Assessment and Remediation of Contaminated Sediments (ARCS) Program
REMEDIATION GUIDANCE DOCUMENT
US Environmental Protection Agency. 1994. ARCS Remediation Guidance Document. EPA 905-B94-003. Chicago, Ill.: Great Lakes National Program Office.
Transport technologies are used to move sediments and treatment residues between components of a remedial alternative. In most cases, the first element of the transport component is to convey sediments dredged during the removal process to the disposal or rehandling site. Sediments may then be transported for pretreatment and then treatment, and treated residues may be transported to a disposal site. Transport is the component that links the other components of a remedial alternative, and may involve several different technologies or modes of transport.
Transport modes can include waterborne, overland, or a combination of these technologies. Waterborne transport modes include pipeline transport, hopper dredges, and barge systems. Overland transport modes include pipeline, railcar, truck trailer, and conveyor systems. In most cases, contaminated sediments are initially moved using a waterborne transport mode (pipeline or barge) during the removal process (one exception is when land-based dredging is used). Hydraulic removal technologies produce contaminated, dredged material slurries that are typically hauled by pipeline transport to either a disposal or rehandling site. Mechanical removal technologies typically produce dense, contaminated dredged material or excavated basin material for rehandling, which is hauled by barge, railcar, truck trailer, or conveyor systems.
Averett et al. (in prep.) provide a literature review of dredged material transport technologies. Other key resources for information on transport technologies include Churchward et al. (1981), Souder et al. (1978), Turner (1984), and USEPA (1979). Much of the information on transport technologies in the literature cited herein was developed for application to municipal sewage sludge, dredged material, and mining materials. The intended applications were generally scaled for very large quantities of materials. In many instances, these materials were transported over long distances, using permanently installed systems as part of long-term operations. In contrast, sediment remediation projects will typically move relatively small quantities of material over short distances and are often short-term operations. The feasibility and costs of transportation modes will be influenced by the scale of the remediation project.
This chapter provides a brief description of the pipeline, barge, railcar, truck trailer, and conveyor transport technologies. Discussions of the factors for selecting the appropriate transport technology and techniques for estimating costs and contaminant losses during transport are also provided. When transport modes are compared and contrasted with each other, the volumes of material being discussed are in-place cubic yards or cubic meters of sediment.
DESCRIPTIONS OF TECHNOLOGIES
Temporary dredge pipelines are the most economically feasible mode for hauling contaminated dredged material slurries and water. For a sediment remedial alternative, pipelines may be used for the discharge from a hydraulic dredge; with the hydraulic pumpout from a tank barge, railcar, or truck trailer; and in routing process water, effluent, or leachate to treatment systems.
The amount of dredged material slurry generated during sediment removal is greatly affected by the contaminated sediment characteristics, removal equipment design, and removal equipment operation. Pipeline transport systems should be hydraulically designed and operated to minimize downtime while effectively moving this slurry. Equipment durability and pipeline routing greatly affect system downtime. Effective slurry transport consists of moving the slurry with minimal particle sedimentation in the line and with good line connections and minimal line wear and corrosion. Other factors being equal, fine-grained dredged material can be less costly to move (i.e., require less energy) than coarse-grained material (Denning 1980; Souder et al. 1978; USEPA 1979).
It is periodically necessary to halt dredging operations to add or remove sections of the pipeline to permit vessel passage or dredge advance, repair leaks, or reroute the line. Therefore, pipeline sections should be quick and easy to assemble, maintain, and dismantle. Although leaks can be welded, extra pipe sections should be readily available onsite to replace both land- and water-based pipeline sections that are clogged or leaking. Frequent monitoring helps to prevent excess leakage (Cullinane et al. 1986a).
Discharge Pipeline
Hydraulic dredge discharge pipelines can be identified by their properties (i.e., construction material, internal diameter, relative strength or schedule number, length, wall thickness, or pressure rating) or method of deployment (i.e., floating, submerged, or overland). Discharge pipelines typically range in length from <3 to >15 km (with boosters) (Cullinane et al. 1986a; Souder et al. 1978; Turner 1984). Souder et al. (1978) indicate that during commercial land reclamation projects slurries have been moved through pipelines of up to 24 km in length, and that a well-designed hydraulic dredge system can theoretically move some slurries >200 km using multiple booster pumps.
Discharge pipe sections are available in a variety of wall thicknesses and standard section lengths. The internal diameter, which is slightly larger than the diameter of the dredge suction line, ranges from 6 to 42 in. (15 to 105 cm; Turner 1984). Internal pipe section linings of cement, plastic, or glass can reduce the abrasion caused by slurry-entrained gravel, sand, and site debris; metal corrosion caused by sediment-bound contaminants and saline transport water; and the internal pipe roughness. In addition, internal abrasion and corrosion can be evenly distributed by periodically rotating each pipe section. External metal pipe corrosion can be controlled with coatings and/or cathodic protection.
Several types of discharge pipelines available for use are discussed below.
Rigid Pipeline--Rigid pipe sections can be constructed of steel, cast and ductile iron, thermoplastic, and fiberglass-reinforced plastic; the steel and iron sections are most commonly used. These sections can be joined by ball, sleeve, or flange joints to form discharge lines of varying lengths. The rigid nature of these sections permits longer, unsupported line spans and reduces the potential for damage while handling. Standard steel and iron pipe section lengths are 20, 30, and 40 ft (6.1, 9.1, and 12.1 m).
