A.25 Hackensack River, NJ

A.25.1 Contact

Regulatory Contact: U.S. District Court of New Jersey

A.25.2 Summary

Environment:	Estuary
Scale:	Full
Contaminants of Concern:	Chromium
Source Control Achieved Prior to Remedy Selection?	Yes
Final Remedy:	Dredging (0.5 acres), cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment. (30 acres), MNR (53 acres)
Expected Recovery Time:	Recovery achieved
MNR viewed as a success?	Not yet determined

A.25.3 Site Description

Study Area 7 is a 34-acre site bordering the Hackensack River, near the confluence with Newark Bay in Jersey City (Hudson County), New Jersey. The primary source of contaminants at this site is chromium ore processing residue used as fill in the Study Area 7 waterfront.

This area has been used for industrial and commercial purposes for over a hundred years. The operation of a sodium dichromium manufacturing facility from 1905-1954 (Mutual Chemical Company of America) led to chromium contamination. Chromium ore processing residue were used as fill material in Study Area 7 (at that time a common practice). Approximately 1 million yd³ of this material were used, leading to elevated chromium concentrations in Hackensack River sediment through historical groundwater seepage and surface runoff.

CSM summary: The primary natural recovery process in Study Area 7 is chemical transformationabiotic or biotic chemical process (such as photolysis, hydrolysis, oxidation/reduction, radioactive decay) that transform an element (Cr(VI) - Cr III) or compound (phenol – CO₂+ H₂O) to a different element or chemical compound. of hexavalent chromium, Cr(VI), to trivalent chromium, Cr(III). Cr(VI) rapidly transforms into Cr(III) under reducing or mildly oxidizing conditions. Cr(III) is much less bioavailable and toxic than CR(VI). Cr(VI) rarely forms in nature due to kinetic constraints, although it is thermodynamically favored under aerobic conditions.

In Study Area 7, Cr(VI) is transformed almost immediately to Cr(III) upon contact with sediments, which were characterized as reducing. A secondary natural recovery process is the physical isolation of buried sediments. By enhancing the primary natural recovery process this further supports the requirement to remedy sediments containing greater than 370 mg/kg total chromium.

Lines of evidence supporting chemical transformation, reduction in bioavailabilityThe relationship between external (or applied) dose and internal (or resulting) dose of the chemical(s) being considered for an effect (NRC 2003)., and mobility (very low bioavailability of chromium in sediments) included indicators of redox conditions in surface sediment, Cr(VI) detection in pore waterWater located in the interstitial compartment (between solid-phase particles) of bulk sediment. samples, sediment resuspensionA renewed suspension of insoluble particles after they have been precipitated. and oxidation test, Cr(VI) detection in subsurface groundwater, biota tissue analyses, and toxicity tests.

Lines of evidence supporting physical isolation processes and sediment stability included sediment trap analysis, radiological tracer measurements, sediment shear strength studies, hydrodynamic modeling, and an analysis of vertical chromium profiles in sediment cores.

A.25.4 Remedial Objectives

The primary concerns are ecological risks from chromium in sediment.

RAOs/project objectives: A remedy must be applied to all sediments, regardless of depth, that exceed the New Jersey Department of Environmental Protection’s effects range-median sediment quality goals of 370 mg/kg, as required by the consent decree governing the site.

A.25.5 Remedial Approach

Final selected remedy: Dredging (0.5 acres), capping (30 acres), and MNR (53 acres)

The recommended remedy alternative involved 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., capping of sediments with total chromium concentrations greater than 2,000 mg/kg, and MNR for the remaining areas. The negotiated remedy involved dredging 2,000 yd³ over 0.5 acres; a 14-acre, 12-inch capA covering over material (contaminated sediment) used to isolate the contaminants from the surrounding environment.; a 15-acre, 6 inch cap; and MNR for 20 acres whose subsurface concentrations exceeded 370 mg/kg. Capping targeted areas where surface sediments total chromium concentrations were greater than 370 mg/kg, while MNR targeted areas where surface sediment concentrations were less than 370 mg/kg but subsurface sediment concentrations exceeded 370 mg/kg.

This remedy was selected because it was determined that chromium was present in a net-depositional area in a form that was geochemically stable and nonbioavailable. In addition, only moderate resuspension was expected during high-energy events. MNR was selected after a detailed comparative risk analysis of several alternatives (no action, three capping remedies, and two dredging remedies). The risk analysis considered the following factors:

• worker risks associated with construction and transportation
• community quality of like impairments (noise, odor, diesel emissions, traffic congestion)
• short-term benthic habitatThe benthic habitat is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some subsurface layers. loss and recovery times
• risk reduction associated with changes in surface sediment concentrations of chromium
• long-term recontamination potential

The risk analysis also took into account both the short-term risk of implementing each remedy as well as the anticipated long-term risk reduction. The analysis showed that MNR provides comparable risk reduction to other remedies. Considering cost as well, it showed that the increasing costs associated with capping dredging did not proportionally decrease risk. Therefore, MNR provided comparable or greater risk reduction to other alternatives while also minimizing cost and the impact of removing the sediment.

The primary lines of evidencePieces of evidence are organized to show relationships among multiple hypotheses or complex interactions among agent, events, or processes. A weight of evidence approach includes the assignment of a numeric weight to each line of evidence. used to investigate MNR included lines of evidence used to support chemical transformation (reduction in bioavailability and mobility) such as indicators of redox conditions, pore water analyses, sediment resuspension and oxidation tests, biota tissue analyses, and toxicity tests. Lines of evidence supporting physical isolation includes sediment trap analysis, radio-isotope analysis, hydrodynamic modeling, sedflume shear strength studies, sediment coring, and vertical chromium profiling.

A.25.6 Monitoring

Monitoring covers sediment stability, physical isolation of chromium concentrations, geochemical stability of Cr(III), and sediment cap integrity. Tide gauges gather data to model shear forces, velocities, and hydrodynamic conditions to determine maximum velocities where MNR performs acceptably. Bathymetric and SPI camera data are used to calculate erosion and changes in sediment bed elevation. Finally, pre-water samples help to determine the risk reduction and monitor the geochemical stability of Cr (III) in surface sediments.

The area will be monitored for 15 years after objectives have been reached, assuming that they are maintained for those 15 years. Or, monitoring will continue through at least two high-energy events.

Expected recovery time: Recovery has been achieved.

RAOs/project objectives achieved?: Recovery has been achieved; current monitoring focuses on verifying performance.

Overall it is not yet determined if MNR is successful. MNR will be considered successful if five years of routine monitoring and 15 years of severe event monitoring show acceptable bed elevations through bathymetric surveys.

Publication Date: August 2014