Final NPS Salt Marsh Background Study Report - Cape Cod National Seashore - Herring River Restoration Project Background Study

VHB

This National Park Service (NPS) background study investigation was conducted to support the Herring River Restoration Project (HRRP). The HRRP Site (the Site) is within Cape Cod National Seashore (CACO) and the towns of Wellfleet and Truro in Barnstable County, Massachusetts. The goal of the project is to re-establish tidal exchange to the Herring River estuary and thereby remediate degraded conditions and restore native wetland habitats. Many restoration activities will require management of sediment, which may include beneficial reuse in adjacent marshes and uplands, burial, or removal off-Site. Elevated concentrations of DDx compounds, dieldrin, and arsenic have been detected in Site sediment samples from areas where habitat restoration methods may involve sediment management and sediment placement back into CACO wetlands. These constituents have been identified as contaminants of potential concern (COPCs) at the Site. The need to manage on-Site or remove sediment off-Site will be determined based on whether concentrations of COPCs exceed background concentrations and/or risk-based screening thresholds. While the Site is not a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Site, and actions conducted as part of the HRRP restoration do not constitute a removal or remedial action under CERCLA, NPS follows the CERCLA process when making decisions regarding potentially contaminated material placed within a Park boundary. Under CERCLA, cleanup levels are not normally set below the identified natural or anthropogenic background concentrations. NPS conducted this background study investigation to obtain data from regional salt marshes on Cape Cod. The purpose of the study is to determine the anthropogenic background concentrations of COPCs measured in HRRP Site samples to help plan future sediment management. To achieve this objective, NPS collected surface sediment samples from three background salt marshes on Cape Cod that represent historical conditions and planned future conditions of the HRRP Site. In accordance with guidance, selected background areas have similar physical, chemical, geological, biological, and land-use characteristics as the restored HRRP Site. They are not influenced by the Site but do include ongoing sources similar to those present at the Site. These selected background areas also have similar land-use histories as the Site: DDx compounds, dieldrin, and arsenic may have been historically introduced into the regional waterway and wetland areas to combat pests and support agriculture throughout Cape Cod and may be ubiquitous to these ecosystems in the region.

Final NPS Salt Marsh Background Study Report - Cape Cod National Seashore - Herring River Restoration Project Background Study

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