Flexible Pipeline--Flexible discharge pipe sections are constructed of either high-density polyethylene (HDPE) or rubber. The flexibility of the materials allows these sections to naturally adjust to wave action and shore contours. Therefore, these pipelines are easier to route than rigid pipelines. In addition, the flexible nature of these pipelines allows long-sweeping and more hydraulically efficient routing. However, flexible pipelines are far less commonly used than rigid pipelines.
Floating Pipeline--Discharge pipelines typically include a floating pipeline connected to the dredge pump(s) at the stern of the dredge hull. The floating pipeline can subsequently be run to a shore-based pipeline routed to the disposal or rehandling site. Because of concerns about obstructions in these pipelines and their overall stability, their use is typically limited to sections that connect the dredge pump to the land-based line. These sections provide for easy dredge movement (i.e., swing and advance). The dredge pump is connected to a floating rigid pipeline by either a rubber hose, swivel elbow, or ball joint(s). These lines are typically anchored at various locations.
Pipeline flotation is accomplished using pontoons or buoyant collars. Pontoons are typically constructed of metal cylinders with tapered ends, mounted to each end of a pipe section. The pontoons are joined together by rigid, wooden or steel beams. The rigid pipe section is attached to wooden pontoon saddles. Tender boats are used to move floating pipeline sections.
Obstruction of the waterway can be minimized by routing the pipeline to and along the shoreline. However, these pipelines should be placed in waters of adequate depth and distance from the shoreline to prevent the lines from dragging on the bottom and/or ramming the shoreline. When obstruction of the waterway is of little concern, the pipeline should be floated in a wide arc so that the dredge can advance without frequent stops to add additional pipe sections (Huston 1970).
Submerged Pipeline--Submerged pipelines can be used in place of floating pipelines in waterways where vessel traffic would require frequent dredge downtime to disconnect the line and permit passage. Submerged pipelines require two stationary points where the ends of the line can be fixed as they rise out of the water. For temporary lines, these points are typically well-moored barges (Huston 1970). Although less susceptible to damaging wave action, submerged pipelines should be used conservatively because inspection for plugs and leakage is difficult.
Shore Pipeline--Relative to floating and submerged pipelines, shore pipelines are made up of shorter (10-15 ft [3-5 m]) and generally lighter pipe sections. Pipe sections are joined and placed aboveground or on a cribbing. These lines should only be covered to protect the line from damage (i.e., traffic crossings, freezing/thaw conditions) because detection of leakage is difficult. Shore pipelines generally flow into a disposal or rehandling site.
Booster Pump
Booster pumps (kinetic or positive displacement) supplement the dredge pump(s) by increasing the distance a slurry can be pumped without particle sedimentation. Booster pumps are used when the output of the dredge pump(s) is so reduced by line routing that the cost of a booster pump is justified by the increased productivity it achieves. Although easier to design, booster pumps do not have to be identical to the dredge pump(s). For dredges that operate with long discharge lines and require booster pumps, Turner (1984) indicated that installing a booster pump on the dredge hull would reduce labor and maintenance costs. This layout would lower the labor costs typical of line booster pumps but would increase material costs for pipelines necessary to withstand increased pressures.
Booster pumps are installed to form a series of identical pumping stations (barge- or land-based) generally spaced uniformly from the dredge to the disposal or rehandling site. At each pumping station, two essentially similar pumps are arranged in series. However, if deemed necessary to optimize the reliability of the operation, an auxiliary spare pump and motor with all pertinent piping, valves, and connections can be provided for emergency use in the event of a major breakdown in the primary equipment. Positive displacement booster pumps used in combination with a centrifugal dredge pump would require a booster pump holding facility because it is practically impossible to match positive displacement pumping rates to centrifugal pumping rates (USEPA 1979).
Transport barges or scows can be defined as cargo-carrying craft that are towed or pushed by a powered vessel on both inland and ocean waters (McGraw-Hill 1984). Barge transport is the most common means of transport for mechanically dredged material. Features of barge transport that are discussed in this section are barge types, tow operations, and loading/unloading operations.
Barge Types
Three types of barges that are applicable to sediment remediation projects are the tank, hopper, and deck barges. The features of these barges are provided in Table 5-1. Tank barges are most frequently used to haul coal, petroleum and petroleum products, agricultural products, iron, steel, and chemicals. Sectionalized compartments provide structural stability to the barge hull, distribute cargo loads more evenly, help prevent cargo from shifting while in tow, and allow each section to carry different types of cargo.
Hopper barges are designed specifically to deliver bulk material to open-water disposal sites, and are the most commonly used barges for transporting dredged material. Early hopper barge designs used mechanically driven chain, cable, sheave, and releases to open the cargo compartment door(s). Recent designs use high-pressure hydraulic systems. Split-hull and continuous compartment bottom and side-dump hopper barges are simultaneously dumped, whereas bottom and side-dump hopper barge sections can be dumped individually.
The Buffalo District studied the leakage from hopper barges and concluded that all hopper barges leak to some degree. They concluded that all hull seams should be carefully shut and stabilized with sandbags, hay bales, and/or plastic liners to help minimize hull leakage.
