Maryland Department of Transportation State Highway Administration (MDOT SHA)
- Stormwater Management (SWM) Planning
- Environmental Site Design (ESD)
- Erosion and Sediment Control
- Wetland Delineation
- Wetland Mitigation
Coastal Resources, Inc. (CRI) provided SWM planning and wetland delineations for the MD 4 Thomas Johnson Bridge project planning study. The project spans both Calvert and St. Mary’s Counties from the MD 2‐4 split in Calvert County to the MD 235 intersection in St. Mary’s County, a project length of approximately four miles. Near the completion of the planning process for this project, the project had been put on hold. When SHA reactivated the project, CRI was tasked with updating the wetland delineations for the project, assisting with the wetland/waters mitigation site search, and updating and expanding the previous SWM report for the preferred alternative using the new Maryland Department of the Environment (MDE) regulations to complete NEPA documentation for the planning study.
Stormwater Planning: CRI delineated and investigated approximately 37 study points. Field visits were required to verify points of interest, flow patterns, and recent land use changes. The impervious areas within the project limits were categorized as new development, redevelopment, or maintenance. Drainage area and land use information was used to perform TR-55 calculations and complete a water quality summary sheet for each study point. This information along with the Maryland Storm Water Design manual and SHA HHD’s SWM Processor software was used to determine the target ESD volume. CRI determined that approximately 60 ESD facilities are required. Potential ESD treatment techniques were investigated to the Maximum Extent Practicable in order to meet requirements for MDE approval and provide computations for the analysis.
CRI set the limit of disturbance (LOD) which considered road grading, facility installation and future erosion and sediment controls. CRI also adapted typical cross sections to show the proposed stormwater facilities both on the shoulder and in the median. The road design was altered so that the ESD facilities are on the inside of the proposed pedestrian trail in order to reduce the amount of offsite runoff to be treated by each facility. The submitted preliminary design plans included drainage area and study point locations, a water quality map, the LOD, ESD facility locations, and any additional protection measures that may be provided.
Wetland Delineation and Mitigation Planning: Due to the time elapsed since the original planning study and changes to regulatory guidance, CRI assisted with wetland delineations to update the previously mapped wetland boundaries within the corridor. All waters of the U.S., including wetlands, were identified using the Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Atlantic and Gulf Coastal Plain Region (Version 2.0) (USACE, November 2010). Wetland and waterway boundaries were surveyed using a handheld Trimble GPS unit, and in accordance with SHA guidance, and GIS mapping was prepared for inclusion in the project mapping. CRI completed data management and quality control of all field data and prepared report text for inclusion in the overall wetland delineation report prepared by the prime consultant. CRI also participated in the agency field review to verify the wetland/waterway boundaries.
CRI assisted the prime contractor with a mitigation site search to identify suitable locations for wetland creation and/or enhancement to compensate for project impact to regulated waters of the U.S. CRI conducted a desktop GIS analysis and reviewed the online Water Resources Registry (WRR) to identify wetland mitigation opportunities in the Lower Patuxent watershed. Based on the desktop analysis, CRI developed a list of potential mitigation sites and provided a summary memo and accompanying map of the potential opportunity locations to the prime consultant. The desktop sites were preliminarily reviewed in the field using windshield surveys to verify land use and landscape position and those sites deemed suitable were recommended for further onsite evaluations in the future.