5. Conventional and Amended Capping

Table 5-3. Representative contaminated sediment capping projects
Project	Contaminants	Site Conditions	Design Thickness (ft)	Cap Material	Year Constructed	Performance	Comments
PAH, NAPL, and Creosote-contaminated Sites
Pacific Sound Resources, Seattle, WA	Polycyclic aromatic hydrocarbons (PAHs), nonaqueous-phase liquid (NAPL), mercury	58-acre capA covering over material (contaminated sediment) used to isolate the contaminants from the surrounding environment.	2.5– 6	Cap material was partly from upland quarry (287,000 yd³) and partly beneficial reuse of sand from navigational dredging (230,000 yd³).	2003–2005	No observed migration of contaminants based upon pore-water sampling in 2010.	Upland borrow-material met grain size specifications and organic content requirements. Site included a steeply sloping (50%) offshore area and deep (-240 ft) water cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment. with dredged material.
Head of Thea Foss Waterway, Tacoma, WA	PAHs, NAPL	21 acres	3	Composite cap included sand, high-density polyethylene (HDPE), and armoring.	2003	Cap recontaminated Appeared to be upstream source controlThose efforts that are taken to eliminate or reduce, to the extent practicable, the release of COCs from direct and indirect ongoing sources to the aquatic system being evaluated. issue	Engineered cap included partial dredging to increase depth, placement of HDPE to control ebullitionThe act, process, or state of bubbling up usually in a violent or sudden display. of NAPL, armoring as scour protection near stormwater outfalls.
Wyckoff-Eagle Harbor, Bainbridge Island, WA	PAHs, creosote, NAPL	East and West Eagle Harbor total cap of 70 acres	1–3	Cap material was a beneficial reuse of sand from navigational dredging.	1994	Cap contained contaminants Cap erosion in ferry lane Source control failures leading to recontamination No evidence of migration based upon pore-water sampling in 2011 (Reible and Lu 2011)	Cap erosion measured within first year of monitoring, seen only in area proximal to heavily used Washington ferry lane. Contaminants also observed in sediment traps. Monitoring demonstrated long-term risk reduction through elimination of liver lesions in English Sole.
PAH, Mercury, Heavy Metal, and SVOC-contaminated Sites
Wyckoff-Eagle Harbor, Bainbridge Island, WA	PAHs, mercury	East and West Eagle Harbor total cap of 70 acres	0.5-foot thin cap over 6 acres and 3‑foot thick cap over 0.6 acre	22,600 tons of sand for thin cap and 7,400 tons of sand for thick cap	1997–partial dredge and cap		To date, post-verification surface sediment samples have met the cleanup criteria established for the project. Ongoing monitoring.
Pier 64, Seattle, WA	PAHs, heavy metals, phthalates, dibenzofuran	—	0.5–1.5	Cap material was a beneficial reuse of sand from navigational dredging.	1994		Thin-layer capping was used to enhance natural recovery and to reduce resuspensionA renewed suspension of insoluble particles after they have been precipitated. of contaminants during pile driving.
New Haven Harbor, CT	PAHs, metals	—	1.6	Silt	1993		Extensive coring study
Port Newark/ Elizabeth, NY	PAHs, metals	—	5.3	Sand	1993		Extensive coring study
Pier 53–55 CSO, Seattle, WA	PAHs, heavy metals	—	1.3–2.6	Cap material was a beneficial reuse of sand from navigational dredging.	1992		Pre-cap infaunal communities were destroyed in the rapid burial associated with cap construction.
GP Lagoon, Bellingham Bay, WA	Mercury	Shallow intertidal lagoon	3	Sand	2001	• No contaminant migration at 3 months • Cap successfully placed	Ongoing monitoring
Experimental Mud Dam, NY	PAHs, metals	—	3.3	Sand	1983		Cores collected in 1990
Mill-Quinnipiac River, CT	PAHs, metals	—	1.6	Silt	1981		Cores collected in 1991
Norwalk, CT	PAHs, metals	—	1.6	Silt	1981		Routine monitoring
Stamford-New Haven, CT	PAHs, metals	—	1.6	Sand	1978		Cores collected in 1990
GP Lagoon, Bellingham, WA	Mercury	Shallow intertidal lagoon	3	Sand	2001	• No contaminant migration at 3 months • Cap successfully placed	Ongoing monitoring
Central Long Island Sound Disposal Site, NY	Multiple harbor sources	—	Unknown	Sand	1979–1983	• Some cores, uniform structure with low-level contaminants • Some cores, no contaminant migration • Some slumping	Extensive coring study at multiple mounds showed cap stable at many locations. Poor recolonization in many areas.
New York Mud Dump Disposal Site, NY	Metals from multiple harbor sources	—	Unknown	12 million yd³ of sand	1980		Cores taken 3.5 years later in 1983 showed cap integrity over relocated sediments in 80 ft of water.
Duwamish Waterway/ Diagonal CSO, Seattle, WA	PCB, phthalates, mercury	7 acres placed on cut-slope	Cap placed over slope on cut-in benches. 3-5 ft	Composite cap included sand for isolation, cobble to rip-rap for erosion control, and habitat material (fish mix).	2003–2004		Armoring for erosion control was required for most of the site. The habitat enhancement layer was placed over areas shallower than -10 ft mean lower low water (MLLW).
Hylebos Waterway, Commence-ment Bay, WA	PCBs, mercury, semi-volatile organic compounds (SVOCs)	800 ft long by 20–25 ft wide	Cap placed over 2:1 cut slope to a total thickness of 3.5 ft	Heavy non-woven geotextile base layer, 1.5 ft of quarry spalls and 2 ft of pit-run compacted sand/ gravel.	2004		Intertidal cap was placed using conventional upland equipment during low tide sequences. Tidal elevations were between +12 and 0 MLLW.
Olympic View Resource Area, WA	PCBs, dioxins	1.3-acre cap	Variable, depending upon cap area (intertidal, subtidal, habitat)	Sand, granular AC (GAC) and river rock	2002		Intertidal – 11,438 tons removal with 14,500 tons of backfill sand. Contaminated subtidal area was capped with approximately 9,000 tons of sand cap material placed from a barge-mounted tremie tube. In some areas, GAC was mixed at 4% by volume (1.5% by weight) as a precautionary barrier.
Convair Lagoon, San Diego, CA	PCBs	5.7-acre cap in 10-acre site; water depth 10–18 ft	2 ft of sand over 1 ft of rock	Sand over crushed rock	1998		Ongoing monitoring for 20–50 years, including diver inspection, cap coring, biological monitoring
Note: Information in this table, particularly in the Performance column, is based on the last monitoring event. The amount of available data on these projects varies widely, monitoring data for many of the sites are limited, and some of the sites have not been monitored for several years. Table based on the following sources: Sumeri, A. 1984. “Capped In-water Disposal of Contaminated Dredged Material: Duwamish Water Site.” In R.L. Montgomery and J.W. Leach (Eds.), Dredging and Dredged Material Disposal, Volume 2. Proceedings of the Conference Dredging ’84, November 14–16, 1984, Clearwater Beach, FL, American Society of Civil Engineers, NY. RETEC. 2003. Feasibility Study for the Lower Fox River and Green Bay, Appendix C. Prepared for the Wisconsin Department of Natural Resources, Madison, Wisconsin. Truitt, C.L. 1986. The Duwamish Waterway Capping Demonstration Project: Engineering Analysis and Results of Physical Monitoring, Final Report. U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report D-86-2, March. USEPA. 1998. Manistique River/Harbor AOC Draft Responsiveness Summary, Section 4: In-place Containment at Other Sites. USEPA Region 5 and Wisconsin Department of Natural Resources (September 25). The Johnson Company, 2002. Draft Summary of Contaminated Sediment Capping Projects. http://johnsonco.com/pcb-contaminated-sediment/