Deck barges are simply a flat work surface and may be used as a work barge (i.e., anchor, derrick, jack-up, mooring, office, pontoon, quarterboat, service, shop, store, or survey barges) or the platform for the dredge. During a sediment remediation project on the Black River in Lorain, Ohio, a single deck barge was used as the platform for a bucket dredge and several dumpsters that were used to contain the dredged sediments. After the dumpsters were filled, the barge was brought to the shore, where the dumpsters were offloaded to flatbed trucks and hauled to a nearby disposal site.
Barge hulls can be of either single- or double-walled construction. The bow and/or stern of a barge hull is either vertical (box-shaped) or raked (angled). Raked hulls provide less tow resistance, thereby resulting in fuel savings, while box-shaped hulls are typically limited to barges on the interior of an integrated tow of multiple barges. Barges operated in moderately high wave areas can be constructed with a notched stern in which the towboat bow fits. This connection provides greater resistance to longitudinal movement along the vessel interface and enhances control under adverse conditions (Churchward et al. 1981).
Tow Operations
In the absence of significant wave action, the best position for a towboat is at the barge stern (Churchward et al. 1981). While the main factor in selecting a towboat is its ability to maneuver and push or tow the barges, the towboat's draft is also an important factor. The towboat draft should be consistent with site and transport route water depths to prevent sediment resuspension from propwash and hull dragging. Towboats are also used to move the dredge floating plant (when not self-propelled).
Although grain- or coal-filled barges are typically moved in large, integrated tows (up to 40 barges), dredged material-filled barges are generally hauled individually. A typical maintenance dredging operation might use two barges (one is filled by the dredge while the other is being transported to or from the disposal or rehandling site). If the distance between the dredging and disposal or rehandling site is long, additional barges and towboats may be used. The objective is to have sufficient barges and towboats available to keep the dredge operating continuously.
Spillage during transport can result from overfilling the barge or from a leaky hull. Risks of spillage are especially great when moving through rough waters. Overfilling can be prevented by filling the barge only to the bottom of the barge coaming. Spillage while in tow can be prevented by placing removable covers over the barge coaming. Barge hulls should be inspected regularly to ensure that they are completely sealed.
Loading/Unloading Operations
Tank and hopper barges are typically loaded by first pulling the barge adjacent to the dredge floating plant. Dredged sediment is frequently splashed or dropped onto the deck of a barge during loading operations. Spillage can be reduced by minimizing the height from which the bucket releases its load. Dredge operators should place the bucket into the cargo compartment before releasing the load and not drop it with any freefall. In addition, tank barges should be loaded uniformly to prevent excessive tilting or overturning.
During maintenance dredging of uncontaminated sediments, supernatant is allowed to overflow during filling to increase the barge's payload (i.e., reduce the amount of water hauled). Because of the potential for contaminant release and the inefficiency of barge overflow for fine-grained sediment, supernatant overflow should not be permitted on contaminated sediment dredging projects. Methods to remove free-standing water from barges, including the use of polymer flocculants, have been investigated by some Corps districts to produce more economical loads with contaminated dredged material (Palermo and Randall 1990).
Most barges can be unloaded using a variety of mechanical equipment, including cable, hydraulic, or electrohydraulic rehandling buckets (Hawco 1993). Backhoes and belt conveyors or bucket line dredges can also be used to unload barges. All unloading facilities should be equipped with drip pans or aprons to collect material spilled while unloading the barge and loading the material onto a railcar, truck trailer, or conveyor or directly into a disposal or rehandling facility.
Mechanically dredged sediments have been unloaded from barges to CDFs using a modified hydraulic dredge or submerged dredge pump. Water from the rehandling site or disposal facility (where available) is added to the barge and mixed in with the sediment to provide a uniform slurry for the rehandling dredge pump.
Railcar transport is widely used in the transport of sewage sludge, but has not been used for the transport of dredged material (according to available literature). However, railcar transport of contaminated sediments may be feasible when travel distances are especially long (i.e., >160 km).
Railcar designs can include tank, hopper, deck, and box cars (Churchward et al. 1981). Mechanically filled tank and hopper railcars are most likely the only economical means of hauling contaminated dredged material. The features of tank and hopper railcars are summarized in Table 5-2. Tank cars might also be used to haul liquid treatment residues. Souder et al. (1978) indicate that railcars of the 70- to 100-net ton class are preferable for hauling bulk materials such as dredged sediment. Tank and hopper railcars can be constructed with permanent or hatched covers to prevent weather effects and spilling or leaking of material or water from the car. Like barges, railcars should be uniformly loaded.
Railcars are pulled by either diesel- or electric-powered locomotives. However, with the exception of switching facilities, railcars must be hauled by a railroad company locomotive, requiring a contract that can take several months to obtain (USEPA 1979). Larger trains (railcar capacity and number of cars) are limited by track system designs and crossing times.
Tank Railcars
Rectangular tank railcars are typically used to haul dense materials. They are unloaded by moving them off the mainline track to an elevated loop track, disassembling the train, and dumping each car using rotary car unloading equipment. The rotary car technique turns the railcar upside down to allow gravity drainage. Swivel tank car connections can be used to avoid disassembling the train during rotary dumping. Rotary dumping equipment is very expensive and generally works best for non-cohesive materials (Souder et al. 1978). Shaker units can be used to help unload the typically cohesive contaminated dredged material.
