation, mechanical dredging, remedial investigation

1 Senior Consulting Engineer, Dalton, Olmsted & Fuglevand, Inc., 1236 NW Finn Hill Road, Poulsbo, WA 98370 USA T: 360-394-7917, Fax: 866 370-9466, Email: [email protected]. 2 Consulting Engineer, Dalton, Olmsted & Fuglevand, Inc., 1236 NW Finn Hill Road, Poulsbo, WA 98370 USA T: 360-394-7917, Fax: 866 370-9466, Email: [email protected]. 3 Senior Consulting Engineer, Dalton, Olmsted & Fuglevand, Inc., 10827 NE 68th Street, Kirkland, WA 98033 USA, T: 425-827-4588, Fax: 866 370-9466, Email: [email protected].

326 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

INTRODUCTION There are numerous factors that affect environmental dredging productivity for precision excavator dredges, including actual effective dredging time, dredging production rate, and volume estimates. These factors are discussed below with regards to actual dredging productivity data three major environmental dredging projects including the Hudson River PCBs Site (New York), Duwamish Waterway (Washington), and Hylebos Waterway (Washington). All three projects were performed using precision fixed arm excavators. This data can be useful for planning and cost estimating for future environmental dredging projects. DREDGING TIME One of the major performance factors affecting schedule and cost for dredging projects is the actual effective time achieved by the dredge on the project. Dredge effective time describes the time when the dredge is generating dredged material, as opposed to non-effective time when the dredge is not generating dredged material, but rather performing preparatory and ancillary activities. These concepts are defined by the U.S. Army Corps of Engineering (USACE), as summarized below:

Effective working time (EWT): “effective working time” is time during the dredging operation when actual material production is taking place.

Noneffective working time (NEWT): “noneffective working time” is time during the dredging operation when the dredge is operational but no material production is taking place, such as during times of minor operating repairs, repositioning of dredge, vessel traffic, and weather.

Dredging time: “dredging time” is the sum of effective working time and noneffective working time.

Percent Effective Working Time (EWT%): “EWT%” is the ratio of the effective time to the dredging time, expressed as a percentage.

As the EWT% increases, the productivity of the dredge theoretically increases. It is important to realize that 100% EWT is not possible as there are always non-effective work activities that must take place, including moving the dredge, refueling, and changing out sediment scows. So although NEWT cannot be reduced to zero, NEWT can be reduced to only that truly necessary for the project, resulting in increased efficiency, production and reduced costs.

Dredging time data was compiled for three different environmental dredging projects: Head of Hylebos Remediation Project, Tacoma, WA; Boeing DSOA Corrective Measure and Habitat Project, Seattle, WA; and Upper Hudson River Project, Fort Edward, NY.

Calculation of Dredging Time Head of Hylebos Remediation Project During both the 2004 Construction Season (CS) and 2005 CS, full-time engineering observers onboard the dredges tracked effective working time and noneffective working time. The time data was recorded near real time into daily dredge logs on Excel spreadsheets by the dredge observer. Boeing DSOA Corrective Measure and Habitat Project For all three construction seasons at the Boeing DSOA Corrective Measure and Habitat Project, the dredging time, including the effective and noneffective work time, was calculated based on electronic daily logs filled out by the Dredge Observer. The Dredge Observer is the oversight engineer who sat alongside the excavator operator full-time for the duration of the project. The electronic logs had a standardized set of activities that comprised all of the operations that took place during the dredging season. One responsibility of the Dredge Observer was to account for the duration of every activity that took place during each work shift in real time. These electronic files were then transferred to a database so the data could be efficiently analyzed. On a daily basis during the project, this data was analyzed and reviewed with project management staff.

327 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Upper Hudson River Project For the Upper Hudson River project, operational activities and associated durations were recorded by the dredging contractor and reported in the daily reports for each dredge unit. Hudson River Project Data was provided by GE for this paper. Dredging Time Data Actual dredging time data was reviewed for these three environmental dredging projects, each using fully instrumented fixed arm excavators. Both the Head of Hylebos project and the Boeing DSOA project had full-time engineers tasked with recording the dredging time in near real-time, as opposed to the Upper Hudson River project, which had the dredging time reported by the contractor. Due to the nature of the task, the reported effective working time for the Upper Hudson River may be higher than what actually occurred. Table 1 summarizes the effective working time for all three projects, as well as the types of excavators, size of buckets, and production volumes for each season. Effective Work Time Trends over Multi-Year Projects Based on the data summarized in Table 1, it is reasonable to expect that the effective time for a project will increase in subsequent years of the project. For both the Head of Hylebos and the Boeing DSOA projects, the EWT%, as well as the production rate in cubic yards per EWT hour, increased with each construction season. For the Upper Hudson River, the EWT% and production increased up to the 2012 season, and then decreased in 2013 as site factors changed.

