Formatted Title:

Lauritzen Channel, California: 35 Years of Pre- and Post-Dredge Monitoring

Background/Objectives:

The Lauritzen Channel (Channel) is a 4-hectare navigation waterway within Richmond Harbor of San Francisco Bay, California, and part of the United Heckathorn Superfund Site (Site). In the 1940s, the U.S. Government used the Channel for shipbuilding, as well as leased the uplands area to pesticide formulators until it sold the Site in 1949. From 1949 to the mid-1960s, technical grade pesticides continued to be formulated and packaged in nearshore areas of the Site. From 1967 to 1980, the Site was used as scrap storage, and since the 1980s, a dry bulk-cargo shipping terminal has operated along the Channel. Environmental monitoring of the Channel that began in the 1980s identified locally elevated contaminant concentrations in fish and shellfish tissue. In the early 1990s, residual contaminants (e.g., soil/sediment containing part-per-thousand contaminant concentrations) were excavated from nearshore upland and intertidal areas of the Site. In 1994, the Record of Decision for Site cleanup was issued, establishing sediment and surface water remediation levels and requiring dredging of all soft sediment from the Channel. In 1996 and 1997, approximately 80,000 cubic meters of contaminated soft sediment were dredged from the Channel and disposed at off-site landfills. EPA verified removal effectiveness by inspecting dredge buckets and advancing post-dredge confirmation cores.

Approach/Activities:

From 1998 to 2023, robust post-dredge monitoring including sediment, surface water, and fish/shellfish tissue chemical analyses was performed to evaluate remedy effectiveness. Since initial monitoring revealed that prior remediation levels were not being achieved, several follow-on source identification studies were conducted. Key lines of evidence informing the overall remedy effectiveness evaluation have included the following: 1) pre- and post-dredging trends of surface sediment, surface water, and fish/shellfish tissue contaminant concentrations; 2) spatial patterns of contaminant concentrations within the Channel; 3) sediment porewater flux evaluations; 4) sediment erosion and deposition assessment; 5) contaminant mass balances within the Channel; and 6) chemical fingerprinting.

Results/Lessons Learned:

An updated conceptual site model will be presented based on multiple lines of evidence, which have identified ongoing contaminant source areas. These ongoing sources will need to be more carefully evaluated to develop an effective source control plan and then designed, constructed, monitored, and adaptively managed as appropriate to ensure long-term remedy success. This presentation will provide an overview of alternatives that would ensure long-term remedy effectiveness for the Site.

Erik Naylor

Affiliation

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Lauritzen Channel, California: 35 Years of Pre- and Post-Dredge Monitoring