Cylindrical railcars are typically used for hauling liquid cargo and could be used for hauling dredged material slurries. These cars are hydraulically filled and are unloaded by moving them to an elevated track to allow gravity drainage through a hatch or valve opening(s) on the car body. Tank cars can also be pumped out.
Hopper Railcars
Similar to tank railcars, hopper railcars are typically unloaded by moving them to an elevated loop track. Hopper railcars are unloaded by opening the bottom-mounted hopper door(s) or hatch(es) to allow gravity drainage (Souder et al. 1978). Unlike rotary unloading, bottom dumping of hopper railcars does not require disassembly from the train prior to unloading and, depending on the material cohesion, the train may not even have to come to a complete stop.
Truck trailer transport is the most common mode of transportation for hauling mechanically dredged material to upland disposal sites. Truck cargo compartments can include van (open and closed tops), flat, tank (liquid or pneumatic cargo), dump, depression deck, rack, or refrigerated (van or tank) types (Churchward et al. 1981). However, only tank and dump compartments are suitable for hauling dredged material and liquid treatment residues. The features of these types of trailers are summarized in Table 5-3.
Tank and dump compartments can be mounted on a single diesel- or gas-powered tractor chassis or mounted on a trailer chassis and towed by a tractor over both paved and unpaved roads. To minimize the number of drivers required and to allow loading to continue while other trucks are en route, it is desirable to use excess trailers. As with barge and railcar transport, mechanically filled trailers are the only economical means of hauling contaminated dredged material by truck. Liquid treatment residues (e.g., contaminated oil residue from solvent or thermal extraction processes) can be hauled in cylindrical tank trailers.
Trailer gates and hatches can be sealed with rubber gaskets, straw, or other materials to prevent leakage or spillage. During a dredging operation at Michigan City, Indiana, the bottom of dump truck flap gates were lined with sand, and a street sweeper was used to clean any drippage on public roads. Dump truck gates fitted with neoprene seals and double redundant locking latch mechanisms were used to haul dredged material during the Starkweather Creek cleanup in 1992 (Fitzpatrick 1993). Like barges and railcars, trailer covers can be installed to minimize odor releases during transport, to prevent spillage from sudden stops or accidents, and to prevent weather damage. Trailers should also be uniformly loaded.
Conveyor systems have been widely used for the transport of sewage sludge and for material transport in mining and mineral processing (USEPA 1979). Within a sediment remedial alternative, conveyors might be used to transport mechanically dredged sediments from barges to disposal or rehandling sites, from rehandling sites to pretreatment and/or treatment systems, between process units of a pretreatment/treatment system, and, for solid residues, from treatment systems to disposal sites or to other transport modes.
Conveyor transport systems include belt, screw, tabular, and chute systems. The features of the belt and screw conveyor systems are summarized in Table 5-4. These conveyor systems typically require a loading or feeder bin from which the material is placed on the conveyor. An unloading or feedout bin may also be required, depending on whether the material is going to a disposal/rehandling site, a pretreatment or treatment unit, or another mode of transport.
Commercially available conveyor systems can be permanently installed or portable. Portable conveyors provide system flexibility and allow material to be placed over a wider area. These systems are most practical for handling small volumes of mechanically dredged material (USEPA 1979; Souder et al. 1978). For example, a small conveyor system was used to transport materials in the pilot-scale demonstration of sediment washing technologies conducted for the ARCS Program at Saginaw Bay, Michigan (USACE Detroit District, in prep.).
Conveyors have low operating costs and move high volumes with minimal noise and air pollution. However, they can be expensive to purchase and very labor intensive and, like pipelines, may require right-of-way permission. Chute systems that lead from one flight to another can become clogged by oversized pieces. Like pumps and pipelines, conveyors are a continuous system; therefore, if one segment fails the whole system fails (Souder et al. 1978).
Chute or inclined plane conveyors or slides have no mechanical parts. Chutes have been used to move mechanically dredged sediments from barges into CDFs adjacent to navigable waterways. Examples of chutes used at the Chicago Area CDF are shown in Figure 5-1. Sediments were unloaded from the barges using a crane and small bucket and placed onto the chute, which carried the sediments into the CDF. In some cases, water was sprayed onto the chute to help move the material. Based on the use of chutes for sewage sludge, it is recommended that the incline be greater than 60deg. for dewatered material and greater than the material's natural angle of repose for dried material. These systems can be open or covered to prevent spillage (USEPA 1979). Relatively shallow slopes (30deg. and less) have been used with slides transporting wet dredged material.
SELECTION FACTORS
The limitations of each transport technology should be considered prior to selecting the contaminated sediment transport mode(s). These limitations might include legal, political, sociological, environmental, physical, technical, and economic practicality. Souder et al. (1978) developed a generalized sequence for selecting alternatives for inland transport of clean dredged material. The selection factors for contaminated sediment transport adapted from Souder et al. (1978) include: compatibility with other remedial components, equipment and route availability, compatibility with environmental objectives, and costs.