Table 5-4. Representative active sediment capping projects
Sediment Project	Contaminants	Site Conditions	Design Thickness (feet)	Cap Material	Year	Performance
Permeability Control Projects
Ottawa River, OH	Metals, PCBs	107,000 ft²	0.5-0.6 ft	AquaBlok	1999	Placement by conveyor, clamshell, and helicopter was demonstrated.
Galaxy/Spectron Little Elk Creek, MD	VOCs, DNAPL	63,000 ft²	0.7 ft	Bentomat CL	1999	Groundwater pumping capacity was increased to reduce hydrostatic pressure on cap. Monitoring has shown upgraded hydraulic control and cap to be effective.
Anacostia River	PAHs, metals and PCBs	Low flow river, 1 acre site (10,000 ft² for permeability1) Characteristic of a material or membrane that allows liquids or gases to pass through it; 2) The rate of flow of a liquid or gas through a porous material. control)	0.5 ft +0.5 ft sand	AquaBlok	2004	Effective placement via clamshell. Reduction of upwelling in AquaBlok capped area, diversion of groundwater further offshore. Gas ebullition led to uplift and deterioration of containment in one area.
Tennessee Products, Chattanooga Creek, TN	PAHs	175,000 ft²	0.5 ft	AquaBlok	2007	Containing mobile NAPL. Monitoring via pore waterWater located in the interstitial compartment (between solid-phase particles) of bulk sediment. showing good containment in 2010-2012.
Penobscot River, ME	PAHs (MGP site)	High flow High tidal river 60,000 ft²		AquaBlok	2010	Designed to eliminate gas ebullition through NAPL, channel gas/NAPL away from river. Monitoring is ongoing.
Sorbing Amendments (Contaminant Migration Control) Projects
Anacostia River	PAHs, metals and PCBs	Low flow river, 1 acre site (10,000 ft² for permeability control)	1) Reactive Core Mat +0.5 ft sand 0.5 ft 2) Apatite+0.5 ft sand	Coke in Reactive Core Mat, Apatite	2003	Placement of Reactive Core Mat and thin layers of bulk material was achieved, and the effect of recontamination from storm drains was monitored (Reible et al. 2006). Long-term monitoring via passive sampling results (Lampert, Lu, and Reible 2013).
McCormick and Baxter Superfund Site, Willamette River, OR	Creosote, NAPL	23 acres	2	Composite cap of organoclay, sand, armoring, and habitat mix. Also organoclay in mats in gas area	2004	No observed contaminant migration based upon pore-water sampling over 5 years and other sampling efforts. The project was completed in 2004; short-term data show cap remains effective; sheens initially observed have been determined to be biological in origin.
Stryker Bay, Duluth MN	PAHs	1,000,000 ft²	Reactive Core Mat (<1”) overlain by sand	AC in Reactive Core Mat	2006, 2010	Excess cap layer built up to encourage consolidation. Retained contaminants during consolidation.
BROS, Logan Township NJ	PAHs	240,000 ft²	Reactive Core Mat (<1”)	Organoclay in Reactive Core Mat	2009 2010	Wetlands with intermittent inundation.
Roxana Marsh, Grand Calumet IN	PAHs	980,000 ft²	Intermixed with sand in 6” cap with overlying sand	Organoclay	2011	Intermixed bulk placement in a slurry with sand. Monitoring is ongoing.
Onondaga Lake, Syracuse NY	VOCs, PAHs, metals	Freshwater lake 200 acres	AC Intermixed in cap	AC bulk placement	Initiated 2012	Demonstrated capability of placing AC in bulk in a mixture (perhaps most difficult amendment to place in this manner due to low density).