This increase in overall EWT% can be attributed both to the steep learning curve experienced by the crew during the first construction season of a project, as well as the ability to review any lessons-learned from the previous season and reevaluate the processes and equipment used before starting the next season.

This is exemplified by the Boeing DSOA project. During the first construction season (CS1), 16% of dredging time was spent on water management (pumping free water off of barges to a water treatment facility and then back into the waterway to meet strict water quality criteria). After CS1 ended, a new more robust water treatment system was constructed, resulting in the following seasons having 3% or less of dredging time spent on water management. Primary Noneffective Work Time Factors One of the primary noneffective worktime categories that show up in each environmental dredging project reviewed is the time to move the dredge, which includes both stepping the dredge to the next set and relocating the dredge within the project area with tug assist. From the three projects looked at, the percentages of time spent moving the dredge ranged from 4% to 17% of total dredging time, with an average of around 10%. This is a non-avoidable task, and should be taken into account during project planning, scheduling and budgeting. As a considerable source of NEWT, the process of moving the dredge should be evaluated and considered during the project as a way to potentially improve EWT%. At the Boeing DSOA, the overall experience of the crew improved over time, resulting in more efficient moves of the dredge later in the project.

Another noneffective worktime category that was a primary factor for all three projects is the time spent waiting for a sediment scow. This is when the dredge is ready and in position to dredge but does not have a barge alongside to dredge into and includes the time required to switch out a loaded sediment barge with an empty one, as well as the time lost due to delays from the transload facility where barges are offloaded to an upland facility, which is often dependent on the upland storage capacity and transportation systems (truck or rail). For the three projects, the percentage of dredging time spent waiting for and changing a sediment scow ranged from 5% to 31%.

Recommendations for Effective Working Time Listed below are several examples of factors to consider when looking to improve effective working time. This can be done routinely during the project as data is available, even on a daily basis. For project spanning multiple construction seasons large improvements can be made by evaluating each season as completed and looking for larger changes than can be done during the actual dredging season that can produce significant improvements.

328 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Table 1. Dredging time data for precision excavator dredges.

Head of Hylebos Waterway Remediation Boeing DSOA Corrective Action and Habitat Project Upper Hudson River Remediation Phase 1 Dredging 2004 CS 2005 CS CS1 (2013) CS2 (2014) CS3 (2014-2015) 2011 2012 2013 2014 (2009)

Excavator and Bucket Size Liebherr 984 w/ 6.5 CYHitachi 800 w/ 4.5 CYKomatsu PC 750 w/ 3 12 dredges (Note Komatsu PC 800 w/ 4 CY bucket 3 dredges (Note B) 4 dredges (Note C) 5 dredges (Note D) 5 dredges (Note E) bucket bucket CY bucket A)

Dredging Volume Cubic Yards 337,000 CY 64,000 CY 35,949 CY 48,513 CY 72,688 CY 286,354 CY 363,332 CY 663,265 CY 628,057 CY 582,917 CY Dredging Time hours 5,456 hrs 780 hrs 1,651 hrs 1,003 hrs 883 hrs 1,252 hrs7,600 hrs 22, 458 hrs 12,346 hrs 15,568 hrs 14,004 hrs 24-hr day equiv. 227.3 days 32.5 days 68.8 days 41.8 days 36.8 days 52.2 days 935.6 days 316.7 days583.5 514.4 days days 648.7 days Production (CY/dredging hour) 54.0 38.8 35.8 54.9 58.112.8 47.8 53.7 40.3 41.6 Effective Working Time Effective Time, hours 2,501 hrs 251 hrs 1,010 hrs 500 hrs 479 hrs712 hrs 10,093 hrs 5,416 hrs 8,743 hrs 10,385 hrs 9,340 hrs Effective Time, 24-hr. day equiv. 104.2 days 10.4 days 42.1 days 20.8 days 20.0 29.7days days 420.5 days 225.7 days 364.3 days 432.7 days 389.2 days % of Dredging Time (%EWT) 45.8% 32.2% 61.2% 49.9% 54.2% 56.9% 44.9% 71.3%66.7% 70.8% 66.7% Production (CY/EWT hour) 122.5 63.4 71.9 101.3 102.128.4 67.1 75.9 60.5 62.4 Noneffective Working Time