The selection of transport modes should be among the last decisions in the planning of a sediment remedial alternative. In many cases, the selection of other remedial components will eliminate all but one or two transport modes for consideration. For example, a remedial alternative involving hydraulic dredging will, with few exceptions, necessitate pipeline transport. Mechanically dredged sediments, on the other hand, can be transported using any of the modes discussed, including pipeline transport (although sediments will have to be slurried).
Some disposal/rehandling facilities can accommodate both hydraulically or mechanically transported sediments. Others, because of limited size or design features, cannot accommodate loadings by hydraulic slurry. Many treatment and pretreatment technologies have rigid restrictions on both the character and rate of feed material delivery. Residues from pretreatment or treatment systems may require continuous handling to subsequent components, or may be stockpiled for bulk handling. Transport modes must therefore be compatible with all components of a remedial alternative.
Equipment Availability
Availability is rarely a limiting factor in the selection of transportation equipment. Most contaminated sediment sites are in urban areas, with transportation equipment available from several sources. At worst, equipment will have to be brought in from a greater distance, increasing the mobilization and demobilization costs.
Pipeline and Barge Transport--Equipment for waterborne transport is readily available for leasing from dredging and marine construction contractors. The availability of specific equipment, including pipelines and barges, will reflect regional markets for their use and the dimensional restrictions (e.g., vertical clearance, width, draft) of regional waterways. Dredging/marine construction trade journals, such as International Dredging Review, Terra et Aqua, World Dredging, Mining and Construction, and The Waterways Journal, contain the names of contractors and advertisements for equipment lease or purchase.
Railcar Transport--Railcars filled with sediments or treatment residues may be added to an existing train route or transported as an entire trainload of railcars or "unit train." Single-car transport can require that a railcar be switched from train to train several times, resulting in increased costs. A unit train operation, commonly applied to hauling coal, is negotiated with a railroad company and is dedicated to carrying only one commodity from one point to another on a tightly regulated and continuing schedule.
A unit train operation could haul from 70 to 140, 100-ton (91 tonne) railcars (approximately 10,000 tonnes of contaminated dredged material) over distances of 80-2,400 km. Souder et al. (1978) recommended haul volumes of greater than 380,000 m[3] and haul distances greater than 80 km to support a unit train operation. A shorter haul distance increases the cost significance of loading and unloading.
Trailer Transport--A variety of truck trailer rigs may be leased or contracted through most large construction companies. There are numerous State and Federal restrictions on the size (vehicle width, height, and length) and weight of truck trailer rigs. Some regulations limit the number of trailers in tow by a tractor. Some weight regulations provide for the maximum weight that can be carried on single and multiple tandem (two grouped) axle groupings. However, most weight restrictions relate the overall or gross weight to the vehicle's wheel base. Most State regulations limit truck trailer loads to about 25 tons (23 tonnes). Other regulations include speed limits; requirements for safety features such as speedometers, brakes, horns, lights, windshield wipers, mirrors, and bumpers; and requirements for liability insurance. Some local ordinances even restrict truck operations to certain hours of the day and to certain routes (Souder et al. 1978).
Conveyor Transport--Conveyor systems are widely used in wastewater treatment and mining applications. Conveyor equipment may be purchased from suppliers to these industries identified in trade journals, including Water and Waste Digest and Waterworld Review. Some types of conveyor equipment may also be available for lease from the manufacturers or from dredging and construction contractors. Chutes and slides are typically fabricated by the dredging/transport contractor from purchased or available material. One dredging contractor split two abandoned railroad tank cars in half lengthwise and welded them into an open slide for transporting dredged material into the Chicago Area CDF (Figure 5-1).
Route Availability
Factors associated with transport routing include route constraints and scheduling. Route constraints include the availability of existing routes, rights-of-way for access, size and weight limits, and site obstructions. Transportation routes should run through areas that would be the least sensitive to accidental releases, where possible. The entire route should be easily accessible for maintenance, monitoring, and spill response. Site obstructions can affect the transport modes, or the transport modes can block traffic flow on existing routes. Scheduling difficulties may result from traffic interruption, overloads, and shutdowns due to harsh weather conditions (Souder et al. 1978). Routing difficulties can result in lengthy transport times, decreased efficiency, and increased costs.
Pipeline Transport--To deploy pipelines for a sediment remediation project, easements and rights-of-way must be obtained for the entire route. The ability to obtain even temporary easements for pipelines will be complicated because of the contaminated nature of the sediments. Pipeline crossings at roads and railroads may require special construction or excavation. Because sediment remediation projects are most likely in highly urbanized/industrialized areas, routing may be a major limitation in the use of pipelines.
Barge Transport--Barge selection, routing, and transit time are greatly affected by channel dimensions, site obstructions, other channel and seasonal conditions, speed limits and other restrictions, traffic congestion, and user fees. In addition to the length, width, and depth of a channel, other factors affecting barge access include lock sizes, bend radii, and structures (e.g., piers, jetties). Barge and tow boat drafts (loaded) should be less than the shallowest channel depth in the dredging area and on the tow route. Site obstructions can include height limitations caused by bridges or power lines and submerged objects such as cables, pipelines, piles, and rock. Transient or seasonal conditions that can affect barge access include water depths, currents, tidal influence, wave action, and icing. The number of barges required for a project will depend on the dredge production rate, haul volume, and travel time (distance, routing, unloading).
