2015 Excellence in Environmental Engineering and Science™ Competition Winner

E3S Honor Award

2015 Honor Award - Small Projects

Remediation of Mirror Lake Using In-Situ Amendment of Activated Carbon to Sediments

Entrant: Delaware Department of Natural Resources and Environmental Control
Engineer in Charge: Douglas G. Streaker, P.E.
Location: Dover, Delaware
Media Contact: Richard W. Greene, Ph.D., 302.739.9939

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Mirror Lake, Dover, DE, with type 3 turbidity curtain in place (view to west).

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Mirror Lake, Dover, DE, with type 3 turbidity curtain in place (view to east).

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SediMite™ being applied to Mirror Lake using a Telebelt.

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SediMite™ Activated Carbon Product

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SediMite™ being applied to Mirror Lake using an Air Horn.

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Intertidal wetland being constructed using sand delivered from Telebelt.


Entrant Profile

Richard Greene is an environmental engineer with the Delaware Department of Natural Resources and Environmental Control (DNREC). He manages Delaware's surface water toxics program. He holds a Ph.D. from the University of Delaware where his research focused on multi-media fate modeling of polychlorinated biphenyls (PCB), including the role of black carbon in reducing bioavailability and bioaccumulation in aquatic food webs.

In his work for DNREC, Greene used radiodated sediment cores and mass balance models to predict that it will take several decades for the PCB concentration in fish from Mirror Lake, Dover, DE to drop to acceptable levels. Looking to speed that trajectory, Greene contacted Professor Upal Ghosh from the University of Maryland Baltimore County to develop a proposal to use activated carbon to sequester contaminants in the lake sediments, thereby interrupting the transfer of PCBs from the sediments to the water column and the fish. Greene also involved Mr. John Cargill, a professional geologist who works for DNREC's site remediation program to engage that program in the innovative sediment clean-up.

Greene arranged for Biohabitats, Inc. to prepare engineering plans and specifications for the full-scale sediment remediation and lake restoration project. Greene also arranged regulatory reviews and community briefings. Cargill retained Brightfields, Inc. to manage construction of the project, including scheduling, site preparation, materials ordering and handling, oversight of labor and demobilization. Ghosh was retained to design and implement a multi-media environmental sampling and analysis plan to document conditions prior to and post-application of the activated carbon.

Project Description

In 2013, the Delaware Department of Natural Resources and Environmental Control (DNREC) embarked on an ambitious project to remediate an urban lake using a novel in-situ treatment approach. This is the first full-scale application of the in-situ remediation technology which uses activated carbon to bind the pollutants in place rather than the traditional approach of dredging and upland disposal. The St. Jones River system, which includes Mirror Lake, has been contaminated from various historic sources of industrial pollutants from the watershed. Elevated concentrations of polychlorinated biphenyls (PCBs) in fish collected from the Saint Jones system first Jed to the issuance of a fish consumption advisory in 1988. Although PCB production was banned in the 1970s and concentrations in environmental media are decreasing over the years, the rate of decrease is slow and recovery is expected to take many more decades based on current model predictions. Conventional approaches for remediation of contaminated sediments include isolating contaminated sediments (capping), or removing contaminated sediments from the environment (dredging) followed by disposal in an off-site hazardous waste landfill. However, both dredging and capping have limitations such as the need for large-scale material handling, high cost, and disruption ofthe existing ecosystem. A recent development in sediment remediation involves amending contaminated sediments with strong sorbents like activated carbon to reduce the bioavailability of toxic chemicals which has been demonstrated in estuarine and river systems at the pilot-scale (Ghosh et al. 2011).

Dr. Richard Greene and Mr. John Cargill from DNREC evaluated several options for remediating Mirror Lake and downstream areas prior to choosing the in-situ treatment technology. Complete removal ofthe contaminated sediments would have cost approximately $1.5 million, not including the significant price for disposal of the contaminated material. Capping the contaminated sediment with clean sediment was also considered. Although cheaper than dredging, the added volume of capping material would have significantly reduced the depth of the lake and changed flow patterns, neither of which was desirable. This led the team in collaboration with Dr. Upal Ghosh from the University of Maryland Baltimore County to evaluate in-situ treatment options, especially the approach of adding sorbent materials to sediments to reduce pollutant bioavailability. Biohabitats, Inc. was retained to prepare the construction plans & specifications and Brightfields Inc. was retained to manage the construction.

