A Watershed Approach to Mitigating Stormwater Impacts (2017)

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1 S U M M A R Y Departments of transportation (DOT) projects often require multiple federal and state per- mits and reviews to ensure that potential adverse environmental impacts are avoided, mini- mized, or mitigated. Most often, DOTs design roadway plans and submit permit applications on a project-by-project and permit-by-permit basis, which limits the ability to streamline efficiencies by taking a more regional or watershed approach to planning and permitting. Movement at the state and federal level is opening the door for DOTs to more readily embrace a watershed approach to selecting mitigation sites based on the prioritization of needs across a broader area. One state DOT example is Maryland’s Watershed Resources Registry (WRR). This need for better, more collaborative watershed-based approaches is further emphasized in the recently updated Red Book (FHWA 2015). This handbook, which replaces the 1988 Red Book “Applying the Section 404 Permit Process to Federal-Aid High- way Projects” (FHWA 1988), provides DOTs and other state and local practitioners with a variety of methods to streamline the National Environmental Policy Act review and other regulatory review processes and encourages increased use of synchronization at the water- shed or regional level to reduce project timelines and environmental impacts. This NCHRP report intends to enable DOTs to embrace the use of a watershed-based stormwater management planning framework by doing the following: • Providing a review of the tools and national datasets currently available to DOTs for use in evaluating on- and off-site mitigation efforts on a watershed basis; • Identifying defensible strategies, metrics, and protocols for demonstrating and compar- ing the different types of mitigation approaches at the project and watershed level; • Preparing a proof-of-concept Microsoft Excel® based tool that DOTs can download to evaluate on- and off-site mitigation options based on a select number of criteria; and • Providing a case study to enable the reader on how to best understand the applicability of using such a tool to locate and evaluate mitigation opportunities. This report would not have been possible without utilizing the good work of numerous NCHRP reports before which have served to lay the groundwork for evaluating DOT projects on a watershed basis. In particular, readers are encouraged to review NCHRP Report 792, NCHRP Report 565, and several of the relevant reports from NCHRP Project 25-25, whose names follow. • Wet Detention Pond Design for Highway Runoff Pollution Control. NCHRP Project 25-12. 2002. http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP25-12_FR.pdf • NCHRP Report 482: Guidelines for Selecting Compensatory Wetlands Mitigation Options. 2002. http://www.trb.org/Main/Blurbs/152077.aspx A Watershed Approach to Mitigating Stormwater Impacts

2 A Watershed Approach to Mitigating Stormwater Impacts • Assessment and Mitigation Strategies for Land Development Impacts of Transporta- tion Improvements. NCHRP Project 25-25/Task 03. 2003. http://apps.trb.org/cmsfeed/ TRBNetProjectDisplay.asp?ProjectID=1540 • NCHRP Report 565: Evaluation of Best Management Practices for Highway Runoff Control. 2006. http://www.trb.org/Main/Blurbs/158397.aspx • Stormwater Treatment with Vegetated Buffers. NCHRP Project 25-25/Task 53. 2009. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=2378 • NCHRP Report 728: Guidelines for Evaluating and Selecting Modifications to Existing Road- way Drainage Infrastructure to Improve Water Quality in Ultra-Urban Areas. 2012. http:// www.trb.org/Main/Blurbs/168015.aspx • Permeable Shoulders with Stone Reservoirs. NCHRP Project 25-25/Task 82. 2013. http:// apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3315 • NCHRP Report 767: Measuring and Removing Dissolved Metals from Storm Water in Highly Urbanized Areas. 2013. http://www.trb.org/Main/Blurbs/170715.aspx • Current Practice of Post-Construction Structural Stormwater Control Implementa- tion for Highways. NCHRP Project 25-25/Task 83. 2013. http://apps.trb.org/cmsfeed/ TRBNetProjectDisplay.asp?ProjectID=3316 • NCHRP Report 792: Long Term Performance and Life-Cycle Costs of BMPs. 2014. http:// www.trb.org/main/blurbs/171471.aspx • NCHRP Report 778: Bridge Stormwater Runoff Analysis and Treatment Options. 2014. http://www.trb.org/Main/Blurbs/170652.aspx • Nutrient (Nitrogen/Phosphorous) Management and Source Control. NCHRP Project 25-25/ Task 85. 2014. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3510 • NCHRP Report 802: Guidance for Achieving Volume Reduction of Highway Runoff in Urban Areas. 2015. http://www.trb.org/Main/Blurbs/172415.aspx • Transferability of Post-Construction Stormwater Quality BMP Effectiveness Studies. NCHRP Project 25-25/Task 92. 2015. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay. asp?ProjectID=3721