The majority of barge traffic in the Great Lakes area is limited to relatively short hauls that run close to lake shorelines. However, barge dimensions allowed in the Great Lakes area are typically larger than those of other inland barges because of larger lock dimensions (Churchward et al. 1981). The potential for substantial wave action generally demands that ocean-going barges (self-propelled or towed) or ships traverse the Great Lakes.
The U.S. Coast Pilot (a National Ocean Service annual report) contains detailed information about navigation regulations and channel restrictions for the Great Lakes and connecting channels. Navigation charts are available from NOAA. Additional information about channel restrictions, traffic, and user fees can be obtained from local harbor authorities, the Corps, or the U.S. Coast Guard.
Railcar Transport--With the exception of short spurs constructed to provide access to a disposal site, economic railcar transport typically demands the use of existing railroad track lines. These track lines are readily available in most industrialized areas. Mainline spur construction, if permitted, would be too expensive for low-volume dredged material transport. In addition, efficient railcar loading and unloading (bottom or rotary dump) facilities are required to make the unit train concept work and to realize the benefits derived from reduced rates on a large haul.
Truck Trailer Transport--There are about 5.6 million km of paved roads in the United States, of which about 912,000 km (25,600 km of interstate) can be considered for a transport system route (Souder et al. 1978). However, unpaved roads can be constructed relatively quickly at nearly any project site. Therefore, truck routes are more flexible and faster to construct than either waterway or railroad track routes. Because terminal points and routes can be changed readily at little cost, truck trailer transport provides a flexibility not found with other modes of transportation.
Transport technologies are inherently designed to contain their cargo during transport. With the exception of volatilization, contaminant losses (e.g., leakage during transport or spillage during loading or unloading) are generally the result of poorly maintained or operated equipment. Most transport modes have one or more controls that can be applied to limit leakage occurring as a result of transport and spills during loading and unloading (e.g., covers, gate seals, splash aprons); however, these controls are only a few of the necessary steps to minimize contaminant losses. Transport equipment should be tested for leaks prior to hauling contaminated material and should be carefully monitored during operation. As with dredging operations, the amount of spillage during rehandling is greatly affected by the time and care taken by equipment operators.
The exteriors of barges, railcars, and truck trailers should be cleaned prior to leaving the loading or unloading facilities. These loading/unloading areas should be designed so that cleaning and runoff water can be collected at a central location and treated as necessary. After final use, barge, railcar, truck trailer, and conveyor interiors can be decontaminated using high-pressure water sprays. Pump/pipeline systems can be decontaminated by pumping several pipeline volumes of clean water through the system.
The applicability of Federal, State, and local environmental laws and regulations on the transport of contaminated sediments and treatment residues should be investigated on a case-specific basis. Federal regulations on the transport of hazardous and toxic materials include the Hazardous Materials Transportation Uniform Safety Act, RCRA, and TSCA. Specific requirements exist for transport, including registration, labeling, packaging, placarding, and material handling (UAB 1993).
Waterborne transport of contaminated materials may also be regulated by the International Maritime Dangerous Goods Code, which identifies some materials as "marine pollutants" with specific stowing requirements (Currie 1991). Federal regulations generally address interstate transport, and State and local regulations covering intrastate transport may differ from the Federal regulations (UAB 1993).
Virtually all transport modes have environmental effects unrelated to their cargo. Towboats, trucks, trains, and conveyors all have exhaust from their diesel- or gas-powered engines or generators. Towboats used to transport barges may cause sediment resuspension along the route, especially at locations where the barge accelerates, decelerates, or changes directions. A number of studies have been conducted to evaluate the physical, biological, and chemical effects of commercial navigation traffic in large waterways (Miller et al. 1987, 1990; Way et al. 1990; Miller and Payne 1992, 1993a,b).
ESTIMATING COSTS
The transport component of a sediment remedial alternative may incorporate several modes of transport to connect different components. For example, the remedial alternative shown schematically in Figure 5-2 uses pipeline transport between the hydraulic dredge and the rehandling facility. Dewatered sediments are removed from the rehandling facility using a front-end loader and placed onto a conveyor for transport to a pretreatment unit (rotary trommel screen). The primary residue of the pretreatment unit is transported to the thermal desorption treatment unit by another conveyor. The oversized residues of the pretreatment unit and the solids residues of the treatment unit are transported to the disposal facility by conveyor. The liquid (organic) residue of the treatment process is placed into a tank trailer for transport to a commercial incinerator. Water from the rehandling, pretreatment, treatment, and disposal units is routed to a wastewater treatment system through pipelines.
For a remedial alternative such as the one shown in Figure 5-2, it is likely that some modes of transport would be subcontracted as parts of other components (e.g., the pipeline would be supplied by the hydraulic dredging contractor), while others (e.g., conveyors) might be subcontracted separately. For most sediment remediation projects, all transport equipment would be leased or contracted. The transport costs would therefore be entirely capital costs, with no operation and maintenance costs.
Churchward et al. (1981) indicate that the main considerations for selection of the transport modes include cost, flexibility, capacity, and speed. A comparative analysis of these characteristics for pump, barge, railcar, and truck trailer transport, as developed by Churchward et al. (1981), is shown in Table 5-5.
