LZ7 Tunnel Rehabilitation

Coastal Resources, Inc. (CRI) conducted a waters of the U.S. (WOTUS) delineation, prepared a preliminary jurisdictional determination (PJD), performed a tree survey, and conducted Unified Stream Methodology (USM) assessments for the LZ7 Tunnel Rehabilitation project in Great Falls, VA.  The project is part of the proposed improvements to the Potomac Interceptor sanitary system and consists of the replacement of Manhole 31, rehabilitation of 133 feet of 78-inch pipe, rehabilitation of 150 feet of 54-inch pipe, replacement of 200 feet of 54-inch pipe, and the construction of a bypass pumping system within the Northern Virginia Regional Park. The study area consisted of two separate areas along the Potomac River.  The northern study area was 4.87 acres, and the southern study area was 3.03 acres.

The two study areas were field investigated to identify and survey the boundaries of WOTUS, including wetlands.  Wetlands were identified in accordance with the Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Eastern Mountains and Piedmont Region, Version 2.0 (USACE 2010). Wetland and upland plots were established for each identified wetland at representative locations throughout the study area to document that the boundary of the wetland was properly determined.  All identified wetland indicators were recorded on a Wetland Determination Data Form. Delineated WOTUS were located using a Trimble Global Navigation Satellite System (GNSS) receiver. All identified WOTUS, including wetlands, were classified according to A Classification of Wetland and Deep-Water Habitats in the United States (USFWS 1979) and a preliminary assessment of each wetland’s function and value was made using The Highway Methodology Workbook Supplement – Wetland Functions and Values; A Descriptive Approach (USACE 1999). Stream conditions were evaluated using the USM (USACE and VDEQ, 2007). USM data forms were completed at each stream reach identified during the wetland delineation. During the field investigation, five nontidal streams and two nontidal wetlands were identified within and adjacent to the study areas. 

Following the fieldwork, CRI prepared a WOTUS delineation report and a USM memo for DC Water approval. The report included descriptions of each delineated system, methodology, data forms, function and value forms, photographs, and a wetland delineation map. CRI submitted a request to the USACE for a PJD and participated in a field visit/pre-application meeting to review the delineated WOTUS.   

In addition, CRI conducted a tree survey within the two study areas. The tree survey included all trees ≥6 inches diameter at breast height (DBH). All trees were GPS-located using a handheld Trimble GPS unit. CRI post-processed the data and prepared a shapefile including tree number, common name, scientific name, size, and condition.


Fairfax County, VA


DC Water

Key Services:

  • Waters of the U.S. Delineation
  • Pre-Application Field Review/ Preliminary JD
  • Tree Survey
  • Unified Stream Methodology (USM) Assessments