Table 5-5. Case studies describing conventional and amended capping experience
Case Study	Contaminant	Site Description	Amendment
Conventional Capping
Wyckoff-Eagle Harbor, Bainbridge Island, WA	Creosote, PCP, PAHs, metals	Subtidal and intertidal areas	NA
Port of Tacoma Piers 24 and 25, WA	PCBs, PAHs, metals	Marine embayment	NA
Grasse River, NY	Metals, PCBs	River	NA
Bellingham Bay, WA	Hg, 4-methylphenol, phenol	Marine embayment	NA
Black Lagoon, Detroit River, MI	PCBs, metals	River lagoon	NA
Bremerton Naval Yard OU B, WA	PCBs, Hg	Marine embayment	NA
Callahan Mining, ME	PCBs, metals	Tidal estuary	NA
Hackensack River, NJ	Chromium	River	NA
Hooker Chemical, Niagara Falls, NY	PAHs	River	NA
Ketchikan Pulp, AK	Arsenic, metals, PCBs, ammonium compounds, 4 methylphenol,H₂S	Marine cove	NA
Koppers Site, Former Barge Canal, Charleston, SC	NAPL, Total PAH	Tidal and non-tidal wetlands, tributary and river	NA
Manistique River & Harbor, MI	PCBs	Tidal River	NA
McCormick & Baxter, CA	PAHs, Dioxins	Marsh, wetland, floodplain	NA
Metal Bank, PA	PCBs, SVOCs, Dioxins	Tidal river	NA
Torch Lake Superfund Site, MI	Metals, PAHs, PCBs, coal tars, Nitrates, ammonia compounds, contamination from explosives	Lake	NA
Amended Capping
Anacostia River	PAHs, metals	River	AquaBlok, Coke Reactive Core Mat, apatiteName given to a group of phosphate minerals, usually referring to hydroxylapatite distributed widely in igneous, metamorphic, and sedimentary rocks, often in the form of cryptocrystalline fragments. Hydroxylapatite is used in chromatographic techniques to purify proteins and other chemicals., and sand
Aberdeen Proving Ground, MD	Chloroform, Carbon Tetrachloride, Tetracholorethene, Pentachloroethane	Tidal Wetland	Reactive Mat
Galaxy/Spectron Inc., Little Elk Creek, Elkton, MD	Chlorinated solvent DNAPL	Creek	Geosynthetic Clay Liner and Bentomat CL
Hudson River Poughkeepsie NY	Coal tar NAPL	Tidal river	Organophilic clay
Penobscot River, ME	Coal tar NAPL	River	Organophilic clay
Pine Street Canal, VT	PAHs, VOCs, Metals, Coal Tar	Canal	Reactive Core Mat containing organophilic clayClay minerals whose surfaces have been ion exchanged with a chemical to make them oil-sorbent. Bentonite and hectorite (plate-like clays) and attapulgite and sepiolite (rod-shaped clays) are treated with oil-wetting agents during manufacturing. Quaternary fatty-acid amine is applied to the clay. Amine may be applied to dry clay during grinding or it can be applied to clay dispersed in water.
McCormick and Baxter Site, Portland, OR	PAHs	Slough	Sand
Port of Portland	Metals, pesticides, PCBs, petroleum products,		Organophilic clay
Stryker Bay, Duluth, MN	PAHs, metals, coal tar	Lake Bay	AC Reactive Core Mat
West Branch Grand Calumet River, Hammond, IN	PAHs, PCBs, metals, coal tar NAPL.	River	Organophilic clay
Zidell- Willamette River, OR	PCBs, metals, PAHs, TBT	River	Organic carbon

Publication Date: August 2014

Permission is granted to refer to or quote from this publication with the customary acknowledgment of the source (see suggested citation and disclaimer).