In comparison with the other components, especially treatment, transport unit costs are relatively low. Therefore, the transport process should be scheduled for continuous operation to ensure that the other, more expensive processes can operate without interruption.
Souder et al. (1978) indicate that cost estimates should be regarded as generalized evaluations of the related costs of selected transportation modes under representative operating conditions. When specific applications are considered, the unique aspects of each application (e.g., terrain, weather conditions, labor rates) should be evaluated individually and more precise costs related to each specific application should be derived. The Corps' Construction Equipment Ownership and Operating Expense Schedule (USACE 1988) contains a method for computing dredging plant operating rates, which includes methods for estimating pipeline and barge transport costs.
Dredged material transport involves three major operations: loading, transport, and unloading. The loading and unloading activities are situation-dependent and are the major cost items for short-distance transport.
Souder et al. (1978) evaluated the costs of transporting large volumes (300,000 to >2.3 million m[3]) of clean dredged material over long distances (up to 500 km) as part of a study conducted by the Dredged Material Research Program. They indicate that, irrespective of the volume of material to be transported, the truck trailer and conveyor transport modes were considerably more expensive than the pipeline, barge, or railcar transport modes. They further concluded that truck trailer transport is labor- and fuel-intensive in comparison to other transport systems. Conveyors have a high investment cost but can move material efficiently. At lower volumes, conveyor costs are much higher than for other systems. However, at high volumes and shorter haul distances (<30 km) conveyor costs are competitive with all other transport modes except the pipeline system (not including conveyor chute systems for unloading facilities).
Based on technical considerations and cost derivation assumptions, Souder et al. (1978) concluded that pipeline transport is the most economical choice in most instances for transport volumes up to 760,000 m[3] and distances up to 160 km. Depending on the transport volume, barge or railcar transport will be the most economical systems for long-distance hauls. Railcar transport becomes more economical at higher volumes. Because of routing limitations, not all haul distances will be the same for each transport system.
Souder et al. (1978) indicated that for haul volumes <380,000 m[3] it is very difficult to realize the economies of scale required to achieve the relatively low transport rates derived in their analysis. If the transport costs developed by Souder et al. (1978) were modified for application to sediment remediation projects, it is likely that the loading/unloading costs for barge, truck trailer, and rail transport would increase because of the controls required to limit spills, and the relative costs of conveyors might be more favorable for the short hauling distances, such as those between remediation components (i.e., <1.5 km).
For projects involving hydraulic dredging and pipeline transport over short distances (<3 km), the costs for pipeline equipment, mobilization, and labor are included in the dredging costs, as described in Chapter 4. Separate transport costs should be developed for pipeline transport over longer distances, or for pipeline transport of sediment or residues independent of the dredging contract.
Souder et al. (1978) developed unit cost information for pipeline transport of various dredged material haul volumes from a rehandling basin to a disposal site at various haul distances. This hypothetical operation involved using a portable dredge to remove the dredged material from the rehandling basin and transporting the material by a permanently installed pipeline, operated by a contractor. However, the unit cost information provided here was adjusted to include only the discharge pipeline, centrifugal booster pump, and related labor costs. No real estate or right-of-way costs were considered.
Unit cost estimates for this hypothetical operation are shown in Figure 5-3. These unit costs include the discharge pipeline and booster pump costs, including installation, maintenance and repair, lay-up time, insurance, and miscellaneous costs. Discharge pipeline costs include annual costs for the purchase of the pipeline. Centrifugal booster pump costs include annual costs for the pump and motor, reduction gears, controls, foundation, and housing, and costs for power and a sealing water supply (Souder et al. 1978).
Barge carriers include major-line, branch-line, and local operations. Barge transport on the Great Lakes is provided under contract rates or long-term charters, with 26 percent of services provided by independent carriers (Churchward et al. 1981). Many dredging firms own barges and will subcontract additional barges as needed for a large job. For a project involving mechanical dredging and barge transport over short distances (i.e., <5 km), the costs for barge transport are included in the dredging costs presented in Chapter 4. If longer haul distances are required, or for barge transport of sediments or residues independent of the dredging contract, additional transport costs need to be estimated.
Souder et al. (1978) developed unit cost information for contracted tank barge transport of various dredged material haul volumes from a rehandling basin to a disposal site at various haul distances. This hypothetical operation involved using a bulldozer and backhoe to excavate the rehandling basin material, placing the material in a dump truck, moving the material from the truck into the tank barge, towing the barge to the disposal site, removing the material from the barge using a rehandling bucket, placing the material into a dump truck, and dumping the material into the disposal site.
Unit cost estimates for this hypothetical operation are shown in Figure 5-4. The cost information assumes that the rehandling basin and disposal site are both 2.4 km, by way of an existing road, from an existing barge mooring dock. As with the pipeline transport operation, this operation assumes that dredged material is transported under ideal conditions. Project-specific conditions may greatly affect these costs. The operation costs include annual costs for barge loading and unloading and the towboat and barge. Loading costs include backhoe, bulldozer, dump truck, and road maintenance costs. Unloading costs include crane and dump truck costs. Transport costs include towboat and barge costs, crew quarters and subsistence pay, and miscellaneous costs.
The cost engineering office of the Detroit District typically uses unit costs in the range of $0.70 to $1.50/yd[3]-mile ($0.57 to $1.23/m[3]-km) for preliminary estimates of barge transport of dredged material in the Great Lakes (Wong 1993).
