DC Water

Key Services

  • NEPA Documentation (EIS)
  • Natural Resources Inventory
  • Wetland Delineation

Project Details

Coastal Resources, Inc. (CRI) assisted the prime engineering consultant with natural resource inventory and assessments in support of the Environmental Impact Statement (EIS) for the Potomac River Combined Sewer Overflow (CSO) Project.  This innovative undertaking is part of the DC Clean Rivers Project to implement DC Water’s CSO Control Consent Decree requirements.  For the Potomac River CSOs, the Consent Decree requires an underground storage tunnel be constructed to provide 58 million gallons of storage and a dewatering pump station sufficient to dewater the tunnel.  The Consent Decree also includes a requirement that low impact development (LID) opportunities be considered with the objective of reducing the size of the Potomac storage facility.

CRI used readily available mapping, aerial photography, research, and GIS data to prepare a Natural Resources Inventory (NRI) and begin drafting portions of an EIS for the project. CRI conducted background research to obtain any existing information on project area natural resources that include vegetation, terrestrial wildlife, aquatic wildlife, T&E species, groundwater, surface waters, floodplains, and wetlands.  Field investigations were conducted to further identify and verify resources present in the project area and desktop mapping was refined to reflect field findings.

Vegetative communities within the study area were identified and mapped according to the Anderson Land Use Classification System (Anderson et al. 1976).  In the field, the successional stages, dominant and co-dominant vegetative species and vegetative structure was verified for each cover type. CRI developed a list of common species of wildlife, and during the field studies, identified the presence of breeding bird habitat, or unique species that may inhabit the project area.

CRI gathered existing published information on aquatic biota within the study area including, but not limited to fish and macroinvertebrate communities. Waterways, watershed limits, Scenic and Wild Rivers, and navigable waters within the study area were identified and CRI compiled existing available water quality data from the U.S. Geological Survey and other agencies that have conducted recent studies in or near the study area.  FEMA floodplain maps identifying any 100-year floodplains were also included in the GIS inventory mapping.  CRI conducted a wetland delineation in accordance with the USACE Regional Supplement to the 1987 Wetland Delineation Manual and surveyed the wetland boundaries using GPS. CRI prepared a wetland delineation report and wetland delineation mapping for the project area for inclusion in the natural resource inventory mapping.

CRI compiled all background and field data into an NRI technical report, which was then used by the project team to develop the Affected Environment portion of the EIS and computation of potential project impacts on natural resources.