Noneffective Time, hours 2955 hrs 529 hrs 641 hrs 503 hrs 404 hrs541 hrs 12,365 hrs 2,184 hrs 3,603 hrs 5,183 hrs 4,664 hrs Noneffective Time, 24-hr. day equiv.123.1 days 22.1 days 26.7 days 21.0 days 16.8 22.5days days 515.2 days 91.0 days 150.1 days 216.0 days 194.3 days % of Dredging Time 54.2% 67.8% 38.8% 50.1% 45.8%55.1% 43.1% 28.7% 29.2% 33.3% 33.3% Noneffective Working Time % of % of % of % of % of % of % of % of % of Dredge 24-hr 24-hr 24-hr 24-hr % of Dredge 24-hr % of Dredge 24-hr 24-hr 24-hr 24-hr 24-hr 24-hr Details Dredge Dredge Dredge Dredge Dredge Dredge Dredge Dredge Time Days Days Days Days Time Days Time Days Days Days Days Days Days Time Time Time Time Time Time Time Time Repairs 14.2% 32.3ys da 19.1% 6.2ys da 4.6% 3.1ys da 2.9% 1.2ys da 0.5% 0.2ys da 1.0% 0.5ys daN/A* N/A* N/A* N/A* 2.9% 14.7ys3.3% da 21.5ys5.5% da 32.0ys da Moving Dredge 16.8% 38.2ys da 9.7% 3.1ys da 10.6% 7.3ys da 9.5% 4.0ys da 6.0% 2.2ys da 9.2% 4.8ys daN/A* N/A* N/A* N/A* 6.6% 33.9ys3.5% da 22.8ys4.2% da 24.8ys da Stepping 13.1% 29.8y das 7.4% 2.4ys da 6.2% 4.3ys da 5.1% 2.1ys da 3.3% 1.2ys da 4.4% 2.3ys da NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Relocating Dredge 3.7% 8.4 ydas 2.1% 0.7ys da 4.4% 3.0ys da 4.4% 1.8ys da 2.7% 1.0ys da 4.7% 2.5ys da NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Changing / Waiting for Sediment Scow8.5% 19.4ys da 7.4% 2.4ys da 5.4% 3.7ys da 15.1% 6.3ys da 26.9% 9.9ys da 16.7% 8.7ys da 31.0% 290.0ys daN/A* N/A* 9.8% 50.5ys da 10.4% 67.6ys da 10.0% 57.2ys da Changing Sediment Scow NA* NA* NA* NA* NA* NA*y 4.7%s2.0 4.3% da 1.6ys da 8.8% 4.6ys da NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Mooring/Adjusting Scow NA* NA* NA* NA* NA* NA*y 1.4%s0.6 1.0% da 0.4ys da 0.6% 0.3ys da NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Waiting for Scow/Transload Delays NA* NA* NA* NA* NA* NA*y 8.7%s 21.7% 3.6 da 8.0ys da 7.2% 3.8ys da NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Computers and Positioning Electronics6.0% 13.6ys da 4.4% 1.4ys da 6.4% 4.4ys da 3.1% 1.3ys da 4.9% 1.8ys da 2.3% 1.2ys daN/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* Maintenance 4.4% 10.1ys da 4.0% 1.3ys da 1.1% 0.7ys da 0.5% 0.2ys da 0.5% 0.2ys da 1.0% 0.5ys daN/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* Other 3.1% 7.0 days 23.5% 7.6 days 5.8% 4.0 days 2.4% 1 days 3.0% 1.1 days 8.2% 4.3 days 15.3% 143.4 days N/A* N/A* 5.1%8 days 26.4 days 7.9% 51.4 days 9.2% 53. Tribal Fishing NA* NA* NA* NA* NA* NA* 0.0% 0 days 0.0% 0 days 3.0% 1.5 days NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Hold for Crew NA* NA* NA* NA* NA* NA* 1.3% 0.5 days 1.7% 0.6 days 2.3% 1.2 days NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Contractor Directed Standby NA* NA* NA* NA* NA* NA* 0.0% 0 days 0.1% 0 days 1.9% 1 days NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Traffic 0.8% 1.8 days 0.1% 0.0 days 0.5% 0.4 days 0.0% 0 days 0.3% 0.1 days 0.0% 0 days N/A* N/A* N/A* N/A* 0.4% 2.1 days 0.4% 2.8 days 0.2% 1.2 days Tug Delay 0.1% 0.1 days 0.1% 0.0 days 0.1% 0.1 days 0.2% 0.1 days 0.5% 0.2 days 1.7% 0.9 days N/A* N/A* N/A* N/A* 1.8% 9.2 days 3.4% 22.0 days 2.3% 13.6 days Additional Mob/Demob 0.2% 0.5 days 0.0% 0.0 days 4.2% 2.9 days N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* Water Management N/A* N/A* N/A* N/A* N/A* N/A* 16.0% 6.7 days 3.0% 1.1 days 1.5% 0.8 days N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* Hold for Water ManagementN/A* N/A* N/A* N/A* N/A* N/A*12.2% 5.1 days 0.0% 0 days 0.0% 0 days NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Dewatering Sediment ScowN/A* N/A* N/A* N/A* N/A* N/A*3.6% 1.5 days 2.5% 0.9 days 1.4% 0.7 days NA* NA* NA* NA* NA* NA* NA* NA* NA* NA* Water Quality N/A* N/A* N/A* N/A* N/A* N/A* 0.0% 0 days 0.0% 0 days 0.0% 0 days N/A* N/A* N/A* N/A* 0.6% 3 days 0.1% 0.7 days 0.0% 0.2 days Weather/Tides N/A* N/A* N/A* N/A* N/A* N/A* 0.2% 0.1 days 0.0% 0 days 1.5% 0.8 days N/A* N/A* N/A* N/A* 2.0% 10.1 days 4.0% 25.9 days 1.7% 9.8 days Los t Time1 N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* 8.7% 81.5 days N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* N/A* - This field was either not applicable, unavailable, or counted under a different category, such as "other" 1 Lost time includes time recorded as "miscellaneous (lost work time)", "major repairs and alterations,"ents" "opposing and "monitoring natural elem related shutdowns" Note A 4 dredges w/ Caterpillar 385 with 5-cy bucket; 1bucket dredge Caterpillar 345 with 2-cy 7 dredges w/ Catgerpillar 320 with 1-cy bucket Note B 3 dredges w/ Caterpillar 385/390 with 5-cy bucket Note C 3 dredges w/ Caterpillar 385/390 with 5-cy bucket; 1 dredge w/ Caterpillar 3059 with 2-cy bucket Note D 3 dredges w/ Caterpillar 385/390 with 5-cy bucket; 2 dredges w/ Caterpillar 3059 with 2-cy bucket Note E 2 dredges w/ Caterpillar 385/390 with 5-cy bucket; 3 dredges w/ Caterpillar 3059 with 2-cy bucket