Railcar rates are quoted by either a class rate or commodity rate. Class rates generally apply to small-volume shipments like single-car transport and occur on an irregular basis. These rates are influenced by route terrain and distance, the number of railcar switches required, and the haul volume. Class rates are readily obtained, but are usually prohibitively expensive for hauling dredged material. Commodity rates generally apply to regularly scheduled shipments of large volumes, like unit train transport, and are obtained from local rail carriers on a case-by-case basis. Commodity rates are lower than class rates (USEPA 1979; Souder et al. 1978).
Souder et al. (1978) developed unit cost information for contracted hopper railcar transport of various dredged material haul volumes from a rehandling basin to a disposal site at various haul distances. This hypothetical operation involved excavating the rehandling basin material using a backhoe and placing it on a conveyor system that emptied into a hopper railcar. The railcars were towed by a locomotive to the elevated loop track at the disposal site where the material was emptied.
Unit cost estimates for this hypothetical operation are shown in Figure 5-5. The operation costs include annual costs for hopper railcar loading and unloading and the locomotive and railcars. Loading costs include a backhoe, portable and fixed conveyor systems (including feed and feedout bins), and elevated loop track construction costs. Unloading costs include elevated loop track construction costs. Transport costs include locomotive and railcar carrier costs.
Tank railcars are usually leased by the month from a private tank car rental company, with a 5-year minimum lease. In 1978, a large tank car rented for $450/month (USEPA 1979). Hopper railcars are usually leased from the carrier.
Souder et al. (1978) developed unit cost information for contracted dump trailer transport of various dredged material haul volumes from a rehandling basin to a disposal site at various haul distances. This hypothetical operation involved using a backhoe to excavate the rehandling basin material and placing the material on a conveyor system that emptied into the dump trailer. The filled trailer was towed on an existing roadway to a newly constructed road leading into the disposal site and emptied.
Unit cost estimates for this hypothetical operation are provided in Figure 5-6. The operation costs include annual costs for loading the dump trailer and transporting it to the disposal site. Similar to railcar loading, trailer loading costs include backhoe and portable and fixed conveyor system (including feed and feedout bin) costs. Transport costs include truck trailer, driver, and fuel costs. Unloading costs are limited to the cost of constructing a temporary road into the disposal site.
The Detroit District uses unit costs between $1.30 and $2.50/yd[3]-mile ($1.07 to $2.05/m[3]-km) for preliminary estimates of truck trailer transport of dredged material (Wong 1994). The Chicago District estimated dump truck trailer unit costs (including truck trailer rental and labor) for 1-, 19-, and 32-mile (1.6- , 30- , and 51-km) haul distances to be $2.21/yd[3] ($2.91/m[3]), $11.25/yd[3] ($14.80/m[3]), and $17.80/yd[3] ($23.42/m[3]), respectively. They also estimated a unit cost of $2.72/yd[3] ($3.58/m[3]) to remove dredged material from a barge and place it into a truck trailer (Engel 1994).
Souder et al. (1978) developed unit cost information for contracted belt conveyor transport of various dredged material haul volumes from a rehandling basin to a disposal site at various haul distances. This hypothetical operation involved using a bulldozer and backhoe to excavate the rehandling basin material and placing the material on a conveyor system that moved the material to the disposal site where it was dumped. The operation assumed that the conveyor was routed over flat terrain and that there were no costs associated with obtaining right-of-ways and other real estate.
Unit cost estimates for this hypothetical operation are provided in Figure 5-7. The operation costs include annual costs for loading and operating (energy and labor costs) a portable and fixed conveyor system. Conveyor loading costs include backhoe and bulldozer costs. Conveyors do not require additional equipment for unloading.
ESTIMATING CONTAMINANT LOSSES
There are a limited number of mechanisms for contaminant loss during the transport of contaminated sediments, and only one mechanism of contaminant loss can be predicted using a priori techniques (Myers et al., in prep.). Contaminant losses during loading and unloading operations are primarily the result of spills and volatilization. The amount of spillage during loading and unloading reflects the level of care taken by the operators and the efficiencies of any controls (e.g., drip aprons). Loading and unloading areas should be designed with systems to collect spillage and water used to wash transport vessels. This water should be routed to wastewater treatment systems. Contaminant losses from such treatment systems are discussed in Chapter 9, Residue Management.
Losses during transport are the result of leaks, volatilization, and accidental spills. The amount of leakage during transport reflects the containment efficiencies of the carrier vehicles. Accidental spills may occur as a result of equipment failure, operator error, or external influences (e.g., meteorological conditions). Although it is not feasible to entirely eliminate spills and leakage from transport systems for contaminated sediments, it is easier to design controls for these mechanisms of contaminant loss than to quantify them.
There is no a priori method for predicting the amounts of contaminants lost by spillage, leaks, and accidents from a transport mode. The only mechanism of contaminant loss that can be predicted is volatilization from transport systems without covers (i.e., barges, trains, trucks, and conveyors). Methods for predicting the loss of volatile and semivolatile organic contaminants from exposed sediments and ponded water have been developed, and are summarized in Myers et al. (in prep.). These predictive methods are almost entirely theoretical and have not yet been field verified. |
