Menominee River Sediment Removal

Significant Project Features

• Installation of 192 piles, 1,500 lf of walers and 171 tie-backs to support 1,500 lf of steel sheet pile vertical barrier wall containment structure to allow for safe dredging of sediments immediately adjacent to wall
• Installation of temporary turbidity curtain and private aids to navigation to clearly mark channel alignment and work zone along navigable river
• Installation of all site infrastructure to support dredging and stabilization efforts, including: temporary office complex and parking; and labor force; temporary roads to maintain safe flow of traffic; sealed containment area for all sediment handling, treatment, staging and loading; dual truck washes and truck scales for material loadout; wastewater treatment plant to process impacted water removed from sediments, stormwater and decon activities
• Mechanical dredging of over 275,000 CY of sediment from Menominee River of varying depths and hardness while maintaining turbidity limits outside work zone. PC800 excavators on float barges were used for sediment removal. Changes in sediment types required using different dredge buckets and removal methods. Soft sediments were removed with a clam bucket while harder material was removed with conventional digging bucket. Specialty digging buckets were also fabricated to remove high blow count sediments. Dredging performed 24 hours per day and 6 days per week to meet the aggressive schedule set by client
• Dewatering, stabilization and chemical treatment of over 395,000 tons of contaminated sediments. Installed, operated and maintained a treatment system to run either liquid or dry ferric sulfate to respond to changes in sediment characteristics. Screened oversize debris from dredge material prior to stabilization and treatment. Sediments stabilized with varying recipes of Portland cement and ferric sulfate to meet RCRA non-hazardous disposal and landfill acceptance criteria. Managed chemical additive inventories to maintain dredging and treatment schedules. Treatment performed 24 hours per day and 6 days per week. Treated sediments staged in storage bins for confirmation of landfill acceptance criteria prior to load out
• Loading and transport of over 470,000 tons of treated sediments to local landfill for disposal. Managed T+D schedule to maintain bin space for treated materials to prevent interruption to dredging and treatment operations
• Installation, O+M of a 150 GPM onsite wastewater treatment plant to process contaminated water from dewatered sediments, storm events and decon activities. WWTP included a series of processes to treat water: pretreatment using coagulation/filtration in geotextile tube filters and separation process, microfiltration prior to treatment in a two‐stage reverse osmosis (RO) system and a Vibratory Shear Enhanced Processing unit to treat process wastewater and reject water. Treated and discharged over 7.5 million gallons of water during project

Project Gallery

History & Location Details

Project Description

The scope of work required to remediate the site involved four (4) operations:

• Mechanical dredging and loading of sediments into scows.
• Delivery of scows to an unloading dock for transfer to a processing area
• Stabilization and characterization of sediment to meet landfill acceptance criteria
• Loadout, transport and offsite disposal of processed sediment

MECHANICAL DREDGING

The primary means of dredging and loading during the 2012 dredge season was a crane with an environmental bucket. Approximately 26,000 CY were mechanically dredged in 2012. Equipment was modified for the 2013 dredge season to accommodate the client’s goal to maximize the potential for completion of the project by the USEPA-enforced deadline of November 1, 2013. Approximately 254,400 CY were removed in 2013. To maintain this aggressive schedule, dredging operations were performed 24 hours per day 6 days per week. Equipment maintenance was performed on the 7th day. Sevenson self-performed the 2013 dredging using two Komatsu PC800 hydraulic excavators from floating platform barges. Each dredge platform consisted of:

• A PC-800 each equipped with a boom and stick capable of reaching 30 feet below the water surface;
• Level cut clamshell bucket (3.5 CY Anvil model);
• Deck barge approximately 150 feet by 40 feet;
• Dredgepack software system, Real Time Kinematic Global Positioning System (RTK GPS);
• Real-time display of bucket position; and
• Spuds raised and lowered using a hydraulic powered system

An Anvil level cut bucket was used to dredge soft sediments. In areas where sediment was identified as “semi-consolidated material” (SCM) Anvil buckets proved to be ineffective. The Anvil dredge bucket could not penetrate the high blow count SCM material. As a result, Sevenson switched to a traditional excavation bucket.

