Sediment Remediation

Forgen personnel have performed numerous projects requiring removal of contaminated sediments from along and within waterways. Hydraulic and mechanical dredging equipment, including excavators working from barges and along shorelines, have been utilized to perform these removals in a safe and compliant manner. Forgen collaborates with clients and consulting engineers to develop and implement the most efficient and cost-effective sediment removal strategies. Work elements common to these projects include protection of dredge areas using turbidity curtains and other protection measures; dredging and dewatering of sediments; dredgeate dewatering and process water disposal; upland staging, dewatering, and conditioning of sediments; and on-site repository placement or off-site disposal. Forgen has worked closely with clients and regulators to implement this ecologically sensitive work within critical biological and seasonal windows sometimes working around the clock to meet stipulated project completion milestones.

Ann Arbor, Michigan

Forgen performed the excavation of impacted soil at a former MGP site along the Huron River in downtown Ann Arbor, Michigan. Primary tasks involved clearing and grubbing of the site, dewatering, installing a trapping cap, and disposing of all impacted material from the site. Parties involved with this project included a major utility company, a local engineering firm, the City of Ann Arbor, and the Michigan DEQ. Given the close proximity of the site to the downtown area, crews had to manage odor control on a daily basis utilizing a Piian misting system. Prior to loaded trucks leaving the site with contaminated material, loads were sprayed with a foaming odor suppressant.

The removal and disposal of upland and river bank soil was required due to the potential source of pocket area concentrations of contaminants. These contaminants represented a potential future source of pollution to the Huron River. The area of sediment to be removed was from a 15 feet wide by 1,000 feet long section along the river.

The excavation phase of the project involved two excavators removing contaminated material in three, 400 feet sections. During excavation from the river, a 400 foot turbidity curtain was used along with a 50 foot carbon filter, sorbent oil boom to capture any contaminated material from flowing downstream. As the excavation progressed along the river, the booms were re-positioned three times throughout the project. Approximately twenty-five loads per day were transported daily and a total of 50,000 cy of coal-tar contaminated material were removed.

Once the excavation phase was concluded, the site was backfilled and capped. A NAPL (Non-Aqueous Phase Liquids) trapping cap and collection system were installed. Site restoration concluded with a six inch layer of top soil, seeding, and the placement of erosion protection shrubs and trees.

Sheboygan, Wisconsin

This project involved the removal of PCB-contaminated sediments from the Sheboygan River in Sheboygan, Wisconsin. Specific tasks included dredging, dewatering, stabilization, transport and disposal of PCB and PAH impacted sediments, post-dredge confirmation sampling and bathymetric surveys, placement of sand cover, and site restoration.

Crews began the first phase of the project, constructing the sediment processing pad where the dredged material was dewatered and stabilized. After the initial processing pad was complete, the team utilized their patented Sed-Vac process to remove sediment next to a bridge in order to install an air curtain prior to dredging operations. The air (turbidity) curtain was a pipeline that was set on the river bottom and air was pumped from the pipe upward to create a barrier of air to contain sediments from escaping beyond the limits of the dredging and still allow boat traffic through the navigation channel.

The overall remediation process involved dredging contaminated material from the river and loading it onto barges which then transported the material to an off-loading platform. From there the material was moved to a sediment processing pad where it was put through “Grizzlys” with shaker screens to separate the debris material. The sediment would continue through the Grizzly into one of two pug mills to stabilize the material by mixing it with Portland Type III cement. After the material was stabilized, loaders transported it to a stockpile area where it was cured for up to 8 to 12 hours. From there it was loaded into trucks and transported to a designated landfill.  

Additionally, this project included handling and treating of approximately 20,000 to 30,000 gallons of barge water per day. A vac truck was used to vacuum the water from the barges and release it into a settling basin. The water was then sent to a sump, treated with a polymer, pumped into clarifier tanks, and processed through bag filters and two carbon filters before being discharged back into the river.

Air monitoring was provided around the perimeter of the processing pad for particulates, WPDES construction site storm water inspections, waste water monitoring and sampling including:

  • Total volume discharged daily
  • Continuous monitoring of pH and turbidity
  • Daily sampling for PCB and PAH
  • Weekly sampling for pesticides, total metals, TSS, ammonia as nitrogen, oil and grease, hexavalent chromium, and low level mercury
  • Submittal of monthly discharge monitoring report to the State

The team also was responsible for post-dredge confirmation sample processing that included a total of 252 shoreline, DMU grid and TSCA core samples.