TMDL SWM BMP Program Planning and Design

Coastal Resources, Inc. (CRI) has provided planning and design services on two TMDL Contracts (1 in Frederick County and 1 in Harford County) for the SHA.  Under these contracts, CRI designed five new SWM BMPs (3 bioretention/rain gardens and 2 bioswales) that maximized water quality treatment at the chosen locations. CRI conducted field investigations and prepared SWM BMP design and contract documents necessary to advertise the project for construction. Specific tasks included:  

Meetings and Coordination:  CRI attended weekly partnering meetings with the project team to discuss project schedule and progress. In addition, CRI participated in milestone design meetings.  

Desktop Evaluations:  CRI conducted desktop evaluation for sites within SHA-owned roadways and facilities within the study area for potential new SWM BMP sites. The evaluations were based on the results of the SHA SWM Site Selection GIS model, provided by SHA, which will have already identified areas having minimal water quality treatment and preliminary site constraints. 

Field Investigations:  Based on the results of the desktop evaluation, CRI conducted field investigation to determine the feasibility of potential SWM BMP sites. For each feasible site, CRI verified the base information against field observations; visually confirmed drainage patterns and land use; identified site constraints such as natural resources, site accessibility, and utilities; investigated downstream outfall conditions; and documented field investigation with photos. 

Wetlands/Waterways and Forest Delineations:  CRI conducted wetland/waterway delineation and prepared mapping for each site as well as a memorandum.  Waters of the U.S. and wetlands boundaries located within the study limits were delineated in accordance with criteria established in the 1987 USACE Wetland Delineation Manual and Regional Supplement guidance from USACE and MDE.  Wetland and stream boundaries were flagged in the field, sketched on site mapping, and surveyed using GPS.  In addition CRI identified impacts to trees/forests as a result of the proposed SWM improvements.  CRI prepared a General Forest Characterization for each forest stand that was impacted by the project, prepared plan(s) depicting the impacts, and quantified impacts.


Frederick and Harford Counties, MD


MDOT State Highway Administration – Environmental Programs Division

Key Services:

  • Concept Design
  • Preliminary Investigation (PI), Final, and Plans, Specifications & Estimate (PS&E) Design
  • H&H Computations
  • Wetland Delineation
  • Tree Surveys
  • Advertisement Phase Services
  • Permitting Support

The Maryland State Highway Administration (SHA) is committed to meeting the requirements of the Chesapeake Bay TMDL through compliance with the requirements established in Maryland’s Watershed Implementation Plan for the Chesapeake Bay Total Maximum Daily Load (WIP).  

Concept Designs:  CRI prepared SWM concept designs (30%) for the new SWM BMP sites.  The following activities were included in the concept design phase:

  • Hydrologic computations for each proposed BMP including drainage area, hydrologic soil group, and land use verification; runoff curve number (RCN) determination; time of concentration determination; and TR-55/TR-20 analysis. 
  • Design computations and preliminary grading for each proposed BMP. BMP type selection and sizing based on the Recommendations of the Expert Panel to Define Removal Rates for Urban Stormwater Retrofit Projects (dated October 9, 2012) and MDE’s Accounting for Stormwater Wasteload Allocations and Impervious Acres Treated (dated June 2011, Draft). 
  • Impervious area treated and load reduction computations based on contributing drainage area characteristics, BMP type/sizing, and BMP pollutant removal efficiencies.
  • Concept plan and concept report including drainage area mapping and all associated computations. 

Contract Documents: CRI prepared contract documents, including specifications, estimate, H&H computations and SWM reports at the 65% (Semi-Final), 90% (Final), and 100% (PS&E) design stages.

Advertisement Phase Services: CRI assisted SHA during the advertisement phase of the project.  Tasks included responding to contractor requests for information and prepare formal response letters; attending the pre-bid meeting; reviewing bid tabulations and providing bid justification; and preparing addendums.

Permitting Support: CRI provided plans for Erosion and Sediment Control review and approval to the Plan Review Division and plans for review and approval to the Highway Hydraulics Division. CRI also determined wetland and forest impacts to determine if a permit would be required for each project.