329 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Factors to Improve Effective Working Time Overall effective working time can be improved for a project using proper planning and adaptive management. Prior to the start of a project, anticipating the appropriate number of barges and tugs and having redundancy in equipment can help to prevent loss of effective working time.

Then during the project, routinely evaluate EWT and NEWT data and look for areas of large time loss and trends. If time waiting for sediment scows is significant, consider if additional tugs or scows will improve situation cost effectively. The real time tracking and display of project assets (tugs, Dredges, Scows) can significantly improve this process.

During a project some ways to increase effective working time include creating an efficient daily dredge plan to reduce the number of dredge moves and working with the Transload facility to understand and anticipate upcoming issues or limitations. For instance, if it can be anticipated that the barge offloading facility is nearing capacity, dredge operations could be switched over to doing Final Pass dredging, which will produce low production volume while still maintaining high effective working time.

Activities that are necessary to dredge operation, such as switching out sediment scows, can be optimized to be more efficient. This can be done by keeping the crew informed of the timeframe when certain activities will take place, so that all required personnel can be ready to execute the task. In high production dredging, using a 3.1 CM (4 CY) bucket, a 229.5 CM (300 CY) sediment barge may take 2 hours to fill. If the tug operator and pile bucks are notified when the barge is 75% full, then they can be in position with an empty barge and the barge switch can take 10 minutes instead of 45 minutes. However, if the tugs are not notified of a potential barge switch at the dredge they may be off doing other necessary, but not necessarily time critical activities at the time a barge swap is required, resulting in increased NEWT.

In between dredging seasons, examining the dredging time from the previous season can be beneficial in finding ways to improve the overall EWT% for the next construction season. The time in between seasons can allow for large changes than may be possible mid season.

Summary of Planning Numbers Based on the data from the three environmental dredging projects looked at, Table 2 summarizes the averages, which can be used for planning purposes on future projects. Table 2. Average effective worktime and production rates for three environmental dredging projects (1 CY=0.765 CM).

