The Diamond Alkali Superfund Site (DASS) includes portions of the Passaic River beginning at the lower Passaic River Study Area (LPRSA), which runs 17.4 miles south from the Dundee Dam to the confluence with the Hackensack River, and the Newark Bay Study Area (NBSA), including Newark Bay, the Arthur Kill, the Kill Van Kull, and tidal portions of the Hackensack River. However, these areas incorporate only a portion of the New York Bight Watershed Estuary, which through tidal action, intricately connects the water bodies of the Passaic River to both the Upper and Lower New York Bays and the Hudson River.

Production of pesticides and other chemical products began at 80 Lister Avenue in the 1940s. In the 1950s and 1960s, the Diamond Alkali Company owned and operated the facility, manufacturing agricultural chemicals, including the herbicides used in the defoliant known as “Agent Orange.” An unwanted by-product of these manufacturing processes was the extremely toxic chemical 2,3,7,8-tetrachlorodibenzo-para-dioxin, (2,3,7,8-TCDD and hereinafter referred to as “TCDD”). TCDD is commonly and interchangeably referred to as “dioxin,” although dioxin(s) is actually a general name for a large group of chemical compounds, with similar chemical structures, that induce toxicity via a common mechanism of action, resulting in a common spectrum of biological responses.

In 1983, environmental sampling by the State of New Jersey and the U.S. Environmental Protection Agency (EPA) at and near 80 Lister Avenue, as well as in the river, revealed high levels of TCDD. The site was subsequently listed on the Superfund National Priorities List (NPL) in 1984. TCDD, pesticides and other hazardous substances were found in the soil and groundwater at 80-120 Lister Avenue. TCDD, polychlorinated biphenyls (PCBs), metals, polycyclic aromatic hydrocarbons (PAHs) and pesticides were also found in sediment of the lower Passaic River. Additional sampling revealed DASS-related hazardous substances throughout Newark Bay and its tributaries, the Hackensack River, the Arthur Kill River tidal strait and the Kill Van Kull tidal strait.

The DASS was listed on the National Priorities List on September 21, 1984. As defined by EPA, the DASS consists of “...the former Diamond Alkali facility at 80-120 Lister Avenue in Newark, New Jersey, the Lower Passaic River Study Area (LPRSA), the Newark Bay Study Area and the areal extent of contamination.” The LPRSA is “...the 17-mile, tidal portion of the Passaic River, from RM [River Mile] 0 to Dundee Dam (RM 17.4), and its watershed, including the Saddle River (RM 15.6), Third River (RM 11.3) and Second River (RM 8.1).”

Remedial activities at the Site are ongoing - a 100% complete design is anticipated to be complete in 2024, and remedial activities beginning in 2025 or 2026. Pursuant to CERCLA NRDAR regulations, in 2004 the Trustees finalized a Preliminary Assessment Screen and Determination for the Diamond Alkali Superfund Site Natural Resource Damage Assessment and Restoration. In 2020, the Trustees finalized an Assessment Plan for the NRDAR. Assessment activities are ongoing and are currently focused in the Lower Passaic River area.