**1. Introduction**

Since the late 1800s, Newark Bay and adjoining waterways located in New Jersey, USA, have been highly industrialized, receiving direct and indirect discharges from numerous industrial facilities. A Remedial Investigation/Feasibility Study (RI/FS) under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA "Superfund") began in 2004 for the Newark Bay Study Area (NBSA)—which has been defined as Newark Bay (the Bay) and portions of the Hackensack River, Arthur Kill, and Kill van Kull (Figure 1).

To initiate the field investigations for the NBSA, Tierra first developed a Preliminary Conceptual Site Model (CSM) [1], based on historical data, and used the model to plan the first two phases of the remedial investigation (RI) [1,2]. The new data generated from these investigations were used to create the revised CSM described herein, to inform additional data needs for the RI. The specific objectives of the CSM include:

• Update the current understanding of the conditions and processes in the NBSA based on the data generated from recent RI investigations [1,2] and secondary data [3,4].


**Figure 1.** Regional map of Newark Bay and the Newark Bay Study Area (NBSA) outlined in green.

The comprehensive NBSA CSM addresses: (1) the general physico-chemical characteristics of the NBSA (including geology and geomorphology, surface water quality, biological communities), as well as (2) contaminant sources, (3) hydrodynamics and sediment transport, (4) contaminant fate and transport, (5) nature and extent of sediment contamination, (6) human and ecological exposure pathways, and (7) identification of data gaps. The focus of this paper is the hydrodynamics and sediment transport components of the NBSA CSM.

### **2. Environmental History of the Newark Bay Study Area**

Newark Bay is situated within a highly industrialized and heavily populated region, adjacent to the cities of Newark and Elizabeth. It is bordered by Newark Liberty International Airport to the west; Jersey City and Bayonne to the east; and Staten Island, New York, to the south. As part of the New York/New Jersey Harbor Estuary, Newark Bay has evolved over more than two centuries into a key shipping port and a convenient site for industrial operations [5–9].

Environmental degradation has occurred in the NBSA over the past two centuries due to a variety of factors—including shoreline and land development [10], wetlands destruction, habitat degradation, garbage and sewage disposal, and releases of contaminants [11]. As a result of urban and industrial practices, the NBSA is contaminated with a number of COPCs—including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides, herbicides, volatile and semivolatile organic compounds (VOCs and SVOCs, respectively), polychlorinated dibenzo-*p*-dioxins and polychlorinated dibenzofurans (PCDDs and PCDFs), and metals [12,13].

#### **3. Conceptual Site Model—Hydrodynamics and Sediment Transport**

The NBSA is a partially mixed estuary that receives large freshwater contributions from the Passaic and Hackensack Rivers at the northern end of the Bay and additional freshwater contributions from a number of other tributaries, combined sewer overflows (CSOs), storm water outfalls (SWOs), and publically owned treatment works (POTWs) distributed throughout the Bay. It also receives salt water contributions through the Kill van Kull and the Arthur Kill tidal straits at the southern end of the Bay. The NBSA and the surrounding area have a long history of human activity that has modified the shorelines and bathymetry of Newark Bay and its tributaries. As a result, the Bay's bathymetry consists of shallow tidal flats adjacent to deeper, dredged navigation channels, which results in a complex bathymetry with sharp elevation gradients. Large bathymetric gradients, highly variable freshwater loading, astronomical tides, and prevailing and event-based meteorological forcing all contribute to the system's complex hydrodynamic and sediment transport patterns and processes.

#### *3.1. Hydrodynamics*

The hydrodynamics of Newark Bay are influenced primarily by three physical processes: (1) freshwater tributary flows; (2) astronomical forcing (including classical estuarine gravitational circulation) through the Kill van Kull and Arthur Kill tidal straits; and (3) local and regional meteorological events [14,15]. These primary influences combine to yield complex, event-driven circulation and make it challenging to identify a long-term average pattern [16].

A substantial amount of dredging has been done over the past 150 years [10], and flows are much different now in Newark Bay from what they were before human activities began. In general, it is understood that, because of the freshwater inputs in the northern end of the Bay, the system is partially mixed and displays the characteristics of classic two-layer estuarine circulation with a landward flow of salt water in the bottom layer and a seaward flow of less saline water in the surface layer [15–18]. High freshwater discharge from the Passaic River increases both vertical stratification and flow rate in the landward-flowing, saline bottom layer in Newark Bay [16].

This estuarine gravitational circulation pattern can be interrupted (*i.e.*, daily-averaged currents become uniform with depth) during periods of very low freshwater discharge from the Passaic River or during strong meteorological events [16,19]. Moreover, the consensus view in published literature is that there is, on average, a counterclockwise circulation around Staten Island [20–22]. In addition, because the Kill van Kull is shorter, straighter, and better aligned with tidal and gravitational forcing, it typically experiences flows about an order of magnitude greater than the Arthur Kill [23]. Because of the complexity and variability of the circulation patterns, it is most efficient to examine individually the responses of the NBSA to each of the primary influences.