Subsequent 1st year Average Years % of Dredging Time (EWT%) 46.9% 64.0% 56.4% Production (CY/dredging hour) 33.7 47.9 43.6 Production (CY/EWT hour)1 73.1 76.1 75.2 Noneffective Worktime Category, % of Dredging Time Waiting for Sediment Scow2 15.5% 14.8% 15.1% Other2 11.1% 6.7% 8.6% Moving Dredge3 12.0% 6.7% 8.5% Water Management4 16.0% 2.3% 6.9% Repairs3 12.1% 2.6% 6.2% Computers and Positioning Electonics5 4.5% 3.6% 4.1% Maintenance5 3.0% 0.8% 2.1% Weather/Tides6 0.2% 1.8% 1.6% Tug Delay3 0.1% 2.0% 1.3% Water Quality6 0.0% 0.2% 0.1% Traffic3 0.3% 0.3% 0.3% 1Note the first season of the Hylebos Waterways project used a dredge with a 6.5 CY bucket, whereas the second season used a 3 CY bucket, which may skew the production calculation.

330 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

2Averages from Hylebos Waterway; Boeing DSOA; and Upper Hudson 2009, 2012, 2013, and 2014 dredging seasons. 3Averages from Hylebos Waterway; Boeing DSOA; and Upper Hudson 2012, 2013, and 2014 dredging seasons. 4Averages from Boeing DSOA project. 5Averages from Hylebos Waterway and Boeing DSOA projects. 6Averages from Boeing DSOA project and Upper Hudson 2012, 2013, and 2014 dredging seasons.

MECHANICAL DREDGING PRODUCTION RATE Overall dredge production rates can have a wide range based on a variety of factors, which include the following:  The contractor’s environmental dredging experience - This is very specific to the manager and crew performing the work. Have they done this type of work before, have they worked together as a team before. Just because a company has a long list of experience, they are only as good as the crew actually onsite. Large numbers of local new hires to reduce costs can significantly diminish the overall experience factor.  Equipment used and level of maintenance - Equipment reliability, including navigation and positioning system, is a major factor in reducing NEWT  Type of material being dredged – dense sand compared to loose silt, sand can be more difficult to dig but silt may pose greater residual risk so need to perform dredging in appropriate manner at appropriate rate.  Amount of debris – debris can significantly reduce production.  Thickness of dredge cuts – thicker cuts often result in higher production and higher EWT%.  Weather – poor weather including high winds and fog can reduce EWT% and production rate  Vessel traffic – vessel traffic can significantly reduce production rate and EWT% as dredging needs to stop to allow traffic to pass.  Distance to offload site – the distance from dredge site to offload site can significantly impact production and EWT% and can increase the number of tugs and barges necessary to support the project.

Production Factors Bucket Cycle Time The bucket cycle time is defined as the time it takes to make a complete pass with the bucket, which includes lowering the bucket to reach the sediment at the bottom of the waterway, adjusting the bucket placement to get it to the correct location and depth, closing the bucket, raising the bucket out of the water, swinging the bucket over the sediment barge, emptying the bucket into the barge, and then swinging the bucket back to its starting position. Several parameters can affect the bucket cycle time, including depth to sediment, and type of material being dredged, accuracy requirements for location, type of equipment, navigation system, and ability of the operator.  Depth to sediment: The farther down the bucket has to travel to get down to required depth, the longer the bucket cycle time will be. This factor can also affect overall effective time because in deeper water, the dredge may not be able to reach as many bucket locations, and therefore will require the dredge to have more frequent moves. This can be managed if the waterway is tidally influenced by putting the dredge in shallower water during high tides and deeper water during low tides.  Type of material being dredged: The type of material being dredged has a large impact on the cycle time. Softer, finer grained sediments produce the fastest cycle times, whereas compact sands and clays often results in bucket refusal, which means the operator has to work a little harder to get the bucket to fully close around the material. The material type also affects the fill factor.  Accuracy requirements: The greater the accuracy requirements, the longer it will take the operator to get the bucket on target. However, with greater accuracy less overall cycles are required and residuals generation is reduced.  Type of equipment: The year and model of the excavator used will affect how quickly the dredge arm can swing to and from the sediment scow.  Navigation System: The functionality of the navigation system is vital to successful operation of an environmental dredging project. It is important to both have a good navigation system, but also to have people who know the system readily available to troubleshoot if needed.