The remediation of the lake sediments was done by uniformly spreading SediMite™, a pelletized form of activated carbon, throughout the lake and the downstream area. Sedimite™, produced by Sediment Solutions (www.sedimite.com), is an agglomerate that incorporates activated carbon (as the treatment agent), sand (to enable it to sink and resist resuspension), and clays (as inert binders). It is designed to withstand dispersal through the water column with minimal release of active ingredients followed by slow disintegration and mixing into the bioactive zone of sediments through natural sediment mixing processes such as bioturbation. SediMite™ was spread from the bank of the lake using a telebeft for most of the area (Fig. 1), and also from boats on the lake through the use of an induction air hom, Vortex spreaders, and by hand. In all, seventy-nine tons of SediMite™ were applied to five acres oflake and channel sediments in ten days. The construction phase of the Mirror Lake Remediation & Restoration Project was completed ahead of schedule and under budget.

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In addition to treating the contaminated sediments, the project also incorporated several ecological restoration features, including: removal of invasive plant species along the banks; conversion of an existing sandbar to an intertidal wetland; reinforcement of an eroding bank with coir logs and mulch; and the installation of two in-stream rock vanes to direct flow and protect the new intertidal wetland. To create the intertidal wetland, 967 cubic yards of sand were placed in Mirror Lake between the low tide and high tide elevations. The new wetland was then protected with matting and planted with an array of native plant species. Sixty-seven volunteers helped on the project, which saved over $100,000 in labor cost. There were no injuries during the project, no permit violations, and no complaints from adjacent land owners.

Sediment and Erosion control methods were implemented according to the Delaware Erosion and Sediment Control Handbook prior to and during lake remediation and restoration work. A turbidity curtain was installed around the perimeter of the intertidal wetland and rock vane work area to keep sediments from traveling up or down stream. At the completion of the remediation and restoration efforts, silt fence, mulch, and stabilized construction entrances were removed and the area was seeded and restored to its prior condition.

The approximately $1 million remediation/restoration project was funded primarily by state sources, plus $73,800 in federal grant funds from the Clean Water Act Section 319 Nonpoint Source for the wetland restoration and coir log installation by federal grant funding. The project also includes Community Transportation Funds from local lawmakers.

Monitoring performed in the Lake water, sediment and fish in the Fall of 2014 (one year after treatment) showed reductions in PCB concentrations in sediment porewater by 60% and in overlying water by 62% compared to levels measured before treatment. PCB concentrations in resident fish in the lake also dropped by approximately 60% compared to levels measure before remediation. Overall, the remediation project has been able to reduce levels of PCBs in fish and it is expected that with the implementation of further controls on ongoing sources, these levels will continue to decrease in the future.


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Intertidal wetland nearing completion during extreme low ide, SediMite™ in foreground.

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Intertidal wetland being protected with coir matting.

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Planting the intertidal wetland with native species (left to right): Former DNREC Secretary Collin O'Mara, Project Co-Leaders John Cargill and Richard Greene, and U.S. Senator Christopher Coons.

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Rock J-vanes installed to divert flow and protect the intertidal wetland.

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Intertidal wetland one year after planting.

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Sediment cores showing activated carbon incorporation one month (~2 inches) after application and one year (~6 inches) after application.

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Passive sampler used to measure dissolved contaminants in the sediments and water column of Mirror Lake before and after activated carbon treatment.

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Electroshocking to collect fish from Mirror Lake for contaminants analysis.

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Mirror Lake Project Team (left to right): Jeffrey Vance (Brightfields), Richard Greene (DNREC Project Co-Leader), John Carbill (DNREC Project Co-Leader), and Upah Ghosh (UMBC)

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State of Delaware Governor Jack Markell at the Mirror Lake press event with U.S. Environmental Protection Agency Region 3 Administrator Sean Garvin (left) and former City of Dover Mayor Carlton Carey (right) in the background.

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Dr. Richard Greene, DNREC Project Co-Leader and initiator of the Mirror Lake Project, declaring victory.


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