Sevenson loaded sediment into water tight, 1,000 CY scows for transport from the dredge operation to the offloading area. The barge dimensions were generally 168 feet long, 40 feet wide and 14 feet high with a draft of approximately 11 feet when fully loaded. Two scows were used during the 2012 dredging season and six scows used during 2013 dredging season. Due to draft restrictions in areas where soft sediments were Sevenson utilized four custom built 100 CY hopper barges.

UNLOADING AND STABILIZATION TREATMENT

Material scows were transported to a barge unloading station when full where water was decanted using a four inch trash pump. Decant water was settled using weir tanks and transferred to the onsite WWTP for treatment. Scows were then unloaded using two Sennebogen excavators with clamshell buckets. Sediment was placed onto a screening system for sizing. Separated material and was conveyed into a storage bin. Oversize debris was removed and staged for shredding. A second set of excavators transferred the screened material from the storage bin and fed pugmills which mixed Portland cement and ferric sulfate (dry or liquid) with the sediment at varying dosages as determined by treatability study analysis. Treated material exiting the pugmills was transferred by wheel loader to staging bins where it was sampled for disposal criteria. Upon approval, the material was loaded out for landfill disposal as a RCRA non-hazardous waste. To maintain the aggressive dredging pace sediment stabilization was performed 24 hours per day, 6 days per week with equipment maintenance performed on the 7th day.

During 2012 dredge season problems developed with the treatment recipes specified by the client. Processed sediment resulted in a wet material which did not meet disposal criteria. During the winter between dredging seasons, Sevenson performed treatability studies on the sediment scheduled for removal during the 2013 dredge season. The studies evaluated options to solve the wet consistency problem. Modifications to the recipe were developed and incorporated into the treatment process based on the results of the study. They included: use of a dry reagent in lieu of wet to provide a more workable end product; bringing in additional equipment to handle and introduce dry reagents; and use of RapidMix pugmills to more effectively blend reagents. As a result the quality of the end product improved. It became an easy to handle, dirt-like material which passed disposal criteria on a more continuous basis. This resulted in time and cost savings to the client as re-treatment was infrequent and avoided the possible hazardous classification. During the 2012 dredge season approximately 35,500 tons were treated and stabilized and during the 2013 dredge season approximately 360,000 tons of dredged material were treated and stabilized.

LOADING, TRANSPORTATION AND DISPOSAL

Upon notification from the site engineer that treated soils met disposal criteria, Sevenson loaded waste material into dump trucks for transport off-site and disposal at a local landfill permitted to accept the waste. In order to maintain sufficient storage space, loading operations utilized two loading excavators, two onsite truck washes and two onsite truck scales and was typically performed 5 days per week using one 12-14 hour shift. A typical loading day saw between 150 and 200 loads sent for disposal. The 2012 dredge season transported and disposed of approximately 48,000 tons of treated materials while the 2013 dredge season saw nearly 17,000 truckloads and over 420,000 tons of treated waste and debris loaded and transported for disposal.

VERTICAL BARRIER WALL SUPPORT

Installation of a driven pile and deadman support system for existing vertical barrier containment wall to allow dredging of sediments immediately adjacent to it. 192 piles were driven and secured in bedrock and over 1500 lf of waler and 171 tiebacks installed to driven pile deadmen to secure wall against movement during dredging activities

WASTEWATER TREATMENT PLANT

Sevenson installed and operated a 150 GPM onsite wastewater treatment plant to handle contaminated water generated from site activities. Contaminated water sources included: dewatering of sediment, contact water from rain events and decon water. The onsite treatment system used a series of processes to treat water: pretreatment using coagulation/filtration in geotextile tube filters and separation process, and microfiltration (“MF”) prior to treatment in a two‐stage reverse osmosis (RO) system. Process wastewater and reject water were then sent to a Vibratory Shear Enhanced Processing (VSEP) unit, which is a specialized membrane system that concentrates the waste stream so the total volume of water being returned to the Menominee River is increased while the total volume of the waste stream being sent offsite for disposal is reduced.