331 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

 Ability of the operator: The cycle time is directly affected by the ability and experience of the operator. Cycle time generally increases from the beginning of a dredging season to the end just from the operator getting more experience. Bucket Size The size of the environmental dredging bucket directly affects the production rate of a mechanical dredge because it affects how much material can be dredged per bucket cycle. A typical bucket size for transportable size excavators is 2 to 6 cubic yards, however sometimes site conditions can make having a smaller bucket beneficial (such as dredging areas with a lot of obstructions). Fill Factor The fill factor is a ratio of the amount of sediment removed per bucket to the volume of the bucket. This factor varies based on type of material, depth of dredge cut, bucket type, and operator skills. The fill factor also impacts the volume of water generated during the dredging project. Higher fill factors result in lower water generation and higher production rates. However, over-penetration of the bucket into soft sediments, which can often happen if too high (over 90%) fill factor is targeted. Such over-penetration can result in significant sediment resuspension and generation of releases and residuals. Fill factor must be balanced between desired depth of cut, production rate and typical objective of managing residuals and producing resulting surface that meets regulatory criteria. Over the course of the project the fill factor will be high during thick bank cuts and low during final cuts to grade, and will tend to average between 50% and 60% depending on site conditions.

Production Rate Calculation The production rate for a mechanical dredge can be calculated using the bucket size, average fill factor, and cycle time. The equations for production rate in cubic yards per hour and cubic yards per day are shown below.

(1) /

/ / # ⁄ % (2)

The typical range of parameters that can be used for planning purposes is shown in Table 3 below.

Table 3. Planning numbers for production calculations for environmental dredging projects (1 CY=0.765 CM).

Recommended Production Factor Planning Numbers Bucket Size, Cubic Yards 2-6 CY Fill Factor 0.5-0.6 Cycle Time, seconds 60-90 s Effective Working Time, EWT% 50%-60%

VOLUME ESTIMATE The volume of sediment removed during an environmental dredging project is a primary factor in estimating the cost of the project. During the early stages of a remediation project, the remedial investigation (RI) and feasibility study (FS) are conducted and an initial estimate of dredging volume can be made. The RI often establishes the extent of sediment contamination and the in-situ volume of impacted sediment. The FS estimates the volume of sediment that will be dredged in order to capture the in-situ volume of impacted sediment. This is done by creating a dredge prism that encompasses the impacted sediment, but also takes into account logistics, bucket size, and allowable overdredging. Table 4 shows the planned and actual dredging volumes for each project, as well as the neat line volume of contaminated sediment.

332 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

As shown in Table 4, for the Head of Hylebos (2004-2005) and the Boeing DSOA (2013-2015) the scaling factor of insitu neat line contaminated sediment volume to the actual final dredge volume was 1.76 and 1.46 respectively. Both of these project has a limited (15.2 cm, 6 inch) design overdredge allowance, a moderate amount of debris (urban setting for each) and a dredge cut thicknesses ranging from 0.61 m to 6.1 m (2 ft to 20 ft).

Based on this a scaling factor of 1.8 to 2.0 x the insitu volume would be a recommended planning scaling factor to use during project planning prior to final design. In projects with significant debris down to full depth of dredge cut, this ratio may be slightly higher. For projects with an area weighted thicker average cut thickness, the scaling factor would be expected to be lower than for a project with a thinner average cut thickness. The same is true for overdredge allowance where a greater overdredge allowance would be expected to result in a higher sacling factor than that realized for projects with a 15.2 cm (6 inch) overdredge allowance.

Table 4. Planned and actual dredging volumes (1 CY=0.765 CM). Scaling Neat line Dredge Actual Factor: Neat contaminated Volume Volume line to Project sediment Estimate1 Dredged Actual volume (CY) (CY) (CY) Volume Dredged Head of Hylebos 230,000 383,000 404,000 1.76 Boeing DSOA 110,223 176,179 161,392 1.46 1Based on the dredge prism, including allowable overdredging

CONCLUSIONS The productivity of an environmental dredge is an important factor to consider during project planning and cost estimating. The productivity of precision excavator dredges can be better estimated by considering the following factors: dredging time, mechanical dredging production rates, and volume estimates. These factors can be better estimated when accounting for specific project details, such as material being dredged, debris, site limitations, and distance to offload site.

CITATION Fuglevand, P.F., Webb, R.S., and Dreher, T.D. “Environmental dredging productivity for precision excavator dredges,” Proceedings of the Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015", Houston, Texas, USA, June 22-25, 2015.

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